阅读说明：本技术 四轮驱动车辆 (Four-wheel drive vehicle ) 是由 高以良幸司 于 2021-04-28 设计创作，主要内容包括：本发明提供一种四轮驱动车辆,该四轮驱动车辆能在进行自动起动控制时抑制或防止由于驱动系统的振动变大而导致的NV的恶化。基于后轮侧分配率(Xr)来相对于规定起动时发动机转速(Nestf)变更起动时目标发动机转速(Nesttgt),起动时目标发动机转速(Nesttgt)被设定为与驱动系统的共振转速(Nx)分离的转速,因此能在进行自动起动控制(CTst)时抑制或避免因发动机的转矩变动导致的驱动系统的共振的产生。(The invention provides a four-wheel drive vehicle capable of suppressing or preventing deterioration of NV due to increase in vibration of a drive system when automatic start control is performed. Since the target engine speed (Nesttgt) at the time of starting is changed from the predetermined engine speed (Nestf) at the time of starting on the basis of the rear wheel side distribution ratio (Xr), and the target engine speed (Nesttgt) at the time of starting is set to a speed that is separated from the resonance speed (Nx) of the drive system, it is possible to suppress or avoid the occurrence of resonance of the drive system due to torque variation of the engine when the automatic start control (CTst) is performed.)

1. A four-wheel drive vehicle (10) is provided with: a drive force source (PU) including at least an engine (12); a drive force distribution device (30) that is capable of transmitting drive force from the drive force source (PU) to main drive wheels (16) and auxiliary drive wheels (14), and that is capable of adjusting a drive force distribution ratio (Rx) that is a ratio of the drive force distributed between the main drive wheels (16) and the auxiliary drive wheels (14); and a control device (130) that performs a driving force distribution control (CTx) that adjusts the driving force distribution ratio (Rx) and performs an automatic start control that automatically starts the engine (12) when a predetermined start condition is satisfied, the four-wheel drive vehicle (10) being characterized in that,

the control device (130) is a device that changes a target engine speed (Netgt) after completion of explosion of the engine (12) in the automatic start control with respect to a predetermined start-time engine speed (Nestf) on the basis of the driving force distribution ratio (Rx), and the control device (130) sets the target engine speed (Netgt) to a speed that is separate from a resonance speed (Nx) of a drive system to which the engine (12) is connected so as to be able to transmit power.

2. Four-wheel drive vehicle (10) according to claim 1,

the control device (130) is a device that sets the target engine rotational speed (Netgt) to a rotational speed that is separated by a prescribed value (DeltaNest) from a resonance rotational speed (Nx) of the drive system calculated based on the drive force distribution ratio (Rx),

the predetermined value (Δ Nest) is a predetermined value for setting the target engine speed (Netgt) that can suppress the amount of change from the predetermined start-time engine speed (Nestf) and can avoid or suppress the occurrence of resonance in the drive system.

3. Four-wheel drive vehicle (10) according to claim 1 or 2,

the prescribed start-time engine speed (Nestf) is an optimum engine speed at which energy efficiency in the four-wheel drive vehicle (10) is optimum.

4. Four-wheel drive vehicle (10) according to any one of claims 1 to 3,

the control device (130) has a control function of changing the driving force distribution ratio (Rx) when the automatic start control is performed so as to separate the resonance rotation speed (Nx) of the drive system from the predetermined start-time engine rotation speed (Nestf) from the driving force distribution ratio (Rx) when the automatic start control is not performed,

the control device (130) selectively changes the target engine speed (Netgt) and the driving force distribution ratio (Rx) based on a vehicle state when performing the automatic start control, and separates the target engine speed (Netgt) from a resonance speed (Nx) of the drive system.

5. Four-wheel drive vehicle (10) according to claim 4,

the control device (130) separates the target engine speed (Netgt) from the resonance speed (Nx) of the drive system by changing the target engine speed (Netgt) when an accelerator operation amount or a drive request amount is equal to or greater than a predetermined amount, and separates the target engine speed (Netgt) from the resonance speed (Nx) of the drive system by changing the drive force distribution ratio (Rx) when the accelerator operation amount or the drive request amount is less than the predetermined amount.

6. Four-wheel drive vehicle (10) according to claim 4 or 5,

the control device (130) separates the target engine speed (Netgt) from the resonance speed (Nx) of the drive system by changing the target engine speed (Netgt) when a yaw rate (Vyaw) is equal to or greater than a predetermined angular rate, and separates the target engine speed (Netgt) from the resonance speed (Nx) of the drive system by changing the driving force distribution ratio (Rx) when the yaw rate (Vyaw) is less than the predetermined angular rate.

7. Four-wheel drive vehicle (10) according to any one of claims 4 to 6,

the control device (130) separates the target engine speed (Netgt) from the resonance speed (Nx) of the drive system by changing the target engine speed (Netgt) when a steering angle (θ sw) is equal to or greater than a predetermined angle, and separates the target engine speed (Netgt) from the resonance speed (Nx) of the drive system by changing the driving force distribution ratio (Rx) when the steering angle (θ sw) is less than the predetermined angle.

8. Four-wheel drive vehicle (10) according to any one of claims 4 to 7,

the control device (130) separates the target engine rotational speed (Netgt) from the resonance rotational speed (Nx) of the drive system by changing the target engine rotational speed (Netgt) when the four-wheel drive vehicle (10) is running in a curve, and separates the target engine rotational speed (Netgt) from the resonance rotational speed (Nx) of the drive system by changing the driving force distribution ratio (Rx) when the four-wheel drive vehicle (10) is running in a straight line.

Technical Field

The present invention relates to a four-wheel drive vehicle configured to be able to adjust the proportion of driving force distributed between main driving wheels and auxiliary driving wheels.

Background

A four-wheel drive vehicle is known, which includes: a driving force source including at least an engine; a driving force distribution device that is capable of transmitting a driving force from the driving force source to main driving wheels and auxiliary driving wheels, and that is capable of adjusting a driving force distribution ratio that is a proportion of the driving force distributed between the main driving wheels and the auxiliary driving wheels; and a control device that performs a driving force distribution control for adjusting the driving force distribution ratio, and performs an automatic start control for automatically starting the engine when a predetermined start condition is satisfied. This is true of a four-wheel drive vehicle described in patent document 1, for example.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2011/042951

Further, when the automatic start control is performed so that the drive system to which the engine is connected to be capable of transmitting power has a predetermined resonance rotation speed determined by, for example, mass and torsional rigidity, resonance of the drive system occurs due to the frequency of torque fluctuation of the engine, and vibration of the drive system increases. Thus, NV may be deteriorated by such vibration of the drive system. The NV is a general term for noise generated by a vehicle and vibration felt by a passenger, for example. In the four-wheel drive vehicle as described above, since the mass and the torsional rigidity of the drive system change according to the driving force distribution ratio, the resonance rotation speed of the drive system changes. Therefore, in the four-wheel drive vehicle as described above, there are problems as follows: when the automatic start control is performed, resonance of the drive system due to torque variation of the engine is likely to occur, and NV is likely to deteriorate.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a four-wheel drive vehicle capable of suppressing or preventing deterioration of NV due to increase in vibration of a drive system when automatic start control is performed.

Means for solving the problems

The first aspect of the invention provides (a) a four-wheel drive vehicle including: a driving force source including at least an engine; a driving force distribution device that is capable of transmitting a driving force from the driving force source to main driving wheels and auxiliary driving wheels, and that is capable of adjusting a driving force distribution ratio that is a proportion of the driving force distributed between the main driving wheels and the auxiliary driving wheels; and a control device that performs a driving force distribution control for adjusting the driving force distribution ratio, and performs an automatic start control for automatically starting the engine when a predetermined start condition is satisfied, wherein (b) the control device is a device that changes a target engine speed after completion of explosion of the engine in the automatic start control with respect to a predetermined start-time engine speed based on the driving force distribution ratio, and sets the target engine speed to a speed that is separated from a resonance speed of a drive system to which the engine is connected so as to be able to transmit power.

A second aspect of the invention provides the four-wheel drive vehicle recited in the first aspect of the invention, wherein the control device sets the target engine speed to a speed separated by a predetermined amount from a resonant speed of the drive system calculated based on the driving force distribution ratio, and the predetermined amount is a predetermined value of the target engine speed that is set to suppress an amount of change from the predetermined start-time engine speed and to avoid or suppress occurrence of resonance in the drive system.

A third aspect of the present invention is the four-wheel drive vehicle according to the first or second aspect of the present invention, wherein the predetermined start-time engine speed is an optimum engine speed at which energy efficiency in the four-wheel drive vehicle is optimum.

A fourth aspect of the invention provides the four-wheel drive vehicle recited in any one of the first to third aspects of the invention, wherein the control device has a control function of changing the target engine speed, and a control function of changing the driving force distribution ratio at the time of the automatic start control with respect to the driving force distribution ratio at the time of the non-automatic start control so that the resonance speed of the drive system is separated from the predetermined start-time engine speed, and wherein the control device alternately changes the target engine speed and the driving force distribution ratio based on a vehicle condition and separates the target engine speed from the resonance speed of the drive system at the time of the automatic start control.

A fifth aspect of the invention provides the four-wheel drive vehicle of the fourth aspect of the invention, wherein the control device separates the target engine speed from the resonant speed of the drive system by changing the target engine speed when an accelerator operation amount or a drive request amount is equal to or greater than a predetermined amount, and separates the target engine speed from the resonant speed of the drive system by changing the driving force distribution ratio when the accelerator operation amount or the drive request amount is less than the predetermined amount.

A sixth aspect of the invention provides the four-wheel drive vehicle of the fourth or fifth aspect of the invention, wherein the control device separates the target engine speed from the resonant speed of the drive system by changing the target engine speed when a yaw rate is equal to or higher than a predetermined angular rate, and separates the target engine speed from the resonant speed of the drive system by changing the driving force distribution ratio when the yaw rate is lower than the predetermined angular rate.

A seventh aspect of the invention provides the four-wheel drive vehicle of any one of the fourth to sixth aspects of the invention, wherein the controller separates the target engine speed from the resonance speed of the drive system by changing the target engine speed when a steering angle is equal to or greater than a predetermined angle, and separates the target engine speed from the resonance speed of the drive system by changing the driving force distribution ratio when the steering angle is smaller than the predetermined angle.

An eighth aspect of the invention provides the four-wheel drive vehicle of any one of the fourth to seventh aspects of the invention, wherein the control device separates the target engine speed from the resonance speed of the drive system by changing the target engine speed when the four-wheel drive vehicle is running in a curve, and separates the target engine speed from the resonance speed of the drive system by changing the driving force distribution ratio when the four-wheel drive vehicle is running in a straight line.

Effects of the invention

According to the first aspect of the invention, the target engine speed in the automatic start control is changed with respect to the predetermined start-time engine speed based on the drive force distribution ratio, and the target engine speed is set to a speed that is separated from the resonance speed of the drive system. This can suppress or prevent deterioration of NV due to increase in vibration of the drive system when the automatic start control is performed.

Further, according to the second aspect of the invention, the target engine speed is set to a speed that is separated by a predetermined value from the resonance speed of the drive system calculated based on the driving force distribution ratio, and therefore the occurrence of resonance of the drive system due to torque variation of the engine is appropriately suppressed or avoided. Further, since the predetermined value is a predetermined value for setting the target engine speed that can suppress the amount of change of the engine speed with respect to the predetermined start-up time and can avoid or suppress the occurrence of resonance in the drive system, the target engine speed is set to the target engine speed that can suppress the amount of change of the engine speed with respect to the predetermined start-up time and the occurrence of resonance in the drive system is appropriately suppressed or prevented when the automatic start-up control is performed.

Further, according to the third aspect of the invention, since the predetermined start-time engine speed is an optimum engine speed at which energy efficiency in the four-wheel drive vehicle is optimum, the target engine speed is separated from the resonance speed of the drive system by changing the target engine speed with respect to the optimum engine speed. This can suppress or prevent deterioration of NV while suppressing deterioration of energy efficiency. Further, if the target engine speed is set to a speed that is separated from the resonance speed of the drive system by a predetermined value, the target engine speed is set such that the amount of change from the optimum engine speed is suppressed, and therefore deterioration of energy efficiency is appropriately suppressed.

Further, according to the fourth aspect of the invention, when the automatic start control is performed, the target engine speed and the driving force distribution ratio are alternatively changed based on the vehicle state, and the target engine speed is separated from the resonant speed of the drive system, so that the influence on the vehicle motion controllability is suppressed while suppressing or preventing deterioration of NV, and the target engine speed is suppressed from being changed from the predetermined start engine speed. If the engine speed at the time of the prescribed start is the optimum engine speed, deterioration of energy efficiency is suppressed.

Further, according to the fifth aspect of the invention, since the target engine speed is separated from the resonant speed of the drive system by changing the target engine speed when the accelerator operation amount or the drive request amount is equal to or greater than the predetermined amount, the vehicle motion controllability by the drive force distribution control is prioritized over the improvement in energy efficiency in a situation where the quick start operation or the quick acceleration operation is performed. On the other hand, when the accelerator operation amount or the drive request amount is smaller than the predetermined amount, the target engine speed is separated from the resonance speed of the drive system by changing the drive force distribution ratio, and therefore, in a situation where the start operation or the accelerator operation is slow, improvement of the energy efficiency is prioritized over controllability of the vehicle motion by the drive force distribution control. This suppresses or prevents deterioration of NV, and also suppresses the influence on the controllability of the vehicle motion, and suppresses the target engine speed from being changed from the engine speed at the time of the predetermined start. If the engine speed at the time of the prescribed start is the optimum engine speed, deterioration of energy efficiency is suppressed.

Further, according to the sixth aspect of the invention, when the yaw rate is equal to or greater than the predetermined angular rate, the target engine speed is separated from the resonant speed of the drive system by changing the target engine speed, and therefore, in a situation where the change in the vehicle posture is large, the vehicle motion controllability by the drive force distribution control is prioritized over the improvement in the energy efficiency. On the other hand, when the yaw rate is smaller than the predetermined angular rate, the target engine speed is separated from the resonant speed of the drive system by changing the driving force distribution ratio, and therefore, in a situation where the change in the vehicle posture is small, improvement of the energy efficiency is prioritized over controllability of the vehicle motion by the driving force distribution control. This suppresses or prevents deterioration of NV, and also suppresses the influence on the controllability of the vehicle motion, and suppresses the target engine speed from being changed from the engine speed at the time of the predetermined start. If the engine speed at the time of the prescribed start is the optimum engine speed, deterioration of energy efficiency is suppressed.

Further, according to the seventh aspect of the invention, since the target engine speed is separated from the resonance speed of the drive system by changing the target engine speed when the steering angle is equal to or greater than the predetermined angle, the controllability of the vehicle motion by the drive force distribution control is prioritized over the improvement of the energy efficiency in a situation where the change in the vehicle posture is large. On the other hand, when the steering angle is smaller than the predetermined angle, the target engine speed is separated from the resonance speed of the drive system by changing the driving force distribution ratio, and therefore, in a situation where the change in the vehicle posture is small, improvement of the energy efficiency is prioritized over vehicle motion controllability by the driving force distribution control. This suppresses or prevents deterioration of NV, and also suppresses the influence on the controllability of the vehicle motion, and suppresses the target engine speed from being changed from the engine speed at the time of the predetermined start. If the engine speed at the time of the prescribed start is the optimum engine speed, deterioration of energy efficiency is suppressed.

Further, according to the eighth aspect of the invention, since the target engine speed is separated from the resonance speed of the drive system by changing the target engine speed when the four-wheel drive vehicle is running in a curve, the controllability of the vehicle motion by the drive force distribution control is prioritized over the improvement of the energy efficiency in a situation where the change in the vehicle posture is large. On the other hand, when the four-wheel drive vehicle is traveling straight, the target engine speed is separated from the resonance speed of the drive system by changing the driving force distribution ratio, and therefore, in a situation where the change in the vehicle posture is small, improvement of the energy efficiency is prioritized over controllability of the vehicle motion by the driving force distribution control. This suppresses or prevents deterioration of NV, and also suppresses the influence on the controllability of the vehicle motion, and suppresses the target engine speed from being changed from the engine speed at the time of the predetermined start. If the engine speed at the time of the prescribed start is the optimum engine speed, deterioration of energy efficiency is suppressed.

Drawings

Fig. 1 is a diagram illustrating a schematic configuration of a four-wheel drive vehicle to which the present invention is applied, and is a diagram illustrating a control function and a main part of a control system for various controls in the four-wheel drive vehicle.

Fig. 2 is a diagram illustrating a schematic configuration of the automatic transmission of fig. 1.

Fig. 3 is an operation chart illustrating a relationship between a shift operation of the mechanical stepped shift portion of fig. 2 and a combination of operations of the engagement device for the shift operation.

Fig. 4 is a collinear chart showing the relative relationship between the rotation speeds of the respective rotating elements in the electric continuously variable transmission unit and the mechanical stepped transmission unit of fig. 2.

Fig. 5 is a skeleton diagram illustrating the structure of the transfer of fig. 1.

Fig. 6 is a diagram showing an example of an AT range shift map for shift control of the stepped transmission unit and a travel mode switching map for switching control of the travel mode, and shows the respective relationships.

Fig. 7 is a flowchart for explaining a main part of the control operation of the electronic control device, and is a flowchart for realizing the control operation of the four-wheel drive vehicle capable of suppressing or preventing deterioration of NV due to increase of vibration of the drive system when the automatic start control is performed.

Fig. 8 is a diagram illustrating an example of a scheme in which the target engine speed at the time of startup and the rear wheel side distribution ratio are alternatively changed based on the accelerator opening degree.

Fig. 9 is a diagram illustrating an example of a scheme in which the target engine speed at the time of startup and the rear wheel side distribution ratio are alternatively changed based on the yaw rate.

Fig. 10 is a diagram illustrating an example of a scheme in which the target engine speed at the time of startup and the rear wheel side distribution ratio are alternatively changed based on the steering angle.

Fig. 11 is a diagram illustrating an example of a scheme in which the target engine rotation speed at the time of start and the rear wheel side distribution ratio are changed based on whether the vehicle is traveling in a curve or a straight line.

Description of reference numerals:

10: a four-wheel drive vehicle is provided with a four-wheel drive,

12: an engine (a driving force source),

14(14L, 14R): a front wheel (an auxiliary driving wheel),

16(16L, 16R): a rear wheel (main driving wheel),

30: a transfer (driving force distribution means),

130: an electronic control device (control device).

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[ example 1]

Fig. 1 is a diagram illustrating a schematic configuration of a four-wheel drive vehicle 10 to which the present invention is applied, and is a diagram illustrating a main portion of a control system for various controls in the four-wheel drive vehicle 10. In fig. 1, a four-wheel drive vehicle 10 is a hybrid vehicle including an engine 12 (see "ENG" in the figure), a first rotary machine MG1, and a second rotary machine MG2 as drive power sources. As described above, the four-wheel drive vehicle 10 is a vehicle provided with a drive power source including at least the engine 12. The four-wheel drive vehicle 10 further includes a pair of left and right front wheels 14L, 14R, a pair of left and right rear wheels 16L, 16R, and a power transmission device 18 that transmits the driving force from the engine 12 and the like to the front wheels 14L, 14R and the rear wheels 16L, 16R, respectively. The rear wheels 16L, 16R are main drive wheels serving as drive wheels in both two-wheel drive running and four-wheel drive running. The front wheels 14L and 14R are sub-drive wheels serving as driven wheels in two-wheel drive running and serving as drive wheels in four-wheel drive running. The four-wheel drive vehicle 10 is a four-wheel drive vehicle based on an FR (front engine/rear drive) type vehicle. In the present embodiment, the front wheels 14L and 14R are referred to as front wheels 14 and the rear wheels 16L and 16R are referred to as rear wheels 16 without making any special distinction. Note that the engine 12, the first rotary machine MG1, and the second rotary machine MG2 are simply referred to as the drive force source PU without being particularly distinguished.

The engine 12 is a driving force source for running of the four-wheel drive vehicle 10, and is a known internal combustion engine such as a gasoline engine or a diesel engine. The engine 12 controls an engine control device 20 including a throttle actuator, a fuel injection device, an ignition device, and the like provided in the four-wheel drive vehicle 10 by an electronic control device 130 described later, thereby controlling an engine torque Te as an output torque of the engine 12.

The first rotary machine MG1 and the second rotary machine MG2 are rotating electric machines having a function as an electric motor (motor) and a function as a generator (generator), and are so-called motor generators. The first rotary machine MG1 and the second rotary machine MG2 are rotary machines that can be driving force sources for running of the four-wheel drive vehicle 10. The first rotary machine MG1 and the second rotary machine MG2 are connected to the battery 24 of the four-wheel drive vehicle 10 via the inverter 22 of the four-wheel drive vehicle 10. The first rotary machine MG1 and the second rotary machine MG2 control the inverter 22 by an electronic control device 130 described later, respectively, to control an MG1 torque Tg as an output torque of the first rotary machine MG1 and an MG2 torque Tm as an output torque of the second rotary machine MG 2. For example, in the case of a positive rotation, the positive torque on the acceleration side is a power running torque, and the negative torque on the deceleration side is a regenerative torque. The battery 24 is a power storage device that exchanges electric power with each of the first rotary machine MG1 and the second rotary machine MG 2. The first rotary machine MG1 and the second rotary machine MG2 are provided in the transmission case 26 as a non-rotating member fitted to the vehicle body.

The power transmission device 18 includes an automatic transmission 28 (see "HV T/M" in the drawings) as a hybrid transmission, a transfer case 30 (see "T/F" in the drawings), a front propeller shaft 32, a rear propeller shaft 34, a front wheel side differential gear device 36 (see "FDiff" in the drawings), a rear wheel side differential gear device 38 (see "RDiff" in the drawings), a pair of left and right front wheel axles 40L, 40R, and a pair of left and right rear wheel axles 42L, 42R. In the power transmission device 18, the driving force from the engine 12 and the like transmitted via the automatic transmission 28 is transmitted from the transfer 30 to the rear wheels 16L, 16R via the rear propeller shaft 34, the rear wheel side differential gear device 38, the rear wheel axles 42L, 42R and the like in this order. Further, in the power transmission device 18, when a part of the driving force from the engine 12 transmitted to the transfer 30 is distributed to the front wheels 14L, 14R side, the distributed driving force is transmitted to the front wheels 14L, 14R via the front propeller shaft 32, the front wheel side differential gear device 36, the front wheel axles 40L, 40R, and the like in this order.

Fig. 2 is a diagram illustrating a schematic configuration of the automatic transmission 28. In fig. 2, the automatic transmission 28 includes an electric continuously variable transmission unit 44, a mechanical step-variable transmission unit 46, and the like, which are arranged in series on a common rotation axis CL1 in the transmission case 26. The electric continuously variable transmission 44 is directly coupled to the engine 12 or indirectly coupled thereto via a damper (damper) or the like (not shown). The mechanical stepped transmission unit 46 is coupled to the output side of the electric continuously variable transmission unit 44. The transfer case 30 is connected to the output side of the mechanical step-variable transmission unit 46. In the automatic transmission 28, the power output from the engine 12, the second rotary machine MG2, and the like is transmitted to the mechanical stepped transmission unit 46, and is transmitted from the mechanical stepped transmission unit 46 to the transfer 30. Hereinafter, the electric continuously variable transmission unit 44 is referred to as a continuously variable transmission unit 44, and the mechanical stepped transmission unit 46 is referred to as a stepped transmission unit 46. In addition, the power is also synonymous with the torque and the force without a special distinction. The continuously variable transmission unit 44 and the step-variable transmission unit 46 are arranged substantially symmetrically with respect to the rotation axis CL1, and the lower half portion is omitted from the rotation axis CL1 in fig. 2. The rotation axis line CL1 is the axial center of the crankshaft of the engine 12, the connecting shaft 48 as an input rotating member of the automatic transmission 28 connected to the crankshaft, the output shaft 50 as an output rotating member of the automatic transmission 28, and the like. The coupling shaft 48 is also an input rotating member of the continuously variable transmission unit 44, and the output shaft 50 is also an output rotating member of the stepped transmission unit 46.

The continuously variable transmission unit 44 includes: a first rotary machine MG 1; and a differential mechanism 54 as a power split mechanism that mechanically distributes the power of the engine 12 to the first rotary machine MG1 and the intermediate transmission member 52 as an output rotating member of the continuously variable transmission portion 44. The second rotary machine MG2 is coupled to the intermediate transmission member 52 so as to be able to transmit power. The continuously variable transmission unit 44 is an electric continuously variable transmission that controls the differential state of the differential mechanism 54 by controlling the operation state of the first rotating machine MG 1. The continuously variable transmission unit 44 operates as an electric continuously variable transmission in which the transmission ratio (also referred to as gear ratio) γ 0 (equal to the engine rotation speed Ne/MG2 rotation speed Nm) is changed. The engine rotation speed Ne is the rotation speed of the engine 12, and is equal to the input rotation speed of the continuously variable transmission unit 44, that is, the rotation speed of the coupling shaft 48. The engine rotation speed Ne is also the input rotation speed of the automatic transmission 28 as a whole in which the continuously variable transmission unit 44 and the stepped transmission unit 46 are combined. The MG2 rotation speed Nm is the rotation speed of the second rotary machine MG2, and is the same as the output rotation speed of the continuously variable transmission unit 44, that is, the value of the rotation speed of the intermediate transmission member 52. The first rotary machine MG1 is a rotary machine capable of controlling the engine rotation speed Ne. The operation control of the first rotary machine MG1 is performed to control the operation state of the first rotary machine MG 1.

The differential mechanism 54 is constituted by a single-pinion planetary gear device, and includes a sun gear S0, a carrier CA0, and a ring gear R0. The engine 12 is power-transmittable coupled to the carrier CA0 via the coupling shaft 48, the first rotary machine MG1 is power-transmittable coupled to the sun gear S0, and the second rotary machine MG2 is power-transmittable coupled to the ring gear R0. In the differential mechanism 54, the carrier CA0 functions as an input element, the sun gear S0 functions as a reaction force element, and the ring gear R0 functions as an output element.

The stepped shift portion 46 is a stepped transmission that constitutes a power transmission path between the intermediate transmission member 52 and the transfer 30. The intermediate transmission member 52 also functions as an input rotating member of the stepped shift portion 46. The second rotary machine MG2 is connected to the intermediate transmission member 52 so as to rotate integrally. The stepped transmission portion 46 is an automatic transmission that constitutes a part of a power transmission path between the drive force source PU for running and the drive wheels (the front wheels 14, the rear wheels 16). The stepped transmission unit 46 is a known planetary gear type automatic transmission including a plurality of sets of planetary gear devices, i.e., the first planetary gear device 56 and the second planetary gear device 58, and a plurality of engagement devices, i.e., a clutch C1, a clutch C2, a brake B1, and a brake B2, including a one-way clutch F1. Hereinafter, the clutch C1, the clutch C2, the brake B1, and the brake B2 are simply referred to as an engagement device CB without being particularly distinguished.

The engagement device CB is a hydraulic friction engagement device including a multi-plate type or single-plate type clutch pressed by a hydraulic actuator, a brake, a band brake pulled by the hydraulic actuator, and the like. In the engagement device CB, the operating states, i.e., the engagement and release states, are switched by the respective hydraulic pressures of the engagement device CB after pressure regulation, which are output from a hydraulic pressure control circuit 60 (see fig. 1) provided in the four-wheel drive vehicle 10.

In the step-variable transmission portion 46, the respective rotary elements of the first planetary gear device 56 and the second planetary gear device 58 are partially coupled to each other directly or indirectly via the engagement device CB and the one-way clutch F1, or are coupled to the intermediate transmission member 52, the transmission case 26, or the output shaft 50. The rotating elements of the first planetary gear device 56 are a sun gear S1, a carrier CA1, and a ring gear R1, and the rotating elements of the second planetary gear device 58 are a sun gear S2, a carrier CA2, and a ring gear R2.

The stepped transmission unit 46 is a stepped transmission that forms any one of a plurality of shift stages (also referred to as "gear stages") having different gear ratios γ AT (AT input rotation speed Ni/output rotation speed No) by engagement of a predetermined engagement device, for example, which is any one of a plurality of engagement devices. That is, the stepped shift portion 46 performs shifting by switching the shift position when any one of the plurality of engagement devices is engaged. The stepped transmission portion 46 is a stepped automatic transmission forming each of a plurality of gears. In the present embodiment, the shift stage formed by the stepped shift portion 46 is referred to as an AT shift stage. The AT input rotation speed Ni is the input rotation speed of the stepped transmission unit 46, which is the rotation speed of the input rotating element of the stepped transmission unit 46, and is the same as the value of the rotation speed of the intermediate transmission element 52 and the value of the MG2 rotation speed Nm. The AT input rotation speed Ni may be represented by the MG2 rotation speed Nm. The output rotation speed No is the rotation speed of the output shaft 50, which is the output rotation speed of the stepped transmission portion 46, and is also the output rotation speed of the automatic transmission 28.

In the stepped shift portion 46, for example, as shown in the engagement operation table of fig. 3, as a plurality of AT gears, AT gears for 4 forward gears of an AT1 speed (a "first gear (1 st)" in the drawing) to an AT4 speed (a "fourth gear (4 th)" in the drawing) are formed. The speed ratio γ AT of the AT1 speed position is the largest, and the speed ratio γ AT is smaller as the AT position is higher. Further, an AT gear for reverse drive ("reverse gear (Rev)" in the drawing) is formed by engagement of the clutch C1 and engagement of the brake B2, for example. That is, when the reverse travel is performed, for example, the AT1 speed is established. The engagement operation table of fig. 3 is a table summarizing the relationship between each AT range and each operation state of the plurality of engagement devices. That is, the engagement operation table in fig. 3 is a table summarizing the relationship between each AT range and a predetermined engagement device that is an engagement device engaged in each AT range. In fig. 3, ". o" indicates engagement, ". Δ" indicates engagement at the time of engine braking or coast down shift of the stepped shift portion 46, and the blank column indicates release.

In the stepped shift portion 46, AT ranges formed in accordance with an acceleration operation by a driver (driver), a vehicle speed Vv, and the like, that is, a plurality of AT ranges are selectively formed, by an electronic control device 130 described later. For example, in the shift control of the stepped shift portion 46, a shift is performed by an engagement switching of any one of the engagement devices CB, that is, a shift is performed by a switching of engagement and release of the engagement devices CB, and a so-called clutch-to-clutch (clutch to clutch) shift is performed.

The four-wheel drive vehicle 10 further includes: a one-way clutch F0, an MOP62 as a mechanical oil pump, an electric oil pump not shown, and the like.

The one-way clutch F0 is a lock mechanism capable of fixing the carrier CA0 to be non-rotatable. That is, the one-way clutch F0 is a lock mechanism capable of fixing the connecting shaft 48, which is connected to the crankshaft of the engine 12 and rotates integrally with the carrier CA0, to the transmission case 26. One of the two relatively rotatable members of the one-way clutch F0 is integrally connected to the connecting shaft 48, and the other member is integrally connected to the transmission case 26. The one-way clutch F0 idles in the normal rotation direction which is the rotation direction during operation of the engine 12, and mechanically and automatically engages in the rotation direction opposite to the rotation direction during operation of the engine 12. Therefore, during idling of the one-way clutch F0, the engine 12 is set to a state in which it can rotate relative to the transmission case 26. On the other hand, when the one-way clutch F0 is engaged, the engine 12 is set in a state where relative rotation with respect to the transmission case 26 is disabled. That is, the engine 12 is fixed to the transmission case 26 by engagement of the one-way clutch F0. Thus, the one-way clutch F0 allows rotation of the carrier CA0 in the normal rotation direction, which is the rotation direction during operation of the engine 12, and prevents rotation of the carrier CA0 in the reverse rotation direction. That is, the one-way clutch F0 is a lock mechanism that can permit rotation of the engine 12 in the normal rotation direction and prevent rotation in the reverse rotation direction.

The MOP62 is coupled to the coupling shaft 48, rotates together with the rotation of the engine 12, and discharges the hydraulic OIL used in the power transmission device 18. Note that, for example, an electric oil pump not shown is driven when the engine 12 is stopped, that is, when the MOP62 is not driven. The hydraulic control circuit 60 is supplied with operating OIL discharged from an MOP62 or an electric OIL pump not shown. The hydraulic OIL is regulated to each hydraulic pressure of the engagement device CB by the hydraulic control circuit 60, and is supplied to the power transmission device 18 (see fig. 1).

Fig. 4 is a collinear chart showing the relative relationship of the rotation speeds of the respective rotating elements in the continuously variable transmission portion 44 and the stepped transmission portion 46. In fig. 4, three vertical lines Y1, Y2, and Y3 corresponding to the three rotational elements constituting the differential mechanism 54 of the continuously variable transmission portion 44 are, in order from the left: the g-axis indicating the rotation speed of the sun gear S0 corresponding to the second rotating element RE2, the e-axis indicating the rotation speed of the carrier CA0 corresponding to the first rotating element RE1, and the m-axis indicating the rotation speed of the ring gear R0 corresponding to the third rotating element RE3 (i.e., the input rotation speed of the stepped transmission unit 46). The four vertical lines Y4, Y5, Y6, and Y7 of the stepped shift portion 46 are, in order from the left: a shaft indicating the rotational speed of the sun gear S2 corresponding to the fourth rotary element RE4, a shaft indicating the rotational speeds of the ring gear R1 and the carrier CA2 coupled to each other corresponding to the fifth rotary element RE5 (i.e., the rotational speed of the output shaft 50), a shaft indicating the rotational speeds of the carrier CA1 and the ring gear R2 coupled to each other corresponding to the sixth rotary element RE6, and a shaft indicating the rotational speed of the sun gear S1 corresponding to the seventh rotary element RE 7. The mutual intervals of the vertical lines Y1, Y2, and Y3 are determined according to the gear ratio ρ 0 of the differential mechanism 54. Further, the mutual intervals of the vertical lines Y4, Y5, Y6, Y7 are determined according to the gear ratios ρ 1, ρ 2 of the first planetary gear device 56 and the second planetary gear device 58, respectively. In the relationship between the vertical axes of the collinear chart, when the sun gear and the carrier are spaced apart from each other by an interval corresponding to "1", the carrier and the ring gear are spaced apart from each other by an interval corresponding to the gear ratio ρ (═ the number of teeth of the sun gear/the number of teeth of the ring gear) of the planetary gear device.

If expressed using the collinear chart of fig. 4, the differential mechanism 54 of the continuously variable transmission portion 44 is configured such that: the engine 12 (see "ENG" in the figure) is coupled to the first rotating element RE1, the first rotary machine MG1 (see "MG 1" in the figure) is coupled to the second rotating element RE2, and the second rotary machine MG2 (see "MG 2" in the figure) is coupled to the third rotating element RE3 that rotates integrally with the intermediate transmission member 52, and transmits the rotation of the engine 12 to the stepped transmission 46 via the intermediate transmission member 52. In the continuously variable transmission unit 44, the relationship between the rotation speed of the sun gear S0 and the rotation speed of the ring gear R0 is indicated by respective straight lines L0e, L0m, and L0R that cross the vertical line Y2.

Further, in the step-variable transmission 46, the fourth rotating element RE4 is selectively linked to the intermediate transmission member 52 via a clutch C1, the fifth rotating element RE5 is linked to the output shaft 50, the sixth rotating element RE6 is selectively linked to the intermediate transmission member 52 via a clutch C2 and is selectively linked to the transmission case 26 via a brake B2, and the seventh rotating element RE7 is selectively linked to the transmission case 26 via a brake B1. In the stepped shift portion 46, the rotation speeds of the "first gear", "second gear", "third gear", "fourth gear", and "reverse gear" in the output shaft 50 are indicated by respective straight lines L1, L2, L3, L4, and LR crossing the vertical line Y5 in accordance with the engagement release control of the engagement device CB.

The straight line L0e and the straight lines L1, L2, L3, and L4 indicated by solid lines in fig. 4 show the relative speeds of the respective rotary elements during forward running in the HV running mode in which hybrid running (HV running) is possible in which at least the engine 12 is used as a drive power source. In this HV running mode, when the negative torque generated by the first rotary machine MG1, that is, the MG1 torque Tg that is a reaction torque, is input to the sun gear S0 with respect to the engine torque Te that is a positive torque input to the carrier CA0 in the differential mechanism 54, an engine direct torque Td that becomes a positive torque in the form of a positive rotation (Te/(1 + ρ 0) — (1/ρ 0) × Tg) appears in the ring gear R0. Then, in accordance with the requested driving force, the total torque of the engine direct torque Td and the MG2 torque Tm is transmitted to the transfer 30 as a driving torque in the forward direction of the four-wheel drive vehicle 10 via the stepped transmission portion 46 in which any AT range from the AT1 speed range to the AT4 speed range is formed. The first rotary machine MG1 functions as a generator when generating negative torque in the positive rotation. The generated electric power Wg of the first rotary machine MG1 is charged to the battery 24, or consumed by the second rotary machine MG 2. The second rotary machine MG2 outputs MG2 torque Tm using all or part of the generated electric power Wg, or using electric power from the battery 24 in addition to the generated electric power Wg.

A straight line L0m indicated by a one-dot chain line in fig. 4 and straight lines L1, L2, L3, and L4 indicated by a solid line in fig. 4 show the relative speeds of the respective rotary elements in forward running in the EV running mode in which the motor running with at least one of the first rotary machine MG1 and the second rotary machine MG2 as the drive power source is possible (EV running) with the operation of the engine 12 stopped. The EV running during the forward running in the EV running mode includes, for example, single-drive EV running in which running is performed using only the second rotary machine MG2 as a drive power source, and dual-drive EV running in which running is performed using both the first rotary machine MG1 and the second rotary machine MG2 as drive power sources. During the single-drive EV running, carrier CA0 is set to zero rotation, and MG2 torque Tm that is positive torque in the form of normal rotation is input to ring gear R0. At this time, the first rotary machine MG1 coupled to the sun gear S0 is in a no-load state and idles in reverse. In the single-drive EV running, the one-way clutch F0 is released, and the coupling shaft 48 is not fixed to the transmission case 26.

In the dual-drive EV running, when MG1 torque Tg which is a negative torque in reverse rotation is input to sun gear S0 in a state where carrier CA0 is set to rotate at zero, one-way clutch F0 is automatically engaged, and rotation of carrier CA0 in the reverse direction is prevented. In a state where carrier CA0 is fixed to be non-rotatable by engagement of one-way clutch F0, reaction torque generated by MG1 torque Tg is input to ring gear R0. In the dual-drive EV running, MG2 torque Tm is input to the ring gear R0, similarly to the single-drive EV running. If MG2 torque Tm is not input when MG1 torque Tg that becomes negative torque in reverse rotation is input to sun gear S0 with carrier CA0 set to zero rotation, single-drive EV running by MG1 torque Tg is also possible. During forward running in the EV running mode, the engine 12 is not driven, the engine rotation speed Ne is set to zero, and AT least one of the MG1 torque Tg and the MG2 torque Tm is transmitted to the transfer 30 as a drive torque in the forward direction of the four-wheel drive vehicle 10 via the stepped transmission portion 46 in which any AT range from the AT1 speed range to the AT4 speed range is formed. During forward running in the EV running mode, MG1 torque Tg is reverse rotation and negative torque power running torque, and MG2 torque Tm is positive rotation and positive torque power running torque.

A straight line L0R and a straight line LR indicated by broken lines in fig. 4 show the relative speeds of the respective rotating elements in the reverse travel in the EV travel mode. During reverse travel in the EV travel mode, MG2 torque Tm, which is negative torque in reverse rotation, is input to the ring gear R0, and this MG2 torque Tm is transmitted to the transfer 30 as drive torque in the reverse direction of the four-wheel drive vehicle 10 via the stepped transmission unit 46 in which the AT1 speed stage is formed. In the four-wheel drive vehicle 10, reverse travel is possible by outputting the MG2 torque Tm for reverse travel, which is opposite in sign to the MG2 torque Tm for forward travel, from the second rotary machine MG2 in a state where, for example, an AT1 speed range, which is a low-range AT range for forward travel, is formed among a plurality of AT ranges by the electronic control device 130 described later. In the reverse travel in the EV travel mode, MG2 torque Tm is a power running torque that is reversed and negative. In the HV travel mode, the second rotary machine MG2 can be reversed as indicated by a straight line L0R, and therefore reverse travel can be performed in the same manner as in the EV travel mode.

Fig. 5 is a skeleton diagram illustrating the structure of the transfer case 30. The transfer case 30 includes a transfer case 64 as a non-rotating member. The transfer case 30 includes a rear wheel-side output shaft 66, a front wheel-driving drive gear 68, and a front wheel-driving clutch 70 in the transfer case 64 around a common rotation axis CL 1. The transfer case 30 includes a front wheel-side output shaft 72 and a front wheel-driving driven gear 74 in the transfer case 64 about a common rotation axis CL 2. The transfer case 30 includes a front wheel drive idle gear 76. The rotation axis CL2 is the axial center of the front propeller shaft 32, the front wheel-side output shaft 72, and the like.

The rear wheel-side output shaft 66 is coupled to the output shaft 50 so as to be capable of transmitting power, and is coupled to the rear propeller shaft 34 so as to be capable of transmitting power. The rear wheel-side output shaft 66 outputs the driving force transmitted from the driving force source PU to the output shaft 50 via the automatic transmission 28 to the rear wheels 16. The output shaft 50 also functions as an input rotating member of the transfer 30 that inputs the driving force from the driving force source PU to the rear wheel-side output shaft 66 of the transfer 30, that is, as a driving force transmission shaft that transmits the driving force from the driving force source PU to the transfer 30. The automatic transmission 28 is an automatic transmission that transmits the driving force from the driving force source PU to the output shaft 50.

The front wheel driving drive gear 68 is provided to be rotatable relative to the rear wheel side output shaft 66. The front wheel driving clutch 70 is a multi-plate wet clutch, and adjusts the transmission torque transmitted from the rear wheel output shaft 66 to the front wheel driving drive gear 68. That is, the front wheel driving clutch 70 adjusts the transmission torque transmitted from the rear wheel side output shaft 66 to the front wheel side output shaft 72.

The front wheel driving driven gear 74 is integrally provided on the front wheel side output shaft 72, and is connected to the front wheel side output shaft 72 so as to be capable of transmitting power. The front wheel driving idle gear 76 meshes with the front wheel driving drive gear 68 and the front wheel driving driven gear 74, respectively, and is coupled between the front wheel driving drive gear 68 and the front wheel driving driven gear 74 so as to be capable of transmitting power.

The front wheel-side output shaft 72 is coupled to the front wheel-driving drive gear 68 via a front wheel-driving idle gear 76 and a front wheel-driving driven gear 74 so as to be capable of power transmission, and is coupled to the front propeller shaft 32 so as to be capable of power transmission. The front wheel-side output shaft 72 outputs a part of the driving force from the driving force source PU, which is transmitted to the front wheel-driving drive gear 68 via the front wheel-driving clutch 70, to the front wheels 14.

The front wheel drive clutch 70 includes a clutch hub 78, a clutch drum 80, a frictional engagement element 82, and a piston 84. The clutch hub 78 is coupled to the rear wheel side output shaft 66 so as to be capable of transmitting power. The clutch drum 80 is coupled to the front wheel drive gear 68 so as to be capable of transmitting power. The frictional engagement element 82 has: a plurality of first friction plates 82a provided so as to be movable relative to the clutch hub 78 in the direction of the rotation axis line CL1 and so as to be incapable of relative rotation with respect to the clutch hub 78; and a plurality of second friction plates 82b provided so as to be movable relative to the clutch drum 80 in the direction of the rotation axis line CL1 and so as not to be rotatable relative to the clutch drum 80. The first friction plates 82a and the second friction plates 82b are arranged so as to alternately overlap in the direction of the rotation axis CL 1. The piston 84 is provided to be movable in the direction of the rotation axis CL1, and abuts against the frictional engagement element 82 to press the first friction plate 82a and the second friction plate 82b, thereby adjusting the torque capacity of the front wheel drive clutch 70. When the piston 84 does not press the frictional engagement element 82, the torque capacity of the front wheel driving clutch 70 becomes zero, and the front wheel driving clutch 70 is released.

The transfer 30 distributes the driving force of the driving force source PU transmitted via the automatic transmission 28 to the rear wheel-side output shaft 66 and the front wheel-side output shaft 72 by adjusting the torque capacity of the front wheel driving clutch 70. When the front wheel driving clutch 70 is released, the power transmission path between the rear wheel-side output shaft 66 and the front wheel driving drive gear 68 is cut off, and therefore the transfer 30 transmits the driving force transmitted from the driving force source PU to the transfer 30 via the automatic transmission 28 to the rear wheels 16 via the rear propeller shaft 34 and the like. Further, when the front wheel driving clutch 70 is in the slip engaged state or the fully engaged state, the power transmission path between the rear wheel-side output shaft 66 and the front wheel driving drive gear 68 is connected, so the transfer 30 transmits a part of the driving force transmitted from the driving force source PU via the transfer 30 to the front wheels 14 via the front propeller shaft 32 or the like, and transmits the remaining part of the driving force to the rear wheels 16 via the rear propeller shaft 34 or the like. The transfer 30 is a drive force distribution device that can transmit the drive force from the drive force source PU to the front wheels 14 and the rear wheels 16.

The transfer case 30 includes an electric motor 86, a worm gear 88, and a cam mechanism 90 as a device for operating the front wheel drive clutch 70.

The worm gear 88 is a gear pair including a worm 92 formed integrally with the motor shaft of the electric motor 86 and a worm wheel 94 formed with teeth meshing with the worm 92. The worm wheel 94 is provided to be rotatable around a rotation axis CL 1. When the electric motor 86 rotates, the worm wheel 94 rotates about the rotation axis CL 1.

The cam mechanism 90 is provided between the worm wheel 94 and the piston 84 of the front wheel driving clutch 70. The cam mechanism 90 includes: a first member 96 connected to the worm gear 94; a second member 98 connected to the piston 84; and a plurality of balls 99 interposed between the first member 96 and the second member 98, and the cam mechanism 90 is a mechanism for converting the rotational motion of the electric motor 86 into a linear motion.

The plurality of balls 99 are arranged at equal angular intervals in the rotational direction around the rotation axis CL 1. Cam grooves are formed in the surfaces of the first member 96 and the second member 98 that contact the balls 99, respectively. Each cam groove is formed so that the first member 96 and the second member 98 are separated from each other in the direction of the rotation axis CL1 in the case where the first member 96 is relatively rotated with respect to the second member 98. Therefore, when the first member 96 is relatively rotated with respect to the second member 98, the first member 96 and the second member 98 are separated from each other, the second member 98 moves in the direction of the rotation axis CL1, and the piston 84 connected to the second member 98 pushes the frictional engagement element 82. When the worm wheel 94 is rotated by the electric motor 86, the rotational motion of the worm wheel 94 is converted into a linear motion in the direction of the rotation axis CL1 via the cam mechanism 90 and transmitted to the piston 84, so that the piston 84 presses the frictional engagement element 82. The torque capacity of the front wheel drive clutch 70 is adjusted by adjusting the pressing force with which the piston 84 presses the frictional engagement element 82. The transfer 30 can adjust the driving force distribution ratio Rx, which is the ratio of the driving force from the driving force source PU distributed between the front wheels 14 and the rear wheels 16, by adjusting the torque capacity of the front wheel driving clutch 70.

The driving force distribution ratio Rx is, for example, the ratio of the driving force transmitted from the driving force source PU to the rear wheels 16 to the total driving force transmitted from the driving force source PU to the rear wheels 16 and the front wheels 14, that is, the rear wheel side distribution ratio Xr. Alternatively, the driving force distribution ratio Rx is, for example, the ratio of the driving force transmitted from the driving force source PU to the front wheels 14 to the total driving force transmitted from the driving force source PU to the rear wheels 16 and the front wheels 14, that is, the front wheel side distribution ratio Xf (═ 1-Xr). In the present embodiment, the rear wheels 16 are main driving wheels, and therefore as the driving force distribution ratio Rx, a rear wheel-side distribution ratio Xr as a main side distribution ratio is used.

When piston 84 does not press frictional engagement element 82, the torque capacity of front wheel drive clutch 70 is zero. At this time, the front wheel driving clutch 70 is released, and the rear wheel side distribution ratio Xr becomes 1.0. In other words, if the total driving force is 100 and the distribution of the driving forces to the front wheels 14 and the rear wheels 16, that is, the distribution of the driving forces to the front and rear wheels is expressed by "the driving force of the front wheels 14 to the driving force of the rear wheels 16", the distribution of the driving forces to the front and rear wheels becomes 0: 100. On the other hand, when the piston 84 presses the frictional engagement element 82, the torque capacity of the front wheel driving clutch 70 becomes larger than zero, and the rear wheel side distribution ratio Xr decreases as the torque capacity of the front wheel driving clutch 70 increases. When the front wheel driving clutch 70 has a torque capacity of being fully engaged, the rear wheel side split ratio Xr becomes 0.5. In other words, the driving force distribution of the front and rear wheels becomes balanced at 50: 50. In this way, the transfer case 30 can adjust the rear wheel side distribution ratio Xr between 1.0 and 0.5, that is, the driving force distribution of the front and rear wheels between 0: 100 and 50: 50 by adjusting the torque capacity of the front wheel driving clutch 70. That is, the transfer 30 can be switched between a two-wheel drive state in which the driving force from the driving force source PU is transmitted only to the rear wheels 16 and a four-wheel drive state in which the driving force from the driving force source PU is transmitted to the rear wheels 16 and the front wheels 14.

Returning to fig. 1, the four-wheel drive vehicle 10 includes a wheel brake device 100. The wheel brake device 100 includes a wheel brake 101, a brake master cylinder not shown, and the like, and applies a braking force generated by the wheel brake 101 to each of the wheels 14 and 16 of the front wheel 14 and the rear wheel 16. The wheel brakes 101 are front brakes 101FL, 101FR provided to each of the front wheels 14L, 14R and rear brakes 101RL, 101RR provided to each of the rear wheels 16L, 16R. The wheel brake device 100 supplies brake fluid pressure to wheel cylinders, not shown, provided in the wheel brakes 101, respectively, in response to, for example, a depression operation of a brake pedal by a driver. In the wheel brake device 100, the master cylinder hydraulic pressure having a magnitude corresponding to the brake operation amount Bra generated from the master cylinder is supplied to the wheel cylinder as the brake hydraulic pressure in the normal state. On the other hand, in the wheel Brake device 100, for example, at the time of ABS (anti-Lock Brake System) control, at the time of sideslip suppression control, at the time of vehicle speed control, or the like, Brake fluid pressure required for each control is supplied to the wheel cylinders to generate braking force by the wheel brakes 101. The brake operation amount Bra is a signal indicating the magnitude of the depression operation of the brake pedal by the driver according to the depression force of the brake pedal. In this manner, the wheel braking device 100 can adjust the braking force generated by the wheel brake 101 that is applied to each of the wheels 14, 16.

The four-wheel drive vehicle 10 is provided with an electronic control device 130 as a controller, and the electronic control device 130 includes a control device of the four-wheel drive vehicle 10 that controls the drive force source PU, the transfer case 30, and the like. Fig. 1 is a diagram showing an input/output system of the electronic control device 130, and is a functional block diagram illustrating a main part of a control function realized by the electronic control device 130. The electronic control device 130 is configured to include, for example, a so-called microcomputer provided with a CPU that performs signal processing using a temporary storage function of the RAM and in accordance with a program stored in advance in the ROM, a RAM, a ROM, an input-output interface, and the like, thereby executing various controls of the four-wheel drive vehicle 10. The electronic control device 130 is configured as various computers including an engine control computer, a shift control computer, and the like as necessary.

Various signals based on detection values obtained by various sensors and the like (for example, the engine rotation speed Ne, the output rotation speed sensor 102, the output rotation speed sensor 104, the MG1 rotation speed sensor 106, the MG2 rotation speed sensor 108, the wheel speed sensor 110, the accelerator opening degree sensor 112, the throttle opening degree sensor 114, the brake pedal sensor 116, the G sensor 118, the shift position sensor 120, the yaw rate sensor 122, the steering sensor 124, the battery sensor 126, the oil temperature sensor 128 and the like) provided in the four-wheel drive vehicle 10 (for example, the engine rotation speed Ne, the output rotation speed No corresponding to the vehicle speed Vv, the MG1 rotation speed Ng as the rotation speed of the first rotary machine MG1, the MG2 rotation speed Nm as the same value as the AT input rotation speed Ni, the wheel speed Nr as the rotation speeds of the respective wheels 14 and 16, the accelerator opening degree θ acc as the accelerator operation amount of the driver indicating the magnitude of the accelerator operation of the driver), and the like are supplied to the electronic control device 130, respectively, A throttle opening degree θ th that is an opening degree of an electronic throttle valve, a brake on signal Bon that is a signal indicating a state in which a brake pedal for operating the wheel brake 101 is being operated by a driver, a brake operation amount Bra, a front-rear acceleration Gx and a left-right acceleration Gy of the four-wheel drive vehicle 10, an operation position POSsh of a shift lever provided to the four-wheel drive vehicle 10, a yaw angular velocity Vyaw that is a change speed of a vehicle rotation angle around a vertical axis passing through a center of gravity of the four-wheel drive vehicle 10, a steering angle θ sw and a steering direction Dsw of a steering wheel provided to the four-wheel drive vehicle 10, a battery temperature THbat of the battery 24, a battery charge-discharge current Ibat, a battery voltage Vbat, an operating OIL temperature THoil that is a temperature of the operating OIL, and the like).

The accelerator operation amount by the driver is an accelerator operation amount that is an operation amount of an accelerator operation member such as an accelerator pedal, for example, and is an output request amount of the four-wheel drive vehicle 10 by the driver. As the output request amount of the driver, in addition to the accelerator opening degree θ acc, a throttle opening degree θ th or the like may be used.

Various command signals (for example, an engine control command signal Se for controlling the engine 12, a rotating machine control command signal Smg for controlling the first rotating machine MG1 and the second rotating machine MG2, a hydraulic control command signal Sat for controlling the operating state of the engagement device CB, an electric motor control command signal Sw for controlling the electric motor 86, a brake control command signal Sb for controlling the braking force generated by the wheel brake 101, and the like) are output from the electronic control device 130 to the respective devices (for example, the engine control command signal Sat, the hydraulic control circuit 60, the electric motor 86, the wheel brake device 100, and the like) included in the four-wheel drive vehicle 10.

The electronic control device 130 includes an AT shift control unit 132 serving as an AT shift control unit, a hybrid control unit 134 serving as a hybrid control unit, and a four-wheel drive control unit 136 serving as a four-wheel drive control unit, in order to realize various controls in the four-wheel drive vehicle 10.

The AT shift control unit 132 performs a shift determination of the stepped shift portion 46 using, for example, an AT range shift map shown in fig. 6, which is a predetermined relationship that is a relationship obtained and stored experimentally or by design in advance, and outputs a hydraulic control command signal Sat for executing a shift control of the stepped shift portion 46 to the hydraulic control circuit 60 as necessary. The AT range shift map is a predetermined relationship having a shift line for determining a shift of the stepped shift portion 46 on two-dimensional coordinates with the vehicle speed Vv and the requested driving force Frdem as variables. Here, the output rotation speed No or the like may be used instead of the vehicle speed Vv. Instead of the requested driving force Frdem, the requested driving torque Trdem, the accelerator opening degree θ acc, the throttle opening degree θ th, and the like may be used. Each shift line in the AT range shift map is an upshift line for determining an upshift as indicated by a solid line and a downshift line for determining a downshift as indicated by a broken line.

The hybrid control unit 134 includes a function as an engine control unit that controls the operation of the engine 12, that is, an engine control unit 134a, and a function as a rotary machine control unit that controls the operations of the first rotary machine MG1 and the second rotary machine MG2 via the inverter 22, that is, a rotary machine control unit 134b, and the hybrid control unit 134 executes hybrid drive control and the like by the engine 12, the first rotary machine MG1, and the second rotary machine MG2 by these control functions.

The hybrid control unit 134 calculates a requested driving force Frdem, which is a driving request amount, by applying the accelerator opening θ acc and the vehicle speed Vv to, for example, a driving request amount map, which is a predetermined relationship. As the drive request amount, in addition to the requested drive force Frdem [ N ], the requested drive torque Trdem [ Nm ] in each drive wheel (front wheel 14, rear wheel 16), the requested drive power Prdem [ W ] in each drive wheel, the requested AT output torque in the output shaft 50, and the like can be used. The hybrid control unit 134 outputs an engine control command signal Se as a command signal for controlling the engine 12 and a rotary machine control command signal Smg as command signals for controlling the first rotary machine MG1 and the second rotary machine MG2 so as to realize a requested drive power Prdem based on the requested drive torque Trdem and the vehicle speed Vv, taking into account the chargeable electric power Win, the dischargeable electric power Wout, and the like of the battery 24. The engine control command signal Se is, for example, a command value of an engine power Pe, which is the power of the engine 12 that outputs the engine torque Te at the engine rotation speed Ne at that time. The rotary machine control command signal Smg is, for example, a command value of the generated power Wg of the first rotary machine MG1 that outputs the MG1 torque Tg at the MG1 rotation speed Ng at the time of command output as the reaction torque of the engine torque Te, and a command value of the consumed power Wm of the second rotary machine MG2 that outputs the MG2 torque Tm at the MG2 rotation speed Nm at the time of command output.

The chargeable power Win of the battery 24 is the maximum power that can be input, which defines the limit of the input power of the battery 24, and indicates the input limit of the battery 24. The dischargeable power Wout of the battery 24 is a maximum power that can be output and that defines a limit on the output power of the battery 24, and indicates the output limit of the battery 24. Chargeable electric power Win and dischargeable electric power Wout of battery 24 are calculated by electronic control device 130, for example, based on battery temperature THbat and state of charge value SOC [% ] of battery 24. The state-of-charge value SOC of the battery 24 is a value indicating a state of charge corresponding to the amount of charge of the battery 24, and is calculated by the electronic control device 130 based on the battery charge/discharge current Ibat, the battery voltage Vbat, and the like, for example.

For example, when the continuously variable transmission unit 44 is operated as a continuously variable transmission and the entire automatic transmission 28 is operated as a continuously variable transmission, the hybrid control unit 134 controls the engine 12 so as to obtain the engine rotation speed Ne and the engine torque Te that achieve the engine power Pe of the requested drive power Prdem and controls the generated power Wg of the first rotary machine MG1 in consideration of the optimum engine operating point or the like, thereby executing the continuously variable transmission control of the continuously variable transmission unit 44 and changing the gear ratio γ 0 of the continuously variable transmission unit 44. As a result of this control, the transmission ratio γ t (═ γ 0 × γ at ═ Ne/No) of the automatic transmission 28 when operating as a continuously variable transmission is controlled. The optimum engine operating point is determined in advance as an engine operating point at which the total fuel efficiency of the four-wheel drive vehicle 10 becomes optimum, taking into account the charge-discharge efficiency of the battery 24 in addition to the fuel efficiency of the engine 12 alone, for example, when the requested engine power Pedem is achieved. The engine operating point is an operating point of the engine 12 represented by the engine rotational speed Ne and the engine torque Te. The engine speed Ne at the optimum engine operating point is the optimum engine speed Neb at which the energy efficiency in the four-wheel drive vehicle 10 becomes optimum.

For example, when the continuously variable transmission unit 44 is shifted like a stepped transmission and the entire automatic transmission 28 is shifted like a stepped transmission, the hybrid control unit 134 performs a shift determination of the automatic transmission 28 using, for example, a stepped shift map which is a predetermined relationship, and performs shift control of the continuously variable transmission unit 44 in such a manner that a plurality of shift stages having different gear ratios γ t are selectively established in cooperation with shift control of the AT shift stage of the stepped transmission unit 46 by the AT shift control unit 132. The first rotary machine MG1 can control the engine rotation speed Ne based on the output rotation speed No, thereby establishing a plurality of shift positions so that the respective gear ratios γ t can be maintained.

Hybrid control unit 134 selectively establishes the EV running mode or the HV running mode as the running mode according to the running state. For example, hybrid control unit 134 establishes the EV running mode when the requested drive power Prdem is in the EV running range in which the requested drive power Prdem is smaller than the predetermined threshold value, and establishes the HV running mode when the requested drive power Prdem is in the HV running range in which the requested drive power Prdem is equal to or greater than the predetermined threshold value. A dashed-dotted line a in fig. 6 is a boundary line between the HV travel region and the EV travel region for switching between the HV travel mode and the EV travel mode. The predetermined relationship having the boundary line shown by the one-dot chain line a in fig. 6 is an example of a running mode switching map configured in two-dimensional coordinates with the vehicle speed Vv and the requested driving force Frdem as variables. Note that, in fig. 6, this traveling mode switching map is shown together with the AT range shift map for convenience.

When the requested drive power Prdem can be realized only by the second rotating machine MG2 when the EV running mode is established, the hybrid control unit 134 causes the four-wheel drive vehicle 10 to run in the single-drive EV running mode by the second rotating machine MG 2. On the other hand, when the requested drive power Prdem cannot be realized only by the second rotary machine MG2 when the EV running mode is established, the hybrid control unit 134 causes the four-wheel drive vehicle 10 to run in the double-drive EV running mode. Even when the requested drive power Prdem can be realized by only the second rotary machine MG2, the hybrid control unit 134 can cause the four-wheel drive vehicle 10 to travel in the double-drive EV travel when the first rotary machine MG1 and the second rotary machine MG2 are used in combination with each other more efficiently than when the second rotary machine MG2 is used alone.

Even when the requested drive power Prdem is in the EV running region, the hybrid control portion 134 establishes the HV running mode in a case where the state of charge value SOC of the battery 24 is smaller than a predetermined engine start threshold value, or in a case where warm-up of the engine 12 is required, or the like. The engine start threshold is a predetermined threshold for determining the state of charge value SOC at which it is necessary to automatically start the engine 12 to charge the battery 24.

The hybrid control unit 134 functionally includes a start control unit 134c that is start control means for performing automatic start control CTst for automatically starting the engine 12 when a predetermined start condition RMst is satisfied. The predetermined start condition RMst is, for example, a case where the HV running mode is established when the operation of the engine 12 is stopped, a case where the vehicle is reset from a known idle stop control, or the like, and the idle stop control is a control for temporarily stopping the engine 12 by stopping the four-wheel drive vehicle 10 when the engine 12 is operated in the HV running mode. The start control unit 134c determines whether or not the predetermined start condition RMst is satisfied, and determines that a request to start the engine 12 is made when determining that the predetermined start condition RMst is satisfied. When it is determined that there is a request to start the engine 12, the start control unit 134c performs the automatic start control CTst.

When the automatic start control CTst is performed, the start control unit 134c increases the engine rotation speed Ne by the first rotary machine MG1, for example, and performs fuel supply to the engine 12 and ignition of the engine 12 when the engine rotation speed Ne becomes equal to or higher than a predetermined ignitable rotation speed Neigf, thereby rotating the engine 12 by itself. The prescribed ignitable rotation speed Neigf is a predetermined engine rotation speed Ne at which the engine 12 can rotate by itself after the initial explosion and is completely exploded, for example. After the engine 12 has exploded and the combustion has stabilized, the start control unit 134c controls the engine rotation speed Ne to a target engine rotation speed Netgt, which is a target value of the engine rotation speed Ne, and completes a series of automatic start control CTst. The target engine speed Netgt after completion of the explosion of the engine 12 in the automatic start control CTst is a predetermined start-time engine speed Nestf predetermined such as an optimum engine speed Neb and an idle stop speed Neidl. In the present embodiment, the target engine speed Netgt after the completion of the explosion of the engine 12 in the automatic start control CTst is referred to as the start-time target engine speed Nesttgt.

The hybrid control unit 134 functionally includes a stop control unit 134d that is stop control means for performing automatic stop control CTsp for automatically stopping the engine 12 when a predetermined stop condition RMsp is satisfied. The predetermined stop condition RMsp is, for example, a case where the EV running mode is established when the engine 12 is operated, a case where the idle stop control is performed by stopping the four-wheel drive vehicle 10 when the engine 12 is operated in the HV running mode, or the like. The stop control unit 134d determines whether or not a predetermined stop condition RMsp is satisfied, and determines that a request to stop the engine 12 is made when determining that the predetermined stop condition RMsp is satisfied. When it is determined that there is a request to stop the engine 12, the stop control unit 134d performs automatic stop control CTsp.

The stop control unit 134d stops the fuel supply to the engine 12 when the automatic stop control CTsp is performed. At this time, the stop control unit 134d may control the MG1 torque Tg so as to rapidly decrease the engine rotation speed Ne and stop the rotation of the engine 12, for example, by applying a torque to the engine 12 to decrease the engine rotation speed Ne.

The four-wheel drive control section 136 performs drive force distribution control CTx that adjusts the rear wheel side distribution ratio Xr. The four-wheel drive control unit 136 sets a target value of the rear-wheel-side distribution ratio Xr according to the running state of the four-wheel drive vehicle 10 determined from the output rotation speed sensor 104, the G sensor 118, and the like, and outputs the electric motor control command signal Sw for controlling the electric motor 86 so that the rear-wheel-side distribution ratio Xr is adjusted to the target value by adjusting the torque capacity of the front-wheel-drive clutch 70.

The four-wheel drive control unit 136 controls the rear-wheel side split ratio Xr to 1.0 (i.e., controls the driving force distribution of the front and rear wheels to 0: 100) by releasing the front-wheel drive clutch 70 during, for example, straight traveling. The four-wheel drive control unit 136 calculates a target yaw rate Vyawtgt based on the steering angle θ sw during turning and the vehicle speed Vv, and adjusts the rear-wheel-side distribution ratio Xr so that the yaw rate Vyaw detected at any time by the yaw rate sensor 122 follows the target yaw rate Vyawtgt.

The power transmission device 18 has a resonance rotation speed Nx predetermined based on, for example, the mass m, the torsional rigidity k, and the like. On the other hand, in the four-wheel drive vehicle 10, the rear-wheel-side distribution ratio Xr is adjusted between 1.0 and 0.5, that is, the driving force distribution of the front and rear wheels is adjusted between 0: 100 and 50: 50. That is, in the four-wheel drive vehicle 10, the power transmission path, i.e., the drive system, to which the engine 12 in the power transmission device 18 is connected in a power transmittable manner varies depending on the rear wheel side distribution ratio Xr. Therefore, in the four-wheel drive vehicle 10, the mass m and the torsional rigidity k of the drive system change according to the rear-wheel side distribution ratio Xr, and the resonance rotation speed Nx of the drive system changes according to the rear-wheel side distribution ratio Xr. Thus, in the four-wheel drive vehicle 10, when the automatic start control CTst is performed, resonance of the drive system occurs due to torque variation of the engine 12, vibration of the drive system tends to increase, and NV tends to deteriorate. In the automatic start control CTst, the resonance of the drive system that occurs when the target engine rotation speed Nesttgt at the time of start is maintained at or near the resonance rotation speed Nx of the drive system is more likely to be a problem than the resonance of the drive system that occurs when the engine rotation speed Ne in the rising process passes through the resonance rotation speed Nx of the drive system. In the present embodiment, the target engine speed Nesttgt at startup is given as the frequency of torque variation of the engine 12 in which resonance of the drive system becomes a problem. The resonance rotation speed Nx of the drive system is a value of a rotation speed of the drive system at which resonance of the drive system occurs, and is, for example, an input rotation speed of the power transmission device 18 corresponding to the rotation speed of the coupling shaft 48 and the engine rotation speed Ne. In the case where the rotational speed of the drive system is always substantially equal to the engine rotational speed Ne, it can be interpreted that the resonance rotational speed Nx of the drive system is also the resonance rotational speed Nx of the engine 12, that is, the value of the engine rotational speed Ne at which the resonance of the drive system occurs.

Therefore, when the automatic start control CTst is performed, the start control unit 134c changes the start target engine speed Nesttgt from the predetermined start engine speed Nestf based on the rear wheel side distribution ratio Xr. The start control unit 134c sets the start-time target engine speed Nesttgt to a speed that is separated from the resonance speed Nx of the drive system.

The electronic control device 130 further includes a vehicle state acquisition unit 138 that is vehicle state acquisition means for realizing the four-wheel drive vehicle 10 that can suppress or prevent deterioration of NV due to increase in vibration of the drive system when performing the automatic start control CTst.

When the start control unit 134c determines that the start of the engine 12 is requested, the vehicle state acquisition unit 138 acquires environmental information necessary for calculating the natural frequency f of the drive system. For example, the vehicle state acquisition portion 138 acquires the rear wheel-side distribution ratio Xr as a value representing the state of the driving force distribution control CTx by the four-wheel drive control portion 136. The natural frequency is synonymous with the resonant frequency.

The vehicle state obtaining portion 138 calculates the mass m of the drive system by applying the rear wheel side distribution ratio Xr to the drive system mass map MAPm, for example. Further, the vehicle state obtaining portion 138 calculates the torsional rigidity k of the drive system by applying the rear wheel side distribution ratio Xr to the drive system torsional rigidity map MAPk, for example. The drive system mass map MAPm is a predetermined relationship between the rear wheel side distribution ratio Xr and the mass m of the drive system. The drive system torsional rigidity map MAPk is a predetermined relationship between the rear wheel side distribution ratio Xr and the torsional rigidity k of the drive system.

The vehicle state acquisition portion 138 calculates the natural frequency f of vibration of the drive system using the mass m and the torsional rigidity k of the drive system corresponding to the rear wheel side distribution ratio Xr. The calculation formula used in calculating the natural frequency f of the drive system is, for example, the calculation formula (1) shown in step S30 in the flowchart of fig. 7 described later. The natural frequency f of the drive system corresponds to the resonance rotational speed Nx of the drive system. That is, the vehicle state acquisition portion 138 calculates the resonant rotation speed Nx of the drive system based on the rear wheel side distribution ratio Xr.

When the automatic start control CTst is performed, the start-time target engine speed Nesttgt is set to a speed that is separated from the resonance speed Nx of the drive system calculated by the vehicle state acquisition unit 138 by a predetermined value Δ Nest. The start-time target engine speed Nesttgt may be set to a higher rotation speed than the resonance rotation speed Nx of the drive system or may be set to a lower rotation speed than the resonance rotation speed Nx of the drive system. The predetermined value Δ Nest is, for example, a predetermined value for setting a start-time target engine speed Nesttgt that can suppress the amount of change from the predetermined start-time engine speed Nestf and can avoid or suppress the occurrence of resonance in the drive system.

Here, a case where the driving force distribution control CTx is in a failure state is considered. The failure state of the driving force distribution control CTx is, for example, a state in which the electric motor control command signal Sw is not normally supplied to the electric motor 86, that is, the driving current, or the like. In this case, since the electric motor 86 is in a freely rotating state, the piston 84 is not pressed against the frictional engagement element 82, and the torque capacity of the front wheel driving clutch 70 is zero. That is, in the failure state of the driving force distribution control CTx, the front wheel driving clutch 70 is released, and the four-wheel drive vehicle 10 is in the two-wheel drive state in which the rear wheel side distribution ratio Xr is 1.0. When the start control unit 134c determines that the request for starting the engine 12 is made, the vehicle state acquisition unit 138 sets the natural frequency f of the drive system to the predetermined natural frequency f when the four-wheel drive vehicle 10 is in the two-wheel drive state, that is, the predetermined natural frequency f when the rear-wheel-side distribution ratio Xr is 1.0, when the drive force distribution control CTx is in the failure state.

Fig. 7 is a flowchart for explaining a main part of the control operation of the electronic control device 130, and is a flowchart for explaining the control operation for realizing the four-wheel drive vehicle 10 capable of suppressing or preventing deterioration of NV due to increase in vibration of the drive system when the automatic start control CTst is performed, and is executed, for example, when a start request of the engine 12 is made.

In fig. 7, first, in step S10 corresponding to the function of the vehicle state obtaining unit 138 (hereinafter, step is omitted), environment information is obtained. Specifically, the rear wheel side distribution ratio Xr is acquired as a value indicating the state of the driving force distribution control CTx. Next, in S20 corresponding to the function of the vehicle state obtaining portion 138, the mass m and the torsional rigidity k of the drive system are calculated based on the rear wheel side distribution ratio Xr. Next, in S30 corresponding to the function of the vehicle state acquisition unit 138, the natural frequency f of the drive system, that is, the resonance rotation speed Nx of the drive system is calculated based on the mass m and the torsional rigidity k of the drive system using equation (1) in the figure. Next, in S40 corresponding to the function of the start control unit 134c, the start-time target engine speed Nesttgt is set to a speed that is separated from the resonance speed Nx of the drive system, and the automatic start control CTst is performed. In the automatic start control CTst, when the engine rotation speed Ne becomes equal to or higher than the predetermined ignitable rotation speed Neigf, fuel supply to the engine 12 and ignition of the engine 12 are performed, the engine 12 rotates by itself after initial explosion, and after the explosion and combustion are stabilized, the engine rotation speed Ne is controlled to the start-time target engine rotation speed Nesttgt.

As described above, according to the present embodiment, the start-time target engine speed Nesttgt is changed from the predetermined start-time engine speed Nestf based on the rear wheel side distribution ratio Xr, and the start-time target engine speed Nesttgt is set to a speed that is separated from the resonance speed Nx of the drive system, so that the occurrence of resonance of the drive system due to torque variation of the engine 12 is suppressed or avoided when the automatic start control CTst is performed. This can suppress or prevent deterioration of NV due to increase in vibration of the drive system when the automatic start control CTst is performed.

Further, according to the present embodiment, the start-time target engine rotational speed Nesttgt is set to a rotational speed that is separated by the predetermined value Δ Nest from the resonance rotational speed Nx of the drive system calculated based on the rear wheel side distribution ratio Xr, and therefore the occurrence of resonance of the drive system due to torque variation of the engine 12 is appropriately suppressed or avoided. Further, the predetermined value Δ Nest is a predetermined value for setting the start-time target engine speed Nesttgt that can suppress the amount of change from the predetermined start-time engine speed Nestf and can avoid or suppress the occurrence of resonance in the drive system, so the start-time target engine speed Nesttgt with the amount of change from the predetermined start-time engine speed Nestf suppressed is set at the time of performing the automatic start control CTst, and the occurrence of resonance in the drive system is appropriately suppressed or avoided.

Further, according to the present embodiment, since the start-time engine rotation speed Nestf is determined to be the optimum engine rotation speed Neb, the start-time target engine rotation speed Nesttgt is changed from the optimum engine rotation speed Neb, thereby separating the start-time target engine rotation speed Nesttgt from the resonance rotation speed Nx of the drive system. This can suppress or prevent deterioration of NV while suppressing deterioration of energy efficiency. Further, if the start-time target engine speed Nesttgt is set to a speed separated from the resonance speed Nx of the drive system by the predetermined value Δ Nest, the start-time target engine speed Nesttgt is set with the amount of change from the optimum engine speed Neb suppressed, so deterioration of energy efficiency is appropriately suppressed.

Next, another embodiment of the present invention will be explained. In the following description, the same reference numerals are given to portions common to the embodiments, and the description thereof is omitted.

[ example 2]

In embodiment 1 described above, the start-time target engine speed Nesttgt is separated from the resonance speed Nx of the drive system by changing the start-time target engine speed Nesttgt. In addition to such a control function, the target engine speed Nesttgt at startup can be separated from the resonant rotation speed Nx of the drive system by changing the resonant rotation speed Nx of the drive system.

When the automatic start control CTst is performed by the start controller 134c, the four-wheel drive controller 136 changes the rear-wheel-side distribution ratio Xr with respect to the rear-wheel-side distribution ratio Xr when the automatic start control CTst is not performed so that the resonance rotation speed Nx of the drive system is separated from the predetermined start-time engine rotation speed Nestf.

The electronic control unit 130 has a control function of changing the rear wheel side distribution ratio Xr when the automatic start control CTst is performed with respect to the rear wheel side distribution ratio Xr when the automatic start control CTst is not performed so that the resonance rotation speed Nx of the drive system is separated from the predetermined start-time engine rotation speed Nestf, in addition to the control function of changing the start-time target engine rotation speed Nesttgt. When the automatic start control CTst is performed, the electronic control unit 130 alternately changes the start-time target engine speed Nesttgt and the rear wheel side distribution ratio Xr based on the vehicle state, and separates the start-time target engine speed Nesttgt from the resonance speed Nx of the drive system.

When the acceleration operation by the driver is large, such as a sudden start operation, a sudden acceleration operation, or the like, it is preferable to suppress the influence on the vehicle motion controllability, so the vehicle motion controllability achieved by the driving force distribution control CTx is prioritized over the improvement in energy efficiency. As shown in fig. 8, when the accelerator opening degree θ acc, which is one parameter indicating the vehicle state, is equal to or greater than the predetermined amount θ accf, the electronic control device 130 prioritizes the driving force distribution control CTx and separates the start-time target engine speed Nesttgt from the resonance speed Nx of the drive system by changing the start-time target engine speed Nesttgt. On the other hand, as shown in fig. 8, when the accelerator opening degree θ acc is smaller than the predetermined amount θ accf, the electronic control device 130 prioritizes the automatic start control CTst at the predetermined start-time engine rotation speed Nestf, and separates the start-time target engine rotation speed Nesttgt from the resonance rotation speed Nx of the drive system by changing the rear wheel side distribution ratio Xr. The prescribed amount θ accf is a predetermined threshold value for suppressing the influence on the vehicle motion controllability while suppressing or preventing deterioration of NV when the automatic start control CTst is performed, and for suppressing the start-time target engine speed Nesttgt from being changed with respect to the prescribed start-time engine speed Nestf, for example.

Alternatively, when the steering operation by the driver is large, it is preferable to suppress the influence on the vehicle motion controllability, so the vehicle motion controllability achieved by the driving force distribution control CTx is prioritized over the improvement in energy efficiency. When the yaw rate Vyaw, which is one of the parameters indicating the vehicle state, is equal to or greater than the predetermined angular rate Vyawf as shown in fig. 9 and/or when the steering angle θ sw, which is one of the parameters indicating the vehicle state, is equal to or greater than the predetermined angle θ swf as shown in fig. 10, the electronic control device 130 prioritizes the driving force distribution control CTx and separates the start-time target engine speed Nesttgt from the resonance speed Nx of the drive system by changing the start-time target engine speed Nesttgt. On the other hand, when the yaw rate Vyaw is smaller than the predetermined angular rate Vyawf as shown in fig. 9 and/or when the steering angle θ sw is smaller than the predetermined angle θ swf as shown in fig. 10, the electronic control device 130 prioritizes the automatic start control CTst at the predetermined start-time engine speed Nestf, and separates the start-time target engine speed Nesttgt from the resonance speed Nx of the drive system by changing the rear-wheel-side distribution ratio Xr. The predetermined angular velocity Vyawf and the predetermined angle θ swf are predetermined thresholds for suppressing the influence on the vehicle motion controllability while suppressing or preventing deterioration of NV when the automatic start control CTst is performed, and for suppressing the change of the start-time target engine speed Nesttgt with respect to the predetermined start-time engine speed Nestf, for example.

Alternatively, in a situation where the driver has performed a steering operation, it is preferable to suppress the influence on the vehicle motion controllability, so the vehicle motion controllability achieved by the driving force distribution control CTx is prioritized over the improvement in energy efficiency. As shown in fig. 11, when the four-wheel drive vehicle 10, which is one of the parameters indicating the vehicle state, is running in a curve, the electronic control device 130 prioritizes the driving force distribution control CTx and separates the start-time target engine speed Nesttgt from the resonance speed Nx of the drive system by changing the start-time target engine speed Nesttgt. On the other hand, as shown in fig. 11, when the four-wheel drive vehicle 10, which is one parameter indicating the vehicle state, is traveling straight, the electronic control device 130 prioritizes the automatic start control CTst at the predetermined start-time engine rotation speed Nestf, and separates the start-time target engine rotation speed Nesttgt from the resonance rotation speed Nx of the drive system by changing the rear-wheel side distribution ratio Xr. The scheme based on whether the four-wheel drive vehicle 10 is performing the change of the target engine rotation speed at the time of starting and the change of the rear wheel side distribution ratio alternatively during the cornering travel or the straight travel may be regarded as a scheme in which the predetermined angular velocity Vyawf is set to a value of zero or a value in the vicinity of zero in the scheme shown in fig. 9, or a scheme in which the predetermined angle θ swf is set to a value of zero or a value in the vicinity of zero in the scheme shown in fig. 10, for example.

At least one of the embodiments shown in fig. 8, 9, 10, and 11 may be implemented.

As described above, according to the present embodiment, when the automatic start control CTst is performed, the change of the start-time target engine speed Nesttgt and the change of the rear wheel side distribution ratio Xr are performed alternatively based on the vehicle state, and the start-time target engine speed Nesttgt is separated from the resonance rotation speed Nx of the drive system, so that the influence on the vehicle motion controllability is suppressed while suppressing or preventing the deterioration of NV, and the change of the start-time target engine speed Nesttgt from the predetermined start-time engine speed Nestf is suppressed. If the engine speed Nestf at the time of the prescribed start is the optimum engine speed Neb, deterioration of the energy efficiency is suppressed.

Further, according to the present embodiment, when the accelerator opening degree θ acc is equal to or greater than the predetermined amount θ accf, the start-time target engine speed Nesttgt is separated from the resonance speed Nx of the drive system by the change in the start-time target engine speed Nesttgt, so in the situation where the quick start operation and the quick acceleration operation are performed, the vehicle motion controllability by the drive force distribution control CTx is prioritized over the improvement in energy efficiency. On the other hand, when the accelerator opening degree θ acc is smaller than the predetermined amount θ accf, the rear wheel side sharing rate Xr is changed to separate the start-time target engine speed Nesttgt from the resonance speed Nx of the drive system, so that improvement of energy efficiency is prioritized over controllability of vehicle motion by the drive force distribution control CTx in a situation where the start operation and the acceleration operation are slow. As a result, the influence on the controllability of the vehicle motion is suppressed while suppressing or preventing deterioration of NV, and the change of the start-time target engine speed Nesttgt from the predetermined start-time engine speed Nestf is suppressed. If the engine speed Nestf at the time of the prescribed start is the optimum engine speed Neb, deterioration of the energy efficiency is suppressed.

Further, according to the present embodiment, when the yaw rate Vyaw is equal to or greater than the predetermined angular rate Vyawf, when the steering angle θ sw is equal to or greater than the predetermined angle θ swf, or when the four-wheel drive vehicle 10 is in cornering, the start-time target engine speed Nesttgt is separated from the resonance speed Nx of the drive system by the change in the start-time target engine speed Nesttgt, so that the vehicle motion controllability by the drive force distribution control CTx is prioritized over the improvement in energy efficiency in such a situation that the change in the vehicle attitude is large. On the other hand, when the yaw rate Vyaw is smaller than the predetermined angular rate Vyawf, when the steering angle θ sw is smaller than the predetermined angle θ swf, or when the four-wheel drive vehicle 10 is traveling straight, the start-time target engine speed Nesttgt is separated from the resonance speed Nx of the drive system by the change of the rear-wheel-side distribution ratio Xr, so that the improvement of the energy efficiency is prioritized over the vehicle motion controllability by the drive force distribution control CTx in a situation where the change in the vehicle attitude is small. As a result, the influence on the controllability of the vehicle motion is suppressed while suppressing or preventing deterioration of NV, and the change of the start-time target engine speed Nesttgt from the predetermined start-time engine speed Nestf is suppressed. If the engine speed Nestf at the time of the prescribed start is the optimum engine speed Neb, deterioration of the energy efficiency is suppressed.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the present invention is applicable to other embodiments.

For example, in embodiment 1 described above, the rear wheel side distribution ratio Xr is shown as an example of a value indicating the state of the driving force distribution control CTx, and the mass m and the torsional rigidity k of the drive system are calculated by applying the rear wheel side distribution ratio Xr to the drive system mass map MAPm and the drive system torsional rigidity map MAPk. For example, the value indicating the state of the driving force distribution control CTx may be a pressing force when the piston 84 abuts on the frictional engagement element 82 to press the first friction plate 82a and the second friction plate 82b, an electric motor control command signal Sw for the electric motor 86, or the like. Further, the mass m and the torsional rigidity k of the drive system may be calculated using a predetermined function in which a value indicating the state of the drive force distribution control CTx is set as an input parameter.

In embodiment 2 described above, the change of the target engine speed Nesttgt at the time of startup and the change of the rear wheel side distribution ratio Xr are alternatively performed based on whether or not the accelerator opening degree θ acc is equal to or greater than the predetermined amount θ accf. For example, the change of the target engine rotation speed Nesttgt at the time of startup and the change of the rear wheel side distribution ratio Xr may be alternatively performed based on whether or not the drive request amount such as the requested drive force Frdem is equal to or greater than a predetermined amount, instead of the accelerator operation amount such as the accelerator opening degree θ acc. The drive request amount is a value calculated based on the accelerator opening degree θ acc, etc., but in automatic drive control, automatic vehicle speed control, etc., for example, a drive request amount that does not depend on the accelerator operation amount by the driver may be used. The drive request amount is useful for a four-wheel drive vehicle having control functions such as automatic driving control and automatic vehicle speed control.

In the above-described embodiment, the four-wheel drive vehicle 10 is a four-wheel drive vehicle based on an FR type vehicle, a time-division type four-wheel drive vehicle that switches between two-wheel drive and four-wheel drive depending on the running state, a hybrid vehicle that uses the engine 12, the first rotary machine MG1, and the second rotary machine MG2 as drive power sources, or a four-wheel drive vehicle that includes the automatic transmission 28 having the continuously variable transmission unit 44 and the stepped transmission unit 46 in series, but is not limited to this configuration. For example, the present invention is applicable to a four-wheel drive vehicle based on an FF (front engine/front drive) type vehicle, a full-time type four-wheel drive vehicle, a parallel hybrid vehicle in which drive power from an engine and a rotary machine is transmitted to drive wheels, a vehicle in which only the engine is used as a drive power source, and the like. Alternatively, the present invention may be applied to a four-wheel drive vehicle including a known planetary gear type automatic Transmission, a synchromesh type parallel two-shaft automatic Transmission including a known DCT (Dual Clutch Transmission), a known belt type continuously variable Transmission, a known electric continuously variable Transmission, or the like as an automatic Transmission. In the case of a four-wheel drive vehicle based on an FF-type vehicle, the front wheels become main drive wheels, the rear wheels become sub-drive wheels, and the front-wheel-side distribution ratio Xf becomes a main-side distribution ratio. In the case of a full-time four-wheel drive vehicle including a central differential gear device (center differential) having a differential limiting clutch, when the differential limiting clutch for limiting the differential motion of the center differential is not operated, for example, the driving force distribution of the front and rear wheels is set to a predetermined driving force distribution such as 30: 70, and the differential limiting clutch is operated, whereby the driving force distribution of the front and rear wheels is changed to 50: 50. In short, the present invention is applicable to a four-wheel drive vehicle including at least a drive power source including an engine, a drive power distribution device capable of transmitting drive power from the drive power source to main drive wheels and auxiliary drive wheels and adjusting a drive power distribution ratio, and a control device performing drive power distribution control and automatic start control.

In the above-described embodiment, the piston 84 constituting the front wheel drive clutch 70 of the transfer case 30 is configured to move toward the frictional engagement element 82 via the cam mechanism 90 to press the frictional engagement element 82 when the electric motor 86 rotates, but the present invention is not limited to this configuration. For example, it may be configured such that when the electric motor 86 rotates, the piston 84 presses the frictional engagement element 82 via a ball screw or the like that converts rotational motion into linear motion. Alternatively, piston 84 may be driven by a hydraulic actuator.

The above-described embodiment is only one embodiment, and the present invention can be implemented by various modifications and improvements based on the knowledge of those skilled in the art.