阅读说明：本技术 四轮驱动力分配装置 (Four-wheel drive force distribution device ) 是由 光本尚训 丹羽智彦 于 2021-05-14 设计创作，主要内容包括：本发明提供四轮驱动力分配装置,用于使车辆的加速性能以及转弯性能提高。在向四轮驱动车辆的各车轮分配驱动力的四轮驱动力分配装置中,当车辆转弯时,基于前内轮(2a)的接地载荷与后内轮(3a)的接地载荷来调整向前内轮(2a)的驱动力分配量与向后内轮(3a)的驱动力分配量。转弯中的前内轮(2a)的接地载荷相对于后内轮(3a)的接地载荷的比例越小,则使向前内轮(2a)的驱动力分配量越小于向后内轮(3a)的驱动力分配量。(The invention provides a four-wheel drive force distribution device for improving the acceleration performance and the turning performance of a vehicle. In a four-wheel drive force distribution device that distributes drive force to each wheel of a four-wheel drive vehicle, when the vehicle is turning, the drive force distribution amount to the front inner wheel (2a) and the drive force distribution amount to the rear inner wheel (3a) are adjusted based on the ground contact load of the front inner wheel (2a) and the ground contact load of the rear inner wheel (3 a). The smaller the proportion of the ground contact load of the front inner wheel (2a) to the ground contact load of the rear inner wheel (3a) during turning is, the smaller the driving force distribution amount to the front inner wheel (2a) is compared with the driving force distribution amount to the rear inner wheel (3 a).)

1. A four-wheel drive force distribution device that distributes drive force to each wheel of a four-wheel drive vehicle,

when the vehicle turns, the driving force distribution amount of the front inner wheel and the driving force distribution amount of the rear inner wheel are adjusted based on the ground contact load of the front inner wheel and the ground contact load of the rear inner wheel, and the smaller the proportion of the ground contact load of the front inner wheel to the ground contact load of the rear inner wheel during turning is, the smaller the driving force distribution amount of the front inner wheel is compared with the driving force distribution amount of the rear inner wheel.

2. The four-wheel drive force distribution device according to claim 1,

the smaller the proportion of the ground contact load of the front inner wheel to the ground contact load of the rear inner wheel during turning is, the smaller the driving force distribution amount to the pair of front wheels is made to be than the driving force distribution amount to the pair of rear wheels.

3. The four-wheel drive force distribution device according to claim 1,

when the vehicle turns, the ratio of the ground contact load of the front inner wheel to the ground contact load of the rear inner wheel is calculated, and the driving force is distributed to the front inner wheel and the rear inner wheel according to the ratio during turning.

4. The four-wheel drive force distribution device according to claim 3,

driving force is distributed to a pair of front wheels and a pair of rear wheels according to the ratio in turning.

5. The four-wheel drive force distribution device according to claim 3,

the vehicle is provided with a front-rear acceleration sensor for detecting acceleration in the front-rear direction of the vehicle and a lateral acceleration sensor for detecting acceleration in the lateral direction of the vehicle, and the ratio of the ground contact load of the front inner wheel to the ground contact load of the rear inner wheel is calculated from the front-rear acceleration detected by the front-rear acceleration sensor and the lateral acceleration detected by the lateral acceleration sensor.

6. The four-wheel drive force distribution device according to claim 3,

a front-rear acceleration is estimated from an engine output torque and a gear ratio between an engine and drive wheels, a lateral acceleration is estimated from a steering angle and a vehicle speed, and a ratio of a ground contact load of a front inner wheel to a ground contact load of a rear inner wheel is calculated from the estimated front-rear acceleration and the estimated lateral acceleration.

7. The four-wheel drive force distribution device according to claim 3,

when the vehicle turns, the change amount of the ground contact load of the front inner wheel and the change amount of the ground contact load of the rear inner wheel are calculated, and the ratio of the ground contact load of the front inner wheel to the ground contact load of the rear inner wheel is calculated from the change amount of the ground contact load of the front inner wheel and the change amount of the ground contact load of the rear inner wheel.

8. The four-wheel drive force distribution device according to claim 3,

when the vehicle turns, braking force is applied to the front inner wheel and the rear inner wheel.

9. The four-wheel drive force distribution device according to claim 8,

during the turning of the vehicle, the braking force applied to the front inner wheel and the rear inner wheel is distributed according to the ratio.

Technical Field

The present invention relates to a four-wheel drive force distribution device.

Background

In a tire used for a vehicle, that is, a wheel, a grip (grip) force on a ground surface increases as a ground contact load of the wheel increases, and the grip force on the ground surface decreases as the ground contact load of the wheel decreases. When the grip force on the ground surface becomes small, if a large driving force is applied to the wheels, the wheels slip, and the vehicle cannot be steered appropriately. On the other hand, when the vehicle turns, the ground contact load of the inner wheel located on the inner side as viewed from the turning center becomes smaller than the ground contact load of the outer wheel located on the outer side as viewed from the turning center, and at this time, if a large driving force is applied to the inner wheel whose ground contact load becomes smaller, the inner wheel slips, and the steering of the vehicle cannot be appropriately performed. In view of this, a two-wheel drive vehicle is known in which the driving force of an inner wheel (drive wheel) is made smaller than the driving force of an outer wheel (drive wheel) when the vehicle turns (see, for example, patent document 1).

Patent document 1: japanese patent laid-open No. 2001 and 063397

In addition, even in a four-wheel drive vehicle, when the vehicle turns, the ground contact load of the inner wheel is smaller than that of the outer wheel, and the ground contact load of the front inner wheel is smaller than that of the rear inner wheel. However, in the case where the above-described two-wheel drive force distribution device is applied to a pair of front wheels, while the above-described two-wheel drive force distribution device is also applied to a pair of rear wheels, the same drive force is applied to the front inner wheels and the rear inner wheels when the vehicle turns, regardless of whether the ground contact load of the front inner wheels is smaller than that of the rear inner wheels. As a result, the front inner wheel having a small ground contact load may slip to cause an understeer state.

Disclosure of Invention

According to the present invention, there is provided a four-wheel drive force distribution device for distributing drive forces to respective wheels of a four-wheel drive vehicle, wherein a drive force distribution amount to a front inner wheel and a drive force distribution amount to a rear inner wheel are adjusted based on a ground contact load to the front inner wheel and a ground contact load to the rear inner wheel during turning of the vehicle, and the smaller a proportion of the ground contact load to the rear inner wheel of the front inner wheel during turning is, the smaller the drive force distribution amount to the front inner wheel is made than the drive force distribution amount to the rear inner wheel.

The drivability of the vehicle can be improved while ensuring a proper steering action of the vehicle.

Drawings

Fig. 1 is an overall view schematically showing a four-wheel drive force distribution device of a vehicle.

Fig. 2 is a diagram showing a relationship between the front wheel-drive torque and the rear wheel-drive torque.

Fig. 3 is an overall view schematically showing another example of the four-wheel drive force distribution device of the vehicle.

Fig. 4 is a diagram showing a friction circle.

Fig. 5A, 5B, and 5C are diagrams for explaining the behavior of the vehicle.

Fig. 6A and 6B are diagrams for explaining a change in the ground contact load of the wheel.

Fig. 7A and 7B are diagrams showing the size of the friction circle of each wheel.

Fig. 8A and 8B are diagrams showing the size of the friction circle of each wheel.

Fig. 9A and 9B are diagrams for explaining the amount of change in the ground contact load of the wheel.

Fig. 10 is a diagram for explaining a method of calculating a ratio of a ground contact load of the front inner wheel to a ground contact load of the rear inner wheel when the vehicle turns.

FIG. 11 shows the front-rear acceleration G_XA line graph of the relationship with the lateral acceleration Gy.

Fig. 12 is a diagram showing an electronic control unit and the like used in embodiment 2.

Fig. 13A and 13B are diagrams showing the relationship between the engine speed, the accelerator opening degree, and the engine output torque, and a method for calculating the lateral acceleration Gy, respectively.

Fig. 14 is a view showing the size of a friction circle of each wheel.

Fig. 15 is a diagram for explaining a method of calculating a ratio between a ground contact load of the front inner wheel and a ground contact load of the rear inner wheel when the vehicle turns.

FIG. 16 shows the front-rear acceleration G_XA line graph of the relationship with the lateral acceleration Gy.

Fig. 17 is a flowchart for performing driving control.

Detailed Description

First, a four-wheel drive force distribution device for a vehicle will be described with reference to fig. 1. The four-wheel drive force distribution device is an example, and various known four-wheel drive force distribution devices capable of arbitrarily distributing drive force to the front and rear wheels may be used instead of the four-wheel drive force distribution device shown in fig. 1. Referring to fig. 1, a vehicle is generally indicated by reference numeral 1. In fig. 1, 2a and 2b denote a pair of front wheels, 3a and 3b denote a pair of rear wheels, 4 denotes an internal combustion engine, and 5 denotes a drive torque distributor. A front drive shaft 6 extends forward from the drive torque distributor 5, and a rear drive shaft 7 extends rearward. The front drive shaft 6 is coupled to the front wheels 2a and 2b via a front differential 8 and corresponding axles 9, and the rear drive shaft 7 is coupled to the rear wheels 3a and 3b via a rear differential 10 and corresponding axles 11.

The drive torque distributor 5 is composed of a planetary gear mechanism, and includes a 1 st sun gear 13 fixed to an output shaft 12 of the internal combustion engine 1, a 2 nd sun gear 14 fixed to the rear drive shaft 7, and a carrier 15 supported so as to be rotatable about the output shaft 12 of the internal combustion engine 1 and the rear drive shaft 7. The carrier 15 rotatably supports a 1 st planetary gear 16 and a 2 nd planetary gear 17 that are meshed with the 1 st sun gear 13 and the 2 nd sun gear 14, respectively, and integrally rotate, and a gear 19 that is meshed with a gear 18 fixed to the front drive shaft 6 and is rotatable around the output shaft 12 of the internal combustion engine 1 is formed at one end of the carrier 15, and a hydraulic clutch mechanism 21 that can adjust a coupling state between a clutch plate 20 fixed to the rear drive shaft 7 and the carrier 15 is formed at the other end of the carrier 15. The hydraulic clutch mechanism 21 is controlled by a hydraulic control device 22.

On the other hand, as shown in fig. 1, hydraulic brake devices 30 are mounted on the front wheels 2a and 2b and the rear wheels 3a and 3b, respectively, and the hydraulic brake devices 30 are connected to a brake control device 32 via corresponding brake oil pipes 31 shown by broken lines. The brake control device 32 includes: a master cylinder that generates a brake hydraulic pressure by a depression operation of a brake pedal; and a brake fluid pressure adjusting device capable of adjusting the generated brake fluid pressure to generate a different brake fluid pressure for each of the brake devices 30 of the front wheels 2a, 2b and the rear wheels 3a, 3 b. That is, the braking force of each front wheel 2a, 2b and each rear wheel 3a, 3b can be independently controlled by the brake control device 32.

Fig. 1 shows an electronic control unit 40 mounted on the vehicle 1. The electronic control unit 40 is constituted by a digital computer, and includes a ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45, and an output port 46, which are connected to each other by a bidirectional bus 41. As shown in fig. 1, a vehicle 1 is mounted with a front-rear acceleration sensor (hereinafter, referred to as a front-rear G sensor) 50 that detects acceleration in the front-rear direction of the vehicle 1, a lateral acceleration sensor (hereinafter, referred to as a lateral G sensor) 51 that detects acceleration in the lateral direction of the vehicle 1, a steering angle sensor 52 that detects a steering angle, and a vehicle speed sensor 53 that detects a vehicle speed, and output signals of the front-rear G sensor 50, the lateral G sensor 51, the steering angle sensor 52, and the vehicle speed sensor 53 are input to the input port 45 via corresponding AD converters 47. On the other hand, the output port 46 is connected to the hydraulic control device 22 and the brake control device 32 via corresponding drive circuits 48.

In fig. 1, the output torque of the internal combustion engine 1 is distributed by the drive torque distributor 5 into the drive torque of the front drive shaft 6 for driving the front wheels 2a and 2b and the drive torque of the rear drive shaft 7 for driving the rear wheels 3a and 3b, and the distribution control of the drive torques is performed by controlling the clutch operating hydraulic pressure of the hydraulic clutch mechanism 21 by the hydraulic control device 22. Fig. 2 shows the relationship among the distribution amount of the front-wheel-drive torque distributed to the front drive shaft 6, the distribution amount of the rear-wheel-drive torque distributed to the rear drive shaft 7, and the clutch operating hydraulic pressure of the hydraulic clutch mechanism 21. In the drive torque distributor 5 shown in fig. 1, when the clutch operating hydraulic pressure of the hydraulic clutch mechanism 21 is reduced and the clutch is in the disengaged state, the output torque of the internal combustion engine 1 is transmitted to the front drive shaft 6 via the 1 st sun gear 13, the 1 st planetary gear 16, and the carrier 15, and is transmitted to the rear drive shaft 7 via the 1 st sun gear 13, the 1 st planetary gear 16, the 2 nd planetary gear 17, and the 2 nd sun gear 14. At this time, the distribution amount of the drive torque of the front drive shaft 6 and the rear drive shaft 7 becomes a constant value corresponding to the number of teeth of the 1 st sun gear 13, the 2 nd sun gear 14, the 1 st planetary gear 16, and the 2 nd planetary gear 17, and in the drive torque distributor 5 shown in fig. 1, at this time, as shown by a point P in the drawing, the distribution amount of the front drive torque distributed to the front drive shaft 6 becomes 0.6, and the distribution amount of the rear drive torque distributed to the rear drive shaft 7 becomes 0.4.

On the other hand, when the clutch operating hydraulic pressure of the hydraulic clutch mechanism 21 increases and the clutch becomes engaged, the output torque of the internal combustion engine 1 is transmitted to the front drive shaft 6 via the 1 st sun gear 13, the 1 st planetary gear 16, and the carrier 15, and is transmitted to the rear drive shaft 7 via the 1 st sun gear 13, the 1 st planetary gear 16, and the carrier 15. In the drive torque distributor 5 shown in fig. 1, the distribution amount of the front wheel drive torque distributed to the front drive shaft 6 is 0.2 and the distribution amount of the rear wheel drive torque distributed to the rear drive shaft 7 is 0.8, as indicated by the point Q in the figure. Therefore, by controlling the clutch operating hydraulic pressure of the hydraulic clutch mechanism 21, the distribution amount of the front-wheel drive torque and the distribution amount of the rear-wheel drive torque can be arbitrarily adjusted within the ranges of P and Q in fig. 2.

Fig. 3 shows another example of the four-wheel drive force distribution device of the vehicle. In this example, the front wheels 2a, 2b and the rear wheels 3a, 3b are driven by independent electric motors 60, respectively. A motor drive control device 61 for controlling each electric motor 60 is mounted on the vehicle 1, and the motor drive control device 61 controls the output torque of each electric motor 60 to be independent output torque.

Next, a force acting on the contact surface of the tire and a friction circle of the tire will be briefly described with reference to fig. 4. In fig. 4, the suffix x represents the front-rear direction of the vehicle, and the suffix y represents the lateral direction of the vehicle. In this way, when the driving torque is applied to the tire to accelerate the vehicle, that is, the longitudinal acceleration G is applied to the vehicle_XA force in the vehicle longitudinal direction, i.e., a longitudinal force Fx, acts on the ground contact surface of the tire. The front-to-back force Fx is proportional to the driving torque applied to the tire. On the other hand, when the vehicle is turned, a centrifugal force, that is, a lateral acceleration Gy is generated in the vehicle, and a lateral force acts on the vehicle. When a lateral force is applied to the vehicle, a lateral force Fy is generated on the contact surface of each tire in a direction opposite to the lateral force, and in this case, in short, a force substantially proportional to the contact load of each tire is generated on the contact surface of each tireThe transverse force Fy. Therefore, a resultant force Fxy of the front-rear force Fx and the lateral force Fy is generated in the contact surface of each tire.

On the other hand, when the ground contact load of the tire is Fz and the coefficient of friction between the tire and the road surface is μ, a circle having Fz · μ as a radius is referred to as a friction circle, and this friction circle is shown in fig. 4. The radius Fz · μ of the friction circle indicates a limit value of a force acting on the contact surface of the tire when the contact surface of the tire starts to slip against the frictional force, and when a resultant force Fxy of the front-rear force Fx and the lateral force Fy exceeds the friction circle, that is, exceeds the limit, the tire starts to slip against the frictional force between the tire and the road surface. Therefore, the size of the friction circle indicates the strength of the grip with respect to the tire. Since the size of the friction circle is proportional to the ground contact load of the tire, the grip force with respect to the tire becomes stronger as the ground contact load of the tire becomes larger. In a vehicle, a resultant force Fxy that exceeds a limit cannot be generated so as to exceed a friction circle on a contact surface of a tire, and the vehicle is usually driven so that the resultant force Fxy generated on the contact surface of the tire does not exceed the friction circle.

Next, referring to fig. 5A to 5C, the behavior of the vehicle, which occurs when the lateral force Fy generated in the contact surface of the tire exceeds the friction circle, that is, when the lateral force Fy generated in the contact surface of the tire exceeds the limit, will be briefly described using a 2-wheel model in which the front wheels 2a and 2b and the rear wheels 3a and 3b are respectively brought close to each other. In fig. 5A to 5C, solid arrow C indicates a target travel line, and broken arrow D indicates an actual travel line. Arrow Fy indicates a lateral force generated in the ground contact surfaces of the front wheels 2a and 2b and the rear wheels 3a and 3b when the vehicle turns. Fig. 5A shows a case where the lateral force Fy does not exceed the friction circle, that is, a case where the lateral force Fy does not exceed the limit, although the lateral force Fy is generated. In this case, the actual travel line D overlaps the target travel line C.

On the other hand, fig. 5B shows a case where the lateral force Fy generated in the ground contact surfaces of the front wheels 2a and 2B and the rear wheels 3a and 3B becomes large and the lateral force Fy generated in the ground contact surfaces of the front wheels 2a and 2B exceeds the friction circle, that is, the limit. In this case, the yaw moment M is generated in the vehicle, and the actual travel line D bulges outward beyond the target travel line C. Such a condition is called understeer (or sideslip). On the other hand, fig. 5C shows a case where the lateral force Fy generated in the contact surface of the front wheels 2a and 2b and the rear wheels 3a and 3b becomes large and the lateral force Fy generated in the contact surface of the rear wheels 3a and 3b exceeds the friction circle, that is, the limit. In this case, a yaw moment M opposite to that in fig. 5B is generated in the vehicle, and the vehicle turns so that the actual travel line D is directed inward from the target travel line C. Such a condition is called oversteer. Among them, if the vehicle is turned, it is extremely dangerous. Therefore, the vehicle is generally designed to first cause understeer (or spin) when a large lateral force Fy is generated, and in the embodiment to which the present invention relates, is also designed to first cause understeer (or spin) when a large lateral force Fy is generated.

Further, as described above, when the driving torque is applied to the tire, the front-rear force Fx is generated on the contact surface of the tire, and the front-rear acceleration G is generated on the vehicle_X. In this case, the more the front-rear force Fx generated on the contact surface of the tire can be increased, the more the front-rear acceleration G can be increased_XThat is, the more the acceleration performance of the vehicle can be improved. On the other hand, when the vehicle is turned, a lateral acceleration Gy is generated in the vehicle, and a lateral force Fy is generated in the contact surface of the tire. In this case, the lateral acceleration Gy, that is, the turning performance of the vehicle can be improved as the lateral force Fy generated in the contact surface of the tire can be increased. Therefore, the more the front-rear force Fx and the lateral force Fy generated in the contact surface of the tire can be increased within the range where the resultant force Fxy of the front-rear force Fx and the lateral force Fy does not exceed the friction circle, the more the acceleration performance and the cornering performance of the vehicle can be improved.

This will be described with reference to fig. 6A to 8B. Fig. 6A is a view when the vehicle 1 is viewed from the lateral direction, fig. 6B is a view when the vehicle 1 is viewed from the front, and fig. 7A to 8B are views when the vehicle 1 is viewed from the upper side. In fig. 6A and 6B, G_XShows an acceleration applied in the front-rear direction of the vehicle during acceleration driving (hereinafter referred to as a front-rear acceleration G)_X) Gy represents an acceleration applied in the lateral direction of the vehicle 1 when the vehicle is turning (hereinafter, referred to as lateral acceleration Gy). First, referring to fig. 7A, fig. 7A shows friction circles with respect to the front wheels 2a, 2b and the rear wheels 3a, 3b when the vehicle 1 is driven straight at a constant speed. As is apparent from fig. 7A, fig. 7A to 8B show the case where the ground contact loads of the front wheels 2a and 2B and the rear wheels 3a and 3B are substantially equal when the vehicle is stopped.

On the other hand, when the vehicle 1 is accelerated by applying a driving torque to the front wheels 2a and 2b and the rear wheels 3a and 3b, a moment Ma as shown in fig. 6A is generated in the vehicle 1, and as a result, the ground contact load of the front wheels 2a and 2b becomes smaller than the ground contact load of the rear wheels 3a and 3 b. Therefore, at this time, as shown in fig. 7B, the diameter of the friction circle with respect to the front wheels 2a, 2B becomes smaller than the diameter of the friction circle with respect to the rear wheels 3a, 3B. At this time, as shown in fig. 7B, the driving torques applied to the front wheels 2a and 2B and the rear wheels 3a and 3B are adjusted so that the front-rear force Fx generated in the contact surfaces of the front wheels 2a and 2B and the rear wheels 3a and 3B becomes a limit, and thus the optimal acceleration performance can be ensured.

On the other hand, fig. 8A shows a case where the vehicle 1 makes a left turn in a constant speed driving state. The front wheels 2a and the rear wheels 3a located inward of the turning center at this time are hereinafter referred to as a front inner wheel 2a and a rear inner wheel 3a, and the front wheels 2b and the rear wheels 3b located outward of the turning center are hereinafter referred to as a front outer wheel 2b and a rear outer wheel 3 b. When the vehicle 1 is turned left, the lateral acceleration Gy is applied to the vehicle 1, and a moment Mb as shown in fig. 6B is generated in the vehicle 1. As a result, the ground contact load of the front inner wheel 2a and the rear inner wheel 3a becomes smaller than the ground contact load of the front outer wheel 2b and the rear outer wheel 3 b. Therefore, at this time, as shown in fig. 8A, the diameter of the friction circle with respect to the front inner wheel 2a and the rear inner wheel 3a becomes smaller than the diameter of the friction circle with respect to the front outer wheel 2b and the rear outer wheel 3 b. Further, as described above, since the lateral force Fy substantially proportional to the ground contact load of each tire is generated in the ground contact surface of each tire, at this time, as shown in fig. 8A, the lateral force Fy substantially proportional to the diameter of the corresponding friction circle is generated in the ground contact surface of each of the front inner wheel 2a, the front outer wheel 2b, the rear inner wheel 3a, and the rear outer wheel 3 b.

As described above, in the embodiment according to the present invention, when the vehicle 1 generates a large lateral acceleration Gy, understeer (or sideslip) is designed to be generated first. On the other hand, when the vehicle 1 is turned left, for example, as shown in fig. 8A, the lateral force Fy generated in the contact surfaces of the front outer wheel 2b and the rear outer wheel 3b is sufficiently larger than the lateral force Fy generated in the contact surfaces of the front inner wheel 2a and the rear inner wheel 3 a. Therefore, in the embodiment of the present invention, as shown in fig. 8A, it is designed such that the lateral force Fy generated in the ground contact surface of the front outer wheel 2b is larger than the lateral force Fy generated in the ground contact surface of the rear outer wheel 3b, so that understeer is generated first when the vehicle 1 is made to turn left, for example.

On the other hand, fig. 8B shows a case where the vehicle 1 makes a left turn in a state of accelerated driving. At this time, the moment Ma as shown in fig. 6A and the moment Mb as shown in fig. 6B are simultaneously generated in the vehicle 1, and as a result, the ground contact load of the front inner wheel 2a becomes minimum and the ground contact load of the rear inner wheel 3a becomes second smallest. In this case as well, as in the case shown in fig. 8A, the lateral force Fy generated in the respective ground contact surfaces of the front inner wheel 2a and the rear inner wheel 3a is reduced. Therefore, at this time, if the driving torques proportional to the ground contact load of the front inner wheel 2a and the ground contact load of the rear inner wheel 3a are applied to the front inner wheel 2a and the rear inner wheel 3a, respectively, the front-rear force Fx generated in the ground contact surface of the front inner wheel 2a and the rear inner wheel 3a can be increased to the vicinity of the limit within the range where the resultant force Fxy of the front-rear force Fx and the lateral force Fy does not exceed the friction circle. If the front-rear force Fx generated in the contact surfaces of the front inner wheel 2a and the rear inner wheel 3a can be increased to the vicinity of the limit, the acceleration performance can be greatly improved.

However, when the vehicle 1 turns left, for example, in a state of accelerated driving, if the front inner wheel 2a and the rear inner wheel 3a are respectively provided with drive torques proportional to the ground contact load of the front inner wheel 2a and the ground contact load of the rear inner wheel 3a, the drive torque applied to the front inner wheel 2a is smaller than the drive torque applied to the rear inner wheel 3 a. In this case, the drive torque applied to the front outer wheel 2b is reduced similarly to the drive torque applied to the front inner wheel 2a, and the drive torque applied to the rear outer wheel 3b is increased similarly to the drive torque applied to the rear inner wheel 3 a. In this way, when the driving torque applied to the front outer wheel 2b is reduced, the resultant force Fxy of the front and rear forces Fx and the lateral force Fy of the front outer wheel 2b does not exceed the friction circle, and a margin is left to the limit of the resultant force Fxy of the front and rear forces Fx and the lateral force Fy of the rear outer wheel 3b, so that the driving torque applied to the rear outer wheel 3b can be increased. Therefore, when the ground load of the front inner wheel 2a and the ground load of the rear inner wheel 3a are focused during the turning of the vehicle, when the ground load of the front inner wheel 2a is larger than the ground load of the rear inner wheel 3a, the driving force distribution amount, which is the distribution amount of the driving torque to the front inner wheel 2a, is larger than the driving force distribution amount, which is the distribution amount of the driving torque to the rear inner wheel 3a, and when the ground load of the front inner wheel 2a is smaller than the ground load of the rear inner wheel 3a, the driving force distribution amount, which is the distribution amount of the driving torque to the front inner wheel 2a, is smaller than the driving force distribution amount, which is the distribution amount of the driving torque to the rear inner wheel 3a, whereby excellent acceleration performance can be ensured.

In view of this, in the present invention, in a four-wheel drive force distribution device that distributes drive force to each wheel of a four-wheel drive vehicle, the drive force distribution amount to the front inner wheel 2a and the drive force distribution amount to the rear inner wheel 3a are adjusted based on the ground contact load of the front inner wheel 2a and the ground contact load of the rear inner wheel 3a when the vehicle 1 turns, and the smaller the proportion of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3a in turning, the smaller the drive force distribution amount to the front inner wheel 2a than the drive force distribution amount to the rear inner wheel 3 a.

In this case, in one embodiment of the present invention, the same driving torque, i.e., the same driving force, is distributed to the front inner wheel 2a and the front outer wheel 2b, and the same driving torque, i.e., the same driving force, is distributed to the rear inner wheel 3a and the rear outer wheel 3 b. That is, the smaller the proportion of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3a during turning, the smaller the driving force distribution amount to the pair of front wheels 2a, 2b is, the smaller the driving force distribution amount to the pair of rear wheels 3a, 3b is.

In addition, in the preferred embodiment of the present invention, the ratio of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3a is calculated at the time of turning of the vehicle, and the driving force is distributed to the front inner wheel 2a and the rear inner wheel 3a according to the ratio at the time of turning. In this case, in the preferred embodiment of the present invention, the driving force is distributed to the pair of front wheels 2a, 2b and the pair of rear wheels 3a, 3b according to the ratio during turning. In view of this, a method of calculating the ratio of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3a during turning will be described with reference to fig. 9A, 9B, and 10.

Fig. 9A is a view of the vehicle 1 as seen from the lateral direction as in fig. 6A, and fig. 9B is a view of the vehicle 1 as seen from the front as in fig. 6B. In fig. 9A and 9B, Hs represents the height of the center of gravity, T represents the vehicle track, L represents the wheel base, wf represents the vehicle load applied to the pair of front wheels 2a, 2B in the vehicle stopped state, wr represents the vehicle load applied to the pair of rear wheels 3a, 3B in the vehicle stopped state, G represents the vehicle load applied to the pair of rear wheels 2a, 2B in the vehicle stopped state, and_Xrepresents the front-rear acceleration, Gy represents the lateral acceleration. Therefore, as shown in fig. 9A and 9B, the ground contact load of each front wheel 2a, 2B in the vehicle stopped state is wf/2, and the ground contact load of each rear wheel 3a, 3B in the vehicle stopped state is wr/2.

Further, assuming that the weight of the vehicle 1 is m, the vehicle 1 is subjected to the longitudinal acceleration G_XWhen the amount of change in the load applied to the front wheels 2a and 2b and the amount of change in the load applied to the rear wheels 3a and 3b are Δ wx, respectively, in fig. 9A, when the vehicle 1 generates the front-rear acceleration G_XThen, a moment Ma (m · G) as shown in fig. 6A_XHs) acts on the vehicle 1. Since 1/2 of the moment Ma generates a moment (Δ wx · L) that causes a change in the load applied to the front wheels 2a and the rear wheels 2b, respectively, and the remaining 1/2 of the moment Ma generates a moment (Δ wx · L) that causes a change in the load applied to the front wheels 2b and the rear wheels 3b, respectively, as shown in fig. 9A, the ground contact load change amount Δ wx of each of the front wheels 2a, 2b and each of the rear wheels 3a, 3b becomes 39wx ═ 1/2 · m · G_X·Hs/L。

On the other hand, when the lateral acceleration Gy is generated in the vehicle 1, a moment Mb (m · Gy · Hs) as shown in fig. 6B acts on the vehicle 1. However, in this case, the distribution ratio of the torque Mb and the longitudinal acceleration G generated in the vehicle 1 are equal to each other_XSlightly different. That is, in the vehicle, the spring force of the suspension device for the front wheels is generally stronger than the spring force of the suspension device for the rear wheels, and in the embodiment according to the present invention, the spring force of the suspension device for the front wheels 2a, 2b is also stronger than the spring force of the suspension device for the rear wheelsSpring force of the suspension means of the wheels 3a, 3 b. Therefore, as shown in fig. 9B, when the lateral acceleration Gy is applied to the vehicle 1, the moment that causes the change in the load applied to the front inner wheel 2a and the front outer wheel 2B is larger than the moment that causes the change in the load applied to the rear inner wheel 3a and the rear outer wheel 3B.

In this case, when Dwf is used as the distribution ratio of the moment Mb, Dwf is used as the distribution ratio of the moment Mb to the moment causing the change in the load applied to the front inner wheel 2a and the front outer wheel 2b, 1 to Dwf is used as the distribution ratio of the moment Mb to the moment causing the change in the load applied to the rear inner wheel 3a and the rear outer wheel 3b, Δ wy is used as the change amount of the ground contact load of the front inner wheel 2a and the front outer wheel 2b, and Δ wz is used as the change amount of the ground contact load of the rear inner wheel 3a and the rear outer wheel 3b, when the lateral acceleration Gy is generated in the vehicle 1, the moment Mb · Dwf generates a moment (Δ wy · T) that causes a change in the load applied to the front inner wheel 2a and the front outer wheel 2b, respectively, and the moment Mb · (1-Dwf) generates a moment (Δ wz · T) that causes a change in the load applied to the rear inner wheel 3a and the rear outer wheel 3b, respectively. Therefore, as shown in fig. 9B, the amount of change in the ground contact load Δ wy between the front inner wheel 2a and the front outer wheel 2B becomes (m · Gy · Hs/L) · Dwf, and as shown in fig. 9B, the amount of change in the ground contact load Δ wz between the rear inner wheel 3a and the rear outer wheel 3B becomes (m · Gy · Hs/L) · (1-Dwf). Here, the distribution ratio Dwf of the moment Mb is, for example, 0.6.

During the turning of the vehicle 1, the front-rear acceleration G is generated in the vehicle 1_XSince the ground contact load of the front inner wheel 2a decreases when the lateral acceleration Gy is generated and the ground contact load of the front inner wheel 2a also decreases when the lateral acceleration Gy is generated, as shown by formula a in fig. 10, the ground contact load variation Δ wf of the front inner wheel 2a becomes (m.gy · Hs) · Dwf and the ground contact load variation Δ wy of the front inner wheel 2a and the front outer wheel 2b when the lateral acceleration Gy is generated and (m.gy · Hs) · Dwf when the front-rear acceleration G is generated in the vehicle 1_XThe ground contact load variation Δ wx of the front wheels 2a and 2b and the rear wheels 3a and 3b at that time is 1/2 · m · G_XThe sum of Hs/L. On the other hand, during the turning of the vehicle 1, the vehicle 1 generates the front-rear acceleration G_XWhen the ground contact load of the rear inner wheel 3a increases and the lateral acceleration Gy occurs, the rear wheelSince the ground contact load of the inner race 3a decreases, as shown by formula a in fig. 10, the ground contact load variation (decrease) Δ wr of the rear inner race 3a is obtained by subtracting the front-rear acceleration G generated in the vehicle 1 from the ground contact load variation Δ wy of the front inner race 2a and the front outer race 2b when the lateral acceleration Gy is generated, which is (m · Gy · Hs/L) · (1-Dwf)_XThe ground contact load variation Δ wx of the front wheels 2a and 2b and the rear wheels 3a and 3b at that time is 1/2 · m · G_XHs/L.

Further, since the ground contact load of the front wheels 2a in the vehicle stopped state is wf/2 as described above, the front-rear acceleration G is generated during the turning of the vehicle 1_XAnd the ground contact load of the front inner wheel 2a at the time of the lateral acceleration Gy is a value (wf/2- Δ wf) obtained by subtracting the ground contact load change Δ wf of the front inner wheel 2a from wf/2. On the other hand, since the ground contact load of the rear wheels 3a in the vehicle stopped state is wr/2, the front-rear acceleration G is generated during the turning of the vehicle 1_XAnd the ground contact load of the rear inner wheel 3a at the time of the lateral acceleration Gy is a value (wr/2- Δ wr) obtained by subtracting the ground contact load change amount Δ wr of the rear inner wheel 3a from wr/2. As described above, in embodiment 1 according to the present invention, the longitudinal acceleration sensor 50 for detecting the acceleration in the longitudinal direction of the vehicle and the lateral acceleration sensor 51 for detecting the acceleration in the lateral direction of the vehicle are provided, and the longitudinal acceleration G detected by the longitudinal acceleration sensor 50 is based on the longitudinal acceleration G_XAnd a ratio of the ground contact load (wf/2- Δ wf) of the front inner wheel 2a to the ground contact load (wr/2- Δ wr) of the rear inner wheel 3a is calculated from the lateral acceleration Gy detected by the lateral acceleration sensor 51, and a driving torque, i.e., a driving force, is distributed to the front inner wheel 2a and the rear inner wheel 3a in proportion to the ground contact load (wf/2- Δ wf) of the front inner wheel 2a and the ground contact load (wr/2- Δ wr) of the rear inner wheel 3 a.

In the embodiment according to the present invention, as shown in formula B of fig. 10, the ground contact load (wf/2- Δ wf) of the front inner wheels 2a and the ground contact load (wr/2- Δ wr) of the rear inner wheels 3a are used to calculate the driving torque of the front inner wheels 2a during turning of the vehicle, that is, the distributed amount Dpf of the driving force and the driving torque of the rear inner wheels 3a, that is, the distributed amount Dpr of the driving force (═ 1-Dpf), and the driving force is distributed to the front inner wheels 2a and the rear inner wheels 3a during turning based on the distributed amounts Dpf and Dpr. Further, in this embodiment 1, the driving force is distributed to the pair of front wheels 2a, 2b and the pair of rear wheels 3a, 3b in accordance with these distribution amounts Dpf and Dpr during turning.

FIG. 11 shows a diagram illustrating the longitudinal acceleration G generated in the vehicle 1 when the resultant Fxy of the longitudinal force Fx and the lateral force Fy of each tire is a limit_XAnd the calculation result of the relationship of the lateral acceleration Gy. In fig. 11, Q1 represents a case where front wheel drive is performed, Q2 represents a case where rear wheel drive is performed, Q3 represents a case where the driving force distribution to the front inner wheel 2a and the front outer wheel 2b and the rear inner wheel 3a and the rear outer wheel 3b is performed according to the ratio of the ground contact load average value of the front inner wheel 2a and the front outer wheel 2b to the ground contact load average value of the rear inner wheel 3a and the rear outer wheel 3b, and Q4 represents a case where the driving force distribution to the front inner wheel 2a and the front outer wheel 2b and the rear inner wheel 3a and the rear outer wheel 3b is performed according to the ratio of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3 a. The relationship shown in FIG. 11 clearly shows the actual front-rear acceleration G_XAnd the lateral acceleration Gy. As is apparent from fig. 11, when the driving forces of the front inner wheel 2a and the front outer wheel 2b and the rear inner wheel 3a and the rear outer wheel 3b are distributed according to the ratio of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3a as shown in Q4, the front-rear acceleration G generated in the vehicle 1 can be set to the limit of the resultant Fxy of the front-rear force Fx and the lateral force Fy of each tire_XAnd the lateral acceleration Gy is maximized, i.e., the acceleration performance and the cornering performance are maximized.

Next, embodiment 2 of the present invention will be described with reference to fig. 12 to 13B. In the embodiment 2, when the distribution amount Dpf of the drive torque to the pair of front wheels 2a, 2B and the distribution amount Dpr of the drive torque to the pair of rear wheels 3a, 3B are calculated using the equations a and B of fig. 10, the front-rear acceleration G is used_XAnd an inferred value of the lateral acceleration Gy. Fig. 12 shows an electronic control unit 40 and the like used in this embodiment 2. As is clear from fig. 12, in embodiment 2, an accelerator opening degree sensor 54 and a detection sensor 54 for detecting an accelerator opening degree may be used instead of the front-rear G sensor 50 and the lateral G sensor 51 shown in fig. 1 and 3A rotation speed sensor 55 that measures the engine rotation speed is input to the input port 45 via the AD converter 47. In embodiment 2, the longitudinal acceleration G is estimated based on the accelerator opening detected by the accelerator opening sensor 54, the engine speed detected by the speed sensor 55, the steering angle detected by the steering angle sensor 52, and the vehicle speed detected by the vehicle speed sensor 53_XAnd lateral acceleration Gy.

First, the front and rear acceleration G is estimated_XThe method of (3) is explained as follows, the driving torque of the tire is obtained by multiplying the output torque of the internal combustion engine by the reduction gear ratio in the driving torque distributor 5 and the differentials 8 and 10, and the front-rear force Fx generated in the ground contact surface of the tire is obtained by dividing the driving torque of the tire by the radius of the tire. The front-rear force Fx is determined by the vehicle weight and the front-rear acceleration G_XThe product of (1) indicates that the radius of the tire and the vehicle weight are constant, and as a result, the longitudinal acceleration G is determined from the output torque of the internal combustion engine and the reduction gear ratio_X. On the other hand, as shown in fig. 13A, the output torque of the internal combustion engine is a function of the accelerator opening degree and the engine speed, and therefore the output torque of the internal combustion engine is obtained from the accelerator opening degree and the engine speed. Therefore, in this 2 nd embodiment, the front-rear acceleration G is calculated from the accelerator opening degree, the engine speed, and the reduction gear ratio_XThe front and rear acceleration G_XIs taken as the front-rear acceleration G_XThe inferred value of (1).

On the other hand, the lateral acceleration Gy is larger as the steering angle at the time of turning action is larger, and larger as the vehicle speed at the time of turning action is larger. That is, the lateral acceleration Gy is a function of the steering angle and the vehicle speed. In this embodiment 2, the lateral acceleration Gy is calculated according to the equation shown in fig. 13B. In the equation shown in fig. 13B, St represents a steering angle, V represents a vehicle speed, L represents a wheel base, n represents a steering gear ratio (a steering angle to a gear ratio of each tire), and K represents a stability factor (a constant determined according to a vehicle). In the 2 nd embodiment, the lateral acceleration Gy is calculated from the steering angle and the vehicle speed using the equation shown in fig. 13B, and the front-rear acceleration G is calculated_XCalculated values before and afterAcceleration G_XThe inferred value of (1).

In this embodiment 2, these front-rear accelerations G are used_XThe estimated value of the lateral acceleration Gy and the estimated value of the forward inner wheel 2a are used to calculate the distributed amount Dpf of the drive torque to the forward inner wheel 2a and the distributed amount Dpr of the drive torque to the rearward inner wheel 3a shown in fig. 10. That is, in embodiment 2, the longitudinal acceleration G is estimated from the engine output torque and the gear ratio between the engine and the drive wheels_XThe lateral acceleration Gy is estimated from the steering angle and the vehicle speed, and the estimated longitudinal acceleration G is used as the basis_XAnd the inferred lateral acceleration Gy to calculate the ratio of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3 a.

Fig. 14 to 16 show an example added to embodiment 1 and embodiment 2. First, referring to fig. 14 showing the same state as fig. 8B, in this embodiment, when the vehicle 1 is made to turn, the yaw moment Mz required to improve the turning performance to the maximum is obtained, and the braking force is applied only to the front inner wheel 2a and the rear inner wheel 3a by the brake control device 32 shown in fig. 1 or 3 so as to generate the yaw moment Mz. At this time, the braking force generated on the contact surface of the tire is represented as a front-rear force Fx in fig. 14. In this case, the braking force is applied to the front inner wheel 2a and the rear inner wheel 3a in proportion to the ground contact load of the front inner wheel 2a and the ground contact load of the rear inner wheel 3a so that the braking force does not exceed the limit of the grip force. That is, in this embodiment, during turning of the vehicle, the braking force applied to the front inner wheel 2a and the rear inner wheel 3a is distributed in accordance with the ratio of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3 a.

Next, a method of distributing the braking force will be described with reference to fig. 15. In fig. 15, equations a and B are the same as those in fig. 10, and therefore, the allocation amount Dpf of the drive torque to the front inner wheel 2a and the allocation amount Dpr of the drive torque to the rear inner wheel 3a during turning of the vehicle are calculated using equations a and B (1 to Dpf). In this embodiment, the braking force is distributed using these distribution amount Dpf and distribution amount Dpr. Thus, in fig. 15, C represents the yaw moment required to improve the turning performance to the maximumMz. As shown in the C diagram, the yaw moment Mz is the front-rear acceleration G_XAs a function of lateral acceleration Gy. Wherein these front and rear accelerations G_XAnd lateral acceleration Gy and front-rear acceleration G used in the formula A_XAnd the lateral acceleration Gy. As shown in the graph C, when the lateral acceleration Gy increases to a certain degree or more, the yaw moment Mz increases, and the longitudinal acceleration G increases_XThe larger the increase amount at this time.

Further, if the vehicle track is T and the braking force generated on the ground contact surface of the inner wheel is Fxi, then when the braking force Fxi is generated on the ground contact surface of the inner wheel, a yaw moment Fxi · T/2 is generated in the vehicle, so that in order to generate the yaw moment Mz, even if the braking force Fxi is 2Mz/T, Fxi · T/2 ═ Mz may be used. In this case, in this embodiment, as shown in equation D of fig. 15, the brake instruction value Fxif for the front inner wheel 2a and the brake instruction value Fxir for the rear inner wheel 3a are allocated based on the allocation amount Dpf and the allocation amount Dpr, respectively. That is, the brake instruction value Fxif for the front inner wheel 2a is (2Mz/T) · Dpf, and the brake instruction value Fxir for the rear inner wheel 3a is (2Mz/T) · Dpr. The brake control device 32 controls the brake fluid pressure of the front inner wheel 2a and the brake fluid pressure of the rear inner wheel 3a based on the brake instruction value Fxif and the brake instruction value Fxir so that the front inner wheel 2a generates the braking force Fxif and the rear inner wheel 3a generates the braking force Fxir.

FIG. 16 shows a graph showing the front-rear acceleration G generated in the vehicle 1 when the turning action is performed_XAnd the calculation result of the relationship of the lateral acceleration Gy. In fig. 16, R1 indicates a case where the control for generating the yaw moment Mz is not performed during the turning of the vehicle, R2 indicates a case where the braking control of only the front inner wheel 2a is performed for generating the yaw moment Mz during the turning of the vehicle, R3 indicates a case where the braking control of only the rear inner wheel 3a is performed for generating the yaw moment Mz during the turning of the vehicle, and R4 indicates a case where the braking force is distributed to the front inner wheel 2a and the rear inner wheel 3a in accordance with the ratio of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3a for generating the yaw moment Mz during the turning of the vehicle. The relationship shown in FIG. 16 clearly shows the actual front-rear acceleration G_XAnd the relation of lateral acceleration Gy. Therefore, as shown in fig. 16, when the braking force is distributed to the front inner wheel 2a and the rear inner wheel 3a according to the ratio of the ground contact load of the front inner wheel 2a to the ground contact load of the rear inner wheel 3a in order to generate the yaw moment Mz when the vehicle turns, as shown by R4, the front-rear acceleration G generated in the vehicle 1 can be increased_XAnd the lateral acceleration Gy, that is, the acceleration performance and the cornering performance can be improved.

Next, an example of the driving control will be described with reference to fig. 17. Fig. 17 shows a routine for executing this driving control, which is executed, for example, in accordance with an interrupt at every certain crank angle.

Referring to fig. 17, first, in step 70, the longitudinal acceleration G is obtained_XAnd lateral acceleration Gy. In this case, in embodiment 1, the front-rear acceleration G is detected by the front-rear G sensor 50_XThe lateral acceleration Gy is detected by the lateral G sensor 51. On the other hand, in embodiment 2, the longitudinal acceleration G is estimated from the accelerator opening degree, the engine speed, and the reduction gear ratio_XThe lateral acceleration Gy is estimated from the steering angle and the vehicle speed. Next, in step 71, the ground contact load variation Δ wf of the front inner wheel 2a and the ground contact load variation Δ wr of the rear inner wheel 3a are calculated using the formula a in fig. 10 or 15. Next, in step 72, the distributed amount Dpf of the drive torque to the front inner wheel 2a and the distributed amount Dpr of the drive torque to the rear inner wheel 3a are calculated. Next, in step 73, the yaw moment Mz is calculated from the C diagram of fig. 15.

Next, at step 74, the brake instruction value Fxif for the front inner wheel 2a and the brake instruction value Fxir for the rear inner wheel 3a are calculated using the expression D in fig. 15. Next, at step 75, the front wheels 2a, 2b and the rear wheels 3a, 3b are driven based on the distribution Dpf of the driving torque to the front inner wheel 2a and the distribution Dpr of the driving torque to the rear inner wheel 3a calculated at step 72. Next, at step 76, the braking action of the front inner wheel 2a and the braking action of the rear inner wheel 3a are performed based on the braking instruction value Fxif for the front inner wheel 2a and the braking instruction value Fxir for the rear inner wheel 3a calculated at step 74. In embodiment 1 and embodiment 2, steps 73, 74, and 76 are omitted.