阅读说明：本技术 车辆控制装置 (Vehicle control device ) 是由 武谷弘隆 中野启太 于 2020-02-25 设计创作，主要内容包括：本发明例如是一种车辆控制装置,具备：驱动力控制部,控制车辆的车轮产生的驱动力；以及制动力控制部,控制所述车轮产生的制动力,其中,通过由所述驱动力控制部产生第一规定量的所述驱动力,并且由所述制动力控制部产生第二规定量的所述制动力,将所述车辆的速度控制为恒定,通过进行由所述驱动力控制部对所述驱动力的控制以及由所述制动力控制部对所述制动力的控制中的一者,对加速和减速均能够进行控制。(The present invention is a vehicle control device, for example, including: a driving force control unit that controls driving force generated by wheels of a vehicle; and a braking force control unit that controls a braking force generated by the wheel, wherein the speed of the vehicle is controlled to be constant by generating the driving force by a first predetermined amount by the driving force control unit and generating the braking force by a second predetermined amount by the braking force control unit, and both acceleration and deceleration can be controlled by performing one of the control of the driving force by the driving force control unit and the control of the braking force by the braking force control unit.)

1. A vehicle control device is provided with:

a driving force control unit that controls driving force generated by wheels of a vehicle; and

a braking force control unit that controls a braking force generated by the wheel,

wherein the speed of the vehicle is controlled to be constant by generating the driving force of a first prescribed amount by the driving force control portion and generating the braking force of a second prescribed amount by the braking force control portion,

the acceleration and deceleration can be controlled by performing one of the control of the driving force by the driving force control unit and the control of the braking force by the braking force control unit.

2. The vehicle control apparatus according to claim 1,

the vehicle includes, as a device for generating braking force for the wheel, a brake device with a braking force retaining mechanism capable of retaining braking force before a disappearance of an energy supply for generating braking force even after the disappearance of the energy supply,

the braking force control unit controls the braking device with the braking force holding mechanism to generate a braking force of a third predetermined amount or more smaller than the second predetermined amount while the vehicle is traveling.

3. The vehicle control apparatus according to claim 2,

the vehicle includes an EPB as the brake device with the braking force holding mechanism and a hydraulic brake device as a device for generating braking force to the wheels, the EPB and the hydraulic brake device being configured to selectively function with one of large braking force,

the braking force control unit determines whether the EPB is operating normally based on a relationship between the driving force and an acceleration of the vehicle when outputting an instruction to control the EPB to generate an electric braking force while the vehicle is traveling.

4. The vehicle control apparatus according to claim 1,

the vehicle includes an EPB and a hydraulic brake device as a device for generating braking force for the wheels, the EPB and the hydraulic brake device being configured to selectively exert a larger braking force,

during the stop of the vehicle, the braking force control unit controls the EPB to generate an electric braking force of a fourth predetermined amount larger than the second predetermined amount, and thereafter controls the EPB to reduce the electric braking force to a third predetermined amount smaller than the second predetermined amount before the vehicle is started.

5. The vehicle control apparatus according to claim 4,

the braking force control unit adjusts the electric braking force by estimating the electric braking force based on a current characteristic of a brake mechanism drive motor in release control for releasing the electric braking force when controlling the EPB to reduce the electric braking force to the third predetermined amount before starting the vehicle.

Technical Field

The present invention relates to a vehicle control device.

Background

In current vehicles, there are increasing cases where a function of autonomously performing speed control during parking is provided. This function recognizes the surrounding situation of the vehicle and the like by various sensors and automatically controls the vehicle speed adjustment up to the parking position.

In this case, the speed of the vehicle is generally adjusted by dynamically controlling the driving force and the braking force in parallel.

Further, patent document 1 discloses that in a system for automatically controlling the speed of a vehicle, when a hydraulic brake fails to generate a braking force due to a failure, an electric brake (parking brake) generates a braking force in a good response instead, thereby improving safety.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 6408585

Disclosure of Invention

Technical problem to be solved by the invention

However, in the conventional technology, when the driving force and the braking force are dynamically controlled in parallel depending on the state of the road such as a slope, control interference may occur due to differences in control responsiveness and accuracy between the respective control responses, and control may be complicated to prevent the control interference. In addition, when there is a failure in the hydraulic brake, if the control device of the electric brake delays the detection of the failure, or if the hydraulic brake and the control device of the electric brake are integrally configured, the electric brake may not be able to realize the braking force as intended.

Therefore, an object of the present invention is to provide a vehicle control device that can simplify control of driving force and braking force and has high safety.

Technical solution for solving technical problem

The present invention is a vehicle control device, for example, including: a driving force control unit that controls driving force generated by wheels of a vehicle; and a braking force control unit that controls a braking force generated by the wheel, wherein the speed of the vehicle is controlled to be constant by generating the driving force by a first predetermined amount by the driving force control unit and generating the braking force by a second predetermined amount by the braking force control unit, and both acceleration and deceleration can be controlled by performing one of control of the driving force by the driving force control unit and control of the braking force by the braking force control unit. In this case, when the speed of the vehicle is controlled to be constant, the first predetermined amount and the second predetermined amount are the same value if the vehicle is traveling on a flat road, and the second predetermined amount is a value different from the first predetermined amount in consideration of the gravitational acceleration if the vehicle is traveling on an uphill or a downhill.

Drawings

Fig. 1 is a schematic diagram showing an overall outline of a vehicle brake device according to a first embodiment.

Fig. 2 is a schematic cross-sectional view of a wheel braking mechanism of a rear wheel system provided in the vehicle braking device according to the first embodiment.

Fig. 3 is a time chart showing an example of the temporal change of each physical quantity at the time of vehicle control in the first embodiment.

Fig. 4 is a flowchart showing a process performed by the vehicle control device of the first embodiment.

Fig. 5 is a time chart showing an example of the temporal change of each physical quantity at the time of vehicle control in the second embodiment.

Fig. 6 is a time chart showing an example of temporal changes in the respective physical quantities when the electric braking force is reduced before the vehicle starts in the second embodiment.

Fig. 7 is a flowchart showing a process performed by the vehicle control device of the second embodiment.

Fig. 8 is a time chart showing an example of the temporal change of each physical quantity at the time of vehicle control in the third embodiment.

Fig. 9 is a flowchart showing a process performed by the vehicle control device of the third embodiment.

Detailed Description

Hereinafter, exemplary embodiments (first to third embodiments) of the present invention are disclosed. The structure of the embodiment shown below, and the action and result (effect) produced by the structure are examples. The present invention can be realized by other configurations than those disclosed in the following embodiments. In addition, according to the present invention, at least one of various effects (including derived effects) obtained by the following structure can be obtained.

(first embodiment)

In the first embodiment, a vehicle Brake device in which a disc Brake type EPB (Electric park Brake) is applied to a rear wheel system will be described as an example. Fig. 1 is a schematic diagram showing an overall outline of a vehicle brake device according to a first embodiment. Fig. 2 is a schematic cross-sectional view of a wheel braking mechanism of a rear wheel system provided in the vehicle braking device according to the first embodiment. Hereinafter, the description will be made with reference to these drawings.

As shown in fig. 1, the vehicle brake device according to the first embodiment includes a service brake 1 (hydraulic brake device) and an EPB 2.

The service brake 1 is a hydraulic brake mechanism that generates a service braking force (hydraulic braking force) by pressing a brake pad 11 with hydraulic pressure toward a disc 12 that rotates integrally with a wheel, based on depression of a brake pedal 3 by a driver. Specifically, the service brake 1 multiplies the depression force corresponding to the depression of the brake pedal 3 by the driver by the multiplying device 4, and then generates the brake fluid pressure corresponding to the multiplied depression force in the master cylinder (hereinafter, referred to as M/C.) 5. Then, the brake fluid pressure is transmitted to wheel cylinders (hereinafter referred to as W/C.) 6 provided in wheel brake mechanisms of the respective wheels, thereby generating a running brake force. Further, an actuator 7 for controlling the brake hydraulic pressure is provided between the M/C5 and the W/C6. The actuator 7 adjusts the service braking force generated by the service brake 1, and performs various controls (e.g., cleat control, etc.) for improving the safety of the vehicle.

Various controls using the actuator 7 are executed by an ESC (Electronic Stability Control) ECU8 that controls the running braking force. For example, the ESC-ECU8 outputs a control current for controlling various control valves, not shown, provided in the actuator 7 and a motor for driving a pump, thereby controlling a hydraulic circuit provided in the actuator 7 and controlling the pressure transmitted to the W/C of the W/C6. This improves the safety of the vehicle, for example, by avoiding wheel slip.

For example, the actuator 7 includes, for each wheel, a pressure increasing control valve that controls the brake fluid pressure generated in the M/C5 or the brake fluid pressure generated by the driving of the pump applied to the W/C6, a pressure reducing control valve that reduces the W/C pressure by supplying the brake fluid in each W/C6 to the reservoir, and the like, and the actuator 7 is configured to be capable of performing pressure increasing, holding, and pressure reducing control on the W/C. Further, the actuator 7 can realize the automatic pressurizing function of the service brake 1, and can automatically pressurize the W/C6 even in a state where there is no brake operation, based on the pump drive and the control of various control valves.

On the other hand, EPB2 generates an electric braking force by driving the wheel brake mechanism by motor 10, and is configured to have EPB-ECU9 (braking force control section) that controls the driving of motor 10. Specifically, for example, the EPB2 presses the brake pad 11 toward the brake disc 12 by driving the motor 10, and generates electric braking force so that the vehicle does not make unintended movement while parked. EPB-ECU9 and ESC-ECU8 transmit and receive information by CAN (Controller Area Network) communication, for example.

The wheel brake mechanism is a mechanical structure that generates braking force in the vehicle brake device of the first embodiment, and first, the wheel brake mechanism of the front wheel system is provided with a structure that generates service braking force by operation of the service brake 1. On the other hand, the wheel brake mechanism of the rear wheel system is provided in a common configuration that generates braking force for both the operation of the service brake 1 and the operation of the EPB 2. The wheel brake mechanism of the front wheel system is a wheel brake mechanism that is generally used in the related art, except for a mechanism that generates an electric braking force based on an operation of the EPB2, with respect to the wheel brake mechanism of the rear wheel system, and therefore, a description thereof will be omitted, and a description thereof will be given below.

In the wheel brake mechanism of the rear wheel system, not only when the service brake 1 is actuated but also when the EPB2 is actuated, the brake pad 11 as a friction member shown in fig. 2 is pressed, and the brake disc 12(12RL, 12RR, 12FR, 12FL) as a friction receiving member is sandwiched by the brake pad 11, so that a frictional force is generated between the brake pad 11 and the brake disc 12, and a braking force is generated.

Specifically, in the brake caliper 13 shown in fig. 1, as shown in fig. 2, the motor 10 directly fixed to the main body 14 of the W/C6 for pressing the brake pad 11 is rotated, whereby the spur gear 15 provided on the drive shaft 10a of the motor 10 is rotated. Then, the brake pads 11 are moved by transmitting the rotational force (output) of the motor 10 to the spur gear 16 meshed with the spur gear 15, and electric braking force by the EPB2 is generated.

In the brake caliper 13, a part of the end surface of the brake disc 12 is accommodated so as to be sandwiched by the brake pads 11 in addition to the W/C6 and the brake pads 11. The W/C6 is configured to generate a W/C pressure in the hollow portion 14a as the brake fluid storage chamber by introducing the brake fluid pressure into the hollow portion 14a of the cylindrical body 14 through the passage 14b, and is configured to include the rotation shaft 17, the thrust shaft 18, the piston 19, and the like in the hollow portion 14 a.

One end of the rotary shaft 17 is connected to the spur gear 16 through an insertion hole 14c formed in the main body 14, and when the spur gear 16 rotates, the rotary shaft 17 rotates in accordance with the rotation of the spur gear 16. A male screw groove 17a is formed in an outer peripheral surface of the rotary shaft 17 at an end opposite to an end connected to the spur gear 16 in the rotary shaft 17. On the other hand, the other end of the rotary shaft 17 is pivotally supported by being inserted into the insertion hole 14 c. Specifically, a bearing 21 is provided in the insertion hole 14c together with the O-ring 20, and the O-ring 20 prevents brake fluid from leaking through between the rotary shaft 17 and the inner wall surface of the insertion hole 14c, and the bearing 21 supports the other end of the rotary shaft 17.

The propeller shaft 18 is formed by a nut formed of a hollow cylindrical member, and has a female screw groove 18a formed in an inner wall surface thereof to be screwed into the male screw groove 17a of the rotary shaft 17. The thrust shaft 18 is configured to have a cylindrical or polygonal columnar shape provided with a rotation prevention key, for example, and is configured not to rotate about the rotation center of the rotation shaft 17 even when the rotation shaft 17 rotates. Therefore, when the rotary shaft 17 is rotated, the rotational force of the rotary shaft 17 is converted into a force that moves the propeller shaft 18 in the axial direction of the rotary shaft 17 by the engagement of the male screw groove 17a and the female screw groove 18 a. When the driving of the motor 10 is stopped, the propulsion shaft 18 is stopped at the same position by the frictional force generated by the engagement of the male screw groove 17a and the female screw groove 18a, and if the driving of the motor 10 is stopped when the target electric braking force is reached, the propulsion shaft 18 is held at the position, and the desired electric braking force can be maintained and self-locking (hereinafter, simply referred to as "locking").

The piston 19 is disposed so as to surround the outer periphery of the propeller shaft 18, is formed of a bottomed cylindrical member or a polygonal cylindrical member, and is disposed so that the outer peripheral surface thereof is in contact with the inner wall surface of the hollow portion 14a formed in the body 14. In order to prevent brake fluid leakage between the outer peripheral surface of the piston 19 and the inner wall surface of the body 14, a structure is provided in which a seal member 22 is provided on the inner wall surface of the body 14 and W/C pressure is applied to the end surface of the piston 19. The seal member 22 is used to generate a reaction force for pulling back the piston 19 at the time of release control after the lock control. Since the seal member 22 is provided, basically, even if the brake pad 11 and the piston 19 are pressed within a range not exceeding the elastic deformation amount of the seal member 22 by the brake disc 12 inclined during the rotation, the brake pad 11 and the piston 19 can be pushed back toward the brake disc 12 side and a predetermined gap (gap C2 in fig. 2) can be maintained between the brake disc 12 and the brake pad 11.

Further, in order that the piston 19 does not rotate about the rotation center of the rotation shaft 17 even if the rotation shaft 17 rotates, when the rotation prevention key is provided on the thrust shaft 18, the piston 19 is provided with a key groove in which the key slides, and when the thrust shaft 18 has a polygonal columnar shape, the piston 19 has a polygonal tubular shape corresponding to the shape of the key groove.

A brake pad 11 is disposed at the tip end of the piston 19, and the brake pad 11 is moved in the left-right direction on the paper surface in accordance with the movement of the piston 19. Specifically, the piston 19 is configured to be movable in the left direction of the drawing sheet in accordance with the movement of the thrust shaft 18, and is configured to be movable in the left direction of the drawing sheet independently of the thrust shaft 18 by applying a W/C pressure to an end portion of the piston 19 (an end portion opposite to the end portion on which the brake pad 11 is disposed). When the push shaft 18 is located at the release position (the state before the motor 10 is rotated) which is the standby position at the time of normal release, if the brake fluid pressure in the hollow portion 14a is not applied (the W/C pressure is 0), the piston 19 is moved in the right direction of the drawing by the elastic force of the seal member 22 which will be described later, and the brake pad 11 is separated from the brake disc 12.

When the motor 10 rotates and the thrust shaft 18 moves from the initial position to the left direction on the paper surface, even if the W/C pressure is zero, the moving thrust shaft 18 regulates the movement of the piston 19 to the right direction on the paper surface, and the brake pad 11 is held at that position. Further, a clearance C1 in fig. 2 indicates a distance between the tip of the propeller shaft 18 and the piston 19. After the release of the EPB is completed, the propulsion shaft 18 is positionally fixed relative to the main body 14.

In the wheel brake mechanism configured as described above, when the service brake 1 is operated, the piston 19 is moved in the paper-left direction based on the W/C pressure generated thereby, and the brake pad 11 is pressed against the brake disc 12, thereby generating a service braking force. When the EPB2 is operated, the drive motor 10 rotates the spur gear 15, and the spur gear 16 and the rotary shaft 17 rotate in association therewith, so that the thrust shaft 18 moves toward the brake disk 12 (in the left direction of the drawing) based on the engagement between the male screw grooves 17a and the female screw grooves 18 a. Then, along with this, the tip end of the propeller shaft 18 abuts on the piston 19 and presses the piston 19, and the piston 19 also moves in the same direction, whereby the brake pad 11 presses the brake disc 12, and electric braking force is generated. Therefore, a common wheel brake mechanism can be formed that generates braking force for both the operation of the service brake 1 and the operation of the EPB 2.

In the vehicle brake device according to the first embodiment, the state of generation of the electric braking force by the EPB2 can be confirmed or the current detection value can be recognized by confirming the current detection value by a current sensor (not shown) that detects the current of the motor 10.

The front-rear G sensor 25 detects G (acceleration) in the front-rear direction (traveling direction) of the vehicle, and sends a detection signal to the EPB-ECU 9.

The M/C pressure sensor 26 detects the M/C pressure in the M/C5, and sends a detection signal to the EPB-ECU 9.

The temperature sensor 28 detects the temperature of a wheel brake mechanism (e.g., a brake disc), and sends a detection signal to the EPB-ECU 9.

The wheel speed sensor 29 detects the rotation speed of each wheel and sends a detection signal to the EPB-ECU 9. Although the wheel speed sensors 29 are actually provided one for each wheel, detailed illustration and description thereof are omitted here.

EPB-ECU9 is constituted by a known microcomputer including a CPU, ROM, RAM, I/O, and the like, and controls the rotation of motor 10 in accordance with a program stored in the ROM or the like to perform parking brake control.

The EPB-ECU9 inputs a signal or the like corresponding to the operation state of an operation SW (switch) 23 provided on an instrument panel (not shown) in the vehicle, for example, and drives the motor 10 according to the operation state of the operation SW 23. Further, the EPB-ECU9 executes lock control, release control, and the like based on the current detection value of the motor 10, and recognizes, based on the control state, that it is in lock control or by lock control so that the wheels are in a locked state, and that it is in release control or by release control so that the wheels are in a released state (EPB released state). Then, the EPB-ECU9 outputs signals for performing various displays to the display lamps 24 provided on the instrument panel.

In the vehicle brake device configured as described above, basically, when the vehicle is traveling, the service brake 1 generates a service braking force to generate a braking force for the vehicle. When the vehicle is stopped by the service brake 1, the driver presses the operation SW23 to operate the EPB2 to generate the electric braking force and maintain the stopped state, or thereafter releases the electric braking force. That is, when the brake pedal 3 is operated by the driver while the vehicle is running as the operation of the service brake 1, the brake fluid pressure generated in the M/C5 is transmitted to the W/C6 to generate a service braking force. In addition, as the operation of the EPB2, the motor 10 is driven to move the piston 19, and the brake pad 11 is pressed against the disc 12 to generate the electric braking force to lock the wheel, or the brake pad 11 is separated from the disc 12 to release the electric braking force to release the wheel.

Specifically, by the lock/release control, the electric braking force is generated or released. In the lock control, the EPB2 is operated by rotating the motor 10 in the forward direction, and the rotation of the motor 10 is stopped at a position where a desired electric braking force is generated by the EPB2, and this state is maintained. Thereby, a desired electric braking force is generated. In the release control, the motor 10 is reversed to operate the EPB2 and release the electric braking force generated by the EPB 2.

In addition, even when the vehicle is traveling, for example, in an emergency, during automatic driving, or when the service brake 1 is broken down, the EPB2 may be effectively used, and therefore, the EPB2 may be used in such cases. For example, EPB2 may be used as a means for generating braking force during automatic driving.

A vehicle control device is provided with: a driving force control unit (not shown) for controlling a driving force generated by wheels of the vehicle; and a braking force control unit (ESC-ECU8, EPB-ECU9) for controlling the braking force generated by the wheels. In the first embodiment, the vehicle control device controls the speed of the vehicle to be constant by generating the driving force of the first predetermined amount by the driving force control unit and generating the braking force of the second predetermined amount by the braking force control unit. When the speed of the vehicle is controlled to be constant, the first predetermined amount and the second predetermined amount have the same value when the vehicle is traveling on a flat ground, and the second predetermined amount has a value different from the first predetermined amount in consideration of the gravitational acceleration when the vehicle is traveling on an uphill or a downhill. Further, both acceleration and deceleration can be controlled by performing one of control of the driving force by the driving force control section and control of the braking force by the braking force control section. That is, the vehicle control device can make the speed of the vehicle constant by controlling the driving force and the braking force so as to balance them, and can realize both acceleration and deceleration by dynamically controlling either one of the driving force and the braking force from this state.

Fig. 3 is a time chart showing an example of the temporal change of each physical quantity at the time of vehicle control in the first embodiment. In fig. 3, (a) shows a vehicle body speed, (b) shows a vehicle body acceleration, (c) shows a driving force, and (d) shows a braking force (hydraulic braking force, electric braking force).

In addition, since the following embodiments show examples of the situation where the vehicle travels on flat ground, the first predetermined amount generated by the driving force control unit and the second predetermined amount generated by the braking force control unit have the same value. As described above, in a situation where the vehicle is traveling on an uphill or a downhill, the first predetermined amount and the second predetermined amount will show different values.

At time t1 when the vehicle is stopped, both the driving force and the braking force are generated, but the stopped state of the vehicle can be maintained by increasing the braking force. Thereafter, when the vehicle is started at time t2, the vehicle can be started by reducing the braking force to the driving force or less while the driving force is fixed. Then, by dynamically controlling the braking force in a state where the driving force is fixed until time t9, the vehicle can be accelerated in a period where the driving force is larger than the braking force and decelerated in a period where the driving force is smaller than the braking force.

Then, at time t9 to time t10, the driving force and the braking force are balanced, whereby the vehicle body acceleration can be made zero and the vehicle body speed can be made constant.

Further, at time t10 to time t13, by dynamically controlling the driving force with the braking force fixed, the vehicle can be accelerated in a period in which the driving force is larger than the braking force, and can be decelerated in a period in which the driving force is smaller than the braking force.

Thereafter, at time t13 to time t14, the driving force and the braking force are balanced, whereby the vehicle body acceleration can be made zero and the vehicle body speed can be made constant.

Further, after time t14, by dynamically controlling the braking force in a state where the driving force is fixed, the vehicle can be accelerated in a period where the driving force is larger than the braking force, and can be decelerated in a period where the driving force is smaller than the braking force.

Fig. 4 is a flowchart showing a process performed by the vehicle control device of the first embodiment. Note that, in the following description, although the description of the driving force control is omitted, the driving force shown in fig. 3 (c) is generated.

During the stop of the vehicle, in step S1 (time t1 in fig. 3), the braking force drive unit (at least any one of ESC-ECU8 and EPB-ECU9) controls the brake device (at least any one of service brake 1 and EPB 2) to generate a braking force of a fourth predetermined amount (the magnitude of the braking force at time t1 to t2 in fig. 3 d) that is greater than the second predetermined amount.

Next, in step S2, the vehicle control device determines whether there is a departure request of the vehicle (for example, based on a departure determination in automatic driving (including automatic parking) at the time of a departure operation by the driver), and proceeds to step S3 in the case of yes, and returns to step S2 in the case of no.

In step S3 (time t2 in fig. 3), the braking force drive unit controls the brake device to reduce the braking force to a third predetermined amount that is smaller than the second predetermined amount (the magnitude of the braking force from time t2 to t3 in fig. 3 (d)).

In step S4, the vehicle control device adjusts the acceleration and speed of the vehicle by controlling one of the driving force and the braking force to be fixed and the other of the driving force and the braking force to be variable (after time t2 in fig. 3).

As described above, according to the vehicle control device of the first embodiment, since the acceleration and the speed of the vehicle can be adjusted by the control of fixing one of the driving force and the braking force and changing the other of the driving force and the braking force, the control of the driving force and the braking force can be simplified and the safety can be improved.

For example, when a vehicle travels on a road that repeats ascending and descending, there is a problem that not only is control complicated, but also the driving force and the braking force are uselessly generated or the control becomes unstable, which deteriorates ride quality, when the driving force and the braking force are dynamically controlled in parallel as in the conventional technique. On the other hand, according to the vehicle control device of the first embodiment, since the acceleration and the speed of the vehicle can be adjusted by the control of fixing one of the driving force and the braking force and changing the other of the driving force and the braking force, the control is simplified, and the occurrence of such a problem can be avoided or reduced.

(second embodiment)

Next, a second embodiment will be explained. The same matters as those in the first embodiment will be omitted as appropriate. The service brake 1 and the EPB2 are configured to selectively act with a large braking force. Specifically, when the motor 10 is stopped in a state where the propeller shaft 18 shown in fig. 2 is moved in the left direction of the paper surface, the electric braking force is maintained even in the absence of the hydraulic pressure, and the hydraulic braking force is generated when there is a hydraulic braking force larger than the electric braking force. Therefore, if the propeller shaft 18 is in a state of being moved to a certain extent in the left direction of the drawing sheet, even when the hydraulic brake device fails, a situation in which the braking force becomes zero can be avoided, and vehicle control with higher safety can be realized.

The EPB2 is an example of a brake device with a braking force holding mechanism that can hold a braking force before the energy supply disappears even after the energy supply for generating a braking force disappears. Further, the braking force control unit can reduce the influence of the normal control by controlling EPB2 to generate the electric braking force of a third predetermined amount or more smaller than the second predetermined amount during the traveling of the vehicle. The braking device with the braking force holding mechanism is not limited to the EPB, and may be configured to hold the hydraulic pressure at the time of failure, for example, by a normally closed solenoid valve or the like. With this configuration, the braking force of the second predetermined amount or more is generated, and the hydraulic pressure can be maintained even when a failure occurs. Here, if the brake device with the braking force holding function is EPB2, the energy refers to the current supplied to rotate the motor 10, and if the brake device with the braking force holding function is an electromagnetic valve, the energy refers to the current supplied to open and close the electromagnetic valve.

Fig. 5 is a time chart showing an example of the temporal change of each physical quantity at the time of vehicle control in the second embodiment. In fig. 5, (a) shows a vehicle body speed, (b) shows a vehicle body acceleration, (c) shows a driving force, and (d) shows a braking force. Further, (e) represents a hydraulic braking force, and (f) represents an electric braking force. Further, since the larger one of the hydraulic braking force and the electric braking force selectively acts as the braking force, that is, the braking force of (d) corresponds to the larger one of the hydraulic braking force of (e) and the electric braking force of (f) at each time.

At time t21 when the vehicle is stopped, both the driving force and the braking force are generated, but the stopped state of the vehicle can be maintained by increasing the braking force. Further, the electric braking force is increased to the fourth predetermined amount at time t21, and is decreased to the third predetermined amount at time t22, and thereafter, this state is maintained. On the other hand, the hydraulic braking force increases to the fourth predetermined amount at time t21, and decreases to the third predetermined amount at time t23 when the vehicle is started. That is, at time t23, the vehicle can be started by reducing the braking force to equal to or less than the driving force while the driving force is fixed. Then, by dynamically controlling the hydraulic braking force in a state where the driving force is fixed until time t30, the vehicle can be accelerated in a time period where the driving force is larger than the braking force and decelerated in a time period where the driving force is smaller than the braking force.

Thereafter, at time t30 to time t31, the hydraulic braking force is maintained to be the same as the driving force, and the driving force and the braking force are balanced, whereby the vehicle body acceleration can be made zero, and the vehicle body speed can be made constant.

Further, at time t31 to time t34, by dynamically controlling the driving force with the braking force fixed, the vehicle can be accelerated in a period in which the driving force is larger than the braking force, and can be decelerated in a period in which the driving force is smaller than the braking force.

Thereafter, at time t34 to time t35, the hydraulic braking force and the driving force are maintained the same, and the driving force and the braking force are balanced, whereby the vehicle body acceleration can be made zero, and the vehicle body speed can be made constant.

Further, after time t35, by dynamically controlling the hydraulic braking force in a state where the driving force is fixed, the vehicle can be accelerated in a period where the driving force is larger than the braking force, and can be decelerated in a period where the driving force is smaller than the braking force.

Here, fig. 6 is a time chart showing an example of temporal changes in the respective physical quantities when the electric braking force is reduced (at time t22 in fig. 5) before the vehicle is started in the second embodiment. In fig. 6, (a) shows an electric braking force, and (b) shows an EPB motor current value (current value of the motor 10).

While the vehicle is stopped, EPB-ECU9 controls EPB2 to generate electric braking force of a fourth predetermined amount greater than the second predetermined amount (time t21 in (f) of fig. 5), and thereafter controls EPB2 to reduce the electric braking force to the third predetermined amount (time t22 in (f) of fig. 5) before the vehicle is started.

In addition, when the EPB2 is controlled to reduce the electric braking force to the third predetermined amount before the vehicle is started, the EPB-ECU9 estimates the electric braking force based on the current characteristic of the motor 10 (brake mechanism driving motor) in the release control for releasing the electric braking force ("EPB motor current value" in fig. 6 (b), for example), and thereby can adjust the electric braking force. That is, the EPB-ECU9 can perform the release control and reduce the electric braking force to a desired value at times t25 to t26 after the lock control is performed at times t21 to t24 of fig. 6 based on the EPB motor current value. In addition, thereafter, EPB-ECU9 can perform release control and reduce the electric braking force to other desired values at times t27 to t28 of fig. 6 based on the EPB motor current value.

Fig. 7 is a flowchart showing a process performed by the vehicle control device of the second embodiment. Here, the time immediately after time t21 in fig. 5 is taken as a starting point. During the stop of the vehicle, in step S11 (time t22 in fig. 5), EPB-ECU9 controls EPB2 to reduce the electric braking force by a third predetermined amount (the magnitude of the electric braking force after time t22 in fig. 5 (d)).

Next, in step S12, the vehicle control device determines whether there is a departure request of the vehicle (for example, based on a departure determination in automatic driving (including automatic parking) or a departure operation by the driver), and if yes, it proceeds to step S13, and if no, it returns to step S12.

In step S13, the vehicle control device adjusts the acceleration and speed of the vehicle by controlling to fix one of the driving force and the braking force and to change the other of the driving force and the braking force while the electric braking force is fixed (after time t22 in fig. 5).

As described above, according to the vehicle control device of the second embodiment, since the acceleration and the speed of the vehicle can be adjusted by controlling to fix one of the driving force and the braking force and to change the other of the driving force and the braking force in a state where the electric braking force is fixed, the control of the driving force and the braking force can be simplified.

Further, by stopping the release operation and adjusting the electric braking force in the middle of the release control, the responsiveness can be improved as compared with the conventional method in which the lock control is performed and the electric braking force is adjusted after the release control is finished.

Further, since the electric braking force is maintained in the state of the third predetermined amount even while the vehicle is traveling, even when the service brake 1 fails (stops due to a failure, a power outage, or the like), the empty stroke and the air gap of the EPB2 are removed, and therefore, the EPB2 can be promptly operated to realize a required braking force.

For example, in an assist system (vehicle control device) of the related art, in order to remove an idle stroke and an air gap of a brake device before performing automatic driving, a parking brake is operated in a range in which a braking action is not generated, and when a failure of a service brake or a service brake device (hydraulic brake device) as a normal brake device is generated, a drive torque of an engine is partially reduced on an uphill slope and a drive torque is fully reduced on a downhill slope. However, this conventional technique does not take such a technical problem into consideration, and the vehicle speed cannot be controlled with high accuracy only by the deceleration control of the drive torque as described above, and therefore the vehicle may not be stopped at a safe place depending on a change in the surrounding situation.

On the other hand, according to the vehicle control device of the second embodiment, even when the hydraulic brake device is not operated, the electric braking force is maintained at the third predetermined amount, so that both acceleration and deceleration of the vehicle can be accurately achieved by dynamically controlling the driving force, and the vehicle can be moved to a desired place (destination, safe place, etc.) that meets the surrounding situation, so that the safety of the occupant can be ensured.

Further, if the electric braking force is generated in a state where there is no hydraulic braking force before the vehicle is started, the backlash in the EPB2 can be reduced with high accuracy without being affected by the hydraulic pressure.

(third embodiment)

Next, a third embodiment will be explained. The same matters as at least one of the first and second embodiments are appropriately omitted from the description. In this third embodiment, while the vehicle is traveling, EPB-ECU9 determines whether EPB2 is operating normally based on the relationship between the driving force and the acceleration of the vehicle when outputting an instruction to control EPB2 to generate electric braking force. That is, when the hydraulic braking force is generated, it is not known how much electric braking force can be generated by EPB2, and therefore, the fault detection of EPB2 is performed as follows.

Fig. 8 is a time chart showing an example of the temporal change of each physical quantity at the time of vehicle control in the third embodiment. The same matters as in fig. 5 will not be described as appropriate. The times t41 to t50, t52 to 59 of fig. 8 correspond to the times t21 to t38 of fig. 5. In fig. 8 (a), (b), (d), and (f), the solid line represents the target value, and the broken line represents the actual value.

As shown in fig. 8 (f), at time t51, EPB2 is disabled, and thereafter, the electric braking force becomes zero. In this case, since the larger one of the hydraulic braking force and the electric braking force selectively acts as the braking force at the time t54 to t55, the actual value of the braking force is different from the target value and becomes zero as shown in fig. 8 (d), and accordingly, the vehicle body speed is also different from the target value as shown in fig. 8 (a), and the vehicle body acceleration is also different from the target value as shown in fig. 8 (b). The EPB-ECU9 can determine that EPB2 is abnormal based on the difference between the actual value and the target value between the vehicle body speed and the vehicle body acceleration.

Fig. 9 is a flowchart showing a process performed by the vehicle control device of the third embodiment. In step S21 (time t54 in fig. 8), the ESC-ECU8 controls the hydraulic brake device (service brake 1) to reduce the hydraulic braking force to a predetermined value (e.g., zero).

Next, in step S22, EPB-ECU9 determines whether or not the difference between the target value and the actual value of the vehicle body speed is equal to or less than a first threshold value (predetermined vehicle body speed threshold value), and if yes, it proceeds to step S23, and if no, it proceeds to step S24.

In step S23, EPB-ECU9 determines whether or not the difference between the target value and the actual value of the vehicle body acceleration is equal to or smaller than a second threshold value (predetermined vehicle body acceleration threshold value), and if yes, it proceeds to step S25, and if no, it proceeds to step S24.

In step S24, EPB-ECU9 determines EPB2 as abnormal. In this case, for example, EPB-ECU9 leaves the fact that EPB2 is abnormal as data in a log, or notifies the driver via display lamp 24 or the like. In step S25, EPB-ECU9 determines EPB2 as normal.

As described above, according to the vehicle control device of the third embodiment, when the electric braking force is generated, it is possible to easily determine whether or not the EPB2 is operating normally only by reducing the hydraulic braking force and examining the difference between the target value and the actual value of the vehicle state quantity (the acceleration and the speed of the vehicle). Therefore, the reliability of the EPB2 is improved.

The embodiments of the present invention have been described above, but the above embodiments are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in other various ways, and various omissions, substitutions, combinations, and changes can be made without departing from the spirit of the invention. Further, specifications (structure, type, number, and the like) such as each structure and shape can be appropriately changed and implemented.

For example, the wheels to be braked by the EPB are not limited to the rear wheels, and may be front wheels. The number of wheels of the vehicle to which the present invention is directed is not limited to four, and may be six or more.