JP5356363B2 - Brake device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fit the responsiveness upon increase and decrease of braking force in a brake-by-wire system to a driver's feeling with a simple structure. <P>SOLUTION: A stroke of a brake pedal is inputted into a manipulated variable braking force conversion circuit 31 as a manipulated variable, the output signal is inputted into an increasing low-pass filter 32 and a decreasing low-pass filter 33, larger one out of respective outputs is selected by a maximum selection circuit 34, a control target value Bmax is created by the larger output out of outputs of the respective lowpass filters, and the control target value Bmax becomes a final braking force target value. A response delay of the braking force target value for a brake manipulated variable can be reduced on the increase side of the brake manipulated variable and enlarged on the decrease side of the brake manipulated variable, and cut-off frequency (time constant) of each low-pass filter is adjusted. With such a simple structure, brake feeling with no discomfort can be provided to a driver. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a vehicle brake device, and more particularly to a vehicle brake device that generates a brake force by brake-by-wire.

  In some electric vehicles and hybrid vehicles, an electric motor is connected to a drive shaft of a drive wheel, and the motor is used as a generator during braking to perform energy regeneration. In such a vehicle, it may be difficult to achieve all braking force with only regenerative braking due to the motor rating, the remaining battery level, etc., and it is driven by so-called brake-by-wire by electronic control. There is a system that performs coordinated control of the hydraulic brake and the regenerative brake.

  In the brake-by-wire, the piston of the hydraulic pressure generating cylinder is driven by an electric motor according to the stroke of the brake pedal, and the brake pedal and the hydraulic pressure generating cylinder are not mechanically connected. Therefore, unlike the case of the brake pedal mechanically connected to the conventional master cylinder, the reaction force accompanying the increase in the brake fluid pressure does not directly occur in the brake pedal, so that the pedal depression force for the operation of the brake pedal is given. Some have a pedal simulator (see, for example, Patent Document 1).

JP 2009-29294 A

  On the other hand, in the system using brake-by-wire, the relationship between the pedal stroke and the pedal effort is adjusted by the pedal simulator, and the relationship between the pedal stroke and the vehicle deceleration and the relationship between the pedal effort and the vehicle deceleration are Adjustment can be made by setting a target value of the total braking force, which is the sum of the control and the regenerative torque of the motor.

  There are various types of brake-by-wire systems, but the dynamic characteristics of the brakes generated by regenerative torque control and brake fluid pressure control are different in response and mechanical hysteresis characteristics from known mechanical brake systems. There is. Therefore, even if the system configured by the brake-by-wire method is set so that the same static characteristics as the mechanical brake system can be obtained, May cause discomfort.

  Note that in the brake-by-wire system having the pedal simulator described above, the braking force target value is calculated based on the pedal operation amount (for example, pedal stroke). It can be mitigated by having eye friction and damping characteristics. However, in this case, there is a problem that the mechanism of the pedal simulator is complicated and the cost of parts tends to be high.

  In addition, in the case of a brake-by-wire system that does not rely on a pedal simulator for dynamic characteristics, it is better to design it with a margin of control by slightly increasing the response to brake pedal operation. Since a feeling is born, it is necessary to reduce the response to the brake pedal operation to match the driver's feeling by some method.

  Also, the deceleration with respect to the pedal stroke and pedal effort may be smaller in the brake-by-wire system than in the mechanical system. When the brake pedal is released, the vehicle may be rebounded from the pitching while decelerating, and the upper body and head of the occupant may be shaken to cause discomfort. If the system responsiveness is lowered to cope with this problem (for example, a damper is provided on the brake pedal to increase the damping), the problem arises that the responsiveness required for the original brake characteristics is sacrificed.

  In the present invention, in order to solve such a problem and realize that the response when the brake force increases or decreases in the brake-by-wire system matches the driver's feeling with a simple configuration. The brake operation amount detection means (11a) for outputting the brake operation amount operated by the driver as a detection signal, and the braking force generation means (5.7) for generating the braking force of the vehicle according to the magnitude of the detection signal 8 · 10), wherein the detection signal has a first low-pass filter (32) having a first cutoff frequency, and the detection signal is lower than the first cutoff frequency. A second low-pass filter (33) having a second cutoff frequency, and the larger one of the output signal of the first low-pass filter and the output signal of the second low-pass filter is selected. And a braking force target value setting means for generating a braking force target value (36) Te, the braking force generating means, and shall be generated the braking force according to the brake force target value.

  According to this, on the increase side of the output signal of the low-pass filter on the side where the detection signal of the brake operation amount increases, the output signal of the first low-pass filter having a higher cutoff frequency is the output signal of the second low-pass filter. The output signal of the second low-pass filter having a lower cut-off frequency is lower than the output signal of the first low-pass filter. Therefore, the response delay of the braking force target value with respect to the brake operation amount can be reduced on the increase side of the brake operation amount and increased on the decrease side of the brake operation amount.

  In particular, it is preferable that a cutoff adjustment means (32a, 33a) for adjusting at least one of the first cutoff frequency and the second cutoff frequency is provided. According to this, the adjustment corresponding to the individual difference of the brake device and the difference of the use environment condition can be easily performed, and a desirable braking force characteristic under a wide use environment can be obtained. The braking force generating means may perform cooperative control of regenerative braking and hydraulic braking.

  As described above, according to the present invention, the brake feeling without any sense of incongruity can be given to the driver with a simple configuration of adjusting the cutoff frequency (time constant) of each low-pass filter.

It is a principal part systematic diagram of the brake system of the motor vehicle to which this invention was applied. 1 is a hydraulic circuit diagram schematically showing a brake device for an automobile to which the present invention is applied. It is a principal part circuit block diagram which shows the control point based on this invention. It is a wave form diagram for demonstrating the control point of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a system diagram of a principal part of a brake system of an electric vehicle or a hybrid vehicle to which the present invention is applied.

  The automobile shown in FIG. 1 has a pair of left and right front wheels 2 disposed on the front side of the vehicle 1 and a pair of left and right rear wheels 3 disposed on the rear side of the vehicle 1. A motor / generator 5 is connected to the front wheel axle 4 connected to the left and right front wheels 2 in a torque transmission relationship. A differential mechanism provided on the front wheel axle 4 is not shown.

  The motor / generator 5 serves as both a vehicle-driving motor and a regenerative generator. The battery 7 as a secondary battery is used as a power source to supply power from the battery 7 and power to the battery 7. (Charging) is controlled, and at the time of deceleration, braking energy generating means for converting regenerative braking energy into electric power and generating regenerative braking force is provided.

  In addition, by providing a control circuit using a CPU, various control of the vehicle is performed, and a control unit (ECU) 6 as a braking force distribution means is provided. The inverter 10 is electrically connected to the control unit 6. In the case of an electric vehicle, this configuration may be left as it is or a motor / generator for driving the rear wheel 3 may be provided. However, in the case of a hybrid vehicle, the front wheel axle 4 has an engine indicated by a two-dot chain line in the figure. (Internal combustion engine) The output shaft of E is connected. In the case of the engine E in the figure, an example of front wheel drive is shown, but four-wheel drive can also be used.

  Each wheel of the front wheel 2 and the rear wheel 3 is constituted by a caliper having a disc 2a, 3a and a wheel cylinder 2b, 3b integrated with the wheel (front wheel 2, rear wheel 3) as friction braking means for performing friction braking. A known disc brake is provided. The wheel cylinders 2b and 3b are connected to a brake fluid pressure generating device 8 constituting a braking force generating means via a known brake pipe. As will be described in detail later, the brake fluid pressure generator 8 is configured by a hydraulic circuit that can distribute the brake pressure by increasing or decreasing the brake pressure for each wheel.

  Each wheel speed sensor 9 is provided as a wheel speed detecting means for detecting a wheel speed corresponding to each wheel of the front wheel 2 and the rear wheel 3, and the brake pedal 11 operated by the driver has a depression amount. A displacement sensor 11a for detecting a brake operation amount is provided. Each detection signal of each wheel speed sensor 9 and displacement sensor 11 a is input to the control unit 6.

  The control unit 6 determines that a braking command has been issued when the output signal of the displacement sensor 11a of the brake pedal 11 is greater than 0, and performs control during braking. In the illustrated example, the braking is performed by regenerative cooperative control in which regenerative braking and hydraulic braking are performed, and therefore, it is assumed to be brake-by-wire.

  Next, the brake fluid pressure generator 8 will be described with reference to FIG. The braking system of the present embodiment does not mechanically transmit the operation of the brake pedal 1 as a braking operation member to the brake fluid pressure generating cylinder to generate the brake fluid pressure, but the operation amount of the brake pedal 11 (pedal displacement) Amount) is detected by a displacement sensor 11a as an operation amount sensor, and brake fluid pressure is generated by a motor drive cylinder 13 as a brake fluid pressure generating cylinder driven by an electric servo motor 12 based on the operation amount detection value. It is constituted by so-called brake-by-wire.

  As shown in FIG. 1, one end of a rod 14 that converts the arc motion into a substantially linear motion is connected to a brake pedal 11 that is rotatably supported by the vehicle body, and the other end of the rod 14 is connected in series. Are engaged so as to push in the first piston 15a of the master cylinder 15. The master cylinder 15 has a second piston 15b arranged in series on the side opposite to the rod 14 with respect to the first piston 15a. Each piston 15a, 15b is spring-biased toward the rod 14 side. Yes. The brake pedal 11 is spring-biased and is stopped by a stopper (not shown) when the brake operation is not performed, and is located at a standby position in the state of FIG.

  The master cylinder 15 is provided with a reservoir tank 16 for exchanging brake fluid according to the displacement of the pistons 15a and 15b. The pistons 15a and 15b are provided with seal members having a known structure for sealing between the oil passages 16a and 16b communicating with the reservoir tank 16, respectively. In the cylinder of the master cylinder 15, a first liquid chamber 17a is formed between the first piston 15a and the second piston 15b, and the second liquid is disposed on the side opposite to the first piston of the second piston 15b. A chamber 17b is formed.

  On the other hand, the motor drive cylinder 13 is displaced in the axial direction by transmitting torque to the electric servo motor 12, the gear box 18 connected to the electric servo motor 12, and the gear box 18 via a ball screw mechanism. There are provided a threaded rod 19 and a first piston 21 a and a second piston 21 b that are coaxially arranged in series with the threaded rod 19.

  Note that one end of a connecting member 27 extending toward the first piston 21a is fixed to the second piston 21b, and the other end of the connecting member 20 is axially relative to the first piston 21a. Is supported so as to be displaceable by a predetermined amount. Thereby, when the first piston 21a moves forward (displacement on the second piston 21b side), it can be displaced separately from the second piston 21b. However, when the first piston 21a moves backward from the advanced state to the initial state of FIG. The second piston 21b is also pulled back to the initial position via the connecting member 20. In addition, each piston 21a * 21b is spring-biased to the rod 19 side by each return spring 27a * 27b provided corresponding to each.

  The motor drive cylinder 13 is provided with oil passages 22a and 22b communicating with the reservoir tank 16 via the communication passage 22, respectively. The pistons 21a and 21b are connected to the oil passages 22a and 22b, respectively. Sealing members having a known structure for sealing the gaps are provided at appropriate positions. In the cylinder of the motor drive cylinder 13, a first hydraulic pressure generating chamber 23a is formed between the first piston 21a and the second piston 21b, and the second piston 21b is arranged on the side opposite to the first piston 21a. A two-hydraulic pressure generating chamber 23b is formed.

  The first fluid chamber 17a of the master cylinder 15 communicates with the first fluid pressure generating chamber 23a of the motor drive cylinder 13 via the normally open electromagnetic valve 24a, and the second fluid chamber 17b is normally opened. The pipes are respectively connected so as to be able to communicate with the second hydraulic pressure generation chamber 23b of the motor drive cylinder 13 through the electromagnetic valve 24b. A master cylinder side brake pressure sensor 25a is connected between the first fluid chamber 17a and the electromagnetic valve 24a, and a motor driven cylinder side brake pressure sensor is connected between the electromagnetic valve 24b and the second fluid pressure generating chamber 23b. 25b is connected.

  In addition, a cylinder type simulator 28 is connected between the second liquid chamber 17b and the electromagnetic valve 24b via a normally closed type electromagnetic valve 24c. The simulator 28 is provided with a piston 28a that divides the inside of the cylinder, a liquid storage chamber 28b is formed on the solenoid valve 24b side of the piston 28a, and a compression coil is provided on the side opposite to the liquid storage chamber 28a side of the piston 28a. A spring 28c is received. When both the solenoid valves 24a and 24b are closed and the solenoid valve 24c is open, the brake pedal 11 is depressed and the brake fluid in the second fluid chamber 17b enters the fluid storage chamber 28b, whereby the compression coil spring 28c. The urging force is transmitted to the brake pedal 11, so that the reaction force against the depression similar to that of a brake device in which a known master cylinder and wheel cylinder are directly connected is obtained.

  Furthermore, the first hydraulic pressure generation chamber 23a and the second hydraulic pressure generation chamber 23b of the motor drive cylinder 13 are respectively provided in plural (four in the illustrated example) wheel cylinders 2b via the VSA device 26 in the present embodiment.・ It is piped to communicate with 3b. The VSA device 26 is a ABS that prevents wheel lock during braking, and a traction control system (TCS) that prevents wheel slipping during acceleration, etc., and suppresses slipping during turning to control the three functions in total. It may be a known stabilization control system, and its description is omitted. The VSA device 26 includes brake actuators using various hydraulic elements that respectively constitute a first system corresponding to each wheel cylinder 2b of the front wheel and a second system corresponding to each wheel cylinder 3b of the rear wheel, And a VSA control unit 26a for controlling them.

  The brake fluid pressure generator 8 configured in this way is comprehensively controlled by the control unit 6. The control unit 6 receives detection signals from the stroke sensor 11a and the brake pressure sensors 25a and 25b, and also receives detection signals from various sensors (not shown) for detecting the behavior of the vehicle. Yes. The control unit 6 controls the brake fluid pressure generated by the motor drive cylinder 13 based on the detection signal from the stroke sensor 11a and in accordance with the running situation determined from the detection signals from the various sensors. Further, in the case of a hybrid vehicle (or an electric vehicle) that is a target vehicle of the present embodiment, regeneration control by a motor / generator is performed, and the control unit 6 performs regeneration in the case of performing regeneration control. The distribution control of the magnitude of the brake hydraulic pressure by the motor drive cylinder 13 is also performed.

  Next, a control procedure during normal braking will be described. FIG. 2 shows a state where the driver is not operating the brake pedal 11. The detection value of the stroke sensor 11a is an initial value (= 0), and no brake fluid pressure generation signal is output from the control unit 6. In this state, as shown in FIG. 2, in the motor drive cylinder 13, the threaded rod 19 is at the most retracted position, and the pistons 21 a. 21b is also retracted, and no brake fluid pressure is generated in both fluid pressure generating chambers 23a and 23b.

  When the brake pedal 11 is depressed and the detected value of the stroke sensor 11a becomes greater than 0, both solenoid valves 24a and 24b are closed and generated in the master cylinder 15 to perform control by brake-by-wire. The hydraulic pressure to be transmitted is blocked from being transmitted to the motor drive cylinder 13 and is also transmitted to the simulator 28 by opening the electromagnetic valve 24c. Then, based on the operation amount detection value (brake operation amount) detected by the stroke sensor 11a, a motor drive command value (operation amount) is output from the control unit 6 to the electric servo motor 12, and the screw is set according to the operation amount. The grooved rod 19, that is, the first piston 21 a is driven in the pushing direction, and a brake fluid pressure corresponding to the amount of depression of the brake pedal 11 (brake operation amount) as an input is generated in the first fluid pressure generating chamber 23 a. At the same time, the second piston 21b is pressed against the urging force of the return spring 27b by being pressed by the hydraulic pressure in the first hydraulic pressure generating chamber 23a, and the brake hydraulic pressure is also generated in the second hydraulic pressure generating chamber 23b. .

  When the driver displaces the brake pedal 11 in the returning direction, the threaded rod 19, that is, the first piston 21 a is returned by the electric servo motor 12 according to the returning direction displacement detected by the stroke sensor 11 a. The braking force can be reduced according to the depression amount of the brake pedal 11. When the brake pedal 11 is returned to the initial position by a return spring (not shown), the control unit 6 opens the electromagnetic valves 24a and 24b. Accordingly, the brake fluid of each wheel cylinder 2b and 3b can return to the reservoir tank 16 via the motor drive cylinder 13, and the braking force is released. When the detection value of the stroke sensor 11a becomes the initial value, the second piston 21b also returns to the initial position via the first piston 21a and the connecting member 20 as described above.

  The brake hydraulic pressure generated in the motor drive cylinder 13 is supplied to the front and rear wheel cylinders 2b and 3b via the VSA device 26, and a braking force is generated to perform normal braking control. In addition, when the braking force distribution control for each wheel by the VSA device 26 is performed, the braking force of each wheel is adjusted according to the control.

  In addition, when the depression amount (brake operation amount) of the brake pedal 11 is small, that is, when the vehicle body deceleration is small, only the regenerative brake may be controlled. In this case, the control unit 6 controls the motor / generator 5 as a generator, and increases or decreases the regenerative brake amount according to the brake operation amount by the brake pedal 11. If the vehicle deceleration becomes insufficient with the regenerative brake alone with respect to the magnitude of the brake operation amount (the magnitude of the deceleration requested by the driver), the motor drive cylinder 13 is moved by the electric servo motor 12 described above. Drive control is performed to perform regenerative cooperative control using a regenerative brake and a hydraulic brake.

  The timing for closing the solenoid valve 24c may be set to the timing when the fluid pressure in the second fluid chamber 17b decreases until the piston 28a can return to the initial position shown in FIG. 2 by the compression coil spring 28c. It can be after a predetermined time has elapsed since the valves 24a and 24b were opened. Alternatively, it may be after the detected value of the motor drive cylinder side brake pressure sensor 25b has become a predetermined value (for example, the hydraulic pressure is close to 0) or less.

  Next, the main part based on this invention of the control unit 6 is demonstrated with reference to FIG. A detection signal from the stroke sensor 11a is input to the operation amount braking force conversion circuit 31 as an operation amount in the control, and the operation amount braking force conversion circuit 31 corresponds to the brake operation amount (pedal stroke) of the brake pedal 11. For example, the braking force value Bo is set by a map or function.

  The braking force value Bo set by the manipulated variable braking force conversion circuit 31 is input in parallel to the increasing low-pass filter 32 as the first low-pass filter and the decreasing low-pass filter 33 as the second low-pass filter. The increase low-pass filter 32 is used for the purpose of slightly reducing the response when the braking force is increased, and is a low-pass filter with a phase delay. The reduction low-pass filter 33 is used for the purpose of slightly reducing the response when the braking force is reduced, and is a low-pass filter with a phase delay. This reduction low-pass filter 33 is suitable for the purpose of calming the pitching rebound behavior of the vehicle.

  Each of the low-pass filters 32 and 33 can also serve as noise removal, and the cut-off frequency as the first cut-off frequency of the increase low-pass filter 32 may be about 5 to 15 Hz. The cutoff frequency as the second cutoff frequency may be about 2 to 4 Hz, which is lower than the cutoff frequency of the increasing low-pass filter 32. The low-pass filters 32 and 33 are connected to adjusters 32a and 33a as cut-off adjusting means for freely setting the respective cut-off frequencies. The adjusters 32a and 33a may be digital switches or variable resistors.

  Each waveform signal of the increase target value Bi filtered by the increase low pass filter 32 and the decrease target value Bd filtered by the decrease low pass filter 33 is input to the maximum value selection circuit 34. In the maximum value selection circuit 34, the control target value Bmax generated by the larger one (maximum value) of both the target values Bi and Bd is output to the braking force control circuit 35 as a braking force target value. In this way, the braking force target value setting unit 36 as the braking force target value setting means is constituted by the operation amount braking force conversion circuit 31, the low bass filters 32 and 33, and the maximum value selection circuit 34. In the present embodiment, the braking force target value setting unit 36 converts the brake operation amount into a braking force value and then inputs the braking operation value to the low-pass filters 32 and 33. However, the present invention is not limited to this. Instead, for example, the braking force target value may be generated based on the respective outputs of the low-pass filters 32 and 33 after the brake operation amount is directly input to the low-pass filters 32 and 33.

  Processing performed by the low-pass filters 32 and 33 and the maximum value selection circuit 34 thus configured will be described with reference to FIG. In FIG. 4, a braking force value Bo with a change in the stroke of the brake pedal 11 as a sine wave is indicated by a two-dot chain line. The waveform obtained by filtering the braking force value Bo by the increasing low-pass filter 32 is indicated by the rising side of the solid line and the broken line, and the waveform obtained by filtering the braking force value Bo by the decreasing low-pass filter 33 is one point. As indicated by the chain line and the descending side of the solid line.

  Then, the maximum value selection circuit 34 selects the maximum value (larger) of the output signals from both the low-pass filters 32 and 33, so that the waveform shown by the solid line in FIG. Is output from. The output waveform from the maximum value selection circuit 34 becomes the final braking force target value and is input to the braking force control circuit 35. The braking force control circuit 35 determines the regenerative braking force by the motor / generator 5 and the hydraulic braking force by the servo motor 12 in a known hybrid vehicle by distributing the braking force target value using a known method. , Perform cooperative control.

  Thus, by using the control target value Bmax having the waveform shown by the solid line in FIG. 4, the control target value Bmax becomes a waveform in which the phase delay Δt1 occurs on the increase side of the waveform with respect to the braking force value Bo. On the waveform decrease side, the waveform decreases with a phase delay Δt2. Since the increase-side phase delay Δt1 is smaller than the decrease-side phase delay Δt2 from the relationship of the cut-off frequency, the response to the input waveform (braking force value Bo) of the control target value Bmax is increased, and the increase side is set to the decrease side. Can also be high.

  As a result, as a control characteristic in the known brake-by-wire system, even if the brake response to the brake pedal operation is set to be hypersensitive in order to provide a margin for the start-up characteristic of the brake force, the normal brake operation Can be dulled to match the driver's feeling, and the driver can perform the brake operation without any discomfort.

  In addition, by setting the phase lag when decreasing to be larger than when increasing braking force, the responsiveness when decreasing can be greatly reduced, and when the brake pedal 11 is released (returned), the vehicle rebounds from pitching during deceleration. In addition to being able to suppress the phenomenon that occurs, when using a disc brake, it is possible to give a firm brake sensation as if the brake pads are sticking to the disc.

  Since each responsiveness when the braking force is increased and when the vehicle is decelerating can be set separately, a good brake feeling can be obtained.When performing regenerative and hydraulic brake cooperative control like a hybrid vehicle, Since the dynamic characteristic with respect to the control target value Bmax that is the total braking force is defined, a consistent brake feeling can be easily obtained regardless of the ratio of the regenerative and hydraulic braking forces.

  In addition, the response level can be set with a simple circuit configuration with two low-pass filters, and the respective cut-off frequencies can be set freely, ensuring high responsiveness when braking force increases and braking. When the force decreases, the convergence of the pitching behavior of the vehicle can be easily performed. Further, since the cut-off frequency can be freely set, individual differences caused by the reaction force characteristics of the brake pedal 11 and the response characteristics of the slave cylinder 13 as an actuator with respect to the braking force, and differences in responsiveness depending on the use environment conditions are determined. Since it can be adjusted separately, a desired braking force characteristic can be obtained in a wider range of use environments.

5 Motor generator (braking force generating means)
7 Battery (braking force generating means)
8 Brake fluid pressure generator (braking force generator)
10 Inverter (braking force generating means)
11a Displacement sensor (brake operation amount detection means)
32 Low pass filter for increase (first low pass filter)
33 Low-pass filter for reduction (second low-pass filter)
32a / 33a adjuster (cut-off adjusting means)
36 Braking force target value setting unit (braking force target value setting means)

Claims (3)

A brake device for a vehicle having brake operation amount detection means for outputting a brake operation amount operated by a driver as a detection signal, and braking force generation means for generating a braking force of the vehicle according to the magnitude of the detection signal. And
A first low-pass filter having a first cut-off frequency for the detection signal;
A second low-pass filter having a second cutoff frequency lower than the first cutoff frequency for the detection signal;
Braking force target value setting means for generating a braking force target value by selecting the larger one of the output signal of the first low-pass filter and the output signal of the second low-pass filter;
The vehicle brake device, wherein the braking force generating means generates the braking force according to the braking force target value.   The vehicle brake device according to claim 1, further comprising a cut-off adjusting unit that adjusts at least one of the first cut-off frequency and the second cut-off frequency.   The vehicular brake device according to claim 1 or 2, wherein the braking force generation means performs cooperative control of regenerative braking and hydraulic braking.

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