JP6497346B2 - Brake control device for vehicle - Google Patents

Description

  The present invention includes a so-called in-line system that includes a differential pressure regulating valve disposed in a fluid path connecting a master cylinder and a wheel cylinder, and a pump that supplies brake fluid to a fluid path on the wheel cylinder side of the differential pressure regulating valve. The present invention relates to a vehicle brake control device applied to a hydraulic brake device of a system.

  Patent Document 1 describes an example of a so-called in-line hydraulic brake device that can adjust a braking force applied to a vehicle in cooperation with a regenerative brake device. The hydraulic braking device includes a differential pressure adjusting valve disposed in a fluid path connecting the master cylinder and the wheel cylinder, and a pump for supplying brake fluid to a fluid path closer to the wheel cylinder than the differential pressure adjusting valve. ing. When the switching control for increasing the hydraulic braking force according to the decrease in the regenerative braking force is performed, the WC pressure, which is the hydraulic pressure in the wheel cylinder, is increased by operating both the differential pressure adjusting valve and the pump. The pressure braking force can be increased.

  In the above hydraulic braking device, the brake fluid in the master cylinder is pumped up by a pump, and the brake fluid can be supplied to the fluid path between the differential pressure adjusting valve and the wheel cylinder. Therefore, when the WC pressure is increased under the condition that the brake operation force that is the operation force of the brake operation member by the driver is constant, the amount of the brake fluid in the master cylinder is reduced by the operation of the differential pressure adjustment valve and the pump. . As a result, the MC pressure that is the hydraulic pressure in the master cylinder and the brake operation amount that is the operation amount of the brake operation member that is drivingly connected to the master cylinder may change. When the MC pressure or the brake operation amount changes in this way, the required braking force calculated based on at least one of the MC pressure and the brake operation amount changes, and the deceleration of the vehicle may vary when the replacement control is performed.

  Therefore, in the hydraulic braking device described in Patent Document 1, when a change in the MC pressure or the brake operation amount is detected in a situation where the brake operation force has not changed, the change amount of the MC pressure or the brake operation amount is calculated. Based on this, the required braking force is corrected. As a result, when switching control is performed under the condition where the brake operating force is not changing, the change in the total value of the regenerative braking force and the hydraulic braking force is suppressed, so that fluctuations in vehicle deceleration are suppressed. can do.

JP 2010-179840 A

  By the way, the switching control includes a first switching control for increasing the hydraulic braking force by reducing the regenerative braking force, and a second switching control for decreasing the hydraulic braking force by increasing the regenerative braking force. When the second switching control is performed, the opening of the differential pressure adjusting valve is increased under the condition that the pump is operated in order to reduce the WC pressure in the wheel cylinder. However, when the second switching control is performed in a situation in which the MC pressure is generated in the master cylinder by the operation of the braking operation member by the driver, the wheel cylinder is not affected even if the opening of the differential pressure adjustment valve is increased. The brake fluid inside is difficult to return to the master cylinder. In this case, since the WC pressure is unlikely to decrease, the total value of the regenerative braking force and the hydraulic braking force becomes larger than the required braking force. As a result, the deceleration of the vehicle may be larger than the deceleration intended by the driver.

  Specifically, for example, when the WC pressure in the wheel cylinder is higher than the MC pressure in the master cylinder by operating the differential pressure adjustment valve and the pump, the brake in the wheel cylinder is increased. The liquid moves to the master cylinder side via the differential pressure adjustment valve. Then, the driver unconsciously counters the movement of the brake operation member being pushed back due to the movement of the brake fluid toward the master cylinder, that is, the driver unconsciously increases the brake operation force to perform braking. The operation reaction force of the operation member is increased, and the MC pressure may be higher than the driver's intention. At this time, as the amount of increase in the operation reaction force of the braking operation member increases, the MC pressure increases, and the WC pressure obtained by adding the command differential pressure, which is a differential pressure corresponding to the opening of the differential pressure adjustment valve, to the MC pressure increases. For this reason, the hydraulic braking force does not decrease than expected. As a result, the deceleration of the vehicle becomes larger than the deceleration intended by the driver.

  An object of the present invention is to appropriately adjust the hydraulic braking force when the control for reducing the hydraulic braking force is performed in a situation where MC pressure is generated in the master cylinder by the operation of the braking operation member by the driver. An object of the present invention is to provide a braking control device for a vehicle that can be reduced.

  A vehicle braking control apparatus for solving the above-described problem is a drive cylinder connected to a braking operation member, and a master cylinder that generates a larger hydraulic pressure as the operation amount of the braking operation member increases, and a plurality of wheels of the vehicle The wheel cylinder connected to the master cylinder via the liquid passage, and the liquid passage connecting the master cylinder and each wheel cylinder are provided to increase the differential pressure between the master cylinder side and the wheel cylinder side. A differential valve for reducing the opening, and a holding valve that is provided in each of the fluid passages connecting the differential pressure regulator and the wheel cylinder, and is closed when the hydraulic pressure in the wheel cylinder is not increased. And a pump that sucks in brake fluid from within the master cylinder and supplies the brake fluid to the fluid path between the differential pressure adjusting valve and each holding valve. It is intended to be a device for adjusting the hydraulic braking force applied to the vehicle by controlling the differential pressure control valve and the pump. In this vehicle braking control device, when the operation of the braking operation member is started, among the holding valves, a part of the holding valves is closed while the remaining holding valves are not closed. Part of the holding valve is closed by the first processing unit, and the hydraulic pressure in the wheel cylinder corresponding to the remaining holding valve by the operation of the differential pressure adjusting valve and the pump (hereinafter, This is also applied to the vehicle by increasing the degree of opening of the differential pressure adjustment valve in a situation where the pressure is also higher than the hydraulic pressure in the master cylinder (hereinafter also referred to as “MC pressure”). And a second processing unit that performs a decompression process for increasing the opening degree of the part of the holding valves when the hydraulic braking force to be reduced is reduced.

  According to the above configuration, when the operation of the braking operation member by the driver is started, some of the plurality of holding valves connected to the differential pressure adjusting valve via the liquid passage are closed. . That is, only the remaining holding valves among the holding valves are opened. Therefore, by supplying brake fluid into the wheel cylinder corresponding to the remaining holding valve, a hydraulic braking force corresponding to the WC pressure in the wheel cylinder is applied to the vehicle.

  In the above configuration, when the braking operation member is operated by the driver, the differential pressure adjusting valve and the pump are operated, and the wheel cylinder corresponding to the remaining holding valve (that is, the holding valve that is not closed). The WC pressure inside may become higher than the MC pressure inside the master cylinder. When it becomes necessary to reduce the hydraulic braking force under such circumstances, not only the opening degree of the differential pressure adjusting valve is increased, but also the above-mentioned part of the holding valves (that is, the valve is closed) by performing the pressure reducing process. The opening of the holding valve is increased. Thereby, the brake fluid in the wheel cylinder corresponding to the remaining holding valves flows out to the wheel cylinder side corresponding to some of the holding valves. Then, the WC pressure in the wheel cylinder corresponding to the remaining holding valves is reduced, and the WC pressure in the wheel cylinders corresponding to some of the holding valves is increased.

  Here, the WC pressure in the wheel cylinder increases as the amount of brake fluid in the wheel cylinder increases, and decreases as the amount of brake fluid decreases. Moreover, the amount of change in the WC pressure when the amount of brake fluid in the wheel cylinder changes by a predetermined amount increases as the WC pressure immediately before the start of change in the amount of brake fluid in the wheel cylinder increases. Prior to the start of the pressure reduction process, the WC pressures in the wheel cylinders corresponding to some of the holding valves are lower than the WC pressures in the wheel cylinders corresponding to the remaining holding valves.

  For this reason, when a part of the holding valves is opened by performing the pressure reducing process, the amount of decrease in the WC pressure in the wheel cylinders corresponding to the remaining holding valves is larger in the wheel cylinders corresponding to the part of the holding valves. It is larger than the increase amount of the WC pressure. As a result, the hydraulic braking force is reduced as a whole vehicle. Therefore, when the control for reducing the hydraulic braking force is performed under the situation where the MC pressure in the master cylinder is increased by the operation of the braking operation member by the driver, the hydraulic braking force is appropriately reduced. Will be able to. In addition, since the brake fluid in the wheel cylinder corresponding to the remaining holding valves flows out to the wheel cylinder side corresponding to some of the holding valves by performing the decompression process, the brake fluid from the wheel cylinder to the master cylinder side is discharged. Movement is suppressed, and as a result, an increase in MC pressure is suppressed.

  Further, in the vehicle braking control apparatus, the second processing unit has a part of the holding valve closed by the first processing unit, and the remaining holding valve is operated by the operation of the differential pressure adjusting valve and the pump. When the WC pressure in the wheel cylinder corresponding to is higher than the MC pressure in the master cylinder, when the hydraulic braking force applied to the vehicle is decreased by increasing the opening of the differential pressure adjustment valve, When it is determined that the MC pressure in the master cylinder has increased due to an increase in the opening degree of the differential pressure regulating valve, it is preferable to start a pressure reduction process for increasing the opening degree of some of the holding valves.

  According to the above configuration, when it is determined that the MC pressure in the master cylinder has increased due to an increase in the opening of the differential pressure adjustment valve, it can be determined that the operation reaction force against the braking operation member has started to increase. The part of the holding valves is opened by performing the decompression process. As a result, the brake fluid is less likely to move from the wheel cylinder corresponding to the remaining holding valve to the master cylinder side, and thus further increase in MC pressure and decrease in the operation amount of the brake operation member are suppressed. Therefore, the hydraulic braking force can be appropriately reduced while suppressing the deterioration of the feeling of the driver who operates the braking operation member.

  Here, the hydraulic braking device includes an auxiliary reservoir and a pressure reducing valve that is provided for each of the wheel cylinders and is opened when the brake fluid in the wheel cylinder is allowed to flow into the auxiliary reservoir. Sometimes. In this case, when the braking operation member is operated by the driver and the WC pressure in the wheel cylinder is high, when the pressure reducing valve is opened, the brake fluid in the wheel cylinder corresponding to the pressure reducing valve assists. Since it is discharged to the reservoir side, the WC pressure in the wheel cylinder can be reduced.

  By the way, the smaller the difference between the WC pressure in the wheel cylinder corresponding to the part of the holding valves and the WC pressure in the wheel cylinder corresponding to the remaining holding valves, the more from the wheel cylinder corresponding to the remaining holding valves. Brake fluid does not easily flow out to the wheel cylinder side corresponding to some holding valves. Then, it becomes difficult to reduce the WC pressure in the wheel cylinder corresponding to the remaining holding valves, that is, it is difficult to reduce the hydraulic braking force.

  Therefore, in the vehicle braking control device applied to the above hydraulic braking device, when the decompression process performed by the second processing unit is the first decompression process, the first decompression process by the second processing unit is performed. It is preferable to include a third processing unit that performs a second pressure reducing process for opening at least one pressure reducing valve among the pressure reducing valves in a state in which the part of the holding valves is opened by performing the above. .

  According to the above configuration, when the second pressure reducing process is performed, at least one of the pressure reducing valves is opened, so that the brake fluid in the wheel cylinder corresponding to the pressure reducing valve flows out to the auxiliary reservoir side. To come. As a result, the WC pressure in the wheel cylinder is reduced, and the brake fluid from the wheel cylinder to the master cylinder side is suppressed by discharging the brake fluid in the wheel cylinder to the auxiliary reservoir side. By suppressing the increase, the hydraulic braking force can be reduced.

The block diagram which shows the outline of a hybrid vehicle provided with brake ECU which is one Embodiment of the braking control apparatus of a vehicle. The schematic diagram which shows the outline of the hydraulic-pressure supply apparatus which comprises the hydraulic-pressure braking device controlled by the brake ECU. The block diagram which shows the outline of the hydraulic braking device. 7 is a flowchart for explaining a processing procedure for calculating a control hydraulic braking force and controlling a differential pressure adjusting valve and a pump based on the control hydraulic braking force when a brake operation is started. The flowchart explaining the process sequence for implementing each pressure reduction process when brake operation is started. The map which shows the relationship between target braking force and target assist amount. The map which shows the relationship between stroke change amount and reference | standard MC pressure change amount. The graph which shows the relationship between the quantity of the brake fluid in a wheel cylinder, and the hydraulic pressure in a wheel cylinder. When the assist control is performed during the brake operation, (a) is a timing chart showing the transition of the braking force, (b) is a timing chart showing the transition of the presence / absence of the assist control, and (c) is the switching control. The timing chart which shows transition of the presence or absence of implementation, (d) is a timing chart which shows transition of the hydraulic pressure in the master cylinder. When a brake operation is started while the vehicle is running, (a) is a timing chart showing the transition of braking force, (b) is a timing chart showing the transition of hydraulic pressure in the master cylinder, and (c) is for the front wheels. Timing chart showing transition of hydraulic pressure in wheel cylinder, (d) shows timing chart showing transition of hydraulic pressure in wheel cylinder for rear wheel, and (e) shows transition of operation of holding valve for rear wheel. (F) is a timing chart showing the transition of the operation of the pressure reducing valve for the rear wheel, (g) is a timing chart showing the transition of the differential pressure command current value with respect to the differential pressure regulating valve, and (h) is the operation of the pump. The timing chart which shows transition of.

Hereinafter, an embodiment embodying a vehicle braking control device will be described with reference to FIGS.
FIG. 1 illustrates an example of a hybrid vehicle including a brake ECU 120 that is a vehicle braking control device of the present embodiment. As shown in FIGS. 1 and 2, the vehicle includes a power unit 10 that applies driving force to the front wheels FL and FR that are driving wheels, a hydraulic braking device 30 that adjusts hydraulic braking force applied to the vehicle, and a power unit. 10 and a vehicle control device 100 for controlling the hydraulic braking device 30.

  Further, as shown in FIG. 1, in the vehicle, a brake mechanism 20 is provided for each of the wheels FL, FR, RL, and RR. The brake mechanism 20 can apply a braking force to the wheels FL, FR, RL, and RR by pressing the friction material 22 against the rotating body 21 that rotates integrally with the wheels FL, FR, RL, and RR. Note that the force that presses the rotating body 21 against the friction material 22, that is, the braking force, increases as the WC pressure Pwc, which is the hydraulic pressure in the wheel cylinders 23a, 23b, 23c, and 23d, increases. The total braking force applied to the wheels FL, FR, RL, and RR by the brake mechanism 20 corresponds to the hydraulic braking force applied to the vehicle.

  The power unit 10 is configured to be able to transmit the driving force from at least one of the engine 11 and the driving motor 12 to the front wheels FL and FR. Further, when the vehicle is braked, the drive motor 12 can generate electric power by transmitting the rotation of the front wheels FL and FR to the drive motor 12. That is, the drive motor 12 can also apply a regenerative braking force BPR, which is a braking force according to power generation, to the vehicle.

  As shown in FIG. 1, the hydraulic brake device 30 includes a hydraulic pressure supply device 32 to which a brake pedal 31 that is an example of a braking operation member is drivingly connected, a hydraulic pressure supply device 32, and wheel cylinders 23 a to 23 d. And a brake actuator 50 disposed between the two. As shown in FIGS. 1 and 2, the hydraulic pressure supply device 32 receives a booster 33 that assists the brake operating force that is the operating force of the brake pedal 31 by the driver, and the brake operating force that is assisted by the booster 33. A master cylinder 34 and an atmospheric pressure reservoir 35 for storing brake fluid.

  As shown in FIG. 2, two master pistons 411 and 412 arranged in the left-right direction in the figure are provided in a bottomed cylindrical housing 40 constituting the master cylinder 34. Each of the master pistons 411 and 412 slides in the braking direction, which is the left direction in the figure, against the urging force from the springs 421 and 422 when the input brake operation force increases. On the other hand, when the input brake operation force is reduced, each master piston 411, 412 slides in the non-braking direction, which is the right direction in the figure, by the urging force from each spring 421, 422.

  Further, the first master chamber 431 in the master cylinder 34 communicates with a first hydraulic circuit 511 described later of the brake actuator 50 and can communicate with the atmospheric pressure reservoir 35 through the first communication path 441. It has become. Further, the second master chamber 432 in the master cylinder 34 communicates with a second hydraulic pressure circuit 512 (described later) of the brake actuator 50 and can communicate with the atmospheric pressure reservoir 35 through the second communication path 442. It has become.

  The communication between the first master chamber 431 and the first hydraulic circuit 511 and the communication between the second master chamber 432 and the second hydraulic circuit 512 are small or large even if the brake operation amount BPInput is large. Even maintained. On the other hand, the communication between each of the master chambers 431 and 432 and the atmospheric pressure reservoir 35 is maintained when the brake operation amount BPInput is less than the invalid operation amount BPInputTH. In this case, the MC pressure Pmc, which is the hydraulic pressure of each master chamber 431, 432 with respect to the atmospheric pressure reservoir 35, is “0”, that is, no MC pressure Pmc is generated, so each master chamber 431, 432 The brake fluid does not flow from the inside to the brake actuator 50 side, that is, the hydraulic circuits 511 and 512.

  On the other hand, communication between the master chambers 431 and 432 and the atmospheric pressure reservoir 35 is blocked by the master pistons 411 and 412 when the brake operation amount BPInput is equal to or greater than the invalid operation amount BPInputTH. In this case, the MC pressure Pmc increases as the brake operation amount BPInput (that is, the brake operation force) increases. That is, when the brake operation amount BPInput becomes equal to or larger than the invalid operation amount BPInputTH, the MC pressure Pmc is generated in the master cylinder 34. And from each master chamber 431,432, so that MC pressure Pmc is high, many brake fluids flow into the brake actuator 50 side, ie, each hydraulic circuit 511,512. In this case, when the brake fluid that has flowed out from the master chambers 431 and 432 flows into the wheel cylinders 23a to 23d, the WC pressure Pwc in the wheel cylinders 23a to 23d increases, and a hydraulic braking amount is applied to the vehicle. Become. In the present specification, such a hydraulic braking force according to the MC pressure Pmc is sometimes referred to as a “reference hydraulic braking force BPB”.

  As shown in FIG. 3, the brake actuator 50 is provided with two systems of hydraulic circuits 511 and 512. A wheel cylinder 23a for the left front wheel and a wheel cylinder 23d for the right rear wheel are connected to the first hydraulic circuit 511, and a wheel cylinder 23b for the right front wheel and the left cylinder are connected to the second hydraulic circuit 512. A wheel cylinder 23c for the rear wheel is connected.

  In each fluid pressure circuit 511, 512, differential pressure regulating valves 521, 522 are provided in fluid passages connecting the master cylinder 34 and the wheel cylinders 23a-23d. The differential pressure regulating valves 521 and 522 are normally open linear solenoid valves, and the opening degree decreases as the input differential pressure command current value Ism increases. Further, in the first hydraulic circuit 511, a path 53a for the left front wheel and a path 53d for the right rear wheel are provided on the wheel cylinders 23a and 23d side of the differential pressure regulating valve 521. Similarly, a path 53b for the right front wheel and a path 53c for the left rear wheel are provided on the wheel cylinders 23b and 23c side of the second hydraulic circuit 512 from the differential pressure regulating valve 522. And in these paths 53a-53d, holding valves 54a, 54b, 54c, 54d, which are normally open solenoid valves that are closed when the WC pressure Pwc in the wheel cylinders 23a-23d is not increased, and the WC pressure Pressure reducing valves 55a, 55b, 55c, and 55d, which are normally closed solenoid valves that are opened when Pwc is decreased, are provided.

  Further, each hydraulic circuit 511, 512 has an auxiliary function for temporarily storing brake fluid flowing out from the wheel cylinders 23a-23d through the pressure reducing valves 55a-55d when the pressure reducing valves 55a-55d are open. The reservoirs 561 and 562 are connected to pumps 581 and 582 that are operated based on the drive of the pump motor 57. The auxiliary reservoirs 561 and 562 are connected to the pumps 581 and 582 through the suction flow paths 591 and 592, and are connected to the liquid path closer to the master cylinder 34 than the differential pressure regulating valves 521 and 522 through the master side flow paths 601 and 602. It is connected. The pumps 581 and 582 are connected to connection portions 621 and 622 between the differential pressure regulating valves 521 and 522 and the holding valves 54a to 54d through the supply flow paths 611 and 612.

  Then, when the pump motor 57 is driven, the pumps 581 and 582 draw the brake fluid from the auxiliary reservoirs 561 and 562 and supply the brake fluid to the supply passages 611 and 612. When no brake fluid remains in the auxiliary reservoirs 561 and 562, the pumps 581 and 582 draw the brake fluid in the master cylinder 34 (that is, the master chambers 431 and 432) through the suction flow paths 591 and 592 and the master side. The brake fluid is pumped through the flow paths 601 and 602, and the brake fluid is supplied to the supply flow paths 611 and 612. Therefore, when the differential pressure regulating valves 521 and 522 and the pumps 581 and 582 are operated, the fluid path on the wheel cylinders 23a to 23d side with respect to the differential pressure regulating valves 521 and 522 and the master side with respect to the differential pressure regulating valves 521 and 522. A differential pressure is generated between the fluid path on the cylinder 34 side. In addition, the said differential pressure becomes large, so that the opening degree of the differential pressure regulation valves 521 and 522 is small.

  That is, in the hydraulic braking device 30, even when the MC pressure Pmc is not generated in the master cylinder 34, that is, when the MC pressure Pmc is “0”, the pumps 581 and 582 and the differential pressure regulating valves 521 and 522 By actuating, the WC pressure Pwc in the wheel cylinders 23a to 23d can be increased, and a hydraulic braking force can be applied to the vehicle. In the present specification, the hydraulic braking force according to the operation of the differential pressure regulating valves 521 and 522 and the pumps 581 and 582 may be referred to as “control hydraulic braking force BPP”.

  As shown in FIG. 1, the vehicle control apparatus 100 is electrically connected to detection systems such as wheel speed sensors 201, MC pressure sensors 202, stroke sensors 203, and brake switches 204 as many as the number of wheels FL, FR, RL, RR. It is connected. The wheel speed sensor 201 detects the wheel speed VW that is the speed of the corresponding wheel FL, FR, RL, RR, and the MC pressure sensor 202 detects the MC pressure Pmc in the master cylinder 34. The stroke sensor 203 detects a brake operation amount BPInput that is an operation amount of the brake pedal 31 by the driver, and the brake switch 204 detects whether or not the brake pedal 31 is operated.

  The vehicle control device 100 includes a power unit control device 110 that controls the power unit 10 and a brake ECU 120 that controls the brake actuator 50 of the hydraulic braking device 30. The power unit control device 110 includes an engine ECU 111 that controls the engine 11 and a motor ECU 112 that controls the drive motor 12. “ECU” is an abbreviation for “Electronic Control Unit”.

  When the brake ECU 120 calculates the required braking force BPTA based on the brake operation amount BPInput, the MC pressure Pmc, and the like, the motor ECU 112 causes the drive motor 12 to generate the regenerative braking force BPR that does not exceed the required braking force BPTA. Generate electricity. In addition, the motor ECU 112 transmits information related to the regenerative braking force BPR applied to the vehicle to the brake ECU 120. Therefore, in this embodiment, the drive motor 12 and the motor ECU 112 constitute an example of a “regenerative braking device” that applies a regenerative braking force BPR to the vehicle.

  Next, referring to the flowchart shown in FIG. 4, when the brake switch 204 detects that the driver is operating the brake, the control hydraulic braking force BPP is calculated and the differential pressure regulating valves 521 and 522 are calculated. A processing procedure for controlling the operation of the pumps 581 and 582 will be described. In the present embodiment, each step of the flowchart of FIG. 4 is executed by the brake ECU 120 at a predetermined calculation cycle.

  As shown in FIG. 4, first, in step S <b> 11, the MC pressure Pmc of the master cylinder 34 detected by the MC pressure sensor 202 and the brake operation amount BPInput detected by the stroke sensor 203 are acquired. Subsequently, in step S12, the target braking force BPT is calculated based on the acquired MC pressure Pmc and the brake operation amount BPInput. The target braking force BPT is set to a larger value as the brake operation amount BPInput increases. In addition to the brake operation amount BPInput, the target braking force BPT may be set to a larger value as the MC pressure Pmc is higher.

  In the present embodiment, when the driver is operating the brake, if the predetermined assist control execution condition is satisfied, the target braking force BPT is increased and corrected so that the deceleration of the vehicle gradually increases. The assist control for deriving the power BPTA is performed. In this assist control, the target assist amount Tα is derived so as to increase as the target braking force BPT increases, and the required braking force BPTA is made equal to the sum of the target braking force BPT and the target assist amount Tα. More specifically, the required braking force BPTA is increased from the target braking force BPT with a predetermined increase gradient, and the final required braking force BPTA is made equal to the sum of the target braking force BPT and the target assist amount Tα. For example, the target assist amount Tα can be derived using the assist map M1 shown in FIG.

  As shown in FIG. 6, an assist map M <b> 1 is stored in the memory of the brake ECU 120. In the assist map M1, the target assist amount Tα increases as the target braking force BPT increases.

  Returning to FIG. 4, in step S <b> 121, it is determined whether or not a predetermined assist control execution condition is satisfied. If the execution condition is satisfied (step S121: YES), the process proceeds to the next step S122. In step S122, the assist map M1 shown in FIG. 6 is used to derive the target assist amount Tα corresponding to the current target braking force BPT, and the process proceeds to step S13 described later. On the other hand, when the execution condition is not satisfied (step S121: NO), in the next step S123, the target assist amount Tα is set to “0”, and the assist amount α described later is set to “0”. Then, the process proceeds to the next step S13.

  In step S13, it is determined whether or not the switching control from the hydraulic braking force to the regenerative braking force is performed. For example, when the regenerative braking force BPR received from the motor ECU 112 is large, the brake ECU 120 can determine that the replacement control is being performed. If the replacement control is not performed (step S13: NO), the process proceeds to the next step S14. In step S14, the current MC pressure Pmc is set to the reference MC pressure Pmcref, the current brake operation amount BPInput is set to the reference operation amount BPInputref, and the process proceeds to the next step S15.

  In step S15, a sum obtained by adding the standard assist addition value AS1, which is a value corresponding to the increase gradient, to the previous value of the assist amount α is set as the current assist amount α. The standard assist addition value AS1 is obtained by multiplying a predetermined increase gradient (which may be referred to as “increase speed”) determined in advance by a calculation interval time which is the time length of the calculation cycle. Can be calculated. By using the standard assist addition value AS1, the assist amount α gradually increases to the target assist amount Tα with a predetermined gradient during the execution of the assist control. The assist control for increasing the assist amount α using the standard assist addition value AS1 in this way may be referred to as “normal assist control”. And after execution of step S15, a process transfers to step S191 mentioned later.

  On the other hand, in step S13, when the replacement control is performed (YES), the process proceeds to the next step S16. The reference operation amount BPInputref and the reference MC pressure Pmcref at the time when the determination result in step S13 becomes “YES” can be regarded as being equal to the brake operation amount BPInput and the MC pressure Pmc immediately before the start of the replacement control. In step S16, the reference operation amount BPInputref is used to calculate a stroke change amount ΔBPInput that is a change amount of the brake operation amount during the execution of the replacement control. Specifically, the difference (= BPInput−BPInputref) obtained by subtracting the reference operation amount BPInputref from the current brake operation amount BPInput is set as the stroke change amount ΔBPInput. In step S17, the reference MC pressure change amount ΔPmcst corresponding to the stroke change amount ΔBPInput is derived by using the map shown in FIG. Thereafter, the process proceeds to the next step S18.

  The map shown in FIG. 7 is a map representing the relationship between the stroke change amount ΔBPInput and the reference MC pressure change amount ΔPmcst. The reference MC pressure change amount ΔPmcst is a predicted value of the change amount of the MC pressure Pmc caused by the change in the brake operation amount BPInput. In the present embodiment, the reference MC pressure change amount ΔPmcst is “0” when the stroke change amount ΔBPInput is equal to “0”, that is, when the brake operation amount BPInput is not changed during the above-described replacement control. Further, the reference MC pressure change amount ΔPmcst becomes a positive value when the stroke change amount ΔBPInput is a positive value, that is, when the brake operation amount BPInput is increased during the replacement control. Specifically, the reference MC pressure change amount ΔPmcst increases as the stroke change amount ΔBPInput increases. On the other hand, the reference MC pressure change amount ΔPmcst becomes a negative value when the stroke change amount ΔBPInput is a negative value, that is, when the brake operation amount BPInput decreases during the replacement control. Specifically, the reference MC pressure change amount ΔPmcst becomes smaller as the absolute value | ΔBPInput | of the stroke change amount is larger.

  Returning to FIG. 4, in step S <b> 18, the sum of the reference MC pressure Pmcref and the reference MC pressure change amount ΔPmcst is obtained, and a first calculation difference (= Pmc− ( It is determined whether or not (Pmcref + ΔPmcst)) is greater than the first change determination value ΔPmcTH1.

  Here, during execution of the switching control, the differential pressure command current value Ism for the differential pressure regulating valves 521 and 522 is decreased in order to decrease the control hydraulic braking force BPP. When the amount of brake fluid discharged from the pumps 581 and 582 is constant, the smaller the differential pressure command current value Ism, the larger the opening of the differential pressure adjustment valves 521 and 522, and therefore the master from the wheel cylinders 23a to 23d side. Brake fluid tends to flow out to the cylinder 34 side. As a result, the MC pressure Pmc in the master cylinder 34 is likely to increase.

  The sum of the reference MC pressure Pmcref and the reference MC pressure change amount ΔPmcst is a so-called normal pressure that is an MC pressure corresponding to the brake operation amount BPInput under the condition that the control for reducing the control hydraulic braking force BPP is not performed. This is the MC pressure corresponding to the brake operation amount BPInput at the time. The fact that the first calculation difference is larger than the first change determination value ΔPmcTH1 can be regarded as an increase in the MC pressure Pmc regardless of the change in the brake operation amount BPInput. Therefore, when the first calculation difference is larger than the first change determination value ΔPmcTH1 in step S18 (YES), the process proceeds to the next step S19. On the other hand, when the first calculation difference is equal to or smaller than the first change determination value ΔPmcTH1 (step S18: NO), the process proceeds to step S15 described above.

  Note that, when the replacement control is being performed and the first calculation difference is larger than the first change determination value ΔPmcTH1, the WC pressure Pwc in the wheel cylinders 23a to 23d is not easily reduced, and the actual control hydraulic pressure control is performed. The power tends to be larger than the control hydraulic braking force BPP calculated by the brake ECU 120. Therefore, in such a case, when normal assist control using the standard assist addition value AS1 is performed, a situation where the deceleration of the vehicle increases excessively is caused. Therefore, in this case, in step S19, the suppression assist addition value AS2 smaller than the standard assist addition value AS1 is used, and the sum obtained by adding the suppression assist addition value AS2 to the previous value of the assist amount α is set to the current assist amount α. set. The suppression assist addition value AS2 may be “0” or a negative value as long as it is smaller than the standard assist addition value AS1. Therefore, the increase gradient of the assist amount α is smaller, that is, the assist amount α is less likely to increase compared to the case where the normal assist control using the standard assist addition value AS1 is performed. As a result, even if the assist control is performed during the replacement control, the vehicle deceleration can be prevented from becoming too large. And after execution of step S19, a process transfers to following step S191.

  In step S191, it is determined whether or not the current assist amount α is larger than the target assist amount Tα. If the current assist amount α is equal to or smaller than the target assist amount Tα (step S191: NO), the process proceeds to step S20 described later. On the other hand, if the current assist amount α is larger than the target assist amount Tα (step S191: YES), the process proceeds to the next step S192. In step S192, the assist amount α is made equal to the target assist amount Tα. This prevents the assist amount α from becoming larger than the target assist amount Tα. When the assist control is not performed, the assist amount α is set to “0” because the target assist amount Tα is “0”. Thereafter, the process proceeds to the next step S20.

  In step S20, the required braking force BPTA is made equal to the sum of the target braking force BPT and the assist amount α (= BPT + α). In step S21, information regarding the calculated required braking force BPTA is transmitted to the motor ECU 112. Then, the motor ECU 112 controls the drive motor 12 to apply the regenerative braking force BPR to the vehicle within a range not exceeding the required braking force BPTA.

  Subsequently, in step S22, information related to the regenerative braking force BPR applied to the vehicle is received. In this regard, in the present embodiment, the brake ECU 120 constitutes an example of a “regeneration acquisition unit” that acquires the regenerative braking force BPR applied to the vehicle by the drive motor 12. Then, in step S23, the required hydraulic braking force BPF is made equal to the difference obtained by subtracting the regenerative braking force BPR from the required braking force BPTA (BPTA-BPR). In step S24, the basic hydraulic braking force BPB is calculated based on the current MC pressure Pmc. The basic hydraulic braking force BPB increases as the MC pressure Pmc increases.

  Subsequently, in step S25, the control hydraulic braking force BPP is made equal to the difference obtained by subtracting the basic hydraulic braking force BPB from the required hydraulic braking force BPF (= BPF−BPB). Then, in the next step S26, the operations of the differential pressure regulating valves 521 and 522 and the pumps 581 and 582 are controlled based on the control hydraulic braking force BPP. At this time, the differential pressure command current value for the differential pressure adjusting valves 521 and 522 becomes larger as the control hydraulic braking force BPP is larger. When the control hydraulic braking force BPP is greater than “0”, the pumps 581 and 582 are operated by the brake ECU 120. However, when the second pressure reduction process described later is performed, the pumps 581 and 582 are stopped even if the control hydraulic braking force BPP is greater than “0”. However, even when the operation of the pumps 581 and 582 is stopped in this way, when the control hydraulic braking force BPP is increased, the pump 581 is used to increase the WC pressure Pwc in the wheel cylinders 23a to 23d. , 582 is resumed.

  Thereafter, in step S27, it is determined whether or not the brake operation has been detected by the brake switch 204. When the brake operation is continued (step S27: NO), the process proceeds to step S11 described above. On the other hand, when the brake operation is finished (step S27: YES), this processing routine is ended.

  Here, with reference to the timing chart shown in FIG. 9, an operation when the assist control is performed during the brake operation by the driver will be described. FIG. 9 shows an example in which the brake operation amount BPInput does not change.

  As shown in FIGS. 9A, 9 </ b> B, 9 </ b> C, and 9 </ b> D, the assist control is started from the first timing t <b> 21 when the assist control execution condition is satisfied. In the period from the first timing t21 to the second timing t22, since the switching control is not performed, the assist amount α is increased by the standard assist addition value AS1 for each calculation cycle. As a result, the required braking force BPTA is increased with a gradient corresponding to the standard assist addition value AS1.

  Then, when the second timing t22 is reached and the switching control is started, the MC pressure Pmc in the master cylinder 34 increases due to the execution of the switching control. However, in the period from the second timing t22 to the third timing t23, the first calculation difference (= Pmc− (Pmcref + ΔPmcst)) is equal to or less than the first change determination value ΔPmcTH1, and thus the standard assist addition value AS1. The assist amount α using, that is, the increase in the required braking force BPTA is continued.

  However, since the first calculation difference becomes larger than the first change determination value ΔPmcTH1 after the third timing t23, the assist amount α is increased using the suppression assist addition value AS2 instead of the standard assist addition value AS1. Will be done. As a result, an increase in the assist amount α, that is, an increase in the required braking force BPTA is suppressed. In the example shown in FIG. 9, the suppression assist addition value AS2 is “0”. Further, the broken line in FIG. 9A indicates a request when the assist amount α is increased using the standard assist addition value AS1 even if the first calculation difference is larger than the first change determination value ΔPmcTH1. The transition of the braking force BPTA is shown.

  When the replacement control is finished at the fourth timing t24 thereafter, the assist amount α is increased using the standard assist addition value AS1 instead of the suppression assist addition value AS2. Then, the assist amount α, that is, the required braking force BPTA is increased. When the assist amount α becomes equal to the target assist amount Tα at the fifth timing t25, the assist amount α is held at a value equal to the target assist amount Tα thereafter.

  Next, referring to the flowchart shown in FIG. 5, when the brake switch 204 detects that the driver is operating the brake operation, the switching control from the hydraulic braking force to the regenerative braking force is performed. A processing procedure for controlling the operation of some of the holding valves 54a to 54d, some of the pressure reducing valves 55a to 55d, and the pumps 581 and 582 will be described. This processing routine is executed in parallel with the processing routine described with reference to FIG. In the present embodiment, each step in the flowchart of FIG. 5 is executed by the brake ECU 120.

  As shown in FIG. 5, first, in step S41, among the holding valves 54a to 54d, the rear-wheel holding valves 54c and 54d are closed. Therefore, in the present embodiment, when the brake operation is started by the driver by the brake ECU 120, among the holding valves 54a to 54d, the rear wheel holding valves 54c and 54d (part of the holding valves) are closed. On the other hand, an example of a “first processing unit” that does not close the front wheel holding valves 54a and 54b (remaining holding valves) is configured. When the process of step S41 is executed, the WC pressure Pwc in the front wheel wheel cylinders 23a and 23b is allowed to increase, but the WC pressure Pwc in the rear wheel wheel cylinders 23c and 23d is not increased. Become.

  In step S42, the MC pressure Pmc in the master cylinder 34 detected by the MC pressure sensor 202 and the brake operation amount BPInput detected by the stroke sensor 203 are acquired. Subsequently, in step S43, it is determined whether or not the switching control from the hydraulic braking force to the regenerative braking force is started. If the replacement control has not yet been started (step S43: NO), the process proceeds to the next step S44. In step S44, the current MC pressure Pmc is set to the reference MC pressure Pmcref, the current brake operation amount BPInput is set to the reference operation amount BPInputref, and the process proceeds to step S42 described above.

  On the other hand, when the above-described replacement control has been started (step S43: YES), the process proceeds to the next step S45. The reference operation amount BPInputref and the reference MC pressure Pmcref at the time when the determination result in step S43 becomes “YES” can be regarded as equal to the brake operation amount BPInput and the MC pressure Pmc immediately before the start of the replacement control. In step S45, the latest MC pressure Pmc of the master cylinder 34 and the latest brake operation amount BPInput are acquired. In step S46, the stroke change amount ΔBPInput, which is the change amount of the brake operation amount during the execution of the substitution control, is obtained by subtracting the reference operation amount BPInputref set in step S44 from the brake operation amount BPInput acquired in step S45. It is done. Subsequently, in step S47, similarly to step S17, the reference MC pressure change amount ΔPmcst corresponding to the stroke change amount ΔBPInput is derived by using the map shown in FIG.

  In step S48, a sum of the reference MC pressure Pmcref and the reference MC pressure change amount ΔPmcst is obtained, and a second calculation difference (= Pmc− (Pmcref + ΔPmcst)), which is a difference obtained by subtracting the sum from the current MC pressure Pmc. Is greater than the second change determination value ΔPmcTH2. It should be noted that the second change determination value ΔPmcTH2 is such that when the second calculation difference is larger than the second change determination value ΔPmcTH2, the differential pressure adjustment valves 521 and 522 are opened regardless of whether or not the brake operation amount BPInput has changed. The value is set in advance so that it can be determined that the MC pressure Pmc is increased due to the increase in the degree. Therefore, the second change determination value ΔPmcTH2 may be equal to the first change determination value ΔPmcTH1 or may be a value slightly different from the first change determination value ΔPmcTH1.

  When the second calculation difference is larger than the second change determination value ΔPmcTH2 (step S48: YES), the MC pressure Pmc increases due to the opening of the differential pressure regulating valves 521 and 522 becoming larger. Therefore, the process proceeds to the next step S49. On the other hand, when the second calculation difference is equal to or smaller than the second change determination value ΔPmcTH2 (step S48: NO), the process proceeds to step S45 described above. That is, during the replacement control, a series of processing from step S45 to S47 is performed until it can be determined that the MC pressure Pmc is increased due to the increase in the opening of the differential pressure regulating valves 521 and 522. Repeatedly.

  In step S49, a first pressure reduction process is performed to increase the opening degree of the rear-wheel holding valves 54c and 54d that are closed. In the first decompression process, the rear wheel holding valves 54c and 54d are closed, and the front wheel wheel cylinders 23a and 23b are operated by the operation of the differential pressure regulating valves 521 and 522 and the pumps 581 and 582. The WC pressure Pwc in the master cylinder 34 is higher than the MC pressure Pmc in the master cylinder 34. Therefore, in the present embodiment, the brake ECU 120 constitutes an example of a “second processing unit”. The first decompression process is performed until the rear wheel holding valves 54c and 54d are fully opened, that is, until the indicated current value for the holding valves 54c and 54d is "0". Thus, when the opening degree of the holding valves 54c and 54d increases, the brake fluid flows out from the front wheel wheel cylinders 23a and 23b to the rear wheel wheel cylinders 23c and 23d.

  Here, an example of the first decompression process will be described. For example, in the first decompression process, when the start condition of the first decompression process is satisfied, that is, the amount of decrease in the brake operation amount BPInput from the time when the determination result in step S48 becomes “YES” is likely to increase. The predicted rate of increase in the opening degree of the holding valves 54c and 54d increases as predicted. That is, when it is predicted that the amount of decrease in the brake operation amount BPInput is likely to increase, the brake fluid tends to flow into the wheel cylinders 23c and 23d for the rear wheels, as compared to when it is not. Therefore, a change in the brake operation amount BPInput during the replacement control can be suitably suppressed.

  When the first decompression process is completed, the process proceeds to the next step S50. In this step S50, it is determined whether or not the switching control from the hydraulic braking force to the regenerative braking force is being continued. If the replacement control has already been completed (step S50; NO), this processing routine is terminated without performing a second decompression process described later. On the other hand, when the replacement control is continued (step S50: YES), the process proceeds to the next step S51.

  In step S51, as in step S45, the latest MC pressure Pmc and the latest brake operation amount BPInput of the master cylinder 34 are acquired. In step S52, the stroke change amount ΔBPInput, which is the change amount of the brake operation amount during the execution of the substitution control, is obtained by subtracting the reference operation amount BPInputref set in step S44 from the brake operation amount BPInput acquired in step S51. It is done. Subsequently, in step S53, the reference MC pressure change amount ΔPmcst corresponding to the stroke change amount ΔBPInput is derived by using the map shown in FIG. 7 as in step S17 and step S47.

  In step S54, a sum of the reference MC pressure Pmcref and the reference MC pressure change amount ΔPmcst is obtained, and a third calculation difference (= Pmc− (Pmcref + ΔPmcst)), which is a difference obtained by subtracting the sum from the current MC pressure Pmc. Is greater than the third change determination value ΔPmcTH3. Note that the third change determination value ΔPmcTH3 is the MC pressure Pmc when the third calculation difference is larger than the third change determination value ΔPmcTH3 because the opening of the differential pressure adjustment valves 521 and 522 is increased. Is set in advance to such a value that it can be determined that is increasing.

  When the third calculation difference is larger than the third change determination value ΔPmcTH3 (step S54: YES), the MC pressure Pmc increases due to the opening of the differential pressure regulating valves 521 and 522 becoming larger. Since it can be determined that the process is being performed, the process proceeds to the next step S55. On the other hand, when the third calculation difference is equal to or smaller than the third change determination value ΔPmcTH3 (step S54: NO), the process proceeds to step S50 described above.

  In step S55, a second decompression process is performed in which, among the decompression valves 55a to 55d, the decompression valves 55c and 55d for the rear wheels are opened and the operations of the pumps 581 and 582 are stopped. In the present embodiment, the second decompression process is performed in a state where the rear-wheel holding valves 54c and 54d are fully opened by performing the first decompression process. When the second pressure reduction process is performed, the brake fluid in the wheel cylinders 23c and 23d for the rear wheels flows out into the auxiliary reservoirs 561 and 562. Therefore, in the present embodiment, the brake ECU 120 constitutes an example of a “third processing unit”.

  Here, an example of the second decompression process will be described. For example, in the second decompression process, the decompression valves 55c and 55d are opened only for a certain period. When the pressure reducing valves 55c and 55d are closed, the amount of decrease in the brake operation amount BPInput during the valve closing period is monitored. At this time, if the decrease amount of the brake operation amount BPInput during the valve closing period becomes equal to or larger than the determination decrease amount, the decompression valves 55c and 55d are opened again for a certain period. Thereafter, the amount of decrease in the brake operation amount BPInput during the valve closing period is monitored again. As described above, in the second pressure reducing process, the opening of the pressure reducing valves 55c and 55d and the monitoring during the valve closing period are repeated. Then, when the replacement control is finished, the second decompression process is also finished. When the second decompression process is thus completed, the present processing routine is terminated.

  Next, with reference to the graph shown in FIG. 8 and the timing chart shown in FIG. 10, the action when the vehicle decelerates by the brake operation by the driver will be described together with the effects. In the example illustrated in FIG. 10, for convenience of explanation, it is assumed that the assist control is not performed.

  As shown in FIGS. 10 (a), (b), (c), (d), (e), (f), (g), and (h), the driver at the first timing t1 while the vehicle is traveling. The brake operation by is started. Then, during the period from the first timing t1 to the second timing t2, the brake operation amount BPInput increases, but the brake operation amount BPInput is less than the invalid operation amount BPInputTH, so the MC pressure Pmc in the master cylinder 34 is “0”. In the example shown in FIG. 10, the application of the regenerative braking force BPR to the vehicle is started at the third timing t3. Therefore, in the period from the first timing t1 to the second timing t2, the control hydraulic braking force BPP becomes equal to the required braking force BPTA (that is, the target braking force BPT). As a result, the operations of the pumps 581 and 582 and the differential pressure regulating valves 521 and 522 are started from the first timing t1, and the differential pressure command current value Ism for the differential pressure regulating valves 521 and 522 is controlled by the control hydraulic braking force BPP. As (= BPTA) increases, it gradually increases. That is, the opening degree of the differential pressure regulating valves 521 and 522 gradually decreases.

  Further, at the first timing t1 when the start of the brake operation is detected, the rear wheel holding valves 54c and 54d are closed. Therefore, as shown in FIGS. 10C and 10D, the WC pressure Pwc in the wheel cylinders 23a and 23b for the front wheels gradually increases, while the WC pressure in the wheel cylinders 23c and 23d for the rear wheels. Pwc is not increased. As a result, a state is created in which the WC pressure Pwc in the wheel cylinders 23a and 23b for the front wheels is higher than the WC pressure Pwc in the wheel cylinders 23c and 23d for the rear wheels.

  Since the brake operation amount BPInput reaches the invalid operation amount BPInputTH at the second timing t2, the MC pressure Pmc in the master cylinder 34 gradually increases as the brake operation amount BPInput increases from the second timing t2. . In this case, the braking force applied to the vehicle is equal to the sum of the control hydraulic braking force BPP and the basic hydraulic braking force BPB.

  Subsequent control at the third timing t3 from the hydraulic braking force to the regenerative braking force is started. Then, as the regenerative braking force BPR increases, the differential pressure command current value Ism for the differential pressure regulating valves 521, 522 decreases, that is, the opening degree of the differential pressure regulating valves 521, 522 increases. At this time, in the hydraulic pressure supply device 32, communication between the master chambers 431 and 432 and the atmospheric pressure reservoir 35 is blocked. Therefore, even if the opening of the differential pressure adjusting valves 521 and 522 is increased in this way, the brake fluid flows out from the front wheel wheel cylinders 23a and 23b to the master cylinder 34 side. Even when it is constant, the MC pressure Pmc in the master cylinder 34 increases. As a result, an operation reaction force with respect to the brake pedal 31 is increased, and the brake operation amount BPInput may be decreased even if the brake operation force of the driver is constant.

  Therefore, in the present embodiment, when it is determined that the MC pressure Pmc is increased due to the increase in the opening degree of the differential pressure regulating valves 521 and 522 at the fourth timing t4, the rear wheel holding valve is used. A first pressure reduction process for opening the valves 54c and 54d is started. At this time, the WC pressure Pwc in the wheel cylinders 23c and 23d for the rear wheels is lower than the WC pressure Pwc in the wheel cylinders 23a and 23d for the front wheels and the MC pressure Pmc in the master cylinder 34. Therefore, the brake fluid in the front wheel wheel cylinders 23a and 23d flows into the rear wheel wheel cylinders 23c and 23d. As a result, the WC pressure Pwc in the wheel cylinders 23a and 23d for the front wheels decreases, and the WC pressure Pwc in the wheel cylinders 23c and 23d for the rear wheels increases.

  Here, FIG. 8 shows the relationship between the amount of brake fluid in the wheel cylinders 23a to 23d and the WC pressure Pwc. As shown in FIG. 8, the greater the amount of brake fluid in the wheel cylinders 23a to 23d, the higher the WC pressure Pwc. However, the amount of change in the WC pressure Pwc when the amount of brake fluid in the wheel cylinders 23a to 23d changes by a predetermined amount increases as the WC pressure Pwc immediately before the start of change in the amount of brake fluid increases.

  Therefore, even if all of the brake fluid flowing out from the front wheel wheel cylinders 23a and 23b flows into the rear wheel wheel cylinders 23c and 23d by the first decompression process, the rear wheel wheel cylinders. The increase amount of the WC pressure Pwc in 23c, 23d is smaller than the decrease amount of the WC pressure Pwc of the wheel cylinders 23a, 23b for the front wheels. Therefore, the control hydraulic braking force BPP can be appropriately reduced by performing the first pressure reduction process during the replacement control. As a result, it is possible to suppress the deceleration of the vehicle from becoming larger than the deceleration intended by the driver.

  Further, since the rear wheel holding valves 54a to 54d are opened by performing the first pressure reduction process, the brake from the inside of the front wheel wheel cylinders 23a, 23b to the master cylinder 34 side is performed during the replacement control. The inflow of liquid is reduced. Therefore, the increase in the operation reaction force of the brake pedal 31 is suppressed as the MC pressure Pmc in the master cylinder 34 is less likely to increase, and the brake operation amount BPInput is less likely to decrease. Therefore, it is possible to suppress the deterioration of the feeling of the driver who operates the brake pedal 31.

  By the way, even if the rear-wheel holding valves 54c and 54d are opened by performing the first pressure reduction process, the WC pressure Pwc in the rear-wheel wheel cylinders 23c and 23d remains in the front-wheel wheel cylinders 23a and 23d. After that, the WC pressure Pwc in the wheel cylinders 23a and 23d for the front wheels is less likely to decrease. Therefore, when the opening of the differential pressure regulating valves 521 and 522 is increased in this state, the amount of brake fluid flowing from the front wheel wheel cylinders 23a and 23b to the master cylinder 34 increases. As a result, the MC pressure Pmc in the master cylinder 34 is increased, the operation reaction force against the brake pedal 31 is increased, and the brake operation amount BPInput tends to decrease.

  Therefore, in the present embodiment, it is determined that the MC pressure Pmc is increased due to the increase in the opening degree of the differential pressure regulating valves 521 and 522 at the fifth timing t5 after the end of the first pressure reduction process. Then, the second pressure reducing process for opening the rear wheel holding valves 54c and 54d is started. In the second decompression process, the operations of the pumps 581 and 582 are stopped. As a result, the brake fluid in the wheel cylinders 23c and 23d for the rear wheels flows into the auxiliary reservoirs 561 and 562 via the pressure reducing valves 55c and 55d. As a result, the WC pressure Pwc in each of the wheel cylinders 23a to 23d is reduced. Note that the brake fluid accumulated in the auxiliary reservoirs 561 and 562 does not contribute to the application of the braking force to the wheels FL, FR, RL, and RR. Therefore, the control hydraulic braking force BPP can be appropriately reduced. Note that the second decompression process is performed until the sixth timing t6 at which the replacement control is finished.

As described above, according to the present embodiment, in addition to the effects described above, the following effects can be further obtained.
During the above replacement control, as shown by the broken line in FIG. 10A, the braking force to be applied to the vehicle even if the first decompression process or the second decompression process is performed. The braking force is slightly larger than the required braking force BPTA. In this regard, in the present embodiment, during the replacement control execution period, in the period in which the first calculation difference (= Pmc− (Pmcref + ΔPmcst)) is greater than the first change determination value ΔPmcTH1, the assist amount is greater than that outside the period. The increase in α is suppressed. Therefore, compared with the case where the assist amount α is determined using the standard assist addition value AS1 even during the period, the deceleration of the vehicle is suppressed while suppressing an excessive increase in the deceleration of the vehicle during the replacement control. It can be adjusted appropriately.

  Further, in the second decompression process, the closing and opening of the decompression valves 55c and 55d are repeated, and abnormal noise resulting from the operation of the decompression valves 55c and 55d is generated from the brake actuator 50. Therefore, in the present embodiment, when the replacement control is started, the first pressure reduction process is performed before the second pressure reduction process. And when implementation of said switching control is complete | finished before the start conditions of a 2nd pressure reduction process are satisfied, a 2nd pressure reduction process is not implemented. Therefore, the generation of noise from the brake actuator 50 during the execution of the replacement control can be suppressed by the amount that the increase in the operation opportunity of the pressure reducing valves 55c and 55d can be suppressed.

  In addition, it is possible to suppress an increase in the opportunity for the pumps 581 and 582 to stop as compared with the case where the second pressure reduction process is performed with priority over the first pressure reduction process. That is, it is possible to prevent the brake actuator 50 from operating in a state where the brake fluid remains in the auxiliary reservoirs 561 and 562.

The above embodiment may be changed to another embodiment as described below.
In the above embodiment, the rear wheel pressure reducing valves 55c and 55d are opened in the second pressure reducing process, but the rear wheel pressure reducing valves 55c and 55d are not the front wheel pressure reducing valves 55a and 55b. May be opened. In the second pressure reducing process, both the rear wheel pressure reducing valves 55c and 55d and the front wheel pressure reducing valves 55a and 55b may be opened. Even in this case, an effect equivalent to that of the above embodiment can be obtained.

  In the second decompression process, if the opening and closing of the decompression valves 55c and 55d are repeated, the decompression valves 55c and 55d may be operated by a method different from the method described in the above embodiment. Good. For example, the amount of increase in the MC pressure Pmc during the valve closing period after the pressure reducing valves 55c and 55d are opened for a certain period is monitored, and when the amount of increase exceeds a specified amount, the pressure reducing valves 55c and 55d are You may make it open a valve for a fixed period. The opening of the pressure reducing valves 55c and 55d for a certain period and the monitoring of the increase amount of the MC pressure Pmc after closing the valve may be repeated.

In the second decompression process, the decompression valves 55c and 55d may be opened for a certain period each time a predetermined time has elapsed since the opening of the decompression valves 55c and 55d was completed.
If the opening degree of the pressure reducing valves 55c and 55d can be adjusted similarly to the holding valves 54a to 54d, the opening degree of the pressure reducing valves 55c and 55d is gradually increased in the second pressure reducing process. Also good. In this case, the increasing speed of the opening of the pressure reducing valves 55c and 55d may be a predetermined speed set in advance, or may be variable according to the changing speed of the MC pressure Pmc, the brake operation amount BPInput, the regenerative braking force BPR, and the like. You may make it make it.

  The second decompression process may be continued when the switching control is still continued when the first decompression process is completed. Further, the second decompression process may be started while the opening degree of the holding valve 54d is increased by performing the first decompression process.

If the first decompression process is performed, the second decompression process may not be performed.
In the above embodiment, the increase rate of the opening degree of some holding valves may be increased as the increase rate of the MC pressure Pmc during the first pressure reduction process is increased. In addition, the increase rate of the opening degree of some holding valves may be increased as the increase rate of the regenerative braking force BPR during the switching control is increased. Further, the increase rate of the opening degree of some holding valves may be a predetermined speed set in advance.

In the first decompression process, some holding valves may be operated so as to repeat valve opening and valve closing. In this case, a two-position valve can be adopted as the holding valve.
During the replacement control, the first pressure reduction process may be started when an increase in the MC pressure Pmc detected by the MC pressure sensor 202 is detected, or the brake detected by the stroke sensor 203 The first decompression process may be started when a decrease in the manipulated variable BPInput is detected. Moreover, you may make it start a 1st pressure reduction process with the start of replacement control.

  When the brake operation is started, the front wheel holding valves 54a and 54b may be closed, and the rear wheel holding valves 54c and 54d may not be closed. In the first decompression process in this case, the closed front-wheel holding valves 54a and 54b are opened. Even if it is such a structure, the effect equivalent to the said embodiment can be acquired.

  The substitution control may be started before the MC pressure Pmc is generated in the master cylinder 34. Until the MC pressure Pmc is generated in this way, the opening of the differential pressure regulating valves 521 and 522 is increased so that the brake fluid is appropriately discharged from the front wheel wheel cylinders 23a and 23b to the master cylinder 34 side. be able to. In this case, even if the brake fluid flows into the master cylinder 34 from the wheel cylinders 23a, 23b, the brake fluid flows out from the master cylinder 34 to the atmospheric pressure reservoir 35. Pmc hardly changes. Therefore, the first decompression process may not be performed when the switching control is completed before the MC pressure Pmc is generated.

  The vehicle including the hydraulic braking device 30 may be a vehicle other than the hybrid vehicle (for example, an electric vehicle) as long as the vehicle includes a regenerative braking device that can apply the regenerative braking force BPR. .

  The vehicle may be a vehicle having only the engine 11 as a power source. In this case, since the regenerative braking force BPR is not applied to the vehicle, in the master cylinder provided in such a vehicle, the communication between the master chamber and the atmospheric pressure reservoir is cut off almost at the same time when the brake operation is started by the driver. It has a configuration. In such a vehicle, the differential pressure adjustment valves 521 and 522 and the pumps 581 and 582 of the brake actuator 50 may be operated by performing the brake assist for assisting the brake operation by the driver. The brake braking force may need to be reduced under such a situation that the WC pressure Pwc in the wheel cylinders 23a to 23d is higher than the MC pressure in the master cylinder due to the execution of the brake assist. Even in this case, a part of the holding valves may be closed at the start of the brake operation, and the first pressure reduction process may be performed when the hydraulic braking force is reduced by performing the control. Even in this case, the hydraulic braking force can be appropriately reduced by performing the first pressure reduction process.

Next, the technical idea that can be grasped from the above embodiment and another embodiment will be added below.
(A) In the hydraulic braking device, the pump sucks brake fluid from the auxiliary reservoir and the master cylinder, and enters the brake fluid into a fluid path between the differential pressure adjusting valve and each holding valve. To supply
In the second pressure reducing process, it is preferable that the third processing unit opens at least one pressure reducing valve among the pressure reducing valves and stops the operation of the pump.

  According to the above configuration, in the second decompression process, the brake fluid that has flowed out of the wheel cylinder into the auxiliary reservoir by opening the decompression valve is stopped by stopping the operation of the pump. It will not be supplied to the liquid path between. That is, since the brake fluid that has flowed out of the wheel cylinder into the auxiliary reservoir stays in the auxiliary reservoir, the braking force applied to the vehicle by the hydraulic braking device can be reduced by performing the second decompression process. it can.

(B) A regenerative acquisition unit that acquires the regenerative braking force applied to the vehicle by the regenerative braking device,
In the second processing unit, the part of the holding valves is closed by the first processing unit, and the second holding unit corresponds to the remaining holding valves by the operation of the differential pressure adjusting valve and the pump. In a situation where the hydraulic pressure in the wheel cylinder is higher than the hydraulic pressure in the master cylinder, the first depressurizing process is performed at the time of performing replacement control that increases the regenerative braking force and decreases the hydraulic braking force. It is preferable to implement.

  According to the above configuration, by increasing the regenerative braking force and reducing the hydraulic braking force, the first pressure reduction process is performed during the replacement control, thereby suppressing an increase in vehicle deceleration during the replacement control. be able to.

  DESCRIPTION OF SYMBOLS 12 ... Drive motor which comprises regenerative braking device, 23a-23d ... Wheel cylinder, 30 ... Hydraulic brake device, 31 ... Brake pedal which is an example of braking operation member, 34 ... Master cylinder, 521, 522 ... Differential pressure adjustment valve 54a to 54d ... holding valve, 55a to 55d ... pressure reducing valve, 561, 562 ... auxiliary reservoir, 581, 582 ... pump, 112 ... motor ECU constituting a regenerative braking device, 120 ... an example of a vehicle braking control device. Brake ECU (first processing unit, second processing unit, third processing unit, and regeneration acquiring unit), FL, FR, RL, RR... Front wheel.

Claims (3)

A master cylinder that is drivingly connected to the brake operation member and generates a larger hydraulic pressure as the operation amount of the brake operation member increases;
A wheel cylinder provided for each of a plurality of wheels of the vehicle and connected to the master cylinder via a liquid path;
A differential pressure adjusting valve that is provided in a liquid passage connecting the master cylinder and each wheel cylinder, and whose opening is reduced when increasing the differential pressure between the master cylinder side and the wheel cylinder side;
A holding valve that is provided in each of the fluid passages connecting the differential pressure regulating valve and the wheel cylinder and is closed when the fluid pressure in the wheel cylinder is not increased;
A brake that sucks in brake fluid from within the master cylinder and supplies the brake fluid to a fluid path between the differential pressure adjusting valve and each holding valve;
A vehicle braking control device that adjusts a hydraulic braking force applied to the vehicle by controlling the differential pressure adjusting valve and the pump,
A first processing unit that closes some of the holding valves and does not close the remaining holding valves when the operation of the braking operation member is started;
The part of the holding valves is closed by the first processing unit, and the hydraulic pressure in the wheel cylinder corresponding to the remaining holding valves is changed by the operation of the differential pressure adjusting valve and the pump. When the hydraulic pressure applied to the vehicle is reduced by increasing the opening of the differential pressure adjusting valve under a situation where the hydraulic pressure in the master cylinder is higher, the opening of the some holding valves And a second processing unit that performs a decompression process for increasing the vehicle braking control device. The second processing unit includes:
The part of the holding valves is closed by the first processing unit, and the hydraulic pressure in the wheel cylinder corresponding to the remaining holding valves is changed by the operation of the differential pressure adjusting valve and the pump. In a situation where the hydraulic pressure in the master cylinder is higher than the hydraulic pressure in the master cylinder, when the opening of the differential pressure adjustment valve is increased to reduce the hydraulic braking force applied to the vehicle,
The vehicle brake control device according to claim 1, wherein the pressure reduction process is started when it is determined that the hydraulic pressure in the master cylinder has increased due to an increase in the opening of the differential pressure regulating valve. The hydraulic braking device includes an auxiliary reservoir, and a pressure reducing valve that is provided for each of the wheel cylinders and is opened when the brake fluid in the wheel cylinder flows out to the auxiliary reservoir side. And
When the decompression process performed by the second processing unit is the first decompression process,
A second pressure reducing valve that opens at least one pressure reducing valve among the pressure reducing valves in a state in which the one or more holding valves are opened by the first pressure reducing process performed by the second processing unit. The vehicle braking control device according to claim 1, further comprising a third processing unit that performs processing.

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