Braking control device

Abstract

A braking control device 70 comprises: a target setting unit 115 that, when stopping a vehicle 10, performs an at-vehicle-stop target setting process which includes decreasing a target regenerative braking force and increasing a target frictional braking force; a correction unit 117 that corrects the target frictional braking force so that a deviation between a target value and an actual value of deceleration of the vehicle 10 is reduced; and a stop control unit 119 that, when the at-vehicle-stop target setting process is being performed, stops the vehicle 10 by operating a regenerative braking unit 20 on the basis of the target regenerative braking force and operating a friction braking unit 40 on the basis of a corrected target frictional braking force.

Description

Braking control device

[0001] The present invention relates to a brake control device applied to a vehicle.

[0002] Japanese Patent Application Laid-Open No. 2006-129999 discloses a control device that performs braking control to suppress sudden changes in the pitch attitude of a vehicle when the vehicle stops. The control device controls a motor generator so that regenerative braking force decreases toward zero when the vehicle speed drops below a predetermined speed. When the vehicle speed reaches zero, the control device increases frictional braking force by operating a hydraulic actuator.

[0003] JP 2016-28913 A

[0004] While a vehicle is traveling, external disturbances that change the deceleration of the vehicle may be input to the vehicle, such as changes in the gradient of the road on which the vehicle is traveling and wind.

[0005] If such a disturbance is input to the vehicle while the above-described braking control is being executed, a discrepancy occurs between the predicted stopping timing and the actual stopping timing, which may result in the start timing of the increase in frictional braking force being earlier or later than the actual stopping timing, which may cause the vehicle behavior to become unstable before and after stopping.

[0006] A braking control device for solving the above problems is applied to a vehicle including a regenerative braking unit that applies a regenerative braking force to the vehicle and a friction braking unit that applies a friction braking force to the vehicle. The braking control device includes: a target setting unit that executes a vehicle-stop target setting process, which includes, when stopping the vehicle, decreasing a target regenerative braking force that is a target for the regenerative braking force and increasing a target friction braking force that is a target for the friction braking force, a correction unit that corrects the target friction braking force so as to reduce a deviation between a target value of deceleration of the vehicle and an actual value of the deceleration, and a stop control unit that, when the vehicle-stop target setting process is being executed, operates the regenerative braking unit based on the target regenerative braking force and operates the friction braking unit based on the target friction braking force corrected by the correction unit, thereby stopping the vehicle.

[0007] The braking control device has the effect of ensuring stability in the vehicle behavior when the vehicle stops.

[0008] Fig. 1 is a schematic diagram showing a configuration of a vehicle equipped with a brake control device of a first embodiment. In Fig. 2, (a) to (f) are timing charts for stopping the vehicle of Fig. 1 in accordance with a braking request. Fig. 3 is a flowchart showing a series of processes executed by the brake control device of Fig. 1. Fig. 4 is a flowchart showing braking control when the vehicle is stationary of Fig. 3. Fig. 5 is a flowchart showing part of a series of processes executed by a brake control device of a second embodiment.

[0009] (First embodiment) A first embodiment of a brake control device will be described below with reference to Figs. 1 to 4. <Overall configuration of vehicle> Fig. 1 shows a vehicle 10 equipped with a brake control device 70. The vehicle 10 further includes a brake operating member 11, a plurality of wheels 13, a regenerative braking unit 20, a friction braking unit 40, and a plurality of sensors. The brake operating member 11 is a member operated by the driver when adjusting the deceleration of the vehicle 10. An example of the brake operating member 11 is a brake pedal.

[0010] <Regenerative Braking Unit> The regenerative braking unit 20 is configured to apply an effective regenerative braking force FbE to the vehicle 10. The regenerative braking unit 20 includes a motor generator 21 that applies the effective regenerative braking force FbE to the axle 14 that rotates integrally with the wheel 13, and a regenerative control device 30 that controls the motor generator 21. The motor generator 21 functions as a generator, thereby applying the effective regenerative braking force FbE to the axle 14.

[0011] The regenerative control device 30 includes a processing circuit 31. An example of the processing circuit 31 is an electronic control device. In this case, the processing circuit 31 includes a CPU and a memory that stores a control program executed by the CPU. The CPU executes the control program stored in the memory, allowing the processing circuit 31 to control the motor-generator 21.

[0012] The regenerative control device 30 is configured to be able to send and receive various information and commands to and from the braking control device 70 via the in-vehicle network. Therefore, when the vehicle is braking, the regenerative control device 30 can operate the motor generator 21 based on the information or commands received from the braking control device 70.

[0013] The processing circuit 31 functions as a regenerative control unit 101 by the CPU executing a control program stored in the memory. The regenerative control unit 101 adjusts the effective regenerative braking force FbE by operating the motor generator 21. That is, the regenerative control unit 101 can adjust the effective regenerative braking force FbE by operating the motor generator 21 based on the target regenerative braking force FbETr, which is a target for the regenerative braking force.

[0014] <Friction Braking Unit> The friction braking unit 40 is configured to apply a friction braking force FbF to the vehicle 10. The friction braking unit 40 includes a plurality of friction brakes 41 provided respectively for the plurality of wheels 13, and a braking actuator 50.

[0015] Each of the multiple friction brakes 41 applies a friction braking force to the corresponding wheel 13. The friction brake 41 has a wheel cylinder 42, a rotating body 43, and a friction portion 44. The rotating body 43 rotates integrally with the wheel 13. Therefore, by pressing the friction portion 44 against the rotating body 43, a friction braking force is applied to the wheel 13. The force pressing the friction portion 44 against the rotating body 43 increases as the wheel pressure, which is the hydraulic pressure in the wheel cylinder 42, increases. Therefore, the friction brake 41 can apply a greater friction braking force to the wheel 13 as the wheel pressure increases. The sum of the friction braking forces applied to the multiple wheels 13 corresponds to the "friction braking force FbF" applied to the vehicle 10.

[0016] The brake actuator 50 is configured to be able to control the wheel pressure of the plurality of wheel cylinders 42. For example, the brake actuator 50 has a pressure source that can supply brake fluid to the plurality of wheel cylinders 42. The pressure source is, for example, an electric pump or an electric cylinder. The brake fluid discharged from the brake actuator 50 is supplied to the wheel cylinders 42 via a supply flow path 51.

[0017] <Sensors> The multiple sensors output signals according to their detection results to the brake control device 70. The multiple sensors include, for example, a brake sensor 61, multiple wheel speed sensors 62, and an acceleration sensor 63. The brake sensor 61 detects information related to the operation of the brake operating member 11 by the driver. An example of the brake sensor 61 is a stroke sensor that detects the amount of operation of the brake operating member 11 by the driver. The operation amount based on the detection signal of the brake sensor 61 is referred to as the "braking operation amount X." The vehicle 10 may also be equipped with a sensor that detects the operating force of the brake operating member 11 by the driver.

[0018] The plurality of wheel speed sensors 62 detect the rotational speeds of the corresponding wheels 13. The rotational speeds of the wheels 13 based on the detection signals of the wheel speed sensors 62 are referred to as "wheel speeds VW." The acceleration sensor 63 detects the longitudinal acceleration of the vehicle 10. The longitudinal acceleration based on the detection signals of the acceleration sensor 63 is referred to as "longitudinal acceleration GX."

[0019] <Brake Control Device> The brake control device 70 activates the brake actuator 50 of the friction braking unit 40. The brake control device 70 is configured to be able to send and receive various information and commands to and from the regenerative control device 30. Therefore, during vehicle braking, the brake control device 70 can adjust the deceleration of the vehicle 10 by operating the brake actuator 50 and cooperating with the regenerative control device 30. In other words, the brake control device 70 can control the total braking force Fb of the vehicle 10 by operating the friction braking unit 40 and the regenerative braking unit 20. In this embodiment, the sum of the effective regenerative braking force FbE and the friction braking force FbF corresponds to the "total braking force Fb."

[0020] The braking control device 70 includes a processing circuit 71. An example of the processing circuit 71 is an electronic control device. In this case, the processing circuit 71 includes a CPU 72, a first memory 73, and a second memory 74. The first memory 73 stores a control program executed by the CPU 72. The second memory 74 stores the calculation results of the CPU 72. When the CPU 72 executes the control program in the first memory 73, the processing circuit 71 can operate the friction braking unit 40 to adjust the friction braking force FbF. Furthermore, the processing circuit 71 can adjust the effective regenerative braking force FbE by transmitting an instruction regarding the regenerative braking force to the regenerative control device 30.

[0021] The following describes the regenerative cooperative control executed by the processing circuit 71. The processing circuit 71 derives a required braking force FbRq, which is a required value of the total braking force Fb. The processing circuit 71 transmits the required braking force FbRq to the regenerative control device 30.

[0022] The processing circuit 31 of the regenerative control device 30 derives the target regenerative braking force FbETr based on the required braking force FbRq. For example, the processing circuit 31 sets the target regenerative braking force FbETr to the smaller of the regenerative braking force limit value and the required braking force FbRq. The regenerative braking force limit value is the upper limit value of the regenerative braking force that can be applied to the vehicle 10, or a regenerative braking force slightly smaller than the upper limit value. The processing circuit 31 operates the motor generator 21 based on the target regenerative braking force FbETr.

[0023] The processing circuit 71 of the brake control device 70 sets a target frictional braking force FbFTr based on the effective regenerative braking force FbE and the required braking force FbRq. If the effective regenerative braking force FbE is equal to the required braking force FbRq, the processing circuit 71 sets the target frictional braking force FbFTr to 0 (zero). On the other hand, if the effective regenerative braking force FbE is less than the required braking force FbRq, the processing circuit 71 sets the target frictional braking force FbFTr to the difference between the required braking force FbRq and the effective regenerative braking force FbE. Then, the processing circuit 71 operates the brake actuator 50 based on the target frictional braking force FbFTr.

[0024] <Functional Units> The processing circuit 71 functions as multiple functional units by the CPU 72 executing the control program in the first memory 73. The multiple functional units include a required braking force derivation unit 111, a stopping-related value acquisition unit 113, a target setting unit 115, a correction unit 117, and a stop control unit 119.

[0025] <Required Braking Force Derivation Unit> The required braking force derivation unit 111 derives the required braking force FbRq. When the driver is operating the brake operating member 11, the required braking force derivation unit 111 derives the required braking force FbRq so that the required braking force FbRq increases as the braking operation amount X increases. When deceleration of the vehicle 10 is requested by another control device or another functional unit, the required braking force derivation unit 111 derives a braking force corresponding to a required value of the deceleration of the vehicle 10 as the required braking force FbRq.

[0026] <Stop-related value acquisition unit> The stop-related value acquisition unit 113 acquires a stop-related value at each predetermined control period when the vehicle 10 is braking. The stop-related value decreases as the vehicle 10 approaches a predetermined stopping position.

[0027] For example, the stopping-related value acquisition unit 113 estimates a stopping position, which is a position where the vehicle 10 will stop, based on the vehicle body speed VS and vehicle body acceleration DVS of the vehicle 10. The vehicle body speed VS is the traveling speed of the vehicle 10. The vehicle body acceleration DVS is a value obtained by time-differentiating the vehicle body speed VS. The stopping-related value acquisition unit 113 may estimate, as the stopping position, the position of the vehicle 10 at the time when the vehicle body speed VS becomes 0 (zero) if the vehicle 10 continues to decelerate at the current vehicle body acceleration DVS. This stopping position corresponds to a "predetermined stopping position." Then, the stopping-related value acquisition unit 113 acquires a stopping distance DS, which is the distance from the current position of the vehicle 10 to the stopping position, as the stopping-related value.

[0028] <Target Setting Unit> The target setting unit 115 sets a target regenerative braking force FbETr and a target frictional braking force FbFTr for each predetermined control cycle when braking the vehicle. When the vehicle 10 is about to be stopped by the application of braking force, the target setting unit 115 executes a vehicle-stop target setting process. In the vehicle-stop target setting process, the target setting unit 115 decreases the target regenerative braking force FbETr and increases the target frictional braking force FbFTr when stopping the vehicle 10.

[0029] When the stopping distance DS becomes equal to or less than the first threshold value DSth1, it can be determined that the vehicle 10 is about to come to a stop. Therefore, when the stopping distance DS becomes equal to or less than the first threshold value DSth1, the brake control device 70 starts stopping braking control. Stopping braking control is braking control that suppresses a sudden change in the pitch attitude of the vehicle 10 due to stopping. When such stopping braking control is executed, the target setting unit 115 executes stopping target setting processing. In the stopping target setting processing, the target setting unit 115 sets the target regenerative braking force FbETr and the target frictional braking force FbFTr so as to satisfy all of the following multiple conditions (A1), (A2), and (A3).

[0030] (A1) The vehicle 10 stops in a state where the sum of the effective regenerative braking force FbE and the frictional braking force FbF is smaller than the requested braking force FbRq. (A2) The target regenerative braking force FbETr is replaced with the target frictional braking force FbFTr so that the frictional braking force FbF increases to a magnitude equal to or greater than the stop-holding braking force Fbh.

[0031] (A3) Decreasing the target regenerative braking force FbETr to 0 (zero) from the time when the changeover from the target regenerative braking force FbETr to the target frictional braking force FbFTr is completed until the vehicle 10 stops.

[0032] Note that even when the vehicle is braking, if the stopping distance DS is greater than the first threshold value DSth1, the above-described regenerative cooperative control is executed instead of the stationary braking control. When the regenerative cooperative control is executed, the target setting unit 115 sets the target frictional braking force FbFTr based on the required braking force FbRq and the effective regenerative braking force FbE. On the other hand, when the regenerative cooperative control is executed, the target regenerative braking force FbETr is set by the regenerative control unit 101, so the target setting unit 115 does not need to set the target regenerative braking force FbETr.

[0033] <Correction Unit> When the vehicle-stop target setting process is being executed, the correction unit 117 corrects the target frictional braking force FbFTr set by the target setting unit 115 so as to reduce the discrepancy between the target value and the actual value of the deceleration of the vehicle 10. On the other hand, when the vehicle-stop target setting process is not being executed, the correction unit 117 does not correct the target frictional braking force FbFTr set by the target setting unit 115. An example of the target value of the deceleration of the vehicle 10 is a value obtained by converting the required braking force FbRq into acceleration. Such a target value is referred to as a "target vehicle body acceleration DVSTr." An example of the actual value of the deceleration of the vehicle 10 is the vehicle body acceleration DVS. For example, the correction unit 117 corrects the target frictional braking force FbFTr by feedback control that receives as input a deviation ΔDVS between the target vehicle body acceleration DVSTr and the vehicle body acceleration DVS. The feedback control preferably includes at least proportional control among proportional control, integral control, and differential control.

[0034] <Stop Control Unit> Before the stationary braking control is started, i.e., when the stationary target setting process has not been executed, the regenerative cooperative control is executed. When the regenerative cooperative control is executed, the stop control unit 119 transmits information on the required braking force FbRq to the regenerative control device 30, i.e., the regenerative control unit 101. In addition, the stop control unit 119 operates the brake actuator 50 based on the target friction braking force FbFTr set by the target setting unit 115.

[0035] When the vehicle-stop target setting process is being executed, the stop control unit 119 stops the vehicle 10 by operating the regenerative braking unit 20 based on the target regenerative braking force FbETr and operating the brake actuator 50 based on the target frictional braking force FbFTr corrected by the correction unit 117. This allows the stop control unit 119 to control the frictional braking force FbF based on the corrected target frictional braking force FbFTr.

[0036] When the stop control unit 119 operates the regenerative braking unit 20 based on the target regenerative braking force FbETr, the stop control unit 119 transmits information about the target regenerative braking force FbETr set by the target setting unit 115 to the regenerative control unit 101. Upon receiving the information, the regenerative control unit 101 operates the motor generator 21 based on the target regenerative braking force FbETr indicated by the information. As a result, the stop control unit 119 can control the effective regenerative braking force FbE by operating the regenerative braking unit 20 based on the target regenerative braking force FbETr.

[0037] <Stationary Braking Control> With reference to FIG. 2 , the stationary braking control executed by the brake control device 70 will be described. As shown in FIGS. 2A to 2F, when a braking request is issued at timing t11, the vehicle 10 is decelerated in accordance with the braking request. In the example shown in FIG. 2 , before timing t12, the stationary distance DS acquired by the stationary-related value acquisition unit 113 is greater than the first threshold value DSth1, and therefore the stationary braking control has not yet started. Therefore, regenerative cooperative control is executed during the period from timing t11 to timing t12. That is, when the required braking force derivation unit 111 derives the required braking force FbRq, information regarding the required braking force FbRq is transmitted to the regenerative control unit 101. If the required braking force FbRq is equal to or less than the regenerative braking force limit value, the regenerative control unit 101 sets the required braking force FbRq to the target regenerative braking force FbETr. The regenerative control unit 101 then operates the motor generator 21 based on the target regenerative braking force FbETr, thereby applying to the vehicle 10 an effective regenerative braking force FbE corresponding to the required braking force FbRq.

[0038] At timing t12, the stopping distance DS becomes equal to or less than the first threshold value DSth1, and thus stopping-state braking control is initiated. When stopping-state braking control is executed, the target setting unit 115 starts a stopping-state target setting process. The stop control unit 119 activates the brake actuator 50 based on the target frictional braking force FbFTr, and activates the regenerative braking unit 20 based on the target regenerative braking force FbETr. That is, the stop control unit 119 transmits information related to the target regenerative braking force FbETr to the regenerative control unit 101. Then, the regenerative control unit 101 activates the motor-generator 21 based on the target regenerative braking force FbETr indicated by the information. As a result, an effective regenerative braking force FbE corresponding to the target regenerative braking force FbETr is applied to the vehicle 10.

[0039] The stationary braking control includes a replacement process, a reduction process, a holding process, and a degeneration process. The replacement process of the stationary braking control is started at timing t12. The replacement process is a process of increasing the frictional braking force FbF to a magnitude equal to or greater than the stationary holding braking force Fbh and reducing the effective regenerative braking force FbE by the increase in the frictional braking force FbF. In this embodiment, the replacement process increases the frictional braking force FbF to the stationary holding braking force Fbh. In this case, in the stationary target setting process, the target setting unit 115 increases the target frictional braking force FbFTr to the stationary holding braking force Fbh. Furthermore, the target setting unit 115 sets the effective regenerative braking force FbE at the start of the replacement process to the initial value of the target regenerative braking force FbETr and reduces the target regenerative braking force FbETr from the initial value by the increase in the target regenerative braking force FbETr.

[0040] The stop control unit 119 operates the brake actuator 50 based on the target frictional braking force FbFTr. This increases the frictional braking force FbF. The stop control unit 119 also transmits information related to the target regenerative braking force FbETr to the regenerative control unit 101. When the regenerative control unit 101 receives this information, the regenerative control unit 101 operates the motor generator 21 based on the target regenerative braking force FbETr indicated by this information. This reduces the effective regenerative braking force FbE by the amount of increase in the frictional braking force FbF.

[0041] Here, an external disturbance may be input to the vehicle 10 while the vehicle 10 is traveling. The external disturbance is a force input to the vehicle 10 from outside the vehicle that changes the deceleration of the vehicle 10. In the example shown in FIG. 2 , the gradient of the road surface on which the vehicle 10 is traveling changes. Specifically, the road surface changes from a horizontal road to a downhill road between timing t12 and timing t13. In this case, the component of gravity acting on the vehicle 10 in the direction along the road surface changes, and therefore the deceleration of the vehicle 10 changes.

[0042] Because the vehicle body acceleration DVS deviates from the target vehicle body acceleration DVSTr, the correction unit 117 corrects the target frictional braking force FbFTr set by the target setting unit 115. In the example shown in FIG. 2, the target frictional braking force FbFTr is increased. In FIG. 2(e), the solid line indicates the change in the target frictional braking force FbFTr corrected by the correction unit 117, and the dashed line indicates the change in the target frictional braking force FbFTr not corrected by the correction unit 117. The stop control unit 119 operates the brake actuator 50 based on the corrected target frictional braking force FbFTr. Therefore, the deviation of the vehicle body acceleration DVS from the target vehicle body acceleration DVSTr is corrected.

[0043] Once the switching process is completed, the effective regenerative braking force FbE is maintained even if the frictional braking force FbF is changed due to the influence of a disturbance input to the vehicle 10. At timing t13, the stopping distance DS becomes equal to or less than the second threshold value DSth2, and a reduction process for the vehicle-stopping braking control is initiated. The second threshold value DSth2 is smaller than the first threshold value DSth1. The reduction process is a process for reducing the effective regenerative braking force FbE to 0 (zero). In this case, the target setting unit 115 reduces the target regenerative braking force FbETr to 0 (zero) so that the effective regenerative braking force FbE becomes 0 (zero) before the vehicle 10 reaches the stopping position. The stop control unit 119 transmits information regarding the target regenerative braking force FbETr to the regenerative control unit 101. The regenerative control unit 101 operates the motor-generator 21 based on the target regenerative braking force FbETr indicated by the information. As a result, the effective regenerative braking force FbE is reduced to 0 (zero).

[0044] On the other hand, the stop control unit 119 activates the brake actuator 50 based on the target friction braking force FbFTr corrected by the correction unit 117. This suppresses fluctuations in the vehicle body acceleration DVS caused by input of disturbances to the vehicle 10.

[0045] When the effective regenerative braking force FbE becomes 0 (zero) at timing t14, the reduction process ends and the maintaining process starts. In this case, the target regenerative braking force FbETr is maintained at 0 (zero). Furthermore, if the magnitude of the disturbance does not change, the target frictional braking force FbFTr, i.e., the frictional braking force FbF, is maintained. If the magnitude of the disturbance changes while the maintaining process is being performed, the correction unit 117 changes the target frictional braking force FbFTr, and therefore the frictional braking force FbF also changes.

[0046] When the stopping distance DS becomes equal to or less than the third threshold value DSth3 at timing t15, the stop control unit 119 can determine that the vehicle 10 has stopped. The third threshold value DSth3 is smaller than the second threshold value DSth2. An example of the third threshold value DSth3 is 0 (zero). When it is determined that the vehicle 10 has stopped, the holding process ends and the degeneration process starts. The degeneration process is a process for increasing the frictional braking force FbF to the required braking force FbRq. In this case, the target setting unit 115 increases the target frictional braking force FbFTr to the required braking force FbRq. The stop control unit 119 operates the brake actuator 50 based on the target frictional braking force FbFTr. As a result, the frictional braking force FbF increases toward the required braking force FbRq. At timing t16, the frictional braking force FbF becomes equal to or greater than the required braking force FbRq, and the degeneration process ends. That is, the vehicle-stopping braking control ends.

[0047] <Series of processes when decelerating the vehicle in accordance with a braking request> A series of processes when decelerating the vehicle 10 in accordance with a braking request will be described with reference to Figures 3 and 4. The processing circuit 71 of the braking control device 70 repeatedly executes this series of processes at predetermined control intervals.

[0048] As shown in FIG. 3, in step S11, the processing circuit 71 determines whether or not a braking request is made. If the processing circuit 71 determines that a braking request is made (S11: YES), the processing circuit 71 proceeds to step S13. On the other hand, if the processing circuit 71 determines that a braking request is not made (S11: NO), the processing circuit 71 proceeds to step S12. In step S12, the processing circuit 71 sets an end flag FLG (described later) to OFF. Thereafter, the processing circuit 71 temporarily ends the series of processes shown in FIG. 3.

[0049] In step S13, the processing circuit 71 derives the required braking force FbRq by functioning as the required braking force derivation unit 111. In the following step S15, the processing circuit 71 obtains the stopping distance DS by functioning as the stopping-related value acquisition unit 113.

[0050] In the next step S17, the processing circuit 71 determines whether the end flag FLG is set to OFF. The end flag FLG is a flag that is set to ON when the stop-time braking control during the current vehicle braking operation has ended. If the end flag FLG is set to OFF (S17: YES), the processing circuit 71 proceeds to step S31. On the other hand, if the end flag FLG is set to ON (S17: NO), the processing circuit 71 proceeds to step S19. If the processing proceeds to step S19, the vehicle 10 has already stopped.

[0051] In step S19, the processing circuit 71 sets the target frictional braking force FbFTr by functioning as the target setting unit 115. Specifically, the processing circuit 71 sets the required braking force FbRq to the target frictional braking force FbFTr.

[0052] In the following step S21, the processing circuit 71 functions as the stop control unit 119 to operate the brake actuator 50 based on the target friction braking force FbFTr set in step S19. Thereafter, the processing circuit 71 temporarily ends the series of processes.

[0053] In step S31, the processing circuit 71 determines whether the stopping distance DS is equal to or less than the first threshold value DSth1. If the stopping distance DS is equal to or less than the first threshold value DSth1, it can be determined that the vehicle 10 is about to stop. If the stopping distance DS is equal to or less than the first threshold value DSth1 (S31: YES), the processing circuit 71 proceeds to step S41. On the other hand, if the stopping distance DS is greater than the first threshold value DSth1 (S31: NO), the processing circuit 71 executes regenerative cooperative control. Specifically, the processing circuit 71 proceeds to step S33.

[0054] In step S33, the processing circuit 71 transmits information regarding the required braking force FbRq to the regenerative control device 30. Then, the processing circuit 31 proceeds to step S35. The processing circuit 31 of the regenerative control device 30 sets a target regenerative braking force FbETr based on the required braking force FbRq indicated by the received information. Then, the processing circuit 31 operates the motor generator 21 based on the target regenerative braking force FbETr.

[0055] In step S35, the processing circuit 71 of the brake control device 70 acquires the effective regenerative braking force FbE. In the following step S37, the processing circuit 71 sets the target frictional braking force FbFTr by functioning as the target setting unit 115. For example, the processing circuit 71 sets the target frictional braking force FbFTr to the larger of the value obtained by subtracting the effective regenerative braking force FbE from the required braking force FbRq, or 0 (zero).

[0056] Then, in step S39, the processing circuit 71 functions as the stop control unit 119 to operate the brake actuator 50 based on the target friction braking force FbFTr. After that, the processing circuit 71 temporarily ends the series of processes.

[0057] In step S41, the processing circuit 71 executes stationary braking control. Specifically, the processing circuit 71 proceeds to step S101 shown in FIG. 4. In step S101, the processing circuit 71 determines whether or not the switching process for stationary braking control has been completed. If the switching process has been completed (S101: YES), the processing circuit 71 proceeds to step S107. On the other hand, if the switching process has not been completed (S101: NO), the processing circuit 71 proceeds to step S103.

[0058] In step S103, the processing circuit 71 derives the stop-maintaining braking force Fbh. For example, when the road surface on which the vehicle 10 is traveling is a slope, the processing circuit 71 derives a braking force as the stop-maintaining braking force Fbh that is greater than when the road surface is not a slope.

[0059] In the following step S105, the processing circuit 71 executes a switching process. Specifically, the processing circuit 71 functions as the target setting unit 115 to increase the target frictional braking force FbFTr toward the vehicle-stop-maintaining braking force Fbh. The processing circuit 71 also decreases the target regenerative braking force FbETr by the increase in the target frictional braking force FbFTr. The processing circuit 71 then functions as the stop control unit 119 to transmit information regarding the target regenerative braking force FbETr to the regenerative control device 30. Thereafter, the processing circuit 71 proceeds to step S117.

[0060] The processing circuit 31 of the regenerative control device 30 operates the motor generator 21 based on the target regenerative braking force FbETr indicated by the received information. In step S107, the processing circuit 71 determines whether the stopping distance DS is equal to or less than the second threshold value DSth2. If the stopping distance DS is equal to or less than the second threshold value DSth2 (S107: YES), the processing circuit 71 proceeds to step S109. On the other hand, if the stopping distance DS is greater than the second threshold value DSth2 (S107: NO), the processing circuit 71 proceeds to step S117.

[0061] In step S109, the processing circuit 71 determines whether the stopping distance DS is equal to or less than the third threshold value DSth3. If the stopping distance DS is equal to or less than the third threshold value DSth3 (S109: YES), the processing circuit 71 proceeds to step S121. On the other hand, if the stopping distance DS is greater than the third threshold value DSth3 (S109: NO), the processing circuit 71 proceeds to step S110.

[0062] In step S110, the processing circuit 71 acquires the effective regenerative braking force FbE. In the following step S111, the processing circuit 71 determines whether the effective regenerative braking force FbE acquired in step S110 is 0 (zero). If the effective regenerative braking force FbE is 0 (zero) (S111: YES), the processing circuit 71 proceeds to step S115. On the other hand, if the effective regenerative braking force FbE is greater than 0 (zero) (S111: NO), the processing circuit 71 proceeds to step S113.

[0063] In step S113, the processing circuit 71 executes a process for reducing the braking control during a stop. Specifically, the processing circuit 71 functions as the target setting unit 115 to reduce the target regenerative braking force FbETr toward 0 (zero). Then, the processing circuit 71 functions as the stop control unit 119 to transmit information about the set target regenerative braking force FbETr to the regenerative control device 30. After that, the processing circuit 71 proceeds to step S117.

[0064] The processing circuit 31 of the regenerative control device 30 operates the motor generator 21 based on the target regenerative braking force FbETr indicated by the received information. In step S115, the processing circuit 71 of the brake control device 70 executes a process for maintaining the stationary braking control. Specifically, the processing circuit 71 functions as the target setting unit 115 to maintain the target regenerative braking force FbETr at 0 (zero). Then, the processing circuit 71 functions as the stop control unit 119 to transmit information regarding the set target regenerative braking force FbETr to the regenerative control device 30. Thereafter, the processing circuit 71 proceeds to step S117.

[0065] In step S117, the processing circuit 71 functions as the correction unit 117 to subtract the vehicle body acceleration DVS from the target vehicle body acceleration DVSTr, thereby deriving the deviation ΔDVS. In the following step S119, the processing circuit 71 functions as the correction unit 117 to correct the target frictional braking force FbFTr by feedback control using the deviation ΔDVS as an input. Then, the processing circuit 71 proceeds to step S125.

[0066] In step S121, the processing circuit 71 determines whether the degeneration process of the stationary braking control has been completed. If the degeneration process has been completed (S121: YES), the processing circuit 71 proceeds to step S127. On the other hand, if the degeneration process has not been completed (S121: NO), the processing circuit 71 proceeds to step S123.

[0067] In step S123, the processing circuit 71 executes a degeneration process. Specifically, the processing circuit 71 functions as the target setting unit 115 to increase the target friction braking force FbFTr toward the required braking force FbRq. Then, the processing circuit 71 proceeds to step S125.

[0068] In step S125, the processing circuit 71 functions as the stop control unit 119 to operate the brake actuator 50 based on the target friction braking force FbFTr. After that, the processing circuit 71 ends the series of processes shown in FIG.

[0069] In step S127, the processing circuit 71 sets the end flag FLG to ON. Then, the processing circuit 71 ends the series of processes shown in Fig. 4. Returning to Fig. 3, after executing the stop braking control in step S41, the processing circuit 71 temporarily ends the series of processes shown in Fig. 3.

[0070] <Functions and Effects of the Present Embodiment> (1-1) The processing circuit 71 of the brake control device 70 executes a vehicle-stop target setting process when stopping the vehicle 10. The vehicle-stop target setting process includes decreasing the target regenerative braking force FbETr and increasing the target frictional braking force FbFTr. The processing circuit 71 controls the frictional braking force FbF by operating the brake actuator 50 based on the target frictional braking force FbFTr. The processing circuit 71 also controls the effective regenerative braking force FbE by operating the regenerative braking unit 20 based on the target regenerative braking force FbETr.

[0071] When the above-described vehicle stop target setting process is being executed, a disturbance that changes the deceleration of the vehicle 10 may be input to the vehicle 10. Here, a comparative example will be described in which the target regenerative braking force FbETr is corrected so as to reduce the difference between the target vehicle body acceleration DVSTr and the vehicle body acceleration DVS. Due to the characteristics of the motor-generator 21, once the rotation of the wheels 13 stops, the motor-generator 21 is unable to apply regenerative braking force to the vehicle 10. In this comparative example, when a disturbance is input to the vehicle 10, the vehicle 10 may stop with the target regenerative braking force FbETr greater than 0 (zero). In this case, the effective regenerative braking force FbE becomes 0 (zero) when the vehicle 10 stops, and therefore the total braking force Fb suddenly decreases when the vehicle 10 stops. This sudden decrease in the total braking force Fb may cause vibrations in the vehicle 10 due to the sudden decrease in the total braking force Fb.

[0072] In this regard, in the brake control device 70, the processing circuit 71 corrects the target frictional braking force FbFTr instead of the target regenerative braking force FbETr so as to reduce the difference between the target vehicle body acceleration DVSTr and the vehicle body acceleration DVS. Then, the processing circuit 71 operates the brake actuator 50 based on the corrected target frictional braking force FbFTr. This prevents the predicted vehicle stop timing from differing from the actual vehicle stop timing.

[0073] Furthermore, since the brake control device 70 does not increase the target regenerative braking force FbETr, the vehicle 10 can be stopped with the target regenerative braking force FbETr kept as small as possible. This prevents the total braking force Fb from suddenly decreasing when the vehicle 10 stops.

[0074] Therefore, the brake control device 70 can ensure stability of the behavior of the vehicle 10 when the vehicle 10 stops. (1-2) The brake control device 70 executes stop-time braking control immediately before the vehicle 10 stops. When stop-time braking control is executed, the processing circuit 71 sets the target regenerative braking force FbETr and the target frictional braking force FbFTr so that the vehicle 10 stops in a state where the sum of the effective regenerative braking force FbE and the frictional braking force FbF is smaller than the required braking force FbRq. The processing circuit 71 then operates the brake actuator 50 based on the target frictional braking force FbFTr and operates the regenerative braking unit 20 based on the target regenerative braking force FbETr. This allows the brake control device 70 to suppress a sudden change in the pitch attitude of the vehicle 10 when the vehicle 10 stops. Furthermore, the brake control device 70 can suppress a decrease in the stability of the vehicle behavior before and after the vehicle 10 stops, which is caused by the execution of stop-time braking control.

[0075] (1-3) When the vehicle is braking but the vehicle-stop target setting process is not being executed, the processing circuit 71 does not execute the process of correcting the target friction braking force FbFTr based on the difference between the target vehicle body acceleration DVSTr and the vehicle body acceleration DVS. This allows the brake control device 70 to suppress a decrease in opportunities to increase the effective regenerative braking force FbE.

[0076] Second Embodiment A second embodiment of the braking control device will be described with reference to Fig. 5. The second embodiment differs from the first embodiment in part of the processing content before the vehicle-stop target setting processing is executed. In the following description, differences from the first embodiment will be mainly described, and the same components as those in the first embodiment will be assigned the same reference numerals and redundant description will be omitted.

[0077] The flow of processing when the regenerative braking cooperative control is executed will be described with reference to Fig. 5. In step S31 of Fig. 3, if the stopping distance DS is greater than the first threshold value DSth1 (S31: NO), the processing circuit 71 of the brake control device 70 proceeds to step S201. In step S201, the processing circuit 71 acquires the effective regenerative braking force FbE.

[0078] In the following step S203, the processing circuit 71 functions as the correction unit 117 to derive the deviation ΔDVS in the same manner as in step S117. In the next step S205, the processing circuit 71 functions as the correction unit 117 to correct the target regenerative braking force FbETr based on the deviation ΔDVS. For example, the processing circuit 71 corrects the target regenerative braking force FbETr by feedback control using the deviation ΔDVS as an input.

[0079] In the following step S207, the processing circuit 71 functions as the stop control unit 119, and transmits information about the target regenerative braking force FbETr corrected in step S205 to the regenerative control device 30. Then, the processing circuit 71 proceeds to step S209.

[0080] When the processing circuit 31 of the regenerative control device 30 receives the information, it operates the motor generator 21 based on the target regenerative braking force FbETr indicated by the information. In step S209, the processing circuit 71 of the braking control device 70 functions as the target setting unit 115 to set the target frictional braking force FbFTr in the same manner as in step S37.

[0081] In the following step S211, the processing circuit 71 functions as the stop control unit 119 to operate the brake actuator 50 based on the target friction braking force FbFTr. After that, the processing circuit 71 temporarily ends the series of processes.

[0082] The brake control device 70 of the second embodiment can achieve the following effects in addition to the effects of the first embodiment. (2-1) Before the vehicle-stop brake control is initiated, the processing circuit 71 of the brake control device 70 corrects the target regenerative braking force FbETr so as to reduce the difference between the target vehicle body acceleration DVSTr and the vehicle body acceleration DVS. The motor generator 21 is operated based on the target regenerative braking force FbETr. This allows the effective regenerative braking force FbE to be maximized when the vehicle 10 is not about to come to a stop. As a result, the brake control device 70 can efficiently recover regenerative energy.

[0083] (Modifications) The above-described embodiments can be modified as follows: The above-described embodiments and the following modifications can be combined with each other within the scope of technical compatibility.

[0084] In the second embodiment, when correcting the target regenerative braking force FbETr based on the deviation ΔDVS, the processing circuit 71 may increase the target frictional braking force FbFTr if the target regenerative braking force FbETr reaches the regenerative braking force limit value.

[0085] In the above embodiments, when the vehicle-stop target setting process is started, the processing circuit 71 corrects the target frictional braking force FbFTr based on the deviation ΔDVS. However, this is not limited to this. Even when the vehicle-stop target setting process is started, the processing circuit 71 does not need to correct the target frictional braking force FbFTr based on the deviation ΔDVS until a predetermined condition is met. For example, the processing circuit 71 may determine that the predetermined condition is met when the stopping distance DS is equal to or less than the second threshold value DSth2. Alternatively, the processing circuit 71 may determine that the predetermined condition is met when the switching process is completed. The processing circuit 71 may determine that the predetermined condition is met when the reduction process is started.

[0086] The vehicle-stop braking control may be a control different from the control described in the above embodiments, as long as it can make the total braking force Fb less than the requested braking force FbRq when the vehicle 10 comes to a stop.

[0087] For example, the vehicle-stop braking control may be a control in which the effective regenerative braking force FbE is reduced to 0 (zero) and then the frictional braking force FbF is increased to the vehicle-stop maintaining braking force Fbh. In this case, the processing circuit 71 may reduce the target regenerative braking force FbETr to 0 (zero) and then increase the target frictional braking force FbFTr in the vehicle-stop target setting process.

[0088] The vehicle-stop braking control may include an increase process for increasing the total braking force Fb to be greater than the required braking force FbRq before the start of the switching process. The vehicle-stop braking control does not need to include a degeneration process as long as the vehicle 10 can be kept stopped.

[0089] In the degeneration processing, the processing circuit 71 does not need to increase the target friction braking force FbFTr to the required braking force FbRq as long as the vehicle 10 can be kept stopped. The processing circuit 71 may acquire a parameter other than the stopping distance DS as the stopping-related value. For example, the processing circuit 71 may acquire the vehicle speed VS of the vehicle 10 as the stopping-related value. Also, for example, the processing circuit 71 may acquire the time required for the vehicle 10 to reach the stopping position as the stopping-related value.

[0090] The processing circuit 71 does not have to execute the vehicle stop braking control immediately before the vehicle 10 is stopped. Even in this case, the processing circuit 71 executes the switching control to switch the effective regenerative braking force FbE to the frictional braking force FbF until the vehicle 10 is stopped. When such switching control is executed, the processing circuit 71 may correct the target frictional braking force FbFTr based on the deviation ΔDVS.

[0091] The processing circuitry 71 may be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware for performing at least some of the various processes, or a combination thereof. Examples of dedicated hardware include an application-specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM, which store program code or instructions configured to cause the CPU to perform processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0092] (Other Technical Ideas) The following describes technical ideas that can be understood from the above-described embodiments and modified examples. [Supplementary Note 1] In the stop-time target setting process, it is preferable that the target setting unit replaces the target regenerative braking force with the target frictional braking force so that the target frictional braking force increases to a magnitude equal to or greater than a stop-maintaining braking force, which is a braking force that can maintain the vehicle at a stop on the road surface on which the vehicle is traveling, and then reduces the target regenerative braking force to 0 (zero).

[0093] [Supplementary Note 2] It is preferable that the correction unit does not correct the target friction braking force set by the target setting unit before the target setting unit executes the stationary-vehicle target setting process.

[0094] [Supplementary Note 3] It is preferable that the correction unit stops the process of correcting the target frictional braking force when it is determined that the vehicle has stopped. [Appendix 4] A braking control device that is applied to a vehicle that includes a regenerative braking unit that applies a regenerative braking force to the vehicle and a friction braking unit that applies a friction braking force to the vehicle, and that performs stationary braking control to stop the vehicle in a state where the sum of the regenerative braking force and the friction braking force is smaller than a required braking force that is a required value for the total braking force of the vehicle, the braking control device comprising: a target setting unit that, when the stationary braking control is being executed, performs stationary target setting processing including reducing a target regenerative braking force that is a target for the regenerative braking force, and increasing a target friction braking force that is a target for the friction braking force; a correction unit that corrects the target friction braking force so that a deviation between a target value of deceleration of the vehicle and an actual value of the deceleration becomes smaller; and a stop control unit that, when the stationary braking control is being executed, operates the regenerative braking unit based on the target regenerative braking force, and operates the friction braking unit based on the target friction braking force corrected by the correction unit.

[0095] It should be noted that the expression "at least one" used in this specification means "one or more" of the desired options. As an example, the expression "at least one" used in this specification means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

Claims

1. A braking control device applicable to a vehicle equipped with a regenerative braking unit that applies regenerative braking force to the vehicle and a friction braking unit that applies friction braking force to the vehicle, comprising: a target setting unit that executes a vehicle-stop target setting process, which includes reducing a target regenerative braking force that is a target for the regenerative braking force and increasing a target friction braking force that is a target for the friction braking force when stopping the vehicle; a correction unit that corrects the target friction braking force so as to reduce the deviation between a target value of the vehicle's deceleration and an actual value of the deceleration; and a stop control unit that, when the vehicle-stop target setting process is being executed, operates the regenerative braking unit based on the target regenerative braking force, and operates the friction braking unit based on the target friction braking force corrected by the correction unit, thereby stopping the vehicle.

2. The braking control device controls the total braking force of the vehicle by activating the regenerative braking unit and the friction braking unit, and the target setting unit sets the target regenerative braking force and the target friction braking force in the stopped target setting process so that the vehicle stops in a state where the sum of the regenerative braking force and the friction braking force is smaller than the required braking force, which is the required value of the total braking force.

3. A braking control device as described in claim 2, further comprising a stopping-related value acquisition unit that acquires a stopping-related value that decreases as the vehicle approaches a predetermined stopping position, and wherein the target setting unit starts the stopping target setting process when the stopping-related value becomes equal to or less than a predetermined threshold value.

4. A braking control device as described in any one of claims 1 to 3, wherein the correction unit corrects the target regenerative braking force set by the target setting unit so that the deviation between the target value of the vehicle's deceleration and the actual value of the deceleration becomes small before the target setting unit executes the stationary target setting process.

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