Braking control device

Abstract

A processing circuit 51 of a braking control device 50 functions as: a control unit M11 that, when a braking force is applied to a vehicle 10 to stop the vehicle, executes reduction correction processing of reducing the vehicle braking force to a predetermined braking force less than a required braking force and then setting the vehicle body speed of the vehicle 10 to 0 (zero); and a setting unit M15 that, when a change in a braking operation being performed by the driver is detected before the start of the reduction correction processing, setting the execution time of the reduction correction processing to a shorter time than when no change in the braking operation is detected.

Description

Braking control device

[0001] The present invention relates to a braking control device that controls braking force applied to a vehicle.

[0002] Patent Document 1 discloses a vehicle control device that performs stopping control to suppress changes in the vehicle's posture when the vehicle is stopped by reducing the braking force applied to the vehicle immediately before the vehicle stops.

[0003] JP 2016-28913 A

[0004] When the braking force is reduced as a result of the execution of the above-described vehicle stop control, if the driver of the vehicle changes his / her braking operation, a deviation may occur between the vehicle behavior intended by the driver and the actual vehicle behavior. If such a deviation occurs, the driver may feel uncomfortable due to the deviation.

[0005] A braking control device for solving the above problem includes a control unit that, when applying braking force to a vehicle to stop it, reduces the braking force applied to the vehicle to a predetermined braking force that is smaller than the required value of the braking force, and then performs a reduction correction process to set the vehicle's body speed to 0 (zero), and a setting unit that, when a change in the braking operation is detected before the reduction correction process starts while the driver of the vehicle is performing a braking operation, sets the execution time of the reduction correction process to a shorter time than when a change in the braking operation is not detected.

[0006] The braking control device has the effect of suppressing changes in the vehicle's attitude when stopped, without making the driver feel uncomfortable, when the driver changes the braking operation during braking.

[0007] FIG. 1 is a schematic diagram showing a configuration of a vehicle equipped with a brake control device according to an embodiment. FIG. 2 is a timing chart showing a case where the braking operation does not change when stopping the vehicle by applying a braking force. FIG. 3 is a diagram showing an example of a map for setting an execution time of a reduction correction process. FIG. 4 is a flowchart showing a series of processes executed by the brake control device of FIG. 1. FIG. 5 is a timing chart showing a case where a reduction in the braking operation amount starts before the reduction correction process starts in a first comparative example. FIG. 6 is a timing chart showing a case where a reduction in the braking operation amount starts before the reduction correction process starts in the brake control device of FIG. 1. FIG. 7 is a timing chart showing a case where an increase in the braking operation amount starts before the reduction correction process starts in a second comparative example. FIG. 8 is a timing chart showing a case where an increase in the braking operation amount starts before the reduction correction process starts in the brake control device of FIG. 1. FIG. 9 is a flowchart showing a part of a series of processes executed by a brake control device according to a modified example. FIG. 10 is a timing chart showing a modified example of stop-time braking control.

[0008] An embodiment of a brake control device will be described below with reference to Figs. 1 to 8. Fig. 1 illustrates a vehicle 10 equipped with a brake control device 50. The vehicle 10 includes a brake operating member 11, a plurality of wheels, a plurality of friction brakes 20, and a brake actuator 30. The plurality of wheels include two front wheels 12 and two rear wheels 13. The brake operating member 11 is a member operated by the driver when applying a braking force to the vehicle 10. An example of the brake operating member 11 is a brake pedal. The driver's operation of the brake operating member 11 is referred to as a "braking operation."

[0009] <Friction Brake> The multiple friction brakes 20 each apply a braking force to a corresponding wheel. The friction brake 20 has a wheel cylinder 21, a rotating body 22, and a friction portion 23. The rotating body 22 rotates integrally with the wheel. Therefore, braking force is applied to the wheel by pressing the friction portion 23 against the rotating body 22. The force pressing the friction portion 23 against the rotating body 22 increases as the wheel hydraulic pressure, which is the hydraulic pressure in the wheel cylinder 21, increases. Therefore, the friction brake 20 can apply a greater braking force to the wheel as the wheel hydraulic pressure increases.

[0010] <Brake Actuator> The brake actuator 30 controls the wheel hydraulic pressure in the plurality of wheel cylinders 21 to control the braking force applied to the wheels 12, 13. For example, the brake actuator 30 has a pressure source that supplies brake fluid to the plurality of wheel cylinders 21. The pressure source is, for example, an electric pump and an electric cylinder. The brake actuator 30 can individually adjust the wheel hydraulic pressure in the wheel cylinder 21 for the front wheels 12 and the wheel hydraulic pressure in the wheel cylinder 21 for the rear wheels 13.

[0011] In the following description, the sum of the braking forces applied to the multiple wheels 12, 13 will also be referred to as the "vehicle braking force BPAl." <Detection System> The detection system of the vehicle 10 includes multiple sensors that output detection signals to the braking control device 50. The multiple sensors include a brake sensor 101, multiple wheel speed sensors 102, and a longitudinal acceleration sensor 103.

[0012] The brake sensor 101 detects information related to the operation of the brake operating member 11 by the driver. An example of the brake sensor 101 is a stroke sensor that detects the amount of operation of the brake operating member 11 by the driver. The amount of operation based on the detection signal of the brake sensor 101 is referred to as the "braking operation amount X." The detection system may also include a sensor that detects the operating force of the brake operating member 11 by the driver.

[0013] A wheel speed sensor 102 is provided for each of the plurality of wheels. Each of the plurality of wheel speed sensors 102 detects the rotational speed of the corresponding wheel. The rotational speed of the wheel based on the detection signal of the wheel speed sensor 102 is referred to as the "wheel speed VW." The traveling speed of the vehicle 10 calculated based on the wheel speeds VW of the plurality of wheels 12, 13 is referred to as the "vehicle speed VS."

[0014] The longitudinal acceleration sensor 103 detects the longitudinal acceleration of the vehicle 10 out of the accelerations acting on the vehicle 10. The longitudinal acceleration of the vehicle 10 based on the detection signal of the longitudinal acceleration sensor 103 is referred to as "longitudinal acceleration Gx."

[0015] <Brake Control Device> The brake control device 50 includes a processing circuit 51. One example of the processing circuit 51 is an electronic control device. In this case, the processing circuit 51 includes a CPU 52, a first memory 53, and a second memory 54. The first memory 53 stores a control program executed by the CPU 52. The second memory 54 stores calculation results of the CPU 52, etc. When the CPU 52 executes the control program in the first memory 53, the processing circuit 51 controls the brake actuator 30 to activate the plurality of friction brakes 20. In other words, the processing circuit 51 can adjust the vehicle braking force BPAl by activating the plurality of friction brakes 20.

[0016] <Outline of braking control at a stop> The processing circuit 51 performs braking control at a stop when the driver is operating the brake operating member 11. The braking control at a stop is braking control for suppressing changes in the posture of the vehicle 10 when the vehicle is stopped.

[0017] Referring to FIG. 2 , the braking control at a stop will be described. FIG. 2 illustrates an example in which the braking operation amount X does not change during the braking control at a stop. While the vehicle 10 is traveling, the driver begins to operate the brake operating member 11 at timing t11. In this case, as shown in FIG. 2B , the processing circuit 51 derives a required braking force BPRq. The required braking force BPRq is a required value for the vehicle braking force BPAl. For example, the processing circuit 51 derives the required braking force BPRq so that the greater the braking operation amount X of the brake operating member 11, the greater the required braking force BPRq. When the vehicle speed VS of the vehicle 10 is greater than the first vehicle speed determination value VSth1, as before timing t12, the processing circuit 51 sets the required braking force BPRq as the command braking force BPTr, as shown in FIG. 2D . Then, the processing circuit 51 controls the brake actuator 30 so that the vehicle braking force BPAl becomes equal to the command braking force BPTr.

[0018] When a braking force is applied to the vehicle 10 in this manner, the vehicle speed VS decreases as shown in Fig. 2A. Also, as shown in Fig. 2C, the absolute value of the longitudinal acceleration Gx increases as the vehicle braking force BPAl increases.

[0019] When the vehicle speed VS reaches the first vehicle speed determination value VSth1 at timing t12, the processing circuit 51 starts stop braking control. The first vehicle speed determination value VSth1 is an example of a threshold value for setting the start timing of stop braking control. From timing t12, the processing circuit 51 starts an increase correction process for the stop braking control. In the increase correction process, the processing circuit 51 sets a braking force greater than the required braking force BPRq as the command braking force BPTr. For example, the processing circuit 51 sets the sum of the required braking force BPRq and the offset value ΔBP as the command braking force BPTr. Then, the processing circuit 51 controls the brake actuator 30 so that the vehicle braking force BPAl becomes the command braking force BPTr. As a result, even if the required braking force BPRq remains the same, the absolute value of the longitudinal acceleration Gx of the vehicle 10 becomes greater by the amount of the offset value ΔBP than before timing t12.

[0020] At timing t13, the vehicle speed VS becomes the second vehicle speed determination value VSth2. A vehicle speed smaller than the first vehicle speed determination value VSth1 is set as the second vehicle speed determination value VSth2. When the vehicle speed VS is equal to or smaller than the second vehicle speed determination value VSth2, it is determined that the vehicle 10 is approaching the stop position PS. The stop position PS is a predicted position where the vehicle 10 will stop. The processing circuit 51 shifts the processing of the stop-time braking control from an increase correction processing to a decrease correction processing. In the decrease correction processing, the processing circuit 51 decreases the command braking force BPTr at a constant rate. Then, the processing circuit 51 controls the brake actuator 30 so that the vehicle braking force BPAl becomes the command braking force BPTr. By performing the decrease correction processing in this manner, the processing circuit 51 causes the vehicle braking force BPAl to become smaller than the required braking force BPRq. As a result, even if the required braking force BPRq remains the same, the absolute value of the longitudinal acceleration Gx of the vehicle 10 gradually decreases.

[0021] At timing t14, the command braking force BPTr becomes equal to the stop-maintenance braking force BPth. The stop-maintenance braking force BPth is set to the minimum braking force necessary to maintain the stop of the vehicle 10 on the current road surface on which the vehicle 10 is traveling, or to a braking force slightly greater than that braking force. This stop-maintenance braking force BPth is an example of a "predetermined braking force." From timing t14, in the reduction correction process, the processing circuit 51 maintains the command braking force BPTr at the stop-maintenance braking force BPth.

[0022] At timing t15, the processing circuit 51 determines that the vehicle 10 has stopped, and therefore transitions the processing of the stop-time braking control from the reduction correction processing to the degeneration processing. In the degeneration processing, the processing circuit 51 increases the command braking force BPTr. For example, the processing circuit 51 increases the command braking force BPTr to the required braking force BPRq. The processing circuit 51 controls the brake actuator 30 based on the command braking force BPTr, thereby increasing the vehicle braking force BPAl. When the command braking force BPTr becomes equal to the required braking force BPRq at timing t16, the processing circuit 51 terminates the stop-time braking control.

[0023] <Functional Configuration of Processing Circuit> The functional configuration of the processing circuit 51 will be described with reference to Fig. 1. The CPU 52 executes the control program in the first memory 53, causing the processing circuit 51 to function as multiple functional units. These multiple functional units are functional units for applying braking force to the vehicle 10 to bring it to a stop. The multiple functional units include, for example, a control unit M11, an acquisition unit M13, and a setting unit M15.

[0024] <Control Unit> The control unit M11 performs stop braking control when applying braking force to the vehicle 10 to stop the vehicle. That is, when a start condition for stop braking control is met, the control unit M11 executes an increase correction process for the stop braking control. In the increase correction process, the control unit M11 sets the command braking force BPTr to a vehicle braking force greater than the required braking force BPRq. An offset value ΔBP, which is an increase correction amount for the command braking force BPTr at this time, is a braking force correction amount for compensating for an extension of the braking distance of the vehicle 10 due to execution of a decrease correction process, which will be described later. The control unit M11 operates the brake actuator 30 based on the command braking force BPTr.

[0025] When a condition for transitioning from the increasing correction process to the decreasing correction process is met during the execution of the increasing correction process, the control unit M11 terminates the increasing correction process and starts the decreasing correction process. In the decreasing correction process, the control unit M11 reduces the commanded braking force BPTr to a stop-maintenance braking force BPth that is smaller than the required braking force BPRq, and then sets the vehicle body speed VS to 0 (zero). At this time, the control unit M11 reduces the commanded braking force BPTr to the stop-maintenance braking force BPth before the vehicle body speed VS becomes 0 (zero). After the commanded braking force BPTr becomes the stop-maintenance braking force BPth, the control unit M11 maintains the commanded braking force BPTr at the stop-maintenance braking force BPth. The control unit M11 operates the brake actuator 30 based on the commanded braking force BPTr at that time.

[0026] When a transition condition from the reduction correction process to the degeneration process is met during the execution of the reduction correction process, the control unit M11 ends the reduction correction process and starts the degeneration process. In the degeneration process, the control unit M11 increases the command braking force BPTr to the required braking force BPRq. The control unit M11 operates the brake actuator 30 based on the command braking force BPTr.

[0027] The acquisition unit M13 acquires at least one of the braking operation amount X and the rate of change dX of the braking operation amount X as the braking operation-related value. For example, the acquisition unit M13 acquires the braking operation-related value each time the increasing correction process is performed. In this embodiment, the acquisition unit M13 acquires at least the braking operation amount X of the braking operation amount X and the rate of change dX of the braking operation amount X.

[0028] <Setting Unit> When the setting unit M15 detects a change in the braking operation before the start of the reduction correction process while the driver is performing the braking operation, the setting unit M15 sets the execution time TMD of the reduction correction process to a shorter time than when no change in the braking operation is detected. For example, the setting unit M15 detects a change in the braking operation based on a change in the braking-related value acquired by the acquisition unit M13 before the start of the reduction correction process. In this embodiment, the acquisition unit M13 acquires the braking-related value X as the braking operation-related value. Therefore, the setting unit M15 detects a change in the braking operation based on a change in the braking operation amount X before the start of the reduction correction process. In this case, the setting unit M15 detects a change in the braking operation when the change amount ΔX in the braking operation amount X from the start of the increase correction process becomes equal to or greater than a first change amount ΔXth1.

[0029] The setting unit M15 sets the execution time TMD of the decrease correction process depending on whether a change in the braking operation is detected before the decrease correction process is started. In this embodiment, when the change ΔX in the braking operation amount X from the start of the increase correction process becomes equal to or greater than the first change ΔXth1, the setting unit M15 sets the execution time TMD to be shorter than when the change ΔX does not become equal to or greater than the first change ΔXth1.

[0030] For example, the setting unit M15 may set the execution time TMD of the reduction correction process using the map shown in FIG. 3 . As shown in FIG. 3 , when the change amount ΔX is less than the first change amount ΔXth1, the setting unit M15 determines that a change in braking operation before the start of the reduction correction process cannot be detected, and sets the reference execution time TMDB as the execution time TMD of the reduction correction process. When the change amount ΔX is equal to or greater than the first change amount ΔXth1 but less than the second change amount ΔXth2, the setting unit M15 sets a shorter time as the change amount ΔX increases as the execution time TMD of the reduction correction process. The second change amount ΔXth2 is smaller than the first change amount ΔXth1. When the change amount ΔX is equal to or greater than the second change amount ΔXth2, the setting unit M15 sets the minimum time TMDMin as the execution time TMD of the reduction correction process. The minimum time TMDMin is shorter than the reference execution time TMDB.

[0031] <Processing flow during vehicle braking> A series of processes performed by the processing circuit 51 when performing braking control at a stop will be described with reference to Fig. 4. The processing circuit 51 repeatedly performs the series of processes shown in Fig. 4 when the driver is performing a braking operation.

[0032] In step S11, the processing circuit 51 determines whether or not a start condition for stop braking control is satisfied. For example, as shown in FIG. 2, the processing circuit 51 determines that the start condition is satisfied when the vehicle body speed VS becomes equal to or less than the first vehicle body speed determination value VSth1 after being greater than the first vehicle body speed determination value VSth1. If the processing circuit 51 determines that the start condition is satisfied (S11: YES), the processing circuit 51 proceeds to step S13. On the other hand, if the processing circuit 51 determines that the start condition is not satisfied (S11: NO), the processing circuit 51 temporarily terminates the series of processes shown in FIG. 4.

[0033] In step S13, the processing circuit 51 acquires the braking operation amount X at that time as a reference operation amount XB. This reference operation amount XB is the braking operation amount X at the start of the increasing correction process. In the following step S15, the processing circuit 51 executes the increasing correction process for the stop-time braking control. In the increasing correction process, the processing circuit 51 sets the sum of the required braking force BPRq and the offset value ΔBP as the command braking force BPTr to compensate for the extension of the braking distance of the vehicle 10 caused by the execution of the decreasing correction process. The processing circuit 51 operates the brake actuator 30 based on the command braking force BPTr.

[0034] In the next step S17, the processing circuit 51 acquires the braking operation amount X at that time. That is, the processing circuit 51 acquires the braking operation amount X during execution of the increasing correction process. Then, in step S19, the processing circuit 51 sets an execution time TMD of the decreasing correction process. Specifically, the processing circuit 51 derives the magnitude of the difference between the braking operation amount X acquired in step S17 and the reference operation amount XB as the change amount ΔX of the braking operation amount. The processing circuit 51 sets the execution time TMD according to the change amount ΔX using, for example, the map shown in FIG. 3 .

[0035] In the following step S21, the processing circuit 51 sets the second vehicle speed determination value VSth2 to a vehicle speed corresponding to the execution time TMD set in step S19. At this time, the processing circuit 51 sets the second vehicle speed determination value VSth2 so that the shorter the execution time TMD, the smaller the value. The stop-time braking control is a control that sets the vehicle speed VS to 0 (zero) during execution of the reduction correction process. Therefore, for example, if the second vehicle speed determination value VSth2 is not reduced even when the execution time TMD is shortened, there is a high possibility that the vehicle speed VS will not become 0 (zero) by the time the reduction correction process ends. Therefore, when the execution time TMD of the reduction correction process is variable as in this embodiment, it is necessary to change the second vehicle speed determination value VSth2 according to the set execution time TMD. Therefore, the processing circuit 51 sets the second vehicle body speed determination value VSth2 so that the vehicle body speed VS becomes 0 (zero) during the holding period in which the command braking force BPTr is held at the vehicle stop maintenance braking force BPth during the execution of the decrease correction process. After setting the second vehicle body speed determination value VSth2, the processing circuit 51 proceeds to step S23.

[0036] In step S23, the processing circuit 51 determines whether a transition condition from the increasing correction processing to the decreasing correction processing is satisfied. For example, the processing circuit 51 determines that the transition condition is satisfied when the vehicle speed VS becomes equal to or less than the second vehicle speed determination value VSth2 after being greater than the second vehicle speed determination value VSth2. The second vehicle speed determination value VSth2 used here is the value set in step S21. If the processing circuit 51 determines that the transition condition is not satisfied (S23: NO), the processing circuit 51 transitions the processing to step S15. That is, the processing circuit 51 executes the increasing correction processing. On the other hand, if the processing circuit 51 determines that the transition condition is satisfied (S23: YES), the processing circuit 51 transitions the processing to step S25.

[0037] In step S25, the processing circuit 51 executes a reduction correction process for the stop-time braking control. In the reduction correction process, the processing circuit 51 reduces the command braking force BPTr to the stop-maintenance braking force BPth. After the command braking force BPTr reaches the stop-maintenance braking force BPth, the processing circuit 51 maintains the command braking force BPTr at the stop-maintenance braking force BPth. Then, the processing circuit 51 operates the brake actuator 30 based on the command braking force BPTr.

[0038] In this embodiment, the processing circuit 51 changes the command braking force BPTr so that the reduction correction process can be completed within the execution time TMD set in step S19. First, the processing circuit 51 sets the length of a reduction period, which is a period during which the command braking force BPTr is reduced to the stop-maintenance braking force BPth, and the length of a holding period, which is a period during which the command braking force BPTr is maintained at the stop-maintenance braking force BPth. Shortening the length of the reduction period tends to increase the rate at which the command braking force BPTr is reduced during the reduction period. Therefore, the processing circuit 51 shortens the length of the holding period as the execution time TMD becomes shorter. Then, during the reduction period, the processing circuit 51 increases the rate at which the command braking force BPTr is reduced as the set reduction period becomes shorter. When the reduction period ends and the command braking force BPTr reaches the stop-maintenance braking force BPth, the processing circuit 51 maintains the command braking force BPTr at the stop-maintenance braking force BPth.

[0039] In the following step S27, the processing circuit 51 determines whether a transition condition from the reduction correction processing to the degeneration processing is satisfied. For example, as shown in FIG. 2, the processing circuit 51 determines that the transition condition is satisfied when it is determined that the vehicle 10 has stopped. Therefore, the processing circuit 51 may determine that the transition condition is satisfied before the actual execution time of the reduction correction processing reaches the execution time TMD. Conversely, the processing circuit 51 may determine that the transition condition is satisfied after the actual execution time of the reduction correction processing exceeds the execution time TMD. If the processing circuit 51 determines that the transition condition is not satisfied (S27: NO), the processing circuit 51 transitions the processing to step S25. That is, the processing circuit 51 executes the reduction correction processing. On the other hand, if the processing circuit 51 determines that the transition condition is satisfied (S27: YES), the processing circuit 51 transitions the processing to step S29.

[0040] In step S29, the processing circuit 51 executes a degeneration process for the stop braking control. In the degeneration process, the processing circuit 51 increases the command braking force BPTr to the required braking force BPRq. Then, the processing circuit 51 operates the brake actuator 30 based on the command braking force BPTr.

[0041] In the next step S31, the processing circuit 51 determines whether the termination condition for the degeneration process is satisfied. For example, if the command braking force BPTr is equal to the required braking force BPRq, the termination condition is deemed to be satisfied. On the other hand, if the command braking force BPTr is less than the required braking force BPRq, the termination condition is deemed to be not satisfied. If the processing circuit 51 determines that the termination condition is not satisfied (S31: NO), the processing circuit 51 proceeds to step S29. That is, the processing circuit 51 executes the degeneration process. On the other hand, if the processing circuit 51 determines that the termination condition is satisfied (S31: YES), the processing circuit 51 terminates the degeneration process. Then, the processing circuit 51 terminates the stop-time braking control and ends the series of processes shown in FIG. 4.

[0042] In this embodiment, the processes of steps S15 and S23 to S31 are executed by the processing circuitry 51 functioning as the control unit M11. The processes of steps S13 and S17 are executed by the processing circuitry 51 functioning as the acquisition unit M13. The processes of steps S19 and S21 are executed by the processing circuitry 51 functioning as the setting unit M15.

[0043] <Actions and Effects of the Present Embodiment When the Braking Operation Amount X is Reduced> A case where the braking operation amount X is reduced before the start of the reduction correction process will be described with reference to Figures 5 and 6. Figure 5 illustrates a first comparative example in which the execution time TMD of the reduction correction process is not changed even if the braking operation amount X is reduced before the start of the reduction correction process. Figure 6 illustrates the present embodiment in which the execution time TMD of the reduction correction process is changed when the braking operation amount X is reduced before the start of the reduction correction process.

[0044] 5A, 5B, and 5C, at timing t21 while the driver is applying a braking force to the vehicle 10, the processing circuit determines that the start condition for stop-time braking control is met. Therefore, the processing circuit starts an increasing correction process. During the increasing correction process, the command braking force BPTr is set to a vehicle braking force greater than the required braking force BPRq. Therefore, the vehicle braking force BPAl becomes greater than the required braking force BPRq.

[0045] At timing t22 during the execution of this increasing correction process, the driver's braking operation changes. Specifically, the braking operation amount X decreases, and the required braking force BPRq decreases as shown in FIG. 5A. As a result, the command braking force BPTr also decreases while remaining greater than the required braking force BPRq. This also decreases the vehicle braking force BPAl.

[0046] At subsequent timing t23, the condition for transitioning from the increasing correction process to the decreasing correction process is met, so the processing circuit terminates the increasing correction process and starts the decreasing correction process. In the decreasing correction process, the command braking force BPTr is reduced to the vehicle stop maintenance braking force BPth. Therefore, the vehicle braking force BPAl decreases toward the vehicle stop maintenance braking force BPth. Then, at timing t24, the command braking force BPTr becomes the vehicle stop maintenance braking force BPth. Therefore, from timing t24 onwards, the command braking force BPTr is maintained at the vehicle stop maintenance braking force BPth. As a result, the vehicle braking force BPAl is maintained.

[0047] In the first comparative example, the vehicle braking force BPAl is decreasing in accordance with the decrease in the braking operation amount X during the execution of the increasing correction process before the start of the decreasing correction process. Then, as shown in FIG. 5C , the decrease in the vehicle braking force BPAl increases due to the decrease in the braking operation amount X being started at timing t23 while the braking operation amount X is decreasing. That is, even though the decrease in the braking operation amount X is constant, the decrease in the vehicle braking force BPAl increases midway through. In the first comparative example, the period from timing t23 to timing t24 is the period during which the vehicle braking force BPAl decreases at a rate greater than the rate corresponding to the decrease in the braking operation amount X. Furthermore, in the first comparative example, the vehicle braking force BPAl does not decrease during the period from timing t24 to timing t25, even though the braking operation amount X is decreasing.

[0048] In other words, in the first comparative example, a discrepancy occurs between the vehicle behavior estimated from the manner in which the driver brakes and the actual vehicle behavior. If this discrepancy occurs for a long period of time, the driver may feel uncomfortable due to the discrepancy.

[0049] <Present Embodiment> As shown in (A), (B), and (C) of FIG. 6, at timing t31 while the driver is applying a braking force to the vehicle 10 by performing a braking operation, the processing circuit 51 starts an increasing correction process for the stop-time braking control. As a result, the vehicle braking force BPAl becomes larger than the required braking force BPRq. At timing t32 while this increasing correction process is being performed, the driver's braking operation changes. Specifically, because the braking operation amount X decreases, the required braking force BPRq decreases as shown in (A) of FIG. 6. As a result, the command braking force BPTr and the vehicle braking force BPAl also decrease as shown in (C) of FIG. 6.

[0050] Timing t33 ​​in FIG. 6 corresponds to timing t23 in FIG. 5 . That is, in the first comparative example, the reduction correction process is started at timing t33. In contrast, in the present embodiment, if a change in braking operation is detected before the start of the reduction correction process, the execution time TMD of the reduction correction process is set to a shorter time than when no change in braking operation is detected. As a result, the start timing of the reduction correction process is delayed compared to the first comparative example. In the example shown in FIG. 6 , the processing circuit 51 executes the reduction correction process between timing t34 and timing t36, which is after timing t33. Specifically, between timing t34 and timing t35, the processing circuit 51 reduces the instructed braking force BPTr to the stop-maintenance braking force BPth. Then, between timing t35 and timing t36, the processing circuit 51 maintains the instructed braking force BPTr at the stop-maintenance braking force BPth.

[0051] The length of the period from timing t34 to timing t36 is shorter than the length of the period from timing t23 to timing t25, which is the execution period of the reduction correction process in the first comparative example. As a result, the length of the period during which a deviation occurs between the vehicle behavior estimated from the manner of the driver's braking operation and the actual vehicle behavior is shorter than in the first comparative example. Therefore, even if the reduction correction process is executed, the driver is less likely to feel uncomfortable due to the occurrence of this deviation. Therefore, even if the reduction correction process begins to decrease the braking operation amount X before the start of the reduction correction process, the brake control device 50 can suppress changes in the attitude of the vehicle 10 when stopped without causing the driver to feel uncomfortable.

[0052] <Actions and Effects of the Present Embodiment When the Braking Operation Amount X is Increasing> A case where the braking operation amount X is increased before the start of the reduction correction process will be described with reference to Figures 7 and 8. Figure 7 illustrates a second comparative example in which the execution time TMD of the reduction correction process is not changed even if the braking operation amount X is increased before the start of the reduction correction process. Figure 8 illustrates the present embodiment in which the execution time TMD of the reduction correction process is changed when the braking operation amount X is increased before the start of the reduction correction process.

[0053] <Second Comparative Example> As shown in (A), (B), and (C) of FIG. 7, at timing t41 while the driver is applying a braking force to the vehicle 10 by performing a braking operation, the processing circuit starts an increasing correction process for the stop-time braking control. As a result, the vehicle braking force BPAl becomes larger than the required braking force BPRq. At timing t42 while this increasing correction process is being performed, the driver's braking operation changes. Specifically, as the braking operation amount X increases, the required braking force BPRq increases, as shown in (A) of FIG. 7. As a result, the command braking force BPTr and the vehicle braking force BPAl also increase, as shown in (C) of FIG. 7.

[0054] At a subsequent timing t43, the condition for transitioning from the increasing correction process to the decreasing correction process is met, so the processing circuit ends the increasing correction process and starts the decreasing correction process. In the decreasing correction process, the command braking force BPTr is reduced to the vehicle stop maintenance braking force BPth. At timing t44, the command braking force BPTr becomes the vehicle stop maintenance braking force BPth. Therefore, the command braking force BPTr is maintained at this value from timing t44 onwards.

[0055] In the second comparative example, the braking operation amount X is increased during the execution of the increasing correction process before the decreasing correction process starts. Therefore, the vehicle speed VS reaches the second vehicle speed determination value VSth2 early. As a result, the execution time of the increasing correction process is shortened. This may result in a longer braking distance of the vehicle.

[0056] Furthermore, if the braking distance is reduced by the increase correction process, the following problem may arise. That is, the decrease correction process may not be able to reduce the command braking force BPTr to the vehicle stop-maintenance braking force BPth because the execution time of the increase correction process is shortened. In this case, the vehicle braking force BPAl is greater than the vehicle stop-maintenance braking force BPth when the vehicle is stopped. As a result, the effect of suppressing changes in the vehicle's posture when the vehicle is stopped is reduced.

[0057] Furthermore, in the second comparative example, the period from time t43 to time t45 is a period in which the vehicle braking force BPAl decreases despite the increase in the braking operation amount X. In other words, the period from time t43 to time t45 is a period in which a deviation occurs between the vehicle behavior estimated from the manner in which the driver brakes and the actual vehicle behavior. If this period in which a deviation occurs is long, the driver may feel uncomfortable due to the occurrence of this deviation.

[0058] <Present Embodiment> As shown in (A), (B), and (C) of FIG. 8, at timing t51 while the driver is applying a braking force to the vehicle 10 by performing a braking operation, the processing circuit 51 starts an increasing correction process for the stop-time braking control. As a result, the vehicle braking force BPAl becomes larger than the required braking force BPRq. At timing t52 while this increasing correction process is being performed, the driver's braking operation changes. Specifically, as the braking operation amount X increases, the required braking force BPRq increases as shown in (A) of FIG. 8. As a result, the command braking force BPTr and the vehicle braking force BPAl also increase as shown in (C) of FIG. 8.

[0059] In this embodiment, if a change in braking operation is detected before the start of the decrease correction process, the execution time TMD of the decrease correction process is set to a shorter time than when no change in braking operation is detected. As a result, the start timing of the decrease correction process is delayed compared to the second comparative example. This causes the execution time of the increase correction process to be longer than in the second comparative example. As a result, the brake control device 50 can suppress an increase in braking distance by extending the execution time of the increase correction process compared to the second comparative example.

[0060] Furthermore, since the execution time of the increasing correction process can be extended, the braking distance can be shortened by executing the increasing correction process compared to the second comparative example. Therefore, in the decreasing correction process executed after the increasing correction process, the command braking force BPTr, i.e., the vehicle braking force BPAl, is reduced to the stop-maintenance braking force BPth. As a result, the brake control device 50 can more effectively suppress changes in the posture of the vehicle 10 while stopped compared to the second comparative example.

[0061] Furthermore, in this embodiment, the period from timing t53 to timing t54 is the execution period of the decrease correction process. In the example shown in FIG. 8 , because the braking operation amount X is increased during the execution of the increase correction process, the length of the period from timing t53 to timing t54 is shorter than the period from timing t43 to timing t45, which is the execution period of the decrease correction process in the second comparative example. Therefore, the length of the period during which a deviation occurs between the vehicle behavior estimated from the driver's braking operation and the actual vehicle behavior is shorter than in the second comparative example. Therefore, even if the decrease correction process is executed, the driver is less likely to feel uncomfortable due to the occurrence of the deviation. Therefore, even if the increase in the braking operation amount X begins before the decrease correction process is started, the brake control device 50 can suppress changes in the posture of the vehicle 10 when stopped without causing the driver to feel uncomfortable.

[0062] <Other Effects> (1) It can be inferred that the greater the change amount ΔX in the braking operation amount before the start of the reduction correction process, the stronger the driver's intention to change the braking mode. Therefore, the brake control device 50 sets a shorter time as the change amount ΔX in the braking operation amount before the start of the reduction correction process as the execution time TMD of the reduction correction process. As a result, the stronger the driver's intention to change the braking mode, the brake control device 50 can shorten the period during which the behavior of the vehicle 10 intended by the driver performing the braking operation diverges from the actual behavior of the vehicle 10.

[0063] (2) As described above, the longer the period during which the vehicle braking force BPAl remains unchanged despite the driver changing the braking operation amount X, the more likely the driver is to feel uncomfortable. Therefore, when the brake control device 50 detects a change in the braking operation before the start of the reduction correction process, it shortens the length of the holding period during which the command braking force BPTr is held at the stop-maintenance braking force BPth, part of the execution time of the reduction correction process, compared to when a change in the braking operation is not detected. As a result, when the brake control device 50 detects a change in the braking operation before the start of the reduction correction process, it can shorten the period during which the vehicle braking force BPAl remains unchanged despite the driver changing the braking operation amount X, making it less likely that the driver will feel uncomfortable.

[0064] <Modifications> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0065] The processing circuit 51 (i.e., the acquisition unit M13) may acquire, as the braking operation-related value, the rate of change dX of the braking operation amount X. Fig. 9 illustrates a part of a series of processes when the execution time TMD of the reduction correction process is set based on the rate of change dX.

[0066] As shown in FIG. 9 , when the processing circuit 51 determines that the start condition for stop-time braking control is satisfied (S11: YES), the processing proceeds to step S131. In step S131, the processing circuit 51 functions as the acquisition unit M13 to acquire the current rate of change dX of the braking operation amount as the reference rate of change dXB. At this time, the processing circuit 51 may acquire the value obtained by time-differentiating the braking operation amount X as the rate of change dX. In the next step S15, the processing circuit 51 executes an increase correction process for stop-time braking control. In the following step S171, the processing circuit 51 functions as the acquisition unit M13 to acquire the current rate of change dX. That is, the processing circuit 51 acquires the rate of change dX during the execution of the increase correction process.

[0067] Then, in step S191, the processing circuit 51 functions as the setting unit M15 to set the execution time TMD according to the magnitude of the difference between the rate of change dX obtained in step S171 and the reference rate of change dXB. The magnitude of the difference between the rate of change dX and the reference rate of change dXB is referred to as the "rate of change." For example, when the rate of change is equal to or greater than a threshold, the processing circuit 51 shortens the execution time TMD compared to when the rate of change is less than the threshold. The threshold is set as a criterion for determining whether a change in braking operation can be detected. As a result, when the processing circuit 51 detects a change in braking operation before the start of the reduction correction process, the processing circuit 51 can set the execution time TMD to a shorter time than when no change in braking operation is detected.

[0068] The processing circuit 51 (i.e., the setting unit M15) may set the execution time TMD of the reduction correction process by taking into account both the change amount ΔX of the braking operation amount obtained before the start of the reduction correction process and the change amount of the change rate.

[0069] When the processing circuit 51 (i.e., the setting unit M15) detects a change in the braking operation before the start of the reduction correction process, it is not necessary to vary the execution time TMD according to the degree of change in the braking operation.

[0070] When the processing circuit 51 (i.e., the setting unit M15) detects a change in the braking operation before the start of the reduction correction process, the processing circuit 51 may shorten the execution time TMD of the reduction correction process by omitting the holding period in which the command braking force BPTr is held at the vehicle stop maintenance braking force BPth. Figure 10 shows a time chart showing the progress of the command braking force BPTr when the holding period is omitted. Even in this case, the execution time of the reduction correction process is shortened, and therefore the same effect as in the above embodiment can be obtained.

[0071] When the processing circuit 51 detects a change in the braking operation before the start of the reduction correction process, if the execution time TMD of the reduction correction process can be shortened, the length of the reduction period for reducing the command braking force BPTr does not need to be shortened. Even in this case, the processing circuit 51 can shorten the execution time TMD of the reduction correction process by shortening the length of the holding period for holding the command braking force BPTr.

[0072] In the above embodiment, the vehicle stop maintenance braking force BPth is set as the predetermined braking force, but this is not limiting. A vehicle braking force different from the vehicle stop maintenance braking force BPth may be set as the predetermined braking force. Furthermore, the magnitude of the predetermined braking force may be changed depending on the situation.

[0073] The braking control at a stop may not necessarily include an increase correction process as long as it includes a decrease correction process. In this case, the reference time is a timing a predetermined time before the start of the decrease correction process. If the processing circuit 51 detects a change in braking operation during the period from the reference time to the start of the decrease correction process, it is preferable to set the execution time of the decrease correction process to a shorter time than when no change in braking operation is detected during that period. In this case, the "predetermined time" may be several seconds.

[0074] If the processing circuit 51 shortens the execution time TMD of the reduction correction process when the braking operation amount X is reduced before the start of the reduction correction process, the processing circuit 51 does not need to change the execution time TMD when the braking operation amount X is increased before the start of the reduction correction process.

[0075] If the processing circuit 51 shortens the execution time TMD of the reduction correction process when the braking operation amount X is increased before the start of the reduction correction process, the processing circuit 51 does not need to change the execution time TMD when the braking operation amount X is decreased before the start of the reduction correction process.

[0076] In the above embodiment, the processing circuit 51 determines the start timing of the increase correction process and the start timing of the decrease correction process of the stop braking control in accordance with changes in the vehicle body speed VS. However, the processing circuit 51 may determine the start timing of each process using a parameter other than the vehicle body speed VS, as long as the parameter value decreases as the vehicle 10 approaches the stop position PS. Examples of the other parameters include a stopping distance and a predicted stopping time. The stopping distance is the distance from the current position of the vehicle 10 to the stop position PS. The predicted stopping time is the time required for the vehicle 10 to stop. An example of the predicted stopping time is TTC. TTC is an abbreviation for "Time To Collision."

[0077] When executing braking control at a stop, the brake control device may control not only the frictional braking force but also the regenerative braking force. In this case, the sum of the total frictional braking force applied to the vehicle 10 and the total regenerative braking force applied to the vehicle 10 is the vehicle braking force BPAl.

[0078] The processing circuitry 51 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.

[0079] <Other Technical Ideas> The following describes technical ideas that can be understood from the above-described embodiment and modified examples. [Supplementary Note 1] It is preferable that the device further includes an acquisition unit that acquires at least one of the amount of braking operation and the rate of change of the amount of braking operation, and the setting unit detects a change in the braking operation based on a transition of the value acquired by the acquisition unit before the start of the reduction correction process.

[0080] [Note 2] In the reduction correction process, it is preferable that the control unit reduces the braking force applied to the vehicle to the predetermined braking force, and after the braking force reaches the predetermined braking force, maintains the braking force at the predetermined braking force and sets the vehicle speed to 0 (zero).

[0081] [Appendix 3] When the setting unit detects a change in the braking operation before the reduction correction process is started, it is preferable that the setting unit sets the time during which the braking force applied to the vehicle is maintained at the specified braking force during the execution of the reduction correction process to a shorter time than when a change in the braking operation is not detected.

[0082] [Appendix 4] When the setting unit detects a change in the braking operation before the reduction correction process is started, it is preferable that the setting unit shortens the execution time of the reduction correction process by omitting the period during which the braking force applied to the vehicle is maintained at the specified braking force.

[0083] [Note 5] When applying braking force to the vehicle to stop it, the control unit is configured to execute an increase correction process before executing the decrease correction process to make the braking force applied to the vehicle greater than the required value of the braking force, and when the setting unit detects a change in the braking operation during execution of the increase correction process, it is preferable to set the execution time of the decrease correction process to a shorter time than when no change in the braking operation is detected.

[0084] 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 brake control device comprising: a control unit that, when applying braking force to a vehicle to stop the vehicle, reduces the braking force applied to the vehicle to a predetermined braking force that is smaller than a required value of the braking force, and executes a reduction correction process to set the vehicle speed of the vehicle to 0 (zero); and a setting unit that, when a driver of the vehicle is performing a braking operation, detects a change in the braking operation before the start of the reduction correction process, sets the execution time of the reduction correction process to a shorter time than when a change in the braking operation is not detected.

2. The brake control device according to claim 1, wherein the setting unit sets the execution time of the reduction correction process to a shorter time as the degree of change in the braking operation before the start of the reduction correction process increases.

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