Braking control device

Abstract

A processing circuit 51 of a braking control device 50 functions as: a control unit M11 that, when bringing a vehicle 10 to a halt by applying a braking force thereto, performs stop-time braking control of bringing the vehicle body speed of the vehicle 10 to 0 (zero) after reducing the vehicle braking force to a prescribed braking force; and a setting unit M15 that, during the execution of the stop-time braking control, sets the time for executing the processing for retaining the stop-time braking control shorter when the moving force acting on the vehicle 10 is larger.

Description

Braking control device

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

[0002] In recent years, control devices have been developed that perform stopping control to suppress changes in the vehicle's posture while the vehicle is stopped by reducing the braking force applied to the vehicle immediately before the vehicle stops. For example, a control device disclosed in Patent Document 1 estimates an estimated stopping timing, which is the timing at which the vehicle speed becomes 0 (zero), during stopping control. The control device then reduces the braking force so that the braking force becomes 0 (zero) at the estimated stopping timing.

[0003] However, the timing when the vehicle speed actually reaches 0 (zero) may occur before the estimated vehicle stop timing. In such a case, the control device may not be able to sufficiently reduce the braking force before the vehicle stops, and therefore may not be able to sufficiently reduce the change in the vehicle's attitude when the vehicle stops.

[0004] In contrast, the control device disclosed in Patent Document 2 sufficiently reduces the braking force before the estimated vehicle stop timing, and then performs stopping control to maintain the braking force. According to this, even if the actual vehicle speed reaches zero before the estimated vehicle stop timing, the braking force is sufficiently small at the time the vehicle speed actually reaches zero. Furthermore, just before the vehicle stops, the rate of reduction in the braking force is zero. This suppresses changes in the vehicle's posture when the vehicle is stopped, even if the actual vehicle speed reaches zero differently from the estimated vehicle stop timing.

[0005] JP 2016-28913 A JP 2022-152781 A

[0006] A force acts on a vehicle to move the vehicle. The force that moves the vehicle is, for example, a driving force transmitted from the vehicle's power source to the wheels, and a component of gravitational acceleration acting on the vehicle traveling on a slope in the downhill direction of the slope. If the stopping control disclosed in Patent Document 2 is executed under conditions in which such a force that moves the vehicle is relatively large, the driver may feel uncomfortable when the vehicle is stopped. For example, the vehicle may start moving after the vehicle speed reaches 0 (zero). Furthermore, on an uphill road, the vehicle may slide downhill.

[0007] A braking control device for solving the above problem is a device that, when applying a braking force to a vehicle to stop it, performs stop braking control by reducing the braking force applied to the vehicle to a predetermined braking force and then setting the vehicle body speed to 0 (zero).The braking control device includes a control unit that, in the stop braking control, executes a reduction process that reduces the braking force applied to the vehicle to the predetermined braking force and a holding process that is executed after the reduction process until the vehicle body speed of the vehicle becomes 0 (zero), and that holds the braking force applied to the vehicle at the predetermined braking force, and a setting unit that sets the execution time of the holding process to be shorter the greater the force acting on the vehicle to move the vehicle during execution of the stop braking control.

[0008] The braking control device described above has the effect of suppressing changes in the vehicle's posture when the vehicle is stopped without giving the driver any sense of discomfort when the vehicle is stopped by performing braking control when the vehicle is stopped.

[0009] FIG. 1 is a schematic diagram showing a configuration of a vehicle equipped with a brake control device of a first embodiment. FIG. 2 is a timing chart showing the process of stopping the vehicle on a level road. FIG. 3 is a diagram showing an example of a map used when setting the execution time of the holding process and the execution time of the decreasing process. FIG. 4 is a flowchart showing a series of processes executed by the brake control device of the first embodiment. FIG. 5 is a timing chart showing the process of stopping the vehicle on a slope in a comparative example. FIG. 6 is a timing chart showing the process of stopping the vehicle on a slope in the brake control device of the first embodiment. FIG. 7 is a flowchart showing the process of performing the brake control device of a second embodiment. FIG. 8 is a timing chart showing the process of stopping the vehicle on a slope in the brake control device of the second embodiment. FIG. 9 is a diagram showing an example of a map used when deriving the reliability of the road surface gradient.

[0010] (First Embodiment) A first embodiment of a brake control device will be described below with reference to Figs. 1 to 6. 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 brake operating member 11 is a member that is 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 plurality of wheels include two front wheels 12 and two rear wheels 13.

[0011] <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.

[0012] <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.

[0013] 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.

[0014] 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.

[0015] 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."

[0016] 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."

[0017] <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.

[0018] <Outline of braking control at stop> The processing circuit 51 performs braking control at stop when applying a braking force to stop the vehicle 10. The braking control at stop is braking control for suppressing changes in the posture of the vehicle 10 when the vehicle is stopped.

[0019] The braking control at a stop will be described with reference to FIG. 2 . FIG. 2 illustrates an example of a case in which the braking control at a stop is performed when the vehicle 10 is stopped on a level road. 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 of 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 becomes. 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 the command braking force BPTr.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] In the following, the process of the reduction correction process for reducing the command braking force BPTr to the vehicle stop maintenance braking force BPth will be referred to as the "reduction process." Also, the process of the reduction correction process for maintaining the command braking force BPTr at the vehicle stop maintenance braking force BPth will be referred to as the "maintenance process." The maintenance process is a process that is started after the reduction process is executed and is executed until the vehicle speed VS becomes 0 (zero). More specifically, it is preferable that the maintenance process be started immediately before the vehicle speed VS becomes 0 (zero).

[0025] At timing t15, the processing circuit 51 determines that the vehicle 10 has stopped, and therefore transitions the stop-time braking control process from a reduction correction process (i.e., a holding process) to a degeneration process. In the degeneration process, 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.

[0026] <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, a moving force derivation unit M13, and a setting unit M15.

[0027] <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. 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.

[0028] When a transition condition from the increasing correction process to the decreasing correction process is satisfied during 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 the vehicle stop maintenance braking force BPth and then sets the vehicle speed VS to 0 (zero). More specifically, the control unit M11 reduces the commanded braking force BPTr to the vehicle stop maintenance braking force BPth by executing a decreasing process within the decreasing correction process. In this embodiment, in the decreasing process, the control unit M11 reduces the commanded braking force BPTr to the vehicle stop maintenance braking force BPth, which is smaller than the required braking force BPRq. The control unit M11 operates the brake actuator 30 based on the commanded braking force BPTr at that time. After the command braking force BPTr reaches the vehicle stop maintenance braking force BPth, the control unit M11 executes a maintenance process of the reduction correction process to maintain the command braking force BPTr at the vehicle stop maintenance braking force BPth. The control unit M11 starts the maintenance process before the vehicle speed VS reaches 0 (zero). The control unit M11 operates the brake actuator 30 based on the command braking force BPTr at that time.

[0029] As will be described in more detail later, in this embodiment, the setting unit M15 sets an execution time TMD for the reduction process. Therefore, the control unit M11 reduces the command braking force BPTr to the vehicle-stop maintenance braking force BPth within the execution time TMD set by the setting unit M15. Therefore, in the reduction process, the control unit M11 derives the difference between the command braking force BPTr at the start of the reduction process and the vehicle-stop maintenance braking force BPth as a braking force difference. The control unit M11 divides the braking force difference by the execution time TMD to derive the reduction rate of the command braking force BPTr. Then, the control unit M11 reduces the command braking force BPTr at this reduction rate.

[0030] When a transition condition from the reduction correction process to the degeneration process is met during the reduction correction process, the control unit M11 terminates 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. At this time, the control unit M11 increases the command braking force BPTr so that the rate of increase of the command braking force BPTr is greater than the rate of decrease of the command braking force BPTr in the reduction process. Then, the control unit M11 operates the brake actuator 30 based on the command braking force BPTr.

[0031] <Moving Force Derivation Unit> The moving force derivation unit M13 derives the moving force FM acting on the vehicle 10 when braking the vehicle 10. The moving force FM is a force that moves the vehicle 10. More specifically, the moving force FM is a force that acts on the vehicle 10 in the front and rear directions.

[0032] The moving force FM includes, for example, the driving force FD of the vehicle 10 and gravity acting on the vehicle 10. The greater the magnitude of the driving force FD, the greater the force tending to move the vehicle 10 in the direction of travel of the vehicle 10. Furthermore, when the vehicle 10 is traveling on a slope, the greater the magnitude of the gravitational acceleration component FG, which is the component of gravity in the downhill direction, i.e., the component on the downhill side of the slope, the greater the force tending to move the vehicle 10 in the downhill direction.

[0033] Therefore, the moving force derivation unit M13 derives the moving force FM so that the value increases as the magnitude of the driving force FD of the vehicle 10 during braking of the vehicle 10 increases. The moving force derivation unit M13 also derives a road surface gradient θ, which is the gradient of the road surface on which the vehicle 10 is traveling. For example, the moving force derivation unit M13 derives the road surface gradient θ so that the value increases as the magnitude of the difference between the derivative of the vehicle body speed VS of the vehicle 10 and the longitudinal acceleration Gx increases. The moving force derivation unit M13 may obtain the road surface gradient θ based on information about the road surface obtained from a navigation device. Furthermore, if the vehicle 10 is equipped with a sensor that detects the degree of inclination of the vehicle body, the moving force derivation unit M13 may obtain the detected value of the sensor as the road surface gradient θ. Furthermore, the moving force derivation unit M13 may derive the road surface gradient θ by analyzing images captured by an on-board camera.

[0034] The moving force derivation unit M13 derives the moving force FM so that the value increases as the magnitude of the road surface gradient θ increases. This is because the magnitude of the gravitational acceleration component FG increases as the magnitude of the road surface gradient θ increases.

[0035] When the vehicle 10 is moving forward on an uphill road, the direction of the driving force FD is opposite to the direction of the gravitational acceleration component FG. Therefore, the moving force derivation unit M13 derives the difference between the magnitude of the gravitational acceleration component FG, which can be estimated from the road surface gradient θ, and the magnitude of the driving force FD as the moving force FM.

[0036] When the vehicle 10 is moving forward on a downhill road, the direction of the driving force FD is the same as the direction of the gravitational acceleration component FG. Therefore, the moving force derivation unit M13 derives the moving force FM as the sum of the magnitude of the gravitational acceleration component FG, which can be estimated from the road surface gradient θ, and the magnitude of the driving force FD.

[0037] <Setting Unit> The setting unit M15 sets the execution time TMH of the holding process of the reduction correction process and the execution time TMD of the decrease process of the reduction correction process based on the moving force FM acting on the vehicle 10 during execution of the stop braking control. Specifically, the setting unit M15 sets the execution time TMH of the holding process to be shorter the greater the moving force FM. Furthermore, the setting unit M15 sets the execution time TMD of the decrease process so that the shorter the execution time TMH of the holding process is, the larger the value becomes.

[0038] 3 illustrates an example of a map for setting the execution time TMH of the holding process and the execution time TMD of the reduction process. As shown in FIG. 3, when the moving force FM is less than the determined moving force FMth, the execution time TMH of the holding process is set to the reference execution time TMH1, and the execution time TMD of the reduction process is set to the reference execution time TMD1. On the other hand, when the moving force FM is equal to or greater than the determined moving force FMth, the execution time TMH of the holding process is set to less than the reference execution time TMH1, and the execution time TMD of the reduction process is longer than the reference execution time TMD1. Specifically, when the moving force FM is equal to or greater than the determined moving force FMth, the greater the moving force FM, the shorter the execution time TMH of the holding process. Furthermore, the shorter the execution time TMH of the holding process, the shorter the execution time TMD of the reduction process.

[0039] 3, the execution time of the reduction correction process, which is the sum of the execution time TMH of the holding process and the execution time TMD of the reduction process, is constant regardless of the magnitude of the moving force FM. However, the execution time of the reduction correction process may be variable depending on the magnitude of the moving force FM. For example, the execution time of the reduction correction process may be set to be shorter as the magnitude of the moving force FM increases.

[0040] <Processing Flow During Vehicle Braking> A series of processes performed by the processing circuit 51 when performing stop braking control will be described with reference to Fig. 4. The processing circuit 51 repeatedly executes the series of processes shown in Fig. 4 when braking the vehicle 10.

[0041] In step S11, the processing circuit 51 derives a moving force FM. In the next step S13, the processing circuit 51 sets an execution time TMH of the holding process based on the moving force FM. The processing circuit 51 also sets an execution time TMD of the decrease process based on the execution time TMH of the holding process.

[0042] In step S15, 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 (S15: YES), the processing circuit 51 proceeds to step S17. On the other hand, if the processing circuit 51 determines that the start condition is not satisfied (S15: NO), the processing circuit 51 temporarily terminates the series of processes shown in FIG. 4.

[0043] In step S17, the processing circuit 51 performs braking control at a stop. Specifically, in step S19, the processing circuit 51 performs an increasing correction process. 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.

[0044] In step S21, 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. If the processing circuit 51 determines that the transition condition is not satisfied (S21: NO), the processing circuit 51 shifts the processing to step S19. 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 (S21: YES), the processing circuit 51 shifts the processing to step S23.

[0045] In step S23, the processing circuit 51 executes a decrease process of the decrease correction process. In the decrease process, the processing circuit 51 decreases the commanded braking force BPTr to the vehicle stop maintenance braking force BPth. Specifically, the processing circuit 51 decreases the commanded braking force BPTr so that the commanded braking force BPTr becomes the vehicle stop maintenance braking force BPth within the execution time TMD of the decrease process set in step S13. Then, the processing circuit 51 operates the brake actuator 30 based on the commanded braking force BPTr at that time.

[0046] In the next step S25, the processing circuit 51 determines whether the command braking force BPTr has become equal to or less than the vehicle stop maintenance braking force BPth. Here, the processing circuit 51 may determine whether the actual execution time of the reduction process has reached the execution time TMD of the reduction process. If the processing circuit 51 determines that the command braking force BPTr has not become equal to or less than the vehicle stop maintenance braking force BPth (S25: NO), the processing circuit 51 proceeds to step S23. That is, the processing circuit 51 executes the reduction process. On the other hand, if the processing circuit 51 determines that the command braking force BPTr has become equal to or less than the vehicle stop maintenance braking force BPth (S25: YES), the processing circuit 51 proceeds to step S27.

[0047] In step S27, the processing circuit 51 executes a holding process of the reduction correction process. In the holding process, the processing circuit 51 holds the command braking force BPTr at the vehicle stop maintenance braking force BPth. Then, the processing circuit 51 operates the brake actuator 30 based on the command braking force BPTr.

[0048] In the next step S29, the processing circuitry 51 determines whether the termination condition for the holding process is satisfied. In this embodiment, the processing circuitry 51 determines that the termination condition for the holding process is satisfied when at least one of the following conditions (A1) and (A2) is satisfied. On the other hand, the processing circuitry 51 determines that the termination condition for the holding process is not satisfied when neither of the following conditions (A1) nor (A2) is satisfied.

[0049] (A1) The actual execution time of the holding process has reached the execution time TMH of the holding process. (A2) It can be determined that the vehicle 10 has stopped. If the processing circuit 51 determines that the termination condition is not met (S29: NO), the processing circuit 51 proceeds to step S27. That is, the processing circuit 51 executes the holding process. On the other hand, if the processing circuit 51 determines that the termination condition is met (S29: YES), the processing circuit 51 proceeds to step S31.

[0050] In step S31, the processing circuit 51 executes a degeneration process. 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.

[0051] In the next step S33, 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 (S33: NO), the processing circuit 51 transitions to step S31. 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 (S33: 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.

[0052] In this embodiment, the processing of step S11 is executed by the processing circuit 51 functioning as the moving force derivation unit M13. The processing of step S13 is executed by the processing circuit 51 functioning as the setting unit M15. The processing of step S17 is executed by the processing circuit 51 functioning as the control unit M11.

[0053] <Actions and Effects of the Present Embodiment> The actions and effects of the present embodiment will be described with reference to Figures 5 and 6. The example shown in Figures 5 and 6 is a case where a braking force is applied to a vehicle 10 traveling on a slope to stop the vehicle. Figure 5 shows a comparative example in which the execution time TMH of the holding process and the execution time TMD of the reduction process are not changed according to the moving force FM. Figure 6 shows the present embodiment in which the execution time TMH of the holding process and the execution time TMD of the reduction process are changed according to the moving force FM.

[0054] Comparative Example As shown by the dashed line in FIG. 5C, when the vehicle 10 is traveling on a slope, the stop-maintenance braking force BPth is greater than when the vehicle 10 is traveling on a level road.

[0055] 5A, 5B, and 5C, at timing t21 while braking force is being applied to the vehicle 10, the processing circuit determines that the start condition for stop braking control is met. Therefore, the processing circuit starts the 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.

[0056] At timing t22, the condition for transitioning from the increasing correction process to the decreasing correction process is met. Therefore, the processing circuit starts the decreasing process of the decreasing correction process. As a result, the vehicle braking force BPAl decreases to the stop-maintaining braking force BPth. Then, at timing t23, the command braking force BPTr becomes the stop-maintaining braking force BPth, so the processing circuit starts the maintaining process of the decreasing correction process. As a result, the vehicle braking force BPAl is maintained. At timing t24, the maintaining process is ended and the degeneration process is started, so the vehicle braking force BPAl increases.

[0057] Here, the vehicle stop maintenance braking force BPth is set based on the magnitude of the road surface gradient θ. Therefore, if the derivation accuracy of the road surface gradient θ is low, the vehicle stop maintenance braking force BPth may deviate from the actual value of the vehicle stop maintenance braking force. In particular, if the vehicle stop maintenance braking force BPth is smaller than the actual value of the vehicle stop maintenance braking force, there is a risk that the vehicle 10 will start moving downhill after the vehicle speed VS becomes 0 (zero) while the vehicle braking force BPAl is being held by the holding process. The greater the gradient of the slope, the greater the magnitude of the gravitational acceleration component FG, i.e., the moving force FM. The greater the moving force FM, the earlier the timing at which the vehicle 10 will start moving downhill.

[0058] If the vehicle braking force BPAl is increased by the degeneration process after the vehicle 10 starts to move downhill in this way, the vehicle 10 will stop. However, the driver may feel uncomfortable if the vehicle 10 stops after starting to move downhill in this way.

[0059] 6A, 6B, and 6C, the processing circuit 51 starts the increasing correction process of the stop-time braking control at timing t31 while a braking force is being applied to the vehicle 10. As a result, the vehicle braking force BPAl becomes larger than the required braking force BPRq.

[0060] In this embodiment, the processing circuit 51 sets the execution time TMH of the holding process prior to execution of the reduction correction process. Specifically, the processing circuit 51 sets the execution time TMH of the holding process so that the larger the moving force FM, the shorter the value of TMH.

[0061] Therefore, when the moving force FM is relatively large, such as when the vehicle 10 is traveling on a slope, the execution time TMH of the holding process is short. In the example shown in Figure 6, the reduction process of the reduction correction process is started at timing t32, thereby reducing the vehicle braking force BPAl. Then, the holding process of the reduction correction process is started at timing t33. The holding process is executed until timing t34, and the reduction process is started at timing t34, thereby increasing the vehicle braking force BPAl.

[0062] The length of the period from timing t33 ​​to timing t34, which is the execution period of the holding process, is shorter than the length of the period from timing t23 to timing t24, which is the execution period of the holding process in the above comparative example. Therefore, even if the vehicle stop maintenance braking force BPth is smaller than the actual value of the vehicle stop maintenance braking force, the possibility that the vehicle 10 will start moving downhill after the vehicle speed VS becomes 0 (zero) while the vehicle braking force BPAl is being held by the holding process is lower than in the above comparative example. Therefore, the driver is less likely to feel uncomfortable as in the comparative example.

[0063] Therefore, when the brake control device 50 performs stop braking control to stop the vehicle 10, it is possible to suppress changes in the posture of the vehicle 10 while the vehicle is stopped without causing discomfort to the driver.

[0064] <Other Effects> (1-1) When the execution time TMH of the holding process is shortened because the moving force FM is relatively large, the brake control device 50 lengthens the execution time TMD of the reduction process. This makes it possible to slow the rate at which the vehicle braking force BPAl is reduced during the reduction process. As a result, when the moving force FM is relatively large, the brake control device 50 can slow the pitching motion of the vehicle 10 during the reduction correction process.

[0065] (1-2) The braking control device 50 derives the moving force FM so that the value increases as the road surface gradient θ increases. Therefore, the braking control device 50 can effectively prevent the vehicle 10 from sliding downhill when stopping the vehicle 10 by performing stop braking control on a slope with a large road surface gradient θ.

[0066] Second Embodiment A second embodiment of the braking control device will be described with reference to Figures 7 and 8. The second embodiment differs from the first embodiment in that stop braking control is selected according to the magnitude of the moving force. 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 designated by the same reference numerals, and redundant description will be omitted.

[0067] In this embodiment, the brake control device 50 is configured to be able to perform first stop braking control and second stop braking control as stop braking control. Each of the first stop braking control and second stop braking control includes an increase correction process, a decrease correction process, and a degeneration process. The decrease correction process of the first stop braking control includes a decrease process and a holding process. The decrease correction process of the second stop braking control includes the decrease process but does not include the holding process.

[0068] <Processing flow during vehicle braking> A series of processes performed by the processing circuit 51 of the brake control device 50 when performing braking control at a stop will be described with reference to Fig. 7. The processing circuit 51 repeatedly executes the series of processes shown in Fig. 7 when braking the vehicle 10.

[0069] In step S51, the processing circuit 51 derives the moving force FM, similar to step S11 above. In the next step S53, the processing circuit 51 determines whether the start condition for stop braking control is met, similar to step S15 above. If the processing circuit 51 determines that the start condition is met (S53: YES), the processing circuit 51 proceeds to step S55. On the other hand, if the processing circuit 51 determines that the start condition is not met (S53: NO), the processing circuit 51 temporarily ends the series of processes shown in FIG. 7.

[0070] In step S55, the processing circuit 51 determines whether the moving force FM is less than a threshold value FMth1. If stop braking control is performed when the moving force FM is relatively large, there is a risk that the vehicle 10 will start moving after the vehicle speed VS temporarily becomes 0 (zero) during the execution of the reduction correction process. Therefore, the threshold value FMth1 is set as a criterion for determining whether the moving force FM is relatively large. If the processing circuit 51 determines that the moving force FM is less than the threshold value FMth1 (S55: YES), the processing circuit 51 proceeds to step S60. On the other hand, if the processing circuit 51 determines that the moving force FM is equal to or greater than the threshold value FMth1 (S55: NO), the processing circuit 51 proceeds to step S80.

[0071] In step S60, the processing circuit 51 performs first stop-time braking control as stop-time braking control. Specifically, in step S61, the processing circuit 51 executes an increasing correction process. The content of this increasing correction process is the same as the increasing correction process executed in step S19 above. In the next step S63, similar to step S21 above, the processing circuit 51 determines whether a transition condition from the increasing correction process to the decreasing correction process is met. If the processing circuit 51 determines that the transition condition is not met (S63: NO), the processing circuit 51 transitions the processing to step S61. That is, the processing circuit 51 executes the increasing correction process. On the other hand, if the processing circuit 51 determines that the transition condition is met (S63: YES), the processing circuit 51 transitions the processing to step S65.

[0072] In step S65, the processing circuit 51 executes the decrease process of the decrease correction process. In the decrease process, the processing circuit 51 decreases the command braking force BPTr to the vehicle stop maintenance braking force BPth. Then, the processing circuit 51 operates the brake actuator 30 based on the command braking force BPTr at that time.

[0073] In the next step S67, the processing circuit 51 determines whether the command braking force BPTr has become equal to or less than the vehicle-stop maintaining braking force BPth. If the processing circuit 51 determines that the command braking force BPTr has not become equal to or less than the vehicle-stop maintaining braking force BPth (S67: NO), the processing circuit 51 proceeds to step S65. That is, the processing circuit 51 executes a reduction process. On the other hand, if the processing circuit 51 determines that the command braking force BPTr has become equal to or less than the vehicle-stop maintaining braking force BPth (S67: YES), the processing circuit 51 proceeds to step S69.

[0074] In step S69, the processing circuit 51 executes the holding process of the subtraction correction process, similar to step S27. In the next step S71, the processing circuit 51 determines whether the vehicle 10 has stopped. If the processing circuit 51 determines that the vehicle 10 has not stopped (S71: NO), the processing circuit 51 proceeds to step S69. That is, the processing circuit 51 executes the holding process. On the other hand, if the processing circuit 51 determines that the vehicle 10 has stopped (S71: YES), the processing circuit 51 proceeds to step S73.

[0075] In step S73, the processing circuit 51 executes the degeneration process, similar to step S31. In the following step S75, the processing circuit 51 determines whether the termination condition for the degeneration process is satisfied, similar to step S33. If the processing circuit 51 determines that the termination condition is not satisfied (S75: NO), the processing circuit 51 shifts the process to step S73. 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 (S75: YES), the processing circuit 51 terminates the degeneration process. Then, the processing circuit 51 terminates the first stop braking control and ends the series of processes shown in FIG. 7.

[0076] In step S80, the processing circuit 51 performs second stop-time braking control as stop-time braking control. Specifically, in step S81, the processing circuit 51 executes an increasing correction process. The content of this increasing correction process is the same as the increasing correction process executed in step S19. In the next step S83, similar to step S21, the processing circuit 51 determines whether a transition condition from the increasing correction process to the decreasing correction process is met. If the processing circuit 51 determines that the transition condition is not met (S83: NO), the processing circuit 51 transitions the process to step S81. That is, the processing circuit 51 executes the increasing correction process. On the other hand, if the processing circuit 51 determines that the transition condition is met (S83: YES), the processing circuit 51 transitions the process to step S85.

[0077] In step S85, the processing circuit 51 executes the decrease process of the decrease correction process. In the decrease process, the processing circuit 51 decreases the command braking force BPTr to the vehicle stop maintenance braking force BPth. Then, the processing circuit 51 operates the brake actuator 30 based on the command braking force BPTr at that time.

[0078] In the next step S87, the processing circuit 51 determines whether the command braking force BPTr has become equal to or less than the vehicle-stop maintaining braking force BPth. If the processing circuit 51 determines that the command braking force BPTr has not become equal to or less than the vehicle-stop maintaining braking force BPth (S87: NO), the processing circuit 51 proceeds to step S85. That is, the processing circuit 51 executes a reduction process. On the other hand, if the processing circuit 51 determines that the command braking force BPTr has become equal to or less than the vehicle-stop maintaining braking force BPth (S87: YES), the processing circuit 51 proceeds to step S89.

[0079] In step S89, the processing circuit 51 executes the degeneration process, similar to step S31. In the following step S91, the processing circuit 51 determines whether the termination condition for the degeneration process is satisfied, similar to step S33. If the processing circuit 51 determines that the termination condition is not satisfied (S91: NO), the processing circuit 51 shifts the process to step S89. 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 (S91: YES), the processing circuit 51 terminates the degeneration process. Then, the processing circuit 51 terminates the second stop braking control and ends the series of processes shown in FIG. 7.

[0080] <Functions and Effects of the Present Embodiment> The functions and effects of the second stop braking control will be described with reference to Fig. 8. The example shown in Fig. 8 is a case where a braking force is applied to the vehicle 10 traveling on a slope to bring the vehicle 10 to a stop.

[0081] As shown in (A), (B), and (C) of Figure 8, at timing t41 while a braking force is being applied to the vehicle 10, the processing circuit 51 determines that the start condition for the stop braking control is met. In this case, the processing circuit 51 can determine that the moving force FM is equal to or greater than the threshold value FMth1, and therefore performs the second stop braking control. That is, from timing t41, the processing circuit 51 starts an increase correction process for the second stop braking control. During the increase 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.

[0082] At timing t42, the condition for transitioning from the increasing correction process to the decreasing correction process is met. Therefore, the processing circuit 51 executes the decreasing process of the decreasing correction process. As a result, the vehicle braking force BPAl is reduced to the stop-maintenance braking force BPth. Then, at timing t43, the command braking force BPTr becomes the stop-maintenance braking force BPth. Then, the processing circuit 51 transitions the process from the decreasing correction process to the degeneration process. In other words, when the second stop-time braking control is implemented, there is no period during which the vehicle braking force BPAl is maintained. At subsequent timing t44, the command braking force BPTr reaches the required braking force BPRq, so the processing circuit 51 terminates the second stop-time braking control.

[0083] In this embodiment, there is no period during which the vehicle braking force BPAl is maintained at the stop-maintenance braking force BPth. Therefore, once the reduction process is executed and the command braking force BPTr reaches the stop-maintenance braking force BPth, the command braking force BPTr is immediately increased toward the required braking force BPRq. As a result, even if the stop-maintenance braking force BPth is smaller than the actual value of the stop-maintenance braking force, the possibility that the vehicle 10 will start moving downhill once the vehicle speed VS reaches 0 (zero) is lower than in the comparative example. Therefore, the driver is less likely to feel uncomfortable as in the comparative example.

[0084] Therefore, when the brake control device 50 performs stop braking control to stop the vehicle 10, it is possible to suppress changes in the posture of the vehicle 10 while the vehicle is stopped without causing discomfort to the driver.

[0085] (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.

[0086] The processing circuit 51 does not have to function as the moving force derivation unit M13. In this case, in the first embodiment, the processing circuit 51 (i.e., the setting unit M15) may set the execution time TMH of the holding process to be shorter as the magnitude of the road surface gradient θ increases. This is because it can be predicted that the moving force acting on the vehicle 10 increases as the magnitude of the road surface gradient θ increases.

[0087] In the second embodiment, the processing circuit 51 (i.e., the setting unit M15) can determine that the moving force is large when the magnitude of the road surface gradient θ is equal to or greater than the gradient threshold value, and therefore can execute the second stop braking control. On the other hand, the processing circuit 51 can determine that the moving force is not large when the magnitude of the road surface gradient θ is less than the gradient threshold value, and therefore can execute the first stop braking control.

[0088] In the first embodiment, the processing circuit 51 (i.e., the setting unit M15) may set the execution time TMH of the holding process to a time that is shorter when the road surface on which the vehicle 10 is traveling is a slope than when the road surface on which the vehicle 10 is traveling is not a slope.

[0089] In the first embodiment, the processing circuit 51 (i.e., the setting unit M15) varies the execution time TMD of the decrease process depending on the execution time TMH of the hold process, but this is not limiting. For example, the processing circuit 51 (i.e., the setting unit M15) may set the execution time TMD of the decrease process to a predetermined time regardless of the length of the execution time TMH of the hold process.

[0090] In various embodiments, the processing circuit 51 (i.e., the control unit M11) may vary the rate of increase of the command braking force BPTr during the degeneration process in accordance with the moving force FM. For example, the processing circuit 51 (i.e., the control unit M11) may set the rate of increase of the command braking force BPTr during the degeneration process so that the rate increases as the moving force FM increases.

[0091] The braking control at a stop does not necessarily have to include the increasing correction process as long as it includes the decreasing correction process and the degenerating process. In the above embodiments, the processing circuit 51 determines the start timing of the increasing correction process and the start timing of the decreasing correction process of the braking control at a stop in accordance with changes in the vehicle speed VS. However, the processing circuit 51 may determine the start timing of each process using a parameter other than the vehicle 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."

[0092] 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.

[0093] In the above embodiments, the processing circuit 51 performs the braking control at a standstill when the vehicle is braked in response to the driver's operation of the brake operating member 11. However, the processing circuit 51 may perform the braking control at a standstill when the vehicle is automatically braked.

[0094] The processing circuit 51 (i.e., the moving force derivation unit M13) may derive the road surface gradient θ based on the magnitude of the difference between the derivative of the vehicle body speed VS of the vehicle 10 and the longitudinal acceleration Gx. Various noise signals are superimposed on the detection signals of the longitudinal acceleration sensor 103 and the wheel speed sensor 102. Therefore, it is difficult to say that the accuracy of deriving the road surface gradient θ is high. For example, even if the road surface is level, a value corresponding to an error component may be derived as the road surface gradient θ. In this case, a value greater than the value that should be set as the stop-maintenance braking force BPth may be derived. Therefore, the processing circuit 51 (i.e., the moving force derivation unit M13) may use the map shown in FIG. 9 when deriving the road surface gradient θ.

[0095] FIG. 9 is a map showing road surface gradient θ and reliability. The road surface gradient based on the magnitude of the difference between the derivative of the vehicle speed VS and the longitudinal acceleration Gx is referred to as the "road surface gradient calculation value θE." In the map, when the road surface gradient calculation value θE is equal to or greater than the first boundary gradient value θth1 and equal to or less than the second boundary gradient value θth2, the reliability α is 0 (zero). For example, the first boundary gradient value θth1 is the value obtained by inverting the sign of the second boundary gradient value θth2. When the road surface gradient calculation value θE is less than the first boundary gradient value θth1, the reliability α increases as the absolute value of the road surface gradient calculation value θE increases. When the road surface gradient calculation value θE is greater than the second boundary gradient value θth2, the reliability α increases as the absolute value of the road surface gradient calculation value θE increases.

[0096] The processing circuit 51 (i.e., the moving force derivation unit M13) then derives the road surface gradient θ as the product of the reliability α derived based on the map shown in Fig. 9 and the road surface gradient calculation value θE. The processing circuit 51 (i.e., the moving force derivation unit M13) then derives a value corresponding to this road surface gradient θ as the moving force FM.

[0097] The predetermined braking force may be a value different from the vehicle stop maintenance braking force BPth. For example, a vehicle braking force BPAl that is slightly larger than the vehicle stop maintenance braking force BPth may be set as the predetermined braking force.

[0098] 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.

[0099] <Other Technical Ideas> The technical ideas that can be understood from the above-described embodiments and modified examples will be described below. [Supplementary Note 1] The stop-time braking control is a process that is performed after the holding process is performed and includes a degeneration process that increases the braking force applied to the vehicle, and it is preferable that the control unit, in the degeneration process, increase the braking force applied to the vehicle at a rate that is greater than the rate at which the braking force applied to the vehicle is reduced during the reduction process.

[0100] [Appendix 2] A braking control device that, when applying a braking force to a vehicle to stop it, performs stop-time braking control by reducing the braking force of the vehicle to a predetermined braking force and then setting the vehicle's body speed to 0 (zero), the braking control device comprising: a control unit that, in the stop-time braking control, executes a reduction process that reduces the braking force applied to the vehicle to the predetermined braking force, and a holding process that is started after the reduction process and before the vehicle's body speed VS becomes 0 (zero), and that holds the braking force applied to the vehicle at the predetermined braking force; and a setting unit that, when the road surface on which the vehicle is traveling is a slope, sets a shorter time as the execution time of the holding process than when the road surface is not a slope.

[0101] [Supplementary Note 3] A braking control device that, when applying a braking force to a vehicle to stop it, performs stop-time braking control by reducing the braking force of the vehicle to a predetermined braking force and then setting the vehicle body speed of the vehicle to 0 (zero), comprising: a control unit that performs, as the stop-time braking control, first stop-time braking control including a reduction process that reduces the braking force applied to the vehicle to the predetermined braking force and a holding process that is started after the reduction process and before the vehicle body speed VS of the vehicle becomes 0 (zero), and that maintains the braking force applied to the vehicle at the predetermined braking force; and second stop-time braking control that includes the reduction process but does not include the holding process, wherein the control unit performs the first stop-time braking control when a moving force that acts on the vehicle to move the vehicle is less than a threshold, and performs the second stop-time braking control when the moving force is equal to or greater than the threshold.

[0102] 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 that performs stop-time braking control, which reduces the braking force applied to the vehicle to a predetermined braking force when stopping the vehicle by applying a braking force to the vehicle, and then sets the vehicle's body speed to 0 (zero), comprising: a control unit that executes a reduction process in the stop-time braking control, which reduces the braking force applied to the vehicle to the predetermined braking force, and a holding process that is executed after the reduction process until the vehicle's body speed becomes 0 (zero), and which holds the braking force applied to the vehicle at the predetermined braking force; and a setting unit that sets the execution time of the holding process to be shorter the greater the force acting on the vehicle to move the vehicle during execution of the stop-time braking control.

2. The brake control device according to claim 1, wherein the setting unit sets the execution time of the decrease process so that the value increases as the execution time of the hold process becomes shorter.

3. A brake control device according to claim 1 or 2, further comprising a moving force derivation unit that derives a force for moving the vehicle that is greater the greater the gradient of the road surface on which the vehicle is traveling.

Images