Braking control device

Abstract

To provide a braking control device, which is configured to suppress a change in attitude of a vehicle which is being stopped, without making a driver feel strangeness, when stopping the vehicle by executing stop-time braking control.SOLUTION: A processing circuit 51 of a braking control device 50 functions as: a control part M11 that decreases vehicle braking force down to predetermined braking force and then executes a stop-time braking control for decreasing the vehicle body speed of a vehicle 10 down to 0 (zero), when applying braking force to the vehicle 10 to stop the vehicle; and a setting part M15 that sets a time for executing a process for holding the stop-time braking control to be shorter as movement force acting on the vehicle 10 is larger during execution of the stop-time braking control.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, a control device has been developed that performs stop control to suppress changes in the posture of a vehicle during stopping by reducing the braking force applied to the vehicle immediately before stopping. For example, the control device disclosed in Patent Document 1 estimates a stop estimation timing, which is the timing when the vehicle speed becomes 0 (zero), in stop control. Then, the control device reduces the braking force so that the braking force becomes 0 (zero) at the stop estimation timing.

[0003] However, the actual timing when the vehicle speed becomes 0 (zero) may be earlier than the stop estimation timing. In such a case, with the above control device, since the braking force cannot be made sufficiently small before stopping, there is a possibility that the change in the posture of the vehicle during stopping cannot be made sufficiently small.

[0004] On the other hand, the control device disclosed in Patent Document 2 performs stop control in which the braking force is sufficiently reduced before the stop estimation timing and then the braking force is held. According to this, even if the actual timing when the vehicle speed becomes 0 (zero) is earlier than the stop estimation timing, the braking force is sufficiently small at the actual timing when the vehicle speed becomes 0 (zero). Furthermore, immediately before stopping, the reduction rate of the braking force is 0 (zero). Thereby, even if the actual timing when the vehicle speed becomes 0 (zero) deviates from the stop estimation timing, the change in the posture of the vehicle during stopping is suppressed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0006] A force for moving the vehicle acts on the vehicle. The force for moving the vehicle is, for example, a driving force transmitted from the power source of the vehicle to the wheels, and a component in the downhill direction of the slope among the gravitational accelerations acting on a vehicle traveling on a slope. When parking control as disclosed in Patent Document 2 is executed in a situation where such a force for moving the vehicle is relatively large, there is a risk of giving the driver a sense of discomfort when the vehicle stops. For example, the vehicle may move after the vehicle speed once becomes zero. Also, on an uphill road, the vehicle may slip downward in the downhill direction of the uphill road.

MEANS FOR SOLVING THE PROBLEMS

[0007] A braking control device for solving the above problems is a device that, when stopping a vehicle by applying a braking force to the vehicle, performs a stop braking control in which the braking force applied to the vehicle is decreased to a predetermined braking force and then the vehicle body speed of the vehicle is set to 0 (zero). The braking control device includes a control unit that executes, in the stop braking control, a decreasing process of decreasing the braking force applied to the vehicle to the predetermined braking force, and a process that is executed until the vehicle body speed of the vehicle becomes 0 (zero) after the decreasing process 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 as the force for moving the vehicle acting on the vehicle during the execution of the stop braking control is larger.

EFFECTS OF THE INVENTION

[0008] The above braking control device has an effect that it can suppress a change in the posture of the vehicle at the time of stopping without giving the driver a sense of discomfort when stopping the vehicle by performing the stop braking control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0010] (First Embodiment) Hereinafter, the first embodiment of the braking control device will be described with reference to FIGS. 1 to 6. Figure 1 illustrates a vehicle 10 equipped with a braking control device 50. The vehicle 10 includes a braking operation member 11, a plurality of wheels, a plurality of friction brakes 20, and a braking actuator 30. The braking operation member 11 is a member that a driver operates when applying a braking force to the vehicle 10. An example of the braking operation member 11 is a brake pedal. The plurality of wheels includes two front wheels 12 and two rear wheels 13.

[0011] <Friction brake> A plurality of friction brakes 20 respectively apply braking force to corresponding wheels. 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, by pressing the friction portion 23 against the rotating body 22, braking force is applied to the wheel. The force for 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] <Braking actuator> The braking actuator 30 controls the braking force applied to the wheels 12, 13 by controlling the wheel hydraulic pressures of a plurality of wheel cylinders 21. For example, the braking actuator 30 has a pressurizing source that supplies brake fluid to a plurality of wheel cylinders 21. The pressurizing source is, for example, an electric pump and an electric cylinder. The braking actuator 30 can individually adjust the wheel hydraulic pressure of the wheel cylinder 21 for the front wheels 12 and the wheel hydraulic pressure of the wheel cylinder 21 for the rear wheels 13.

[0013] In the following description, the sum of the braking forces applied to the plurality of wheels 12, 13 is also referred to as "vehicle braking force BPAl". <Detection system> The detection system of the vehicle 10 includes a plurality of sensors that output detection signals to the braking control device 50. The plurality of sensors include a brake sensor 101, a plurality of wheel speed sensors 102, and a longitudinal and lateral acceleration sensor 103.

[0014] The brake sensor 101 detects information related to the operation of the braking operation member 11 by the driver. An example of the brake sensor 101 is a stroke sensor that detects the operation amount of the driver's braking operation member 11. The operation amount based on the detection signal of the brake sensor 101 is referred to as "braking operation amount X". Note that the detection system may have a sensor that detects the operation force of the driver's braking operation member 11.

[0015] The wheel speed sensor 102 is provided for each of a plurality of wheels. The plurality of wheel speed sensors 102 respectively detect the rotational speed of the corresponding wheels. The rotational speed of the wheels based on the detection signal of the wheel speed sensor 102 is referred to as "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 "vehicle body speed VS".

[0016] The longitudinal acceleration sensor 103 detects the longitudinal acceleration of the vehicle 10 among 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. An example of the processing circuit 51 is an electronic control unit. In this case, the processing circuit 51 has 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 the calculation results of the CPU 52 and the like. By the CPU 52 executing the control program in the first memory 53, the processing circuit 51 controls the brake actuator 30 to operate the plurality of friction brakes 20. That is, the processing circuit 51 can adjust the vehicle braking force BPAl by operating the plurality of friction brakes 20.

[0018] <Outline of braking control at stop> When the processing circuit 51 stops the vehicle 10 by applying a braking force, it performs braking control at stop. The braking control at stop is braking control for suppressing changes in the posture of the vehicle 10 when stopping.

[0019] Referring to FIG. 2, the braking control at stop will be described. FIG. 2 shows an example of the case where the braking control at stop is performed when stopping the vehicle 10 on a horizontal road. At timing t11 when the vehicle 10 is running, the driver starts operating the braking operation member 11. In this case, as shown in (B) of FIG. 2, 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 such that the value increases as the braking operation amount X of the braking operation member 11 increases. When the vehicle body speed VS of the vehicle 10 is greater than the first vehicle body speed determination value VSth1 as before timing t12, as shown in (D) of FIG. 2, the processing circuit 51 sets the required braking force BPRq as the instructed braking force BPTr. Then, the processing circuit 51 controls the braking actuator 30 so that the vehicle braking force BPAl becomes the instructed braking force BPTr.

[0020] When the braking force is applied to the vehicle 10 in this way, as shown in (A) of FIG. 2, the vehicle body speed VS decreases. Also, as shown in (C) of FIG. 2, the absolute value of the longitudinal and lateral acceleration Gx increases as the vehicle braking force BPAl increases.

[0021] When the vehicle body speed VS reaches the first vehicle body speed determination value VSth1 at timing t12, the processing circuit 51 starts the braking control at stop. The first vehicle body speed determination value VSth1 is an example of a threshold value for setting the start timing of the braking control at stop. From timing t12, the processing circuit 51 starts the incremental correction process of the braking control at stop. In the incremental correction process, the processing circuit 51 sets a braking force greater than the required braking force BPRq as the instructed 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 instructed braking force BPTr. Then, the processing circuit 51 controls the braking actuator 30 so that the vehicle braking force BPAl becomes the instructed braking force BPTr. Thereby, even if the required braking force BPRq is the same, the absolute value of the longitudinal and lateral acceleration Gx of the vehicle 10 becomes greater than before timing t12 by the amount of the offset value ΔBP.

[0022] At timing t13, the vehicle body speed VS becomes the second vehicle body speed determination value VSth2. A vehicle body speed smaller than the first vehicle body speed determination value VSth1 is set as the second vehicle body speed determination value VSth2. When the vehicle body speed VS is equal to or lower than the second vehicle body speed determination value VSth2, it can be considered that the vehicle 10 has approached the stop position PS. The stop position PS is the predicted position where the vehicle 10 stops. The processing circuit 51 shifts the processing of the stop-time braking control from the plus correction processing to the minus correction processing. In the minus correction processing, the processing circuit 51 decreases the indicated braking force BPTr at a constant speed. Then, the processing circuit 51 controls the braking actuator 30 so that the vehicle braking force BPAl becomes the indicated braking force BPTr. By executing the minus correction processing in this way by the processing circuit 51, the vehicle braking force BPAl becomes smaller than the required braking force BPRq. As a result, even if the required braking force BPRq is the same, the absolute value of the longitudinal acceleration Gx of the vehicle 10 gradually becomes smaller.

[0023] At timing t14, the indicated braking force BPTr becomes equal to the stop-maintaining braking force BPth. As the stop-maintaining braking force BPth, the minimum braking force required to maintain the stop of the vehicle 10 on the current traveling road surface of the vehicle 10, or a braking force slightly larger than the braking force, is set. This stop-maintaining braking force BPth is an example of the "predetermined braking force". From timing t14, in the minus correction processing, the processing circuit 51 holds the indicated braking force BPTr at the stop-maintaining braking force BPth.

[0024] Hereinafter, in the minus correction processing, the process of decreasing the indicated braking force BPTr to the stop-maintaining braking force BPth is referred to as the "decrease process". Also, in the minus correction processing, the process of holding the indicated braking force BPTr at the stop-maintaining braking force BPth is referred to as the "holding process". The holding process is a process that starts after the execution of the decrease process and is a process that is executed until the vehicle body speed VS becomes 0 (zero). More specifically, the holding process is preferably started immediately before the vehicle body speed VS becomes 0 (zero).

[0025] At timing t15, in order for the processing circuit 51 to determine that the vehicle 10 has stopped, the process of the stop-time braking control shifts from the subtractive correction process (i.e., the holding process) to the degradation process. In the degradation process, the processing circuit 51 increases the commanded braking force BPTr. For example, the processing circuit 51 increases the commanded braking force BPTr to the required braking force BPRq. By controlling the braking actuator 30 based on the commanded braking force BPTr by the processing circuit 51, the vehicle braking force BPAl increases. When the commanded braking force BPTr becomes equal to the required braking force BPRq at timing t16, the processing circuit 51 ends the stop-time braking control.

[0026] <Functional configuration of the processing circuit> Referring to FIG. 1, the functional configuration of the processing circuit 51 will be described. By the CPU 52 executing the control program of the first memory 53, the processing circuit 51 functions as a plurality of functional units. These plurality of functional units are functional units for stopping the vehicle 10 by applying a braking force thereto. The plurality of functional units include, for example, a control unit M11, a driving force derivation unit M13, and a setting unit M15.

[0027] <Control unit> When applying a braking force to the vehicle 10 to stop it, the control unit M11 performs stop-time braking control. That is, when the start condition of the stop-time braking control is satisfied, the control unit M11 executes an additive correction process. In the additive correction process, the control unit M11 sets the commanded braking force BPTr to a vehicle braking force greater than the required braking force BPRq. The offset value ΔBP, which is the additive correction amount of the commanded braking force BPTr at this time, is a correction amount of the braking force for compensating for the extension of the braking distance of the vehicle 10 caused by the execution of the subtractive correction process described later. The control unit M11 operates the braking actuator 30 based on the commanded braking force BPTr.

[0028] During the execution of the augmentation correction process, when the transition condition from the augmentation correction process to the reduction correction process is satisfied, the control unit M11 ends the augmentation correction process and starts the reduction correction process. In the reduction correction process, the control unit M11 reduces the commanded braking force BPTr to the holding braking force BPth for stopping and then sets the vehicle body speed VS to 0 (zero). Specifically, the control unit M11 reduces the commanded braking force BPTr to the holding braking force BPth for stopping by executing the reduction process in the reduction correction process. In the present embodiment, the control unit M11 reduces the commanded braking force BPTr to the holding braking force BPth for stopping, which is smaller than the required braking force BPRq, in the reduction process. The control unit M11 operates the brake actuator 30 based on the commanded braking force BPTr at that time. After the commanded braking force BPTr reaches the holding braking force BPth for stopping, the control unit M11 holds the commanded braking force BPTr at the holding braking force BPth for stopping by executing the holding process in the reduction correction process. The control unit M11 starts the holding process before the vehicle body speed VS becomes 0 (zero). The control unit M11 operates the brake actuator 30 based on the commanded braking force BPTr at that time.

[0029] As will be described in detail later, in the present embodiment, the execution time TMD of the reduction process is set by the setting unit M15. Therefore, the control unit M11 reduces the commanded braking force BPTr to the holding braking force BPth for stopping within the execution time TMD set by the setting unit M15. Thus, in the reduction process, the control unit M11 derives the difference between the commanded braking force BPTr at the start of the reduction process and the holding braking force BPth for stopping as the braking force difference. The control unit M11 derives the value obtained by dividing the braking force difference by the execution time TMD as the reduction speed of the commanded braking force BPTr. Then, the control unit M11 reduces the commanded braking force BPTr at the reduction speed.

[0030] During the execution of the subtraction correction process, when the transition condition from the subtraction correction process to the degradation process is satisfied, the control unit M11 ends the subtraction correction process and starts the degradation process. In the degradation process, the control unit M11 increases the commanded braking force BPTr to the required braking force BPRq. At this time, the control unit M11 increases the commanded braking force BPTr such that the increase rate of the commanded braking force BPTr is greater than the decrease rate of the commanded braking force BPTr in the decrease process. Then, the control unit M11 operates the brake actuator 30 based on the commanded 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 the vehicle 10 is braked. The moving force FM is the force that moves the vehicle 10. More specifically, the moving force FM is the force acting on the vehicle 10 in the vehicle forward or vehicle rear direction with respect to the vehicle 10.

[0032] The moving force FM includes, for example, the driving force FD of the vehicle 10 and the gravitational force acting on the vehicle 10. The greater the magnitude of the driving force FD, the greater the force that attempts to move the vehicle 10 in the traveling direction of the vehicle 10. Also, when the vehicle 10 is traveling on a slope, the greater the magnitude of the gravitational acceleration component FG, which is the component of the gravitational force in the downhill direction on the lower side of the slope of the slope, the greater the force that attempts to move the vehicle 10 in the downhill direction.

[0033] Therefore, the moving force derivation unit M13 derives the moving force FM such that the value increases as the magnitude of the driving force FD of the vehicle 10 increases when the vehicle 10 is braked. Further, the motive force derivation unit M13 derives the road surface gradient θ, which is the gradient of the traveling road surface of the vehicle 10. For example, the motive force derivation unit M13 derives the road surface gradient θ such that the larger the magnitude of the difference between the differential value of the vehicle body speed VS of the vehicle 10 and the longitudinal acceleration Gx, the larger the value. The motive force derivation unit M13 may acquire the road surface gradient θ based on the information about the road surface obtained from the navigation device. Also, when the vehicle 10 is equipped with a sensor for detecting the degree of inclination of the vehicle body, the motive force derivation unit M13 may acquire the detection value of the sensor as the road surface gradient θ. Further, the motive force derivation unit M13 may derive the road surface gradient θ by analyzing the image captured by the in-vehicle camera.

[0034] The motive force derivation unit M13 derives the motive force FM such that the larger the magnitude of the road surface gradient θ, the larger the value. This is because the larger the magnitude of the road surface gradient θ, the larger the magnitude of the gravitational acceleration component FG described above.

[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 motive force derivation unit M13 derives, as the motive force FM, the magnitude of the difference between the magnitude of the gravitational acceleration component FG that can be estimated from the road surface gradient θ and the magnitude of the driving force FD.

[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 motive force derivation unit M13 derives, as the motive force FM, the sum of the magnitude of the gravitational acceleration component FG that 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 in the deceleration correction process and the execution time TMD of the decreasing process in the deceleration correction process based on the motive force FM acting on the vehicle 10 during the execution of the stop-time braking control. Specifically, the setting unit M15 sets the execution time TMH of the holding process to be shorter as the motive force FM is larger. Also, the setting unit M15 sets the execution time TMD of the decreasing process such that the value becomes larger as the execution time TMH of the holding process is shorter.

[0038] FIG. 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 determination 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 greater than or equal to the determination moving force FMth, the execution time TMH of the holding process is set to be 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 greater than or equal to the determination moving force FMth, the greater the moving force FM, the shorter the execution time TMH of the holding process. And the shorter the execution time TMH of the holding process, the shorter the execution time TMD of the reduction process.

[0039] Note that in the example shown in FIG. 3, the execution time of the subtraction 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 subtraction correction process may vary depending on the magnitude of the moving force FM. For example, the execution time of the subtraction correction process may be made shorter as the magnitude of the moving force FM increases.

[0040] <Flow of processing during vehicle braking> Referring to FIG. 4, a series of processes when the processing circuit 51 performs stop braking control will be described. The processing circuit 51 repeatedly executes a series of processes shown in FIG. 4 when the vehicle 10 is braked.

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

[0042] In step S15, the processing circuit 51 determines whether the start condition for the stop-time braking control is satisfied. For example, as shown in FIG. 2, when the vehicle body speed VS decreases from a state where it is greater than the first vehicle body speed determination value VSth1 to a value less than or equal to the first vehicle body speed determination value VSth1, the processing circuit 51 determines that the start condition is satisfied. When the processing circuit 51 determines that the start condition is satisfied (S15: YES), the process proceeds to step S17. On the other hand, when the processing circuit 51 determines that the start condition is not satisfied (S15: NO), the series of processes shown in FIG. 4 is temporarily terminated.

[0043] In step S17, the processing circuit 51 performs the stop-time braking control. Specifically, in step S19, the processing circuit 51 executes the additional correction process. In the additional correction process, the processing circuit 51 sets the sum of the required braking force BPRq and the offset value ΔBP as the indicated braking force BPTr in order to compensate for the extension of the braking distance of the vehicle 10 caused by the execution of the subtractive correction process. The processing circuit 51 operates the brake actuator 30 based on the indicated braking force BPTr.

[0044] In step S21, the processing circuit 51 determines whether the transition condition from the additional correction process to the subtractive correction process is satisfied. For example, when the vehicle body speed VS decreases from a state where it is greater than the second vehicle body speed determination value VSth2 to a value less than or equal to the second vehicle body speed determination value VSth2, the processing circuit 51 determines that the transition condition is satisfied. When the processing circuit 51 determines that the transition condition is not satisfied (S21: NO), the process proceeds to step S19. That is, the processing circuit 51 executes the additional correction process. On the other hand, when the processing circuit 51 determines that the transition condition is satisfied (S21: YES), the process proceeds to step S23.

[0045] In step S23, the processing circuit 51 executes the decreasing process among the subtraction correction processes. In the decreasing process, the processing circuit 51 decreases the commanded braking force BPTr to the holding braking force for stopping BPth. Specifically, the processing circuit 51 decreases the commanded braking force BPTr such that the commanded braking force BPTr becomes the holding braking force for stopping BPth within the execution time TMD of the decreasing 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 commanded braking force BPTr has become less than or equal to the holding braking force for stopping BPth. Here, the processing circuit 51 may determine whether the actual execution time of the decreasing process has become the execution time TMD of the decreasing process. When the processing circuit 51 determines that the commanded braking force BPTr is not less than or equal to the holding braking force for stopping BPth (S25: NO), the process proceeds to step S23. That is, the processing circuit 51 executes the decreasing process. On the other hand, when the processing circuit 51 determines that the commanded braking force BPTr has become less than or equal to the holding braking force for stopping BPth (S25: YES), the process proceeds to step S27.

[0047] In step S27, the processing circuit 51 executes the holding process among the subtraction correction processes. In the holding process, the processing circuit 51 holds the commanded braking force BPTr at the holding braking force for stopping BPth. Then, the processing circuit 51 operates the brake actuator 30 based on the commanded braking force BPTr.

[0048] In the next step S29, the processing circuit 51 determines whether the end condition of the holding process has been satisfied. In the present embodiment, the processing circuit 51 determines that the end condition of the holding process has been satisfied when at least one of the following conditions (A1) and (A2) is satisfied. On the other hand, when neither of the following conditions (A1) and (A2) is satisfied, the processing circuit 51 determines that the end condition of the holding process has not been satisfied.

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

[0050] In step S31, the processing circuit 51 executes the degradation process. In the degradation process, the processing circuit 51 increases the commanded braking force BPTr to the required braking force BPRq. Then, the processing circuit 51 operates the brake actuator 30 based on the commanded braking force BPTr.

[0051] In the next step S33, the processing circuit 51 determines whether the end condition of the degradation process is satisfied. For example, when the commanded braking force BPTr becomes equal to the required braking force BPRq, it is regarded that the end condition is satisfied. On the other hand, when the commanded braking force BPTr is less than the required braking force BPRq, it is regarded that the end condition is not satisfied. When the processing circuit 51 determines that the end condition is not satisfied (S33: NO), the process proceeds to step S31. That is, the processing circuit 51 executes the degradation process. On the other hand, when the processing circuit 51 determines that the end condition is satisfied (S33: YES), the degradation process ends. Then, the processing circuit 51 ends the stop-time braking control and ends the series of processes shown in FIG. 4.

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

[0053] <Actions and Effects of the Present Embodiment> Referring to FIGS. 5 and 6, the operation and effects of the present embodiment will be described. The examples shown in FIGS. 5 and 6 are cases where the vehicle 10 traveling on a slope is stopped by applying a braking force. FIG. 5 shows a comparative example in which the execution time TMH of the holding process and the execution time TMD of the decreasing process are not changed according to the moving force FM. FIG. 6 shows the present embodiment in which the execution time TMH of the holding process and the execution time TMD of the decreasing process are changed according to the moving force FM.

[0054] <Comparative example> As shown by the dashed line in FIG. 5(C), when the vehicle 10 is traveling on a slope, the braking force BPth for maintaining a stop is greater than when the vehicle 10 is traveling on a horizontal road.

[0055] As shown in FIGS. 5(A), 5(B), and 5(C), at the timing t21 when the braking force is being applied to the vehicle 10, the processing circuit determines that the start condition for the braking control at stop is satisfied. Therefore, the processing circuit starts the augmentation correction process. During the execution of the augmentation correction process, the commanded 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 the timing t22, the transition condition from the augmentation correction process to the decrementation correction process is satisfied. Therefore, the processing circuit starts the decreasing process among the decrementation correction processes. As a result, the vehicle braking force BPAl decreases to the braking force BPth for maintaining a stop. Then, since the commanded braking force BPTr becomes the braking force BPth for maintaining a stop at the timing t23, the processing circuit starts the holding process among the decrementation correction processes. As a result, the vehicle braking force BPAl is held. When the timing t24 is reached, since the holding process ends and the degradation process starts, the vehicle braking force BPAl increases.

[0057] Here, the parking 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 parking maintenance braking force BPth may deviate from the actual value of the parking maintenance braking force. In particular, if the parking maintenance braking force BPth is smaller than the actual value of the parking maintenance braking force, there is a possibility that the vehicle 10 may start to move in the downhill direction after the vehicle body speed VS once becomes 0 (zero) while the vehicle braking force BPAl is being held by the holding process. The steeper the slope of the slope road, the greater the magnitude of the gravitational acceleration component FG, that is, the greater the moving force FM. The greater the moving force FM, the earlier the start timing of the movement of the vehicle 10 in the downhill direction tends to be.

[0058] And when the vehicle braking force BPAl is increased by the degradation process after the vehicle 10 starts to move in the downhill direction in this way, the vehicle 10 will stop. However, the driver may feel a sense of discomfort with respect to the vehicle 10 stopping after starting to move in the downhill direction in this way.

[0059] <This Embodiment> As shown in FIGS. 6(A), (B), and (C), at the timing t31 when the braking force is being applied to the vehicle 10, the processing circuit 51 starts the supplementary correction process for the braking control at stop. As a result, the vehicle braking force BPAl becomes greater 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 the execution of the reduction correction process. Specifically, the processing circuit 51 sets the execution time TMH of the holding process so that the value becomes shorter as the moving force FM is greater.

[0061] Therefore, when the moving force FM is relatively large, such as when the vehicle 10 is traveling on a slope road, the execution time TMH of the holding process becomes shorter. In the example shown in FIG. 6, when the decreasing process in the subtractive correction process starts from timing t32, the vehicle braking force BPAl decreases. Then, the holding process in the subtractive correction process starts from timing t33. The holding process is executed until timing t34, and since the degenerate process starts from timing t34, the vehicle braking force BPAl increases.

[0062] The length of the time from timing t33 to timing t34, which is the execution period of the holding process, is shorter than the length of the time from timing t23 to timing t24, which is the execution period of the holding process in the above comparative example. Therefore, even if the stop maintenance braking force BPth is smaller than the actual value of the stop maintenance braking force, while the vehicle braking force BPAl is being held by the holding process, the possibility that the vehicle body speed VS once becomes 0 (zero) and then the vehicle 10 starts to move in the downhill direction is lower than in the above comparative example. Therefore, the possibility that the driver feels a sense of discomfort as in the case of the comparative example is reduced.

[0063] Therefore, when the braking control device 50 stops the vehicle 10 by performing the braking control at the stop, it is possible to suppress a change in the posture of the vehicle 10 at the stop without giving the driver a sense of discomfort.

[0064] <Other effects> (1-1) When the braking control device 50 shortens the execution time TMH of the holding process because the moving force FM is relatively large, it lengthens the execution time TMD of the decreasing process. Thereby, the decreasing speed of the vehicle braking force BPAl during the execution of the decreasing process can be reduced. As a result, when the moving force FM is relatively large, the braking control device 50 can moderate the pitching motion of the vehicle 10 during the execution of the subtractive correction process.

[0065] (1-2) The braking control device 50 derives the moving force FM so that its value increases as the road surface gradient θ increases. For this reason, when the braking control device 50 stops the vehicle 10 by performing the braking control at the stop on a downhill road with a large road surface gradient θ, it can enhance the effect of suppressing the slip-down of the vehicle 10 in the downhill direction.

[0066] (Second Embodiment) A second embodiment of the braking control device will be described with reference to FIGS. 7 and 8. Note that in the second embodiment, it is different from the first embodiment in that stop-time braking control according to the magnitude of the moving force is selected. In the following description, the parts different from the first embodiment will be mainly described, and the same members as those in the first embodiment will be denoted by the same reference numerals and redundant descriptions will be omitted.

[0067] In the present embodiment, the braking control device 50 is configured to be able to perform first stop-time braking control and second stop-time braking control as stop-time braking control. Each of the first stop-time braking control and the second stop-time braking control includes augmentation correction processing, reduction correction processing, and degeneracy processing. The reduction correction processing of the first stop-time braking control includes reduction processing and holding processing. The reduction correction processing of the second stop-time braking control includes reduction processing but does not include holding processing.

[0068] <Flow of Processing During Vehicle Braking> Referring to FIG. 7, a series of processes when the processing circuit 51 of the braking control device 50 performs stop-time braking control will be described. The processing circuit 51 repeatedly executes the series of processes shown in FIG. 7 when the vehicle 10 is braked.

[0069] In step S51, the processing circuit 51 derives the moving force FM in the same manner as in step S11 above. In the next step S53, the processing circuit 51 determines whether or not the start condition of the stop-time braking control is satisfied in the same manner as in step S15 above. When the processing circuit 51 determines that the start condition is satisfied (S53: YES), the process proceeds to step S55. On the other hand, when the processing circuit 51 determines that the start condition is not satisfied (S53: NO), the series of processes shown in FIG. 7 is temporarily terminated.

[0070] In step S55, the processing circuit 51 determines whether the moving force FM is less than the threshold value FMth1. If the stop braking control is implemented in a state where the moving force FM is relatively large, there is a possibility that the vehicle 10 starts to move after the vehicle body speed VS once becomes 0 (zero) during the execution of the subtraction correction process. Therefore, the criterion for determining whether the moving force FM is relatively large is set as the threshold value FMth1. When the processing circuit 51 determines that the moving force FM is less than the threshold value FMth1 (S55: YES), the process proceeds to step S60. On the other hand, when the processing circuit 51 determines that the moving force FM is greater than or equal to the threshold value FMth1 (S55: NO), the process proceeds to step S80.

[0071] In step S60, the processing circuit 51 performs the first stop braking control as the stop braking control. Specifically, in step S61, the processing circuit 51 executes the addition correction process. The content of this addition correction process is the same as the addition correction process executed in step S19 above. In the next step S63, the processing circuit 51 determines whether the transition condition from the addition correction process to the subtraction correction process is satisfied, similar to step S21 above. When the processing circuit 51 determines that the transition condition is not satisfied (S63: NO), the process proceeds to step S61. That is, the processing circuit 51 executes the addition correction process. On the other hand, when the processing circuit 51 determines that the transition condition is satisfied (S63: YES), the process proceeds to step S65.

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

[0073] In the next step S67, the processing circuit 51 determines whether or not the commanded braking force BPTr has become less than or equal to the stop maintenance braking force BPth. When the processing circuit 51 determines that the commanded braking force BPTr has not become less than or equal to the stop maintenance braking force BPth (S67: NO), the process proceeds to step S65. That is, the processing circuit 51 executes a decreasing process. On the other hand, when the processing circuit 51 determines that the commanded braking force BPTr has become less than or equal to the stop maintenance braking force BPth (S67: YES), the process proceeds to step S69.

[0074] In step S69, the processing circuit 51 executes a holding process, which is part of the subtraction correction process, in the same manner as in step S27 above. In the next step S71, the processing circuit 51 determines whether or not the vehicle 10 has stopped. When the processing circuit 51 determines that the vehicle 10 has not stopped (S71: NO), the process proceeds to step S69. That is, the processing circuit 51 executes a holding process. On the other hand, when the processing circuit 51 determines that the vehicle 10 has stopped (S71: YES), the process proceeds to step S73.

[0075] In step S73, the processing circuit 51 executes a degeneracy process in the same manner as in step S31 above. In the subsequent step S75, the processing circuit 51 determines whether or not the end condition of the degeneracy process has been satisfied in the same manner as in step S33 above. When the processing circuit 51 determines that the end condition has not been satisfied (S75: NO), the process proceeds to step S73. That is, the processing circuit 51 executes a degeneracy process. On the other hand, when the processing circuit 51 determines that the end condition has been satisfied (S75: YES), the degeneracy process ends. Then, the processing circuit 51 ends the first stop-time braking control and ends the series of processes shown in FIG. 7.

[0076] In step S80, the processing circuit 51 performs the second stop braking control as the stop braking control. Specifically, in step S81, the processing circuit 51 executes the augmentation correction process. The content of this augmentation correction process is the same as the augmentation correction process executed in step S19 above. In the next step S83, the processing circuit 51 determines whether or not the transition condition from the augmentation correction process to the reduction correction process is satisfied, in the same manner as in step S21 above. If the processing circuit 51 determines that the transition condition is not satisfied (S83: NO), the process proceeds to step S81. That is, the processing circuit 51 executes the augmentation correction process. On the other hand, if the processing circuit 51 determines that the transition condition is satisfied (S83: YES), the process proceeds to step S85.

[0077] In step S85, the processing circuit 51 executes the reduction process among the reduction correction processes. In the reduction process, the processing circuit 51 reduces the commanded braking force BPTr to the holding braking force BPth for stopping. Then, the processing circuit 51 operates the brake actuator 30 based on the commanded braking force BPTr at that time.

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

[0079] In step S89, the processing circuit 51 executes a degradation process in the same manner as in step S31. In the subsequent step S91, the processing circuit 51 determines whether the end condition of the degradation process is satisfied in the same manner as in step S33. If the processing circuit 51 determines that the end condition is not satisfied (S91: NO), the process proceeds to step S89. That is, the processing circuit 51 executes the degradation process. On the other hand, if the processing circuit 51 determines that the end condition is satisfied (S91: YES), the degradation process ends. Then, the processing circuit 51 ends the second stop-time braking control and ends the series of processes shown in FIG. 7.

[0080] <Actions and effects of this embodiment> Referring to FIG. 8, the actions and effects when the second stop-time braking control is performed will be described. The example shown in FIG. 8 is a case where the vehicle 10 traveling on a slope is stopped by applying a braking force.

[0081] As shown in FIGS. 8(A), 8(B), and 8(C), at the timing t41 when the braking force is being applied to the vehicle 10, the processing circuit 51 determines that the start condition of the stop-time braking control is satisfied. In this case, since the processing circuit 51 can determine that the moving force FM is equal to or greater than the threshold value FMth1, the second stop-time braking control is performed. That is, from the timing t41, the processing circuit 51 starts the additional correction process of the second stop-time braking control. During the execution of the additional correction process, the commanded braking force BPTr is set to a vehicle braking force that is greater than the required braking force BPRq. Therefore, the vehicle braking force BPAl becomes greater than the required braking force BPRq.

[0082] The transition condition from the augmentation correction process to the reduction correction process is satisfied at timing t42. Therefore, the processing circuit 51 executes the reduction process among the reduction correction processes. As a result, the vehicle braking force BPAl decreases to the stop maintenance braking force BPth. Then, at timing t43, the commanded braking force BPTr becomes the stop maintenance braking force BPth. Then, the processing circuit 51 shifts the process from the reduction correction process to the degradation process. That is, when the second stop-time braking control is performed, no period during which the vehicle braking force BPAl is held is provided. At subsequent timing t44, since the commanded braking force BPTr reaches the required braking force BPRq, the processing circuit 51 ends the second stop-time braking control.

[0083] In the present embodiment, no period during which the vehicle braking force BPAl is held at the stop maintenance braking force BPth is provided. Therefore, when the commanded braking force BPTr becomes the stop maintenance braking force BPth by executing the reduction process, the commanded braking force BPTr immediately increases 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 starts to move in the downhill direction after the vehicle body speed VS once becomes 0 (zero) is lower than in the above comparative example. Therefore, the possibility that the driver feels an uncomfortable feeling as in the case of the comparative example is reduced.

[0084] Therefore, when stopping the vehicle 10 by performing the stop-time braking control, the braking control device 50 can suppress a change in the posture of the vehicle 10 at the time of stopping without giving an uncomfortable feeling to the driver.

[0085] (Modification example) The above-described plurality of embodiments can be modified and implemented as follows. The above-described plurality of embodiments and the following modification examples can be implemented in combination with each other within a range that is not technically contradictory.

[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 is larger. This is because it can be predicted that the moving force acting on the vehicle 10 is larger as the magnitude of the road surface gradient θ is larger.

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

[0088] ·In the first embodiment, when the traveling road surface of the vehicle 10 is a slope, the processing circuit 51 (i.e., the setting unit M15) may set the execution time TMH of the holding process to be shorter than when the traveling road surface 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 reduction process according to the execution time TMH of the holding process, but is not limited thereto. For example, the processing circuit 51 (i.e., the setting unit M15) may set a predetermined time as the execution time TMD of the reduction process regardless of the length of the execution time TMH of the holding process.

[0090] ·In a plurality of embodiments, the processing circuit 51 (i.e., the control unit M11) may vary the increasing speed of the commanded braking force BPTr during the degeneration process according to the moving force FM. For example, the processing circuit 51 (i.e., the control unit M11) may set the increasing speed of the commanded braking force BPTr during the degeneration process such that the value increases as the moving force FM increases.

[0091] ·If the stop-time braking control includes the subtraction correction process and the degeneration process, it does not have to include the addition correction process. · In the above-described multiple embodiments, the processing circuit 51 determines the start timing of the supplementary correction process and the start timing of the reduction correction process of the stop-time braking control in accordance with the change in the vehicle body speed VS. However, if it is a parameter whose value decreases as the vehicle 10 approaches the stop position PS, the processing circuit 51 may determine the start timing of each process using a parameter other than the vehicle body speed VS. Examples of other parameters include the stop distance and the stop prediction time. The stop distance is the distance from the current position of the vehicle 10 to the stop position PS. The stop prediction time is the time required for the vehicle 10 to stop. An example of the stop prediction time is TTC. TTC is an abbreviation for "Time To Collision".

[0092] · When executing the stop-time braking control, the braking 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 sum of the total regenerative braking force applied to the vehicle 10 becomes the vehicle braking force BPAl.

[0093] · In the above-described multiple embodiments, the processing circuit 51 performs the stop-time braking control when the vehicle is braked due to the operation of the braking operation member 11 by the driver. However, the processing circuit 51 may perform the stop-time braking control during automatic braking.

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

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

[0096] Then, the processing circuit 51 (that is, the driving force derivation unit M13) derives the product of the reliability α derived based on the map shown in FIG. 9 and the road surface gradient calculation value θE as the road surface gradient θ. Then, the processing circuit 51 (that is, the driving force derivation unit M13) may derive a value corresponding to such a road surface gradient θ as the driving force FM.

[0097] · The predetermined braking force may be a value different from the parking maintenance braking force BPth. For example, a vehicle braking force BPAl slightly greater than the parking maintenance braking force BPth may be set as the predetermined braking force.

[0098] · The processing circuit 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 executing at least a part of various processes, or a combination thereof. Examples of the dedicated hardware include an ASIC (Application Specific Integrated Circuit) which is an integrated circuit for a specific purpose. The processor includes a CPU and memories such as a RAM and a ROM, and the memories store program codes or instructions configured to cause the CPU to execute processes. The memory, that is, the storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0099] <Other technical ideas> Describe the technical idea that can be grasped from the above-described plurality of embodiments and modification examples. [Appendix 1] The stop-time braking control is a process after the execution of the holding process, and includes a degradation process of increasing the braking force applied to the vehicle. In the degradation process, the control unit preferably increases the braking force applied to the vehicle at a speed higher than the decreasing speed of the braking force applied to the vehicle during the execution of the decreasing process.

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

[0101] [Appendix 3] A braking control device that performs stop-time braking control to stop the vehicle by applying a braking force to the vehicle, in which after reducing the braking force of the vehicle to a predetermined braking force, the vehicle body speed of the vehicle is set to 0 (zero). As the stop-time braking control, a first stop-time braking control including a decreasing process of reducing the braking force applied to the vehicle to the predetermined braking force, and a process that is subsequent to the decreasing process and is started before the vehicle body speed VS of the vehicle becomes 0 (zero), and that holds the braking force applied to the vehicle at the predetermined braking force, and a second stop-time braking control that includes the decreasing process but does not include the holding process, and a control unit that performs the control. When the driving force, which is the force for moving the vehicle acting on the vehicle, is less than the threshold value, the control unit performs the first stop braking control, and when the driving force is equal to or greater than the threshold value, the control unit performs the second stop braking control. A braking control device.

[0102] Note 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 the 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.

Explanation of Reference Numerals

[0103] 10…Vehicle 11, 12…Wheels 20…Friction Brake 30…Braking Actuator 50…Braking Control Device 51…Processing Circuit M11…Control Unit M13…Driving Force Derivation Unit M15…Setting Unit

Claims

1. When stopping a vehicle by applying a braking force to the vehicle, a braking control device that performs a stop braking control for reducing the braking force applied to the vehicle to a predetermined braking force and then setting the vehicle body speed of the vehicle to 0 (zero), in the stop braking control, a control unit that executes a reduction process for reducing the braking force applied to the vehicle to the predetermined braking force, and a process that is executed until the vehicle body speed of the vehicle becomes 0 (zero) after the reduction process, 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 as the force for moving the vehicle acting on the vehicle during the execution of the stop braking control is larger. Braking control device.

2. The setting unit sets the execution time of the reduction process so that the value increases as the execution time of the holding process is shortened. The braking control device according to Claim 1.

3. A moving force deriving unit that derives a larger force as the gradient of the traveling road surface of the vehicle is larger, as the force for moving the vehicle. The braking control device according to Claim 1 or Claim 2.

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