Brake control system

Abstract

To quickly stop a vehicle that has decelerated by applying regenerative braking force and then started moving again in the opposite direction of its previous movement after coming to a complete stop. [Solution] The processing circuit 71 of the braking control device 70 functions as a reverse movement detection unit 203 that detects when the vehicle 10 starts moving in the reverse direction after the vehicle 10 has stopped during the execution of stopping control, and a braking control unit 205 that, when it is detected that the vehicle 10 has started moving in the reverse direction, sets a target friction braking force that is larger the greater of the regenerative braking force and the requested braking force at the time the vehicle 10 stopped, and operates the friction braking unit 40 based on the target friction braking force to stop the vehicle 10.

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a braking control device that controls regenerative braking force and friction braking force applied to a vehicle. The braking control device reduces the regenerative braking force such that the regenerative braking force becomes zero when the vehicle stops, immediately before the vehicle stops due to the application of braking force. Then, when the vehicle stops, the braking control device increases the friction braking force. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2016-28913 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] When reducing the regenerative braking force such that the regenerative braking force becomes zero when the vehicle stops, the braking control device predicts the stop position or stop timing of the vehicle. Then, a regenerative braking unit that adjusts the regenerative braking force operates so that the regenerative braking force becomes zero at the predicted stop position or stop timing. However, if the vehicle stops before the stop position predicted by the braking control device, or stops earlier than the predicted stop timing, the regenerative braking force may still not be zero when the vehicle actually stops.

[0005] Here, when applying regenerative braking force to the vehicle, the regenerative braking unit outputs torque in a direction that restricts the rotation of the wheel to the axle of the wheel. This torque is torque that rotates the wheel and the axle in the reverse direction.

[0006] Therefore, if the regenerative braking force is greater than 0 (zero) at the time the vehicle stops, the torque mentioned above is being input to the axle at that time of stopping, which may cause the vehicle, once stopped, to start moving again in the opposite direction to the direction of movement before stopping. [Means for solving the problem]

[0007] The braking control device for solving the above problems is applied to a vehicle comprising a regenerative braking unit that applies regenerative braking force to the vehicle and a friction braking unit that applies friction braking force to the vehicle. The braking control device performs stopping control to stop the vehicle by activating the regenerative braking unit and the friction braking unit. The braking control device comprises a reverse movement detection unit that detects when the vehicle starts moving in the reverse direction after it has stopped during the execution of the stopping control, and a braking control unit that, when the reverse movement detection unit detects that the vehicle has started moving in the reverse direction, sets a target friction braking force that is larger the greater of the two braking forces, namely the regenerative braking force at the time the vehicle stopped and the required braking force for the vehicle, and performs reverse movement suppression control to stop the vehicle by activating the friction braking unit based on the target friction braking force. [Effects of the Invention]

[0008] The above-described braking control device has the effect of being able to stop the movement of a vehicle early when, after a vehicle that has been decelerated by applying regenerative braking force has come to a complete stop, the vehicle starts moving again in the opposite direction of its previous movement. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing a vehicle equipped with a braking control device according to an embodiment. [Figure 2] Figures 2(a) to 2(f) are timing charts showing examples of the changes in various parameters when the smooth stop process is executed just before the vehicle in Figure 1 comes to a complete stop. [Figure 3]Figure 3 is a flowchart showing the processing flow when a smooth stop process is executed in the braking control device shown in Figure 1. [Figure 4] Figures 4(a) to 4(f) are timing charts showing the changes in various parameters when a vehicle that has come to a stop begins to move in reverse during the execution of the smooth stop process. [Modes for carrying out the invention]

[0010] An embodiment of a braking control device will be described with reference to Figures 1 to 4. <Overall vehicle configuration> Figure 1 shows a vehicle 10 equipped with a braking control device 70. The vehicle 10 further comprises a braking operating member 11, a plurality of wheels 13, a regenerative braking unit 20, a friction braking unit 40, and a plurality of sensors. The braking operating member 11 is a member operated by the driver when adjusting the deceleration of the vehicle 10. An example of the braking operating member 11 is a brake pedal. In Figure 1, only one of the plurality of wheels 13 is shown.

[0011] <Regenerative braking section> The regenerative braking unit 20 is configured to apply regenerative braking force to the vehicle 10. The regenerative braking unit 20 includes a motor generator 21, a rotation angle sensor 22 for detecting the rotational speed of the output shaft of the motor generator 21, and a regenerative control device 30 for controlling the motor generator 21. The motor generator 21 functions as a generator, thereby applying regenerative braking force to the vehicle 10. The actual value of the regenerative braking force applied to the vehicle 10 by the regenerative braking unit 20 is referred to as "effective regenerative braking force FbE".

[0012] An example of a rotation angle sensor 22 is a resolver. The rotation angle sensor 22 outputs a detection signal to the regenerative control device 30 according to the rotation speed of the output shaft. The rotation angle of the motor generator 21 that can be derived based on the detection signal of the rotation angle sensor 22 is referred to as the "motor rotation angle θmt".

[0013] The regenerative control device 30 includes a processing circuit 31. An example of the processing circuit 31 is an electronic control device. In this case, the processing circuit 31 has a CPU and a memory that stores a control program executed by the CPU. The CPU executes the control program in the memory, enabling the processing circuit 31 to control the motor generator 21.

[0014] The regenerative control device 30 is configured to send and receive various information and commands to and from the braking control device 70 via the in-vehicle network. Therefore, when the vehicle is braking, the regenerative control device 30 can operate the motor generator 21 based on the information or commands received from the braking control device 70.

[0015] The processing circuit 31 functions as a regenerative control unit 101 when the CPU executes a memory control program. The regenerative control unit 101 adjusts the effective regenerative braking force FbE by operating the motor generator 21. In other words, the regenerative control unit 101 can adjust the effective regenerative braking force FbE by operating the motor generator 21 based on the target regenerative braking force FbETr, which is the target of the regenerative braking force.

[0016] <Friction brake part> The friction braking unit 40 is configured to apply friction braking force to the vehicle 10. The friction braking unit 40 comprises a plurality of friction brakes 41, each individually provided for a plurality of wheels 13, and a braking actuator 50. In Figure 1, only one of the plurality of friction brakes 41 is shown.

[0017] Each of the plurality of friction brakes 41 generates a friction braking force at the corresponding wheel 13. The friction brake 41 includes a wheel cylinder 42, a rotating body 43, and a friction portion 44. The rotating body 43 rotates integrally with the wheel 13. Therefore, pressing the friction portion 44 against the rotating body 43 generates a friction braking force at the wheel 13. The force pressing the friction portion 44 against the rotating body 43 increases as the wheel pressure, which is the hydraulic pressure in the wheel cylinder 42, becomes higher. Therefore, the friction brake 41 can generate a larger friction braking force at the wheel 13 as the wheel pressure becomes higher. The sum of the friction braking forces generated by the plurality of wheels 13 corresponds to "the friction braking force FbF applied to the vehicle 10".

[0018] The braking actuator 50 is configured to be capable of controlling the wheel pressure of the plurality of wheel cylinders 42. For example, the braking actuator 50 has a pressure source capable of supplying brake fluid to the plurality of wheel cylinders 42. The pressure source is, for example, an electric pump or an electric cylinder. The brake fluid discharged from the braking actuator 50 is supplied to the wheel cylinders 42 via a supply flow path 51.

[0019] <Sensor> The plurality of sensors output signals corresponding to detection results to the braking control device 70. The plurality of sensors include, for example, a brake sensor 61, a plurality of wheel speed sensors 62, and an acceleration sensor 63. The brake sensor 61 detects information related to the operation of the braking operation member 11 by the driver. An example of the brake sensor 61 is a stroke sensor that detects the operation amount of the braking operation member 11 by the driver. The operation amount based on the detection signal of the brake sensor 61 is referred to as "braking operation amount Ba". Note that the vehicle 10 may be provided with a sensor that detects the operating force of the braking operation member 11 by the driver.

[0020] The plurality of wheel speed sensors 62 detect the rotational speed of the corresponding wheels 13. Specifically, each wheel speed sensor 62 outputs a pulse signal corresponding to the rotational speed of the corresponding wheel 13 as a detection signal. The pulse generation period in the pulse signal becomes longer as the rotational speed of the wheel 13 decreases. The rotational speed of the wheel 13 obtained based on the detection signal of the wheel speed sensor 62 is referred to as "wheel speed VW". An example of the wheel speed sensor 62 is a sensor that generates pulses at a period corresponding to the rotational speed regardless of the rotational direction of the wheel 13.

[0021] The acceleration sensor 63 detects the longitudinal acceleration of the vehicle 10. The longitudinal acceleration obtained based on the detection signal of the acceleration sensor 63 is referred to as "longitudinal acceleration GX". <Braking Control Device> The braking control device 70 operates the braking actuator 50 of the friction braking unit 40. The braking control device 70 is configured to be able to transmit and receive various types of information and commands to and from the regenerative control device 30. Therefore, during vehicle braking, the braking control device 70 can adjust the deceleration of the vehicle 10 by cooperating with the regenerative control device 30 while operating the braking actuator 50. That is, the braking control device 70 can control the total braking force Fb of the vehicle 10 by operating the friction braking unit 40 and the regenerative braking unit 20. The total braking force Fb is the sum of the executed regenerative braking force FbE and the friction braking force FbF.

[0022] The braking control device 70 includes a processing circuit 71. An example of the processing circuit 71 is an electronic control device. In this case, the processing circuit 71 includes a CPU 72, a first memory 73, and a second memory 74. The first memory 73 stores a control program executed by the CPU 72. Calculation results of the CPU 72 are stored in the second memory 74. When the CPU 72 executes the control program stored in the first memory 73, the processing circuit 71 can operate the friction braking unit 40 to adjust the friction braking force FbF. Further, the processing circuit 71 can adjust the executed regenerative braking force FbE by transmitting an instruction related to regenerative braking force to the regenerative control device 30.

[0023] <Smooth Stop Processing> The processing circuit 71 of the braking control device 70 performs a smooth stop process just before the vehicle 10, which is decelerating by the application of braking force, comes to a complete stop. The smooth stop process is a process that reduces the change in the vehicle 10's posture when the vehicle 10 stops. In this smooth stop process, the processing circuit 71 coordinates the regenerative braking unit 20 and the friction braking unit 40.

[0024] Refer to Figure 2 to explain an example of smooth stop processing. When the vehicle 10 is decelerating due to the application of braking force, the processing circuit 71 estimates the stopping position of the vehicle 10 based on the vehicle speed VS and vehicle acceleration DVS. The vehicle speed VS is the calculated value of the vehicle's travel speed based on the wheel speed VW. The vehicle acceleration DVS is the time derivative of the vehicle speed VS. The processing circuit 71 estimates the stopping position of the vehicle 10 when the vehicle speed VS becomes 0 (zero) as the vehicle decelerates at the current vehicle acceleration DVS. The processing circuit 71 then derives stopping-related values ​​that decrease as the vehicle 10 approaches the stopping position. For example, the processing circuit 71 derives the stopping distance DS, which is the distance from the vehicle 10's current position to the above-mentioned stopping position, as a stopping-related value.

[0025] As shown in Figures 2(a) to (f), the processing circuit 71 operates the friction braking unit 40 and the regenerative braking unit 20 based on the required braking force FbRq applied to the vehicle 10. In the example shown in Figure 2, before timing t11, at least the regenerative braking force is applied to the vehicle 10, causing the vehicle 10 to decelerate. At timing t11, the processing circuit 71 determines that the conditions for executing the smooth stop process have been met because the derived stopping distance DS is less than or equal to the first threshold DSth1. The first threshold DSth1 is the criterion for determining whether the vehicle 10 is about to come to a complete stop.

[0026] The smooth stop process includes substitution control, reduction correction control, and degeneration control. The reduction correction control is an example of "stopping control" that stops the vehicle 10 by activating the regenerative braking unit 20 and the friction braking unit 40.

[0027] When the conditions for executing the smooth stop process are met at timing t11, the processing circuit 71 starts the substitution control for the smooth stop process. The substitution control is a control that substitutes the active regenerative braking force FbE with the friction braking force FbF. In the substitution control, the processing circuit 71 sets the holding braking force FbH to the target friction braking force FbFTr and then operates the braking actuator 50 of the friction braking unit 40. As a result, the processing circuit 71 can make the friction braking force FbF substantially equal to the holding braking force FbH.

[0028] The holding braking force FbH is the lower limit of the braking force required to maintain the vehicle 10's stop on the road surface where the vehicle 10 is located, or a braking force slightly greater than that lower limit. For example, the processing circuit 71 derives the holding braking force FbH such that its value increases as the absolute value of the road surface gradient increases.

[0029] When the processing circuit 71 operates the braking actuator 50 as described above, it sends an instruction to the regenerative control device 30 of the regenerative braking unit 20 to reduce the regenerative braking force by the amount of the increase in frictional braking force FbF.

[0030] When the regenerative control device 30 receives the above instruction, the processing circuit 31 of the regenerative control device 30 reduces the target regenerative braking force FbETr by the amount of the increase in friction braking force FbF. Then, the processing circuit 31 operates the motor generator 21 based on the target regenerative braking force FbETr. As a result, the effective regenerative braking force FbE decreases in proportion to the increase in friction braking force FbF. In other words, while suppressing the increase in total braking force Fb, a portion of the effective regenerative braking force FbE is replaced with friction braking force FbF.

[0031] When the processing circuit 71 of the braking control device 70 determines that the friction braking force FbF has become equal to the holding braking force FbH, it terminates the substitution control. At timing t12 after the execution of the substitution control, if the stopping distance DS becomes less than or equal to the second threshold DSth2, the processing circuit 71 starts the reduction correction control. The second threshold DSth2 is greater than 0 (zero) and less than the first threshold DSth1. In the reduction correction control, the processing circuit 71 sends an instruction to the regenerative control device 30 to reduce the regenerative braking force to 0 (zero). At this time, the processing circuit 71 should send an instruction to the regenerative control device 30 to reduce the regenerative braking force at a reference reduction speed. The reference reduction speed is set so that the effective regenerative braking force FbE becomes 0 (zero) before the stopping distance DS becomes 0 (zero).

[0032] When the regenerative control device 30 receives the instruction, the processing circuit 31 of the regenerative control device 30 reduces the target regenerative braking force FbETr toward 0 (zero). Then, the processing circuit 31 operates the motor generator 21 based on the target regenerative braking force FbETr. As a result, the effective regenerative braking force FbE decreases.

[0033] Furthermore, in the reduction correction control, the processing circuit 71 of the braking control device 70 maintains a state in which the target friction braking force FbFTr is equal to the held braking force FbH. Then, the processing circuit 71 operates the braking actuator 50 based on the target friction braking force FbFTr.

[0034] At timing t14, while the reduction correction control is being executed, the regenerative braking force FbE becomes 0 (zero). Since the vehicle 10 has not yet stopped at timing t14, the processing circuit 71 continues the reduction correction control. At this time, the processing circuit 71 maintains a state in which the target friction braking force FbFTr is equal to the holding braking force FbH, and then operates the braking actuator 50 based on the target friction braking force FbFTr. Therefore, if the holding braking force FbH is maintained at a constant value, the friction braking force FbF is also maintained.

[0035] In the example shown in Figure 2, the counting condition for the pulse count CNTp is met at timing t13, between timing t12 and timing t14. For example, the processing circuit 71 may determine that the counting condition is met when the stopping distance DS is less than or equal to the third threshold DSth3. In this case, the third threshold DSth3 is greater than 0 (zero) and less than the second threshold DSth2. When the counting condition is met, as shown in Figure 2(f), the processing circuit 71 updates the pulse count CNTp so that it increases by 1 each time a pulse is input from the wheel speed sensor 62 to the braking control device 70. When the wheel 13 is rotating, pulses are input from the wheel speed sensor 62 to the braking control device 70 at intervals corresponding to its rotational speed.

[0036] At timing t15, while the deceleration correction control is being executed, no pulses are input from the wheel speed sensor 62 to the braking control device 70. As a result, from timing t15 onward, the processing circuit 71 maintains the pulse count CNTp. At timing t16, when the duration of the state in which the pulse count CNTp is maintained reaches the determination time, the processing circuit 71 determines that the vehicle 10 has stopped. At this point, the processing circuit 71 terminates the deceleration correction control and starts degraded control.

[0037] In degenerate control, the processing circuit 71 increases the friction braking force FbF. For example, the processing circuit 71 increases the target friction braking force FbFTr to the required braking force FbRq. Then, the processing circuit 71 operates the braking actuator 50 based on the target friction braking force FbFTr. This increases the friction braking force FbF. When the target friction braking force FbFTr reaches the required braking force FbRq at timing t17, the processing circuit 71 terminates the degenerate control. That is, the processing circuit 71 terminates the smooth stop process.

[0038] <Functional configuration of the braking control system> Referring to Figure 1, the functional configuration of the braking control device 70 will be explained. The processing circuit 71 of the braking control device 70 functions as a plurality of functional units when the CPU 72 executes the control program of the first memory 73. The plurality of functional units include a request setting unit 201, a residual regenerative braking force output unit 202, a reverse detection unit 203, a stop determination unit 204, and a braking control unit 205.

[0039] The request setting unit 201 sets the requested braking force FbRq at predetermined control cycles. When the braking operation member 11 is operated, the request setting unit 201 sets the requested braking force FbRq such that the value increases as the braking operation amount Ba increases. When deceleration of the vehicle 10 is requested from another on-board control device, the request setting unit 201 sets the requested braking force FbRq to the braking force according to that request.

[0040] The residual regenerative braking force derivation unit 202 derives the effective regenerative braking force FbE immediately before stopping as the residual regenerative braking force FbER when the vehicle 10 stops. When the rotation of wheel 13 stops, regenerative braking force is no longer actually generated by wheel 13. Therefore, if a braking request is issued, the residual regenerative braking force derivation unit 202 monitors the trend of the effective regenerative braking force FbE. The residual regenerative braking force derivation unit 202 then derives, for example, the value just before the vehicle speed VS becomes 0 (zero) as the residual regenerative braking force FbER.

[0041] The reverse movement detection unit 203 detects that after the vehicle 10 has stopped during the execution of the attenuation correction control, the vehicle 10 has started moving in the opposite direction to its previous direction of movement. Hereafter, the movement of the vehicle 10 in the reverse direction will be described as "the vehicle 10 is moving in reverse."

[0042] An example of a reverse movement detection process, which detects when vehicle 10 moves in reverse, will be explained. As explained using Figure 2, when deceleration correction control is being performed, if the stopping distance DS becomes less than or equal to the third threshold DSth3 and the conditions for counting the pulse count CNTp are met, the counting of the pulse count CNTp begins. If vehicle 10 does not move in reverse after stopping, the pulse count CNTp is maintained because the state in which the rotation of the wheels 13 has stopped is maintained. However, if vehicle 10 starts moving in the reverse direction after it has stopped, the input of pulses from the wheel speed sensor 62 to the braking control device 70 continues. As a result, the pulse count CNTp continues to increase even after it has reached the reference value CNTb.

[0043] Therefore, in the reverse movement detection process, the reverse movement detection unit 203 detects that the vehicle 10 is moving in reverse based on the pulse signal output from the wheel speed sensor 62. For example, the reverse movement detection unit 203 detects that the vehicle 10 is moving in reverse if the number of pulses CNTp is greater than the reference value CNTb. More specifically, the reverse movement detection unit 203 sets the sum of the reference value CNTb and the offset value as the determination value CNTth, and then determines whether the number of pulses CNTp is equal to or greater than the determination value CNTth. The reverse movement detection unit 203 then detects that the vehicle 10 is moving in reverse if the number of pulses CNTp is equal to or greater than the determination value CNTth.

[0044] The stop determination unit 204 determines whether or not the vehicle 10 has stopped. For example, the stop determination unit 204 determines that the vehicle 10 has stopped if, under the condition that the pulse count CNTp is equal to or greater than the reference value CNTb, the duration of the state in which the pulse count CNTp is maintained exceeds a predetermined measurement time.

[0045] When a braking request is received, the braking control unit 205 adjusts the total braking force Fb by coordinating the regenerative braking unit 20 and the friction braking unit 40. For example, the braking control unit 205 transmits information regarding the requested braking force FbRq to the regenerative control unit 30.

[0046] The regenerative control unit 101 of the regenerative control device 30 derives a target regenerative braking force FbETr based on the requested braking force FbRq indicated by the received information. For example, the regenerative control unit 101 sets the target regenerative braking force FbETr to the smaller of the regenerative braking force limit value and the requested braking force FbRq. The regenerative braking force limit value is the upper limit of the regenerative braking force that can be applied to the vehicle 10, or a regenerative braking force slightly smaller than that upper limit value. The regenerative control unit 101 operates the motor generator 21 based on the target regenerative braking force FbETr.

[0047] The braking control unit 205 sets the target friction braking force FbFTr based on the effective regenerative braking force FbE and the required braking force FbRq. If the effective regenerative braking force FbE is equal to the required braking force FbRq, the braking control unit 205 sets the target friction braking force FbFTr to 0 (zero). On the other hand, if the effective regenerative braking force FbE is less than the required braking force FbRq, the braking control unit 205 sets the target friction braking force FbFTr to the difference between the required braking force FbRq and the effective regenerative braking force FbE. Then, the braking control unit 205 operates the braking actuator 50 based on the target friction braking force FbFTr. If the conditions for executing the smooth stop process are met while this control is being executed, the braking control unit 205 starts the smooth stop process.

[0048] When the braking control unit 205 is performing the reduction correction control for smooth stop processing, the reverse detection unit 203 may detect that the vehicle 10 is moving in reverse. In this case, the braking control unit 205 stops the reduction correction control and performs reverse suppression control. In reverse suppression control, the braking control unit 205 sets the target friction braking force FbFTr based on one of the braking forces, which is the residual regenerative braking force FbER (executed regenerative braking force FbE at the time the vehicle 10 stops) and the requested braking force FbRq, such that the value increases as the other braking force increases. In this embodiment, the braking control unit 205 sets the target friction braking force FbFTr based on the residual regenerative braking force FbER, such that the value increases as the residual regenerative braking force FbER increases. Then, the braking control unit 205 stops the vehicle 10 by operating the braking actuator 50 of the friction braking unit 40 based on the target friction braking force FbFTr. As a result, the braking control unit 205 can apply a friction braking force FbF greater than the holding braking force FbH to the vehicle 10.

[0049] If the stop determination unit 204 determines that the vehicle 10 has stopped while reverse suppression control is being executed, the braking control unit 205 terminates the reverse suppression control and executes degraded control of the smooth stop process. As a result, when the vehicle 10 is stopped, the braking control unit 205 can make the friction braking force FbF substantially equal to the required braking force FbRq.

[0050] <Processing flow in the braking control system> Refer to Figure 3 to explain the process flow when performing a smooth stop operation. When the vehicle 10 is decelerating due to the application of braking force, the processing circuit 71 of the braking control device 70 sequentially executes a number of processes according to the processing flow shown in Figure 3.

[0051] In step S11, the processing circuit 71 determines whether the execution conditions for the substitution control of the smooth stop process have been met. For example, if the stopping distance DS is less than or equal to the first threshold DSth1, it indicates that the execution conditions for the substitution control have been met. If the execution conditions for the substitution control have not yet been met (S11: NO), the processing circuit 71 repeatedly performs the determination in step S11 until the execution conditions are met. On the other hand, if the execution conditions are met (S11: YES), the processing circuit 71 proceeds to step S13.

[0052] In step S13, the processing circuit 71 functions as a braking control unit 205 to perform substitution control for the smooth stop process. In substitution control, the processing circuit 71 increases the friction braking force FbF to the holding braking force FbH by activating the friction braking unit 40, and decreases the active regenerative braking force FbE by the amount of the increase in the friction braking force FbF by activating the regenerative braking unit 20.

[0053] In the following step S15, the processing circuit 71 determines whether the substitution control has finished. When the friction braking force FbF reaches the holding braking force FbH, the processing circuit 71 can determine that the substitution control has finished. If the processing circuit 71 determines that the substitution control has not finished (S15: NO), the processing circuit 71 continues the substitution control by moving the process to step S13. On the other hand, if the processing circuit 71 determines that the substitution control has finished (S15: YES), the processing circuit 71 moves the process to step S17.

[0054] In step S17, the processing circuit 71 determines whether the execution conditions for the undercorrection control are met. If the execution conditions for the undercorrection control are not met (S17: NO), the processing circuit 71 repeatedly performs the determination in step S17 until the execution conditions are met. On the other hand, if the execution conditions are met (S17: YES), the processing circuit 71 proceeds to step S19.

[0055] In step S19, the processing circuit 71 performs reduction correction control by functioning as a braking control unit 205. In reduction correction control, the processing circuit 71 reduces the effective regenerative braking force FbE to 0 (zero) by activating the regenerative braking unit 20, and maintains a state in which the friction braking force FbF is substantially equal to the held braking force FbH by activating the friction braking unit 40.

[0056] During step S21 of the execution of the reduction correction control, the processing circuit 71, by functioning as a reverse detection unit 203, determines whether or not it has detected that the vehicle 10 is moving in reverse. If the processing circuit 71 detects that the vehicle 10 is moving in reverse (S21: YES), the processing circuit 71 proceeds to step S23. On the other hand, if the processing circuit 71 does not detect that the vehicle 10 is moving in reverse (S21: NO), the processing circuit 71 proceeds to step S25.

[0057] In step S23, the processing circuit 71 performs reverse suppression control by functioning as a braking control unit 205. In reverse suppression control, the processing circuit 71 increases the friction braking force FbF by activating the friction braking unit 40. Then, the processing circuit 71 proceeds to step S25.

[0058] In step S25, the processing circuit 71 functions as a stop determination unit 204 to determine whether or not the vehicle 10 has stopped. If the processing circuit 71 determines that the vehicle 10 has stopped (S25: YES), the processing circuit 71 proceeds to step S29. On the other hand, if the processing circuit 71 determines that the vehicle 10 has not stopped (S25: NO), the processing circuit 71 proceeds to step S27.

[0059] In step S27, the processing circuit 71 determines whether or not it is performing reverse suppression control. If the processing circuit 71 is performing reverse suppression control (S27: YES), the processing circuit 71 continues to perform reverse suppression control by moving the process to step S23. On the other hand, if the processing circuit 71 is not performing reverse suppression control (S27: NO), the processing circuit 71 continues to perform undercorrection control by moving the process to step S19.

[0060] In step S29, the processing circuit 71 performs degenerate control by functioning as a braking control unit 205. In degenerate control, the processing circuit 71 increases the friction braking force FbF toward the required braking force FbRq by activating the friction braking unit 40.

[0061] In the subsequent step S31, the processing circuit 71 determines whether the friction braking force FbF is substantially equal to the required braking force FbRq. For example, the processing circuit 71 only needs to determine that the friction braking force FbF is substantially equal to the required braking force FbRq if the target friction braking force FbFTr is greater than or equal to the required braking force FbRq. If the processing circuit 71 determines that the friction braking force FbF is less than the required braking force FbRq (S31: NO), the processing circuit 71 continues the execution of the degenerate control by moving the process to step S29. On the other hand, if the processing circuit 71 determines that the friction braking force FbF is substantially equal to the required braking force FbRq (S31: YES), the processing circuit 71 terminates the degenerate control. That is, the processing circuit 71 terminates the smooth stop process.

[0062] <Operation and Effects of This Embodiment> Referring to Figure 4, the operation and effects of this embodiment will be described. As shown in Figures 4(a) to (f), at timing t21 while the vehicle 10 is decelerating due to the application of regenerative braking force, the processing circuit 71 determines that the conditions for executing the smooth stop process have been met. Then, the processing circuit 71 starts the smooth stop process substitution control. Through the substitution control, the friction braking force FbF is increased to the holding braking force FbH, and the effective regenerative braking force FbE is decreased by the amount of the increase in the friction braking force FbF.

[0063] At timing t22, after the substitution control is completed, the processing circuit 71 determines that the conditions for executing the subtraction correction control have been met, and therefore starts the subtraction correction control. In Figure 4(b), the dashed line shows the progression of the vehicle acceleration DVS that the braking control device 70 assumed at the start of the smooth stop process. On the other hand, the solid line shows the progression of the actual vehicle acceleration DVS. In other words, in the example shown in Figure 4, the deceleration of the vehicle 10 is greater than that assumed by the braking control device 70. Therefore, the vehicle 10 stops earlier than the stopping position predicted by the processing circuit 71. As a result, the vehicle 10 stops at timing t23 when the effective regenerative braking force FbE is still greater than 0. In other words, the residual regenerative braking force FbER is greater than 0.

[0064] Here, the motor generator 21 of the regenerative braking unit 20 outputs a rotation restricting torque TqE to the axle 14 of the wheel 13, which is a torque that restricts the rotation of the wheel 13 when applying regenerative braking force to the vehicle 10. The direction of rotation of the wheel 13 and axle 14 during deceleration of the vehicle 10 is described as the "forward rotation direction," and the direction opposite to the forward rotation direction is described as the "reverse rotation direction." The rotation restricting torque TqE is the torque that rotates the wheel 13 and axle 14 in the reverse direction. The larger the target regenerative braking force FbETr, the larger the rotation restricting torque TqE. Therefore, when the remaining regenerative braking force FbER is greater than 0 (zero), the rotation restricting torque TqE is output to the axle 14. When the rotation restricting torque TqE is large, the rotation of the wheel 13 may temporarily stop, and then the wheel 13 and axle 14 may start rotating in the reverse direction. In other words, if the residual regenerative braking force FbER is greater than 0 (zero), there is a possibility that the vehicle 10 may move in reverse after coming to a complete stop.

[0065] In the example shown in Figure 4, the counting condition for the pulse count CNTp is met at timing t23, so the processing circuit 71 starts updating the pulse count CNTp. If the vehicle 10 comes to a complete stop and then reverses direction, the updating of the pulse count CNTp continues even if the pulse count CNTp exceeds the reference value CNTb.

[0066] At timing t24 in this state, the processing circuit 71 detects that the vehicle 10 is moving in reverse. Therefore, the processing circuit 71 stops the deceleration correction control and starts reverse suppression control. As a result, the state in which the friction braking force FbF is held is released, and the friction braking force FbF is increased. As a result, the vehicle 10 stops moving in reverse and comes to a stop. Thus, the processing circuit 71 can stop the vehicle 10 from moving in reverse early when the vehicle 10, which has been decelerated by the application of regenerative braking force, comes to a stop and then starts moving in reverse.

[0067] In the example shown in Figure 4, the processing circuit 71 determines that the vehicle 10 has stopped at timing t25, so the processing circuit 71 terminates the reverse suppression control and starts the degenerate control. When the degenerate control starts, the friction braking force FbF is increased toward the required braking force FbRq. When the friction braking force FbF becomes substantially equal to the required braking force FbRq, the processing circuit 71 terminates the smooth stop process.

[0068] <Example of changes> The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0069] The processing circuit 71, i.e., the reverse movement detection unit 203, may detect that the vehicle 10 is moving in reverse using a method different from the method described in the above embodiment, as long as it can detect that the vehicle 10 is moving in reverse based on the pulse signal output from the wheel speed sensor 62. For example, when the vehicle 10 stops due to the application of braking force, the pulse generation period included in the pulse signal gradually lengthens. Then, when the vehicle 10, which has stopped, begins to move in reverse, the pulse generation period gradually shortens. Therefore, the processing circuit 71 may detect that the vehicle 10 is moving in reverse when it detects that the pulse generation interval has shortened after it had lengthened.

[0070] The vehicle 10 may be equipped with a wheel speed sensor that outputs a detection signal corresponding to the rotation speed and direction of rotation of the wheel 13. In this case, the processing circuit 71, i.e., the reverse movement detection unit 203, can detect that the vehicle 10 is moving in reverse when the rotation direction of the wheel 13 changes, based on the detection signal from the wheel speed sensor.

[0071] When the vehicle 10 stops due to the application of braking force, the longitudinal acceleration GX fluctuates around a value corresponding to the gradient of the road surface on which the vehicle 10 has stopped. The longitudinal acceleration corresponding to the gradient of the road surface is referred to as the acceleration convergence value. Therefore, the processing circuit 71, i.e., the reverse movement detection unit 203, should detect that the vehicle 10 is moving in reverse when the longitudinal acceleration GX fluctuates around the acceleration convergence value. In other words, the processing circuit 71 can detect that the vehicle 10 is moving in reverse based on the longitudinal acceleration GX, which is the value detected by the acceleration sensor 63, and information regarding the gradient of the road surface.

[0072] The rotation angle sensor 22 of the regenerative braking unit 20 outputs a detection signal corresponding to the rotation speed and direction of the output shaft of the motor generator 21. If the braking control device 70 can receive information regarding the rotation speed and direction of the output shaft of the motor generator 21 from the regenerative control device 30 of the regenerative braking unit 20, the processing circuit 71, i.e., the reverse movement detection unit 203, may be configured to detect that the vehicle 10 is moving in reverse based on the received information. Specifically, when the rotation direction of the output shaft of the motor generator 21 changes, the polarity of the detection signal of the rotation angle sensor 22 changes. For example, the polarity is positive before the vehicle 10 stops, while the polarity becomes negative when the vehicle 10 starts to move in reverse. Therefore, the processing circuit 71 may be configured to detect that the vehicle 10 is moving in reverse when the polarity of the detection signal of the rotation angle sensor 22 reverses.

[0073] The processing circuit 71, i.e., the reverse movement detection unit 203, may detect the reverse movement of the vehicle 10 even if smooth stop processing is not being performed, if it is attempting to stop the vehicle 10 by applying braking force. For example, when the braking control unit 205 is performing regenerative substitution control as a stop control, which reduces the effective regenerative braking force FbE toward 0 (zero) and increases the friction braking force FbF by the amount of the reduction in the effective regenerative braking force FbE, the reverse movement detection unit 203 may detect the reverse movement of the vehicle 10. If the reverse movement of the vehicle 10 is detected while regenerative substitution control is being performed, it is preferable for the braking control unit 205 to stop the vehicle 10 by performing reverse movement suppression control.

[0074] The processing circuit 71, i.e., the braking control unit 205, may set a target friction braking force FbFTr that increases as the required braking force FbRq increases in reverse suppression control, and activate the braking actuator 50 based on the target friction braking force FbFTr to stop the vehicle 10. Even in this case, as in the above embodiment, the processing circuit 71 can increase the friction braking force FbF, so that when the vehicle 10, which has stopped once, starts to reverse, the reverse movement of the vehicle 10 can be stopped early.

[0075] The regenerative braking unit may be configured to include a power unit comprising at least one motor generator and an engine, provided that it can provide regenerative braking force to the vehicle 10.

[0076] The braking control device 70 may be configured to include multiple processing circuits. For example, among the multiple processing circuits, the first processing circuit executes some of the multiple functional units 201 to 205. The functional unit realized by the first processing circuit is the first functional unit. In this case, a second processing circuit, separate from the first processing circuit, functions as a functional unit separate from the first functional unit among the multiple functional units 201 to 205.

[0077] The processing circuit 71 may be configured as a circuit including one or more processors that operate according to a computer program, one or more dedicated hardware circuits such as dedicated hardware that performs at least some of the various processes, or a combination thereof. Examples of dedicated hardware include application-specific integrated circuits (ASICs). The processor includes a CPU and memory such as RAM and ROM, where the memory stores program code or instructions configured to cause the CPU to perform the processes. The memory, i.e., storage medium, includes any available medium that can be accessed by a general-purpose or dedicated computer.

[0078] <Other technological ideas> The technical concepts that can be understood from the above embodiments and modified examples are described below. [Note 1] The vehicle is equipped with a stop determination unit that determines whether or not the vehicle has stopped, The braking control unit, If the stop determination unit determines that the vehicle has stopped during the execution of the reduction correction control, a degenerate control is executed to increase the friction braking force toward the required braking force. It is preferable to execute the reverse suppression control if, during the execution of the reduction correction control, the vehicle starts moving in the reverse direction before the stop determination unit determines that the vehicle has stopped, and then execute the degradation control after the vehicle has stopped.

[0079] In this specification, the expression "at least one" means "one or more" of the desired options. For example, if there are two options, the expression "at least one" means "only one option" or "both of the two options." As another example, if there are three or more options, the expression "at least one" means "only one option" or "a combination of two or more arbitrary options." [Explanation of Symbols]

[0080] 10... Vehicles 13...Wheel 20...Regenerative braking section 22... Rotation angle sensor 21…Motor Generator 40...Friction brake part 41… Friction brakes 50... Brake actuator 62... Wheel speed sensor 63...Accelerometer 70... Brake control device 71…Processing circuit 203...Reverse detection unit 205... Brake Control Unit

Claims

1. A braking control device applied to a vehicle comprising a regenerative braking unit that applies regenerative braking force to the vehicle and a friction braking unit that applies friction braking force to the vehicle, which performs stopping control to stop the vehicle by activating the regenerative braking unit and the friction braking unit, A reverse movement detection unit detects when the vehicle starts moving in the reverse direction after it has stopped during the execution of the aforementioned stop control, The system includes a braking control unit that, when the reverse movement detection unit detects that the vehicle has started moving in the reverse direction, sets a target friction braking force that is larger than the regenerative braking force at the time the vehicle stopped and the required braking force for the vehicle, and then operates the friction braking unit based on the target friction braking force to stop the vehicle, thereby performing reverse movement suppression control. Brake control device.

2. The braking control unit performs a reduction correction control as the stopping control, which stops the vehicle when the sum of the regenerative braking force and the friction braking force is less than the required braking force. The braking control device according to claim 1.

3. The vehicle has a wheel speed sensor that outputs a pulse signal including pulses that occur at a period corresponding to the rotational speed of the vehicle's wheels. The reverse movement detection unit detects that the vehicle has started moving in the reverse direction when it detects that the number of pulses output from the wheel speed sensor is greater than a reference value which is the number at which the vehicle is estimated to have stopped, or when the interval between pulses becomes longer and then shorter. A braking control device according to claim 1 or claim 2.

4. The regenerative braking unit comprises a motor generator and a rotation angle sensor for detecting the rotation angle of the motor generator. The reverse movement detection unit detects that the vehicle has started moving in the reverse direction when the polarity of the detection signal output from the rotation angle sensor is reversed. A braking control device according to claim 1 or claim 2.

5. The vehicle is equipped with an acceleration sensor that detects the longitudinal acceleration of the vehicle, The reverse movement detection unit detects that the vehicle has started moving in the reverse direction based on the value detected by the acceleration sensor and information regarding the gradient of the road surface on which the vehicle is located. A braking control device according to claim 1 or claim 2.

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