Brake control system

Abstract

When switching control is performed to stop a vehicle, this prevents the vehicle from moving in the opposite direction to its previous direction of movement once it has stopped. [Solution] The braking control device 70 is applied to a vehicle 10 which is equipped with wheels 13, a regenerative braking unit 20, and a friction braking unit 40. The braking control device 70 performs substitution control when stopping the vehicle 10. When substitution control is performed, the braking control device 70 functions as a residual regenerative braking force derivation unit 202 which derives the residual regenerative braking force, which is a predicted value of the regenerative braking force at the time the vehicle 10 stops, and a braking control unit 204 which operates the friction braking unit 40 so that the vehicle 10 stops with a friction braking force that is greater the greater the residual regenerative braking force.

Description

[[Technical Field]]

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

[0002] Patent Document 1 discloses a braking control device that controls regenerative braking force and frictional 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 the braking force. Then, when the vehicle stops, the braking control device increases the frictional braking force. [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Application 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 predicted 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, there is a possibility that the regenerative braking force has not yet become zero at the time 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 rotation of a 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 wheels, 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. When stopping the vehicle, the braking control device performs substitution control by activating the regenerative braking unit and the friction braking unit to decrease the regenerative braking force and increase the friction braking force. The braking control device comprises a residual regenerative braking force derivation unit that derives a residual regenerative braking force, which is a predicted value of the regenerative braking force at the time the vehicle stops, based on information related to the rotation of the wheels and the rate of decrease of the regenerative braking force when the substitution control is being executed, and a braking control unit that sets a target friction braking force that is larger the greater the residual regenerative braking force, and activates the friction braking unit so that the vehicle stops with the target friction braking force applied to the vehicle. [Effects of the Invention]

[0008] The above-mentioned braking control device has the effect of preventing a vehicle that has come to a complete stop from moving in the opposite direction to its previous direction of movement when a vehicle substitution control is performed just before the vehicle comes to a complete stop. [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 the first embodiment. [Figure 2] Figures 2(a) to 2(e) are timing charts showing an example of the changes in various parameters when vehicle swapping control is performed just before the vehicle in Figure 1 comes to a stop. [Figure 3]Figure 3 is a flowchart showing the first half of the series of processes executed when a braking request occurs in the braking control device shown in Figure 1. [Figure 4] Figure 4 is a flowchart showing the latter half of the series of processes executed when a braking request occurs in the braking control device shown in Figure 1. [Figure 5] Figures 5(a) to 5(d) are timing charts showing examples of the changes in various parameters when the braking control device in Figure 1 performs substitution control. [Figure 6] Figure 6 is a flowchart showing a portion of the series of processes executed when a braking request occurs in the braking control device of the second embodiment. [Modes for carrying out the invention]

[0010] (First Embodiment) A first embodiment of the braking control device will be described with reference to Figures 1 to 5. <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 corresponding to the rotation speed of the output shaft. The rotation angle of the output shaft 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 value 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 frictional 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, by pressing the friction portion 44 against the rotating body 43, a frictional braking force is generated at the wheel 13. The force that presses 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 frictional braking force at the wheel 13 as the wheel pressure becomes higher. The sum of the frictional braking forces generated by the plurality of wheels 13 corresponds to "the frictional 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 pressurization source that can supply brake fluid to the plurality of wheel cylinders 42. The pressurization 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 cylinder 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 include a sensor that detects the operating force of the braking operation member 11 applied by the driver.

[0020] Multiple wheel speed sensors 62 detect the rotational speed of the corresponding wheel 13. Specifically, the wheel speed sensors 62 output pulse signals as detection signals corresponding to the rotational speed of the corresponding wheel 13. The lower the rotational speed of the wheel 13, the longer the generation period of the pulses included in the pulse signal. The rotational speed of the wheel 13 based on the detection signals of the wheel speed sensors 62 is referred to as "wheel speed VW".

[0021] The acceleration sensor 63 detects the longitudinal acceleration of the vehicle 10. The longitudinal acceleration based on the detection signal from the acceleration sensor 63 is referred to as "longitudinal acceleration GX". <Braking control device> The braking control device 70 activates the braking actuator 50 of the friction braking unit 40. The braking control device 70 is configured to send and receive various information and commands with the regenerative braking control device 30. Therefore, when the vehicle is being braked, the braking control device 70 can adjust the deceleration of the vehicle 10 by operating the braking actuator 50 and coordinating with the regenerative braking control device 30. In other words, 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 effective 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. The second memory 74 stores the calculation results of the CPU 72. By the CPU 72 executing the control program in the first memory 73, the processing circuit 71 can operate the friction braking unit 40 and adjust the friction braking force FbF. The processing circuit 71 can also adjust the effective regenerative braking force FbE by transmitting instructions regarding regenerative braking force to the regenerative control device 30.

[0023] <Regenerative Cooperative Control> The regenerative cooperative control performed by the braking control device 70 will be described below. The processing circuit 71 of the braking control device 70 derives the required braking force FbRq, which is the required value of the total braking force Fb. The processing circuit 71 transmits information regarding the required braking force FbRq to the regenerative control device 30.

[0024] The processing circuit 31 of the regenerative control device 30 functions as a regenerative control unit 101 and derives a target regenerative braking force FbETr based on the requested braking force FbRq indicated by the received information. For example, the processing circuit 31 sets the target regenerative braking force FbETr to the smaller of the regenerative braking force limit value and the 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 processing circuit 31 operates the motor generator 21 based on the target regenerative braking force FbETr.

[0025] The processing circuit 71 of the braking control device 70 sets the target friction braking force FbFTr based on the effective regenerative braking force FbE and the required braking force FbRq. The target friction braking force FbFTr is the target value of the friction braking force FbF. If the effective regenerative braking force FbE is equal to the required braking force FbRq, the processing circuit 71 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 processing circuit 71 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 processing circuit 71 operates the braking actuator 50 based on the target friction braking force FbFTr.

[0026] <Substitution control> Referring to Figure 2, the substitution control performed by the braking control device 70 will be explained. The processing circuit 71 of the braking control device 70 performs substitution control to reduce the effective regenerative braking force FbE and increase the frictional braking force FbF when stopping the vehicle 10 by applying braking force. The "substitution control" referred to here is substitution control that is performed just before the vehicle 10 comes to a complete stop.

[0027] In the example shown in Figure 2, before the timing t11 when the substitution control is initiated, only the regenerative braking force among the regenerative braking force and friction braking force is applied to the vehicle 10. Then, at the timing t13 after the substitution control is completed, the vehicle 10 comes to a stop.

[0028] As shown in Figures 2(a) to (e), at timing t11 while the vehicle 10 is decelerating due to the application of braking force, the processing circuit 71 determines that the execution conditions for the substitution control have been met. For example, the processing circuit 71 determines that the execution conditions have been met when the vehicle speed VS of the vehicle 10 is less than or equal to the start determination speed VSth. The vehicle speed VSth is set as the vehicle speed that serves as the criterion for determining whether or not the vehicle 10 is traveling at an extremely low speed. The vehicle speed VS is a calculated value of the vehicle 10's travel speed derived based on the wheel speeds VW of the multiple wheels 13. When the execution conditions are met, the processing circuit 71 sends a command to the regenerative control device 30 of the regenerative braking unit 20 to reduce the regenerative braking force to 0 (zero).

[0029] When the processing circuit 31 of the regenerative control device 30 receives the above command, it reduces the target regenerative braking force FbETr at a predetermined speed. Then, the processing circuit 31 operates the motor generator 21 based on the latest value of the target regenerative braking force FbETr. As a result, the effective regenerative braking force FbE decreases.

[0030] The processing circuit 71 of the braking control device 70 acquires the effective regenerative braking force FbE at predetermined intervals. The processing circuit 71 sets the difference between the required braking force FbRq and the effective regenerative braking force FbE as the target friction braking force FbFTr. When substitution control is performed, the effective regenerative braking force FbE gradually decreases, as shown in Figure 2(d). Therefore, even if the required braking force FbRq is maintained, as shown in Figure 2(a), the target friction braking force FbFTr gradually increases. The processing circuit 71 then operates the braking actuator 50 based on this target friction braking force FbFTr. As a result, the processing circuit 71 can increase the friction braking force FbF while decreasing the effective regenerative braking force FbE.

[0031] In the example shown in Figure 2, the effective regenerative braking force FbE becomes 0 (zero) at timing t12, which is before the timing t13 when the vehicle 10 stops. Therefore, the processing circuit 71 replaces the effective regenerative braking force FbE with the friction braking force FbF, i.e., terminates the replacement control. Then, at timing t13, the vehicle 10 stops.

[0032] <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 multiple functional units when the CPU 72 executes the control program of the first memory 73. These multiple functional units include a request setting unit 201, a residual regenerative braking force extraction unit 202, a stop determination unit 203, and a braking control unit 204.

[0033] 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.

[0034] The residual regenerative braking force derivation unit 202 derives the residual regenerative braking force FbER at predetermined intervals when substitution control is being performed. The residual regenerative braking force FbER is a predicted value of the effective regenerative braking force FbE at the time the vehicle 10 stops.

[0035] Here, the substitution control is a control that substitutes the effective regenerative braking force FbE with the friction braking force FbF so that the effective regenerative braking force FbE becomes 0 (zero) before the vehicle 10 comes to a stop. However, if the calculated vehicle speed VS is smaller than the actual vehicle speed, or if the deceleration of the vehicle 10 is larger than expected, the vehicle 10 may come to a stop before the effective regenerative braking force FbE becomes 0 (zero).

[0036] Therefore, the residual regenerative braking force derivation unit 202 derives the residual regenerative braking force FbER based on information regarding the rotation of the wheels 13 and the rate of decrease of the effective regenerative braking force FbE. For example, the residual regenerative braking force derivation unit 202 predicts the stopping time of the vehicle 10 based on the wheel speed VW and the wheel acceleration DVW, which is the time derivative of the wheel speed VW. The residual regenerative braking force derivation unit 202 may derive the time when the wheel speed VW becomes 0 (zero) if the current wheel acceleration DVW is maintained as the predicted stopping time. Then, the residual regenerative braking force derivation unit 202 estimates the effective regenerative braking force FbE still applied to the vehicle 10 at the predicted stopping time based on the current effective regenerative braking force FbE and the rate of decrease of the effective regenerative braking force FbE. The residual regenerative braking force derivation unit 202 derives the residual regenerative braking force FbER based on the estimated value of the effective regenerative braking force FbE. That is, if the estimated value of the effective regenerative braking force FbE is greater than 0 (zero), the residual regenerative braking force derivation unit 202 derives this estimated value as the residual regenerative braking force FbER. On the other hand, if the estimated value of the effective regenerative braking force FbE is less than 0 (zero), the residual regenerative braking force derivation unit 202 derives 0 (zero) as the residual regenerative braking force FbER. In this case, the wheel speed VW and wheel acceleration DVW correspond to "information regarding the rotation of the wheel 13".

[0037] The stop determination unit 203 determines whether or not the vehicle 10 has stopped. For example, the stop determination unit 203 determines that the vehicle 10 has stopped when the duration of the state in which the vehicle speed VS is 0 (zero) reaches a predetermined stop determination time.

[0038] As described above, the detection signal from the wheel speed sensor 62 is a pulse signal corresponding to the rotational speed of the wheel 13. Therefore, when the wheel 13 is rotating, the braking control device 70 receives pulses from the wheel speed sensor 62 at a frequency corresponding to the rotational speed of the wheel 13. On the other hand, when the rotation of the wheel 13 stops, that is, when the vehicle 10 stops, the braking control device 70 no longer receives pulses from the wheel speed sensor 62.

[0039] Therefore, the stop determination unit 203 may determine that the vehicle 10 has stopped if a predetermined measurement time has elapsed since the last pulse was input from the wheel speed sensor 62 to the brake control device 70 and no further pulse is input.

[0040] When a braking request is received, the braking control unit 204 performs the above-mentioned regenerative cooperative control based on the requested braking force FbRq. In this state, when the vehicle speed VS falls below the start determination speed VSth, the braking control unit 204 performs substitution control.

[0041] When the braking control unit 204 is performing substitution control, it operates the braking actuator 50 of the friction braking unit 40 so that the vehicle 10 stops with a friction braking force FbF that is greater the greater the remaining regenerative braking force FbER. For example, when the braking control unit 204 is performing substitution control, it performs a determination process at predetermined control cycles to determine whether the remaining regenerative braking force FbER is greater than a threshold FbERth.

[0042] 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 after the vehicle 10 comes to a complete stop, the vehicle 10 may move in the opposite direction to its previous movement.

[0043] Therefore, when the vehicle 10 stops, the effective regenerative braking force FbE is greater than 0 (zero), and a braking force equal to or less than that is set as the threshold FbERth, which serves as the criterion for determining whether the vehicle 10 will move in the opposite direction. For example, 0 (zero) is set as the threshold FbERth. Of course, a braking force greater than 0 (zero) may also be set as the threshold FbERth.

[0044] The braking control unit 204 performs a stopping increase process to activate the braking actuator 50 of the friction braking unit 40 so that the vehicle 10 stops when the sum of the remaining regenerative braking force FbER and the friction braking force FbF is greater than the required braking force FbRq, provided that the remaining regenerative braking force FbER is greater than the threshold FbERth. On the other hand, the braking control unit 204 does not perform the stopping increase process when the remaining regenerative braking force FbER is less than or equal to the threshold FbERth.

[0045] In one example of the stopping increase process, the braking control unit 204 increases the target friction braking force FbFTr. For example, the braking control unit 204 increases the target friction braking force FbFTr so that at the predicted stopping time, the target friction braking force FbFTr is equal to the sum of the remaining regenerative braking force FbER and the required braking force FbRq. Then, the braking control unit 204 operates the braking actuator 50 based on the target friction braking force FbFTr. As a result, the braking control unit 204 can stop the vehicle 10 with a friction braking force FbF that increases as the remaining regenerative braking force FbER increases.

[0046] When the braking control unit 204 is performing the stopping increase processing, if the stopping determination unit 203 determines that the vehicle 10 has stopped, the braking control unit 204 terminates the stopping increase processing. Then, the braking control unit 204 sets the requested braking force FbRq to the target friction braking force FbFTr and operates the braking actuator 50 based on the said target friction braking force FbFTr.

[0047] <Braking control processing> Referring to Figures 3 and 4, a series of processes executed by the processing circuit 71 of the braking control device 70 when a braking request occurs will be described. The series of processes shown in Figures 3 and 4 will be referred to as the "braking control process". When a braking request occurs, the processing circuit 71 executes the braking control process.

[0048] As shown in Figure 3, in step S11, the processing circuit 71 acquires various information necessary for braking control of the vehicle 10. For example, the processing circuit 71 acquires the wheel speed VW, wheel acceleration DVW, vehicle speed VS, longitudinal acceleration GX, and braking operation amount Ba.

[0049] In the subsequent step S13, the processing circuit 71 functions as a request setting unit 201 to set the requested braking force FbRq. In the next step S15, the processing circuit 71, functioning as a braking control unit 204, determines whether the conditions for executing the substitution control are met. If the processing circuit 71 determines that the conditions are not met (S15: NO), the processing circuit 71 proceeds to step S17.

[0050] In step S17, the processing circuit 71 functions as a stop determination unit 203 to determine whether or not the vehicle 10 has stopped. If the processing circuit 71 determines that the vehicle 10 has stopped (S17: YES), the processing circuit 71 proceeds to step S37. On the other hand, if the processing circuit 71 determines that the vehicle 10 has not stopped (S17: NO), the processing circuit 71 proceeds to step S19.

[0051] In step S19, the processing circuit 71 performs the regenerative cooperative control described above by functioning as the braking control unit 204. Then, the processing circuit 71 proceeds to step S11.

[0052] On the other hand, if the processing circuit 71 determines in step S15 that the execution condition is met (S15: YES), the processing circuit 71 starts the substitution control by functioning as the braking control unit 204.

[0053] Specifically, in step S21, the processing circuit 71 functions as a braking control unit 204 and instructs the regenerative control device 30 of the regenerative braking unit 20 to reduce the effective regenerative braking force FbE. Then, the processing circuit 71 proceeds to step S23.

[0054] In step S23, the processing circuit 71 obtains the current effective regenerative braking force FbE. In the subsequent step S24, the processing circuit 71 functions as a request setting unit 201 to set the requested braking force FbRq.

[0055] In the next step S25, the processing circuit 71 functions as a braking control unit 204 and sets the difference between the latest value of the requested braking force FbRq and the actual regenerative braking force FbE as the target friction braking force FbFTr.

[0056] In the subsequent step S27, the processing circuit 71 derives the residual regenerative braking force FbER by functioning as a residual regenerative braking force derivation unit 202. That is, the processing circuit 71 derives the residual regenerative braking force FbER when substitution control is being performed.

[0057] Then, in step S29, the processing circuit 71 determines whether the remaining regenerative braking force FbER is greater than the threshold FbERth. If the remaining regenerative braking force FbER is greater than the threshold FbERth (S29: YES), the processing circuit 71 proceeds to step S31. On the other hand, if the remaining regenerative braking force FbER is less than or equal to the threshold FbERth (S29: NO), the processing circuit 71 proceeds to step S33.

[0058] In step S31, the processing circuit 71, functioning as a braking control unit 204, increases and corrects the target friction braking force FbFTr derived in step S25. Then, the processing circuit 71 proceeds to step S33.

[0059] In step S33, the processing circuit 71 functions as a braking control unit 204 and activates the braking actuator 50 based on the target friction braking force FbFTr. Activating the braking actuator 50 based on the target friction braking force FbFTr set in step S31 corresponds to the "stopping increase processing". Then, the processing circuit 71 proceeds to step S35.

[0060] In step S35, the processing circuit 71 functions as a stop determination unit 203 to determine whether or not the vehicle 10 has stopped. If the processing circuit 71 determines that the vehicle 10 has not stopped (S35: NO), the processing circuit 71 proceeds to step S23. In this case, the processing circuit 71 continues the substitution control. On the other hand, if the processing circuit 71 determines that the vehicle 10 has stopped (S35: YES), the processing circuit 71 proceeds to step S37.

[0061] As shown in Figure 4, in step S37, the processing circuit 71 functions as a request setting unit 201 to set the requested braking force FbRq. In the following step S39, the processing circuit 71, acting as a braking control unit 204, sets the requested braking force FbRq to the target friction braking force FbFTr. In the next step S41, the processing circuit 71, acting as a braking control unit 204, activates the braking actuator 50 based on the target friction braking force FbFTr.

[0062] In the following step S43, the processing circuit 71 determines whether or not there is a braking request. For example, if the requested braking force FbRq is greater than 0 (zero), it is considered that there is a braking request. On the other hand, if the requested braking force FbRq is 0 (zero), it is considered that there is no braking request. If the processing circuit 71 determines that there is a braking request (S43: YES), the processing circuit 71 proceeds to step S37. On the other hand, if the processing circuit 71 determines that there is no braking request (S43: NO), the processing circuit 71 terminates the braking control process.

[0063] <Operation and Effects of This Embodiment> The operation and effects of this embodiment will be explained with reference to Figure 5. As shown in Figures 5(a) to (d), 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 substitution control have been met, and therefore the processing circuit 71 starts the substitution control. At timing t21, the processing circuit 71 predicts that the vehicle 10 will stop at timing t24 and instructs the regenerative control device 30 of the regenerative braking unit 20 to reduce the regenerative braking force.

[0064] The processing circuit 71 predicts the stopping time of the vehicle 10 based on information related to the rotation of the wheels 13, when the effective regenerative braking force FbE decreases and the friction braking force FbF increases due to the substitution control. That is, the processing circuit 71 determines the predicted stopping time while the substitution control is being executed. At timing t22 during the execution of the substitution control, the processing circuit 71 determines timing t23, which is earlier than timing t24, as the predicted stopping time. Furthermore, the processing circuit 71 derives the predicted value of the effective regenerative braking force FbE at timing t23 as the remaining regenerative braking force FbER, based on the effective regenerative braking force FbE and the rate of decrease of the effective regenerative braking force FbE.

[0065] In the example shown in Figure 5, the processing circuit 71 determines that the remaining regenerative braking force FbER is greater than the threshold FbERth (=0), and therefore starts the stopping increase process. During the stopping increase process, the processing circuit 71 increases the target friction braking force FbFTr. As a result, as shown in Figures 5(c) and 5(d), the rate of decrease of the effective regenerative braking force FbE remains unchanged, while the rate of increase of the friction braking force FbF becomes larger compared to before timing t22. Consequently, as shown in Figure 5(b), the total braking force Fb becomes greater than the required braking force FbRq.

[0066] Then, the vehicle 10 actually stops at a timing slightly before timing t23. The dashed line in Figure 5(d) shows the progression of the friction braking force FbF when the substitution control is performed as usual. As shown in Figure 5(d), when residual regenerative braking force FbER is generated, the processing circuit 71 can stop the vehicle 10 with a friction braking force FbF that is larger the larger the residual regenerative braking force FbER is applied to the vehicle 10. As a result, even if a rotational limiting torque TqE is output to the axle 14 because the effective regenerative braking force FbE was not 0 (zero) when the vehicle 10 actually stopped, the vehicle 10, once stopped, is prevented from moving in the opposite direction of its previous movement due to the application of friction braking force.

[0067] When the processing circuit 71 determines that the vehicle 10 has stopped, it sets the required braking force FbRq to the target friction braking force FbFTr and then activates the braking actuator 50. This allows the processing circuit 71 to maintain the vehicle 10 in a stopped state.

[0068] (Second Embodiment) A second embodiment of the braking control device will be described with reference to Figure 6. Note that the execution conditions for the stopping-time increase process differ in the second embodiment from those of the first embodiment. In the following description, the differences from the first embodiment will be primarily explained, and identical component components are denoted by the same reference numerals to avoid redundant explanations.

[0069] <Braking control processing> Referring to Figure 6, the braking control processing performed by the braking control device 70 of the second embodiment will be explained, focusing on the parts that differ from the braking control processing performed by the braking control device 70 of the first embodiment.

[0070] In step S27, the processing circuit 71 functions as a residual regenerative braking force derivation unit 202 to derive the residual regenerative braking force FbER. In the following step S29, if the remaining regenerative braking force FbER is greater than the threshold FbERth (S29: YES), the processing circuit 71 proceeds to step S30. On the other hand, if the remaining regenerative braking force FbER is less than or equal to the threshold FbERth (S29: NO), the processing circuit 71 proceeds to step S33.

[0071] In step S30, the processing circuit 71 determines whether the current friction braking force FbF is less than the remaining regenerative braking force FbER. If the processing circuit 71 determines that the friction braking force FbF is less than the remaining regenerative braking force FbER (S30: YES), the processing circuit 71 proceeds to step S31. On the other hand, if the processing circuit 71 determines that the friction braking force FbF is greater than or equal to the remaining regenerative braking force FbER (S30: NO), the processing circuit 71 proceeds to step S33.

[0072] In other words, the processing circuit 71 performs the stopping increase process when the residual regenerative braking force FbER is greater than the threshold FbERth and the friction braking force FbF is less than the residual regenerative braking force FbER. On the other hand, the processing circuit 71 does not perform the stopping increase process when the residual regenerative braking force FbER is greater than the threshold FbERth, but the friction braking force FbF is greater than or equal to the residual regenerative braking force FbER.

[0073] <Operation and Effects of This Embodiment> The braking control device 70 of the second embodiment can obtain the following effects in addition to the same effects as the first embodiment described above.

[0074] In the braking control device 70 of the second embodiment, the processing circuit 71 does not perform the stopping increase process if the friction braking force FbF is already equal to or greater than the residual regenerative braking force FbER, even if the residual regenerative braking force FbER is greater than the threshold FbERth. In other words, if it is possible to prevent the vehicle 10 from moving in the opposite direction of its previous movement after it has stopped without applying a larger friction braking force FbF to the vehicle 10, the processing circuit 71 does not perform the stopping increase process. Therefore, the braking control device 70 of the second embodiment can prevent the friction braking force FbF from becoming excessive in order to prevent the vehicle 10 from moving in the opposite direction after it has stopped.

[0075] (Example of change) The above embodiments can be implemented with the following modifications. The above embodiments and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0076] A braking force greater than 0 (zero) may be set to the threshold FbERth. In the above embodiment, the processing circuit 71, i.e., the residual regenerative braking force derivation unit 202, determines the predicted stopping time of the vehicle 10 based on the change in wheel speed VW when substitution control is being performed. The processing circuit 71 then derives the actual regenerative braking force FbE at the predicted stopping time as the residual regenerative braking force FbER. The processing circuit 71 may derive the residual regenerative braking force FbER by a method other than the above method, as long as it can derive the residual regenerative braking force FbER.

[0077] The processing circuit 71, i.e., the braking control unit 204, may increase the target friction braking force FbFTr in the stopping increase processing using a method different from the method described in the above embodiment, provided that it is possible to increase the target friction braking force FbFTr. For example, the processing circuit 71 may set the target friction braking force FbFTr in the stopping increase processing such that the sum of the decrease rate of the effective regenerative braking force FbE and a predetermined offset value becomes the increase rate of the target friction braking force FbFTr.

[0078] 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.

[0079] 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 204. 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 other than the first functional unit among the multiple functional units 201 to 204.

[0080] 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.

[0081] (Other technological ideas) This section describes the technical concepts that can be understood from the above-mentioned multiple embodiments and modifications. [Note 1] The vehicle is equipped with a stop determination unit that determines whether or not the vehicle has stopped. Preferably, if the braking control unit determines that the vehicle has stopped while the stopping-increase process is being executed, it terminates the stopping-increase process and operates the friction braking unit so that the friction braking force becomes equal to the required braking force.

[0082] 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]

[0083] 10... Vehicles 13...Wheel 20...Regenerative braking section 21…Motor Generator 40...Friction brake part 41… Friction brakes 50... Brake actuator 70... Brake control device 71…Processing circuit 101...Regenerative Control Unit 201...Requirement setting section 202...Residual regenerative braking force derivation section 203...Stop judgment section 204... Brake Control Unit

Claims

1. A braking control device applied to a vehicle comprising wheels, a regenerative braking unit for applying regenerative braking force to the vehicle, and a friction braking unit for applying friction braking force to the vehicle, wherein when stopping the vehicle, the device performs substitution control to reduce the regenerative braking force and increase the friction braking force by activating the regenerative braking unit and the friction braking unit, When the substitution control is being performed, a residual regenerative braking force derive unit derives a residual regenerative braking force, which is a predicted value of the regenerative braking force at the time the vehicle stops, based on information related to the rotation of the wheels and the rate of decrease of the regenerative braking force. The system includes a braking control unit that sets a target friction braking force that is larger the greater the residual regenerative braking force, and operates the friction braking unit so that the vehicle comes to a stop when the target friction braking force is applied to the vehicle. Brake control device.

2. The system includes a request setting unit that sets a required braking force, which is the required value of the total braking force, which is the sum of the regenerative braking force and the friction braking force. The braking control unit, when the remaining regenerative braking force is greater than a threshold, performs a stopping increase process by activating the friction braking unit to increase the friction braking force so that the vehicle stops when the sum of the remaining regenerative braking force and the friction braking force is greater than the required braking force. The braking control device according to claim 1.

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