Braking control device

Abstract

To reduce power consumption when a vehicle is stopped. [Solution] A brake control device 80 is applied to a vehicle 10 equipped with a hydraulic braking device 50 and an electric parking device 60. A processing circuit 81 of the brake control device 80 includes a stop control unit 113 that activates the hydraulic braking device 50 so that the vehicle 10 is stopped by applying hydraulic braking force, a hold control unit 115 that executes stop hold control, including activating the electric parking device 60 so that the parking braking force increases toward a holding braking force that is greater than the hydraulic braking force at the time the vehicle 10 is stopped, and activating the hydraulic braking device 50 so that the hydraulic braking force decreases to 0 (zero), and a setting unit 117 that sets at least one of the increase rate of the parking braking force and the holding braking force when the stop hold control is being executed, based on the required braking force.

Description

[Technical Field]

[0001] The present invention relates to a brake control device applied to a vehicle. [Background technology]

[0002] The braking control device disclosed in Patent Document 1 is applied to a vehicle equipped with a hydraulic braking device and an electric parking device. The hydraulic braking device is equipped with an electric brake actuator and can apply hydraulic braking force to the vehicle in accordance with the operation of the brake actuator. The hydraulic braking device can maintain the hydraulic braking force by energizing a solenoid valve equipped in the brake actuator to keep the solenoid valve operating.

[0003] When the brake hold control is permitted under the condition that the vehicle is stopped by applying hydraulic braking force, the braking control device applies parking braking force to the vehicle by operating the electric parking device. At this time, the braking control device also applies hydraulic braking force to the vehicle according to the difference between the target braking force and the parking braking force. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2022-173338 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned braking control device can maintain the vehicle in a stopped state by applying both parking braking force and hydraulic braking force. However, in a braking system equipped with both a hydraulic braking device and an electric parking device as described above, it is required to reduce power consumption when the vehicle is stopped. [Means for solving the problem]

[0006] A brake control device for solving the above problem is applied to a vehicle equipped with a hydraulic braking device having an electric operating unit that operates to adjust hydraulic pressure in wheel cylinders and applies hydraulic braking force to the vehicle according to the hydraulic pressure in the wheel cylinders, and an electric parking device having an electric motor that increases the parking braking force applied to the vehicle by driving the electric motor. The brake control device includes a stop control unit that operates the hydraulic braking device so that the vehicle is stopped by applying the hydraulic braking force, a hold control unit that executes stop hold control, including operating the electric parking device so that the parking braking force increases toward a hold braking force that is greater than the hydraulic braking force at the time the vehicle is stopped and operating the hydraulic braking device so that the hydraulic braking force decreases to 0 (zero), and a setting unit that sets at least one of the increase rate of the parking braking force and the hold braking force during execution of the stop hold control, based on a required braking force that is a required value of the braking force of the vehicle. [Effects of the Invention]

[0007] The braking control device has the effect of reducing power consumption when the vehicle is stopped. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a vehicle equipped with a braking control device according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view that schematically shows a friction brake for a second wheel provided on the vehicle of FIG. 1 and a parking actuator of an electric parking device. [Figure 3] 3(a) to 3(f) are timing charts when the braking control device of the first embodiment applies braking force to stop the vehicle. [Figure 4] FIG. 4 is a flowchart showing a series of processes executed when adjusting the braking force applied to the vehicle in the brake control device of the first embodiment. [Figure 5]FIG. 5 is a flowchart showing the vehicle stop maintenance control of FIG. [Figure 6] FIG. 6 is a flowchart showing a series of processes executed when the brake control device of the first embodiment detects movement of the vehicle after determining that the vehicle has stopped. [Figure 7] 7(a) to 7(c) are timing charts showing the sequence of steps shown in FIG. 6 when they are executed. [Figure 8] 8(a) to 8(c) are timing charts when the brake control device of the second embodiment detects the movement of the vehicle after determining that the vehicle has stopped. [Figure 9] FIG. 9 is a flowchart showing a part of a series of processes executed when adjusting the braking force applied to the vehicle in the brake control device of the third embodiment. [Figure 10] FIG. 10 is a flowchart showing the vehicle stop maintenance control in the brake control device of the fourth embodiment. [Figure 11] 11(a) to 11(d) are timing charts for when the series of processes shown in FIG. 10 are executed. [Figure 12] FIG. 12 is a block diagram showing a braking control device according to the fifth embodiment. [Figure 13] FIG. 13 is a flowchart showing a part of a series of processes executed when adjusting the braking force applied to the vehicle in the brake control device of the fifth embodiment. [Figure 14] 14(a) to 14(f) are timing charts for when the series of processes shown in FIG. 13 are executed. DETAILED DESCRIPTION OF THE INVENTION

[0009] (First embodiment) A first embodiment of the braking control device will be described with reference to FIGS. <Overall vehicle configuration> Figure 1 shows a vehicle 10 equipped with a braking control device 80. The vehicle 10 further comprises a braking operating member 11, multiple wheels, a regenerative braking device 20, a braking system, and multiple sensors.

[0010] The brake operating member 11 is a member that is operated by the driver when adjusting the deceleration of the vehicle 10. An example of the brake operating member 11 is a brake pedal. Multiple wheels include multiple first wheels 12 and multiple second wheels 13. An example of a first wheel 12 is a front wheel. An example of a second wheel 13 is a rear wheel. Note that in Figure 1, only one of the multiple first wheels 12 and only one of the multiple second wheels 13 are illustrated.

[0011] <Regenerative braking device> The regenerative braking system 20 is configured to apply an effective regenerative braking force FxE to the vehicle 10. In the example shown in Figure 1, the regenerative braking system 20 can apply an effective regenerative braking force FxE to the axle 12a of the first wheel 12. The regenerative braking system 20 includes a motor generator 21 and a regenerative control device 30 that controls the motor generator 21. The motor generator 21 functions as a generator, thereby applying an effective regenerative braking force FxE to the axle 12a.

[0012] 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.

[0013] The regenerative control device 30 is configured to send and receive various information and commands to and from the braking control device 80 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 80.

[0014] 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 FxE by operating the motor generator 21. In other words, the regenerative control unit 101 can adjust the effective regenerative braking force FxE by operating the motor generator 21 based on the target regenerative braking force FxETr, which is the target of the regenerative braking force.

[0015] <Braking system> The braking system comprises multiple friction brakes 40 individually provided for multiple wheels 12, 13, a hydraulic braking device 50, and an electric parking device 60.

[0016] As shown in Figures 1 and 2, each of the multiple friction brakes 40 has a wheel cylinder 41, a rotating body 42, and a friction part 43. The rotating body 42 rotates together with the wheel. Therefore, by pressing the friction part 43 against the rotating body 42, a frictional braking force is applied to the wheel. The force pressing the friction part 43 against the rotating body 42 increases as the wheel pressure, which is the hydraulic pressure inside the wheel cylinder 41, increases. Therefore, the friction brake 40 can apply a greater frictional braking force to the wheel as the wheel pressure increases. Hereafter, the frictional braking force applied to the wheel by the wheel pressure will be referred to as "hydraulic braking force". The sum of the hydraulic braking forces applied to the multiple wheels 12, 13 will be referred to as the "hydraulic braking force FxR" applied to the vehicle 10.

[0017] The hydraulic braking system 50 is configured to adjust the hydraulic braking force FxR by controlling the wheel pressure of multiple wheel cylinders 41. The hydraulic braking system 50 includes a pressurizing unit 51. The pressurizing unit 51 has a supply source for supplying brake fluid. Examples of supply sources include electric cylinders and electric pumps. Multiple supply channels 55 are connected to the pressurizing unit 51 for supplying brake fluid to the wheel cylinders 41. The pressurizing unit 51 can adjust the wheel pressure of the wheel cylinders 41 by supplying brake fluid to the wheel cylinders 41 via the supply channels 55.

[0018] The hydraulic braking device 50 is equipped with multiple solenoid valves 52, each installed in one of the multiple supply passages 55. The multiple solenoid valves 52 are normally open solenoid valves. The solenoid valves 52 are closed by energizing their solenoids. When the solenoid valves 52 are closed, the outflow of brake fluid from the wheel cylinder 41 corresponding to the solenoid valve 52 is restricted, thereby maintaining wheel pressure.

[0019] Furthermore, the pressurizing unit 51 and the multiple solenoid valves 52 correspond to the electrically operated "actuated parts" that operate to adjust the wheel pressure. As shown in Figures 1 and 2, the electric parking device 60 has a plurality of parking actuators 61. The plurality of parking actuators 61 are integrated with the friction brakes 40 of the corresponding second wheels 13. The parking actuator 61 has an electric motor 62 and a conversion mechanism 63 that converts the rotational motion of the rotating shaft 62a of the electric motor 62 into linear motion and transmits it to the piston 41a of the wheel cylinder 41. When the piston 41a moves linearly due to the driving of the electric motor 62, the friction part 43 of the friction brake 40 is pressed against the rotating body 42. This applies a friction braking force to the second wheel 13. In other words, the electric parking device 60 can increase the friction braking force by driving the electric motor 62. Hereafter, the friction braking force applied to the second wheel 13 by the operation of the parking actuator 61 will be referred to as "parking braking force". The sum of the parking braking forces applied to the plurality of second wheels 13 will be referred to as "parking braking force FxP" applied to the vehicle 10.

[0020] The conversion mechanism 63 of the parking actuator 61 has a self-locking function. In other words, if the driving force of the electric motor 62 is not transmitted to the conversion mechanism 63, the components of the conversion mechanism 63 will not operate. Therefore, even if the power supply to the electric motor 62 is stopped while the parking braking force FxP has increased due to the operation of the electric motor 62, the parking braking force FxP can be maintained by the self-locking function of the conversion mechanism 63.

[0021] <Sensor> As shown in Figure 1, the multiple sensors output signals to the braking control device 80 according to the detection results. The multiple sensors include, for example, a brake sensor 71, multiple wheel speed sensors 72, and an acceleration sensor 73. The brake sensor 71 detects information related to the driver's operation of the braking control member 11. An example of the brake sensor 71 is a stroke sensor that detects the amount of operation of the driver's braking control member 11. The amount of operation based on the detection signal of the brake sensor 71 is referred to as "braking operation amount X". The vehicle 10 may also be equipped with a sensor that detects the operating force of the driver's braking control member 11.

[0022] Multiple wheel speed sensors 72 detect the rotational speed of the corresponding wheel. For example, a wheel speed sensor 72 outputs a pulse signal as a detection signal corresponding to the rotational speed of the corresponding wheel. The rotational speed of the wheel based on the detection signal of the wheel speed sensor 72 is referred to as "wheel speed VW".

[0023] The acceleration sensor 73 detects the longitudinal acceleration of the vehicle 10. The longitudinal acceleration based on the detection signal from the acceleration sensor 73 is referred to as "longitudinal acceleration GX". <Brake control device> As shown in Figure 1, the braking control device 80 adjusts the braking force of the vehicle 10 by controlling the regenerative braking device 20, the hydraulic braking device 50, and the electric parking device 60. The braking control device 80 is equipped with a processing circuit 81. An example of the processing circuit 81 is an electronic control device. In this case, the processing circuit 81 has a CPU 82, a first memory 83, and a second memory 84. The first memory 83 stores the control program executed by the CPU 82. The second memory 84 stores the calculation results of the CPU 82, etc.

[0024] The processing circuit 81 performs regenerative cooperative control when it decelerates the vehicle 10 in accordance with a braking request. When the vehicle 10 is about to come to a stop due to the deceleration of the vehicle 10 accompanying the execution of regenerative cooperative control, the processing circuit 81 performs stopping control. When the vehicle 10 has come to a stop due to the execution of stopping control, the processing circuit 81 performs stopping hold control.

[0025] Referring to Figure 3, regenerative braking control, stopping control, and stopping hold control will be explained. When a braking request is made to the vehicle 10, for example, when the driver starts to operate the brake operating member 11, the processing circuit 81 starts deriving the required braking force FxRq as shown in Figure 3(a). The required braking force FxRq is a required value of the total braking force Fx. Then, the processing circuit 81 starts regenerative cooperative control.

[0026] In regenerative cooperative control, the processing circuit 81 transmits the requested braking force FxRq to the regenerative control device 30. The processing circuit 31 of the regenerative control device 30 derives a target regenerative braking force FxETr based on the requested braking force FxRq, as shown in Figure 3(d). For example, the processing circuit 31 sets the target regenerative braking force FxETr to the smaller of the regenerative braking force limit value and the requested braking force FxRq. 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 FxETr.

[0027] In regenerative braking coordinated control, the processing circuit 81 of the braking control device 80 sets the target hydraulic braking force FxRTr based on the effective regenerative braking force FxE and the required braking force FxRq, as shown in Figure 3(e). The target hydraulic braking force FxRTr is the target value of the hydraulic braking force FxR. If the effective regenerative braking force FxE is equal to the required braking force FxRq, the processing circuit 81 sets the target hydraulic braking force FxRTr to 0 (zero). On the other hand, if the effective regenerative braking force FxE is less than the required braking force FxRq, the processing circuit 81 sets the target hydraulic braking force FxRTr to the difference between the required braking force FxRq and the effective regenerative braking force FxE. Then, the processing circuit 81 operates the hydraulic braking device 50 based on the target hydraulic braking force FxRTr.

[0028] When regenerative cooperative control is being performed, the vehicle body acceleration DVS of vehicle 10 becomes a negative value, as shown in Figure 3(b). In other words, vehicle 10 is decelerating. Then, at timing t11, the processing circuit 81 determines that vehicle 10 is about to come to a stop. For this reason, at timing t11, the processing circuit 81 switches the control from regenerative cooperative control to stopping control.

[0029] When the vehicle 10 is decelerating due to the application of braking force, the processing circuit 81 estimates the stopping position of the vehicle 10 based on the vehicle speed VS and vehicle acceleration DVS. The vehicle speed VS is the vehicle speed of the vehicle 10. The vehicle acceleration DVS is the time derivative of the vehicle speed VS. The processing circuit 81 estimates the stopping position of the vehicle 10 at the point when the vehicle speed VS becomes 0 (zero) if the vehicle 10 continues to decelerate at the current vehicle acceleration DVS. The processing circuit 81 obtains the stopping distance DS, which is the distance from the current position of the vehicle 10 to the said stopping position. Then, when the stopping distance DS becomes less than or equal to the first threshold DSth1, the processing circuit 81 determines that the vehicle 10 is about to stop.

[0030] The vehicle stop control includes an increase process, a replacement process, a decrease process, and a maintenance process. When the vehicle stop distance DS becomes equal to or smaller than the first threshold value DSth1, the processing circuit 81 starts the increase process of the vehicle stop control.

[0031] In the increase process, the processing circuit 81 increases the total braking force Fx of the vehicle 10 to a value greater than the required braking force FxRq, as shown in Figure 3(c). The total braking force Fx is the sum of the effective regenerative braking force FxE, the hydraulic braking force FxR, and the parking braking force FxP. When stop control is being performed, the parking braking force FxP is 0 (zero). Therefore, during the execution of stop control, the total braking force Fx is the sum of the effective regenerative braking force FxE and the hydraulic braking force FxR. In the example shown in Figure 3, the effective regenerative braking force FxE at timing t11 is smaller than the above regenerative braking force limit value. Therefore, in the increase process, the processing circuit 81 increases the effective regenerative braking force FxE by activating the regenerative braking device 20. As a result, the absolute value of the vehicle acceleration DVS increases, as shown in Figure 3(b).

[0032] When the stopping distance DS falls below the second threshold DSth2 at timing t12, the processing circuit 81 switches the processing from the increase processing to the substitution processing. The second threshold DSth2 is greater than 0 (zero) and less than the first threshold DSth1. In the substitution processing, as shown in Figures 3(d) and 3(e), the processing circuit 81 increases the hydraulic braking force FxR to the stopping braking force FxH and decreases the effective regenerative braking force FxE by the amount of the increase in hydraulic braking force FxR. The stopping braking force FxH is the minimum braking force that can stop the vehicle 10, or a braking force slightly greater than that minimum value. For example, the processing circuit 81 sets the stopping braking force FxH to ​​be greater the greater the gradient of the road surface on which the vehicle 10 is traveling.

[0033] The processing circuit 81 operates the hydraulic braking device 50 so that the hydraulic braking force FxR increases to the stopping braking force FxH. The processing circuit 81 also sends an instruction to the regenerative braking device 20 to reduce the target regenerative braking force FxETr by the amount of the increase in hydraulic braking force FxR. The processing circuit 31 of the regenerative braking device 20 then reduces the target regenerative braking force FxETr based on this instruction. The processing circuit 31 then operates the motor generator 21 based on the target regenerative braking force FxETr. As a result, the processing circuit 81 can reduce the effective regenerative braking force FxE by the amount of the increase in hydraulic braking force FxR.

[0034] When the stopping distance DS falls below the third threshold DSth3 at timing t13, the processing circuit 81 of the braking control device 80 switches the processing from substitution processing to reduction processing. The third threshold DSth3 is greater than 0 (zero) and less than the second threshold DSth2. In the reduction processing, the processing circuit 81 reduces the effective regenerative braking force FxE to 0 (zero) before the vehicle 10 comes to a stop. At this time, the processing circuit 81 instructs the regenerative braking device 20 to set the target regenerative braking force FxETr to 0 (zero) before the vehicle 10 comes to a stop.

[0035] When the effective regenerative braking force FxE becomes 0 (zero) due to the reduction process at timing t14, the processing circuit 81 switches the process from reduction to holding. In the holding process, the processing circuit 81 holds the target hydraulic braking force FxRTr at the stopping braking force FxH. This allows the processing circuit 81 to maintain the hydraulic braking force FxR.

[0036] If the processing circuit 81 determines that the vehicle 10 has stopped while the holding process is being executed, it terminates the stopping control. For example, the processing circuit 81 determines that the vehicle 10 has stopped when the stopping distance DS becomes less than or equal to the fourth threshold DSth4. The fourth threshold DSth4 is smaller than the third threshold DSth3. An example of the fourth threshold DSth4 is 0 (zero).

[0037] When the processing circuit 81 determines at timing t15 that the vehicle 10 has stopped due to the execution of the stop-time control, it starts the stop-maintenance control. The stop-maintenance control is a control that increases the total braking force Fx compared to the time when it was determined that the vehicle 10 had stopped. When the vehicle 10 is stopped, the effective regenerative braking force FxE is 0 (zero). Therefore, the total braking force Fx during the execution of the stop-maintenance control is the sum of the hydraulic braking force FxR and the parking braking force FxP.

[0038] In the vehicle stop maintenance control, the processing circuit 81 increases the parking braking force FxP toward the maintenance braking force FxPH, as shown in Fig. 3(f). The processing circuit 81 sets the maintenance braking force FxPH to a braking force greater than the hydraulic braking force FxR at the time when it is determined that the vehicle 10 has stopped. Therefore, it can be said that the maintenance braking force FxPH is greater than the vehicle stop braking force FxH.

[0039] The processing circuit 81 increases the target parking braking force FxPTr according to the instructed increase rate ΔFxPTr, which will be described later. The target parking braking force FxPTr is the target value of the parking braking force FxP. Then, the processing circuit 81 drives the electric motor 62 of the electric parking device 60 based on the target parking braking force FxPTr. When the target parking braking force FxPTr reaches the holding braking force FxPH at timing t17, the processing circuit 81 determines that the parking braking force FxP has reached the holding braking force FxPH. Then, the processing circuit 81 stops driving the electric motor 62. As a result, power is stopped to the electric motor 62.

[0040] Furthermore, in the vehicle stop-hold control, the processing circuit 81 reduces the target hydraulic braking force FxRTr to 0 (zero). Then, the processing circuit 81 activates the hydraulic braking device 50 based on the target hydraulic braking force FxRTr. This allows the processing circuit 81 to reduce the hydraulic braking force FxR to 0 (zero). In this case, in order to suppress the movement of the vehicle 10 due to the reduction in hydraulic braking force FxR, the processing circuit 81 starts reducing the hydraulic braking force FxR from a timing t16, which is later than the timing t15, which is the start timing of the increase in parking braking force FxP. That is, after the hydraulic braking force FxR becomes 0 (zero), the processing circuit 81 can stop supplying power to the solenoid valve 52 for maintaining wheel pressure.

[0041] <Functional configuration of the braking control system> Referring to Figure 1, the functional configuration of the braking control device 80 will be described. When the CPU 82 executes the control program of the first memory 83, the processing circuit 81 functions as multiple functional units for performing stopping control and stopping hold control. The multiple functional units include an acquisition unit 111, a stopping control unit 113, a holding control unit 115, a setting unit 117, and a movement suppression unit 119.

[0042] <Acquisition part> The acquisition unit 111 acquires parameters necessary for executing the vehicle stop control and the vehicle stop maintenance control. For example, the acquisition unit 111 acquires the braking operation amount X, the vehicle speed VS, the vehicle acceleration DVS, the longitudinal acceleration GX, the stopping distance DS, and the effective regenerative braking force FxE.

[0043] The acquisition unit 111 acquires the required braking force FxRq. For example, when the driver is operating the brake operating member 11, the acquisition unit 111 acquires the required braking force FxRq so that the magnitude of the required braking force FxRq increases as the braking operation amount X increases. Even when the driver is not operating the brake operating member 11, a request to decelerate the vehicle 10 may be made by another control device or another functional unit. In this case, the acquisition unit 111 acquires a braking force corresponding to the request to decelerate the vehicle 10 as the required braking force FxRq.

[0044] The acquisition unit 111 acquires the road surface gradient θ, which is the gradient of the road surface on which the vehicle 10 is located. For example, the acquisition unit 111 can acquire the road surface gradient θ as the absolute value of the difference between the vehicle acceleration DVS and the longitudinal acceleration GX.

[0045] The acquisition unit 111 acquires the motor temperature TPepb. One example of the motor temperature TPepb is the temperature of the electric motor 62 of the electric parking device 60. In this case, the acquisition unit 111 may acquire, as the motor temperature TPepb, an estimated value of the temperature of the components of the electric motor 62 based on the magnitude of the current supplied to the electric motor 62, the time for which the electric motor 62 has been energized, and the like. Of course, if the electric motor 62 is provided with a temperature sensor, the acquisition unit 111 may acquire, as the motor temperature TPepb, a value detected by the temperature sensor. For example, the acquisition unit 111 may acquire, as the motor temperature TPepb, an estimated value or a detected value of the temperature of an element in the drive circuit of the electric motor 62.

[0046] <Stop control unit> The stop control unit 113 executes a stop control, that is, the stop control unit 113 executes an increase process, a replacement process, a decrease process, and a holding process in this order.

[0047] In the increasing process, the stopping control unit 113 operates the regenerative braking device 20 and the hydraulic braking device 50 so that at least the effective regenerative braking force FxE, of the hydraulic braking force FxR and the effective regenerative braking force FxE, is applied to the vehicle 10.

[0048] The stopping control unit 113 operates the regenerative braking device 20 and the hydraulic braking device 50 in order to control the hydraulic braking force FxR and the effective regenerative braking force FxE during the substitution process and the reduction process. In the holding process, the stopping control unit 113 operates the hydraulic braking device 50 so that the vehicle 10 stops by applying only the hydraulic braking force FxR out of the hydraulic braking force FxR and the effective regenerative braking force FxE.

[0049] <Holding control section> The holding control unit 115 performs a stationary holding control. In the stationary holding control, the holding control unit 115 operates the electric parking device 60 so that the parking braking force FxP increases toward the holding braking force FxPH. The holding control unit 115 also operates the hydraulic braking device 50 so that the hydraulic braking force FxR decreases to 0 (zero).

[0050] As will be described in detail later, the increase rate of the parking braking force FxP and the holding braking force FxPH when the vehicle stop holding control is being executed are set by the setting unit 117. The holding control unit 115 increases the target parking braking force FxPTr at the command increase rate ΔFxPTr until the target parking braking force FxPTr reaches the holding braking force FxPH. Then, the holding control unit 115 drives the electric motor 62 based on the target parking braking force FxPTr. When the target parking braking force FxPTr reaches the holding braking force FxPH, the holding control unit 115 determines that the parking braking force FxP has reached the holding braking force FxPH and stops the supply of electricity to the electric motor 62.

[0051] <Settings section> The setting unit 117 sets at least one of the increase rate of the parking braking force FxP and the holding braking force FxPH when the vehicle stop maintenance control is being executed, based on the required braking force FxRq and the road surface gradient θ. In this embodiment, the setting unit 117 sets both the increase rate of the parking braking force FxP and the holding braking force FxPH when the vehicle stop maintenance control is being executed, based on the required braking force FxRq and the road surface gradient θ.

[0052] For example, the setting unit 117 sets the indicative increase speed ΔFxPTr, which is the indicative value for the rate at which the parking braking force FxP increases, such that the magnitude decreases as the required braking force FxRq decreases. The setting unit 117 sets the indicative increase speed ΔFxPTr such that the magnitude decreases as the absolute value of the road surface gradient θ decreases.

[0053] For example, the setting unit 117 sets the maintained braking force FxPH so that the magnitude decreases as the required braking force FxRq decreases. The setting unit 117 sets the maintained braking force FxPH so that the magnitude decreases as the absolute value of the road surface gradient θ decreases. In this case, it is preferable that the setting unit 117 sets the maintained braking force FxPH so that the maintained braking force FxPH is equal to or greater than the sum of the stopping braking force FxH and a tolerance value Fxα, which will be described later.

[0054] <Movement suppression part> When movement of the vehicle 10 is detected under conditions in which stop-holding control is being executed, the movement suppressing unit 119 executes an increase control to stop the movement of the vehicle 10 by increasing at least one of the hydraulic braking force FxR and the parking braking force FxP. In this embodiment, in the increase control, the movement suppressing unit 119 stops the movement of the vehicle 10 by increasing only the parking braking force FxP out of the hydraulic braking force FxR and the parking braking force FxP. At this time, the movement suppressing unit 119 corrects the command increase speed ΔFxPTr set by the setting unit 117 by increasing it, and corrects the holding braking force FxPH set by the setting unit 117 by increasing it.

[0055] Here, the movement of vehicle 10 means that wheels 12 and 13 rotate. The wheel speed sensor 72 outputs a pulse signal as a detection signal corresponding to the rotational speed of the corresponding wheel.

[0056] Therefore, the movement suppression unit 119 counts the number of pulses input from the wheel speed sensor 72 to the braking control device 80 from the moment it is determined that the vehicle 10 has stopped, that is, from the moment the stop-holding control is started. This number of pulses is referred to as the "slip detection counter CNT". The movement suppression unit 119 then detects that the vehicle 10 is moving when the slip detection counter CNT becomes equal to or greater than the count determination value CNTth.

[0057] Furthermore, if the movement of the vehicle 10 can be detected while the vehicle is in a stationary position, it is not necessary to use the pulse signal from the wheel speed sensor 72. For example, the movement suppression unit 119 may detect the movement of the vehicle 10 based on the change in longitudinal acceleration GX.

[0058] <Vehicle braking process> Referring to Figure 4, the processing flow executed by the processing circuit 81 of the braking control device 80 when a braking request occurs will be explained. This processing flow is the vehicle braking process. When a braking request occurs, the processing circuit 81 repeatedly executes the vehicle braking process.

[0059] In step S11, the processing circuit 81 functions as an acquisition unit 111 to acquire the required braking force FxRq. In the following step S13, the processing circuit 81 functions as an acquisition unit 111 to acquire the road surface gradient θ. In the next step S15, the processing circuit 81 functions as an acquisition unit 111 to acquire the motor temperature TPepb. In the following step S17, the processing circuit 81 functions as an acquisition unit 111 to acquire the stopping distance DS.

[0060] Then, in step S19, the processing circuit 81 determines whether the stopping distance DS is less than or equal to the first threshold DSth1. If the stopping distance DS is less than or equal to the first threshold DSth1 (S19: YES), the processing circuit 81 proceeds to step S23. On the other hand, if the stopping distance DS is greater than the first threshold DSth1 (S19: NO), the processing circuit 81 proceeds to step S21.

[0061] In step S21, the processing circuit 81 executes the above-described regenerative cooperative control, and then temporarily ends the vehicle braking process. In step S23, the processing circuit 81 determines whether the vehicle 10 is stopped. If the stopping distance DS is equal to or less than the fourth threshold value DSth4, the processing circuit 81 determines that the vehicle 10 is stopped. On the other hand, if the stopping distance DS is greater than the fourth threshold value DSth4, the processing circuit 81 determines that the vehicle 10 is not stopped. If the processing circuit 81 determines that the vehicle 10 is stopped (S23: YES), the processing circuit 81 shifts the processing to step S31. On the other hand, if the processing circuit 81 determines that the vehicle 10 is not stopped (S23: NO), the processing circuit 81 shifts the processing to step S25.

[0062] In step S25, the processing circuit 81 functions as the stopping control unit 113 to execute the above-described stopping-time control. Specifically, if the stopping distance DS is equal to or less than the first threshold value DSth1 and greater than the second threshold value DSth2, the processing circuit 81 executes an increasing process for the stopping-time control. If the stopping distance DS is equal to or less than the second threshold value DSth2 and greater than the third threshold value DSth3, the processing circuit 81 executes a switching process for the stopping-time control. If the stopping distance DS is equal to or less than the third threshold value DSth3 and the effective regenerative braking force FxE is greater than 0 (zero), the processing circuit 81 executes a decreasing process for the stopping-time control. If the stopping distance DS is equal to or less than the third threshold value DSth3 and the effective regenerative braking force FxE is 0 (zero), the processing circuit 81 executes a maintaining process for the stopping-time control.

[0063] In the following step S27, the processing circuit 81 sets the command increasing speed ΔFxPTr by functioning as the setting unit 117. At this time, the processing circuit 81 sets the command increasing speed ΔFxPTr based on the required braking force FxRq and the road surface gradient θ.

[0064] In the next step S29, the processing circuit 81 functions as a setting unit 117 to set the holding braking force FxPH. At this time, the processing circuit 81 sets the holding braking force FxPH based on the required braking force FxRq and the road surface gradient θ. After that, the processing circuit 81 temporarily terminates the vehicle braking process.

[0065] In step S31, the processing circuit 81 determines whether the motor temperature TPepb at the time it is determined that the vehicle 10 has stopped is equal to or greater than the temperature determination value TPth. If the motor temperature TPepb at the time it is determined that the vehicle 10 has stopped is equal to or greater than the temperature determination value TPth (S31: YES), the processing circuit 81 proceeds to step S33. On the other hand, if the motor temperature TPepb at the time it is determined that the vehicle 10 has stopped is less than the temperature determination value TPth (S31: NO), the processing circuit 81 proceeds to step S35.

[0066] In step S33, the processing circuit 81 performs degraded control by functioning as a holding control unit 115. In degraded control, the processing circuit 81 operates the hydraulic braking device 50 so that the hydraulic braking force FxR increases to the required braking force FxRq. After that, the processing circuit 81 temporarily terminates the vehicle braking process.

[0067] In step S35, the processing circuit 81 performs stop-hold control by functioning as a hold-control unit 115. Details of the stop-hold control in step S35 will be described later. After that, the processing circuit 81 temporarily terminates the vehicle braking process.

[0068] <Stopping and holding control> The vehicle stop control in step S35 will be described in detail with reference to FIG. In step S101, the processing circuit 81 determines whether the parking braking force FxP is greater than the holding braking force FxPH. If the processing circuit 81 determines that the parking braking force FxP is equal to or less than the holding braking force FxPH (S101: NO), the processing circuit 81 proceeds to step S103. On the other hand, if the processing circuit 81 determines that the parking braking force FxP is greater than the holding braking force FxPH (S101: YES), the processing circuit 81 proceeds to step S105.

[0069] In step S103, the processing circuit 81 operates the electric parking device 60 based on the instructed increasing speed ΔFxPTr. That is, the processing circuit 81 increases the target parking braking force FxPTr at the instructed increasing speed ΔFxPTr. Then, the processing circuit 81 drives the electric motor 62 based on the target parking braking force FxPTr. After that, the processing circuit 81 proceeds to step S111.

[0070] In step S105, the processing circuit 81 maintains the parking brake force FxP by stopping the power supply to the electric motor 62. Then, the processing circuit 81 proceeds to step S111.

[0071] In step S111, the processing circuit 81 derives the lower limit parking braking force FxPL1 by subtracting the allowable value Fxα from the parking braking force FxP. Here, the controllability of the parking braking force FxP is lower than the controllability of the hydraulic braking force FxR. In other words, even if the electric parking device 60 is operated so that the parking braking force FxP becomes the holding braking force FxPH, the actual value of the parking braking force varies relatively widely. The allowable value Fxα is a value that corresponds to this variation in the actual value of the parking braking force. Therefore, if the lower limit parking braking force FxPL1 is equal to or less than the stopping braking force FxH, there is a possibility that the vehicle 10 will start moving when the hydraulic braking force FxR becomes 0 (zero).

[0072] Therefore, in step S111, the processing circuit 81 determines whether the lower limit parking braking force FxPL1 is greater than the stopping braking force FxH. If the processing circuit 81 determines that the lower limit parking braking force FxPL1 is greater than the stopping braking force FxH (S111: YES), the processing circuit 81 proceeds to step S113. On the other hand, if the processing circuit 81 determines that the lower limit parking braking force FxPL1 is less than the stopping braking force FxH (S111: NO), the processing circuit 81 terminates the series of processes shown in Figure 5.

[0073] In step S113, the processing circuit 81 determines whether the hydraulic braking force FxR is 0 (zero). If the hydraulic braking force FxR is 0 (S113: YES), the processing circuit 81 terminates the series of processes shown in Figure 5. On the other hand, if the hydraulic braking force FxR is greater than 0 (S113: NO), the processing circuit 81 proceeds to step S115.

[0074] In step S115, the processing circuit 81 activates the hydraulic braking device 50 so that the hydraulic braking force FxR decreases. Then, the processing circuit 81 completes the series of processes shown in Figure 5. <Movement Restriction Processing> Referring to Figure 6, the movement restriction process performed by the processing circuit 81 will be explained. The processing circuit 81 repeatedly performs the movement restriction process at predetermined control cycles when the vehicle is braking. By functioning as a movement suppression unit 119, the processing circuit 81 performs the processes of multiple steps S201, S203, and S205 that constitute the movement restriction process.

[0075] In step S201, the processing circuit 81 determines whether or not it is performing stop-hold control. If the processing circuit 81 is not performing stop-hold control (S201: NO), the processing circuit 81 terminates the movement restriction process. If the processing circuit 81 is performing stop-hold control (S201: YES), the processing circuit 81 proceeds to step S203.

[0076] In step S203, the processing circuit 81 determines whether or not it has detected the rotation of the wheels 12 and 13. The processing circuit 81 counts the slip-down detection counter CNT. The processing circuit 81 determines that it has detected the rotation of the wheels 12 and 13 if both of the following two conditions (A1) and (A2) are met.

[0077] (A1) The slippage detection counter CNT is increased. (A2) The slippage detection counter CNT is equal to or greater than the count determination value CNTth. If the processing circuit 81 determines that it has detected the rotation of wheels 12 and 13 (S203: YES), the processing circuit 81 proceeds to step S205. On the other hand, if the processing circuit 81 determines that it has not detected the rotation of wheels 12 and 13 (S203: NO), the processing circuit 81 terminates the movement restriction process.

[0078] In step S205, the processing circuit 81 performs an increase control. In the increase control, the processing circuit 81 increases and corrects the holding braking force FxPH set in step S29 of Figure 4. The processing circuit 81 also increases and corrects the instructed increase speed ΔFxPTr set in step S27 of Figure 4. As a result, the processing circuit 81 can stop the vehicle 10 from moving by increasing the parking braking force FxP. After that, the processing circuit 81 temporarily terminates the movement restriction process.

[0079] <Actions and Effects of This Embodiment> (1-1) When the vehicle 10 is stopped by the application of hydraulic braking force FxR, the braking control device 80 performs stop-hold control. In stop-hold control, the braking control device 80 increases the parking braking force FxP toward the holding braking force FxPH and reduces the hydraulic braking force FxR to 0 (zero).

[0080] Here, when the hydraulic braking force FxR becomes 0 (zero), the hydraulic braking device 50 can stop supplying power to the solenoid valve 52. Also, the electric parking device 60 can maintain the parking braking force FxP even if it stops supplying power to the electric motor 62.

[0081] The braking control device 80 can maintain the vehicle 10 at a standstill with only the parking braking force FxP applied, out of the two hydraulic braking forces FxR and parking braking force FxP. This allows the braking control device 80 to reduce the power consumption of the braking system when the vehicle 10 is stopped.

[0082] Generally, the electric parking system 60 applies a relatively large parking braking force FxP to the vehicle 10 so that it can maintain its stop regardless of the road surface on which it is stopped. This parking braking force FxP is referred to as the "upper limit parking braking force FxPL2".

[0083] In response to this, the brake control device 80 sets the holding braking force FxPH based on the required braking force FxRq. That is, depending on the magnitude of the required braking force FxRq, the vehicle 10 may be held stopped in a state in which a parking braking force FxP smaller than the upper limit parking braking force FxPL2 is applied to the vehicle 10. In this respect as well, the brake control device 80 can reduce the power consumption of the electric parking device 60 when holding the vehicle 10 stopped.

[0084] The brake control device 80 can vary the rate of increase of the parking braking force FxP while the vehicle stop maintenance control is being executed, based on the required braking force FxRq. As a result, depending on the magnitude of the required braking force FxRq, the rate of increase of the parking braking force FxP while the vehicle stop maintenance control is being executed can be made smaller than the rate of increase of the parking braking force FxP during normal operation of the electric parking device 60. A smaller rate of increase of the parking braking force FxP means that the rotation speed of the rotary shaft 62a of the electric motor 62 is lower, and therefore the operating noise of the parking actuator 61 caused by driving the electric motor 62 can be reduced.

[0085] (1-2) The response speed of the parking brake force FxP is smaller than that of the hydraulic brake force FxR. Therefore, if the parking brake force FxP is large when the vehicle 10 is stopped, a delay in the vehicle 10's departure may occur when the vehicle 10 is subsequently started.

[0086] Therefore, in the braking control device 80, the holding braking force FxPH is set such that the smaller the required braking force FxRq, the smaller the holding braking force FxPH. The smaller the required braking force FxRq when the vehicle 10 is stopped, the smaller the parking braking force FxP when the vehicle 10 is stopped can be. As a result, when the vehicle 10 is to start moving afterward, the parking braking force FxP can be reduced to 0 (zero) relatively quickly. Consequently, the braking control device 80 can suppress delays in the starting of the vehicle 10 when the vehicle 10 is to start moving.

[0087] (1-3) In stop-hold control, the braking control device 80 delays the start of reducing the hydraulic braking force FxR to 0 (zero) in response to the increase in parking braking force FxP toward the holding braking force FxPH. This allows the braking control device 80 to reduce the hydraulic braking force FxR after the parking braking force FxP has become relatively large. Therefore, it is possible to suppress the decrease in the total braking force Fx after the vehicle 10 has come to a stop due to the decrease in hydraulic braking force FxR. Thus, the braking control device 80 can suppress the vehicle 10 from starting to move even when the hydraulic braking force FxR is reduced to 0 (zero).

[0088] (1-4) If the magnitude of the road surface gradient θ at the time it is determined that the vehicle 10 has stopped is greater than the magnitude of the road surface gradient θ at the time the stopping control is initiated, the vehicle 10 may start moving due to insufficient braking force while the stopping control is being executed.

[0089] When the braking control device 80 detects movement of the vehicle 10 while performing stop-hold control, it increases the parking braking force FxP to stop the vehicle 10 from moving. In other words, when the braking control device 80 determines that movement of the vehicle 10 has been detected while performing stop-hold control, it performs an increase control.

[0090] In the example shown in Figures 7(a) to 7(c), the processing circuit 81 of the braking control device 80 determines that the vehicle 10 has stopped at timing t21 and starts stop-hold control. At timing t22, while the stop-hold control is being executed, the sliding detection counter CNT becomes equal to or greater than the count determination value CNTth, so the processing circuit 81 determines that movement of the vehicle 10 has been detected and starts increase control. That is, the processing circuit 81 increases the holding braking force FxPH and the instructed increase speed ΔFxPTr.

[0091] From timing t22 onward, the processing circuit 81 sets a target parking braking force FxPTr based on the increased and corrected holding braking force FxPH and the instructed increase speed ΔFxPTr. Then, the processing circuit 81 operates the electric parking device 60 based on this target parking braking force FxPTr. As a result, the processing circuit 81 can increase the parking braking force FxP earlier. This allows the braking control device 80 to maintain the vehicle 10 in a stopped state.

[0092] (1-5) The braking control device 80 sets the holding braking force FxPH to increase as the road surface gradient θ increases. In stop-hold control, the braking control device 80 increases the parking braking force FxP toward the holding braking force FxPH. As a result, even when the vehicle 10 stops on a road surface with a large road surface gradient θ, the braking control device 80 can maintain the stopped state of the vehicle 10 by applying the parking braking force FxP.

[0093] (1-6) The motor temperature TPepb is likely to increase as the operation frequency of the electric parking device 60 increases. If the electric motor 62 is driven while the motor temperature TPepb is high, the product life of the parking actuator 61 is likely to be shortened.

[0094] The braking control device 80 does not perform stop-hold control if the motor temperature TPepb is equal to or greater than the temperature determination value TPth. In other words, the braking control device 80 does not drive the electric motor 62 if the motor temperature TPepb is equal to or greater than the temperature determination value TPth. This allows the braking control device 80 to prevent a shortening of the product life of the parking actuator 61.

[0095] (1-7) If the braking control device 80 does not perform stop-hold control, and determines that the vehicle 10 has stopped, it performs degenerate control. In degenerate control, the braking control device 80 increases the hydraulic braking force FxR to the required braking force FxRq. As a result, even if the electric parking device 60 cannot be activated, the braking control device 80 can maintain the state in which the vehicle 10 is stopped by activating the hydraulic braking device 50.

[0096] (Second embodiment) A second embodiment of the braking control device will be described with reference to Figure 8. Note that the second embodiment differs from the first embodiment in the content of the increasing control. In the following description, the differences from the first embodiment will be mainly explained, and the same reference numerals will be used for components identical to those in the first embodiment to avoid redundant explanations.

[0097] Referring to Figure 8, the increasing control performed by the braking control device 80 of this embodiment will be described. As shown in Figures 8(a) to 8(c), the processing circuit 81 of the braking control device 80 determines at timing t31 that the vehicle 10 has stopped due to the application of hydraulic braking force FxR. Then, the processing circuit 81 functions as a holding control unit 115 and performs a stop holding control. This allows the processing circuit 81 to increase the parking braking force FxP.

[0098] When the slide detection counter CNT becomes equal to or greater than the count determination value CNTth while the vehicle stop maintenance control is being executed, the processing circuit 81 determines that movement of the vehicle 10 has been detected. In the example shown in FIG. 8, the processing circuit 81 determines that movement of the vehicle 10 has been detected at timing t32. Therefore, the processing circuit 81 functions as the movement suppression unit 119 and starts the increase control from timing t32. In the increase control, the processing circuit 81 increases the hydraulic braking force FxR, as shown in FIG. 8(a). This stops the vehicle 10 from moving.

[0099] <Actions and Effects of This Embodiment> In this embodiment, in addition to the effects (1-1) to (1-3) and (1-5) to (1-7) of the first embodiment described above, the following effects can be further obtained.

[0100] (2-1) When the brake control device 80 determines that movement of the vehicle 10 is detected while the vehicle stop maintenance control is being executed, the brake control device 80 increases the hydraulic braking force FxR. That is, the brake control device 80 can maintain the vehicle 10 in a stopped state by increasing both the hydraulic braking force FxR and the parking braking force FxP.

[0101] (Third embodiment) A third embodiment of the braking control device will be described with reference to Fig. 9. The third embodiment differs from the above-described embodiments in that the command increasing speed and the maintained braking force are changed even while the vehicle stop maintenance control is being executed. In the following explanation, differences from the above-described embodiments will be mainly described, and the same reference numerals will be used to designate the same components as those in the above-described embodiments, and redundant explanations will be omitted.

[0102] Figure 9 shows a part of the vehicle braking process performed by the processing circuit 81 of the braking control device 80 in this embodiment. In step S23, if the processing circuit 81 determines that the vehicle 10 has stopped (S23:YES), the processing proceeds to step S31. In step S31, if the motor temperature TPepb is less than the temperature determination value TPth (S31:NO), the processing circuit 81 proceeds to step S301.

[0103] In step S301, the processing circuit 81, by functioning as a setting unit 117, changes the setting of the instructed acceleration rate ΔFxPTr. Specifically, the processing circuit 81 changes the setting of the instructed acceleration rate ΔFxPTr based on the requested braking force FxRq. For example, if the requested braking force FxRq becomes smaller than the time at which the processing circuit 81 determined that the vehicle 10 had stopped, it decreases the instructed acceleration rate ΔFxPTr. If the requested braking force FxRq becomes larger than the time at which the processing circuit 81 determined that the vehicle 10 had stopped, it increases the instructed acceleration rate ΔFxPTr.

[0104] In the subsequent step S303, the processing circuit 81, by functioning as a setting unit 117, changes the setting of the holding braking force FxPH. Specifically, the processing circuit 81 changes the setting of the holding braking force FxPH based on the required braking force FxRq. For example, if the required braking force FxRq becomes smaller than the time when the processing circuit 81 determined that the vehicle 10 had stopped, it corrects the holding braking force FxPH by decreasing it. If the required braking force FxRq becomes larger than the time when the processing circuit 81 determined that the vehicle 10 had stopped, it corrects the holding braking force FxPH by increasing it. After that, the processing circuit 81 proceeds to step S35.

[0105] The vehicle stop maintenance control in step S35 is the same as that in the above-described embodiments, and therefore the subsequent processing flow will be omitted. <Actions and Effects of This Embodiment> In this embodiment, in addition to the effects (1-1) to (1-7) of the first embodiment, the following effects can be further obtained.

[0106] (3-1) When the required braking force FxRq changes while the parking braking force FxP is increasing due to the execution of the vehicle stop maintenance control, the brake control device 80 changes the setting of the command increasing speed ΔFxPTr in accordance with the change in the required braking force FxRq. This allows the brake control device 80 to increase the parking braking force FxP at a speed commensurate with the required braking force FxRq at that time.

[0107] (3-2) If the required braking force FxRq changes while the parking braking force FxP is increasing due to the execution of the vehicle stop maintenance control, the brake control device 80 changes the setting of the holding braking force FxPH in accordance with the change in the required braking force FxRq. This allows the brake control device 80 to increase the parking braking force FxP to a magnitude commensurate with the required braking force FxRq at that time.

[0108] (Fourth embodiment) A fourth embodiment of the brake control device will be described with reference to Figures 10 and 11. The fourth embodiment differs from the above-described embodiments in the content of the vehicle stop maintenance control. In the following description, differences from the above-described embodiments will be mainly described, and the same components as those in the above-described embodiments will be designated by the same reference numerals, and redundant description will be omitted.

[0109] <Stopping and holding control> The vehicle stop maintenance control executed by the brake control device 80 of this embodiment will be described with reference to Fig. 10. When the processing circuit 81 of the brake control device 80 determines in step S31 of Fig. 4 that the motor temperature TPepb is less than the temperature determination value TPth, the processing circuit 81 executes the vehicle stop maintenance control. The processing circuit 81 functions as the maintenance control unit 115, thereby executing the processes of a plurality of steps S401 to S427 that constitute the vehicle stop maintenance control.

[0110] In step S401, the processing circuit 81 determines whether the total braking force Fx is less than or equal to the holding braking force FxPH. The total braking force Fx corresponds to the "total braking force," which is the sum of the hydraulic braking force FxR and the parking braking force FxP. If the processing circuit 81 determines that the total braking force Fx is less than or equal to the holding braking force FxPH (S401: YES), the processing circuit 81 proceeds to step S403. On the other hand, if the processing circuit 81 determines that the total braking force Fx is greater than the holding braking force FxPH (S401: NO), the processing circuit 81 proceeds to step S421.

[0111] In step S403, the processing circuit 81 activates the electric parking device 60 based on the instructed increase rate ΔFxPTr, similar to step S103 in Figure 5. This allows the processing circuit 81 to increase the parking braking force FxP.

[0112] In the next step S405, the processing circuit 81 sets the target hydraulic braking force FxRTr. Specifically, the processing circuit 81 sets the target hydraulic braking force FxRTr to the sum of the value obtained by subtracting the parking braking force FxP from the holding braking force FxPH and the stopping braking force FxH. The stopping braking force FxH can be considered as the hydraulic braking force FxR at the time it is determined that the vehicle 10 has stopped.

[0113] Then, in step S407, the processing circuit 81 activates the hydraulic brake device 50 based on the target hydraulic braking force FxRTr set in step S405. This allows the processing circuit 81 to increase both the hydraulic braking force FxR and the parking braking force FxP until the total braking force Fx reaches the holding braking force FxPH. After that, the processing circuit 81 completes the series of processes shown in Figure 10.

[0114] In step S421, the processing circuit 81 determines whether the hydraulic braking force FxR is greater than 0 (zero). If the hydraulic braking force FxR is greater than 0 (S421: YES), the processing circuit 81 proceeds to step S423. On the other hand, if the hydraulic braking force FxR is 0 (zero) (S421: NO), the processing circuit 81 proceeds to step S427.

[0115] In step S423, the processing circuit 81 activates the electric parking device 60 based on the instructed increase rate ΔFxPTr, similar to step S103 in Figure 5. This allows the processing circuit 81 to increase the parking braking force FxP. In the subsequent step S425, the processing circuit 81 activates the hydraulic braking device 50 so that the hydraulic braking force FxR decreases. At this time, the processing circuit 81 decreases the hydraulic braking force FxR at the same decrease rate as the increase rate of the parking braking force FxP. In other words, the processing circuit 81 replaces the hydraulic braking force FxR with the parking braking force FxP. After that, the processing circuit 81 completes the series of processes shown in Figure 10.

[0116] In step S427, the processing circuit 81 stops the power supply to the electric motor 62 of the electric parking device 60. This allows the processing circuit 81 to maintain the parking braking force FxP. Then, the processing circuit 81 completes the series of processes shown in Figure 10.

[0117] <Actions and Effects of This Embodiment> With reference to FIG. 11, the operation and effect after it is determined that the vehicle 10 has stopped will be described.

[0118] As shown in Figures 11(a) to 11(d), the vehicle 10 stops at timing t41 when the hydraulic braking force FxR is applied. At this point, the processing circuit 81 starts stop-holding control.

[0119] In stop-hold control, the processing circuit 81 increases the target parking braking force FxPTr at an instructed increase rate ΔFxPTr. Then, the processing circuit 81 activates the electric parking device 60 based on the target parking braking force FxPTr. Furthermore, the processing circuit 81 also increases the target hydraulic braking force FxRTr. Then, the processing circuit 81 activates the hydraulic braking device 50 based on the target hydraulic braking force FxRTr. In other words, the processing circuit 81 operates the hydraulic braking device 50 and the electric parking device 60 so that both the hydraulic braking force FxR and the parking braking force FxP increase until the total braking force Fx reaches the holding braking force FxPH.

[0120] The responsiveness of the parking brake force FxP is lower compared to the responsiveness of the hydraulic brake force FxR. Therefore, in the braking control device 80 of this embodiment, in stop-hold control, increases not only the parking brake force FxP but also the hydraulic brake force FxR. As a result, the braking control device 80 can suppress the movement of the vehicle 10 due to the response delay of the parking brake force FxP.

[0121] At the subsequent timing t42, the processing circuit 81 determines that the total braking force Fx has reached the holding braking force FxPH. Therefore, the processing circuit 81 increases the target parking braking force FxPTr while decreasing the target parking braking force FxPTr. Then, the processing circuit 81 activates the electric parking device 60 based on the target parking braking force FxPTr, and activates the hydraulic braking device 50 based on the target hydraulic braking force FxRTr.

[0122] As mentioned above, the rate of increase of the target parking braking force FxPTr and the rate of decrease of the target hydraulic braking force FxRTr are equal. Therefore, fluctuations in the total braking force Fx can be suppressed.

[0123] In the example shown in Figure 11, the hydraulic braking force FxR becomes 0 (zero) at timing t43. Therefore, the processing circuit 81 stops the power supply to the electric motor 62 of the electric parking device 60. In this embodiment, the braking control device 80 reduces the hydraulic braking force FxR to 0 (zero) when it determines that the parking braking force FxP has become relatively large. Therefore, the braking control device 80 does not need to continue supplying power to the solenoid valve 52 of the hydraulic braking device 50 while the vehicle 10 is stopped. Consequently, the braking control device 80 can reduce the power consumption of the braking system during the period when the vehicle 10 is stopped.

[0124] (Fifth embodiment) A fifth embodiment of the braking control device will be described with reference to Figures 12 to 14. Note that the fifth embodiment differs from the above embodiments in that the processing circuit of the braking control device functions as an indicator acquisition unit. In the following description, the differences from the above embodiments will be mainly described, and the same reference numerals will be used for components identical to those in the above embodiments to avoid redundant explanations.

[0125] <Brake control device> As shown in Figure 12, the processing circuit 81 of the braking control device 80A includes a CPU 82, a first memory 83, and a second memory 84. By executing the control program in the first memory 83, the CPU 82 enables the processing circuit 81 to function as multiple functional units for performing stopping control and stopping hold control. These multiple functional units include an acquisition unit 111, a stopping control unit 113, a holding control unit 115, a setting unit 117, and a movement suppression unit 119, as well as an indicator acquisition unit 121.

[0126] The index acquisition unit 121 acquires an index that correlates with the length of the stopping time, which is the time from when the vehicle 10 stops until the vehicle 10 starts moving. More specifically, the index is the correlation value of the predicted time from the current time to the time when the vehicle 10 is expected to start moving, assuming that the vehicle 10 is currently stopped. In this embodiment, the index acquisition unit 121 acquires the required braking force FxRq as the index. The larger the required braking force FxRq, the longer the time required to reduce the required braking force FxRq to 0 (zero). Therefore, the index acquisition unit 121 acquires the required braking force FxRq as the index.

[0127] The holding control unit 115 executes the above-described stop-hold control when the length of the stopping time indicated by the indicator is greater than or equal to the time determination value. On the other hand, the holding control unit 115 does not execute the stop-hold control when the length of the stopping time indicated by the indicator is less than the time determination value. The time determination value is the criterion for determining whether or not the vehicle 10 will start moving immediately. In this embodiment, the holding control unit 115 executes the stop-hold control when the required braking force FxRq at the time it is determined that the vehicle 10 has stopped is greater than the determined braking force Fxth, while it does not execute the stop-hold control when the required braking force FxRq is less than or equal to the determined braking force Fxth.

[0128] As mentioned above, the responsiveness of the parking brake force FxP is lower than that of the hydraulic brake force FxR. Therefore, if it is expected that the vehicle 10 will start moving soon, it is not advisable to apply the parking brake force FxP to the vehicle 10.

[0129] <Vehicle braking process> Figure 13 shows a part of the vehicle braking process performed in this embodiment. In step S31 of Figure 4, if the motor temperature TPepb at the time it is determined that the vehicle 10 has stopped is less than the temperature determination value TPth (S31:NO), the processing circuit 81 proceeds to step S501 of Figure 13.

[0130] In step S501, the processing circuit 81 functions as an index acquisition unit 121 and acquires the required braking force FxRq as an index at the time it is determined that the vehicle 10 has stopped. In the subsequent step S503, the processing circuit 81 determines whether the requested braking force FxRq obtained in step S501 is greater than the determination braking force Fxth. If the requested braking force FxRq is greater than the determination braking force Fxth, it can be assumed that the vehicle 10 will not start for some time. On the other hand, if the requested braking force FxRq is less than or equal to the determination braking force Fxth, it can be assumed that the vehicle 10 may start immediately. In other words, the determination braking force Fxth is the braking force corresponding to the above time determination value.

[0131] In step S503, if the required braking force FxRq is greater than the determined braking force Fxth (S503: YES), the processing circuit 81 determines that the length of the stop time indicated by the index is equal to or greater than the time determination value. Therefore, the processing circuit 81 proceeds to step S35 in Fig. 4. Then, the processing circuit 81 functions as the hold control unit 115 to execute the stop hold control.

[0132] On the other hand, in step S503, if the required braking force FxRq is less than or equal to the determined braking force Fxth (S503: NO), the processing circuit 81 proceeds to step S505. In step S505, the processing circuit 81 determines whether the hydraulic braking force FxR is less than the current required braking force FxRq. If the hydraulic braking force FxR is less than the current required braking force FxRq (S505: YES), the processing circuit 81 proceeds to step S507. On the other hand, if the hydraulic braking force FxR is equal to or greater than the current required braking force FxRq (S505: NO), the processing circuit 81 proceeds to step S509.

[0133] In step S507, the processing circuit 81 activates the hydraulic braking device 50 so that the hydraulic braking force FxR increases toward the current required braking force FxRq. After that, the processing circuit 81 temporarily terminates the vehicle braking process.

[0134] In step S509, the processing circuit 81 operates the hydraulic braking device 50 so that the hydraulic braking force FxR follows the current required braking force FxRq. After that, the processing circuit 81 temporarily terminates the vehicle braking process.

[0135] <Actions and Effects of This Embodiment> Referring to Figure 14, the operation and effects of this embodiment will be described. As shown in Figures 14(a) to 14(f), the vehicle 10 stops at timing t52 when the hydraulic braking force FxR is applied. In the example shown in Figure 14, the required braking force FxRq begins to decrease from timing t51, which is before timing t52. At timing t52, the required braking force FxRq is less than or equal to the judgment braking force Fxth.

[0136] Therefore, even if the processing circuit 81 determines that the vehicle 10 has stopped, it does not perform stop-hold control. Specifically, the processing circuit 81 does not increase the parking braking force FxP. Instead, the processing circuit 81 adjusts the hydraulic braking force FxR to follow the requested braking force FxRq.

[0137] In the example shown in Figure 14, the required braking force FxRq continues to decrease even after the vehicle 10 has come to a stop. Then, at timing t53, the required braking force FxRq becomes 0 (zero). Therefore, the processing circuit 81 operates the hydraulic braking device 50 so that the hydraulic braking force FxR becomes 0 (zero) at timing t53.

[0138] The braking control device 80A does not perform stop-hold control if it is predicted that the vehicle 10 will start moving again soon after it has stopped. In other words, the braking control device 80A does not apply parking braking force FxP to the vehicle 10, but instead applies hydraulic braking force FxR to the vehicle 10. Therefore, the braking control device 80A can suppress the feeling of dragging when the vehicle 10 starts moving, compared to when parking braking force FxP is applied when the vehicle 10 is stopped.

[0139] (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.

[0140] In the fifth embodiment described above, the processing circuit 81 (i.e., the index acquisition unit 121) may acquire parameters other than the required braking force FxRq as indicators. For example, the index acquisition unit 121 may acquire the braking operation amount X as the indicator.

[0141] The brake control device 80A may be applied to a vehicle that can acquire information from outside the vehicle. The "information from outside the vehicle" here includes, for example, information about when a traffic light will turn green and information about whether a preceding vehicle has started moving. In this case, the processing circuit 81 analyzes the acquired information from outside the vehicle to estimate whether the stopping time of the vehicle 10 will be short. If the processing circuit 81 can estimate that the stopping time of the vehicle 10 will be short, it may maintain the stopping of the vehicle 10 by using the hydraulic braking force FxR without executing the stop-maintenance control.

[0142] In the above-described embodiments, the processing circuit 81 may perform stop-hold control when it determines that the vehicle 10 has stopped, regardless of whether the motor temperature TPepb is high or not.

[0143] In the above embodiments, the processing circuitry 81 does not have to function as the movement suppressing unit 119. In the above-described embodiments, if the processing circuit 81 (i.e., the setting unit 117) sets the holding braking force FxPH based on the required braking force FxRq, it may set the holding braking force FxPH without considering the road surface gradient θ.

[0144] In the above embodiments, if the processing circuit 81 (i.e., the setting unit 117) sets the command increasing speed ΔFxPTr based on the required braking force FxRq, it is not necessary to set the held braking force FxPH based on the required braking force FxRq. In this case, the processing circuit 81 may set the held braking force FxPH to the required braking force FxRq. Furthermore, the processing circuit 81 may set the held braking force FxPH to the sum of the stopping braking force FxH and the allowable value Fxα, or a braking force greater than the sum.

[0145] If the processing circuit 81 (i.e., the setting unit 117) sets the holding braking force FxPH based on the requested braking force FxRq, it does not need to set the indicative increase rate ΔFxPTr based on the requested braking force FxRq.

[0146] In the fourth embodiment described above, the processing circuit 81 may start decreasing the hydraulic braking force FxR after the total braking force Fx has reached the holding braking force FxPH and the parking braking force FxP has increased to the holding braking force FxPH.

[0147] The stopping control may be a different control from the control described in the above embodiments, as long as the hydraulic braking force FxR can be reduced to less than the required braking force FxRq when the vehicle 10 comes to a stop.

[0148] For example, the vehicle stop control does not have to include the increasing process of making the total braking force Fx greater than the requested braking force FxRq before the switching process starts. Furthermore, for example, the vehicle stop control may operate the regenerative braking device 20 so that the effective regenerative braking force FxE becomes 0 (zero) when the vehicle 10 stops.

[0149] The braking control device does not need to execute the vehicle stop control immediately before the vehicle 10 comes to a stop. The processing circuit 81 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.

[0150] (Other technological ideas) The technical ideas that can be understood from the above-described embodiments and modifications will be described. [Note 1] the setting unit sets the holding braking force based on the required braking force, It is preferable that the setting unit sets the holding braking force such that its magnitude decreases as the required braking force decreases.

[0151] [Appendix 2] the setting unit sets an increase rate of the parking braking force during execution of the vehicle stop maintenance control based on the required braking force, It is preferable that the setting unit sets the rate at which the parking braking force increases during the execution of the stop-hold control such that the magnitude decreases as the required braking force decreases.

[0152] [Appendix 3] In the vehicle stopping control, it is preferable that the holding control unit delays the start of reducing the hydraulic braking force to 0 (zero) in response to the parking braking force beginning to increase toward the holding braking force.

[0153] [Appendix 4] When the holding control unit does not perform the stop-holding control, it is preferable that it holds the vehicle stopped using only the hydraulic braking force among the hydraulic braking force and the parking braking force.

[0154] The expression "at least one" used herein means "one or more" of the desired options. As an example, the expression "at least one" used herein means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" used herein means "only one option" or "any combination of two or more options" if the number of options is three or more. [Explanation of symbols]

[0155] 10... Vehicles 40...Friction brake 41...Wheel cylinder 50...Hydraulic braking device 51…Pressurizing unit (an example of an operating part) 52...Solenoid valve (an example of an actuator) 60…Electric parking system 61…Parking Actuator 62… Electric motor 80, 80A… Brake control device 81…Processing circuit 113... Stopping Control Unit 115...Holding control unit 117...Settings section 119…Movement suppression unit 121…Indicator acquisition part

Claims

1. The present invention is applied to a vehicle equipped with a hydraulic braking device having an electric operating unit that operates to adjust the hydraulic pressure of a wheel cylinder and applies a hydraulic braking force to the vehicle according to the hydraulic pressure, and an electric parking device having an electric motor and increasing the parking braking force applied to the vehicle by driving the electric motor, a stop control unit that activates the hydraulic braking device so that the vehicle is stopped by applying the hydraulic braking force; a hold control unit that executes stop hold control, including operating the electric parking device so that the parking braking force increases toward a holding braking force that is greater than the hydraulic braking force at the time the vehicle is stopped, and operating the hydraulic braking device so that the hydraulic braking force decreases to 0 (zero); a setting unit that sets at least one of an increase rate of the parking braking force and the holding braking force when the stop holding control is performed, based on a required braking force that is a required value of the braking force of the vehicle. Braking control device.

2. When the required braking force changes while the parking braking force is increasing due to the execution of the stop-hold control, the setting unit changes the setting of the increase rate of the parking braking force in accordance with the change in the required braking force. The braking control device according to claim 1 .

3. the stop control unit stops the vehicle in a state in which the hydraulic braking force is made smaller than the required braking force by operating the hydraulic braking device, In the vehicle stop maintenance control, the maintenance control unit the hydraulic braking device and the electric parking device are operated so that both the hydraulic braking force and the parking braking force increase until a total braking force, which is the sum of the hydraulic braking force and the parking braking force, reaches the holding braking force; After the total braking force reaches the holding braking force, the electric parking device is operated so that the parking braking force increases toward the holding braking force, and the hydraulic braking device is operated so that the hydraulic braking force decreases to 0 (zero). The braking control device according to claim 1 .

4. a movement suppression unit that, when movement of the vehicle is detected under the condition that the stop-hold control is being executed, stops the movement of the vehicle by increasing at least one of the hydraulic braking force and the parking braking force; The braking control device according to any one of claims 1 to 3.

5. the setting unit sets the holding braking force based on the required braking force and a gradient of a road surface on which the vehicle is stopped, The setting unit sets the holding braking force so that the magnitude of the holding braking force increases as the gradient of the road surface increases. The braking control device according to any one of claims 1 to 3.

6. The hold control unit does not execute the stop hold control when the temperature of the electric parking device is equal to or higher than a temperature determination value. The braking control device according to any one of claims 1 to 3.

7. an index acquisition unit that acquires an index that correlates with the length of a stop time, which is the time from when the vehicle stops to when the vehicle starts; The hold control unit does not execute the stop maintenance control when the length of the stop time indicated by the indicator is less than a time determination value. The braking control device according to any one of claims 1 to 3.

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