Brake control method and brake control device

Abstract

In a brake control method, during execution of braking control, in which a brake action and a brake release action are alternately repeated by a parking brake device driven by a motor (10) while a vehicle is traveling, a determination is made as to whether or not an acceleration amount (α2 × t2) of the vehicle in the brake release action is equal to or greater than a deceleration amount (α1 × t1) of the vehicle in the brake action, and the execution of antilock control is limited when the acceleration amount (α2 × t2) is equal to or greater than the deceleration amount (α1 × t1).

Description

Technical Field

[0001] The present invention relates to a brake control method and a brake control device.

Background Art

[0002] Patent Document 1 describes a brake control method for a vehicle equipped with an anti-lock control mechanism. The motor-driven parking brake device described in Patent Document 1 is called an electronic parking brake (EPB). In an EPB, a brake pad that converts the rotation of a motor into linear motion and transmits it contacts and separates from a brake rotor to apply or release a brake to the vehicle.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an EPB, since the rotation of the motor moves the brake pad, the control responsiveness is lower than that of a vehicle behavior control device (VDC) that moves the brake pad by a cylinder. In addition to the main function of parking brake during parking, the EPB has a function of performing anti-lock control as an emergency brake during driving. However, when performing braking control with anti-lock control in the EPB, the period of the brake release operation in the anti-lock control becomes longer. When the friction coefficient of the road surface is low and the deceleration due to the brake decreases, the vehicle may be re-accelerated by the creep torque during the period of the brake release operation in the anti-lock control.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress re-acceleration of a vehicle during braking control accompanied by anti-lock control by a motor-driven parking brake device.

Means for Solving the Problems

[0006] In order to solve the above-described problems, in a braking control method according to one aspect of the present invention, it is determined whether an acceleration amount during a brake release operation of a vehicle is equal to or greater than a deceleration amount during a brake operation of the vehicle. The brake release operation and the brake operation of the vehicle are alternately repeated during the running of the vehicle in the anti-lock control of the braking control by the motor-driven parking brake device. During the execution of the braking control accompanied by the anti-lock control, it is determined whether the acceleration amount of the vehicle during the brake release operation is equal to or greater than the deceleration amount of the vehicle due to the brake operation, and when the acceleration amount is equal to or greater than the deceleration amount, the execution of the anti-lock control is restricted.

Effects of the Invention

[0007] According to the present invention, it is possible to suppress re-acceleration of a vehicle during braking control accompanied by anti-lock control by a motor-driven parking brake device.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

DETAILED DESCRIPTION OF THE INVENTION

[0009] With reference to the drawings, embodiments, variations thereof, and specific examples to which an embodiment or its variation is applied will be described. In the description of the drawings, the same reference numerals are given to the same parts and the description thereof is omitted.

[0010] (First Embodiment) With reference to FIG. 1, a configuration example of a main part of a vehicle equipped with a parking brake device to which a brake control method according to a first embodiment of the present invention is applied will be described.

[0011] The vehicle shown in FIG. 1 travels on four wheels (not shown) in the front, rear, left, and right by the power of the power train 1. The power train 1 may have, for example, an electric power source such as a motor, or may have a power source by an internal combustion engine such as a reciprocating engine. FIG. 1 shows an example in the case of driving the front two wheels by the power of the power train 1. The wheels driven by the power of the power train 1 may be the rear two wheels or all four wheels.

[0012] When the brake on the wheels of the vehicle shown in FIG. 1 is released, the vehicle moves due to the creep phenomenon even if the accelerator pedal is not depressed. When the power train 1 uses a clutch mechanism (not shown) with an engine (not shown) and a fluid coupling, the creep phenomenon is caused by the creep torque transmitted from the idling engine to the wheels via the clutch mechanism.

[0013] The creep phenomenon does not occur structurally, for example, in vehicles that do not use a fluid coupling in the clutch mechanism, electric vehicles (EVs) that use a power source other than the engine as the power source of the power train 1, etc. In vehicles where the creep phenomenon does not occur, during the release of the brake, the wheels may be driven by a low torque generated in the power train 1 by control to generate a pseudo-creep phenomenon. In the following embodiments, the torque generated in the power train 1 for this pseudo-creep phenomenon is also included in the category of creep torque. The value of the creep torque may be detected by a sensor or the like, or may be obtained by calculation or estimation.

[0014] The vehicle shown in FIG. 1 is provided with a motor-driven parking brake device. The parking brake device has an ECU (Electronic Control Unit) 2, a switch 3, wheel speed sensors 4 to 7 corresponding to the front, rear, left, and right wheels (not shown), and actuators 8 and 9 corresponding to the rear two wheels.

[0015] The ECU 2 can be realized using, for example, a microcomputer. The microcomputer can be configured to include a CPU (Central Processing Unit), a memory, and an output unit.

[0016] By installing a computer program in the memory of the microcomputer and causing the CPU to execute it, the ECU 2 can constitute a brake control device that functions as an information processing unit including a determination unit and a restriction unit described later.

[0017] In this embodiment, an example is shown in which the information processing by each information processing unit of the motor-driven parking brake device is realized by software. It is also possible to prepare dedicated hardware for executing the information processing of each information processing unit to constitute each information processing unit. The dedicated hardware can include, for example, an application-specific integrated circuit (ASIC) arranged to execute the functions described in the embodiments to be described later, and devices such as conventional circuit components.

[0018] When a sensor (not shown) detects that the vehicle occupant has operated the switch 3 in the vehicle, the ECU 2 calculates the vehicle speed from the wheel speeds of the four wheels of the vehicle detected by the front, rear, left, and right wheel speed sensors 4 to 7. The switch 3 can be, for example, a lever-type switch arranged on the center console in the vehicle together with the shift lever. The occupant operating the switch 3 can be, for example, the driver in the driver's seat or a passenger in the passenger seat.

[0019] When the vehicle speed calculated in response to the operation of the switch 3 is equal to or less than the stop determination speed V1 and the vehicle is determined to be in a stopped state, the ECU 2 operates the actuators 8 and 9 to apply brakes to the rear two wheels.

[0020] The actuators 8 and 9 each have, for example, a motor 10, a speed reducer 11, a feed screw 12, a nut 13, and a piston 14 as shown in FIG. 2. In each of the actuators 8 and 9, when the motor 10 rotates the feed screw 12 via the speed reducer 11, the nut 13 engaged with the feed screw 12 linearly moves the piston 14 in the axial direction of the feed screw 12. The piston 14 moves the brake pad 15 closer to and away from the brake rotor 16 by linearly moving in the axial direction of the feed screw 12.

[0021] When the brake pad 15 is pressed against the brake rotor 16, the rear two wheels of the vehicle can be braked with a braking force corresponding to the pressing force of the brake pad 15 against the brake rotor 16. By rotating the feed screw 12 to linearly move the piston 14 and changing the pressing force of the brake pad 15 against the brake rotor 16, the braking force of the brake applied to the rear two wheels can be increased or decreased. When the brake pad 15 is separated from the brake rotor 16, the brake applied to the rear two wheels can be released.

[0022] When the ECU 2 in FIG. 1 determines that the vehicle is in a stopped state and activates each of the actuators 8 and 9, when the braking force of the brake applied to the rear two wheels reaches the parking braking force required to maintain the vehicle in a stopped state, the operation of each of the actuators 8 and 9 is stopped. By stopping the operation of each of the actuators 8 and 9, the rear two wheels can be maintained in a state where the parking braking force is applied.

[0023] When the ECU 2 determines that the vehicle speed calculated by the operation of the switch 3 exceeds the stop determination speed V1 and the vehicle is in a running state, it is determined that the occupant has operated the switch 3 to start emergency braking control to brake the running vehicle. The operation of the switch 3 by the occupant corresponds to the operation of the parking brake device by the occupant.

[0024] When performing emergency brake control on a moving vehicle, the ECU2 operates each actuator 8, 9 until the braking force applied to the rear two wheels reaches a predetermined braking force, which is different from the case of applying the parking braking force to a stationary vehicle. While the occupant is operating the switch 3 in a moving vehicle, the ECU2 continues to operate each actuator 8, 9 for applying brakes to the rear two wheels.

[0025] During emergency brake control, if the ECU2 detects from the wheel speeds detected by the wheel speed sensors 6, 7 that the rear two wheels are locked, it executes emergency brake control as braking control with anti-lock control. In the emergency brake control with anti-lock control, the ECU2 intermittently operates each of the actuators 8, 9 to alternately repeat the brake operation and the brake release operation by the motor-driven parking brake device.

[0026] In the brake operation, the ECU2 sets the braking force applied to the rear two wheels to a predetermined braking force. In the brake release operation, the ECU2 sets the braking force applied to the rear two wheels to zero to release the emergency brake on the rear two wheels.

[0027] The ECU2 in FIG. 1 calculates the vehicle speed during emergency brake control from the wheel speeds detected by the wheel speed sensors 4 to 7. If the ECU2 determines that the vehicle speed during emergency brake control has become equal to or lower than the stop determination speed V1 and the vehicle has reached a stopped state, it operates the actuators 8, 9 until the vehicle reaches a stopped state with the parking braking force applied to the rear two wheels, and then stops the operation of the actuators 8, 9 in the stopped state. If the ECU2 detects that the occupant has stopped operating the switch 3 before the vehicle speed during emergency brake control becomes equal to or lower than the stop determination speed V1, it operates each actuator 8, 9 until the braking force applied to the rear two wheels disappears to release the brake and terminates the emergency brake control.

[0028] During emergency braking control with anti-lock control, each time the parking brake device repeatedly alternates between a braking operation and a brake release operation, actuators 8 and 9 convert the rotation of the motor 10 in FIG. 2 into linear motion to move the brake pad 15. The responsiveness of the anti-lock control in which the parking brake device repeatedly performs a braking operation and a brake release operation becomes extremely lower than the control in the case of moving the brake pad 15 by a cylinder or the like that moves in a linear motion.

[0029] When the responsiveness of the anti-lock control is low, compared to the case where the responsiveness is high, the time required to return the state of the parking brake device from the brake release operation to the braking operation increases, the start of the braking operation is delayed, and the deceleration of the vehicle during emergency braking control decreases.

[0030] On a high μ road where the friction coefficient with the tire is high, even if the deceleration of the vehicle during emergency braking control decreases, the braking force (EPB braking force) of the parking brake device shown in the lower graph of FIG. 3 acts during the braking operation, and the vehicle decelerates at a greater deceleration than on a low μ road where the friction coefficient is low. On a high μ road, since the vehicle decelerates at a greater deceleration than on a low μ road, the creep torque T shown in the middle graph of FIG. 3 is generated due to the decrease in the vehicle speed V, and even if it is transmitted to the wheels during the brake release operation, the vehicle speed V does not increase.

[0031] On a high μ road, since the vehicle speed V does not increase due to the creep torque T, the vehicle speed V decreases to a speed below the stop determination speed V1 shown in the upper graph of FIG. 3 due to the EPB braking force during the braking operation. On a high μ road, even if emergency braking control with anti-lock control is executed, the vehicle can be brought to a stop state at an appropriate speed. When the vehicle comes to a stop state, as shown in the lower part of FIG. 3, the magnitude of the EPB braking force is maintained at the parking braking force.

[0032] On a low - μ road, when the deceleration of the vehicle during emergency brake control decreases, even if the EPB braking force shown in the lower graph of Fig. 4 acts during the braking operation, as shown in the upper graph of Fig. 4, the deceleration of the vehicle becomes smaller than that on a high - μ road. On a low - μ road, since the vehicle decelerates at a lower deceleration than on a high - μ road, when the creep torque T shown in the middle graph of Fig. 4 is generated due to the decrease in vehicle speed V and is transmitted to the wheels during the brake release operation, the vehicle speed V increases.

[0033] On a low - μ road, since the vehicle speed V increases due to the creep torque T, it becomes difficult for the vehicle speed V to decrease to a speed below the stop determination speed V1 shown in the upper graph of Fig. 4 with the EPB braking force during the braking operation. When the emergency brake control with anti - lock control is executed during driving on a low - μ road, it is assumed that it takes time to stop the vehicle and it becomes difficult to stop the vehicle at an appropriate speed.

[0034] During the emergency brake control with anti - lock control, when the acceleration amount during the brake release operation of the vehicle becomes equal to or greater than the deceleration amount during the brake operation of the vehicle, the ECU2 of the present embodiment restricts the execution of the anti - lock control.

[0035] The acceleration amount during the brake release operation of the vehicle can be obtained, for example, based on the operation time t2 of the brake release operation in the EPB braking force shown in the lower graph of Fig. 5 and the acceleration α2 during the brake release operation of the vehicle. The operation time t2 of the brake release operation is the time of the brake release operation in one cycle of the anti - lock control. The acceleration α2 during the brake release operation of the vehicle is the acceleration when the creep torque T shown in the middle graph of Fig. 5 is transmitted to the wheels during the brake release operation and the vehicle speed V increases.

[0036] In this embodiment, the ECU 2 multiplies the acceleration α2 in the brake release operation of the vehicle by the operation time t2 of the brake release operation to obtain the acceleration amount α2×t2 in the brake release operation of the vehicle. The operation time t2 of the brake release operation may be, for example, the length of the brake release operation when performing anti-lock control under standard conditions, or may be predetermined as the length of the brake release operation. The acceleration amount in the brake release operation of the vehicle may be obtained by a method other than multiplying the acceleration α2 in the brake release operation of the vehicle by the operation time t2 of the brake release operation.

[0037] The deceleration amount in the braking operation of the vehicle can be obtained, for example, based on the operation time t1 of the braking operation in the EPB braking force shown in the lower graph of FIG. 5 and the deceleration α1 in the braking operation of the vehicle. The operation time t1 of the braking operation is the time of the braking operation in one cycle of the anti-lock control. The deceleration α1 in the braking operation of the vehicle is the deceleration when the vehicle speed V decreases due to the EPB braking force acting during the braking operation.

[0038] In this embodiment, the ECU 2 multiplies the deceleration α1 in the braking operation of the vehicle by the operation time t1 of the braking operation to obtain the deceleration amount α1×t1 in the braking operation of the vehicle. The operation time t1 of the braking operation may be, for example, the length of the braking operation when performing anti-lock control under standard conditions, or may be predetermined as the length of the braking operation. The deceleration amount in the braking operation of the vehicle may be obtained by a method other than multiplying the deceleration α1 in the braking operation of the vehicle by the operation time t1 of the braking operation.

[0039] In this embodiment, while restricting the execution of the anti-lock control, the ECU 2 aborts the brake release operation and continues the braking operation. When the execution of the anti-lock control is restricted and the braking operation is continued, the increase in the vehicle speed V during the brake release operation due to the creep torque T generated by the decrease in the vehicle speed V disappears. By eliminating the increase in the vehicle speed V due to the creep torque T, the vehicle speed V decreases to a speed below the stop determination speed V1 by the EPB braking force during the braking operation, as shown in the upper graph of FIG. 5.

[0040] On a high - μ road, even if the creep torque T is transmitted to the wheels during the brake release operation and the vehicle speed V does not increase, it is meaningful to continue the anti - lock control without restriction even if the acceleration amount during the vehicle's brake release operation is greater than or equal to the deceleration amount during the brake operation. It may be limited to the case where the road surface during running is a low - μ road when restricting the anti - lock control when the acceleration amount during the vehicle's brake release operation becomes greater than or equal to the deceleration amount during the brake operation.

[0041] Whether the road surface during running is a low - μ road or not can be determined based on the friction coefficient μ of the running road surface on which the vehicle is running. The friction coefficient μ of the running road surface can be detected, for example, based on the slope of the vehicle speed V when the ECU2 starts the emergency brake control. The frame on the upper graph in FIG. 5 shows an example of the detection period Dp of the vehicle speed V used to detect the friction coefficient μ.

[0042] The friction coefficient μ of the running road surface may be detected by calculation based on the wheel speeds of the driving wheels detected by the wheel speed sensors 4 and 5 of the front two wheels and the EPB braking force during the detection period Dp. The friction coefficient μ of the running road surface may be detected by estimation based on the acceleration of the vehicle detected by an acceleration sensor (not shown) and the EPB braking force during the detection period Dp. The method for obtaining the friction coefficient μ of the running road surface is not limited to the methods described above.

[0043] An example of the procedure when the ECU2 executes the brake control method according to the present embodiment will be described with reference to the flowchart in FIG. 6. The ECU2 determines whether it has detected an operation of the switch 3 by a sensor (not shown) by the vehicle occupant (Is there an EPB switch operation?) (step S101). If it has not detected an operation of the switch 3 (NO in step S101), it ends a series of processes. If it has detected an operation of the switch 3 (YES in step S101), the ECU2 determines whether the vehicle speed V is a speed higher than the stop determination speed V1 (step S103).

[0044] When the vehicle speed V does not exceed the stop determination speed V1 (NO in step S103), the ECU2 executes parking braking (step S105), applies parking braking force to the rear two wheels by the respective actuators 8 and 9, and then ends a series of processes. When the vehicle speed V exceeds the stop determination speed V1 (YES in step S103), the ECU2 starts emergency brake control and operates the respective actuators 8 and 9 so that a predetermined braking force by the emergency brake is applied (step S107).

[0045] The ECU2 detects the friction coefficient μ of the driving road surface (step S109) and detects the creep torque T of the power train 1 (step S111). The creep torque T can be detected by calculation, for example, based on a control value indicating the output of the power train 1. The ECU2 calculates the operation times t1 and t2 of standard brake operation and brake release operation (step S113). The operation times t1 and t2 of standard brake operation and brake release operation may be, for example, those determined in advance and stored in a memory (not shown) of the ECU2. The order of step S109 to step S113 may be reversed.

[0046] The ECU2 calculates the deceleration (emergency brake deceleration) α1 in the brake operation of the vehicle and the acceleration (power train acceleration) α2 in the brake release operation of the vehicle (step S115). The deceleration α1 in the brake operation of the vehicle is the deceleration by the EPB braking force acting during the brake operation on the road surface with the friction coefficient μ detected in step S109. The acceleration α2 of the vehicle is the acceleration during the brake release operation by the creep torque T detected in step S111.

[0047] ECU2 determines whether the deceleration amount α1×t1 during the braking operation of the vehicle exceeds the acceleration amount α2×t2 during the brake release operation of the vehicle (step S117). If the deceleration amount α1×t1 of the vehicle exceeds the acceleration amount α2×t2 (YES in step S117), it is determined that the acceleration amount α2×t2 is not greater than or equal to the deceleration amount α1×t1, and the anti-lock control is continued (step S119), and a series of processes are terminated. If the deceleration amount α1×t1 of the vehicle does not exceed the acceleration amount α2×t2 (NO in step S117), it is determined that the acceleration amount α2×t2 is greater than or equal to the deceleration amount α1×t1, and the anti-lock control is prohibited (step S121), and a series of processes are terminated.

[0048] When ECU2 has already executed the emergency brake control involving anti-lock control, in step S119, the ongoing anti-lock control is continued. When ECU2 has not executed the emergency brake control involving anti-lock control, in step S119, the anti-lock control is continued by setting an enable flag that enables the anti-lock control.

[0049] The enable flag can be, for example, a flag that ECU2 refers to when the conditions for executing the emergency brake control involving anti-lock control are satisfied. When the referred enable flag is set, ECU2 executes the emergency brake control involving anti-lock control. Even if the conditions for executing the emergency brake control involving anti-lock control are satisfied, if the referred enable flag is not set at that time, ECU2 does not execute the emergency brake control involving anti-lock control.

[0050] When ECU2 has already executed the emergency brake control involving anti-lock control, in step S121, the ongoing anti-lock control is stopped to prohibit the anti-lock control. When ECU2 has not executed the emergency brake control involving anti-lock control, in step S121, the anti-lock control is prohibited by clearing the enable flag.

[0051] ECU2 may determine whether the vehicle deceleration amount α1×t1 in step S117 exceeds the acceleration amount α2×t2 based on whether the creep torque T detected in step S111 is less than or equal to the torque threshold T1 shown in the middle graph of FIG. 5. The torque threshold T1 can be determined, for example, based on the value of the deceleration torque acting on the vehicle due to the EPB braking force and the ratio of the operation times t1 and t2 of the standard braking operation and the brake release operation. The deceleration torque of the vehicle due to the EPB braking force can be obtained, for example, based on the deceleration amount of the vehicle due to the EPB braking force and the known vehicle weight.

[0052] When the creep torque T detected in step S111 is less than or equal to the torque threshold T1, ECU2 can determine that the vehicle deceleration amount α1×t1 exceeds the acceleration amount α2×t2 and the acceleration amount α2×t2 is not greater than or equal to the deceleration amount α1×t1. When the creep torque T detected in step S111 is not less than or equal to the torque threshold T1, ECU2 can determine that the vehicle deceleration amount α1×t1 does not exceed the acceleration amount α2×t2 and the acceleration amount α2×t2 is greater than or equal to the deceleration amount α1×t1.

[0053] By executing the process of step S117 in FIG. 6, ECU2 can function as a determination unit. According to the result of the determination in step S117, by executing the processes of step S119 and step S121, ECU2 can function as a restriction unit.

[0054] In this embodiment, ECU2 determines whether the acceleration amount α2×t2 is greater than or equal to the deceleration amount α1×t1 based on whether the deceleration amount α1×t1 in the vehicle braking operation exceeds the acceleration amount α2×t2 in the vehicle brake release operation. Based on the result of the determination, ECU2 identifies a scene where vehicle re-acceleration is assumed in the emergency braking control with anti-lock control. Anti-lock control is prohibited in the scene where vehicle re-acceleration is assumed to prevent vehicle re-acceleration.

[0055] When the ECU2 prohibits anti-lock control in a scene where re-acceleration of the vehicle is assumed, the anti-lock control is continued on a high-friction road to eliminate the locked state, and on a low-friction road, the prohibition of anti-lock control improves the stopping performance of the vehicle by emergency braking control. In the braking control method of the present embodiment, it is possible to achieve both improvement in vehicle behavior on a high-friction road and improvement in the stopping performance of the vehicle on a low-friction road.

[0056] In the braking control method of the present embodiment, when the ECU2 executes the braking control method according to the present embodiment by the processing of the procedure in FIG. 6, it is possible to prevent the vehicle from re-accelerating during emergency braking control involving anti-lock control by the motor-driven parking brake device. By suppressing the re-acceleration of the vehicle during emergency braking control, even on a low-friction road with a low friction coefficient between the tire and the road surface, the speed of the vehicle can be reduced to a stopped state at an appropriate speed by emergency braking control involving anti-lock control.

[0057] In the braking control method of the present embodiment, the ECU2 executes the processing of the procedure after step S107 only when it is confirmed that the vehicle occupant has operated the switch 3 during driving. In the braking control method of the present embodiment, it is possible to prevent the execution of the processing related to the prohibition of anti-lock control in a state other than during emergency braking control.

[0058] In the braking control method of the present embodiment, the ECU2 obtains the deceleration amount in the braking operation of the vehicle by multiplying the deceleration α1 in the braking operation of the vehicle by the operation time t1 of the braking operation. Further, the ECU2 obtains the acceleration amount in the brake release operation of the vehicle by multiplying the acceleration α2 in the brake release operation of the vehicle by the operation time t2 of the brake release operation. Both the deceleration amount in the braking operation of the vehicle and the acceleration amount in the brake release operation can be easily obtained using values that can be detected or measured in the vehicle, known values, etc.

[0059] (Second Embodiment) In the first embodiment, the ECU 2 determines whether or not the vehicle occupant has operated the switch 3 during travel. When it is determined that the vehicle occupant has operated the switch 3 during travel, the ECU 2 determines whether or not the acceleration amount in the vehicle brake release operation is equal to or greater than the deceleration amount in the vehicle braking operation. However, the determination as to whether or not the vehicle occupant has operated the switch 3 during travel may be omitted. When this determination is omitted, the ECU 2 determines whether or not the acceleration amount in the vehicle brake release operation is equal to or greater than the deceleration amount in the vehicle braking operation regardless of whether or not the switch 3 has been operated.

[0060] The brake control method according to the second embodiment of the present invention can be realized using the configuration shown in FIGS. 1 and 2, similarly to the brake control method of the first embodiment. However, in the brake control method of the second embodiment, the ECU 2 in FIG. 1 does not perform the procedures of steps S101 and S103 in FIG. 6, but executes the procedures after step S107. When the ECU 2 in FIG. 1 executes the brake control method of the second embodiment by the procedures after step S107, the brake control device according to the second embodiment of the present invention can be configured. In the brake control method and the brake control device of the second embodiment, the processing load on the ECU 2 can be reduced.

[0061] (Third Embodiment) In each of the above-described embodiments, when the ECU 2 determines that the vehicle speed V exceeds the stop determination speed V1 and the vehicle is in a traveling state, the ECU 2 unconditionally determines whether or not the acceleration amount in the vehicle brake release operation is equal to or greater than the deceleration amount in the vehicle braking operation. However, the ECU 2 may determine whether or not the acceleration amount in the vehicle brake release operation is equal to or greater than the deceleration amount in the vehicle braking operation only when the vehicle speed V has decreased to the speed at which the creep torque T is generated.

[0062] The acceleration amount in the brake release operation of the vehicle is generated by the creep torque T generated by the decrease in the vehicle speed V. If the vehicle speed V has not decreased to the speed at which the creep torque T is generated, the acceleration amount in the brake release operation of the vehicle will not occur. When the vehicle speed V has not decreased to the speed at which the creep torque T is generated, it is not necessary to determine whether the acceleration amount in the brake release operation of the vehicle is greater than or equal to the deceleration amount in the brake operation of the vehicle by the process of step S117 in FIG. 6.

[0063] The brake control method according to the third embodiment of the present invention can be realized using the configurations shown in FIGS. 1 and 2, similar to the brake control methods of the first and second embodiments. However, in the brake control method of the third embodiment, before determining whether the acceleration amount in the brake release operation of the vehicle is greater than or equal to the deceleration amount in the brake operation of the vehicle, the ECU 2 determines whether the vehicle speed V is lower than a predetermined determination speed. The predetermined determination speed can be, for example, the reference speed V2 shown in the upper graph of FIG. 7. FIG. 7 shows an example when the road surface during vehicle travel is a low-μ road.

[0064] The reference speed V2 is higher than the speed at which the creep torque T in the middle graph of FIG. 7 is generated in the vehicle. The determination of whether the vehicle speed V is lower than the reference speed V2 can be performed, for example, in step S108 between step S107 and step S109 of FIG. 6, as shown in the flowchart of FIG. 8.

[0065] When the vehicle speed V is lower than the reference speed V2 (YES in step S108), the ECU 2 transfers the process to step S109 of FIG. 6. When the vehicle speed V is not lower than the reference speed V2 (NO in step S108), the series of processes is terminated. The ECU 2 determines whether the acceleration amount in the brake release operation of the vehicle is greater than or equal to the deceleration amount in the brake operation of the vehicle by the process of step S117 in FIG. 6 only when the vehicle speed V is lower than the reference speed V2.

[0066] In the braking control method of the third embodiment, when the vehicle speed V has not decreased to the speed at which the creep torque T is generated, the ECU2 omits the execution of the procedure necessary to determine whether the acceleration amount in the brake release operation of the vehicle is greater than or equal to the deceleration amount in the braking operation. The procedure to be omitted can be, for example, steps S109 to S115 in FIG. 6. When the ECU2 in FIG. 1 executes the braking control method of the third embodiment described above, it can constitute a braking control device according to the third embodiment of the present invention. In the braking control method and the braking control device of the third embodiment, the processing load on the ECU2 can be reduced.

[0067] (Fourth Embodiment) In each of the above-described embodiments, the ECU2 determines whether the acceleration amount in the brake release operation of the vehicle is greater than or equal to the deceleration amount in the braking operation of the vehicle regardless of whether the road surface during traveling is a low-μ road or a high-μ road. However, the ECU2 may determine whether the acceleration amount in the brake release operation of the vehicle is greater than or equal to the deceleration amount in the braking operation of the vehicle only when the road surface during traveling is a low-μ road.

[0068] When the road surface during traveling is a high-μ road, the deceleration amount in the braking operation of the vehicle exceeds the acceleration amount in the brake release operation of the vehicle due to the creep torque T even if the vehicle speed V decreases and the creep torque T is generated. When the road surface during traveling is a high-μ road, it becomes unnecessary to determine whether the acceleration amount in the brake release operation of the vehicle is greater than or equal to the deceleration amount in the braking operation of the vehicle by the processing in step S117 of FIG. 6.

[0069] The brake control method according to the fourth embodiment of the present invention can be realized using the configurations shown in FIGS. 1 and 2, similar to the brake control methods of the first to third embodiments. However, in the brake control method of the fourth embodiment, before determining whether the acceleration amount during the brake release operation of the vehicle is equal to or greater than the deceleration amount during the brake operation of the vehicle, the ECU2 determines whether the friction coefficient μ of the running road surface is equal to or less than a reference friction coefficient μ1 which is a predetermined threshold value. The reference friction coefficient μ1 is a friction coefficient serving as a criterion for determining whether the running road surface is a low-μ road or a high-μ road. The determination of whether the friction coefficient μ of the running road surface is equal to or less than the reference friction coefficient μ1 can be made, for example, at step S110 between step S109 and step S111 in FIG. 6, as shown in the flowchart of FIG. 9.

[0070] When the friction coefficient μ of the running road surface is equal to or less than the reference friction coefficient μ1 (YES at step S110), the ECU2 determines that the acquired friction coefficient μ is equal to or less than a predetermined threshold value, and transfers the process to step S111 in FIG. 6. When the friction coefficient μ of the running road surface exceeds the reference friction coefficient μ1 (NO at step S110), the series of processes is terminated. The ECU2 determines whether the acceleration amount during the brake release operation of the vehicle is equal to or greater than the deceleration amount during the brake operation of the vehicle by the process of step S117 in FIG. 6 only when the friction coefficient μ is equal to or less than the reference friction coefficient μ1.

[0071] In the brake control method of the fourth embodiment, when the friction coefficient μ is not so low that the acceleration amount during the brake release operation of the vehicle becomes equal to or greater than the deceleration amount during the brake operation as the vehicle speed V decreases, the ECU2 omits the execution of some procedures. The procedures to be omitted are the procedures necessary for determining whether the acceleration amount during the brake release operation of the vehicle is equal to or greater than the deceleration amount during the brake operation, and can be, for example, steps S111 to S115 in FIG. 6. When the ECU2 in FIG. 1 executes the brake control method of the fourth embodiment described above, it can constitute a brake control device according to the fourth embodiment of the present invention. In the brake control method and the brake control device of the fourth embodiment, the processing load on the ECU2 can be reduced.

[0072] (Fifth Embodiment) In each of the above-described embodiments, when the ECU 2 determines that the acceleration amount in the brake release operation of the vehicle is equal to or greater than the deceleration amount in the brake operation by the process of step S117 in FIG. 6, the anti-lock control is prohibited in step S121 in FIG. 6. However, instead of prohibiting the anti-lock control during emergency braking, the ECU 2 may limit it.

[0073] The brake control method according to the fifth embodiment of the present invention can be realized using the configurations shown in FIGS. 1 and 2, similarly to the brake control methods of the first to fourth embodiments. However, in the brake control method of the fifth embodiment, the ECU 2 Brake operation When the deceleration amount in does not exceed the acceleration amount in the brake release operation (NO in step S117 of FIG. 6), instead of prohibiting the anti-lock control, it limits it.

[0074] When the ECU 2 determines NO in step S117 of FIG. 6 and determines that the acceleration amount in the brake release operation of the vehicle is equal to or greater than the deceleration amount in the brake operation, as shown in FIG. 10, the content of the anti-lock control is changed to the restricted content (step S122). By changing the content of the anti-lock control in step S122, the ECU 2 restricts the anti-lock control. After changing the content of the anti-lock control during emergency braking to the restricted content in step S122, a series of processes are terminated.

[0075] The restriction of the anti-lock control can be performed, for example, by reducing the brake release amount in the brake release operation compared to when the anti-lock control is not restricted. When the brake release amount in the brake release operation is reduced, as in the restricted region Ra of the anti-lock control shown in the lower graph of FIG. 11, at the operation time t2 of the brake release operation, a lower EPB braking force than the operation time t1 of the brake operation is applied to the rear two wheels of the vehicle. FIG. 11 shows an example when the road surface during vehicle travel is a low-μ road.

[0076] In the brake control method of the fifth embodiment, even if the acceleration amount during the brake release operation of the vehicle due to the creep torque T shown in the middle graph of FIG. 11 is equal to or greater than the deceleration amount during the brake operation of the vehicle, the re-acceleration of the vehicle can be suppressed by the EPB braking force. That the re-acceleration of the vehicle can be suppressed due to the limitation of the anti-lock control can be clarified, for example, by comparing the graph of the vehicle speed V shown in the upper part of FIG. 11 with the graph of the vehicle speed V shown in the upper part of FIG. 4.

[0077] In the part of the brake release operation after the creep torque T occurs in the graph of the vehicle speed V shown in the upper part of FIG. 4, the re-acceleration of the vehicle occurs due to the occurrence of the creep torque T. The vehicle speed Vt2 in the part of the brake release operation in the anti-lock control limit region Ra shown in the upper graph of FIG. 11 also shows that the vehicle is re-accelerated due to the occurrence of the creep torque T. However, in the anti-lock control limit region Ra, since the EPB braking force during the brake release operation is not set to zero, the magnitude of the re-acceleration is suppressed compared to the case where the anti-lock control is executed.

[0078] Also, in the brake control method of the fifth embodiment, even if the anti-lock control is restricted, the EPB braking force during the brake release operation is lower than that during the brake operation. Therefore, even if the anti-lock control is restricted, the lock can be released during the brake release operation.

[0079] In the fifth embodiment, the ECU 2 executes the process of the procedure in which step S121 in FIG. 6 is replaced with step S122 in FIG. 10, thereby executing the brake control method of the fifth embodiment. The ECU 2 in FIG. 1 can constitute a brake control device according to the fifth embodiment of the present invention when executing the brake control method of the fifth embodiment. In the brake control method and the brake control device of the fifth embodiment, the re-acceleration of the vehicle during the emergency brake control involving the anti-lock control by the motor-driven parking brake device can be suppressed.

[0080] Note that each of the above-described embodiments is an example of the present invention. Therefore, the present invention is not limited to each of the above-described embodiments, and various modifications can be made according to the design and the like as long as they do not deviate from the technical idea of the present invention even in forms other than the above-described embodiments.

Explanation of Reference Numerals

[0081] 2 ECU (Parking Brake Device, Determination Unit, Limitation Unit) 3 Switch (Parking Brake Device) 4 - 7 Wheel Speed Sensors (Parking Brake Device) 8, 9 Actuator (Parking Brake Device) 10 Motor T Creep Torque T1 Torque Threshold t1 Brake Operation Time t2 Brake Release Operation Time V Vehicle Speed V2 Reference Speed (Predetermined Determination Speed) α1 Deceleration α2 Acceleration μ Friction Coefficient μ1 Reference Friction Coefficient (Predetermined Threshold)

Claims

1. Braking control by a motor-driven parking brake device, during the execution of the braking control involving antilock control that alternately repeats a braking operation and a brake release operation while the vehicle is running, determining whether an acceleration amount in the brake release operation of the vehicle is equal to or greater than a deceleration amount in the braking operation of the vehicle, when the acceleration amount is equal to or greater than the deceleration amount, restricting the execution of the antilock control, A braking control method.

2. Determining whether the speed of the vehicle during running is lower than a predetermined determination speed, and when the speed during running is lower than the predetermined determination speed, determining whether the acceleration amount is equal to or greater than the deceleration amount. The braking control method according to claim 1.

3. The braking control involving the antilock control is an emergency braking control for braking the running vehicle by an operation of the parking brake device by an occupant of the vehicle. The braking control method according to claim 1 or 2.

4. When the emergency brake is activated, obtaining a friction coefficient of the running road surface of the vehicle, and when the obtained friction coefficient is equal to or less than a predetermined threshold value, determining whether the acceleration amount is equal to or greater than the deceleration amount. The braking control method according to claim 3.

5. Obtaining the deceleration amount based on an operation time of the braking operation in one cycle of the antilock control and a deceleration in the braking operation of the vehicle. The braking control method according to any one of claims 1 to 4.

6. Obtaining the acceleration amount based on an operation time of the brake release operation in one cycle of the antilock control and an acceleration in the brake release operation of the vehicle. The braking control method according to any one of claims 1 to 5.

7. Restricting the antilock control by reducing a brake release amount in the brake release operation as compared to when the antilock control is not restricted. The braking control method according to any one of claims 1 to 6.

8. Braking control by a motor-driven parking brake device, during the execution of the braking control involving antilock control that alternately repeats a braking operation and a brake release operation while the vehicle is running, a determination unit that determines whether an acceleration amount in the brake release operation of the vehicle is equal to or greater than a deceleration amount in the braking operation of the vehicle, A limiting unit that restricts execution of the antilock control when, as a result of determination by the determination unit, the acceleration amount is greater than or equal to the deceleration amount; A brake control device including the same.

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