Brake control system

Abstract

Regarding the braking control system of a vehicle that performs anti-lock braking control, it suppresses vehicle behavior that is contrary to the driver's intentions. [Solution] The braking control device 50 includes a control unit M21 that performs anti-lock brake control. The braking control device 50 also includes an acquisition unit M11 that acquires lateral acceleration and yaw angular acceleration. The control unit M21 starts a prohibition process to prohibit the execution of anti-lock brake control for the rear wheels 13 if the absolute value of the lateral acceleration is greater than or equal to a prohibition determination value, and terminates the prohibition process when the absolute value of the yaw angular acceleration, which was greater than or equal to a turning tendency determination value during the execution of the prohibition process, falls below the turning tendency determination value.

Description

Technical Field

[0001] The present invention relates to a braking control device.

Background Art

[0002] Patent Document 1 describes an anti-lock brake control executed during a vehicle's turning.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In motorsports or the like, a driver may intentionally cause the rear wheels of a vehicle to skid. In a control device as described in Patent Document 1, intentional skidding by the driver is not considered. For this reason, even if the driver intentionally performs an operation that induces skidding, the anti-lock brake control may intervene and suppress the skidding contrary to the driver's intention. Thus, there were cases where the driver could not perform the desired driving.

Means for Solving the Problems

[0005] A braking control device for solving the above problems includes a control unit that performs anti-lock brake control to suppress the locking of the wheels by adjusting the braking force applied to the wheels of the vehicle, and an acquisition unit that acquires the lateral acceleration and yaw angular acceleration of the vehicle. The control unit initiates a prohibition process to prohibit the execution of the anti-lock brake control on the rear wheels if the absolute value of the lateral acceleration is greater than or equal to a prohibition determination value which is a determination value for prohibiting the anti-lock brake control. The prohibition process is terminated when the absolute value of the yaw angular acceleration during the prohibition process falls from a state in which it is greater than or equal to a turning tendency determination value which is a determination value indicating that the vehicle is turning to a state below the turning tendency determination value. [Effects of the Invention]

[0006] It can suppress vehicle behavior that goes against the driver's intentions. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram showing the braking control device in the first embodiment and a vehicle equipped with the braking control device. [Figure 2] Figure 2 is a flowchart showing the processing flow performed by the braking control device shown in Figure 1. [Figure 3] Figure 3 is a flowchart showing the processing flow performed by the braking control device shown in Figure 1. [Figure 4] Figure 4 shows the region in which the braking control device shown in Figure 1 prohibits the execution of anti-lock braking control for the rear wheels, based on the relationship between the vehicle's lateral acceleration and deceleration. [Figure 5] Figure 5 shows an example of a change in the region where anti-lock brake control is prohibited in relation to the vehicle's lateral acceleration and deceleration. [Figure 6] Figure 6 is a schematic diagram showing the braking control device in the second embodiment and a vehicle equipped with the braking control device. [Figure 7]Figure 7 is a flowchart showing the processing flow performed by the braking control device shown in Figure 6. [Figure 8] Figure 8 is a flowchart showing the processing flow performed by the braking control device shown in Figure 6. [Figure 9] Figure 9 is a timing chart showing an example of the control mode by the braking control device in Figure 6. [Modes for carrying out the invention]

[0008] (First Embodiment) The braking control device of the first embodiment will be described with reference to the drawings. Figure 1 shows a braking control device 50 and a vehicle 10 equipped with the braking control device 50.

[0009] An example of a vehicle 10 is described. For example, vehicle 10 includes a braking operating member 11, a steering member 14, multiple wheels, multiple friction brakes 20, and a braking actuator 30. The braking operating member 11 is a member operated by the driver when applying braking force to vehicle 10. An example of the braking operating member 11 is a brake pedal. The steering member 14 is a member operated by the driver when turning vehicle 10. An example of the steering member 14 is a steering wheel. The multiple wheels include two front wheels 12 and two rear wheels 13.

[0010] <Friction brakes> Multiple friction brakes 20 each apply braking force to their corresponding wheels. Each friction brake 20 comprises a wheel cylinder 21, a rotating body 22, and a friction part 23. The rotating body 22 rotates integrally with the wheel. Therefore, braking force is applied to the wheel by pressing the friction part 23 against the rotating body 22. The force pressing the friction part 23 against the rotating body 22 increases with increasing wheel hydraulic pressure, which is the fluid pressure inside the wheel cylinder 21. Therefore, the friction brake 20 can apply greater braking force to the wheel as the wheel hydraulic pressure increases.

[0011] <Braking Actuator> The braking actuator 30 controls the braking force applied to the wheels by controlling the wheel hydraulic pressure of a plurality of wheel cylinders 21. For example, the braking actuator 30 has a pressure source that supplies brake fluid to the plurality of wheel cylinders 21. The pressure source is, for example, an electric pump and an electric cylinder. The braking actuator 30 can individually adjust the wheel hydraulic pressure of the wheel cylinder 21 corresponding to each wheel.

[0012] <Detection system> As shown in FIG. 1, the detection system of the vehicle 10 includes a plurality of sensors that output detection signals to the braking control device 50. The plurality of sensors include, for example, a brake operation amount sensor 101, a wheel speed sensor 102, a steering angle sensor 104, a longitudinal acceleration sensor 111, a lateral acceleration sensor 112, and a yaw rate sensor 113.

[0013] The brake operation amount sensor 101 detects information related to the operation of the braking operation member 11 by the driver. An example of the brake operation amount sensor 101 is a stroke sensor that detects the operation amount of the driver's braking operation member 11. The operation amount of the braking operation member 11 based on the detection signal of the brake operation amount sensor 101 is referred to as "brake operation amount BR".

[0014] The wheel speed sensors 102 are provided for each of the plurality of wheels. The plurality of wheel speed sensors 102 respectively detect the rotational speed of the corresponding wheels. The rotational speed of the wheels based on the detection signal of the wheel speed sensor 102 is referred to as "wheel speed VW". The traveling speed of the vehicle 10 calculated based on the wheel speeds VW of the plurality of wheels is referred to as "vehicle body speed VS". In the present embodiment, a value obtained by reversing the positive and negative signs of the calculation result of differentiating the vehicle body speed VS of the decelerating vehicle 10 with respect to time is defined as "deceleration DVS".

[0015] The steering angle sensor 104 detects the angle of the steering member 14. The angle of the steering member 14 based on the detection signal of the steering angle sensor 104 is referred to as "steering angle θ". The longitudinal acceleration sensor 111 detects the longitudinal acceleration of the vehicle 10 among the accelerations acting on the vehicle 10.

[0016] The lateral acceleration sensor 112 detects the lateral acceleration of the vehicle 10 among the accelerations acting on the vehicle 10. The lateral acceleration of the vehicle 10 derived based on the detection signal of the lateral acceleration sensor 112 is referred to as "lateral acceleration Gy". The lateral acceleration Gy indicates that an acceleration is generated in the right or left direction of the vehicle 10 depending on the sign of the lateral acceleration Gy. For example, a positive lateral acceleration Gy indicates that an acceleration in the right direction is generated with respect to the vehicle 10, and a negative lateral acceleration Gy indicates that an acceleration in the left direction is generated with respect to the vehicle 10.

[0017] The yaw rate sensor 113 detects the angular velocity with respect to the yaw axis of the vehicle 10. The angular velocity derived based on the detection signal of the yaw rate sensor 113 is referred to as "yaw rate Yr". The value obtained by differentiating the yaw rate Yr with respect to time is referred to as "yaw angular acceleration DYr". The yaw angular acceleration DYr corresponds to the change amount of the yaw rate Yr per unit time.

[0018] <Brake control device> As shown in FIG. 1, the brake control device 50 includes a processing circuit 51. An example of the processing circuit 51 is an electronic control unit. In this case, the processing circuit 51 has, for example, a CPU 52, a first memory 53, and a second memory 54. The first memory 53 stores a control program executed by the CPU 52. The second memory 54 stores the calculation results of the CPU 52 and the like. By the CPU 52 executing the control program of the first memory 53, various functions can be realized.

[0019] <Functional configuration of the processing circuit> Referring to FIG. 1, the functional configuration of the processing circuit 51 will be described. By the CPU 52 executing the control program of the first memory 53, the processing circuit 51 functions as a plurality of functional units. Examples of the functional units include an acquisition unit M11 and a control unit M21. The functional unit may include a calculation unit M12.

[0020] The acquisition unit M11 calculates and acquires various parameters of the vehicle 10 based on the detection signals from the detection system. The calculation unit M12 can calculate a reference value for the yaw angular acceleration in the vehicle 10 based on the steering angle θ and vehicle speed VS by using a vehicle model in which the vehicle characteristics of the vehicle 10 are stored. The vehicle model is stored, for example, in the first memory 53. The yaw angular acceleration estimated based on the steering angle θ and vehicle speed VS is called the "yaw angular acceleration reference value DYr*".

[0021] The control unit M21 can control the braking actuator 30 to activate the friction brake 20. By activating the friction brake 20, the control unit M21 can adjust the braking force applied to the wheels of the vehicle 10.

[0022] [ABS control] The control unit M21 can perform anti-lock brake control during braking of the vehicle 10 by adjusting the braking force applied to the wheels to prevent the wheels from locking. Hereafter, anti-lock brake control will be referred to as "ABS control". The control unit M21 can perform ABS control individually for each wheel.

[0023] The control unit M21 determines, for example, that a wheel may lock up if its slip ratio exceeds a slip threshold. When the wheel slip ratio exceeds the slip threshold, the control unit M21 performs ABS control on that wheel. ABS control eliminates wheel slip by repeatedly performing depressurization (reducing braking force) and pressure increase (increasing braking force). The slip threshold is an example of a threshold for initiating anti-lock brake control by determining the occurrence of deceleration slip. The control unit M21 may also be configured to initiate ABS control based on wheel acceleration. For example, the control unit M21 initiates ABS control when it detects a decrease in wheel acceleration. Specifically, if the wheel acceleration is a negative value, ABS control can be initiated when the absolute value of the wheel acceleration exceeds a wheel acceleration determination value. The wheel acceleration determination value is another example of a threshold for initiating anti-lock brake control.

[0024] [Rear wheel ABS disabled] The control unit M21 can perform a prohibition process to prohibit the execution of ABS control for the rear wheels 13 of the vehicle 10. This prohibition process is sometimes called the rear wheel ABS prohibition process. When the rear wheel ABS prohibition process is started, the control unit M21 will not start ABS control for the rear wheels 13 even if the slip ratio exceeds the slip threshold until the rear wheel ABS prohibition process is terminated. The rear wheel ABS prohibition process is a process that prohibits the execution of ABS control for both rear wheels 13 of the vehicle 10. Since the rear wheel ABS prohibition process is a process that prohibits the execution of ABS control for the rear wheels 13, the execution of ABS control for the front wheels 12 is not prohibited even while the rear wheel ABS prohibition process is being performed. The conditions for starting the rear wheel ABS prohibition process and the conditions for terminating the rear wheel ABS prohibition process will be described later.

[0025] <Processing flow to initiate the rear wheel ABS disabling process> Referring to Figure 2, the series of processes performed by the processing circuit 51 will be explained. The processing circuit 51 repeatedly executes the processes shown in Figure 2 at predetermined control cycles.

[0026] In step S101, the processing circuit 51, by functioning as an acquisition unit M11, acquires the deceleration DVS and lateral acceleration Gy. After that, the processing circuit 51 proceeds to step S102.

[0027] In step S102, the processing circuit 51 determines whether the absolute value of the deceleration DVS is greater than or equal to the deceleration threshold DVSth. If the absolute value of the deceleration DVS is greater than or equal to the deceleration threshold DVSth (S102: YES), the processing circuit 51 terminates the series of processes shown in Figure 2. On the other hand, if the absolute value of the deceleration DVS is less than the deceleration threshold DVSth (S102: NO), the processing circuit 51 proceeds to step S103.

[0028] The deceleration threshold DVSth is set as a value that, if the absolute value of the deceleration DVS is greater than or equal to the deceleration threshold DVSth, indicates that vehicle 10 is decelerating rapidly. The deceleration threshold DVSth is set to a value that has been calculated in advance through experiments or other means.

[0029] In step S103, the processing circuit 51 determines whether the absolute value of the lateral acceleration Gy is greater than or equal to the prohibition threshold Gyth1. If the absolute value of the lateral acceleration Gy is less than the prohibition threshold Gyth1 (S103: NO), the processing circuit 51 terminates the series of processes shown in Figure 2. On the other hand, if the absolute value of the lateral acceleration Gy is greater than or equal to the prohibition threshold Gyth1 (S103: YES), the processing circuit 51 proceeds to step S104.

[0030] The prohibition threshold Gyth1 is a threshold value used to prohibit anti-lock brake control. The prohibition threshold Gyth1 is set as a value that allows the vehicle 10 to be determined to be turning if the absolute value of the lateral acceleration Gy is greater than or equal to the prohibition threshold Gyth1. Preferably, the prohibition threshold Gyth1 is large enough that it can be determined that the driver of the vehicle 10 is trying to skid the rear wheels 13 if the absolute value of the lateral acceleration Gy is greater than or equal to the prohibition threshold Gyth1. The prohibition threshold Gyth1 is set to a value that has been calculated in advance through experiments or the like.

[0031] In step S104, the processing circuit 51, by functioning as the control unit M21, initiates the rear wheel ABS disable process. As a result, even if the slip ratio of the rear wheel 13 exceeds the slip threshold, ABS control for the rear wheel 13 will not be initiated. Once the rear wheel ABS disable process is initiated, the processing circuit 51 terminates the series of processes shown in Figure 2.

[0032] <Processing flow for terminating the rear wheel ABS disabling process> Referring to Figure 3, a series of processes executed by the processing circuit 51 during the rear wheel ABS disabling process will be explained. When the rear wheel ABS disabling process is being performed, the processing circuit 51 repeatedly executes the processes shown in Figure 3 at predetermined control cycles.

[0033] In step S201, the processing circuit 51 performs an acquisition process by functioning as an acquisition unit M11. For example, the processing circuit 51 acquires the yaw angular acceleration DYr. The processing circuit 51 may also acquire a yaw angular acceleration reference value DYr*. After performing the acquisition process, the processing circuit 51 proceeds to step S202.

[0034] In step S202, the processing circuit 51 determines whether the restriction release condition is met. If the restriction release condition is not met (S202: NO), the processing circuit 51 terminates the series of processes shown in Figure 3. On the other hand, if the restriction release condition is met (S202: YES), the processing circuit 51 proceeds to step S203.

[0035] Examples of conditions for lifting the ban include the following conditions 1 and 2. The processing circuit 51 determines that the conditions for lifting the ban are met if either condition 1 or condition 2 is met, or if both condition 1 and condition 2 are met.

[0036] Condition 1 is met when the absolute value of the yaw angular acceleration DYr decreases from a state where it is greater than or equal to the turning tendency determination value DYrth to a state where it is less than or equal to the turning tendency determination value DYrth, based on the change in the yaw angular acceleration DYr. The turning tendency determination value DYrth is set as a value that allows the vehicle 10 to be determined to be in a straight line state or close to a straight line state when the absolute value of the yaw angular acceleration DYr is less than the turning tendency determination value DYrth. The turning tendency determination value DYrth is set to a value that has been calculated in advance through experiments, etc.

[0037] Condition 2 is met when the difference between the measured yaw angular acceleration DYr and the reference yaw angular acceleration reference value DYr* is greater than or equal to the deviation judgment value, based on a comparison between the measured yaw angular acceleration DYr and the reference yaw angular acceleration reference value DYr*. The difference between the yaw angular acceleration DYr and the reference yaw angular acceleration reference value DYr* can be calculated, for example, by subtracting the smaller value from the larger value of yaw angular acceleration DYr and reference yaw angular acceleration reference value DYr*. When the vehicle 10 is turning while its rear wheels 13 are skidding, the yaw angular acceleration DYr will deviate to some extent from the reference yaw angular acceleration reference value DYr*. When the vehicle 10 spins, the difference between the yaw angular acceleration DYr and the reference yaw angular acceleration reference value DYr* becomes larger. The deviation judgment value is set to a value that, if the difference between the yaw angular acceleration DYr and the reference yaw angular acceleration reference value DYr* is greater than or equal to the deviation judgment value, indicates that the vehicle 10 may be spinning. In this context, a spin indicates that the driver is having difficulty controlling the turning behavior of vehicle 10. The deviation judgment value is set to a value calculated in advance through experiments, etc.

[0038] In step S203, the processing circuit 51 terminates the rear wheel ABS disable process by functioning as the control unit M21. As a result, when the slip ratio of the rear wheel 13 exceeds the slip threshold, ABS control for the rear wheel 13 is initiated. After terminating the rear wheel ABS disable process, the processing circuit 51 terminates the series of processes shown in Figure 3.

[0039] <Operation and Effects of the First Embodiment> Figure 4 shows the prohibited region A1 in which the braking control device 50 initiates rear wheel ABS disabling processing in relation to the lateral acceleration Gy and deceleration DVS of the vehicle 10.

[0040] According to the braking control device 50, if the absolute value of the lateral acceleration Gy is greater than or equal to the prohibition judgment value Gyth1, the rear wheel ABS prohibition process is initiated, which prohibits the execution of ABS control for the rear wheels 13. In other words, as shown in Figure 4, if the lateral acceleration Gy is less than or equal to the value obtained by multiplying the prohibition judgment value Gyth1 by -1, "-Gyth1", or if the lateral acceleration Gy is greater than or equal to the prohibition judgment value Gyth1, the rear wheel ABS prohibition process is initiated. Therefore, when the driver is turning the vehicle 10 and intentionally trying to cause the rear wheels 13 to skid, the execution of ABS control for the rear wheels 13 is suppressed.

[0041] If ABS control for the rear wheels 13 is disabled, the ABS control will not intervene even if the slip ratio of the rear wheels 13 increases. As a result, the state of a high slip ratio for the rear wheels 13 can be maintained. This prevents the vehicle 10 from behaving contrary to the driver's intention when the driver is trying to turn the vehicle 10 and intentionally cause the rear wheels 13 to skid. Therefore, the vehicle 10 can be driven in the manner desired by the driver.

[0042] According to the braking control device 50, if the absolute value of the lateral acceleration Gy is less than the prohibition judgment value Gyth1, the rear wheel ABS prohibition process is not initiated. In other words, as shown in Figure 4, if the lateral acceleration Gy is greater than the value obtained by multiplying the prohibition judgment value Gyth1 by -1 ("-Gyth1") and less than the prohibition judgment value Gyth1, the rear wheel ABS prohibition process is not initiated. Here, a configuration in which ABS control is not performed on the rear wheels 13 regardless of the lateral acceleration Gy is considered as a comparative example. According to the braking control device 50 of this embodiment, unlike the comparative example, if the absolute value of the lateral acceleration Gy is less than the prohibition judgment value Gyth1, ABS control can be enabled to intervene. Therefore, if the slip ratio of the wheels becomes greater than or equal to the slip threshold when the absolute value of the lateral acceleration Gy is less than the prohibition judgment value Gyth1, the ABS control can be executed, which is expected to have the effect of suppressing the locking of the rear wheels 13.

[0043] In the braking control device 50, if the absolute value of the deceleration DVS is greater than or equal to the deceleration threshold DVSth, the rear wheel ABS prohibition process is not initiated even if the absolute value of the lateral acceleration Gy is greater than or equal to the prohibition judgment value Gyth1. This allows ABS control to intervene regardless of the lateral acceleration Gy in cases where the deceleration is excessively large, for example, when the vehicle 10 is decelerating suddenly.

[0044] The rear wheel ABS disabling process is terminated when the absolute value of the yaw angular acceleration DYr decreases from a state where it is greater than or equal to the turning tendency determination value DYrth to a state where it is less than or equal to the turning tendency determination value DYrth. When the rear wheels 13 of the vehicle 10 skid sideways during a turn, the absolute value of the lateral acceleration Gy gradually decreases, while the absolute value of the yaw angular acceleration DYr increases. Furthermore, as the skid of the rear wheels 13 is resolved and the vehicle 10 returns to a straight-ahead state, the yaw angular acceleration DYr approaches "0". Therefore, it is possible to determine whether or not the skid of the rear wheels 13 has been resolved based on the change in the yaw angular acceleration DYr. Accordingly, the braking control device 50 can terminate the rear wheel ABS disabling process when the driver's intentional skid operation ends.

[0045] The rear wheel ABS disabling process is terminated when the difference between the yaw angular acceleration DYr and the yaw angular acceleration reference value DYr* exceeds a certain deviation threshold. By detecting that the measured value of the yaw angular acceleration deviates from the reference value, ABS control can be enabled to intervene if it becomes difficult for the driver to control the turning behavior of the vehicle 10.

[0046] (Second Embodiment) A braking control device of the second embodiment will now be described. Regarding the second embodiment, explanations of components common to the first embodiment will be omitted as appropriate.

[0047] Figure 6 shows the vehicle 10 described in the first embodiment in more detail. Figure 6 shows the two front wheels 12 of the vehicle 10, namely the left front wheel 12L and the right front wheel 12R. It also shows the two rear wheels 13 of the vehicle 10, namely the left rear wheel 13L and the right rear wheel 13R.

[0048] In Figure 6, the wheel speed sensors 102 corresponding to each wheel are shown as wheel speed sensors 102a, 102b, 102c, and 102d, corresponding to the left front wheel 12L, right front wheel 12R, left rear wheel 13L, and right rear wheel 13R, respectively.

[0049] The vehicle 10 is equipped with a drive unit 40, a drive control device 60, and a drive operating member 15. The drive unit 40 is equipped with a power source for the vehicle 10. Examples of the power source for the vehicle 10 include an internal combustion engine and a motor generator. The drive unit 40 is equipped with a transmission mechanism that transmits the driving force generated by the power source of the vehicle 10 to the wheels. The vehicle 10 shown in Figure 6 can transmit driving force to the left front wheel 12L, the right front wheel 12R, the left rear wheel 13L, and the right rear wheel 13R. In other words, the vehicle 10 is a four-wheel drive vehicle.

[0050] The drive operation member 15 is operated by the driver when applying driving force to the vehicle 10. An example of the drive operation member 15 is the accelerator pedal. The detection system of the vehicle 10 further includes an accelerator pedal operation amount sensor 105. The accelerator pedal operation amount sensor 105 detects the amount of operation of the drive control member 15 by the driver. The amount of operation of the drive control member 15 based on the detection signal of the accelerator pedal operation amount sensor 105 is called the "accelerator pedal operation amount AC".

[0051] The drive control device 60 can control the drive unit 40. The drive control device 60 includes a processing circuit. By controlling the drive unit 40, the drive control device 60 can adjust the driving force applied to the wheels of the vehicle 10. The drive control device 60 can adjust the driving force, for example, based on the accelerator pedal input AC.

[0052] Vehicle 10 is equipped with an in-vehicle network 19. Each processing circuit in vehicle 10 is configured to transmit and receive various types of information via the in-vehicle network 19. For example, the braking control device 50 and the drive control device 60 can transmit and receive various types of information via the in-vehicle network 19.

[0053] <Braking control device> In addition to all the functions described in the first embodiment, the braking control device 50 further implements the following functions.

[0054] [Estimation of road surface friction coefficient] The calculation unit M12 of the braking control device 50 can calculate the road surface friction coefficient μ. The road surface friction coefficient μ is an estimated value of the friction coefficient of the road surface on which the vehicle 10 is traveling. For example, the road surface friction coefficient μ can be obtained by dividing the vehicle deceleration Gx during ABS control by the acceleration due to gravity g. The vehicle deceleration Gx can be derived based on the detection signals of the front and rear acceleration sensors 111.

[0055] 〔ESC〕 The control unit M21 of the braking control device 50 can perform yaw control to suppress excessive oversteer and understeer behavior of the vehicle 10 by individually adjusting the longitudinal force applied to each wheel. Hereafter, yaw control will be referred to as "ESC".

[0056] The control unit M21 controls the behavior of the vehicle 10 by adjusting the driving force and braking force of each wheel based on, for example, the target yaw rate and the actual yaw rate. The control unit M21 starts ESC, for example, when the oversteer tendency based on the yaw rate Yr exceeds a threshold. The control unit M21 also starts ESC, for example, when the understeer tendency based on the yaw rate Yr exceeds a threshold.

[0057] During ESC (Electronic Stability Control), for example, the calculation unit M12 calculates a target value for braking force according to the ESC. The control unit M21 adjusts the braking force based on the target value. Specifically, for each wheel, the ESC calculation pressure PwcESC is calculated as the target value for wheel hydraulic pressure in the wheel cylinder 21. The calculated ESC calculation pressure PwcESC is set as the target WC pressure PwcTar. The braking force is adjusted by controlling the wheel hydraulic pressure based on the target WC pressure PwcTar. The ESC calculation pressure PwcESC is calculated as the target value for braking force according to the ESC.

[0058] Furthermore, while ESC is in operation, the calculation unit M12 calculates a target value for the driving force according to the ESC. The control unit M21 instructs the drive control device 60 to adjust the driving force based on the target value of the driving force. The calculation unit M12 uses a dynamic model of the vehicle 10's motion when calculating target values ​​for braking force and driving force according to the ESC. The dynamic model of the vehicle 10's motion includes, for example, the influence of the road surface friction coefficient μ.

[0059] [ESC restriction processing] The control unit M21 can perform ESC limiting processing to limit the magnitude of the braking force on the rear wheels adjusted by the ESC while the rear wheel ABS disabling process is being performed.

[0060] During the execution of the ESC limit process, the braking forces applied to the left rear wheel 13L and the right rear wheel 13R are limited based on the brake operation amount BR, respectively. Here, the required value of the wheel hydraulic pressure calculated to generate the wheel hydraulic pressure corresponding to the brake operation amount BR is referred to as the required WC pressure PwcReq. The calculation unit M12 calculates the limited WC pressure PwcLim based on the required WC pressure PwcReq. By setting the limited WC pressure PwcLim as the target WC pressure PwcTar by the control unit M21, the braking forces applied to the left rear wheel 13L and the right rear wheel 13R are limited based on the brake operation amount BR, respectively. The limited WC pressure PwcLim corresponds to the limit value based on the brake operation amount BR. When the limited WC pressure PwcLim is greater than the ESC calculated pressure PwcESC, the control unit M21 sets the ESC calculated pressure PwcESC as the target WC pressure PwcTar.

[0061] Since the ESC limit process is a process that limits the braking forces of the left rear wheel 13L and the right rear wheel 13R adjusted by the ESC, the braking forces of the left front wheel 12L and the right front wheel 12R adjusted by the ESC are not limited. That is, even while the ESC limit process is being executed, for the left front wheel 12L and the right front wheel 12R, the ESC calculated pressure PwcESC calculated for each is set as the target WC pressure PwcTar.

[0062] <Flow of the process when the ESC limit process is executed> Referring to FIG. 7, a series of processes executed by the processing circuit 51 will be described. When the braking operation member 11 is operated, the processing circuit 51 repeatedly executes the processes shown in FIG. 7 at every predetermined control cycle.

[0063] In step S301, the processing circuit 51 determines whether the ESC is being executed. If the ESC is not being executed (S301: NO), the processing circuit 51 temporarily ends the series of processes shown in FIG. 7. On the other hand, if the ESC is being executed (S301: YES), the processing circuit 51 proceeds to step S302.

[0064] In step S302, the processing circuit 51 determines whether or not the rear wheel ABS disable process is currently being performed. If the rear wheel ABS disable process is not being performed (S302: NO), the processing circuit 51 terminates the series of processes shown in Figure 7. On the other hand, if the rear wheel ABS disable process is being performed (S302: YES), the processing circuit 51 proceeds to step S303.

[0065] In step S303, the processing circuit 51 performs an acquisition process by functioning as an acquisition unit M11. For example, the processing circuit 51 acquires the accelerator operation amount AC, the requested WC pressure PwcReq, and the rear wheel ESC calculation pressure PwcESC. After performing the acquisition process, the processing circuit 51 moves the process to step S304.

[0066] In step S304, the processing circuit 51 calculates the limiting WC pressure PwcLim. Referring to Figure 8, the processing flow of the processing circuit 51 that is executed in step S304, namely the processing when calculating the limit WC pressure PwcLim, will be explained.

[0067] In step S401 of Figure 8, the processing circuit 51 determines whether the accelerator operation amount AC is greater than the accelerator judgment value ACth. The accelerator judgment value ACth is a value that is set in advance as a threshold value that the drive control device 60 uses to control the driving force based on the accelerator operation amount AC when the accelerator operation amount AC is greater than the accelerator judgment value ACth. In this case, if the accelerator operation amount AC is greater than the accelerator judgment value ACth, it means that the drive operating member 15 is being operated by the driver, or more precisely, that there is a request for driving force. Therefore, by determining whether the accelerator operation amount AC is greater than the accelerator judgment value ACth, it is possible to determine whether the drive operating member 15 is being operated.

[0068] In step S401, if the accelerator operation amount AC is less than or equal to the accelerator judgment value ACth (S401: NO), the processing circuit 51 proceeds to step S402. In step S402, the processing circuit 51 sets the value of the requested WC pressure PwcReq as the limiting WC pressure PwcLim. After that, the processing circuit 51 completes the series of processes shown in Figure 8.

[0069] In step S401, if the accelerator operation amount AC is greater than the accelerator judgment value ACth (S401: YES), the processing circuit 51 proceeds to step S403.

[0070] In step S403, the processing circuit 51 calculates the limit WC pressure PwcLim based on the accelerator operation amount AC. For example, the processing circuit 51 sets the limit WC pressure PwcLim as the value obtained by adding a correction amount X to the value of the requested WC pressure PwcReq. The correction amount X is calculated to be larger the larger the accelerator operation amount AC is, for example. After calculating the limit WC pressure PwcLim, the processing circuit 51 completes the series of processes shown in Figure 8.

[0071] Returning to Figure 7, once the limiting WC pressure PwcLim is calculated in step S304, the processing circuit 51 proceeds to step S305. In step S305, the processing circuit 51 sets the target WC pressure PwcTar. The processing circuit 51 compares the ESC calculated pressure PwcESC and the limit WC pressure PwcLim and sets the smaller value as the target WC pressure PwcTar. Once the target WC pressure PwcTar is set, the processing circuit 51 completes the series of processes shown in Figure 7.

[0072] Furthermore, if a negative determination is made in step S302, that is, if ESC is being performed but the rear wheel ABS disabling process is not being performed, the ESC calculation pressure PwcESC is set as the target WC pressure PwcTar.

[0073] <Operation and Effects of the Second Embodiment> According to the second embodiment, similar to the first embodiment, when the driver is turning the vehicle 10 and intentionally causing the left rear wheel 13L and the right rear wheel 13R to skid, the ABS control is suppressed for the left rear wheel 13L and the right rear wheel 13R. Furthermore, when ESC is implemented, the braking force applied to each of the left rear wheel 13L and the right rear wheel 13R in accordance with the ESC is reduced and limited.

[0074] Referring to Figure 9, an example of the progression of the limiting WC pressure PwcLim calculated during the ESC limiting process is explained. Figure 9(a) shows the required WC pressure PwcReq, ESC calculation pressure PwcESC, and limited WC pressure PwcLim for one of the rear wheels, either the left rear wheel 13L or the right rear wheel 13R.

[0075] Figure 9(b) shows the change in accelerator pedal input AC. The accelerator pedal input AC is greater than the accelerator judgment value ACth from timing t11 onwards. The accelerator pedal input AC is less than or equal to the accelerator judgment value ACth during the period before timing t11.

[0076] As shown in Figure 9(a), during the period before timing t11, the limiting WC pressure PwcLim is equal to the required WC pressure PwcReq. After timing t11, the limiting WC pressure PwcLim is greater than the required WC pressure PwcReq by the amount of correction X corresponding to the accelerator operation amount AC.

[0077] The control unit M21 compares the ESC calculation pressure PwcESC and the limiting WC pressure PwcLim for each of the left rear wheel 13L and the right rear wheel 13R. For each of the left rear wheel 13L and the right rear wheel 13R, the control unit M21 sets the smaller of the ESC calculation pressure PwcESC and the limiting WC pressure PwcLim as the target WC pressure PwcTar. In the example shown in Figure 9, during the period before timing t12, the limiting WC pressure PwcLim is smaller than the ESC calculation pressure PwcESC, so the limiting WC pressure PwcLim is set as the target WC pressure PwcTar. After timing t12, the limiting WC pressure PwcLim is larger than the ESC calculation pressure PwcESC, so the ESC calculation pressure PwcESC is set as the target WC pressure PwcTar.

[0078] If the rear wheel ABS is disabled, i.e., if rear wheel lock-up is permitted, and ESC is implemented, the braking actuator 30 may be controlled to apply a large braking force to the locked rear wheel. Also, for example, in a configuration that calculates the road surface friction coefficient μ while ABS control is being performed, if the rear wheel ABS is disabled, i.e., if rear wheel lock-up is permitted, the road surface friction coefficient μ cannot be calculated. If ESC is implemented at this time, the target value of the braking force corresponding to ESC may become excessively large. In such cases, according to this embodiment, by setting the limiting WC pressure PwcLim as the target WC pressure PwcTar, the upper limit of the braking force applied to the rear wheel becomes the braking force requested by the driver.

[0079] When the rear wheel ABS disabling process is in effect and the drive operating member 15 is operated in addition to the braking operating member 11, driving force is applied to the rear wheels according to the accelerator operation amount AC. Therefore, the probability of the rear wheels locking up is low. Accordingly, in this embodiment, when ESC is implemented while the rear wheel ABS disabling process is in effect and both the braking operating member 11 and the drive operating member 15 are operated, the limiting WC pressure PwcLim is corrected according to the accelerator operation amount AC. This makes it possible to increase the braking force applied to the rear wheels according to the accelerator operation amount AC. As a result, the braking force can be adjusted in order to achieve vehicle behavior control by ESC.

[0080] As described above, the braking control device 50 of the second embodiment can suppress excessive oversteer and understeer behavior of the vehicle 10 while allowing the vehicle 10 to be driven in the manner desired by the driver.

[0081] (Example of change) Each of the above embodiments can be implemented with the following modifications. Each embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0082] In each of the above embodiments, the system is configured not to start the rear wheel ABS disable process if the absolute value of the deceleration DVS is greater than or equal to the deceleration threshold DVSth. This determination based on the deceleration DVS can also be omitted. For example, in the processing flow shown in Figure 2, the process can be configured to proceed from step S101 to step S103 by omitting the process in step S102. In this way, regardless of the magnitude of the deceleration DVS, the decision of whether or not to start the rear wheel ABS disable process may be made based on the absolute value of the lateral acceleration Gy. In this case, it is not necessary to obtain the deceleration DVS in the process of step S101.

[0083] • In each of the above embodiments, a configuration in which the prohibition judgment value Gyth1 is a fixed value was illustrated. Alternatively, the prohibition judgment value Gyth1 may be a variable value. For example, the prohibition judgment value Gyth1 may be a variable value that is set to be larger the greater the deceleration DVS is.

[0084] Figure 5 shows the prohibition threshold Gyth1, which is set to increase as the deceleration DVS increases, and the prohibited area A1 in this case. With this configuration, the area in which the rear wheel ABS prohibition process is not initiated can be made larger as the deceleration DVS increases.

[0085] The braking control device may change the likelihood of ABS control being performed on the rear wheels 13 based on the lateral acceleration Gy. For example, if the absolute value of the lateral acceleration Gy is greater than or equal to the limit judgment value Gyth2 and less than the prohibition judgment value Gyth1, ABS control on the rear wheels 13 is less likely to be performed compared to the case where the absolute value of the lateral acceleration Gy is less than the limit judgment value Gyth2. The limit judgment value Gyth2 is a value smaller than the prohibition judgment value Gyth1. In the above configuration, if the absolute value of the lateral acceleration Gy is less than the limit judgment value Gyth2, the rear wheel ABS prohibition process is not started.

[0086] A configuration that makes it difficult to perform ABS control on the rear wheel 13 may include, but is not limited to, the following: When the absolute value of the lateral acceleration Gy is greater than or equal to the limit judgment value Gyth2, the slip threshold for ABS control on the rear wheel 13 is increased compared to when the absolute value of the lateral acceleration Gy is less than the limit judgment value Gyth2. This makes it difficult to initiate ABS control on the rear wheel 13 when the absolute value of the lateral acceleration Gy is greater than or equal to the limit judgment value Gyth2. In this configuration, the slip threshold for ABS control on the rear wheel 13 may be increased as the absolute value of the lateral acceleration Gy, which is greater than or equal to the limit judgment value Gyth2, approaches the prohibition judgment value Gyth1. In a configuration that initiates ABS control when the value to be judged is greater than or equal to the threshold for initiating ABS control, such as the slip threshold-based configuration described above, ABS control becomes less likely to be performed by correcting the threshold for initiating ABS control to a larger value. On the other hand, in a configuration where ABS control is initiated when the value to be judged is less than the threshold for initiating ABS control, correcting the threshold for initiating ABS control to a smaller value makes it less likely for ABS control to be executed.

[0087] • In the above modification example, the limit judgment value Gyth2 is a fixed value. The limit judgment value Gyth2 may also be a variable value. The limit judgment value Gyth2 may be a variable value that is set to be larger the greater the deceleration DVS is, for example. Figure 5 shows the limit judgment value Gyth2 set to be larger the greater the deceleration DVS is, and the limit region A2 in this case, which makes it difficult to perform ABS control for the rear wheel 13.

[0088] In a configuration where the restriction value Gyth2 is set, the prohibition value Gyth1 may be the same value as the prohibition value Gyth1 in a configuration where the restriction value Gyth2 is not set. In a configuration where the restriction value Gyth2 is set, the prohibition value Gyth1 may be a larger value than the prohibition value Gyth1 in a configuration where the restriction value Gyth2 is not set.

[0089] The restriction judgment value Gyth2 may be smaller than the prohibition judgment value Gyth1 in a configuration without the restriction judgment value Gyth2. The restriction judgment value Gyth2 may also be the same as the prohibition judgment value Gyth1 in a configuration without the restriction judgment value Gyth2.

[0090] In the embodiments described above, conditions 1 and 2 were given as examples of conditions for lifting the prohibition. Condition 2 is not required to be included as a condition for lifting the prohibition. That is, it is possible to determine that the condition for lifting the prohibition is met if condition 1 is met, and that the condition for lifting the prohibition is not met if condition 1 is not met, based solely on condition 1.

[0091] In the second embodiment, a configuration is shown in which the series of processes shown in Figure 7 are repeatedly executed when the braking operation member 11 is operated. Alternatively, the series of processes shown in Figure 7 may be repeatedly executed while the vehicle 10 is braking. Furthermore, the series of processes shown in Figure 7 may be repeatedly executed when the conditions for starting ABS control for the rear wheels are met. For example, the series of processes shown in Figure 7 may be repeatedly executed when the slip ratio of the rear wheels is equal to or greater than the slip threshold.

[0092] In step S401 shown in Figure 8, the accelerator determination value ACth is exemplified as a value that can determine whether or not the drive operating member 15 is being operated. Alternatively, the accelerator determination value ACth may be a value that can determine whether or not enough driving force is being applied to release the lock of the rear wheels.

[0093] As shown in Figure 8, step S402 is illustrated by a configuration in which the value of the requested WC pressure PwcReq is set as the limiting WC pressure PwcLim. The limiting WC pressure PwcLim calculated in step S402 does not necessarily have to be equal to the requested WC pressure PwcReq. For example, the limiting WC pressure PwcLim may be a value obtained by adding a value smaller than the correction amount X to the value of the requested WC pressure PwcReq.

[0094] In step S403 shown in Figure 8, the correction amount X is calculated to be a larger value the larger the accelerator pedal input AC is. Alternatively, the correction amount X may be a fixed value that is set in advance.

[0095] As shown in Figure 8, step S403 is illustrated by a configuration in which the limited WC pressure PwcLim is calculated by adding a correction amount X to the value of the requested WC pressure PwcReq. Alternatively, the limited WC pressure PwcLim may be calculated by multiplying the value of the requested WC pressure PwcReq by a correction amount Y. The correction amount Y is a value calculated so that it is larger the larger the accelerator operation amount AC is. The correction amount Y may also be a fixed value that is set in advance.

[0096] In the second embodiment, an example is given of a configuration in which the wheel hydraulic pressure is controlled based on the target WC pressure PwcTar as the ESC. Alternatively, the wheel hydraulic pressure may be controlled based on the calculated ESC pressure PwcESC. Furthermore, as the ESC limiting process, an example is given of a configuration in which the smaller of the calculated ESC pressure PwcESC and the limiting WC pressure PwcLim is set as the target WC pressure PwcTar, and then the wheel hydraulic pressure is controlled based on the target WC pressure PwcTar. Alternatively, the wheel hydraulic pressure may be controlled based on the smaller of the calculated ESC pressure PwcESC and the limiting WC pressure PwcLim.

[0097] Vehicle 10 is not limited to a four-wheel drive vehicle. Vehicle 10 may be a front-wheel drive vehicle or a rear-wheel drive vehicle. In the case of rear-wheel drive, the driving force is directly transmitted to the rear wheels. In the case of front-wheel drive, the driving force transmitted to the front wheels acts as a propulsive force on vehicle 10, thereby indirectly transmitting the driving force to the rear wheels.

[0098] The processing circuit 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 memory stores program code or instructions configured to cause the CPU to perform the processes. Memory, or storage medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. [Explanation of symbols]

[0099] 10... Vehicles 11... Braking operating member 12…Front wheel 13... Rear wheel 14… Steering components 15…Drive operating member 20… Friction brakes 30... Brake actuator 40…Drive system 50... Brake control device 60…Drive control device 101...Brake operation amount sensor 102...Wheel speed sensor 104... Steering angle sensor 105...Accelerator pedal input sensor 112...Lateral acceleration sensor 113... Yaw rate sensor M11…Acquisition part M12…Calculation part M21... Control Unit

Claims

1. A control unit that performs anti-lock brake control to suppress the locking of the wheels by adjusting the braking force applied to the wheels of the vehicle, The system includes an acquisition unit that acquires the lateral acceleration and yaw angular acceleration of the vehicle, The control unit initiates a prohibition process to prohibit the execution of the anti-lock brake control for the rear wheels if the absolute value of the lateral acceleration is equal to or greater than a prohibition determination value, which is a determination value for prohibiting the anti-lock brake control. The control unit terminates the prohibition process when the absolute value of the yaw angular acceleration during the prohibition process falls from a state in which it is equal to or greater than a turning tendency determination value, which is a determination value indicating that the vehicle is turning, to a state in which it is less than or equal to the turning tendency determination value. Brake control device.

2. The acquisition unit further acquires the deceleration of the vehicle, The control unit will not initiate the prohibition process if the absolute value of the deceleration is equal to or greater than the deceleration threshold, even if the absolute value of the lateral acceleration is equal to or greater than the prohibition determination value. The braking control device according to claim 1.

3. The yaw angular acceleration acquired by the acquisition unit is an actual value based on the detection signal from the yaw rate sensor. The system further includes a calculation unit that calculates a reference value for the yaw angular acceleration of the vehicle based on the steering angle of the vehicle and the vehicle speed of the vehicle. The control unit terminates the prohibition process if the deviation between the measured value of the yaw angular acceleration and the reference value is greater than or equal to the deviation determination value. The braking control device according to claim 1 or 2.

4. The control unit sets a threshold for initiating the anti-lock brake control, and if the absolute value of the lateral acceleration is greater than or equal to a limiting judgment value which is smaller than the prohibition judgment value, and less than the prohibition judgment value, the control unit corrects the threshold to a larger value compared to the case where the absolute value of the lateral acceleration is less than the limiting judgment value, making it less likely for the anti-lock brake control to be performed on the rear wheels. The braking control device according to claim 1 or 2.

5. The control unit can calculate a target value for the braking force to be applied to each wheel of the vehicle in order to suppress excessive oversteer and understeer behavior of the vehicle, and perform skid suppression control that adjusts the braking force applied to each wheel of the vehicle based on the target value. If the skidding control is performed while the prohibition process is in progress, the braking force applied to the rear wheels by the skidding control is limited based on the amount of operation of the vehicle's braking control member. The braking control device according to claim 1 or 2.

6. When the control unit performs the skidding suppression control while the prohibition process is being carried out, it applies braking force to the rear wheels based on the smaller of the target value and the limit value based on the amount of operation of the braking operating member. The braking control device according to claim 5.

7. When the vehicle's drive control member and brake control member are being operated while the prohibition process is being performed, the limit value is corrected to be larger the larger the amount of operation of the drive control member. The braking control device according to claim 6.

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