JP7848632B2 - Brake control system - Google Patents

Description

This invention relates to a vehicle braking control device.

Patent Document 1 discloses an electric parking brake system and a control device for the electric parking brake system, configured to press a friction material against a rotating body that rotates integrally with the wheel, using the drive of an electric motor. The friction material is pressed against the rotating body as a linear motion member, which is generated by converting the rotational motion of the electric motor into linear motion, moves.

The control device disclosed in Patent Document 1 is configured to suppress excessive movement of a linear motion member by estimating its position.

Japanese Patent Publication No. 2021-102413

In vehicles equipped with an electric parking brake system, the electric parking brake system may be activated while the vehicle is in motion. For example, in addition to the hydraulic pressure from the hydraulic brake system pressing the friction material against the rotating body, the electric parking brake system may also generate a load that presses the friction material against the rotating body. In such cases, the load applied to the friction material against the rotating body involves both the load generated by the electric parking brake system and the load generated by the hydraulic pressure. Therefore, the position of the linear motion member and the magnitude of the EPB load may not always correlate. For example, the position of the linear motion member at which the EPB load begins to occur when no hydraulic pressure is present is different from the position of the linear motion member at which the EPB load begins to occur when hydraulic pressure is present.

The braking control device disclosed in Patent Document 1 does not consider the case where braking force is generated by both a hydraulic braking system and an electric parking brake system. Therefore, there is room for improvement in the control when braking force is generated by both a hydraulic braking system and an electric parking brake system.

A braking control device for solving the above problems is a braking control device applied to a vehicle having a hydraulic braking device that generates a load on a rotating body that rotates integrally with the wheel by adjusting the hydraulic pressure in the wheel cylinder, thereby generating a braking force on the wheel, and an electric parking brake device that generates a load on the rotating body in accordance with the rotational motion of an electric motor, wherein when braking the vehicle, the friction material pressed against the rotating body is adjusted by the electric parking brake device in addition to the load generated by the hydraulic braking device to generate a braking force. The system comprises an assist control unit that performs assist control using a vehicle braking system, a load detection unit that detects the occurrence of an EPB load by acquiring a value corresponding to the load generated by the electric parking brake system, and a slip detection unit that detects deceleration slip of the wheels. The system's essence is that when deceleration slip of the wheels is detected, the assist control unit, if the occurrence of an EPB load is detected, performs a release process to drive the electric motor in a direction that reduces the EPB load, while not performing the release process if the occurrence of an EPB load is not detected.

When wheel deceleration slip is detected, it is known that, for example, anti-lock brake control is performed to suppress wheel lock. Even during the execution of assistive control, if wheel deceleration slip is detected, it is preferable to adjust the braking force to suppress wheel lock. However, even if a release process is performed while assistive control is being executed and no EPB load is generated, this release process does not contribute to a reduction in braking force. Furthermore, unnecessary release processes may cause the electric parking brake system to operate excessively in a direction that reduces the EPB load.

According to the above configuration, if wheel deceleration slip is detected and EPB load is also detected, the release process is executed. Conversely, if wheel deceleration slip is detected but EPB load is not detected, the release process is not executed. Therefore, the release process can be executed at an appropriate time. This prevents excessive release processing.

Figure 1 is a schematic diagram showing one embodiment of a braking control device and the vehicle that is controlled by the braking control device. Figure 2 is a flowchart showing the processing flow performed by the braking control device shown in Figure 1 during the execution of assistive control using the electric parking brake system. Figure 3 is a flowchart showing the processing flow performed by the braking control device shown in Figure 1 during the execution of assistive control using the electric parking brake system. Figure 4 is a timing chart showing the transitions of various states when deceleration slip occurs while assist control is being performed on a vehicle to which the braking control device shown in Figure 1 is applied. Figure 5 is a timing chart showing the transitions of various states when deceleration slip occurs while assist control is being performed on a vehicle to which the braking control device shown in Figure 1 is applied. Figure 6 is a timing chart showing the transitions of various states when deceleration slip occurs while assist control is being performed on a vehicle to which the braking control device shown in Figure 1 is applied. Figure 7 is a timing chart showing the transitions of various states when deceleration slip occurs while assist control is being performed on a vehicle to which the braking control device shown in Figure 1 is applied.

The following describes a control device 10, which is one embodiment of a braking control device, with reference to Figures 1 to 7.
Figure 1 shows a control device 10 as a braking control device and a vehicle 90 to which the control device 10 is applied.

Vehicle 90 is, for example, a four-wheeled vehicle. Figure 1 shows an example of one of the wheels 91 of vehicle 90.
Vehicle 90 is equipped with a hydraulic braking system 80. The hydraulic braking system 80 is used as a service brake. Vehicle 90 is equipped with a braking operating member 92 that can be operated by the driver of vehicle 90. For example, the braking operating member 92 is a brake pedal. By operating the braking operating member 92, the driver can generate braking force via the hydraulic braking system 80 and brake vehicle 90. The operation of the braking operating member 92 corresponds to a braking request by the driver.

Vehicle 90 is equipped with an electric parking brake system 70. The electric parking brake system 70 can be used as a parking brake. As described later, the electric parking brake system 70 can also be activated while the vehicle 90 is in motion.

<Hydraulic braking system>
The hydraulic braking system 80 includes a hydraulic pressure generator. The hydraulic braking system 80 includes a hydraulic actuator 84. The hydraulic braking system 80 includes a braking mechanism corresponding to each wheel. The braking mechanism can apply braking force to the corresponding wheel.

The braking mechanism consists of a rotating body 89 that rotates integrally with the wheel 91, and a brake caliper 85. The brake caliper 85 consists of a wheel cylinder 86, a piston 87 located within the wheel cylinder 86, and a friction material 88 that can be pressed against the rotating body 89. The friction material 88 is attached to the surface of the piston 87 facing the rotating body 89. The wheel cylinder 86 has a supply/discharge hole 86a for supplying brake fluid into the wheel cylinder 86. An example of a braking mechanism is a disc brake.

The braking mechanism can generate frictional braking force on the wheel 91 in accordance with the hydraulic pressure in the wheel cylinder 86. Hereafter, the hydraulic pressure in the wheel cylinder 86 may also be referred to as WC pressure. The braking mechanism is configured such that the higher the WC pressure, the greater the force pressing the friction material 88 against the rotating body 89. In other words, the braking mechanism can impart greater braking force to the wheel 91 as the WC pressure increases. Hereafter, the force with which the friction material 88 presses against the rotating body 89 in accordance with the WC pressure will be referred to as hydraulic load.

The hydraulic braking system 80 comprises a power booster 81, a master cylinder 82, and a reservoir tank 83 in which brake fluid is stored. The hydraulic pressure generating device consists of the power booster 81, the master cylinder 82, and the reservoir tank 83.

The power assist device 81 assists the operation of the braking operating member 92 and transmits the assisted operating force to the master cylinder 82. Any known power assist device can be appropriately used as the power assist device 81. For example, examples of power assist devices include negative pressure boosters, hydraulic boosters, and electric boosters.

The master cylinder 82 generates hydraulic pressure in response to the operation of the braking operating member 92. Hereafter, the hydraulic pressure generated by the master cylinder 82 may be referred to as MC pressure. The master cylinder 82 pumps an amount of brake fluid corresponding to the MC pressure to the hydraulic actuator 84.

The hydraulic actuator 84 is positioned between the master cylinder 82 and the wheel cylinder 86. Brake fluid is supplied from the master cylinder 82 to the wheel cylinder 86 via the hydraulic actuator 84. The hydraulic actuator 84 has a brake fluid passage. The brake fluid passage is connected to the wheel cylinder corresponding to each wheel. The hydraulic actuator 84 is composed of, for example, multiple solenoid valves arranged in the passage, a pump arranged in the passage, and a pump drive motor for driving the pump.

<Electric Parking Brake System>
The electric parking brake system 70 shares some components with the braking mechanism of the hydraulic brake system 80.

The electric parking brake system 70 includes an electric motor 71. The electric parking brake system 70 also includes an output shaft member 74 that rotates in response to the drive of the electric motor 71. The electric parking brake system 70 includes a transmission mechanism 72 that transmits the driving force of the electric motor 71 to the output shaft member 74. The rotational shaft member 71a of the electric motor 71 is connected to the transmission mechanism 72 as an input shaft. The transmission mechanism 72 includes, for example, a reduction gear mechanism.

The electric parking brake system 70 is equipped with a conversion mechanism 73. The conversion mechanism 73 is a mechanism that converts the rotational motion of the electric motor 71 into linear motion.
An example of a conversion mechanism 73 is a lead screw, which consists of a screw shaft and a nut. The electric parking brake device 70 includes, for example, a linear motion member 75 that constitutes the conversion mechanism 73. The conversion mechanism 73 consists of an output shaft member 74 and a linear motion member 75. The output shaft member 74 corresponds to a screw shaft. That is, a male thread is formed on the outer circumferential surface of the output shaft member 74. The linear motion member 75 is attached to the output shaft member 74. The linear motion member 75 corresponds to a nut. That is, the linear motion member 75 is cylindrical with a female thread formed on its inner circumferential surface. In the conversion mechanism 73, the male thread of the output shaft member 74 and the female thread of the linear motion member 75 are engaged. Therefore, when the output shaft member 74 rotates, the linear motion member 75 moves in a direction extending along the axis of the output shaft member 74. The linear motion member 75 is subjected to linear motion by the conversion mechanism 73. The direction in which the linear motion member 75 moves is determined by the direction of rotation of the output shaft member 74, and is one or the other of the directions extending along the axis of the output shaft member 74.

The conversion mechanism 73 is equipped with a self-locking mechanism. The self-locking mechanism maintains the position of the linear motion member 75 even when a force is applied to it in the direction of linear motion, while the rotation of the output shaft member 74 is stopped. The self-locking mechanism is realized, for example, by the frictional force resulting from the engagement of the male thread of the output shaft member 74 and the female thread of the linear motion member 75.

In the electric parking brake system 70, the linear motion member 75 is located within the wheel cylinder 86. The electric parking brake system 70 generates a load that presses the friction material 88 against the rotating body 89 by the linear motion member 75 pressing the friction material 88 against the rotating body 89 via the piston 87. This load generated by the electric parking brake system 70 is sometimes referred to as the EPB load below.

Furthermore, the electric parking brake system 70 is not limited to a configuration in which the linear motion member 75 directly contacts the piston 87 when the EPB load is applied. The electric parking brake system 70 may also have a configuration in which a presser is interposed between the linear motion member 75 and the piston 87. For example, the presser is separable from the linear motion member 75 and the piston 87. Another example of a presser is one attached to the tip of the linear motion member 75.

The electric parking brake device 70 is configured such that when the rotating shaft member 71a of the electric motor 71 rotates in a first direction, the linear motion member 75 moves toward the piston 87. Conversely, when the rotating shaft member 71a of the electric motor 71 rotates in a second direction, opposite to the first direction, the electric parking brake device 70 is configured such that the linear motion member 75 moves toward the piston 87. Hereinafter, the direction in which the linear motion member 75 moves toward the piston 87 in the direction extending along the axis of the output shaft member 74 will be referred to as the pressing direction.

The electric parking brake system 70 is provided, for example, in each braking mechanism corresponding to the rear wheels of the vehicle 90. The electric parking brake system 70 may also be provided in each braking mechanism corresponding to the front wheels of the vehicle 90. The electric parking brake system 70 may be provided in all braking mechanisms, or in just one braking mechanism.

The electric parking brake system 70 includes a control unit 30. The control unit 30 can individually adjust the load applied to each wheel by the electric parking brake system 70. The control unit 30 includes peripheral circuits. The control unit 30 is composed of a control device 10 and peripheral circuits. The drive circuit 20 shown in Figure 1 is an example of the peripheral circuits included in the control unit 30.

The drive circuit 20 is a circuit that supplies power to the electric motor 71. The drive circuit 20 is connected to the on-board battery installed in the vehicle 90. The drive circuit 20 is controlled by the control device 10.

The drive circuit 20 is equipped with means for detecting the current value Im flowing through the electric motor 71. For example, the drive circuit 20 includes a current detection circuit. The drive circuit 20 may also include a current sensor.

The drive circuit 20 may include means for detecting the voltage value applied to the electric motor 71. For example, the drive circuit 20 may include a voltage sensor. The drive circuit 20 may also include a voltage detection circuit.

<Various Sensors>
The vehicle 90 is equipped with various sensors. Figure 1 shows, as an example of various sensors, a wheel speed sensor SE1, a pressure sensor SE2, and a manipulated variable sensor SE3. Detection signals from the various sensors are input to the control device 10.

The wheel speed sensor SE1 is a sensor that detects wheel speed. A wheel speed sensor SE1 is installed on each wheel.
The pressure sensor SE2 is a sensor that detects the hydraulic pressure corresponding to the braking force applied by the hydraulic braking device 80. One example of the pressure sensor SE2 is a sensor that detects MC pressure. Another example of the pressure sensor SE2 is a sensor that detects WC pressure. Based on the detection signal from the pressure sensor SE2, the control device 10 can obtain the hydraulic pressure corresponding to the braking force applied by the hydraulic braking device 80.

The control amount sensor SE3 is a sensor that detects the amount of manipulation of the braking control member 92. Based on the detection signal from the control amount sensor SE3, the control device 10 can acquire the amount of manipulation of the braking control member 92. One example of the amount of manipulation is the amount of displacement of the braking control member 92 caused by the driver's operation. Another example of the amount of manipulation is the operating force applied to the braking control member 92 by the driver.

<Other control units>
The vehicle 90 may include other control units. For example, as shown in Figure 1, the vehicle 90 may include a hydraulic control unit 40. The vehicle 90 may also include a support control unit 50. Each control unit is connected to each other so as to be able to communicate via an in-vehicle network 99. Each control unit includes a processing circuit for realizing its respective function.

The support control unit 50 can perform driver assistance control that automatically adjusts the driving speed of the vehicle 90. Examples of driver assistance control include autonomous driving, automatic parking, adaptive cruise control, lane keeping assist, downhill assist, and collision avoidance braking.

The hydraulic control unit 40 can control the hydraulic braking device 80.
The hydraulic control unit 40, for example, has a function to determine whether or not a malfunction has occurred in the hydraulic braking device 80. For example, the hydraulic control unit 40 can detect a malfunction in the power assist device 81. One method of determination is to determine that a malfunction has occurred when the hydraulic braking force BPP is smaller than the target braking force BPT, and the difference between the target braking force BPT and the hydraulic braking force BPP is greater than a determination value. Here, the target braking force BPT is a value corresponding to the braking request. The target braking force BPT is the target value of the braking force to be applied to the vehicle 90. For example, the target braking force BPT can be calculated based on the amount of operation of the braking operating member 92. The hydraulic braking force BPP is an estimated value of the braking force applied by the hydraulic braking device 80. For example, the hydraulic braking force BPP can be calculated based on the detection signal from the pressure sensor SE2. The determination value can be a value calculated in advance through experiments or the like.

The hydraulic control unit 40 may also have a function to control the hydraulic actuator 84. For example, it may have a function to control the brake fluid supplied to each wheel cylinder 86 and adjust the WC pressure individually.

The hydraulic control unit 40 may also have a function to adjust the WC pressure in accordance with the driving support control performed by the support control unit 50.
The hydraulic control unit 40 may also have a function to calculate the wheel speed of each wheel 91 based on the detection signal from the wheel speed sensor SE1. The hydraulic control unit 40 can also calculate the vehicle speed based on the wheel speeds. The vehicle speed indicates the travel speed of the vehicle 90.

The hydraulic control unit 40 may also have a function to calculate the slip amount of each wheel 91. The slip amount of the wheels 91 can be calculated based on the vehicle speed and the wheel speed.
The hydraulic control unit 40 may also have a function to determine whether or not deceleration slip is occurring in each wheel 91. For example, it can determine that deceleration slip is occurring if the amount of slip exceeds a predetermined determination amount.

The hydraulic control unit 40 can also perform anti-lock brake control. Hereinafter, anti-lock brake control will be referred to as ABS control. ABS control is a control system that suppresses wheel lock-up by reducing the amount of slip of the wheels 91 through adjustment of the braking force when braking the vehicle 90. For example, the hydraulic control unit 40 can start ABS control when it detects deceleration slip. When the hydraulic control unit 40 starts ABS control, it activates the hydraulic braking device 80 to adjust the WC pressure according to the amount of slip.

<Control device>
The control device 10 is a processing circuit composed of multiple functional units that perform various types of control. Figure 1 shows, as an example of functional units, a slip detection unit 11, a hydraulic pressure detection unit 12, a load detection unit 13, a motor control unit 14, and an assist control unit 15. Each functional unit of the control device 10 is capable of sending and receiving information from one another.

The slip detection unit 11 detects deceleration slip of the wheel 91. For example, the slip detection unit 11 can acquire information indicating whether or not deceleration slip is occurring. Alternatively, the slip detection unit 11 can determine whether or not deceleration slip is occurring. For example, the slip detection unit 11 can detect the occurrence of deceleration slip when the slip amount exceeds a predetermined threshold. The slip amount can be obtained from a value calculated by the hydraulic control unit 40. The slip detection unit 11 may also calculate the slip amount.

The hydraulic pressure detection unit 12 detects the hydraulic pressure generated by the operation of the hydraulic braking device 80. For example, the hydraulic pressure detection unit 12 acquires the MC pressure. The hydraulic pressure detection unit 12 detects the presence of hydraulic pressure when the MC pressure is greater than "0". The hydraulic pressure detection unit 12 may also be configured to acquire the WC pressure and detect the presence of hydraulic pressure when the WC pressure is greater than "0".

The load detection unit 13 detects the occurrence of an EPB load by acquiring a value corresponding to the EPB load.
As an example, the load detection unit 13 acquires the current value Im flowing through the electric motor 71. The load detection unit 13 is configured to detect the occurrence of an EPB load when the absolute value of the current value Im is greater than a predetermined threshold value, which is the current determination value Imth. In this example, the current value Im corresponds to a value corresponding to the EPB load. The current determination value Imth is, for example, equal to the magnitude of the current flowing through the electric motor 71 when no EPB load is present. That is, the no-load current value of the electric motor 71 can be used for the current determination value Imth. The current determination value Imth may also be a value greater than the current value flowing through the electric motor 71 when no EPB load is present.

The load detection unit 13 acquires the current value Im, taking into account the inrush current flowing through the electric motor 71, and the value is obtained after the inrush current has subsided. For example, the load detection unit 13 acquires the current value Im each time voltage is applied to the electric motor 71. For example, the load detection unit 13 acquires the current value Im immediately before the voltage application is stopped.

As another example, the load detection unit 13 may acquire a value corresponding to the EPB load based on the total load applied to the friction material 88 against the rotating body 89 and the hydraulic pressure detected by the hydraulic pressure detection unit 12. For example, the value obtained by subtracting the hydraulic pressure load from the total load corresponds to the EPB load. For example, the total load can be detected by a load sensor.

The motor control unit 14 drives the electric motor 71 using PWM (Pulse Width Modulation) control. Specifically, the motor control unit 14 generates a drive signal and outputs this drive signal to the drive circuit 20. The electric motor 71 is driven by the switching of the drive circuit 20 in response to the drive signal. The motor control unit 14 sets a target current value Imt as the target value for the electric motor 71's current Im. The motor control unit 14 calculates the duty cycle in the drive signal based on the target current value Imt. The motor control unit 14 generates the drive signal based on the duty cycle.

The electric motor 71 is driven by an apply process and a release process. The apply process is the process of applying a voltage to the electric motor 71 so that the rotating shaft member 71a of the electric motor 71 rotates in a first direction. In other words, the apply process is the process of applying a voltage to the electric motor 71 so that the electric motor 71 rotates in a direction that increases the load on the linear motion member 75 that presses against the piston 87. In other words, the apply process is the process of driving the electric motor 71 in a direction that increases the load on the friction material 88 that presses against the rotating body 89. The release process is the process of applying a voltage to the electric motor 71 so that the rotating shaft member 71a of the electric motor 71 rotates in a second direction. In other words, the release process is the process of applying a voltage to the electric motor 71 so that the electric motor 71 rotates in a direction that decreases the load on the linear motion member 75 that presses against the piston 87. In other words, the release process is the process of driving the electric motor 71 in a direction that reduces the load pressing the friction material 88 against the rotating body 89. For example, in the apply process, a positive voltage is applied to the electric motor 71. In this case, in the release process, a negative voltage is applied to the electric motor 71.

The assist control unit 15 can perform assist control. Assist control can generate braking force by combining the load generated by the hydraulic braking device 80 with the load generated by the electric parking brake device 70 when braking the vehicle 90. In assist control, the friction material 88 pressed against the rotating body 89 is assisted by the linear motion member 75 of the electric parking brake device 70.

<Assistance control>
I will explain the assistance control in more detail.
Assistance control is initiated, for example, by the assistance control unit 15 when the start condition is met. The assistance control unit 15 determines that the start condition is met when the braking force applied by the hydraulic braking device 80 during braking of the vehicle 90 cannot meet the target braking force corresponding to the braking request. Note that "during braking of the vehicle 90" refers to the state in which braking force is applied to the vehicle 90 while the vehicle 90 is in motion.

An example of a starting condition is explained below. For example, the assistance control unit 15 determines that the starting condition is met when a malfunction occurs in the hydraulic braking device 80. An example of a malfunction in the hydraulic braking device 80 is a malfunction of the power assist device 81. Whether or not a malfunction has occurred in the hydraulic braking device 80 can be determined, for example, by obtaining the result of the malfunction determination performed by the hydraulic control unit 40.

For example, the assist control unit 15 can acquire the values of the target braking force BPT and the hydraulic braking force BPP during braking, and determine that the start condition is met if a discrepancy occurs between the target braking force BPT and the hydraulic braking force BPP. For instance, whether or not there is a discrepancy between the target braking force BPT and the hydraulic braking force BPP can be determined by whether or not the discrepancy is greater than a certain threshold value. The threshold value used here may be the same as the threshold value used to determine the failure of the hydraulic braking device 80, or a different value may be adopted.

Furthermore, the assist control may be initiated regardless of whether the initiation conditions are met, if it is permitted to activate the electric parking brake 70 while the vehicle 90 is in motion. For example, it can be determined that it is permitted to activate the electric parking brake 70 when the EPB switch is operated to the ON position. The EPB switch is, for example, a switch that can be operated by the driver of the vehicle 90.

In one example of assistive control, the assistive control unit 15 calculates a target current value Imt as the target value for the current Im flowing through the electric motor 71 through an apply process. Based on the calculated target current value Imt, the assistive control unit 15 drives the electric motor 71 via the motor control unit 14.

For example, the assist control unit 15 calculates the target current value Imt as follows: The assist control unit 15 calculates the difference obtained by subtracting the hydraulic braking force BPP from the target braking force BPT. The assist control unit 15 calculates the target value of the EPB load so that a braking force equivalent to this difference can be applied by the EPB load. The assist control unit 15 calculates the target current value Imt that allows the target value of the EPB load to be applied.

In one example of assistive control, the assistive control unit 15 executes an apply process when the current value Im is less than or equal to the target current value Imt. The assistive control unit 15 can also execute a release process when the current value Im is greater than the target current value Imt.

The assistance control is terminated by the assistance control unit 15, for example, when the termination condition is met.
Let me explain an example of a termination condition. The assistance control unit 15 can determine that the termination condition has been met, for example, when the vehicle 90 stops. Here, the stopping of the vehicle 90 means, for example, when the vehicle 90 goes from a state where it is moving to a state where the vehicle speed of the vehicle 90 is "0". The stopping of the vehicle 90 may include the state just before the vehicle speed becomes "0" and the vehicle speed is slightly greater than "0". It is also possible to determine whether the vehicle 90 has stopped based on the wheel speed, the longitudinal acceleration of the vehicle 90, etc., rather than just the vehicle speed.

The assistance control unit 15 can also determine that the termination condition has been met, for example, when the vehicle speed falls below the predetermined speed. In other words, the assistance control may be terminated during deceleration before the vehicle 90 has come to a complete stop.

The assistance control unit 15 can also determine, for example, that the termination condition has been met when the braking request is released. For instance, it can determine that the braking request has been released when the operation of the braking operation member 92 is released.

The assistance control unit 15 has a function to control the electric parking brake device 70 to suppress wheel locking when deceleration slip is detected during the execution of assistance control. An example of the processing flow performed by the assistance control unit 15 during the execution of assistance control is shown in Figure 2.

The processing routine shown in Figure 2 is executed repeatedly at predetermined intervals during the execution of the assistance control.
When this processing routine is started, in step S101, the assistance control unit 15 first determines whether or not deceleration slip is occurring. If the slip detection unit 11 does not detect deceleration slip (S101: NO), the assistance control unit 15 terminates this processing routine. On the other hand, if the slip detection unit 11 detects deceleration slip (S101: YES), the assistance control unit 15 proceeds to step S102. During the period from the start to the end of this processing routine, the electric motor 71 is not controlled using the target current value Imt.

In step S102, the assistance control unit 15 determines whether or not hydraulic pressure is being generated. If hydraulic pressure is detected by the hydraulic pressure detection unit 12 (S102: YES), the assistance control unit 15 proceeds to step S103.

In step S103, the assistance control unit 15 determines whether or not an EPB load is occurring. Specifically, it determines that an EPB load is occurring if the load detection unit 13 determines that the absolute value of the current value Im is greater than the current determination value Imth. That is, if the absolute value of the current value Im is greater than the current determination value Imth (S103: YES), the assistance control unit 15 proceeds to step S104.

In step S104, the assist control unit 15 performs a release process. When voltage is applied to the electric motor 71 as part of the release process, the linear motion member 75 moves in a direction that reduces the EPB load. After a specified period has elapsed since the start of voltage application due to the release process, the assist control unit 15 terminates the voltage application. Subsequently, the assist control unit 15 terminates this processing routine.

On the other hand, in step S103, if the absolute value of the current Im is less than or equal to the current determination value Imth, i.e., if no EPB load is generated (S103: NO), the assist control unit 15 proceeds to step S105.

In step S105, the assistance control unit 15 puts the electric parking brake device 70 into standby mode without applying voltage to the electric motor 71. Afterward, the assistance control unit 15 terminates this processing routine.

If the hydraulic pressure detection unit 12 does not detect hydraulic pressure during step S102 (S102: NO), the assistance control unit 15 proceeds to step S104. After performing the release process, the assistance control unit 15 terminates this processing routine.

As shown in Figure 3, the assist control unit 15 can also terminate the assist control if deceleration slip continues during the execution of the assist control.
Figure 3 shows the processing flow executed by the assistance control unit 15 during the execution of assistance control. The processing routine shown in Figure 3 is repeatedly executed at predetermined intervals during the execution of assistance control.

When this processing routine is started, in step S201, the assist control unit 15 first determines whether or not deceleration slip is continuing.
"Continuing deceleration slip" means, for example, that even if a release process is performed as part of step S104, which is executed when deceleration slip is detected, the deceleration slip has not been resolved. For example, the assist control unit 15 can determine that deceleration slip is continuing if the deceleration slip has not been resolved even after a predetermined number of release processes have been repeatedly performed. The predetermined number of times is not particularly limited, but for example, it may be two or more times. Alternatively, the assist control unit 15 can also determine that deceleration slip is continuing if a predetermined time has elapsed since the detection of deceleration slip without the deceleration slip being resolved. In this case, the assist control unit 15 may have the electric parking brake 70 on standby as part of step S105 until the predetermined time has elapsed. That is, the assist control unit 15 can also determine that deceleration slip is continuing if the deceleration slip has not been resolved even after a predetermined time has elapsed with the electric parking brake 70 on standby since the detection of deceleration slip.

If deceleration slip is not continuing (S201: NO), the assist control unit 15 terminates this processing routine.
On the other hand, if deceleration slip continues during the process in step S201 (S201: YES), the assist control unit 15 moves the process to step S202. In step S202, the assist control unit 15 terminates the assist control. That is, it terminates the generation of EPB load during braking. At this time, the assist control unit 15 moves the linear motion member 75 in the opposite direction to the pressing direction by a release process. The release process when terminating the assist control moves the linear motion member 75 to, for example, its initial position. The initial position of the linear motion member 75 is, for example, the position obtained by applying a voltage to the electric motor 71 for a predetermined time so that the linear motion member 75 moves away from the piston 87. When the assist control unit 15 terminates the assist control, it terminates this processing routine.

<Mechanism of Action and Effects>
The operation and effects of this embodiment will now be described.
Figures 4 and 5 show the transitions of various states when deceleration slip occurs while applying the assist control.

Figures 6 and 7 show the transitions of various states when deceleration slip occurs during the release process in assist control. Figures 6 and 7 illustrate, for example, the case where the ratio of hydraulic braking force BPP to target braking force BPT is increasing. An increase in the ratio of hydraulic braking force BPP to target braking force BPT means, for example, that the hydraulic braking force BPP is increasing while the target braking force BPT remains constant.

Figures 4(a), 5(a), 6(a), and 7(a) show the status of the hydraulic braking system 80. Specifically, periods during which hydraulic pressure is detected by the hydraulic braking system 80 are indicated as "hydraulic pressure present." Periods during which hydraulic pressure is not detected by the hydraulic braking system 80 are indicated as "hydraulic pressure absent."

Figures 4(b), 5(b), 6(b), and 7(b) show the control modes of the electric parking brake system 70. Specifically, the period during which the apply process is being executed is indicated as "Apply." The period during which the release process is being executed is indicated as "Release." The period during which neither the apply nor release process is being executed is indicated as "Standby."

Figures 4(c), 5(c), 6(c), and 7(c) show the changes in the magnitude of the current flowing through the electric motor 71.
Figures 4(d), 5(d), 6(d), and 7(d) show whether or not deceleration slip is detected. Specifically, periods during which deceleration slip is detected are indicated as "Deceleration slip present," and periods during which deceleration slip is not detected are indicated as "Deceleration slip absent."

In the examples shown in Figures 4 to 7, ABS control is initiated when deceleration slip is detected. That is, when deceleration slip is detected, the hydraulic braking system 80 is activated to adjust the WC pressure according to the amount of slip.

First, in the example shown in Figure 4, as shown in Figure 4(b), the apply process is performed during the period from timing t11 to timing t14. Regarding this apply process, as shown in Figure 4(c), the current value Im after the inrush current has subsided remains smaller than the current determination value Imth. That is, at this point, although the linear motion member 75 is moving in the pressing direction due to the apply process, the linear motion member 75 is not pressing the friction material 88 against the rotating body 89 via the piston 87, and the load on the electric motor 71 is small.

At timing t12, hydraulic pressure is detected as shown in Figure 4(a). At timing t13, deceleration slip is detected as shown in Figure 4(d). That is, the amount of slip increases with increasing braking force.

During the execution of assist control, if deceleration slip of the wheel 91 is detected, it is preferable to adjust the braking force to suppress wheel 91 locking. However, even if a release process is performed when no EPB load is generated during the execution of assist control, the movement of the linear motion member 75 due to the release process does not contribute to a reduction in braking force. Furthermore, unnecessary release processing may cause the linear motion member 75 to move excessively in the direction of reducing the EPB load. Excessive movement of the linear motion member 75 may cause it to interfere with other members. Also, if the linear motion member 75 moves in the direction of reducing the EPB load due to unnecessary release processing, the generation of the EPB load may be delayed when the next apply process is performed. In other words, the responsiveness of the electric parking brake system 70 may be reduced.

In this regard, according to the control device 10, if deceleration slip is detected (S101: YES), hydraulic pressure is detected (S102: YES), and EPB load is not detected (S103: NO), the release process is not executed (S105). Therefore, the release process is not executed after timing t14. By keeping the electric parking brake system 70 in standby mode without executing the release process in this way, excessive movement of the linear motion member 75 can be suppressed. Furthermore, a decrease in the responsiveness of the electric parking brake system 70 can be suppressed. Note that deceleration slip in the case where hydraulic pressure is detected but EPB load is not detected, as described above, can be eliminated by ABS control.

Next, in the example shown in Figure 5, as shown in Figure 5(b), the apply process is performed during the period from timing t21 to timing t24. Regarding this apply process, as shown in Figure 5(c), the current value Im after the inrush current converges remains smaller than the current judgment value Imth until timing t22. At timing t22, hydraulic pressure is detected as shown in Figure 5(a). As shown in Figure 5(c), the current value Im gradually increases during the period from timing t22 to timing t24. That is, the load on the electric motor 71 is increasing. The magnitude of the current value Im reaches the current judgment value Imth at timing t23. That is, the EPB load is detected at timing t23. At timing t23, deceleration slip is detected as shown in Figure 5(d). That is, the amount of slip is increasing with the increase in braking force.

In the control device 10, if deceleration slip is detected (S101: YES), hydraulic pressure is detected (S102: YES), and EPB load is detected (S103: YES), the release process is executed (S104). Therefore, as shown in Figure 5(b), the release process is executed during the period from timing t25 to timing t26. As a result, the linear motion member 75 is moved in a direction that reduces the EPB load. This reduces the EPB load. In the example shown in Figure 5(c), the magnitude of the current value Im after the inrush current associated with the release process from timing t25 converges remains smaller than the current determination value Imth. As a result, after timing t26, the release process is not executed because the EPB load is not detected.

Next, in the example shown in Figure 6, as shown in Figure 6(b), the release process is performed during the period from timing t31 to timing t32. Regarding this release process, as shown in Figure 6(c), the current value Im after the inrush current converges remains smaller than the current judgment value Imth. Hydraulic pressure is detected from timing t31 onwards, as shown in Figure 6(a). Deceleration slip is detected from timing t32 onwards, as shown in Figure 6(d).

According to the control device 10, if deceleration slip is detected (S101: YES), hydraulic pressure is detected (S102: YES), and EPB load is not detected (S103: NO), the release process is not executed (S105). Therefore, the release process is not executed after timing t32.

Next, in the example shown in Figure 7, as shown in Figure 7(b), the release process is performed during the period from timing t41 to timing t42. Regarding this release process, as shown in Figure 7(c), the current value Im after the inrush current converges remains greater than the current determination value Imth. The current value Im gradually decreases. This indicates that the EPB load gradually decreases and the load on the electric motor 71 gradually decreases during the period from timing t41 to timing t42. Furthermore, the current value Im remains greater than the current determination value Imth even at timing t42, when the release process is completed. That is, the EPB load is still present at timing t42. Hydraulic pressure is detected from timing t41 onwards, as shown in Figure 7(a). Deceleration slip is detected from timing t42 onwards, as shown in Figure 7(d).

In the control device 10, if deceleration slip is detected (S101: YES), hydraulic pressure is detected (S102: YES), and EPB load is detected (S103: YES), the release process is executed (S104). Therefore, as shown in Figure 7(b), the release process is executed during the period from timing t43 to timing t44. As a result, the linear motion member 75 is moved in a direction that reduces the EPB load. This reduces the EPB load. Therefore, as shown in Figure 7(c), the magnitude of the current value Im associated with the release process temporarily becomes larger than the current determination value Imth after the inrush current converges, but then decreases to a value smaller than the current determination value Imth. As a result, after timing t44, the release process is not executed because the EPB load is not detected.

Furthermore, when the control device 10 detects deceleration slip during the execution of assist control, if no hydraulic pressure is detected (S102: NO), a release process is performed (S104). The absence of hydraulic pressure during the execution of assist control suggests that the braking force is being applied solely by the EPB load. Therefore, the braking force can be reduced by performing the release process. This reduces the amount of slip and suppresses wheel lock-up.

As described above, the control device 10 can determine whether a deceleration slip is being caused by the electric parking brake 70 when one occurs, and can then perform a release operation at an appropriate time. That is, if the deceleration slip is caused by the EPB load, the amount of slip can be reduced by performing a release operation. On the other hand, if the deceleration slip is caused by the hydraulic load, unnecessary release operations can be suppressed. This prevents excessive movement of the linear motion member 75. Furthermore, it prevents a decrease in the responsiveness of the electric parking brake 70.

(Example of change)
This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

* In the above embodiment, a disc brake was used as an example of the braking mechanism. However, the braking mechanism is not limited to this; a drum brake may also be used. Any drum brake to which an electric parking brake device is applied, configured to assist the friction material pressed against the rotating body in accordance with hydraulic pressure, can be used, as in the above embodiment.

The processing circuits of the control device 10, the hydraulic control unit 40, and the support control unit 50 can be configured as follows: A processing circuit can be configured as a circuit comprising one or more processors that execute various processes according to a computer program. A processing circuit can be configured as a circuit comprising one or more hardware circuits that execute various processes. A processing circuit can be configured as a circuit combining one or more processors that execute some of the various processes and one or more hardware circuits that execute the remaining processes.

A processor comprises a processing unit such as a CPU. A processor also comprises memory such as RAM and ROM. Memory stores program code or instructions configured to cause the processing unit to execute processes. Memory, or storage medium, includes any available medium accessible by a general-purpose or dedicated computer. An example of hardware circuitry is an ASIC, which is an application-specific integrated circuit.

- Some or all of the functions realized by the processing circuits of the hydraulic control unit 40 and the support control unit 50 may be realized by the control device 10.
- Some of the functions implemented by the control device 10 may be implemented by other processing circuits connected to the control device 10.

10...Control device 11...Slip detection unit 13...Load detection unit 14...Motor control unit 15...Assistance control unit 30...Control unit 40...Hydraulic control unit 70...Electric parking brake device 71...Electric motor 73...Conversion mechanism 74...Output shaft member 75...Linear motion member 80...Hydraulic brake device 86...Wheel cylinder 88...Friction material 89...Rotating body 90...Vehicle 91...Wheel

Claims (2)

A braking control device applicable to a vehicle having a hydraulic braking device that generates a braking force on the wheel by adjusting the hydraulic pressure in the wheel cylinder to create a load on a rotating body that rotates integrally with the wheel, thereby creating a load on the wheel that presses a friction material against it, and an electric parking braking device that generates a load on the rotating body that presses the friction material against it in accordance with the rotational motion of an electric motor, wherein
An assist control unit that performs assist control to assist the friction material pressed against the rotating body by the electric parking brake device so that a braking force is generated by the load generated by the hydraulic brake device in addition to the load generated by the electric parking brake device when braking the vehicle,
A load detection unit detects the occurrence of an EPB load by obtaining a value corresponding to the EPB load, which is defined as the load generated by the aforementioned electric parking brake device.
The system includes a slip detection unit that detects the deceleration slip of the aforementioned wheels,
When the deceleration slip of the wheel is detected, the assist control unit performs a release process to drive the electric motor in a direction that reduces the EPB load if the occurrence of the EPB load is detected, while the braking control device does not perform the release process if the occurrence of the EPB load is not detected. The load detection unit acquires the current value flowing through the electric motor and is configured to detect the occurrence of the EPB load when the current value is greater than a specified threshold.
The braking control device according to claim 1, wherein the specified threshold value is greater than or equal to the current value flowing to the electric motor when the EPB load is not occurring.