Brake control system

Abstract

To improve responsiveness of a braking force when a target value of the braking force fluctuates with respect to a braking control device compensating braking of a vehicle by activating an electric parking braking device.SOLUTION: A control device 10 is applied to a vehicle 90 having a hydraulic braking device 80 and an electric parking braking device 70. The control device 10 is provided with an assist control unit 13 that, if a braking requirement cannot be satisfied by the braking force of the hydraulic braking device 80, executes an assist control for causing the electric parking braking device 70 to generate a load corresponding to a difference between a target braking force and the braking force applied by the hydraulic braking device 80. The assist control unit 13 performs apply processing for applying, to an electric motor 71, a voltage for causing the electric motor 71 to drive in a direction for increasing load from the electric parking braking device 70, the assist control unit performing the apply processing even after an actual braking force has reached the target braking force.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] <000^009>Patent Document 1 discloses a control device that brakes a vehicle by the braking force generated by an electric parking brake device when a brake booster device is in a state of functional constraint or non-function. That is, a configuration for compensating for the functional constraint or non-function of the brake booster device by the electric parking brake device is disclosed.

[0003] As an electric parking brake device, for example, a device that applies a mechanism for converting the rotational motion of an electric motor into a linear motion to a brake caliper, as disclosed in Patent Document 2, is known. More specifically, in the electric parking brake device disclosed in Patent Document 2, a linear motion member that is linearly moved by the driving force of an electric motor is disposed inside a piston in the brake caliper.

[0004] In an electric parking brake device, it is known that a self-locking mechanism is adopted as disclosed in Patent Document 2. The self-locking mechanism is a mechanism that holds the position of a linear motion member without the linear motion member moving even when a force acts on the linear motion member in the direction in which the linear motion member moves. In an electric parking brake device provided with such a self-locking mechanism, after moving the linear motion member to a desired position by driving an electric motor, the power supply to the electric motor is stopped and the position of the linear motion member is held by the self-locking mechanism.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] In an electric parking brake system like the one disclosed in Patent Document 2, if control is performed to compensate for vehicle braking using the electric parking brake system as in Patent Document 1, the following problems arise. When compensation is provided by an electric parking brake system, for example, if the hydraulic pressure increases, it becomes necessary to move the linear motion member in order to continue assisting the piston. In this case, if the position of the linear motion member is held by a self-locking mechanism, even if power is supplied to the electric motor after the hydraulic pressure changes, a delay time occurs between the change in hydraulic pressure and the start of movement of the linear motion member. In other words, when the position of the linear motion member is held by a self-locking mechanism and power is stopped from the electric motor, it may not be possible to provide assistance by the linear motion member in a responsive manner in response to the change in hydraulic pressure.

[0007] Thus, when using an electric parking brake system to compensate for vehicle braking, there was room for improvement in the responsiveness of the braking force. [Means for solving the problem]

[0008] A braking control device for solving the above problems is a vehicle having a hydraulic braking device which generates braking force on the wheel in accordance with the load applied to the friction material applied to the wheel, comprising: a rotating member that rotates integrally with the wheel; a friction material pressed against the rotating member; a cylinder supplied with brake fluid; and a piston that presses the friction material against the rotating member in accordance with the hydraulic pressure in the cylinder; and an electric parking brake device which comprises: an electric motor; a conversion mechanism that converts the rotational motion of the electric motor into linear motion; and a linear motion member that is moved linearly by the conversion mechanism and is located inside the cylinder, thereby generating a load applied to the friction material applied to the rotating member by the linear motion member pressing the friction material against the rotating member via the piston, and the vehicle being able to generate braking force by the hydraulic braking device in accordance with the braking request. A braking control device applied to and controlling the electric parking brake device comprises: a motor control unit that outputs a drive signal for driving the electric motor; and an assist control unit that, when the braking force applied by the hydraulic brake device during braking of the vehicle cannot meet the target braking force corresponding to the braking request, performs assist control to cause the electric parking brake device to generate a load corresponding to the difference between the target braking force and the braking force applied by the hydraulic brake device, by assisting the linear motion member in pressing the friction material against the rotating member, wherein the assist control unit performs an apply process in the assist control by applying a voltage to the electric motor that drives the electric motor in a direction that increases the load on which the linear motion member is pressed against the piston, and the essence of the device is to continue performing the apply process even after the actual braking force acting on the vehicle has reached the target braking force.

[0009] According to the above configuration, the electric motor will remain energized even after the difference between the target braking force and the hydraulic braking force is eliminated by the assist control. In other words, the state in which the electric motor is not energized during the execution of the assist control is not continuously maintained. Therefore, responsiveness can be ensured when moving the position of the linear motion member in accordance with the increase or decrease in the target braking force during the execution of the assist control. [Brief explanation of the drawing]

[0010] [Figure 1] 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] Figure 2 is a flowchart showing the processing flow of the assist control performed by the braking control device. [Figure 3] Figure 3 illustrates the current values ​​flowing to the electric motor while maintaining braking force during the assist control performed by the braking control device. [Figure 4] Figure 4 illustrates the current flowing through the electric motor when the braking force is increased during the assist control performed by the braking control device. [Figure 5] Figure 5 shows the changes in current value and load as adjusted by the assist control performed by the braking control device. [Figure 6] Figure 6 shows the changes in current value and load when assistance is provided by an electric parking brake system, as a comparative example. [Figure 7] Figure 7 is a schematic diagram illustrating the state of an electric parking brake system when assistance is provided by the electric parking brake system, as a comparative example, and the corresponding load. [Modes for carrying out the invention]

[0011] An embodiment of the braking control device will be described below with reference to Figures 1 to 5. Figure 1 shows the control device 10 as a braking control device and the vehicle 90 to which the control device 10 is applied.

[0012] 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.

[0013] Vehicle 90 is equipped with an electric parking brake system 70. The electric parking brake system 70 can be used as a parking brake. <Hydraulic braking system> The hydraulic braking system 80 is equipped with a hydraulic pressure generator. The hydraulic braking system 80 is equipped with a hydraulic actuator 84. The hydraulic braking system 80 is equipped with a braking mechanism corresponding to each wheel. The braking mechanism can apply braking force to the corresponding wheel.

[0014] The braking mechanism consists of a rotating member 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 inside the wheel cylinder 86, and a friction material 88 that can be pressed against the rotating member 89. The friction material 88 is attached to the surface of the piston 87 that faces the rotating member 89. The wheel cylinder 86 has a supply and discharge hole 86a for supplying brake fluid into the wheel cylinder 86. An example of a braking mechanism is a disc brake.

[0015] 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 with which the friction material 88 presses against the rotating member 89. In other words, the braking mechanism can impart a 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 member 89 in accordance with the WC pressure will be referred to as the hydraulic load Pb.

[0016] The hydraulic braking device 80 includes a power booster 81, a master cylinder 82, and a reservoir tank 83 in which brake fluid is stored. The hydraulic generating device is constituted by the power booster 81, the master cylinder 82, and the reservoir tank 83.

[0017] The power booster 81 can assist the operation of the braking operation member 92 and transmit the boosted operating force to the master cylinder 82. As the power booster 81, a known power booster can be appropriately adopted. For example, examples of the power booster include a vacuum booster, a hydraulic booster, an electric booster, and the like.

[0018] The master cylinder 82 generates hydraulic pressure in response to the operation of the braking operation member 92. Hereinafter, the hydraulic pressure generated by the master cylinder 82 may also be referred to as the MC pressure. The master cylinder 82 pumps a corresponding amount of brake fluid according to the MC pressure to the hydraulic actuator 84.

[0019] The hydraulic actuator 84 is disposed 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 includes a flow path for brake fluid. The flow path for brake fluid is connected to a wheel cylinder corresponding to each wheel. The hydraulic actuator 84 is constituted by, for example, a plurality of solenoid valves disposed in the flow path, a pump disposed in the flow path, and a pump drive motor for driving the pump.

[0020] 〈Electric parking brake device〉 The electric parking brake device 70 shares a part of the configuration with the braking mechanism in the hydraulic braking device 80.

[0021] The electric parking brake system 70 includes an electric motor 71. The electric parking brake system 70 includes an output shaft 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 74. The rotation shaft 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 mechanism.

[0022] 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 will be described. The electric parking brake device 70 includes, for example, a linear motion member 75 that constitutes a conversion mechanism 73. The conversion mechanism 73 consists of an output shaft 74 and a linear motion member 75. A male screw is formed on the outer circumferential surface of the output shaft 74. The linear motion member 75 is attached to the output shaft 74. The linear motion member 75 is, for example, cylindrical and has a female screw formed on its inner circumferential surface. The male screw of the output shaft 74 and the female screw of the linear motion member 75 are engaged. Therefore, when the output shaft 74 rotates, the linear motion member 75 moves in a direction extending along the output shaft 74. The linear motion member 75 is moved in a linear motion by the conversion mechanism 73. The direction in which the linear motion member 75 moves is determined to be one or the other of the directions extending along the output shaft 74, depending on the rotation direction of the output shaft 74.

[0023] The conversion mechanism 73 is equipped with a self-locking mechanism. The self-locking mechanism is a mechanism that maintains the position of the linear motion member 75 even if a force is applied to the linear motion member 75 in the direction of linear motion when the rotation of the output shaft 74 is stopped. The self-locking mechanism is realized, for example, by the frictional force produced by the meshing of the male thread of the output shaft 74 and the female thread of the linear motion member 75.

[0024] In the electric parking brake system 70, the linear motion member 75 is located inside the wheel cylinder 86. In the electric parking brake system 70, the linear motion member 75 presses the friction material 88 against the rotating member 89 via the piston 87, thereby generating a load that presses the friction material 88 against the rotating member 89. Hereinafter, this load will be referred to as the EPB load Pc.

[0025] The electric parking brake 70 is not limited to a configuration in which the linear motion member 75 directly contacts the piston 87 when the EPB load Pc is applied. The electric parking brake 70 may also be configured 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.

[0026] The electric parking brake 70 is configured such that when the rotating shaft 71a of the electric motor 71 rotates in a first direction, the linear motion member 75 moves toward the piston 87. On the other hand, when the rotating shaft 71a of the electric motor 71 rotates in a second direction, which is opposite to the first direction, the electric parking brake 70 is configured such that the linear motion member 75 moves toward the piston 87. Hereinafter, the direction toward which the linear motion member 75 moves toward the piston 87 in the direction extending along the output shaft 74 will be referred to as the pressing direction.

[0027] The electric parking brake 70 is provided, for example, in each braking mechanism corresponding to the rear wheels of the vehicle 90. The electric parking brake 70 may also be provided in each braking mechanism corresponding to the front wheels of the vehicle 90. The electric parking brake 70 may be provided in all braking mechanisms, or in just one braking mechanism.

[0028] The electric parking brake system 70 includes a control unit 30. The control unit 30 can control the EPB load Pc. 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.

[0029] 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.

[0030] The drive circuit 20 may include means for detecting the current value Im flowing through the electric motor 71. For example, the drive circuit 20 may include a current sensor. The drive circuit 20 may also include a current detection circuit.

[0031] 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.

[0032] <Various Sensors> Vehicle 90 is equipped with various sensors. Figure 1 shows examples of these sensors, including the manipulated variable sensor SE1, the pressure sensor SE2, and the rotation angle sensor SE3. Detection signals from these sensors are input to the control device 10.

[0033] The control amount sensor SE1 is a sensor that detects the amount of operation of the braking operating member 92. Based on the detection signal from the control amount sensor SE1, the control device 10 can obtain the amount of operation of the braking operating member 92. One example of the amount of operation is the amount of displacement of the braking operating member 92 caused by operation by the driver. Another example of the amount of operation is the operating force applied to the braking operating member 92 by the driver.

[0034] The pressure sensor SE2 is a sensor that detects the hydraulic pressure corresponding to the braking force applied by the hydraulic braking device 80. For example, the pressure sensor SE2 is a sensor that detects MC pressure. For example, 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.

[0035] The rotation angle sensor SE3 is a sensor that detects the rotation angle of the electric motor 71. Based on the detection signal from the rotation angle sensor SE3, the control device 10 can obtain the rotation angle of the electric motor 71. Based on the rotation angle of the electric motor 71, the motor rotation speed Nm can be calculated.

[0036] <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 processing circuits to implement its respective function.

[0037] 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.

[0038] 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 system 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 the determination value. Here, the target braking force BPT is the 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 system 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.

[0039] 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 each WC pressure individually.

[0040] 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. <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 a functional unit, an acquisition unit 11, a motor control unit 12, and an assistance control unit 13. Each functional unit of the control device 10 is capable of sending and receiving information from one another.

[0041] The acquisition unit 11 can acquire state variables for controlling the electric parking brake device 70. For example, the acquisition unit 11 calculates state variables. The acquisition unit 11 may also acquire state variables calculated by other functional units and other processing circuits.

[0042] Let's explain some examples of state variables. Examples of state variables include target braking force BPT, hydraulic braking force BPP, current value Im, motor rotation speed Nm, and information on whether or not a malfunction has occurred in the hydraulic braking device 80.

[0043] The motor control unit 12 drives the electric motor 71 using PWM (Pulse Width Modulation) control. That is, the motor control unit 12 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 12 sets a target current value Imt as the target value for the current value Im of the electric motor 71. The motor control unit 12 calculates the duty cycle of the drive signal based on the target current value Imt. The motor control unit 12 generates a drive signal based on the duty cycle.

[0044] There are two processes for driving the electric motor 71: an apply process and a release process. The apply process is the process of applying a voltage to the electric motor 71 that drives the electric motor 71 so that its rotating shaft 71a rotates in a first direction. In other words, the apply process is the process of applying a voltage to the electric motor 71 that drives it in a direction that increases the load on the linear motion member 75 that presses against the piston 87. The release process is the process of applying a voltage to the electric motor 71 that drives the electric motor 71 so that its rotating shaft 71a rotates in a second direction. In other words, the release process is the process of applying a voltage to the electric motor 71 that drives it in a direction that decreases the load on the linear motion member 75 that presses against the piston 87. 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.

[0045] The assist control unit 13 can perform assist control. Assist control activates the electric parking brake 70 when braking the vehicle 90, thereby applying braking force to the vehicle 90 via the electric parking brake 70. In assist control, the friction material 88 pressed against the rotating member 89 is assisted by the linear motion member 75.

[0046] In one example of assist control, the assist control unit 13 calculates a target current value Imt as the target value of the current value Im flowing through the electric motor 71 through an apply process. Based on the calculated target current value Imt, the assist control unit 13 drives the electric motor 71 via the motor control unit 12.

[0047] For example, the assist control unit 13 calculates the target current value Imt as follows: The assist control unit 13 calculates the difference between the target braking force BPT and the hydraulic braking force BPP as the difference Dp. The assist control unit 13 calculates the target value of the EPB load Pc so that a braking force equivalent to the difference Dp can be applied by the EPB load Pc. The assist control unit 13 calculates the target current value Imt so that the target value of the EPB load Pc can be applied.

[0048] <Assistance control> Using Figure 2, an example of the process flow in which the assistance control unit 13 performs assistance control will be explained. This processing routine is repeatedly executed at predetermined intervals during braking of the vehicle 90.

[0049] When this processing routine is started, in step S101, the assistance control unit 13 first determines whether the start condition for assistance control is met. The assistance control unit 13 determines that the start condition is met if 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.

[0050] An example of a starting condition is described below. For example, the assistance control unit 13 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 in 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.

[0051] For example, the assist control unit 13 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 there is a discrepancy between the target braking force BPT and the hydraulic braking force BPP. For example, 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 determination value. The determination value used here may be the same as the determination value used when determining the failure of the hydraulic braking device 80, or a different value may be adopted.

[0052] If the start condition is not met (S101: NO), the assistance control unit 13 terminates this processing routine. If the start condition is met (S101: YES), the assistance control unit 13 proceeds to step S102.

[0053] In step S102, the assistance control unit 13 determines whether the current value Im is less than or equal to the target current value Imt. For example, if the current value Im within the determination time from the start of applying voltage to the electric motor 71 is less than or equal to the target current value Imt (S102: YES), the assistance control unit 13 proceeds to step S103. That is, if the current value Im is equal to the target current value Imt, or if the current value Im is less than the target current value Imt, the assistance control unit 13 proceeds to step S103. Here, the inrush current flowing through the electric motor 71 is taken into consideration, and it is determined whether the current value Im after the inrush current has subsided is less than or equal to the target current value Imt within the determination time. The determination time can be a value calculated in advance by experimentation, for example.

[0054] In step S103, the assist control unit 13 causes the motor control unit 12 to perform the apply process. For example, the assist control unit 13 outputs one pulse at each specified interval. More specifically, the assist control unit 13 calculates the duty cycle at which the motor rotation speed Nm becomes "0" when the current value Im reaches the target current value Imt, and outputs a pulse based on the duty cycle. An example of a specified interval is a constant value. The specified interval may be a value that changes depending on the situation. For example, the specified interval can be adjusted based on road surface μ, vehicle speed, etc.

[0055] When the apply process is performed by the process in step S103, the assistance control unit 13 moves the process to step S105. On the other hand, in the process of step S102, if the current value Im is greater than the target current value Imt (S102: NO), the assistance control unit 13 proceeds to step S104. For example, if the current value Im within the determination time from when voltage is first applied to the electric motor 71 becomes greater than the target current value Imt, the assistance control unit 13 proceeds to step S104.

[0056] In step S104, the assist control unit 13 instructs the motor control unit 12 to perform a release process. An example of the release process is described below. For example, the assist control unit 13 outputs a single pulse as the release process. More specifically, it outputs a single pulse as the release process when a predetermined interval has elapsed since the output of the pulse output in the apply process.

[0057] When the release process is performed by the process in step S104, the assistance control unit 13 moves the process to step S105. In step S105, the assistance control unit 13 determines whether or not the termination condition for assistance control has been met.

[0058] An example of a termination condition is described below. The assistance control unit 13 can determine that the termination condition has been met, for example, when the vehicle 90 comes to a stop. Here, the vehicle 90 coming to a stop means, for example, when the vehicle 90 goes from being in motion to a state where its speed is "0". The vehicle 90 coming to a stop may include the state just before the speed becomes "0" and when the speed is slightly greater than "0". In addition to vehicle speed, it is also possible to determine whether the vehicle 90 has come to a stop based on wheel speed, longitudinal acceleration of the vehicle 90, etc.

[0059] The assist control unit 13 can also determine, for example, that the termination condition has been met when the braking request is released. For example, it can determine that the braking request has been released when the operation of the braking operation member 92 is released.

[0060] If the termination condition is met (S105:YES), the assistance control unit 13 terminates this processing routine. On the other hand, if the termination condition is not met (S105:NO), the assistance control unit 13 returns to step S102.

[0061] This section explains an example of when the termination condition is met and the assistive control is terminated. For example, if the vehicle speed is not "0" when the braking request is released, i.e., if the vehicle 90 is still moving, the assist control unit 13 terminates the assist control. Subsequently, the assist control unit 13 performs a release process to set the EPB load Pc to "0". As another example, if the vehicle 90 comes to a stop, the assist control unit 13 terminates the assist control. Subsequently, the assist control unit 13 performs a release process to set the EPB load Pc to "0". Alternatively, if the assist control is terminated when the vehicle 90 comes to a stop, the assist control unit 13 may continue to apply the EPB load Pc through a self-locking mechanism without performing a subsequent release process.

[0062] Here, using Figures 3 and 4, we will explain an example of the apply process performed in assistive control. Figure 3 illustrates a case where the load on the electric motor 71 is constant during the illustrated period. For example, this is an example where the linear motion member 75 assists the piston 87, generating an EPB load Pc, and the target braking force BPT is constant. As shown in Figure 3, the assist control unit 13 repeatedly energizes and deenerges the electric motor 71 by performing an apply process at specified intervals so that the current value Im flowing to the electric motor 71 becomes the target current value Imt. In the example shown in Figure 3, an inrush current flows at the start of output in each of the four illustrated pulses. In each pulse, the current value Im reaches the target current value Imt within the judgment time after the inrush current has subsided.

[0063] Figure 4 illustrates a case where the load on the electric motor 71 increases over time, starting from a low load state. For example, this is an example where the linear motion member 75 is not in contact with the piston 87, and then the linear motion member 75 begins to be pressed against the piston 87, gradually increasing the EPB load Pc. As shown in Figure 4, when the load on the electric motor 71 is low, the assist control unit 13 has a small current value Im after the inrush current converges, and has not reached the target current value Imt. As the load on the electric motor 71 increases, the current value Im also increases. When the current value Im becomes larger than the target current value Imt, as described above, the release process is performed following the apply process where the current value Im became larger than the target current value Imt.

[0064] As a result of the above assistive control being performed, the electric motor 71 is driven to maintain a constant position of the linear motion member 75 as long as the difference Dp is constant. On the other hand, if the difference Dp fluctuates, the electric motor 71 is driven so that the piston load follows the fluctuation of the difference Dp. Furthermore, the electric motor 71 is energized even after the current value Im reaches the target current value Imt, that is, after the actual braking force acting on the vehicle 90 reaches the target braking force BPT.

[0065] <Mechanism of Action and Effects> The operation and effects of this embodiment will now be described. Figure 5 shows the changes in current value Im and piston load when assist control is performed in the event of a failure in the power assist device 81. In the example shown in Figure 5, assist control is started at timing t11.

[0066] During the period up to timing t12, as shown in Figure 5(b), the hydraulic load Pb generated by the hydraulic braking device 80 in accordance with the braking request is load P11. As shown in Figure 5(a), an inrush current flows at timing t11. Once the inrush current subsides, the current value Im remains at the steady-state current Imb until timing t12.

[0067] In the example shown in Figure 5, the linear motion member 75 and the piston 87 come into contact at timing t12. After timing t12, the load on the electric motor 71 increases as the linear motion member 75 is pressed against the piston 87. As a result, after timing t12, the current value Im gradually increases, as shown in Figure 5(a). Consequently, an EPB load Pc is added after timing t12, as shown in Figure 5(b). After timing t12, the sum of the hydraulic load Pb and the EPB load Pc is the piston load Pa. As shown in Figure 5(a), at timing t13, the current value Im increases to the target current value Imt. As shown in Figure 5(b), at timing t13, the piston load Pa reaches load P12.

[0068] During the period from timing t13 to timing t14, the target braking force BPT is kept constant. Therefore, as shown in Figure 5(b), the piston load Pa is also kept at load P12. According to the control device 10, even after timing t13, the current value Im is kept constant as shown in Figure 5(a) by performing the apply process at specified intervals.

[0069] In the example shown in Figure 5, the increase in the target braking force BPT begins at timing t14. For example, the amount of operation of the braking operating member 92 is increased. Consequently, as shown in Figure 5(b), the hydraulic load Pb increases from timing t14 onward.

[0070] The hydraulic braking force BPP is increased as the target braking force BPT is increased. In other words, the piston 87 is moving in the pressing direction. In this case as well, according to the control device 10, the electric motor 71 is driven so that the current value Im flowing to the electric motor 71 becomes the target current value Imt, as shown in Figure 5(a). As a result, the linear motion member 75 also moves in the pressing direction from timing t14 onwards. Therefore, even from timing t14 onwards, the sum of the hydraulic load Pb and the EPB load Pc is equal to the piston load Pa. Subsequently, the piston load Pa reaches load P13.

[0071] In the example shown in Figure 5, the operation of the braking operating member 92 is released at timing t15 after the piston load Pa reaches load P13. Furthermore, the vehicle 90 is stopped at timing t15. As a result, the assist control is terminated. Therefore, as shown in Figure 5(a), the power supply to the electric motor 71 is terminated after timing t15. After timing t15, the electric parking brake device 70 operates as a parking brake. That is, the position of the linear motion member 75 is held by the self-locking mechanism. The example shown in Figure 5 is an example in which the braking request is terminated when the vehicle 90 is stopped at timing t15. The example shown in Figure 5 is an example in which the EPB load Pc continues to be applied by the self-locking mechanism after timing t15 following the termination of the assist control.

[0072] Next, a comparative example will be described using Figures 6 and 7. The comparative example is similar to this embodiment in that it operates an electric parking brake to compensate for the target braking force BPT. The comparative example differs from this embodiment in that it holds the position of the linear motion member by a self-locking mechanism.

[0073] In the example shown in Figure 6, the assistive control is initiated at timing t21. As shown in Figure 6(a), an inrush current flows at timing t21. Once the inrush current subsides, the current value Im remains at a steady-state current Imb until timing t22. During the period up to timing t22, as shown in Figure 6(b), the hydraulic load Pb generated in accordance with the braking requirement is load P21.

[0074] In the example shown in Figure 6, the linear motion member and the piston come into contact at timing t22. After timing t22, the load on the electric motor increases as the linear motion member is pressed against the piston. As a result, after timing t22, the current value Im gradually increases, as shown in Figure 6(a). Consequently, an EPB load Pc is added after timing t22, as shown in Figure 6(b). After timing t22, the sum of the hydraulic load Pb and the EPB load Pc equals the piston load Pa. As shown in Figure 6(a), at timing t23, the current value Im increases to the target current value Imt. As shown in Figure 6(b), at timing t23, the piston load Pa reaches load P22.

[0075] In the comparative example, as shown in Figure 6(a), the current value Im reaches the target current value Imt at timing t23, and the power supply to the electric motor is temporarily terminated. During the period from timing t23 to timing t24, the target braking force BPT is kept constant. Therefore, as shown in Figure 6(b), the piston load Pa is also kept at load P22.

[0076] In the example shown in Figure 6, the target braking force BPT begins to increase at timing t24. Consequently, as shown in Figure 6(b), the hydraulic load Pb increases from timing t24 onward.

[0077] The hydraulic braking force BPP increases as the target braking force BPT increases. In other words, the piston moves in the pressing direction. At this time, the position of the linear motion member does not change, so the EPB load Pc decreases from timing t24 onwards. Power is supplied to the electric motor again at timing t25. From timing t27 onwards, the load on the electric motor increases as the linear motion member is pressed against the piston. For this reason, from timing t27 onwards, the current value Im gradually increases as shown in Figure 6(a). As a result, as shown in Figure 6(b), the EPB load Pc is added from timing t27 onwards. From timing t27 onwards, the sum of the hydraulic load Pb and the EPB load Pc again equals the piston load Pa. As shown in Figure 6(a), at timing t28, the current value Im reaches the target current value Imt, and power is temporarily supplied to the electric motor.

[0078] Figure 7 shows a schematic diagram of an electric parking brake system in which the piston 101, a component of the comparative example's hydraulic brake system, is assisted by the electric parking brake system, and illustrates the piston load in that state.

[0079] Figure 7 illustrates a piston 101 that supplies brake fluid to a fluid chamber 102, an output shaft 103 rotated by an electric motor, and a linear motion member 104 that moves linearly in accordance with the rotation of the output shaft 103. Figure 7 shows solid arrows indicating the direction of pressure applied by the piston 101. A friction material is attached to the piston 101. The piston 101 presses the friction material against the rotating member due to the piston load. That is, the friction material and the rotating member are arranged in order on the side of the piston 101 that is in the direction of pressure. The friction material and the rotating member are not shown in Figure 7.

[0080] Furthermore, Figure 7 shows the EPB load Pc, which is the load generated by the electric parking brake system, as a solid white arrow. The hydraulic load Pb, which is the load generated by hydraulic pressure, is shown as a dashed white arrow. The sum of the EPB load Pc and the hydraulic load Pb corresponds to the pressing force that the piston 101 exerts on the friction material against the rotating member. This pressing force corresponds to the braking force applied to the wheel.

[0081] Figure 7(a) shows the state in which the end of the linear motion member 104 on the pressing direction side is in contact with the piston 101. As indicated by the white arrow, the piston load reflects the EPB load Pc and the hydraulic load Pb. The sum of the EPB load Pc and the hydraulic load Pb in the state shown in Figure 7(a), i.e., the piston load value, is indicated as the first load P1.

[0082] During the period from timing t23 to timing t24 as illustrated in Figure 6, the comparative electric parking brake device is in the state shown in Figure 7(a). Figure 7 shows the position of the end of the linear motion member 104 on the pressing direction side as the initial nut position Xn in the state shown in Figure 7(a). Figure 7 also shows the position of the end of the piston 101 on the pressing direction side as the initial piston position Xc in the state shown in Figure 7(a).

[0083] Figure 7(b) shows a state where the hydraulic pressure is higher than the state illustrated in Figure 7(a). The position of the linear motion member 104 is maintained at the same position as in Figure 7(a). As indicated by the white arrows, the hydraulic load Pb has increased compared to the state shown in Figure 7(a). At this time, since the position of the linear motion member 104 is maintained at the initial nut position Xn, the EPB load Pc decreases as the hydraulic load Pb increases. That is, the sum of the EPB load Pc and the hydraulic load Pb does not change from the first load P1. The end of the piston 101 remains at the initial piston position Xc.

[0084] When the hydraulic load Pb increases further from the state shown in Figure 7(b) and exceeds the first load P1, the piston 101 begins to move in the pressing direction. That is, the end of the piston 101 moves from the initial piston position Xc in the pressing direction. Figure 7(c) shows the state in which the end of the piston 101 has moved from the initial piston position Xc.

[0085] As shown in Figure 7(c), when the piston 101 moves away from the linear motion member 104, the EPB load Pc becomes "0". In the state shown in Figure 7(c), the hydraulic load Pb is equal to the piston load.

[0086] During the period from timing t24 to timing t26 as illustrated in Figure 6, the comparative electric parking brake device progresses from the state shown in Figure 7(b) to the state shown in Figure 7(c). Figure 7(d) shows the state after the linear motion member 104 has been moved in the pressing direction from the initial nut position Xn, as shown in Figure 7(c). The EPB load Pc is generated again due to the contact between the linear motion member 104 and the piston 101. In the state shown in Figure 7(d), the magnitude of the hydraulic load Pb is the same as in the state shown in Figure 7(c). In the state shown in Figure 7(d), the piston load reaches a second load P2, which is greater than the first load P1, due to the addition of the EPB load Pc to the hydraulic load Pb.

[0087] During the period from timing t27 to timing t28 as illustrated in Figure 6, the comparative electric parking brake device is in the state shown in Figure 7(d). As described above, in the comparative example, when assisting with the electric parking brake, there is a period when the braking force does not increase even when the hydraulic pressure begins to rise, as illustrated in Figure 7(b). Therefore, there is a period when the piston load Pa does not increase, as illustrated in Figure 6 from timing t24 to timing t26. In other words, when the position of the linear motion member is held by a self-locking mechanism and the power supply to the electric motor is stopped, as in the comparative example, it may not be possible to provide responsive assistance with the EPB load Pc in response to fluctuations in hydraulic pressure.

[0088] Furthermore, as illustrated in Figure 7(c), there is a period between when the hydraulic pressure begins to increase and when the braking force begins to increase during which the EPB load Pc is temporarily eliminated. Because the EPB load Pc is eliminated and then reapplied, the manner in which the piston load Pa increases from load P22 to load P24 is no longer linear, as is the case during the period from timing t26 to timing t28 illustrated in Figure 6. Since the load increases from load P22 to load P23 before increasing to load P24, this may destabilize the behavior of the vehicle 90. For example, the pitching motion of the vehicle 90 may increase.

[0089] In contrast, according to the control device 10 of this embodiment, as long as the current value Im is less than or equal to the target current value Imt, the apply process is repeatedly executed until the termination condition is met (S102, S103, and S105). Therefore, until the termination condition is met, the electric motor 71 is energized even if the current value Im reaches the target current value Imt. Until the termination condition is met, the electric motor 71 is energized even if the difference Dp is eliminated. Until the termination condition is met, the electric motor 71 is energized even while the position of the linear motion member 75 is maintained. In this way, the load corresponding to the difference Dp can be continuously applied to the piston 87 without continuing to stop the power supply to the electric motor 71 during the execution of assist control. This makes it possible to quickly move the linear motion member 75 when the target braking force BPT increases during the execution of assist control. The linear motion member 75 can be moved to follow the piston 87 which moves in accordance with the increase in the hydraulic load Pb. In other words, responsiveness to variations in the differential Dp can be ensured.

[0090] The control device 10 ensures responsiveness to fluctuations in the differential Dp. As a result, the condition in which the EPB load Pc is temporarily eliminated, as illustrated in Figure 7(c) as a comparative example, becomes less likely to occur. This makes it easier to linearly increase the piston load Pa, unlike the period from timing t26 to timing t28 illustrated in Figure 6 as a comparative example. This suppresses instability in the behavior of the vehicle 90 during the execution of assist control.

[0091] When maintaining a constant braking force during the execution of assistive control, it is preferable not to move the linear motion member 75 by applying voltage during the apply process, that is, not to fluctuate the EPB load Pc. According to the control device 10, even if the linear motion member 75 moves while the braking force is being maintained, if the current value Im becomes greater than the target current value Imt, a release process is executed (S104). This prevents the EPB load Pc from becoming excessive.

[0092] (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.

[0093] In the above embodiment, an example was shown in which pulse output is performed at specified intervals as an apply process in assist control. Alternatively, the system may be configured to continue supplying power to the electric motor 71 by high-frequency duty cycle control so that the current value Im becomes the target current value Imt. High-frequency duty cycle control is a control method that increases the frequency of PWM control by changing the duty cycle to a smaller value compared to the normal duty cycle. For example, if the drive circuit 20 is equipped with a high-frequency generator, high-frequency duty cycle control can be performed.

[0094] The control device 10 may have a function to learn the time from the occurrence of the inrush current until it converges. The control device 10 may also have a function to learn the magnitude of the inrush current. The control device 10 may adjust the specified interval based on the learning results. For example, by using the learning results of the inrush current, it becomes possible to shorten the interval at which the apply processing is performed without moving the linear motion member 75. This improves the accuracy of setting the motor rotation speed Nm to "0" when the current value Im is the target current value Imt.

[0095] In the above embodiment, the case where the power assist device 81 fails was described as an example of when the start condition for assist control is met. The start condition is not limited to this. For example, even if a failure occurs in a part of the hydraulic braking device 80 other than the power assist device 81, it may be determined that the start condition is met.

[0096] In driver assistance control, the control that adjusts the vehicle's speed using the braking force of the hydraulic brake system 80 is an example of control that has a braking request. That is, even if the braking request of the driver assistance control cannot be met, it can be determined that the start condition has been met. When driver assistance control is being performed, the termination of the driver assistance control corresponds to the resolution of the braking request. For example, it can be determined that the termination condition has been met when the vehicle 90 reaches the target point set by the driver assistance control.

[0097] Furthermore, any control that allows for setting a target value for hydraulic braking force and intervening in the adjustment of hydraulic braking force can be said to have a braking request. Even if the braking request cannot be satisfied by these controls, it can be determined that the start condition has been met. In other words, the assistive control described in the above embodiment can be applied.

[0098] The processing circuits of the control device 10, the hydraulic control unit 40, and the support control unit 50 may have any of the following configurations: [a] A circuit comprising one or more processors that perform various processes according to a computer program. The processor comprises a processing unit. Examples of processing units include a CPU, DSP, and GPU. The processor comprises memory. Examples of memory include RAM, ROM, and flash memory. Memory stores program code or instructions configured to cause the processing unit to perform the processes. Memory, i.e., computer-readable media, includes any available media that can be accessed by a general-purpose or dedicated computer. [b] A circuit comprising one or more hardware circuits that perform various processes. Examples of hardware circuits include an ASIC (Application Specific Integrated Circuit), a CPLD (Complex Programmable Logic Device), and an FPGA (Field Programmable Gate Array). [c] A circuit comprising a processor that performs a part of the various processes according to a computer program, and hardware circuits that perform the remaining parts of the various processes.

[0099] 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. [Explanation of Symbols]

[0100] 10...Control device 12…Motor Control Unit 13…Assistance Control Unit 20…Drive circuit 30…Control Unit 70…Electric parking brake system 71… Electric motor 72…Transmission mechanism 73...Conversion mechanism 74…Output shaft 75…Linear motion member 80... Hydraulic braking system 81...Boosting device 82…Master cylinder 83... Reservoir Tank 84... Hydraulic actuator 85...Brake caliper 86... Wheel Cylinder 87... Piston 88…Friction material 89... Rotating member 90... Vehicles 91...Wheel

Claims

1. A hydraulic braking device comprising a rotating member that rotates integrally with the wheel, a friction material pressed against the rotating member, a cylinder supplied with brake fluid, and a piston that presses the friction material against the rotating member according to the hydraulic pressure in the cylinder, wherein a braking force is generated on the wheel according to the load applied to the friction material pressing against the rotating member, This electric parking brake system is a vehicle having an electric motor, a conversion mechanism that converts the rotational motion of the electric motor into linear motion, and a linear motion member that is moved linearly by the conversion mechanism and is located inside the cylinder, wherein the linear motion member presses the friction material against the rotating member via the piston, thereby generating a load that presses the friction material against the rotating member, and is applicable to the vehicle having the hydraulic brake system that can generate braking force in response to braking requests. A braking control device for controlling the aforementioned electric parking brake, A motor control unit that outputs a drive signal for driving the electric motor, The system includes an assist control unit that, when the braking force applied by the hydraulic braking device during braking of the vehicle cannot meet the target braking force corresponding to the braking request, performs assist control to cause the linear motion member to assist the friction material pressed against the rotating member so that the electric parking brake device generates a load corresponding to the difference between the target braking force and the braking force applied by the hydraulic braking device, The assist control unit performs an apply process in which, in the assist control, it applies a voltage to the electric motor that drives the electric motor in a direction that increases the load on the linear motion member that presses against the piston, and continues to perform the apply process even after the actual braking force acting on the vehicle has reached the target braking force. Brake control device.

2. The current value that generates the load corresponding to the aforementioned difference by driving the electric motor is set as the target current value. When the assist control unit performs the apply process in the assist control, it repeats the energization and de-energization of the electric motor by performing the apply process at predetermined intervals so that the current value flowing to the electric motor becomes the target current value. The braking control device according to claim 1.

3. The assistance control unit, If the current flowing through the electric motor is less than or equal to the target current value, the apply process is performed while, If, as a result of performing the apply process, the current flowing through the electric motor becomes greater than the target current, a release process is performed by applying a voltage to the electric motor that drives it in a direction that reduces the load on the linear motion member pressing against the piston, instead of performing the apply process at the specified intervals. The braking control device according to claim 2.

Images