WO2023171723A1

WO2023171723A1 - Braking control device

Info

Publication number: WO2023171723A1
Application number: PCT/JP2023/008897
Authority: WO
Inventors: 達也浦野; 照薫浦岡
Original assignee: 株式会社アドヴィックス
Priority date: 2022-03-08
Filing date: 2023-03-08
Publication date: 2023-09-14
Also published as: JP2023130657A

Abstract

A control device 10 is applied to a vehicle 90 that has 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 the 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 the load from the electric parking braking device 70, the assist control unit performing the apply processing even after the actual braking force has reached the target braking force.

Description

Brake control device

The present invention relates to a brake control device.

Patent Document 1 discloses a control device that brakes a vehicle using the braking force generated by an electric parking braking device when the brake booster is in a functionally restricted state or in a non-functional state. That is, a configuration is disclosed in which the functional restriction or inability of the brake booster is compensated for by the electric parking braking device.

As an electric parking brake device, one in which a mechanism for converting the rotational motion of an electric motor into linear motion is applied to a brake caliper, as disclosed in Patent Document 2, for example, is known. More specifically, in the electric parking brake system disclosed in Patent Document 2, a linearly moving member to which the driving force of an electric motor is transmitted and linearly moves is arranged within a piston in a brake caliper.

A known electric parking brake device employs a self-locking mechanism as disclosed in Patent Document 2. The self-locking mechanism is a mechanism in which the position of the translational member is maintained without the translational member moving even if a force acts on the translational member in the direction in which the translational member moves. In an electric parking brake system equipped with such a self-locking mechanism, after the linearly moving member is moved to a desired position by driving the electric motor, power to the electric motor is stopped and the self-locking mechanism moves the linearly moving member to a desired position. Hold position.

Patent No. 6563456 Japanese Patent Application Publication No. 2018-118524

When the electric parking brake device as disclosed in Patent Document 2 performs control to compensate for braking of the vehicle using the electric parking brake device as in Patent Document 1, the following problems occur.
If, for example, the hydraulic pressure is increased while compensation is being performed by the electric parking brake system, it becomes necessary to move the linearly moving member in order to continue assisting the piston with the linearly moving member. At this time, if the position of the linear moving member is held by the self-lock mechanism, even if the electric motor starts to be energized after the fluid pressure fluctuates, the linear moving member will not start moving due to the fluid pressure fluctuation. will cause a delay time. In other words, if the position of the linearly moving member is held by a self-locking mechanism and the electric motor is not energized, assistance by the linearly moving member cannot be provided in a responsive manner in response to fluctuations in hydraulic pressure. There was a case.

As described above, when using an electric parking brake system to compensate for the braking of a vehicle, there is room for improvement in the responsiveness of the braking force.

A braking control device for solving the above problems includes a rotating member that rotates integrally with a wheel, a friction material that is pressed against the rotating member, a cylinder to which brake fluid is supplied, and a brake control device that operates according to the hydraulic pressure in the cylinder. a piston that presses the friction material against the rotating member; a hydraulic braking device that generates a braking force on the wheel according to the load with which the friction material is pressed against the rotating member; an electric motor; It is composed of a conversion mechanism that converts the rotational motion of the electric motor into linear motion, and a linear motion member that is linearly moved by the conversion mechanism and is disposed within the cylinder, and the linear motion member and an electric parking braking device that presses the friction material against the rotating member via the piston to generate a load that presses the friction material against the rotating member, and the vehicle A brake control device that is applied to the vehicle capable of generating a braking force by the hydraulic braking device and controls the electric parking brake device, the motor outputting a drive signal for driving the electric motor. a control unit; and when the target braking force corresponding to the braking request cannot be satisfied by the braking force applied by the hydraulic braking device during braking of the vehicle, the target braking force and the braking force applied by the hydraulic braking device; an assistance control unit that executes assistance control in which the linear motion member assists the friction material pressed against the rotating member so that the electric parking brake system generates a load corresponding to the difference between the braking force and the , wherein, in the assisting control, the assisting control unit performs an application process of applying a voltage to the electric motor to drive the electric motor in a direction that increases the load with which the direct-acting member is pressed against the piston. The gist thereof is to perform the apply processing even after the actual braking force actually acting on the vehicle reaches the target braking force.

According to the above configuration, the electric motor is 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 de-energized does not continue while the assisting control is being performed. Therefore, responsiveness can be ensured when the position of the direct-acting member is moved as the target braking force increases or decreases during execution of assisting control.

FIG. 1 is a schematic diagram showing an embodiment of a brake control device and a vehicle to be controlled by the brake control device. FIG. 2 is a flowchart showing the flow of assistance control processing executed by the brake control device. FIG. 3 is a diagram illustrating the value of the current flowing through the electric motor in a state where the braking force is maintained in the assistance control executed by the braking control device. FIG. 4 is a diagram illustrating the current value flowing through the electric motor in a state where the braking force is increased in the assistance control executed by the braking control device. FIG. 5 is a diagram showing changes in the current value and changes in the load that are adjusted by the assistance control executed by the brake control device. FIG. 6 is a diagram showing changes in current value and load when assistance is provided by an electric parking brake system as a comparative example. FIG. 7 is a diagram illustrating the state of the electric parking brake device and the corresponding load when assistance is provided by the electric parking brake device as a comparative example.

Hereinafter, one embodiment of a brake control device will be described with reference to FIGS. 1 to 5.
FIG. 1 shows a control device 10 as a brake control device and a vehicle 90 to which the control device 10 is applied.

Vehicle 90 is, for example, a four-wheeled vehicle. FIG. 1 illustrates one wheel 91 among the wheels included in a vehicle 90.
The vehicle 90 includes a hydraulic braking device 80. The hydraulic braking device 80 is used as a service brake. The vehicle 90 includes a brake operation member 92 that can be operated by the driver of the vehicle 90. For example, the brake operating member 92 is a brake pedal. By operating the brake operation member 92, the driver can generate a braking force via the hydraulic braking device 80 to brake the vehicle 90. The operation of the brake operation member 92 corresponds to a brake request by the driver.

The vehicle 90 includes an electric parking brake device 70. The electric parking brake device 70 can be used as a parking brake.
<Hydraulic braking device>
The hydraulic braking device 80 includes a hydraulic pressure generating device. The hydraulic braking device 80 includes a hydraulic actuator 84. The hydraulic braking device 80 includes a braking mechanism corresponding to each wheel. The braking mechanism can apply braking force to the corresponding wheel.

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

The braking mechanism can generate frictional braking force on the wheels 91 according to the hydraulic pressure in the wheel cylinders 86. Hereinafter, the hydraulic pressure within 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 member 89. That is, the braking mechanism can apply a greater braking force to the wheels 91 as the WC pressure is higher. Hereinafter, the force with which the friction material 88 is pressed against the rotating member 89 in response to the WC pressure will be referred to as hydraulic load Pb.

The hydraulic braking device 80 includes a booster 81, a master cylinder 82, and a reservoir tank 83 in which brake fluid is stored. The hydraulic pressure generator includes a booster 81, a master cylinder 82, and a reservoir tank 83.

The booster 81 can assist the operation of the brake operating member 92 and transmit the assisted operating force to the master cylinder 82. As the booster 81, a known booster can be appropriately employed. For example, examples of the booster include a negative pressure booster, a hydraulic booster, an electric booster, and the like.

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

The hydraulic actuator 84 is arranged between the master cylinder 82 and the wheel cylinder 86. Brake fluid is supplied from master cylinder 82 to wheel cylinder 86 via hydraulic actuator 84 . The hydraulic actuator 84 includes a flow path for brake fluid. The brake fluid flow path is connected to a wheel cylinder corresponding to each wheel. The hydraulic actuator 84 includes, for example, a plurality of electromagnetic valves disposed in the flow path, a pump disposed in the flow path, a pump drive motor for driving the pump, and the like.

<Electric parking brake device>
The electric parking brake device 70 shares a part of the structure with the brake mechanism in the hydraulic brake device 80.

The electric parking brake device 70 includes an electric motor 71. The electric parking brake device 70 includes an output shaft 74 that rotates in accordance with the drive of an electric motor 71. The electric parking brake device 70 includes a transmission mechanism 72 that transmits the driving force of an electric motor 71 to an output shaft 74. A rotating shaft 71a of an electric motor 71 is connected to the transmission mechanism 72 as an input shaft. The transmission mechanism 72 includes, for example, a speed reduction mechanism.

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

The conversion mechanism 73 includes a self-locking mechanism. In the self-locking mechanism, when the rotation of the output shaft 74 is stopped, the position of the linearly moving member 75 is maintained even if a force is applied to the linearly moving member 75 in the direction in which the linearly moving member 75 moves linearly. It is a mechanism that The self-locking mechanism is realized, for example, by the frictional force caused by the engagement between the male thread of the output shaft 74 and the female thread of the direct-acting member 75.

In the electric parking brake device 70, the linear motion member 75 is arranged within the wheel cylinder 86. In the electric parking brake device 70, the direct-acting member 75 presses the friction material 88 against the rotating member 89 via the piston 87, thereby generating a load that causes the friction material 88 to be pressed against the rotating member 89. Hereinafter, this load will be referred to as EPB load Pc.

Note that the electric parking brake device 70 is not limited to a configuration in which the direct-acting member 75 directly contacts the piston 87 when the EPB load Pc is applied. The electric parking brake device 70 may have a configuration in which a pusher is interposed between the linear motion member 75 and the piston 87. For example, the pusher can be separated from the linear motion member 75 and the piston 87. Another example of the presser is attached to the tip of the translational member 75.

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

The electric parking brake device 70 is provided, for example, in each brake mechanism corresponding to a rear wheel among the wheels included in the vehicle 90. The electric parking brake device 70 may be provided in each brake mechanism corresponding to a front wheel among the wheels included in the vehicle 90. The electric parking brake device 70 may be provided in all braking mechanisms, or may be provided in one braking mechanism.

The electric parking brake device 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 includes the control device 10 and peripheral circuits. The drive circuit 20 shown in FIG. 1 is an example of a peripheral circuit 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 an on-vehicle battery mounted on a vehicle 90. The drive circuit 20 is controlled by the control device 10.

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 include a current detection circuit.

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 include a voltage detection circuit.

<Various sensors>
Vehicle 90 is equipped with various sensors. FIG. 1 shows an operation amount sensor SE1, a pressure sensor SE2, and a rotation angle sensor SE3 as examples of various sensors. Detection signals from various sensors are input to the control device 10.

The operation amount sensor SE1 is a sensor that detects the operation amount of the brake operation member 92. Based on the detection signal from the operation amount sensor SE1, the control device 10 can acquire the operation amount of the brake operation member 92. An example of the operation amount is the displacement amount of the brake operation member 92 that is displaced by the driver's operation. Another example of the operation amount is the operation force applied to the brake operation member 92 by the driver.

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

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 acquire 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.

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

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

The hydraulic control unit 40 can control the hydraulic braking device 80.
For example, the hydraulic control unit 40 has a function of determining whether or not the hydraulic braking device 80 has malfunctioned. For example, the hydraulic control unit 40 can detect a failure of the booster 81. For example, if 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 larger than the determination value, a failure has occurred. There is a way to determine if there is. Here, the target braking force BPT is a value corresponding to a braking request. Target braking force BPT is a target value of braking force to be applied to vehicle 90. For example, the target braking force BPT can be calculated based on the amount of operation of the brake operation 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. As the determination value, a value calculated in advance through experiments or the like can be used.

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

The hydraulic pressure control unit 40 may have a function of adjusting the WC pressure according to driving support control executed by the support control unit 50.
<Control device>
The control device 10 is a processing circuit made up of a plurality of functional units that perform various controls. FIG. 1 shows an acquisition section 11, a motor control section 12, and an assistance control section 13 as examples of functional sections. Each functional unit included in the control device 10 is capable of transmitting and receiving information to and from each other.

The acquisition unit 11 can acquire state quantities for controlling the electric parking brake device 70. For example, the acquisition unit 11 calculates the state quantity. The acquisition unit 11 may acquire state quantities calculated by other functional units, other processing circuits, and the like.

An example of state quantity will be explained. Examples of the state quantities include target braking force BPT, hydraulic braking force BPP, current value Im, motor rotational speed Nm, and information on whether or not a failure has occurred in hydraulic braking device 80.

The motor control unit 12 drives the electric motor 71 by PWM (Pulse Width Modulation) control. That is, the motor control unit 12 generates a drive signal and outputs the drive signal to the drive circuit 20. The electric motor 71 is driven by switching the drive circuit 20 according to the drive signal. The motor control unit 12 sets a target current value Imt as a target value of the current value Im of the electric motor 71. The motor control unit 12 calculates the duty ratio of the drive signal based on the target current value Imt. The motor control unit 12 generates a drive signal based on the duty ratio.

Processes for driving the electric motor 71 include apply processing and release processing. The apply process is a process of applying a voltage to the electric motor 71 to drive the electric motor 71 so that the rotating shaft 71a of the electric motor 71 rotates in the first direction. That is, the apply process is a process in which a voltage is applied to the electric motor 71 to drive the electric motor 71 in a direction that increases the load with which the linear motion member 75 is pressed against the piston 87 . The release process is a process of applying a voltage to the electric motor 71 to drive the electric motor 71 so that the rotating shaft 71a of the electric motor 71 rotates in the second direction. That is, the release process is a process in which a voltage is applied to the electric motor 71 to drive the electric motor 71 in a direction that reduces the load with which the linear motion member 75 is pressed against the piston 87 . For example, in the apply process, a positive voltage is applied to the electric motor 71. In this case, a negative voltage is applied to the electric motor 71 in the release process.

The assistance control unit 13 can perform assistance control. In the assistance control, when braking the vehicle 90, the electric parking brake device 70 is operated, and the braking force by the electric parking brake device 70 can be applied to the vehicle 90. In the assistance control, the friction material 88 pressed against the rotating member 89 is assisted by the linear motion member 75 .

In an example of assistance control, the assistance control unit 13 calculates a target current value Imt as a target value of the current value Im flowing through the electric motor 71 through the apply process. The assistance control section 13 causes the motor control section 12 to drive the electric motor 71 based on the calculated target current value Imt.

For example, the assistance control unit 13 calculates the target current value Imt as follows. The assisting control unit 13 calculates the difference between the target braking force BPT and the hydraulic braking force BPP as a difference Dp. The assist control unit 13 calculates a target value of the EPB load Pc so that a braking force corresponding to the difference Dp can be applied by the EPB load Pc. The assisting control unit 13 calculates a target current value Imt at which the target value of the EPB load Pc can be applied.

<Assistance control>
An example of the flow of processing in which the assistance control unit 13 executes assistance control will be described with reference to FIG. 2. This processing routine is repeatedly executed at predetermined intervals while the vehicle 90 is braking.

When this processing routine is started, first in step S101, the assisting control unit 13 determines whether or not the starting condition for assisting control is satisfied. The assistance control unit 13 determines that the start condition is satisfied when the target braking force corresponding to the braking request cannot be satisfied by the braking force applied by the hydraulic braking device 80 during braking of the vehicle 90.

An example of starting conditions will be explained. For example, the assistance control unit 13 determines that the start condition is satisfied when the hydraulic braking device 80 has malfunctioned. An example of failure of the hydraulic braking device 80 is failure of the booster 81. Whether or not a failure has occurred in the hydraulic braking device 80 can be determined, for example, by obtaining the result of failure determination performed by the hydraulic pressure control unit 40.

For example, the assistance control unit 13 acquires the values of the target braking force BPT and the hydraulic braking force BPP during braking, and determines that the start condition is satisfied when a discrepancy occurs between the target braking force BPT and the hydraulic braking force BPP. It can also be determined that For example, whether or not there is a deviation between the target braking force BPT and the hydraulic braking force BPP can be determined based on whether or not the width of the deviation is larger than a determination value. The determination value used here may be the same value as the determination value used when determining failure of the hydraulic braking device 80, or may be a different value.

If the start condition is not satisfied (S101: NO), the assistance control unit 13 temporarily ends this processing routine. If the start condition is satisfied (S101: YES), the assistance control unit 13 moves the process to step S102.

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 after starting to apply voltage to the electric motor 71 is equal to or less than the target current value Imt (S102: YES), the assistance control unit 13 shifts the process 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 smaller than the target current value Imt, the assistance control unit 13 shifts the process to step S103. Note that, in consideration of the inrush current flowing through the electric motor 71, it is determined here whether the current value Im after the inrush current converges is equal to or less than the target current value Imt within the determination time. For example, a value calculated in advance through experiments or the like can be used as the determination time.

In step S103, the assistance control unit 13 causes the motor control unit 12 to perform an apply process. For example, the assistance control unit 13 outputs one pulse at each prescribed interval. More specifically, the assist control unit 13 calculates a duty ratio 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 ratio. let An example of the prescribed interval is a constant value. The prescribed interval may be a value that changes depending on the situation. For example, it is conceivable to adjust the specified interval based on road surface μ, vehicle speed, etc.

After executing the apply process through 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 larger than the target current value Imt (S102: NO), the assistance control unit 13 shifts the process to step S104. For example, if the current value Im within the determination time after starting to apply voltage to the electric motor 71 becomes larger than the target current value Imt, the assisting control unit 13 shifts the process to step S104.

In step S104, the assistance control unit 13 causes the motor control unit 12 to perform a release process. An example of release processing will be explained. For example, the assistance control unit 13 outputs one pulse as a release process. More specifically, one pulse is output as a release process when a predetermined interval has elapsed from the output point of the pulse output in the apply process.

After executing the release process through 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 the conditions for ending assistance control are satisfied.

An example of termination conditions will be explained. For example, the assistance control unit 13 can determine that the termination condition is satisfied when the vehicle 90 has stopped. Here, stopping the vehicle 90 means, for example, that the vehicle speed of the vehicle 90 changes from a state where the vehicle 90 is running to a state of "0". Stopping the vehicle 90 may include a state where the vehicle speed is just before reaching "0" and the vehicle speed is slightly higher than "0". It is also possible to determine whether the vehicle 90 has stopped based not only on the vehicle speed but also on the wheel speed, longitudinal acceleration of the vehicle 90, and the like.

The assistance control unit 13 can also determine that the termination condition is satisfied, for example, when the braking request is canceled. For example, when the operation of the brake operation member 92 is canceled, it can be determined that the brake request is canceled.

If the termination condition is satisfied (S105: YES), the assistance control unit 13 terminates this processing routine. On the other hand, if the termination condition is not satisfied (S105: NO), the assistance control unit 13 shifts the process to step S102 again.

An example in which the assist control is ended when the end condition is satisfied will be described.
As an example, if the vehicle speed is not "0" when the braking request is canceled, that is, if the vehicle 90 is running, the assistance control unit 13 ends the assistance control. Thereafter, the assistance control unit 13 sets the EPB load Pc to "0" by performing a release process. As another example, when the vehicle 90 stops, the assistance control unit 13 ends the assistance control. Thereafter, the assistance control unit 13 sets the EPB load Pc to "0" by performing a release process. Alternatively, when the assistance control ends when the vehicle 90 stops, the assistance control section 13 can continue to apply the EPB load Pc by the self-lock mechanism without performing the release process thereafter.

Here, an example of an apply process performed in assistance control will be described using FIGS. 3 and 4.
FIG. 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 to generate the EPB load Pc, and the target braking force BPT is constant. As shown in FIG. 3, the assistance control unit 13 performs an apply process at regular intervals so that the current value Im flowing through the electric motor 71 becomes the target current value Imt, thereby controlling the energization and energization of the electric motor 71. Stop and repeat. In the example shown in FIG. 3, an inrush current flows at the start of output in each of the four pulses illustrated. In each pulse, the current value Im reaches the target current value Imt within the determination time after the inrush current converges.

FIG. 4 illustrates a case where the load on the electric motor 71 increases over time from a low load state. For example, this is an example in which the linear moving member 75 starts to be pressed against the piston 87 from a state where the linear moving member 75 is not in contact with the piston 87, and the EPB load Pc gradually increases. As shown in FIG. 4, when the load on the electric motor 71 is small, the current value Im that flows after the inrush current converges is small and does not reach 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 processing is performed following the apply processing in which the current value Im becomes larger than the target current value Imt.

As a result of executing the above-mentioned assisting control, the electric motor 71 is driven so as to keep the position of the direct-acting member 75 constant while the difference Dp is constant. On the other hand, when the difference Dp changes, the electric motor 71 is driven so that the piston load follows the change in 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 actually acting on the vehicle 90 reaches the target braking force BPT.

<Action and effect>
The operation and effects of this embodiment will be explained.
FIG. 5 shows changes in the current value Im and the piston load when assisting control is executed when the booster 81 has failed. In the example shown in FIG. 5, assistance control is started from timing t11.

In the period up to timing t12, as shown in FIG. 5(b), the hydraulic load Pb generated by the hydraulic braking device 80 in accordance with the braking request is the load P11.
As shown in FIG. 5(a), an inrush current flows at timing t11. After the rush current converges, the current value Im remains at the steady current Imb until timing t12.

In the example shown in FIG. 5, the direct-acting member 75 and the piston 87 come into contact at timing t12. After timing t12, as the direct-acting member 75 is pressed against the piston 87, the load on the electric motor 71 increases. Therefore, after timing t12, the current value Im gradually increases, as shown in FIG. 5(a). As a result, as shown in FIG. 5(b), the EPB load Pc is applied after timing t12. After timing t12, the sum of the hydraulic load Pb and the EPB load Pc becomes the piston load Pa. As shown in FIG. 5(a), the current value Im increases to the target current value Imt at timing t13. As shown in FIG. 5(b), at timing t13, the piston load Pa reaches the load P12.

During the period from timing t13 to timing t14, target braking force BPT is held constant. Therefore, as shown in FIG. 5(b), the piston load Pa is also maintained at the load P12. According to the control device 10, the apply process is performed at regular intervals even after timing t13, so that the current value Im is maintained constant as shown in FIG. 5(a).

In the example shown in FIG. 5, the target braking force BPT starts increasing at timing t14. For example, the amount of operation of the brake operation member 92 is increased. Along with this, as shown in FIG. 5(b), the hydraulic load Pb is increased after timing t14.

By increasing the target braking force BPT, the hydraulic braking force BPP is increased. That is, the piston 87 is moving in the pressing direction. Also in this case, according to the control device 10, the electric motor 71 is driven so that the current value Im flowing through the electric motor 71 becomes the target current value Imt, as shown in FIG. 5(a). As a result, after timing t14, the linearly moving member 75 is also moving in the pressing direction. Therefore, even after timing t14, the sum of the hydraulic load Pb and the EPB load Pc is the piston load Pa. After that, the piston load Pa reaches the load P13.

In the example shown in FIG. 5, the operation of the brake operation member 92 is canceled at timing t15 after the piston load Pa reaches the load P13. Furthermore, the vehicle 90 is stopped at timing t15. This completes the assistance control. Therefore, as shown in FIG. 5A, after timing t15, the electric motor 71 is no longer energized. After timing t15, the electric parking brake device 70 operates as a parking brake. That is, the position of the linearly moving member 75 is held by the self-locking mechanism. The example shown in FIG. 5 is an example in which the braking request is canceled with the vehicle 90 stopped at timing t15. The example shown in FIG. 5 is an example in which the self-lock mechanism continues to apply the EPB load Pc after timing t15 after the end of the assisting control.

Next, a comparative example will be described using FIGS. 6 and 7. The comparative example is similar to the present embodiment in that the electric parking brake system is operated to compensate for the target braking force BPT. The comparative example differs from the present embodiment in that the position of the translational member is held by a self-locking mechanism.

In the example shown in FIG. 6, assistance control is started from timing t21.
As shown in FIG. 6(a), an inrush current flows at timing t21. After the rush current converges, the current value Im remains at the steady current Imb until timing t22. In the period up to timing t22, as shown in FIG. 6(b), the hydraulic load Pb generated in accordance with the braking request is the load P21.

In the example shown in FIG. 6, the direct-acting member and the piston come into contact at timing t22. After timing t22, the load on the electric motor increases as the direct-acting member is pressed against the piston. Therefore, after timing t22, the current value Im gradually increases, as shown in FIG. 6(a). As a result, as shown in FIG. 6(b), the EPB load Pc is applied after timing t22. After timing t22, the sum of the hydraulic load Pb and the EPB load Pc becomes the piston load Pa. As shown in FIG. 6A, the current value Im increases to the target current value Imt at timing t23. As shown in FIG. 6(b), at timing t23, the piston load Pa reaches the load P22.

In the comparative example, as shown in FIG. 6A, when the current value Im reaches the target current value Imt at timing t23, the energization of the electric motor is temporarily terminated. During the period from timing t23 to timing t24, target braking force BPT is held constant. Therefore, as shown in FIG. 6(b), the piston load Pa is also maintained at the load P22.

In the example shown in FIG. 6, the increase in target braking force BPT is started at timing t24. Along with this, as shown in FIG. 6(b), the hydraulic load Pb is increased after timing t24.

By increasing the target braking force BPT, the hydraulic braking force BPP is increased. That is, the piston is moving in the pressing direction. At this time, since the position of the linearly moving member does not change, the EPB load Pc decreases after timing t24. Energization of the electric motor is restarted at timing t25. After timing t27, the load on the electric motor increases as the direct-acting member is pressed against the piston. Therefore, after timing t27, the current value Im gradually increases, as shown in FIG. 6(a). As a result, as shown in FIG. 6(b), the EPB load Pc is applied after timing t27. After timing t27, the sum of the hydraulic load Pb and the EPB load Pc becomes the piston load Pa again. As shown in (a) of FIG. 6, the current value Im reaches the target current value Imt at timing t28, and the energization of the electric motor is temporarily terminated.

FIG. 7 is a schematic diagram showing an electric parking brake device in a state where the piston 101, which is a component in a hydraulic brake device of a comparative example, is assisted by the electric parking brake device, and the piston load in that state. are doing.

FIG. 7 shows a piston 101 that supplies brake fluid to a fluid chamber 102, an output shaft 103 that is rotated by an electric motor, and a linear motion member 104 that is a linear motion member that moves linearly in accordance with the rotation of the output shaft 103. and is illustrated. In FIG. 7, solid line arrows indicating the pressing direction by the piston 101 are displayed. A friction material is attached to the piston 101. The piston 101 presses the friction material against the rotating member by the piston load. That is, a friction material and a rotating member are arranged in this order on the side of the piston 101 in the pressing direction. In FIG. 7, illustration of the friction material and the rotating member is omitted.

Furthermore, in FIG. 7, the EPB load Pc, which is the load generated by the electric parking brake system, is indicated by a solid white arrow. A hydraulic load Pb, which is a load caused by hydraulic pressure, is indicated by a dashed white arrow. The total load of the EPB load Pc and the hydraulic load Pb corresponds to the pressing force with which the piston 101 presses the friction material against the rotating member. The pressing force corresponds to the braking force applied to the wheels.

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

In the period from timing t23 to timing t24 illustrated in FIG. 6, the electric parking brake system of the comparative example is in the state shown in FIG. 7(a).
In FIG. 7, the position of the end of the translation member 104 in the pressing direction in the state shown in FIG. 7A is shown as an initial nut position Xn. In FIG. 7, the position of the end of the piston 101 in the pressing direction in the state shown in FIG. 7A is shown as an initial piston position Xc.

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

When the hydraulic load Pb is further increased from the state shown in FIG. 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 in the pressing direction from the initial piston position Xc. FIG. 7C shows a state in which the end of the piston 101 has moved from the initial piston position Xc.

As shown in FIG. 7(c), when the piston 101 and the direct-acting member 104 are separated by movement of the piston 101, the EPB load Pc becomes "0". In the state shown in FIG. 7(c), the hydraulic load Pb is equal to the piston load.

In the period from timing t24 to timing t26 illustrated in FIG. 6, the electric parking brake system of the comparative example goes through the state shown in FIG. 7(b) and reaches the state shown in FIG. 7(c).
FIG. 7(d) shows a state in which the linear motion member 104 is moved from the initial nut position Xn in the pressing direction from the state shown in FIG. 7(c). The EPB load Pc is generated again due to the contact between the direct-acting member 104 and the piston 101. In the state shown in FIG. 7(d), the magnitude of the hydraulic load Pb is equal to the state shown in FIG. 7(c). In the state shown in FIG. 7(d), the EPB load Pc is added to the hydraulic load Pb, so that the piston load has reached the second load P2, which is larger than the first load P1.

In the period from timing t27 to timing t28 illustrated in FIG. 6, the electric parking brake system of the comparative example is in the state shown in FIG. 7(d).
As described above, in the case of the comparative example, when assisting with the electric parking brake system, there is a period in which the braking force does not increase even if the hydraulic pressure starts to increase, as illustrated in FIG. 7(b). Therefore, there is a period from timing t24 to timing t26 illustrated in FIG. 6 in which the piston load Pa does not increase. In other words, when the position of the linearly moving member is held by the self-locking mechanism and the power supply to the electric motor is stopped as in the comparative example, the assistance by the EPB load Pc is not responsive to fluctuations in fluid pressure. There were times when I couldn't do it well.

Further, as illustrated in FIG. 7(c), there is a period in which the EPB load Pc is temporarily eliminated after the hydraulic pressure starts to increase until the braking force starts to increase. Since the EPB load Pc is reapplied after being eliminated, the manner in which the piston load Pa increases from load P22 to load P24 is linear, as in the period from timing t26 to timing t28 illustrated in FIG. It will no longer be. Since the load increases once from load P22 to load P23 and then increases to load P24, there is a risk that the behavior of vehicle 90 may become unstable. For example, there is a possibility that the pitching motion of the vehicle 90 may increase.

On the other hand, according to the control device 10 of the present embodiment, while the current value Im is equal to or lower than the target current value Imt, the apply process is repeatedly executed until the termination condition is satisfied (S102, S103, and S105). ). Therefore, until the end condition is satisfied, the electric motor 71 is continued to be energized even if the current value Im reaches the target current value Imt. Until the termination condition is satisfied, the electric motor 71 continues to be energized even if the difference Dp is resolved. Until the termination condition is satisfied, the electric motor 71 continues to be energized while the position of the linear motion member 75 is maintained. In this way, the load corresponding to the difference Dp can continue to be applied to the piston 87 without continuing the state in which the electric motor 71 is de-energized during execution of the assisting control. Thereby, when the target braking force BPT is increased during execution of assisting control, the linearly moving member 75 can be moved quickly. The linear member 75 can be moved to follow the piston 87, which moves as the hydraulic load Pb increases. That is, responsiveness to fluctuations in the difference Dp can be ensured.

According to the control device 10, responsiveness to fluctuations in the difference Dp can be ensured. For this reason, a state in which the EPB load Pc is temporarily eliminated, as illustrated in FIG. 7C as a comparative example, is 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 FIG. 6 in the comparative example. This can prevent the behavior of the vehicle 90 from becoming unstable during execution of the assistance control.

When the braking force is held constant during execution of assisting control, it is preferable not to move the linear member 75 due to the voltage application performed in the apply process, that is, to not vary the EPB load Pc. According to the control device 10, even if the linear motion member 75 moves while the braking force is maintained, when the current value Im becomes larger than the target current value Imt, a release process is executed (S104). This can prevent the EPB load Pc from becoming excessive.

(Example of change)
This embodiment can be modified and implemented as follows. This embodiment and the following modified examples can be implemented in combination with each other within a technically consistent range.

- In the above embodiment, an example was shown in which pulses are output at prescribed intervals as the apply process in assist control. Alternatively, the electric motor 71 may be continuously energized by high frequency duty control so that the current value Im becomes the target current value Imt. High frequency duty control is control in which the duty ratio is changed to be smaller than the normal duty ratio, and the frequency of PWM control is increased. For example, if the drive circuit 20 includes a high frequency generator, high frequency duty control can be performed.

- The control device 10 may have a function of learning the time from when an inrush current occurs until it converges. The control device 10 may have a function of learning the magnitude of the inrush current. The control device 10 may adjust the prescribed interval based on the learning result. For example, by using the inrush current learning results, it becomes possible to shorten the interval at which the application process is performed without moving the direct-acting member 75. Thereby, it is possible to improve the accuracy of setting the motor rotation speed Nm to "0" when the current value Im is the target current value Imt.

- In the above embodiment, the case where there is a failure in the booster 81 has been described as an example in which the conditions for starting the assist control are satisfied. The starting conditions are not limited to these. For example, even if a failure occurs in a portion of the hydraulic braking device 80 other than the booster 81, it may be determined that the start condition is satisfied.

In the driving support control, the control that adjusts the traveling speed of the vehicle 90 by the braking force of the hydraulic braking device 80 is an example of control that has a braking request. That is, even when the braking request of driving support control cannot be satisfied, it can be determined that the start condition is satisfied. If driving support control is being performed, ending the driving support control corresponds to cancellation of the braking request. For example, it can be determined that the end condition is satisfied when the vehicle 90 reaches the target point set by the driving support control.

In addition, any control that can intervene in adjusting the hydraulic braking force by setting a target value of the hydraulic braking force can be said to be a braking request. Even when the braking request cannot be satisfied by these controls, it can be determined that the start condition is satisfied. That is, the assistance control in the above embodiment can be applied.

- The control device 10, which is a processing circuit, the processing circuit included in the hydraulic pressure control unit 40, and the processing circuit included in the support control unit 50 may have any of the configurations [a] to [c] below. [a] A circuit that includes one or more processors that execute various processes according to a computer program. The processor includes a processing device. Examples of processing devices are CPUs, DSPs, GPUs, and the like. The processor includes memory. Examples of memory are RAM, ROM, flash memory, and the like. The memory stores program code or instructions configured to cause the processing device to perform operations. Memory or computer-readable media includes any available media that can be accessed by a general purpose or special purpose computer. [b] A circuit that includes one or more hardware circuits that perform various processes. Examples of hardware circuits include ASIC (Application Specific Integrated Circuit), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). [c] A circuit that includes a processor that executes a part of various processes according to a computer program, and a hardware circuit that executes the remaining processes among the various processes.

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

Claims

A rotating member that rotates together with the wheel, a friction material that is pressed against the rotating member, a cylinder that is supplied with brake fluid, and a piston that presses the friction material against the rotating member according to hydraulic pressure in the cylinder. a hydraulic braking device that generates a braking force on the wheel according to the load that the friction material is pressed against the rotating member;
It is composed of 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 linearly moved by the conversion mechanism and is disposed within the cylinder, an electric parking braking device in which the linearly moving member presses the friction material against the rotating member via the piston, thereby generating a load that causes the friction material to be pressed against the rotating member; Applied to the vehicle capable of generating a braking force by the hydraulic braking device in response to a braking request,
A brake control device that controls the electric parking brake device,
a motor control unit that outputs a drive signal for driving the electric motor;
When the target braking force corresponding to the braking request cannot be satisfied by the braking force applied by the hydraulic braking device during braking of the vehicle, the target braking force and the braking force applied by the hydraulic braking device and an assistance control unit that executes assistance control in which the linear motion member assists the friction material pressed against the rotating member so that the electric parking brake device generates a load corresponding to the difference between
In the assisting control, the assisting control unit performs an apply process of applying a voltage to the electric motor to drive the electric motor in a direction that increases the load with which the direct-acting member is pressed against the piston; A brake control device that performs the apply processing even after the actual braking force actually acting on the vehicle reaches the target braking force.
A current value that causes a load corresponding to the difference to be generated by driving the electric motor is set as a target current value,
When performing the apply process in the support control, the assist control unit performs the apply process at regular intervals so that a current value flowing through the electric motor becomes the target current value. The brake control device according to claim 1, wherein the motor is repeatedly energized and de-energized.
The assistance control section includes:
If the current value flowing through the electric motor is less than or equal to the target current value, while performing the apply process,
If the current value flowing through the electric motor becomes larger than the target current value as a result of performing the apply process, instead of performing the apply process at each specified interval, the direct-acting member may The brake control device according to claim 2, wherein a release process is performed to apply a voltage to the electric motor to drive the electric motor in a direction that reduces the load pressed against the piston.