Electric braking device

Abstract

An electric braking device comprises a piston (6D) driven by a rotary linear motion device (8), which in turn is driven by an electric motor (7A). The piston (6D) is configured to press brake pads (6C) against a disc rotor (4) and to hold the brake pads (6C) in a pressure position by stopping the electric motor (7A). A parking brake control device (24) is configured to determine, when a request (application command) to hold the brake pads (6C) is received, a judgment point for assessing whether to stop the electric motor (7A) based on a change trend in a current value of the electric motor (7A). When the judgment point is reached, the parking brake control device (24) assesses whether or not to stop the electric motor (7A).

Description

TECHNICAL AREA

[0001] The present invention relates to an electric braking device configured to exert a braking force on a vehicle, for example an automobile. STATE OF THE ART

[0002] An electric braking device, arranged in a vehicle, for example an automobile, is known which is configured to apply a braking force when the vehicle is stopped or parked, for example, based on the drive (rotation) of an electric motor (Patent Reference 1). Patent Reference 1 describes a braking device configured to detect, when an electric motor is driven in an application direction (brake application direction), that the application is complete when a current value is equal to or greater than a threshold value for a predetermined time period, and stops the electric motor. LITERATURE LIST PATENT LITERATURE

[0003] PTL 1: JP 2016-124403 A SUMMARY OF THE INVENTIONAL ENGINEERING TASK

[0004] In the related prior art, it is possible that the variation in the current value at the time of application completion (hereinafter also referred to as "arrival current") cannot be suppressed while simultaneously maintaining robustness against false detection of application completion due to current fluctuations. That is, it is difficult to suppress both false detection of application completion and variation in the current value at the time of application completion despite current fluctuations during the application. SOLUTION TO THE TASK

[0005] An objective of the present invention is to provide an electric braking device capable of counteracting fluctuations in an arrival current (i.e., thrust). to suppress while ensuring robustness against power fluctuations.

[0006] According to one embodiment of the present invention, an electric braking device is provided, comprising: an electric braking device unit in which a piston, driven by a rotation-linear motion device which is driven by an electric motor, is configured to press a braking element against a braked element and to hold the braking element in a pressure position by stopping the electric motor; and a control unit configured to control the electric motor, wherein the control unit is configured to determine, when a request is made to hold the braking element, an evaluation point for assessing whether the electric motor should be stopped, based on a change trend of a current value of the electric motor, and when the evaluation point is reached, it assesses whether the electric motor should be stopped.

[0007] Furthermore, according to one embodiment of the present invention, an electric braking device is provided, comprising: an electric braking device in which a piston, driven by a rotation-linear motion device, which is driven by an electric motor, is configured to press a braking element against a braked element and to hold the braking element in a pressure position by stopping the electric motor;and a control unit configured to control the electric motor, wherein the control unit is configured to determine, when a request is made to hold the brake element, an evaluation point in time for assessing whether a rotational position of the electric motor has reached a position where holding the brake element is complete, based on a change trend of a current value of the electric motor, and that when the evaluation point is reached, it assesses whether holding the brake element is complete.

[0008] According to the electric braking device of an embodiment of the present invention, it is possible to suppress the fluctuation of the arrival current (i.e., the thrust) while simultaneously ensuring robustness against the current fluctuation. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a conceptual representation of a vehicle with an electric braking device mounted thereon according to a first embodiment of the present invention. Fig. Figure 2 is an enlarged vertical cross-sectional view of a disc brake with an electric parking brake function, located on one side of the rear wheel. Fig. 1 is arranged. Fig. Figure 3 is a block diagram illustrating a parking brake control device. Fig. 1 together with a rear disc brake and other parts. Fig. Figure 4 is a flowchart illustrating the control processing of the parking brake control device in the first embodiment. Fig. Figure 5 is a characteristic curve diagram illustrating an example of a current change over time in the first embodiment. Fig. Figure 6 is a flowchart illustrating the control processing of a parking brake control device in a second embodiment of the present invention. Fig. Figure 7 is a characteristic curve diagram illustrating an example of a current change over time in the second embodiment. Fig. Figure 8 is a flowchart illustrating the control processing of a parking brake control device in a third embodiment of the present invention. Fig. Figure 9 is a characteristic curve diagram illustrating an example of a current change and a current difference value change over time in the third embodiment. Fig. Figure 10 is a flowchart illustrating the control processing of a parking brake control device in a fourth embodiment of the present invention. Fig. Figure 11 is a characteristic curve diagram illustrating an example of a relationship between an estimated motor rotational speed and a current in the fourth embodiment. DESCRIPTION OF THE EXECUTION FORMS

[0009] With reference to the accompanying drawings, an example of a case in which an electric braking device according to embodiments of the present invention is mounted on a four-wheeled automobile is now described. In the Fig. 4, Fig. 6, Fig. 8 and Fig. In the 10 flowcharts shown, each step is marked by the use of the notation “S” (for example, step 1 = “S1”).

[0010] Fig. 1 to Fig. Figure 5 are diagrams illustrating a first embodiment of the present invention. Fig. 1. A total of four wheels, including, for example, left and right front wheels 2 (FL, FR) and left and right rear wheels 3 (RL, RR), are arranged on the underside (road-facing side) of a vehicle body 1, which forms the vehicle's body. The wheels (the front wheels 2 and the rear wheels 3, respectively) together with the vehicle body 1 constitute the vehicle. The vehicle is equipped with a braking system for applying a braking force. The vehicle's braking system will now be described.

[0011] A disc rotor 4 is arranged on each of the front wheels 2 and the rear wheels 3 as a braked element (rotating element), configured to rotate with each wheel (each front wheel 2 and each rear wheel 3). A braking force is applied to the disc rotor 4 for each front wheel 2 by a front wheel disc brake 5, which is a hydraulic disc brake. A braking force is applied to the disc rotor 4 for each rear wheel 3 by a rear wheel disc brake 6, which is a hydraulic disc brake with an electric parking brake function.

[0012] The pair (set) of rear wheel disc brakes 6, arranged according to the left and right rear wheel 3, is a hydraulic pressure braking device (hydraulic brake) configured to apply a braking force by pressing the brake pads 6C (see Fig. 2) presses against the disc rotor 4 by hydraulic pressure. As in Fig. As shown in Figure 2, the rear wheel disc brakes 6, for example, comprise a mounting element 6A, referred to as the carrier, a brake caliper 6B, which serves as the wheel cylinder, a pair of brake pads 6C, which serve as the braking element (friction element, friction lining), and a piston 6D, which serves as the pressure element. In this case, the brake caliper 6B and the piston 6D form a cylinder assembly, that is, a cylinder assembly configured such that it moves by hydraulic pressure and presses the brake pads 6C against the disc rotor 4.

[0013] The mounting element 6A is attached to a non-rotating part of the vehicle and is shaped to span an outer circumferential side of the disc rotor 4. The brake caliper 6B is positioned on the mounting element 6A to allow the disc rotor 4 to move axially. The brake caliper 6B comprises a cylinder main body section 6B1, a claw section 6B2, and a bridge section 6B3 that connects the cylinder main body section 6B1 and the claw section 6B2. A cylinder (cylinder bore) 6B4 is arranged in the cylinder body 6B1, and the piston 6D is inserted into the cylinder 6B4. The brake pads 6C are movably mounted on the mounting element 6A and positioned to be in contact with the disc rotor 4. The piston 6D is configured to press the brake pads 6C against the disc rotor 4.

[0014] The brake caliper 6B drives the brake pads 6C through the piston 6D by supplying (adding) hydraulic pressure (brake hydraulic pressure) to the cylinder 6B4, based, for example, on the actuation of a brake pedal 9. At this point, the brake pads 6C on both sides of the disc rotor 4 are pressed against the jaw section 6B2 of the brake caliper 6B and the piston 6D. As a result, a braking force is exerted on the rear wheel 3, which rotates together with the disc rotor 4.

[0015] The rear disc brakes 6 further comprise an electric actuator 7 and a rotation-linear motion device 8. The electric actuator 7 includes, for example, an electric motor 7A, which serves as the electric motor, and a speed reducer (not shown) configured to slow the rotation of the electric motor 7A. The electric motor 7A serves as the drive source for driving the piston 6D. The rotation-linear motion device 8 forms a holding device (pressure element holding device) configured to hold the pressure force of the brake pads 6C.

[0016] In this case, the rotary-linear motion device 8 comprises a rotary-linear motion element 8A configured to convert the rotation of the electric motor 7A into an axial displacement (linear displacement) of the piston 6D and to drive the piston 6D. The rotary-linear motion element 8A is, for example, composed of a screw element 8A1, which consists of a rod-shaped body with a male screw formed on it, and a linear motion element 8A2, which serves as the drive element and has a female screw bore formed on an inner circumferential side. The rotary-linear motion device 8 is configured to convert the rotation of the electric motor 7A into an axial displacement of the piston 6D and to hold the piston 6D driven by the electric motor 7A.That is, the rotary-linear motion device 8 exerts a thrust force on the piston 6D through the electric motor 7A, drives the brake pads 6C through the piston 6D to press the brake pads 6C against the disc rotor 4, and maintains the thrust force of the piston 6D.

[0017] The rear disc brakes 6 form an electric braking device by incorporating the rotary-linear motion device 8 and the electric motor 7A. The electric braking device is configured such that it converts the rotational force of the electric motor 7A, via the reduction gear and the rotary-linear motion device 8, into a thrust force and applies or releases the braking force by applying the thrust force to the piston 6D, which presses against the brake pads 6C. That is, in the electric braking device, the piston 6D, driven by the rotary-linear motion device 8, which in turn is driven by the electric motor 7A, presses the brake pads 6C against the disc rotor 4 and holds the brake pads 6C in the applied position by stopping the electric motor 7A. The electric braking device, together with the parking brake control device 24 described later, forms the electric braking system.

[0018] The rear disc brakes 6 are configured such that they drive the piston 6D by means of the brake hydraulic pressure generated by actuation of the brake pedal 9, thereby exerting a braking force on the wheels (rear wheels 3) and thus on the vehicle by pressing the disc rotor 4 with the brake pads 6C. Furthermore, as described later, the rear disc brakes 6 exert a braking force (parking brake or auxiliary brake, as required) on the vehicle by causing the electric motor 7A to drive the piston 6D via the rotary-linear motion device 8 in response to an operating request, for example, based on a signal from a parking brake switch 23.

[0019] This means that the rear disc brakes 6 drive the electric motor 7A and press and hold the brake pads 6C against the disc rotor 4 by driving the piston 6D through the rotationally linear motion element 8A. In this case, the rear disc brakes 6 can maintain the vehicle's braking by driving the piston 6D through the electric motor 7A in response to a parking brake request signal (request signal), which is a request to apply the parking brake. Additionally, the rear disc brakes 6 can decelerate the vehicle by supplying hydraulic pressure from a hydraulic pressure source (master cylinder 12, which will be described later, and optionally a hydraulic pressure supply device 16) in response to actuation of the brake pedal 9.

[0020] As described above, the rear wheel disc brakes 6 have a rotation-linear motion device 8 which presses the brake pads 6C against the disc rotor 4 by means of the electric motor 7A and maintains the contact force of the brake pads 6C, and can press the brake pads 6C against the disc rotor 4 by means of hydraulic pressure which is supplied separately to the brake pads 6C by means of the electric motor 7A.

[0021] Meanwhile, the pair (set) of front-wheel side disc brakes 5, arranged according to the left and right front wheels 2, are configured essentially in the same way as the rear-wheel disc brakes 6, with the exception of the device relating to the actuation of the parking brake. That is to say, as in Fig. As shown in Figure 1, the front wheel disc brakes 5 comprise, for example, a mounting element (not shown), a brake caliper 5A, brake pads (not shown), and a piston 5B, but not, for example, the electric actuator 7 (electric motor 7A) and the device for the rotational linear movement 8 for applying and releasing the parking brake. However, the front wheel disc brakes 5 are the same as the rear wheel disc brakes 6 in that the front wheel disc brakes 5 are configured to drive the piston 5B by hydraulic pressure, generated, for example, by actuation of the brake pedal 9, in order to exert a braking force on the wheels (front wheels 2) and thus on the vehicle.That is, the front wheel disc brakes 5 are a hydraulic braking device (hydraulic brake) configured to apply a braking force by pressing the brake pads against the disc rotor 4 by means of hydraulic pressure.

[0022] The front disc brakes 5, like the rear disc brakes 6, can be disc brakes with an electric parking brake function. Furthermore, in the embodiments, the hydraulic disc brakes 6, including the electric motor 7A, are used as an electric braking device (electric parking brake). However, the electric braking device is not limited to this; for example, electric disc brakes with an electric caliper, electric drum brakes configured to apply a braking force by pressing a shoe against a drum via an electric motor, disc brakes with an electric drum parking brake, and a cable-operated electric parking brake configured to operate by applying a parking brake through the pulling of a cable by an electric motor can also be used.This means that various types of electric braking devices can be used as electric braking devices, as long as the electric braking device can press (drive) a friction element (lining, shoe) against a rotating element (rotor, drum) based on the drive of an electric motor (electric actuator) and can hold and release the pressure force.

[0023] The brake pedal 9 is located on a front side wall of the vehicle body 1. The driver operates the brake pedal 9 by pressing on it during braking. Based on the actuation of the brake pedal 9, a braking force is applied to or released from each of the disc brakes 5 and 6 as the regular brake (service brake). The brake pedal 9 comprises a brake light switch, a pedal switch (brake switch), and a brake actuation detection sensor (brake sensor) 10, for example, a pedal travel sensor.

[0024] The brake actuation detection sensor 10 is configured to detect the presence or absence of actuation of the brake pedal 9 and the amount of this actuation, and to output a corresponding detection signal to an ESC control unit 17. The detection signal from the brake actuation detection sensor 10 is transmitted via a vehicle data bus 20 or a communication line (not shown) that connects, for example, the ESC control unit 17 and the parking brake control unit 24 (is output to the parking brake control unit 24).

[0025] The actuation of the brake pedal 9 is transmitted via an amplifier 11 to a master cylinder 12, which acts as a hydraulic source (hydraulic pressure source). The amplifier 11 is designed as a vacuum amplifier (atmospheric pressure amplifier) ​​or as an electric amplifier and is arranged between the brake pedal 9 and the master cylinder 12. The amplifier 11 amplifies the pedal force and transmits the amplified pedal force to the master cylinder 12 when the brake pedal 9 is actuated.

[0026] At this point, the master cylinder 12 generates hydraulic pressure using brake fluid supplied (refilled) from a main reservoir 13. The main reservoir 13 serves as the operating fluid reservoir in which the brake fluid is stored. The device for generating the hydraulic pressure by the brake pedal 9 is not limited to the configuration described above and can be a device configured to generate this hydraulic pressure in response to the actuation of the brake pedal 9, for example, a brake-by-wire device.

[0027] The hydraulic pressure generated in the master cylinder 12 is conveyed, for example, via a pair of cylinder-side hydraulic pressure lines 14A and 14B to the hydraulic pressure supply unit 16 (hereinafter referred to as "ESC 16"). The ESC 16 is located between the disc brakes 5 and 6 and the master cylinder 12. The ESC 16 is configured to deliver the hydraulic pressure output by the master cylinder 12 via the cylinder-side hydraulic lines 14A and 14B to each of the disc brakes 5 and 6 via the brake-side line sections 15A, 15B, 15C, and 15D. This means that the regulator 16 supplies each of the disc brakes 5 and 6 (brake calipers 5A and 6B) arranged on each wheel (each front wheel 2 and each rear wheel 3) with hydraulic pressure (brake hydraulic pressure) according to the actuation of the brake pedal 9. This allows the braking force to be applied to each wheel (each front wheel 2 and each rear wheel 3) independently of each other.

[0028] The ESC 16 is a hydraulic pressure control device that regulates the hydraulic pressure of the hydraulic brakes (front disc brakes 5 and rear disc brakes 6). For this purpose, the ESC 16 comprises a plurality of control valves, a hydraulic pump configured to pressurize the brakes, an electric motor configured to drive the hydraulic pump, and a hydraulic pressure control reservoir configured to temporarily store excess brake fluid (none of these parts are shown). Each control valve and the electric motor of the ESC 16 are connected to the ESC control unit 17, and the ESC 16 includes the ESC control unit 17.

[0029] The opening and closing of each control valve of the ESC 16 and the drive of the electric motor are controlled by the ESC control unit 17. That is, the ESC control unit 17 is an ESC control unit (ESC ECU) configured to control the ESC 16. The ESC control unit 17 contains a microcomputer. The microcomputer is configured to electrically drive and control the controller 16 (the solenoid coil of each control valve and the controller's electric motor). In this case, for example, the ESC control unit 17 contains a computing circuit configured to control the hydraulic pressure supply of the ESC 16 and to detect a malfunction of the ESC 16, as well as a drive circuit configured to drive the electric motor and each control valve (neither of these parts are shown).

[0030] The ESC control device 17 individually controls and regulates each control valve of the ESC 16 and the electric motor for the hydraulic pump (solenoid coil). As a result, the ESC control device 17 individually controls the reduction, holding, increase, or pressurization of the brake hydraulic pressure (wheel cylinder hydraulic pressure) supplied to each of the disc brakes 5 and 6 via the brake-side pipe sections 15A to 15D for each of the disc brakes 5 and 6.

[0031] In this case, the ESC control unit 17 can perform the following controls (1) to (8), for example by controlling the operation of the ESC 16. (1) Brake force distribution control for the appropriate distribution of the braking force to each of the wheels 2 and 3 in accordance with a ground contact load, for example when the vehicle brakes (2) Anti-lock braking system (hydraulic ABS control) for automatically adjusting the braking force of each of the wheels 2 and 3 during braking to prevent locking (slipping) of each of the wheels 2 and 3. (3) Vehicle stabilization control for suppressing understeer and oversteer in order to stabilize the behavior of the vehicle by detecting the lateral slip of each of the wheels 2 and 3 during driving and automatically controlling the braking force applied to each of the wheels 2 and 3 appropriately, irrespective of the degree of application of the brake pedal 9. (4) Hill start assist control to assist with starting by maintaining the braking state on an incline (especially uphill) (5) Traction control that prevents each of the wheels 2 and 3 from spinning when starting off, for example (6) Control of the following vehicle to maintain a certain distance from the vehicle in front (7) Control of lane avoidance by keeping in a lane (8) Obstacle avoidance control (automatic braking control and collision damage mitigation braking control) to avoid a collision with an obstacle in the direction of travel of the vehicle

[0032] During normal operation, based on brake application by the driver, the ESC 16 delivers the hydraulic pressure generated by the master cylinder 12 directly to the disc brakes 5 and 6 (the brake calipers 5A and 6B). Meanwhile, for example when the anti-lock brake control is activated, the pressure boost control valve closes to maintain the hydraulic pressure of the disc brakes 5 and 6, and when the hydraulic pressure of the disc brakes 5 and 6 is reduced, the pressure reduction control valve opens and the hydraulic pressure of the disc brakes 5 and 6 is released to escape to the hydraulic pressure control reservoir.

[0033] To perform stabilization control (gap prevention control) during driving, the hydraulic pump is operated by the electric motor when the hydraulic pressure supplied to the disc brakes 5 and 6 is increased or pressurized, with the supply control valve in a closed state, and the brake fluid delivered by the hydraulic pump is supplied to the disc brakes 5 and 6. At this time, brake fluid in the main reservoir 13 is supplied to the suction side of the hydraulic pump from the side of the master cylinder 12.

[0034] The ESC control unit 17 is supplied with electrical energy via a power supply line 19 from a battery 18 (or a generator driven by the engine), which is a power source of the vehicle. As shown in Fig. As shown in Figure 1, the ESC control unit 17 is connected to the vehicle data bus 20. It is also possible to use a known ABS unit instead of the ESC 16. Furthermore, it is also possible to connect the master cylinder 12 and the brake-side line sections 15A to 15D directly without the ESC 16 (i.e., to omit the ESC 16).

[0035] The vehicle data bus 20 forms a Controller Area Network (CAN) which is mounted as a serial communication unit on the vehicle body 1. A large number of electronic devices mounted on the vehicle (for example, various types of control units, including the ESC control unit 17 and the parking brake control unit 24) perform multiplex communication with each other within the vehicle via the vehicle data bus 20.In this case, the vehicle information transmitted to the vehicle data bus 20 includes, for example, information (vehicle information) based on detection signals (output signals) from, for example, the brake actuation detection sensor 10, an ignition switch, a seat belt sensor, a door lock sensor, a door opening sensor, a seat occupancy sensor, a vehicle speed sensor, a steering angle sensor, an accelerator pedal sensor (accelerator pedal actuation sensor), a throttle position sensor, an engine rotation sensor, a stereo camera, a millimeter wave radar, an inclination sensor (gradient sensor), a transmission sensor (transmission data), an acceleration sensor (G-sensor), a wheel speed sensor, and an inclination sensor configured to detect movement in a vehicle tilt direction.Other examples of vehicle information transmitted to the vehicle data bus 20 include acquisition signals (information) from a W / C pressure sensor 21 configured to acquire wheel cylinder pressure and an M / C pressure sensor 22 configured to acquire master cylinder pressure.

[0036] Next, the parking brake switch 23 and the parking brake control device 24 will be described.

[0037] In the vehicle body 1, a parking brake switch (PKB-SW) ​​23 is located near the driver's seat (not shown). This switch serves as the control unit for the electric parking brake. The parking brake switch 23 acts as an operating unit that is operated by the driver. In response to an operating command from the driver, the parking brake switch 23 sends a signal (actuation request signal) to the parking brake control unit 24. This signal corresponds to an actuation request for the parking brake (either an application request to hold the brake or a release request).This means that the parking brake switch 23 sends an operating request signal (apply request signal as a holding request signal or release request signal) to the parking brake control device 24 to cause the piston 6D, and thus the brake pads 6C, to perform an application (holding) or release operation based on the drive (rotation) of the electric motor 7A. The parking brake control device 24 is a parking brake control unit (parking brake ECU).

[0038] When the parking brake switch 23 is actuated by the driver towards the brake side (actuation side), that is, when an actuation request (brake holding request) to apply a braking force to the vehicle is received, an actuation request signal (parking brake request signal or actuation command) is issued by the parking brake switch 23. In this case, electrical energy is supplied to the electric motor 7A of the rear wheel disc brakes 6 via the parking brake control device 24 to rotate it towards the brake side. At this point, the rotary linear motion device 8 drives (pushes) the piston 6D based on the rotation of the electric motor 7A towards the disc rotor side 4 and holds the driven piston 6D. As a result, the rear wheel disc brakes 6 are in a state in which a braking force is applied as a parking brake (or auxiliary brake), that is, they are in an applied (brake holding) state.

[0039] When the parking brake switch 23 is actuated by the driver to the brake release side (release side), that is, when a release request (brake release request) to release the vehicle's braking force is received, a release request signal (parking brake release request signal or release command) is issued by the parking brake switch 23. In this case, electrical energy is supplied to the electric motor 7A of the rear wheel disc brakes 6 via the parking brake control unit 24 to rotate it in the direction opposite to the brake side. At this point, the rotary linear motion device 8 releases the piston 6D from its position by rotating the electric motor 7A (releasing the pressure force through the piston 6D). As a result, the rear wheel disc brakes 6 are in a state where the braking force is released as a parking brake (or auxiliary brake), that is, they are in a released state (brake release state).

[0040] The parking brake can be automatically applied based on an automatic application request issued by the parking brake control device 24 based on an application assessment logic, for example, when the vehicle has been stopped for a predetermined period of time (e.g., when the vehicle is assessed as stopped because a condition in which the detection speed of the vehicle speed sensor is less than 5 km / h has persisted for a predetermined period of time due to deceleration while driving), when the engine is stopped, when the gearshift lever is moved into a 'P' (Park) position, when the door is opened, and when the seat belt is unfastened.Furthermore, the parking brake can be automatically released (automatically released) based on an automatic release request issued by the parking brake control device 24, based on parking brake release logic, when the vehicle is moving (for example, when the vehicle is judged to be moving because a state in which the vehicle speed sensor's detection speed is 6 km / h or more has been maintained for a predetermined period due to acceleration from a stationary state), when the accelerator pedal is pressed, when the clutch pedal is pressed, and when the gearshift lever is moved to a position other than "P" or "N". Automatic application and release can be configured as a switch fault assistance function that automatically applies or releases the braking force when the parking brake switch 23 is faulty.

[0041] Furthermore, when the parking brake switch 23 is activated while driving, more precisely when a dynamic parking brake is requested (dynamic activation), for example, in the event of urgent use of the parking brake as an auxiliary brake while driving, the braking force can be applied and released by the ESC 16 in accordance with the activation of the parking brake switch 23. In this case, for example, the parking brake control unit 24 sends a braking command corresponding to the activation of the parking brake switch 23 (e.g., a hydraulic pressure request signal or a target hydraulic pressure signal) to the ESC control unit 17 via the vehicle data bus 20 or the communication line.As a result, the ESC 16 applies a braking force based on the hydraulic pressure while the parking brake switch 23 on the brake side is actuated (while operation continues on the brake side), based on the braking command from the parking brake control unit 24. When the process is complete, the braking force based on the hydraulic pressure is released.

[0042] If the parking brake switch 23 is actuated while driving, the braking force can be applied and released, for example, by the drive of the electric motor 7A of the rear wheel disc brakes 6, instead of being applied and released by the ESC 16. In this case, for example, the parking brake control unit 24 applies the braking force while the parking brake switch 23 is actuated towards the brake side (while operation continues towards the brake side), and when the operation is complete, the parking brake control unit 24 releases the braking force. At this point, the parking brake control unit 24 can be configured to automatically apply and release the braking force (perform ABS control) depending on the state of the wheels (each rear wheel 3), that is, whether the wheels are locked (slipping) or not. The control device

[0043] The parking brake control device 24 (electric brake control device) forms an electric brake device together with the electric motor 7A and the rotary-linear motion device 8 of the rear wheel disc brakes 6. The parking brake control device 24 is configured to control the drive of the electric motor 7A. For this purpose, the parking brake control device 24 includes, as shown in Fig. Figure 3 shows an arithmetic circuit (CPU) 25, which is built, for example, from a microcomputer, and a memory 26. The parking brake control unit 24 is supplied with electrical energy from the battery 18 (or a generator driven by the engine) via the power supply line 19.

[0044] The parking brake control unit 24 controls the drive of the electric motors 7A and 7A of the rear wheel disc brakes 6 and 6 and generates a braking force (parking brake or auxiliary brake) when the vehicle is parked or stopped (and, if necessary, while driving). That is, the parking brake control unit 24 actuates (activates and releases) the disc brakes 6 and 6 as a parking brake (auxiliary brake as needed) by controlling the left and right electric motors 7A and 7A. For this purpose, an input side of the parking brake control unit 24 is connected to the parking brake switch 23 and an output side of the parking brake control unit 24 is connected to the electric motors 7A and 7A of the disc brakes 6 and 6.The parking brake control device 24 includes the computing circuit 25 to detect, for example, an actuation by the driver (actuation of the parking brake switch 23), to decide whether the electric motors 7A and 7A should be driven or not, and to decide whether the electric motors 7A and 7A should be stopped or not, as well as motor drive circuits 28 and 28 for controlling the electric motors 7A and 7A.

[0045] The parking brake control device 24 drives the left and right electric motors 7A and 7A based on an operating request (apply or release request) generated by the driver by actuating the parking brake switch 23, an operating request based on the parking brake's apply / release evaluation logic, or an operating request based on the ABS control, and engages (holds) or releases the left and right disc brakes 6 and 6. At this time, the piston 6D and the brake pads 6C in the rear wheel disc brakes 6 are held or released by the rotary linear motion device 8 based on the drive of each electric motor 7A.In this way, the parking brake control device 24 drives and controls the electric motor 7A to drive the piston 6D (and thus the brake pads 6C) in response to the operating request signal for a holding operation (applying) or a releasing operation (releasing) of the piston 6D (and thus the brake pads 6C).

[0046] As in Fig. As shown in Figure 3, the computing circuit 25 of the parking brake control unit 24 is connected, in addition to the memory 26 which serves as a storage unit, to, for example, the parking brake switch 23, the vehicle data bus 20, a voltage sensor unit 27, the motor control circuits 28, and current sensor units 29. Various types of vehicle state variables required for controlling (actuating) the parking brake, i.e., various types of vehicle information, can be obtained from the vehicle data bus 20. Furthermore, the parking brake control unit 24 can output information and commands to various types of control units, including the ESC control unit 17, via the vehicle data bus 20 or the communication line.

[0047] The vehicle information acquired from the vehicle data bus 20 can also be acquired by directly connecting a sensor configured to acquire the information to the parking brake control unit 24 (the arithmetic circuit 25 of the parking brake control unit 24). Furthermore, the arithmetic circuit 25 of the parking brake control unit 24 can be configured such that an actuation request based on the aforementioned assessment logic or the ABS control is input from another control unit (for example, the ESC control unit 17) connected to the vehicle data bus 20. In this case, the application / release assessment based on the aforementioned assessment logic and the ABS control of the parking brake can be performed by another control unit, for example, the ESC control unit 17, instead of the parking brake control unit 24.This means that it is possible to integrate the control content of the parking brake control unit 24 into the ESC control unit 17.

[0048] The parking brake control device 24 includes the memory 26, which serves as a storage unit and comprises, for example, flash memory, ROM, RAM, or EEPROM. The memory 26 is configured to store the logic mentioned above for assessing the application / release of the parking brake and the ABS control program. Furthermore, the memory 26 stores, for example, a processing program for executing the operation described in Fig. 4. Processing sequence shown and described later, that is, a processing program used for control processing when applying the electric parking brake.

[0049] In these embodiments, the parking brake control device 24 is separate from the ESC control device 17, but the parking brake control device 24 and the ESC control device 17 can be configured integrally (that is, integrated as a single brake control device). Furthermore, the parking brake control device 24 controls two rear disc brakes 6 and 6, left and right, but the parking brake control device 24 can be arranged for each of the left and right rear disc brakes 6 and 6. In this case, each parking brake control device 24 can be integrally formed with the rear disc brake 6.

[0050] As in Fig. As shown in Figure 3, the parking brake control device 24 comprises, for example, the voltage sensor unit 27, which is configured to detect the voltage from the power supply line 19; the left and right motor drive circuit 28, which is configured to drive the left and right electric motors 7A and 7A, respectively; and the left and right current sensor unit 29, which is configured to detect the motor current of the left and right electric motors 7A and 7A, respectively. The voltage sensor unit 27, the motor drive circuits 28, and the current sensor units 29 are each connected to the arithmetic circuit 25.Consequently, in the arithmetic circuit 25 of the parking brake control device 24, when the parking brake is applied or released, for example, the decision (decision to end the application and decision to end the release) to stop the drive of electric motor 7A can be made based on (a change in) the current value of electric motor 7A, which is detected by the current sensor units 29. In the example shown, the voltage sensor unit 27 is configured to detect (measure) the supply voltage, but the voltage sensor unit can be configured, for example, to measure the voltage between the terminals of electric motors 7A and 7A independently for the left and right sides.

[0051] Incidentally, if, when the parking brake is applied, the electric motor's current (motor current), which is proportional to the thrust force, continuously exceeds a threshold value for the completion of the application, which is preset for a predetermined period (for example, 30 ms or 3 control cycles), the application can be considered complete and the electric motor 7A can be stopped. However, the current value increases during a predetermined period from when the threshold value for the completion of the application is exceeded until the application is deemed complete (the electric motor 7A is stopped). This increasing current value varies depending on the slope of the motor current.Consequently, the current value (arriving current) changes at the time of application termination, that is, the current value (arriving current) immediately before the electric motor 7A actually stops, also depending on the slope of the motor current at the time of application, and the thrust can vary. If it is possible to reduce the fluctuation of the thrust during full application, the generation of excessive thrust can be suppressed, and the brake calipers 6B of the rear disc brakes 6 and 6 can be made smaller and lighter. For this reason, for example, if the application is deemed complete and the electric motor 7A is stopped at the same time as the current value exceeds the threshold for the completion of the application, the variation in thrust can be suppressed.However, if the current value fluctuates, for example due to noise, and temporarily exceeds the threshold for the application to complete, there is a possibility that the application will be incorrectly assessed as complete.

[0052] Therefore, the following configuration is adopted in the embodiments so that fluctuations in thrust can be suppressed while simultaneously ensuring robustness against an erroneous assessment of application completion when the current value has fluctuated. That is, in the first embodiment, the time required for the motor current value to reach the application completion threshold is estimated from the changes in the current (motor current) of the electric motor 7A over time, and the assessment that the application is complete is only permitted after this time has elapsed. This ensures robustness against current fluctuations, and the fluctuation of the arrival current (thrust) is suppressed by the assessment that the application is complete during a control cycle that exceeds the current threshold.

[0053] This means that the parking brake control device 24 is a control unit configured to control the electric motor 7A. The parking brake control device 24 determines an evaluation point (time) to assess, upon a request to hold the brake pads 6C (application command), whether the electric motor 7A should be stopped or not (holding of the brake pads 6C is complete). In this case, the parking brake control device 24 determines (calculates) the evaluation point for assessing whether the electric motor 7A should be stopped or not, based on a change trend (quantity of change or slope) of the current value (motor current I) of the electric motor 7A. When the determined evaluation point is reached, the parking brake control device 24 assesses whether the electric motor 7A should be stopped or not.

[0054] This means that the parking brake control device 24 determines (calculates) the stopping time of the electric motor 7A based on the change trend of the current value of the electric motor 7A while the electric motor 7A is being driven in the application direction based on an application command. When the determined time is reached, the parking brake control device 24 judges that the electric motor 7A should be stopped and stops the electric motor 7A. In this case, the parking brake control device 24 judges that the electric motor 7A should be stopped when the current value of the electric motor 7A is equal to or greater than a predetermined value (current threshold IF for application completion).Furthermore, the parking brake control device 24 determines the assessment point for evaluating whether or not the electric motor 7A should be stopped, based on the change trend of the current value of the electric motor 7A, if there has been an increase in the current value after a predetermined time period (inrush current mask time) has elapsed since the electric motor 7A was driven. The control of the application drive of the electric motor 7A by the parking brake control device 24, that is, the one in . Fig. The control processing shown in section 4 will be described in detail later.

[0055] The four-wheeled automobile braking system according to the embodiments has the configuration described above, and the operation of this braking system will now be described next.

[0056] When the driver of the vehicle presses and depresses the brake pedal 9, the force applied is transmitted via the brake booster 11 to the master cylinder 12, and hydraulic brake pressure is generated in the master cylinder 12. The hydraulic brake pressure generated in the master cylinder 12 is supplied via the cylinder-side hydraulic pressure lines 14A and 14B, the ESC 16, and the brake-side line sections 15A, 15B, 15C, and 15D to each of the disc brakes 5 and 6 to exert a braking force on each of the left and right front wheels 2 and each of the left and right rear wheels 3.

[0057] In this case, in each of the disc brakes 5 and 6, the pistons 5B and 6D slide towards the brake pads 6C when the hydraulic brake pressure in the brake calipers 5A and 6B increases, and the brake pads 6C are pressed against the disc rotors 4 and 4. As a result, a braking force based on the hydraulic brake pressure is applied. When the brake pedal is released, the supply of hydraulic brake pressure to the brake calipers 5A and 6B stops, causing the pistons 5B and 6D to move away from (retract from) the disc rotors 4 and 4. Consequently, the brake pads 6C separate from the disc rotors 4 and 4, and the vehicle returns to a non-braking state.

[0058] When the vehicle driver activates the parking brake switch 23 to the brake side (actuation side), the electric motor 7A of the left and right rear disc brakes 6 is energized by the parking brake control unit 24, and the electric motor 7A rotates and is driven. In the rear disc brakes 6, the rotary motion of the electric motor 7A is converted into a linear motion by the rotary-linear motion device 8, and the piston 6D is driven by the rotary-linear motion element 8A. As a result, the disc rotor 4 is pressed against the brake pads 6C. At this point, the rotary-linear motion device 8 (linear motion element 8A2) maintains a braking state by means of a frictional force (holding force), which is generated, for example, by screw engagement. Consequently, the rear disc brakes 6 are applied as a parking brake.This means that even after the power supply to the electric motor 7A has been stopped, the piston 6D is held in the braking position by the rotary linear motion device 8.

[0059] When the driver moves the parking brake switch 23 to the release side, current is supplied from the parking brake control device 24 to the electric motor 7A, causing the motor to rotate in reverse. As a result of this current supply, the electric motor 7A rotates in the opposite direction to that which occurs when the parking brake is applied. At this point, the holding force by the rotary linear motion device 8 is released, and the piston 6D can be moved away from the disc rotor 4. This releases the rear wheel disc brakes 6 from their function as a parking brake.

[0060] Next, the control processing carried out by the computing circuit 25 of the parking brake control device 24 is described with reference to Fig. 4 described. The control processing of Fig. 4 is executed repeatedly in a predetermined control cycle (for example, 10 msec) during the period in which the parking brake control device 24 is, for example, energized.

[0061] When the parking brake control device 24, which is an electronic control unit (ECU), is activated, the control processing of Fig. 4. In step S1, the parking brake control device 24 assesses whether an application operating flag is ON or not. The application operating flag is an assessment flag used to determine whether an application process is being carried out or not, and is switched on during the application process, that is, when the electric motor 7A is driven in the application direction. Specifically, the application operating flag is switched ON during the processing of step S3 and OFF during the processing of step S11, which is described later.

[0062] If step S1 is evaluated as "NO", meaning if the application operating flag is evaluated as OFF, processing continues to step S2. If step S1 is evaluated as "YES", meaning if the application operating flag is evaluated as ON, processing continues to step S4. In step S2, it is evaluated whether an application command exists or not. In step S2, it is evaluated whether an actuation command has been issued, for example, by the parking brake switch 23 or based on the parking brake actuation evaluation logic. If step S2 is evaluated as "YES", meaning if it is determined that an application command exists, processing continues to step S3. If step S2 is evaluated as "NO", meaning if it is determined that no actuation command exists, processing returns to the beginning. That is, the processing returns to the start, and the processing after step S1 is repeated.

[0063] In step S3, the application operating flag is switched to ON. Additionally, electric motor 7A is driven in the application direction. In step S3, along with the activation of the application operating flag, when electric motor 7A begins to drive in the application direction, processing continues to step S4. In step S4, it is determined whether a variable t_hat, used to determine the point in time for assessing application completion (i.e., an estimated arrival time t_hat), has already been calculated during this application operation. If step S4 is assessed as "NO," meaning that the estimated arrival time t_hat has not yet been calculated, processing continues to step S5. If step S4 is assessed as "YES," meaning that the estimated arrival time t_hat has been calculated, processing continues to step S9.

[0064] In step S5, it is determined whether the inrush current mask time has elapsed. The inrush current mask time is the time since the electric motor 7A began operating in the direction of application. The inrush current mask time is defined as the time within which the inrush current stabilizes sufficiently. If step S5 is evaluated as "NO," meaning that the inrush current mask time has not elapsed, the processing returns to the start. This is to prevent the inrush current from influencing the estimation (calculation) of the estimated arrival time t_hat in the following steps S6 and S7. If, in the meantime, step S5 is evaluated as "YES," meaning that the inrush current mask time has elapsed, the processing continues to step S6.

[0065] In step S6, it is assessed whether the current of electric motor 7A, i.e., the motor current I, remains equal to or greater than a change trend assessment threshold Ia for a predetermined time "ta" or longer. If step S6 is assessed as "NO," meaning that the motor current I was no longer equal to or greater than the change trend assessment threshold Ia for the predetermined time "ta" or longer, the processing returns to the start. Meanwhile, if step S6 is assessed as "YES," meaning that the motor current I remains equal to or greater than the change trend assessment threshold Ia for the predetermined time "ta" or longer, the processing proceeds to step S7.In this case, if the change trend assessment threshold Ia, that is, the current value threshold Ia for the start of the assessment of a current change over time, is set to a high value, there is a possibility that the current change over time will not be calculated until the motor current I reaches the application completion current threshold IF. If the change trend assessment threshold Ia is set low, the current change over time at the time of application completion assessment cannot be accurately represented, for example, due to the nonlinearity of the pad stiffness. Therefore, the change trend assessment threshold Ia is set to meet the conditions described above, for example, to 3 A.If the predetermined time "ta", that is, the predetermined time "ta" which specifies the interval for evaluating the current change over time, is set to a short value, the evaluation is easily affected by noise, for example. Conversely, if the predetermined time "ta" is set to a long value, the motor current I can reach the threshold IF for the application termination current before a change in the motor current I over time is detected. Therefore, the predetermined time "ta" is set to satisfy the conditions described above, for example, to 30 ms.

[0066] In step S7, the slope of the current change, that is, the current change over time ΔI / ta, is calculated from the amount of increase in the current ΔI during the predetermined time 'ta' after the motor current I reaches a value equal to or greater than the change trend assessment threshold Ia. In step S8, which follows step S7, the estimated arrival time t_hat, which is the time the motor current I takes to reach the application termination current threshold IF, is calculated (estimated) based on the current change over time ΔI / ta obtained in step S7. The estimated arrival time t_hat is obtained from the following formula (1). t_hat=IF−(I a+Δ I)Δ I / ta

[0067] Then, in step S8, a counter for the elapsed time "t" since the calculation of the estimated arrival time t_hat is set to 0. This elapsed time counter counts the time that has passed since it was set to 0. In step S8, along with the calculation of the estimated arrival time t_hat, when the elapsed time counter "t" starts counting, the processing returns to the beginning. Meanwhile, if step S4 is evaluated as "YES," meaning it is determined that the estimated arrival time t_hat has been calculated, the processing continues to step S9. In step S9, it is evaluated whether the elapsed time counter "t" is equal to or greater than the estimated arrival time t_hat.If step S9 is evaluated as "NO", meaning that the counter for the elapsed time "t" is not equal to or greater than the estimated arrival time t_hat, processing returns to the start. Meanwhile, if step S9 is evaluated as "YES", meaning that the counter for the elapsed time "t" is equal to or greater than the estimated arrival time t_hat, processing continues to step S10. In step S10, it is evaluated whether the motor current I is equal to or greater than the application termination current threshold IF. If step S10 is evaluated as "NO", meaning that the motor current I is not equal to or greater than the application termination current threshold IF, processing returns to the start.If step S10 is evaluated as "YES", meaning that the motor current I is determined to be equal to or greater than the application termination current threshold IF, processing proceeds to step S11. In step S11, the application termination flag is set to ON, and other flags (for example, the application operation flag) are cleared (set to OFF). Additionally, any timers (for example, the elapsed time counter "t") are cleared (switched OFF). Furthermore, the electric motor 7A is stopped, and processing returns to the start.

[0068] In Fig. Figure 5 illustrates an example of the current change over time during an application process in the first embodiment. When an application command is issued by the parking brake switch 23 or based on the parking brake's application evaluation logic, the parking brake control device 24 begins, for example, to drive the electric motor 7A (step S3). If the inrush current stabilizes immediately after the electric motor 7A starts driving and the current value becomes Ia or higher, the parking brake control device 24 calculates the current slope ΔI / ta based on the magnitude of the current increase ΔI from the time the current value becomes Ia or higher until the predetermined time "ta" has elapsed (step S7).The parking brake control unit 24 then calculates the estimated arrival time t_hat from the present time until the current value reaches the application termination current threshold IF, based on the current slope ΔI / ta (step S8). When the elapsed time counter t becomes equal to or greater than the estimated arrival time t_hat, and it is determined that the current value has reached the application termination current threshold IF (steps S9 and S10), the parking brake control unit 24 stops the electric motor 7A (step S11). Therefore, as in . Fig. Figure 5 shows that the electric motor 7A can be stopped, regardless of the thickness of the lining, when the current value reaches the threshold IF for the application termination current. This prevents the braking force of the parking brake (thrust force based on the drive of the electric motor 7A) from becoming too high or too low.

[0069] As described above, the parking brake control device 24, according to the first embodiment, determines an evaluation time (estimated arrival time t_hat) for assessing whether or not to stop the electric motor 7A, based on a change trend (ΔI / ta) of the current value of the electric motor 7A. Therefore, it is possible to determine the evaluation time taking current fluctuations into account. This allows the electric motor 7A to be stopped at the correct time and the arrival current to be suppressed at the time of a current fluctuation, i.e., excessive or insufficient thrust. As a result, fluctuations in thrust can be reduced and excessive thrust suppressed, thereby improving responsiveness, reducing operating noise, making the electric brake device (brake caliper 6B) smaller and lighter, and reducing costs.

[0070] According to the first embodiment, the parking brake control device 24 assesses, upon reaching the assessment time, that the electric motor 7A must be stopped if the current value (motor current I) of the electric motor 7A is equal to or greater than a predetermined value (application termination current threshold IF). Therefore, the electric motor 7A can be stopped in a state where the current value is equal to or greater than the predetermined value (application termination current threshold IF), thus preventing insufficient thrust.

[0071] According to the first embodiment, the parking brake control device 24 determines the assessment time (estimated arrival time t_hat) for judging whether or not to stop the electric motor 7A, based on the change trend of the current value of the electric motor 7A if there has been an increase in the current value after a predetermined time interval (after the inrush current mask time) has elapsed since the electric motor 7A was driven. Therefore, the assessment time can be determined while avoiding the inrush current when starting the drive of the electric motor 7A.

[0072] Fig. 6 and Fig. Figure 7 shows a second embodiment of the present invention. A feature of the second embodiment is that the completion current threshold (IF) is calculated based on the change trend of the current value, and it is determined whether the electric motor should be stopped after a predetermined time interval has elapsed since the calculated completion current threshold. In the second embodiment, parts identical to those of the first embodiment are designated by the same reference numerals, and their descriptions are omitted.

[0073] In the second embodiment, the application completion is determined (i.e., the application is considered complete and the electric motor 7A is stopped) when the motor current I continuously exceeds a threshold IF2 for a predetermined time "tb" (for example, 30 ms = 3 control cycles). This ensures robustness. Furthermore, in the second embodiment, the current threshold IF2 for assessing completion is corrected based on the change in motor current over time, so that the motor current value is constant when the electric motor 7A stops; that is, the electric motor 7A stops at the application completion current threshold IF. This suppresses variation in the arrival current.

[0074] In the second embodiment, the parking brake control device 24 determines the time at which the electric motor 7A is to be stopped based on the change trend of the current value (motor current I) of the electric motor 7A when the electric motor 7A is driven in the application direction by the application command. In this case, the parking brake control device 24 determines (calculates) the threshold value IF2 for the assessment of the termination current, which becomes the threshold value IF for the termination current of the application when the predetermined time "tb" has elapsed. Based on the completion assessment current threshold value IF2, the parking brake control device 24 assesses that the electric motor 7A is to be stopped after the predetermined time "tb" and stops the electric motor 7A.

[0075] Fig. Figure 6 illustrates the control processing in the second embodiment, that is, the control processing carried out in the computing circuit 25 of the parking brake control device 24. In the second embodiment, the processing program for executing the operation described in Figure 6 is... Fig. The processing sequence shown in section 6 is stored in memory 26 of the parking brake control device 24. Step S1, step S2, step S3, step S5, step S6, step S7 and step S11 of the Fig. 6 are the same processing as that of step S1, step S2, step S3, step S5, step S6, step S7 and step S11 of the Fig. 4 in the first embodiment, and therefore the description of these steps is omitted here.

[0076] In step S21, which follows a "YES" result in step S1 or step S3, it is assessed whether the current threshold IF2 for the completion assessment has been calculated. If step S21 is assessed as "NO," meaning it is determined that the current threshold IF2 for the completion assessment has not been calculated, processing continues to step S5. Meanwhile, if step S21 is assessed as "YES," meaning it is determined that the current threshold IF2 for the completion assessment has been calculated, processing continues to step S23. In step S22, which follows step S7, the current threshold IF2 for the final assessment is calculated.In particular, in step S22, the current threshold IF2 for the completion assessment is calculated based on the "current change over time ΔI / ta" and the "predetermined time tb" obtained in step S7, from the time the current threshold IF2 for the completion assessment is exceeded until the application is deemed complete. The current threshold IF2 for the completion assessment is calculated using the following formula (2). That is, based on formula (2), if the current change ΔI / ta increases, the current threshold IF2 for the completion assessment decreases, so that the current value at the time the application is completed becomes the current threshold IF for the application's completion. IF2=IF−Δ It a×tb

[0077] Meanwhile, in step S23, which follows "YES" in step S21, it is assessed whether the motor current I has continuously exceeded the threshold for the completion assessment current IF2 for the predetermined time "tb" or longer. If step S23 is assessed as "NO," meaning that the motor current I has not continuously exceeded the current threshold IF2 for the predetermined time "tb" or longer, the processing returns to the start. If, meanwhile, step S23 is assessed as "YES," meaning that the motor current I has continuously exceeded the current threshold IF2 for the predetermined time "tb" or longer, the processing continues to step S11. If the current change is determined in step S22, the voltage applied to the electric motor 7A can be used as an alternative characteristic of the current change over time.

[0078] In Fig. Figure 7 illustrates the current change over time during an application process in the second embodiment. For example, when an application command is issued by the parking brake switch 23, the parking brake control device 24 begins to drive the electric motor 7A (step S3). When the inrush current stabilizes immediately after the electric motor 7A starts driving and the current value becomes Ia or higher, the parking brake control device 24 calculates the current slope ΔI / ta based on the magnitude of the current increase ΔI from the moment the current value becomes Ia or higher until the predetermined time "ta" has elapsed (step S7).Then, the parking brake control device 24 calculates the completion assessment current threshold IF2 based on the "current slope ΔI / ta" and the "predetermined time 'tb' from the time the completion assessment current threshold IF2 is exceeded until the application completion assessment is determined" (step S22). If the parking brake control device 24 determines that the motor current I has continuously exceeded the completion assessment current threshold IF2 for the predetermined time 'tb' or more (step S23), the parking brake control device 24 stops the electric motor 7A (step S11). Therefore, as in . Fig. Figure 7 shows that the electric motor 7A can be stopped, regardless of the thickness of the lining, when the current value reaches the threshold IF for the application termination current. This prevents the braking force of the parking brake (thrust force based on the drive of the electric motor 7A) from becoming too high or too low.

[0079] In the second embodiment, the assessment point for determining whether or not to stop electric motor 7A is determined in steps S21, S22, and S23 as described above, and it is determined that electric motor 7A should be stopped at the specified assessment point (electric motor 7A is stopped). There is no significant difference in the basic action of the second embodiment compared to the first embodiment described above. That is, as with the first embodiment, it is also possible in the second embodiment to suppress fluctuations in the incoming current (i.e., the thrust) while ensuring robustness against current fluctuations.

[0080] Fig. 8 and Fig. Figure 9 shows a third embodiment of the present invention. A feature of the third embodiment is that the judgment timing for deciding whether or not to stop (or stop immediately) the electric motor is determined based on a change trend in the current value (current differential value), and when the judgment timing is reached, it is decided to stop the electric motor. In the third embodiment, parts identical to those of the first embodiment are designated with the same reference numbers, and their description is omitted.

[0081] In the third embodiment, if the motor current I exceeds the application termination current threshold IF, the application termination decision is determined to be established when it is confirmed that the current has not fluctuated within the immediately preceding predetermined time interval (i.e., the application termination is assessed, and the electric motor 7A is stopped). This ensures robustness to current fluctuations and suppresses arrival current variability by deciding that the application termination is determined on a control cycle that exceeds the application termination current threshold IF.

[0082] In the third embodiment, the parking brake control device 24 determines the point in time at which the electric motor 7A is to be stopped based on a current differential value “i”, which is the rate of change of the current value (motor current I) of the electric motor 7A when the electric motor 7A is driven by the application command in the application seal. In this case, the parking brake control device 24 decides that the electric motor 7A should be stopped when the rate of change, that is, the magnitude of the change in the current differential value “i” of the motor current I in a period “tc” immediately before reaching the current threshold value IF for termination of the application, is small (the difference between the maximum imax and the minimum imin of the current differential value is less than a predetermined value icor), and the electric motor 7A is stopped immediately.However, if the amount of change in the current differential value “i” in the period “tc” immediately before reaching the application termination current threshold IF is large (difference between maximum imax and minimum imin of the current differential value is equal to or greater than the predetermined value icor), it is not decided that the electric motor 7A should be stopped, and the parking brake control device 24 stops the electric motor 7A at a current threshold obtained by adding a predetermined additional current amount IΔF to the application termination current threshold IF.

[0083] Fig. Figure 8 is a representation of the control processing in the third embodiment, that is, the control processing that is carried out in the computing circuit 25 of the parking brake control device 24. In the third embodiment, the processing program for executing the in Fig. The processing sequence shown in section 8 is stored in memory 26 of the parking brake control device 24. Steps S1, S2, S3 and S11 of Fig. 8 are the same processing as those of step S1, step S2, step S3 and step S11 of Fig. 4 in the first embodiment, and therefore the description of these steps is omitted here.

[0084] In step S31, which follows "YES" in step S1 or step S3, it is assessed whether the inrush current mask time has expired or not, so that the application is not considered complete at the inrush current. The processing of step S31 is the same as that of step S5 in Fig. 4. If step S31 is evaluated as "NO", meaning that the inrush current mask time has not yet elapsed, processing returns to the start. If step S31 is evaluated as "YES", meaning that the inrush current mask time has elapsed, processing continues with step S32. Fig. In the first embodiment described above, the inrush current stabilizes when it is determined that the estimated arrival time t_hat has been calculated in step S4, and therefore processing step S31 after "YES" in step S4 is not required. In the third embodiment, however, there is no such condition, and therefore processing step S31 is required.

[0085] In step S32, it is assessed whether the motor current I is equal to or greater than the threshold of the application termination current IF. The processing of step S32 is the same as that of step S10 in Fig. 4. If step S32 is evaluated as "NO", meaning that the motor current I is not equal to or greater than the application termination current threshold IF, processing returns to the start. If step S32 is evaluated as "YES", meaning that the motor current I is equal to or greater than the application termination current threshold IF, processing continues to step S33.

[0086] In step S33, it is assessed whether the difference between the maximum imax and the minimum imin of the current difference value during the immediately preceding predetermined time "tc" is less than the predetermined value icor. If step S33 is assessed as "YES," meaning that the difference between the maximum imax and the minimum imin of the current difference value during the immediately preceding predetermined time "tc" is less than the predetermined value icor, processing continues to step S11. Meanwhile, if step S33 is assessed as "NO," meaning that the difference between the maximum imax and the minimum imin of the current difference value during the immediately preceding predetermined time "tc" is not less than the predetermined value icor, processing proceeds to step S34.In step S34, the second assessment of the application termination is performed: whether the motor current I is equal to or greater than the sum of the application termination current threshold IF and the additional current amount IΔF. If step S34 is assessed as "NO," meaning that the motor current I is not equal to or greater than the sum of the application termination current threshold IF and the additional current amount IΔF, processing returns to the start. If step S34 is assessed as "YES," meaning that the motor current I is found to be equal to or greater than the sum of the application termination current threshold IF and the additional current amount IΔF, processing proceeds to step S11.The additional current amount IΔF is an additional current to ensure the thrust by preventing the assessment of the application completion from failing and continuing to supply current if the current continues to fluctuate, and can, for example, be set to 3 A.

[0087] In Fig. Figure 9 illustrates an example of the current change over time at the moment of actuation in the third embodiment. When an application command is issued by the parking brake switch 23 or based on the parking brake application evaluation logic, the parking brake control unit 24, for example, begins to drive the electric motor 7A (step S3). If the inrush current is established immediately after the start of the drive of the electric motor 7A and the current value becomes equal to or greater than the threshold of the application termination current IF (step S32), it is evaluated whether the "difference between the maximum imax and the minimum imin of the current differential value" during the immediately preceding predetermined time "tc" is less than the predetermined value icor or not (step S33).If it is determined that the "difference between the maximum imax and the minimum imin of the current differential value" is less than the predetermined value icor, the parking brake control device 24 determines that the electric motor 7A should be stopped and stops the electric motor 7A (step S11). Meanwhile, if it is determined that the "difference between the maximum imax and the minimum imin of the current differential value" is equal to or greater than the predetermined value icor, the parking brake control device 24 determines whether the motor current I is equal to or greater than "the sum of the application termination current threshold IF and the additional current IΔF" (step S34).In this case, if it is determined that the motor current I is equal to or greater than "the sum of the threshold of the application termination current IF and the additional current amount IΔF", the parking brake control device 24 determines that the electric motor 7A should be stopped and stops the electric motor 7A (step S11). This prevents the braking force of the parking brake (thrust based on the drive of the electric motor 7A) from becoming too high or too low.

[0088] In the third embodiment, the assessment point for determining whether or not electric motor 7A should be stopped (whether or not electric motor 7A should be stopped immediately because the current value is equal to or greater than the threshold of the application termination current IF) is determined in steps S31, S32, S33, and S34 as described above, and it is determined that electric motor 7A should be stopped at the determined assessment point (electric motor 7A is stopped). There is no particular difference in the basic action of the third embodiment compared to the first and second embodiments described above. That is, as with the first and second embodiments, it is also possible in the third embodiment to suppress fluctuations in the arrival current (i.e., the thrust) while ensuring robustness against current fluctuations.

[0089] Fig. 10 and Fig. Figure 11 shows a fourth embodiment of the present invention. A feature of the fourth embodiment is that the assessment point for determining whether the electric motor has reached the rotational position (or whether the electric motor should be stopped immediately) is determined based on a change trend in the current, and when the assessment point is reached, a decision is made to stop the electric motor. In the fourth embodiment, parts identical to those of the third embodiment are designated with the same reference numbers, and their descriptions are omitted.

[0090] In the fourth embodiment, when the motor current I exceeds the application termination current threshold IF, the application termination decision is determined to be established when it is confirmed that the current value for the motor speed has not fluctuated (i.e., the application termination is assessed, and the electric motor 7A is stopped). This ensures robustness to current fluctuations and suppresses arrival current fluctuation by determining that the application termination is established on a control cycle that exceeds the application termination current threshold IF. In this case, the current fluctuation is assessed based on the current value for the motor speed, and therefore the assessment can be performed by eliminating the influence of changes in motor speed due to fluctuations in the supply voltage.

[0091] The motor speed can be estimated based on the current I and the voltage V of the electric motor 7A. In this case, the motor speed can be calculated by integrating the speed of the electric motor 7A, i.e., the motor speed ω. The motor speed ω can be obtained from the following formula (3), where D and R are coefficients, V is the voltage between the motor terminals, and I is the current value (motor current). In this case, the accuracy of the estimate can be improved by using the voltage between the motor terminals instead of the supply voltage. Alternatively, the motor speed can be measured by attaching a rotary angle sensor. The motor speed can also be calculated from the value of the linear motion sensor. ω=D (V−RI)

[0092] In the fourth embodiment, the parking brake control device 24 determines an evaluation point (time) to assess, upon a request to hold the brake pads 6C (application command), whether the rotational position of the electric motor 7A at which holding the brake pads 6C is complete has been reached. In this case, the parking brake control device 24 determines (calculates) the evaluation point to assess whether the rotational position of the electric motor 7A at which holding the brake pads 6C is complete has been reached, based on a change trend (quantity of change or slope) of the current value (motor current I) of the electric motor 7A. When the determined evaluation point is reached, the parking brake control device 24 assesses that holding the brake pads 6C is complete.

[0093] In particular, when the electric motor 7A is driven in the application direction based on an application command, the parking brake control device 24 determines the stopping time of the electric motor 7A based on the change trend of the current value (motor current I) of the electric motor 7A, that is, a difference Idiff between a predicted value of the motor speed from the current value and the motor speed in a normal state. In this case, the parking brake control device 24 judges that the electric motor should be stopped when the difference Idiff between a predicted value estimated from the current change from an immediately preceding predetermined motor speed φa when the application termination current threshold IF is reached and the normal state is small (the difference Idiff is equal to or less than the predetermined threshold Imgn), and immediately stops the electric motor 7A.If the difference Idiff between the predicted value, estimated from the current change from the immediately preceding predetermined motor speed φa when the application termination current threshold IF is reached, and the normal state is large (the difference Idiff is greater than the predetermined threshold Imgn), it is not decided that the electric motor 7A should be stopped, and the parking brake control device 24 stops the electric motor 7A at a current threshold obtained by adding the predetermined additional current IΔF to the application termination current threshold IF.

[0094] Fig. Figure 10 is a representation of the control processing in the fourth embodiment, that is, the control processing that is carried out in the computing circuit 25 of the parking brake control device 24. In the fourth embodiment, the processing program for executing the in Fig. The processing sequence shown in 10 is stored in memory 26 of the parking brake control device 24. Step S1, step S2, step S3 and step S11 of Fig. 10 are the same processing as those of step S1, step S2, step S3 and step S11 of Fig. 4 of the first embodiment, and step S31, step S32 and step S34 of Fig. 10 are the same processing as those of step S31, step S32 and step S34 of Fig. 8 of the third embodiment, and therefore the description of these steps is omitted here.

[0095] In step S41, it is assessed whether the difference Idiff between the predicted value, estimated from the current change from the immediately preceding predetermined engine speed φa and the normal state, is equal to or less than a predetermined threshold value Imgn. If step S41 is assessed as "YES", meaning that the difference Idiff is assessed as equal to or less than the predetermined threshold value Imgn, processing proceeds to step S11. If step S41 is assessed as "NO", meaning that the difference Idiff is assessed as equal to or less than the predetermined threshold value Imgn, processing proceeds to step S11. Fig. Figure 11 is a characteristic curve plotting the current value against the estimated motor speed at the time of application. Under normal conditions, the current value increases linearly, as shown by the alternating long and short dashed line 31, and therefore the difference Idiff from the predicted value (dashed line 32), estimated from the current change from the immediately preceding predetermined motor speed φa, approaches zero. However, during current fluctuation, the current value is not linear, and the difference Idiff from the predicted value increases. The motor speed is a displacement proportional to the thrust, and therefore, if the difference Idiff from the predicted value is large, the thrust for the same current value will be small. Consequently, if the application is considered complete in a state where the difference Idiff from the predicted value is large, the thrust will be less than a target value.To avoid this condition, step S41 assesses whether the difference Idiff between the predicted value, estimated from the current change from the immediately preceding predetermined motor rotation amount φa, and the normal state is equal to or less than the predetermined threshold Imgn. If the difference Idiff from the predicted value is greater than the predetermined threshold Imgn, processing proceeds to step S34. The difference Idiff from the predicted value at the time of application completion correlates with the difference between the thrust estimated from the motor current value I and the actual thrust. Therefore, the threshold Imgn is adjusted so that the decrease in thrust due to current fluctuation remains within the safety margin for the minimum thrust required to ensure the vehicle is held and the thrust that is the target at the time of application.

[0096] In the fourth embodiment, the assessment point for determining whether or not to stop electric motor 7A (whether to stop immediately or not because the current value is equal to or greater than the threshold of the application termination current IF) is determined in step S41 as described above, and it is assessed that electric motor 7A should be stopped at the determined assessment point (electric motor 7A is stopped). There is no particular difference in the basic action of the fourth embodiment from the third embodiment described above. That is, as in the first through third embodiments, it is also possible in the fourth embodiment to suppress fluctuations in the arrival current (i.e., thrust) while ensuring robustness against current fluctuations.In the fourth embodiment, the motor speed is used to decide whether or not to stop the electric motor 7A. That is, the decision to stop the electric motor 7A is made based on the estimated motor speed (the difference Idiff between the predicted value, estimated from the current change in the immediately preceding predetermined motor speed φa, and the normal state). As in the first through third embodiments, it is also possible in the fourth embodiment to suppress both the erroneous detection of the application termination and the change in thrust force at the time of application termination.

[0097] In the first to fourth embodiments, cases are described in which it is assessed whether the electric motor should be stopped or not when the application is complete. That is, in the first to fourth embodiments, cases are described in which the flag for the completion of the application is set in step S11 of Fig. 4, Fig. 6, Fig. 8 and Fig.10 is set to ON. However, the present invention is not limited to this. For example, the application termination flag in step S11 can be left off, and the electric motor can be re-energized later. That is, the application termination flag can be used to assess whether or not the electric motor should be stopped in the case of a configuration where the excitation is temporarily stopped during the application (the electric motor is temporarily stopped and then re-energized during the application). Furthermore, the assessment of whether or not to stop the electric motor in the first to fourth embodiments can be used when starting from a state in which thrust has been generated.In these cases, even if the thrust is generated gradually during application or if the thrust increase is temporarily halted, the electric motor can be stopped at the appropriate time, and the incoming current during a current fluctuation—that is, the excess or deficiency of thrust—can be suppressed. Examples of situations where thrust is generated gradually or thrust increase is temporarily halted include situations where wheel lock-up when the parking brake is applied while driving and situations where sudden wheel lock-up during brake force control with a roller dynamo is to be prevented.

[0098] In each embodiment, an exemplary case was described in which the rear disc brakes 6 are hydraulic disc brakes with an electric parking brake function and the front disc brakes 5 are hydraulic disc brakes without an electric parking brake function. However, the present invention is not limited to this. For example, the rear disc brakes 6 can be hydraulic disc brakes without an electric parking brake function and the front disc brakes 5 can be hydraulic disc brakes with an electric parking brake function. Furthermore, both the front disc brakes 5 and the rear disc brakes 6 can be hydraulic disc brakes with an electric parking brake function. In short, the brakes of at least one pair of left and right wheels of the vehicle can be configured as electric parking brakes.

[0099] In each embodiment, hydraulic disc brakes 6 with an electric parking brake were described as an example of the electric braking device. However, the braking device is not limited to one type of disc brake and can be configured as a drum-type braking device. Furthermore, various types of electric parking brake configurations can be assumed, for example, a drum-in-disc brake with a drum-like electric parking brake within the disc brake, and a configuration in which the parking brake is held by an electric motor pulling a cable. It should also be understood that each embodiment is exemplary and that the configurations described in different embodiments can be partially substituted or combined.

[0100] For example, the aspects described below can be taken into account in an electric braking device based on the embodiments described above.

[0101] As a first aspect, an electric braking device is provided, comprising: an electric braking device in which a piston, driven by a rotation-linear motion device which is driven by an electric motor, is configured to press a braking element against a braked element and to hold the braking element in a pressure position by stopping the electric motor; and a control unit configured to control the electric motor, wherein the control unit is configured to determine, when a request is made to hold the braking element, an evaluation point for assessing whether to stop the electric motor based on a change trend of a current value of the electric motor, and when the evaluation point is reached, it assesses whether to stop the electric motor.

[0102] According to the first aspect, the assessment point for deciding whether or not to stop the electric motor is determined based on the change trend of the electric motor's current value. Therefore, it is possible to determine the assessment point taking current fluctuations into account. This allows the electric motor to be stopped at an appropriate time, and the arrival current during a current fluctuation—that is, the excess or deficiency of thrust—is suppressed. As a result, fluctuations in thrust can be reduced and excessive thrust suppressed, thereby improving responsiveness, reducing operating noise, making the electric braking device (caliper) smaller and lighter, and reducing costs.

[0103] According to the second aspect, the control unit is configured to decide, upon reaching the assessment point, that the electric motor may be stopped if the current value of the electric motor is equal to or greater than a predetermined value. According to this second aspect, the electric motor can be stopped in the state where the current value is equal to or greater than the predetermined value, thus preventing insufficient thrust.

[0104] According to a third aspect of the first or second aspect, the control unit is configured so that, if the current value increases after a predetermined time has elapsed since the electric motor started, it determines the assessment point for evaluating whether the electric motor should be stopped, based on the change trend of the electric motor's current value. According to the third aspect, the assessment point can be determined while avoiding inrush current when the electric motor starts to run.

[0105] As a fourth aspect, an electric braking device is provided, comprising: an electric braking device in which a piston driven by a rotation-linear motion device, which is driven by an electric motor, is configured to press a braking element against a braked element and to hold the braking element in a pressure position by stopping the electric motor;and a control unit configured to control the electric motor, wherein the control unit is configured to determine, when a request is made to hold the brake element, an evaluation point in time for assessing whether a rotational position of the electric motor has reached a position where holding the brake element is complete, based on a change trend of a current value of the electric motor, and that when the evaluation point is reached, it assesses whether holding the brake element is complete.

[0106] According to this fourth aspect, the assessment point for determining whether the electric motor has reached the rotational position at which the holding of the braking element is complete can be determined based on the change trend of the electric motor's current value. Therefore, it is possible to determine the assessment point taking current fluctuations into account. This allows the electric motor to be stopped at an appropriate time, and the arrival current during a current fluctuation—that is, the over- or under-run of the thrust force—can be suppressed. Consequently, fluctuations in thrust can be reduced and excessive thrust suppressed, thereby improving responsiveness, reducing operating noise, making the electric braking device (caliper) smaller and lighter, and reducing costs.

[0107] Note that the present invention is not limited to the embodiments described above and includes various other modifications. For example, in the embodiments described above, the configurations are described in detail to clearly describe the present invention, but the present invention is not necessarily limited to an embodiment that includes all the configurations described. Furthermore, part of the configuration of one particular embodiment may replace the configuration of another embodiment, and the configuration of another embodiment may also be added to the configuration of one particular embodiment. Furthermore, another configuration may be added to, deleted from, or replace part of the configuration of any of the embodiments.

[0108] The present application claims priority based on Japanese patent application No. 2018-242708, filed on December 26, 2018. All disclosed contents, including the specification, scope of claims, drawings, and abstract of Japanese patent application No. 2018-242708, filed on December 26, 2018, are incorporated herein by reference in their entirety. REFERENCE MARK LIST

[0109] 4 Disc rotor (braked element), 6 Rear wheel disc brake (electric braking device), 6C Brake pad (brake element), 6D Piston, 7A Electric motor, 8 Rotation linear motion device, 24 Parking brake control unit (control unit)

Claims

[1] An electric braking device comprising: an electric braking device unit in which a piston, driven by a rotary linear motion device driven by an electric motor, is configured to press a braking element against a braked element and to hold the braking element in a pressure position by stopping the electric motor; and a control unit configured to control the electric motor, wherein the control unit is configured such that, when a request is made to hold the brake element, it determines an assessment point in time to assess whether the electric motor should be stopped, based on a change trend of a current value of the electric motor, and that when the assessment point is reached, it assesses whether the electric motor should be stopped. [2] Electric braking device according to claim 1, wherein the control unit is configured to assess, upon reaching the assessment time, that the electric motor may be stopped if the current value of the electric motor is equal to or greater than a predetermined value. [3] Electric braking device according to claim 1 or 2, wherein the control unit is configured to determine, when the current value is increased after a predetermined time period has elapsed since the start of the drive of the electric motor, the assessment time for judging whether the electric motor should be stopped, based on the change trend of the current value of the electric motor. [4] An electric braking device comprising: an electric braking device unit in which a piston, driven by a rotary linear motion device driven by an electric motor, is configured to press a braking element against a braked element and to hold the braking element in a pressure position by stopping the electric motor; and a control unit configured to control the electric motor, wherein the control unit is configured such that, when a request is made to hold the brake element, it determines an evaluation point in time to assess whether a rotational position of the electric motor has reached a position at which holding the brake element is complete, based on a change trend of a current value of the electric motor, and that when the evaluation point is reached, it assesses whether holding the brake element is complete.

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