Electric driving device

Abstract

To improve the durability of an electric braking device.SOLUTION: A suction control unit (10) of an electric braking device (1) executes a control for decreasing the forward-movement speed of a piston (P) as a target pressure value increases, in which the control is executed at least for a period after a hydraulic pressure on a hydraulic chamber side with respect to a switching valve (NC1) increases to the proximity of the target pressure value, in a period in which a forward-movement control is executed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electric braking system. [Background technology]

[0002] In an electric braking system using an electric cylinder, if the brake fluid in the wheel cylinder is released to a reservoir when anti-lock brake control is performed to reduce pressure, the total amount of brake fluid in the hydraulic chamber, the wheel cylinder, and the piping between the hydraulic chamber and the wheel cylinder, which are separated by the cylinder and piston of the electric cylinder, decreases when the anti-lock brake control is performed. As a result, when attempting to generate a predetermined pressure in the wheel cylinder, if the total amount of brake fluid is reduced, the piston position of the electric cylinder advances compared to when the total amount of brake fluid is not reduced. This can cause bottoming, in which the piston of the electric cylinder hits the bottom of the cylinder when the piston of the electric cylinder advances to send brake fluid from the hydraulic chamber to the wheel cylinder to increase the vehicle's braking force. Patent Document 1 describes a refill control to prevent this phenomenon, which returns the piston of the electric cylinder toward its starting position and sucks brake fluid back into the hydraulic chamber from the reservoir. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5800437 Summary of the Invention [Problem to be solved by the invention]

[0004] In refill control, after brake fluid is drawn back from the reservoir, the piston of the electric cylinder is advanced to restore the pressure in the hydraulic chamber defined by the cylinder and piston to the pressure at the start of refill control. Here, if the piston advances at high speed during refill control, the pressure in the hydraulic chamber may overshoot. If an overshoot occurs when the target pressure in the hydraulic chamber is high when the piston advances, excessive load is placed on the electric cylinder, potentially reducing the durability of the electric cylinder. An object of one aspect of the present disclosure is to improve the durability of an electric braking device. [Means for solving the problem]

[0005] In order to solve the above problems, an electric braking device according to one aspect of the present disclosure is an electric braking device that adjusts the hydraulic pressure in a wheel cylinder by discharging brake fluid from a hydraulic chamber defined by the cylinder and the piston to the outside of the hydraulic chamber or by drawing brake fluid from outside the hydraulic chamber into the hydraulic chamber when a piston in a cylinder is driven by an electric motor, and that has a reservoir connected to the hydraulic chamber, and a control circuit for controlling the cutoff and opening of the discharge brake fluid, which is the brake fluid discharged from the hydraulic chamber to the wheel cylinder side, and the draw brake fluid, which is the brake fluid drawn from the wheel cylinder side to the hydraulic chamber. and a suction control unit that uses the switching valve to block the discharge brake fluid and the suction brake fluid, moves the piston backward using the electric motor to suck the brake fluid from the reservoir into the hydraulic chamber, and then performs forward control to move the piston forward until the hydraulic pressure in the hydraulic chamber reaches a target pressure value, wherein the suction control unit controls to decrease the forward speed of the piston in the forward control as the target pressure value increases, at least during the period during which the forward control is being performed, after the hydraulic pressure on the hydraulic chamber side relative to the switching valve has increased to near the target pressure value. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, the durability of an electric braking device can be improved compared to conventional devices. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a hydraulic circuit diagram for explaining an electric braking device according to an embodiment of the present disclosure. FIG. [Figure 2] 5 is a flowchart showing a flow of refill control in an electric braking device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Configuration of electric braking device) Fig. 1 is a diagram illustrating an electric braking device according to an embodiment of the present disclosure. The electric braking device 1 shown in Fig. 1 includes a control unit 10, a reservoir 11, and an electric cylinder 12. The electric braking device 1 is mounted on a vehicle having a plurality of wheels W. Each wheel W is provided with a caliper having a wheel cylinder WC. The reservoir 11, the electric cylinder 12, and the wheel cylinder WC are connected to a hydraulic circuit having a first flow path F1, a second flow path F2, and a third flow path F3.

[0009] The first flow path F1 is a flow path between the reservoir 11 and the electric cylinder 12. Brake fluid is stored in the reservoir 11. The brake fluid stored in the reservoir 11 is supplied to the electric cylinder 12 via a first flow path F1. A check valve CV1 is arranged in the first flow path F1. The check valve CV1 opens when the pressure on the electric cylinder 12 side of the check valve CV1 becomes lower than the pressure on the reservoir 11 side of the check valve CV1, that is, when the pressure on the electric cylinder 12 side of the check valve CV1 becomes negative pressure, thereby allowing the flow of brake fluid from the reservoir 11 to the electric cylinder 12. On the other hand, the flow of brake fluid from the electric cylinder 12 to the reservoir 11 is restricted.

[0010] The electric cylinder 12 has a cylinder C, a piston P, an electric motor M, and a rotation angle sensor R. The piston P moves linearly within the cylinder C in response to the drive of the electric motor M, changing the volume of a hydraulic chamber H defined by the cylinder C and the piston P. As the piston P moves forward within the cylinder C, brake fluid within the hydraulic chamber H is discharged to the wheel cylinder WC. The rotation angle sensor R detects the rotation angle of the rotor of the electric motor M. The position of the piston P of the electric cylinder 12 can be obtained based on the detection result of the rotation angle sensor R.

[0011] The second flow path F2 is a flow path between the hydraulic chamber H of the electric cylinder 12 and the wheel cylinder WC. A normally closed solenoid valve NC1, a normally open solenoid valve NO1, and a check valve CV2 are arranged in the second flow path F2. The check valve CV2 opens when the pressure on the wheel cylinder WC side of the check valve CV2 becomes lower than the pressure on the electric cylinder 12 side of the check valve CV1, allowing the flow of brake fluid from the electric cylinder 12 to the wheel cylinder WC. Meanwhile, it restricts the flow of brake fluid from the wheel cylinder WC to the electric cylinder 12. The solenoid valve NC1 is arranged in parallel with the check valve CV2. The solenoid valve NO1 is arranged in series with the check valve CV2 and the solenoid valve NC1, and is located closer to the wheel cylinder WC than the check valve CV2 and the solenoid valve NC1. The solenoid valve NC1 is an example of a switching valve. By switching the second flow path F2 between the hydraulic chamber H of the electric cylinder 12 and the wheel cylinder WC between a blocked state and a connected state, the discharge brake fluid, which is the brake fluid discharged from the hydraulic chamber to the wheel cylinder side, and the suction brake fluid, which is the brake fluid sucked into the hydraulic chamber from the wheel cylinder side, are switched between blocked and open.

[0012] When the solenoid valve NO1 is closed, the second flow path F2 is shut off. When the solenoid valves NO1 and NC1 are open, the second flow path F2 is in a communication state. When the solenoid valve NO1 is open and the solenoid valve NC1 is closed, the brake fluid does not flow in the direction from the wheel cylinder WC toward the electric cylinder 12.

[0013] The sensor SE1 is disposed between the solenoid valves NC1 and NO1 and measures the brake fluid pressure Pr2 in the flow path between the solenoid valves NC1 and NO1. The sensor SE1 may also function as a temperature sensor and may further measure the temperature of the brake fluid.

[0014] The third flow path F3 is a flow path between the wheel cylinder WC and the reservoir 11. A normally closed solenoid valve NC2 is disposed in the third flow path F3. When the solenoid valve NC2 is closed, the third flow path F3 is blocked. When the solenoid valve NC2 is open, the third flow path F3 is connected.

[0015] The control unit 10 is an example of a suction control unit, and is, for example, an ECU including a microcomputer. The control unit 10 is used for antilock brake control that prevents the wheels W from locking during braking. The antilock brake control has, for example, a pressure reduction mode in which the hydraulic pressure in the wheel cylinder WC (brake hydraulic pressure Pr3) is reduced by closing the solenoid valve NO1 and opening the solenoid valve NC2, a pressure retention mode in which the hydraulic pressure in the wheel cylinder WC is maintained by closing the solenoid valve NO1 and the solenoid valve NC2, and a pressure increase mode in which the hydraulic pressure in the wheel cylinder WC is increased by opening the solenoid valve NO1 and closing the solenoid valve NC2 and then driving the electric cylinder 12.

[0016] In the pressure reduction mode, brake fluid is returned from the wheel cylinder WC to the reservoir 11 via the third flow path F3, thereby reducing the total amount of brake fluid in the hydraulic chamber H, the wheel cylinder WC, and the hydraulic path between the check valve CV1 and the solenoid valve NC2. This event may cause bottoming, in which the piston P of the electric cylinder 12 collides with the bottom surface B of the cylinder C, so the control unit 10 performs refill control (suction control).

[0017] (Refill control) In the refill control, the control unit 10 closes the solenoid valve NC1 to block the second flow path F2. Then, the control unit 10 moves the piston P of the electric cylinder 12 backward to draw brake fluid from the reservoir 11 into the hydraulic chamber H of the electric cylinder 12.

[0018] The amount of brake fluid sucked from the reservoir 11 to the hydraulic chamber H of the electric cylinder 12 per unit time varies depending on the amount of retraction of the piston P of the electric cylinder 12.

[0019] After the brake fluid is drawn into the hydraulic chamber H of the electric cylinder 12, the control unit 10 performs forward control to advance the piston P of the electric cylinder 12. When the hydraulic pressure in the hydraulic chamber H reaches a target pressure value by advancing the piston P, the solenoid valve NC1 is opened. For example, the hydraulic pressure in the hydraulic chamber H may be determined to have reached the target pressure value based on the hydraulic pressure in the hydraulic chamber H estimated from the current flowing through the motor M (detected by a current sensor, not shown). Alternatively, the hydraulic pressure in the hydraulic chamber H may be determined to have reached the target pressure value based on an increase in the detection value of the sensor SE1, which occurs when the brake fluid on the electric cylinder 12 side flows into the wheel cylinder WC through the check valve CV2 due to the advancement of the piston P. Alternatively, the hydraulic pressure in the hydraulic chamber H may be determined to have reached the target pressure value based on the detection value of a pressure sensor, not shown, located on the electric cylinder 12 side of the solenoid valve NC1. Here, the target pressure value is the target value of the hydraulic pressure in the hydraulic chamber H during forward control. The target pressure value may be, for example, the hydraulic pressure on the wheel cylinder WC side of the solenoid valve NC1 during forward control, or the hydraulic pressure in the hydraulic chamber H immediately before the piston P is retracted during refill control. The target pressure value may also be the pressure at which the hydraulic pressure in the hydraulic chamber H begins to rise. This is because, even if the piston P is advanced to an extent that the gas region generated in the hydraulic chamber H due to the retraction of the piston P is eliminated by the forward control, it is possible to prevent the brake fluid on the wheel cylinder WC side of the solenoid valve NC1 from flowing into the hydraulic chamber H.

[0020] In the refill control, when the piston P is advanced at high speed, the hydraulic pressure in the hydraulic chamber H of the electric cylinder 12 may overshoot the target pressure value. If the hydraulic pressure in the hydraulic chamber H overshoots when the target pressure value is high, excessive load is applied to each component of the electric cylinder 12. Therefore, during the period when the advance control is being performed, the control unit 10 reduces the advance speed of the piston P for the period after the hydraulic pressure on the hydraulic chamber H side relative to the solenoid valve NC1 has increased to near the target pressure value.

[0021] FIG. 2 is a flowchart showing the flow of refill control in the electric braking device according to one embodiment of the present disclosure. In S100, the control unit 10 determines whether or not to start refill control. The conditions for starting refill control may be, for example, at least one of the following: the piston P has advanced beyond a predetermined position (i.e., the amount of fluid in the hydraulic chamber H has decreased); and the likelihood of increasing the pressure in the wheel cylinder WC is low. If the control unit 10 determines not to start refill control (S100: NO), it executes S100 again. If the control unit 10 determines to start refill control (S100: YES), it proceeds to the processing of S200.

[0022] In S200, the control unit 10 closes the solenoid valve NC1. Then, the process proceeds to S300. Note that the control unit 10 may store the detection value of the sensor SE1 before closing the solenoid valve NC1, and set this stored value as the target pressure value.

[0023] In the next step S300, the control unit 10 drives the motor M of the electric cylinder 12 to move the piston P backward by a predetermined backward amount. In the next S400, the control unit 10 determines whether to end the retraction of the piston P. When the piston P has reached a predetermined retraction amount, it determines that the retraction of the piston P has ended (S400: YES), and when the piston P has not reached the predetermined retraction amount (S400: NO), the process returns to S300.

[0024] In the next S500, the control unit 10 drives the motor M of the electric cylinder 12 to move the piston P forward at a predetermined speed, and then proceeds to the processing of S600. Note that the control unit 10 may wait for a predetermined period of time after the piston P has completed moving backward until the piston P starts moving forward.

[0025] In S600, the control unit 10 determines whether the pressure in the hydraulic pressure chamber H has reached a first threshold value. The control unit 10 determines whether the hydraulic pressure in the hydraulic pressure chamber H, estimated from the current flowing through the motor M, has reached the first threshold value. Here, the first threshold value is a predetermined value smaller than the target pressure value, and is a pressure value at which the pressure in the hydraulic pressure chamber H may exceed the target pressure value if the piston P is driven forward at the speed determined in S500 even after exceeding the first threshold value. The first threshold value corresponds to a value close to the target pressure value. If the control unit 10 determines that the pressure in the hydraulic pressure chamber H has reached the first threshold value (S600: YES), the control unit 10 proceeds to S700. If the control unit 10 determines that the pressure in the hydraulic pressure chamber H has not reached the first threshold value (S600: NO), the control unit 10 returns to S500. In S700, the control unit 10 reduces the forward speed of the piston P below the predetermined speed determined in S500. Here, the higher the target pressure value, the more the control unit 10 reduces the forward speed of the piston P. After the processing of S700 is completed, the process proceeds to S800.

[0026] In S800, the control unit 10 determines whether to terminate the forward movement of the piston P. For example, when the hydraulic pressure in the hydraulic pressure chamber H estimated from the current flowing through the motor M reaches a target pressure value, the control unit 10 determines to terminate the forward movement of the piston P (S800: YES), opens the solenoid valve NC1 (S900), and terminates the refill control. The target pressure value is, for example, the hydraulic pressure on the wheel cylinder WC side of the solenoid valve NC1 during the forward movement control (S500 to S800), i.e., the brake hydraulic pressure Pr2 acquired from the sensor SE1. Note that the target pressure value may be the hydraulic pressure in the hydraulic pressure chamber H immediately before the piston P is retracted in S300. Alternatively, the target pressure value may be a value at which the hydraulic pressure in the hydraulic pressure chamber H begins to rise after the piston P is advanced in S500, i.e., a value greater than atmospheric pressure by a predetermined value.

[0027] For example, when the hydraulic pressure in the hydraulic chamber H estimated from the current flowing through the motor M has not reached the target pressure value, the control unit 10 determines that the forward movement of the piston P should not be terminated (S800: NO) and executes S800 again.

[0028] [Modification] In the above embodiment, the forward speed of the piston P is set to be lower as the measurement result of the brake fluid pressure Pr2, which is the target pressure value, is higher, but the present invention is not limited to this. The forward speed of the piston P during forward control may be changed depending on the hydraulic pressure at another position as long as it is a target pressure value. For example, the forward speed of the piston P during forward control may be set lower as the hydraulic pressure Pr3 in the wheel cylinder WC increases.

[0029] In the above embodiment, the speed of the piston P is reduced when the pressure in the hydraulic chamber H reaches the first threshold value in S600, but this is not limiting. The speed of the piston P may be reduced in accordance with the target pressure value from the time when the piston P starts to move forward.

[0030] In the above embodiment, the speed of the piston P is reduced once at S700, but this is not limiting. For example, the speed of the piston P may be changed as appropriate depending on the detected hydraulic pressure on the wheel cylinder WC side relative to the solenoid valve NC1 during forward travel control.

[0031] In antilock brake control in a mode other than the pressure reduction mode, when brake fluid is drawn from the reservoir 11 to the hydraulic chamber H of the electric cylinder 12, the forward speed of the piston P may be slowed to suppress overshoot.

[0032] In the above embodiment, in S600 and S800, it is determined whether or not to terminate the forward movement of the piston P based on the brake fluid pressure estimated from the current flowing through the motor M. However, the criterion for determining whether or not to terminate the forward movement of the piston P is not limited to the brake fluid pressure estimated from the current flowing through the motor M. For example, the forward movement of the piston P may be terminated when the value of a pressure sensor provided on the electric cylinder 12 side of the solenoid valve NC1 becomes equal to or greater than a target pressure value.

[0033] 〔summary〕 According to one aspect of the present disclosure, an electric braking device adjusts hydraulic pressure in a wheel cylinder by discharging brake fluid from a hydraulic chamber defined by the cylinder and the piston to the outside of the hydraulic chamber or by drawing brake fluid from outside the hydraulic chamber into the hydraulic chamber when a piston in a cylinder advances or retreats based on the drive of an electric motor. The electric braking device includes a reservoir connected to the hydraulic chamber, and a switch for switching between blocking and opening the discharge brake fluid, which is the brake fluid discharged from the hydraulic chamber to the wheel cylinder side, and the suction brake fluid, which is the brake fluid drawn into the hydraulic chamber from the wheel cylinder side. and a suction control unit that uses the switching valve to block the discharge brake fluid and the suction brake fluid, uses the electric motor to move the piston backward to suck the brake fluid from the reservoir into the hydraulic chamber, and then performs forward control to move the piston forward until the hydraulic pressure in the hydraulic chamber reaches a target pressure value, and the suction control unit performs control to slow the forward speed of the piston in the forward control as the target pressure value increases, at least during the period during which the forward control is being performed, after the hydraulic pressure on the hydraulic chamber side relative to the switching valve has increased to near the target pressure value.

[0034] In suction control, with the selector valve blocking the discharge brake fluid and the suction brake fluid, the piston is retracted to draw brake fluid from the reservoir into the hydraulic chamber, and then the piston is advanced until the hydraulic pressure in the hydraulic chamber reaches a target pressure value. When advancing the piston, if the piston advances too quickly, the pressure on the hydraulic chamber side of the selector valve may exceed the target pressure value, potentially reducing the durability of the electric braking device. Therefore, by lowering the piston advance speed, at least near the target pressure value, the higher the target pressure value, the more effectively the pressure on the hydraulic chamber side of the selector valve can be prevented from overshooting, thereby preventing an excessive increase in pressure on the hydraulic chamber side of the selector valve. This improves the durability of the electric braking device.

[0035] [Additional Notes] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. [Explanation of symbols]

[0036] 1 Electric braking device 10 Control Unit 11 Reservoir 12 Electric cylinder C cylinder CV1, CV2 check valves H Hydraulic chamber M Electric Motor NC1, NC2, NO1 solenoid valves P piston R rotation angle sensor SE1 Sensor WC Wheel Cylinder

Claims

[Claim 1] An electric braking device that adjusts hydraulic pressure in a wheel cylinder by discharging brake fluid from a hydraulic pressure chamber defined by the cylinder and the piston to the outside of the hydraulic pressure chamber or by drawing brake fluid from the outside of the hydraulic pressure chamber into the hydraulic pressure chamber when a piston in a cylinder moves forward or backward based on the drive of an electric motor, a reservoir connected to the hydraulic chamber; a switching valve that switches between blocking and opening the discharge brake fluid, which is the brake fluid discharged from the hydraulic chamber to the wheel cylinder side, and the suction brake fluid, which is the brake fluid sucked into the hydraulic chamber from the wheel cylinder side; a suction control unit that blocks the discharge brake fluid and the suction brake fluid by the switching valve, moves the piston backward by the electric motor to suction the brake fluid from the reservoir into the hydraulic pressure chamber, and then performs forward control to move the piston forward until the hydraulic pressure in the hydraulic pressure chamber reaches a target pressure value, The suction control unit executes control to decrease the forward speed of the piston during the forward control as the target pressure value increases, at least during a period after the hydraulic pressure on the hydraulic pressure chamber side of the switching valve has increased to a value close to the target pressure value during the period during which the forward control is being performed.

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