Electric braking device

Abstract

To provide an electric braking device in which refill control can be efficiently executed.SOLUTION: An electric braking device (1) includes: a reservoir (11) connected to a hydraulic chamber (H) of an electric cylinder (12); and a suction control part for executing suction control in which a piston (P) is retreated by an electric motor (M), and a brake fluid is thereby sucked from the reservoir (11) into the hydraulic chamber (H), and for changing a retreat speed or a retreat amount of the piston (P) according to a viscosity of the brake fluid in the suction control.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] However, in refill control, if the viscosity of the brake fluid is high, the suction speed of the brake fluid is reduced compared to when the viscosity is low, and it may not be possible to suction a sufficient amount of brake fluid according to the amount the piston is returned (retraction amount), which is inefficient. An object of one aspect of the present disclosure is to provide an electric braking device that can execute refill control more efficiently than conventional devices. [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 partitioned by the cylinder and the piston out of the hydraulic chamber or sucking brake fluid from outside the hydraulic chamber into the hydraulic chamber as a piston in a cylinder moves forward or backward based on the drive of an electric motor, and is equipped with a reservoir connected to the hydraulic chamber, and a suction control unit that performs suction control to suck brake fluid from the reservoir into the hydraulic chamber as the electric motor moves the piston backward, and that changes the backward speed or the amount of backward movement of the piston in the suction control depending on the viscosity of the brake fluid. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, refill control can be performed more efficiently than conventionally. [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. On the other hand, 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.

[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 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 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 and the viscosity of the brake fluid.

[0019] After the brake fluid is drawn into the hydraulic chamber H of the electric cylinder 12, the control unit 10 advances the piston P of the electric cylinder 12, and when it determines that the hydraulic pressure in the hydraulic chamber H has returned to the value before the suction, it opens the solenoid valve NC1. For example, it may be determined that the hydraulic pressure in the hydraulic chamber H has returned to the value before the suction 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, it may be determined that the hydraulic pressure in the hydraulic chamber H has returned to the value before the suction based on the increase in the detection value of the sensor SE1 caused by the brake fluid on the electric cylinder 12 side flowing into the wheel cylinder WC through the check valve CV2 due to the advancement of the piston P. Alternatively, it may be determined that the hydraulic pressure in the hydraulic chamber H has returned to the value before the suction based on the detection value of a pressure sensor, not shown, provided on the electric cylinder 12 side of the solenoid valve NC1.

[0020] The time from when the piston P is retracted to start sucking brake fluid until the piston P starts moving forward (hereinafter referred to as the refill time) has an upper limit from the viewpoint of stability of vehicle behavior. If the viscosity of the brake fluid is high, it may not be possible to suck a sufficient amount of brake fluid from the reservoir 11 into the hydraulic chamber H of the electric cylinder 12 within the refill time in relation to the amount of retraction of the piston P.

[0021] The actual amount of brake fluid actually drawn during the refill time is set to X1, and the target amount of brake fluid to be drawn in accordance with the amount of retraction of the piston P when there is no upper limit to the refill time is set to X2. In this case, the amount of retraction of the piston P that corresponds to the difference X2-X1 between the target amount X2 and the actual amount X1 does not contribute to an increase in the amount of brake fluid in the hydraulic chamber H.

[0022] Furthermore, even if a sufficient amount of brake fluid cannot be sucked in within the refill time, after the refill time, the piston P will be advanced to eliminate the gas area that has been created in the hydraulic chamber H by the retreat of the piston P. The larger the difference X2-X1 between the target amount X2 and the actual amount X1, the longer the time required for operations that do not contribute to the suction of brake fluid, such as creating a gas area by the retreat of the piston P and eliminating the gas area by the advance of the piston P.

[0023] Therefore, the control unit 10 changes the amount of retraction of the piston P depending on the viscosity of the brake fluid. For example, the control unit 10 changes the amount of retraction of the piston P depending on the viscosity of the brake fluid so that the target amount X2 approaches the actual amount X1. Specifically, it is preferable to reduce the amount of retraction of the piston P as the viscosity of the brake fluid increases.

[0024] 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.

[0025] 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 use it as a determination condition in S700, which will be described later.

[0026] In the next step S300, the control unit 10 calculates the amount of retraction of the piston P based on the viscosity of the brake fluid. The viscosity of the brake fluid varies depending on the type and temperature of the brake fluid. Therefore, the control unit 10 may measure the temperature of the brake fluid using the sensor SE1 or a temperature sensor (not shown) provided in the first flow path F1 and estimate the viscosity of the brake fluid. The control unit 10 may also estimate the viscosity based on the actual values of the amount of retraction and amount of advancement of the piston P during refill control.

[0027] In the next step S400, the control unit 10 drives the motor M of the electric cylinder 12 to move the piston P backward by the amount determined in S400. In the next step S500, the control unit 10 determines whether or not to end the backward movement of the piston P. When the piston P has reached the amount of backward movement determined in S400, the control unit 10 determines that the backward movement of the piston P should be ended (S500: YES). When the piston P has not reached the amount of backward movement determined in S400 (S500: NO), the process returns to S400. In the next step S600, the control unit 10 drives the motor M of the electric cylinder 12 to move the piston P forward, and then proceeds to the process of S700. Note that the control unit 10 may wait for a predetermined period of time after the backward movement of the piston P is completed before starting to move the piston P forward.

[0028] In S700, the control unit 10 determines whether to terminate the forward movement of the piston P. For example, when the hydraulic pressure in the hydraulic chamber H estimated from the current flowing through the motor M reaches a predetermined value, the control unit 10 determines to terminate the forward movement of the piston P (S700: YES), opens the solenoid valve NC1 (S800), and terminates the refill control. The predetermined value is, for example, the brake hydraulic pressure in the flow path between the solenoid valve NC1 and the check valve CV1 immediately before the piston P is retracted in S400. The predetermined value may also be the current brake hydraulic pressure in the flow path between the solenoid valve NC1 and the solenoid valve NO1, or a pressure value at which it can be determined that the pressure in the hydraulic chamber H has begun to rise. When the hydraulic pressure estimated from the current flowing through the motor M has not reached the predetermined value, the control unit 10 determines not to terminate the forward movement of the piston P (S700: NO), and returns to the processing of S600.

[0029] [Modification] In the above embodiment, the control unit 10 changes the amount of retraction of the piston P in the refill control in accordance with the viscosity of the brake fluid. However, in the refill control, the parameter that the control unit 10 changes in accordance with the viscosity of the brake fluid is not limited to only the amount of retraction of the piston P. For example, the control unit 10 may change the retraction speed of the piston P in accordance with the viscosity of the brake fluid. Specifically, the higher the viscosity of the brake fluid, the slower the retraction speed of the piston P is preferably. Changing the retraction speed of the piston P within the refill time can also change the amount of retraction of the piston P within the refill time, thereby achieving the same effects as those of the above embodiment. Furthermore, if the viscosity of the brake fluid is high and the retraction speed of the piston P is fast, air bubbles may form in the brake fluid. When the viscosity of the brake fluid is high, the generation of air bubbles can be suppressed by slowing down the retraction speed of the piston P. This can suppress wear on parts and the generation of abnormal noise caused by the bursting of air bubbles generated in the brake fluid.

[0030] In the above embodiment, at S700, 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 reaches or exceeds a predetermined value.

[0031] 〔summary〕 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 partitioned by the cylinder and the piston out of the hydraulic chamber or by sucking brake fluid from outside the hydraulic chamber into the hydraulic chamber as a piston in a cylinder moves forward or backward based on the drive of an electric motor, and is equipped with a reservoir connected to the hydraulic chamber, and a suction control unit that performs suction control to suck brake fluid from the reservoir into the hydraulic chamber as the electric motor moves the piston backward, and that changes the backward speed or the amount of backward movement of the piston in the suction control depending on the viscosity of the brake fluid.

[0032] According to the above embodiment, the piston P can be retracted by an amount that matches the amount of brake fluid that can be sucked within the refill time, and the driving force that contributes little to the suction of brake fluid can be reduced during the retraction of the piston P and the advancement of the piston P after the retraction, thereby enabling efficient refill control. This increases the amount of brake fluid that can be sucked relative to the input energy required to execute the suction control.

[0033] [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]

[0034] 1 Electric braking device 10 Control Unit 11 Reservoir 12 Electric cylinder C cylinder H Hydraulic chamber M Electric Motor P piston 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 suction control unit that performs suction control in which the electric motor retracts the piston to draw brake fluid from the reservoir into the hydraulic chamber, and that changes a retraction speed or a retraction amount of the piston in accordance with the viscosity of the brake fluid during the suction control; An electric braking device comprising:

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