Electric braking device

Abstract

To estimate a viscosity of a brake fluid without an additional configuration as compared to the prior art.SOLUTION: An electric braking device (1) estimates a viscosity of a brake fluid on the basis of: a first displacement amount of a piston (P) when the piston (P) is retreated by an electric motor (M) from a time point of blocking the brake fluid by a switching valve (NC1), and the brake fluid in a reservoir (11) is sucked into a hydraulic chamber (H); and a second displacement amount of the piston when the piston is advanced after completion of retreat of the piston until it is determined that a pressure in the hydraulic chamber has returned to a pressure before the retreat of the piston.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 will be slower than if 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 moved back (retraction amount). One aspect of the present disclosure aims to make it possible to estimate the viscosity of brake fluid without any additional configuration in order to estimate the amount of sucked brake fluid. [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 sucking brake fluid from the outside of the hydraulic chamber into the hydraulic chamber as a piston in a cylinder advances or retreats based on the drive of an electric motor, the electric braking device comprising: a reservoir connected to the hydraulic chamber; a discharge brake fluid that is the brake fluid discharged from the hydraulic chamber to the wheel cylinder side; and a suction brake fluid that is the brake fluid sucked from the wheel cylinder side to the hydraulic chamber. The device is equipped with a switching valve that switches between blocking and opening the rake fluid, a position acquisition unit that acquires the position of the piston, and a viscosity estimation unit that estimates the viscosity of the brake fluid based on a first displacement amount that is the displacement amount of the piston when the discharge brake fluid and the suction brake fluid are blocked by the switching valve and the piston is moved backward by the electric motor from the point of blocking to suck the brake fluid in the reservoir into the hydraulic chamber, and a second displacement amount that is the displacement amount of the piston when the piston is moved forward from the completion of backward movement until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston was moved backward. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, the viscosity of brake fluid can be estimated without any additional configuration, as compared to the related art. [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] 10 is a map showing the relationship between the displacement difference |L1-L2| and the viscosity of the brake fluid in an electric braking device according to an embodiment of the present disclosure. [Figure 3]4 is a flowchart illustrating a flow of viscosity estimation 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] The solenoid valve NC1 is an example of a switching valve, and switches between a blocked state and a connected state of the second flow path F2 between the hydraulic chamber H of the electric cylinder 12 and the wheel cylinder WC, thereby 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 sucked into the hydraulic chamber from the wheel cylinder side. 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] (Position acquisition part) The control unit 10 acquires the position of the piston P of the electric cylinder 12 based on the detection result of the rotation angle sensor R.

[0021] (Viscosity estimation part) The control unit 10 functions as a viscosity estimation unit that estimates the viscosity of the brake fluid. When functioning as the viscosity estimation unit, the control unit 10 acquires a first displacement amount L1 and a second displacement amount L2 (details of which will be described later) and estimates the viscosity of the brake fluid based on the displacement difference |L1-L2| between the first displacement amount L1 and the second displacement amount L2. The control unit 10 estimates the viscosity by, for example, multiplying the difference between the displacement difference |L1-L2| at the reference viscosity and the displacement difference |L1-L2| at the current viscosity by a predetermined gain. Note that the displacement difference |L1-L2| at the reference viscosity also changes with respect to the target pressure (pressure before the piston starts to retract). Therefore, it is preferable to read the value from a map such as that shown in FIG. 2, which is stored in advance in memory. Note that in FIG. 2, for the same viscosity, the displacement difference |L1-L2| increases as the pressure before the piston starts to retract. This is because, when the first displacement amount L1 is constant, the lower the pressure before the start of backward movement, the lower the target pressure when the piston P advances, and the shorter the stroke L2 when the piston P advances. By estimating the viscosity here, the control unit 10 can hold the latest viscosity estimation result.

[0022] The first displacement amount L1 is the amount of displacement of the piston P during the time from when the flow path between the hydraulic chamber H of the electric cylinder 12 and the wheel cylinder WC is blocked to when the piston P is retracted to a predetermined position. For example, the predetermined position is determined depending on the accuracy required for viscosity estimation. The second displacement amount L2 is the displacement amount of the piston P from when the piston P starts to move forward until the pressure in the hydraulic chamber H returns to the pressure before the piston P moved backward.

[0023] FIG. 3 is a flowchart showing a flow of estimating the viscosity of the brake fluid 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 viscosity estimation. The condition for starting viscosity estimation may be, for example, that the probability of increasing the wheel cylinder WC pressure is low. If the control unit 10 determines not to start viscosity estimation (S100: NO), it executes S100 again. If the control unit 10 determines to start viscosity estimation (S100: YES), it proceeds to the process of S200.

[0024] In S200, the control unit 10 advances the piston P of the electric cylinder 12 by a predetermined amount, and then proceeds to the processing of S300. The predetermined amount in S200 is an amount necessary to ensure that the piston P is retracted for viscosity estimation. Note that if the retraction amount necessary for viscosity estimation has already been ensured, it is preferable to skip S200 and proceed to the processing of S300. In S300, the control unit 10 closes the solenoid valve NC1. Then, the process proceeds to S400. 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 S800, which will be described later.

[0025] In the next step S400, the control unit 10 drives the motor M of the electric cylinder 12 to move the piston P back by a predetermined amount. The predetermined amount is determined depending on the accuracy required for viscosity estimation. The predetermined amount in step S400 may be the same as the amount of piston P moving back in the refill control described above.

[0026] In the next S500, the control unit 10 determines whether or not to end the retraction of the piston P. When the piston P reaches the predetermined amount determined in S400, it determines that the retraction of the piston P is to end (S500: YES), and proceeds to the processing of S600. When the piston P has not reached the predetermined amount determined in S400 (S500: NO), the processing returns to the processing of S400. In the next step S600, the control unit 10 acquires the first displacement amount L1 of the piston P. In the next step S700, the control unit 10 drives the motor M of the electric cylinder 12 to move the piston P forward, and then the process proceeds to step S800.

[0027] In S800, the control unit 10 determines whether or not 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 predetermined value, the control unit 10 determines to terminate the forward movement of the piston P (S800: YES) and acquires a second displacement amount L2 of the piston P (S900). The predetermined value in S800 is a pressure at which it can be determined that the pressure in the hydraulic pressure chamber has returned to the pressure before the piston retracted, and is, for example, the brake hydraulic pressure (detection value of the sensor SE1) in the flow path between the solenoid valve NC1 and the check valve CV1 immediately before S300 is performed. Alternatively, the predetermined value may be the current brake hydraulic pressure in the flow path between the solenoid valve NC1 and the solenoid valve NO1. In the next step S1000, the control unit 10 estimates the viscosity of the brake fluid based on the first displacement amount L1 acquired in S600 and the second displacement amount L2 acquired in S900, and then ends the viscosity estimation. Note that the predetermined value in S900, i.e., the pressure at which it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston retracted, may be a pressure value at which it is determined that the pressure in the hydraulic chamber H has started to rise. In this case, it is preferable to estimate the viscosity after correcting the displacement difference |L1-L2| at the current viscosity. For example, when the brake fluid pressure estimated from the current flowing through the motor M has not reached a predetermined value, the control unit 10 determines not to end the forward movement of the piston P (S800: NO) and returns to the processing of S700. Note that a process of opening the solenoid valve NC1 may be provided after S1000.

[0028] [Modification] In the above embodiment, in S800, it is determined whether 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 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.

[0029] 〔summary〕 According to one aspect of the present disclosure, an electric braking device 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 the hydraulic chamber into the hydraulic chamber when a piston in the 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 cut-off valve for blocking discharge brake fluid, which is brake fluid discharged from the hydraulic chamber to the wheel cylinder side, and a cut-off valve for blocking brake fluid intake, which is brake fluid drawn from the wheel cylinder side to the hydraulic chamber. a position acquisition unit that acquires the position of the piston; and a viscosity estimation unit that estimates the viscosity of the brake fluid based on a first displacement amount that is the displacement amount of the piston when the discharge brake fluid and the suction brake fluid are blocked by the switch valve and the piston is moved backward by the electric motor from the point of blocking to suck the brake fluid in the reservoir into the hydraulic chamber, and a second displacement amount that is the displacement amount of the piston when the piston is moved forward from the completion of the backward movement until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston was moved backward.

[0030] According to the above embodiment, the viscosity estimation unit shuts off the discharge brake fluid and the suction brake fluid using the switching valve before the piston retracts, and then retracts the piston to draw brake fluid from the reservoir into the hydraulic chamber. Here, even if the first displacement amount, which is the amount of retraction of the piston, is the same, the amount of brake fluid drawn from the reservoir into the hydraulic chamber varies depending on the viscosity of the brake fluid. As a result, the second displacement amount, which is the amount of displacement of the piston when the piston is advanced from the completion of retraction until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston retracted, varies depending on the viscosity of the brake fluid, even if the first displacement amount is the same. Therefore, by measuring the first and second displacement amounts, the viscosity of the brake fluid can be estimated using a position acquisition unit included in a typical braking device.

[0031] In one aspect of the electric braking device of the present disclosure, the electric braking device is configured to perform suction control to suck the brake fluid in the reservoir into the hydraulic chamber by blocking the discharge brake fluid and the suction brake fluid using the switching valve, then retracting the piston using the electric motor, and then advancing the piston until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston retracted, and releasing the discharge brake fluid and the suction brake fluid using the switching valve, and the viscosity estimation unit estimates the viscosity of the brake fluid based on the first displacement amount and the second displacement amount obtained during the suction control processing.

[0032] The viscosity estimation shown in FIG. 3 is preferably performed during the refill control described above. During refill control, the piston P of the electric cylinder 12 cannot be advanced to send brake fluid to the wheel cylinder WC, i.e., braking force cannot be increased. Therefore, refill control is not performed unless necessary. Therefore, refill control is performed when the piston P is advanced beyond a predetermined position, which indicates a high possibility of bottoming. Therefore, if the viscosity estimation of the present disclosure is performed during refill control, the piston P is advanced beyond the predetermined position, making the process of S200 in FIG. 3 unnecessary. In addition, in refill control, the solenoid valve NC1 is closed, the piston is retracted, and then the piston is advanced until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston retracted. Therefore, viscosity estimation and the operation of the electric cylinder are common. Furthermore, in refill control, the amount of brake fluid that can be sucked varies depending on the viscosity of the brake fluid. Therefore, since the viscosity estimated in the present disclosure can be used in refill control, the present disclosure and refill control are highly compatible technologies.

[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 CV1, CV2 check valves H Hydraulic chamber L1 First displacement L2 Second displacement M Electric Motor NC1, NC2, NO1 solenoid valves P piston SE1 Sensor WC Wheel Cylinder

Claims

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 position acquisition unit that acquires a position of the piston; a viscosity estimating unit that estimates the viscosity of the brake fluid based on a first displacement amount, which is the displacement amount of the piston when the discharge brake fluid and the suction brake fluid are blocked by the switching valve and the piston is moved backward by the electric motor from the point of blocking to suck the brake fluid in the reservoir into the hydraulic chamber, and a second displacement amount, which is the displacement amount of the piston when the piston is moved forward from the completion of backward movement until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston was moved backward; An electric braking device comprising:

2. the electric braking device is configured to perform suction control to suck the brake fluid in the reservoir into the hydraulic chamber by blocking the discharge brake fluid and the suction brake fluid with the selector valve, retracting the piston with the electric motor, and then advancing the piston until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston retracted, and releasing the discharge brake fluid and the suction brake fluid with the selector valve; The viscosity estimation unit estimates the viscosity of the brake fluid based on the first displacement amount and the second displacement amount acquired during the suction control process. The electric braking device according to claim 1 .

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