Electric braking device

Abstract

An electric braking device (1) estimates the viscosity of a brake fluid on the basis of a first displacement amount of a piston (P) when the piston is retracted by an electric motor (M) from the point of time when the brake fluid is blocked by a switching valve (NC1) and the brake fluid in a reservoir (11) is suctioned into the hydraulic chamber (H), and a second displacement amount of the piston when the piston is advanced until it is determined that the pressure in the hydraulic chamber has returned to a pressure before the piston retraction after the completion of the piston retraction.

Description

electric braking device

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

[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, in which the piston of the electric cylinder returns to its starting position and sucks brake fluid back into the hydraulic chamber from the reservoir.

[0003] Patent No. 5800437

[0004] However, in the refill control, when the viscosity of the brake fluid is high, the suction speed of the brake fluid is slower than when the viscosity is low, and it may not be possible to suction a sufficient amount of brake fluid corresponding to the amount of return of the piston (retraction amount). One aspect of the present disclosure aims to be able to estimate the viscosity of the brake fluid in order to estimate the amount of suctioned brake fluid without any additional configuration.

[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.

[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.

[0007] 1 is a hydraulic circuit diagram for explaining an electric braking device according to an embodiment of the present disclosure; 2 is a map showing the relationship between the displacement difference |L1-L2| and the viscosity of the brake fluid in the electric braking device according to an embodiment of the present disclosure; 3 is a flowchart showing a flow of viscosity estimation in the electric braking device according to an embodiment of the present disclosure;

[0008] (Configuration of electric braking device) Fig. 1 is a diagram for explaining an electric braking device according to one 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. The wheels W are provided with calipers each 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 the 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 check valve CV1 restricts the flow of brake fluid from the electric cylinder 12 to the reservoir 11.

[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 brake fluid to flow from the electric cylinder 12 to the wheel cylinder WC. Meanwhile, the check valve CV2 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. By switching the second flow path F2 between the hydraulic chamber H of the electric cylinder 12 and the wheel cylinder WC between a closed 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 from the wheel cylinder side to the hydraulic chamber, are switched between being blocked and being opened. When the solenoid valve NO1 is closed, the second flow path F2 is blocked. When the solenoid valve NO1 and the solenoid valve NC1 are open, the second flow path F2 is connected. When the solenoid valve NO1 is open and the solenoid valve NC1 is closed, brake fluid does not flow from the wheel cylinder WC toward the electric cylinder 12.

[0013] The sensor SE1 is disposed between the solenoid valve NC1 and the solenoid valve NO1, and measures the brake fluid pressure in the flow path between the solenoid valve NC1 and the solenoid valve 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, which prevents the wheels W from locking during braking. The antilock brake control includes, for example, a pressure reduction mode in which the hydraulic pressure in the wheel cylinders WC is reduced by closing the solenoid valve No. 1 and opening the solenoid valve NC2, a pressure retention mode in which the hydraulic pressure in the wheel cylinders WC is maintained by closing the solenoid valves No. 1 and NC2, and a pressure increase mode in which the hydraulic pressure in the wheel cylinders WC is increased by opening the solenoid valve No. 1 and closing the solenoid valve NC2 and then operating 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] 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 retracts the piston P of the electric cylinder 12 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. When the control unit 10 determines that the hydraulic pressure in the hydraulic chamber H has returned to the value before the suction, the control unit 10 opens the solenoid valve NC1. For example, the control unit 10 may determine 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, the control unit 10 may determine 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 in the electric cylinder 12 flowing into the wheel cylinder WC through the check valve CV2 due to the advancement of the piston P. Alternatively, the control unit 10 may determine 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, located on the electric cylinder 12 side of the solenoid valve NC1.

[0020] (Position Acquisition Unit) 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 Unit) 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 viscosity from a map such as that shown in FIG. 2 that is stored in advance in memory. Note that in FIG. 2, for a given viscosity, the displacement difference |L1-L2| increases as the pressure before the piston starts to retract increases. 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 store the latest viscosity estimation result.

[0022] The first displacement amount L1 is the amount of displacement of the piston P from the time when the flow path between the hydraulic pressure chamber H of the electric cylinder 12 and the wheel cylinder WC is blocked until 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 amount of displacement of the piston P from the time when the piston P starts to move forward until the pressure in the hydraulic pressure chamber H returns to the pressure before the piston P retracted.

[0023] 3 is a flowchart showing the flow of brake fluid viscosity estimation in an electric braking system according to an embodiment of the present disclosure. In S100, the control unit 10 determines whether or not to start viscosity estimation. A condition for starting viscosity estimation may be, for example, a low probability of increasing the wheel cylinder WC pressure. 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 processing 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 the amount required to retract the piston P for viscosity estimation. If the retraction amount required for viscosity estimation has already been secured, it is preferable to proceed to the processing of S300 without executing S200. In S300, the control unit 10 closes the solenoid valve NC1. Thereafter, the processing proceeds to S400. The control unit 10 may store the detection value of the sensor SE1 before closing the solenoid valve NC1, and use the stored value as a determination condition for 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 following 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 is determined that the retraction of the piston P is to end (S500: YES), and the process proceeds to S600. When the piston P has not reached the predetermined amount determined in S400 (S500: NO), the process returns to S400. In the following S600, the control unit 10 acquires a first displacement amount L1 of the piston P. In the following S700, the control unit 10 drives the motor M of the electric cylinder 12 to advance the piston P, and the process proceeds to S800.

[0027] 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 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 H has returned to the pressure before the piston retracted. For example, the predetermined value is the brake fluid pressure (detected value of the sensor SE1) in the flow path between the solenoid valve NC1 and the check valve CV1 immediately before S300 is executed. Alternatively, the predetermined value may be the current brake fluid pressure in the flow path between the solenoid valve NC1 and the solenoid valve NO1. Next, in 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 terminates the viscosity estimation. The predetermined value in S900, i.e., the pressure at which it is determined that the pressure in the hydraulic chamber H 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 begun 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 hydraulic pressure estimated from the current flowing through the motor M has not reached the predetermined value, the control unit 10 determines that the advancement of the piston P has not ended (S800: NO) and returns to the processing of S700. Note that a process of opening the solenoid valve NC1 may be performed after S1000.

[0028] In the above embodiment, at 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] An electric braking device according to one aspect of the present disclosure is an electric braking device that 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 sucking brake fluid from outside the hydraulic chamber into the hydraulic chamber as a result of a piston in a cylinder being driven by an electric motor, and that 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 suction brake fluid, which is brake fluid sucked 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 piston displacement 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 then releasing the discharge brake fluid and the suction brake fluid using the switching valve, and the viscosity estimating 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 under conditions such as when the piston P is further advanced than 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 further advanced than the predetermined position, making 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 utilized 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.

Claims

1. In an electric braking device that adjusts the hydraulic pressure in a wheel cylinder by discharging the brake fluid in a hydraulic chamber partitioned by the cylinder and the piston to the outside of the hydraulic chamber or sucking the brake fluid outside the hydraulic chamber into the hydraulic chamber as the piston in the 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 releasing 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 from the wheel cylinder side into the hydraulic chamber; a position acquisition unit that acquires the position of the piston; a viscosity estimation 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 retracted by the electric motor to suck the brake fluid in the reservoir into the hydraulic chamber from the time of the blocking, and a second displacement amount, which is the displacement amount of the piston when the piston is advanced until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston retraction after the piston retraction is completed. An electric braking device comprising the above components.

2. The electric braking device according to claim 1, wherein the electric braking device is configured to perform suction control for sucking the brake fluid in the reservoir into the hydraulic chamber by blocking the discharge brake fluid and the suction brake fluid with the switching valve, retracting the piston with the electric motor, advancing the piston until it is determined that the pressure in the hydraulic chamber has returned to the pressure before the piston retraction, and then releasing the discharge brake fluid and the suction brake fluid with 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 acquired during the process of the suction control.

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