Braking device

Abstract

To improve the accuracy of adjusting the hydraulic pressure of the wheel cylinder. [Solution] The braking device comprises an electric cylinder 20 and a processing circuit 40. The hydraulic chamber 26 of the electric cylinder 20 is connected to the wheel cylinder 10 via an output port 28 that is always in communication with it, and is connected to the reservoir 32 via an input port 27 that is disconnected from the hydraulic chamber 26 when the piston 23 is positioned in the forward direction beyond a predetermined position in the cylinder 21, and is in communication with the hydraulic chamber 26 when the piston 23 is positioned in the backward direction beyond the predetermined position. When the hydraulic pressure of the wheel cylinder 10 is reduced, the processing circuit 40 moves the piston 23 in the backward direction beyond the predetermined position, and performs a discharge process by controlling the drive of the electric motor 24 to discharge brake fluid from the hydraulic chamber 26 to the reservoir 32 via the input port 27, while adjusting the opening ratio of the input port 27 to the hydraulic chamber 26.

Description

Technical Field

[0001] The present invention relates to a braking device.

Background Art

[0002] Patent Document 1 discloses a vehicular braking device that includes an electric cylinder in which a hydraulic chamber defined by a cylinder and a piston is formed inside the cylinder, and the piston is driven by an electric motor. An input port and an output port are formed in the cylinder of the electric cylinder. The hydraulic chamber is configured to be isolated from the reservoir when the piston is positioned further forward than the input port, and to be connected to the reservoir via the input port when the piston is positioned further rearward than the input port. The electric cylinder is configured to supply brake fluid in the hydraulic chamber to a wheel cylinder via the output port as the piston moves forward to reduce the volume of the hydraulic chamber.

[0003] Further, in the conventional braking device described above, when there is no braking request, the piston is normally positioned at a standby position on the forward side relative to the input port. As a result, the hydraulic chamber and the reservoir are isolated, so that outflow of brake fluid from the reservoir when a brake pipe ruptures is suppressed. On the other hand, even in a state where there is no braking request, if a specific state such as expansion of the brake fluid occurs, the piston is retracted from the standby position to bring the hydraulic chamber into communication with the reservoir.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0005] In the conventional braking system described above, brake drag is suppressed by opening the input port and returning the brake fluid to the reservoir when the brake fluid expands. However, there is still room for improvement in the method of connecting the hydraulic chamber and the reservoir when the piston of the electric cylinder is retracted. [Means for solving the problem]

[0006] A braking device that solves the above problems includes: a reservoir for storing brake fluid supplied to a wheel cylinder; an electric cylinder configured such that when the piston is driven by an electric motor, the piston moves forward in the cylinder, causing the brake fluid in the hydraulic chamber partitioned by the inner wall of the cylinder and the piston to be discharged into a fluid passage connected to the wheel cylinder via an output port opening in the cylinder, and when the piston is retracted beyond a predetermined position within the piston's range of motion, the reservoir and the hydraulic chamber are in communication via an input port opening in the cylinder, and when the piston is forward beyond the predetermined position within the range of motion, the communication between the reservoir and the hydraulic chamber via the input port is blocked by the piston; and a processing circuit that performs a discharge process by controlling the drive of the electric motor to discharge the brake fluid from the hydraulic chamber to the reservoir via the input port, while adjusting the opening ratio of the input port to the hydraulic chamber, when the hydraulic pressure of the wheel cylinder is reduced. [Effects of the Invention]

[0007] The above braking system has the effect of improving the precision of adjusting the hydraulic pressure of the wheel cylinders. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the configuration of the first embodiment of the braking device. [Figure 2]In the braking system shown in Figure 1, Figure 2(A) is a graph showing the relationship between the piston position of the electric cylinder and the braking pressure, and Figure 2(B) is a graph showing the relationship between the piston position of the electric cylinder and the opening rate of the input port. [Figure 3] Figure 3 is a flowchart of the processes performed by the processing circuit for discharge treatment in the braking device shown in Figure 1. [Figure 4] Figure 4(A) is a time chart showing the change in piston position, Figure 4(B) shows the change in the input port opening rate, and Figure 4(C) shows the change in braking pressure before and after the discharge treatment is performed in the braking device shown in Figure 1. [Figure 5] Figure 5(A) is a time chart showing the change in piston position, Figure 5(B) shows the change in the opening rate of the input port, and Figure 5(C) shows the change in braking pressure before and after the discharge treatment in the second embodiment of the braking device. [Modes for carrying out the invention]

[0009] (First Embodiment) The first embodiment of the braking device will be described in detail below with reference to Figures 1 to 4. <Regarding the configuration of the braking system> First, the configuration of the braking device of this embodiment will be described with reference to Figure 1. The braking device of this embodiment is mounted on a vehicle. The braking device of this embodiment comprises a wheel cylinder 10, a reservoir 32 for storing brake fluid supplied to the wheel cylinder 10, an electric cylinder 20, and a processing circuit 40.

[0010] The wheel cylinder 10, together with the friction material 11 and the rotating body 12, constitutes a friction brake that generates frictional braking force at the wheel. The friction brake generates frictional braking force at the wheel by pressing the friction material 11 against the rotating body 12, which rotates integrally with the wheel, in response to the supply of hydraulic pressure to the wheel cylinder 10. The force with which the friction material 11 presses against the rotating body 12 increases as the hydraulic pressure inside the wheel cylinder 10 increases. Therefore, the higher the hydraulic pressure inside the wheel cylinder 10, the greater the frictional braking force generated at the wheel. In the following explanation, the hydraulic pressure inside the wheel cylinder 10 will be referred to as the braking pressure Pwc. Furthermore, in the following explanation, the braking pressure Pwc will be expressed as gauge pressure, i.e., the differential pressure from atmospheric pressure. Although Figure 1 depicts a disc-type friction brake as the friction brake on which the wheel cylinder 10 is installed, other types of friction brakes, such as drum-type brakes, may also be used.

[0011] The electric cylinder 20 comprises a cylinder body 22 having a cylinder 21, a piston 23, an electric motor 24, and a conversion mechanism 25. The piston 23 is slidably mounted inside the cylinder 21. Inside the cylinder 21, a hydraulic chamber 26 is partitioned by the inner wall of the cylinder 21 and the piston 23. The volume of the hydraulic chamber 26 changes depending on the position of the piston 23 inside the cylinder 21. The conversion mechanism 25 converts the rotation of the output shaft of the electric motor 24 into the linear movement of the piston 23. As a result, the position of the piston 23 inside the cylinder 21 can be changed by the electric motor 24. In the following description, the direction of linear movement of the piston 23 inside the cylinder 21 when reducing the volume of the hydraulic chamber 26 will be described as the forward direction FD. The direction opposite to the forward direction FD will be described as the backward direction RD. The backward direction RD is the direction of linear movement of the piston 23 inside the cylinder 21 when increasing the volume of the hydraulic chamber 26. In the following explanation, linear movement of piston 23 in the forward direction FD will be referred to as "piston 23 forward," and linear movement of piston 23 in the reverse direction RD will be referred to as "piston 23 backward."

[0012] The cylinder body 22 has two ports, an input port 27 and an output port 28, which connect the hydraulic chamber 26 to the outside. The input port 27 is connected to the reservoir 32 via a second fluid passage 31. The output port 28 is connected to the wheel cylinder 10 via a first fluid passage 33. The output port 28 is always in communication with the hydraulic chamber 26, regardless of the position of the piston 23 within the cylinder 21. Therefore, the hydraulic chamber 26 of the electric cylinder 20 is always in communication with the wheel cylinder 10. In contrast, the input port 27 switches between being open to the hydraulic chamber 26 and being closed to the hydraulic chamber 26 by the piston 23, depending on the position of the piston 23 within the cylinder 21. Specifically, the piston 23 is provided with a communication hole 29 that connects the outer peripheral wall that slides against the cylinder 21 and the inner peripheral wall that constitutes the wall surface of the hydraulic chamber 26. A primary cup 35 for sealing is provided on the inner circumferential wall of the cylinder 21 in the portion forward FD of the input port 27. When a portion of the opening of the communication hole 29 is located backward RD of the primary cup 35, the input port 27 and the hydraulic chamber 26 communicate through the communication hole 29. In this case, the input port 27 is open to the hydraulic chamber 26. On the other hand, when the entire opening of the communication hole 29 is located forward FD of the primary cup 35, the communication between the input port 27 and the hydraulic chamber 26 is blocked by the piston 23. In this case, the input port 27 is closed to the hydraulic chamber 26. When the input port 27 is open, the hydraulic chamber 26 communicates with the reservoir 32 via the second fluid passage 31. When the input port 27 is closed, the hydraulic chamber 26 is isolated from the reservoir 32.

[0013] The processing circuit 40 includes a CPU 41 and a memory 42. The memory 42 stores a control program executed by the CPU 41 and control data referenced during the execution of the control program. The processing circuit 40 controls the operation of the electric cylinder 20 by having the CPU 41 execute the control program. A braking pressure sensor 43 and a brake sensor 45 are connected to the processing circuit 40. The braking pressure sensor 43 is a sensor that detects the hydraulic pressure inside the wheel cylinder 10, i.e., the braking pressure Pwc. The brake sensor 45 is a sensor that detects the amount of operation of the braking operating member 46 by the driver of the vehicle. An example of the braking operating member 46 is the brake pedal. The drive circuit 44 for the electric motor 24 drives the electric motor 24 in response to a command from the processing circuit 40. The drive circuit 44 has a function to detect the motor rotation angle, which is the rotation angle of the output shaft of the electric motor 24. The drive circuit 44 then transmits the motor rotation angle detection result to the processing circuit 40.

[0014] In the electric cylinder 20, a stopper (not shown) determines the furthest retracted position, which is the end of the retraction direction RD of the piston 23's range of motion. The piston position Z, described later, represents the motor rotation angle required for the piston 23 to move forward from the furthest retracted position to that position. The processing circuit 40 calculates the piston position Z based on the detected motor rotation angle.

[0015] <Regarding the operation of the electric cylinder 20> Next, the operation of the electric cylinder 20 will be explained with reference to Figure 2. Figure 2(A) shows the relationship between the piston position Z and the braking pressure Pwc when the braking pressure Pwc is increased, as shown by a solid line. Figure 2(B) shows the relationship between the piston position Z and the opening ratio θ of the input port 27. As shown in Figure 1, strictly speaking, the area sealed by the primary cup 35 and the piston 23 and the end of the opening of the input port 27 are separated in the axial direction of the piston 23. Therefore, the reservoir 32 and the hydraulic chamber 26 communicate through the communication hole 29 via the gap between the inner circumference of the cylinder 21 and the outer circumference of the piston 23. However, since the gap between the inner circumference of the cylinder 21 and the outer circumference of the piston 23 is minute, the flow rate of brake fluid flowing through this gap is minute. Therefore, in terms of the piston position Z and the opening ratio θ of the input port 27, the area sealed by the primary cup 35 and the piston 23 and the end of the opening of the input port 27 (the end on the right side of the page in Figure 1) can be considered to be at the same position in the axial direction of the piston 23. Therefore, in this embodiment, the opening ratio θ is the ratio of the area of ​​the opening of the input port 27 relative to the cylinder 21 that does not overlap with the outer peripheral wall of the piston 23. When the opening ratio θ is 0%, the input port 27 is closed to the hydraulic chamber 26. When the opening ratio θ is not 0%, at least a part of the input port 27 is open to the hydraulic chamber 26. And when the opening ratio θ is 100%, the entire input port 27 is open to the hydraulic chamber 26.

[0016] When the piston position Z is 0, that is, when the piston 23 is in its fully retracted position, the opening ratio θ of the input port 27 is 100%. At this time, the hydraulic chamber 26 is in communication with the reservoir 32 via the input port 27 and the second fluid passage 31. On the other hand, the wheel cylinder 10 is always in communication with the hydraulic chamber 26 via the first fluid passage 33 and the output port 28. At this time, the wheel cylinder 10 is in communication with the reservoir 32. Therefore, when the opening ratio θ is maintained at 100%, the hydraulic pressure of the wheel cylinder 10, i.e., the braking pressure Pwc, is "0", which is equal to atmospheric pressure in absolute pressure.

[0017] When the piston 23 is advanced from its most retracted position, the opening ratio θ of the input port 27 is maintained at 100% until the position "Z1" in the figure is reached. In the following description, the position "Z1" is referred to as the fully open position. When the piston 23 is further advanced from the fully open position Z1, the opening ratio θ of the input port 27 gradually decreases. Then, when the position "Z2" in the figure is reached, the opening ratio θ of the input port 27 becomes 0%, and the input port 27 is in a state of being closed relative to the hydraulic chamber 26. In the following description, the position "Z2" in the figure is referred to as the refill start position.

[0018] When the piston 23 is further advanced from the refill start position Z2, the brake fluid in the hydraulic chamber 26 is discharged to the first fluid passage 33 via the output port 28. When the piston 23 advances to the position "Z4" in the figure, the hydraulic pressure of the wheel cylinder 10, that is, the braking pressure Pwc, starts to rise. As a result, the friction material 11 is pressed against the rotating body 12, and a friction braking force is generated at the wheel. In the following description, "Z4" is referred to as the zero point position.

[0019] When the piston 23 is advanced in the range of the forward direction FD beyond the zero point position Z4, brake fluid is discharged from the hydraulic chamber 26 to the first fluid passage 33 via the output port 28, so the braking pressure Pwc increases. When the piston 23 is retracted in the range of the forward direction FD beyond the zero point position Z4, brake fluid is drawn from the first fluid passage 33 into the hydraulic chamber 26 via the output port 28, so the braking pressure Pwc decreases.

[0020] Here, consider a situation where the temperature of the brake fluid is kept constant and there is no leakage of brake fluid due to breakage of the first fluid passage 33 or the like. The braking pressure Pwc in this case is uniquely determined by the piston position Z in the range of the forward direction FD beyond the zero point position Z4. The memory 42 of the processing circuit 40 stores the correspondence relationship between the piston position Z and the braking pressure Pwc obtained in advance through actual measurement, calculation, or the like. In the case of the present embodiment, the correspondence relationship between the piston position Z and the braking pressure Pwc stored in the memory 42 corresponds to the reference relationship.

[0021] <Regarding Normal Braking Pressure Control> Next, the normal braking pressure control performed by the processing circuit 40 will be described. Based on the detection results of the amount of operation of the braking operating member 46 by the brake sensor 45, the processing circuit 40 calculates the target braking pressure, which is the target value of the braking pressure Pwc. When the target braking pressure is "0", that is, when there is no braking request, the processing circuit 40 controls the drive of the electric motor 24 to keep the piston 23 stationary at a predetermined standby position Z3. The standby position Z3 is set to a piston position Z that is FD in the forward direction from the refill start position Z2 and RD in the reverse direction from the zero point position Z4.

[0022] When the target braking pressure is greater than 0, i.e., during a braking request, the processing circuit 40 calculates the piston position Z at which the braking pressure Pwc is equal to the target braking pressure, based on the correspondence between the piston position Z and the braking pressure Pwc stored in the memory 42. Furthermore, the processing circuit 40 compares the calculated position with the current piston position Z and calculates the rotation direction and rotation angle of the electric motor 24 required to move the piston 23 to the target piston position. Then, the processing circuit 40 commands the electric motor 24 to perform rotational drive according to the calculation result.

[0023] As described above, in normal braking pressure control, the processing circuit 40 controls the drive of the electric motor 24 to move the piston 23 within the range of forward direction FD from the refill start position Z2, thereby adjusting the braking pressure Pwc, which is the hydraulic pressure of the wheel cylinder 10. Specifically, the processing circuit 40 increases the braking pressure Pwc by moving the piston 23 forward within the above range, and decreases the braking pressure Pwc by moving the piston 23 backward within the above range.

[0024] <Regarding refill processing> However, the relationship between the piston position Z and the braking pressure Pwc may change due to wear of the friction material 11 or thermal expansion of the brake fluid. In the normal braking pressure control described above, the braking pressure Pwc is controlled based on the relationship between the braking pressure Pwc and the piston position Z stored in the memory 42. Therefore, if the relationship between the braking pressure Pwc and the piston position Z deviates from the relationship stored in the memory 42, the braking pressure Pwc cannot be controlled accurately. The processing circuit 40 performs a refill process to correct the deviation in the relationship between the piston position Z and the braking pressure Pwc.

[0025] Another example of a change in the relationship between piston position Z and braking pressure Pwc is when brake fluid is unintentionally drawn from reservoir 32 into hydraulic chamber 26 when the piston 23 of electric cylinder 20 is retracted. Yet another example is a system in which a master cylinder operated by the driver's pedal operation is connected to electric cylinder 20 via a solenoid valve, in which case the operation of the master cylinder is sudden and the solenoid valve does not close in time, causing brake fluid to unintentionally flow from the master cylinder to electric cylinder 20.

[0026] During the refill process, when there is no braking request, the processing circuit 40 drives the electric cylinder 20 to move the piston 23 from the standby position Z3 to a position RD further back than the refill start position Z2. As a result, the hydraulic chamber 26 communicates with the reservoir 32 via the input port 27 and the second fluid passage 31. Consequently, any excess brake fluid is returned to the reservoir 32, or any insufficient brake fluid is replenished from the reservoir 32, thereby correcting any discrepancy in the correspondence between the piston position Z and the braking pressure Pwc. After a predetermined time has elapsed, the processing circuit 40 drives the electric motor 24 to return the piston 23 to the standby position Z3, thus ending the refill process. The processing circuit 40 performs the refill process, for example, when it starts up, or when a discrepancy in the above correspondence is detected from the braking pressure Pwc detection results.

[0027] <Regarding waste disposal> Furthermore, the processing circuit 40 performs discharge processing as part of the processing related to brake pressure control when braking is requested. Discharge processing is performed when reducing the brake pressure Pwc in brake pressure control when braking is requested.

[0028] Figure 3 shows a flowchart of the process performed by the processing circuit 40 for discharge treatment. During braking pressure control, the processing circuit 40 repeatedly executes the process shown in Figure 3 at predetermined control cycles while commanding the electric motor 24 to retract the piston 23 in order to reduce the braking pressure Pwc. The "S" preceding the symbols in the figure represents a step.

[0029] When the process shown in Figure 3 is started, the processing circuit 40 first acquires the current braking pressure Pwc and piston position Z in step 100. Next, in step 102, the processing circuit 40 calculates the piston position Z corresponding to the current braking pressure Pwc in the correspondence stored in memory 42 as the assumed piston position Ze. Then, in the following step 104, the processing circuit 40 subtracts the current piston position Z from the assumed piston position Ze and calculates the value of the relationship deviation ΔZ as the value of the subtracted value.

[0030] In the next step 106, the processing circuit 40 calculates a second threshold X2 based on the relationship deviation amount ΔZ. The processing circuit 40 calculates a larger value for the second threshold X2 as the relationship deviation amount ΔZ is larger. In this embodiment, the processing circuit 40 calculates a value for the second threshold X2 that is greater than the value obtained by subtracting the refill start position Z2 from the zero point position Z4.

[0031] Next, in step 108, the processing circuit 40 determines whether the relationship deviation amount ΔZ is greater than or equal to the first threshold X1. The first threshold X1 is set to a predetermined positive value. If the processing circuit 40 determines that the relationship deviation amount ΔZ is greater than or equal to the first threshold X1 (YES), it proceeds to step 110. If it determines that it is less than the first threshold X1 (NO), it terminates the processing shown in Figure 3 for the current control cycle.

[0032] If the process proceeds to step 110, the processing circuit 40 subtracts the refill start position Z2 from the current piston position Z and determines whether the subtracted value is less than or equal to the second threshold X2. The value obtained by subtracting the refill start position Z2 from the current piston position Z represents the distance from the refill start position Z2 to the current piston position Z. If the processing circuit 40 determines that the value is less than or equal to the second threshold X2 (YES), it proceeds to step 112. If it determines that the value exceeds the second threshold X2 (NO), it terminates the process shown in Figure 3 for the current control cycle.

[0033] If the process proceeds to step 112, the processing circuit 40 calculates the target opening rate θt based on the relationship deviation amount ΔZ in step 112. The processing circuit 40 calculates the target opening rate θt as a value that is larger as the relationship deviation amount ΔZ is larger, within the range of values ​​greater than 0% and less than 100%. The target opening rate θt represents the target value of the opening rate θ of the input port 27 to be achieved in the discharge process.

[0034] Next, in step 114, the processing circuit 40 commands the electric motor 24 to move the piston 23 to a position where the opening rate θ of the input port 27 is set to the target opening rate θt. Then, the processing circuit 40 completes the process shown in Figure 3 for this control cycle.

[0035] <Operation and Effects of the First Embodiment> If an opportunity to perform refilling is not available, or if the correspondence between the brake fluid and piston position Z cannot be optimized during refilling, the normal brake pressure control described above may be performed with a discrepancy in the correspondence between the brake pressure Pwc and piston position Z. Furthermore, during the execution of the normal brake pressure control described above, a discrepancy in the correspondence may also occur due to thermal expansion of the brake fluid due to a rise in temperature.

[0036] Here, we consider the case where the correspondence between the braking pressure Pwc and the piston position Z changes from the relationship shown by the solid line in Figure 2(A) to the relationship shown by the dashed line. In this case, the change in the correspondence is a change toward the side where the braking pressure Pwc is higher when the piston position Z is the same. When such a change in the correspondence occurs, even if the piston 23 is retracted to the standby position Z3 after the braking pressure Pwc is generated, the braking pressure Pwc does not decrease to 0. Therefore, residual pressure is generated in the wheel cylinder 10 after the braking request is released, which may cause brake drag. In the braking device of this embodiment, the processing circuit 40 performs discharge processing when reducing the braking pressure Pwc when braking pressure control is performed with the above-mentioned deviation in the correspondence occurring.

[0037] Figure 4 shows an example of the control behavior before and after the discharge process in the braking device of this embodiment. Figure 4(A) shows the change in piston position Z, Figure 4(B) shows the change in the opening ratio θ of the input port 27, and Figure 4(C) shows the change in braking pressure Pwc. Figure 4 also shows the control behavior in the process of reducing the braking pressure Pwc when braking pressure control is performed in response to a braking request while a corresponding relationship deviation of a magnitude such that the relationship deviation amount ΔZ is greater than or equal to the first threshold X1 occurs.

[0038] Figure 4(A) shows the progression of piston position Z when normal braking pressure control is performed without discharge processing, indicated by a dashed line. Figure 4(C) also shows the progression of braking pressure Pwc when normal braking pressure control is performed without discharge processing, indicated by a dashed line. In normal braking pressure control, the processing circuit 40 reduces the braking pressure Pwc to 0 by retracting the piston 23 to the standby position Z3. However, in this case, due to a discrepancy in the correspondence between braking pressure Pwc and piston position Z, the piston position Z reaches the standby position Z3 at time t4, and the braking pressure Pwc does not decrease to 0.

[0039] In contrast, in this embodiment, at time t1, when the piston 23 retracts to a position where the distance to the refill start position Z2 is less than or equal to the second threshold X2, the processing circuit 40 starts the discharge process. When the discharge process starts, the processing circuit 40 starts moving the piston 23 to a position Zt in the retraction direction RD from the refill start position Z2. Position Zt is the piston position Z at which the opening rate θ of the input port 27 is equal to the target opening rate θt calculated by the processing circuit 40 based on the misalignment amount ΔZ. At the time t2 thereafter, when the piston 23 reaches position Zt, the processing circuit 40 fixes the piston position Z so that the opening rate θ of the input port 27 is maintained at the target opening rate θt. As a result, the input port 27 is in communication with the hydraulic chamber 26, and the brake fluid in the hydraulic chamber 26 is discharged to the second fluid passage 31 via the input port 27. The amount of brake fluid present in the hydraulic chamber 26, the first fluid passage 33, and the wheel cylinder 10 decreases by the amount that has been discharged. Therefore, even if the piston position Z is fixed after time t2, the braking pressure Pwc gradually decreases. Then, at the subsequent time t3, the braking pressure Pwc decreases to 0.

[0040] The processing circuit 40 terminates the discharge process when a predetermined time has elapsed since the start of the discharge process, or when it confirms that the braking pressure Pwc has dropped to 0. After terminating the discharge process, the processing circuit 40 controls the drive of the electric motor 24 to advance the piston 23 to the standby position Z3.

[0041] Furthermore, the processing circuit 40 diagnoses whether there is any fluid leakage due to a rupture in the first fluid passage 33, etc., based on the detection results of the brake pressure sensor 43, etc. If the discharge process is performed when fluid leakage occurs, the brake fluid in the reservoir 32 will leak to the outside. For this reason, if the processing circuit 40 diagnoses that fluid leakage has occurred, it prohibits the execution of the discharge process.

[0042] In the discharge process, when the piston 23 is moved to a position where the opening ratio θ of the input port 27 is 100%, the braking pressure Pwc decreases rapidly, and the frictional braking force generated by the wheels decreases sharply, which may cause the driver to feel discomfort. In contrast, in this embodiment, the processing circuit 40 controls the rate at which the braking pressure Pwc decreases by adjusting the opening ratio θ of the input port 27 during the discharge process. Therefore, even if there is a discrepancy in the correspondence between the braking pressure Pwc and the piston position Z, it is possible to reduce the braking pressure Pwc at an appropriate rate.

[0043] (1) In the braking device of this embodiment, when the braking pressure Pwc, which is the hydraulic pressure of the wheel cylinder 10, is reduced, the processing circuit 40 moves the piston 23 in the backward direction RD from the refill start position Z2, and while adjusting the opening ratio θ of the input port 27 with respect to the hydraulic chamber 26, it drives and controls the electric motor 24 to discharge brake fluid from the hydraulic chamber 26 to the second fluid passage 31 via the input port 27. As a result, even if there is a discrepancy in the correspondence between the braking pressure Pwc and the piston position Z, it is possible to reduce the braking pressure Pwc at an appropriate speed, and thus the hydraulic pressure of the wheel cylinder 10 can be adjusted with precision.

[0044] (2) If the discharge process is performed when the relationship deviation amount ΔZ is not very large, the braking pressure Pwc may drop to 0 too early. In contrast, in this embodiment, the processing circuit 40 performs the discharge process on the condition that the relationship deviation amount ΔZ is greater than or equal to the first threshold X1. Therefore, in normal braking pressure control, the discharge process can be performed only when the deviation of the above correspondence is greater than a certain amount.

[0045] (3) If the discharge process is started when the distance from the refill start position Z2 to the current piston position Z is greater than a certain threshold, the braking pressure Pwc will drop sharply after the discharge process starts because the braking pressure Pwc is high before the process begins. Also, if the discharge process is started when the distance from the refill start position Z2 to the current piston position Z is smaller than a certain threshold, the timing at which the braking pressure Pwc drops to 0 may be delayed too long. In contrast to this, in this embodiment, the processing circuit 40 starts the discharge process when it confirms that the distance from the refill start position Z2 to the current piston position Z is less than or equal to the second threshold X2. Therefore, the discharge process can be started at an appropriate time.

[0046] (4) When the relationship deviation ΔZ is large, even if the flow rate of brake fluid discharged from the hydraulic chamber 26 to the first fluid passage 33 via the input port 27 during the discharge process is the same, the time required for the braking pressure Pwc to decrease will be longer. In contrast, in this embodiment, the processing circuit 40 calculates the target opening rate θt, which is the target value of the opening rate θ of the input port 27 realized in the discharge process, so that the larger the relationship deviation ΔZ, the larger the target opening rate θt becomes. Therefore, it is possible to suppress the increase in the time required for the braking pressure Pwc to decrease when the relationship deviation ΔZ is large.

[0047] (5) In this embodiment, the processing circuit 40 calculates a second threshold X2 such that the value increases as the relative deviation ΔZ increases. As a result, the larger the relative deviation ΔZ, the more the piston position Z at which the discharge process begins will be at the forward position FD. Therefore, this also helps to suppress the increase in the time required for the braking pressure Pwc to decrease when the relative deviation ΔZ is large.

[0048] (6) If the braking pressure Pwc does not decrease to 0 even after the braking request is released, that is, if residual pressure remains in the wheel cylinder 10, brake drag will occur. In contrast, in this embodiment, the processing circuit 40 sets the value of the second threshold X2 to a value greater than the value obtained by subtracting the refill start position Z2 from the zero point position Z4. As a result, the discharge process is started earlier than when the piston 23 retracts to the zero point position Z4. Since the reduction of the braking pressure Pwc to eliminate residual pressure can be started during the braking request, the occurrence of brake drag can be effectively suppressed.

[0049] (Second Embodiment) Next, a second embodiment of the braking device will be described with reference to Figure 5. The braking device of this embodiment is configured to perform discharge processing in a manner different from that of the first embodiment. In the following description, the differences from the first embodiment will be mainly described, and the same reference numerals will be used for components identical to those in the first embodiment to avoid redundant explanations.

[0050] Figure 5 shows an example of the control mode during the switching process performed by the processing circuit 40 in the braking device of this embodiment. Figure 5(A) shows the change in piston position Z during the switching process, Figure 5(B) shows the change in the opening ratio θ of the input port 27 during the switching process, and Figure 5(C) shows the change in braking pressure Pwc during the switching process.

[0051] In the braking device of this embodiment, the processing circuit 40 controls the drive of the electric motor 24 so that, during discharge processing, the input port 27 alternates between a closed state in which it is isolated from the hydraulic chamber 26 and an open state in which it is in communication with the hydraulic chamber 26. Specifically, as shown in Figure 5(A), the processing circuit 40 alternately switches between the closed state and the open state by repeatedly moving the piston 23 forward from the fully open position Z1 to the refill start position Z2 and moving the piston 23 backward from the refill start position Z2 to the fully open position Z1. The processing circuit 40 also includes a period during which the piston 23 is stopped at the refill start position Z2 and a period during which the piston 23 is stopped at the fully open position Z1.

[0052] In this embodiment, during the discharge process, the input port 27 is kept intermittently open to the hydraulic chamber 26. During the period when the input port 27 is open to the hydraulic chamber 26, the brake fluid in the hydraulic chamber 26 is discharged to the second fluid passage 31 via the input port 27, causing the braking pressure Pwc to decrease. On the other hand, during the period when the input port 27 is closed to the hydraulic chamber 26, the discharge of brake fluid from the hydraulic chamber 26 to the second fluid passage 31 is stopped, causing the decrease in braking pressure Pwc to stagnate. Therefore, the braking pressure Pwc during the discharge process decreases in the manner shown in Figure 5(C).

[0053] Here, the ratio of the period during which the input port 27 is open to the hydraulic chamber 26 during discharge processing is denoted as the opening ratio ω. The opening ratio ω can be calculated, for example, as the ratio of period T to period L shown in Figure 5(B). Period L is the period from when the piston 23 retracts from the refill start position Z2 to the fully open position Z1 until the next similar retraction of the piston 23 occurs. Period T is the period during which the state in which the piston 23 is located in the retraction direction RD from the refill start position Z2 is maintained, that is, the period during which the state in which the input port 27 is open to the hydraulic chamber 26 is maintained.

[0054] The average rate of decrease in braking pressure Pwc during discharge processing increases as the opening ratio ω of the input port 27 to the hydraulic chamber 26 increases. The processing circuit 40 controls the rate of decrease while reducing the braking pressure Pwc during discharge processing by adjusting the opening ratio ω of the input port 27 to the hydraulic chamber 26 and discharging the brake fluid in the hydraulic chamber 26 to the second fluid passage 31 via the input port 27. In this embodiment, the processing circuit 40 calculates the target opening ratio ωt of the input port 27 to the hydraulic chamber 26 during discharge processing based on the relationship deviation amount ΔZ, such that the value increases as the relationship deviation amount ΔZ increases. The processing circuit 40 then controls the drive of the electric motor 24 so that the switching between the open and closed states of the input port 27 to the hydraulic chamber 26 is performed at an opening ratio ω corresponding to the target opening ratio ωt.

[0055] The opening rate ω during discharge processing can be adjusted, for example, by fixing the period during which the input port 27 is kept in an open state while changing the period during which the input port 27 is kept in a closed state, or by fixing the period during which the input port 27 is kept in a closed state while changing the period during which the input port 27 is kept in an open state. The opening rate ω during discharge processing can also be adjusted by changing both the period during which the open state is maintained and the period during which the closed state is maintained. Furthermore, the opening rate ω during discharge processing can also be adjusted by fixing the sum of the periods during which the open state is maintained and the closed state is maintained, and changing the ratio of the periods during which the open state is maintained and the closed state is maintained within that sum.

[0056] The braking device of this embodiment can also achieve the same effects as those described in (1) to (6) above. (Other embodiments) The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0057] In the second embodiment, when controlling the drive of the electric motor 24 for the repeated forward and backward movement of the piston 23 during the discharge process, the piston 23 may be advanced to a position FD in the forward direction from the refill start position Z2. Alternatively, the piston 23 may be retracted to a position other than the fully closed position Z1, as long as it is at a position RD in the backward direction from the refill start position Z2. In short, as long as it is possible to alternately switch between the open state and the closed state of the input port 27 to the hydraulic chamber 26, the content of the drive control of the electric motor 24 during the discharge process may be changed as appropriate.

[0058] ·Instead of the relationship deviation amount ΔZ in the above embodiment, the discharge process may be performed using the relationship deviation amount ΔP calculated in the following manner. Based on the correspondence relationship stored in memory 42, the value of the braking pressure Pwc corresponding to the current piston position Z in that correspondence relationship is calculated as the assumed braking pressure Pe. The assumed braking pressure Pe is subtracted from the current braking pressure Pwc, and the subtracted value is calculated as the value of the relationship deviation amount ΔP. The relationship deviation amount ΔP calculated in this way is also a value that corresponds to the magnitude of the deviation in the correspondence relationship between the braking pressure Pwc and the piston position Z toward the side where the braking pressure Pwc is higher at the same piston position Z. That is, at least one of the following two amounts can be used as the relationship deviation amount. One is the amount of deviation of the actual hydraulic pressure of the wheel cylinder 10 toward the side where the hydraulic pressure is higher relative to the hydraulic pressure of the wheel cylinder 10 determined from the reference relationship. The other is the amount of deviation of the actual position of the piston 23 toward the backward direction RD relative to the position of the piston 23 determined from the reference relationship. The reference relationship here represents the correspondence between the hydraulic pressure of the wheel cylinder 10 and the position of the piston 23, which serves as the reference.

[0059] The target release ratios θt and ωt in the discharge process may be calculated based on the brake fluid temperature. The brake fluid temperature can be obtained, for example, by directly detecting it using a temperature sensor or by estimating it based on the operating status of the braking system. When the brake fluid temperature is high, the amount of thermal expansion of the brake fluid increases, and the discrepancy in the correspondence between the braking pressure Pwc and the piston position Z also increases. Therefore, regarding the relationship between brake fluid temperature and thermal expansion, it is desirable to set larger values ​​for the target release ratios θt and ωt as the brake fluid temperature increases. On the other hand, when the brake fluid temperature is low, the viscosity of the brake fluid increases. Even if the release ratios θ and ω are the same, the flow rate of brake fluid discharged from the hydraulic chamber 26 to the first fluid passage 33 via the input port 27 during the discharge process is less when the viscosity of the brake fluid is high than when it is low. Therefore, regarding the relationship between brake fluid temperature and viscosity, it is desirable to set larger values ​​for the target release ratios θt and ωt as the brake fluid temperature decreases. Therefore, when calculating the target release ratios θt and ωt based on the brake fluid temperature, it is desirable to adopt a calculation method that takes into account the relationship between the brake fluid temperature, thermal expansion, and viscosity.

[0060] • In the discharge process, the second threshold X2 may be calculated based on the temperature of the brake fluid. In this case, considering that the amount of thermal expansion of the brake fluid increases as the temperature rises, and the relationship deviations ΔZ and ΔP increase, the second threshold X2 should be calculated so that it becomes a larger value as the temperature of the brake fluid rises.

[0061] When the relative displacement amounts ΔZ and ΔP are large, the decrease in braking pressure Pwc during discharge processing is large, so it is desirable to start discharge processing earlier than when the relative displacement amounts ΔZ and ΔP are small. On the other hand, when performing discharge processing, the processing circuit 40 retracts the piston 23 to the position RD in the reverse direction from the refill start position Z2, opens the input port 27 to the hydraulic chamber 26, and then adjusts the opening ratio θ and ω. If the motor rotation speed when retracting the piston 23 to the position RD in the reverse direction from the refill start position Z2 after the start of such discharge processing is increased, the timing at which the decrease in braking pressure Pwc begins during discharge processing can be advanced. For this reason, it is good to increase the motor rotation speed when retracting the piston 23 after the start of discharge processing as the relative displacement amounts ΔZ and ΔP are larger. Also, as mentioned above, the relative displacement amounts ΔZ and ΔP are large when the brake fluid temperature is high. For this reason, it is also good to increase the motor rotation speed when retracting the piston 23 after the start of discharge processing as the brake fluid temperature is higher.

[0062] The calculation of the second threshold X2 based on the relationship deviation ΔZ, ΔP during discharge processing, or the brake fluid temperature, may be omitted. For example, the discharge processing may be carried out by omitting the process in step 106 of Figure 3. In this case, a fixed value may be set for the second threshold X2.

[0063] The calculation of the relationship deviation ΔZ, ΔP during discharge processing, or the target release ratio θt, ωt based on the brake fluid temperature, may be omitted. For example, the discharge processing may be carried out in a manner that omits the process in step 112 of Figure 3. In this case, fixed values ​​may be set for the target release ratio θt, ωt.

[0064] In the above embodiment, the discharge process was performed on the condition that the relationship deviation amounts ΔZ and ΔP were greater than or equal to a first threshold X1. The conditions for performing such a discharge process may be changed as appropriate. For example, the discharge process may be performed on the condition that the temperature of the brake fluid is above a predetermined value.

[0065] In the above embodiment, the discharge process was initiated when the distance from the refill start position Z2 to the current piston position Z became less than or equal to the second threshold X2. These conditions for initiating the discharge process may be changed as appropriate.

[0066] In the above embodiment, the rate at which the braking pressure Pwc decreases during discharge processing was controlled by adjusting the opening ratios θ and ω of the input port 27 relative to the hydraulic chamber 26. The opening ratio θ is defined as the ratio of the area of ​​the portion of the opening of the input port 27 relative to the cylinder 21 that does not overlap with the outer circumference of the piston 23. The opening ratio ω is defined as the ratio of the time during which the input port 27 is open relative to the hydraulic chamber 26 during discharge processing. In the present invention, the opening ratio of the input port 27 relative to the hydraulic chamber 26 is defined as follows: Here, the ratio of the area of ​​the portion of the opening of the input port 27 relative to the cylinder 21 that does not overlap with the outer wall of the piston 23 at a certain point during discharge processing is defined as the instantaneous opening ratio of the input port 27 relative to the hydraulic chamber 26. The opening ratio of the input port 27 relative to the hydraulic chamber 26 during discharge processing is the time integrated value of the instantaneous opening ratio over a predetermined period during discharge processing, or a value proportional to that time integrated value.

[0067] · Following the above definition, the adjustment of the opening ratio of the input port 27 to the hydraulic chamber 26 during discharge processing can also be performed in the following manner. Similar to the second embodiment, the drive control of the electric motor 24 is performed to repeatedly move the piston 23 forward and backward so that the closed state and the open state of the input port 27 to the hydraulic chamber 26 alternately switch. The holding time of the closed state and the holding time of the open state are fixed values. In this case as well, the average rate of decrease of the braking pressure Pwc during discharge processing can be changed by changing the opening ratio θ, which is defined as the ratio of the above area, while the open state is being held. Therefore, discharge processing can also be performed by adjusting the opening ratio in this manner.

[0068] The discharge process may be terminated when the relationship deviation Δ falls below a predetermined threshold. For example, the discharge process may be terminated when the difference between the braking pressure Pwc and atmospheric pressure falls below a predetermined threshold during the discharge process.

[0069] • The discharge process may be terminated if the braking pressure Pwc becomes lower than the target braking pressure during the discharge process. The processing circuit 40 may be configured as a circuit including one or more processors that operate according to a computer program, one or more dedicated hardware circuits such as dedicated hardware that performs at least some of the various processes, or a combination thereof. Examples of dedicated hardware include application-specific integrated circuits (ASICs). The processor includes a CPU and memory such as RAM and ROM, where the memory stores program code or instructions configured to cause the CPU to perform the processes. The memory, i.e., storage medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. [Explanation of Symbols]

[0070] 10 Wheel Cylinder 20 Electric Cylinder 21 Cylinders 23 pistons 24 Electric motors 26. Hydraulic chamber 27 Input Ports 28 output ports 31 2nd liquid path 32 Reservoirs 33 1st liquid path 40 Processing Circuits

Claims

1. A reservoir that stores the brake fluid supplied to the wheel cylinder, An electric cylinder is configured such that, when an electric motor drives a piston forward within the cylinder, the brake fluid in the hydraulic chamber partitioned by the inner wall of the cylinder and the piston is discharged into a fluid passage connected to the wheel cylinder via an output port opening into the cylinder, and when the piston is retracted beyond a predetermined position within the piston's range of motion, the reservoir and the hydraulic chamber are in communication via an input port opening into the cylinder, and when the piston is advanced beyond the predetermined position within the range of motion, the communication between the reservoir and the hydraulic chamber via the input port is blocked by the piston. A processing circuit that performs a discharge process, which, when reducing the hydraulic pressure of the wheel cylinder, retracts the piston beyond the predetermined position and controls the drive of the electric motor to discharge the brake fluid from the hydraulic chamber to the reservoir via the input port, while adjusting the opening ratio of the input port to the hydraulic chamber. A braking system equipped with [a specific feature].

2. The braking device according to claim 1, wherein the opening ratio is the ratio of the area of ​​the portion of the opening of the input port relative to the cylinder that does not overlap with the outer circumference of the piston.

3. The processing circuit drives the electric motor to repeatedly move the piston forward and backward so that, during the discharge process, the input port is closed to the hydraulic chamber and the input port is open to the hydraulic chamber alternately. The opening ratio is the ratio of the duration of the open state to the sum of the duration of the closed state and the duration of the open state. The braking device according to claim 1.

4. The braking device according to claim 1, wherein the processing circuit performs the discharge process on the condition that at least one of the following is greater than or equal to a first threshold: the amount of deviation of the wheel cylinder's hydraulic pressure, determined from a reference relationship which is the relationship between the hydraulic pressure of the wheel cylinder and the position of the piston, and the actual hydraulic pressure of the wheel cylinder, toward the side where the hydraulic pressure of the wheel cylinder is higher; and the amount of deviation of the piston's position, determined from the reference relationship, and the actual position of the piston, toward the side where the piston is retracted.

5. The braking device according to claim 1, wherein the processing circuit starts the discharge process when the distance from the predetermined position to the position of the piston becomes less than or equal to a second threshold.

6. The braking device according to claim 5, wherein the second threshold value is set to a value that is larger the greater at least one of the following: the amount of deviation toward the side where the hydraulic pressure of the wheel cylinder is higher between the hydraulic pressure of the wheel cylinder determined from a reference relationship which is the relationship between the hydraulic pressure of the wheel cylinder and the position of the piston and the actual hydraulic pressure of the wheel cylinder, and the amount of deviation toward the side where the piston is retracted between the position of the piston determined from the reference relationship and the actual position of the piston.

7. The braking device according to claim 1, wherein, in the discharge process, the processing circuit controls the drive of the electric motor to increase the greater the amount of deviation of the wheel cylinder's hydraulic pressure, determined from a reference relationship which is the relationship between the hydraulic pressure of the wheel cylinder and the position of the piston, and the actual hydraulic pressure of the wheel cylinder toward the side where the hydraulic pressure of the wheel cylinder is higher, and the amount of deviation of the piston, determined from the reference relationship which is the position of the piston, and the actual position of the piston toward the side where the piston is retracted.

8. The braking device according to claim 1, wherein the processing circuit controls the drive of the electric motor by changing the opening ratio based on the temperature of the brake fluid.

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