Brake equipment

Abstract

To provide brake equipment capable of inhibiting foreign matter, which exists within a reservoir, from flowing out toward the side of a supply liquid passage after the completion of ABS control.SOLUTION: Brake equipment 40 comprises a first control part 51 that executes limit processing for making a decrease rate of supply pressure lower than a rate corresponding to a decrease rate of a required brake force, when the required brake force is decreased after the completion of ABS control.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] By-wire braking systems have been known for some time. For example, a braking system described in Patent Document 1 includes a wheel cylinder that generates a braking force corresponding to the hydraulic pressure of brake fluid on a wheel, and an upstream unit and a downstream unit that adjust the hydraulic pressure of the wheel cylinder. The downstream unit includes a plurality of solenoid valves, a pump, and a reservoir.

[0003] When a braking request is made to the vehicle, the upstream unit supplies brake fluid to the wheel cylinder via the downstream unit. In this way, the upstream unit generates braking force at the wheel according to the braking request. If deceleration slip occurs at the wheel while the vehicle is braking, the downstream unit initiates ABS control to eliminate the deceleration slip. Specifically, during ABS control, the downstream unit adjusts the braking force generated at the wheel by controlling multiple solenoid valves and pumps. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-154482 Summary of the Invention [Problem to be solved by the invention]

[0005] During ABS control, brake fluid discharged from the wheel cylinder when the hydraulic pressure in the wheel cylinder is reduced flows into the reservoir. Therefore, if brake fluid remains in the reservoir when ABS control ends, the brake fluid in the reservoir must be returned to the upstream unit after the control ends. However, minute foreign matter may be present in the reservoir. In this case, when the brake fluid in the reservoir is returned to the upstream unit after ABS control ends, it is preferable that the foreign matter does not flow out of the reservoir along with the brake fluid. [Means for solving the problem]

[0006] A braking device that solves the above problem includes a first braking unit that adjusts the supply pressure, which is the hydraulic pressure of brake fluid supplied to a wheel cylinder, based on the output of an electric motor; a second braking unit that is arranged between the first braking unit and the wheel cylinder and is configured to be able to adjust the WC pressure, which is the hydraulic pressure of the wheel cylinder, when brake fluid is supplied from the first braking unit to the wheel cylinder; a first control unit that controls the first braking unit to increase the supply pressure to increase the amount of brake fluid in the wheel cylinder when a required braking force increases, and to decrease the supply pressure to decrease the amount of brake fluid in the wheel cylinder when the required braking force decreases; and a second control unit that controls the second braking unit to perform ABS control to suppress deceleration slippage by adjusting the WC pressure when deceleration slippage occurs in a wheel, wherein the second braking unit has a supply fluid path that connects the first braking unit and the wheel cylinder, and a second control unit that controls the supply fluid path that connects the first braking unit and the wheel cylinder, and adjusts the WC pressure to increase the amount of brake fluid in the wheel cylinder when a required braking force decreases. The brake fluid supply system includes an adjustment unit provided in a fluid path that adjusts the amount of brake fluid supplied to the wheel cylinder and the amount of brake fluid discharged from the wheel cylinder by operation of the adjustment unit, a reservoir that stores brake fluid discharged from the wheel cylinder by operation of the adjustment unit, a discharge fluid path that connects the adjustment unit to the reservoir, a first return fluid path that connects the discharge fluid path to the supply fluid path, a pump provided in the first return fluid path that discharges brake fluid toward the supply fluid path, a second return fluid path that connects the reservoir to a portion of the supply fluid path between the first braking unit and the adjustment unit, and a valve mechanism provided in the second return fluid path that creates a flow of brake fluid from the reservoir to the supply fluid path when the fluid pressure on the reservoir side is higher than the fluid pressure on the supply fluid path side, and the second control unit stops driving the pump when the ABS control ends, and the first control unit performs a limiting process to slow down the rate of reduction of the supply pressure below a rate corresponding to the rate of reduction of the required braking force when the required braking force is reduced after the ABS control ends. [Effects of the Invention]

[0007] The braking device can suppress foreign matter present in the reservoir from flowing out toward the supply fluid path after the ABS control ends. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a braking device. [Figure 2] FIG. 2 is a flowchart illustrating the flow of processing performed by the first control unit of the braking device. [Figure 3] 3(a) to 3(d) are timing charts illustrating the operation of the braking device. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of the braking device will now be described. <Configuration of this embodiment> 1, a vehicle 10 includes a plurality of wheels 20, a plurality of wheel cylinders 30, and a braking device 40. The plurality of wheels 20 includes a right front wheel 21, a left front wheel 22, a right rear wheel 23, and a left rear wheel 24.

[0010] <Wheel cylinder> The multiple wheel cylinders 30 include a wheel cylinder 31 corresponding to the right front wheel 21, a wheel cylinder 32 corresponding to the left front wheel 22, a wheel cylinder 33 corresponding to the right rear wheel 23, and a wheel cylinder 34 corresponding to the left front wheel 22. The wheel cylinders 30 generate braking force on the wheels 20 according to the hydraulic pressure of the supplied brake fluid. In the following description, the hydraulic pressure of the wheel cylinders 30 will also be referred to as "WC pressure."

[0011] <Brake device> The braking device 40 includes a first braking unit 100, a second braking unit 200, a first control unit 51, and a second control unit 52.

[0012] <First braking unit> The first braking unit 100 adjusts the supply pressure Ps, which is the hydraulic pressure of the brake fluid supplied to the wheel cylinder 30. The first braking unit 100 includes an electric cylinder 110, a first supply fluid passage 121, a hydraulic pressure sensor 122, a brake operating member 131, and a brake sensor 132.

[0013] The electric cylinder 110 is a device that generates a supply pressure Ps electrically. The electric cylinder 110 includes a cylinder body 111, a piston 112, an electric motor 113, and a linear motion conversion mechanism 114.

[0014] The cylinder body 111 is cylindrical. The cylinder body 111 houses a piston 112. The cylinder body 111 and the piston 112 form a hydraulic chamber 115 filled with brake fluid. The piston 112 is slidable along the inner wall surface of the cylinder body 111. The linear motion conversion mechanism 114 converts the rotational motion of the output shaft of the electric motor 113 into linear motion of the piston 112. The piston 112 moves in the forward direction X1 or the backward direction X2 based on the power transmitted from the electric motor 113. The volume of the hydraulic chamber 115 decreases as the piston 112 moves in the forward direction X1, and increases as the piston 112 moves in the backward direction X2.

[0015] The first supply fluid path 121 connects the hydraulic chamber 115 of the first brake unit 100 and the second brake unit 200. The first supply fluid path 121 constitutes a part of the "supply fluid path." The hydraulic pressure sensor 122 is provided in the first supply fluid path 121. The hydraulic pressure sensor 122 detects the hydraulic pressure of the brake fluid in the first supply fluid path 121. The hydraulic pressure sensor 122 outputs a signal corresponding to the detected value to the first control unit 51.

[0016] The brake operating member 131 is, for example, a brake pedal. The brake operating member 131 is operated by the driver when the driver requests braking of the vehicle 10. The brake sensor 132 is a sensor that detects the operation amount or operation force of the brake operating member 131. The brake sensor 132 outputs a signal corresponding to the detected value to the first control unit 51.

[0017] <Second braking unit> The second brake unit 200 includes a front wheel pressure regulating mechanism 201, a rear wheel pressure regulating mechanism 202, a second supply fluid passage 230, and a pump motor 241.

[0018] The second brake unit 200 individually adjusts the WC pressure of the plurality of wheel cylinders 30 via a second supply fluid path 230. The second supply fluid path 230 includes a second supply fluid path 231 connecting the first supply fluid path 121 and the wheel cylinders 31, 32 of the front wheels 21, 22, and a second supply fluid path 232 connecting the first supply fluid path 121 and the wheel cylinders 33, 34 of the rear wheels 23, 24. In this respect, the second brake unit 200 is disposed between the first brake unit 100 and the plurality of wheel cylinders 30. In addition, in this embodiment, the second supply fluid paths 231, 232, together with the first supply fluid path 121, constitute a "supply fluid path."

[0019] <Front wheel pressure adjustment mechanism> The front-wheel pressure adjusting mechanism 201 adjusts the WC pressure in the wheel cylinders 31, 32 of the front wheels 21, 22, thereby generating a braking force corresponding to the WC pressure on the front wheels 21, 22. The front-wheel pressure adjusting mechanism 201 has a differential pressure adjusting valve 211, a holding valve 212, a pressure reducing valve 213, a reservoir 214, a pump 215, a check valve 216, a discharge fluid path 221, a first return fluid path 222, and a second return fluid path 223.

[0020] The differential pressure adjustment valve 211 is provided in the second supply fluid path 231. The differential pressure adjustment valve 211 is a normally open linear electromagnetic valve. The differential pressure adjustment valve 211 adjusts the differential pressure between the fluid pressure on the electric cylinder 110 side of the differential pressure adjustment valve 211 and the fluid pressure on the wheel cylinder 30 side.

[0021] The holding valve 212 is provided in the second supply fluid path 231 between the differential pressure adjustment valve 211 and the wheel cylinder 30. The holding valve 212 is a normally open solenoid valve that closes when energized and opens when de-energized. For example, the holding valve 212 is closed to restrict an increase in WC pressure. The pressure reducing valve 213 is provided in the discharge fluid path 221. The discharge fluid path 221 is a fluid path that connects the reservoir 214 to a portion of the second supply fluid path 231 between the holding valve 212 and the wheel cylinder 30. The pressure reducing valve 213 is a normally closed solenoid valve that opens when energized and closes when de-energized. For example, the pressure reducing valve 213 opens to allow brake fluid to flow out of the wheel cylinder 30. The holding valve 212 and the pressure reducing valve 213 adjust the amount of brake fluid supplied to and discharged from the wheel cylinder 30 by their respective operations. In this respect, the retention valve 212 and the pressure reducing valve 213 correspond to the "adjustment unit."

[0022] Reservoir 214 has a storage chamber 214a that can store brake fluid. Reservoir 214 has a movable wall 214b that can be displaced in a direction that changes the volume of storage chamber 214a, and a coil spring 214c that urges movable wall 214b in a direction that reduces the volume of storage chamber 214a. When brake fluid flows into reservoir 214, movable wall 214b is displaced in a direction that increases the volume of storage chamber 214a. At this time, coil spring 214c is elastically compressed and deformed in response to the displacement of movable wall 214b. On the other hand, when brake fluid flows out of reservoir 214, the restoring force of coil spring 214c displaces movable wall 214b in a direction that reduces the volume of storage chamber 214a. In the following description, the amount of brake fluid stored in reservoir 214 will simply be referred to as the fluid volume Lq of reservoir 214.

[0023] The pump 215 is provided in the first return fluid path 222. The first return fluid path 222 is a fluid path that connects the discharge fluid path 221 with a portion of the second supply fluid path 231 between the differential pressure adjustment valve 211 and the holding valve 212. The pump 215 is driven by a pump motor 241. The pump 215 sucks brake fluid from the discharge fluid path 221 and discharges it into the second supply fluid path 231.

[0024] The check valve 216 has a valve element 216a that opens and closes the second return fluid path 223. The second return fluid path 223 is a fluid path that connects the reservoir 214 and a portion of the second supply fluid path 231 between the electric cylinder 110 and the differential pressure adjustment valve 211. The valve element 216a is biased by a spring (not shown) in a direction that closes the second return fluid path 223. The check valve 216 restricts the flow of brake fluid from the electric cylinder 110 toward the reservoir 214 in the second return fluid path 223. On the other hand, the check valve 216 allows the flow of brake fluid from the reservoir 214 toward the electric cylinder 110 in the second return fluid path 223 when the fluid pressure on the reservoir 214 side is higher than the fluid pressure on the electric cylinder 110 side. In this respect, the check valve 216 corresponds to a "valve mechanism."

[0025] In this embodiment, the check valve 216 and the reservoir 214 are configured as an integrated unit, but in the above-mentioned respect, it can be said that the check valve 216 is provided in the second return fluid path 223. Note that in other embodiments, the check valve 216 and the reservoir 214 may be configured as separate units. Also, the check valve 216 can be replaced with a solenoid valve.

[0026] <Rear wheel pressure adjustment mechanism> The rear-wheel pressure regulating mechanism 202 regulates the WC pressure in the wheel cylinders 30 of the rear wheels 23, 24, thereby generating a braking force corresponding to the WC pressure on the rear wheels 23, 24. Similar to the front-wheel pressure regulating mechanism 201, the rear-wheel pressure regulating mechanism 202 has a differential pressure regulating valve 211, a holding valve 212, a pressure reducing valve 213, a reservoir 214, a pump 215, a check valve 216, a discharge fluid path 221, a first return fluid path 222, and a second return fluid path 223. The second supply fluid path 232 in the rear-wheel pressure regulating mechanism 202 corresponds to the second supply fluid path 230 in the front-wheel pressure regulating mechanism 201. The hydraulic circuit for wheel cylinder 33 of right rear wheel 23 has the same configuration as the hydraulic circuit for wheel cylinder 31 of right front wheel 21, and the hydraulic circuit for wheel cylinder 34 of left rear wheel 24 has the same configuration as the hydraulic circuit for wheel cylinder 32 of left front wheel 22. The rear-wheel pressure regulating mechanism 202 shares a pump motor 241 with the front-wheel pressure regulating mechanism 201.

[0027] <First control section> The first control unit 51 is an electronic control device. The first control unit 51 has a CPU and a memory. In the first control unit 51, the CPU executes a program stored in the memory, thereby controlling the first braking unit 100.

[0028] The first control unit 51 calculates a required braking force BPR required of the vehicle 10 based on the detection result of the brake sensor 132. Then, the first control unit 51 drives the electric cylinder 110 so that the supply pressure Ps of the electric cylinder 110 becomes a target supply pressure, which is a supply pressure according to the required braking force BPR. In detail, the first control unit 51 drives the electric cylinder 110 so that the hydraulic pressure detected by the hydraulic pressure sensor 122 becomes the target supply pressure.

[0029] When the required braking force BPR increases, the first control unit 51 moves the piston 112 of the electric cylinder 110 in the forward direction X1, thereby causing brake fluid to flow out of the electric cylinder 110. In this case, the brake fluid flowing out of the electric cylinder 110 is supplied to the wheel cylinder 30 via the first supply fluid path 121 and the second supply fluid path 230. As a result, the WC pressure increases, and the braking force generated on the wheel 20 increases. On the other hand, when the required braking force BPR decreases, the first control unit 51 moves the piston 112 of the electric cylinder 110 in the backward direction X2, thereby causing brake fluid to flow into the electric cylinder 110. In this case, the brake fluid in the wheel cylinder 30 returns to the electric cylinder 110 via the first supply fluid path 121 and the second supply fluid path 230. As a result, the WC pressure decreases, and the braking force generated on the wheel 20 decreases.

[0030] <Second control section> The second control unit 52 is an electronic control device. The second control unit 52 has a CPU and a memory. In the second control unit 52, the CPU executes a program stored in the memory, thereby controlling the second braking unit 200. The second control unit 52 is capable of communicating with the first control unit 51 via an in-vehicle network.

[0031] The second control unit 52 calculates the slip amount Slp of each of the plurality of wheels 20 by comparing the wheel speeds VW of the plurality of wheels 20 with the vehicle body speed VS. The slip amount Slp is a value indicating the degree of deceleration slip of the wheel 20. For example, the second control unit 52 can calculate the slip amount Slp by subtracting the wheel speed VW from the vehicle body speed VS. Next, the second control unit 52 compares the slip amount Slp of the plurality of wheels 20 with a predetermined reference slip amount Slpth. If there is a wheel 20 whose slip amount Slp exceeds the reference slip amount Slpth, the second control unit 52 determines that deceleration slip is occurring in that wheel 20.

[0032] If it is determined that deceleration slip is not occurring in the wheel 20, the second control unit 52 does not start antilock brake control to suppress deceleration slip. In this case, the second control unit 52 does not energize the differential pressure adjustment valve 211, the holding valve 212, and the pressure reducing valve 213. Therefore, when the required braking force BPR changes, the fluid paths through which brake fluid flows are limited to the first fluid supply path 121 and the second fluid supply path 230. Hereinafter, antilock brake control will be referred to as "ABS control."

[0033] When it is determined that deceleration slip has occurred in the wheel 20, the second control unit 52 starts ABS control. When the slip amount Slp of the slipping wheel, which is the wheel experiencing deceleration slip, is greater than a reference slip amount Slpth, the second control unit 52 closes the pressure retention valve 212 and then performs a pressure reduction process to open the pressure reduction valve 213. When the slip amount Slp of the slipping wheel is smaller than the reference slip amount Slpth, the second control unit 52 closes the pressure reduction valve 213 and then performs a pressure increase process to open the pressure retention valve 212. When implementing ABS control, the second control unit 52 continues driving the pump 215 using the pump motor 241.

[0034] When pressure reduction processing is performed, brake fluid is discharged from the wheel cylinder 30 of the slipping wheel to the drain fluid passage 221 via the pressure reduction valve 213. In this case, the WC pressure in the wheel cylinder 30 of the slipping wheel decreases, thereby reducing the braking force acting on the slipping wheel. As a result, the amount of slip Slp in the slipping wheel is reduced. Furthermore, the brake fluid discharged from the wheel cylinder 30 of the slipping wheel to the drain fluid passage 221 is discharged by the pump 215 to the second supply fluid passage 230. If the flow rate of brake fluid discharged from the wheel cylinder 30 of the slipping wheel to the drain fluid passage 221 is greater than the flow rate that the pump 215 can pump, brake fluid corresponding to the difference between the two flow rates flows into the reservoir 214. In other words, the fluid volume Lq in the reservoir 214 increases during pressure reduction processing.

[0035] When the pressure increase process is performed, brake fluid flows from the second supply fluid line 230 into the wheel cylinder 30 of the slipping wheel via the retention valve 212. In this case, the WC pressure in the wheel cylinder 30 of the slipping wheel increases, thereby increasing the braking force acting on the slipping wheel. Furthermore, when the pressure increase process is performed, brake fluid does not flow from the wheel cylinder 30 of the slipping wheel to the discharge fluid line 221. Therefore, the fluid volume Lq in the reservoir 214 decreases while the pressure increase process is being performed.

[0036] While the ABS control is being performed, the second control unit 52 determines whether or not an end condition for the ABS control is satisfied. The end condition for the ABS control is, for example, when the vehicle 10 has stopped or when the deceleration slip of the slipping wheel has been resolved. If the end condition for the ABS control is not satisfied, the second control unit 52 repeatedly performs the pressure reduction process and the pressure increase process. On the other hand, if the end condition for the ABS control is satisfied, the second control unit 52 stops the supply of electricity to the holding valve 212 and the pressure reduction valve 213 and stops the pump motor 241.

[0037] As described above, during the pressure reduction process, brake fluid is discharged from the wheel cylinder 30 of the slipping wheel to the discharge fluid path 221. The amount of brake fluid discharged to the discharge fluid path 221 is proportional to the amount of decrease in WC pressure that occurs during the pressure reduction process. During ABS control, the pump 215 continues to discharge brake fluid from the discharge fluid path 221 to the second supply fluid path 230. Therefore, the second control unit 52 can estimate the fluid level Lq in the reservoir 214 during ABS control by adding the amount of brake fluid discharged from the wheel cylinder 30 during the pressure reduction process and subtracting the discharge volume of the pump 215. The second braking unit 200 may also include a fluid level sensor that detects the fluid level Lq in the reservoir 214. In this case, the second control unit 52 can obtain the fluid level Lq in the reservoir 214 based on the detection result of the fluid level sensor.

[0038] <Restriction processing by the first control section> In the second brake unit 200, if the ABS control termination condition is satisfied while the pressure reduction process is being performed, there is a possibility that brake fluid will remain in the reservoir 214. In this case, when the supply pressure Ps decreases as the required braking force BPR decreases, the fluid pressure in the first supply fluid path 121 and the second supply fluid path 230 decreases. As a result, the fluid pressure in the second return fluid path 223 on the second supply fluid path 230 side of the check valve 216 becomes lower than the fluid pressure in the second return fluid path 223 on the reservoir 214 side of the check valve 216. As a result, the brake fluid remaining in the reservoir 214 flows into the second supply fluid path 230 via the check valve 216. At this time, the flow rate of the brake fluid passing through the check valve 216 is proportional to the rate of change of the fluid pressure in the second return fluid path 223 on the second supply fluid path 230 side of the check valve 216, i.e., the rate of decrease in the supply pressure Ps. Therefore, when the rate at which the supply pressure Ps decreases is high, the flow rate of the brake fluid passing through the check valve 216 also increases. Note that even if a solenoid valve is used instead of the check valve 216, the same applies when the solenoid valve is opened.

[0039] Incidentally, minute foreign matter may be present in reservoir 214. Examples of minute foreign matter include metal chips generated during machining of components of reservoir 214. In this case, when the brake fluid in reservoir 214 is returned to second fluid supply path 230 via check valve 216 after ABS control ends, it is preferable that the foreign matter does not flow out of reservoir 214 along with the brake fluid so as not to affect other components of braking device 40.

[0040] Therefore, when the required braking force BPR is reduced after the end of ABS control, the first control unit 51 performs a limitation process to reduce the rate at which the supply pressure Ps is reduced below a rate corresponding to the rate at which the required braking force BPR is reduced. In this way, when the required braking force BPR is reduced after the end of ABS control, the first control unit 51 reduces the flow rate of the brake fluid passing through the check valve 216.

[0041] If the fluid volume Lq in the reservoir 214 at the end of ABS control is large, a larger amount of brake fluid passes through the check valve 216 when the supply pressure Ps decreases as the operation of the brake operating member 131 is released than if the fluid volume Lq in the reservoir 214 is small. In this regard, the larger the fluid volume Lq in the reservoir 214 at the end of ABS control, the higher the possibility that foreign matter will leak out of the reservoir 214 when the supply pressure Ps decreases. Therefore, when the required braking force BPR is reduced after the end of ABS control, the first control unit 51 determines whether to permit or prohibit the restriction process based on the fluid volume Lq in the reservoir 214 at the end of ABS control. More specifically, the first control unit 51 permits the implementation of the restriction process when the fluid volume Lq in the reservoir 214 at the end of ABS control is equal to or greater than a predetermined set fluid volume Lqth. On the other hand, if the fluid volume Lq in the reservoir 214 at the end of ABS control is less than the set fluid volume Lqth, the first control unit 51 prohibits the implementation of the restriction process. The set fluid volume Lqth is a fixed value that is set in advance based on experiments, simulations, etc. The set fluid volume Lqth may also be a variable value that depends on factors such as temperature that affect the viscosity of the brake fluid.

[0042] The required braking force BPR decreases after the end of ABS control, for example, when the vehicle 10 resumes traveling or when the vehicle 10 is parked. When the vehicle 10 resumes traveling, if the restriction process is implemented from the timing when the required braking force BPR decreases, the driver may feel a dragging sensation in the brakes compared to when the restriction process is not implemented. In other words, the driver may feel that the vehicle 10 is not accelerating as expected even though the driver is not operating the brake operating member 131.

[0043] Therefore, the first control unit 51 determines the timing to start the restriction process based on the magnitude of the supply pressure Ps under the condition that the required braking force BPR is reduced after the end of ABS control, i.e., under the condition that the supply pressure Ps is reduced after the end of ABS control. Specifically, the first control unit 51 does not start the restriction process when the supply pressure Ps is higher than the set hydraulic pressure Psth. On the other hand, the first control unit 51 starts the restriction process when the supply pressure Ps is equal to or lower than the set hydraulic pressure Psth.

[0044] The set hydraulic pressure Psth is set to be equal to or greater than the pre-pressure of the reservoir 214. The set hydraulic pressure Psth is a fixed value that is set in advance based on experiments, simulations, etc. The set hydraulic pressure Psth may be a variable value that depends on the magnitude of the required driving force at the start of the restriction process, etc.

[0045] <Restriction processing by the first control section> The following describes the flow of processing that the first control unit 51 performs after the ABS control ends. After the ABS control ends, the first control unit 51 repeatedly performs this processing until the required braking force BPR becomes "0".

[0046] 2, the first control unit 51 determines whether the fluid volume Lq in the reservoir 214 at the end of ABS control is equal to or greater than the set fluid volume Lqth (S11). If the fluid volume Lq in the reservoir 214 at the end of ABS control is less than the set fluid volume Lqth (S11: NO), the first control unit 51 ends this process. In this case, the first control unit 51 does not perform the restriction process. If the first control unit 51 does not perform the restriction process, the supply pressure Ps becomes a target supply pressure corresponding to the required braking force BPR.

[0047] If the fluid volume Lq in the reservoir 214 at the time of ending ABS control is equal to or greater than the set fluid volume Lqth (S11: YES), the first control unit 51 determines whether or not the supply pressure Ps is higher than the set fluid pressure Psth (S12). If the supply pressure Ps is higher than the set fluid pressure Psth (S12: YES), the first control unit 51 ends this process. On the other hand, if the supply pressure Ps is equal to or less than the set fluid pressure Psth (S12: NO), the first control unit 51 starts the restriction process (S13). Thereafter, the first control unit 51 determines whether or not the end condition for the restriction process is satisfied (S14). The end condition for the restriction process is satisfied, for example, when the braking force generated on the wheel 20 becomes "0." If the end condition for the restriction process is not satisfied (S14: NO), the first control unit 51 proceeds to step S14. In this case, the first control unit 51 continues the restriction process. On the other hand, if the condition for ending the restriction process is met (S14: YES), the first control unit 51 ends this process. That is, the first control unit 51 ends the restriction process.

[0048] <Actions and Effects of This Embodiment> The operation and effect of this embodiment will be described with reference to Fig. 3. Fig. 3(a) to Fig. 3(d) show the changes in the required braking force BPR, the vehicle speed VS, the hydraulic pressure, and the fluid volume Lq in the reservoir 214 when the vehicle 10 is about to come to a stop due to the execution of ABS control.

[0049] 3(a) to 3(d), the tenth timing t10 ​​is the timing at which ABS control ends. Therefore, the period up to the tenth timing t10 ​​is the period before the end of ABS control, and the period after the tenth timing t10 ​​is the period after the end of ABS control.

[0050] During the period prior to the tenth timing t10, the required braking force BPR is maintained constant, and therefore the supply pressure Ps is the target supply pressure corresponding to the required braking force BPR. In other words, as shown by the solid line or the two-dot chain line in FIG. 3C, the WC pressure in the wheel cylinder 30 of the wheel 20 other than the slipping wheel is equal to the supply pressure Ps. Meanwhile, as shown by the dashed line in FIG. 3C, the WC pressure in the wheel cylinder 30 of the slipping wheel experiencing deceleration slip increases or decreases while remaining lower than the supply pressure Ps due to ABS control. For example, during the pressure reduction process from the first timing t1 to the second timing t2, the WC pressure decreases and the fluid volume Lq in the reservoir 214 increases. Furthermore, during the pressure increase process from the second timing t2 to the third timing t3, the WC pressure increases and the fluid volume Lq in the reservoir 214 decreases. Furthermore, because braking forces are generated on multiple wheels 20, the vehicle speed VS gradually decreases.

[0051] At tenth timing t10, when ABS control ends as the vehicle 10 comes to a stop, the holding valve 212 remains open and the pressure-reducing valve 213 remains closed. Therefore, as shown by the dashed-dotted line in FIG. 3C, the WC pressure in the wheel cylinder 30 of the slipping wheel where deceleration slip occurred becomes equal to the supply pressure Ps. Also, at tenth timing t10, the pump motor 241 stops operating. Therefore, the brake fluid stored in the reservoir 214 cannot return to the second supply fluid line 230 via the pump 215. Also, at tenth timing t10, the fluid pressure on the second return fluid line 223, closer to the second supply fluid line 230 than the check valve 216, is higher than the fluid pressure on the discharge fluid line 221 than the check valve 216. In other words, the supply pressure Ps is higher than the fluid pressure in the reservoir 214. Therefore, the brake fluid stored in the reservoir 214 cannot return to the second fluid supply line 230 via the check valve 216. As a result, after the ABS control ends and under the condition that the required braking force BPR is maintained, the fluid volume Lq in the reservoir 214 is maintained constant. Also, in the example shown in Fig. 3, at the tenth timing t10, the fluid volume Lq in the reservoir 214 is equal to or greater than the set fluid volume Lqth.

[0052] At an eleventh time point t11, the required braking force BPR begins to decrease as the driver's operation amount of the brake operating member 131 decreases. When the required braking force BPR begins to decrease at the eleventh time point t11, the supply pressure Ps begins to decrease at a rate corresponding to the rate at which the required braking force BPR is decreasing. As a result, the braking force generated on the wheels 20 begins to decrease. At a twelfth time point t12, the supply pressure Ps becomes equal to the set hydraulic pressure Psth.

[0053] Here, a first comparative example will be described in which the restriction process is not executed after the end of ABS control. In the first comparative example, even after the twelfth timing t12, the supply pressure Ps decreases at a rate corresponding to the rate of decrease of the required braking force BPR, as shown by the two-dot chain line in FIG. 3(c). The rate at which brake fluid flows from the reservoir 214 to the second return fluid path 223 is determined by the difference between the supply pressure Ps and the fluid pressure in the reservoir 214. Therefore, the higher the rate at which the supply pressure Ps decreases, the more likely it is that the fluid volume Lq in the reservoir 214 will decrease at a relatively high rate. As a result, the flow rate of the brake fluid discharged from the reservoir 214 toward the check valve 216 will be relatively high. Therefore, foreign matter is more likely to flow out of the reservoir 214 along with the brake fluid.

[0054] In contrast, as shown by the solid line in FIG. 3(c), in this embodiment, the restriction process begins at the twelfth timing t12 when the supply pressure Ps becomes equal to the set hydraulic pressure Psth. Therefore, after the twelfth timing t12, the rate of decrease of the supply pressure Ps becomes slower than the rate corresponding to the decrease of the required braking force BPR. In the example shown in FIG. 3, the rate of decrease of the required braking force BPR is constant before and after the twelfth timing t12. Therefore, the rate of decrease of the supply pressure Ps after the twelfth timing t12 is slower than the rate of decrease of the supply pressure Ps before the twelfth timing t12. As a result, the rate of decrease of the fluid volume Lq in the reservoir 214 tends to be relatively slow, and the flow rate of the brake fluid discharged from the reservoir 214 toward the check valve 216 tends to be slow. Therefore, foreign matter is less likely to flow out of the reservoir 214 along with the brake fluid. In other words, foreign matter is prevented from flowing out of the reservoir 214 toward the second supply hydraulic line 230.

[0055] Thereafter, at the thirteenth timing t13, the required braking force BPR becomes "0." In this embodiment, in order to slow down the rate of decrease of the supply pressure Ps, the decrease in the supply pressure Ps, i.e., the decrease in the braking force, continues even after the thirteenth timing t13. Then, at the fourteenth timing t14, which is after the thirteenth timing t13, the braking force generated on the wheels 20 becomes "0." In other words, the limitation process ends at the fourteenth timing t14.

[0056] Consider a second comparative example in which the rate of decrease of the supply pressure Ps is slowed from the eleventh time t11 when the required braking force BPR starts to decrease. In this comparative example, the period from the time when the required braking force BPR becomes "0" to the time when the braking force actually generated on the wheels 20 also becomes "0" is lengthened. In other words, in this comparative example, when the driver operates the accelerator operating member from the thirteenth time t13 when the required braking force BPR becomes "0", the driver may feel a strong dragging sensation of the brakes.

[0057] In contrast, in this embodiment, the rate of decrease of the supply pressure Ps is slowed from the twelfth time t12 when the supply pressure Ps becomes the set hydraulic pressure Psth. Therefore, the period from the time when the required braking force BPR becomes "0" to the time when the braking force actually generated on the wheels 20 becomes "0" is unlikely to be long. As a result, in this embodiment, even if the driver operates the accelerator operation member from the thirteenth time t13 when the required braking force BPR becomes "0", the driver is unlikely to feel a dragging sensation of the brakes. Therefore, the braking device 40 can suppress the outflow of foreign matter from the reservoir 214 while suppressing the occurrence of a dragging sensation of the brakes.

[0058] Furthermore, in this embodiment, the fluid volume Lq of the reservoir 214 at the tenth timing t10 ​​when ABS control ends is equal to or greater than the set fluid volume Lqth, and therefore the restriction process is permitted. In contrast, if the fluid volume Lq of the reservoir 214 at the tenth timing t10 ​​when ABS control ends is less than the set fluid volume Lqth, the restriction process is not permitted. In other words, the braking device 40 does not perform the restriction process if there is a low possibility that foreign matter will leak from the reservoir 214 after ABS control ends. Therefore, the braking device 40 can prevent the restriction process from being performed more than necessary.

[0059] <Example of change> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0060] The first control unit 51 may determine whether to permit or prohibit the implementation of the restriction process based on the deceleration of the vehicle 10 during ABS control in a situation where the required braking force BPR is reduced after the end of ABS control. Depending on the vehicle 10, the greater the deceleration, the stronger the brake dragging sensation felt by the driver when the restriction process is implemented. Alternatively, the smaller the deceleration, the stronger the brake dragging sensation felt by the driver when the restriction process is implemented. With the above configuration, the first control unit 51 can implement the restriction process based on the deceleration if the driver is unlikely to feel the brake dragging sensation, and not implement the restriction process if the driver is likely to feel the brake dragging sensation. In other words, the braking device 40 can balance the driver's drivability with the prevention of foreign matter from leaking from the reservoir 214.

[0061] The first control unit 51 or the second control unit 52 may estimate the hydraulic pressure in the reservoir 214 at the end of ABS control based on the content of the processing being performed at the end of ABS control and the duration of the processing. Then, in a situation where the required braking force BPR is reduced after the end of ABS control, the first control unit 51 may start the limiting processing at the timing when the supply pressure Ps becomes equal to or lower than the estimated hydraulic pressure in the reservoir 214. This modification makes it possible to start the limiting processing at an appropriate timing.

[0062] The first control unit 51 may perform the restriction process if the ABS control ends before the vehicle speed VS becomes "0". The first control unit 51 may start the restriction process after the supply pressure Ps becomes less than the set hydraulic pressure Psth. In other words, the first control unit 51 may start the restriction process regardless of the set hydraulic pressure Psth.

[0063] In the restriction process, the first control unit 51 may change the rate at which the supply pressure Ps is reduced based on values ​​that indicate various states of the vehicle 10. For example, in the restriction process, the first control unit 51 may set a difference in the rate at which the supply pressure Ps is reduced depending on whether the vehicle speed VS or the acceleration is high or low.

[0064] During ABS control, the second control unit 52 may perform a holding process to close the holding valve 212 and the pressure reducing valve 213 when the slip amount Slp of the slipping wheel is equal to the reference slip amount Slpth.

[0065] The pressure source of the first braking unit 100 may be configured to include a device other than the electric cylinder 110, as long as it can pressurize the brake fluid by driving the electric motor. The other pressure source may be, for example, a pump such as a gear pump.

[0066] The first brake unit 100 and the second brake unit 200 may be provided with a filter that captures foreign matter in the portion through which the brake fluid flows. The vehicle 10 may be equipped with a driving assistance device that performs driving assistance control such as automatic driving and pre-crash braking. In this case, the first control unit 51 may control the first braking unit 100 based on the required braking force BPR transmitted from the driving assistance device. In other words, even if the driver does not operate the brake operating member 131, the first control unit 51 may perform the limitation process as long as the required braking force BPR decreases after the end of ABS control.

[0067] The first control unit 51 and the second control unit 52 are not limited to processing circuits that include a CPU and a ROM and execute software processing. For example, the first control unit 51 and the second control unit 52 may include dedicated hardware circuits that execute at least some of the various processes executed in the above-described embodiment. An example of a dedicated hardware circuit is an ASIC. ASIC is an abbreviation for "Application Specific Integrated Circuit." In other words, the first control unit 51 and the second control unit 52 may have any of the following configurations (a) to (c):

[0068] (a) A processing circuit comprising a processing device that executes all of the above processes according to a program, and a program storage device such as a ROM that stores the program. (b) A processing circuit comprising a processing device and a program storage device that executes part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing.

[0069] (c) A processing circuit having dedicated hardware circuitry for performing all of the above processes. Here, there may be a plurality of software execution devices each having a processing device and a program storage device, and a plurality of dedicated hardware circuits. [Explanation of symbols]

[0070] 10...Vehicle 20(21~22)…Wheel 30 (31-34)... Wheel cylinder 40...braking device 51...First control section 52...Second control section 100...First braking unit 113...Electric motor 121...First supply liquid path (supply liquid path) 200...Second braking unit 212...Retention valve (adjustment part) 213... Pressure reducing valve (adjustment part) 214...Reservoir 215...Pump 216...Check valve (valve mechanism) 221...Drainage path 222...First return liquid path 223...Second return liquid path 230(231,232)…Second supply liquid path (supply liquid path)

Claims

1. a first braking unit that adjusts a supply pressure, which is a hydraulic pressure of brake fluid supplied to a wheel cylinder, based on an output of the electric motor; a second brake unit disposed between the first brake unit and the wheel cylinder, and configured to adjust a WC pressure, which is a hydraulic pressure in the wheel cylinder, when brake fluid is supplied from the first brake unit to the wheel cylinder; a first control unit that controls the first brake unit to increase the supply pressure to increase the amount of brake fluid in the wheel cylinder when the required braking force increases, and to decrease the supply pressure to decrease the amount of brake fluid in the wheel cylinder when the required braking force decreases; a second control unit that controls the second brake unit when deceleration slip occurs in a wheel, thereby performing ABS control to suppress the deceleration slip through adjustment of the WC pressure, The second braking unit includes: a supply fluid passage connecting the first braking unit and the wheel cylinder; an adjusting unit provided in the fluid supply passage for adjusting the amount of brake fluid supplied to the wheel cylinder and the amount of brake fluid discharged from the wheel cylinder; a reservoir that stores brake fluid discharged from the wheel cylinder by operation of the adjusting unit; a discharge path connecting the adjusting unit and the reservoir; a first return liquid path connecting the discharge liquid path and the supply liquid path; a pump provided in the first return fluid path and configured to discharge brake fluid toward the supply fluid path; a second return fluid path connecting a portion of the supply fluid path between the first braking unit and the adjustment unit and the reservoir; a valve mechanism provided in the second return fluid line for allowing a flow of brake fluid from the reservoir to the supply fluid line when the fluid pressure on the reservoir side is higher than the fluid pressure on the supply fluid line side; the second control unit stops driving the pump when the ABS control ends, When the required braking force is reduced after the ABS control is terminated, the first control unit performs a limiting process to reduce the rate of reduction of the supply pressure to a rate lower than a rate corresponding to the rate of reduction of the required braking force. Braking device.

2. The first control unit starts the limiting process when the supply pressure becomes equal to or lower than a set hydraulic pressure under a condition in which the required braking force is reduced after the ABS control is terminated.

2. The braking device of claim 1.

3. The first control unit determines whether to permit the implementation of the restriction process based on the deceleration of the vehicle during the implementation of the ABS control under a condition in which the required braking force is reduced after the ABS control is terminated. The braking device according to claim 1 or 2.

4. The first control unit, under a situation in which the required braking force is reduced after the ABS control is terminated, If the amount of brake fluid in the reservoir at the end of the ABS control is equal to or greater than a set fluid amount, the execution of the restriction process is permitted; If the amount of brake fluid in the reservoir at the end of the ABS control is less than the set fluid amount, the execution of the limiting process is prohibited. The braking device according to claim 1 or 2.

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