JP2016188037A - Brake system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently boost pressure up to a high fluid pressure area while avoiding an increase in size of a slave cylinder and to excellently secure brake fluid to be supplied for a wheel brake.SOLUTION: There are provided: a hydraulic passage leading from a master cylinder 10 to a wheel brake; a changeover valve provided for the hydraulic passage; a communication passage communicating from the slave cylinder 20 with the changeover valve; a cutoff valve which is provided for the communication passage and can cut off the communication passage; a return passage 9b leading from the wheel brake to the slave cylinder 20; a pressure accumulation chamber which is provided for the return passage 9b and accumulates the brake fluid let out to the return passage 9b from the wheel brake when the pressure of the wheel brake is reduced; and control means performing liquid absorption control. The control means performs control to close the cutoff valve and cause an electric actuator to drive a piston 22 in a decompression direction during the liquid absorption control. When reducing the pressure of the wheel brake, the brake fluid accumulated in the pressure accumulation chamber flows in the slave cylinder through the return passage 9b by the liquid absorption control.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a brake system used for a vehicle.

Conventionally, for example, a brake-by-wire system as shown in Patent Document 1 is known as a brake system that generates hydraulic pressure in accordance with an operation amount of a brake operator.
This brake system includes an input device, a slave cylinder, and a hydraulic pressure control device, and includes two brake systems. The input device includes a master cylinder that generates hydraulic pressure by a piston connected to the brake operator, and a stroke simulator that applies a pseudo operation reaction force to the brake operator. The slave cylinder includes an electric motor as an electric actuator and a piston driven by the electric motor.

  In this brake system, the electric motor of the slave cylinder is driven according to the operation amount of the brake operator, and the hydraulic pressure is applied to the wheel brake by the slave cylinder piston driven by the electric motor. Further, during anti-lock brake control, the hydraulic pressure control device is operated to adjust the brake hydraulic pressure acting on the wheel brake.

JP2012-106637A

  Since the brake system of Patent Document 1 is configured to increase the hydraulic system by driving the slave cylinder, it is possible to increase the pressure appropriately to the high hydraulic pressure region by increasing the stroke of the slave cylinder piston provided in the slave cylinder. it can. That is, by increasing the stroke amount of the slave cylinder piston, a brake system having a boosting function corresponding to the driver's required hydraulic pressure can be obtained. However, if the stroke amount of the slave cylinder piston is increased, the axial length of the cylinder is increased, resulting in an increase in the size of the slave cylinder and an increase in the size of the brake system. Also, during anti-lock brake control, control to increase, hold, or reduce the hydraulic pressure acting on the wheel brake is frequently performed, so that the slave cylinder may become large in order to secure brake fluid to be supplied to the wheel brake. was there.

  It is an object of the present invention to provide a brake system capable of suitably increasing pressure to a high hydraulic pressure region while avoiding an increase in the size of a slave cylinder and ensuring adequate brake fluid to be supplied to a wheel brake. Let it be an issue.

The brake system of the present invention, which was created to solve such a problem, has a master cylinder that generates a hydraulic pressure to be applied to a wheel brake by the driver's operation of the brake operator, and an operation amount of the brake operator. And a slave cylinder that generates hydraulic pressure by an electric actuator that is driven accordingly. The brake system includes a hydraulic pressure path from the master cylinder to the wheel brake, a switching valve provided in the hydraulic pressure path, a communication path from the slave cylinder to the switching valve, and provided in the communication path. And a shutoff valve capable of shutting off the communication path. Further, the brake system is provided in a return flow path from the wheel brake to the slave cylinder, and in the return flow path, and stores brake fluid that has escaped from the wheel brake to the return flow path when the wheel brake is depressurized. A pressure accumulating chamber; and a control means for performing liquid suction control for sucking brake fluid into the slave cylinder. The control means closes the shut-off valve and controls to drive the piston in the pressure reducing direction by the electric actuator during liquid absorption control. At the time of the pressure reduction, the brake fluid stored in the pressure accumulating chamber flows into the slave cylinder through the return flow path by liquid suction control.
Here, “the piston is driven in the pressure reducing direction by the electric actuator” means that the piston is driven in the pressure reducing direction from the position where the piston is driven in the pressure applying direction from the initial position.

  In such a brake system, when pressure reduction control is performed to reduce the hydraulic pressure acting on the wheel brake when the wheel brake is reduced, the brake fluid released from the wheel brake flows into the return flow path and is stored in the pressure accumulation chamber. When the liquid suction control is executed by the control means, the shut-off valve is closed and the slave piston is driven in the pressure reducing direction. As a result, the hydraulic pressure chamber of the slave cylinder becomes negative pressure, and the brake fluid stored in the pressure accumulating chamber is sucked into the slave cylinder through the return channel. Therefore, even if the axial length of the slave cylinder is set to be relatively short, the brake fluid for repressurization can be replenished in the hydraulic pressure chamber by the liquid suction control. As a result, a brake system that can increase the pressure suitably to the high hydraulic pressure region while avoiding an increase in the size of the slave cylinder can be obtained. Moreover, even if the wheel brake pressure reduction control is frequently performed, the brake fluid released to the return flow path can be sucked into the slave cylinder by the liquid suction control, and the necessary brake fluid is suitably secured. be able to. Therefore, even if the pressure reduction control of the wheel brake continues for a long time, the hydraulic pressure acting on the wheel brake can be suitably increased, and an efficient brake system can be obtained.

  Furthermore, since the brake fluid in the pressure accumulating chamber is stored in a state where pressure is applied, when the fluid pressure chamber of the slave cylinder becomes negative during the suction control, suction by the slave cylinder and extrusion by the pressure accumulating chamber are performed. The brake fluid flows smoothly into the fluid pressure chamber of the slave cylinder. As a result, quick liquid absorption is realized, and for example, it is possible to suitably ensure the brake liquid to be supplied to the wheel brake during antilock brake control.

  The control means comprises: a reservoir tank for storing brake fluid; a replenishment path extending from the reservoir tank to the return flow path; and a cut valve provided in the replenishment path and capable of blocking the replenishment path. During the decompression, the cut valve may be closed. If it does in this way, a replenishment path will be interrupted | blocked by a cut valve at the time of pressure reduction of a wheel brake, and the brake fluid stored in the pressure accumulation chamber by pressure reduction control will be suitably liquid-absorbed (refluxed) to the hydraulic pressure chamber of a slave cylinder.

  The control means may continue to maintain the closing control of the cut valve while the antilock brake control is continued. In this way, the brake fluid is sucked into the slave cylinder from the reservoir tank at the time of normal braking or special braking such as sudden braking that requires the maximum system hydraulic pressure. Therefore, it is possible to suitably increase the pressure to the high hydraulic pressure region while avoiding an increase in the size of the slave cylinder.

  In addition, an acquisition means for acquiring the brake fluid amount or the hydraulic pressure stored in the pressure accumulation chamber is provided, and the control means absorbs when the brake fluid amount or the hydraulic pressure acquired by the acquisition means exceeds a predetermined value. Liquid control should be performed. If it does in this way, the timing for performing liquid absorption control can be specified easily based on the amount of brake fluid stored in the pressure accumulation chamber, or the hydraulic pressure. Therefore, efficient liquid absorption control can be performed.

  The acquisition means may be a pressure sensor installed in the return channel. In this way, the amount of brake fluid stored in the pressure accumulating chamber by the pressure sensor can be easily specified.

The return flow path may be provided with a check valve that allows only brake fluid to flow from the pressure accumulation chamber side to the slave cylinder side. In this manner, the brake fluid stored in the pressure accumulating chamber can be sucked into the slave cylinder through the check valve by reducing the pressure in the fluid pressure chamber of the slave cylinder during the liquid suction control of the antilock brake control. . Further, the check valve can suitably prevent the hydraulic pressure generated in the slave cylinder from being transmitted to the pressure accumulating chamber side.
In the configuration including the reservoir tank, the supply path, and the cut valve, the brake fluid in the reservoir tank can be sucked into the slave cylinder through the supply path during high load brake control. Also, the check valve can suitably prevent the hydraulic pressure generated in the slave cylinder from being transmitted to the reservoir tank side.

  In addition, by making the shut-off valve a normally open solenoid valve, it is not necessary to energize the shut-off valve during normal braking in which hydraulic pressure is generated in the wheel brake by the slave cylinder. Therefore, power consumption can be minimized.

  According to the present invention, it is possible to obtain a brake system that can suitably increase the pressure to a high hydraulic pressure region while avoiding an increase in the size of the slave cylinder, and that can suitably ensure the brake fluid supplied to the wheel brake.

1 is a hydraulic circuit diagram showing a brake system according to an embodiment of the present invention. (A) (b) is explanatory drawing which shows typically the structure of a switching valve and a cutoff valve. It is a figure which shows the relationship between the stroke amount of a slave cylinder, and a pressure. FIG. 2 is a hydraulic circuit diagram when the brake system shown in FIG. 1 is started. It is a flowchart in the case of reaching liquid absorption control. It is a figure which shows the relationship between a request | requirement hydraulic pressure and required stroke amount. It is a time chart which shows the timing of liquid absorption control when the system maximum wheel cylinder pressure is requested | required. It is a time chart which shows the timing of the liquid absorption control at the time of regular brakes. It is a time chart which shows the timing of the liquid absorption control at the time of anti-lock brake control.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the brake system A includes a by-wire brake system that operates when a prime mover (such as an engine or an electric motor) is started, and a hydraulic brake that operates when the prime mover is stopped. It is equipped with both the system.

  The brake system A mainly includes a master cylinder 10, a slave cylinder 20, and a hydraulic pressure control device 30 as control valve means. The brake system A can be mounted not only on an automobile that uses only an engine (internal combustion engine) as a power source, but also on a hybrid automobile that uses a motor together, an electric vehicle that uses only a motor as a power source, a fuel cell automobile, and the like.

  The master cylinder 10 is a tandem type having two pistons 11 and 12. The master cylinder 10 generates hydraulic pressure that is applied to the wheel brakes FL, RR, RL, FR by the depression force of the brake pedal P (brake operator) (in accordance with the operation amount). A stroke simulator 40 is connected to the master cylinder 10. The stroke simulator 40 applies a pseudo operation reaction force to the brake pedal P.

The slave cylinder 20 generates hydraulic pressure by driving the electric motor 24 (electric actuator) according to the operation amount of the brake pedal P. The hydraulic pressure generated by the slave cylinder 20 (hereinafter referred to as “generated hydraulic pressure”) acts on the wheel brakes FL, RR, RL, FR.
The hydraulic pressure control device 30 controls the hydraulic pressure acting on the wheel brakes and assists in stabilizing the vehicle behavior.
In the brake system A of the present embodiment, the master cylinder 10, the slave cylinder 20, and the hydraulic pressure control device 30 are provided in one base 1, and are configured as an integral unit.

  In the base body 1, a first brake system K1 and a second brake system K2 are provided. The first brake system K1 is provided with a first hydraulic pressure passage 2a that leads from the master cylinder 10 to the two wheel brakes FL, RR, and the second brake system K2 includes the remaining wheel brakes RL, FR from the master cylinder 10. A second hydraulic pressure path 2b leading to is provided. Further, a branch hydraulic pressure path 3, a common hydraulic pressure path 4, a first series path 5a, a second communication path 5b, a supply path 9a, and a return liquid path 9b are formed in the base body 1. A first pressure sensor 6 is provided in the first hydraulic pressure path 2a. A second pressure sensor 7 is provided in the common hydraulic pressure path 4.

  The master cylinder 10 includes a first piston 11 and a second piston 12 inserted into a bottomed cylindrical cylinder hole 10a, and two first and second elastic members 17a and 17b accommodated in the cylinder hole 10a. It is equipped with. The master cylinder 10 is provided with a reservoir tank 15 for storing brake fluid.

A first pressure chamber 16 a is formed between the bottom surface 10 b of the cylinder hole 10 a and the first piston 11. A first elastic member 17a, which is a coil spring, is interposed in the first pressure chamber 16a.
A second pressure chamber 16 b is formed between the first piston 11 and the second piston 12. A second elastic member 17b, which is a coil spring, is interposed in the second pressure chamber 16b.
A plurality of cup seals 10c, 10c are mounted on the inner peripheral surface of the cylinder hole 10a.

The end of the second piston 12 is connected to the brake pedal P via a push rod P1. The first piston 11 and the second piston 12 receive the depression force of the brake pedal P, slide in the cylinder hole 10a, and pressurize the brake fluid in both the pressure chambers 16a and 16b. The brake fluid pressurized in both pressure chambers 16a and 16b is output through output ports 18a and 18b provided in the cylinder hole 10a.
The first hydraulic pressure path 2a is connected to the output port 18a, and the second hydraulic pressure path 2b is connected to the output port 18b. The first hydraulic pressure path 2 a and the second hydraulic pressure path 2 b are connected to the downstream hydraulic pressure control device 30.
The master cylinder 10 is assembled with a stroke sensor ST that detects the stroke of the second piston 12.

  The stroke simulator 40 includes a simulator piston 42 inserted into the simulator cylinder hole 41, and two elastic members 43 and 44 interposed between the bottom surface 41 b of the simulator cylinder hole 41 and the simulator piston 42. .

  A pressure chamber 45 is formed in the simulator cylinder hole 41. The pressure chamber 45 is provided between the introduction port 46 and the simulator piston 42 and is connected to the second pressure chamber 16b of the master cylinder 10 via the branch hydraulic pressure path 3, the second hydraulic pressure path 2b, and the output port 18b. Leads to. Accordingly, when hydraulic pressure is generated in the second pressure chamber 16 b of the master cylinder 10 by operating the brake pedal P, the simulator piston 42 of the stroke simulator 40 moves against the urging force of the elastic members 43 and 44. Thereby, a pseudo operation reaction force is applied to the brake pedal P. The reservoir tank communication passage 9 is connected to the back pressure chamber 47 in which the elastic members 43 and 44 are disposed via a port 47a. The reservoir tank communication path 9 communicates with the reservoir tank 15 via the port 19 of the master cylinder 10.

  The slave cylinder 20 includes one slave cylinder piston 22 inserted into the cylinder hole 21, an elastic member 23 accommodated in the cylinder hole 21, an electric motor 24, and a drive transmission unit 25.

A fluid pressure chamber 26 is formed between the bottom 21b of the cylinder hole 21 and the slave cylinder piston 22 (hereinafter referred to as piston 22). An elastic member 23 that is a coil spring is disposed in the hydraulic chamber 26.
The fluid pressure chamber 26 communicates with the first fluid pressure passage 2a via the common fluid pressure passage 4 and the first series passage 5a, and the second fluid pressure passage 2b via the common fluid pressure passage 4 and the second communication passage 5b. Leads to.

The electric motor 24 is an electric servo motor. The electric motor 24 includes a coil portion 24a and a rotating portion 24c supported by a bearing 24b. A magnet 24d is attached to the rotating portion 24c.
A drive transmission unit 25 is provided inside the rotation unit 24c. The drive transmission unit 25 converts the rotational driving force of the electric motor 24 into a linear axial force. The drive transmission unit 25 includes a rod 25a that is in contact with the piston 22, and a plurality of balls 25b disposed between the rod 25a and the rotation unit 24c. A spiral thread groove is formed on the outer peripheral surface of the rod 25a, and a plurality of balls 25b are accommodated in the thread groove so as to roll. The tip of the rod 25a (the portion facing the piston 22) is formed in a hemispherical shape. The rotating part 24c is screwed into the plurality of balls 25b. Thus, the ball screw mechanism is provided between the rotating part 24c and the rod 25a.
The electric motor 24 is driven and controlled by an electronic control unit 70 as a control means mounted on the base 1. A rotation angle sensor (not shown) is attached to the electric motor 24. The detection value of the rotation angle sensor is input to the electronic control unit 70. The electronic control unit 70 calculates the stroke amount of the piston 22 of the slave cylinder 20 based on the detection value of the rotation angle sensor.

When the rotating portion 24c of the electric motor 24 rotates, a linear axial force is applied to the rod 25a by the ball screw mechanism provided between the rotating portion 24c and the rod 25a, and the rod 25a moves forward and backward. .
When the rod 25a moves to the piston 22 side, the piston 22 receives the input from the rod 25a and moves forward (moves in the pressurizing direction) in the cylinder hole 21, and the brake fluid in the hydraulic chamber 26 is pressurized. The Further, when the rod 25a moves to the side opposite to the piston 22, the piston 22 moves backward (moves in the pressure reducing direction) in the cylinder hole 21 by the biasing force of the elastic member 23, and the brake fluid in the hydraulic chamber 26 flows. Depressurized.

  The hydraulic pressure control device 30 appropriately controls the hydraulic pressure applied to each wheel cylinder W of the wheel brakes FL, RR, RL, FR. The hydraulic pressure control device 30 has a configuration capable of executing antilock brake control, and is connected to each wheel cylinder W via a pipe. Further, a return fluid path 9 b is connected to the hydraulic pressure control device 30.

The wheel brakes FL, RR, RL, FR are connected to the outlet port 301 of the base 1 via pipes, respectively. In a normal state, the hydraulic pressure output from the slave cylinder 20 corresponding to the depression force of the brake pedal P is applied to the wheel cylinders W of the wheel brakes FL, RR, RL, FR through the hydraulic pressure paths 2a, 2b. Is done.
In the following, in the hydraulic control device 30, the system connected to the first hydraulic path 2a is referred to as “first hydraulic system 300a”, and the system connected to the second hydraulic path 2b is referred to as “second hydraulic system 2a”. It is referred to as “hydraulic system 300b”.

  The first hydraulic system 300a is provided with two control valve devices V corresponding to the wheel brakes FL and RR. Similarly, the second hydraulic system 300b includes the wheel brakes RL and FR. Correspondingly, two control valve devices V are provided.

  The control valve device V is a valve that controls the flow of hydraulic pressure from the slave cylinder 20 to the wheel brakes FL, RR, RL, FR (specifically, the wheel cylinder W), and the hydraulic pressure acting on the wheel cylinder W ( (Hereinafter referred to as “wheel cylinder pressure”) can be increased, held or reduced. Therefore, the control valve device V includes an inlet valve 31, an outlet valve 32, and a check valve 33.

  One inlet valve 31 is provided for two hydraulic pressure paths from the first hydraulic pressure path 2a to the wheel brakes FL and RR, and two hydraulic pressure paths from the second hydraulic pressure path 2b to the wheel brakes RL and FR. It is arranged one by one. The inlet valve 31 is a normally-open proportional solenoid valve (linear solenoid valve), and the pressure difference between the upstream and downstream of the inlet valve 31 (opening of the inlet valve 31) depends on the value of the drive current flowing through the coil of the inlet valve 31. The valve pressure can be adjusted. The inlet valve 31 is normally open, thereby allowing hydraulic pressure to be applied from the slave cylinder 20 to each wheel cylinder W. Further, the inlet valve 31 is closed under the control of the electronic control device 70 when the wheel is about to be locked, and the hydraulic pressure applied to each wheel cylinder W is shut off.

  The outlet valve 32 is a normally closed electromagnetic valve disposed between each wheel cylinder W and the return liquid passage 9b. The outlet valve 32 is normally closed, but is opened under the control of the electronic control unit 70 when the wheel is about to lock. When the outlet valve 32 is opened, the brake fluid acting on each wheel cylinder W is depressurized.

  The check valve 33 is connected to each inlet valve 31 in parallel. The check valve 33 is a valve that allows only brake fluid to flow from the wheel cylinder W side to the slave cylinder 20 side (master cylinder 10 side). Accordingly, even when the inlet valve 31 is closed, the check valve 33 allows the brake fluid to flow from each wheel cylinder W side to the slave cylinder 20 side.

  In such a hydraulic pressure control device 30, the wheel control pressure of each wheel cylinder W is adjusted by controlling the opening / closing states of the inlet valve 31 and the outlet valve 32 by the electronic control device 70. For example, when the brake pedal P is depressed in a normal state where the inlet valve 31 is open and the outlet valve 32 is closed, the hydraulic pressure from the slave cylinder 20 is transmitted to the wheel cylinder W as it is, and the wheel cylinder pressure is increased. Further, when the inlet valve 31 is closed and the outlet valve 32 is opened, the brake fluid is released from the wheel cylinder W to the return fluid passage 9b and flows out, and the wheel cylinder pressure is reduced and reduced. Furthermore, in a state where both the inlet valve 31 and the outlet valve 32 are closed, the wheel cylinder pressure is maintained.

Next, each hydraulic path formed in the substrate 1 will be described.
The two first hydraulic pressure paths 2 a and the second hydraulic pressure path 2 b are both hydraulic pressure paths starting from the cylinder hole 10 a of the master cylinder 10.
The first hydraulic pressure passage 2 a communicates with the first pressure chamber 16 a of the master cylinder 10. On the other hand, the second hydraulic pressure passage 2 b communicates with the second pressure chamber 16 b of the master cylinder 10. The first hydraulic pressure path 2a communicates with the wheel brakes FL and RR on the downstream side. On the other hand, the second hydraulic pressure path 2b communicates with the wheel brakes RL and FR on the downstream side.

  The branch hydraulic pressure path 3 is a hydraulic pressure path from the second hydraulic pressure path 2 b to the pressure chamber 45 of the stroke simulator 40. The branch hydraulic pressure path 3 is provided with a normally closed electromagnetic valve 8 as a valve. The normally closed solenoid valve 8 opens and closes the branch hydraulic pressure path 3.

  The two first series passages 5 a and the second communication passage 5 b are both hydraulic pressure paths starting from the hydraulic pressure chamber 26 of the slave cylinder 20. The first series passage 5 a and the second communication passage 5 b merge with the common hydraulic pressure passage 4 and are connected to the cylinder hole 21. The first series passage 5a is a flow path from the hydraulic pressure chamber 26 to the first hydraulic pressure path 2a, while the second communication path 5b is also a flow path from the hydraulic pressure chamber 26 to the second hydraulic pressure path 2b.

  A first switching valve 51, which is a three-way valve, is provided at a connection portion between the first hydraulic pressure passage 2a and the first series passage 5a. The first switching valve 51 is a 2-position 3-port solenoid valve. As shown in FIG. 2A, the first switching valve 51 includes a first position where the valve body 51a is seated on the first valve seat 51c, and the valve body 51a is the first position as shown in FIG. The second position for seating on the two-valve seat 51d can be selected. In the first position, the upstream side of the first hydraulic pressure path 2a (master cylinder 10 side) and the downstream side of the first hydraulic pressure path 2a (hydraulic pressure control device 30 side, wheel brakes FL, RR) communicate with each other. The passage to the first series passage 5a is blocked. That is, the wheel brakes FL and RR when the first switching valve 51 is in the first position communicate with the master cylinder 10 but are disconnected from the slave cylinder 20 (become non-communication state). In the first position, since the coil 51e is in a non-energized state, the valve body 51a is seated on the first valve seat 51c by the urging force of the return spring 51b. In the second position, as shown in FIG. 2 (b), the communication to the upstream side of the first hydraulic pressure path 2a is blocked, and the first series path 5a and the downstream side of the first hydraulic pressure path 2a Communicate. That is, the wheel brakes FL and RR when the switching valve 51 is in the second position are disconnected from the master cylinder 10 (become in a non-communication state) but are in communication with the slave cylinder 20. In the second position, since the coil 51e is energized, the valve body 51a is seated on the second valve seat 51d by the magnetic force of the coil 51e.

On the other hand, the 2nd switching valve 52 which is a three-way valve is provided in the connection part of the 2nd hydraulic pressure path 2b and the 2nd communicating path 5b. The second switching valve 52 is a 2-position 3-port solenoid valve. As shown in FIG. 2A, the second switching valve 52 has a first position where the valve body 51a is seated on the first valve seat 51c, and the valve body 51a is the first position as shown in FIG. The second position for seating on the two-valve seat 51d can be selected. In the first position, the upstream side (master cylinder 10 side) of the second hydraulic pressure passage 2b and the downstream side (hydraulic pressure control device 30 side, wheel brakes RL, FR) of the second hydraulic pressure passage 2a communicate with each other. The path to the second communication path 5b is blocked. That is, the wheel brakes RL and FR when the second switching valve 52 is in the first position communicate with the master cylinder 10 but are disconnected from the slave cylinder 20 (become non-communication state). In the first position, since the coil 51e is in a non-energized state, the valve body 51a is seated on the first valve seat 51c by the urging force of the return spring 51b. Further, at the second position, as shown in FIG. 2B, the communication to the upstream side of the second hydraulic path 2b is blocked, and the second communication path 5b and the downstream side of the second hydraulic path 2b Communicate. That is, the wheel brakes RL and FR when the switching valve 52 is in the second position are disconnected from the master cylinder 10 (become in a non-communication state) but are in communication with the slave cylinder 20. In the second position, since the coil 51e is energized, the valve body 51a is seated on the second valve seat 51d by the magnetic force of the coil 51e.
Note that the positions of the first switching valve 51 and the second switching valve 52 are switched by the electronic control unit 70. Incidentally, in the first switching valve 51 and the second switching valve 52, the valve body 51a is in the first position at the time of starting the system or in the backup mode in which the hydraulic pressure is directly applied from the master cylinder 10 to the wheel cylinder W. In the first switching valve 51 and the second switching valve 52, the valve body 51a is in the second position, for example, during normal brake control in which hydraulic pressure is applied from the slave cylinder 20 to the wheel cylinder W.

  A first shut-off valve 61 is provided in the first series passage 5a. The first shut-off valve 61 is a normally open solenoid valve, and opens and closes the first series passage 5a. As shown in FIG. 2A, when the coil 61e is not energized, the valve body 61a is separated from the valve seat 61c by the urging force of the return spring 61b, and the first series passage 5a communicates. As shown in FIG. 2B, when the coil 61e is energized, the valve body 61a is seated on the valve seat 61c by the magnetic force, and the first series passage 5a is blocked. The valve element 61a of the first shut-off valve 61 at the time of closing is pressed against the valve seat 61c from the slave cylinder 20 side which is the upstream side (hydraulic pressure generation source side). The electronic control unit 70 opens and closes the first shut-off valve 61 (energization control for the coil 61e).

  A second shutoff valve 62 is provided in the second communication passage 5b. The second shut-off valve 62 is a normally open solenoid valve, and opens and closes the second communication path 5b. As shown in FIG. 2A, when the coil 61e is not energized, the urging force of the return spring 61b separates the valve body 61a from the valve seat 61c, and the second communication path 5b communicates. Further, as shown in FIG. 2B, when the coil 61e is energized, the valve body 61a is seated on the valve seat 61c by the magnetic force, and the second communication path 5b is shut off. The valve body 61a of the second shut-off valve 62 when the valve is closed is pressed against the valve seat 61c from the slave cylinder 20 side that is the upstream side (hydraulic pressure generation source side). The electronic control device 70 opens and closes the second shut-off valve 62 (energization control for the coil 61e).

The two pressure sensors 6 and 7 both detect the magnitude of the brake fluid pressure. Information (detected values) acquired by the pressure sensors 6 and 7 is input to the electronic control unit 70.
One pressure sensor 6 is disposed in the first hydraulic pressure path 2 a between the master cylinder 10 and the first switching valve 51. The pressure sensor 6 functions as a master pressure sensor that detects the hydraulic pressure generated in the master cylinder 10.
The other pressure sensor 7 is disposed in the common hydraulic pressure path 4. The pressure sensor 7 detects the hydraulic pressure generated in the slave cylinder 20.

  As shown in FIG. 1, the replenishment path 9a is a flow path starting from the reservoir tank 15 and extending from the reservoir tank 15 to the return flow path 9b. A cut valve 93 is provided in the supply path 9a. The cut valve 93 opens and closes the supply passage 9a. The cut valve 93 is a normally open solenoid valve, and is closed by the control (energization control) of the electronic control device 70 when the wheel brake is depressurized in the antilock brake control, and shuts off the supply path 9a. While the antilock brake control continues, the valve closed state is maintained (during the antilock control mode). Further, the cut valve 93 is open (non-energized controlled) except during anti-lock brake control, thereby allowing brake fluid to flow from the reservoir tank 15 to the return flow path 9b.

  The return flow path 9 b is a liquid path from the hydraulic pressure control device 30 to the slave cylinder 20. The brake fluid escaped from each wheel cylinder W flows into the return fluid passage 9b through the outlet valve 32 of the fluid pressure control device 30 during the pressure reduction control of the antilock brake control. A pressure sensor 91 and a reservoir 92 are provided in the return flow path 9b. The pressure sensor 91 corresponds to an acquisition unit in the claims. The reservoir 92 corresponds to a pressure accumulation chamber in the claims.

  The detection value of the pressure sensor 91 is input to the electronic control unit 70 and used to calculate the amount of brake fluid stored in the reservoir 92. In this case, the electronic control unit 70 calculates the amount of brake fluid stored in the reservoir 92 from the detection value of the pressure sensor 91 based on a map stored in advance.

  The reservoir 92 communicates with the return flow path 9b through the hydraulic pressure path 9e. The reservoir 92 has a function of temporarily storing the brake fluid that has escaped to the return fluid passage 9b during the pressure reduction control of the antilock brake control. The reservoir 92 includes a reservoir piston 921 inserted into the reservoir hole 92a, and an elastic member 922 interposed between the bottom surface 92b of the reservoir hole 92a and the reservoir piston 921. The reservoir 92 stores the brake fluid released to the return flow path 9b by the urging force of the elastic member 922 in a pressure accumulation state. The brake fluid stored in the reservoir 92 is sucked into the slave cylinder 20 during the suction control.

  The return flow path 9b is connected to the common hydraulic pressure path 4 via the branch return flow path 9c. A check valve 9d is provided in the branch return flow path 9c. The check valve 9d only allows inflow of brake fluid from the reservoir 92 side (reservoir tank 15 side) to the common hydraulic pressure path 4 side (slave cylinder 20 side).

  When the piston 22 of the slave cylinder 20 is in the initial position, the brake fluid in the reservoir tank 15 passes through the supply passage 9 a, the return passage 9 b, the supply port 20 a of the slave cylinder 20, and the supply hole 22 a of the piston 22. Will be replenished. Further, during special braking such as sudden braking described later (during high load braking), the brake fluid in the reservoir tank 15 is supplied to the replenishment passage 9a, the return passage 9b, the branch return passage 9c by the liquid absorption control. The fluid is sucked into the fluid pressure chamber 26 through the fluid pressure path 4 and the connection hole 20 b of the slave cylinder 20. Further, during the anti-lock brake control, the brake fluid stored in the reservoir 92 of the return flow path 9b is sucked into the slave cylinder 20 through the return flow path 9b, the branch return flow path 9c, and the common hydraulic pressure path 4 by the liquid absorption control. To be liquidated. In addition, after the antilock brake control is completed, the brake fluid stored in the reservoir 92 is returned from the return fluid passage 9b to the reservoir tank 15 through the replenishment passage 9a.

  The electronic control device 70 accommodates a control board (not shown) therein and is attached to the side surface of the base 1. The electronic control unit 70 opens and closes the normally closed solenoid valve 8 based on information (detected values) obtained from the various sensors such as the pressure sensors 6 and 7 and the stroke sensor ST, a program stored in advance, and the like. The operation of the electric motor 24, the operation of both switching valves 51 and 52, the opening and closing of both shut-off valves 61 and 62, and the opening and closing of the control valve device V of the hydraulic pressure control device 30 are controlled.

  The electronic control unit 70 controls the operation of the first switching valve 51, the second switching valve 52, the first cutoff valve 61, and the second cutoff valve 62 while driving and controlling the electric motor 24. Further, the electronic control unit 70 has a function of determining whether or not the hydraulic pressure generated by the slave cylinder 20 has increased to a hydraulic pressure corresponding to the operation amount of the brake pedal P (function as a determination unit). Specifically, the electronic control unit 70 refers to the map shown in FIG. 3 as a program stored in advance, and the hydraulic pressure detected by the pressure sensor 7 corresponds to the operation amount of the brake pedal P. It is determined whether or not it has risen to (detected by the stroke sensor ST) (whether or not it has risen to a preprogrammed judgment value). Then, the electronic control unit 70 controls the slave cylinder, the two switching valves 51 and 52, and the both shut-off valves 61 and 62 based on the determination result. Details of the control based on the determination of the electronic control unit 70 will be described later.

  The electronic control device 70 has a function of performing liquid absorption control. The liquid absorption control is a control for actively absorbing the brake fluid through the return flow path 9b and securing the brake fluid in the slave cylinder 20. For example, the liquid absorption control is executed when it is desired to secure the brake fluid in order to pressurize the slave cylinder 20 to the high hydraulic pressure region. In addition, when the hydraulic pressure generated by the slave cylinder 20 is the hydraulic pressure required by the driver (this state is referred to as “steady”), the brake fluid is sucked in advance in preparation for the subsequent pressurization. Liquid control is performed. Furthermore, at the time of anti-lock brake control, the liquid absorption control is executed when the brake fluid is secured in advance in preparation for pressure increase. Details of the liquid absorption control will be described later.

Next, the operation of the brake system will be outlined.
(Normal brake control)
In the brake system A, when the system is activated, the normally closed electromagnetic valve 8 of the branch hydraulic pressure passage 3 is opened. In this state, the hydraulic pressure generated in the master cylinder 10 by the operation of the brake pedal P is transmitted to the stroke simulator 40 without being transmitted to the wheel cylinder W. Then, the hydraulic pressure in the pressure chamber 45 is increased, and the simulator piston 42 moves toward the bottom surface 41b against the urging force of the elastic members 43 and 44, whereby the stroke of the brake pedal P is allowed, and the pseudo operation is performed. A reaction force is applied to the brake pedal P.

  When the stroke sensor ST detects that the brake pedal P has been operated, the first switching valve 51 and the second switching valve 52 are excited and the valve body 51a moves to the second position as shown in FIG. (See FIG. 2 (b)). By this movement, the downstream side (wheel brake side) of the first hydraulic pressure passage 2a communicates with the first series passage 5a, and the second switching valve 52 causes the downstream side of the second hydraulic pressure passage 2b and the second communication passage 5b to communicate with each other. Leads to. That is, the master cylinder 10 and the wheel cylinder W are disconnected (non-communication state), and the slave cylinder 20 is in communication with the wheel cylinder W.

Further, when the depression of the brake pedal P is detected by the stroke sensor ST, the electric motor 24 of the slave cylinder 20 is driven by the electronic control unit 70, and the piston 22 of the slave cylinder 20 moves to the bottom 21b side. The brake fluid in the hydraulic chamber 26 is pressurized.
The electronic control unit 70 generates the hydraulic pressure generated by the slave cylinder 20 (the hydraulic pressure detected by the pressure sensor 7) and the hydraulic pressure output from the master cylinder 10 (the hydraulic pressure corresponding to the operation amount of the brake pedal P). The rotation speed of the electric motor 24 is controlled based on the comparison result. In this way, the brake system A increases the hydraulic pressure.

  The generated hydraulic pressure of the slave cylinder 20 is transmitted to each wheel cylinder W via the hydraulic pressure control device 30, and each wheel cylinder W is operated to apply a braking force to each wheel.

  When the depression of the brake pedal P is released, the electric motor 24 of the slave cylinder 20 is reversely driven by the electronic control unit 70, and the piston 22 is returned to the electric motor 24 side by the elastic member 23. As a result, the pressure in the hydraulic chamber 26 is reduced, and the operation of each wheel cylinder W is released.

  In the state where the slave cylinder 20 does not operate (for example, when the ignition is turned off or electric power cannot be obtained), the first switching valve 51, the second switching valve 52, and the normally closed solenoid valve 8 return to the initial state. (See FIG. 1). When the first switching valve 51 and the second switching valve 52 return to the initial state, the first hydraulic pressure path 2a communicates and the second hydraulic pressure path 2b communicates. In this state, the hydraulic pressure generated in the master cylinder 10 is directly transmitted to each wheel cylinder W.

(Liquid absorption control)
Next, liquid absorption control will be described. The liquid suction control is control for sucking brake fluid from the reservoir tank 15 or the reservoir 92 in order to secure brake fluid in the hydraulic pressure chamber 26 of the slave cylinder 20. The hydraulic chamber 26 has a normal (normal) brake control (first shut-off valve) except for special braking such as sudden braking or when antilock brake control is frequently continued. 61, during the brake control when the second shut-off valve 62 is open), a necessary amount of brake fluid is secured.
First, liquid absorption control at the time of special braking such as sudden braking that requires the maximum system generated hydraulic pressure will be described. During special braking such as sudden braking, a hydraulic pressure higher than the hydraulic pressure during normal brake control is required. In this case, in the slave cylinder 20, the piston 22 that has slid in the pressure direction in the cylinder hole 21 is returned in the pressure-reducing direction at a position just before contacting the bottom 21b of the cylinder hole 21 (returned to the electric motor 24 side). Liquid absorption control is performed. Hereinafter, a detailed description will be given with reference to FIGS. FIG. 5 is a flowchart for explaining the liquid suction control that requires the system maximum wheel cylinder pressure, and FIG. 6 is a map showing the relationship between the required hydraulic pressure and the required stroke amount.

First, in step S21 of FIG. 5, the detected value ST1 of the stroke sensor ST is input to the electronic control unit 70, and in step S22, the driver's required hydraulic pressure P3 based on the detected value ST1 is calculated.
Thereafter, in step S23, the required stroke amount STW of the piston 22 corresponding to the required hydraulic pressure P3 is calculated based on the map shown in FIG.

  Thereafter, in step S24, it is determined whether or not the calculated required stroke amount STW exceeds the normal maximum stroke amount (limit stroke amount) STL. The limit stroke amount STL is set, for example, as a movement distance when the piston 22 moves from an initial position to a position just before contacting the bottom portion 21b of the cylinder hole 21 during pressurization. That is, in step S24, it is determined whether or not the driver's required hydraulic pressure P3 can be generated with a stroke amount within the limit stroke amount STL.

  If it is determined in step S24 that the required stroke amount STW is smaller than the limit stroke amount STL (step S24, No), the process returns to step S21 and the following steps S22 and S23 are repeated.

  If it is determined in step S24 that the required stroke amount STW is larger than the limit stroke amount STL (step S24, Yes), the process proceeds to step S25, and the return amount STB of the piston 22 is calculated. That is, when the driver's required hydraulic pressure P3 cannot be met with the limit stroke amount STL, the piston 22 is once returned in the pressure reducing direction to perform pressurization in order to pressurize beyond the limit stroke amount STL. The return amount STB can be calculated based on the map shown in FIG.

  Thereafter, in step S26, pressurization driving of the slave cylinder 20 is started. In the subsequent step S27, the stroke amount STR (total stroke amount) of the slave cylinder 20 is input.

  Thereafter, in step S28, it is determined whether or not the input stroke amount STR is equal to or greater than the limit stroke amount STL. If it is determined in step S28 that the input stroke amount STR is not greater than or equal to the limit stroke amount STL (No in step S28), the process returns to step S27.

  In step S28, when the input stroke amount STR becomes equal to or larger than the limit stroke amount STL (step S28, Yes), the process proceeds to step S29, and the liquid absorption control is started.

  When shifting to the liquid absorption control, the electronic control unit 70 controls the first cutoff valve 61 and the second cutoff valve 62 to be closed. In this case, the first shut-off valve 61 and the second shut-off valve 62 are closed by the valve body 61a from the slave cylinder 20 side toward the wheel brake side (being closed by receiving the urging force of the return spring 61b). When the valve is closed, the valve body 61a is smoothly seated on the valve seat 61c under the fluid pressure from the slave cylinder 20 side (see FIGS. 2A and 2B). The hydraulic pressure downstream of the first shut-off valve 61 and the second shut-off valve 62 is held by closing the first shut-off valve 61 and the second shut-off valve 62.

  Thereafter, the electric motor 24 is driven in the pressure reducing direction (return direction) by the return amount STB calculated in step S25. Then, the piston 22 is returned in the pressure-reducing direction, and the hydraulic chamber 26 is depressurized to a negative pressure state while the hydraulic pressure of the wheel cylinder W is maintained. As a result, the brake fluid is sucked from the reservoir tank 15 into the hydraulic pressure chamber 26 through the replenishment path 9a, the return flow path 9b, the branch return flow path 9c, and the common hydraulic pressure path 4. In this case, the amount of brake fluid that is absorbed is based on the return amount STB, and is an amount that can supplement pressurization.

Thereafter, in step S30, the piston 22 is driven again in the pressurizing direction, and the first cutoff valve 61 and the second cutoff valve 62 are controlled to open. As a result, the pressure of the wheel cylinder W (hereinafter referred to as “wheel cylinder pressure V1”) is increased again, and the wheel cylinder pressure V1 corresponding to the driver's required hydraulic pressure P3 is obtained.
The opening timing of the first shut-off valve 61 and the second shut-off valve 62 may be determined by, for example, driving the piston 22 in the return direction and then driving the piston 22 in the pressurizing direction. The valve opens at the timing when the generated hydraulic pressure SCV of the slave cylinder 20 becomes equal to the hydraulic pressure (wheel cylinder pressure V1) on the downstream side of the shutoff valve 62, or opens at the timing just before it becomes the same pressure. It is good to do. By opening the valve at this timing, since there is no differential pressure between the upstream side and the downstream side of the first cutoff valve 61 and the second cutoff valve 62, the valve opening operation can be performed smoothly. Natural boosting characteristics can be obtained. It should be noted that the valve can be opened at a timing after the generated hydraulic pressure SCV of the slave cylinder 20 becomes equal to the hydraulic pressure downstream of the first cutoff valve 61 and the second cutoff valve 62. In this case, it is preferable to open the valve until it reaches a pressure obtained by adding the load of the return spring 61b to the generated hydraulic pressure SCV.

  FIG. 7 is a time chart showing the timing of liquid absorption control when the maximum system wheel cylinder pressure V1M is requested. As shown in FIG. 7, when the piston 22 of the slave cylinder 20 is driven in the pressurizing direction and the stroke amount STR reaches the limit stroke amount STL at the time T1, the liquid suction control is started (the start timing of the hydraulic pressure control). ). That is, the wheel cylinder pressure V1 is increased without liquid absorption control up to the normal pressure maximum value VM (illustrated by a thick broken line).

In the liquid suction control, as described above, the electric motor 24 is driven in the pressure reducing direction (return direction) by the return amount STB calculated in step S25, and the brake fluid is sucked into the hydraulic pressure chamber 26 (time T1). To time T2).
On the other hand, the first cutoff valve 61 and the second cutoff valve 62 are closed at time T1. As a result, the wheel cylinder pressure V1 is maintained from time T1 to time T2.

  At time T2, when the piston 22 is driven again in the pressurizing direction and the stroke amount STR (total stroke amount) increases again, the wheel cylinder pressure V1 starts to rise. At time T4, the system increases to the maximum wheel cylinder pressure V1M, and the pressurization exceeding the limit stroke amount STL is supplemented.

  In the brake system A of the present embodiment, since the liquid suction control is provided, the maximum hydraulic pressure of the system can be increased without securing the axial length of the slave cylinder 20 more than necessary.

  Next, liquid suction control performed at a timing that does not affect the hydraulic pressure generated by the slave cylinder 20 will be described with reference to FIG. The liquid absorption control in FIG. 8 is based on the premise that the piston 22 (see FIG. 1) does not reach the limit stroke during normal braking. In the liquid absorption control of FIG. 8, when the wheel cylinder pressure V1 is increased to the driver's required hydraulic pressure and the operation of the brake pedal P does not change (in the holding state), the liquid absorption control is performed. It is. Note that if the driver's operation of the brake pedal P changes during the liquid absorption control, for example, if the brake pedal P is further depressed or released, the liquid absorption control is stopped. Hereinafter, liquid absorption control by the electronic control unit 70 will be described in detail.

  When the brake pedal P is depressed by the driver, the driver's required hydraulic pressure P3 (not shown) is calculated based on the detection value ST1 of the stroke sensor ST in the same manner as described above. Based on the required hydraulic pressure P3, the required stroke amount STW is calculated from the map shown in FIG. Thereafter, the slave cylinder 20 is driven based on the required stroke amount STW, and the piston 22 is pressure-driven in the pressurizing direction. Then, the wheel cylinder pressure V1 increases as the stroke amount STR increases.

  Thereafter, when the depression of the brake pedal P is held at time t1, and this holding state is continued for a predetermined time, a liquid absorption control flag is set at time t2 (the electronic control device 70 needs to execute the liquid absorption control). The first shut-off valve 61 and the second shut-off valve 62 are closed. As a result, the wheel cylinder pressure V1 is held.

  Thereafter, at time t3, the piston 22 is driven to depressurize in the depressurizing direction. The return amount STB can be obtained based on the necessary stroke amount STW, for example. When the piston 22 is driven to depressurize in the depressurization direction, the hydraulic pressure SCV generated in the slave cylinder 20 decreases (time t3 → time t4), and the hydraulic chamber 26 enters a negative pressure state. As a result, the brake fluid is sucked into the hydraulic pressure chamber 26 from the reservoir tank 15 through the replenishment path 9a, the return flow path 9b, the branch return flow path 9c, and the common hydraulic pressure path 4 (see FIG. 1).

  At time t4, the piston 22 is driven in the pressurizing direction, and the generated hydraulic pressure SCV of the slave cylinder 20 is the same as the wheel cylinder pressure V1 (the hydraulic pressure downstream of the first cutoff valve 61 and the second cutoff valve 62). Pressurized to become. When the generated hydraulic pressure SCV of the slave cylinder 20 becomes the same as the wheel cylinder pressure V1 at time t5, the first cutoff valve 61 and the second cutoff valve 62 are opened.

  Thereafter, when the brake pedal P is depressed again by the driver at time t6, the wheel cylinder pressure V1 increases in accordance with the increase in the stroke amount STR. Then, at time t7, the depression of the brake pedal P is held, and when this holding state is continued for a predetermined time, the suction control flag is set at time t8, and the first cutoff valve 61 and the second cutoff valve 62 are turned on. The valve is closed. As a result, the wheel cylinder pressure V1 is held.

  At time t9, the piston 22 is driven to depressurize in the depressurizing direction. The return amount STB can be obtained, for example, based on the required stroke amount STW due to the increase in the stroke amount STR from time t6 to time t7. When the piston 22 is driven to depressurize in the depressurization direction, the generated hydraulic pressure SCV of the slave cylinder 20 decreases (time t9 → time t10), and the hydraulic chamber 26 enters a negative pressure state. As a result, the brake fluid is sucked into the hydraulic pressure chamber 26 from the reservoir tank 15 through the replenishment path 9a, the return flow path 9b, the branch return flow path 9c, and the common hydraulic pressure path 4 (see FIG. 1).

  In this state, when the brake pedal P is depressed by the driver at time t10, the liquid absorption control is stopped. With the suspension of the liquid suction control, the first cutoff valve 61 and the second cutoff valve 62 are opened at time t10.

  The generated hydraulic pressure SCV of the slave cylinder 20 is increased at once by the depression of the brake pedal P, and the generated hydraulic pressure SCV of the slave cylinder 20 is increased again (time t11).

  Thereafter, the depression of the brake pedal P is held at time t12. When this holding state is continued for a predetermined time, the suction control flag is set at time t13 in the same manner as described above, and the first shutoff valve 61 and the first shutoff valve 61 The two shutoff valve 62 is closed. As a result, the wheel cylinder pressure V1 is held.

  At time t14, the piston 22 is driven in the pressure reducing direction. The return amount STB in this case can be obtained, for example, based on the required stroke amount STW due to the increase in the stroke amount STR from time t11 to time t12. When the piston 22 is driven in the depressurization direction, the generated hydraulic pressure SCV of the slave cylinder 20 decreases again (time t14 → time t15), and the hydraulic pressure chamber 26 enters a negative pressure state. As a result, the brake fluid is sucked into the hydraulic pressure chamber 26 from the reservoir tank 15 through the replenishment path 9a, the return flow path 9b, the branch return flow path 9c, and the common hydraulic pressure path 4 (see FIG. 1).

  In this state, when the driver releases the depression of the brake pedal P at time t15, the liquid absorption control is stopped. Then, with the suspension of the liquid suction control, the first cutoff valve 61 and the second cutoff valve 62 are opened at time t15.

  At time t15, the generated hydraulic pressure SCV of the slave cylinder 20 is increased in the pressurizing direction so as to be equal to the wheel cylinder pressure V1 (the hydraulic pressure downstream of the first cutoff valve 61 and the second cutoff valve 62). The piston 22 is once driven (time t15 → time t17). Thereafter, the piston 22 is driven in the pressure reducing direction, and the wheel cylinder pressure V1 is reduced.

  Next, liquid absorption control during antilock brake control will be described with reference to FIG. During anti-lock brake control, control for increasing, holding, or reducing the hydraulic pressure acting on the wheel brake is frequently performed, so it is necessary to secure brake fluid to be supplied to the wheel brake. The liquid absorption control shown in FIG. 9 is performed when the brake fluid amount BR stored in the reservoir 92 of the return flow path 9b reaches a hydraulic pressure that is greater than or equal to a predetermined pressure during antilock brake control. Is. That is, when the brake fluid amount BR reaches a predetermined fluid pressure, the fluid absorption control is performed assuming that the stroke amount STR of the piston 22 has reached the limit stroke amount STL. Hereinafter, liquid absorption control by the electronic control unit 70 will be described in detail.

  As shown in FIG. 9, when the brake pedal P is depressed by the driver at time t21, the driver's required hydraulic pressure P3 (not shown) is calculated based on the detection value ST1 of the stroke sensor ST in the same manner as described above. Is done. Based on the required hydraulic pressure P3, the required stroke amount STW is calculated from the map shown in FIG. Then, the slave cylinder 20 is driven based on the required stroke amount STW, and the piston 22 is pressurized and driven in the pressurizing direction. Then, the wheel cylinder pressure V1 increases as the stroke amount STR increases.

  Thereafter, when the wheel is about to enter a locked state at time t22, the anti-lock brake control is executed by the hydraulic pressure control device 30. The antilock brake control is realized by appropriately selecting a hydraulic pressure acting on the wheel cylinder W in a reduced pressure state, an increased pressure state, or a holding state in which the hydraulic pressure is kept constant. Note that the electronic controller 70 determines whether to select the reduced pressure, the increased pressure, or the held state based on information such as a wheel speed obtained from a wheel speed sensor provided in the vicinity of the wheel. When the anti-lock brake control is started, that is, when the pressure reduction of the wheel brake is started, the electronic control device 70 closes the cut valve 93 of the supply path 9a shown in FIG.

  In the anti-lock brake control, when the reduced pressure state is selected at time t22, the inlet valve 31 and the outlet valve 32 of the hydraulic pressure control device 30 shown in FIG. The brake fluid is released to the return fluid passage 9b through the outlet valve 32. That is, a part of the brake fluid supplied from the slave cylinder 20 to the wheel cylinder W is released to the return fluid passage 9b. For this reason, for example, in the anti-lock brake control, when the pressure reduction state is selected at time t23 and then the pressure increase state is selected at time t24, etc., in order to ensure the fluid pressure necessary for pressure increase, The stroke amount STR of the piston 22 is increased.

  The brake fluid released to the return flow path 9b is temporarily stored in the reservoir 92 of the return flow path 9b. The amount of brake fluid stored in the reservoir 92 is specified by the detection value of the pressure sensor 91. The electronic control unit 70 acquires the detection value of the pressure sensor 91, and calculates the brake fluid amount BR stored in the reservoir 92 based on the detection value. The electronic control unit 70 monitors whether or not the calculated brake fluid amount BR has reached a predetermined fluid pressure.

  Thereafter, the anti-lock brake control is continued and the pressure increasing state is repeatedly selected. When the brake fluid amount BR stored in the reservoir 92 reaches a predetermined fluid pressure at time t25, the electronic control device 70 performs the fluid suction control. Is called. In the liquid suction control, the first shut-off valve 61 and the second shut-off valve 62 are closed (time t25), and the piston 22 is driven to depressurize in the depressurization direction (return direction) based on the return amount STB calculated in the same manner as described above. (Time t26). Then, the hydraulic chamber 26 is depressurized to a negative pressure state, and the brake fluid stored in the reservoir 92 is sucked into the hydraulic chamber 26 through the return channel 9b, the branch return channel 9c, and the common hydraulic channel 4. To be liquidated. As a result, a desired generated hydraulic pressure SCV necessary for pressure increase is ensured (a stroke amount STR exceeding an allowable limit is ensured).

  When the liquid suction is completed, the piston 22 is pressurized and driven in the pressurizing direction, and the generated hydraulic pressure SCV of the slave cylinder 20 is the wheel cylinder pressure V1 (the hydraulic pressure downstream of the first cutoff valve 61 and the second cutoff valve 62). The pressure is increased to the same pressure. Thereafter, the first shut-off valve 61 and the second shut-off valve 62 are controlled to open (time t27), and the liquid suction control is finished (time t28). In the subsequent antilock brake control, when the brake fluid amount BR reaches the predetermined fluid pressure again, the fluid suction control is performed in the same manner as described above, and the desired generated fluid pressure SCV necessary for the pressure increase is obtained. Secured.

As described above, the liquid absorption control when the brake fluid amount BR reaches the predetermined hydraulic pressure has been described. You may make it perform. In this case, since the liquid suction control is performed at a timing other than the pressure increase control, the brake fluid can be effectively ensured during the antilock brake control.
Further, when the stroke amount STR of the piston 22 reaches the allowable limit, the liquid suction control may be performed assuming that the brake fluid amount BR has reached a predetermined hydraulic pressure.

  Further, the electronic controller 70 is provided with a road surface friction coefficient estimating means capable of estimating the road surface friction coefficient, and the liquid absorption control is performed at a timing when the road surface friction coefficient estimated by the road surface friction coefficient estimation means becomes less than a predetermined value. You may comprise. In this case, for example, the brake fluid can be effectively secured when the anti-lock brake control (decompression control, holding control) is continued for a relatively long time on a low μ road with a low road surface friction coefficient.

  In the brake system according to the present embodiment described above, the brake fluid released during the pressure reduction control is stored in the reservoir 92 and sucked into the slave cylinder 20, so that the axial length of the slave cylinder 20 is relatively long. Even if it is set short, the brake fluid for re-pressurization can be suitably supplied into the hydraulic chamber 26. As a result, the brake system A that can appropriately increase the pressure to the high hydraulic pressure region while avoiding an increase in the size of the slave cylinder 20 is obtained. Moreover, even when the pressure increasing, holding, or pressure reducing control is frequently performed during the anti-lock brake control, the brake fluid released to the return flow path 9b can be sucked into the slave cylinder 20 by the liquid suction control. The necessary brake fluid can be suitably secured. Therefore, even if the antilock brake control continues for a long time, the hydraulic pressure acting on the wheel brake can be suitably increased, and an efficient brake system can be obtained.

  Further, since the brake fluid is stored in the reservoir 92 in a state where pressure is applied, if the fluid pressure chamber 26 of the slave cylinder 20 becomes negative during the suction control, suction on the slave cylinder 20 side and suction on the reservoir 92 side are performed. The brake fluid smoothly flows into the hydraulic chamber 26 by the extrusion. As a result, quick liquid absorption is realized, and it is possible to suitably secure the brake liquid that acts on the wheel brakes FL, RR, RL, FR during the antilock brake control.

  In addition, since the replenishment path 9a from the reservoir tank 15 to the return flow path 9b is blocked by the cut valve 93 during the anti-lock brake control, the return flow path 9b is closed and the brake stored in the reservoir 92 by liquid absorption control. The liquid is preferably sucked (refluxed) into the hydraulic chamber 26 of the slave cylinder 20.

  In addition, since the cut valve 93 is opened at a time other than the anti-lock brake control, the reservoir tank is used for a normal brake that is opened or a special brake such as a sudden brake that requires the maximum system hydraulic pressure. The brake fluid is sucked into the slave cylinder 20 from 15. Therefore, it is possible to increase the pressure suitably to the high hydraulic pressure region while avoiding the enlargement of the slave cylinder 20.

  Moreover, since the timing of liquid absorption control can be specified based on the detection value of the pressure sensor 91, liquid absorption control can be performed efficiently. Further, since the timing of liquid absorption control can be specified by a simple means of providing the pressure sensor 91, the system configuration is simplified.

Further, since the check valve 9d is provided in the return flow path 9b, the brake pressure stored in the reservoir 92 is reduced by reducing the hydraulic pressure chamber 26 of the slave cylinder 20 during the liquid suction control of the antilock brake control. The liquid can be sucked into the slave cylinder 20 through the check valve 9d. Further, the check valve 9d can suitably prevent the hydraulic pressure generated in the slave cylinder 20 from being transmitted to the reservoir 92 side.
Further, during the high load brake control, the brake fluid in the reservoir tank 20 can be sucked into the slave cylinder 20 through the supply passage 9a. Further, the check valve 9d can suitably prevent the hydraulic pressure generated in the slave cylinder 20 from being transmitted to the reservoir tank 20 side.

  Further, since the first shut-off valve 61 and the second shut-off valve 62 are normally open solenoid valves, the first shut-off valve 61 and the second shut-off valve 61 and the second shut-off valve 61 and There is no need to energize the second shutoff valve 62. Therefore, power consumption can be minimized.

  The liquid absorption control may be configured to be performed at a timing when the amount of increase in the driver's required hydraulic pressure becomes equal to or less than a predetermined value. If it does in this way, liquid absorption control can be performed suitably at the timing which does not have an influence on brake feeling.

  Further, the liquid absorption control may be configured to be performed at a timing when the absolute value of the driver's required hydraulic pressure becomes equal to or greater than a predetermined value. In this way, for example, boosting can be performed satisfactorily at the time of brake assist control with a boosting greater than that during normal braking.

  Further, the pressure sensor 91 for the return flow path 9b is not necessarily provided. In this case, the amount of brake fluid stored in the reservoir 92 may be estimated by the electronic control unit 70 based on the operation status of the slave cylinder 20 and the opening / closing operation status of each outlet valve 32.

  In addition, the brake fluid amount may not be converted from the sensor value (hydraulic pressure), and the sensor value (hydraulic pressure) may be used as it is and compared with a predetermined threshold value to perform the liquid absorption control. .

1 Base 5a First passage (communication passage)
5b Second communication path (communication path)
9a Supply path 9b Return path 9d Check valve 10 Master cylinder 15 Reservoir tank 20 Slave cylinder 22 Piston 26 Fluid pressure chamber 30 Fluid pressure control device 40 Stroke simulator 51 First switching valve (switching valve)
52 Second switching valve (switching valve)
61 First shut-off valve (shut-off valve)
62 Second shutoff valve (shutoff valve)
70 Electronic control device (control means)
92 Reservoir (pressure accumulation chamber)
91 Pressure sensor (acquisition means)
93 Cut valve A Brake system P Brake pedal (brake operator)
FL, RR, RL, FR Wheel brake W Wheel cylinder

Claims (7)

A master cylinder that generates a hydraulic pressure to be applied to a wheel brake by an operation of a driver's brake operator, and a slave cylinder that generates a hydraulic pressure by an electric actuator that is driven according to an operation amount of the brake operator. A brake system,
A hydraulic path from the master cylinder to the wheel brake;
A switching valve provided in the hydraulic pressure path;
A communication path leading from the slave cylinder to the switching valve;
A shut-off valve provided in the communication path and capable of blocking the communication path;
A return flow path from the wheel brake to the slave cylinder;
A pressure accumulating chamber that is provided in the return flow path and stores brake fluid that has escaped from the wheel brake to the return flow path when the wheel brake is depressurized;
Control means for performing liquid suction control for sucking brake fluid into the slave cylinder,
The control means is configured to execute control for closing the shutoff valve and driving the piston in a pressure reducing direction by the electric actuator during liquid suction control,
During the pressure reduction, the brake fluid stored in the pressure accumulating chamber flows into the slave cylinder through the return flow path by liquid absorption control. The brake system according to claim 1,
A reservoir tank for storing brake fluid;
A supply path from the reservoir tank to the return flow path;
A cut valve provided in the supply path and capable of blocking the supply path;
The said control means closes the said cut valve at the time of the said pressure reduction, The brake system characterized by the above-mentioned. The brake system according to claim 2,
The control system is characterized in that while the anti-lock brake control continues, the control means continues to maintain the valve closing control of the cut valve. The brake system according to any one of claims 1 to 3,
An acquisition means for acquiring a brake fluid amount or a hydraulic pressure stored in the pressure accumulation chamber;
The said control means performs a liquid absorption control, when the brake fluid quantity or hydraulic pressure acquired by the said acquisition means becomes more than predetermined, The brake system characterized by the above-mentioned. The brake system according to claim 4, wherein
The brake system according to claim 1, wherein the acquisition means is a pressure sensor disposed in the return flow path. The brake system according to any one of claims 1 to 5,
The brake system according to claim 1, wherein the return flow path is provided with a check valve that allows only brake fluid to flow from the pressure accumulation chamber side to the slave cylinder side. The brake system according to any one of claims 1 to 6,
The brake system according to claim 1, wherein the shut-off valve is a normally open solenoid valve.

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