JP6245655B2 - Brake system - Google Patents

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 boost the hydraulic system by driving the slave cylinder, it can be suitably boosted to a high hydraulic pressure region by increasing the stroke amount of the slave cylinder piston provided in the slave cylinder. Can do. 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, includes a slave cylinder that generates hydraulic pressure by an electric actuator that is driven in accordance with the operation of the brake operator. The brake system includes: a fluid path that leads from the slave cylinder to the wheel brake; a shut-off valve that is provided in the fluid path and that can shut off the fluid path; a reservoir tank that stores brake fluid; And a control means for executing liquid absorption control for absorbing brake fluid from the supply path. The control means executes control for closing the shut-off valve and driving the slave cylinder in the pressure reducing direction by the electric actuator as liquid absorption control when the fluid amount of the slave cylinder decreases due to pressure reduction of the wheel brake. To do. Further, the control means includes road surface friction coefficient estimating means capable of estimating a road surface friction coefficient during anti-lock brake control. The control means is configured to set the timing for performing liquid absorption control based on the road surface friction coefficient estimated by the road surface friction coefficient estimation means .

In such a brake system, when the fluid amount of the slave cylinder decreases due to the pressure reduction of the wheel brake, the shut-off valve is closed and the slave cylinder is driven in the fluid pressure reduction direction. As a result, the pressure in the slave cylinder (hydraulic pressure chamber) becomes negative, and the brake fluid is sucked into the slave cylinder from the replenishment path. Therefore, even if the axial length of the slave cylinder is set to be relatively short, the brake fluid for repressurization can be replenished into the slave cylinder 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. In addition, the anti-lock brake control is frequently controlled to increase, hold, or reduce the hydraulic pressure acting on the wheel brakes, and even if the fluid volume in the slave cylinder decreases, it is supplied to the wheel brakes by liquid absorption control. The brake fluid to be secured can be suitably secured.
In addition, the liquid suction control performed when the liquid amount of the slave cylinder decreases is not limited to the liquid suction control performed when the liquid amount of the slave cylinder decreases, and the liquid amount of the slave cylinder decreases. Liquid absorption control performed at a later predetermined timing is also included.
Further, since the control means is configured to set the timing for performing liquid absorption control based on the road surface friction coefficient estimated by the road surface friction coefficient estimation means, for example, anti-lock brake control on a low μ road having a low road surface friction coefficient Brake fluid can be effectively secured when (decompression control, holding control) is continued for a relatively long time.

  Moreover, the said control means is good to perform liquid absorption control, when the stroke amount of the said slave cylinder becomes more than predetermined. In this way, the liquid absorption control is performed only when a high hydraulic pressure is required, and 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. A brake system capable of suitably securing the brake fluid supplied to the wheel brake for the lock brake control is obtained.

  The electric actuator may be an electric motor, and the stroke amount of the slave cylinder may be specified based on a rotation angle sensor that detects a rotation angle of the electric motor. If it does in this way, the exact stroke amount can be specified based on the rotation angle of an electric motor, and the timing for performing liquid absorption control can be specified easily.

  Moreover, the said control means is good to perform liquid absorption control, when the control state of a wheel becomes holding | maintenance control or pressure reduction control. Thus, by performing liquid absorption when the control state of the wheel is other than the pressure increase control, it is possible to effectively secure the brake liquid during the antilock brake control.

  The control means may perform liquid absorption control when the relationship between the hydraulic pressure increased by the slave cylinder and the stroke amount of the slave cylinder does not satisfy a predetermined relationship. If it does in this way, brake fluid can be replenished in a slave cylinder by liquid absorption control, and the hydraulic pressure raised by a slave cylinder can be made into the predetermined hydraulic pressure corresponding to the stroke amount of a slave cylinder.

  Further, it is preferable that a check valve that allows only brake fluid to flow from the reservoir tank side to the slave cylinder side is provided in the supply path. In this way, when the pressurizing operation of the slave cylinder is released, the brake fluid in the reservoir tank can be supplied to the slave cylinder through the supply path. 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, since the shut-off valve is a normally open solenoid valve, it is not necessary to energize the shut-off valve during normal braking in which the slave cylinder generates hydraulic pressure in the wheel brake. 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 which shows the procedure of a diagnosis when the reduction | decrease of brake fluid arises. 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, two first elastic members 13 and a second elastic member 14 housed in the cylinder hole 10a, It is equipped with. The master cylinder 10 is provided with a reservoir tank 15 for storing brake fluid. The reservoir tank 15 includes first supply ports 15a and 15b for supplying brake fluid to the master cylinder 10, and a second supply port 15c independent of the first supply ports 15a and 15b. A supply channel 9a and a return channel 9b are connected to the second supply port 15c.

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 passage 9 communicates with the reservoir tank 15 via the port 19 and the first supply port 15b 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 hydraulic chamber 26 is formed between the bottom 21 b of the cylinder hole 21 and the slave cylinder piston 22 (hereinafter simply 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 hemispherical (see FIG. 2 (a)). 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. If the inlet valve 31 is closed and the outlet valve 32 is opened, the brake fluid flows out from the wheel cylinder W to the return fluid passage 9b, 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 the slave cylinder 20 is shut off (becomes a 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 (not in communication) 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 the slave cylinder 20 is shut off (becomes a 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 (not in communication) 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 element 61a of the second shut-off valve 61 when the valve is closed 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 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.

  The supply path 9 a is a liquid path from the reservoir tank 15 to the slave cylinder 20. The replenishment path 9a is connected to the common hydraulic path 4 via the branch replenishment path 9c. The branch replenishment path 9c is provided with a check valve 9d that allows only brake fluid to flow from the reservoir tank 15 side to the common hydraulic pressure path 4 side (slave cylinder 20 side). Normally, the brake fluid is supplied from the reservoir tank 15 to the slave cylinder 20 through the supply path 9a. Further, during the liquid suction control described later, the brake fluid is sucked into the slave cylinder 20 from the reservoir tank 15 (second supply port 15c) through the supply path 9a, the branch supply path 9c, and the common hydraulic pressure path 4.

  The return liquid path 9 b is a liquid path from the hydraulic pressure control device 30 to the reservoir tank 15. Brake fluid escaped from each wheel cylinder W flows into the return fluid passage 9b via the outlet valve 32 of the fluid pressure control device 30. The brake fluid released to the return fluid passage 9b is returned to the reservoir tank 15 from the return fluid passage 9b through the second supply port 15c.

  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 refers to the map shown in FIG. 3 as a program stored in advance, and the hydraulic pressure generated by the slave cylinder 20 corresponds to the stroke amount of the piston 22 of the slave cylinder 20. A function (a function as a determination unit) for determining whether or not the value has increased to a predetermined value programmed in advance is provided. 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 suction control is a control for positively sucking the brake fluid into the slave cylinder 20 from the replenishment path 9 a and securing the brake fluid in the slave cylinder 20. For example, when it is desired to secure the brake fluid to pressurize the slave cylinder 20 up to the high hydraulic pressure region, or when the generated hydraulic pressure of the slave cylinder 20 becomes the driver's required hydraulic pressure (hereinafter, this state is referred to as “steady state”). In this case, it is executed when the brake fluid is secured in advance for the subsequent pressurization. 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.

(Brake control when brake fluid decreases)
Next, in the state where the electric motor 24 of the slave cylinder 20 is driven, the brake control when the brake fluid in either the first hydraulic pressure path 2a or the second hydraulic pressure path 2b is decreased is a flowchart of FIG. Will be described with reference to FIG. In this case, the brake fluid reduction is diagnosed through the following three steps.

First, in step S1, a detection value P2 of the pressure sensor 7 and a pre-programmed determination value P5 (see FIG. 3) are input to the electronic control unit 70.
Thereafter, in step S2, the electronic control unit 70 determines whether or not the detection value P2 of the pressure sensor 7 has increased to the determination value P5. That is, it is determined whether the generated hydraulic pressure (detected value P2) of the slave cylinder 20 has increased to a hydraulic pressure corresponding to the stroke amount of the piston 22 of the slave cylinder 20. If it is determined in step S2 that the detection value P2 of the pressure sensor 7 has increased to the determination value P5 (step S2, Yes), the process returns to step S1 and the following steps S1 and S2 are repeated.

In step S2, when it is determined that the detection value P2 of the pressure sensor 7 has not increased to the determination value P5 (step S2, No, when it is determined to be abnormal), the process proceeds to step S3, where the brake fluid is discharged. Begin first-stage diagnosis for reduction.
In the first stage diagnosis, first, the shut-off valves 61 and 62 are closed in step S3, and the slave cylinder 20 is pressurized in step S4 (the electric motor so that the piston 22 moves toward the bottom 21b). 24 is driven).

If the slave cylinder 20 is driven to pressurize, it is determined in step S5 whether or not the detection value P2 of the pressure sensor 7 has increased (recovered) compared to before the both shut-off valves 61 and 62 are closed.
If it is determined in step S5 that the detection value P2 of the pressure sensor 7 has not increased (No in step S5), the process proceeds to step S7, where the hydraulic pressure is directly applied from the master cylinder 10 to the wheel cylinder W. Start control in backup mode. That is, when it is determined in step S5 that the detection value P2 of the pressure sensor 7 has not increased, the brake fluid is reduced in the path from the first cutoff valve 61 and the second cutoff valve 62 to the slave cylinder 20 side. Therefore, the excitation of the first switching valve 51 and the second switching valve 52 is released. Thereby, as shown in FIG. 2A, the valve bodies 51a are respectively switched to the first position. By this switching, the first hydraulic pressure path 2a communicates and the second hydraulic pressure path 2b communicates. That is, the wheel brake communicates with the master cylinder 10 and is disconnected from the slave cylinder 20.
If it is determined in step S5 that the detected value P2 of the pressure sensor 7 has not increased (No in step S5), the normally closed electromagnetic valve 8 in the branch hydraulic pressure path 3 is closed (master). Stop the flow from the cylinder 10 to the stroke simulator 40). As a result, the hydraulic pressure generated in the master cylinder 10 is directly transmitted to the wheel cylinder W (wheel brake) via the first hydraulic pressure path 2a and the second hydraulic pressure path 2b.

  In step S5, when it is determined that the detection value P2 of the pressure sensor 7 is increasing (step S5, Yes), the second stage diagnosis is started. In this case, the process proceeds to step S6, the first shut-off valve 61 is kept closed, and the second shut-off valve 62 is opened. Thereafter, in step S8, the slave cylinder 20 is driven under pressure.

After the pressure driving, in step S9, it is determined whether or not the detected value P2 of the pressure sensor 7 has increased (recovered) compared to before the first shut-off valve 61 is closed (second stage).
If it is determined in step S9 that the detection value P2 of the pressure sensor 7 has increased (step S9, Yes), the process proceeds to step S10, and the process proceeds to the brake control mode of the second brake system K2. That is, when the detected value P2 of the pressure sensor 7 is increased by closing the first shutoff valve 61, the brake fluid may be decreased in the path of the first brake system K1, In the second brake system K2, the pressure increase by the slave cylinder 20 is continued. That is, braking (brake control mode) by the slave cylinder 20 is ensured by the second brake system K2. The first hydraulic pressure path 2a and the slave cylinder 20 are continuously disconnected.

  On the other hand, if it is determined in step S9 that the detection value P2 of the pressure sensor 7 has not increased (No in step S9), a third-stage diagnosis is started. In this case, the process proceeds to step S11, where the first cutoff valve 61 is opened and the second cutoff valve 62 is closed. Thereafter, in step S12, the slave cylinder 20 is driven to be pressurized.

After the pressure driving, in step S13, it is determined whether or not the detection value P2 of the pressure sensor 7 has increased (recovered) compared to before step S12.
In step S13, when it is determined that the detection value P2 of the pressure sensor 7 has increased (step S13, Yes), the process proceeds to step S14, and the process proceeds to the brake control mode of the first brake system K1. That is, when the detection value P2 of the pressure sensor 7 is increased by closing the second shutoff valve 62, the brake fluid may be decreased in the path of the second brake system K2. In the first brake system K1, the pressure increase by the slave cylinder 20 is continued. That is, braking (brake control mode) by the slave cylinder 20 is ensured by the first brake system K1. The second hydraulic pressure path 2b and the slave cylinder 20 are continuously disconnected.

  In Step S13, when it is determined that the detection value P2 of the pressure sensor 7 does not increase (No in Step S13), the process proceeds to Step S7, and the hydraulic pressure is directly applied from the master cylinder 10 to the wheel cylinder W. Start control in backup mode.

  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 a control for sucking brake fluid from the reservoir tank 15 in order to secure the brake fluid in the hydraulic pressure chamber 26 of the slave cylinder 20. In the hydraulic chamber 26, a necessary amount of brake fluid is secured in normal (ordinary) brake control except during special braking such as sudden braking.
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. 6 is a flowchart for explaining the liquid suction control that requires the system maximum wheel cylinder pressure, and FIG. 7 is a map showing the relationship between the generated hydraulic pressure of the slave cylinder and the required stroke amount.

First, in step S21 of FIG. 6, 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 step S27, the stroke amount STR (total stroke amount) of the piston 22 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 hydraulic pressure from the slave cylinder 20 (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 9 a 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 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. 8 is a time chart showing the timing of liquid suction control when the system maximum wheel cylinder pressure V1M is requested. As shown in FIG. 8, 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. Then, at time T3, 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 generated hydraulic pressure of the slave cylinder 20 will be described with reference to FIG. The liquid absorption control in FIG. 9 is based on the premise that the piston 22 (see FIG. 1) does not reach the limit stroke at the time of regular braking. In the liquid absorption control of FIG. 9, the liquid absorption control is performed when the operation of the brake pedal P does not change (in the holding state) after the wheel cylinder pressure V1 is increased to the driver's required hydraulic pressure. 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 through the replenishment path 9a 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 through the replenishment path 9a 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 through the replenishment path 9a 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. 10 performs liquid absorption control when the stroke amount STR of the piston 22 reaches an allowable limit (limit stroke amount) during antilock brake control. Hereinafter, liquid absorption control by the electronic control unit 70 will be described in detail.

  As shown in FIG. 10, when the driver depresses the brake pedal P 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 be locked 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.

  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 holding state is selected at time t23 and then the pressure increasing state is selected at time t24, etc., in order to ensure the hydraulic pressure necessary for pressure increasing, The stroke amount STR of the piston 22 is increased.

  Thereafter, when the stroke amount STR reaches the allowable limit at time t25, liquid absorption control is performed. 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 depressurized (returned at time t26) based on the return amount STB calculated in the same manner as described above. Direction). Then, the hydraulic chamber 26 is depressurized to a negative pressure state, and the brake fluid is sucked into the hydraulic chamber 26 from the reservoir tank 15 through the replenishment path 9a and the common hydraulic path 4. As a result, a stroke amount STR exceeding the allowable limit is secured, and a desired generated hydraulic pressure SCV is secured.

  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 stroke amount STR reaches the allowable limit again, the liquid absorption control is performed in the same manner as described above, and the stroke amount STR exceeding the allowable limit is secured.

  The liquid absorption control when the stroke amount STR reaches the allowable limit has been described above. However, the liquid absorption control is not limited to this, and the liquid absorption control is performed at the timing when the antilock brake control becomes the holding control or the pressure reduction control. It may be. 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, the electronic control unit 70 is provided with a road surface friction coefficient estimating means capable of estimating the road surface friction coefficient, and the timing for performing the liquid absorption control is changed based on the road surface friction coefficient estimated by the road surface friction coefficient estimating means. It may be configured. In this case, for example, when it is estimated that anti-lock brake control (decompression control, holding control) is continued for a relatively long time on a low μ road having a low road surface friction coefficient, the stroke amount STR falls within the allowable limit. By performing the liquid absorption control at a predetermined timing earlier than the arrival, the brake fluid can be effectively secured. The predetermined timing may be, for example, a timing when the holding control is performed after a predetermined stroke or a timing when the pressure reducing control is performed.
The road surface friction coefficient can be estimated based on, for example, the wheel brake fluid pressure at the time of depressurization of the antilock brake control or the return tendency (wheel acceleration) of the wheel during the depressurization.

According to the brake system of the present embodiment described above, the connection between the master cylinder 10 and the slave cylinder 20 with respect to the wheel brake can be switched by the first switching valve 51 and the second switching valve 52, and Since the communication can be shut off by the first shut-off valve 61 and the second shut-off valve 62, the hydraulic pressure acting on the wheel brake can be brought into various states without having a complicated configuration, and the system situation and the vehicle Efficient hydraulic pressure control suitable for the situation becomes possible.
And since efficient hydraulic pressure control is attained without having a complicated structure, the enlargement as a system can be suppressed.
In addition, the hydraulic pressure of each system K1, K2 can be increased separately, and the hydraulic pressure acting on each system K1, K2 from the slave cylinder 20 can be shut off separately, so that efficient hydraulic pressure control is possible. Is possible.

  Further, since the pressure in the first series passage 5a and the second communication passage 5b can be increased by one hydraulic pressure chamber 26 provided in the slave cylinder 20, efficient hydraulic pressure control by the single hydraulic pressure chamber 26 is possible. Become. Moreover, the enlargement as a system can be suppressed.

  Further, by providing the pressure sensor 7, the hydraulic pressure generated in the slave cylinder 20 can be detected by one pressure sensor 7. Therefore, the system configuration is simplified, and efficient hydraulic pressure detection is possible.

Further, when the pressurizing operation of the slave cylinder 20 is released, the brake fluid in the reservoir tank 15 can be efficiently replenished to the slave cylinder 20 (hydraulic pressure chamber 26) through the replenishment path 9a.
Further, since the check valve 9d is provided in the branch supply path 9c, the check valve 9d can suitably prevent the hydraulic pressure generated in the slave cylinder 20 from being transmitted to the reservoir tank 15 side.

  Further, since the replenishment path 9a is connected to the common hydraulic pressure path 4, it is not necessary to provide a port for the replenishment path in the slave cylinder 20, so that the configuration is simple. Even in this case, the check valve 9d can suitably prevent the hydraulic pressure generated in the slave cylinder 20 from being transmitted to the reservoir tank 15 side. The replenishment path 9a may be directly connected to the first series path 5a and the second communication path 5b. Further, the supply path 9 a may be connected to the port 19 of the master cylinder 10.

  In addition, 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 are used during normal braking in which the slave cylinder 20 generates hydraulic pressure in the wheel brake. There is no need to energize the two shutoff valves 62. Therefore, power consumption can be minimized.

  Further, since the valve elements 61a of the first shut-off valve 61 and the second shut-off valve 62 are pressed against the valve seat 61c from the slave cylinder 20 side, the first shut-off valve 61 and the second shut-off valve are applied when the slave cylinder 20 is pressurized. 62 can be smoothly closed without resistance.

  In addition, since the return fluid passage 9b leading from the outlet valve 32 to the reservoir tank 15 is provided, when the fluid pressure of the wheel cylinder W is reduced, the fluid passes through a reservoir or the like for temporarily storing brake fluid. Therefore, the brake fluid can be suitably returned to the reservoir tank 15. Therefore, smooth brake fluid flow can be realized.

  Moreover, since the return flow path 9b is directly connected to the reservoir tank 15 via the second supply port 15c, the brake fluid can be directly returned to the reservoir tank 15 without passing through other components. Therefore, smoother brake fluid flow can be realized.

  In addition, since the master cylinder 10, the slave cylinder 20, and the hydraulic pressure control device 30 can be attached to the vehicle as an integrated unit, an increase in size and complexity of the system can be suppressed.

  In addition, the electronic controller 70 causes the hydraulic pressure increased by the slave cylinder 20 in either the first brake system K1 or the second brake system K2 to correspond to a predetermined fluid corresponding to the stroke amount STR of the piston 22 of the slave cylinder 20. When it is determined that the pressure is lower than the pressure, the shutoff valve of that system is closed and the shutoff valve of the other system is opened. Therefore, even when an abnormality occurs in which the brake fluid decreases in one of the two brake systems K1 and K2, the boost performance of the other system can be suitably ensured by driving the slave cylinder 20. Therefore, the hydraulic pressure control of the other system can be preferably continued.

  Further, an abnormality is detected based on a detected value when one of the first shut-off valve 61 and the second shut-off valve 62 is closed and the slave cylinder 20 is driven, and a detected value when the other is closed and the slave cylinder 20 is driven. Therefore, it is possible to efficiently detect the presence or absence of an abnormality in the hydraulic pressure of each system with one pressure sensor 7. Further, since the abnormality can be determined by one pressure sensor 7, the system configuration is simplified, and the cost can be reduced, and the system can be downsized.

Furthermore, in this embodiment, after making a determination based on the detection value when both the first cutoff valve 61 and the second cutoff valve 62 are closed and the slave cylinder 20 is driven, the first cutoff valve 61 and the second cutoff valve The determination can be made based on the detected value when one of the 62 is closed and the slave cylinder 20 is driven, and the detected value when the other is closed and the slave cylinder 20 is driven. Therefore, after determining whether or not there is an abnormality on the slave cylinder 20 side, it is possible to determine whether or not there is an abnormality in the hydraulic pressure by closing the shut-off valve in order, and thus whether there is an abnormality on the slave cylinder 20 side and each system The presence or absence of an abnormality in the hydraulic pressure can be efficiently detected by one pressure sensor 7.
Further, when the determination is made in the reverse order, it is possible to determine whether there is an abnormality on the slave cylinder 20 side after closing the shut-off valves in order and determining whether there is an abnormality in the hydraulic pressure. Therefore, also in this case, it is possible to efficiently detect the presence / absence of an abnormality in the hydraulic pressure of each system and the presence / absence of an abnormality on the slave cylinder 20 side by one pressure sensor 7.

  Further, if the detected value when both the first shut-off valve 61 and the second shut-off valve 62 are closed and the slave cylinder 20 is driven is lower than a predetermined hydraulic pressure corresponding to the stroke amount STR of the piston 22 of the slave cylinder 20 When the determination is made, the first switching valve 51 and the second switching valve 52 are respectively switched so that the wheel cylinder W communicates with the master cylinder 10 and is disconnected from the slave cylinder 20 side. The wheel cylinder W can be suitably boosted by the hydraulic pressure from Therefore, the brake system A which functions suitably as a fail safe is obtained.

Further, the first shutoff valve 61 and the second shutoff valve 62 are closed by the liquid suction control, the piston 22 is driven in the pressure reducing direction, and the brake fluid is sucked from the replenishment path 9a by the negative pressure. Therefore, even if the axial length of the slave cylinder 20 is set to be relatively short, the brake fluid in the hydraulic chamber 26 can be secured by the liquid suction control. 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.
In addition, even if the anti-lock brake control is frequently controlled to increase, hold, or reduce the hydraulic pressure acting on the wheel cylinder W, the brake fluid supplied to the wheel cylinder W is suitably secured by the liquid absorption control. can do.

  In addition, since the liquid absorption control is performed when the stroke amount STR of the piston 22 of the slave cylinder 20 becomes equal to or greater than a predetermined value (the timing when the normal maximum stroke amount (limit stroke amount) STL is reached), a high hydraulic pressure is required. Liquid absorption control is performed only when the Therefore, it is possible to obtain the brake system A that can appropriately increase the pressure to the high hydraulic pressure region while avoiding the enlargement of the slave cylinder 20.

  In addition, since the stroke amount STR of the piston 22 of the slave cylinder 20 is specified based on a rotation angle sensor that detects the rotation angle of the electric motor 24, an accurate stroke amount can be specified based on the rotation angle of the electric motor 24. The timing for performing liquid absorption control can be easily specified.

  The liquid absorption control may be configured to determine that the liquid absorption control needs to be executed when the pressure increase amount of the driver's required hydraulic pressure is 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 determine that the liquid absorption control needs to be executed 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 liquid absorption control may be configured to be performed when the control state of the wheel (wheel brake) becomes the holding control or the pressure reduction control. If it does in this way, brake fluid can be effectively secured at the time of anti-lock brake control by performing liquid absorption when the control state of a wheel is other than pressure increase control.

  Further, the liquid suction control may be performed when the relationship between the hydraulic pressure increased by the slave cylinder 20 and the stroke amount STR of the piston 22 of the slave cylinder 20 does not satisfy a predetermined relationship. . In this way, the brake fluid can be supplied into the slave cylinder 20 by the fluid suction control, and the fluid pressure increased by the slave cylinder 20 is set to a predetermined fluid corresponding to the stroke amount STR of the piston 22 of the slave cylinder 20. Pressure.

DESCRIPTION OF SYMBOLS 1 Base body 2a 1st hydraulic pressure path 2b 2nd hydraulic pressure path 4 Common hydraulic pressure path 5a 1st serial path 5b 2nd communicating path 6 1st pressure sensor 7 2nd pressure sensor 9a Replenishment path 9b Returning liquid path 9d Check valve 10 Master cylinder 15 Reservoir tank 20 Slave cylinder 22 Piston 24 Electric motor 30 Fluid pressure control device (control valve means)
51 1st switching valve 52 2nd switching valve 61 1st cutoff valve 62 2nd cutoff valve 70 Electronic controller A Brake system K1 1st brake system K2 2nd brake system P Brake pedal (brake operator)
FL, RR, RL, FR Wheel brake ST Stroke sensor W Wheel cylinder

Claims (7)

A brake system including a slave cylinder that generates hydraulic pressure by an electric actuator that is driven according to an operation amount of a brake operator,
A fluid path leading from the slave cylinder to the wheel brake;
A shut-off valve provided in the liquid path and capable of blocking the liquid path;
A reservoir tank for storing brake fluid;
A supply path for supplying brake fluid from the reservoir tank to the slave cylinder;
Control means for performing liquid suction control for sucking brake fluid from the replenishment path,
The control means executes control for closing the shut-off valve and driving the slave cylinder in the pressure reducing direction by the electric actuator as liquid absorption control when the fluid amount of the slave cylinder decreases due to pressure reduction of the wheel brake. Is a configuration to
Further, the control means includes road surface friction coefficient estimating means capable of estimating a road surface friction coefficient during anti-lock brake control,
The said control means sets the timing which performs liquid absorption control based on the road surface friction coefficient estimated by the said road surface friction coefficient estimation means, The brake system characterized by the above-mentioned. The brake system according to claim 1,
The brake system according to claim 1, wherein the control unit performs liquid absorption control when a stroke amount of the slave cylinder becomes a predetermined amount or more. The brake system according to claim 2,
The electric actuator is an electric motor;
The brake system according to claim 1, wherein the stroke amount of the slave cylinder is specified based on a rotation angle sensor that detects a rotation angle of the electric motor. The brake system according to any one of claims 1 to 3,
The said control means performs a liquid absorption control, when the control state of a wheel becomes holding | maintenance control or pressure reduction control, The brake system characterized by the above-mentioned. The brake system according to any one of claims 1 to 4, wherein
The brake system according to claim 1, wherein the control means performs liquid absorption control when a relationship between a hydraulic pressure increased by the slave cylinder and a stroke amount of the slave cylinder does not satisfy a predetermined relationship. The brake system according to any one of claims 1 to 5 ,
The brake system according to claim 1, wherein a check valve is provided in the replenishment path to allow only a brake fluid to flow from the reservoir tank 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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