Vehicle brake system
A vehicle brake system includes a slave cylinder configured to drive an electric motor and generate a brake fluid pressure by moving pistons with a ball screw shaft; normally open type master cut valves that communicate/shut off between the slave cylinder and a master cylinder; and a control unit that controls the electric motor to close the master cut valves and limit a displacement of the ball screw shaft on the basis of a reference position during operation of a VSA device.
1. A vehicle brake system comprising:
a master cylinder to which a brake operation by a driver is input;
a slave cylinder including a cylinder body, a piston and a shaft member disposed in the cylinder body, the shaft member extending and retracting in the cylinder body with being retractable up to a top dead point, the slave cylinder configured to drive an electric actuator having the shaft member to generate a brake fluid pressure by moving the piston by the shaft member;
a master cut valve that opens and closes a communication between the slave cylinder and the master cylinder;
a controller that controls the electric actuator and the master cut valve; and
an automatic brake device which has an upstream side connected to the master cut valve and is configured to generate the brake fluid pressure regardless of the brake operation by the driver,
wherein, during operation of the automatic brake device, the controller closes the master cut valve and controls the electric actuator to limit an extending displacement of the shaft member from the top dead point by the electric actuator such that the shaft member does not reach a bottom dead point located opposite to the top dead point.
2. The vehicle brake system according to claim 1 , wherein a maximum distance of the extending displacement limited by the controller is determined to be in a range in which a predetermined braking force can be generated in response to the brake operation by the driver in a state that the controller stops the electric actuator and opens the master cut valve in occurrence of abnormality.
3. The vehicle brake system according to claim 2 , further comprising a displacement detector that directly or indirectly detects the displacement of the shaft member, wherein the controller closes the master cut valve, calculates the extending displacement of the shaft member based on a signal from the displacement detector and controls the electric actuator to limit the extending displacement not to exceed the maximum distance.
4. The vehicle brake system according to claim 1 , wherein the controller limits the displacement of the shaft member from the top dead point so as to reduce a fluid loss necessary to retract the shaft member to the top dead point after the master cut valve is opened.
5. A vehicle brake system controlling method, the vehicle brake system comprising:
a master cylinder to which a brake operation by a driver is input;
a slave cylinder including a cylinder body, a piston and a shaft member disposed in the cylinder body, the shaft member extending and retracting in the cylinder body with being retractable up to a top dead point, the slave cylinder configured to drive an electric actuator having the shaft member to generate a brake fluid pressure by moving the piston by the shaft member;
a master cut valve that opens and closes a communication between the slave cylinder and the master cylinder;
a controller that controls the electric actuator and the master cut valve; and
an automatic brake device which has an upstream side connected to the master cut valve and is configured to generate the brake fluid pressure regardless of the brake operation by the driver,
the method comprising:
detecting operation of the automatic brake device; and
during the operation of the automatic brake device, closing the master cut valve and controlling the electric actuator to limit an extending displacement of the shaft member from the top dead point by the electric actuator such that the shaft member does not reach a bottom dead point located opposite to the top dead point.