Hydraulic brake system

A hydraulic brake system, comprising:

• a brake operation member to be operated by a driver;
• a brake device provided for a wheel and configured to generate a braking force having a magnitude in accordance with a pressure of a working fluid supplied thereto;
• a master cylinder including a housing including a partition portion which partitions an interior of the housing into two fluid chambers and which has an opening, an input piston disposed in the housing rearward of the partition portion and connected to the brake operation member to move forward toward the partition portion by an operation of the brake operation member, a pressurizing piston having a main body portion which is disposed in the housing forward of the partition portion and which has a flange formed at a rear end of the main body portion, an inter-piston chamber defined between the input piston and the pressurizing piston utilizing the opening of the partition portion, a pressurizing chamber which is defined forward of the pressurizing piston and in which the working fluid to be supplied to the brake device is pressurized by a forward movement of the pressurizing piston, an input chamber which is defined between the flange of the pressurizing piston and the partition portion and to which is introduced the working fluid for applying a force to the pressurizing piston that moves the pressurizing piston forward, and an opposing chamber defined forward of the flange of the pressurizing piston and opposed to the input chamber with the flange interposed therebetween, a pressure receiving area of the pressurizing piston on which a pressure of the working fluid in the inter-piston chamber acts being made equal to a pressure receiving area of the pressurizing piston on which a pressure of the working fluid in the opposing chamber acts;
• a communication passage which connects the inter-piston chamber and the opposing chamber to each other and to which a low-pressure source is connected;
• a communication switching valve disposed at a portion of the communication passage nearer to the inter-piston chamber than a connected portion of the communication passage at which the low-pressure source is connected, a state of the communication switching valve being switched between an open state in which communication between the inter-piston chamber and the opposing chamber is allowed and a closed state in which the communication is shut off;
• a low-pressure-source shut-off valve disposed between the communication passage and the low-pressure source, a state of the low-pressure-source shut-off valve being switched between an open state in which communication between the communication passage and the low-pressure source is allowed and a closed state in which the communication is shut off;
• a stroke simulator disposed at a portion of the communication passage nearer to the opposing chamber than the connected portion and including a fluid chamber connected to the communication passage, the stroke simulator being configured to elastically pressurize the working fluid in the fluid chamber;
• a high-pressure source configured to supply the working fluid having a high pressure;
• a regulator configured to regulate, to a regulated pressure, a pressure of the working fluid having the high pressure supplied from the high-pressure source and to supply the pressure-regulated working fluid to the input chamber of the master cylinder, the regulator including a regulated-pressure chamber in which the working fluid having the regulated pressure is stored, a valve mechanism including a valve member which is movable in an axial direction of the regulator and which is configured to receive the pressure of the working fluid in the regulated-pressure chamber from one-end side of the regulator in the axial direction, the valve mechanism being configured such that, when the valve member is located at an end position in a movable range of the valve member, the end position being located on-the an other-end side of the regulator in the axial direction, communication between the low-pressure source and the regulated-pressure chamber is allowed while communication between the high-pressure source and the regulated-pressure chamber is shut off and such that, when the valve member moves forward toward the one-end side of the regulator in the axial direction, the communication between the low-pressure source and the regulated-pressure chamber is shut off while the communication between the high-pressure source and the regulated-pressure chamber is allowed, a pilot piston disposed rearward of the valve member, a first-pilot-pressure chamber which is defined rearward of the pilot piston and to which is introduced the working fluid pressurized in the pressurizing chamber of the master cylinder, and a second-pilot-pressure chamber defined between the pilot piston and the valve member;
• a pressure adjuster configured to adjust a pressure of the working fluid to a predetermined level and to supply the pressure-adjusted working fluid to the second-pilot-pressure chamber of the regulator;
• and
• a controller configured to control the communication switching valve and the low-pressure-source shut-off valve to switch the state of each of the communication switching valve and the low-pressure-source shut-off valve between the open state and the closed state and control the regulated pressure by controlling the pressure adjuster to adjust a second pilot pressure which is a pressure of the working fluid in the second-pilot-pressure chamber,
• wherein the controller is configured to control the pressure adjuster to adjust the second pilot pressure to switch a pressure-regulating state of the regulator from a first pressure-regulating state in which the pilot piston comes into contact with the valve member and moves with the valve member by a first pilot pressure which is a pressure of the working fluid in the first-pilot-pressure chamber, so that the regulated pressure is regulated to a level in accordance with the first pilot pressure to a second pressure-regulating state in which the valve member moves in a state in which the pilot piston is separated away from the valve member by the second pilot pressure, so that the regulated pressure is regulated to a level in accordance with the second pilot pressure,
• wherein the controller is configured to switch a pressurizing state of the master cylinder selectively between a first pressurizing state in which the pressurizing piston moves forward depending on both of a pressure of the working fluid in the inter-piston chamber and a pressure of the working fluid in the input chamber by shutting off the communication between the inter-piston chamber and the opposing chamber with the communication switching valve placed in the closed state and by allowing communication between the opposing chamber and the low-pressure source with the low-pressure-source shut-off valve placed in the open state and a second pressurizing state in which the pressurizing piston moves forward depending on only the pressure of the working fluid in the input chamber by allowing the communication between the inter-piston chamber and the opposing chamber with the communication switching valve placed in the open state and by shutting off communication between:
• the inter-piston chamber and the opposing chamber;
• and the low-pressure source with the low-pressure-source shut-off valve placed in the closed state, and
• wherein, when the pressurizing state of the master cylinder is switched from the first pressurizing state to the second pressurizing state after initiation of the operation of the brake operation member, the controller executes a pressurizing-state switching control in which switching of the state of the low-pressure-source shutoff valve from the open state to the closed state and switching of the state of the communication switching valve from the closed state to the open state are carried out after the pressure-regulating state of the regulator has been switched from the first pressure-regulating state to the second pressure-regulating state by controlling the pressure adjuster to increase the second pilot pressure before switching from the first pressurizing state to the second pressurizing state.