Brake system for vehicle

A brake system for a vehicle, comprising:

• a pedal to which a braking input is applied;
• an actuator part configured to generate a braking hydraulic pressure in response to the braking input applied to the pedal and including a first actuator having a first hydraulic chamber and a second actuator having a second hydraulic chamber;
• wheel brakes connected with the first actuator and the second actuator;
• and
• a sub-cylinder including two sub-pistons for forming a third hydraulic chamber and a fourth hydraulic chamber, which are two hydraulic chambers continuously disposed within a housing;
• wherein the sub-cylinder includes a first sub-piston located centrally and a second sub-piston connected to the pedal,
• wherein the sub-cylinder includes an inlet side structure with a stepped portion,
• wherein a portion of the sub-cylinder where the second sub-piston is connected to the pedal has a smaller outer diameter than another portion of the sub-cylinder that extends toward the fourth hydraulic chamber,
• wherein the first hydraulic chamber is connected with the third hydraulic chamber by a flow path in which a first valve is installed, the second hydraulic chamber is connected with the fourth hydraulic chamber by a flow path in which a second valve is installed, and pressure balancing is performed by the sub-cylinder when a difference between braking hydraulic pressures generated by the first actuator and the second actuator occurs,
• wherein the fourth hydraulic chamber is connected with a first flow path proximate to the first sub-piston and a second flow path,
• wherein the first flow path and the second flow path are connected with the second valve, and
• wherein the first sub-piston divides the third hydraulic chamber and the fourth hydraulic chamber, and when the first flow path is closed by the first sub-piston by a pressure difference between the third hydraulic chamber and the fourth hydraulic chamber, a braking force by the pressure balancing is transmitted to the second hydraulic chamber through the second flow path.