2. Pressure increase (High pressure)
In contrast to the time when the pressure is low, when the pressure is high, the booster pressure that is applied to the rubber reaction disc increases. Accordingly, the rubber reaction disc deforms and causes a return force in the rightward direction to be applied to the spool valve via the reaction rod. Therefore, in contrast to the time when the pressure is low, a greater reaction force is transmitted to the brake pedal. As a result, a variable servo mechanism is realized, in which the servo ratio is lower during high pressure than during low pressure.
This is a state in which the force that is applied via the brake pedal and the master cylinder pressure are in balance. The forces that are applied to the front and the rear of the regulator piston, in other words, forces that are generated by the master cylinder pressure and the regulator pressure become balanced. This causes the spool valve to close both port Bfrom the booster chamber to the accumulator and port Ato the reservoir. As a result, the brake is in the holding state.
4. Pressure reduce
When the pressure that is applied to the brake pedal is relaxed, the master cylinder pressure decreases. Then, the regulator piston’s return (rightward) force becomes relatively greater, causing the regulator piston to retract and the spool valve to also retract. As a result, the port Abetween the reservoir tank and the booster chamber opens. The booster pressure becomes reduced in this state, creating a balance that corresponds to the force that is newly applied via the brake pedal. This process is performed repetitively to reduce the booster pressure and the master cylinder pressure in accordance with the force that is applied via the brake pedal.
5. During power supply malfunction
If the accumulator pressure is affected by any malfunction, no hydraulic pressure will be supplied to the booster chamber. For this reason, a power assist cannot be provided to the force that is applied via the brake pedal and the pressure to the rear brakes cannot be increased. However, the pressure to the front brakes will be increased at the master cylinder piston in accordance with the pedal effort applied to the brake pedal.