2023 changes:
Master cylinder assembly and electric booster assembly
The vacuum pump has been discontinued and a master cylinder assembly and an electric booster assembly have been adopted on new model vehicles.
The master cylinder assembly and electric booster assembly integrate parts such as a motor and control unit, and have a compact construction equivalent to existing negative pressure brake boosters.
Also, an electric brake booster that responds more to increased pressure is used to increase the response of pre-collision braking and adaptive cruise control.
■ Construction and operation
The master cylinder assembly and electric booster assembly consist of a servo mechanism, servo control mechanism, master cylinder mechanism and brake pedal shock sensor.
| mECHANISM | Construction and operation |
| Servo mechanism | • The servo mechanism consists of a motor, gear unit and valve body. • The torque generated by the motor is reduced by the gear unit and rotates the shaft nut. When the spindle nut rotates, the spindle is pushed out, which pushes out the master cylinder piston via the valve body and reaction disc. |
| Servo control mechanism | • The servo control mechanism consists of parts such as the electric brake booster control unit and the brake pedal stroke sensor. • The electric brake booster control unit calculates the differential stroke of the control target based on the signals from the sensor of the brake pedal stroke and controls the engine. |
| Master cylinder mechanism | • The master cylinder mechanism is the same mechanism as the master cylinder used in negative pressure brake boosters. |
| Brake pedal shock sensor | • The brake pedal shock sensor is installed inside the power amplifier assembly and detects the driver pressing the brake pedal. |
– Operation
Brake pedal pressure from the driver is read by the brake pedal shock sensor, and then the motor is controlled to drive the master cylinder via the gear unit, which generates brake fluid pressure. However, note that the same reaction disc as a negative pressure brake booster is adopted for building pedal reaction force, realizing a natural braking feel.
– Brake performance
Even with a short stroke, a higher depression force gradient can be established to provide controllability and stiffness. This achieves peace of mind by applying braking instantly when it is depressed, and a sportier braking feel through short stroke and stiffness.
– Control cooperation with EyeSight
Adaptive cruise control and pre-collision brake assist are activated using the master cylinder assembly and the electric booster assembly. In addition to increased pressure with the VDC unit motor, a more responsive electric brake booster has been adopted to increase the responsiveness of Pre-Collision Braking and Adaptive Cruise Control.
