Power Brake Booster Description and Operation

The brake booster is an electromechanical brake booster that replaces a vacuum booster including its vacuum supply. It is designed to make hybrid and electric vehicles more efficient by providing situation-dependent support when a driver initiates braking.

The brake booster unit takes the driver applied brake demand and transforms this into an amplified brake pressure and does not rely on vacuum to function. The brake booster unit is designed to operate together with an electronic stability control module which is normally responsible for ABS, traction control and stability control.

Since the brake booster unit operates electromechanically, it does not require vacuum from the engine and recovers almost all the energy lost in typical braking. It uses electrical current only during braking.

The brake booster unit consists of a PSM motor for force build up, and ECU for the control of the brake booster, a stage gear control to transmit the motor torque to the output pressure in the master cylinder, a vehicle interface to connect the brake booster and the vehicle, a pedal coupling unit to couple the brake booster with the vehicle pedal unit, a pedal travel sensor to detect the driver brake request, TMC to connect the brake booster with the braking system and a reservoir to support the braking system with brake fluid.

For maximum efficiency, a hybrid or EV must recover as much energy as possible when braking. Ideally, a vehicle would be slowed down purely by the electric motor, avoiding the loss of valuable energy through braking. The system recovers almost all the energy lost in typical braking operations by ensuring deceleration rates of up to 0.3 g are achieved using the electric motor alone. If the brakes are applied harder, the brake booster system generates the additional braking pressure needed in the traditional way, using the brake master cylinder.

The brake booster unit is purely electromechanical, without brake fluid, which means it can be rotated flexibly about the longitudinal axis.