Conceptual

Toyota Electronically Controlled Brake System

The Prius uses Toyota's ECB, a brake-by-wire system: the pedal normally moves only a stroke simulator while an ECU commands an electro-hydraulic actuator (pump, accumulator, solenoid valves) to apply exactly the friction pressure needed after regenerative braking is subtracted. There is no vacuum booster; a mechanical hydraulic fallback exists only for system failure.