Final answer:
Hydraulic power brake assist units are typically used in diesel engine vehicles and operate on hydraulic systems and Pascal's Principle to amplify braking force.
Step-by-step explanation:
Hydraulic power brake assist units are essential for vehicles that cannot use vacuum brakes, typically found in diesel engines. These systems leverage hydraulic systems and Pascal's Principle to operate. In a hydraulic power brake system, the driver pushes the brake pedal, applying a force that is amplified through the system. The force applied at the pedal is magnified by a lever and further increased by the hydraulic system. This pressure is then evenly transmitted to wheel cylinders via the incompressible hydraulic fluid, ensuring that each wheel experiences the same stopping force.
These systems often incorporate a motorized pump, which carries out the majority of the system's work, creating the necessary force to assist in braking. The hydraulic nature of these systems makes them quite powerful and efficient, by increasing the force that can be applied to the braking mechanism even though work (force times distance) remains constant; the distance the wheel cylinders move is smaller than the distance the pedal cylinder moves. This powerful feature enables vehicles, such as bulldozers and those with insufficient vacuum for traditional brakes, to utilize hydraulic brakes effectively.