Automobile Engineering

Subject : Chassis and transmission system

Topic : Brake - MASTER CYLINDER


 

    The master cylinder is the heart of the hydraulic braking system. It consists of a piston, a compression chamber filled with hydraulic fluid, and a reservoir that holds the fluid itself. The piston is connected to the brake pedal by a push rod. The primary and secondary seals are provided on the front and rear of the piston. In addition a return spring is provided in front of the piston. The reservoir is connected to the compression chamber by two holes of different diameters.

    The smaller hole is called the bypass or compensation port ‌, and the larger hole is called the intake or recuperation port. The pressurized brake fluid enters the pipeline through a check valve from the compression chamber.

WORKING

    The push rod piston moves forward against the pressure of the return spring when force is applied to the brake pedal. 

    When the intake port ‌ and the bypass port are closed during the movement of the piston, pressure is exerted on the filled fluid in the compression chamber, which in turn enters the pipeline inside the check valve and acts on the pistons in the wheel cylinder and calipers.

    The piston is pushed back by the pressure of the return spring as the force is withdrawn from the brake pedal. However, due to the pressure of the spring, the check valve will remain closed. In addition, due to the inertia experienced by the brake fluid, the brake fluid returns to the vacuum compression chamber. If this vacuum is not removed there is a possibility of air entering there.

    Due to the atmospheric pressure experienced in the reservoir, the fluid reaches the perimeter of the piston through the intake port, and enters the compression chamber by compressing the primary seal through the holes in the front of the piston. Thus the vacuum in the compression chamber is eliminated and the brake fluid enters the compression chamber back from the pipeline by raising the check valve. But the compression chamber will be filled with fluid arriving through the intake port. The excess fluid then returns to the reservoir via the bypass port and the brakes are released.