The automobile braking system reduces wheel rotating speed in order to reduce speed of the vehicle. When brakes are applied on a moving vehicle, the kinetic energy of motion of the vehicle is transformed into heat generated by the friction between the brake lining and the rotating drum (or disc). The heat generated is dissipated into the surrounding air. The braking systems which are commonly used in all automobiles is shown in figure, and is discussed below:
1. Parking brake
It is used to hold the vehicle stationary, when applied. At the time of parking, the braking is necessary to prevent the vehicle from rolling off due to road gradient or blowing wind. The brake manually operates on the rear wheels through cables or mechanical linkage from an auxiliary foot lever (or a hand pull). It is held on by a ratchet until released by some means such as a push button or a lever.
2. Service brake (Main system)
The most automotive service brakes are hydraulic brakes. The hydraulic action begins when force is applied to the brake pedal. This force creates pressure in the master cylinder, either directly or through a power booster. It serves to displace hydraulic fluid stored in master cylinder. The displaced fluid transmits the pressure through the fluid filled brake lines to the wheel cylinders that actuate the brake shoe (or pad mechanism). The actuation of these mechanisms forces the brake pads and linings against the rotors (front wheels) or drums (rear wheels) to stop the wheels.
The master cylinder of a brake system converts pedal force into hydraulic pressure to operate the brakes. When the brake pedal is depressed, pistons in the master cylinder are activated, causing pressure to act on the brake fluid. When the brake pedal is released, return springs move the pistons back to their original positions.
Generally, all the vehicles utilize tandem master cylinders. This type of master cylinder serves two independent hydraulic lines. Since both hydraulic lines are independent, therefore, the fluid loss or other abnormalities in one line do not cause all the brakes to fail.
The master cylinder is fitted with a brake fluid reservoir. The fluid in the reservoir compensates for variations in the fluid level that accompany movement of pistons and for permanent changes in the quantity of fluid in the brake lines that occur as the brake pads become worn.
Note: When the brake pads are worn, the caliper piston must have longer stroke so that pads make a contact with the disc. Thus, more fluid is required in the brake line.
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