Internal expanding shoe brakes are the generally used braking system in automobiles. In an automobile, the wheel is fitted on a wheel drum. The brake shoes are fitted in contact with inner surface of this drum to apply brakes.
The construction of mechanical disk brake is shown in picture. The whole assembly contains of a pair of brake shoes with brake linings, two anchor pins and retractor spring, a cam and a brake drum. Brake linings are attached on outer surface of each brake shoe.
The brake shoes are hinged at one end by means of anchor pins. Last end of brake shoe is functioned by a cam to expand it out counter direction to brake drum. Retracting springs provided are used for bringing the shoes to their original position when brakes are not applied. The brake drum closes inside it the entire mechanism to protect it from dust and sand. A plate holds the total assembly and fits to car axle. It also acts as a base to fasten the brake shoes and other operating mechanism.
How Brakes are Applied and Released
When brake pedal is pressed, the cam turns through brake linkages. Brake shoes expand towards brake drum due to turning of cam. The brake linings, rub against brake drum and therefore motion of wheels is stopped. The pedal force is transmitted to the brake shoes through a mechanical linage. This device also multiplies the force to apply the brakes effectively. When force on brake pedal is removed, the retractor spring brings the shoes back to original position and brakes are released.
Working of disk brake
Modern motor cars are fitted with disc brakes instead of conventional drum type brakes. Front wheels are generally has disc brakes whereas rear wheel are provided with drum brakes. A disc brake contains a rotating disc and two friction pads which are actuated by hydraulic braking system as described earlier. The friction pads stay free on each side of disc when brakes are not applied. When brakes are applied they rub in contradiction to the disc to stop the vehicle. The working of this brake is the same method as that of hydraulic brakes. But the way of stopping the vehicle is not the same as that of drum brakes.
Working of disk brakes
In a disc brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston in turn crushes two brake pads against the disc, that is being attached to wheel, making it to stop or slow down.
Advantage of Disc Brakes
- Main advantage of disc brakes is their resistance to wear as the discs remain cool even after repeated brake applications.
- Brake pads are easily replaceable.
- The condition of brake pads can be checked without much dismantling of brake system.
Disadvantage of Disc Brakes
- More force is needed be applied as the brakes are not self-emerging.
- Pad wear is more.
- Hand brakes are not much effective if disc brakes are used in rear wheels also.
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