Drum Brakes a Type of Mechanical Brake | Construction and Working of a Drum Brake System

Drum Brakes a Type of Mechanical Brake

The details of the drum brake a type manually operated mechanical brake system can be seen in the picture

01 - CROSS SECTION OF A DRUM BRAKE - MECHANICAL BRAKE CONSTRUCTION AND WORKING.

In the motor vehicle, the wheel is attached to a drum. The drum encloses the entire brake mechanism and keeps out dust and moisture. The inner side of the drum is open. The backing plate at the open side of the brake drum completes the brake enclosure and holds the brake assembly. The backing plate is attached to the vehicle axle housing. The backing plate acts as the base for fastening the brake shoes and the operating mechanism. The wheel attaching bolts on the brake drum connect the wheel and the drum.The front coil spring suspension and the drum type brake mechanism in partly disassembled view can be seen in the picture

Construction and working of a drum brake system

01 - COMPONENTS OF A DRUM BRAKE - MECHANICAL BRAKE CONSTRUCTION AND WORKING

The details of the drum brake system can be seen in the picture. The brake shoes which are roughly semicircular are made to contact the inside surface of the brake drum. In the most designs, two shoes are used with each drum to form a complete brake mechanism at each wheel. The brake shoes have brake linings on their outer surfaces. Each brake shoe is hinged at one end by an anchor pin. The anchor pin is fixed to the backing plate. The other end of each shoe rests on a cam. This can be turned by the camshaft which passes through a hole in the backing plate. The camshaft can be operated by the brake pedal through suitable linkages.

When the cam is turned, the brake shoes expand outward, the brake linings come into contact with the brake drum. Brake lining increases the coefficient of friction and also prevents wearing away of the metal. The force of friction is opposite to the direction of drum rotation. The friction between the drum surface and the shoe linings serves to stop or slow down the drum rotation and hence the wheel rotation.

Working of a drum brake

The friction force that comes into action also tends to make the shoes to revolve with the drum. The latter action is prevented by the pin and the cam. The pin is therefore called the anchorage pin.

01 - STEP BY STEP WORKING OF DRUM BRAKE - WORKING PRINCIPLE OF DRUM BRAKE

The magnitude of the friction force, multiplied by the radius of the drum, gives the torque tending to stop the drum, that is, the braking torque. The entire mechanical linkage between the brake pedal and the shoes operates to transmit pedal force to the brake shoes, and to multiply. The pedal force through leverage produces effective braking force against the drum.

The retracting spring are held between the brake shoes. These retracting springs draw the shoes away from the drum when the cam is turned and moved to the release position.

This system in which the shoes are mounted to rub against the inside surface of the brake drum, is called internal expanding brake. In this system, each part of the linkage must be free to move. The joints must be properly lubricated to reduce friction and wear. Otherwise erratic and unequal braking action may result.

Construction and Working of Disk Brakes in an Automobile | Disk Brakes a Type of Mechanical Braking System

Mechanical Braking System

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.

01 - COMPONENTS OF A DISK BRAKE - MECHANICAL BRAKE CONSTRUCTION AND WORKING

Construction and Working of Disk Brakes in an Automobile

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.

01 - WORKING OF A DISK BRAKE - MECHANICAL BRAKE AND ITS CONSTRUCTION AND WORKING

Construction and 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.

Construction and Working of Disk Brakes in an Automobile

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.