Disk brake drum brake and hydraulic brake systems

CONSTRUCTION AND WORKING OF disk BRAKES in an automobile | disk brakes a type of mechanical braking system

MECHANICAL BRAKES

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.

  Drum brakes a type of mechanical brake | Construction and working of a drum brake system

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

  Hydraulic Brake System OF AN AUTOMOBILE | CONSTRUCTION AND WORKING OF HYDRAULIC BRAKING SYSTEM | COMPONENTS OF AN OIL BRAKE SYSTEM

   

  Hydraulic Brake Systems

  Hydraulic operation of brakes has been the universal design for more than 60 years. The complete hydraulic system consists of master cylinder; steel lines, rubber hoses, various pressure-control valves, and brake apply devices at each wheel.

  

  Master Cylinder

  The master cylinder is the start of the brake hydraulic system. It actually is a cylindrical pump. The cylinder is closed at one end, and the flexible pushrod extends from the other end. The pushrod moves a pair of in-line pistons that produce the pumping action. The brake pedal lever moves the pushrod this moves the pistons to draw fluid from a reservoir on top of the master cylinder. Piston action forces the fluid under pressure through outlet ports to the brake lines. All master cylinders for vehicles built since 1967 have two pistons and pumping chambers. Motor vehicle safety standards involve this dual-brake system to provide hydraulic system operation in case one wheel brake assembly loses fluid. Because the brake hydraulic system is closed, all the lines and cylinders are full of fluid at all times. The master cylinder develops system pressure the amount of fluid moved is only in less value.

  

  Split Systems

  Modern-day vehicles have split brake systems. The pre-1970s vehicle had a single hydraulic system serving all four wheels. A leak anywhere in the system will result in a complete braking failure. The split system is designed to prevent total system failure. This required the use of a dual-piston master cylinder and the inclusion of various valves. A split system is fed by one piston in the master cylinder and feeds two wheel brakes of the vehicle.

  

  There are two types of split systems: diagonal and front/rear. The diagonal system has one system feeding a front-wheel brake and the rear opposing side wheel brake, that is left front and right rear. The second triangle split is to the other wheel brakes. One side or split feeds the rear-wheel brakes and the other feeds the front wheels. Both of these types have advantages and disadvantages, but each prevents complete system failure from a single leak.

  Brake Lines and Hoses

  The rigid lines or pipes of a brake hydraulic system are made of steel tubing for system safety. Flexible rubber hoses join the wheel brakes to the rigid 7lines on the vehicle body or frame. The front brakes have a rubber hose at each wheel to allow for steering movement. Rear brakes may have different hoses at each wheel or a single hose connected to a line on the body or frame if the vehicle has a rigid rear axle. Brake lines and hoses contain the high-pressure fluid, and the fluid acts like a solid rod to transfer force to the wheel cylinders and caliper pistons.

  Wheel Cylinders and Caliper Pistons

  

  Technically, the wheel cylinders of drum brakes and the caliper pistons of disc brakes are “slave” cylinders because they operate in response to the master cylinder. These hydraulic cylinders at the wheels change hydraulic pressure back into mechanical force to apply the brakes. Most late-model systems with drum brakes have a single, two-piston cylinder at each wheel. Hydraulic pressure enters the cylinder between the two pistons and forces them outward to act on the brake shoes. The shoes move outward, the lining contacts the drums to stop the car. The caliper pistons for disc brakes also act in response to hydraulic pressure that enters a fluid chamber in the caliper. Hydraulic pressure in stationary caliper is applied to one or two pistons on each side of the caliper to force the pads against the rotor. Pressure is applied to a single piston in a movable caliper on the inboard side to force the inboard pad against the rotor. Hydraulic pressure is equal in all directions in a closed chamber. This equal pressure creates a reaction force that moves the outboard side of the caliper inward so that both pads grip the rotor.