Brakes
Brakes are mechanical devices used to stop the vehicle quickly within a short distance.
when the brakes are applied on a moving vehicle, the kinetic energy of the vehicle is transformed into heat generated by the friction between the brake lining and drums.
The heat generated is dissipated into the surrounding air.
The force of friction between the linings and the drums depends upon the coefficient of friction of the two materials, force applied between the sliding surfaces, the roughness of the surfaces, and the material of which the surface are made.
Purposes of brakes
1. To stop the vehicle in the shortest possible distance and time.
2. To slow down the vehicle.
3. To park the vehicle.
4. To control the speed of the vehicle.
Requirements of a good braking system
1. The brakes should stop the vehicle in the shortest possible distance and time.
2. The brakes should work equally good (or) on bad roads.
3. Pedal effort applied by the driver should not be more.
4.Brakes should work equally good in all weather.
5. It should have less wearing parts.
6. It should require little maintenance.
7. Brakes, when applied, should not disturb steering geometry.
8. When brakes are applied, the vehicle should not pull to one side.
9. There should be minimum sound when brakes are applied.
Classification of brakes
1. According to the application
(1) Foot brake (or) service brake
(2) Hand brake (or) parking brake
2. According to the method of braking contact
(1) Drums brakes
a) External contracting brakes
b) Internal expanding brakes
(2) Caliper (or) disc brakes
3. According to the mode of operation
(1) Mechanical brakes
(2) Hydraulic brakes
(3) Vacuum brakes
(4) Vacuum assisted hydraulic brakes
(5) Air brakes
(6) Air assisted hydraulic brakes
Mechanical brakes
The brakes which are operated mechanically by means of levers, linkages, pedals, cams, bell crank are known as mechanical brakes.
In mechanical brake system, a brake drum is attached concentric to the axle hub where as on the axle casing is mounted a back plate.
In case of front axle, the back plate is bolted to the steering knuckle.
It provides a support for the expands anchor and brake shoes. It also protects the drum and shoe assembly from mud and dust.
Friction lining are mounted on the brake shoes.
One (or) two retractor springs are used which serve to keep the shoes away from the drum when the brakes are not applied.
The brake shoes are anchored at one end where as on the other end force is applied by means of some brake actuating mechanism, which force the brake shoe against the revolving drum, there by applying the brakes.
An adjuster is also provided to compensate for wear of friction lining with use.
The internal expanding and external contracting brakes are two main classes of mechanical actuating drum, brake system.
Brake shoe
These are made of steel usually in 'T' section which is considered strong. They are either cast (or) fabricated.
Two types of shoe on the left and a secondary shoe on the right are provided.
On the brake shoe, the specially treated asbestos brake lining is fixed with the help of rivets now a days in some of the vehicles lining are pasted and pressed on brake shoes with the synthetic resin adhesive.
The brake lings are usually 28 to 63 mm wide and from 4 to 10 mm thick in the case os passenger motor vehicles.
Brake drum
The brake drum rotates with the road wheel and provides a contacting surface for the brake shoes to come into contact for braking action.
Brake drums are usually made of cast iron. In some cases brake drums are made of steel (or) aluminium having inner liner of cast iron.
The diameter of the brakes drums usually range between 200mm and 37mm.
In most cases fins are provides at the outer surface of the brake drum for the rapid dissipation of heat and thus help in its cooling.
Brake lining
The following two types of lining are employed with the brake shoes.
a) organic b) metallic
a) organic lining
It is of two types moulded and woven. The moulded type in made from a thoroughly mixed components of asbestos, filler materials and powdered resins.
The compound is moulded in dies to form into shape and is placed under heat and pressure until a hard like board is formed.
It is then art and bent into individual segments for attached to the brake shoes.
These linings have good wear resistance. The woven type organic lining is woven from strands of asbestos and threads of other materials and impregnated with a rubber compounds.
b) Metallic lining
It is made of sintered metal and is composed of finely powdered copper or iron, graphite and some amount of inorganic fillers and friction modifiers.
After thoroughly mixing the constituents a lubricating oil is added to avoid separation of different materials. It is then made into the required form by means of a special process.
Metallic linings are used for extreme braking conditions as encountered in police cars, fire brigade vehicles and sports cars under such extreme service, the frictional qualities of the metallic linings are more constant than that of organic lining.
Servo brake system
Long journey can be very tired for the driver. Then even the simple application of brakes can become a great strain.
For this reason servo brakes are introduced which state that any mechanism which adds to the driver 's effort in applying the brakes is called a servo mechanism this mechanism is used to reduce the drivers effort.
Hydraulic brake system
Brakes operated by means of hydraulic pressure are known as hydraulic brakes. They work on the principle of pascal's law which states that " pressure applied to a liquid is transmitted equally in all directions".
Most of the cars today use hydraulically operated foot brakes on the all the four wheels with an additional hand brake mechanically operated on the rear wheels.
Advantages of hydraulic brake
1. Simple in construction
2. Equal raking effort to all the four wheels
3. Increased braking system
4. Self lubrication
5. Low wear rate
6. High mechanical advantage
7. friction losses are low
8. Application of brake is very smooth
Disadvantage
1. The braking system fails if there is any leakage in the brake lines.
2. If the brake fluid leaks out on the brake shoes they will be ruined
0 Comments