BRAKES 11 6. NESSECITY OF ABS with EBD Whenever the brakes are applied, the Vehicle wheels transmit this braking force to the road surface. To achieve optimal deceleration each wheel should be braked to the point of imminent lock. In this manner maximum possible braking force would be imparted to the road surface. However, if a wheel is braked be- yond this level it will lock which can result in the vehicle skidding and the driver losing control. EBD: During normal braking there is always a level of load transfer from the rear axle to the front. During this occurrence it is necessary to ensure that the rear axle wheels do not reach the point of lock before the front axle wheels. On vehicles without ABS and EBD this is achieved through the use of a pressure conscious regulating valve (PCRV) which limits the pressure to the rear axle to give a front first locking sequence. The PCRV allows only a predetermined pressure to the rear wheels to avoid locking of the rear axle wheels before the front axle wheels. As a mechanical fixed ratio component it cannot adapt to the condition of the vehicle brakes, tires or to the road or vehicle load conditions, and hence it cannot achieve ideal braking at the rear axel To enable optimum braking at the rear axle while maintaining vehicle stability during braking EBD is provided. It enables the distribution of brake force between the front and rear axle brakes to be adjusted throughout the vehicle life, irrespective of the condition of the vehicle brakes, tires; or to the road, vehicle load conditions. In the case of EBD failure, the driver will be alerted. ABS: In emergency braking conditions and when driving on wet or slippery road surfaces like snow and Ice, gravel, steel plates and bridges etc. it is possible that the braking forces at the wheel exceed those possible wheel locking limits. This will result in wheel locking (stopping rotating). If one or more wheels locks during braking, the vehicle can go into a skid and no longer be controlled by the drive as he will have lost steer ability. To avoid the wheels from locking and prevent the vehicle from skidding ABS is provided. It prevents the wheels from locking and maintains the steerability of the vehicle thereby helping the driver to maintain stability of the vehicle while bringing it to a stop in the safest possible way. In the case of ABS failures, the driver will be alerted and the conventional braking circuit will still be operational. 7. VACUUM BRAKE BOOSTER General: Vehicle is equipped with a mechanical vacuum booster to assist driver’s pedal effort. This is achieved by using vacuum from engine inlet manifold (for petrol engines) or vacuum pump (for diesel engines). A diaphragm is provided between the two shells of the booster, the difference of pressure on two sides of diaphragm (one side vacuum and another side atmospheric pressure) gives mechanical advantage. This amplifies the driver’s pedal effort while braking. The unit is connected to the brake pedal and the master cylinder. The vacuum booster input push rod is connected to brake pedal while the output push rod operates the master cylinder. If failure of vacuum occurs, the two push rods act as a single rod and the brakes will work in the conventional manner, but more pedal effort will be required and the fatigue of the driver will increase. NOTE: The booster assembly and TMC assembly are coupled with the help of fasteners. The mating dimensions of booster and TMC are factory set hence: 1. Do not alter the height of the output rod of the vacuum booster unit at any stage and ensure booster output rod is correctly aligned to the primary piston bore during assembly of TMC to the booster. 2. Once the booster assembly is removed from vehicle, at the time of refitting on vehicle, the gasket at the mounting face of the booster should be replaced with a new one. 3. Booster assembly is a non-serviceable unit and it should never be tampered with.
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