ANTI LOCK BRAKING SYSTEM (ABS) 1 ANTI-LOCK BRAKING SYSTEM (ABS) 6.2.1 GENERAL INFORMATION 6.2.1.1 NECESSITY OF ABS WITH EBD Whenever the brakes are applied, the road 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 beyond this level it will lock which can result in the vehicle skidding and the driver loosing control. EBD During normal braking there is always a level of load transfer from the rear axle to the front. Due to 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 load sensing pressure valve (LSPV) which limits the pressure to the rear axle to give a front first locking sequence. The LSPV 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, tyres, road or the vehicle load conditions, and hence it cannot achieve ideal braking at the rear axle 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 at any point of time, depending on the condition of the vehicle brakes, tyres; the road, or vehicle load conditions. In the case of EBD failure the driver will be alerted .It is unsafe to drive the vehicle with EBD not working. 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 to transmit to the road surface. This will result in wheel locking (stopping rotating). If one or more wheels lock under braking the vehicle can go into a skid and no longer be controlled by the driver as he/she will have lost steerability. 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 case of ABS failures the driver will be alerted and the conventional braking circuit will still be operational. NOTE ABS ECU calculates the Vehicle Speed and Odometer signals. If ABS ECU fails vehicle speed and odometer will not function.
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