SAFARI

11 ANTI-LOCK BRAKES ABS 4. ANTI LOCK BRAKE SYSTEM - THEORY Anti lock Brake system (ABS) is a closed loop system, which modulates the brake pressure in response to the brake slip rate of the wheel so as to prevent the control led wheel or wheels from becoming fully locked above a preset minimum speed. During emergency braking situations at high speeds, panic braking will be applied under conditions like - Un-anticipated obstacle and mistakes committed by other drivers and pedestrians or braking under more critical driving conditions such as driving on wet and slippery road surfaces like ice etc the wheels tends to lock which in turn will skid. This will lead to loss of steerability and stability of the vehicle as it loses traction. Wheel slip : The vehicle can stop in relation to how well the tyre contact surface grips the road. At 0% slip, the tyre rotates freely and at 100% slip, the tyre and wheel are locked and the weight of the vehicle pushes the locked tyres along the road surface. In this situation, vehicle stability and steerability will be lost. During gradual braking, the %slip will be in between 10 to 20% and at this condition vehicle stopping distance and steering control will be at their best. This optimum slip (10 to 20 %) is required for achieving maximum braking performance & for stopping the wheel. The theory behind ABS is simple. Whenever a driver brakes, the wheels of the vehicle have to transfer this braking force to the ground surface for achieving braking. As long as driver brakes gradually, the braking force is transferred through the tyres to the ground surface & optimum braking is achieved. But when driver applies panic braking, the tyres will stop rotating instantaneously (locking condition). The vehicle drags all the 4 wheels in the same direction (at the point of braking) & also driver cannot steer the vehicle so as to avoid any accident. To avoid the wheels from getting locked & skidding while panic braking, Antilock brakes system is provided. The main benefits of ABS are in the area of vehicle stability and steerability. i.e. This system prevents the wheel locking during emergency braking situations and thereby helps the driver to maintain A : Stable Range B : Unstable range 1 : Dry Asphalt 2: Wet Concrete 3. Snow 4. Polished Ice stability of the vehicle & also in bringing the vehicle to a complete stop with a minimum possible stopping distance in the safest possible way. The purpose of ABS 5.3, 4-sensor 4-wheel, vertical split system is to provide 1. Enhanced steering control by enabling the vehicle to move in a driver’s intended direction, even during panic braking. 2. Enhanced braking stability by making the most of available traction on all surfaces. 3. It’s operational throughout the vehicles entire speed range, effective down to the speed of 2.75 km/ h. It is capable of rapid adaptation to changes in surface traction. ( Dry road with patches of ice) and capable of slowing down the yaw effect on the vehicle when vehicle is driven on a µ split track, so that even an average driver can initiate compensatory counter steer. ECU continually monitors the operating status of ABS. Incase of ABS failure driver will be alerted and conventional braking will still be operational without ABS. Fig. 3