ABS(Antilock braking system) M.Mathankumar, M.Mohankumar, B.E-Mechanical Engineering, K.S.R College of engineering, Thiruchencode.

Antilock Braking System ABSTRACT: Antilock braking systems (ABS) are electronic systems that monitor and control wheel slip during vehicle braking. ABSs can improve vehicle control during braking, and reduce stopping distances on slippery (split or low coefficient of friction) road surfaces by limiting wheel slip and minimizing lockup. Rolling wheels have much more traction than locked wheels. Reducing wheel slip improves vehicle stability and control during braking, since stability increases as wheel slip decreases.  

Why Anti Lock Braking System Need? A skidding wheel (where the tire contact patch is sliding relative to the road) has less traction than a non-skidding wheel By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two ways: You'll stop faster, and you'll be able to steer while you stop

Components of Antilock Braking System ABS Controller Wheel Speed sensors Pump Valves

Location of anti-lock brake components

ABS Controller The controller is a computer in the car. It receives inputs from: Wheel Speed Sensors (Each Wheel’s Speed) Brake Switch (Brake Pedal Operation) Vehicle Speed Sensor (Vehicle Speed) And Controls: The solenoid valves (8 Nos) Pump Motor Assembly

Wheel Speed Sensors The speed sensors are located at each wheel, or in some cases in the differential These sensors measure the speed of the respective wheel on which it is fitted Which provides the information, when a wheel is about to lock up.

Solenoid Valves There is a valve in the brake line of each brake controlled by the ABS. The valve has three positions: The valve is open; pressure from the master cylinder is passed right through to the brake. The valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder. The valve releases some of the pressure from the brake.

Pump Motor Outlet Solenoid valves release pressure from the brake lines. When a valve reduces the pressure in a line, the pump operates to get the pressure back up for the respective line. Thus it help ‘lock and brake’ of the wheel to effect Antilock brake functioning

Anti-lock brake pump and valves

How ABS works ?... An ABS consists of several key components: Electronic control unit, wheel speed sensors, modulator valves. Here’s how these components work together: 1. Wheel speed sensors constantly monitor and send electrical pulses to the ECU at a rate proportional to the wheel speed. 2. When the pulse rates indicate impending wheel lockup, the ECU signals the modulator valve(s) to reduce and/or hold the brake application pressure to the wheel(s) in question. 3. The ECU then adjusts pressure, seeking one which gives maximum braking without risking wheel lockup. 4. When the ECU acts to modulate the brake pressure, it will also turn off the retarder (if so equipped) until the risk of lockup is over. 5. The ECU continually checks itself for proper operation. If it detects a malfunction/failure in the electrical/electronic system, it will shut down that part of the ABS affected by the problem or the entire ABS depending upon the system and the problem.

Antilock Braking System

Advantages Disadvantages It allows the driver to maintain directional stability and control over steering during braking Safe and effective Automatically changes the brake fluid pressure at each wheel to maintain optimum brake performance. ABS absorbs the unwanted turbulence shock waves and modulates the pulses thus permitting the wheel to continue turning under maximum braking pressure. Disadvantages It is very costly Maintenance cost of a car equipped with ABS is more.

Conclusion Statistics show that approximately 40 % of automobile accidents are due to skidding. These problems commonly occur on vehicle with conventional brake system which can be avoided by adding devices called ABS If there is an ABS failure, the system will revert to normal brake operation. Normally the ABS warning light will turn on and let the driver know there is a fault