What is ABS ?
front right and rear left are fed from the other part of the tandem master cylinder.
The wheel sensors operate on the Hall principle and give an electric current output which is considered to have advantages over the more usual voltage signal from wheel sensors. The ABS control computer is incorporated into the ABS modulator and, with the aid of sensor inputs, provides the controlling actions that are designed to allow safe braking in emergency stops.
Block diagram of ABS
Starting at the top left corner of Figure there are two hydraulic accumulators
(A1 and A2) which act as pressure reservoirs for hydraulic fluid. Below these is the modulator pump which is under computer control. At the bottom of the diagram are the four wheel brakes and above these are the inlet and outlet valves (labeled C and D, respectfully) which, under computer control, determine how braking is applied when the ABS system is in operation.
ABS is not active below 7 km/h and normal braking only is available at lower speeds. When ABS is not operating, the inlet valves rest in the open position (to permit normal braking) and the outlet valves rest in the closed position. At each inlet valve there is a pressure sensitive return valve that permits rapid release of pressure when the brake pedal is released and this prevents any dragging of the brakes.
Why do you need Anti-lock Brakes?
Imagine, you are driving a car without the Anti-lock Braking System (ABS) on a slippery road (e.g. after a rain or snow). Suddenly, you notice something on the road right in front of you. You hit the brakes hard and try to steer aside, but the car doesn't react to the steering anymore and just skids out of control. This happens, because all the wheels are locked up while you are holding down the brake pedal. As a result, you lose the ability to steer the vehicle (upper photo).
The ABS system is designed to help in situations like this. The Anti-lock Braking system prevents the wheels from locking up, helping you maintain steering control during hard braking. In a similar situation, driving a car equipped with the ABS, it would be easier for you to steer your vehicle while braking.
Working principle of ABS
Depressing the brake pedal operates the brakes in the normal way. For example, should the wheel sensors indicate to the computer that the front right wheel is about to lock, the computer will start up the modulator pump and close the inlet valve C4(ref to fig above). This prevents any further pressure from reaching the right front brake. This is known as the ‘pressure retention phase’. If the wheel locks up, the computer will register the fact and send a signal that will open the outlet valve
D4 so that pressure is released. This will result in some rotation of the right front wheel. This is known as the ‘pressure reduction phase’. If the sensors indicate that
the wheel is accelerating, the computer will signal the outlet valve D4(ref to fig above) to close and the inlet valve C4(ref to fig above) to open and further hydraulic pressure will be applied. This is known as the ‘pressure increase phase’. These three phases of ABS braking, i.e.
pressure retention, pressure release and pressure increase, will continue until the threat of wheel lock has ceased or until the brake pedal is released.
We can also say that it prevents our tyres to lock suddenly when we break hard but split our breaking in number of small locking and un-locking help us to prevent skidding and to find better stability !
For better understanding refer to our video attached
What are various advantages of ABS over normal breaks !
1They eliminate or greatly reduce the possibility of brake lock up and therefore provide a better chance of steering out of trouble.
2. ABS brakes were designed to combat the problem of tire lock up and uncontrolled spins. Since brakes are most effective at slowing the car at a point just before wheel lock up, a system that provides for wheel braking while preventing wheel lock up is very desirable.
3. Due to rotating wheel, it helps you to steer away the vehicle from the object while applying brakes at the same time.
Is even more effective in sand, snow, water, and mud where loss of traction is even higher, as on these surfaces, with normal braking system, it is even easier to lock wheels and loose traction but ABS works excellent in these conditions also and stops the vehicle in a much shorter distance.
Categories:
automobile,
mechanical
sir i m very thankfull to you !! for adding vedio it has made me much more clear about ABS