ABS of Automobiles
Image credits: Photo by user Eduardo Spares via Unsplash
ABS (Anti-lock Breaking System) is a technology widely used in cars these days. It helps to stop a car in rapid motion very quickly and safely without allowing tires to slip on the road. The importance of ABS technology can be analysed from the fact that an average driver with ABS enabled car can stop it earlier than an experienced one, provided that both of them starts retarding from same speed on similar surfaces. The main purpose of using ABS in cars is to prevent slippage.
- Principle of ABS:-
The ABS works on the principle that the tyre sliding on the road will take more time to stop than the tyre rolling as well as sliding between the threshold braking limits.
It may be simplified by saying that when a tyre is continuously sliding on the road, it will have less grip on the road than a rolling tyre.
Construction of ABS: An ABS may be divided into four major components which contributes significantly in executing the action of ABS. These are listed below:
- Speed sensor
- ECU
- Valves in brake line
- Pump
Speed sensors: These are the input units of an ABS. The ABS shall be informed of the time the wheel is to be locked. And how much brake fluid pressure must be reduced to prevent the wheel from being locked while continuing the retardation of speed. This information is gathered through the speed sensors. They are used on the vehicle’s tires. The sensors transmit the data gathered to the ECU; which then interprets the data, control the opening of the brake line valve accordingly so that the car may stop quickly within the limit of threshold braking and without slipping on the road.
ECU: ECU is the brain of ABS. It collects information on the speed of the tyres from the speed sensors and then takes measures on how to stop the car at the minimum achievable time. It does this by controlling the opening and closing of the brake line valve used in the tyres.
Brake line valves: These are the mechanical components of an ABS. They allow the brake fluid to enter the brake system used on all tyres, which forces them to stop their rotational motion.
Pump: When the pressure on the brake shoes is required to be reduced, an amount of brake fluid must have to be taken back from the brake line. This is done by the pump. The reserve for the fluid is the master cylinder.
What happens in an automobile without the ABS?
Assume that you are travelling on a straight road amidst a forest at about 98 km/h. All of a sudden, you find a cow on the highway. It is obvious that you will be baffled by such a situation and you press the brake paddle with complete force. As a result, the tyres will be jammed and due to the huge momentum of the car, it will start skidding down the road. We understand that rolling friction is always less than static friction. Therefore the car will take more time to stop than expected in this situation. Also, you cannot steer the car while it is skidding on the road.
The above mentioned problem is solved by the ABS.
Working of ABS: When the driver presses the brake paddle suddenly facing an obstacle very close to the car on the road, the tyres tends to be locked by the brake shoes. Due to this sudden change in tyre rotation, ABS becomes effective. The speed sensors send the data about the speed change to the ECU. ECU, then open the brake line valve just before the tire begins to slide off the road. Therefore, the locking is stopped and the tire tends to turn again. After a short rotation, the ECU opens the brake valve and further increases the pressure on the brake shoes. When the allowable deceleration is reached and the tyre is about to be locked again, the ECU removes the brake fluid and the tyre has a tendency to turn again. This reciprocal process of increasing and decreasing the pressure on the brake shoes of the tires continues until the car stops completely. The process of increasing and decreasing the brake line pressure is monitored by the ECU so rapidly that it can compete up to 14 cycles in one second. Consequently, the car takes considerably less time to stop without sliding on the road.
How to know if the ABS is operating?
The driver experiences pulsing jolts through the brake paddle while the ABS is running. This is due to a rapid shift in brake shoe pressure from the opening and closing of the brake line valves.
The ABS is very useful while driving the car on the ice where the traction between the road and tyre is very low.
