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Anti-lock braking systems |
Crumple zones, Anti-roll bars, Side impact beams, Engine sub frame, Collapsible steering column, Hydraulic assist brakes, so on and so forth. These are some of the latest additions in the cars we see today, these are features that make a car safer and the passengers actively or passively help in either avoiding fatalities or, the event of a crash in itself. One such technology which can help reduce the risk of the crash itself is Anti-lock brakes, or more commonly known as ABS.
Recently, this technology has been made available in many cars, such as the Safari Dicor, Maruti Suzuki Swift and so on, but the technology has made its presence felt even at the Budget cars end, The Hyundai Santro Xing has been available with ABS for a long time now and the Maruti Suzuki Wagon R features the same, post the introduction of its Euro-3 Model.
As always, what I describe here is how most systems work in general. Since different manufactures have their own versions of ABS, specifications and part names will differ. The ABS may be integrated to all the four wheels and is able to apply the optimum amount of pressure on the brakes, according to the available grip on the particluar tyre. When the wheels lock, all steering ability of the vehicle is lost and as a result, so is control. Thus, since the wheels don't lock, the driver is able to steer away from an obstacle while constantly slowing down considerably
Wheel slip increases along with brake pressure. But, the factor is that tire grip peaks just before it locks and falls to a much lower value as soon as the wheel locks. ABS is designed to keept the tires performing in the maximum grip zone as often as possible; this is done by applying enough pressure on the tire to maintain it at almost lock condition without letting it lock!! Complex isn't it..
There are many parts that make up the antilock braking system. This system takes information from the sensors placed at the brakes which sense the speed of the individual wheel in comparison with that of other wheels; if the speed of the wheel is drastically less when compared to others, this tire has locked up. This information is passed onto the control module which reacts by reducing the pressure on this brake which allows for the locked wheel to start rolling again; or in some systems, pressure is completely released allowing the wheel to rotate and a slightly lower pressure is then applied to the wheel and throught the process the wheel lock is kept under check.
The master cylinder controls the hydraulic pressure in the braking cylinder; the essentially hydraulic system connects the master cylinder to the brake cylinders that are at each wheel. The hydraulic fluid passes through a valve present in the master cylinder and a fluid chamber to get to the brake cylinder present in the brake caliper. When the brakes are engaged under normal use without ABS, the valve is open, and the pressure in the chamber is the same as the pressure in the master cylinder. This parameter gets varied as soon as ABS kicks in.
When the sensor detects imminent locking, the control valve moves as a result of instructions from the ABS computer. The control valve determines the pressure in the cavity in front of the actuator by controlling amount of brakes applied. The greater pressure in front of the actuator causes it to slide back. This closes the valve between the master cylinder and the chamber.
When it is detected that locking will no longer occur, the control valve returns back to its initial position. This results in the drop in pressure in the braking system. Now, the ABS is switched off and hence normal braking continues.
Antilocks help motorists by preventing the wheel from stopping before the vehicle does, A vehicle ABS remains under control during
Emergency braking and one can continue to steer while braking as hard as possible. This benefit is most felt in the wet, but on the dry, non ABS vehicle tend to take lesser braking distance. The benefit is most felt on a wet sunday afternoon, when all of a sudden a buffalo might want a lift!!
If ever you were to be in a situation where you are actually using the ABS on your car, a light will come on; on the dash and there will be a pulsating feeling to the brake pedal; don't get alarmed at stop braking... This is happening due to the rapid changes in pressure according to avaiable grip on the brakes.
When all of a vehicle's wheels lock, the vehicle skids forward and perhaps somewhat left or right, depending on the coefficient of friction between each tire and the road. When only the rear wheels lock, the tendency is for the vehicles back end to move faster than the front. This results in a lateral motion as the rear end tries to pass the front end and the vehicle can spin out of control. When front wheels lock, the result is basically a straight line skid but there is no steering control.
The final question then, do we really need anti-lock brakes in our cars?
The answer is a resounding yes, simply because they are very well suited to our Indian conditions, as they are able to cope with the varying degrees of friction available with the various facets of out Indian roads, so to speak. So, make sure that this feature, features on your next cars' equipment list, you never know when you might need it.
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![ABS](javascript:openwin("largephoto.asp?imagename=abs.jpg&imagetitle=Antilock brakes"))
