An anti-lock braking system is a safety system that allowsthe wheels on a motor vehicle to continueinteracting tractively with the road surface as directed by driversteering inputs while braking, preventing the wheels from lockingup (that is, ceasing rotation) and therefore avoiding skidding.An ABS generally offers improved vehicle control and decreasesstopping distances on dry and slippery surfaces for many drivers;however, on loose surfaces like gravel or snow-coveredpavement, an ABS can significantly increase braking distance,although still improving vehicle control.Since initial widespread use in production cars, anti-lock brakingsystems have evolved considerably. Recent versions not onlyprevent wheel lock under braking, but also electronically controlthe front-to-rear brake bias. This function, depending on itsspecific capabilities and implementation, is known as electronicbrakeforce distribution (EBD), traction control system,emergency brake assist, or electronic stability control (ESC).
The ABS was first developed for aircraft use in 1929 by theFrench automobile and aircraft pioneer, Gabriel Voisin, asthreshold braking on airplanes is nearly impossible. Thesesystems use a flywheel and valve attached to a hydraulicline that feeds the brake cylinders. The flywheel is attachedto a drum that runs at the same speed as the wheel. Innormal braking, the drum and flywheel should spin at thesame speed.
A typical ABS includes a central electronic control unit (ECU),four wheel speed sensors, and at least two hydraulic valves withinthe brake hydraulics. The ECU constantly monitors therotationalspeed of each wheel; if it detects a wheel rotating significantlyslower than the others, a condition indicative of impending wheellock, it actuates the valves to reduce hydraulic pressure to the brakeat the affected wheel, thus reducing the braking force on thatwheel; the wheel then turns faster. Conversely, if the ECU detects awheel turning significantly faster than the others, brake hydraulicpressure to the wheel is increased so the braking force is reapplied,slowing down the wheel. This process is repeated continuously andcan be detected by the driver via brake pedal pulsation. Some anti-lock system can apply or release braking pressure 16 times persecond.
The ECU is programmed to disregard differences inwheel rotative speed below a criticalthreshold, because when the car is turning, the twowheels towards the center of the curve turn slowerthan the outer two. For this samereason, a differential is used in virtually all roadgoingvehicles.If a fault develops in any part of the ABS, a warninglight will usually be illuminated on the vehicleinstrument panel, and the ABS will be disabled untilthe fault is rectified.
Modern electronic stability control (ESC or ESP) systems are anevolution of the ABS concept. Here, a minimum of twoadditional sensors are added to help the system work: these area steering wheel angle sensor, and a gyroscopic sensor. Thetheory of operation is simple: when the gyroscopic sensordetects that the direction taken by the car does not coincidewith what the steering wheel sensor reports, the ESC softwarewill brake the necessary individual wheel(s) (up to three with themost sophisticated systems), so that the vehicle goes the waythe driver intends. The steering wheel sensor also helps in theoperation of Cornering Brake Control (CBC), since this will tellthe ABS that wheels on the inside of the curve should brakemore than wheels on the outside, and by how much.
The ABS equipment may also be used to implementa traction control system(TCS) on acceleration of thevehicle. If, when accelerating, the tire loses traction,the ABS controller can detect the situation and takesuitable action so that traction is regained. Moresophisticated versions of this can also control throttlelevels and brakes simultaneously.
There are four main components to an ABS :Speed sensors, Valves, a Pump, and a Controller.
Speed sensors:The anti-lock braking system needs some way of knowingwhen a wheel is about to lock up. The speed sensors,which are located at each wheel, or in some cases in thedifferential, provide this information.Valves:There is a valve in the brake line of each brake controlledby the ABS. On some systems, the valve has threepositions:In position one, the valve is open; pressure fromthe master cylinder is passed right through to the brake.In position two, the valve blocks the line, isolating thatbrake from the master cylinder. This prevents thepressure from rising further .In position three, the valvereleases some of the pressure from the brake.
Pump:Since the valve is able to release pressure from thebrakes, there has to be some way to put that pressureback. That is what the pump does; when a valve reducesthe pressure in a line, the pump is there to get thepressure back up.Controller:The controller is an ECU type unit in the car whichreceives information from each individual wheel speedsensor, in turn if a wheel loses traction the signal is sentto the controller, the controller will then limit thebrakeforce (EBD) and activate the ABS modulator whichactuates the braking valves on and off.
Four-channel, four-sensor ABSThis is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.Three-channel, four-sensor ABSThere is a speed sensor on all four wheels and a separate valve for each of the front wheels, but only one valve for both of the rear wheels.
Three-channel, three-sensor ABSThis scheme, commonly found on pickup trucks with four-wheelABS, has a speed sensor and a valve for each of the front wheels,with one valve and one sensor for both rear wheels. The speedsensor for the rear wheels is located in the rear axle. This sys-temprovides individual control of the front wheels, so they can bothachieve maximum braking force. The rear wheels, however, aremonitored together; they both have to start to lock up before theABS will activate on the rear. With this system, it is possible that oneof the rear wheels will lock during a stop, reducing brakeeffectiveness. This system is easy to identify, as there are noindividual speed sensors for the rear wheels.
One-channel, one-sensor ABSThis system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rearwheels, and one speed sensor, located in the rear axle. Thissystem operates the same as the rear end of a three-channel system. The rear wheels are monitored togetherand they both have to start to lock up before the ABS kicksin. In this system it is also possible that one of the rearwheels will lock, reducing brake effectiveness. This systemis also easy to identify, as there are no individual speedsensors for any of the wheels.
Apache is the first bike in India that comes equippedwith ABS and we should salute TVS for taking this bigleap in rider safety as this “will” avoid a lotof accidents and save a lot of lives ,and for a countrylike India where almost 1.2 lakh people every year diesdue to road accident this could be a big step. For just9 thousand over the price of the normal ApacheRTR180