ABS: Anti-Lock Braking System

February 20,2000

If you’ve been driving long enough, you’ve probably experienced that most dreaded moment: the Panic Stop. You’re driving down the Ortigas-Rosario flyover and when you reach the ground level, a very slow car suddenly cuts in. You’re keeping to 30 km/h in a school zone, when, without looking, a kid steps into your path just a few meters ahead. In these situations, you would be fortunate if you can call on something to help you stop in the shortest distance possible while still allowing you to steer the car. No it’s not your guardian angel-it’s the electronic-hydraulic safety device known as the Anti-lock Braking System (ABS).

How it works

ABS consists of rotation sensors on each wheel, and a hydraulic pump integrated into the brake system, and a computer. The sensors tell the computer if a wheel has locked up-that is, stopped rotating-and the computer tells the hydraulic pump to release the pressure in the brake line to allow the wheel to rotate again, then applies and releases pressure repeatedly. In short, the ABS pumps your brakes for you, but at a rate beyond what is possible for any human, even the Michael Schumachers among you-as much as 30 times per second. Also, the ABS pumps each wheel individually, which not even Commander Data can do, unless he has four brake pedals to activate.

4-sensor 3-channel ABS means that there’s a sensor on each of the four wheels, while the system can actuate three hydraulic lines: the front wheels are pumped individually, while the rear wheels are pumped together. No, the spare tire doesn’t get one, no matter how prominently you display it on your tailgate. Nowadays, most systems are 4-sensor, 4-channel.

ABS is effective in decreasing stopping distances, as it allows the driver to use the full braking potential of the car. Maximum stopping power of the tires occurs when they are at imminent lock-up: just about to lock up but still rotating. ABS allows the driver to achieve this when he uses the system. Since it doesn’t allow the tires to lockup, the driver retains control of the steering.

How to actuate

If your car has ABS, remember that for the system to be effective, you must use full pressure on the brake pedal. When needed, don’t hesitate to slam full force on the brakes. You will probably hear a grinding sound and you might feel the pedal pulsate under your foot. Do not lift off! The grinding and pulsating tell you that the ABS pump is doing its job of braking and releasing each wheel quickly to avoid lockup. Use full braking force and concentrate on steering the car.

Another mistake that leads to accidents is that the driver hesitates in applying full force to the brakes. Studies have shown that drivers usually depress the pedal lightly, then a few fractions of a second later, use full force. In those fractions of a second, the car would have traveled several tens of meters, and the car won’t be able to stop on time. To correct this, manufacturers such as Mercedes and BMW have incorporated a Brake Assist system, which detects a potential panic stop and applies full force to the brakes, even if the driver is not applying full pressure on the brake pedal. I wonder if they’ve considered what happens to the trailing car when Brake Assist intervenes, but then if it is a genuine panic stop, you won’t have time to worry about the vehicle behind you anyway.

Other functions such as traction control

Since the ABS sensors and hardware are already present in many cars, some manufacturers have added some control features merely by tweaking the ABS software.

Since the ABS can detect the rotation speed of a wheel, it can be programmed to brake a wheel that is spinning too fast compared to the others. This is traction control. In some systems, the traction control software can also instruct the engine computer to reduce torque. In the Mercedes M-class 4×4, the front, rear and center differentials are all open. With an open differential, when one wheel gets stuck, say in deep mud, it usually spins uncontrollably and the whole vehicle bogs down. However, the M-class uses its ABS system to brake the spinning wheel, thus transferring torque to the wheel or wheels that have traction. Theoretically, this allows the M-class to keep moving even if only one wheel has grip-all without the weight and complexity of locking differentials. There’s no button to press-simply step on the gas for all it’s worth.

All cars should have ABS
As far as safety features go, ABS is one of the most important ones you can fit into your car. Unfortunately, the current market leader doesn’t offer ABS as standard or even as an option, on any of its 1.6 or 2.0 models. Despite its steep prices across the line, only its 2.3-liter, P1,100,000+ car has this feature. Forget about traction control for now-can’t we just get basic ABS?!

Don’t expect our government to help here-heck, it can’t even discipline those gigantic buses along EDSA, let alone worry about some tiny hydraulic pump in certain passenger cars. So who can help? Insurance companies? If they allow a reduction in premium if your car has ABS, perhaps they can influence manufacturers to offer this feature, and buyers to demand it.

A few carmakers do include ABS in most of their new models, notably Ford and Toyota. The way buyers are voting with their checkbooks, though, they’re telling the manufacturers: ABS? What’s ABS?

Word of caution

Despite its proven effectiveness in track testing, a US insurance-industry study has shown that ABS does not actually reduce the incidents or severity of accidents in cars so equipped. Surprised?

The study shows that: (1) drivers do not really know how to activate their ABS brakes. When they sense the ABS actuation-the grinding noise and pedal pulsation-they back off the brake pedal, thus actually increasing their stopping distance. (2) drivers who have ABS become overconfident and tend to drive faster and closer to the car in front, thus canceling out whatever extra margin the ABS provides.

So if your car does have ABS, remember to use full force when necessary, and maintain sufficient distance from the car in front as if your car didn’t have ABS. Only a few fortunate ones among you will have that extra bit of safety ready to help when you press on the brake pedal.

Text By Jason Ang | Photos by motioncars.com

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