At the Mercedes test track in Stuttgart, Germany, workers drive these elegant autos at high speeds through slalom courses.
Going ninety miles an hour, the driver slams on the brakes and nimbly maneuvers the car through a series of orange pylons. Why don’t these pricey vehicles flip off course like so many Matchbox cars in the hands of a four-year-old? Because of the quick response of anti-lock brakes.
Today it is not only luxury models that can give you the additional safety of antilock brakes. General Motors, for instance, includes them as standard equipment on many of its Pontiacs, Cadillacs, Buicks, and Chevrolets and offers them as optional equipment on other models.
The heart of the anti-lock braking system (ABS) is a computer inside the vehicle. A sensor located on the inside of the wheel monitors how fast the wheels are turning and feeds this information continuously to the computer. The sensor has calibrations, or small teeth, that run smoothly when the wheels of the car are turning properly.
If you brake gradually, your brakes will perform on their own as usual. But if you suddenly jam on the brakes, regardless of how fast you may be going, the sensor in milliseconds registers that the teeth are not moving uniformly and signals the computer that the wheels are about to lock. The computer, in turn, activates a hydraulic modulator that forces hydraulic fluid to the braking system, initiating a sort of stuttering effect. The brake disks clamp and unclamp incredibly fast, up to fifteen times per second.
The result is a rapid pumping action, like that which you may have practiced yourself on slippery snowy roads, but of course much faster. The point is, the wheels continue to roll slightly, preventing the hazardous lockup that can send you spiraling off the road. With this system, too, you can generally stop in a shorter distance and also maintain your ability to steer.
The concept underlying ABS arose back in the early fifties when Dunlop Tire Company in England developed an anti-lock braking system called Maxaret for aircraft. In the sixties the Japanese incorporated the system in some of their high-speed trains. Today, in automobiles, these brakes are becoming widespread and are gradually being phased in as standard equipment.
Any drawbacks? It’s fine if your car has them, but in the event of a quick stop on a congested highway, you’d better hope the driver behind you has them too.
During normal braking, the sensor on the wheel moves smoothly and monitors how fast the wheels are turning. When you slam on the brakes for a sudden stop, the sensor informs the computer, which in turn signals the brake modulator to initiate a rapid braking action, the anti-lock brake system.