1971

Anti-Lock Brakes

When we hear screeching tires, it often means that a driver has made a panic stop and has lost control of the vehicle. The tires are sliding rather than rolling. Steering input has no effect and the car is following a ballistic path carried by its momentum.

What if we kept the tires rolling during a panic stop? The screeching noise would disappear and the driver would maintain some control. Stopping distances would also go down. Engineers went to work and the anti-lock braking system was born and popularized in the 1970s. The first autos sold with the anti-lock braking system (ABS) were commercially available beginning in 1971.

The basic idea behind anti-lock braking is very simple. Rotation sensors monitor all four wheels. When the driver presses the brake pedal, a computer checks the rotation rates. If it sees any of the wheels locking up, it pulses the brake on that wheel to keep it rolling. The driver feels a buzz in the brake pedal as the computer rapidly pulses the hydraulic pressure in the brake line to keep the wheel spinning.

Engineers seek efficiency and reuse. Once there is a computer on board that can sense wheel rotation and control braking, what else can the system do? It can, for instance, detect a tire that is going flat. Its rate of rotation will be different from the others. Another useful capability is traction control. If one tire starts spinning uncontrollably, the ABS can apply the brake on that wheel to keep it from spinning. More power gets transferred to the wheel that has grip. There is also stability control, made possible by the addition of a steering sensor and gyroscopes. If the driver turns the steering wheel but the car does not respond, the computer can apply the brakes on the inside of the turn.

Between anti-lock braking, traction control, and stability control, engineers have greatly improved the safety of cars.

The thing engineers cannot do is to keep a driver from being a knucklehead. If someone is driving too fast on an icy road, he is probably going to crash. Engineers compensate for knuckleheads with airbags.

SEE ALSO Automobile Airbag (1953).

Pictured: Close-up of an anti-lock braking system.