ANTI-LOCK BRAKES - HOW THEY WORK

Advances in electronics technology in the Seventies and Eighties allowed car manufacturers to develop highly reliable anti-lock braking systems that could be economically installed in a wide variety of vehicles.

ABS - Recent history
One manufacturer's name is synonymous with the recent history of ABS. Bosch was the first company in the world to begin manufacturing ABS in serious production in 1978 following a ten-year period of development. Since then the company has produced millions of ABS units now fitted to cars worldwide.
To begin with ABS was mostly found in luxury cars but by 1999, up to 86% of all compact cars produced in Western Europe, and up to 30 percent of smaller cars were equipped with it. Today, virtually every new car is fitted with ABS brakes.
This high usage is due not only to rising customer demand for the feature but also to its falling price. This has been made possible not only due to the extra volumes being produced but also thanks to increasing development which has made ABS less expensive and more flexible to integrate into the braking systems of vehicles. The core of ABS, the hydraulic pressure modulator and the electronic control unit, are much lighter and smaller today. The latest hydraulic pressure modulator has less than a third of the volume and weight of the first generation unit.

So how does ABS work?

With an anti-lock braking system, computerised sensors located at each wheel monitor deceleration when the brake is applied. The sensor will detect any wheel lockup and trigger the hydraulic system to automatically pump the brakes up to 15 times per second. Cadence braking is the term used to describe how ABS works.

It's possible to cadence brake yourself - though of course, not at 15 times per second. The driver presses down on the brake pedal until he or she senses that wheel lockup is imminent. At that point, the driver eases up on the pedal pressure just enough to avoid the feel of lockup before repeating the process.

Cadence braking should not be confused with pumping the brakes. In cadence braking, the driver is applying pressure to the brakes all of the time. When pumping the brakes however, each pedal pressure and release can eventually cause wheel lockup. Unfortunately, cadence braking requires practice, and it's a technique with which most drivers are unfamiliar. For ordinary road users then, the way that ABS eliminates the need for the driver to manually pump the brake pedal is of huge benefit.

The dynamic t...