Anti-lock brakes have been a standard feature on most passenger vehicles in the United States for so long now that they are easy to take for granted. While the roots of this important safety system run deep into the early days of the last century, the technology was absent from automobiles for much of its history.
If you needed to stop your car suddenly before anti-lock brake systems (ABS) were adopted, you had the option to either slam on the brake pedal and put your vehicle into a skid, or leave the pedal alone and run full force into something. Okay, there was an in-between option; you could furiously pump your brake pedal in an attempt to prevent the wheels from locking up and the tires from sliding on the pavement. Some drivers would even try to measure exactly how much pressure to apply so as to slow down sharply without locking up the wheels. Good luck employing that strategy when the car in front of you stops suddenly or a playground ball bounces out into the street!
Anti-lock brakes solve the problem of tires skidding when you stop. The problem is that, when you hit the brakes, the tires stop much faster than the rest of your car. The momentum of your vehicle keeps moving forward, dragging the tires along with it. When this happens (in most cases) it takes longer to stop. More importantly, you lose any ability to steer because your tires need to keep rolling for your steering wheel to have any effect. ABS works to rapidly “pulse” the brake calipers (a caliper is a clamping device that is a component of your brake system) so that they squeeze and release the brake pads up to fifteen times per second. This slows your wheels down to precisely the point where your tires are about to lose traction (the point where friction and braking power are at their peak) without stopping the wheels completely.
The advantage of anti-lock brakes is a vehicle that is capable of stopping sooner in an urgent situation and remains under the steering control of its driver. Even in those circumstances where ABS does not stop your car in a shorter distance (on gravel roads or some slippery surfaces), you can at least, as one automotive expert put it, “point your car at what you want to hit.” You can still steer, so you stay in control.
Early ABS technology
The earliest applications of the concept of ABS can be traced back to the beginning of the twentieth century when a system was pioneered for use on rail vehicles. The idea moved from trains to planes, and by the twenties, French and German companies were developing systems for use on aircraft. These early ABS enterprises eventually resulted in a thirty percent improvement in braking performance and fewer burned or burst tires on the runway.
Try as they may though, automotive companies were unable early on to adapt the idea for practical use on cars. A lack of technology in the 1920s prevented engineers from developing commercially-viable ABS systems. Creating a system that was affordable proved to be too complex; making one that was simple was too expensive. The high price tag of ABS was far more difficult to justify on a car than on a plane.
By the nineteen fifties, an aviation anti-skid system, the Dunlop Maxaret, was finding widespread use in the U.K. and across Europe, eventually becoming standard on many aircraft. The system not only allowed aircraft to stop sooner and saved on tires, it also allowed planes to carry more weight. In the later part of the decade, Maxaret even made its way to motorcycles, where skidding was a factor in a high number of crashes, though at the time it did not see production use.
A mechanical ABS system did see limited automotive use in the sixties, but it was confined to experimental vehicles and race cars.
Compared to trains and aircraft, automobiles presented a unique challenge for automotive engineers, besides the cost. In order for ABS to accurately detect the acceleration and deceleration of a car’s wheels on irregular surfaces and while cornering, more sensors and faster signal processing were required.
Through the nineteen-fifties and sixties, automakers worked to design and test anti-lock brake systems for their vehicles. In 1953, for example, the head of design at Mercedes-Benz applied for a patent on a system. A decade later they began work on their first electro-hydraulic brake control system, and, in 1966, they partnered with the electronics company that would later be known as Bosch. The result of that partnership was the 1970 premiere of a somewhat successful analog-electronic system.
Other manufacturers followed suit. Some, such as General Motors and Ford, added rear-wheel ABS to their luxury lines in the early seventies. Nissan and Toyota in Japan produced systems as well. Rear-wheel ABS, though, had only marginal benefits, since most of the stopping power on a car – and all of the steering – comes from the front wheels.
A defining moment came in 1971 when Chrysler, working with the Bendix Corporation, came up with the first four-wheel electronically-controlled ABS system, “Sure Brake,” and added it to their Imperial line. Using electronics to control the system allowed for faster response. Unfortunately, while the technology was effective, marketing was not and Sure Brake disappeared by the mid-seventies.
Mercedes, on the other hand, kept at it with the belief that four-wheel multi-channel ABS was possible with a digital controller. In 1978, they introduced their second generation “Anti-Bloc” system that closely resembles the systems in operation today. Their ad brochure boasted the following:
“The anti-lock braking system uses a computer to monitor the change in rotational speed of each wheel during braking. If the speed slows too quickly (such as when braking on a slippery surface) and the wheel risks locking, the computer automatically reduces the brake pressure. The wheel accelerates again and the brake pressure is increased again, thereby braking the wheel. This process is repeated several times in a matter of seconds.”
Since that time, every major auto manufacturer has added the feature to its vehicles, first as an option, then as standard equipment. Lincoln became one of the first automotive companies to offer standard four-wheel ABS to their lineup in 1993.
Long gone are the days when you might need to pump your brakes to avoid a crash. Indeed, you should not pump the pedal of a car equipped with ABS; just put the pedal to the floor and let the safety system do the work. You now have a better option than locking up the wheels and hoping for the best.
Columbia Auto Care & Car Wash | Author: Mike Ales | Copyright
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