Like many technologies found in cars, Anti-lock Braking Systems (ABS) were originally developed for aircraft. It’s not a good idea for a plane to lock its wheels on landing!
The first systems were developed in the 1920s by Gabriel Voisin a French car and aircraft engineer specifically for planes. One of the earliest systems was developed by Dunlop, the tyre company. Called Maxaret, it was originally developed for aircraft as well and was popular because it helped reduce the braking distance of a plane by up to 30%. With this success, Jensen decided to fit a version to the FF, one of the first all-wheel drive cars offered to the public. The car was a gem but the Maxaret system had a unique “feature” – which was to push the brake pedal back towards the driver when the system kicked in. This was due to the relief valve being plumbed into the master pump thus working against the driver’s input. This would presumably make the driver push harder, so it was probably a good thing to do.
The concept of ABS is the automating of a braking theory called Cadence Braking. This is something that was taught to race car drivers to get the maximum from their brakes. Basically, the driver “pumps” the brakes to reduce the distance to stoppage. The maximum braking pressure is applied to the brake disc a fraction of a second before the disc locks up, so by lifting off and applying the pressure again quickly means that you get the optimal brake performance. ABS automates that concept so that the driver doesn’t need to, and it smoothes out the process. The electronics can do it much faster than a human can.
The electronic units in the ABS are constantly monitoring each wheel and detecting if the speed differs from any other one. If it is too fast then it will apply more braking pressure and if too slow, it will release any pressure being applied. Fundamentally, it works in the background and acts quicker than the driver can react naturally. When an emergency brake situation is required, it can deliver the Cadence Braking concept up to 15 times a second, which dramatically reduces the time that a vehicle would stop.
Chrysler and Mercedes both developed systems in the 1960s and 1970s that were more reliable and it is the Mercedes design that has become a standard for most vehicles today. Chrysler fitted a system to the 1971 Imperial which prompted Ford and GM to compete on their high end cars. Nissan and Toyota were also busy at the same time getting cars out for the Japanese market.
Today’s systems use a lot of electronic sensors to determine speed, grip and direction and they are usually fitted in conjunction with traction control or electronic stability systems. However, as I discovered with a rental car, if the suspension is sloppy it completely negates the power of ABS. If the car’s weight moves and wheels become light, then they will lock up because there is no balance in the chassis.
Most cars today will have some form of ABS and many sports and touring motorcycles are now fitted with the technology to help the riders in difficult conditions. I have noticed that riding on dirt, you need to switch off ABS and traction control as this interferes with the bikes natural desire to move on the loose surface. It is actually safer to let the bike move whilst adjusting your weight (i.e. centre of gravity) for smoother riding.
One thing to remember is that ABS will not “save” you – a degree of competency is still required by the driver to assess the conditions and react accordingly. What ABS and other systems can do is to limit the damage that may occur by helping the driver to deal with the situation. However …. the driver needs to understand their car and when the systems kick in, it is possible to provide input (i.e. steering) that could reduce the effectiveness of the supporting systems. For examples, just look at YouTube!