by Richard Russell
In my humble opinion ABS, or Antilock Braking Systems, are the most significant safety advance since the invention of the brake itself.
ABS requires no conscious thought, training or additional maintenance. Drivers simply have to react as they normally would in an emergency – jam on the brakes. But with ABS they retain steering control. Without ABS the front wheels lock up and the vehicle slides without control directly into the object the driver wanted to avoid. ABS detects when a wheel is about to lock up under heavy braking and modulates brake pressure to that wheel preventing it from doing so.
ABS has its detractors, and there is a great deal of misinformation out there. But for the average driver, ABS will come to the rescue several times each year in normal driving conditions while airbags will be used once every 157 years! ABS is an active safety system – it requires action by the driver to help prevent a crash. Airbags, on the other hand, are passive safety devices that require no action but do not come into effect until after a crash has occurred.
Let’s address the naysayers and misinformation first:
- ABS is no better than a fancy way to pump the brakes. Partially true – but radically different. When we pump the brakes in a non-ABS-equipped vehicle we apply brake pressure to all four wheels simultaneously. ABS can deal with each wheel individually, allowing the others to go about their job.
- ABS reduces braking distances. Not necessarily. ABS simply allows the driver to retain control of steering during maximum braking. Properly applied braking in a non-ABS vehicle can bring a vehicle to a full stop just as quickly as an ABS-equipped vehicle.
- Statistics are proving that ABS-equipped vehicles are involved in more run-off-road crashes and result in more injuries and deaths than non-ABS-equipped vehicles. True – but with a proviso. Before ABS, drivers facing an emergency generally locked their brakes and slid into an object – usually another vehicle. In attempting to steer away, they would discover the locked front wheels did not allow them to do so. With ABS they are doing the same thing but the vehicle is now responding to their steering input and turning – heading into the ditch or nearest offroad object because the driver doesn’t take the secondary action of actually steering around the problem. The same statistics used by the insurance industry and others to question the efficacy of ABS also shows the number of rear-end collisions with ABS-equipped cars to have declined.
As with any technology new developments and more sophisticated systems enter the market at the high end of the price spectrum working their way down as production costs decrease. Today we have everything from rudimentary ABS to elaborate systems that include more advanced ABS, traction and stability control.
There are generally three things that determine the proficiency of ABS: the number of individual wheels it controls, the number of sensors and rapidity with which the brakes are applied. Let’s work our way up the ABS ladder:
- Rear wheel ABS – found only on light trucks and some early sport utes based on the same trucks. A rudimentary system that can cause great problems if you mistakenly think you have four wheel ABS. A single-channel, single sensor system detects rear wheel lock up and modulates pressure to the rear wheels accordingly. BUT it does not involve the front or steering wheels. Many people have crashed because they thought they had four-wheel ABS and acted accordingly – locking the front wheels and losing steering control.
- 3-sensor, 3-channel systems – generally an entry-level system. Far better than no ABS at all and until a few years ago the best there was. Three channel systems provide for control of the two individual front wheels (2 channels) and both rear wheels through the third channel. There are three sensors – one at each front wheel and one for both rear wheels.
- 3-channel, 4-sensor systems – A sensor for each individual wheel and three channels controlling the front wheels individually and the rears as a pair.
- 4-channel, 4-sensor systems – one sensor and one channel per wheel allowing the system to modulate pressure to each individual wheel.
Throughout the entire range the number of times per second pressure can be applied and released can vary from a half-dozen to as much as 30 in the most recent and elaborate systems.
Further up the price ladder, more elaborate systems use information from the sensors to accomplish more. The same sensors that detect impending lockup can, for example, be programmed to detect the opposite: wheel slippage or spinning. The control system then applies the brakes at that wheel to prevent it from spinning – voila – traction control. In more elaborate systems the sensors talk to the engine control computer telling it to reduce power until the wheel regains traction. Generally the lower cost, lower-speed systems apply the brakes to a spinning wheel at low speeds only since doing so at high speeds might cause stability problems. By combining brake application at low speeds and reduced engine output at higher speeds, we get all-speed traction control.
The most recent advances in this technology are stability control and brake assist. Stability control prevents the vehicle from spinning out by utilizing a combination of ABS, steering and yaw sensors to detect when a vehicle is not going in the desired direction. In such cases individual brake pressure is applied to the appropriate wheels to bring it back in line – a subject for another time.
Brake assist is a method of maximizing the benefits of ABS. Studies in Europe have found that when drivers sense a problem they do not immediately apply enough pressure to activate the ABS system. Instead the normal driver faced with an emergency will hit the brake pedal quickly and then assess the situation. Following this “assessment” they will either release the brakes or realize they need to apply more pressure. This delay, while infinitesimal in terms of time – can prove deadly in terms of increased stopping distance. Brake assist monitors the speed and effort of the initial stab at the brake pedal. If it is judged to be a quick emergency-type application the system will apply full pressure and activate the ABS system immediately – while the driver is “assessing” the situation. If the driver lets off the brake pedal, the system will release pressure immediately. If, on the other hand the driver figures the scene ahead requires full braking, that will already have been done for him. The difference is amazing – tests indicate that from 50 km per hour brake assist can reduce braking distances by as much as 10 metres – almost two car lengths.
The advent of ABS has allowed the development of systems that prevent the average driver from getting into serious trouble.