New Braking Systems Proliferate
Question: I am told by car salesmen that there are two kinds of anti-lock brake systems and that one is better than the other, but that is the limit of their knowledge. Which system is superior? Are they worth the extra cost?--E.F.
Answer: Anti-lock brake systems are judged to be a major improvement in vehicle safety that will eventually become standard equipment on most cars. So, the auto industry, the technical community and the marketplace have made the judgment that they are worth the extra cost.
Anti-lock systems were installed on 9% of domestic cars in 1989. By the year 2000, they will be on 90% of new cars.
Why the big switch? Under certain difficult stopping conditions, anti-lock systems can reduce braking distances by 20% and prevent loss of vehicle steering. On wet ice, the most difficult stopping surface, the systems can prevent wild spins.
In a panic stop in which you jam your foot on the brake pedal, a central computer will immediately begin comparing the speed with which your wheels are rotating and the speed of the vehicle. If there is a difference, then the tire is locking up.
The system then reduces the pressure or rapidly pulsates the brake, similar to the action of a motorist pumping a brake. But anti-lock system can pulsate the brake 12 times per second, far faster than a human could.
But the cost is not yet clear, ranging from $600 to more than $1,000. That’s not the whole story, however.
The systems can require very sophisticated maintainance and in the worst case can require very costly spare parts. One national brake expert estimated that some electronically controlled hydraulic components on the newer systems cost more than $1,000 to replace.
Eventually, high costs will come down once these systems are mass-produced, but for the time being they are not cheap to buy or maintain.
The salesmen were correct that ABS brakes come in several basic designs, and so far there is no uniform standard among manufacturers. Judging the capability of these systems is nearly impossible for the consumer.
Various systems provide for anti-lock capabilities only at the front or rear wheels. Some systems have only a single sensor in the front. And one system provides for a single sensor for the entire car. By one estimate, there are seven different configurations in common usage, each with different stopping characteristics.
In addition, there are so-called integrated and non-integrated systems. In the non-integrated systems, which are also called add-on systems, the ABS consists of a typical power brake vacuum booster and its booster pump, along with an accumulator, a master cylinder, a computer, wheel speed sensors and a valve block that distributes the hydraulic pressure to each wheel.
The integrated system, which predominates today, combines some of these components so that the valve or modulator block gets its power from a power booster unit. It eliminates the separate master cylinder, valve block and associated vacuum power devices.
