ANTI-LOCK BRAKES - THE ORIGINS

Anti-lock braking was first designed for trains in the early 1900s, and developed for jet aircraft after World War II. In the late 1960s, motor manufacturers began to adapt ABS for use in luxury cars. However, early prototype systems were severely limited by the mechanical and analogue technologies of the time.

Advances in electronics technology in the Seventies and Eighties however, 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 manufacturer in the world to begin manufacturing ABS in series production in 1978 following a ten-year period of development. The first millionth ABS was produced eight years following production startup. By 1996 Bosch had supplied 25 million systems and the figure rose to more than 40 million in 1998.
The 50 millionth ABS unit rolled off the production line of Bosch`s Immenstadt (Allgäu) plant in Germany at the end of July. Every workday more than 40,000 of these electronic safety systems leave Bosch`s 17 production facilities located in Germany and abroad. This amounts to more than a third of all such systems produced around the globe today.
In 1999, Bosch-produced ABS systems will be fitted to 92% of the passenger cars produced in Germany, 67% of passenger cars in western Europe, 74% in North America, 62% in Japan and 55% worldwide. In the beginning, ABS was mostly found in top-of-the range cars but by1999, up to 86% of all compact cars produced in western Europe and up to 30 percent of even smaller cars were equipped with it.
This extra usage is due not only to rising customer demand for the feature but also to the 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 in the brake system. 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.
How ABS Works
Applying excessive pressure on the brake pedal, or panic-slamming the brake pedal, can cause wheels to lockup and possibly send the vehicle careering into a terrifying skid. Excessive brake pedal pressure often occurs in an emergency or in adverse weather conditions, such as on wet or icy roads. With an anti-lock braking system, computerised sensors located at each wheel will 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.
Of course, 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. Racing drivers will tell you that the ‘manual’ way still gives them a greater feeling of control – which is why ABS is rarely, if ever, fitted to competition cars.
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 is 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 technology in ABS allows the driver to be master of cadence braking. All the driver has to do is apply pressure on the brake pedal and the ABS system will mechanically cadence brake evenly and smoothly. This will allow the driver to maintain control of the vehicle and shorten the stopping distance. He or she will know that the system is working thanks to the absence of the kind of screeching sound that most drivers are accustomed to hearing when they apply excessive pressure on their brakes.
The Key Technical Elements Of ABS
* Wheel Speed Sensors: These measure wheel speed and then transmit this information to an electronic control unit.
* The Electronic Control Unit (ECU): This receives information from the sensors, determines when a wheel is about to lockup and activates the brake pressure modulator. Also, it detects any malfunction of the ABS.
* The Brake Pressure Modulator: This reduces, holds and restores pressure to one or more brakes, independent of the driver's brake pedal effort.
In the event of a malfunction in the anti-lock system, a warning lamp on the instrument panel alerts the driver that the ABS system is in need of repair. However, the vehicle's normal brakes will still function.
Different Types Of ABS
First the good news. Most modern ABS ‘4-Channel’ systems are basically the same, controlling all four wheels of the vehicle. So, in principle at least, the ABS system on a Nissan Micra should work as effectively as that on a Mercedes S600, allowing for and taking into account the weight of the vehicles in question. The differences come in the amount of extra electronic hard or softwear connected to the basic ABS layout. In the Mercedes for example, the basic anti-lock braking system might also be an integral part of a traction control set-up and/or an electronic stability programme that will correct the car if driven into a corner too fast.
There are differences however. Some anti-lock systems fitted to older cars are less effective ‘3-Channel’ set-ups. Some trucks meanwhile, have rear wheel anti-lock systems (RWAL), controlling only the two rear wheels; this is obviously not as effective in terms of stability and control during braking but is a cheaper solution.