This article explains features and advancements in the antilock braking systems (ABS). The ABS campaign is an example of the way that advertisements can inadvertently make engineering design seem like a process of fulfilling corporate visions. An antilock braking system monitors the rotating speed of an automobile’s wheels and, when it detects a too-rapid deceleration, momentarily releases the pressure applied to the brake. As ABS developed as a device, so did the community working on it. The problem at hand and the community addressing it were defined and evolved simultaneously. Initially, a community of about 50 researchers and design engineers formed around the problem of skidding automobiles. Electrical engineers from electronics firms, including Siemens and American Microsystems, joined the community by presenting papers at conferences on the use of purpose-design, solid-state microprocessors in cars. The challenge of introducing electronic control to the automobile industry, questionably reliable new technologies in general, was therefore shared by several companies that all moved to include integrated circuits and microprocessors in their designs. The real history of ABS presents a much more engaging picture of how engineers really bring products to market.
Antilock braking systems for automobiles first entered Americans’ public consciousness through advertising campaigns in the late 1980s and early 1990s. American television viewers were introduced to this new technology, which would help them triumph over dangerous roads and unpredictable fellow drivers. Antilock systems, commonly called ABS, were presented as a great idea whose time had come.
Automobile companies, most notably Daimler-Benz, took credit for these developments. Daimler claimed that the invention was driven so clearly by its interest in public safety that the corporation would not pursue any patent infringement suits over its competitors’ systems.
Through these advertising campaigns, ABS created the impression that it was bursting onto the scene and that its design was driven by a corporate, humanitarian vision. Neither of these claims is inaccurate, but the picture presented through the advertisements effaces the difficult and lengthy process of actually designing a workable, affordable antilock braking system for automobiles.
The ABS campaign is an example of the way that advertisements can inadvertently make engineering design seem like a process of fulfilling corporate visions. Yet nearly any design engineer will attest to the intellectual challenges that product design presents, precisely because of the difficulty of transforming ideas and visions into workable, affordable, mass-producible things. Still, many studies of design focus on understanding the side of invention that Thomas Edison famously referred to as 1 percent inspiration.
Far less literature about engineering design focuses on Edison's other factor—the 99 percent perspiration. What design engineers worked on for over 25 years in the case of ABS was the 99 percent perspiration, and the real story of ABS does not follow the Madison Ave. scripts very well. It involves failures and misunderstandings, community building and knowledge generation, corporations and agencies, and lots of engineers.
Today's electronically controlled ABS is a good design. A good design is one that, once invented and introduced to the mass market, seems obvious: its function is easy to understand and it is socially desirable. These features are precisely what car companies wanted to sell to consumers. They did not want to sell the complexities of the design itself, or the novelties (and potential bugs) of using microprocessors in automobiles for the first time.
They could not sell the precursor devices that started to appear back in the 1960s. Daimler did not want to sell the 30 years of development required before its Teldix-designed, Bosch-built ABS system hit the market in 1978. The company did not want its potential consumers to ask “What took so long?” or “Is this finally the one?”
As a result, in public presentations at least, the engineering process behind ABS had to be obscured. Yet that process is very illustrative of the challenges and joys of engineering design. And the most notable feature of ABS design is the community that produced it.
As ABS developed as a device, so did the community working on it. Still, before several companies and agencies began their work there was no pre-existing ABS community. The problem at hand and the community addressing it were defined and evolved simultaneously.
Initially, a community of about 50 researchers and design engineers formed around the problem of skidding automobiles; they first met at the International Skid Prevention Conference of 1958 in Charlottesville, Va. There was no predetermined solution to skidding, and initially a wide array of answers was considered, including road design, tire design, better driver training, as well as improved braking systems (which included many types of projects, including brake distribution, disc brake systems, self-energizing systems, and different kinds of hydraulic assist).
The notion that skidding was a real problem on roads emerged from the British Road Research Laboratory (RRL) in the early 1950s. Britain kept national statistics on automotive safety and early in the post-World War II period British researchers determined that skidding caused a significant number of accidents— approximately 16,000, or 27 percent of accidents on wet roads in 1957. Although accidents were increasing as the number of cars on the road increased, skidding accidents were actually increasing at a higher rate than automobile miles. The British government originally undertook the study on skidding to determine the nature of the problems and what solutions might improve the situation, from speed limits to different road signage to new approaches to driver education.
How to Avoid a Skid
An antilock braking system monitors the rotating speed of an automobile's wheels and, when it detects a too-rapid deceleration, momentarily releases the pressure applied to the brake. Because the adjustment keeps the wheel from losing traction with the road, ABS permits a driver to steer as the vehicle slows. ABS shortens stopping distance, if braking efficiency is high enough, because on most surfaces kinetic friction is greater than static friction.
Systems differ. Some ABS designs for four-wheel vehicles, for instance, have a speed sensor monitoring each wheel separately. Others may have one sensor monitoring both rear wheels.
The speed sensor data are read by a controller, which can detect an extraordinary deceleration and send a command to a valve that will shut off the pressure from the master cylinder to the brake of the wheel. As soon as the wheel spins at an appropriate rate, a pump returns pressure to the brake.
Some antilock braking systems can cycle as many as 15 times a second.
After examining cars on the road, though, several researchers at the RRL began to focus on ways to improve the automobile itself and make it less likely to skid. They examined devices designed to prevent skidding on aircraft. The laboratory's director, W. H. Glanville, created a project team under the direction of engineer R. D. Lister to retrofit a Dunlop Maxaret device from an airplane to a 1950 Morris 6 automobile.
The Maxaret, introduced in 1952, consisted of a small rubber-tired wheel positioned against the inside rim of the plane's wheel. Inside the wheel were a drum, a flywheel, and a drive spring. The spring held the drum in contact with the flywheel. When the plane's wheel decelerated too rapidly, the spring retracted and the drum stopped spinning. A valve then closed the supply line to the brake actuator, and pressure was exhausted. This released the brake until the wheel's angular velocity returned to the same rate as the flywheel, at which point the spring would reset and recouple the flywheel and drum.
Both the automobile and the Maxaret had to be significantly modified for the experiment, because the Morris had drum brakes and was considerably smaller than the aircraft for which the Maxaret was designed. In addition, the automobile had to be outfitted with all sorts of measurement apparatus, whose results led to increasingly sophisticated mathematical models of skidding vehicles.
The results of the Maxaret retrofit were disappointing to Lister. While the wheels did not lock up and cause skidding, the distance the car took to stop was much longer, especially at speeds less than 35 miles per hour. The modified Maxaret did not achieve nearly enough braking efficiency.
Even worse, the pulsing of the brakes caused some fairly violent vibrations in the car—vibrations that would certainly be a deterrent to street use of the device. Lister explained the vibration problem as one of mismatched scale. The device was designed for a much larger vehicle (a plane), and the inertia of the valve opening and closing caused the car to jerk.
Designing a similar system explictly on automobile scale promised a much smoother operation. Lister, a government employee, partnered his lab with Dunlop to develop such an automotive antiskid system from the ground up. By 1958 they had a prototype for a Jaguar Mark VII (which was chosen in part because it had disc brakes).
Dunlop put the Maxaret for automobiles on the market by 1966, hardly overnight even with the retrofit prototype acting as a kind of blueprint for the project. The automobile Maxaret's most famous installation was on the innovative Jensen FF. It effectively modulated wheel lock-up and therefore minimized skidding, but it never succeeded in shortening a car's stopping distance. Its biggest problem was its cost; it was prohibitively expensive, costing over £2,000 (considerably more than the £600 cost of an entire Volkswagen Beetle in 1966).
Engineers knew that improving road safety would require a significant percentage of cars to be resistant to skidding. Clearly the Maxaret would not be the device to make roads safer. Still, it was a start to building a better braking system; one that spurred other companies to begin their own R&D projects and therefore a catalyst to growing the ABS community.
Dunlop's Maxaret proved that an antiskid device could be developed and even sold, but it failed to achieve anything like the kind of market saturation engineers and executives alike knew was needed. As the community reoriented itself toward marketable devices (and defined the solution set to the skidding problem more narrowly as an improved braking device), community members were more and more commonly based in the corporate, rather than government, sector.
Although many firms from both Europe and the U.S. initiated R&D projects focused on ABS in the 1960s, the most important corporate participant to come on board was Teldix GmbH, a small avionics company in Heidelberg, West Germany. Teldix produced electronics for the American Starfighter 104 plane. In 1963 the company began to consider expanding into automotive electronics, a field that was just beginning.
Heinz Leiber, a mechanical engineer and Teldix's director of development, had been working on aviation navigation, where he had led the R&D of a number of high-speed, high-pressure, low-inertia valves. In the context of early 1960s ABS research, these valves promised a smoother modulating system, able to pulse up to 10 times faster than Dunlop's.
But engineers at Teldix were not looking to simply duplicate Dunlop's system with a better valve. They had more design criteria to meet.
Like Dunlop, they were not initially focused on making a design that would be affordable. But they added a crucial design criterion that the device they developed should reduce stopping distances on both wet and dry pavement, something no firm had achieved. This criterion would be extremely challenging.
To meet this desire, engineers at Teldix had to change the way they thought about skidding. Rather than producing a system that reacted to a wheel locking up, Leiber and a growing group of colleagues at Teldix designed a system that detected and regulated imminent skidding. This meant that their system could produce a much higher braking efficiency and still allow the driver to maintain directional control.
Leiber and his colleagues at Teldix designed an electronic, adaptive control module that could either directly detect or calculate the angular deceleration of each of the car's wheels and then compare decelerations. The system could also compare the angular deceleration of the wheel with the linear deceleration of the vehicle. Wheels that were decelerating too quickly could then be pulsed off and on using the high-speed valves the company developed for aviation applications.
Proprietary, but also Collective
In 1967 Teldix hired Hans Jürgen Gerstenmeier to design the circuits that the electronic control system required. Teldix's system used new mathematical models of vehicle dynamics which had been produced by engineers and applied mathematicians at other firms, agencies, and universities. These new models were based on data from the measuring apparatus that had been attached to cars testing prototypes of ABS. Although antilock systems were proprietary technologies, the ABS community was contributing collectively to developing the state of the art.
Furthermore, design choices at Teldix shaped the ABS community even outside that firm. When Teldix devised a system that would regulate instead of react to wheel lock-up, it raised the bar for the whole community.
ABS designers from other firms knew about this decision through conferences at which Teldix engineers presented their new designs, and from journal and magazine articles. Engineers at other companies employed electrical engineers and started to focus on systems with sophisticated electronic control.
Electrical engineers from electronics firms, including Siemens and American Microsystems, joined the community by presenting papers at conferences on the use of purpose-design, solid state microprocessors in cars. The challenge of introducing electronic control to the automobile industry, which was gunshy of electronics and of unproven, questionably reliable new technologies in general, was therefore shared by several companies that all moved to include integrated circuits and microprocessors in their designs. To do so would require close R&D partnerships with the automobile companies that would constitute the market for ABS devices.
Most ABS in the 1960s and early 1970s were, in fact, developed in partnership between a brake producer and an automobile manufacturer. Kelsey-Hayes partnered with Ford, Bendix with Chrysler, Alfred Teves with BMW, Bendix-DBA with Citroën, and Teldix with Daimler-Benz. Only General Motors kept the whole project in house. The partnerships enlarged the ABS community to include automotive engineers, an important step in overcoming the automobile manufacturers’ skepticism.
Several competing antilock braking systems were introduced to the market between 1966 and 1972, including the 1969 Lincoln Mark III and Ford Thunderbird using the Kelsey-Hayes Sure-Track system and the 1971 Chrysler Imperial with the Bendix Sure-Brake system.
But Teldix and Daimler did not introduce their system, and even by 1973 it was still an advanced prototype built on a breadboard in a 40 by 20 centimeter case.
To produce this system commercially, Teldix and Daimler brokered another partnership, with Robert Bosch GmbH, a firm that pioneered mass-produced electronics in the automobile with fuel injection systems in the late 1960s. Bosch was experienced in mass-producing electronics and had a strong reputation for reliability with the automobile manufacturers. As a result, mass production brought another group of engineers into the ABS community, whose expertise was critical to ABS's market success.
By 1975, when Bosch bought a 50 percent interest in Teldix and transferred the project and its engineers to Bosch's K-1 division, the ABS community was large, diverse, and focused on device designs rather than on general questions like skidding.
The economic climate of the mid-1970s was a poor time to introduce new, relatively expensive automotive technologies. The Bosch ABS, seemingly market ready in 1975, did not appear on the Mercedes S-class sedan until the 1978 model year.
One step remained in closing the design around this electronic adaptively controlled system. Even in 1978 Bosch's system was an add-on to an existing braking system. By the early 1980s, Alfred Teves GmbH had produced an integrated ABS, that is, an all-in-one system that included both the full hydraulic braking system and ABS.
Engineers Hans Christopf Klein and Werner Fink argued that integrated ABS would be more durable and reliable than Bosch's add-on. They were still trying to convince the automobile manufacturers to adopt the system. Neither the ABS manufacturers nor the automobile companies seemed to be rushing the technology to market.
Certain and Secure
By the end of the 1980s manufacturers were sold on the idea, and ABS became a way to market their cars to consumers. This advertising gambit required a strategy that drew attention to ABS. Cars started to sport badges on their trunks reading “ABS.” Television and print advertising campaigns emphasized the desirability of ABS through slogans such as Bosch's “Eines ist sicher!” a German pun that means both “One thing is certain” and “One thing is secure.”
ABS's time had come, but the long wait was not mentioned by the ads. It is apparent why these campaigns took the character that they did, but in doing so they intentionally obscured the lengthy and difficult path that ABS required. They inadvertently created public expectations for quick fixes by obscuring the challenges design engineers face in getting reliable products to market.
Perhaps at their worst, such ad campaigns overshadow the complex, social activity that is engineering design, which may have real consequences in attracting the next generation of young engineers. The real history of ABS presents a much more engaging picture of how engineers really bring products to market.