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25 YEARS OF AUTOMOTIVE ABS by Julian Edgar Anti-Lock Braking Systems (ABS) are now a quarter of a century old. In that time the systems have saved countless dollars in panel damage, a huge number of injuries and prevented many deaths. German company Bosch has been instrumental in developing the technology and seeing it widely adopted by car manufacturers around the world. Here we take a look at the development. 36  Silicon Chip www.siliconchip.com.au    Bosch ABS Milestones 1936: Bosch registers a patent for a “mechanism to prevent locking of the wheels of a motor vehicle”. 1970: ABS 1 models perform all required functions; but reliability of the control unit is not yet adequate. 1978: First fitting of ABS 2 as option at Mercedes-Benz and shortly thereafter at BMW. As the first ‘active’ car control system with major implications for safety, ABS required extensive development prior to its release. Here early vehicle testing by Bosch is shown. 1981: 100,000th ABS system supplied; ABS now also in commercial vehicles. 1985: Bosch ABS fitted for the first time in U.S. vehicles. In the 25 years since Bosch ABS went into production, the mass of the control system has dropped from 6.3 to 1.6kg, the number of components in the Electronic Control Unit has dropped from 140 to 16, and the amount of memory has risen from 2 to 128kB! 1986: One million Bosch ABS delivered. 1987: Production of Traction Control System (TCS) for passenger cars starts. 1989: With the ABS 2E, the control unit is attached directly to the hydraulic unit. 1992: 10 million ABS systems from Bosch. 1993: Start of production of ABS 5.0 from Bosch. 1995: Production of Bosch ABS 5.3 starts (with attached microhybrid control unit); production start of Electronic Stability Control. While slow to gather momentum, the proportion of new cars sold worldwide with ABS as standard has skyrocketed over the last 15 years. Just under 70 per cent of all new cars now have ABS as standard. www.siliconchip.com.au 1998: Bosch begins volume production of ABS 5.7 1999: 50 million Bosch ABS systems. 2001: Bosch ABS version 8 launched. 2003: 25 years of series production of Bosch ABS February 2004  37 CONTROL UNIT HISTORY 1970 Bosch subsidiary Teldix started working on ABS in 1964 and by 1970 had developed a system controlled entirely by electronics. The basic structure of this design, named ABS 1, is still to be found in nearly all ABS systems. But the reliability and durability of the electronic control unit - with its roughly 1000 analog components and the safety switches - were not good enough for volume production. 1978 The advent of digital technology and integrated control circuits allowed the number of electronic components to be reduced to 140. After 14 long years of development, everything was finally in place in 1978: the second generation of Bosch’s ABS – ABS 2 – began to be fitted as optional equipment, at first in Mercedes-Benz’s ‘S’-class cars and shortly afterwards in BMW’s 7-series vehicles. 1983 Based on the first ABS, the following 1983 generation 2S was more compact and efficient. However still only 0.3 per cent of new vehicles worldwide were then being fitted with ABS. 1987 In 1987, Bosch produced the first traction control system (TCS) for passenger vehicles. It was based on ABS2S and was upgraded with the required hydraulics and electronic elements. TCS helps to improve acceleration on smooth or slippery surfaces, and also increases stability by reducing engine power when corners are taken too fast. 1989 In 1989, Bosch started the mass production of ABS 2E. For the first time, developers succeeded in integrating a control unit ECU manufactured in hybrid technology. Bosch Not the First 1993 More compact and powerful solenoid valves are characteristic of the 1993 generation 5 ABS. The integrated electronic control unit ECU also had more functions. 38  Silicon Chip Despite Bosch developing the technology that has allows ABS to be implemented in millions of cars, it was not the first company to be involved in fitting ABS to a passenger car. The first car with ABS was the 1966-71 Jensen Interceptor FF, which used Dunlop Maxaret antilock brakes originally developed for fighter aircraft landing on aircraft carriers. www.siliconchip.com.au 1995 The 1995 ABS 5.3 was the first to be fitted with an ECU in micro hybrid technology. Total weight and size were further reduced. 1998 2001 1978 The brake control system of the 1998 generation 5.7 is optimised for the use in Electronic Stability Control systems. 2001 The direct comparison of hydraulic and electronic control units in the ABS2 from 1978 (left) and the integrated ABS8 of the latest generation show how the latter is much more compact. ABS 8 – the current generation – first appeared in 2001. It uses a modular design, which allows various degrees of complexity of the brake control system – ABS, Traction Control and Electronic Stability – to be manufactured in very similar ways. How ABS Works The hydraulic unit is the central component of an ABS system. Each of the four wheels has a speed sensor, which measures the rotational speed of the wheel. This information is monitored by an electronic control unit, which opens and closes the magnetic valves in the hydraulic unit at the right time. If a wheel is about to lock under heavy braking, the system reduces the hydraulic pressure on that particular wheel until the threat of locking is past. Once the wheel is turning freely again, the hydraulic pressure is increased. This variation in pressure continues until the driver reduces the force on the brake pedal or until the tendency to lock is overcome – when there is more grip on the road surface, for instance. Depending on the particular system, there is a certain amount of feedback movement at the brake pedal. www.siliconchip.com.au sc February 2004  39