ABS: The car goes digital

Oct 10, 2018

The car is now more intelligent than ever. And development is advancing at a faster pace than ever before: In the current stock technology used at Mercedes-Benz, the networked assistance systems show how the car as the driver’s partner will play an active part in the future of mobility. This technology status is a result of a unique innovation structure that stretches back to the invention of the motor car in 1886. The Intelligent Drive philosophy unveiled in 2013 is thus also based on Mercedes-Benz’s brand and technology history. Its holistic approach combines a wealth of assistance systems aimed primarily at enhancing safety and comfort. The history of digital assistance systems is an important foundation of Intelligent Drive. It started 40 years ago with the anti-lock braking system (ABS) developed by Mercedes-Benz and Bosch, which had its world premiere in August 1978 in S-Class model series 116.

This introduction of digital technology to the car was the first chapter of a global success story as digital assistance systems have been redefining the partnership between driver and car ever since: the vehicle supports its driver increasingly comprehensively and increasingly intelligently. Mercedes-Benz plays a leading and defining role in this innovation process. In the past 40 years, the Stuttgart brand has collaborated with various partners to develop numerous assistance systems that often become the benchmark for the entire industry,

including ABS as well as the Electronic Stability Program ESP® (1995) and DISTRONIC adaptive cruise control, which premiered in 1998 – exactly 20 years ago. It’s not only the technology that’s changing, so is the view of vehicle safety: at the start of the 2000s, Mercedes-Benz combined active and passive safety to create an integral system, which led to the development of the Intelligent Drive concept at the start of the 2010s. This now already includes numerous intuitive and intelligent technologies for the future of mobility.

1978: Standard version of ABS unveiled

For the driver, the anti-lock braking system unveiled in 1978 was primarily a milestone in active safety: Maintaining full control over the car’s steering even under emergency braking, because the wheels do not lock – only vastly experienced drivers were able to achieve this before ABS was introduced 40 years ago. Now the vehicle itself performed the intricate work of controlling braking – an absolute sensation at the time. Even during emergency braking, the driver still had an opportunity to deliberately avoid other road users and obstacles, and prevent possible accidents.

In the history of technology for modern cars, ABS has another meaning that is at least just as important. Because this was the system that saw Mercedes-Benz and technology partner Bosch introduce digital technology to the car. To gauge the enormity of this innovation, it is necessary to consider the state of the art in production technology at the time: ABS is from an era of electrics and analogue electronics. As a genuine digital assistance system, ABS was a trailblazer for future developments.

The origins of ABS go right back to the early 1950s. In 1953, Hans Scherenberg, then design chief at Mercedes-Benz, applied for a patent on a system to stop a vehicle’s wheels locking under braking. Although similar solutions had already existed in aviation (anti-skid) and on the railways (Knorr anti-slip protection) since the 1950s, the car was a particularly complex system as it had to contend with a wide variety of road surfaces. For example, the ABS sensors needed to register the rotational deceleration and acceleration of the wheels without error, including when cornering, on irregular surfaces and in very dirty conditions.

It took many years of intensive knowledge exchange between the in-house R&D team and partners in industry for the basic idea of series production-ready ABS to take shape. In 1963, the Advance Development department at Daimler-Benz AG adopted a new approach to developing in-house components for an electronic/hydraulic braking control system. In 1966, the company started collaborating with the Heidelberg electronics specialist Teldix, which was later taken over by Bosch. The result premiered in 1970, when Hans Scherenberg, now development chief at Daimler-Benz, presented the “ Mercedes-Benz/Teldix Anti-Bloc System” to the media at the test track in Untertürkheim. The presentation delivered the proof that the system worked.

Scherenberg also announced preparations for production while abating the hopes for a quick production breakpoint. This is because the developers realised that digital control was the right way forward for ABS fit for large-scale production. It was more reliable, less complex and also far more effective than the analogue electronics used in 1970. Together with Bosch, responsible for the digital control unit, this led to the digital, second-generation ABS.

Head of the ABS project at Mercedes-Benz was engineer Jürgen Paul, who had been working for the Stuttgart-based company since 1969. As a sensor expert and key developer for the electronic assistance systems, he became the “father” of ABS and the solutions based on it. Paul later recalled the breakthrough moment in ABS development, stating that it was the decision to go with digital microelectronics rather than analogue electronics.

The change took some time, but it proved to be the key to success. That’s because the use of integrated circuits allowed the sensor data at all four wheels to be acquired and processed in the shortest time, enabling calculation of the necessary solenoid valve activation for regulating the braking pressure. ABS was also tested in the Mercedes-Benz Experimental Safety Vehicles (ESF) in the early and mid-1970s. The Auto 2000 research vehicle of 1981 had the now standard ABS on board along with the innovative electronic traction control systems and the proximity regulating radar.

The ABS anti-lock braking system developed to production standard was unveiled in August 1978. It was initially available as optional equipment for the S-Class model series 116 at an additional cost of DM 2,217.60. As of August 1980, ABS was available as an option for all Mercedes-Benz passenger car model series at an additional cost of DM 2,429.50. From October 1992, ABS finally became standard for all Mercedes-Benz passenger car models.

Safety as the guiding principle

ABS is now considered a given in most regions of the world, regardless of manufacturer. This is down to the innovation culture at Mercedes-Benz and the impetus in-house accident research has given the developers since May 1969. Daimler-Benz performs pioneering work with these systematic accident analyses. The findings are incorporated into the development of new solutions and used to further develop practical test procedures and standards.

The effect of the anti-lock braking system goes beyond its use to ensure optimum braking while maintaining vehicle steerability as the data supplied by its sensors can also be used by other assistance systems such as the anti-slip control (ASR), the Electronic Stability Program ESP®, Brake Assist BAS, the electronically controlled automatic transmission, the DISTRONIC adaptive cruise control, and many more.

Mercedes-Benz presented the ASR and ASD (automatic locking differential) traction systems at the International Motor Show in Frankfurt (IAA) in 1985. They were the first systems whose software was developed by the in-house electrics/electronics development department itself. The ASD limits the compensation movement of the other wheel in the differential respectively with a disc lock as soon as the on-board electronics register that a driven wheel is spinning. It was optionally available for all model series 201 and 124 vehicles as well as for the new six-cylinder models in S-Class model series 126 (260 SE and 300 SE) straight after the show. At this time, the additional cost was DM 1539. ASD was included as standard in the 4MATIC vehicles in model series 124 presented at the same time.

ASR was introduced simultaneously in the S-Class eight-cylinder models. When a wheel is spinning, this assistance system not only applies the brakes, it also cuts the engine torque by reducing the throttle by a specific amount. This function was possible thanks to the electronic accelerator (EGAS) created based on the cruise control. Both traction systems really came into their own in rear-wheel-drive vehicles on slippery roads.

The 1985 International Motor Show (IAA) also marked the premiere of the newly developed 4MATIC traction system for the six-cylinder models in model series 124. This quickly engaging and disengaging four-wheel-drive system ensures that full ABS functionality and the accustomed handling characteristics are maintained: the car’s default setting was two-wheel drive. If traction is lost, 4MATIC acts in three stages to first engage four-wheel drive, then the additional inter-axle differential, and finally the additional rear inter-wheel differential.

Two-wheel drive with ABS function is re-engaged automatically on braking. To control the individual operating states, the control unit continuously records the speeds of both front wheels, the rear propshaft speed, the steering angle, and the brake actuation status – the latter by means of a contact on the brake switch.

After the press trial drive in northern Sweden in February 1986, German car magazine ‘Auto Motor und Sport’ concluded: “4MATIC has all the ingredients to offer sensible drivers advantages on slippery surfaces. Besides constantly optimum distribution of the forces and the resulting outstanding traction, the four-wheel-drive Mercedes displays no weaknesses whatsoever when it comes to braking and handling characteristics.”

Mercedes-Benz introduced a newly designed 4MATIC system in E-Class model series 210 in 1997. It differed from the previous version by virtue of the permanent all-wheel drive with a rear-biased torque distribution of 35 to 65 percent. The differential locks were now replaced by the 4ETS (Electronic Traction System), which applied the brakes automatically if one or more wheels started to spin.

Safety and comfort

The realisation of the ABS anti-lock braking system in 1978 was an important first step in the development of the car from a driving machine controlled by the driver into a hearing, seeing, feeling, independently reacting, and in future autonomously driving mobility system. The central theme of this development at Mercedes-Benz is always the need for greater safety – and for greater comfort as supporting drivers with assistance systems also enhances their wellbeing dramatically. From a physiological safety perspective, this is in turn a key element of driving safety.

A prime example of this link between safe and comfortable driving is the cruise control, which premiered at Mercedes-Benz in the same decade as ABS. From 1975, it was optionally available for S-Class model series 116 as well as for SL and SLC model series 107 in conjunction with automatic transmission. The cruise control was developed mainly in response to demand in the North American market. The ‘P’ cruise control with analogue-electronic controller, pneumatic actuator, and Bowden cable was initially developed into ‘E’ cruise control (electromotive actuator) and finally into digital ‘IC’ cruise control (with integrated circuits).