Automatic locking differential (ASD), acceleration skid control (ASR) and 4MATIC all-wheel drive
Developments based on sensor technology for the anti-lock braking system (ABS)
Stuttgart – On a test ground in Rovaniemi, Finland, Daimler-Benz AG presented from February 3 – 8, 1986 important steps of passenger car safety: automatic locking differential (ASD), acceleration skid control (ASR) and the automatically engaging 4MATIC four-wheel drive. These exploited the possibilities offered by electronic technology to improve active vehicle safety.
In a press release for the Frankfurt International Motor Show (IAA) in 1985 the company wrote: “State-of-the-art automotive mechanics and hydraulics combined with intelligent electronics now open up perspectives in the field of traction control systems that go far beyond conventional traction systems currently available. Three stepped electronically controlled automatic systems, tuned to meet various requirements, represent both the result and content of the Mercedes-Benz vehicle dynamics concept, which sets new standards in the relationship between the human and the vehicle – automatic locking differential (ASD), acceleration skid control (ASR) [and] Mercedes-Benz 4MATIC.”
The introduction of electronic vehicle dynamics systems began with the anti-lock braking system ABS, which celebrated its world premiere in the Mercedes-Benz S-Class (W 116 series) in 1978.
The systems presented on the IAA 1985 the first time built on this system, using the sensory technology made available through ABS: a common feature of all these systems was to use advanced microelectronics and hydraulics to record and limit wheel slip with the aim of improving the so-called longitudinal dynamics of the motor vehicle. Other systems to make use of the ABS signals include the revolutionary Electronic Stability Program (ESP®, 1995), Brake Assist (BAS, 1996) and the electrohydraulic Sensotronic Brake Control system (SBCTM, 2001).
What was written about the three vehicle dynamic systems in the press release is as valid today as it was then: “The unique benefit of this Mercedes-Benz development is that they minimise the possibilities of incorrect or impaired human reactions. The recognition, decision-making and response are objectively accurate, timely and quicker than those of a human being – moreover they do not tire or distract the driver, nor mislead him into inappropriate action.”
ABS: The anti-lock braking system (ABS) is an electronic protection system designed to prevent wheels from locking and to aid safe steering and braking.
ASD: The automatic locking differential (ASD) functions electrohydraulically. It serves as a start-off assistant and locks the differential 100 percent to improve traction in the event of wheel spin. This is achieved by a control unit which measures the speed of the driven and non-driven wheels. The system was replaced by an electronic acceleration skid control in the 1990s.
ASR: Acceleration skid control (ASR) counteracts wheel spin and lateral sliding of the vehicle under acceleration by controlling the interplay of longitudinal forces between the tyres and road surface. In so doing it has an impact both on braking and on engine torque. In this way the system stabilises start-off on surfaces with little static friction, for example ice, snow, wet cobbles or gravel.
BAS: The Brake Assist System (BAS) is an anticipatory assistant for automatic power braking which reduces stopping distance.
ESP®: The Electronic Stability Program (ESP®) is a fully automatic, active-dynamic driving safety system, which works interactively with ABS, ASR, BAS, and uses controlled braking impulses to reduce the risk of skidding or rollover.
SBCTM: As a situation-actuated control system, Sensotronic Brake Control (SBC) ensures optimum brake pressure of the electrohydraulic high-pressure brake.
4MATIC: Introduced in 1985, the automatically engaging 4MATIC four-wheel drive has three selectable settings as required. The advantages of the 4MATIC lie in its greater directional stability and road adhesion, thanks to maximum traction at all wheels resulting from the four-wheel drive, two differential locks, engagement in extreme curves and the safe and precise functioning of its self-regulating and intelligent electronics. Today 4MATIC all-wheel drive is permanent and therefore operates without response time.