On a frozen lake near Rovaniemi, Finland, the then Daimler-Benz AG presented acceleration skid control (ASR) for passenger cars and commercial vehicles, the automatically engaged four-wheel drive (4MATIC) for passenger cars and the automatic locking differential (ASD) – important elements of automotive safety – from February 3 – 8, 1986.
Time and again, Daimler-Benz had been setting new standards in safe motoring. The list of innovations is a long one, including the rigid safety passenger cell (1951), the airbag (1981) and the Electronic Stability Program (ESP®, 1995) – each one of these a milestone developed by the company and meanwhile a standard feature throughout the motor industry.
The anti-lock braking system (ABS, 1978) is equally a development by Daimler-Benz. The system retains full steerability during emergency braking – and it was the first of a whole series of dynamic handling control systems which build upon, and interact with, each other. These include acceleration skid control (ASR) and four-wheel drive (4MATIC) as well as ESP®. These systems use the ABS sensors and the ABS data to deploy their additional functions. Incidentally, the specification of ESP® includes the fitting of ABS, ASR and Brake Assist (BAS) which identifies an emergency braking situation and automatically activates maximum braking efficiency.
ASR prevents the spinning of the driven wheels under acceleration. This is achieved by means of brief, automatic brake pulses, well metered in response to the sensor data on wheel speed, steering angle and the car’s rotary movement and lateral acceleration. In addition, engine torque is reduced as required. This improves traction on slippery ground and stability in critical driving maneuvers. ASR became available in 1985, initially in the Mercedes-Benz S-Class (W 126).
Four-wheel drive, 4MATIC, improves traction and dynamic handling on wet roads, ice, snow and poor road surfaces, as well as when starting off and accelerating. The key element of 4MATIC is a single-stage transfer case with open central differential for rotational-speed compensation between the axles. It is directly connected to the automatic transmission and forms a complete drive unit together with engine, torque converter and front-axle drive. 4MATIC engages front-wheel drive and the differential locks in situations in which normal rear-wheel drive would no longer suffice to propel the car. The Mercedes-Benz 124 series was the first in 1985 to include cars with the 4MATIC four-wheel drive, namely models 300 D, 260 E, 300 E, 300 TD and 300 TE.
The automatic locking differential (ASD), equally presented in Finland, became available in 1985 as additional equipment of numerous passenger car models with rear-wheel drive from the W 201 and W 124 series. When one of the wheels spins, ASD channels more drive torque to the wheel with good tire-to-road adhesion – a particularly comfortable feature being the fact that the driver does not have to engage the system himself.