Handling vehicles safely round the bend

A plastic potentiometer has helped out in the design of a new DCS system for BMW

Much work has been done in automotive design in recent years to improve vehicle handling under arduous driving conditions. Systems such as ABS and traction control are playing a key role in making vehicles more controllable, and therefore more safe. Any new development that improves the dynamic handling of a vehicle is to be applauded. Now, lucky BMW drivers will have an on-board `intelligent` control system which will help the car driver to maintain course.

BMW reports that the dynamic stability control (DSC) unit is now a standard feature in several of its models. The DSC supplements the brake and motor management systems and is said to be particularly cost effective.

Part of the DSC comprises a conductive plastic potentiometer unit with a hollow shaft over the bottom end of the steering column, from where several varying measurements are recorded, evaluated and transmitted to other on-board vehicle systems. The DSC forms an `intelligent’ control system which works with the steering and braking system to improve the dynamic handling of the vehicle, ion particular supporting the driver in critical situations such as swerving

The steering angle sensor is a two-plate design. The sensor is a Novotechnik manufactured unit and has two plastic resistance wiper pick-ups transposed at a 90 degrees angle, each delivering a signal voltage between 0 and 4.5V. The actual rotary steering angle, the rotary direction and the composite steering angle are all computed from the two individual voltages. Evaluating electronics transfer the steering angle information over a CAN-bus interface to the control electronics with a resolution of 0.7 degrees.

This information is then used to determine the reference speed through curves in the road, or in other unstable driving conditions, as well as providing the input which enables the superimposed vehicle controller to calculate the driver’s intended course. Output information from the steering angle sensor is available to all other management systems within the vehicle in addition to the DSC system. When correctly connected, changes in temperature and humidity have practically no effect on measurement accuracy.

Available from Variohm, the conductive plastic potentiometers used in the DCS are inexpensive, robust, insensitive to environmental influences, and exact, which makes them ideal for fitting to vehicles. Another important feature of the sensors is their low power consumption, which makes them ideal for use with batter power supplies and so suits them for use in mobile application such as this.

Variohm Components Tel: 01327 351004