Steering angle sensor takes CAN onboard

A Bosch Automotive OE Division product story

Edited by the Engineeringtalk editorial team Oct 13, 2005

Bosch is currently developing a new generation of steering angle sensors which differ from their predecessors in having a modular construction.

Bosch is currently developing a new generation of steering angle sensors which differ from their predecessors in having a modular construction.

This allows different versions to be produced to cover a range of different functional requirements.

The simplest version is a competitively priced absolute measurement sensor with a range of measurement of +/-90 degrees.

The most high-performance version is a +/-780 degree multiturn sensor featuring customer-specific programmable signal processing with built-in redundancy.

The new generation of Bosch sensors with the designation LWS 5 can thus be used for a wide range of applications.

The very different requirements of the electronic stability program (ESP), an electric or electro-hydraulic power steering system, adaptive lights or a parking assistance system can in each case be met with a precisely matched version.

The sensors are fully compatible with the previous LWS 3 model, so that they can be fitted to existing systems without any modification.

The functional principle of the LWS-5 sensors relies on two resistance bridges positioned at 90 degrees to each other, the bridge parts consisting of GMR (giant magnetoresistance) elements.

In the simple version, when the steering wheel is turned, a measurement cog wheel rotates over a GMR element.

An integrated microcontroller uses the change in the bridge voltage to accurately calculate a steering angle of up to +/-90 degrees.

No external control unit is required.

The LWS 5 version is used for measuring larger steering angles; it has not one, but two, measuring cog wheels with a differing number of teeth.

This expands the precise range of measurement (according to the Nonius process) to +/-780Grad, which allows more than four complete turns of a steering rod to be measured.

Because the sensor versions the steering angle data is stored at a resolution of 0.1 degrees only in the relative position of the two measurement cog wheels to each other, the new Bosch sensor - like its predecessors - requires no quiescent power supply when the engine is switched off.

Nonetheless, the sensor immediately registers the current steering angle as soon as the ignition is switched on.

In addition to the increased range of measurement, the Nonius process also offers additional safety, because in the interaction of the two cog wheels there are only a certain number of plausible steering angle settings.

If measurements diverge from these, they are noted in the interface protocol as invalid.

The wide-ranging monitoring functions cover the entire signal chain from the cog wheels to the measurement of the steering angle and the emission of the signal.

Further safety elements of the LWS 5 are redundant microcontrollers working on the master/slave principle and the systems for monitoring them.

An LWS 5 is fitted as standard with a CAN interface.

Customer-specific interfaces and individual programming of the microcontroller are possible.

The new steering angle sensor is expected to be available from the end of 2006.