A Non Contact Strain Gage Torque Sensor for Automotive Servo Driven Steering Systems

Tapping of one or more torques (ranges 10 Nm and 60 Nm) on the steering column for the purpose of servo control must satisfy high accuracy requirements on the one hand and high safety requirements on the other hand. A suggestion for developing a low-cost solution to this problem is described below: Strain gages optimally satisfy both these requirements: However, for cost reasons, these are not applied directly to the steering column but to a prefabricated, flat steel rod which is laser welded to the torque rod of the steering column. The measuring direction of the strain gages is under 45° to the steering column axis. The strain gages are either vacuum metallized onto the support rod as a thin film or laminated in a particularly low-cost way by means of a foil-type intermediate carrier.

The relatively low output signals of the measuring resistor bridge are amplified on site (on the steering column) with an integrated electronic evaluation circuit and converted into a frequency-analog, highly interference-proof signal. Signal output and power supply may be connected to the fixed parts of the body neither by collector rings nor by cables. Both connections are made totally non-contact by means of a very simple and low-cost rotary transformer which surrounds the steering column concentrically and has two separate winding chambers. In this case, it is practically impossible for air gap fluctuations and similar interferences to falsify the frequency-analog measuring signal.