Erich Dipl Ing Dr Zabler

A NON CONTACT STRAIN GAGE TORQUE SENSOR FOR AUTOMOTIVE SERVO DRIVEN STEERING SYSTEMS

Abstract Tapping of one or more torques (ranges 10 N m and 60 N m) on the steering column of an automobile for the purpose of servo control must satisfy both high accuracy requirements and high safety requirements. 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 that 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. Neither collector rings nor cables are needed to connect the signal output and power supply to the fixed parts of the body. 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.