Automotive power steering is prime app for non-contacting torque sensors

September 11, 2013 // By Christoph Hammerschmidt
Automotive electronics supplier Bourns has added to its range of non-contacting torque sensors for electric power assisted steering (EPAS) applications. The new models include a torque-only sensor that measures the relative shift angle between two rotating shafts to determine how much power assistance is required; a torque angle sensor that collectively measures torque, steering wheel angle and speed; and a torque index sensor that includes an additional switch that functions by counting the number of turns of the steering shaft. This torque index sensor enables a more cost-effective solution when the total EPAS system cost is considered.

The non-contacting models feature clock spring-free and Hall Effect (HE)-based technology, which allows measurement without the constraints of a connecting cable for the transmission of power and output signals.

The torque-only sensor (TOS) measures the relative shift angle between two rotating shafts linked by a torsion bar. This angular data is converted into a voltage output and is fed to the EPAS electronic control unit (ECU) to determine how much power assistance is required. This sensor is ideal for applications where a steering angle sensor is already discretely fitted to the column electronic architecture or mounted below the airbag housing. It is particularly useful for column EPAS applications that benefit from the elimination of the connecting cable.

The torque angle sensor (TAS) has the ability to collectively measure torque, steering wheel angle and speed with a number of steering wheel turns. The upper portion of the sensor contains components for differential torque measurement, and the lower housing uses a set of satellite gears to measure the rate and number of steering wheel turns. The steering angle sensor output is absolute and offers true power-off capability. This sensor is an optimal solution for vehicles that require both torque and steering angle feedback. The TAS sensor design effectively replaces the need to fit two discrete devices.

The torque index sensor (TIS) offers a cost-effective solution that features an additional HE switch that functions by counting the number of turns of the steering shaft for comparative analysis with an EPAS motor. A motor position sensor (MPS) obtains the relative value of angles from the steering assist motor and by comparing this information; the TIS sensor can accurately determine the absolute value of the steering angle without the use of a discrete steering angle sensor.

Bourns; www.bourns.com.