Application of Passive SAW Resonant Sensors to Contactless Measurement of the Output Engine Torque in Passenger Cars

An engine output torque measurement system employing 433 MHz SAW resonators as sensing elements is presented. Either one or two SAW sensing elements incorporating three or five one-port resonators are attached to a flexplate that couples the crankshaft to the torque converter of a car with automatic transmission. An optimum design of the flexplate is described that minimizes the influence of extraneous mechanical forces. Design of the large diameter RF rotary coupler, as well as torque and temperature calibration characteristics of the sensor, is presented. An interrogation algorithm and its influence on system bandwidth are discussed. Experimental results of dynamic tests characterizing accuracy of the torque measurement are presented.