Winterthur, Switzerland — Intended for vehicle dynamics applications such as development of control systems for dynamic stability, traction control, and ABS, the Rotating Wheel Torquemeter (RWT) measures the driving and braking torque acting on passenger car wheels. Designed by Kistler Instrument Corp., the sensor system fits to the vehicle with a set of car-specific hub and rim adapters.
Three components make the RWT: a torque sensor, a transceiver head for telemetric signal transmission, and the control unit. Eight piezoelectric quartz shear force sensors, preloaded between two flanges, comprise the torque sensor. Optimized for low mass, high rigidity, and temperature variations, the sensor offers two selectable measuring ranges (±3,000 and±300 Nm) for maximum signal resolution.
In addition to sensing the torque signal, the RWT offers a provision for installing four K-type thermocouple elements on the torque sensor's rotating element. These, for example, can be used to monitor temperatures on the brake disk. Amplifiers for the charges and thermocouple signals are integrated into the torque sensor.
Telemetric signal transmission carries measured data from the transceiver head to the control unit, located inside the vehicle. The transceiver head includes all the necessary components for data acquisition, telemetry, and telecommand: processor, signal conditioning circuits, a 16-bit-A/D converter with eight-channel multiplexer, and sender/receiver module with antenna.
Sampling rate is 1,000 samples/sec for torque, or eight samples/sec for temperature. To save battery power, the transceiver head is set to sleep mode; any movement of the head wakes it up again.
The control unit includes a 32-bit processor, digital-, serial-, CAN- or analog interfaces, as well as radio links with the transceiver head. One control unit can serve as many as four transceiver heads. The radio links are based on a DECT transceiver module as used in cordless phones. Several such systems can operate simultaneously without interference.
Synchronization delay between the control unit and each transceiver head is less than one msec. The control unit accepts commands through ACAN-bus or RS-232C interface. Measured data, converted into physical units, is output through the CAN or RS-232C interface. An analog output–one per transceiver head–is also available.
In summary, the new Rotating Wheel Torquemeter measures real-life road conditions with special emphasis on:
Power transmission measurements
Coast down tests
Contact Kistler Instrument Corp ., 75 John Glenn Dr., Amherst, NY 14228; Tel: (716) 691-5100; www.kistler.ch/