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Engine Control + Torque Sensor = Improved Fuel Economy
Technique uses the existing shaft for low cost measurement
Randy Frank, Contributing Editor -- Design News, December 10, 2007
In spite of all the sensors found on vehicles, a torque sensor is not one of them. “All OEMs today use torque sensors in their lab and instrumentation systems to develop products, but today, passenger cars and light trucks are not using torque sensing in serial production,” says Paul Cain, director of marketing — Transportation Products for Custom Sensors and Technologies Inc. “Engine control module engineers and transmission engineers are seeking a high accuracy torque technology in their assembly, but the price points of torque sensors have historically been too high.” A production-viable technology from BEI Duncan Electronics Div., called BEITORQ, could change this.
Using patented technology licensed from NCTEngineering GmbH, Pulsed Current Modulated Encoding (PCME) establishes a permanent magnetically encoded region inside an existing shaft, as long as the shaft is made from a ferro-magnetic material. Applying a mechanical force causes the shaft to radiate a magnetic field that is measured by the sensor. As the torque is increased on the shaft the magnetic field is also increased outside this encoded region. The coils then “read” this changing magnetic field. The sensor assembly is designed to reject unwanted external magnetic field signals, such as those from the earth’s magnetic field. The sensor operates in air, water and oil with only 5 mA current consumption, provides a high signal bandwidth of 10 kHz and accepts large alignment tolerances of 0.5 mm. With a temperature range up to 210C, ideal applications are automotive and industrial environments.
In vehicles, a torque sensor mounted at the crankshaft can monitor dynamic torque sensing on the engine as a primary sensor for next-generation engine control modules to optimize fuel economy and eliminate other sensors. Additionally, these torque sensors are under development in transmission applications in both the input and output shaft locations. To use it effectively, a torque sensor requires a different architecture in the control module. While it is not a trivial system design change, the benefits could offset the effort in a new engine or transmission management system. With the pressure for improved fuel economy and soaring gas prices, torque sensing could supply a means for improvement over accepted design methodology. Today, strong interest in diesel engines could provide one of the first applications.
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