Measuring and testing – Dynamometers – Responsive to multiple loads or load components
Reexamination Certificate
1999-10-21
2001-08-07
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to multiple loads or load components
Reexamination Certificate
active
06269702
ABSTRACT:
TECHNICAL FIELD
This invention relates to an apparatus and method for measuring torque, and more particularly, a structure and method that will measure the torque output of a rotating shaft.
BACKGROUND OF THE INVENTION
Engine crankshaft torque is an important factor in engine and vehicle performance. Fuel economy, drivability and operational smoothness in a vehicle driven by an automatic transmission are functions of transmission shift points and engine control parameters. Crankshaft torque is taken into account in order to optimize these shift points. The design and proper function of the drive train also must take into account crankshaft torque.
Crankshaft torque has been typically measured in test cells using highly specialized expensive dynamometer equipment and setups. The equipment, however, is large and very sensitive, making it totally unsuitable for vehicular applications.
Also, other attempts to measure engine crankshaft torque were made by machining “flats” into the engine crankshaft and installing stress or strain gauges onto the flats. As torque load is applied to the crankshaft, the strain gauges sense the induced stress load at their locations on the flats. The resulting signals from the strain gauges are compared with the torque calibration data, from which the torque values are inferred.
Such torque measuring devices are plagued by several problems. Life limiting modifications to the engine crankshaft are required for their installation, in addition to the difficulties and impracticalities of having to install sensors and physically load and calibrate each individual crankshaft, thereby disqualifying their use in commercial production vehicles. They also suffer from inaccuracy due to their inability to distinguish between stresses caused by torsional loads and stresses caused by non-torsional loads (i.e., axial loads, shear/radial loads, bending loads, or skew/misalignment loads).
The size constraints and accuracy problems inherent in prior art torque measuring devices (especially those utilizing slip rings) have greatly contributed to a resulting design cycle for the automobile drive train that is longer than the design cycle typical of the other primary automotive systems. The installation disadvantages of prior art torque measurement devices have also effectively precluded their incorporation into commercial production vehicles.
SUMMARY OF THE INVENTION
According to principles of the present invention, a method and apparatus for measuring torque of a rotating shaft is provided. In one embodiment, the apparatus includes a transducer assembly that is attached to a shaft. The transducer assembly includes a first plate member, a plurality of webs extending from the first plate member and a second plate member connected to the webs. A plurality of strain gauges are mounted on the transducer assembly at selected locations and in selected patterns to form a sensing circuit. The first plate is rigidly coupled to the shaft. As torque is applied to the shaft, the transducer assembly also rotates. The torsional load from the shaft causes stress in the first plate member, the web members, and the second plate member. The strain gauges are placed in locations of the transducer through which the load passes as it is carried by the transducer assembly. The strain gauges respond to this stress and generate signals that provide a measure of the induced stress. The signals transmitted from the sensing circuit are compared with calibration data, and the torque value is inferred.
In one embodiment, the strain gauges are arranged in opposing pairs on the transducer assembly and electrically connected as a Wheatstone bridge. In this embodiment, strain resulting from non-torsional loads is canceled from the measured signal, thereby improving torque measurement accuracy.
In another embodiment, the strain gauges are located on thinned regions in the transducer assembly. The thinned regions are fashioned for the purpose of creating areas of localized high stress. Preferably, they are designed to provide constant stress across each individual strain gauge.
In another embodiment, the transducer assembly includes a decoupling aperture. The decoupling aperture may include holes or slits, and may be disposed at any location throughout the transducer assembly. Appropriate application of the decoupling aperture minimizes hysteresis due to warping and bending of the transducer assembly.
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Throop, M.J. and McWatt, D.G., “Slipping Torque Converter Clutch Interface Temperature, Pressure and Torque Measurement Using Inductively Powered Radiotelemetry”Ford Motor Company, Paper No. 970679.
Carlson David V.
Noori Max
Seed IP Law Group PLLC
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