Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
1999-11-23
2001-09-18
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06289748
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to rotating shaft torque sensors.
2. Description of the Related Art
Sensors to measure the torque imposed on rotating shafts, such as but not limited to shafts in vehicles, are used in many applications. For example, it might be desirable to measure the torque on rotating shafts in a vehicle's transmission, or in a vehicle's engine (e.g., the crankshaft), or in a vehicle's automatic braking system (ABS) for a variety of purposes known in the art.
To this end, magnetostrictive torque sensors have been provided wherein a sensor is positioned in a surrounding relationship with a rotating shaft, with an air gap being established between the sensor and shaft to allow the shaft to rotate without rubbing against the sensor. A magnetic field is generated in the sensor by passing electric current through an excitation coil of the sensor. This magnetic field permeates the shaft and returns back to a pick-up coil of the sensor.
The output of the pick-up coil is an electrical signal that depends on the total magnetic reluctance in the above-described loop. Part of the total magnetic reluctance is established by the air gap, and part is established by the shaft itself, with the magnetic reluctance of the shaft changing as a function of torque on the shaft. Thus, changes in the output of the pick-up coil can be correlated to the torque experienced by the shaft.
As understood herein, the air gap, heretofore necessary to permit relative motion between the shaft and sensor, nonetheless undesirably reduces the sensitivity of conventional magnetostrictive torque sensors. As further understood herein, it is possible to eliminate the air gap between a shaft and a magnetostrictive torque sensor, thereby increasing the sensitivity of the sensor vis-a-vis conventional sensors. Moreover, the present invention recognizes that a phenomenon known in the art as “shaft run-out” can adversely effect conventional magnetostrictive torque sensors, and that a system can be provided that is relatively immune to the effects of shaft run-out. Accordingly, the present invention provides the solutions set forth herein.
SUMMARY OF THE INVENTION
A torque sensing system for generating an electrical signal representative of torque on a shaft defining a longitudinal axis and a radial dimension includes at least one excitation coil that is connectable to a source of electricity to generate magnetic flux. The flux permeates the shaft when the excitation coil is juxtaposed with the shaft. At least one pickup coil is configured to receive magnetic flux from the shaft, with the flux defining a flux path from the excitation coil to the pickup coil. Preferably three bearings engage the shaft and are disposed in the flux path such that no air gap exists in the flux path.
In a preferred embodiment, the bearings and coils are held in a hollow housing that surrounds the shaft. Within the housing a pickup coil is disposed radially outwardly of an associated excitation coil and is aligned with the excitation coil. Also, the bearings include plural rollers.
In one embodiment as shown and described further below in reference to
FIGS. 2 and 3
, a bearing inner ring is disposed between the rollers and the shaft such that the rollers directly contact the bearing inner ring to rollably engage the shaft with the housing. In this embodiment, first, second, and third high permeability regions are on the shaft, and the high permeability regions are longitudinally separated from each other by flux directing regions. Each bearing is aligned in the radial dimension with a respective high permeability region. In contrast, each excitation/pickup coil pair is radially aligned with a respective flux directing region.
As disclosed in greater detail below, the flux directing regions include plural slots that define an oblique angle relative to the axis, preferably an angle of 45°. In a particularly preferred embodiment, first and second flux directing regions have slots formed in them, with the slots in the first flux directing region being orthogonal to the slots in the second flux directing region.
In an alternate embodiment as shown and described further below in reference to
FIGS. 4 and 5
, no inner ring is provided, such that the rollers directly contact the shaft. In this embodiment, the rollers are arranged in sets. Each set of rollers includes front and rear pickup rollers that are aligned parallel to the axis of the shaft, and a middle excitation roller is disposed longitudinally between the pickup rollers and is offset from the line defined by the pickup rollers by an angle of 45°.
In still another embodiment as shown and described further below in reference to
FIGS. 6 and 7
, a torque sensing system for generating an electrical signal representative of torque on a shaft includes a sensor housing surrounding the shaft, and plural pairs of excitation/pickup coils arranged as in the above two embodiments. In this embodiment, the coils are magnetically coupled not by rollers, but by plural poles that slide along the shaft as the shaft rotates. In any case, no air gap is present in the flux path.
Preferably, in this last embodiment four sensor cores are provided on the shaft, and each core includes front and rear pickup poles and a longitudinally intermediate excitation pole that is offset from the line defined by the pickup poles by 45°. With this pole arrangement, each sensor core forms a “V” shape in the longitudinal dimension. As intended herein, each sensor core is made of powder metal that includes spherical powder constituents. Preferably, each constituent has a diameter of less than three microns.
In another aspect, a system for measuring torque on a shaft includes the shaft, and at least one excitation coil is juxtaposed with the shaft. Also, the system includes at least one pickup coil juxtaposed with the shaft. In accordance with present principles, an airless flux path is defined from the excitation coil, to the shaft, and back to the pickup coil, such that the pickup coil generates a signal representative of torque on the shaft.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which:
REFERENCES:
patent: 4541674 (1985-09-01), Mitschang
patent: 4541819 (1985-09-01), Mazziotti
patent: 4887461 (1989-12-01), Sugimoto et al.
patent: 5526704 (1996-06-01), Hoshina et al.
patent: 6083137 (2000-07-01), Kato et al.
Lin Yingjie
Moreno Daniel J.
Rodriguez Lorenzo Guadalupe
Delphi Technologies Inc.
Dobrowitsky Margaret A.
Fuller Benjamin R.
Thompson Jewel V.
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