Abstract:
A magnetostrictive sensor for outputting a signal representative of torque on a shaft includes one or more excitation coils that generate magnetic flux which permeates the shaft and pickup coils that detect the flux after the flux passes through the shaft. Torque on the shaft affects the magnetic flux passing through the shaft. A coupling member such as plural rollers or powder metal poles are disposed in the flux path and touch the shaft such that no air gap exists in the flux path. Consequently, the sensor is comparatively sensitive, and is not unduly effected by shaft run-out.

Description:
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&#39;s transmission, or in a vehicle&#39;s engine (e.g., the crankshaft), or in a vehicle&#39;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: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side view of a vehicle incorporating the present torque sensing system; 
     FIG. 2 is a schematic side cross-section view of a first embodiment of the torque sensing system, in operable engagement with a rotating shaft; 
     FIG. 3 is a schematic transverse cross-section view of the system shown in FIG. 2; 
     FIG. 4 is a schematic side cross-section view of a second embodiment of the torque sensing system, in operable engagement with a rotating shaft; 
     FIG. 5 is a schematic transverse cross-section view of the system shown in FIG. 4; 
     FIG. 6 is a schematic side cross-section view of a third embodiment of the torque sensing system, in operable engagement with a rotating shaft; and 
     FIG. 7 is a schematic transverse cross-section view of the system shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to FIG. 1, a torque sensing system is shown, generally designated  10 . As shown, the system  10  is disposed in a surrounding relationship with a shaft  12  to sense the torque imposed on the shaft  12 . In one exemplary embodiment, the shaft  12  is a rotating shaft within a vehicle  14 . For instance, the shaft  12  can be an ABS shaft, engine shaft, or transmission shaft, although it is to be appreciated that the principles set forth herein apply equally to other vehicular and non-vehicular rotating shafts. 
     Now referring to FIGS. 2 and 3, a first embodiment of the system  10  is shown. As shown, the system  10  includes a hollow sensor housing  16  that is configured for surrounding the shaft  12 . In the preferred embodiment, excitation coils  18  that are longitudinally spaced from each other are held in the housing  16  as shown, it being understood that each excitation coil  18  can be connected to a source of electricity to generate magnetic flux, represented by flux lines  20  in FIG.  2 . In accordance with magnetostrictive principles known in the art, the flux permeates the shaft  12  when the excitation coils  18  are juxtaposed with the shaft  12 . 
     As also shown best in the exemplary embodiment of FIG. 2, disposed radially outwardly of each excitation coil  18  and aligned therewith in the radial dimension can be a respective pickup coil  22  that is configured to receive magnetic flux from the shaft  12 . The skilled artisan will appreciate that the flux defines a flux path from each excitation coil  18  to its respective pickup coil  22 . Other flux sensors can be used within the scope of the present invention, e.g., Hall effect sensors can be used, or inductance changes in the excitation coil  18  can be measured and used, or other inductance change sensors known in the art can be used. 
     In accordance with the present invention, to magnetically couple the excitation coils with the pickup coils without an air gap in the flux path, thereby promoting sensor sensitivity, one or more, preferably three, bearings  24  are disposed in the flux path in physical contact with the shaft  12 . The bearings  24  can be slide bearings but in the embodiment shown the bearings  24  are roller bearings. Accordingly, as shown in FIG. 3 the bearings  24  include plural rollers  26  that rollably engage an inner bearing ring  28  that is on the shaft  12 . In this way, the rollers  26  rollably couple the shaft  12  with the housing  16 . As intended by the present invention, the middle bearing  24  is essentially an excitation bearing and the left and right bearings  24  are pickup bearings. In other words, flux passes through the middle bearing  24  first, then to the left and right bearings, and then to the pickup coils  22 . 
     FIG. 2 best shows that first, second, and third high magnetic permeability regions  30  are on the shaft  12  and are radially aligned with respective bearings  24 . Accordingly, the high permeability regions are longitudinally separated from each other. 
     Between adjacent high permeability regions  30  and, thus radially aligned with respective sets of coils  18 / 22  are flux directing regions  32  that are configured for directing flux from the excitation coils  18  through the rollers  26  and back to the pickup coils  22 . In the preferred embodiment, the flux directing regions include plural slots  34  each of which defines an oblique angle a relative to the longitudinal axis “L” of the shaft  12 . In a particularly preferred embodiment, the angle α is forty five degrees (45°). Moreover, to correctly direct the flux, the slots  34  in the left-most flux directing region  32  shown in FIG. 2 are orthogonal to the slots in the right-most flux directing region  32 . 
     FIGS. 4 and 5 show an alternate system, generally designated  100 . In the system  100  as shown in FIGS. 4 and 5, a hollow housing  102  holds plural excitation coils  104  with respective pickup coils  106 . Also, the system  100  includes as many as three sets of three rollers each that can fit around the shaft, with each set establishing a bearing that includes a middle roller  108  and two side rollers  110 . Pairs of coils  104 ,  106  are longitudinally staggered between adjacent roller sets as shown. The side rollers  110  can be thought of as front and rear rollers, since they are longitudinally spaced from each other. In any case, the rollers  108 ,  110  directly contact a shaft  112 , with the rollers  108 ,  110  being disposed in the flux path, designated by flux lines  114 , between the coils  104 ,  106 . 
     While the side rollers  110  of a set are in a line that is parallel to the longitudinal axis  116  of the shaft  112 , the middle roller  108  of each set is not aligned with the side rollers  110 , as best shown in FIG.  2 . Instead, the middle rollers  108  are offset from their respective side rollers  110  on the circumference of the shaft  112 , to appropriately direct flux. More specifically, a line along the circumference of the shaft  112  from the middle roller  108  to either side roller  110  defines an angle α with respect to the axis  116  of forty five degrees (45°). It may now be appreciated that in accordance with present principles, the side rollers  110  are essentially pickup rollers and the middle rollers  108  are essentially excitation rollers. 
     FIGS. 6 and 7 show yet another torque sensing system, generally designated  200 , which, like the systems  10 , 100  described above, has no air gap in the flux path. A hollow sensor housing  202  surrounds a shaft  204 , and the housing  202  holds two pairs of excitation coils  206  and associated pickup coils  208  arranged as set forth above in relation to the system  10  shown in FIGS. 2 and 3. 
     As shown, plural, preferably four, sensor cores  210  are held in the housing  202  to slidably contact the shaft  204  and thereby magnetically couple the shaft  204  and the coils  206 ,  208 . Each sensor core  210  includes front and rear pickup poles  212 ,  214  and an excitation pole  216  longitudinally intermediate the pickup poles  212 ,  214  as shown best in FIG.  6 . As shown, the coils  206 ,  208  are nested between the excitation pole  216  and respective pickup poles  212 ,  214 . 
     In cross-reference to FIGS. 6 and 7 regarding the preferred embodiment, the front and rear pickup poles  212 ,  214  of a sensor core  210  define a line that is parallel to the longitudinal axis  218  of the shaft  204 , whereas the excitation pole  216  of the core is offset from the pickup poles to appropriately direct flux, denoted by flux lines  220 . Accordingly, each sensor core  210  forms a “V” shape in the longitudinal dimension as shown in FIG.  6 . Consequently, a line between a pickup pole  212 / 214  and its associated excitation pole  216  establishes an angle α of 45° with respect to the axis  218 . 
     In the preferred embodiment, the sensor cores  210  are made of highly permeable powder metal having spherical powder constituents, or a ferromagnetic plastic material, or any material that is softer than the shaft. The powder constituents are very small, preferably having diameters of less than three microns (&lt;3 μ). 
     With the flux coupling members (i.e., rollers, poles, or bearings) of the present invention being disposed in the flux path and touching the shaft, no air gap exists in the flux path. Consequently, the present sensors are comparatively more sensitive than conventional magnetostrictive sensors, and are also less susceptible to performance degradation in the presence of shaft run-out than are conventional magnetostrictive sensors. 
     While the particular SHAFT TORQUE SENSOR WITH NO AIR GAP as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to the elements of the above-described preferred embodiment that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for”.