Abstract:
A torque sensor system comprising, an inner tooth, an outer tooth disposed on an outer yoke member centered on an axis spaced radially from the inner tooth, a plate member, a retainer member operative to retain the outer yoke member and the plate member, a magnet member centered on the axis disposed between the inner tooth and the outer tooth, an air gap partially defined by the plate member and the outer yoke member, and a magnetosensitive element disposed in the air gap operative to sense a magnetic flux induced by an angular displacement of the magnet member relative to the inner tooth and the outer tooth.

Description:
BACKGROUND 
       [0001]    Determining a relative position (angular displacement) of two shafts is beneficial in control systems. The relative positions of shafts may be used to determine a torque induced on components. 
         [0002]    For example, power steering systems use a torque applied to one shaft to control a torque applied to a second shaft. The amount of torque applied to the first shaft may be determined by an angle displacement sensor. 
         [0003]    Previous angle displacement sensors use a rotor having a ring magnet that is attached to a first shaft. The ring magnet is surrounded by a stator assembly having teeth that is attached to a second shaft. When a torque is applied to the first shaft, magnetic flux crosses from the ring magnet to the teeth and forms a differential flux across an air gap in the stator assembly. The differential flux is proportional to the relative angular displacement between the first and second shafts. The differential flux is measured by a magnetosensitive element, such as, for example, a Hall Effect sensor. The measurement of the differential flux is used to determine the torque applied to the ring magnet. 
         [0004]    Previous torque sensors are relatively large, sensitive to mechanical build variations and expensive to manufacture. A compact, reliable, and easily manufactured position sensor that is insensitive to mechanical variation that may be used to sense torque on a shaft is desired. 
       SUMMARY 
       [0005]    The above described and other features are exemplified by the following Figures and Description in which a torque sensor system comprising, an inner tooth, an outer tooth disposed on an outer yoke member centered on an axis spaced radially from the inner tooth, a plate member, a retainer member operative to retain the outer yoke member and the plate member, a magnet member centered on the axis disposed between the inner tooth and the outer tooth, an air gap partially defined by the plate member and the outer yoke member, and a magnetosensitive element disposed in the air gap operative to sense a magnetic flux induced by an angular displacement of the magnet member relative to the inner tooth and the outer tooth. 
         [0006]    An alternate embodiment of a torque sensor system comprising, an inner tooth, an outer tooth disposed on an outer yoke member centered on an axis spaced radially from the inner tooth, a retainer member operative to retain the outer yoke member, a magnet member centered on the axis disposed between the inner tooth and the outer tooth, a lower flux collector, an upper flux collector, an air gap partially defined by the lower flux collector and the upper flux collector, and a magnetosensitive element disposed in the air gap operative to sense a magnetic flux induced by an angular displacement of the magnet member relative to the inner tooth and the outer tooth. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Referring now to the Figures wherein like elements are numbered alike: 
           [0008]      FIG. 1  illustrates a partially cut-away perspective view of a torque sensor. 
           [0009]      FIG. 2  illustrates a perspective view of an exemplary embodiment of the inner teeth, the inner yoke, the outer teeth, the outer yoke, the cover, and the retainer assembly of  FIG. 1 . 
           [0010]      FIG. 3  illustrates a top down cut away view of a portion of the torque sensor of  FIG. 1 . 
           [0011]      FIG. 4  illustrates a graph of the performance curves of the magnetic portion of  FIG. 1 . 
           [0012]      FIG. 5  illustrates a perspective partially cut away view of an alternate embodiment of a torque sensor. 
           [0013]      FIG. 6  illustrates a perspective view of the shaft and inner teeth of  FIG. 5 . 
           [0014]      FIG. 7  is a perspective view of another alternate exemplary embodiment of a torque sensor. 
           [0015]      FIG. 8  is a perspective view of another alternate exemplary embodiment of a torque sensor. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Torque sensors are used to determine an amount of torque applied to a shaft. Previous torque sensors used expensive components such as, for example, sintered NdFeB magnets and were undesirably large as well as being sensitive to mechanical build variations. Embodiments of a compact and less expensive torque sensor that is insensitive to build variations are described below. 
         [0017]    In this regard,  FIG. 1  illustrates a partially cut-away perspective view of a magnetic portion of a torque sensor  100 . The torque sensor  100  includes a multi-pole magnet  102  connected to a first shaft  104  with a magnet retainer  103 . The magnet  102  is disposed between an inner pole portion and an outer pole portion. The inner pole portion includes inner teeth  107  that are formed on an inner yoke  105 , and the outer pole portion includes outer teeth  109  formed on an outer yoke  111 . The inner yoke  105  is connected to a second shaft  112 . The inner yoke  105  and the outer yoke  111  are connected with a non-magnetic retainer  113  that may be formed by, for example, over molded plastic material. The retainer secures a cover  114 . A measurement gap (air gap)  115  is defined by the outer yoke  111 , the retainer  113 , and the cover  114 . A magnetosensitive element  118 , such as, for example, one or more Hall Effect sensors is disposed in the airgap  115  and remains stationary relative to the rotation of the retainer  113 , the cover  114 , and the shafts  104  and  112 . The magnetosensitive element  118  may be connected to a processor (not shown) that receives signals from the magnetosensitive element  118 . 
         [0018]    The illustrated embodiment includes a magnet  102  that may include, for example a ring magnet, an arcuate magnet, or other shaped magnets. The magnet  102  may be formed from any type of magnetic material, for example, NdFeB, SmCo or ferrite. The magnet  102  may be manufactured using various techniques, for example, sintering, compression molding or injection molding. The yokes and teeth may be formed from ferrous metal, for example, laminate SiFe or powdered metal SiFe. The shafts  104  and  112  may be formed from, for example, machined steel stock. 
         [0019]      FIG. 2  illustrates perspective view of an exemplary embodiment of the inner teeth  107 , inner yoke  105 , the outer teeth  109 , the outer yoke  111 , the cover  114 , and the retainer  113  assembly. 
         [0020]      FIG. 3  illustrates a top down cut away view of the inner teeth  107 , inner yoke  105 , the outer teeth  109 , the outer yoke  111 , the magnet  102 , and the second shaft  112 . In operation, when the magnet  102  is in the position shown in  FIG. 3 , the net flux in the air gap  115  is zero. When a torque is applied to the first shaft  104  (of  FIG. 1 ), the first shaft  104  turns the magnet  102  relative to the inner teeth  107  and the outer teeth  109 . As the magnet  102  moves relative to the inner teeth  107  and the outer teeth  109 , a non-zero net magnetic flux flows through the air gap  115 . The magnitude of the net magnetic flux changes proportionally to the angle between the magnet  102  and the inner teeth  107  and the outer teeth  109 . The polarity of the net magnetic flux in the air gap  115  is dependent on the direction of rotation between the magnet  102  and the inner teeth  107  and the outer teeth  109 . For example, if the net magnetic flux in the air gap  115  is positive when the magnet  102  rotates clockwise relative to the inner teeth  107  and the outer teeth  109  then the net magnetic flux in the air gap  115  is negative when the magnet  102  rotates counterclockwise relative to the inner teeth  107  and the outer teeth  109 . 
         [0021]    Referring to  FIG. 1 , in the zero net flux position (the position shown in  FIG. 3 ) 50% of the magnetic flux flows in a path from the magnet  102  through the inner teeth  107 , through the inner yoke  105 , through the second shaft  112  through the cover  114 , across the airgap  115  to the outer yoke  111  through the outer teeth  109 , and back to the magnet  102 . The other 50% of the magnetic flux flows in an opposing path from the magnet  102  through the outer teeth  109 , through the outer yoke  111 , across the air gap  115  to the cover  114 , through the second shaft  112  to the inner yoke  105  and inner teeth  107 , and back to the magnet  102 . In a zero torque condition, no net flux is present in the air gap  115 ; as the magnet  102  rotates relative to the inner teeth  107  and the outer teeth  109 , the net flux increases or decreases dependent on the rotation of the magnet  102  relative to the inner teeth  107  and the outer teeth  109 , the increase and decrease in net flux is measured by the magnetosensitive element  118 . The magnetosensitive element  118  measures changes in the magnetic flux. In the illustrated embodiment, the magnetosensitive element  118  outputs a voltage that varies with the magnitude and direction of the net flux. The net flux measurement is used to determine the torque applied to the first shaft  102 . 
         [0022]      FIG. 4  illustrates an example of the performance curves of the torque sensor  100 . As the angle of displacement (between the magnet  102  and the inner teeth  107  and the outer teeth  109 ) changes, the net flux in measurement gap  115  changes. The resultant net flux in measurement gap  115  is highly linear to approximately 4 degrees of angular displacement with the linearity increasing slightly at angles beyond 4 degrees. 
         [0023]      FIG. 5  illustrates perspective partially cut away view of an alternate embodiment of a torque sensor  500 . The torque sensor  500  is similar in operation to the torque sensor  100  (of  FIG. 1 ) described above. However, the torque sensor  500  includes inner teeth  107  that are formed on the second shaft  512 . The inner teeth  107  may be formed on the second shaft  512  using, for example, a machining process. The torque sensor  500  does not include an inner yoke  111 . The retainer  513  is connected to the outer yoke  511 , the cover  114  and the second shaft  512 . 
         [0024]      FIG. 6  illustrates a perspective view of the shaft  512  (of  FIG. 5 ) and inner teeth  107 . 
         [0025]      FIG. 7  is a perspective view of an alternate exemplary embodiment of a torque sensor  700 . The torque sensor  700  is similar in operation to the torque sensors described above. The illustrated embodiment includes the shaft  512 , however embodiments may alternatively include the shaft  112  and inner yoke  111  and inner teeth  107  as described above in  FIG. 1 . The torque sensor  700  includes a lower flux collector  720  that is spaced from the outer yoke  111  by a small air gap of, for example, 1 mm. The torque sensor  700  includes an upper flux collector  722  that is spaced from the second shaft  512  by a small air gap of, for example, 1 mm. The air gap  115  is partially defined by the lower flux collector  720  and the upper flux collector  722 . The magnetosensitive elements  118  are disposed in the air gap  115 . The lower flux collector  720  and the upper flux collector  722  are retained by a housing member (not shown). The air gap  115  defines a radial arc, for example, 60 degrees. 
         [0026]    In operation torque applied to the second shaft  512  rotates the inner teeth, the outer yoke  111 , and the outer teeth  109  that are connected with a retainer (not shown). The housing member and the lower flux collector  720  and the upper flux collector  722  remain stationary relative to the rotation of the second shaft  512 , the inner teeth  107 , the outer yoke  111 , and the outer teeth  109 . The torque sensor  700  provides an increase in the net flux in the air gap  115  as the angle of displacement (between the magnet  102  and the inner teeth  107 , and the outer teeth  109 ) changes by concentrating the net flux in a smaller angular area, than the torque sensor  100 . The torque sensor  700  provides better rotational accuracy. The design of the torque sensor  700  allows for more variation in the placement of magnetosensitive elements  118  without affecting the performance of the torque sensor  700  in terms of linearity and rotational accuracy. 
         [0027]      FIG. 8  illustrates an alternate exemplary embodiment of a torque sensor  800 . The torque sensor is similar in operation to the torque sensor  700  described above. The torque sensor  800  includes the lower flux collector  720  and the upper flux collector  722  that define the air gap  115  that extends in a 360 degree radial arc. 
         [0028]    The technical effects and benefits of the system and methods described above allow the measurement of torque applied to a shaft. 
         [0029]    While the invention has been described with reference to exemplary embodiments, it will be understood by those of ordinary skill in the pertinent art that various changes may be made and equivalents may be substituted for the elements thereof without departing from the scope of the present disclosure. In addition, numerous modifications may be made to adapt the teachings of the disclosure to a particular object or situation without departing from the essential scope thereof. Therefore, it is intended that the Claims not be limited to the particular embodiments disclosed as the currently preferred best modes contemplated for carrying out the teachings herein, but that the Claims shall cover all embodiments falling within the true scope and spirit of the disclosure.