Abstract:
A magnetometer assembly ( 22 ) for a torque transducer ( 10 ) includes inner and outer coils ( 34,38,36,40 ) wrapped and supported on a bobbin assembly ( 22 ). The bobbin assembly ( 22 ) includes upper and lower axial portions ( 21,23 ) divided by a middle flange ( 28 ). The middle flange ( 28 ) includes a plurality of notches ( 32 ) that are disposed equal angularly about an axis ( 18 ). A plurality of corresponding magnetic strips ( 42 ) extend axially through each of the notches ( 32 ) and through the entire length of the magnetometer assembly ( 22 ). The magnetic strips ( 42 ) are disposed between an inner and outer coil assembly ( 34,38,36,40 ) and becomes saturated in the presence of a magnetic field. Divergent magnetic fields created by torque applied to a torque transducer element ( 12 ) disposed within the magnetometer assembly ( 22 ) and detected and measured to provide an indication of applied torque.

Description:
BACKGROUND OF THE INVENTION 
   This invention generally relates to a magnetometer for a torque sensor. More particularly, this invention relates to a magnetometer including several coils disposed relative to each for measuring torque related divergent magnetic fields. 
   Conventional torque sensors include a torque transducer element that responds to the application of torque by generating a magnetic field. Such generated or changed magnetic fields are detected by a magnetometer. The torque transducer element typically includes a magnetoelastic material that responds to the application of torque by generating a magnetic field. The application of torque to the magnetoelastic material creates shear stresses within the magnetized regions causing the direction of the magnet field generated by the torque transducer element to shift from a substantially circumferential direction to a helical direction. The helical shifting of the magnetic field is detected as an axial component of the magnetic field. The axial component of the magnetic field is proportional to the applied torque and provides an accurate and reliable indication of torque applied to a torque element. 
   Sensing of the magnetic field and specifically the axial components of the distortions in the magnetic field caused by torque is accomplished through the use of magnetic field sensors. A commonly used type of magnetic field sensors is a flux gate sensor, which is fabricated as a coil of fine wire surrounding a core of magnetically-saturable material, and is supplied with an alternating current. The alternating current provides for the periodic magnetic saturation of magnetic elements. The magnetic field produced by the torque transducer shaft is superimposed on the periodic magnetic field generated by the coils. The superimposing the magnetic field produced by the torque transducer shaft creates an asymmetry in the magnetic saturation of the coils. Changes in the inductance of the coils due to the magnetic saturation results in a voltage that is induced to the coils. It is this voltage that is measured to determine the amplitude and direction of torque applied to the torque transducer element. 
   A known prior art magnetic field sensor includes a bobbin having an upper and lower axial section provided by a central flange. The upper and lower coils are isolated from each other and are induced with an alternating current to produce a magnetic field. Magnetically saturatable strips are disposed between the coil and the torque transducer element. These magnetic strips are magnetically saturated by the alternating current that is produced within the coils. The magnetic strips are disposing parallel to the shaft and the axis of rotation. The magnetic strips are fabricated from a material that possesses a very abrupt magnetic saturation characteristic, meaning that the magnetic strips are quickly saturatable in the presence of a magnetic field and in the absence of the magnetic field quickly demagnetize. 
   Disadvantageously prior art magnetic field sensors require precise alignment to eliminate distortion caused by impinging magnetic fields. The required specific and precise alignment increases cost and complexity and reduces durability and dependability of the torque sensor. 
   Accordingly, it is desirable to design and develop a durable easy to produce and accurate magnetic field sensor that is compatible with torque transducer elements having a shaft supporting a magnetoelastic material. 
   SUMMARY OF THE INVENTION 
   An example magnetometer according to this invention includes first and second inner coils that are supported on a common bobbin and that are both connected to first and second outer coil. Between the inner and outer coils is a plurality of magnetic strips. The magnetic strips are alternately magnetized and demagnetized to produce a magnetic field that is utilized to measure distortion caused by torque applied to a torque transducer element. 
   The magnetometer assembly according to this invention includes a bobbin that is divided into an upper axial portion and a lower axial portion. The upper and low axial portions are divided by a middle flange. Each axial portion includes an inner coil and an outer coil. The inner coil and outer coils are electrically connected. The inner and outer coils are wound in such a manner as to produce correspondingly opposing and equal magnetic fields. 
   Between the inner and outer coils is a plurality of magnetic strips. Each of the magnetic strips is magnetically saturatable and includes a very high length to diameter ratio that extends axially the length of the upper and lower coils. The middle flange may include a corresponding plurality of notches to allow the magnetic strips to extend the entire length of the bobbin. 
   A magnetic field is produced by an alternating current energizing the coils to periodically saturate the magnetic strips at the positive and negative peaks of the alternating waveform. When a torque is applied to the torque transducer element, a divergent magnetic field is created. The divergent magnetic field is superimposed on the magnetic strips in a different manner in the upper and lower portions of the magnetometer assembly. Each of the upper and lower coils is in electrical communication with a central node. Voltage at the central node is observed and is indicative of a difference in magnitude and amplitude of the magnetic field between the upper and lower coils and is in turn indicative of torque applied to the shaft. 
   Accordingly, the magnetometer of this invention provides for the simple efficient and economic sensing of magnetic fields produced by a torque transducer element in a simple and cost effective bobbin assembly. 
   These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial cut away view of a portion of an example torque sensor according to this invention. 
       FIG. 2  is a perspective view of an example magnetometer according to this invention. 
       FIG. 3  is a schematic cross-sectional view of an example magnetometer according to this invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a torque sensor assembly  10  according to this invention is illustrated and includes a torque transducer element  12  that supports a magnetoelastic ring  16 . The torque transducer element  12  includes the shaft  14  that supports the magnetoelastic ring  16 . The torque transducer element  12  is rotatable about an axis  18 . Torque within the torque transducer element  12  is transmitted to the magnetoelastic ring  16 . The magnetoelastic ring  16  possesses a magnetic field along a circumferential magnetic easy direction indicated by arrows  20  when in a default non-torqued condition. 
   The torque sensor assembly  10  includes a magnetometer  22 . The magnetometer  22  comprises a bobbin  24  that has an upper axial portion  21  and a lower axial portion  23  that are separated by a middle flange  28 . Each of the upper and lower portions  21 , 23  includes an inner coil and an outer coil. The upper portion  21  includes the inner coil  34  and the outer coil  36 . The lower portion  23  includes an inner coil  38  and an outer coil  40 . The inner coils  34  and  38  are electrically connected at a central node  50  ( FIG. 3 ). Further, each of the inner coils  34 ,  38  are electrically connected to the outer coils  36 ,  40 . Disposed between each of the inner coils  34 ,  38  and outer coils  36 ,  40  are a plurality of axially orientated magnetic strips  42 . 
   The magnetic strips  42  are disposed axially along the length of the bobbin  24 . The magnetic strips  42  are preferably wires or strips that have an extremely large length to diameter ratio. 
   The inner coils  34  and  38  produce a magnetic field in the presence of an alternating current that is opposite to a magnetic field that is produced by the outer coils  36 ,  40 . The oppositely produced magnetic fields of the inner coils  34 ,  38  and outer coils  36 ,  40  provides for a desired low inductance that could not otherwise be created with individual coils. 
   Each of the inner coils  34 ,  38  and outer coils  36 ,  40  are wound utilizing approximately  200  turns of magnet wire. The specific size of the magnet wire and number of turns utilized to produces the coils is application specific and a worker skilled in the art would understand how to size such a coil to provide the desired magnetic properties for a specific application. In the example illustrated in  FIG. 1  each of the inner and outer coils  34 , 38 , 36 , 40  posses approximately  200  windings. Further, the inner coils  34 , 38  are disposed radially proximate to the shaft  14  of the transducer element  12 . It is desirable to locate the inner coils  34 , 38  in close relationship with the torque transducer element  12  in order to provide desired accuracy and sensing of any magnetic field distortions produced by torque applied to the torque transducer element  12 . 
   Further, no matter how many turns are provided for producing and configuring each of the inner coils  34 ,  38  and outer coils  36 ,  40  each of the coils will have an equal number of turns. The advantage of this means of construction is that the equal number of turns and the utilization of a single bobbin by which to support those turns reduces complexity and increases durability. 
   Referring to  FIG. 2 , the magnetometer assembly  22  is illustrated in a perspective view without the torque transducer  12  and includes the plurality of magnetic strips  42  that are disposed equal angularly about the bobbin  24 . The equal angular distribution of the magnetic strips provides a uniform magnetic saturation for each of the magnetic strips  42 . This equal angular distribution is facilitated by a corresponding plurality of equally angular distributed notches  32  in the middle flange  28 . As appreciated, the specific number and spacing of the magnetic strips  42  is application sensitive. The number of magnetic strips  42  provides a means of tailoring a desired sensitivity that may be adjusted by changing the number and spacing between each of the magnetic strips  42 . 
     FIG. 2  illustrates equal angular distribution and spacing between each of the magnetic strips  42 . The spacing between magnetic strips  42  is indicated by the radial lengths  44  that are disposed such that each of the magnetic strips  42  are positioned parallel to the axis  18 . 
   Referring to  FIG. 3 , the magnetometer assembly  22  is shown schematically in cross-section to illustrate the various electrical connections between the coils and their relationship to the magnetic strips  42  disposed there between. Referring to the upper portion  21  of the bobbin  26 , the inner coil assembly  34  is electrically connected to the outer coil assembly  36 . However, each of the inner coil assemblies  34  and outer coil assemblies  36  are wound in such a manner as to produce magnetic fields of opposite orientation. Further, each of the upper coil assemblies  34 ,  36  are produced with an exact, identical number of winding to produce magnetic fields of equal magnitude. 
   Referring now to the lower portion  23  of the magnetometer assembly  22 , the lower inner coil assembly  38  is electrically connected to the outer coil assembly  40 . The electrical connection is shown as node  48 . Again, the inner coil  38  and outer coil  40  are fabricating utilizing identical sizes and grades of wire with identical numbers of turns. The inner coil  38  and outer coil  40  produce a magnetic field of equal but opposite orientations. 
   Disposed between the inner and outer coil assemblies  34 , 38 , 36 , 40  of both the upper portion  21  and lower portion  23  of the magnetometer assembly  22  are the magnetic strips  42 . 
   The coils  34 ,  36 ,  38 ,  40  are attached to an alternating current source as is indicated at  52 . The alternating current source  52  provides an alternating current utilized to produce a periodic saturation of the magnetic strips  42 . The alternating current is produced by application of a square voltage waveform to produce positive and negative peaks at which the magnetic strips  42  become magnetically saturated. 
   Referring now to  FIGS. 1 and 3 , in operation, the coils  34 , 36 , 38 , 40  generate a magnetic field onto which is superimposed the magnetic field generated by the torque transducer element  12 . The magnetic field generated by the torque transducer element  12  is divergent in nature and will be detected differently at different axial portions of the magnetic strips  28 . As the magnetic field within the upper and lower portions  21 ,  23  of the magnetometer  22  are equal; a different saturation in the magnetic strips  42  within the upper and lower portions  21 , 23  of the magnetometer assembly  22  will be detected as a voltage at a common node  50 . 
   Accordingly, at the common node or connection point  50  between the upper and lower portions  21 , 23  of the magnetometer assembly  22  a pulse voltage wave form with a frequency different than that being utilized to drive the coils will be detected. The phase and amplitude of the voltage signal generated and detected at the node  50  is indicative and related to the amplitude and the direction of the divergent magnetic field and thereby the torque applied to the torque transducer element  12 . 
   Accordingly, in operation each of the coils  34 ,  36 ,  38 ,  40  are excited by the alternating current at amplitude that creates saturation in the magnetic strips  42 . Each of the magnetic strips  42  is saturated magnetically at the positive and negative peaks of the alternating current waveform. When torque is applied to the torque transducer element  12  a divergent magnetic field by the magnetoelastic ring  16  is superimposed upon the magnetic field produced within the magnetic strips  42 . This superimposed imposition of the magnetic field onto the magnetically saturated strips  42  produces an asymmetry in the magnetic saturation between the upper and lower portions  21 , 23  of the magnetometer  22 . The voltage waveform produced by the asymmetry can be observed at the common node  50  and will comprise an even ordered harmonic. The even ordered harmonics of the voltage waveform includes a frequency and a phase along with equally utilized characteristics to determine the amplitude of the magnetic field and thereby the torque applied to the torque transducer element  12 . 
   Accordingly, the magnetometer  22  developed and described in this invention provides for the accurate and durable measurement of a magnetic field produced by the torque transducer element  12  utilizing a bobbin and common coil winding techniques. 
   Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.