Magnetic speed sensor

Abstract

A speed sensor for a vehicle wheel has a rotating tone wheel with a stationary magnetic sensor having a pair of sensing poles positioned proximate the tone wheel teeth. Coil means are wound on the poles and the poles are magnetized to induce a signal voltage in the coil means corresponding to wheel speed. The poles are phased relative to the teeth on the tone wheel to reduce noise voltage components in the wheel speed signal voltage due to axial misalignment and vibration of the tone wheel. The poles may be phased 180° relative to one another with respect to the teeth on the tone wheel so that one pole is in registry with a tooth when the other pole is in registry with a space between two teeth. With this arrangement the combined reluctance of the poles is approximately constant.

What is claimed is: 
     
       1. A speed sensor for a vehicle wheel comprising a tone wheel driven by the vehicle and subject to axial misalignment and vibration, the tone wheel being made of magnetic material and having a plurality of teeth, and sensing means having a pair of poles of magnetic material proximate the tone wheel teeth, coil means on the poles, and a permanent magnet having one of its poles connected to the poles on the sensing means for magnetizing the poles on the sensing means to induce a signal voltage in the coil means corresponding to wheel speed upon rotation of the tone wheel relative to the sensing means, the poles on the sensing means being phased relative to the teeth on the tone wheel to reduce noise voltage components in the wheel speed signal voltage due to axial misalignment and vibration of the tone wheel, and a substantially U-shaped shield connected to the other pole of the permanent magnet and enclosing a substantial portion of the sensing means from electromagnetic noise, a portion of the U-shaped shield being positioned adjacent the tone wheel remote from the teeth to provide a return path for magnetic flux. 
     
     
       2. A speed sensor as described in claim 1 in which the poles on the sensing means are spaced relative to the tone wheel teeth so that one of the poles is in registry with a tooth when the other pole is in registry with a space between two teeth. 
     
     
       3. A speed sensor as described in claim 1 in which the poles on the sensing means are phased 180° relative to one another with respect to the teeth on the tone wheel. 
     
     
       4. A speed sensor as described in claim 1 in which the coil means includes a separate coil wound on each sensing pole and the coils are connected in series opposition. 
     
     
       5. A speed sensor as described in claim 1 in which the poles on the sensing means are phased relative to the teeth on the tone wheel so the combined reluctance of the poles is approximately constant. 
     
     
       6. A speed sensor for a vehicle wheel comprising a tone wheel driven by the vehicle and subject to axial misalignment and vibration, the tone wheel being made of magnetic material and having a plurality of teeth, and sensing means having a pair of poles of magnetic material proximate the tone wheel teeth, coil means on the poles, and a permanent magnet having one of its poles connected to both poles of the sensing means for magnetizing the poles to induce a signal voltage in the coil means corresponding to wheel speed upon rotation of the tone wheel relative to the sensing means, the poles on the sensing means being phased relative to the teeth on the tone wheel to reduce noise voltage components in the wheel speed signal voltage due to axial misalignment and vibration of the tone wheel, and the sensing means including a third pole connected to the other pole of the permanent magnet and positioned proximate the tone wheel remote from the teeth to provide a return path for magnetic flux. 
     
     
       7. A speed sensor as described in claim 6 in which the pair of poles on the sensing means are spaced relative to the tone wheel teeth so that one of the poles is in registry with a tooth when the other pole is in registry with a space between two teeth. 
     
     
       8. A speed sensor as described in claim 6 in which the pair of poles on the sensing means are phased 180° relative to one another with respect to the teeth on the tone wheel. 
     
     
       9. A speed sensor as described in claim 6 in which the coil means includes a separate coil wound on each sensing pole of the pair and the coils are connected in series opposition. 
     
     
       10. A speed sensor as described in claim 6 in which the pair of poles on the sensing means are phased relative to the teeth on the tone wheel so the combined reluctance of the poles is approximately constant. .Iadd. 11. A speed sensor as claimed in claim 1, in which the coil means includes a separate coil wound on each pole piece and the coils are connected in series opposition. .Iaddend..Iadd. 12. A speed sensor for a vehicle wheel comprising a tone wheel driven by the vehicle, the tone wheel being made of magnetic material and having a plurality of equally-spaced teeth defining spaces therebetween, and sensing means mounted adjacent said tone wheel, said sensing means comprising a pair of pole pieces located adjacent said teeth, and a permanent magnet located between said pole pieces for providing a flux path therebetween, said magnet having a pair of opposite ends having opposite magnetic polarities, one of the opposite ends of said magnet being magnetically connected to one of the pole pieces, the other of the opposite ends of the magnet being magnetically connected to the other of said pole pieces, and coil means associated with the pole pieces for providing an output signal in response to changes in the magnetic flux in said pole pieces. .Iaddend..Iadd. 13. A speed sensor as claimed in claim 12, in which the axis of the permanent magnet is parallel to the axis of rotation of the tone wheel. .Iaddend..Iadd. 14. A speed sensor as claimed in claim 12, in which the axis of the permanent magnet is parallel to the plane in which the tone wheel rotates. .Iaddend..Iadd. 15. A speed sensor for a vehicle wheel comprising a tone wheel driven by the vehicle, the tone wheel being made of magnetic material and having a plurality of equally-spaced teeth defining spaces therebetween, and sensing means mounted adjacent said tone wheel, said sensing means comprising a pair of pole pieces located adjacent said teeth, and a permanent magnet defining an axis and a pair of ends of opposite magnetic polarity, said magnet being located between said pole pieces and disposed so that the axis of the magnet extends parallel to the plane in which said tone wheel rotates, one end of the magnet being magnetically connected to one of the pole pieces so that said one pole piece is magnetized at the polarity of said one end of the magnet, the other end of the magnet being magnetically connected to the other pole piece so that the other pole piece is magnetized at the polarity of the other end of the magnet and opposite to the polarity of the one pole piece, and coil means associated with the pole pieces for providing an output signal in response to changes in the magnetic flux in said pole pieces. .Iaddend..Iadd. 16. A speed sensor as claimed in claim 15, in which the pole pieces are spaced relative to the teeth of the tone wheel so that the phase difference between the flux in said pole pieces is 180°. .Iaddend..Iadd. 17. A speed sensor as claimed in claim 15, in which the pole pieces are spaced relative to the tone wheel so that one of the pole pieces is in registry with a tooth when the other pole piece is in registry with a space between two teeth. .Iaddend..Iadd. 18. A speed sensor as claimed in claim 17, in which the coil means includes a separate coil wound on each pole piece and the coils are connected in series opposition. .Iaddend. .Iadd. 19. A speed sensor for a vehicle wheel comprising a tone wheel driven by the vehicle, the tone wheel being made of magnetic material and having a plurality of equally-spaced teeth defining spaces therebetween, and sensing means mounted adjacent said tone wheel, said sensing means comprising a pair of pole pieces located adjacent said teeth, said pole pieces being spaced so that the axis of one of said pole pieces is always in registry with one of said spaces when the axis of the other pole piece is in registry with one of said teeth, and the axis of said other pole piece is always in registry with one of said spaces when the axis of said one pole piece is in registry with one of said teeth, regardless of the angular position of the tone wheel, so that the phase difference between the flux in said pole pieces is 180° , means magnetically connecting said pole pieces to define a flux path between the pole pieces, said last-mentioned means including means for magnetizing the pole pieces so that the pole pieces have opposite polarity, and coil means associated with the pole pieces for providing an output signal in response to changes in magnetic flux in said pole pieces. .Iaddend.