Method and apparatus for sensing relative position between two relatively rotatable members

Claims

Having described a preferred embodiment of the invention, the following is claimed:

1. An apparatus for sensing the relative rotational position between first and second relatively rotatable members, comprising:

a transmitter disk having a planar surface and being mountable to said first member so that said planar surface of said transmitter disk is substantially perpendicular the an axis of rotation of the first and second members, said transmitter disk having a conductive material mounted to said planar surface and patterned in the form of a circle having a sinusoidally modified diameter; and

a receiving disk having a planar surface and being mountable to said second member so that said planar surface of said receiving disk is substantially perpendicular the an axis of rotation of the first and second members, said receiving disk having a conductive material mounted thereon and arranged in a pattern so as to receive a signal from said transmitter disk and output a signal indicative of the relative rotational position of the first and second members.

2. The apparatus of claim 1 wherein said pattern of conductive material mounted on said receiving disk is in the form of a circle having a square wave modified diameter.

3. The apparatus of claim 1 wherein said receiving disk includes three separate layers, each layer having a conductive material pattern on each side of the layer, the layers being electrically insulated from each other by an insulating material.

4. The apparatus of claim 3 wherein the patterns on each layer of said receiving disk has its conductive material pattern electrically offset from those on an adjacent layer by 120 electrical degrees.

5. The apparatus of claim 3 wherein the patterns of conductive material on opposite sides of a layer are offset from each other by 180 electrical degrees.

6. The apparatus of claim 1 further including a rotary coupling transformer operatively mounted between a stationary member and the first rotary member, a primary coil of said rotary coupling transformer being electrically connectable to a sinusoidal drive signal, a secondary coil of said rotary coupling transformer being electrically connected to the conductive layer of said transmitting disk for providing a drive signal to said transmitting disk.

7. The apparatus of claim 1 wherein said transmitter disk and said receiving disk each include an associated backing member mounted thereto and made from a material having a magnetic permeability greater than one.

8. The apparatus of claim 7 wherein said backing members are made from a material having a magnetic permeability equal to 40.

9. An apparatus for sensing the relatively rational position between a stator and a rotor of a variable reluctance motor, said apparatus comprising:

a transmitter disk having a planar surface and being mountable to said rotor so that said planar surface of said transmitter disk is substantially perpendicular the an axis of rotation of said rotor, said transmitter disk having a conductive material mounted to said planar surface and patterned in the form of a circle having a sinusoidal modified diameter; and

a receiving disk having a planar surface and being mountable to said stator so that said planar surface of said receiving disk is substantially perpendicular the an axis of rotation of the rotor, said receiving disk having a conductive material mounted thereon and arranged in a pattern so as to receive a signal from said transmitter disk and output a signal indicative of the relative rotational position of said rotor relative to said stator;

means for coupling a transmitting signal to said conductive layer of said transmitter disk; and

means for receiving an output signal from said conductive material of said receiving disk.

10. The apparatus of claim 9 wherein said receiving disk includes three disk layers, each disk layer having a conductive material patterns on side, each disk layer being electrically insulated from an adjacent layer by an insulated layer and electrically offset from a conductive pattern on an adjacent disk layer by 120 degrees, said receiving means monitoring the output of the three patterns and determining relative position in response to the three output signals.

11. The apparatus of claim 9 wherein said means for coupling includes a rotary coupling transformer operatively mounted between a motor housing and the rotor member, a primary coil of said rotary coupling transformer being electrically connectable to a sinusoidal drive signal, a secondary coil of said rotary coupling transformer being electrically connected to the conductive layer of said transmitting disk for providing a drive signal to said transmitting disk.

12. The apparatus of claim 9 wherein said transmitter disk and said receiving disk each include an associated backing member mounted thereto and made from a material having a magnetic permeability greater than one.

13. The apparatus of claim 12 wherein said backing members are made from a material having a magnetic permeability equal to 40.

14. The apparatus of claim 9 wherein said pattern of conductive material mounted on said receiving disk is in the form of a circle having a square wave modified diameter.

15. A method for sensing the relative rotational position between first and second relatively rotatable members, comprising:

(a) providing a transmitter disk having a planar surface;

(b) securing a conductive material to the planar surface of the transmitter disk in a circular pattern having a sinusoidal diameter;

(c) mounting said transmitter disk to said first member so that said planar surface of said transmitter disk is substantially perpendicular the an axis of rotation of the first and second members; and

(d) providing a receiving disk having a planar surface;

(e) securing a conductive material to the planar surface of the receiving disk in a pattern so as to receive a signal from the transmitter disk and output of a signal indicative of the relative rotational position of the first and second members; and

(f) mounting said receiving disk to said second member so that said planar surface of said receiving disk is substantially perpendicular the an axis of rotation of the first and second members.

16. The method of claim 15 wherein said step of securing a conductive material to said receiving disk includes securing coil patters to each side of three disk layers and electrically insulating each layer from adjacent layers and securing the layers together so that the patterns are electrically offset from each other by 120 degrees.

17. The method of claim 15 further including the steps of mounting a rotary coupling transformer operatively between a stationary member and the first rotary member, connecting a primary coil of said rotary coupling transformer to a sinusoidal drive signal, and connecting a secondary coil of said rotary coupling transformer to the conductive layer of said transmitting disk for providing a drive signal to said transmitting disk.

18. The method of claim 15 wherein the step of securing a conductive material to the planar surface of the receiving disk includes forming said pattern in a circle with a squarewave diameter.

19. A method sensing the relative rational position between a stator and a rotor of a variable reluctance motor, said method comprising the steps of:

(a) providing a transmitter disk having a planar surface;

(b) mounting said transmitter disk to said rotor so that said planar surface of said transmitter disk is substantially perpendicular to an axis of rotation of said rotor;

(c) securing a conductive material to said planar surface of said transmitter disk in a circular pattern having a sinusoidal diameter;

(d) providing a receiving disk having a planar surface;

(e) mounting said receiving disk to said stator so that said planar surface of said receiving disk is substantially perpendicular the an axis of rotation of the rotor;

(f) securing a conductive material to said planar surface of said receiving disk in a circular pattern with a squarewave diameter so as to receive a signal from said transmitter disk and output a signal indicative of the relative rotational position of said rotor relative to said stator;

(g) coupling a transmitting signal to said conductive layer of said transmitter disk; and

(h) receiving an output signal from said conductive material of said receiving disk.

20. The method of claim 19 wherein said step of securing a conductive material to said planar surface of said receiving disk in a pattern so as to receive a signal from said transmitter disk and output a signal indicative of the relative rotational position of said rotor relative to said stator includes securing coil patterns to each side of three separate disk layers and electrically insulating the three layers from each other, and electrically offsetting each of the patterns from a pattern on an adjacent disk by 120 electrical degrees, and wherein the method further includes the steps of monitoring the output of the three disk layers, and determining the relative position in response to the three output signals.

21. The apparatus of claim 19 wherein the step of coupling includes the step of mounting a rotary coupling transformer between a motor housing and the rotor member, connecting a primary coil of said rotary coupling transformer to a sinusoidal drive signal, connecting a secondary coil of said rotary coupling transformer to the conductive layer of said transmitting disk for providing a drive signal to said transmitting disk.

22. An apparatus for sensing position of a rotor relative to a stator in a variable reluctance motor, said apparatus comprising:

a first disk having a planar surface, said first disk mounted to said rotor so that said planar surface of said first disk is substantially perpendicular to the axis of rotation of the rotor;

a second disk having a planar surface, said second disk being mounted so as to be stationary relative to the stator and adjacent said first disk with said planar surface of said first and second disks being substantially parallel;

a transmitter coil carried by one of said first and second disks, said transmitter coil being in a circular shape having a diameter modified by a sinusoid;

a receiving coil carried by the other of said first and second disks;

means for generating a drive signal and coupling said drive signal to said transmitter coil; and

means for monitoring the output of said receiving coil and for determining the relative rotation between the rotor and the stator in response to the monitored signal.

23. The apparatus of claim 22 wherein said means for generating a drive signal and coupling said drive signal to said transmitter coil includes a rotary transformer having its primary coil mounted stationary relative to said stator and its secondary mounted to said rotor, said secondary of said rotary transformer being electrically connected to the transmitter coil, said transmitter coil being carried by the disk mounted to said rotor.

24. The apparatus of claim 22 wherein said pattern of conductive material mounted on said receiving disk is in the form of a circle having a square wave modified diameter.

25. An apparatus for sensing position of a rotor relative to a stator in a variable reluctance motor, said apparatus comprising:

a first disk having a planar surface, said first disk mounted to said rotor so that said planar surface of said first disk is substantially perpendicular to the axis of rotation of the rotor;

a second disk having a planar surface, said second disk being mounted so as to be stationary relative to the stator and adjacent said first disk with said planar surface of said first and second disks being substantially parallel;

a transmitter coil carried by one of said first and second disks, said transmitter coil being two coils, each in the shape of a circle having a sinusoidal diameter and being mounted to an associated side of one of the disks with the sinusoids being 180 degrees out of phase;

a receiving coil carried by the other of said first and second disks;

means for generating a drive signal and coupling said drive signal to said transmitter coil; and

means for monitoring the output of said receiving coil and for determining the relative rotation between the rotor and the stator in response to the monitored signal.

26. An apparatus for sensing position of a rotor relative to a stator in a variable reluctance motor, said apparatus comprising:

a first disk having a planar surface, said first disk mounted to said rotor so that said planar surface of said first disk is substantially perpendicular to the axis of rotation of the rotor;

a second disk having a planar surface, said second disk being mounted so as to be stationary relative to the stator and adjacent said first disk with said planar surface of said first and second disks being substantially parallel;

a transmitter coil carried by one of said first and second disks;

a receiving coil carried by the other of said first and second disks, said receiving coil including three disk layers, each layer having a receiving coil pattern having the same shape and mounted to said other of said first and second disks in electrically insulated layers, said receiving coil patterns being offset from an adjacent disk receiving coil pattern by 120 electrical degrees;

means for generating a continuous alternating current drive signal and coupling said continuous alternating current drive signal to said transmitter coil; and

means for monitoring the output of said receiving coil and for determining the relative rotation between the rotor and the stator in response to the monitored signal.

27. A method for sensing position of a rotor relative to a stator in a variable reluctance motor, said method comprising the steps of:

(a) providing a first disk having a planar surface;

(b) mounting said first disk to said rotor so that said planar surface of said first disk is substantially perpendicular to the axis of rotation of the rotor;

(c) providing a second disk having a planar surface;

(d) mounting said second disk so as to be stationary relative to the stator and adjacent said first disk with said planar surface of said first and second disks being substantially parallel;

(e) providing a transmitter coil and mounting said transmitter coil in the shape of a circle having a sinusoidal diameter to one of said first and second disks;

(f) providing a receiving coil and mounting said receiving coil to the other of said first and second disks;

(g) generating a drive signal;

(h) coupling said drive signal to said transmitter coil;

(i) monitoring the output of said receiving coil; and

(j) determining the relative rotation between the rotor and the stator in response to the monitored signal.

28. The apparatus of claim 27 wherein said step of generating a drive signal and coupling said drive signal to said transmitter coil includes providing a rotary transformer, mounting a primary coil of said rotary transformer to a stationary member, stationary relative to said stator, mounting the secondary of the rotary transformer to said rotor, connecting said secondary of said rotary transformer to the transmitter coil, and mounting said transmitter coil to said disk mounted to said rotor.

29. The method of claim 27 wherein the step of providing a receiving coil includes mounting a receiving coil in the shape of a circle having a squarewave diameter.

30. A method for sensing position of a rotor relative to a stator in a variable reluctance motor, said method comprising the steps of:

(a) providing a first disk having a planar surface;

(b) mounting said first disk to said rotor so that said planar surface of said first disk is substantially perpendicular to the axis of rotation of the rotor;

(c) providing a second disk having a planar surface;

(d) mounting said second disk so as to be stationary relative to the stator and adjacent said first disk with said planar surface of said first and second disks being substantially parallel;

(e) providing transmitter coils, each in the shape of a circle having a sinusoidal diameter and mounting said transmitter coils to an associated side of one of said first and second disks so that their circles are 180 degrees out of phase relative to each other;

(f) providing a receiving coil and mounting said receiving coil to the other of said first and second disks;

(g) generating a drive signal;

(h) coupling said drive signal to said transmitter coil;

(i) monitoring the output of said receiving coil; and

(j) determining the relative rotation between the rotor and the stator in response to the monitored signal.

31. A method for sensing position of a rotor relative to a stator in a variable reluctance motor, said method comprising the steps of:

(a) providing a first disk having a planar surface;

(b) mounting said first disk to said rotor so that said planar surface of said first disk is substantially perpendicular to the axis of rotation of the rotor;

(c) providing a second disk having a planar surface;

(d) mounting said second disk so as to be stationary relative to the stator and adjacent said first disk with said planar surface of said first and second disks being substantially parallel;

(e) providing a transmitter coil and mounting said transmitter coil to one of said first and second disks;

(f) providing a receiving coil and mounting said receiving coil to the other of said first and second disks so that said receiving coil includes three coil patterns having the same shape mounted in three separate electrically insulated layers and offset from each other by 120 electrical degrees;

(g) generating a continuous alternating current drive signal;

(h) coupling said continuous alternating current drive signal to said transmitter coil;

(i) monitoring the output of said receiving coil; and

(j) determining the relative rotation between the rotor and the stator in response to the monitored signal.

TECHNICAL FIELD

The present invention is directed to a method and apparatus for sensing the relative rotational position between two relatively rotatable members. The invention has particular use for sensing the relative position of a rotor and stator in a variable reluctance motor for control of the motor's commutation in an electric assist steering system for vehicles.

BACKGROUND OF THE INVENTION

There are many known power assist steering systems for automotive vehicles. Some provide steering assist by using hydraulic power and others by using electric power.

Electric power assist steering systems that utilize a rack and pinion gear set provide power assist by using an electric motor to either (i) apply rotary force to a steering input shaft connected to a pinion gear, or (ii) apply linear force to a steering member having the rack teeth thereon. The electric motor in such systems is typically controlled in response to (i) a driver's applied torque to the vehicle steering wheel, and (ii) sensed vehicle speed.

In U.S. Pat. No. 3,983,953, an electric motor is coupled to the input steering shaft and energized in response to the torque applied to the steering wheel by the vehicle operator. An electronic control system includes a torque sensor and a vehicle speed sensor. A computer receives the output signals provided by both sensors. The computer controls the amount of the assistance provided by the motor dependent upon the applied steering torque and the sensed vehicle speed.

U.S. Pat. No. 4,415,054 (now U.S. Reissue Pat. No. 32,222, hereinafter, "the Drutchas steering gear") utilizes an D.C. electric assist motor driven through an H-bridge arrangement. The motor includes a rotatable armature encircling a steering member which has a thread convolution portion thereon and a portion having straight cut rack teeth thereon. Rotation of the electric assist motor armature causes linear movement of the steering member through a ball-nut drive arrangement in combination with the thread convolution portion of the steering member. A torque sensing device is coupled to the steering column to sense driver applied input torque to the steering wheel. The torque sensing device uses a magnetic Hall-effect sensor arrangement for sensing relative rotation between the input and output shafts across a torsion bar. An electronic control unit monitors the signal from the torque sensing device and controls the electric assist motor in response thereto.

U.S. Pat. No. 4,660,671 discloses an electric controlled steering system that is based on the Drutchas steering gear. In the arrangement disclosed in the '671 patent, the D.C. motor is axially spaced from the ball-nut and is operatively connected thereto through a connection tube. The electronic controls includes a plurality of diagnostic features that monitor the operation of the steering system. If an error in the operation of the electric steering system is detected, the power assist system is disabled and steering reverts to an unassisted mode.

Known electric steering systems have used a D.C. permanent magnet motor driven through a H-bridge drive circuit. It is desirable to use a variable reluctance motor for an electric assist steering system because of its smaller size and larger torque-to-inertia ratio. Proper commutation of a variable reluctance motor requires a "knowledge" of the rotor's position relative to the stator.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for sensing the relative rotational position between two relatively rotatable members.

In accordance with one embodiment of the present invention, an apparatus is provided for sensing the relative rotational position between first and second relatively rotatable members. The apparatus comprises a transmitter disk having a planar surface and being mountable to said first member so that said planar surface of said transmitter disk is substantially perpendicular the an axis of rotation of the first and second members. The transmitter disk has a conductive material mounted to said planar surface and patterned in the form of a circle whose diameter is modified by a multi-pole sinusoid. A receiving disk has a planar surface and is mountable to said second member so that said planar surface of said receiving disk is substantially perpendicular the axis of rotation of the first and second members. The receiving disk has a conductive material mounted thereon and arranged in a circular pattern whose diameter is modified by a square wave so as to receive a signal from the transmitter disk and output a signal indicative of the relative rotational position of the first and second members.

In accordance with another embodiment of the present invention, a method is provided for sensing the relative rotational position between first and second relatively rotatable members, comprising the steps of: (a) providing a transmitter disk having a planar surface; (b) securing a conductive material to the planar surface of the transmitter disk in a circular pattern with a diameter modified by a sinusoid; (c) mounting said transmitter disk to said first member so that said planar surface of said transmitter disk is substantially perpendicular to an axis of rotation of the first and second members; (d) providing a receiving disk having a planar surface; (e) securing a conductive material to the planar surface of the receiving disk in a circular pattern with a diameter modified by a squarewave so as to receive a signal from the transmitter disk and output of a signal indicative of the relative rotational position of the first and second members; and (f) mounting said receiving disk to said second member so that said planar surface of said receiving disk is substantially perpendicular to the an axis of rotation of the first and second members.

In accordance with a preferred embodiment of the present invention an apparatus is provided for sensing position of a rotor relative to a stator in a variable reluctance motor, said apparatus comprising a first disk having a planar surface, said first disk mounted to said rotor so that said planar surface of said first disk is substantially perpendicular to the axis of rotation of the rotor. A second disk is provided having a planar surface, said second disk being mounted so as to be stationary relative to the stator and adjacent said first disk with said planar surface of said first and second disks being substantially parallel. A transmitter coil is carried by one of said first and second disks. A receiving coil is carried by the other of said first and second disks. Means are provided for generating a drive signal and coupling said drive signal to said transmitter coil. Means are also provided monitoring the output of said receiving coil and for determining the relative rotation between the rotor and the stator in response to the monitored signal. The transmitter coil is preferably a circular shape having a diameter in the form of two sinusoids 180 degrees out of phase, each sinusoid being mounted to an associated side of its disk and electrically insulated from the other sinusoidal pattern. The receiving coil preferably includes three dual coil circular patterns mounted to associated disk layers. Each disk has a square wave pattern on each side, the patterns on one disk being 180 mechanical degrees out of phase with each other. The square wav