Position sensor, position sensor arrangement and method of operating the same by measuring the angular orientation of a local magnetic field vector

• US 8,305,073 B2
• Filed: 04/23/2008
• Issued: 11/06/2012
• Est. Priority Date: 04/23/2008
• Status: Active Grant

• Current Assignee: Getrag Ford Transmissions GmbH
• Original Assignee: Getrag Ford Transmissions GmbH
• Inventors: Kather, Lutz
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US12/108,216
• Publication Number:
  US 20090267594A1
• Time in Patent Office: 1,658 Days
• Field of Search: 324/207.25, 324/207.2, 324/207.21, 324/174
• US Class Current: 324/207.25
• CPC Class Codes: G01B 7/30 for measuring angles or tapers; for testing the alignment of axes

Abstract

A position sensor, a position sensor arrangement and a method of operating the position sensor and position sensor arrangement is described, working on the basis of magnetic field sensing sensors maximizing reliability against defects and external interference signals and providing redundancy, in particular for shift-by-wire systems in automobiles. The invention includes various aspects and preferred embodiments including individual sensors that can either only measure the direction of the magnetic field or in addition to that the absolute value of the magnetic field. The specific embodiments depend on the desired diagnostic options, redundancy and compensation capabilities both as to interfering magnetic fields and sensor failures or non-plausible output signals of individual sensors. An evaluation unit can be provided for compensating measurement deviations. Goals are to make the position sensor compact in size, cost effective, maximize reliability against defects and external interference signals, have diagnostic ability and provide redundancy.

Claims

1. Position sensor for a contactless determination of a position by means of redundant magnet-sensitive sensor elements, comprising:

a giver unit and a sensor unit that is movable in relation to the giver unit within a predetermined position determination range, wherein

the giver unit comprises permanent magnet areas disposed in a ring or ring segment pattern and comprises an alternating pole sequence in the direction of the relative movement, so that for the sensor unit an inhomogeneous, alternating magnetic field results,

the sensor unit comprises at least two magnet-sensitive sensor elements that generate one or more electrical output signals that are at least dependent on the respective local magnetic field direction, and that are disposed at different positions adjacent to the surface of the giver unit, wherein the predetermined position determination range and the pole sequence of the giver unit are to interact such that each sensor element during a relative motion between giver and sensor unit over the entire given determination range senses a change of the magnetic field direction of maximally 360 deg., so that each sensor element over the given position determination range generates an output signal that is definite for each particular relative position between giver and sensor unit, and

at least two pairs of poles on the giver unit and at least two sensor elements are provided, wherein each sensor element is arranged in the magnetic sphere of influence of another pole of the giver unit,

wherein at least one of the sensor elements is a multidimensionally measuring sensor element that measures an angular orientation of the magnetic field in at least 2 dimensions for determining the direction of a respective local magnetic field vector; and

the sensors are connectable to a data processing unit for computing an interference vector and determining corrected vectors by subtracting that interference vector from measured real magnetic field vectors.

2. The position sensor according to claim 1, wherein all of the sensor elements are multidimensionally measuring sensor elements that measure the angular orientation of the magnetic field in at least 2 dimensions for determining the direction of the respective local magnetic field vector.

3. The position sensor according to claim 1, wherein the position sensor is to measures an angle of the rotation, wherein the giver unit is designed as a ring magnet with a number of pairs of poles N of at least two, and wherein the predetermined position determination range is an angle of 360/N degrees or less.

4. The position sensor according to claim 3, wherein the magnetic field of the giver unit is rotationally symmetrically with regard to a rotation around an angle of 360/N degrees, and that the sensor elements are arranged at such respective angular positions along the inner or outer circumference of the ring magnet that these are offset with respect to each other by an angle of approximately 360/N degrees or of approximately 180/N degrees, wherein in the latter case all sensor elements are positioned within an angular range of in total 180 degrees.

5. The position sensor according to claim 1, wherein each of the sensor elements comprises a predetermined axis of reference in relation to which the magnetic field direction is measured, wherein the angular orientation of the reference axis of at least one sensor element deviates from the angular orientation of the reference axis of at least another sensor element, wherein all reference axes differ in orientation and the reference axes of all sensor elements are oriented such that over the entire given measuring range each sensor generates a different absolute value of the output signals distinguishing from all other sensors.

6. The position sensor according to claim 1, wherein at least one of the sensor elements is to measure the absolute value as well as the angular orientation of the respective local magnetic field vector.

7. The position sensor according to claim 1, wherein all of the sensor elements are to measure the absolute value as well as the angular orientation of the respective local magnetic field vector.

8. Position sensor arrangement with a position sensor according to claim 1 and an evaluating processor unit connected to the position sensor, wherein the evaluating processor unit is to compute the relative position between sensor unit and giver unit from the sensor output signals and to determine a plausibility signal for the sensor output signals and correct an output signal from one sensor element that is determined as incorrect on the basis of the output signals of the remaining sensor elements.

9. The position sensor arrangement according to claim 6, further comprising an evaluation unit that is to compute from the output signals of the individual sensor elements respective sensor-specific relative positions based on a stored functional interrelation, to compare the relative positions derived from the individual sensor elements, and in case of deviations exceeding a given threshold value, mark the respective relative position as non-plausible.

10. The position sensor arrangement according to claim 6, further comprising sensor elements that are completely or partly to measure the absolute value as well as the angular orientation of the respective local magnetic field vector;

and an evaluation unit that is to compute on the basis of the magnetic field vectors measured by the individual sensor elements a computed geometrical center, to compute a difference vector between the computed geometrical center and the position of an actual center of the sensor arrangement, and to correct the respective individual magnetic field vectors by means of this difference vector.

11. The position sensor arrangement according to claim 6, further comprising an evaluation unit is connected to a read-only-memory and is to store during a learning phase for each of the sensor elements the respective absolute value of the magnet field vector and the related magnetic field orientation for one or several predetermined relative positions as a data set belonging together, and during the actual operation determine from the measured magnetic field direction for the individual sensor elements an estimated absolute value of the magnetic field vector, and in case of a deviation between the estimated value and measured value exceeding a threshold value, to discard the measured value of the respective sensor output value as non-plausible.

12. The position sensor arrangement according to claim 6, wherein the position sensor comprises three sensor elements, wherein in case the relative positions determined from the output signals of two sensor elements coincide within a predetermined measuring tolerance and the output signal of the third sensor element appears non-plausible, the output signal from the third sensor element is not considered for determination of the relative position.

13. A method for a contactless determination of a position by means of redundant magnet-sensitive sensor elements, comprising the steps of:

providing and fixing a giver unit comprising permanent magnet areas disposed in a ring or ring segment pattern and comprises an alternating pole sequence in a direction of relative movement, so that for the sensor unit an inhomogeneous, alternating magnetic field results,

providing and moving a sensor unit having at least 2 sensor elements in the direction of relative movement in relation to the giver unit along a predetermined rotational movement path within a predetermined position determination range of less than 360 degrees,

measuring an angular orientation of the magnetic field in at least 2 dimensions for determining the direction of respective local magnetic field vectors by at least one of the 2 sensor elements,

correlating the angular orientation of the local magnetic field vectors to the relative movement position between the giver unit and the sensor unit; and

computing an interference vector and determining corrected vectors by subtracting that interference vector from measured real magnetic field vectors.

14. The method for a contactless determination of a position by means of redundant magnet-sensitive sensor elements according to claim 13, wherein the correlating step is performed by obtaining the relative movement position between the giver unit and the sensor unit from a value gathered from a prestored table that was obtained by training through measuring an number of relative movement position externally and sensing the 2 correlating local magnetic field vectors orientations for the respective relative movement position.

15. The method for a contactless determination of a position by means of redundant magnet-sensitive sensor elements according to claim 13, comprising the step of additionally measuring the absolute value of the respective local magnetic field vector.

16. The method for a contactless determination of a position by means of redundant magnet-sensitive sensor elements according to claim 13, comprising the steps of calculating a mean angle from the correlated angle for the relative movement position between the giver unit and the sensor unit.

17. The method for a contactless determination of a position by means of redundant magnet-sensitive sensor elements according to claim 13, comprising the steps of determining whether the corrected vectors all correlate to the same angle of rotation and in the affirmative determine that all sensor elements are working properly.

18. The method for a contactless determination of a position by means of redundant magnet-sensitive sensor elements according to claim 13, comprising the steps of providing at least 3 sensor elements and determining whether the corrected vectors all correlate to the same angle of rotation, wherein in case one corrected vector for one particular sensor element is still outside a permissible range of tolerance, correlating the uncorrected measured real magnetic field vectors of all sensor elements with an angle of rotation, and determine a particular sensor element as defective that has a deviating correlating angle of rotation deviating from the correlating angles of rotation for the other sensor elements.