Rotation angle detector

1. A rotation angle detector comprising:

a magnet arranged to rotate around a rotation axis, and

a magnetic detection circuit provided with

a first pair of magnetic detection elements arranged to be in combination sensitive to a first magnetic field in circumferential direction to said rotation axis and to a second magnetic field in normal direction to said first magnetic field and arranged away from said rotation axis, and configured to detect magnetic flux of said magnet,

a second pair of magnetic detection elements arranged to be in combination sensitive to said first magnetic field in circumferential direction to said rotation axis and to said second magnetic field in normal direction to said first magnetic field, wherein said second pair of magnetic detection elements is arranged with a predetermined interval from said first pair of magnetic detection elements in the circumferential direction to said rotation axis, and

a signal processing unit configured to output a signal representative of a rotation angle of said magnet based on outputs of said first and said second pair of magnetic detection elements.

2. The rotation angle detector as in claim 1 , wherein said signal processing unit is arranged to determine a first magnetic flux density difference in said normal direction and a second magnetic flux density difference in said circumferential direction, from outputs of said first pair of magnetic detection elements and said second pair of magnetic detection elements, and to output a signal representative of said rotation angle of said magnet based on said first and said second magnetic flux density difference.

3. The rotation angle detector as in claim 2 , wherein said signal processing unit is arranged to determine a maximum value of an amplitude of said first magnetic flux density difference and a maximum value of an amplitude of said second magnetic flux density difference based on a rate of change in said amplitudes of said first and said second magnetic flux density difference, and arranged to normalize said amplitudes of said first and said second magnetic flux density difference in accordance with the maximum values of said amplitudes of said first and said second magnetic flux density difference.

4. The rotation angle detector as in claim 1 , wherein said first pair of magnetic detection elements is replaced by a first set of two pairs of magnetic detection elements and said second pair by a second set of two pairs of magnetic detection elements.

5. The rotation angle detector as in claim 4 , wherein said signal processing unit is arranged to determine, from outputs of said first set of two pairs of magnetic detection elements and said second set of two pairs of magnetic detection elements, a third magnetic flux density difference in a radial direction of said rotation and a second magnetic flux density difference in said circumferential direction of said rotation, and to output a signal representative of said rotation angle of said magnet, based on said third magnetic flux density difference and said second magnetic flux density difference.

6. The rotation angle detector as in claim 5 , wherein said signal processing unit is arranged to determine a maximum value of an amplitude of said third magnetic flux density difference and a maximum value of an amplitude of said second magnetic flux density difference based on a rate of change in said amplitudes of said third magnetic flux density difference and said second magnetic flux density difference, and arranged to normalize said amplitude of said third magnetic flux density difference and said amplitude of said second magnetic flux density difference in accordance with said maximum value of said amplitude of said third magnetic flux density difference and said maximum value of said amplitude of said second magnetic flux density difference.

7. The rotation angle detector as in claim 1 , wherein said magnet has a magnetization direction in a direction orthogonal to said rotation axis.

8. The rotation angle detector as in claim 1 , wherein said magnet is divided into two parts by a plane passing through said rotation axis and said two parts are parallel to said rotation axis direction and magnetized in mutually opposite directions.

9. The rotation angle detector as in claim 1 , wherein said magnet is divided into a plurality of parts by a plane passing through said rotation axis in accordance with a rotation angle to be detected, and said plurality of parts are parallel to said rotation axis direction and magnetized in mutually opposite directions.

10. The rotation angle detector as in claim 1 , wherein said magnet is formed only at a partial angle around a central axis.

11. The rotation angle detector as in claim 1 , wherein said magnetic detection elements of said first pair are arranged in a region overlapping with said magnet.

12. The rotation angle detector as in claim 1 , wherein said magnetic detection elements of said first pair are arranged in a region not overlapping with said magnet.

13. An attitude control device comprising the rotation angle detector as in claim 1 .

14. An automatic steering device comprising a rotation angle detector as in claim 1 .

15. A throttle device comprising a rotation angle detector as in claim 1 .