Device for determining the position of a magnetic element using linear hall-effect cells

1. A method for determining the position of a magnetic element ( 50 ) using a device ( 1 ), said magnetic element ( 50 ) being able to be moved in at least two directions relative to a longitudinal axis (A), a first direction, called the main direction (Z), and a second direction, called the secondary direction (X), said device comprising:

a position sensor ( 60 ) comprising two sets of two Hall-effect cells measuring the same magnetic field generated by the magnetic element, a first set comprising a first cell ( 70 a ) and a second cell ( 70 b ) along a first axis (B) substantially perpendicular to the longitudinal axis (A), and a second set comprising a third cell ( 70 c ) and a fourth cell ( 70 d ) along a second axis (C) substantially parallel to the first axis (B), the magnetic element being moveable relative to said two sets of two Hall-effect cells;

means ( 90 ) for measuring voltages output by each Hall-effect cell;

first means ( 91 ) for calculating the position of the magnetic element in the main direction (Z); and

second means ( 92 ) for calculating the position of the magnetic element in the secondary direction (X), said method being characterized in that it comprises steps of:

measuring a voltage output by each Hall-effect cell using the measuring means ( 90 );

calculating, using the second calculating means ( 92 ), a value P calculated from a geometric mean √{square root over (V 1 2 +V 2 2 )}, √{square root over (V 3 2 +V 4 2 )} depending on four measured voltages V 1 ,V 2 ,V 3 ,V 4 , where V 1 is the voltage across the terminals of the first cell ( 70 a ), V 2 the voltage across the terminals of the second cell ( 70 b ), V 3 the voltage across the terminals of the third cell ( 70 c ), and V 4 the voltage across the terminals of the fourth cell ( 70 d ); and

determining the position of the magnetic element ( 50 ) in the secondary direction (X) using the calculated value P.

2. The method as claimed in claim 1 , in which the value P is calculated such that it equals:

either a ratiometric ratio P 1 given by

P

1

=

V

1

2

+

V

2

2

k

⁢

V

1

2

+

V

2

2

+

V

3

2

+

V

4

2

,

where k is a preset constant;

or a ratiometric ratio P 2 given by

P

2

=

V

3

2

+

V

4

2

k

⁢

V

3

2

+

V

4

2

+

V

1

2

+

V

2

2

,

the choice depending on the result of a comparison between the two geometric means.

3. The method as claimed in claim 2 , in which the value P is chosen such that:

P=P 1 when √{square root over ( V 1 2 +V 2 2 )}≦√{square root over ( V 3 2 +V 4 2 )};

P= 2 −P 1 when √{square root over ( V 1 2 +V 2 2 )}≧√{square root over ( V 3 2 +V 4 2 )}.

4. The method as claimed in claim 2 , comprising a step of calibrating the value of at least one of the following elements:

size of the magnetic element ( 50 );

distance separating, on the longitudinal axis, the two sets,

depending on a relationship describing the variation in the geometric mean of each set, said geometric means themselves depending on the position of the magnetic element ( 50 ) relative to said sets.

5. The method as claimed in claim 2 , comprising a step of determining the position of the magnetic element ( 50 ) in the main direction (Z) by calculating an arctangent between the first voltage V 1 and the second voltage V 2 and/or by calculating an arctangent between the third voltage V 3 and the fourth voltage V 4 , using the first calculating means ( 91 ).

6. The method as claimed in claim 3 , comprising a step of calibrating the value of at least one of the following elements:

size of the magnetic element ( 50 );

distance separating, on the longitudinal axis, the two sets,

depending on a relationship describing the variation in the geometric mean of each set, said geometric means themselves depending on the position of the magnetic element ( 50 ) relative to said sets.

7. The method as claimed in claim 3 , comprising a step of determining the position of the magnetic element ( 50 ) in the main direction (Z) by calculating an arctangent between the first voltage V 1 and the second voltage V 2 and/or by calculating an arctangent between the third voltage V 3 and the fourth voltage V 4 , using the first calculating means ( 91 ).

8. The method as claimed in claim 1 , comprising a step of calibrating the value of at least one of the following elements:

size of the magnetic element ( 50 );

distance separating, on the longitudinal axis, the two sets,

depending on a relationship describing the variation in the geometric mean of each set, said geometric means themselves depending on the position of the magnetic element ( 50 ) relative to said sets.

9. The method as claimed in claim 8 , comprising a step of determining the position of the magnetic element ( 50 ) in the main direction (Z) by calculating an arctangent between the first voltage V 1 and the second voltage V 2 and/or by calculating an arctangent between the third voltage V 3 and the fourth voltage V 4 , using the first calculating means ( 91 ).

10. The method as claimed in claim 1 , comprising a step of determining the position of the magnetic element ( 50 ) in the main direction (Z) by calculating an arctangent between the first voltage V 1 and the second voltage V 2 and/or by calculating an arctangent between the third voltage V 3 and the fourth voltage V 4 , using the first calculating means ( 91 ).

11. The method as claimed in claim 10 , in which the main direction (Z) is that of the rotation of the magnetic element about the longitudinal axis (A), and the secondary direction (X) is that of the translation of the magnetic element along said longitudinal axis (A).

12. The method as claimed in claim 1 , in which the main direction (Z) is that of the rotation of the magnetic element about the longitudinal axis (A), and the secondary direction (X) is that of the translation of the magnetic element along said longitudinal axis (A).

13. The method according to claim 1 for detecting the rotation and translation of a gear ratio selector ( 20 ) of a gearbox ( 30 ) of an automotive vehicle, which comprises placing the magnetic element ( 50 ) on the gear ratio selector ( 20 ) of axis, the longitudinal axis (A).

14. A device ( 1 ) for determining the position of a magnetic element ( 50 ), implementing the method as claimed in claim 1 , said magnetic element being able to be moved in at least two directions relative to a longitudinal axis (A), a first direction, called the main direction (Z), and a second direction, called the secondary direction (X), characterized in that the device comprises:

a position sensor comprising two sets of two Hall-effect cells measuring the same magnetic field generated by the magnetic element, a first set comprising a first cell ( 70 a ) and a second cell ( 70 b ) along a first axis (B) substantially perpendicular to the longitudinal axis (A), and a second set comprising a third cell ( 70 c ) and a fourth cell ( 70 d ) along a second axis (C) substantially parallel to the first axis (B), the magnetic element being moveable relative to said two sets of two Hall-effect cells;

means ( 90 ) for measuring voltages output by each Hall-effect cell;

first means ( 91 ) for calculating the position of the magnetic element in the main direction (Z); and

second means ( 92 ) for calculating the position of the magnetic element in the secondary direction (X).