Pulse-controlled electric power-assisted steering system

• US 20030057902A1
• Filed: 09/26/2002
• Published: 03/27/2003
• Est. Priority Date: 09/26/2001
• Status: Active Grant

• Current Assignee: SNR Roulements
• Original Assignee: SNR Roulements
• Inventors: Desbiolles, Pascal, Nicot, Christophe, Friz, Achim
• Granted Patent: US 6,686,713 B2
• Time in Patent Office: Days
• US Class Current: 318/254
• CPC Class Codes: B62D 15/0235 by measuring or deriving directly at the electric power steering motor
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position

Abstract

The invention relates to an electric power-assisted steering system making it possible to apply an assist torque for the angular displacement of the wheels of a vehicle, said torque being applied by an electronically commutated motor (2) comprising P phases and N pairs of poles, said system also comprising a device for controlling the motor (2) comprising a circular multipole encoder (17) comprising a main multipole track (17a) and a multipole commutation track (17b) comprising magnetic singularities (17b1-17b6) equidistributed angularly, a fixed sensor (19) capable of delivering square digital signals A, B in quadrature, and a signal C in the form of 2*P*N pulses per revolution of the rotor (3), a circuit for commutating (20) the currents in the phase windings of the motor (2) and a control circuit (21) for the commutation circuit (20).

Claims

1. An electric power-assisted steering system making it possible to apply an assist torque for the angular displacement of the wheels of a vehicle, said torque being applied by an electronically commutated motor (2) comprising P phases and N pairs of poles, said system also comprising a device for controlling the motor (2) comprising:

a circular multipole encoder (17) intended to perform, together with the rotor (3) of the motor (2), a plurality of revolutions around its axis of rotation, said encoder (17) comprising a main multipole track (17a) and a multipole commutation track (17b) comprising magnetic singularities (17b1-17b6) equidistributed angularly, the main (17a) and commutation (17b) tracks being concentric on the encoder (17);

a fixed sensor (19) disposed opposite and at air gap distance from the encoder (17), said sensor (19) comprising at least three sensing elements, at least two of which are positioned opposite the main track (17a) so as to deliver square digital signals A, B in quadrature, and at least one of which is positioned opposite the commutation track (17b) so as to deliver a signal C in the form of 2*P*N pulses per revolution of the rotor (3);

a circuit for commutating (20) the currents in the phase windings of the motor (2) having 2*P*N switches (T1-T6);

a control circuit (21) for the commutation circuit (20) which;

from the signal C supplies commutation signals for the switches (T1-T6); and

from the signals A, B and according to a torque set point (Γ

) defines a current set point (Iref) which controls the current (Im) supplying the phase windings of the motor (2),

2. A system according to claim 1, characterised in that the encoder (17) is associated with the rotating ring (27) of an anti-friction bearing (30) allowing the rotation of the rotor (3), the commutation track (17b) comprising 2*P*N magnetic singularities (17b1-17b6).

3. A system according to claim 1, characterised in that it comprises, associated with the motor (2), a reduction gear (40) of ratio M between the rotation of the rotor (3) and that of the column (1), the encoder (17) being associated with the rotating ring (41) of an output anti-friction bearing (42) of the reduction gear (40) and the commutation track (17b) comprising 2*P*N*M magnetic singularities.

4. A system according to claim 2 or 3, characterised in that the sensor (19) is associated with the fixed ring of the anti-friction bearing (30, 42) having the encoder (17).

5. A system according to any one of claims 1 to 4, characterised in that it comprises a steering column (1), the motor (2) applying a force on the transmission shaft of the column (1).

6. A system according to any one of claims 1 to 4, characterised in that it comprises a steering column (1) associated with a rack pinion (10), the motor (2) applying a force on the rack pinion (10).

7. A system according to any one of claims 1 to 4, characterised in that it comprises a steering rack (11), the motor (2) applying a force on said rack (11) or on a member (15) associated collinearly with said rack (11).

8. A system according to any one of claims 1 to 7, characterised in that the control circuit (21) comprises a regulation loop controlled by the current set point (Iref) originating from an electronic circuit (22), said control circuit (21) being capable of modulating the commutation signals in terms of width and duration by means of an AND logic function (26).

9. A system according to any one of claims 1 to 8, characterised in that the control circuit (21) is implemented in the form of a microprocessor (25) integrating at least one commutation logic for the commutation circuit (20).

10. A system according to any one of claims 1 to 9, characterised in that the encoder (17) is formed from a multipole magnetic ring on which there are magnetised a plurality of pairs of equidistributed North and South poles (18) with a constant angular width so as to form the main track (17a) and commutation track (17b), a magnetic singularity (17b1-17b6) being formed from two pairs of poles which are different from the others.

11. A system according to claim 10, characterised in that the sensing elements are chosen from amongst the group comprising Hall effect sensors, magnetoresistors and giant magnetoresistors.

12. A system according to any one of claims 1 to 9, characterised in that the encoder (17) is formed from a target on which the reference (17a) and commutation (17b) tracks have been etched so as to form an optical pattern analogous to a multipole magnetic pattern, the sensing elements then being formed from optical detectors.

13. A system according to claim 11 or 12, characterised in that the sensor (19) comprises a plurality of aligned sensing elements which are disposed opposite and at air gap distance from the main track (17a).

14. A system according to any one of claims 1 to 13, characterised in that the sensor (19) comprises an interpolator increasing the resolution of the output signals.

15. A system according to any one of claims 1 to 14, characterised in that the sensor (19) is integrated in an ASIC type circuit.