Pulse-controlled electric power-assisted steering system

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).