Limp aside steering assist with estimated motor current

1. An electromechanical motor vehicle power steering mechanism for assisting steering of a motor vehicle by conferring torque generated by an electric motor to a steering mechanism, the mechanism comprising:

a steering controller which receives signals representative of at least the vehicle velocity (v) and the torque (T TS ) applied to a steering wheel and a rotor position signal to determine a target motor torque (T d ),

a motor controller which receives the target motor torque (T d ) from the steering controller and transfers it into target voltages (U α,d , U β,d ) expressed in a coordinate system fixed to the stator;

a motor driver which transforms the target voltages (U α,d , U β,d ) into motor currents (I U ,I V ,I W );

at least one current measurement unit which measures the motor currents (I U ,I V ,I W );

a current estimation unit which estimates the target currents (I dest ,I qest =I 1 , est ) and a diagnostic unit which compares the estimated target currents (I dest ,I qest =I 1 , est ) to measured currents (I q1 ,I d1 =I 1 , I q2 ,I d2 =I 2 ), which are transformed from the measured motor currents (I U1 , I V1 , I W1 , I U2 , I V2 , I W2 ) into the two-dimensional d-q coordinate system in order to identify and remedy occurring faults; and

a coordinate transformation unit, transforming the measured motor currents (I U1 , I V1 , I W1 , I U2 , I V2 , I W2 ) into measured currents (I q1 ,I d1 =I 1 , I q2 ,I d2 =I 2 ) expressed in the two-dimensional d-q coordinate system.

2. The electromechanical motor vehicle power steering mechanism according to claim 1 wherein the motor driver comprises an inverter which transforms the voltages (U α,d ,U β,d ) into three-phase voltages (U U , U V , U W =U 2 ).

3. The electromechanical motor vehicle power steering mechanism according to claim 1 wherein the current estimation unit comprises a motor model unit, which is fed by estimated voltages (U Uest , U Vest , U West ) based on the voltages (U U , U V , U W ) outputted by the inverter.

4. The electromechanical motor vehicle power steering mechanism according to claim 3 wherein the mechanism comprises two redundant current measurement units.

5. The electromechanical motor vehicle power steering mechanism according to claim 3 wherein the motor model unit comprises a coordinate transformation which transforms the estimated motor currents into a two-dimensional rotating reference frame (I dest , I qest =I 1 ) fixed to the rotor of the motor.

6. The electromechanical motor vehicle power steering mechanism according to claim 4 wherein the rotational angular velocity (ω) of the rotor and the estimated target voltages (U Uest , U Vest , U West ) and the estimated winding temperature (T Coil ) are at least input parameters for the motor model unit.

7. The electromechanical motor vehicle power steering mechanism of claim 6 wherein the motor driver comprises two shunts to reconstruct the motor currents (I U ,I V ,I W ).

8. The electromechanical motor vehicle power steering mechanism according to claim 1 wherein the diagnostic unit behaves as current feedback control, feeding an actual current (I 2 ) back into the main loop of the motor control circuit.

9. A method for current feedback control in an electromechanical motor vehicle power steering mechanism, said method comprising the steps of:

receiving at least signals representative of the vehicle velocity (v) and the torque (T TS ) applied to a steering wheel and a rotor position signal

determining on the basis of the received signals a target motor torque (T d ) transferring the target motor torque (T d ) into target voltages (U α,d , U β,d ) expressed in a coordinate system fixed to the stator;

transforming the target voltages (U α,d , U β,d ) into motor currents (I U ,I V ,I W );

measuring the motor currents in at least one current measurement unit;

estimating the target currents (I dest ,I qest =I 1 , est ) in a current estimation unit;

comparing the estimated target currents (I dest ,I qest =I 1 , est ) to the measured motor currents (I U1 , I V1 , I W1 , I U2 , I V2 , I W2 ) in a diagnostic unit; and

feeding back an actual motor current (I q,fb ;I d,fb =I 2 ) into the main loop;

wherein the rotational angular velocity (ω) of the rotor, the estimate voltages (U Uest , U Vest , U West ) based on the target voltages (U α,d , U β,d ) and the estimated winding temperature (T Coil ) are input parameters for the motor model unit.

10. The method for current feedback control according to claim 9 wherein the mechanism comprises two redundant current measurement units.

11. An electromechanical motor vehicle power steering mechanism for assisting steering of a motor vehicle by conferring torque generated by an electric motor to a steering mechanism, the mechanism comprising:

a steering controller which receives signals representative of at least the vehicle velocity (v) and the torque (T TS ) applied to a steering wheel and a rotor position signal to determine a target motor torque (T d ),

a motor controller which receives the target motor torque (T d ) from the steering controller and transfers it into target voltages (U α,d , U β,d ) expressed in a coordinate system fixed to the stator;

a motor driver which transforms the target voltages (U α,d , U β,d ) into motor currents (I U ,I V ,I W );

at least one current measurement unit which measures the motor currents (I U ,I V ,I W );

a current estimation unit which estimates the target currents (I dest ,I qest =I 1 , est ) and a diagnostic unit which compares the estimated target currents (I dest ,I qest =I 1 , est ) to measured currents (I q1 ,I d1 =I 1 , I q2 ,I d2 =I 2 ), which are transformed from the measured motor currents (I U1 , I V1 , I W1 , I U2 , I V2 , I W2 ) into the two-dimensional d-q coordinate system in order to identify and remedy occurring faults; and

a coordinate transformation unit, transforming the measured motor currents (I U1 , I V1 , I W1 , I U2 , I V2 , I W2 ) into measured currents (I q1 ,I d1 =I 1 , I q2 ,I d2 =I 2 ) expressed in the two-dimensional d-q coordinate system;

wherein the motor driver comprises an inverter which transforms the voltages (U α,d , U β,d ) into three-phase voltages (U U , U V , U W =U 2 ).

12. The electromechanical motor vehicle power steering mechanism according to claim 11 wherein the current estimation unit comprises a motor model unit, which is fed by estimated voltages (U Uest , U Vest , U West ) based on the voltages (U U , U V , U W ) outputted by the inverter.

13. The electromechanical motor vehicle power steering mechanism according to claim 12 wherein the mechanism comprises two redundant current measurement units.

14. The electromechanical motor vehicle power steering mechanism according to claim 12 wherein the motor model unit comprises a coordinate transformation which transforms the estimated motor currents into a two-dimensional rotating reference frame (I dest , I qest =I 1 ) fixed to the rotor of the motor.

15. The electromechanical motor vehicle power steering mechanism according to claim 14 wherein the rotational angular velocity (ω) of the rotor and the estimated target voltages (U Uest , U Vest , U West ) and the estimated winding temperature (T Coil ) are at least input parameters for the motor model unit.

16. The electromechanical motor vehicle power steering mechanism of claim 15 wherein the motor driver comprises two shunts to reconstruct the motor currents (I U ,I V ,I W ).

17. An electromechanical motor vehicle power steering mechanism for assisting steering of a motor vehicle by conferring torque generated by an electric motor to a steering mechanism, the mechanism comprising:

a steering controller which receives signals representative of at least the vehicle velocity (v) and the torque (T TS ) applied to a steering wheel and a rotor position signal to determine a target motor torque (T d ),

a motor controller which receives the target motor torque (T d ) from the steering controller and transfers it into target voltages (U α,d , U β,d ) expressed in a coordinate system fixed to the stator;

a motor driver which transforms the target voltages (U α,d , U β,d ) into motor currents (I U ,I V ,I W );

at least one current measurement unit which measures the motor currents (I U ,I V ,I W ); and

a current estimation unit which estimates the target currents (I dest ,I qest =I 1 , est ) and a diagnostic unit which compares the estimated target currents (I dest ,I qest =I 1 , est ) to measured currents (I q1 ,I d1 =I 1 , I q2 ,I d2 =I 2 ), which are transformed from the measured motor currents (I U1 , I V1 , I W1 , I U2 , I V2 , I W2 ) into the two-dimensional d-q coordinate system in order to identify and remedy occurring faults;

wherein the diagnostic unit behaves as current feedback control, feeding an actual current (I 2 ) back into the main loop of the motor control circuit.

18. The electromechanical motor vehicle power steering mechanism according to claim 17 further comprising: a coordinate transformation unit, transforming the measured motor currents (I U1 , I V1 , I W1 , I U2 , I V2 , I W2 ) into measured currents (I q1 ,I d1 =I 1 , I q2 ,I d2 =I 2 ) expressed in the two-dimensional d-q coordinate system.

19. The electromechanical motor vehicle power steering mechanism according to claim 18 wherein the motor driver comprises an inverter which transforms the voltages (U α,d , U β,d ) into three-phase voltages (U U , U V , U W =U 2 ).

20. The electromechanical motor vehicle power steering mechanism according to claim 19 wherein the current estimation unit comprises a motor model unit, which is fed by estimated voltages (U Uest , U Vest , U West ) based on the voltages (U U , U V , U W ) outputted by the inverter.