Determining of the absolute angular position of a steering wheel by means of an incremental measurement and the measurement of the differential velocity of wheels

Abstract

The system for determining the absolute angular position θ of a steering wheel ( 1 ) of a motor vehicle with respect to the chassis thereof comprises a device for incrementally measuring the relative angular position δ of the steering wheel, a device ( 2 ) for measuring the differential velocity Δ V/V of the wheels mounted on the same axle and a processing device ( 8 ) for sampling the angular positions and differential velocities at a period t. Said device comprises computing means suitable to determine at moments tn: the estimate θ* (t n ) of an absolute angular position θ(t n ) according to the differential velocity Δ V/V, the mean difference offset(t n ) between the angular positions θ* (t n ) and δ (t i ), wherein i is a variant ranging from 0 to n and the absolute angular position θ(t n ) by the addition between the mean difference offset(t n ) and the angular position δ(t n ).

1 . A method for determining the absolute angular position  of the steering wheel ( 1 ) of a motor vehicle with respect to the chassis of said vehicle, by means of a system including: 
 a device for incremental measurement of the relative angular position ™ of the steering wheel, including: 
 o an encoder ( 5 ) intended to be set in rotation together with the steering wheel ( 1 ), said encoder including a main multipolar track;  
 o a fixed sensor ( 6 ) arranged with respect to and at a gap distance from the encoder ( 5 ), including at least two sensitive elements positioned with respect to the main track so as to deliver two periodic electrical signals S 1 , S 2 , in quadrature, the sensor ( 6 ) including a suitable electronic circuit ( 7 ), so as to deliver the relative angular position ™ of the steering wheel ( 1 ) based on the signals S 1 , S 2 ;  
   a device ( 2 ) for measuring the differential speed  V/V of the wheels on the same axle;    a processing device ( 8 ) that is able to sample, in a period t, the angular positions ™(t i ) and the differential speeds  V/V(t i ), said device including calculation means suitable, at every t n  instant, for: 
 o determining an estimate  *(t n ) of the absolute angular position  (t n ) according to the differential speed  V/V(t n );  
 o determining the average offset(t n ) difference between the angular positions  *(t i ) and ™(t i ), where i varies from 0 to n;  
 o determining the absolute angular position  (t n ) by adding the average offset(t n ) difference and the angular position ™(t n ).  
   
   
   
       2 . A system according to  claim 1 , characterised in that the multipolar track is formed by a multipolar ring on which multiple pairs of north and south poles are magnetised and evenly distributed with a constant angular width.  
   
   
       3 . A system according to  claim 1  or  2 , characterised in that the electronic circuit ( 7 ) includes an interpolator that allows the output signal resolution to be increased.  
   
   
       4 . A method for determining the angular position  by means of a system according to any one of the claims from  1  to  3 , said method including repeated steps that contemplate: 
 measuring the angular position ™(t i ) and the differential speed  V/V(t i );    determining an estimate  *(t n ) of the absolute angular position  (t n ) according to the differential speed  V/V(t n );    determining the difference in the average of the vectors {circumflex over (θ)}*(t n )=[ *(t 0 ), . . . , (t n )] and {circumflex over (θ)}(t n )=[™(t 0 ), . . . , ™(t n )] so as to obtain the average offset(t n ) difference;    determining the absolute angular position  (t n ) by adding the average offset(t n ) difference and the angular position ™(t n ) .    
   
   
       5 . A method according to  claim 4 , characterised in that the measurement of the differential speed  V/V(t i ) is taken on the non-drive wheels.  
   
   
       6 . A method according to  claim 4  or  5 , characterised in that it is implemented under set driving conditions.  
   
   
       7 . A method according to  claim 6 , characterised in that the driving conditions include a maximum rotation speed of the steering wheel and/or a minimum speed of the vehicle.