System for determining at least one rotation parameter of a rotating member

Abstract

The invention relates to a system comprising a coder that has an alternation of North and South magnetic poles separated by transitions extending along a helix of pitch p and of angle α, the magnetic track having Npp pairs of North and South poles and a polar width Lp measured along a normal to the transitions which are: Npp=πa/l, and Lp=p·cos α. The invention also includes at least one sensor able to detect the rotating magnetic field in a plane perpendicular to the magnetic track and to the transitions by means of a mounting of at least two sensitive magnetic elements. The mounting being disposed at a radial reading distance from the magnetic track and being arranged to deliver signals in quadrature.

What is claimed is: 
     
         1 . A system for determining at least one rotation parameter of a rotating member, the system comprising:
 a coder with a body having a cylindrical periphery with a radius around an axis of revolution (X), the periphery having an alternation of North and South magnetic poles of width l which are separated by transitions, each one of the transitions extending along an helix of pitch p and of angle □ to form a multipolar magnetic track which is able to emit a periodic magnetic field which is rotating in a plane perpendicular to the magnetic track and to the transitions, the track having N pp  pairs of North and South poles and a polar width L p  measured along a normal (N) to the transitions which are: N pp =□a/l, and L p =p·cos □;   at least one sensor able to detect the rotating magnetic field emitted by the coder by means of a mounting of at least two sensitive magnetic elements, the mounting being disposed at a radial reading distance from the magnetic track and being arranged to deliver signals (V 01 , V 02 ; V′ 01 , V′ 02 ) in quadrature;   wherein the system comprises two sensors of which the mountings are spaced by a distance e measured along the normal (N) to the transitions by delivering respectively signals (V 01 , V 02 ; V′ 01 , V′ 02 ) in quadrature, the system further comprising a circuit for subtracting the signals in order to form signals (SIN, COS) in quadrature.   
     
     
         2 . The system according to  claim 1 , wherein the mounting comprises two Wheatstone bridge circuits of four sensitive elements, the circuits being disposed in a plane perpendicular to the magnetic track as to detect the magnetic field rotating in the plane which is emitted by the track. 
     
     
         3 . The system according to  claim 1 , wherein each sensitive element comprises at least one pattern with a tunnel magneto resistance material base of which the resistance varies according to the magnetic field detected. 
     
     
         4 . The system according to  claim 1 , wherein the distance e: e=L p  modulo 2L p . 
     
     
         5 . The system according to  claim 1 , wherein the distance e:
 0.55L p <e<0.82L p , modulo 2L p ; or   1.18L p <e<1.45L p , modulo 2L p .   
     
     
         6 . The system according to  claim 6 , wherein the distance e is substantially equal to ⅔L p  or 4/3L p  modulo 2L p .