Method for determining the angular position of the steering wheel of an automobile vehicle electric power-assisted steering system
The method consists in: determining in which actually sector the booster motor is located, a sector of the booster motor being defied by two successive poles; determining a relative angle position of the steering wheel in relation to the booster motor; identifying a sector, known as neutral, in which the booster motor is located when the rotation speeds of the rear wheels, i.e. right and left of the vehicle, are equal; determining an angle offset of the steering wheel corresponding to a neutral angle position of the steering wheel; determining an absolute angle position of the steering wheel which is equal to the difference between the relative angle position of the steering wheel and the offset angle thereof.
1. A method for determining the angular position of the steering wheel ( 2 ) of an automobile vehicle electric power-assisted steering system, the steering system comprising an assistance electric motor ( 8 ) controlled by an on-board electronic processor ( 10 ), the assistance electric motor ( 8 ) comprising a plurality (n) of stator poles distributed around its circumference, a measurement of the instantaneous angular position (θ) between two successive poles of the assistance electric motor ( 8 ) being carried out by a sensor, notably of the resolver type ( 13 ) or using the Hall effect, characterized in that it consists in
determining in which current sector (tr_motor), a sector of the assistance motor ( 8 ) being bounded by two successive poles, the assistance motor ( 8 ) is situated, the passage from one sector to another, preceding or following respectively, being identified when the separation between two measurements from the sensor ( 13 ) of the instantaneous angular position (θ) of the assistance motor ( 8 ) is, respectively, less than a first predetermined value or greater than a second predetermined value;
determining a relative angular position (Angle_steer_rel) of the steering wheel ( 2 ), with respect to the assistance motor ( 8 ), as a function of a reduction ratio (reduction_ratio) between the assistance motor ( 8 ) and the steering column ( 3 ), and of a reference instantaneous angular position (θ 0 ) of the assistance motor ( 8 ) within one sector, in particular by the formula:
Angle_steer
_rel
=
1
reduction_ratio
×
(
tr_motor
n
×
360
+
(
θ
-
θ
0
)
)
identifying a sector, referred to as neutral sector (tr_motor_neutral), in which the assistance motor ( 8 ) is situated when the rotation speeds of the right-hand rear wheel (v rear R) and left-hand rear wheel (v rear L) of the vehicle are equal;
determining an angular offset (Angle_offset) of the steering wheel ( 2 ), corresponding to a neutral angular position of the steering wheel, as a function of the current sector (tr_motor), of the neutral sector (tr_motor_neutral), and of the reduction ratio (reduction_ratio) between the assistance motor ( 8 ) and the steering column ( 3 ), in particular by the formula:
Angle_Offset
=
360
n
×
(
tr_motor
-
tr_motor
_neutral
reduction_ratio
)
;
determining an absolute angular position (Angle_steer_absolute) of the steering wheel ( 2 ), which is equal to the difference between the relative angular position (Angle_steer_rel) of the steering wheel ( 2 ) and its angular offset (Angle_offset).
2. The method as claimed in claim 1 , wherein in that an estimation, referred to as mechanical estimation (Lr_motor_neutral_wheels), of the neutral sector, proportional to the difference between a turning angle (α wheels) at the steering wheel ( 2 ) and the relative angular position (Angle_steer_rel) of the steering wheel ( 2 ), is carried out, in particular by the formula:
tr_motor
_neutral
_wheels
=
α
wheels
-
angle_steer
_rel
(
360
/
n
)
the turning angle (α wheels) at the steering wheel ( 2 ) being determined by calculation as a function of the speed of the vehicle (v), of the wheel-base of the vehicle (L), of the under-steer gradient (K), of the demultiplication (D) of the steering system, and of the turning radius (R), in particular by the formula:
α
wheels
=
D
(
L
R
+
K
v
2
R
)
.
3. The method as claimed in claim 2 , wherein in that the turning radius (R) is determined by calculation as a function of the rotation speeds of the right-hand rear wheel (v rear R) and left-hand rear wheel (v rear L) of the vehicle, in particular by the formula:
R
=
Base_Rear
2
×
vrearR
+
vrearL
vrearR
-
vrearL
where Base_Rear denotes a predetermined constant.
4. The method as claimed in claim 1 , wherein in that a statistical estimation (tr_motor_neutral_statistical) of the neutral sector is carried out by determining, whenever the rotation speeds of the right-hand rear wheel (v rear R) and left-hand rear wheel (v rear L) of the vehicle are equal, the number of occurrences of the assistance motor ( 8 ) within each sector, the neutral sector (tr_motor_neutral_statistical) being the sector with the greatest number of occurrences (Occ_max) of the assistance motor ( 8 ).
5. The method as claimed in claim 4 , wherein the statistical estimation of the neutral sector (tr_motor_neutral_statistical) is validated if the number of occurrences (Occ_max) of the assistance motor ( 8 ) within this sector is greater than at least one predetermined threshold.
6. The method as claimed in claim 2 , wherein a statistical estimation (tr_motor_neutral_statistical) of the neutral sector is carried out by determining, whenever the rotation speeds of the right-hand rear wheel (v rear R) and left-hand rear wheel (v rear L) of the vehicle are equal, the number of occurrences of the assistance motor ( 8 ) within each sector, the neutral sector (tr_motor_neutral_statistical) being the sector with the greatest number of occurrences (Occ_max) of the assistance motor ( 8 ), and wherein the identification of the neutral sector is validated when the statistical estimation (tr_motor_neutral_statistical) and mechanical estimation (tr_motor_neutral_wheels) return the same value (tr_motor_neutral).