Estimation of the ageing of a power steering
A method for estimating the ageing of a steering mechanism during which the ageing of the steering mechanism is assessed by calculating a value called «ageing value» according to an ageing function (old, old2, ene) which corresponds to the integral, over time, of an expression which is weighted by a stress indicator (T m (u), T s (u)) the value of which at each considered instant (u) is representative of the intensity of a stress force (T m , T s ), such as the operating force exerted by the assist motor, which is undergone by the steering mechanism at the considered instant.
1. A method for managing a power steering comprising a steering mechanism, the method comprising:
determining an age of the steering mechanism by estimating ageing of the steering mechanism by calculating an ageing value according to an ageing function (old, old2, ene) which corresponds to an integral, over time, of an expression which is weighted by a stress indicator (T m (u), T s (u)), the stress indicator having a value at each considered instant in time (u) representative of an intensity of a stress force (T m , T s ) undergone by the steering mechanism at each considered instant in time, and
correcting, based on the determined age, initial settings of at least one of (i) an assist law of the power steering, (ii) a friction model used by the assist law of the power steering, and (iii) at least one elasticity chart which characterizes one or both of a stiffness of a movable member of the steering mechanism and a stiffness of a kinematic linkage between two movable members of the steering mechanism.
2. The method according to claim 1 , further comprising
modifying, based on the ageing value as a parameter, a friction model for assessing internal friction that resists steering operations of the power steering, so as to dynamically adjust, over time, based on the age of the steering mechanism, a friction compensation.
3. The method of claim 2 wherein modifying a friction model so as to dynamically adjust a friction compensation over time comprises reducing the friction compensation with an increasing ageing of the steering mechanism.
4. The method according to claim 1 , wherein, as the steering mechanism comprises at least one actuating member, which is linked to at least one effector member, by at least one drive kinematic chain, the stress indicator (T m (u), T s (u)) is representative of
an intensity of at least one operating force (T m , T s ) which is exerted by the at least one actuating member when the at least one actuating member includes a single actuating member, or
the intensity of the at least one operating force simultaneously exerted respectively by several actuating members, on respective drive kinematic chains when the at least one actuating member includes the several actuating members.
5. The method according to claim 4 , wherein, the at least one actuating member is at least one of a steering wheel and an assist motor.
6. The method according to claim 4 , wherein, the at least one effector member is a wheel steered by the steering mechanism.
7. The method according to claim 4 , wherein the stress indicator is selected from the group consisting of a motor torque setpoint (T m ) which is applied to an assist motor, a measurement of an assist torque (T assist ) which is actually delivered by the assist motor, and a measurement of a steering wheel torque (T s ) which is exerted by a driver on a steering wheel.
8. The method according to claim 1 , wherein, as the steering mechanism comprises an assist motor, the ageing value is calculated according to a first ageing function (old) representative of the ageing related to an action of the assist motor, the first ageing function being given by:
old
(
t
)
=
∫
0
t
T
m
(
u
)
d
u
,
where T m (u) represents a motor torque setpoint applied to the assist motor, or a measurement of an assist torque delivered by the assist motor, at the instant in time u.
9. The method according to claim 1 , wherein, as the steering mechanism comprises a steering wheel, the ageing value is calculated according to a second ageing function (old2) representative of the ageing related to an action of the steering wheel, the ageing function being given by:
old
2
(
t
)
=
∫
0
t
T
s
(
u
)
d
u
,
where T s (u) represents a measurement of a steering wheel torque which is exerted by a driver on the steering wheel, at the instant in time u.
10. The method according to claim 1 , wherein, the ageing value is calculated according to an ageing function an integrand of which contains a product of (i) the stress indicator (T m (u), T s (u)) representative of an intensity of a force, exerted by an actuating member of the steering mechanism, and (ii) a speed of displacement of the actuating member of the steering mechanism.
11. The method according to claim 10 , wherein the actuating member of the steering mechanism is an assist motor, so that the ageing value is calculated according to a third ageing function (ene) representative of an energy delivered by the assist motor, the third ageing function being given by:
ene
(
t
)
=
∫
0
t
T
m
(
u
)
·
ω
m
(
u
)
d
u
,
where T m (u) represents a motor torque setpoint or a measurement of an assist torque delivered by the assist motor at the instant in time u, and ω m (u) represents a speed of rotation of a shaft of the assist motor at the instant in time u.
12. The method according to claim 10 , wherein the stress indicator (T m (u), T s (u)) is representative of an intensity of a torque exerted by the actuating member of the steering mechanism.
13. The method according to claim 10 , wherein the actuating member of the steering mechanism is at least one of a steering wheel and an assist motor.
14. The method according to claim 10 , wherein the speed of displacement of the actuating member is the speed of rotation (ω m ) of the actuating member of the steering mechanism.
15. The method according to claim 1 , further comprising assessing an absolute ageing of the steering mechanism, by calculating the ageing function over a global time period [0, t] an origin of which corresponds to a first entry into service of the steering mechanism or, to a first road use of a vehicle equipped with the steering mechanism.
16. A motor vehicle equipped with a power steering system driven by a control module designed to implement the method according to claim 1 .
17. A non-transitory data medium readable by a computer and containing a computer program, the program comprising instructions for the computer to execute the method according to claim 1 , when the non-transitory data medium is read by the computer.