# US 11,993,327 B2 · Method for estimating and adjusting friction to be adjusted, and controlling hysteresis of a steering wheel torque, and corresponding power steering system

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- Number: US 11,993,327 B2
- Document ID: US11993327B2
- Status: Granted
- Kind: B2
- Application number: 17/689,063
- Filed: 2022-03-08
- Published: 2022-09-29
- Granted: 2024-05-28
- Earliest claimed: 2021-03-24
- Assignees: Jtekt Europe
- Applicants: Jtekt Europe
- Inventors: Nicolas Baudouin; Pierre Larminy
- Web page: https://patentgrep.com/patent/US11993327B2

## CPC

- B62D 6/008: {Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications}
- B62D 5/0481: {monitoring the steering system, e.g. failures}
- B62D 6/10: characterised by means for sensing {or determining} torque
- B62D: MOTOR VEHICLES; TRAILERS (steering, or guiding on a desired track, of agricultural machines or implements A01B69/00; wheels, castors, axles, increasing wheel adhesion B60B; vehicle tyres, tyre inflation or tyre changing B60C; connections between vehicles of a train or the like B60D; vehicles for use on rail and road, amphibious or convertible vehicles B60F; suspension arrangements B60G; heating, cooling, ventilating or other air treating devices B60H; windows, windscreens, non-fixed roofs, doors or similar devices, protective coverings for vehicles not in use B60J; propulsion plant arrangements, auxiliary drives, transmissions, controls, instrumentation or dashboards B60K; electric equipment or propulsion of electrically-propelled vehicles B60L; power supply for electrically-propelled vehicles B60M; passenger accommodation not otherwise provided for B60N; adaptations for load transportation or to carry special loads or objects B60P; arrangement of signalling or lighting devices, the mounting or supporting thereof or circuits therefor, for vehicles in general B60Q; vehicles, vehicle fittings or vehicle parts not otherwise provided for B60R; servicing, cleaning, repairing, supporting, lifting, or manoeuvring, not otherwise provided for, B60S; brake arrangements, brake control systems or parts thereof B60T; air-cushion vehicles B60V; motor-cycles, accessories therefor B62J, B62K; testing of vehicles G01M)

## Abstract

Method for determining a friction to be adjusted in a power steering system or for modifying a hysteresis of a steering wheel torque applied to a steering wheel of the power steering system, the method including the following steps of: determining a speed, from a measurement of a speed of a part of the power steering system and/or a measurement of the steering wheel torque; determining the friction to be adjusted on the basis of a modified LuGre model, said modified LuGre model determining the friction to be adjusted as a function of a state of the system, a time derivative of the state being determined as a function of said state of the system, the speed, a first gain, and a coulomb friction, according to an equation of the form: z . = v ⁡ ( 1 - α ⁡ ( z , v ) ⁢ σ 0 ⁢ z F c ⁢ sign ⁢ ( v ) ) . [ Math ⁢ 1 ]

## Claims

### Claim 1

A method for determining a friction to be adjusted (F) in a power steering system, the method comprising the following steps:
determining a speed (v), from a measurement of a speed (v) of a part of the power steering system and/or from a measurement of a steering wheel torque (T3) applied to a steering wheel of the power steering system;
determining the friction to be adjusted (F) on the basis of a modified LuGre model (LM),
said modified LuGre model (LM) determining the friction to be adjusted (F) as a function of a state (z) of the system, a time derivative (ż) of the state (z) being determined as a function of said state (z) of the system, the speed (v), a first gain (σ0), a second gain (β), and a coulomb friction (Fc), according to an equation of the form:
z
.
=
v
⁡
(
1
-
α
⁡
(
z
,
v
)
⁢
σ
0
⁢
z
F
c
⁢
sign
⁢
(
v
)
)
⁢
in
⁢
which
:
[
Math
⁢
1
]
α
⁡
(
z
,
v
)
=
{
α
⁢
(
z
)
if
⁢
sign
⁢
(
z
)
=
sign
⁢
(
v
)
0
if
⁢
sign
⁢
(
z
)
≠
sign
⁢
(
v
)
[
Math
⁢
2
]
where sign (z) is the sign of the quantity z and sign (v) is the sign of the quantity v, and in which,
α
⁡
(
z
)
=
{
0
if
⁢
❘
"\[LeftBracketingBar]"
z
❘
"\[RightBracketingBar]"
≤
z
b
⁢
a
1
2
⁢
(
sin
(
π
⁢
❘
"\[LeftBracketingBar]"
z
❘
"\[RightBracketingBar]"
-
z
max
(
1
+
β
)
2
z
max
(
1
-
β
)
)
+
1
)
if
⁢
z
b
⁢
a
≤
❘
"\[LeftBracketingBar]"
z
❘
"\[RightBracketingBar]"
≤
z
max
1
if
⁢
⁢
❘
"\[LeftBracketingBar]"
z
❘
"\[RightBracketingBar]"
≥
z
max
⁢
with
,
[
Math
⁢
3
]
z
max
=
F
c
σ
0
⁢
and
⁢
with
,
[
Math
⁢
4
]
z
b
⁢
a
=
β
·
z
max
.
[
Math
⁢
5
]

### Claim 2 (depends on 1)

The method according to claim 1, wherein the Coulomb Friction F, and/or the first gain (σ0), and/or the second gain β vary according to one or more of the following variables: a longitudinal speed of the vehicle, a lateral acceleration of the vehicle, a yaw rate of the vehicle, a steering wheel angle or a power steering motor angle, a steering wheel speed or a power steering motor speed, a temperature of the power steering system, an external temperature, a steering wheel torque, a motor torque.

### Claim 3 (depends on 1)

The method according to claim 1, the step of determining the speed comprises the measurement of a first speed (v1), by an angular speed sensor of an assist motor and the estimation of a second speed (v2) from a measurement of the steering wheel torque (T3), said measurement of the steering wheel torque being carried out by a torque sensor, the determined speed (v) being a sum the first speed (v1) and the second speed (v2).

### Claim 4 (depends on 1)

The method according to claim 1, wherein the friction to be adjusted (F) is determined from an intermediate friction rate (w), the intermediate friction rate (w) being determined on the basis of the modified LuGre model (LM) and the speed (v), the friction to be adjusted (F) being determined according to a step of calculating a product of the intermediate friction rate (w) by a difference between an estimated dynamic friction (FRI) and a desired dynamic friction (FRC), the estimated dynamic friction (FRI) being estimated from at least the intermediate friction rate (w).

### Claim 5 (depends on 3)

The method according to claim 3, wherein the estimation of the second speed (v2) comprises the following steps of:
measuring of the steering wheel torque (T3) with the torque sensor configured to measure the steering wheel torque (T3) between the steering wheel and the rack of the electric power steering,
time derivation of the steering wheel torque measurement (T3),
multiplying the time derivative by a stiffness coefficient to obtain the second speed (v2), called torque speed.

### Claim 6 (depends on 1)

A method for adjusting a friction to be adjusted (F) in a power steering system, the method comprising the following steps of:
estimating the friction to be adjusted (F) using the method according to claim 1,
controlling an assist motor to apply a target steering wheel torque (Cc) which adjusts the friction to be adjusted (F) estimated in the previous step.

### Claim 7 (depends on 6)

The method according to claim 6, the step of controlling the assist motor comprising the following steps of:
(E5) determining the target steering wheel torque (Cc) from a difference between the estimate of the friction to be adjusted (F), and an estimator of the rack force or «rack force estimator» representing a set of forces opposing the movement (RFE);
(E6) closed loop controlling (BF) the assist motor on the basis of the target steering wheel torque (Cc) and the measured steering wheel torque (T3).

### Claim 8 (depends on 1)

A method for controlling a hysteresis of a steering wheel torque (T3) by modifying the hysteresis of a target steering wheel torque (Cc) by adding to a first target steering wheel torque a friction determined according to the method according to claim 1, said method comprising the following steps of:
determining the friction to be adjusted (F) using the method according to claim 1,
determining the target steering wheel torque (Cc) by adding the friction to be adjusted (F) to the first target steering wheel torque (Cc), said first target steering wheel torque being determined from an angle of the steering wheel,
closed loop controlling (BF) the assist motor on the basis of the target steering wheel torque (Cc) and the measured steering wheel torque (T3).

### Claim 9 (depends on 1)

A power steering system (1) configured to implement a method for determining a friction to be adjusted (F) according to claim 1, or to implement a method for adjusting a friction (F) comprising the following steps of:
estimating the friction to be adjusted (F) using the method according to claim 1,
controlling an assist motor to apply a target steering wheel torque (Cc) which adjusts the friction to be adjusted (F) estimated in the previous step, or to implement a method for controlling a hysteresis of a steering wheel torque (T3) by modifying the hysteresis of a target steering wheel torque (Cc) by adding to a first target steering wheel torque a friction determined according to the method according to claim 1, said method comprising the following steps of:
determining the friction to be adjusted (F) using the method according to claim 1,
determining the target steering wheel torque (Cc) by adding the friction to be adjusted (F) to the first target steering wheel torque (Cc), said first target steering wheel torque being determined from an angle of the steering wheel,
closed loop controlling (BF) the assist motor on the basis of the target steering wheel torque (Cc) and the measured steering wheel torque (T3).

### Claim 10 (depends on 9)

A vehicle comprising a power steering system according to claim 9.