Adaptive rear-wheel steer open-loop control for vehicle-trailer system
View Patent ↗A rear-wheel steering control system for a vehicle/trailer combination that adaptively changes an open-loop feed-forward command signal for different trailers or the same trailer with different configurations based only on vehicle parameters. The system includes a hand-wheel sensor for providing a hand-wheel angle signal of a hand-wheel position of the vehicle, a vehicle speed sensor for providing a vehicle speed signal of the vehicle, and a vehicle yaw rate sensor for providing a measured vehicle yaw rate signal of the vehicle. The system also determines if a vehicle yaw rate has reached a steady state and uses the steady-state yaw rate signal to calculate the rear-wheel steering command. In one embodiment, the system updates feed-forward rear/front values for a plurality of predetermined vehicle speeds when determining the proper rear-wheel steering command.
1. A control system for providing an open-loop rear-wheel steering assist signal for a vehicle/trailer combination, said system comprising:
a hand-wheel angle sensor for providing a hand-wheel angle signal of the position of a vehicle hand-wheel;
a vehicle speed sensor for providing a vehicle speed signal of the speed of the vehicle;
a vehicle yaw rate sensor for providing a measured vehicle yaw rate signal of the yaw rate of the vehicle; and
a controller responsive to the hand-wheel angle signal, the vehicle speed signal and the vehicle yaw rate signal, said controller generating the open-loop steering assist signal, said controller adapting the open-loop steering assist signal for different trailers or the same trailer with different configurations based only on vehicle parameters and without any trailer parameters.
2. The system according to claim 1 wherein the controller calculates a vehicle steady-state yaw rate value used for adapting the rear-wheel steering assist signal based on the yaw rate signal.
3. The system according to claim 2 wherein the controller includes a rear-wheel steering processor responsive to the vehicle speed signal and the hand-wheel angle signal, said rear-wheel steering processor generating nominal rear-wheel steering values, said controller further including a rear-wheel adapter processor responsive to the vehicle speed signal and the vehicle steady-state yaw rate value, said rear-wheel adapter processor generating new feed-forward rear/front (R/F) ratio values for rear-wheel steering control.
4. The system according to claim 3 wherein the controller further includes an adapter for updating the new feed-forward rear/front (R/F) ratio values for the rear-wheel steering control.
5. The system according to claim 4 wherein the controller further includes a multiplier for multiplying the updated feed-forward rear/front (R/F) values and the hand-wheel angle signal and generating a rear-wheel steering command signal that provides the rear-wheel steering assist signal.
6. The system according to claim 1 wherein the controller adapts and stores new feed-forward rear/front (R/F) ratio value for a plurality of predetermined vehicle speeds for the trailer based on the vehicle parameters where the rear-wheel steering values provide the steering assist signal.
7. The system according to claim 1 wherein the vehicle parameters include the mass of the vehicle, the distance from the center of gravity of the vehicle to a front axle of the vehicle, the distance from the center of gravity of the vehicle to a rear axle of the vehicle, a corning stiffness of front wheels of the vehicle and a corning stiffness of rear wheels of the vehicle.
8. The system according to claim 7 wherein the controller calculates the open-loop steering signal with the equation:
K
f
(
u
)
=
-
C
f
(
a
1
+
c
)
u
2
G
(
δ
f
,
δ
r_cmd
,
r
ss
)
-
C
f
(
m
1
a
1
u
2
+
ca
1
C
r
+
cb
1
C
r
-
a
1
b
1
C
r
-
b
1
2
C
r
)
C
r
(
c
-
b
1
)
u
2
G
(
δ
f
,
δ
r_cmd
,
r
ss
)
-
C
r
(
m
1
b
1
u
2
+
ca
1
C
f
+
cb
1
C
f
+
a
1
b
1
C
f
+
a
1
2
C
f
)
where K f (u) is a steering ratio value, C f is the cornering stiffness of the front wheels of the vehicle, a is the distance from the center of gravity to the front axle of the vehicle, c is the distance from the center of gravity of the vehicle to a hitch point between the vehicle and the trailer, u is the vehicle speed signal, G is a function, δ f is a front-wheel steer angle of the vehicle signal, δ r — cmd is a rear-wheel steering command signal, r ss is a vehicle steady-state yaw rate signal, m is the mass of the vehicle, C r is the cornering stiffness of the rear wheels of the vehicle, and b is the distance from the center of gravity of the vehicle to the rear axle of the vehicle.
9. A control system for providing an open-loop rear-wheel steering assist signal for a vehicle/trailer combination, said system comprising:
a hand-wheel angle sensor for providing a hand-wheel angle signal of the hand-wheel position of a vehicle hand-wheel;
a vehicle speed sensor for providing a vehicle speed signal of the speed of the vehicle;
a vehicle yaw rate sensor for providing a measured vehicle yaw rate signal of the yaw rate of the vehicle;
a steady-state processor responsive to the vehicle yaw rate signal, said steady state processor determining if the vehicle yaw rate signal has reached steady state and generating a vehicle yaw rate steady-state signal;
a rear-wheel steering processor responsive to the vehicle speed signal and the hand-wheel angle signal, said rear-wheel steering processor generating nominal rear-wheel steering values;
a rear-wheel adapter processor responsive to the vehicle speed signal and the vehicle steady-state signal, said rear-wheel adapter processor generating new feed-forward rear/front (R/F) ratio values;
an adapter for updating the nominal rear-wheel steering values with the new feed-forward rear/front (R/F) ratio values; and
a multiplier for multiplying the updated feed-forward rear/front (R/F) ratio values and the hand-wheel angle signal and generating a rear-wheel steering command signal that provides the rear-wheel steering assist signal.
10. The system according to claim 9 wherein the system adapts and stores the new feed-forward rear/front (R/F) ratio values for a plurality of predetermined vehicle speeds for the trailer based only on the vehicle parameters.
11. The system according to claim 10 wherein the vehicle parameters include the mass of the vehicle, the distance from the center of gravity of the vehicle to a front axle of the vehicle, the distance from the center of gravity of the vehicle to a rear axle of the vehicle, a corning stiffness of front wheels of the vehicle and a corning stiffness of rear wheels of the vehicle.
12. The system according to claim 11 wherein the controller calculates the open-loop steering signal with the equation:
K
f
(
u
)
=
-
C
f
(
a
1
+
c
)
u
2
G
(
δ
f
,
δ
r_cmd
,
r
ss
)
-
C
f
(
m
1
a
1
u
2
+
ca
1
C
r
+
cb
1
C
r
-
a
1
b
1
C
r
-
b
1
2
C
r
)
C
r
(
c
-
b
1
)
u
2
G
(
δ
f
,
δ
r_cmd
,
r
ss
)
-
C
r
(
m
1
b
1
u
2
+
ca
1
C
f
+
cb
1
C
f
+
a
1
b
1
C
f
+
a
1
2
C
f
)
where K f (u) is a steering ratio value, C f the cornering stiffness of the front wheels of the vehicle, a is the distance from the center of gravity to the front axle of the vehicle, c is the distance from the center of gravity of the vehicle to a hitch point between the vehicle and the trailer, u is the vehicle speed signal, G is a function, δ f is a front-wheel steer angle of the vehicle signal, δ r — cmd is a rear-wheel steering command signal, r ss is a vehicle steady-state yaw rate signal, m is the mass of the vehicle, C r is the cornering stiffness of the rear wheels of the vehicle, and b is the distance from the center of gravity of the vehicle to the rear axle of the vehicle.
13. A method for providing an open-loop rear-wheel steering assist signal for a vehicle/trailer combination, said method comprising:
providing a hand-wheel angle signal of the position of a vehicle hand-wheel;
providing a vehicle speed signal of the speed of the vehicle;
providing a measured vehicle yaw rate signal of the yaw rate of the vehicle; and
adapting the open-loop steering signal for different trailers or the same trailer with different configurations using only vehicle parameters and without any trailer parameters by using the hand-wheel angle signal, the vehicle speed signal and the vehicle yaw rate signal.
14. The method according to claim 13 wherein adapting the open-loop steering signal includes using a vehicle steady-state yaw rate value based on the yaw rate signal.
15. The method according to claim 13 wherein adapting the open-loop steering signal includes generating nominal rear-wheel steering values and new feed-forward rear/front (R/F) ratio values.
16. The method according to claim 15 wherein adapting the open-loop steering signal includes updating the nominal rear-wheel steering values and with the new feed-forward rear/front (R/F) ratio values and generating adapted rear-wheel steering command values.
17. The method according to claim 16 wherein adapting the open-loop steering signal includes multiplying the updated new feed-forward rear/front (R/F) ratio values and the hand-wheel angle signal, and generating a rear-wheel steering command signal that provides the rear-wheel steering assist signal.
18. The method according to claim 13 wherein adapting the open-loop steering signal includes adapting and storing feed-forward rear/front (R/F) values for a plurality of predetermined vehicle speeds based on the vehicle parameters.
19. The method according to claim 13 wherein the vehicle parameters include the mass of the vehicle, the distance from the center of gravity of the vehicle to a front axle of the vehicle, the distance from the center of gravity of the vehicle to a rear axle of the vehicle, a corning stiffness of front wheels of the vehicle and a corning stiffness of rear wheels of the vehicle.
20. The method according to claim 19 wherein adapting the open-loop steering signal includes calculating the open-loop steering signal with the equation:
K
f
(
u
)
=
-
C
f
(
a
1
+
c
)
u
2
G
(
δ
f
,
δ
r_cmd
,
r
ss
)
-
C
f
(
m
1
a
1
u
2
+
ca
1
C
r
+
cb
1
C
r
-
a
1
b
1
C
r
-
b
1
2
C
r
)
C
r
(
c
-
b
1
)
u
2
G
(
δ
f
,
δ
r_cmd
,
r
ss
)
-
C
r
(
m
1
b
1
u
2
+
ca
1
C
f
+
cb
1
C
f
+
a
1
b
1
C
f
+
a
1
2
C
f
)
where K f (u) is a steering ratio value, C f is the cornering stiffness of the front wheels of the vehicle, a is the distance from the center of gravity to the front axle of the vehicle, c is the distance from the center of gravity of the vehicle to a hitch point between the vehicle and the trailer, u is the vehicle speed signal, G is a function, δ f is a front-wheel steer angle of the vehicle, δ r — cmd is a rear-wheel steering command signal, r ss is a vehicle steady-state yaw rate signal, m is the mass of the vehicle, C r is the cornering stiffness of the rear wheels of the vehicle, and b is the distance from the center of gravity, of the vehicle to the rear axle of the vehicle.