Torque-based on-center feel for electric power steering
View Patent ↗A control system for controlling an electric power steering system is provided. The control system includes a first module configured to compute an on-center torque adjustment compensation based on a sensed handwheel torque. The on-center torque adjustment compensation is configured to compensate for inertia of a steering actuator motor using a frequency-based methodology. The control system also includes a second module configured to generate a command signal to control the steering actuator motor of the electric power steering system based on the on-center torque adjustment compensation.
1. A control system for controlling an electric power steering system, the control system comprising:
a first module configured to compute an on-center torque adjustment compensation based on a sensed handwheel torque, the on-center torque adjustment compensation configured to compensate for inertia of a steering actuator motor at a handwheel on-center condition using a frequency-based methodology, the on-center torque adjustment compensation models a difference between an input driver handwheel torque and the sensed handwheel torque for the handwheel on-center condition with the steering actuator motor engaged versus the steering actuator motor disengaged, wherein the on-center torque adjustment compensation further comprises a gain function and a base transfer function applied to the sensed handwheel torque, the base transfer function configured to implement a multi-order transfer function for a plurality of corner frequencies, the base transfer function comprises a product of the corner frequencies as an s-squared numerator term, where s is a complex frequency, and the base transfer function produces no on-center torque adjustment compensation at a zero frequency; and
a second module configured to generate a command signal to control the steering actuator motor of the electric power steering system based on the on-center torque adjustment compensation.
2. The control system of claim 1 , wherein the on-center torque adjustment compensation is further configured to compensate for torque measurement dynamics and sampling effects of the sensed handwheel torque.
3. The control system of claim 1 , wherein the on-center torque adjustment compensation is further configured to compensate for torque measurement dynamics and sampling effects of a speed of the steering actuator motor.
4. The control system of claim 3 , wherein the command signal to the steering actuator motor is further based on the speed of the steering actuator motor.
5. The control system of claim 1 , further comprising a third module configured to determine an assist torque for handwheel off-center conditions, wherein the second module is further configured to generate the command signal based on a summation of the assist torque and the on-center torque adjustment compensation.
6. The control system of claim 1 , wherein the base transfer function is characterized by an equation:
s
2
P
1
P
2
(
s
+
P
1
)
(
s
+
P
2
)
,
where s is a complex frequency, and P 1 and P 2 define the corner frequencies.
7. The control system of claim 1 , wherein the gain function is based on one or more of a vehicle speed and the sensed handwheel torque.
8. The control system of claim 1 , wherein the on-center torque adjustment compensation approximates a frequency-based model of a transfer function representative of a motor model of the steering actuator motor, a mass plant model of the electric power steering system, torque measurement dynamics and sampling effects of the sensed handwheel torque, torque measurement dynamics and sampling effects of a speed of the steering actuator motor, and a delay time associated with the command signal.
9. A method for controlling an electric power steering system, the method comprising:
computing an on-center torque adjustment compensation based on a sensed handwheel torque, the on-center torque adjustment compensation configured to compensate for inertia of a steering actuator motor at a handwheel on-center condition using a frequency-based methodology, the on-center torque adjustment compensation models a difference between an input driver handwheel torque and the sensed handwheel torque for the handwheel on-center condition with the steering actuator motor engaged versus the steering actuator motor disengaged, wherein the on-center torque adjustment compensation further comprises a gain function and a base transfer function applied to the sensed handwheel torque, the base transfer function configured to implement a multi-order transfer function for a plurality of corner frequencies, the base transfer function comprises a product of the corner frequencies as an s-squared numerator term, where s is a complex frequency, and the base transfer function produces no on-center torque adjustment compensation at a zero frequency; and
generating a command signal to control the steering actuator motor of the electric power steering system based on the on-center torque adjustment compensation.
10. The method of claim 9 , further comprising compensating for torque measurement dynamics and sampling effects of the sensed handwheel torque.
11. The method of claim 9 , further comprising compensating for torque measurement dynamics and sampling effects of a speed of the steering actuator motor.
12. The method of claim 11 , wherein the command signal to the steering actuator motor is further based on the speed of the steering actuator motor.
13. The method of claim 9 , further comprising:
determining an assist torque for handwheel off-center conditions; and
generating the command signal based on a summation of the assist torque and the on-center torque adjustment compensation.
14. The method of claim 9 , wherein the base transfer function is characterized by an equation:
s
2
P
1
P
2
(
s
+
P
1
)
(
s
+
P
2
)
,
where s is a complex frequency, and P 1 and P 2 define the corner frequencies.
15. The method of claim 9 , wherein the gain function is based on one or more of a vehicle speed and the sensed handwheel torque.
16. The method of claim 9 , wherein the on-center torque adjustment compensation approximates a frequency-based model of a transfer function representative of a motor model of the steering actuator motor, a mass plant model of the electric power steering system, torque measurement dynamics and sampling effects of the sensed handwheel torque, torque measurement dynamics and sampling effects of a speed of the steering actuator motor, and a delay time associated with the command signal.
17. A control system for controlling an electric power steering system, the control system comprising:
a first module configured to compute an on-center torque adjustment compensation based on a sensed handwheel torque, the on-center torque adjustment compensation configured to compensate for inertia of a steering actuator motor at a handwheel on-center condition using a frequency-based methodology, the on-center torque adjustment compensation models a difference between an input driver handwheel torque and the sensed handwheel torque for the handwheel on-center condition with the steering actuator motor engaged versus the steering actuator motor disengaged, wherein the on-center torque adjustment compensation further comprises a gain function and a base transfer function applied to the sensed handwheel torque, the base transfer function configured to implement a multi-order transfer function for a plurality of corner frequencies, the base transfer function is characterized by an equation:
s
2
P
1
P
2
(
s
+
P
1
)
(
s
+
P
2
)
,
where s is a complex frequency, and P 1 and P 2 define the corner frequencies; and
a second module configured to generate a command signal to control the steering actuator motor of the electric power steering system based on the on-center torque adjustment compensation.