Damping methods and systems for electric power steering

1. A control system for controlling an electric power steering system, the control system comprising:

a first module that estimates a damping force based on an assist torque and a handwheel velocity as a summation of a first term, a second term, a third term, and a fourth term, the first term based on the handwheel velocity, the second term based on a product of the absolute value of the assist torque and the handwheel velocity, the third term based on the handwheel velocity squared and having a same sign as the handwheel velocity, and the fourth term based on a product of the handwheel velocity squared and a negative value of the assist torque, thereby providing an asymmetrical damping characteristic for an assist torque component of the estimated damping force; and

a second module that generates a control signal based on the estimated damping force.

2. The system of claim 1 , wherein the first module estimates the damping force based on a plurality of parameters.

3. The system of claim 2 , further comprising a third module that scales the plurality of parameters, and wherein the first module estimates the damping force based on the scaled plurality of parameters.

4. The system of claim 3 , wherein the third module scales the plurality of parameters based on a vehicle speed.

5. The system of claim 1 , further comprising a third module that limits the assist torque or force, and wherein the first module estimates the damping force based on the limited assist torque or force.

6. A method of controlling an electric power steering system, the method comprising:

receiving a steering assist torque and a handwheel velocity at a control module of the electric power steering system;

estimating, by a first module of the control module of the electric power steering system, a damping force based on the steering assist torque and the handwheel velocity as a summation of a first term, a second term, a third term, and a fourth term, the first term based on the handwheel velocity, the second term based on a product of the absolute value of the steering assist torque and the handwheel velocity, the third term based on the handwheel velocity squared and having a same sign as the handwheel velocity, and the fourth term based on a product of the handwheel velocity squared and a negative value of the steering assist torque, thereby providing an asymmetrical damping characteristic for a steering assist torque component of the estimated damping force; and

generating, by a second module of the control module of the electric power steering system, a control signal based on the estimated damping force.

7. The method of claim 6 , wherein the estimating the damping force is based on a plurality of parameters.

8. The method of claim 7 , further comprising scaling the plurality of parameters, and wherein the estimating the damping force is based on the scaled plurality of parameters.

9. The method of claim 8 , wherein the scaling the plurality of parameters is based on a vehicle speed.

10. The method of claim 6 , wherein the estimating the damping force is based on a limited value of assist torque or force.

11. A system, comprising:

an electric power steering system; and

a control module that estimates a damping force based on assist torque or force and handwheel velocity as a summation of a first term, a second term, a third term, and a fourth term, the first term based on the handwheel velocity, the second term based on a product of the absolute value of the assist torque and the handwheel velocity, the third term based on the handwheel velocity squared and having a same sign as the handwheel velocity, and the fourth term based on a product of the handwheel velocity squared and a negative value of the assist torque, thereby providing an asymmetrical damping characteristic for an assist torque component of the estimated damping force, and that generates a control signal to the electric power steering system based on the estimated damping force.

12. The system of claim 11 , wherein the control module estimates the damping force based on a plurality of parameters.

13. The system of claim 12 , wherein the control module scales the plurality of parameters, and estimates the damping force based on the scaled plurality of parameters.

14. The system of claim 13 , wherein the control module scales the plurality of parameters based on vehicle speed.

15. The system of claim 11 , wherein the control module estimates the damping force based on a limited value of the assist torque.