System and method of initial aligning wheels of vehicle steer-by-wire systems

1. A method of initial aligning wheels of a vehicle steer-by-wire system with two independent front road wheels in real time, the method comprising:

sensing absolute and relative steering wheel angles, absolute and relative left road wheel angles, and absolute and relative right road wheel angles;

generating wheel aligning reference angles including a steering wheel aligning reference angle, a left road wheel aligning reference angle, and a right road wheel aligning reference angle;

generating a switch control signal to determine operating states of the steer-by-wire system defining an initial alignment state and a nominal control state, the switch control signal being generated based on the steering wheel and road wheel aligning reference angles between the relative angles and absolute angles by using a logic operation with a switch threshold;

maintaining the initial alignment state wherein the steering wheel and road wheel aligning reference angles are connected to be input signals in the steer-by-wire control system, if one of the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle is greater than the switch threshold between initial alignment state and nominal control state;

aligning the left road wheel, the right road wheel, and the steering wheel based on the steering wheel aligning reference angle, the lef: road wheel aligning reference angle, and the right road wheel aligning reference angle; and

switching to the nominal control state wherein the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle are connected to be input signals in the steer-by-wire control system, if the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle is less then the switch threshold for the initial alignment state and nominal control state;

wherein the steering wheel aligning reference angle θ s-alg , the left road wheel aligning reference angle θ rl-alg , and the right road wheel aligning reference angle θ rr-alg are given as:

θ s-alg =θ s-abs −θ s +θ init

θ rl-alg =θ rl-abs −θ rl +θ init

θ rr-alg =θ rr-abs −θ rr +θ init

whereθ init is a constant to represent the desired alignment angle, θ s and θ s-abs are relative and absolute steering wheel angles, θ rl and θ rl-abs are relative and absolute left road wheel angle, and θ rr and θ rr-abs are relative and absolute right road wheel angle.

2. The method of claim 1 further comprising:

providing a steering wheel control sub-system to generate road wheel reference angles and to produce steering feel for a vehicle driver;

providing a road wheel control sub-system to control actual road wheel angles to track road wheel reference angles; and

providing an initial alignment unit to align the road wheels and steering wheel, the initial alignment unit generating the wheel aligning reference angles to be input signals of the steer-by-wire system and a switch control signal to determine the operating states of steer-by-wire system, initial alignment unit including signal summing operators in communication with signal switches and a logic operation unit.

3. The method of claim 2 wherein the wheel aligning reference angles are determined by using signal summing operators in the initial alignment unit.

4. The method of claim 2 wherein signal switches in the initial alignment unit implements the signals switching between the steering wheel reference angle and steering wheel aligning reference angle, the left road wheel reference angle and left road wheel aligning reference angle, and the right road wheel reference angle and right road wheel aligning reference angle.

5. The method of claim 2 wherein the control signal of switches is provided by the logic operation unit the initial alignment unit, wherein the logic operation unit generates the switch control signal according to differences between the relative angles and absolute angles by using the logic operation.

6. The method of claim 5 wherein the logic operation determines whether the differences between the relative angles and absolute angles are larger or smaller than the switch threshold which represents a range near zero.

7. The method of claim 5 wherein the wheel aligning reference angles of the initial alignment unit are imputted to the steering wheel control sub-system and road wheel control sub-system, if the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle are greater than the switch threshold.

8. The method of claim 5 wherein the wheel reference angles of the initial alignment unit are inputted to the steering wheel control sub-system and road wheel control sub-system, if the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle are smaller than the switch threshold.

9. The method of claim 2 further comprising resetting the relative steering wheel angle, the left road wheel angle, and the right: road wheel angle, when the operating states of steer-by-wire system changes from the initial alignment state to nominal control state.

10. The method of claim 9 wherein the switch control signal in the initial alignment unit determines the operating states of steer-by-wire system.

11. The method of claim 1 wherein the real time initial alignment method only changes the reference input signals of the steering wheel control sub-system and the road wheel control sub-system, and the structure and parameters of the steering wheel control sub-system and road wheel control sub-system are not affected by the initial alignment.

12. The method of claim 1 wherein the return rates of the steering wheel and road wheels in the process of initial alignment can be adjusted by adjusting the gains of the steering wheel control sub-system and road wheel control sub-system.

13. A method of aligning wheels of a vehicle steer-by-wire system with two independent front road wheels in real time, the method comprising:

sensing absolute and relative steering wheel angles, absolute and relative left road wheel angles, and absolute and relative right road wheel angles;

generating a steering wheel aligning reference angle, a left road wheel aligning reference angle, and a right road wheel aligning reference angle;

maintaining the initial alignment state wherein the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle are connected to be input signals in the steer-by-wire control system, if one of the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle is greater than a switch threshold between initial alignment state and nominal control state; and

aligning the left road wheel, the right road wheel, and the steering wheel based on the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle;

wherein the steering wheel aligning reference angle θ s-alg , the left road wheel aligning reference angle θ rl-alg , and the right road wheel aligning reference angle θ rr-alg , are given as:

θ s-alg =θ s-abs −θ s +θ init

θ rf-alg =θ rf-abs −θ rf +θ init

θ rr-alg =θ rf-abs −θ rr +θ init

where θ init is a constant to represent the desired alignment angle, θ s and θ s-abs are relative and absolute steering wheel angles, θ rf and θ rf-abs are relative and absolute left road wheel angle, and θ rr and θ rr-abs are relative and absolute right road wheel angle.

14. A system of initial aligning wheels of a vehicle steer-by-wire system with two independent front road wheels in real time, the system comprising:

a steering wheel control sub-system to generate road wheel reference angles and to produce steering feel for a vehicle driver;

a road wheel control sub-system to control actual road wheel angles to track road wheel reference angles; and

an initial alignment unit to align the road wheels and steering wheel, the initial alignment unit generating a steering wheel aligning reference angle, a left road wheel aligning reference angle, and a right road wheel aligning reference angle to be the input signals of the steer-by-wire system and a switch control signal to determine the operating states of steer-by-wire system, the switch control signal being generated based on the steering wheel and road wheel aligning reference angles between the relative angles and absolute angles by using a logic operation with a switch threshold, and the initial alignment unit including the signal summing operators in communication with signal switches controlled by the switch control signal and a logic operation unit;

wherein the wheel aligning reference angles of the initial alignment unit are inputted to the steering wheel control sub-system and road whee control sub-system, if the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle are greater than the switch threshold.

15. The system of claim 14 wherein the wheel reference angles of the initial alignment unit are inputted to the steering wheel control sub-system and road wheel control sub-system, if the steering wheel aligning reference angle, the left road wheel aligning reference angle, and the right road wheel aligning reference angle are smaller than the switch threshold.

16. The system of claim 14 wherein the steering wheel aligning reference angle θ s-alg , the left road wheel aligning reference angle θ rf-alg , and the right road wheel aligning reference angle θ rf-alg are given as:

θ s-alg =θ s-abs −θ s +θ init

θ rf-alg =θ rf-abs −θ rf +θ init

θ rr-alg =θ rr-abs −θ rr +θ init

whereθ unit is a constant to represent the desired alignment angle, θ s and θ s-abs are relative and absolute steering wheel angles, θ rf and θ rf-abs are relative and absolute left road wheel angle, and θ rr and θ rr-abs are relative and absolute right road wheel angle.