Abstract
Research and/or Engineering Questions/Objective
Four wheels independently steering-by-wire vehicle can switch among a variety of shift patterns, such as front-wheel steering, rear-wheel steering, four-wheel steering, pivot turning, oblique moving and transverse moving. This technology minimizes the space limitations of the vehicle travelling and greatly expands the application field of electric vehicles but the vehicle must be completely still when switching to other modes. For this reason, a method of steering modes switching smoothly control of four wheels independently steering-by-wire vehicle is developed in this paper.
Methodology
The steering instantaneous center of the vehicle moves respectively in the lines where the centers of front or rear wheel spread along under the front wheel steering or rear wheel steering mode when the vehicle drives in steady-state and it moves in the coordinate system plane under four-wheel steering mode. And it can be drawn that a four-wheel steering transition is needed for the switching among steering modes. Assuming that the process of turning meets Ackerman law. And the turning radius or the path should be constant while switching among different modes happens. That means turning the switching among the modes into the steering instantaneous center’s movement in a circle which is drawn with the center of the mass of the vehicle and the steering radius in the coordinate system plane. Results In the paper the velocity of the center of the mass of vehicle is almost fixed under the process of steering modes switched dynamically. At the same time, steering radius keeps fixed and the sideslip angle of center of mass changes in a reasonable range of 5°. They all meet the desired effect of the designed control algorithm. The driver had no obvious feelings during the experiment, and the algorithm is then verified effective.
Limitations of this study
An important limitation of the current study is the limited test condition in the proof of algorithm. Furthermore, the trace of the center of the mass of the vehicle is hardly be observed and thus some parameters’ detection are only valid in simulation.
What does the paper offer that is new in the field including in comparison to other work by the authors?
A method of steering modes switching smoothly control of four wheels independently steering-by-wire vehicle is developed in this paper is new and it works well without vehicle stopping.
Conclusions
A control method of smooth transition among a variety steering modes without stopping for four-wheel independently steering-by-wire vehicle has been developed. It turns the process of switching into the path planning of vehicle steering instantaneous center movement. And the above-mentioned method is then verified to be effective by simulation and experiment on the vehicle.
Key Words : four wheel independently steering-by-wire, steering mode switching, smooth transition, path planning