Abstract
In order to develop an innovative omnidirectional non-homonymic flexible chassis (FC), the four-wheel steering control method of FC was designed by a new concept called off-centered steering (OCS) and the automatic tracking steering system was analyzed. Novelty of this wheel concept lies in the non-conventional positioning of the steering axis and wheel axis. Additionally, the steering axis of steerable wheel was motorized with an on/off electrometrical brake to overcome a hyper-motorization issue inherent to the wheel’s geometrical properties and hold the steering position. Based on the off-centered steering characteristics of FC, the Wheatstone bridge was applied in the steering control system. The bridge resistances are used to track target steering angles and the actual steering angle, respectively. The output voltage of the bridge is exploited to adjust the wheel’s speed so that steering and automatic tracking could be achieved. Experiments at different speeds, loadings, and target steering angles were conducted. Results showed that the chassis can indeed be controlled independently and its steering range is from –90° to 90°, which indicated the automatic tracking steering system was effective. The electromagnetic lock (EL) can significantly improve the stability of the chassis and reduce the vibration. Loading has no significant effect on the accuracy of the steering angle and the time it takes to complete steering tasks. The time taken to complete a forward steering task showed a linear relationship with the required angles, but was independent of rotation speed; for backward steering, time was related to both target angles and rotation speed. The results presented in this research may provide a reference for the steering control strategies of the four-wheel individual drive and four-wheel (4WID/4WIS) vehicle in the future. Keywords: electric vehicles, flexible chassis, four-wheel steering, automatic tracking, control system DOI: 10.25165/j.ijabe.20171005.2525 Citation: Song S J, Li Y N, Qu J W, Zhou W, Guo K Q. Design and test of flexible chassis automatic tracking steering system. Int J Agric & Biol Eng, 2017; 10(5): 45–54.
Highlights
IntroductionAttention from researchers, developers, and consumers as a response to the global energy crisis[1,2]
Electric vehicles (EVs) have garnered increasing attention from researchers, developers, and consumers as a response to the global energy crisis[1,2]
2.2 Determination of angle range According to the flexible chassis (FC) operation and road conditions, this study was mainly focused on the low-speed steering Ackerman principle in terms of determining the respective off-centered axis steering angle range in different motion situations. (The high-speed model, our other ostensible option, is not appropriate for the FC.)
Summary
Attention from researchers, developers, and consumers as a response to the global energy crisis[1,2]. The FC is a 4WID/4WIS EV with in-wheel motors (IWM) that is suited to narrow roads within semi-closed or closed environments at low speed due to its omni-directional running capability. Steering control has proven a challenging endeavor in terms of the 4WID/4WIS electric chassis. This research proposed an automatic tracking steering system based on an off-centered steering axis without using a steering motor. IWM speed is controlled by the output voltage of the bridge, i.e., changes in the relative angle of the wheel and the chassis frame to facilitate automatic tracking steering. FC can change its direction using differential steering, or by changing the direction of its articulations, making the chassis omni-directional and allowing it to move in tight areas (narrow environment). Many other configurations can be imagined and the 12 DOF on FC gives the chassis great flexibility and versatility in its locomotion capabilities
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