Load Estimation of an Open-Link Locomotion Module for Robotic and Commercial Multi-Wheel Applications 2013-01-2358
An open-link locomotion module, comprising a driving wheel with an electric motor, a system of electro-hydraulic suspension, and an electro-hydraulic power steering system, is presented in this paper as the basis for the modular design of unmanned (robotic) ground vehicles. The open-link-type configuration allows the module to be functionally integrated and engineered with a system of similar modules and thus virtually allows to compile vehicles with any required number of driving wheels. The overall dimensions and carrying capacity of the tire used in the module, as well as technical characteristics of the suspension and power steering systems make possible to employ the module for commercial ground vehicle applications.
This paper considers technical issues related to designing the locomotion module. In particular, the interaction of the suspension and steering systems is studied while the systems form the normal reaction of the wheel and influence the resistance moment in the tire-road contact patch. The suspension characteristics influence the wheel normal reaction, tire deflections, and the over roll area of the tire patch. An increased tire patch area has a positive effect on stability of motion of the module and the vehicle as a whole. However, friction in the tire-road contact also goes up and increases power losses to steer the wheel. This can degrade module and vehicle handling performance.
Theoretical and experimental studies (conducted on a test bench and a real automobile built from a set of the locomotion modules) have shown that the problem of increasing stability on motion and improving handling performance of the module can be solved by (i) defining and determining the friction/resistance moment of the tire as a function of the normal reaction of the wheel; (ii) computing the pressure of the working liquid pr in the electro-hydraulic power steering system that is sufficient to overcome the resistance moment; and (iii) by means of functional fusion of the suspension and steering control systems, in which stiffness and damping characteristics are controlled and thus generate a tire patch, which ensures the preset characteristics of module stability and handling. In addition, ride smoothness requirements are also observed.