Improved Wheel Performance on Sand by Controlled Circumferential Rigidity

摘要

An analysis of experimentally determined stress distributions beneath tires on sand revealed a strong tendency for the normal stresses to be greater in areas of higher-than-average tire rigidity, i.e. along the periphery of the contact patch where the tire rigidity is augmented by tire sidewall stiffness and/or local tire flexing. The question arose as to whether the observed phenomenon could be used advantageously by directly controlling the tire rigidity pattern, and thus favorably influence stress distribution, with the net result of improved tire performance. An experimental wheel was built to test this principle; its performance is described in this report. The control of local tire rigidity was achieved by a system of six nonrotating hydraulic jacks inside the wheel acting against a fixed flexible shoe, along which the inner surface of the tire slid as it rotated. Tests with sand at two strength levels showed that the wheel with favorable rigidity distribution (increasing rigidity to the rear of the soil-wheel interface) developed up to 25 percent more pull than the wheel with unfavorable rigidity distribution. The greater pull was paralleled by an efficiency increase of the same order. These experimental results are explained by theoretical computations based on the variation of assumed stress distribution as a function of the rigidity pattern. The experimental wheel was built to check a principle rather than to be used as a means of locomotion, but the prospect of applying the principle of controlled rigidity in practice is shown to be promising. (Author)