A Precise Prediction Model of Traveling Performance

for a Rigid Wheel on Sandy Ground

Masaaki OMINE^＊1, Masami UENO^＊2, Koichiro FUKAMI^＊2

*1 Hokuriku National Agricultural Experiment Station, 1-2-1, Inada, Joetsu, Niigata, 943-0193 JAPAN

*2 College of Agriculture, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa, 903-0213 JAPAN

Abstract

Drawbar pull, torque, traveling resistance and so on are able to be easily estimated if we know at once ground contact stresses acting on a rolling wheel. Therefore, it is one of the main subjects to predict precisely the stresses in the field of traveling performance of off-the-road vehicles.

Some models based on the M. G. Bekker's empirical equation describing the relationship between pressure and sinkage of a footing are widely used for the prediction of distribution of ground contact stress to analyze the traveling performances of a wheel. Although these models are simple and useful in a practical sense, improvements are necessary for precise prediction because of the some faults. For example, the deviation of normal stress distribution with slippage cannot be expressed.

In this study, the parabolic distribution model for normal stress was modified by taking into consideration the effect of slippage. Furthermore, the Janosi's model for tangential stress was extended to represent a peak within the tangential stress - slip displacement relation. A prediction system for ground contact stresses, drawbar pull, torque and time series of these quantities of a wheel was developed by using these models. Predicted results were confirmed good applicability by the comparison with experimental results of traveling tests by a model rigid wheel on the sandy ground.

Methods

A test apparatus for the wheel traveling problem consists of a soil bin, a wheel and its driving unit, a carriage and its driving unit, a data acquisition and processing devices and peripheral devices. Diameter of the wheel is 300mm,width is 410mm, and the surface of it is coated by 5mm-thick rubber mat. A/D convertment of mechanical quantities picked up by each sensor is carried out by a data acquisition device and the data are transferred to a personal computer through GPIB. "Toyoua standard sand" with air-dried condition was used for the soil bin test. Initial void ratio of soil layer was regulated about 0.62 in average. In the experiment, at first, the wheel went down slowly with non-rotating, and then the wheel and the carriage were driven simultaneously. The former and the latter were denoted as the initial sinkage stage and the traveling or rolling stage respectively. The level of slippage was arranged by setting the relative speed for the wheel and the carriage. Before the initial sinkage, the wheel was put on the surface that lightly touched on the soil surface, and the initial balance of some sensors were set. The procedure of test was displayed on the CRT screen by test supporting system so that we could easily carried out the setting of initial balance of sensors, of slippage levels, of initial weight and soon.

Conclusion

The proposed prediction system of traveling performances for a rigid wheel is able to give satisfactory results. Some kinds of modification should be required to represent the tangential stress at the low slippage. This may be achieved by the estimation of the slip displacement. It is necessary to analyze the soil deformation beneath the wheel especially that of contact zone.

References

1) M.G.Bekker (1960) : Off-the-Road Locomotion, The University of Michigan Press, p.25-40.

2) J.Y.Wong (1989) : Terramechanics and Off-Road Vehicles, ELSEVIER, p.84-122

3) Y. Nohse, K. Hashiguchi, M. Ueno, T. Shikanai, H.Izumi and F.Koyama (1991) : A measurement of basic mechanical quantities of off-the-road traveling performance, J. of Terramechanics, Vol.28, p.358-370.