Abstract
There are very few studies on the relation between running speed and rolling resistance of vehicles. Even though the running resistance of vehicles has been studied for a long time, especially in the field of automobile engineering, it is only known experimentally, using the method of costing performance test. In this paper the behavior of tractor wheels, especially the dynamic sinkage of tractor wheels (or vertical defomation of tires) is discussed theoretically.
The sinkage of wheels is very important when considering the running resistance which interrupts travel. The purpose of this study is to find the relation between sinkage of vehicles and running speed, and to apply the results to classify the soil characteristics which will give some effects on trafficability of tractor. It can also be applied to fluid mechanics in the same way.
In the field of automobile engineering, a coasting test is held very often to estimate the performance of the car by deriving the coefficient of rolling resistance. However, it is very diffictlt to apply this method on heavy work machines such as tractors.
Assuming that the tractor is running at constant speed v0 (initial speed), the same depth of sinkage will be kept on homogeneous soil. Substituting the normal running speed v into the initial speed v0 in costing test, hd (dynamic sinkage) is hd=v2/2gc
Total sinkage (or vertical displacement of tire) is expressed as the summation of hs and hd.
Measurement items are:
(1) tractor velocity
(2) static sinkage, hs
(3) dynamic sincage, hd
(4) total sinkage, ht
Total speed was obtained by measuring the time in which the tractor ran more than 5m. Static sinkage hs and total sinkage ht were gotten with a measure and hd was calculated from the equation ht-hs.
To have an experimental proof of this theory with high accuracy, there are some difficulties such as the necessity of much soil which has the same property and wide area as the test field. Generally, as soil is not homogeneous, many errors will be involved in measurement. If the experiment will be held with a pretty high accuracy it is very useful for results to classify the soil variety and its characteristics.
In this paper, the dynamic sinkage (deformation of tire) is not so important when the tractor runs, but from the view point of classification of soil which can be applied to the trafficability of tractor and the similarity to the fluid mechanics, because the dynamic sinkage (or deformation) phenomenon will be similar to the head loss of the fluid flow in the pipe which has different areas at both ends.
