Studies on the Lugs of Garden Tractor Wheel (1)

The Characteristics of Lugs on Sand of Sand Hill

Abstract

We studied some characteristics of various wheel lugs by means of the indoor experimental apparatuses. The soil used for our, experiments was dry sand of sand hill.
The preparatory experiment was taken first to measure the soil reaction acting upon a lug which rotates in the fixed apparatus (slippage 100%), and the main experiment next to measure at the same time the soil reaction acting upon a lug, the torque of the test wheel, and the drawber force when the test wheel is running by using some strain gauges. Test car has three wheels which two rear wheels of them run on the rails and one front wheel for the tests runs on the surface in the soil bin. There are also two time-markers for measuring of the running speed in parallel with a rail.
The significant results obtained from this preparatory experiment are following:
1) The max. value of the reaction occurs before the tip of lug reaches to the deepest point, and it appears to be near by the point when the angle of lug is smaller, but to occur reversely a little earlier when the lug rotates faster.
2) The more the width of lug and the angle of lug increase, the more the max. value of reaction increases. Arid the rate of increase becomes larger when the working depth is deeper, but it is smaller than the rate of width of lug.
3) The reaction increases considerably when the radius of rotation of lug becomes larger, but the influence of the working speed is not so much.
The principal results obtained from the main experiment are following:
1) The behaviour of the soil reaction acting upon a lug is different by the kinds of lugs and the drawber forces, and there appears negative reaction at the end of the behaviour when the drawber force is small.
2) The max. drawber horsepower are obtained between 20% and 30% of slippage, and the values become larger when the width of lug and the angle of lug and the height of lug and wheel weight are large respectively.
3) If the lug is high enough, the drawber forces increase with the wheel weights, but the coefficients of traction decrease with them.
4) When the height of lug is small, the larger width is more effective to make the drawber force increase, but when the height of lug is larger, the width of lug must be narrow to make the lug penetrate deep enough in the sand for remarkable increasing of the drawber force.