TRACTIVE PERFORMANCE OF FOUR WHEEL DRIVE TRACTORS.

摘要

The purpose of this research was to investigate the effects of various static weight distributions, hitch point locations, drawbar loads and traction surfaces on the torque split between the front and rear axles and traction efficiency of four wheel drive tractors. An automatic hitch position control system to control the distribution of axle torques was proposed.; Scale model four wheel drive tractors were used in these investigations. Because of the impossibility of scaling soils according to modelling laws, distortion of scale model results was expected. Therefore, two models built to different scales were tested to investigate any scaling effects. Prediction equations for four wheel drive tractors were developed to estimate slip-pull, axle torque distribution and traction efficiency from the behavior of these scale model tractors.; Results indicated that the portion of the total drawbar load contributed by each axle depended upon the rolling radii of the tires, dynamic load on the axle and soil strength. Variations in the distribution of axle torques did not have a significant effect on traction efficiency. Gross pull of the models was not significantly affected by the strength of the clay loam soil. The major effect of soil strength was on rolling resistance. Results from the 1/10.9 scale model were highly distorted. However, the 1/5.7 scale model provided reasonable results. Slip-pull, axle torque distribution and traction efficiency equations for the 1/5.7 scale model can be satisfactorily used to predict the behavior of prototype four wheel drive tractors. From these equations, tractor behavior can be estimated in terms of drawbar power available, slip, distribution of engine power between the axles and traction efficiency.; The automatic hitch position control system will not be necessary to achieve maximum traction efficiency because of the insensitivity of traction efficiency to various axle torque distributions. The major benefit of automatically controlling axle torque distributions would be to maintain an equal or predetermined distribution of power between the axles. This will prevent overloading and excessive wear of drive trains. Satisfactory operation, however, can be achieved by proper ballasting and hitching the vehicle for given operating conditions.