PERFORMANCE SIMULATION OF TWO-WHEEL DRIVE AND FOUR-WHEEL DRIVE TRACTORS

Decreasing fossil fuel supplies require the development of new conservation programs for energy consuming industries including agriculture. Conservation programs for agriculture include new tractor technologies. Computer simulation of agricultural tractors to determine performance would reduce new technology development time and costs. Mathematical models were developed to determine the gross vehicle motions and drive train motions using Lagrange\u27s equation. The tractor motions were constrained to the vertical plane in the forward direction of travel. Generalized coordinates used were forward displacement, downward displacement perpendicular to the forward direction and pitch displacement. The drive train model was developed considering the drive train as lumped masses connected by torsional springs without damping. The tires were considered torsional springs with damping. Generalized coordinates used were engine angular displacement, clutch angular displacement, angular displacement of the wheel rims and angular displacement of the tire peripheries. The mathematical models were combined into a computer simulation program. Model validation was done by simulating the lugging ability test conducted at the Nebraska Tractor Testing Laboratory. Standard errors of estimate of the simulated data were 1.06 mph, 0.43 percent and 388 rpm for the forward velocity, wheel slippage and engine speed respectively. The average time requirement per run was 96.7 seconds. Because of the high time requirement and poor simulation accuracy, a simplified drive train model was developed neglecting the potential stored in the axles and shafts. The simulated data using the simplified drive train model had standard errors of estimate of 0.26 mph, 0.14 percent and 114 rpm for forward velocity, wheel slippage, and engine speed respectively. The average time requirement per run was 28.7 seconds. The model was demonstrated by comparing the performance of equally powered two-wheel drive tractors with single drive wheels, two-wheel drive tractor with dual drive wheels and four-wheel drive tractors with single drive wheels. The addition of extra drive wheels on a two-wheel drive tractor significantly increased forward velocity, decreased wheel slippage, decreased engine speed and increased fuel efficiency. The addition of an extra drive axle significantly decreased wheel slippage, decreased engine speed and increased fuel efficiency