DESIGN OF AN INTEGRATED TRACTOR CONTROL SYSTEM BY SIMULATION OF A TRACTOR IN MOTION (AGRICULTURE, DIESEL)

Productivity and minimizing costs are key factors in agricultural operations. To assist the farmer in achieving these goals, electronic instrumentation and controls are finding widespread use on agricultural machinery. The electronic packages are generally modular, taking on a single task such as transmission control. A trend is developing to combine the individual control functions, and therefore integrate control.; Mathematical subsystem models were used to describe the tractor motion, engine, drive train, hitch system, tractive forces, and farming implement. A model was constructed to describe the entire engine performance map, including the governor curves. The hitch system is mathematically described for link positions and force interactions. A dynamic model was formulated to represent the hydraulics.; The mathematical subsystem models were assembled into an overall simulation model. Validation of the tractor model is accomplished by comparison to Nebraska Tractor test data. The residual mean square errors are found to be 4.4% for wheel slip, 3.2% for engine speed, 3.5% for drawbar power, 7.5% for fuel consumption, and 4.0% for power take-off power. The overall model provides flexibility for simulations including motion resistance, the entire engine performance map, draft control, hitch position control, and forward gear shifts.; Application of the simulation model to the design process is shown, towards the development of an integrated tractor control system. Control schemes are formulated to maximize tractive efficiency, fuel economy, and productivity. For the tractor modeled, the results show: (1) Maximum tractive efficiency is obtained by operating at 80% rated torque. (2) Maximum fuel economy is obtained by operating at 80% torque, but at reduced throttle settings. (3) Maximum productivity is obtained by operating at 80% torque, and wide-open throttle. (4) Maximum productivity results in a 15.3% gain in ground speed over maximum fuel economy. (5) Maximum fuel economy results in a 22.7% savings in fuel consumption over maximum productivity.; In order to implement the integrated system concept, there is a need for inexpensive and reliable sensors. In particular, sensors are required for fuel flow measurement and engine load detection.