MICROPROCESSOR-BASED DIGITAL CONTROL FOR IMPROVING TRACTOR OPERATING EFFICIENCY

The purpose of this study was to develop a simultaneous engine and slip control system to improve the overall operating efficiency of farm tractors. For this control system, the engine control goal was defined by a minimum specific fuel consumption curve obtained from a laboratory engine performance mapping test. The slip control goal was defined by the optimum wheel slip which is variable depending on terrain and soil conditions. The variable optimum slip was derived from static and dynamic analysis of the tractive system.; An ARMA (auto-regressive, moving-average) model was established to describe the engine-governor system dynamics. The least square method was used in model identification and parameter estimation. Compensator control algorithms were based on the ARMA model.; Control system hardware, including a data acquisition system, a throttle adjusting mechanism with control circuit, and a power-shift control circuit, was developed. Forth language was used for software implementation of the control algorithms. A Motorola 6809 microprocessor was employed as the CPU (central processing unit) of the system. Hardware was installed on a two-wheel drive 1896 tractor (Case international model 1896).; Extensive engine control tests were conducted under laboratory conditions. A direct control algorithm and several compensator control algorithms were tested under different load conditions. Comparison of tests with and without control showed reduction in specific fuel consumption with the use of the control system. Significant improvement in control accuracy was obtained using the compensator designs. Limitations of this control system included engine surge during the control tests when throttle movement limits were not set, and the inability of the system to maintain optimum engine speed under heavy load conditions.; A procedure to estimate engine torque based on throttle position and engine speed was developed during this study. Laboratory and field engine control tests indicated that the procedure is effective.; Engine and slip control were tested under field conditions. Disking tests were conducted on different test routes. Results of tests with no control, with engine control alone, with slip control alone, and with simultaneous engine and slip control were compared to evaluate control system performance. Tests with a constant optimum slip setting were unsuccessful in improving tractor efficiency. Tests with the variable optimum slip setting showed improvements in overall operating efficiency and productivity of the tractor.