Implement control and its effect on the dynamic performance of tractor-implement combinations

Tractors incorporate draught, controls for two reasons, to limit variations in implement depth and to limit fluctuations in the load, i.e. the draught force, imposed on the tractor by the implement. Efficient operation of this control is important because many farmers demand a consistent tillage depth and also, if the load is controlled, the tractor can be operated at its maximum output without excessive wheel slip or engine stall. The work for this thesis involved a theoretical investigation of draught control response and its effect on overall tractor performance. A computer model was devised to simulate draught control and its effect on dynamic performance of the tractor-implement combination. Input data for the simulation was provided by laboratory measurements. Two series of field work were carried out to measure response of a linkage force sensing experimental control to sinusoidal and random draught variations and the response of a control which sensed driveline torque. Comparisons between measured and predicted results, confirmed the validity of the theoretical analysis. Suggestions for improving control performance, particularly stability, are made and the likely improvement predicted using the computer simulation. Other possible methods of implement control or improvements to draught controls are discussed in relation to the likely requirements of future tractors.