HYDRAULIC CONTROL SYSTEM DESIGN FOR FULL-TOROIDAL TRACTION DRIVE INFINITELY VARIABLE-SPEED TRANSMISSION OF A TRACTOR

摘要

This study was carried out to develop an infinitely variable-speed transmission(IVT) for agricultural tractor. A full-toroidal variator mechanism with four discs and six rollers was selected as a device changing speed ratio continuously. In the step of system layout design, the specifications of roller cylinders and end-load cylinder were determined. The planetary gear and the six pairs of gears were designed to establish the maximum vehicle speed of 50km/h. Also the hydraulic clutch, the silent chain, the hydraulic manifold and the electronic controller were developed. Then the instrumentation system, the hydraulic power control system and the control scheme were developed. Experimental tests in the bench and on the farming field were conducted to validate the performance of the prototype IVT. The speed of the vehicle was continuously changed to follow the speed set by a driver under various operating conditions. With the reduction ratio of the variator from 2.0 to 1.0, the settling time was about 0.52 seconds which was satisfactory value for working with a tractor. It was also proved that the tractor could work with continuously variable-speed under heavy load disturbances of plowing.