Hydraulic Torque Converters in Tractors

Abstract

Using a sequence of graphs the characteristic features are developed of the performance of a tractor fitted with a hydraulic torque converter. In particular an attempt is made to relate the performance through the hydraulic unit to the performance of the internal-combustion engine that provides the input torque and speed. The essential feature of coupling the input impeller to the engine is the consequence that the engine runs virtually at constant output, that is, constant torque, speed, and fuel consumption; and it does so virtually irrespective of changes in load on the output runner. The characteristic features of the runner or output member are an approximately linear and therefore ‘stepless’ torque/speed performance, and a highly variable efficiency and power output, approximately parabolic with output speed. The output from this inherent stepless torque conversion is compared with the stepped conversions of the conventional gear transmissions. At maximum power throughput the efficiency of the hydraulic unit is about 85 per cent, compared with about 90 per cent plus, for the orthodox gear transmission. The performances of both types of tractor on formal tests of the Nebraska† type are also compared. Methods of automatic control of the combined engine/converter, for example, to give a constant output speed, are suggested.