Transmissions with three power-flows for trucks and tractors

Abstract

Trucks, agricultural machinery and tractors are equipped with transmissions consisting of main 3-speed or 4-speed gearbox with fixed axles of gears and a planetary splitter and/or a planetary range change unit. These planetary gear sets reduce the rotation speed or work in direct gear depending on the driving conditions of the machine. The splitter and range change unit are also providing up to 4 times extension of the number of gear ratios realized by transmission. If the planetary gear set in such transmissions will work as differential drive, it will allow increasing the number of gear ratios in the combined planetary-layshaft transmissions and the number of operating regimes of the tractor consequently. As a result, the gears with fixed axles can work separately in one-stream operation mode of the planetary gear set (reducer or direct gear) and in a two-stream mode - in parallel with other layshaft gears, when the planetary gear set is working as a differential drive. It was shown that combined two-stream planetary-layshaft transmissions consist of simple gear trains, have high efficiency and provide more overall gear ratios, if compared with transmissions consisted of the gear trains of one type. Two planetary gear sets operating as differential drives increase the number of parallel power-flows to three, which allow further improvements of the functionality of transmissions. In addition, if in two-stream transmissions 50-60 % of the input power is transmitted along the paths, then in three-stream transmissions this percentage is reduced by a factor of 1.5 or 2. The purpose of the paper is to analyse structural schemes of planetary-layshaft transmissions with three power-flows, to determine their general characteristics and to develop a method for synthesis of the kinematic diagrams of these transmissions.