Power flows and efficiency analysis of out- and input coupled IVT

Abstract

Since late 1995, when the high-powered (194 kW) Fendt Favorit 926 equipped with a ´´Vario´´ transmission was launched, power machines with CVT (Continuously Variable Transmission) have appeared on the palette of all major tractor manufacturing companies as well. The CVT unit in the transmission of these power machines is not included directly in the power flow, but in one of the power branches after a split. By modifying the gear ratio of a properly selected CVT unit, the transmission can be geared neutral and the direction of progress of the vehicle can be changed. The transmission structure produced so is called power split IVT (Infinitely Variable Transmission). The paper presents the ways of producing an IVT drive and analyzes the Fendt ``Vario´´ driving mechanism with OC-RSC structure and the same elements but with IC-RSC structure. There is detailed analysis on both structures on power flows (power split, positive/negative power circulating), the Geared Neutral and the backward operational stages, taking into account the significant states from efficiency calculation point of view, together with changes thereof in function of output revolution. Based on these investigations it is highlighted that the entire range of the course of the vehicle can be covered by an output coupled system adjusting the gear of the CVT unit within the high-efficiency range. The task is the same for input coupled systems, to be realized by planetary gears installed after the IVT unit and by the proper control of their engagement.