Evaluation of functionality and mass of two IVT-drives in helicopter-compound split drivetrains

Abstract

The research described in this paper is part of the international research project VARI-SPEED. The aim of this project is to enable main rotor speed variation of rotorcraft in order to reduce the required propulsion power, which enables modern and ecologically efficient aviation. Application of an infinitely variable transmission, capable of speed ratios from ?? to 0, inside the helicopters compound-split module allows for seamless change of rotor speed within a ratio spread of 1.5. This study investigates whether two continuously variable transmission concepts based on the principle of the freewheel and the NuVinci traction drive satisfy the boundary conditions with regard to speed ratio range, mass and power transmission capability for a helicopter of the CS29 class. The general functionality is described for both transmission concepts and kinematic as well as force models are given in order to allow for a rough design, which acts as a base for the mass calculation. Validation for the freewheel gearbox is performed via multi-body dynamics simulation in SIMPACK and gear design in KISSsoft. The design of the traction drive is accomplished by implementation of a parametric model in MATLAB and fully automatic optimization by genetic algorithm. Although the freewheel gearbox allows a transmission ratio of ?? to ?1, the necessary speed ratio of ?? to 0 could not be achieved. The traction drive concept, although capable of the required transmission ratio, is impaired significantly by recirculating power and much greater mass than the reference hydraulic variator unit utilized in previous publications. These findings are important for choosing the best infinitely variable transmission for application in the compound split drivetrain investigated in VARI-SPEED