Abstract
Including a friction variator, the continuously variable transmission (CVT) can steplessly adapt the transmission ratio to take any value between two limits. For that, automotive propulsion systems incorporating CVTs ensure comfort, dynamic performance, driveability and may reduce the fuel consumption, chemical pollution and greenhouse effect emissions through a more efficient use of the engines. Unfortunately, the efficiency of the friction CVTs is generally smaller as the gear transmissions efficiency.
Intending to reduce the CVTs’ efficiency disadvantage, new CVT solutions are studied or already used in automotive applications. Many of these ideas deal with new structures of the power flows inside the CVT. Such transmissions able to change the number and orientation of its power flows, known as “multi-regime CVTs”, can increase their overall efficiency because only a part of the input power passes through the variator, another part passing, with minor losses, through conventional mechanical path, as gears or drive chains.
This paper presents the main problems involved by the use of multi-regime CVT and also proposes some solutions for these. Aspects on transmission’s kinematics and dynamics, as transmission ratio, efficiency, torque conversion, geared neutral, power circulation and couplings management are discussed. It is also indicated a way to transform a CVT in an infinitely variable transmission (IVT).
Keywords: friction variator, CVT, power-split, multi-regime, IVT, power circulation, kinematics, dynamics