Implicit regulation for automotive variators

Abstract

A well-known practice uses mechanical variators to realize the so-called continuously variable transmissions (CVTs) for automotive application. A remarkable problem for one of the most used CVTs is given by the hydraulic control of the axial thrust on the half-pulleys that is necessary for torque transmission. It involves a heavy decrease in transmission efficiency. In the present paper, the possible production of the required axial thrust by a simple spring to eliminate hydraulic losses is analysed. It is shown that the power capacity of such a regulated variator is near to the maximum possible, and the belt torque loss is always considerably lower than the sum of the belt and pump losses of a standard controlled CVT. Moreover, it is not much greater than a slip limit controlled CVT for medium-low vehicle speeds, and slightly lower for higher speeds. Finally, the power capacity by the spring thrust is evaluated when the variator is used in split power transmissions, considering several configurations and steady ideal operation.

On the Feasibility of Independently Controllable Transmissions

“…Infinitely variable transmissions [20][21][22][23] have been successfully applied as vehicle transmission.…”

Design and analysis of a modified power-split continuously variable transmission

“…Other designs actually placed less of a load on the CVT for a true power-split design (Mucino et al, 1997). It was recognized through this research that the qualities of extended ratio range and extended power envelope were inversely proportional (Beccari and Cammalleri, 2001).…”

“…This creates a loading condition on the belt, which is a combination of a buckling load over the axial surface of the belt and a tensile load on the belt between the two pulleys (Kluger and Fussner, 1997). The power is transmitted from the tensile force on the belt as a result of the friction force created by the sheaves pressure on the belt, so the belt stress is the limiting factor in the power capacity of a V-belt CVT (Beccari and Cammalleri, 2001). The split-conical sheave design of the V-Belt CVT requires some source of axial force in order for the transmission to transmit power efficiently.…”

“…While technical development has brought the CVT back into the realm of automotive design, it still suffers from such problems as poor launch feel or reduced high speed fuel economy because of limited ratio coverage and torque capacity (Vahabzadeh, 1990), and the CVT has shorter transmission life at high power densities when compared to conventional transmissions (Hewko, 1986). These problems can be overcome by combining the CVT with one or more epicyclic gears to create a power-split transmission (Beccari and Cammalleri, 2001).…”

“…It is recognized that the power capacities of CVTs still fall far short of the power output of large-displacement engines used in larger automobiles. These power capacities can be extended when the CVT is combined with an epicyclic gear set (Beccari and Cammalleri, 2001), and the life of the CVT can be extended if its transmitted power is kept to a minimum (Hewko, 1986) 1.1 Problem Statement and Thesis Objectives…”