CVT Rolling Traction Drives—A Review of Research Into Their Design, Functionality, and Modeling

[+] Author and Article Information
S. Akehurst, D. A. Parker

 University of Bath, UK

S. Schaaf

 InterSyn Technologies, USA

J. Mech. Des 128(5), 1165-1176 (Oct 03, 2005) (12 pages) doi:10.1115/1.2214737 History: Received December 21, 2004; Revised October 03, 2005

In this paper we detail a review of the current state of published work regarding the modeling of rolling traction drive Continuously Variable Transmissions (CVTs). An overview of CVTs operating by traction through small contact areas is performed, the layouts and kinematics of leading examples are reviewed, including the factors affecting design optimization. Properties of the traction contacts are considered in detail, with particular attention to elastohydrodynamic lubrication and asperity contact. Factors affecting the traction coefficient are reviewed and fundamental empirical predictions are contrasted with modern modeling computations. Finally measurements of the rheology of traction fluids are considered, leading to a definition of ideal properties and the development of proprietary fluids.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 2

(a) Schematic of the Motion CVT; (b) schematic of the Kopp variator

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Figure 3

(a) Layout of Milner CVT (9); (b) a full toroidal CVT ratio changed by steering of rollers, as indicated by arrows. Drive to end elements and drive out from the center element. This particular view is a dual cavity version of the full toroidal CVT.

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Figure 4

Effects of various operating conditions of EHL contact performance as predicted by Nikas (16), (a) effect of contact load; (b) effect of slide-roll ratio at a constant Hertzian pressure; (c) effect of ellipticity ratio; (d) effect of surface roughness; (e) effect of fluid bulk temperature

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Figure 5

Evaluation of spin by Cretu and Glovena (34), (a) typical traction contact; (b) spin test rig

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Figure 6

Results presented by Nonishi (43) for traction contacts, (a) effect of slip/roll ratio; (b) effect of contact pressure and speed on transmissible torque

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Figure 7

(a) Traction curves for both directions (Sharif (46)); (b) viscosities from the Yasutomi equation (50) using experimental data from Bair and Winer (48). Results from the test rig using Santotrac 50 fluid.

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Figure 9

Elastic shear modulus and limiting shear stress of Santotrac 50. (a) Elastic shear modulus at various pressures and temperatures (Fang (52)); (b) elastic shear moduli from other authors (Fang (52)); (c) limiting shear stress at various pressures and temperatures.

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Figure 10

Measurements of traction performance (Newell (47)) using fluid P1. (a) Effects of spin on traction curve at 90°C, U=11m∕s, Pmax=2GPa; (b) effect of rolling speed; (c) effect of contact conformity.

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Figure 1

(a) Effect of contact pressure on film thickness and traction coefficient (Hewko (1)); (b) effect of creep on traction coefficient (Hewko (1))

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Figure 8

(a) Typical rheological behavior of lubricant under EHL conditions; (b) typical traction curve for Santotrac 50, ph=2.5GPa, T=40°C, u=2.0m∕s. Experimental measurements by Fang (52).



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