How Traction CVTs Work

The traction or toroidal continuously variable transmission (T-CVT) is commonly used for traction drives in automotive applications. The word toroidal comes from torus, which means a doughnut or inner tube shape. The red and gray discs in the bottom part of the diagram below can be imagined as doughnuts stretched into a vortex-like shape. As shown in the top part of the diagram, Nissan's Extroid CVT unit includes two variators for varying the engine speed, each made up of a set of discs and rollers.

Traction Continuously Variable Transmissions

When the power roller makes contact with the outer edge of input disc and the inner edge of the output disc, the output disc rotates faster than the input disc. This is a higher-speed position as shown at left in the diagram. Its reverse orientation is a lower-speed position.

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