Building a better CVT? - WIP - Brief Article

Automotive Design & Production, Sept, 2002 by Kermit Whitfield

Continuously variable transmissions [CVTs] fall in the category of technologies that are theoretically elegant, but difficult to implement. And though automakers from Audi to Honda to Saturn have shown increased interest in CVTs in recent years, application rates remain low. Part of the problem is that, because current CVT designs are friction-dependent, tremendous pressure is placed on the unlubricated bands and pulleys that send engine torque to the wheels. This leads to premature part wear, and has kept CVTs mainly in the realm of small, low torque and horsepower cars. But inventor Lawrence Anderson thinks he can change all that.

Anderson has come up with something he calls "floating sprocket bars" that are spring-loaded and mounted radially on the pulleys of current variable diameter pulley designs. He claims the bars greatly reduce the pressure placed on the drive system and cut wear through better lubrication by transforming variable-pulley CVTs From Friction- to positive-drive. However, Anderson's design also replaces the drive belt with a beaded chain that catches and drives each sprocket bar. [His working model uses a light switch chain to represent this component.]

Anderson believes his invention will eliminate the need for the high-pressure hydraulic system used in conventional CVTs thus reducing the overall transmission size and weight to "roughly equivalent to a four-speed gearbox in a small car," and allowing automakers to apply CVTs to high-torque engines.

Lawrence Anderson's variation on the CVT theme uses spring-loaded "floating sprocket bars" driven by a beaded chain. The bars pivot, allowing them to smoothly accept the uniform spacing of the chain even as the gear ratio changes.