THE CVT CONCEPT AND TECHNOLOGY ARE NOT NEW: CVT WAS CONCEPTUALIZED BY LEONARDO DA VINCI IN THE LATE 15TH CENTURY, AND IT WAS AVAILABLE ON THE SUBARU JUSTY FROM THE LATE 1980s THROUGH MID-1990s – THE FIRST CAR WITH A CVT FOR THE U.S. AUTOMOBILE MARKET. FOR THE 2010 MODEL YEAR, A STATE-OF-THE-ART, ELECTRONICALLY CONTROLLED CVT WILL BE AVAILABLE ON SELECT, ALL-NEW LEGACY AND OUTBACK MODELS.
A continuously variable transmission functions as if it had an infinite number of gear ratios. Its changes from ratio to ratio are step-less, contributing to the powertrain's smooth operation. Among its benefits, a CVT wastes less power in transmitting engine torque to the drive wheels. Its efficiencies result in the excellent fuel economy ratings of the non-turbocharged 2010 Subaru Legacy and Outback models equipped with CVT.
The Subaru Lineartronic CVT utilizes an electronically controlled, hydraulically operated pair of adjustable pulleys and a link chain that runs between them. Using a metal chain allows the Subaru design to be more compact.
The pulleys are V-shaped, and the chain rides within each pulley at the point that fits the chain's width. The distances between the sides of the pulleys are adjustable. The powertrain electronic control module varies hydraulic pressure to pull the pulley sides apart or push them together, causing the chain to ride higher or lower in the valley of the V.
The width of the chain remains constant, so making the drive pulley narrower causes the chain to move out from the pulley's hub. At the same time, the driven pulley's sides move apart, and the chain moves closer to that pulley's hub.
When the driving gear is smaller and the driven gear is larger, the CVT functions as if in conventional low gear. Driving through a small gear gives the vehicle starting and pulling power.
When the driving gear is larger and the driven gear is smaller, the CVT functions as if in conventional high gear. This configuration acts like overdrive.
If engine speed is constant, the variations in the diameters of the two pulleys make the vehicle speed up or slow down. In effect, varying pulley sizes change the gear ratio of the transmission -- without changing mechanical gears. During normal driving, there is no conventional "shifting." Passengers do not feel the change.
Because the forward gear ratio range is continuously variable and step-less, it provides a smooth, linear transfer of power and torque. The Subaru system utilizes a wide range of pulley ratios, which enable the CVT to handle a large range of speed and load conditions. In addition, the Lineartronic CVT can be programmed to hold gear ratios at the driver's discretion.