Continuously Variable Transmission
Continuously Variable Transmission
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 LEGACY AND OUTBACK MODELS, A STATE-OF-THE-ART, ELECTRONICALLY CONTROLLED CVT WILL BE AVAILABLE ON SELECT 2012 SUBARU IMPREZA 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 2012 Subaru Impreza models equipped with CVT.
HOW CVT WORKS
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.
The Subaru Lineartronic CVT features a manual mode system that simulates a six-speed manual transmission. When in this "virtual" manual mode, the driver can use paddle levers on the steering wheel to select one of six programmed "speeds." These six speeds are ratios intended for various driving conditions.
Shifting to a lower ratio is accomplished by tapping the downshift when the vehicle is in "Drive." The manual downshift holds the chosen ratio until the engine's rev limit is reached.
BENEFITS OF CVT
The Lineartronic CVT has several benefits:
Smooth operation: Continuous, step-less variation of the width of the drive and driven pulleys takes place without mechanical gear changes. Other than the response of the powertrain relative to driver input, there is no sense of upshifting or downshifting. The end result is smooth operation, which contributes to passenger comfort.
Fuel efficiency: The control modules for the engine and transmission keep the engine in its optimal power range, changing CVT pulley ratios to achieve improved fuel economy and performance.
Improved response: By eliminating gear changes, the step-less CVT enables the powertrain to be more responsive to changes in throttle application and vehicle speed. For example, there is no gear hunting when driving uphill.
Fun to drive: By simulating the operation of a manual transmission, the Lineartronic CVT's manual mode increases driver involvement and makes the vehicle more fun to drive.
Interior comfort: By incorporating chain drive in the CVT's design, Subaru was able to engineer a more compact unit. That enabled increased space for the passenger cabin, with more leg room, in particular.
Altogether, the Subaru Lineartronic CVT adds to the premium driving experience of the 2012 Impreza models.