GM's Hydra-Matic 6L80 Six Speed Automatic Delivers Balanced Performance, Economy For Full-Size SUV's
Manufactured at GM's Toledo, Ohio and Ypsilanti, Mich. manufacturing plants
One of the most sophisticated transmissions in the industry with clutch-to-clutch operation
Wide 6.04:1 ratio spread delivers excellent balance of performance and fuel economy
Approximately 9-percent reduction in engine rpm at 60 mph (compared to the 4L60 four-speed transmission) for enhanced fuel economy and NVH characteristics
Tow/haul mode and auto grade braking for optimal towing performance
Manual range selection for driver-selectable performance
A new GM Hydra-Matic 6L80 rear-wheel drive six-speed electronically controlled automatic transmission designed for the performance requirements of trucks debuts in GM's 2007 full-size SUVs. It is one of the most technologically advanced transmissions in the industry, featuring clutch-to-clutch operation, manual range selection and an integrated 32-bit electro-hydraulic controller.
The 6L80 is available on vehicles equipped with the Vortec 6.2L V-8 engine. A wide, 6.04:1 overall ratio - including two overdrive gears - helps deliver an excellent balance of performance and fuel economy. It is similar to the six-speed "paddle shift" automatic transmission introduced on the 2006 Corvette, but has been tailored for the heavy-duty requirements of SUVs and trucks.
"There are no compromises with the Hydra-Matic 6L80 transmission - it delivers great performance and enables improved fuel economy on the highway, all with smooth, almost imperceptible operation," said Jeff Baran, chief engineer for six-speed rear-wheel drive transmissions. "Complementing its sophisticated performance characteristics is the tough capability necessary for the demanding duty cycle of trucks and the tasks their drivers ask of them."
The Hydra-Matic 6L80's six forward gears have smaller "steps" between them, compared to a conventional four-speed automatic, which bolsters both performance and the feeling of smoothness. Shorter steps between the gears help the transmission quickly find the best gear for the vehicle speed and road conditions, with less back-and-forth hunting on grades - a trait that is particularly helpful when towing.
The smaller steps also enable a steep, 4.02:1 first gear, which provides an improved-performance launch feel. The two overdrive gears include a 0.85:1 ratio in fifth gear and a 0.67:1 ratio in sixth. With two overdrive gears, engine rpm is reduced by approximately 9 percent at 60 mph - a reduction to about 1,500 rpm. Lower engine rpm can bolster fuel economy because less fuel is used. A lower-rpm cruising speed also enhances smoothness and reduces noise heard in the vehicle's cabin.
Clutch-to-clutch operation
The 6L80's sophistication is exemplified by clutch-to-clutch operation that reduces complexity and packaging. It also enhances the performance feel of the transmission, as shifts feel more immediate and precise.
Clutch-to-clutch operation is achieved with three planetary gears, two stationary clutches and three rotating clutches. It is a simple, less complex design that enables the six-speed transmission to be packaged in a size not much larger than a four-speed automatic. Only the first-to-second upshift is a freewheeling action, where the second gear clutch engages while the first gear one-way clutch spins freely. This allows a greater degree of smoothness at lower vehicle speeds.
Internal controller and driver-selectable features
A new, 32-bit electro-hydraulic control module optimizes transmission performance according to a variety of vehicle inputs, while also enabling features including tow/haul mode, auto grade braking and manual range selection. The controller is located entirely within the transmission and operates while immersed in transmission fluid. Locating the controller internally shields the controller from outside elements.
Tow/haul mode is a driver-selectable feature that provides optimal shift characteristics specific for towing or hauling a heavy load. The feature is complemented by manual range selection, which allows the driver to block out upper gears and select desired gears for unique driving conditions, such as towing on a steep grade. The manual range selection feature increases the feeling of control by holding the gear pre-selected by the driver. Electronic safeguards prevent the transmission from being shifted in a manner that could cause engine damage or loss of vehicle control. Auto grade braking is available when the tow/haul mode is selected and the transmission is not in the range selection mode.
GM's first Hydra-Matic six-speed RWD 6L80 was initially introduced in the 2006 Chevy Corvette and Cadillac STS-V and XLR-V. For 2007, GM is offering the 6L80 in the 2007 Cadillac Escalade and GMC Yukon Denali SUVs. GM will produce more than one million six-speed automatic transmissions annually by 2008, and more than three million annually by 2010.