GM's plan to offer one million vehicles annually with six-speed automatics by 2008 accelerates in 2006 and 2007 with nearly 40 global vehicle applications of the fuel-saving transmissions. Models of the 2007 Cadillac STS and SRX, as well as the Saturn Aura, Outlook and Pontiac G6, highlight the vehicles offered with new six-speed automatics.
Other models already on sale include the GMC Yukon Denali family, the Cadillac XLR-V, STS-V and Escalade lineup, and the Chevrolet Corvette. GM's full-size heavy duty pickups are also equipped with an Allison 1000 six-speed automatic when equipped with the Duramax 6.6L turbo-diesel engine.
New 2007 model year six-speed automatic transmission variants include the Hydra-Matic 6T70 and 6T75 for front and all-wheel drive vehicles, as well as the Hydra-Matic 6L50 for rear and all-wheel drive vehicles. The 6L50 benefits from the expertise developed with the larger 6L80 rear-wheel drive six-speed transmission (initially in the 2006 model year), and is the second variant in the Hydra-Matic rear-wheel drive six-speed transmission family.
Advantages of a six-speed automatic include improved fuel economy, performance and a shift feel that is seamless to the customer. The six-speed automatic enables a reduced engine rpm at highway cruising speeds. A lower engine speed reduces engine wear and noise, and improves fuel economy.
"It's a best-of-both-worlds scenario with the six-speed automatic, delivering great performance and enabling improved fuel economy," said Jim Lanzon, executive director of transmission engineering for GM Powertrain. "It is almost like having two transmissions in one - the high numerical first gear provides tremendous off-the-line acceleration, but the transmission is able to use the six gears to evenly distribute the torque and settle at an overdrive gear that helps deliver great fuel economy."
Vehicle performance is enhanced with a six-speed, because smaller "steps" are used between gears, compared to a conventional four-speed automatic. This allows the transmission to quickly find the best gear for the vehicle speed and road conditions - there's less back-and-forth hunting on grades, for example. GM's new Hydra-Matic six-speeds also use technically advanced clutch-to-clutch operation, which reduces mass, complexity and enables compact packaging. A wide, 6.04:1 overall ratio on most of GM's six-speeds, compared to 4.0 of typical four-speed automatics, delivers both great performance and improved fuel economy.
"The mechanical simplicity of the clutch-to-clutch shift operation in our new six-speed automatic transmission families, along with a conscious effort to reduce part complexity, is providing us greater flexibility and the ability to launch with a broad application across the GM portfolio," said Lanzon. "By 2010, GM will introduce 10 new variants of six-speed automatic transmissions, producing three million six-speeds annually."
GM's six-speed transmissions also provide tremendous flexibility to customize features for each vehicle brand, such as tapshift range selection, auto grade braking and a tow/haul mode.
