|The 6L80 RWD six-speed automatic.|
GM is making a big push with its six-speed automatic transmissions. The company plans to offer one million vehicles annually with six-speed automatic transmissions by 2008, and three million by 2010. For model years 2006 and 2007, six-speeds will appear in nearly 40 global vehicles.
Advantages of a six-speed automatic include fuel economy improvement of up to 4% and power improvement of up to 7% compared to a four-speed automatic, and delivering a shift feel that is seamless to the customer. The six-speed automatic enables a reduced engine rpm at highway cruising speeds, thereby reducing engine wear and noise, and also helping fuel economy.
With a six-speed, 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.
The company recently introduced three new members of the six-speed family. Most of GM’s six-speeds feature a wide, 6.04:1 overall ratio compared to 4.0 of typical four-speed automatics.
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 new 6T70 and 6T75 six-speed automatics are designed for front- and all-wheel drive vehicles. The transmissions are based on a common design, with the 6T75 rated for higher torque capacity. The 6T70 debuts on the Saturn Aura and on a Pontiac G6 model; the 6T75 will be offered on the Saturn Outlook.
The 6T70/75’s clutch-to-clutch operation and 6.04:1 overall ratio help the transmission deliver up to 7% improved performance and up to 4% improved fuel economy when compared with current front-wheel drive four-speed automatics.
Both transmissions use a very high numerical 4.48:1 first gear, which helps deliver exceptional launch feel, and a 0.74:1 overdrive sixth gear, which reduces engine rpms at high speeds, thereby reducing engine noise and vibrations. Fifth gear is 1:1 direct drive.
GM co-developed the 6T70/75 with Ford Motor to reach production in less time and to reduce development costs for each company by as much as 50%. A common on-axis design and many common components are shared between GM and Ford Motor Co. The controls, calibrations and operation of the transmissions are unique to each company.
GM also announced an additional $332 million investment in the Warren Transmission Plant to support production of the new six-speeds.
The new 6L50 six-speed transmission debuts in certain 2007 Cadillac STS rear- and all-wheel drive performance sedans and the V-8-powered SRX crossover SUV. The 6L50 is the second model of four new variants in the RWD six-speed transmission family. The 6L50 is designed with the same modular flexibility as the larger 6L80 and is fully compatible by using the same advanced electronic controls. As with the 6L80, the 6L50’s gearset configuration enables the same 6.04 wide overall ratio.
The 6L80 six-speed automatic transmission was the first of four variants in the rear-wheel drive transmission family designed with modular flexibility and compatibility with advanced electronic controls.
It also features clutch-to-clutch operation, manual range selection and an integrated 32-bit electro-hydraulic controller. It debuted in 2006 on the Cadillac XLR-V, STS-V and Chevrolet Corvette, where it is offered with paddle-shift control.
The 6L80 also is tailored for the heavy-duty requirements of SUVs and trucks, and is offered on GM’s 2007 full-size SUVs equipped with the Vortec 6.2L V-8, such as the GMC Yukon Denali and Cadillac Escalade.
With two overdrive gears, engine rpm is reduced by approximately 9% at 60 mph—a reduction of about 1,350 rpm.