YPSILANTI, Michigan - A new Hydra-Matic 6L50 six-speed automatic transmission for rear and all-wheel drive vehicles becomes the second six-speed transmission variant in production at GM’s Ypsilanti, Mich. Transmission Operations. The 6L50 benefits from the expertise developed with the larger 6L80 rear-wheel drive six-speed transmission, which is also produced at YTO and initially launched in the 2006 model year.
The 6L50 will debut in certain 2007 Cadillac STS rear- and all-wheel drive performance sedans and the V-8 powered SRX crossover SUV.
The 6L80 debuted in 2006 on the Cadillac XLR-V, STS-V and Chevrolet Corvette. It is also 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.
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 a 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 six-speed variants for front-, rear- and all-wheel drive models, 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.
New 6L50 RWD and AWD six-speed
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.
As with other GM six-speeds, the 6L50 delivers smaller steps between gears, enabling the vehicle to quickly find the best gear. A higher numerical first gear delivers strong acceleration from a standstill and two overdrive gears enable improved fuel economy through lower engine rpms at cruising speed. Also, the lower rpm achieved with the sixth gear reduces engine noise and vibration on the highway.
The 6L50 also uses the Driver Shift Control feature, which allows the driver to shift the transmission like a clutchless manual gearbox. Also, the transmission is calibrated to override the automatic gear selection during closed-throttle and high-lateral acceleration maneuvers, rapidly downshifting with nearly synchronous engine speed matching for quick power-up when the throttle is reopened. This gives the feel of a manual transmission during deceleration. Electronic safeguards prevent over-revving.
6L80 RWD six-speed
The Hydra-Matic 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.
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. In all applications, the 6L80 has a wide, 6.04:1 overall ratio - including two overdrive gears - that helps deliver up to 7 percent improved 0 - 60 mph performance and up to 4 percent improved fuel economy.
The 6L80’s six forward gears have smaller “steps” between them, which bolsters both performance and the feeling of smoothness. The smaller steps also enable a steep, 4.02:1 first gear, which provides an improved-performance launch feel. And with two overdrive gears, engine rpm is reduced by approximately 9 percent at 60 mph - a reduction of about 1,350 rpm.
A 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 integrated within the transmission.
Tow/haul mode is a driver-selectable feature of the 6L80 that reduces shift busyness when 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.