GM 6L transmission

The series was first launched with the 6L 80 in the 2006 Cadillac STS-V, with the remaining three versions all first appearing in 2007 model year vehicles. The 6L 90 was a strengthened and uprated version of the 6L 80, used primarily in heavy-duty truck/van applications. The 6L 50 was used on V8-powered versions of the Cadillac STS sedan and Cadillac SRX crossover, and replaced the 5L 40-E and 5L 50 in GM's lineup. The 6L 45 was a smaller version of the 6L 50, used in certain BMW vehicles and the Cadillac ATS, as part of either rear-wheel drive and all-wheel drive powertrains. == Production ==

The 6L 80 and 6L 90 were assembled at GM Powertrain plants in Ypsilanti, MI (Willow Run Transmission), Toledo, Ohio (Toledo Transmission) and Silao, Guanajuato, Mexico, while the smaller 6L 45 and 6L 50 were produced at those same Toledo and Silao plants, as well as at a GM Powertrain plant in Strasbourg, France. All four models feature clutch to clutch shifting, eliminating the one-way clutches used on older transmission designs. == Planetary gearset concept ==

Improved fuel economy The main objective in replacing the predecessor model was to improve vehicle fuel economy with extra speeds and a wider gear span to allow the engine speed level to be lowered (downspeeding), which is a decisive factor in improving energy efficiency and thus reducing fuel consumption. In addition, the lower engine speed level improves the noise-vibration-harshness comfort and the exterior noise is reduced. It has a torque converter lock-up for all 6 forward gears, which can be fully disengage when stationary, largely closing the fuel efficiency gap between vehicles with automatic and manual transmissions. Reduced manufacturing complexity In order to avoid a further increase in manufacturing complexity while expanding the number of gear ratios, ZF switched from the conventional design method—in which the planetary gearset concept was limited to a purely serial or in-line power flow—to a more modern design method that utilizes a planetary gearset concept with combined parallel and serial power flow. This was only possible thanks to computer-aided design and has resulted in a globally patented gearset concept. The 6L is based on the 6HP from ZF, which was the first transmission designed according to this new paradigm. After gaining additional gear ratios only with additional components, this time the number of components has to decrease while the number of ratios still increase. The resulting progress is reflected in a much better ratio of the number of gears to the number of components used compared to existing layouts. Quality The ratios of the 6 gears are nicely evenly distributed in all versions. Exceptions are the large step from 1st to 2nd gear and the almost geometric steps from 3rd to 4th to 5th gear. They cannot be eliminated without affecting all other gears. As the large step is shifted due to the large span to a lower speed range than with conventional gearboxes, it is less significant. As the gear steps are smaller overall due to the additional gear(s), the geometric gear steps are still smaller than the corresponding gear steps of conventional gearboxes. Overall, therefore, the weaknesses are not overly significant. As the selected gearset concept saves up to 2 components compared to 5-speed transmissions, the advantages clearly outweigh the disadvantages. The layout brings the ability to shift in a non-sequential manner – going from gear 6 to gear 2 in extreme situations simply by changing one shift element (actuating clutch E and releasing brake A). In a Lepelletier gearset, a conventional planetary gearset and a composite Ravigneaux gearset are combined to reduce both the size and weight as well as the manufacturing costs. Like all transmissions realized with Lepelletier transmissions, the 6L also dispenses with the use of the direct gear ratio and is thus one of the very few automatic transmission concepts without such a ratio. == Applications ==