Predicting the demand for 6-speed automatic transmissions will continue to grow to more than 30% of new vehicles sold by 2012, General Motors Corp. initiated production of a new family of Hydra-Matic 6-speed rear-wheel drive automatic transmissions at its Ypsilanti Transmission Operations adjacent to the historic Willow Run transmission plant in Ypsilanti, MI. The 6L80 makes its debut in the '06 Chevrolet Corvette, Cadillac STS-V and XLR-V, along with GM's all-new '07 full-size SUVs, marking the end of a 3-year, $450-million investment for the 1-million ft.2 facility, which used to build B24 bombers for the U.S. military during World War II. Engineers developed the transmissions around a modular manufacturing concept, allowing nearly 47% of components to be shared among the four variants, which enables any of the variants to run sequentially down the same assembly line. "All four variants are manufactured using the same process, thanks to the use of a common power flow, common architecture and common control systems," says Kent Sears, GM Powertrain's vice president of Manufacturing. "We basically made minor changes to the length and the width of the transmissions for each of the variants in order to handle a larger or smaller gear based on the torque handling required." GM estimates the new 6-speed family (which will include a front-wheel drive and heavy-duty variants) can cut 0-60 mph performance times by as much as 7% and boost fuel economy by upwards of 4%, thanks to its two overdrive gears and wide, 6.04:1 gear ratio spread. The two overdrive gears help to reduce engine rpm by approximate 9% at 60 mph, which provides the foundation for the fuel economy boost. "Right now, we think the 6-speed we are building here has optimized fuel economy and launch," says Sears.
The Ypsilanti facility utilizes CNC machining, instead of a transfer line, with the machines arranged in a cell format. The cell design helps to integrate the piece flow process, boosting efficiency. The result will be a reduction in man-hours per transmission to 3.3 hours per unit, down dramatically from the traditional 4 to 4.5-hour level. "Here we have a team operating the cell and the person goes from machine to machine as the part goes around the cell. It is single-piece flow," says Kingsley Wooten, plant manager at the Ypsilanti facility. There are a total of three business teams that fabricate and sub-assemble the transmission component (gears and shafts, prismatic, and assembly). The sub-assemblies are integrated into the transmission case on the main line to produce the finished transmission. All of the material in the plant is delivered to the teams at the stations on a just-in-time basis via automated guided vehicles. All transmissions are hot-tested for up to four minutes, running through all the gears at varying rpm levels.
The new transmission technology should help GM achieve its goal of having more than three million 6-speeds on the market by 2010. But the 6L80 won't be found only under the hood of GM products. Sears says BMW has already signed up to take the 6-speed for a future product, with other OEMs ready to ante up as well. GM has been providing transmissions to more than 250 OEMs around the world, including BMW and Volvo.-KMK