GM’s Unprecedented Launch of Six-Speed Transmissions Shifts into High Gear

PONTIAC, Mich. - Transmission engineers at General Motors Corp. have given new meaning to the term “overdrive.” By using high-tech computerized tools, they launched nine new fuel-saving six-speed transmission models - the industry’s largest lineup - in just four short years. Furthermore, their use of this technology has shaved as much as six months and $15 million from the typical transmission development process.

GM transmission engineers use sophisticated math modeling, among other advanced tools, to not only design the transmission components, but also to predict and test their reliability, analyzing functions such as oil pressure and flow, lubrication distribution and shift quality.

“We are using computer-based tools in powertrain development for our global engine and transmission programs and seeing terrific results,” said Tom Stephens, group vice president, GM Powertrain and Quality. “On our six-speed transmissions alone, we launched nine models in four years whereas we previously averaged three or four transmissions every decade.”

Stephens said this pace of product development and first-time quality is having an impact in GM’s gasoline and diesel engines, where analytical models also are used early in the process to improve design and functional performance.

“On our new 4.5L V-8 diesel, for example, analytical models were used to design and evaluate nearly 500 different piston shape designs during a 10-day period before we picked the best one. To evaluate this many designs without computer tools would have been unrealistic in terms of timing and cost to do with actual parts,” said Stephens.

GM’s computer modeling and use of common parts on the four rear-wheel-drive (RWD) transmission models reduced development time as much as 50 percent. In fact, 47 percent of the parts are shared among all of the RWD models; and the 6L90 transmission (used in GM’s full-size pickups) shares 75 percent of its components with the 6L80 transmission (used in GM’s full-size sport utility vehicles, the Chevrolet Corvette, Cadillac XLR-V and STS-V, among other models).

GM engineers use the high-tech tools early in the development process to identify whether the computer analysis is sufficient and if physical parts still need to be fabricated and tested. In some areas, simulated tests took only 48 hours versus several weeks, helping to eliminate, in some cases, the need for costly and time-consuming prototypes.

Development of the six-speeds began in 2003, with the first of the RWD models being launched in 2006. GM’s extensive use of computer math modeling tools has enabled the company to develop the various six-speed models in parallel. “Our use of computer tools has improved the first-time quality of our transmission prototypes by five times over past programs,” said Jim Lanzon, executive director of GM Powertrain’s Transmission Engineering. “We’ve eliminated one of three pre-production hardware builds - essentially a complete set of prototype transmissions - and the associated physical tests.”

Lanzon said the new 6T40 front-wheel-drive six-speed model launching in GM Daewoo’s Boryeong facility this month was developed by GM Powertrain’s Transmission Engineering in Ypsilanti, Mich., and the math model was sent to GM Daewoo in Korea for final development and manufacturing.

“The 6T40 transmission was built in Korea from our math models, placed in the first vehicle and performed beautifully,” said Lanzon.

Among GM’s first six-speed models were RWD transmissions introduced in 2006 in the Chevrolet Corvette, Cadillac XLR-V and STS-V. All of the six-speed automatics for RWD and FWD/AWD were designed for maximum application flexibility, allowing them to be used in the greatest number of vehicles in GM’s vehicle portfolio.

Shared traits among the new six-speed automatics reduce complexity, size and mass, including clutch-to-clutch operation that enables the six-speed to be packaged into approximately the same space of a four-speed automatic. The transmissions also share an overall 6.04:1 gear ratio, which contributes to their signature balance of performance and fuel economy.