GM Uses Math to Trim 6-Speed's Cost, Development Time

General Motors Corp. says math-based tools allowed it to shave $150 million from the development of its current 6-speed transmission lineup, a launch that began in 2004 and now numbers nine gearboxes.

“Two to three (transmissions) in a decade would be a big deal,” says Jim Lanzon, executive director-transmission engineering at GM Powertrain. “But to do 10 in four years or so takes a lot of tools, a lot of know-how and disciplined execution.”

The 10th 6-speed arrives next year. GM declines to pinpoint vehicles that will get the new gearbox, but its lineup of 6-speeds currently includes four rear-wheel-drive applications and five front-/all-wheel-drive setups.

Six-speed gearboxes account for 20% of GM's transmission installations worldwide, and that should double to 40% next year, Lanzon says.

According to Ward's data, 6-speed manuals appeared in 1.5% of GM's '07 model year cars produced in North America for the U.S. market through January 2007, while 6-speed automatics accounted for 4.1% of all installations.

A 6-speed manual went into only 0.1% of GM's '07 model year trucks for the U.S., the data shows, but the automatic appeared in 9.6% of the truck portfolio.

On top of the cost savings, GM has trimmed an average six months of development time on each new 6-speed it rolls out. That includes eliminating one of three pre-production hardware builds per program, which is equal to a complete set of prototype transmissions, GM says.

First-time quality of its prototypes is five times better, officials say.

GM won't divulge how much it spent up front to get the software tools and computing power necessary to book the back-end savings, but it's part of a larger initiative called “Road-to-Lab-to-Math.”

The idea is to continually push the amount of development time engineers spend out in the field into the laboratory. Likewise, GM wants more development time pushed from the lab to the analysts that run GM's computer-aided engineering (CAE) math modeling tools.

“It's a process within a process,” says Steve Ackerman, director-Transmission Hardware Release Center at GM. But in the end, the approach drives engineers out of the vehicle and into a math environment, he says.

And every new transmission developed advances GM's analytical capabilities. Before GM started its 6-speed program, the transmission group had just over 100 CAE analysis routines at its disposal. Today it can call up more than 300.

GM says it leverages CAE not only to design the transmissions' components, but also to predict parts and system behavior and identify performance variations in the production vehicle and manufacturing process. Each 6-speed family — RWD and FWD/AWD — underwent more than 250 different computer analyses.

For instance, to test valve body sealing on the Hydra-Matic 6T70 — a transmission that appears on nearly 40% of '07 Saturn Aura sedans — GM's CAE analysts borrowed 3-dimensional design geometry from their computer-aided design colleagues to build a math model of the five components that make up the subsystem.

The goal was to investigate the effects of geometry, bolt-loading and bolting sequence and the performance of different seal materials. Each of those are exercises engineers previously would have performed on the bench or at the test track at substantially higher cost.

Ackerman says feedback on the production transmissions point to a quality gain.

“Our products are doing quite well,” he says. “Our field information says we're as good if not better than anyone out there.”

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