New 9-Speed Pushes Tech Limit, GM Says

The new 9-speed yielded GM 60 new patents and required 800 prototypes. The most unique element of the unit is an industry-first deployment of a selectable 1-way clutch.

James M. Amend, Senior Editor

December 7, 2016

5 Min Read
GMrsquos HydraMatic 9T50 9speed automatic
GM’s Hydra-Matic 9T50 9-speed automatic.

DETROIT – General Motors releases details on its all-new 9-speed automatic transmission, a technology and patent-packed gearbox the automaker expects will spur a 2% fuel-economy gain and impress customers with smooth drivability.

“This thing is going to excite our customers,” says Scott Kline, assistant chief engineer for the Hydra-Matic 9T50 9-speed automatic. “When you get in it, you can tell it is a premium product.”

Chris Meagher, executive director-Transmission and Electrification Hardware Engineering at GM, calls the transmission entering the market in the ’17 Chevy Malibu midsize sedan and coming to the ’17 Chevy Cruze Diesel small sedan this summer and ’18 Chevy Equinox midsize CUV later in the year a major step toward meeting future global fuel-economy and emissions regulations.

But as pivotal an efficiency role as automatic transmissions with greater than the traditional six forward gears can play, it is unlikely GM will go much beyond nine speeds for front-wheel-drive vehicles and a 10-speed automatic due soon for its rear-wheel-drive applications.

“We don’t see the benefit of going higher than 10 forward speeds,” Meagher tells WardsAuto following a presentation on the technologies here.

But never say never, he adds, noting that when GM deployed its revolutionary lineup of 6-speed automatic transmissions a decade ago no one imagined hardware and software technology would advance so dramatically to permit 9- and 10-speed executions.

“So you never really know for sure,” he admits.

Like the old 6-speed units, which GM refined over the years and expects to continue applying to its vehicles into the near future, the 9-speed was developed through a partnership with crosstown rival Ford.

Both automakers also derive 10-speed variants from the work. Ford brought that gearbox to market recently in the F-150 large pickup, while GM got first dibs on the 9-speed. GM’s first application of the 10-speed will be in the ’17 Chevy Camaro ZL1, a 640-hp supercharged version of the sports coupe due later this year in the U.S.

“Think of it as two-for-one,” Meagher says of the cost savings from developing the units with a partner.

The GM and Ford transmissions are nearly identical from a hardware perspective, although some parts differ because each automaker links to its engines differently. Each uses its own parts code and is free to source the parts from suppliers of its own choosing.

The GM and Ford units differ greatly from a driving dynamics perspective. Each automaker deploys its own software to the transmissions to impart a specific character to each vehicle using them.

Meagher says the global nature of the 9-speed program and worldwide popularity of vehicles getting the gearbox over the next several years will push volumes high. He declines to offer a production outlook, but WardsAuto forecasting partner AutoForecast Solutions projects global penetration of the unit will rise from 478,518 units in 2017 to 2.16 million in 2023.

That means the 9-speed likely someday will replace the current 6-speed altogether, with the latter sticking around until volume deployment of the former brings economies of scale. The 6-speed also may be a good fit for a period in emerging markets where cost sensitivity is more acute.

As for now, a fourth model also will receive the 9-speed soon, perhaps on a redesigned GMC Terrain midsize CUV. GM expects 10 vehicle models to use it by the end of 2017. It is built at GM’s San Luis Potosi, Mexico, manufacturing operation after a recent $131 million investment to accommodate its production.

The 6-speed automatic transmission remains the popular gearbox in the U.S., appearing on 54.8% of light vehicles in the ’16 model year, according to WardsAuto data.

High-Tech Gearbox

The new 9-speed yielded GM 60 new patents and required 800 prototypes. It is the same size as the old 6-speed and weighs about 22 lbs. (10 kg) more. The most unique element of the unit is an industry-first deployment of a selectable 1-way clutch, which can hold torque or operate freely depending on the situation.

“It took a good bunch of the development work,” Kline says of the single clutch, which handles duties historically performed by two clutches. As such, the innovation reduces overall weight and size, making it easier to package for transverse applications.

“There were a lot of smart people working on it,” Kline says.

The 9T50 uses an on-axis design, where the gears are in line with the crankshaft, to further optimize packaging.

It also employs a stop-start accumulator, which ensures smooth re-engagement of the transmission at restart.

Unique shift controls include automatic grade braking, where a lower gear will hold vehicle speed while traveling downhill or coasting, while active oil management electronically monitors conditions to deliver precise pressure and volume for optimal efficiency.

The unit is filled with Castrol-brand DEXRON-VI fluid to eliminate service changes under normal driving conditions. GM says the fluid features consistent viscosity, consistent shift performance and reduced degradation.

In-house logics software inside a 32-bit transmission control module handles all shift events for smooth, precise ratio changes, GM says. It also monitors transmission performance and compensates for wear in parts such as the clutch plate to maintain consistent performance over time.

“This transmission shifts very smoothly, very precisely,” Kline says.

The controller is mounted outside the gearbox to reduce packaging and manufacturing complexity, and it pulls vehicle-specific calibration from the cloud to be added to the core program as the car or truck exits the assembly line. It also enables manual shift control and grade logic, GM says.

The 9T50 features a wider 7.6:1 overall ratio, compared with 6.0:1 in its 6-speed predecessor, a deep 4.69 first gear for off-the-line performance and a tall 0.62 top gear for fuel-efficient, low-rpm highway cruising and optimal NVH.

Sixth gear is equivalent to eighth gear on the new transmission, too, so compared with the 6-speed the 9-speed offers two fuel-saving overdrive gears. Seventh gear is the direct-drive gear, while ninth gear is in use up to 52% of the time.

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