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NYIAS: GM Debuts new FWD 6-Speed Auto

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NEW YORK – The new Hydra-Matic 6T70 and 6T75 six-speed automatic transmissions are making their debut in the all-new 2007 front-wheel drive Saturn Aura midsize sedan and the front- or all-wheel drive 2007 Saturn Outlook crossover SUV. General Motors co-developed this transaxle with Ford Motor Co., the result being a new six-speed featuring state-of-the-art dimensions and enabling both spacious packaging and potential safety design opportunities.

The 6T70/75’s clutch-to-clutch operation allows for reduced complexity and compact packaging, which enables the transmission’s three gearsets to be on the same axis as the engine crankshaft. This reduces the amount of room necessary in the engine compartment for the drivetrain, both front-to-back and top-to-bottom. The compact size allows vehicle designers to optimize interior room, as well as lower the hoodline for aerodynamic efficiency.

The spread of ratios between first and sixth gear is a wide 6.04:1 overall ratio. This means a lower first gear helps the engine accelerate the vehicle from a stop, and the high top gear lets the engine operate as slowly as possible during cruising. As a result, performance is improved by approximately 6 percent to 8 percent, and fuel economy is improved by 2 percent to 4 percent, when compared to a four-speed automatic transmission. The first gear is a very low 4.48:1, while the sixth gear is a 0.74:1 overdrive, which reduces rpm at high speeds, thereby reducing engine noise and vibrations. Fifth gear is a 1:1 direct drive ratio. The final drive ratios can be tailored to each vehicle’s performance requirements, and the design allows a wide variety of final drive ratios. For the Saturn Outlook, the final drive ratio is 3.16:1, while the Aura sedan uses a taller 2.77:1 ratio.

The 6T70/75 is rated for engines up to 315 horsepower and 280 lb.-ft. of torque, and with its larger transfer gears, a five-pinion input carrier and beefier structural ribbing on its aluminum case, the 6T75 can handle engines up to 315 horsepower and 300 lb.-ft. of torque.

The co-development by GM and Ford meant that many common components of the transmission are shared, along with the on-axis design; but the controls, calibrations and operation of the transmission are unique to each company. Costs and development time were reduced in some areas by 50 percent because of the co-development process.

“The additional gear states are almost like having two transmissions in one,” said Bob Vargo, assistant chief engineer for the new transaxle. “The low first gear provides tremendous off-the-line acceleration, but the transmission is able to use the middle gears to evenly distribute the torque and offers an overdrive sixth gear that helps deliver great fuel economy.”

Because there are six gears instead of four, the difference between ratios is less than in a four-speed automatic, giving the vehicle more options for using the best ratio for speed and load conditions. For example, with the transmission in an optimum ratio on a hill, the engine will not need to downshift or upshift unnecessarily. Driver Shift Control further reduces shift events by allowing the driver to select a desired gear for certain road conditions, such as steep and long hills, and automatic grade braking for descending hills. Automatic grade braking reduces brake pedal usage by calculating the rate of acceleration while descending a hill, and retaining a lower gear in the transmission.

The electronic controls are designed so that the shift feel is calibrated specifically to either the new midsize sedans or the new midsize crossover vehicles through the timing of the shifts and torque converter lockup speeds. The space-saving hyper-elliptical, narrow section torque converter uses a single-plate lockup clutch that employs GM’s proprietary ECCC (electronic converter clutch control) to dampen driveline vibrations.

The Hydra-Matic 6T70/75’s highlights:

  • Dimensions of 357 mm in length and 197 mm in width approach those of some manual transmissions, and are among the most compact for a six-speed automatic, and for front- and all-wheel drive vehicles with transverse-mounted powertrains
  • Clutch-to-clutch shift operation for all shifts except 1-2 reduces mechanical complexity and mass, and is calibrated for smooth shift feel
  • Integrated transmission electro-hydraulic control module (TEHCM) with driver shift control (DSC), auto grade braking for consistent speed in hilly terrain and while towing or fully loaded
  • Internal control module reduces powertrain complexity
  • Heat-treated gears are honed for a more precise fit, reducing noise, vibration and harshness
  • Hyper-elliptical, narrow-section torque converter enhances packaging and maintains efficiency
  • Reduced number of seals for stronger input shaft design
  • Adjustable capacity vane-type fluid pump enhances fuel economy
Although used in some low-volume, high-performance sports cars and luxury sedans, six-speed transmissions are rare in midsize sedans and most high-volume midsize SUVs. GM and Ford Motor Co. recognized a need for a transmission that could accommodate increased powertrain performance while delivering excellent fuel economy. The compact size and reduced complexity afforded by the clutch-to-clutch, on-axis design allowed engineers to provide improved performance and economy with six forward speeds.

With its wide ratio spread and capacity for high-torque engines, the 6T70/75 has the capability to transfer more torque to the drive wheels, particularly in the all-wheel drive Outlook. It also helps vehicles to feel livelier at lower speeds for a given engine, particularly at launch or when starting from a stoplight.

The 6T70/75’s advanced clutch-to-clutch operation is designed for smooth shift feel and packaging efficiency. All shifts except 1-2 (the transmission “free wheels” in first) feature clutch-to-clutch operation. The sophisticated electronic controls allow timing the clutch-to-clutch engagements and disengagements so that the transfer of power from one gear to the next is transparent to the driver. The three conventional planetary gears, with three stationary clutches and two rotating clutches, can be packaged in a smaller space without additional freewheeling mechanisms. It’s a simple, less complex design that enables the packaging of six gears in the space of a four-speed automatic.

A sophisticated transmission electro-hydraulic control module (TEHCM) is mounted inside the 6T70/75, reducing vehicle complexity. Similar to the control system used in the Hydra-Matic six-speed rear-wheel drive transmissions, the TEHCM offers improved quality through its hard-wired connections and pre-calibration during the controller’s manufacture.

The unit is located entirely within the transmission and operates while bathed in transmission fluid. Locating the controller internally facilitates the modular design and assembly strategy while also shielding the unit from the outside environment. Temperatures are consistent inside the transmission.

GM’s proprietary model-based controls strategy reaches a greater level of sophistication in the new transverse six-speed transmission family, said Vargo. The 32-bit system incorporates three levels of “learning” that actually allow the components to adapt to one another.

It is not uncommon to have a transmission-control module that adapts to the specific transmission with which it is mated; however, the 6T70/75 accomplishes this with two steps: when the control module assembly is manufactured, and when it is installed inside the transmission.

As with other GM transmissions, the programming optimizes performance characteristics according to a variety of vehicle inputs. Finally, the new six-speed automatic adds another level of adaptability. Certain components within the major subsystems that make up the transmission “learn” from one another – via the controller software – in a unique form of self-adaptation that maximizes the interface of all the “networked” components. This procedure takes place as the transmission “tests” itself and the interaction of its internal components before it is shipped from the assembly plant.

The TEHCM also enables performance-oriented and driver-controllable shift features, including driver shift control (DSC) “tap shift” and auto-grade braking for the midsize SUV and Performance Algorithm Shifting (PAS) for the midsize sedan. PAS recognizes a driver’s particular style of throttle and brake application and essentially “reads his or her mind” and predicts which gear will be most advantageous for performance driving or economical cruising.

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315HP and 300lb-ft is more than enough for almost any FWD application.

Even though the UV8 was supposed to go into the Lambdas, I don't know if there's really a need if the 3.6L is going to make 280-290HP.

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Could let the LS4 have a little bit more power also.

That's what I was wondering.

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with that power capacity are the fiero fans gonna say something about this...? :scratchchin:

just waiting for something along the lines of

"drop the G6 and make rearengine fiero!!" :pbjtime:

it would interesting to see that done, once. and go from there :lol:

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315HP and 300lb-ft is more than enough for almost any FWD application.

Even though the UV8 was supposed to go into the Lambdas, I don't know if there's really a need if the 3.6L is going to make 280-290HP.

You will still have certain consumers that will want a V8....either for power or PERCEIVED power....and for refinement, ease of towing, or performance.

Plus, a V8 Enclave would give Buick a step UP over competitiors such as RX and MDX.

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any related info on if it's heavier than the current 4 speeds? saying it's the same sizegive or take a little doesn't mention the weight, thatd be great to have it reduced just for something extra, even if it is insignificant. lol

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You will still have certain consumers that will want a V8....either for power or PERCEIVED power....and for refinement, ease of towing, or performance.

Plus, a V8 Enclave would give Buick a step UP over competitiors such as RX and MDX.

This is true. Ask my father. His Bonnie can outrun my Olds in most situations thanks to the blower, but...I've a V8. :thumbsup:

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You didn't notice this was for release on April 11, did you?

GM didn't notice it was on their website then, did they? :AH-HA_wink:

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sure hope this doesn't have too many early bugs... would hate to see the Aura and/or Outlook get a reputation for bugs like, say, the Olds Aurora. Great car design, but numerous early bugs kill image & resale. :(

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I'm sure GM tested the tranny thoroughly--I would hope so considering it took so long for them to get it out on the market!

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Finally! GM has a new 6-speed transmission. Wonder what they're (the media) going to nag about when the Aura comes out.

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Guest Josh

Doesn't matter about the hybrids. For Saturn to get a FWD 6 Speed is impressive. Chevrolet doesn't even have a FWD 6 Speed.

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Doesn't matter about the hybrids. For Saturn to get a FWD 6 Speed is impressive. Chevrolet doesn't even have a FWD 6 Speed.

Neither does Buick or Cadillac.

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Neither does Buick or Cadillac.

i beg to differ...the xlr-v has a 6A...

edit: my sometimers disease made me forget about the 'scalade

Edited by rodd62

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i beg to differ...the xlr-v has a 6A...

I assume he made a joke. Cadillac doesn't have a FWD 6 speed because none of the vehicles are FWD with the exception of the DTS.. which still only has a 4 speed.

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