http://www.cheersandgears.com/forums...showtopic=7495

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.

 

I particularly love how the transmission sits next to the engine, rather wrapping around with the barrell behind the engine like on current GM FWD cars. That is, keeping in mind that the engine sits sideways, so "next to the engine" from the vehicle's standpoint is actually behind the engine, i.e. at the back of the crank. On the current fwd vehicles, the engine sits sideways, the tranny is driven from the back of the crank, and a chain transfers the power to the meat of the transmission, whose main body wraps around to the right of the engine (between engine and firewall).

Hopefully this means we can reduce some of the huge tall hood/front overhang problem (see current Grand Prix for example) in future FWD cars. The Buick Bengal concept gave a teaser of that effect by putting the transmission barrell in front of the transverse engine, so the tallest part of the powertrain - the engine - was farther away from the front end, and the output of the tranny - and thus the axles - was closer to the front.

By the way, I believe that much of the planetary geartrain layout and the control strategy for these trannies, like the new rwd six speeds, is based on the outstanding Allison transmission planetary layout and control system.

 

Is there any indication that the new trannies can handle more power than the ones they replace?

Seems like GM's drivetrain achillies heel has always been weak hydramatic hardware (i.e. theearly '90s 3.4L twin dual cammer was capable of close to 300hp but the tranny wasn't even close to that).

 

Will this trans make its way into the Saturn sky anytime soon? What about the redline version? I might replace the Audi with a Sky Redline in a year or so but only if available with a 6-speed auto (wife requires an auto, and I'd be more accepting of an automatic if it had 6 gears).

 

Not this is the FWD tranny. The 6 speed RWD tranny is not going into the Sky for a while.

 

Sky gets the 5 speed auto.

 

Re: Sky Redline. I'm sure you'll find the 5 speed auto quite satisfying if you have the Redline engine (260+ hp and a similar amount of torque), in terms of number of gears. Dunno about manumatic capability though.

 

Hurray. It's about time.

 

From everyone that has the non-redline has said, it works VERY nice...

We will see what they say when the Redline arrives, I am getting the manual in my RL