New Hydra-Matic 6T70 Six-Speed Automatic Delivers Performance and Fuel Economy

Innovative, efficient transmission to debut on 2007 Saturn Aura

  • First GM Powertrain front-wheel drive 6-speed automatic transmission
  • Advanced clutch-to-clutch operation and wide 6.04:1 overall ratio spread
  • Co-developed by GM and Ford Motor Co.
  • Applicable to FWD and AWD powertrain layouts
  • Torque capacity to 280 lb.-ft.
  • Shift speeds up to 7000 rpm
  • 32-bit intelligent controller included in sophisticated internal transmission electro-hydraulic control module (TEHCM)
  • Built at GM Powertrain’s assembly plant in Warren, Mich.

MILFORD, Mich. – General Motors new Hydra-Matic 6T70 six-speed automatic transmission, an advanced transmission with clutch-to-clutch shift operation for front- and all-wheel drive vehicles, will debut in the all-new 2007 Saturn Aura midsize sedan. Co-developed with Ford Motor Co., the new six-speed joins the already announced Hydra-Matic six-speed rear-wheel drive family of automatics and Allison 1000 six-speed automatic as part of GM’s mission to produce 3 million six-speed automatics annually by 2010.

The 6T70’s clutch-to-clutch operation allows for reduced complexity and compact packaging. A wide, 6.04:1 overall ratio spread helps the transmission deliver both performance and fuel economy, enabling up to 8 percent improved performance and up to 4 percent improved fuel economy when compared with current front-wheel drive four-speed automatics.

“The 6T70 offers the best of both worlds – the excitement of a performance transmission and the economy expected of an overdrive,” said Robert Vargo, assistant chief engineer, new front-wheel drive transmissions. “The joint development effort allowed both companies to maximize time and engineering talent to answer a common need for a fuel-efficient transmission that meets the performance needs of high-output, transverse-mount powertrains.”

Co-development of the transmission allowed it to reach production in less time and enabled each company to reduce development costs by as much as 50 percent. A common design and many common components are shared between GM and Ford six-speed variants, but each company developed its own controls and calibrations to tailor the shift feel of the transmission to fit their brand characteristics.

Rated for engines up to 315 horsepower and 280 lb.-ft. of torque, the 6T70 helps maximize powertrain performance and economy through its wide 6.04:1 ratio – the spread in gear ratios between first gear and sixth gear. This configuration allows for a “steep” 4.48:1 first gear, which helps deliver exceptional launch feel, and a 0.74:1 overdrive sixth gear – the “tall” overdrive gear lowers rpm at high speeds, reducing noise, vibration and harshness. Fifth gear is 1:1 or direct drive.

“The additional gear states are almost like having two transmissions in one,” said Vargo. “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 delivers great fuel economy.”

Shorter steps between the gears, compared with a four-speed automatic, enhance performance and feel, as the transmission quickly finds the best gear for the vehicle speed and road conditions – there’s less “hunting” (shift busyness) on grades, for example. Also, the 6T70 offers the capability of driver shift control (DSC), which allows the driver to use tap-up, tap-down shifting to select the desired gear for specific road conditions, such as driving up a steep hill.

The Hydra-Matic 6T70’s highlights also include:

  • Compact dimensions of 357 mm in length and 197 mm in width for packaging convenience in a variety of front- and all-wheel drive vehicles with transverse-mounted powertrains – one the most compact transmissions in its competitive set
  • Clutch-to-clutch shift operation for all shifts except 1-2 reduces mechanical complexity and mass while enhancing shift feel
  • Integrated transmission electro-hydraulic control module (TEHCM) with driver shift control and performance algorithm shifting for shift feel and timing tailored to the driver
  • Internal control module reduces powertrain complexity
  • Auto grade braking and shift mode capability
  • Heat-treated gears are honed for a more precise fit, reducing noise, vibration and harshness
  • Narrow torque converter enhances packaging and maintains efficiency
  • Simple, less complex design has reduced number of seals
  • Adjustable capacity vane-type pump enhances fuel economy compared with non-adjustable gear-type pump

Although used in some low-volume high-performance sports cars and luxury sedans, six-speed transmissions are rare in most high-volume midsize cars and 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 design allowed engineers to answer the call for performance and economy with six forward speeds.

With its wide ratio and strong capacity, the 6T70 has the capability to transfer more torque to the drive wheels, particularly in all-wheel drive applications. It also helps vehicles such as SUVs to feel livelier at lower speeds, particularly at launch or when stepping away from a stoplight.

The 6T70’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. This is achieved through three planetary gears, with three stationary clutches and two rotating clutches. 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, reducing vehicle complexity. Similar to the control system used in the Hydra-Matic 6-speed rear-wheel drive transmissions, the TEHCM offers improved quality through its hard-wired connections and pre-calibration.

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.

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

Although it is not uncommon to have a transmission-control module that adapts to the specific transmission with which it is mated, and to also have programming that optimizes transmission performance characteristics according to a variety of vehicle inputs, the new Hydra-Matic six-speed automatic adds another level of adaptability. Certain components within the major subsystems that make up the transmission also “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 enables a host of performance-oriented and driver-controllable shift features, including performance algorithm shifting (PAS), driver shift control (DSC) “tap shift” and auto-grade braking.

The Hydra-Matic 6T70 is manufactured at GM’s Warren Transmission plant. It debuts in summer 2006, when production begins on the 2007 Saturn Aura.

Hydra-Matic 6T70 (MH2) six-speed automatic

Type:

six-speed transverse, electronically controlled, automatic overdrive transmission

Maximum engine horsepower

315

Maximum engine torque:

280 lb-ft

Maximum gearbox torque:

380 lb-ft

Gear ratios:

First:

4.48

Second:

2.87

Third:

1.84

Fourth:

1.41

Fifth:

1.00

Sixth:

0.74

Reverse:

2.88

Maximum shift speed:

7000 rpm

5-position quadrant:

P, R, N, D, (M)

Case material:

die-cast aluminum

Shift pattern:

(2) three-way on/off solenoids

Shift quality:

five variable bleed solenoids

Torque converter clutch:

variable bleed solenoid

Converter size:

258 mm

Transmission weight (kg / lb):

102 / 273 (wet)

Fluid type:

DEXRONŽ VI

Fluid capacity (L / qt):

9.0 / 9.5

Assembly site:

Warren, Mich.

Additional features:

Clutch-to-clutch operation (except 1-2); integrated transmission electro-hydraulic control module with driver shift control and performance algorithm shifting








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