2010 - 6T40 and 6T45 Features and Benefits

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2010 Hydra-Matic 6T40 (MH8-FWD) Hydra-Matic 6T45 (MH7-FWD, MHC-AWD)

2010 Model Year Summary
Hydra-Matic 6T40 / 6T45 six-speed automatic front- or all-wheel-drive transmission

● Six-Speed Automatic Transmission
● New North American Applications: Chevrolet Equinox (MH7, MHC), GMC Torrent (MH7, MHC), and Buick LaCrosse (MH7); Carryover: Chevrolet Malibu (MH8)
● Contemporary On-Axis Design
● Advanced Clutch-To-Clutch Shift Operation
● Tuned For Quick Launch And Fuel Efficient Cruising
● Compact Dimensions Aid Packaging
● Hyper-elliptical Torque Converter Saves Space
● IX Gear Pump Lowers NVH Levels and Improves Hydraulic Efficiency
● Ground And Honed Gears For Precision Fit And Lower NVH Levels
● Unique Input Shaft Eliminates Costly Machining And Adds Strength

Full description of new features and benefits

Six-speed automatic transmission
Two versions of the transverse six-speed automatic transaxle (6T40 / 6T45) have been debuted, featuring a notably wide ratio spread, and the ability to handle different levels of engine torque and vehicle applications. The 6T40 / 6T45 have been designed to address high feature and high value segments with combination of 6-speed, advanced features, and low piece cost. Availability of wide ratio spread allows improved fuel economy and improved performance. The 6T40 / 6T45 transmission has an output chain, and also features a compact low cost 1 piece case.

New applications:
Chevrolet Equinox (MH7, MHC) and GMC Torrent (MH7, MHC) are scheduled to go on sale in the summer of 2009 using the 6T45 (FWD and AWD), which is mated to the 2.4 LAF Ecotec and is rated to handle 315 N-m of engine torque. Additionally, Buick LaCrosse (MH7) will go in production at the end of 2009 using the 6T45, which is mated to the 2.4 LAF Ecotec. The 6T40 / 6T45 will also continue to be offered in 2010 Chevrolet Malibu (MH8).

Carryover from model year 2009 features and benefits are listed below:

Innovative on-axis design
Instead of “folding” the transmission around the end of a transversely mounted engine, which has been one of the dominant GM transaxle design conventions, the 6T40 and 6T45 contain all of their gearing in line with the crankshaft centerline of the engine. The advantages of this layout can translate to a shorter overall vehicle length, more interior room in a vehicle, and lower powertrain height.

Advanced clutch-to-clutch shift operation
To save space compared to “freewheeling” gear change mechanisms, the shifts are accomplished by applying and disengaging clutches simultaneously during each gear change. Sophisticated electronics help enable the precision needed to time the clutches for each shift. The first-to-second gear shift uses a freewheeling mechanism, however, which tends to be smoother during shifts between gears with large ratio differences, such as first and second gears.

Tuned for quick launch and fuel efficient cruising
Because of the wide ratio spread, first gear is a very high ratio, which provides brisk acceleration from a stop. Sixth, however, is an overdrive ratio, which keeps the engine revolutions as low as possible for highway cruising, reducing engine friction losses and improving fuel economy.

Compact dimensions aid packaging
State-of-the-art dimensions enable spacious packaging and enhance potential safety design opportunities. In addition, styling opportunities for lower hood lines are also enabled by the compact dimensions of the 6T40 and 6T45.

Hyper-elliptical torque converter saves space
The 205k, 236mm torque converter in 6T40 (MH8) and 6T45 (MH7) uses a single plate lockup clutch and features an oval cross-section shape, called “hyper-elliptical”. This shape reduces the thickness of the torque converter, reducing the space it needs and keeping the overall width of the engine and transmission as narrow as possible for packaging advantages. The single-plate lockup clutch makes use of GM’s electronic controlled capacity clutch (ECCC) technology to help dampen engine vibrations and ensure smooth operation.

IX gear pump lowers nvh levels and improves hydraulic efficiency
A compact on-axis, fixed displacement IX Gear type fluid pump provides hydraulic pressure for the shift events and lubrication. The pump features an IX gear (Drive/Driven) with a machined crescent in the pocket, which reduces internal leakage and optimizes hydraulic efficiency. The inlet jet nozzle feature in the IX gear type pump provides for increased pump suction pressure which has demonstrated to lower powertrain NVH levels.

Ground and honed gears for precision fit and lower NVH levels
To minimize gear noise as well as vibration, the helical gears are ground and honed to ensure exact dimensions and tolerances. With closer tolerances, the gears are less prone to characteristic whining or humming, and overall the transmission operates as quietly as possible.

Unique input shaft bushings eliminate machining
The input shaft requires no machining for grooves to contain fluid seals, which allows the shaft to retain maximum strength for its size and minimize cost.

Low maintenance
The 6T40/6T45 is filled for life with DEXRON®-VI premium fluid, which during normal use need not be replaced. DEXRON®-VI is validated to improve durability and shift stability over the life of the transmission. DEXRON® VI, was developed to have a more consistent viscosity profile; a more consistent shift performance in extreme conditions; and less degradation over time. Internal GM tests have demonstrated DEXRON® VI delivers more than twice the durability and stability in friction tests compared to existing fluids. The DEXRON®-VI fluid was designed specifically and validated for the new family of GM six-speed automatic transmissions.

Overview
The concept behind the new six-speed front- and all-wheel-drive transaxle family is to enable compact packaging not possible before with a powerful transverse powertrain layout. The gearsets are on the same axis as the engine crankshaft centerline, which makes the entire powertrain unit much shorter fore-to-aft. This allows chassis designers the ability to enhance crush zones, to increase interior space, and lower the hood line of the vehicle compared to a conventional off-axis transaxle.

The primary difference between two variations of the six-speed automatic transaxle being the 6T45 has greater torque handling capability. The output chain is 1.25-in wide in 6T45, versus 1-in wide for the 6T40. The input gearset of the 6T45 uses five pinion gears, versus four pinions for the 6T40. In addition, the case of the 6T45 is slightly larger and includes a heavier ribbed case for strength.

Three planetary gearsets are used with three stationary clutches and two rotating clutches, which save space compared to freewheeling designs. Freewheeling mechanisms allow perfect timing between shifts, but also take up more space and add more components to the transmission. However, due to the electronic controls, the clutch-to-clutch concept of the 6T40 / 6T45 delivers the same accurate shift timing. Gear changes from second to sixth gear ratios are accomplished with a precise clutch-to-clutch action, where the clutch is engaged in one gear at exactly the same time it is released in another. The first-to-second upshift, however, is a freewheeling action, where the second gear clutch engages while the first gear one-way clutch spins freely. This allows a greater degree of smoothness at lower vehicle speeds.

Adaptive shift controls include automatic grade braking, which commands the transmission to remain in a lower gear if the vehicle is decelerating or coasting on a downgrade. This takes advantage of engine braking to prevent unwanted acceleration. This reduces the need for the driver to brake during a hill descent. The control module receives input that monitors brake pedal usage, vehicle acceleration rate, throttle position, and even whether a trailer is connected to the vehicle.

The wide overall ratio spread of 6.11:1 allows a “steep” first gear, as well as a “tall” overdrive top gear for low-rpm highway cruising. Acceleration is maximized, as is fuel economy. Engine noise is also lower during cruising. Sixth gear is a tall “overdrive” gear, for example.

The transmission control module (TCM) in the 6T40 / 6T45 allows the modules to exist reliably inside the transmission, where temperatures remain mostly constant compared to a body-mounted module. The smaller size of the module means the transmission case can be more compact. The transmission and module are assembled together, so no additional connections are necessary during vehicle assembly.

The 32-bit transmission control module (TCM) monitors transmission performance and compensates for normal wear in components such as clutch plates, so transmission performance remains consistent for the life of the transmission. The control module also “tests” the components of the transmission following assembly to optimize the interaction of the components. The module is compatible with all future global applications and the design can accommodate different modules. All of the module strategy is developed by GM Powertrain.

The Hydra-Matic 6T40 / 6T45 was developed as part of the small 6-speed transmission family for global applications and is being produced in Asia Pacific region (GMDAT, Korea, and SGM, China) with subsequent manufacture in North America (SLP, Mexico).

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2010 Hydra-Matic 4T45 (MN5, ME7 Hybrid )

2010 Model Year Summary
Hydra-Matic 4T45 four-speed FWD electronically controlled automatic transmission.

There are no planned performance upgrades for the 2010 Model Year, activities will be centered on quality improvements

FULL DESCRIPTIONS OF FEATURES AND BENEFITS

Low maintenance
The 4T45 transaxle uses DEXRON® VI fluid, and is "fill-for-life", with no maintenance scheduled for normal operation. DEXRON® VI, was developed to behave more consistently during temperature and other environmental variations, as well as to provide even lubrication of the moving surfaces of the transmission and more stable shift performance in extreme conditions. Durability is also increased with the new fluid.

Overview
The Hydra-Matic 4T45 ( MN5 ), is an electronically controlled four-speed transaxle that achieves industry benchmark levels of reliability and shift quality. Precisely calibrated electronic controls enable the transmission to adapt to a variety of driving conditions providing the driver with consistent shift quality. All 4T45 transaxles use the proprietary GM ECCC (Electronic Controlled Capacity Clutch) technology for torque converter lock-up functions. ECCC allows a very small degree of controlled slip in the torque converter lockup clutch to isolate drivetrain pulses and contribute to smooth delivery of power. The transaxle's low-noise operation is a result of the high helix angle gears, an enclosed bell housing, and the random-pattern chain. Mass has been reduced through optimized case design and use of lightweight materials. Driver Shift Control (DSC) function is available that allows easier manual shifting of the gear ranges. On some models the floor-mounted shift lever can be moved rearward and to the right to enable the DSC, and momentary movements of the lever forward and rearward can respectively upshift and downshift the transaxle. Electronic controls prevent downshifting at speeds which would cause the engine to over-rev, and automatically downshift when the vehicle comes to a stop. The 4T45 has a modified channel plate and valve body which allows the ability to electronically change shifts as signaled by the driver pushing a switch on the gear selector lever. To use the feature in the Malibu application, for example, the driver shifts the gear selector from D to the D3 position, then pushes the selector switch to downshift to D2 and then D1. Upshifting from D1 to D2 and D3 is accomplished through the selector switch as well.

On the 4T45 ( ME7 ), hybrid applications, there are several different operating conditions, including an engine-off condition while the vehicle is stopped at a stoplight, battery recharge on deceleration, and electric motor assist on acceleration. To accommodate the electric motor and the duty cycle of engine-off operation, the 4T45 has been modified to enable normal operation by utilizing an electrically powered hydraulic auxiliary pump to maintain pressure to the Forward clutch. The Pressure Switch Manifold has also been modified for additional diagnostic capability..