C7 Corvette fuel economy and performance is about to get even better!

[Rob]

As outlined in the SAE paper below, an 8-speed automatic transmission is coming to the C7 Corvette platform, the fuel economy and already stellar performance of the C7 Corvette platform is about to get even better!

General Motors Rear Wheel Drive Eight Speed Automatic Transmission

Paper #: 2014-01-1721
Published: 2014-04-01
Author(s): James Michael Hart, Tejinder Singh, William Goodrich

Abstract: General Motors Rear Wheel Drive Eight Speed Automatic Transmission General Motors shall introduce a new rear wheel drive eight speed automatic transmission, known as the 8L90, in the 2015 Chevrolet Corvette. The rated turbine torque capacity is 1000 Nm. This transmission replaces the venerable 6L80 six speed automatic transmission. The objectives behind creation of this transmission are improved fuel economy, performance, and NVH. Packaging in the existing vehicle architecture and high mileage dependability are the givens. The architecture is required to offer low cost for a rear drive eight speed transmission while meeting the givens and objectives. An eight speed powerflow, invented by General Motors, was selected. This powerflow yields a 7.0 overall ratio spread, enabling improved launch capability because of a deeper first gear ratio and better fuel economy due to lower top gear N/V capability, relative to the 6L80. The eight speed ratios are generated using four simple planetary gearsets, two brake clutches and three rotating clutches. The resultant on-axis transmission architecture utilizes a squashed torque converter, an off-axis pump and four close coupled gearsets. The three rotating clutches have been located forward of the gearsets to minimize the length of oil feeds which provides for enhanced shift response and simplicity of turbine shaft manufacturing. The transmission architecture features a case with integral bell housing for enhanced powertrain stiffness. A unique pump drive design allows for off-axis packaging very low in the transmission. The pump is a binary vane type which effectively allows for two pumps in the packaging size of one. This design and packaging strategy not only enables low parasitic losses and optimum priming capability but also provides for ideal oil routing to the controls system, with the pump located in the valve body itself. The transmission controller is externally mounted, enabling packaging and powertrain integration flexibilities. The controller makes use of three speed sensors which provide for enhanced shift response and accuracy. Utilization of aluminum and magnesium components throughout the transmission yields competitive mass. The dedicated compensator feed circuit, used in GM six speed designs, was supplanted by a lube-fed design in order to simplify oil routing and enhance shift response. Packaging is within that of the GM 6L80 design, allowing for ease of application integration. The overall result is a robust, compact, and cost effective transmission which offers significant fuel economy and performance benefit, over its six speed counterpart, and shall provide an attractive balance of overall metrics in the automatic transmission market.

 

[KANE]

When in doubt... gear it out!!!

 

[elegant]

When Tadge Juechter spoke about this at the April NCM Bash (and since) he said that using their Cray supercomputer, they modeled more than six speeds with the automatic transmission and that neither fuel economy nor performance increased with more gears, however, due to "bragging rights that other manufacturers have with their seven and eight speed automatics, that we may have to do the same at some point."

Guess that time is here. Believe that the greater number of gears will improve economy and performance is GM's big sedans, SUV's and pickups, and it wouldn't do for the Corvette to have a six speed auto when others in the GM line with had eight speed autos.

 

[67vet]

Sounds like there are more chances for components to leak after many miles of use.

 

[KANE]

Sounds like there are more chances for components to leak after many miles of use.

I thought the same thing too.



But then again..."more" isn't bad when (and if) they are designed "right". Personally, I'm more comfortable with more parts- provided the engineering, forethought, and materials are executed properly than if there were less parts, more shortcuts/trade-offs, and less durability.

Take a modern LSx engine over a GEN I 305. More parts on the LSx... but it is designed and made very, very well from the factory. more so than a smog era 350 too!

 

[Huskerman]

I think a 6M and a 6A are great and all I need.........a 7M is why bother in my book, I mean what next a Roadranger 13 with a button to push and then go back through the pattern again.......... But I can see the marketing side to it also and if it gives the idea of saving more fuel I suppose that is a good thing.....but performance wise I don't think they make much if any difference.......

 

[LLC5]

Every .1 mpg is very helpful in CAFE which shoots up dramatically in a couple of years. An 8 speed auto will probably give a little better performance and mpg, but not a huge amount. Still, if for some reason I had to have an auto transmission in a C7, then I would probably wait for the 8 speed......