[elegant]

Thanks to Runge Kutta for finding this paper published by the Society of Automotive Engineers. The key sentence is bolded:

General Motors Rear Wheel Drive Eight Speed Automatic Transmission: General Motors shall introduce a new rear wheel drive eight speed automatic transmission in the 2015 Chevrolet Corvette.

NO picture is currently available .

Paper #:
2014-01-1721
Published: (To be presented 2014-04-01)
Author(s):
James Michael Hart
Tejinder Singh
William Goodrich
Affiliated:
General Motors Co.
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 (737 foot/pounds torque). 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.
Event:
SAE 2014 World Congress & Exhibition
Sector:
Automotive
Topic:
Transmissions

Thank you Runge for your continued skill in finding and sharing this information.

 

[Mgorski]

So will it be better performance over the six speed. Or mainly better fuel economy. - I would imagine having to shift a lot wouldn't help. But that also means you're at the optimal RPM at all times because there are 8 gears. On the other hand the LT1 has a relatively flat power band, yes? (I could be false)

Also what's the torque rating for the 6 speed is it a stronger transmission because it has less moving parts?

I need reasons not to change my mind!!! Lol as many I'm sure will

 

[jsvette]

Just speculating, but perhaps this will be an option and or available with the yet to be announced higher output engine...

 

[elegant]

Just speculating, but perhaps this will be an option and or available with the yet to be announced higher output engine...

Think you are correct. I am amazed that it is rated to 737 foot/pounds TQ.

Also interesting is how this square with Tadge's statement (which he has made many times) since the January 13th Reveal, that they computer modeled automatic transmissions with more than six speeds and that they do NOT increase either performance, nor fuel economy, but at some point (paraphrasing here) "that due to other car companies getting bragging rights about their eight speed auto trans, we might have to eventually do something just to keep up with their bragging rights."

 

[glen e]

I have owned 6 8-speed tranny's with BMW for the last 4 years and they are nice. (My co demo gets replaced every 6 months) However, they are used (and really needed) in smaller engines that need to stay in the most efficient mode to get the best mpg. They are shifting a lot...silently, efficiently, but always shifting, as they are computer controlled. Even on a flat grade.

I would love one but do not feel at all slighted, (or shafted) with the current A6. With this amount of TQ in the motor, it can EASILY, comfortably live in 6 speeds. I'm very happy with the current A6, it shifts when it's supposed to, and will rip smoke all the way down the street if I want.

I expect many will feel terrible/angry that they bought the A6 this year, but it's really an unnecessary feeling....It's a nice upgrade, but not a gamechanger for the C7 program.

 

[LT1xL82]

Just speculating, but perhaps this will be an option and or available with the yet to be announced higher output engine...

I suspect you are correct. With the torque rating, it would be a natural. To my mind, it would be insane not to have an automated transmission option for the performance variant(s).

 

[zimm888]

Agree with glen e, let's read up on it first get some reviews before we all start crying that we have a 14'. Give them some time to figure out any issues with it as well.

 

[Lipstic]

I'll just wait two or three years, let them work out the bugs and then go for it. I agree with Glen, do not feel slighted at all, but there will be many who will, some will run out and trade their 2014 for a 2015 and take a bath on the deal.

 

[Buzz]

Choices, Choices..................

I had a 2009 with paddleshift and was not happy with the constant upshifting and downshifting on inclines and downgrades; an 8 sp may make it smoother and less noticeable but it will be hard to pass up an 7sp manual just for the fun factor! Thanks, John for finding this tidbit for us. Finding it easier to wait for my 2015 as they add more goodies!

 

[Redc7]

There maybe a few reasons for the new 8-speed however the primary reason companies are going with an 8-speed is fuel economy as our government continues to push the auto manufactures to increase fuel economy in their fleet. Performance, I doubt, you will see much difference however my other assumption with this new tranny is because of the Z06 whose torque rating will be much higher than the LT1 and current 6-speed may not be able to handle it.

 

[jsvette]

I have zero issues about what they may or may not put in or changes they may make to the 2015 C7. I am ecstatic about RedHot- the way she looks and handles. It is exactly what I had hoped for and 'am having a fantastic time with her.