GM Releases Details for New 8-Speed 8L90 Hydramatic Automatic Transmission

[FenwickHockey65]

New 8-Speed Enables Quicker, More Efficient Corvette
GM-designed, patented paddle-shift gearbox rivals dual-clutch performance
General Motors

2014-08-20

DETROIT – The all-new, GM-developed Hydra-Matic 8L90 paddle-shift eight-speed automatic transmission offered in the 2015 Corvette Stingray and Z06 enhances performance and efficiency, while delivering exceptional refinement and world-class shift responsiveness that rivals the world’s best dual-clutch transmissions.

In fact, in the 2015 Corvette Stingray, it enables a class-leading 29-mpg EPA highway estimate – a 3.5-percent increase in fuel economy over the previous six-speed automatic – and a quicker 0-60 time of 3.7 seconds, all while delivering wide-open-throttle upshifts quicker than those of the dual-clutch transmission offered in the Porsche 911.

“GM’s new 8L90 eight-speed automatic represents a rare win-win-win scenario for customers,” said Kavoos Kaveh, global chief engineer for eight-speed automatic transmissions. “It offers greater performance and efficiency, while weighing less than the transmission it replaces. That’s a rare accomplishment in the industry today – and one for which GM has been awarded more than two dozen patents.”

With four simple gearsets for optimal efficiency and five clutches (two brake clutches and three rotating clutches), creative packaging enables the new eight-speed automatic to fit the same space as the previous six-speed automatic – and the powerflow only uses two open clutches for low spin losses, which enhances efficiency. Extensive use of aluminum and magnesium also make it more than eight pounds (4 kg) lighter than the six-speed.

The greater overall performance and efficiency enabled by the 8L90 in the Corvette is due primarily to a new, wider 7.0 overall gear ratio spread, which enhances off-the-line performance with a more aggressive first gear ratio – 4.56 vs. 4.03 on the six-speed – helping achieve the quicker 0-60 time.

The top gear ratio is 0.65 vs. the six-speed’s 0.67. Combined with a new, numerically lower 2.41 rear axle ratio in the Stingray vs. the 2.56 gear used with previous six-speed automatic models, engine rpm is reduced by 8 percent (123 rpm) on the highway at 70 mph. The lower engine speed reduces fuel consumption, while a new torque converter design enhances refinement, particularly during low-speed gear changes.

Stingray models equipped with the Z51 Performance Package feature a more aggressive 2.73 axle ratio, while the Corvette Z06 features the 2.41 axle ratio.

World-class performance

Designed and built by GM, the paddle-shift 8L90 transmission delivers world-class shift times that rival the best dual-clutch designs.

“The Corvette’s new eight-speed automatic delivers the comfort and drivability of a true automatic transmission, as well as lightning-fast shifts and the manual control that enhance the performance-driving experience,” said Kaveh. “It was designed to enhance the driving experience, with performance on par with dual-clutch designs, but without sacrificing refinement.”

For performance driving, the transmission offers full manual control via steering wheel paddles. A new transmission-controls system and unique algorithms deliver shift performance that rivals the dual-clutch/semi-automatic transmissions found in many supercars – but with the smoothness and refinement that comes with a conventional automatic fitted with a torque converter.

In fact, a new, Gen II transmission controller analyzes and executes commands 160 times per second, and wide-open throttle upshifts are executed up to eight-hundredths of a second quicker than those of the dual-clutch transmission offered in the Porsche 911.

Smaller steps between gears, compared to the previous six-speed automatic (see chart above), keep the engine within the sweet spot of the rpm band, making the most of its horsepower and torque to optimize performance and efficiency. Additionally, a torque converter design with a turbine damper complements performance with excellent refinement at low engine speeds.

Unique clutch and torque converter specifications matched to the torque capacity of the Stingray’s LT1 6.2L naturally aspirated engine and the Z06’s LT4 supercharged engine distinguish the applications for the different Corvette models.

Architectural and design features

More than 550 computer-aided engineering analysis were made during the development of the 8L90 to ensure strength, durability, performance and refinement. The architecture features a one-piece case with an integral bell housing for enhanced powertrain stiffness, as well as a detachable extension for the Corvette’s rear transaxle arrangement.

Similar to GM’s six-speed automatic design, the eight-speed’s architecture locates the grounding clutches rearward of the middle of the structure, outside the gearsets. However, the grounding clutches are splined to the case, eliminating the center support, which reduces weight.

This architecture also features a turbine shaft node that reaches to the outside of the barrel, enabling easy execution of a high-resolution magnetic speed sensor. The turbine shaft itself is very short, keeping oil channel drill lengths to a minimum. The rotating clutches are located near the front of the transmission, with short oil feed channels, supporting the transmission’s very fast shifts.

Additional design and performance features include:

• Clutch compensators are fed by lubrication oil rather than the dedicated and regulated feed design of the 6L80. There are two benefits of this new design feature: The reduction of one oil channel between the valve body and the rotating clutches, which reduces the number of rotating oil seals and oil channels within the turbine shaft; and, secondly, the capability for rapid discharge of oil in the compensators during clutch apply, for greater control.
• An industry-first off-axis, chain-driven binary vane-type pump – located within the valve body – effectively allows for two pumps in the packaging size of a single, which contributes to lower parasitic losses and optimal priming capability, as well as ideal oil routing to the controls system.
• The binary pump enables a 60-percent reduction in pump torque at points that represent large portions of the operating duty cycle, compared to the 6L80 six-speed, which is a significant contributor to the overall efficiency gains offered by the 8L90.
• The binary pump is located very low in the sump, for greater cold prime operation – as low as -40 F (-40 C) and excellent high-speed operation with stable line pressure.
• Thanks to a new torque converter clutch friction lining and a new control strategy, the 8L90’s squashed torque converter uses conventional dual-path converter feeds.
• New synthetic fluid with improved cold temperature performance and reduced friction characteristics.

Shift time quickness and improved responsiveness are accomplished with the new Gen II controls system. VFS solenoid technology and three internal speed sensors give the 8L90 the capability for world-class shift performance. The new transmission controller is mounted external to the transmission and has a processor that executes hundreds of calculations and commands every 6.25 milliseconds.

The 8L90 is built at GM’s Toledo, Ohio, transmission facility.

[PYROLYSIS]

I was really hoping, as I'm sure GM was, that they would be able to knock down 30MPG highway for the auto Stingray. That is a very minor disappointment compared to everything else this tranny can do, and it's still an improvement over the six speed. Nicely done.

[Silverlsinva]

I wonder if the 6th gen Camaro will get this tranny. I kinda think it will since it doesn't come out for over a year.

[FenwickHockey65]

Should also point out that automatic Corvettes are now faster than the manuals.

[ShnOmac]

Originally Posted by Silverlsinva

I wonder if the 6th gen Camaro will get this tranny. I kinda think it will since it doesn't come out for over a year.

I'm curious how much this thing would add to the price tag of a Camaro......

[NASTY99Z28]

I thought the vette had an eco mode that allowed over 30mpg's?

[PYROLYSIS]

Originally Posted by NASTY99Z28

I thought the vette had an eco mode that allowed over 30mpg's?

It does but the EPA requires them to list it in Touring mode, the mode that is most used by customers. Like the 7 speed manual, it will achieve 30MPG hwy very easily.

[King T]

Originally Posted by FenwickHockey65

Should also point out that automatic Corvettes are now faster than the manuals.

I noticed that too.

The countdown begins Fen....

[FenwickHockey65]

Popular Mechanics did over 37 MPG hypermiling a C7 so...

[King T]

(Motor Authority)





2015 Chevrolet Corvette 8-Speed Automatic First Drive

What do you do when Chevy hands you the keys to a 2015 Corvette Stingray and an open run at the Milford Road Course? You flog it for all you’re worth, whether you know the track or not.

That’s just what we did yesterday.

Of course, this wasn’t your usual 7-speed manual Stingray. Nor was it the old 6-speed automatic. No, for 2015, the Stingray gets an all-new, GM-designed and built 8-speed automatic that it claims will slay Porsche’s PDK dual-clutch.

But wait, you say. How can a slushbox rival--let alone beat--a real dual-clutch ‘box? According to GM, it starts with shift speed.

And we’re not talking about half-a-second-later, hit-the-paddle-and-wait shift speed, but the total time from the request for the shift at the paddle to the actual engagement of the next gear under power. GM says its new 8-speed Hydra-Matic 8L90 shifts gears 0.08 seconds quicker than Porsche’s PDK at wide-open throttle. That might not sound like a lot, but in the world of lightning-quick gear changes, 80 milliseconds is a lifetime.

But how does it drive? Great, actually, both on the street and on the track, though we’d like to spend some more time with the car than the few hours we had yesterday to suss out any less-obvious characteristics or edge cases that might be hiding behind the very good first impression.

Around town, the 8-speed’s many ratios and smooth shifting equate to an easy, comfortable ride, whether in Eco, Tour, or Sport modes. On track, in Track mode (which affects not only the Performance Traction Management system’s settings, but the interoperation of those settings with the transmission’s behavior), even very advanced drivers will find the “D” selector on the transmission as useful and as accurate a method of gear selection as the “M” position and the paddle shifters mounted to the steering wheel. It’s a very smart algorithm that keeps the car in the right gear to deliver maximum acceleration at any time.

On the torturous Milford Road Course, an assemblage of the most harrowing turns from the most hardcore tracks in the world, there’s no hiding deficiencies—whether they're in the driver or the car. Keeping the vehicle in a state of constant upset, there are direction changes, off-camber lunges, blind crests, the Karussell-like “Toilet Bowl,” and more to unsettle the suspension and drivetrain and push any driver to their limit.

When you only have a handful of laps to learn the track and the car, you worry less about line and more about listening to what the car is doing. That’s what we did, and we found the 8-speed to be a really welcome companion on track, whether you're letting the transmission's brain select the gears or doing it yourself with the paddles. For our own money, we’d still opt for the 7-speed manual, especially with 2015’s improved automatic rev-matching algorithms, but we won’t be looking down our noses at anyone who chooses the 8-speed auto instead.

In fact, we might be looking at their tail lights. Thanks to a low 4.56 first gear ratio, the 2015 Stingray’s 8-speed gearbox helps the car get to 60 mph 0.1 second faster than the manual at 3.7 seconds, and run the quarter-mile 0.1 seconds quicker at 11.9 seconds, too. Despite the increased acceleration, the 8-speed also gets better gas mileage than the stick, improving highway economy by 3.5 percent to 29 mpg.

You might be thinking that 29 mpg is awfully close to 30 mpg. You’d be right. In fact, the actual test figure for EPA certification came down to 29.4932 mpg, just short of rounding to 30 mpg. With the car headed to production right now, Chevy decided to let the car go to market for 2015 with the 29 mpg rating, but expects the 2016 model to hit the 30 mpg mark thanks to revised tuning. When that happens, the Stingray may well be the world’s first 30-mpg car that also does 0-60 mph in under 4.0 seconds.

How’s that for a "slushbox"?

[King T]

(Motor Trend)




2015 Chevrolet Corvette Stingray Eight-Speed Automatic First Drive

We know, we know. Manuals rule. Automatics drool. It’s one of the core arguments among the purest of the purists. But for GM and its crown jewel, the Corvette Stingray, this dispute is not if an automatic will be offered, but rather, which automatic will be offered. Facts are facts: 63% of the 37,000-plus 2014 Corvettes sold had a six-speed automatic. The rest, well, you know what they had.

Such telling data is precisely why GM is sinking copious time, money, and effort into an updated eight-speed gearbox. It’s dubbed the Hydra-Matic 8L90 and it’s all GM, baby. More than 24 patents were awarded to the company’s brainiacs during its creation. It’s more efficient and more capable than the current six-speed 6L80 it replaces. But, before we get into its specifics, there’s another reason why the 8L90 came to fruition: Z06. Yes, if you haven’t heard by now, the forthcoming Z06 will have a torque-converter-packing, planetary automatic transmission option.

“Really, this transmission was engineered around the upcoming Z06,” admitted Tadge Juechter, Corvette chief engineer. “Corvettes are extremely tightly packaged with the transmission in the back, so we’re bearing-limited in longitudinal space. So essentially, this transmission is custom designed for our package space, as well as the performance capabilities of the car. Our priority was that it had to be able to withstand the 650 foot-pounds of torque and 650 horsepower.”

Juechter and his team turned to Kavoos Kaveh, global chief engineer for GM’s eight-speed automatic, to take on the task of building not just a gearbox for the Z06 and its crazy power, but a gearbox for the Stingray, other Corvette variants, and GM’s 6.2-liter-powered SUVs and trucks.

Kaveh’s goals were simple, at least on paper: It had to be more efficient; it had to fit inside the Corvette chassis’ already extremely cozy constraints; it had to be lighter; and, if that wasn’t enough, it had to withstand all the stresses that come with the various applications.

Amazingly, Kaveh and his team worked within the 6L80’s existing space. They gave the 8L90 smaller step sizes (for better off-the-line go); four simple gear sets with a 7.0 overall gear ratio spread (4.56:1 first gear); a chain-driven, off-axis, binary vane pump (high output for performance, low output for fuel economy); synthetic Dexron 6HP fluid; and a torque converter turbine damper (to improve low-speed clutch smoothness). Just two open clutches reduce power flow losses now.

Its updated Gen II controls include a T87 electronic control module (four times faster than Gen I), three speed sensors for more accurate multi-step shifts, and high and low variable force solenoids to better the accuracy of clutch pressure. The gearbox is eight pounds lighter due to its liberal application of magnesium and aluminum. Its piston housing and channel plate are made of the former, pricey metal; its case with bell housing, clutch pistons, input carrier, and rotating clutch housings are all aluminum. Its input carrier shell uses high-strength low-alloy steel to shed mass.

The end result is a Stingray that is up to five percent better on GM’s highway fuel economy test cycles in Tour mode (not Eco mode). That means 29 mpg — or 29.4932 mpg, if you want to get exact — compared to this year’s 28 mpg EPA rating.

“We have an Eco mode in the car, and you have an Eco mode on the label, but we expect more people to drive in Tour, Sport, Track, so we label the car based on the Tour mode,” explained Juechter.

He says that with additional fine tuning and testing, they’ll get to 30, no problem. “We’re going into production, so we don’t have time to tweak or retest for this year, so we’re going in with a 29 (mpg) label. In Eco Mode, it would do solidly in the 30s. And probably next year, we’ll come back and tweak the calibration of the transmission to (officially) get to 30 miles per gallon. In Corvettes, you can actually get the number that’s on the label.” Still, as is sits, that means it’s as efficient as its EPA-rated 2015 counterpart having a seven-speed manual.

But get this: It’s also quicker. In fact, the 8L90-equipped Stingray is quickest Corvette in a straight line (until the Z06 arrives) with a 0-60 mph dash in 3.7 seconds and quarter-mile run 11.9 seconds (no word on trap speed). Added Juechter: “(Those times) should be easily replicated. We’ve had cars in the 3.6s — even some cars in the 3.5s, but we’re going to market with the 3.7 as the performance (figure).”

Wide open throttle second-to-third upshifts are 0.08 seconds quicker than those of its benchmark, Porsche’s seven-speed PDK, says Kaveh (0.45 vs. 0.53). Downshifts from WOT at 60 mph in Sport mode are just as quick (0.95 seconds) too. The PDK also nips at the Hydra-Matic’s heels during WOT first-to-second upshifts (0.49 vs. 0.52).

To experience the gearbox’s character, Chevrolet set us loose on its 2.9-mile twisty, undulating, blind-corner-filled track at the Milford Proving Grounds. Nil-to-wee sprints in Track mode, automatic shifts, were quite telling: The gearbox knocked off gears at its indicated 6500 rpm abruptly, spectacularly, with an accompanying violent explosion that only a 6.2-liter V-8 with quad pipes could produce.

As corners neared, downshifts were again crisp. Deep inside corners, gears held with no moments of confusion or hesitation — it was as if the CPU was more intuitive than reactive; more organic than robotic — which ballooned my confidence and allowed me to pinpoint the longish nose.

While Chevy’s numbers beg to differ, the 8L90 in Track mode simply didn't feel as quick as the PDK when operated via its plastic paddles. Don’t get me wrong, clicking off a WOT upshift is a glorious, stupidly fast affair. It is much the same for downshifts. Yet, Porsche, with its well-honed cohesion of an extra clutch and different structural packaging, still has the upper hand in smoothness and feel while on track.

Even still, the 8L90 was impressive, especially when off the track. We drove more than 40 miles in highway and city settings around Milford. Smoothness was the name of its game. Intuitiveness was too. Multi-step highway passes in automatic mode required no pauses on its part. The ‘Vette just flew. Then it calmly upshifted into a gear best suited for casual cruising.

So, you may be thinking, why no dual-clutch? There were a few reasons why, says Juechter: Structural tunnel packaging, vehicle balance, durability, and fuel economy. It needed to be shared within General Motors as well.

“There was no DCT or advanced transmission in the world that would just fit in that package and that would live behind the upcoming Z06 with 650 horsepower. So we were faced with a conundrum: We could have designed our own DCT, which could have worked for us, but it would not be useful anywhere else in General Motors. It wouldn't be good for heavy duty trucks and things like that. DCTs are great for some things, but they’re not great for a lot of clutch slipping.

One of the big fuel economy advantages of this car is being able to run in four-cylinder mode. DCT are not terribly compatible with AFM (Active Fuel Management). So having a torque convertor as a torsional damper in the system actually helps to use four-cylinder operation. That’s a big fuel economy enabler. Between those two factors, we, GM, elected to say ‘Ok, were going to do a planetary eight-speed transmission with a torque convertor, but we’re going to model it after DCT performance characteristics.’’

That election resulted in a very stunning, very capable, lightning-quick automatic transmission. It is gearbox that will surely have potential buyers scratching their heads, wondering if a five-, six-, or seven-speed manual is their way to go. Now, that’s saying something.

[BaylorCamaro]

In fact, a new, Gen II transmission controller analyzes and executes commands 160 times per second, and wide-open throttle upshifts are executed up to eight-hundredths of a second quicker than those of the dual-clutch transmission offered in the Porsche 911.]

That's insane if true! I remember reading that the 6L90 in the ZL1 was supposed to have shift speeds "close" to the PDK, but for them to out shift the PDK is pretty darn impressive.

[Silverlsinva]

Its cool that Gm I kinda sticking with the "old school" approach with certain things on cars OHV big displacement Engines Vs. OHC smaller more technical engines and regular auto Vs. Dual clutch tranny's that match and or beat the competition.

[shine2013]

Just too beautiful a thought. Not sure if this is nationwide, but where I'm at Corvettes get dumped on by the import crowd who claim American cars can't perform/keep up with imports.