Eric Reeves

Tremec’s (who supplies Chevy with transmissions) acquisition of Hoerbiger Drivetrain Mechatronics can and should yield the technology for a DCT unit in the new C8 Corvette/ME. This new transmission can and should work with a 9,000RPM motor limit. Something the DOHC motor might achieve. Has anyone here thought about this?

rgregory

There are plenty of suppliers that make transaxles already I can’t see the trans being any issue or any major cost no development required just integrate it into the car.

toddlaing

I would say that is will be a pretty big disappointment if it does not have a DCT. If they really intend to benchmark the Porsche TurboS PDK type competition a DCT is a must. Especially at a 100k plus price point.

OnPoint

I wouldn't be surprised to see a DCT with a torque converter. That seems to be the direction of some with the DCTs in order to eliminate some of the DCTs bad behavior at slow speeds/parking lot crawls/stop and go.

rgregory

But I honestly don’t feel DCT is anymore than a paper bragging point. My Gallardo is just a single clutch and it shifts pretty fast and is fun. You are talking millisecond, maybe 0.04 seconds quicker to 60 with a DCT vs a single clutch (assuming 1 shift). I would prefer a good single clutch with good longevity to a complicated DCT.

rgregory

That wouldn’t be a DCT. Torque converters take the place of clutches, you have one or the other.

But I agree with what you are saying, GM doesn’t want cars in for warranty repair for fried clutches and many corvette buyers would drive an automated clutch car stupidly. Torque converters even though I don’t like them are safer and cheaper.

OnPoint

Better tell that to transmission engineers - as they've been building DCTs with 'em:

Here is a clip of an article, I'm sure you can find:

Dual-clutch transmissions—essentially two parallel gearboxes that hand off power from one to the other, and do it more efficiently and quicker than either planetary automatics or conventional manual transmissions—seem like a dream technology for engineers seeking both performance and fuel economy.

But computer management of their clutches is tricky, and drivers accustomed to the silky launch provided by a torque converter-equipped planetary automatic are frequently disappointed by the driving dynamics of DCTs. The cars can lurch when trying to move at parking-lot speeds, and a DCT can make inch-perfect parallel parking frustrating.

Honda has traditionally built its own automatic transmissions (uniquely without planetary gearsets), a strategy that has led to its transmissions sometimes falling behind industry fashion in the number of gear ratios. In the case of the Acura TSX, that meant only five speeds at a time when six is standard and 9-speed automatics are available.

The 2015 Acura TLX replaces the TSX and the TL, and offers a ZF-sourced 9-speed automatic transmission (the 9HP) with the optional 3.5-L V6. The base car pairs its 2.4-L I4 with a Honda-developed 8-speed DCT, which features the novel twist of a torque converter in place of a clutch. Honda claims it's the first production DCT so equipped.

This gives the DCT-equipped TLX the smooth low-speed driving dynamics of a traditional automatic transmission with a gearbox that is more efficient, according to Chris Kipfer, the Assistant Large Project Manager responsible for drivetrain.

Honda's product planners and engineers interviewed drivers of cars equipped with DCTs, and “the main thing they talked about was how unrefined and unsporty they are,” said Kipfer. “The main issue is the low-speed launch.”

Incorporating a torque converter into the unit not only provides internal NVH benefits that help deliver the low-speed refinement most drivers seek, but its inherent torque multiplication boosts off-the-line acceleration. In fact, the TLX 2.4-L car accelerates to 60 mph 1.5 s faster than the TSX did, thanks in large part to the use of a torque converter, he noted.

OnPoint

Actually appears GM is already looking at DCT/torque converter transmissions:

https://www.google.com/url?sa=t&rct=...pxsa1JFWQ7xMIL

From that piece:

GM Explores Torque Converter DCT
June-2013-TRF01-GMDCT-pic-12

Though dual clutch transmissions have been very successful in sports- and performance-oriented passenger cars, the feedback from buyers of luxury cars and family vehicles has not always been so positive. Criticisms have centered on drivability and launch performance, particularly in North America, where drivers are accustomed to the extreme smoothness of planetary automatics and CVTs.

Intent on combining the DCT’s fuel efficiency with a conventional automatic’s ultra-smooth driving characteristics, GM engineers presented a paper at this year’s SAE Congress proposing a seven-speed DCT working behind a hydraulic torque converter in place of the conventional flywheel. As well as improving launch quality, the DCTC arrangement would also counter the other perceived drawbacks of DCT – its lack of sustained creep ability on grades, and its launch shudder and limited thermal capacity.

The GM researchers also cited as a benefit the proposed transmission’s lower demands on its lubricant when compared to a conventional wet clutch DCT (wDCT): “Additionally, for wDCTs, high quality lubricating oil is required to achieve adequate friction and cooling characteristics which requires interval changes, leading to increased initial and routine maintenance costs.“

Operating Strategy

In terms of operating strategy, the torque converter (TC) is only used when launching from rest in first gear. After that, the lock-up clutch (TCC) remains engaged, although there is flexibility to allow slip of around 75 rpm to mitigate gear rattle and facilitate the use of low engine speeds for improved fuel efficiency.

The TC design investigated by the GM engineers is smaller than a conventional TC, but the housing containing the TC and the twin multiplate clutches is about 25 mm longer axially than on a standard DCT. In addition to the main benefit of eliminating the risk of launch shudder, as the shifting clutches do not slip, the authors cite other potential advantages of the arrangement. These include improved transient response and acceleration (thanks to the reduced inertia), the decoupling of the engine and transmission to allow engine idle without the aid of a clutch, and torque multiplication to improve engine starting under stop-start operation.

The latter will help ease some of the complex compromises surrounding dual mass flywheel design and NVH under restart, say the engineers, and DCTC users will perceive quicker vehicle acceleration response following an auto restart from rest.
On the all-important question of fuel economy, GM accepts that there will be extra energy losses in any torque converter. However, the paper shows that with the extra flexibility provided by the TC, the final drive ratio can be adjusted to derive maximum benefit from the TC’s ability to deal with NVH issues and to allow lower engine speeds through controlled slip. This is a useful advantage for the latest-generation downsized and downspeeded engines.

“Steady state operation at lowered transmission input speeds and high loads is made possible by controlled slip to attenuate rattle or provide NVH isolation which is not possible with dry clutches without loss of torque transfer or thermal concerns,” says the paper. “Drive quality is enhanced further in the engine downspeeded region by means of the torque converter facilitating improved torque transfer compared to dry or wet clutches alone. When a downshift is necessary while operating at low speed (around 1000 rpm transmission input), the TCC can be fully released, causing engine speed to flare, lower SR (speed ratio) to create torque multiplication, all the while engine torque capability is increasing. This leads to improved vehicle acceleration when requested, but also enables operating in a region that improves fuel economy.”

Conclusions

Overall, says GM, the most extreme of the final drive ratio options investigated allows the DCTC to actually improve (by 0.25 percent) on the fuel economy of a dry clutch DCT, with further potential improvements utilizing still-taller final drive ratios. Compared to a six-speed planetary automatic, the economy benefit is between 1 and 2 percent but, as the engineers explain in their summary, more is possible:

“The improved drive quality possible with the DCTC’s torque converter can enable aggressive shift and TCC pattern constraints that were shown to provide a 0.25 percent increase in fuel economy. A further increase in efficiency for a DCT utilizing a torque converter would be to relocate the shifting clutches of the DCTC concept to inside the transmission structure. The DCTC concept or use of a torque converter with shifting clutches internal to the transmission structure has the potential to be an enabler for DCT technology to achieve improved fuel economy and drive quality.”

rgregory

Lol that is just marketing gymics to make people think they have a DCT. DCT= dual clutch transmission. How can it be a DCT if there is no clutch?

OnPoint

They still have clutches.

By the way, the current A8 has five clutches - and a torque converter.

rgregory

Of course automatic transmissions have internal clutches but they are there for different purpose. These clutches are not used for taking off from a start.

OnPoint

And the DCTs with TCs still have clutches as well.

Would actually be a nice development if it gets perfected.

rgregory

It is still not the same. Marketing can twist it however they want. How many people with paddle shift automatics think they have a SMG transmission?

A DCT is a transmission with 2 clutches. The transmission is same concept as all manuals with gears and synchronizers except have dual input paths.

Clutches in automatic transmissions are used to engage the gears in the way shift forks would in a Manual but instead with fluid pressure and the clutch packs. These clutches only slip to make for smooth shifts they are not used to engage drive from a dead stop that is why there is a torque converter.

OnPoint

The GM piece above wasn't a marketing piece. The DCTs utilizing a TC essentially are replacing the flywheel with a flywheel/TC with the rest of the DCT architecture remaining DCT. It provides an interface utilized at slow speed operation to smooth low speed DCT operation. Once underway, the TC is in lock-up mode and the DCT performs like a DCT.

But - you're free to think of them however you want.

rgregory

I don’t care how they make it work. Like I posted above I agreed that GM would most likely go the route of a torque converter. I have a Gallardo and when they first came out owners were burning up clutches in 5k miles because they were driving them like automatics. GM would not want to deal with this.

Either way I thought in the article GM called it DCTC not just DCT they made a distinction.

OnPoint

Of course they made a distinction in referencing it, because they added a TC to a DCT, and utilized a nomenclature to speak of it.

Another thought, though and going in a different direction, would be whether they forgo a DCT altogether. Seems lately manufacturers have been backing off a bit on DCTs (at least outside the performance niche) and focusing a good deal of investment in the continued improvement of the old-fashioned TC automatics. The A10 in the Camaro is a good example.

Will be interesting to see if given continued improvement/development of the slushbox whether they simply stay on that path.

Either way - whether they go with a more traditional automatic (albeit highly developed), or with a DCT, I think we'll see a TC either way (A10 or its equivalent having a TC being a given of course).

JerriVette

Would be nice if GM offered a dct...in the c8. It offers a direct fast shift even at part throttle etc...whereas GM s A10 shifts as fast as a dct only when driven like one would at the track flat out ...

Technically speaking the A10 equals the high performance of a dct but street high performance driving leaves the A10 behind the dct ..

GM will either care about the difference or it won't...

It's not lap times but rather how the driver feels connnected to the car...

Dct has this in spades and the A10 not nearly as much

rgregory

I’ll just start that I do not like automatics. However a lot of the issues comes down to software and a few changes. I have driven 2016 Camaros with the auto and steering wheel shifters, compared to my car with SMG it is so slow to react. Down shifts in particular seems so slow. Another issue is that dam torque converter feel.

The torque converter issue though could be overcome. Use the torque converter to get off the line then lock it competely. That would make engine braking and all other aspects feel like a manual.

NoOne

Here is an easy explanation.

A DCT is already in the next gear. A TC trans, even a multi-clutch unit with a TC is not.

Think of a DCT as 2 transmissions. Trans 1 is in 2nd, Trans 2 is in 3rd, it just switches to the one already in the next gear.

I've driven AMG's 9 speed multi-clutch and it is the closest to a DCT I've driven, UP and DOWN shifts.

Until you've driven a DCT you won't get it, and until you've driven on hard, in whatever sport mode that makes it downshift, rev match, and all the rest of the crap you still won't get it.

My DCT is my S4 was always in the right gear, did exactly what I wanted it without me ever touching the gear lever or paddles. All the marketing in the world and a TC trans simply cannot do or respond like a DCT.

I didn't say shift, I said respond. Fast upshifts are fine, but smooth, multiple gear downshifts that do not upset the chassis or the car have yet to be done in a TC trans.

The AMG 9 speed came very close but AMG doesn't call it a DCT and also doesn't say it has a torque converter so I'm not exactly sure what it is.

vetteman41960

I also owned a Gallardo. The issues with the single
clutch are that first there is the issue of premature wear. I had to spend 6k for a new clutch in the Gallardo at 9k miles.
In addition it absolutely horrible in auto mode very clunky and unpleasant to drive in auto mode.

Then there is the delay from a dead stop while the clutch engaged. The hesitation drove me nuts.

Also having to baby the clutch to prevent premature wear. As you know that at a stop you either put the car in neutral by pulling both paddles back or if you stopped for more than 10 second with your foot on the brake the computer will out the car in neutral.


I now have a Callaway SC 757 with A8. While the paddle response is horrible delay it's great for just regular driving around town.


I also own a 14 458 Italia. Car has duel clutch DCT by Getreg. It's is aa comfortable in auto mode in the Callaway. There is no delay from a dead stop. No need to put car in neutral at a stop.

The DCT shifts are lighting quick both in upshift and downshift at any speed.

GM claim that the A8 is a fact a a DCT is just not true. While the A8 will up shift while in auto when wide open, there is no speed or mode that a manual shift comes anywhere near the time from pulling the paddle and the shift happening as quickly as a DCT. In the 458 there is virtually no delay. And absolutely no delay a human could detect at any speed up or down shift.

I will be highly dissapointed If the C8 mid engine high performance model does not have a DCT.

Maybe GM could use a A8 or A10 in the entry level Corvette. But there is no way they will get Ferrari or Porsche or Lamborghini buyers to even consider the top of line C8 mid engine without a proper DCT.

For those who have never driven a well sorted DCT I promise that the A8 is not even close to the performance weather in auto mode or paddle shift.

Lets hope GM gives us the option of a DCT even if it's a 8k or 10k option. Once you drive a well sorted DCT a TC Trans just won't cut it in a high performance sports car.