Dual-Clutch Transmissions (DCT)

[The Critic]

http://www.dctfacts.com/widc_pg1a.asp

I drove a 2009 VW Jetta TDI today with the DSG. The DSG is VW's version of a dual-clutch transmission. It's essentially two manual transmissions contained within one unit and does not use a torque converter.

If these units prove to be reliable (and so far they have), I think they could be the transmission of the future if they continue to deliver better efficiency than a traditional 6-speed automatic.

The performance of the DSG is simply unreal. It shifts extremely quick, quicker than any transmission (including GM and Aisin 6-speed autos) that I have driven. Under normal driving, you cannot feel the shifts, you can only hear the audible change in engine RPM. The programming was also extremely responsive on this particular vehicle.

Has anyone else driven a dual-clutch transmission? What are your thoughts on it? Do you folks think that DCTs will become the "transmission of the future?"

 

[JTK]

Does the driver still have to mash a clutch pedal? I don't get how it works lacking a TC?

 

[The Critic]

Originally Posted By: JTK
Does the driver still have to mash a clutch pedal? I don't get how it works lacking a TC?

For a driver, a DCT operates in the same manner as a normal automatic. There's no clutch pedal. Here's a video on how it works:

http://www.motorauthority.com/video-how-volkswagens-dsg-works.html

 

[crinkles]

i like the idea of it and since i was a teenager i thought why don't they just let the clutch do the declutching itself.

but yeah great idea and have not heard of many problems. the boxes require special fluids though (read $$$).

smart idea and if buying a VW i would probably try and opt for one if I am in that price bracket

 

[ffracer]

The idea is that in a manual clutch transmission:

1-Most drivers don't have the coodrination (or attention span) to time the clutch pedal, let alone match the revs on the downshift.
2-While a manual is better than a torque converter or CVT in almost every respect, other than ease of use, it provides little value in 1st and early 2nd gear to get moving. More efficient, but very jumpy, unless you are really good. It takes a lot of driver skill. Once learned, a non-issue.

The DSG works on four levels:

1-Varies the gear ratio in 1-2 gear (traffic mode) for both efficiency and ease
2-Works as a F1/Indycar-style paddle shifter timed clutch above 2nd. Effectively a manual with an F1/indycar paddle shifter. Fun, fast, and efficient.
3-Can operate like a full automatic.
4-Since it is a manual except the 1st-2nd gear variable, it is really cheap to make and the clutch last pretty much the life of the car.

Overall, it somewhat the best of both, although, you can't quickly and easily go to instant neutral (clutch pedal) on snowy roads or when you are going airborne (!).

I agree that this will be the future, as it is efficient and can be made cheaper, plus it will be used in hybrids to blend the power and return the control to the driver. Very similar to the Automated manual (paddle shift) gearboxes found in BMWs, Ferraris, and F1/Indycars.

 

[Audi Junkie]

It does not disengage the lower gear until the higher gear is engaging, providing continuous thrust. Hot stuff.

 

[d00df00d]

DCTs are different from BMW SMG, Ferrari F1, and Formula 1 race car transmissions. Those types are essentially traditional manuals with robots controlling the clutch. DCTs have two clutches that engage alternately. Very different. Much more complex, but with much more flexibility to be smooth.

CVT is the theoretical ideal because it can always be at the right ratio at all times. Unfortunately, the technology isn't quite mature for performance applications. People also seem to feel uncomfortable when there is no shift shock and the RPMs don't vary much during acceleration, so not everyone likes the feel of a CVT. Until those problems are resolved, DCT is by far the best alternative.

However, it still does not solve the only real problems left with non-manual transmissions:

1. It won't let you coast or engine brake as you please
2. It won't let you skip gears

Still, I suspect DCT will win over a fair number of people from manual transmissions, either because they are tired of shifting or because they can be convinced by the sales pitch ("it's WAY faster than shifting yourself!"). This will be a great thing for the manufacturers because it will eliminate a lot of variables with respect to wear and tear (no more clutch dumps or clumsy/missed shifts), and help keep warranty issues under control.

As for me, until an automated system becomes available that gives me the option of skipping gears and controlling the clutch myself, I will stick with a manual, no ifs, ands, or buts.

 

[ffracer]

Originally Posted By: d00df00d
DCTs are different from BMW SMG, Ferrari F1, and Formula 1 race car transmissions. Those types are essentially traditional manuals with robots controlling the clutch. DCTs have two clutches that engage alternately. Very different. Much more complex, but with much more flexibility to be smooth.

CVT is the theoretical ideal because it can always be at the right ratio at all times. Unfortunately, the technology isn't quite mature for performance applications. People also seem to feel uncomfortable when there is no shift shock and the RPMs don't vary much during acceleration, so not everyone likes the feel of a CVT. Until those problems are resolved, DCT is by far the best alternative.

However, it still does not solve the only real problems left with non-manual transmissions:

1. It won't let you coast or engine brake as you please
2. It won't let you skip gears

Still, I suspect DCT will win over a fair number of people from manual transmissions, either because they are tired of shifting or because they can be convinced by the sales pitch ("it's WAY faster than shifting yourself!"). This will be a great thing for the manufacturers because it will eliminate a lot of variables with respect to wear and tear (no more clutch dumps or clumsy/missed shifts), and help keep warranty issues under control.

As for me, until an automated system becomes available that gives me the option of skipping gears and controlling the clutch myself, I will stick with a manual, no ifs, ands, or buts.


All good points and I agree, but the DSG's idea was to maximize the value of 1-2 gear shift in traffic. The variablility does not factor in after 2nd gear. Other than that, a regular manual (driven by someone who knows how to use it) will work - something I prefer.

 

[JTK]

Being the lesser tallented type, I'm still having a hard time grasping this and I've owned lots of manuals and ATs. If the driver isn't actually doing the clutching and shifting, what's the advantage of a DCT? Quicker, firmer shifts? There's all kinds of "paddle shift" equipped planetary gear, torque converter AT's available that you can 'shift yourself' all day long? Honda AT's already have the manual style sliding gear sets going for them.

Joel

 

[chrome]

Originally Posted By: JTK
Being the lesser tallented type, I'm still having a hard time grasping this and I've owned lots of manuals and ATs. If the driver isn't actually doing the clutching and shifting, what's the advantage of a DCT? Quicker, firmer shifts? There's all kinds of "paddle shift" equipped planetary gear, torque converter AT's available that you can 'shift yourself' all day long? Honda AT's already have the manual style sliding gear sets going for them.


What DCT differs from the more traditional automatic transmission (including Honda's) is the absence of a torque converter. A TC is fairly inefficient especially when the difference in input and output shaft speed is great. This is especially true in lower gears, whereas in higher gears you get the converter lock-up.

DCT uses automated clutches, two of them, instead of a single TC. Therefore, they can transmit torque seamlessly, as the 1st clutch won't disengage until the 2nd clutch engages. This improves efficiency, and response.

 

[Gary Allan]

Quote:
what's the advantage of a DCT?


Lower hp losses through the transmission. The rest is "consumer acceptance" (that includes the road racer types).

I would think the simplest setup for the adaptive crowd would be a TC w/lock up feature mated to a manual. Super high stall for lower powered engines. A simplified fluid circuit should limit pump losses. It would never work in our (or any) "market". Not enough broad spread appeal.

 

[ffracer]

Originally Posted By: JTK
Being the lesser tallented type, I'm still having a hard time grasping this and I've owned lots of manuals and ATs. If the driver isn't actually doing the clutching and shifting, what's the advantage of a DCT? Quicker, firmer shifts? There's all kinds of "paddle shift" equipped planetary gear, torque converter AT's available that you can 'shift yourself' all day long? Honda AT's already have the manual style sliding gear sets going for them.

Joel


The DCT works like this:

1-Full automatic mode (operates to driver like an AT) or
2-Full manual mode from 2nd up using paddles/buttons - no clutch pedal, just up/down sequentially - computer matches reves. The 1-2 gear is varied to get the take off and very low speed driving smoother and more efficient - (feels somewhat like a automatic torque converter in 2nd gear at slow speeds). Once the 2nd gear is in place, further acceleration is identical to a clutch transmission, just you have to hit the upshift button when desired and downshifts later when desired, like a Tipttronic.

The benefit is that is almost the same as a stick shift clutch gearbox mechanically (cheap and reliable and most efficient/responsive), except for the automated varied 1st-2nd gear, no clutch pedal or stick, and the ability to go full automatic.

It drives like a Tiptronic with out the torque converter efficiency loss, but with much better response.

 

[saaber1]

some DSG videos etc. I copied from another thread FYI: There is also a good porsche pdk video out there somewhere on BITOG/youtube.
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Have had my 6 speed DSG (VW GTI) for seven months now and I use manual mode all the time except when I need my hands free for something important like drinking coffee ha ha or when stuck in traffic.

The manual mode is just so much more fun and you can keep the revs right where you want them all the time. On downshifts it rev matches perfectly and the shifts are pretty much instantaneous. Have always been a manual tranny guy but this DSG is just incredible.

BTW keeping it in the automatic sport mode is not too bad either although I prefer manual mode. In "s" mode the car lives in the high rpm range and downshifts aggressively. When accelerating hard, it shifts just past the redline. Amazing.

Some old DSG videos/articles for those interested. Hope these links still work.

7 speed dry clutch dsg http://www.youtube.com/watch?v=WVWP7TYhP0c&feature=related

Good article but some mistakes in it http://blogcritics.org/archives/2006/11/08/091620.php

Jason Plato of Fitth Gear test drives the dsg (about 1:15 into the video is where good dsg discussion starts) http://www.youtube.com/watch?v=5EdjEE0edPw

test of manual vs dsg gti http://www.youtube.com/watch?v=gmMNRQ1GJ3o

Edited by saaber1 (02/03/09 05:26 PM)

 

[Palut]

How do these work at very low speeds? Is first gear very low, or does it constantly engage and release the clutch?

 

[The Critic]

Originally Posted By: Palut
How do these work at very low speeds? Is first gear very low, or does it constantly engage and release the clutch?

I only took a very quick test drive (the car was showing 5 miles remaining on the range), but I didn't notice anything when I accelerated from a stoplight. However, when I made a sudden deceleration to make a last minute lane change, I did feel/hear a clunk from the transmission. It felt more like a manual than an auto.

 

[saaber1]

When starting on a hill you should hold it with the ebrake just like a manual tranny (and it will roll backward a little just like a manual). You don't have to use the ebrake for drivability (it will move forward fine if you simply go from brake to gas pedal), it just prolongs the clutch life.

Starting on hills without ebrake on the DSG or a manual leads to fast clutch death. My wife burned my clutch out on my boxster S manual this way in short order and they are not cheap. Needless to say for the GTI DSG I insisted on her using the ebrake.