Entering the mainstream on the first Golf R32, dual-clutch transmissions combine the best bits of manual and auto 'boxes
13 May 2019

Dual-clutch transmissions (DCTs) hit the big time after Volkswagen first introduced one on the Golf R32 back in 2003. 

To date, VW has made well over 26 million of its direct shift gearboxes (DSGs), and it’s not alone. The standard had previously always been the torque converter automatic (slush) gearbox and, on a few small cars, perhaps a teeth-grindingly awful continuously variable transmission (CVT)

DCTs are fun to use because they shift gear with no interruption of torque from the engine. In a conventional manual gearbox, de-clutching interrupts the torque to disengage each gear and engage the next. Torque is reinstated by closing the clutch again and opening the throttle. 

In a DCT, each clutch is allocated to roughly half the gears. So, for instance, as first gear is engaged and driving through ‘clutch one’, second gear is pre-selected through ‘clutch two’, which stays open. When the driver selects second gear, clutch one opens and clutch two closes, taking up the drive simultaneously with no interruption of torque. And so on. 

Software algorithms control things and try to predict the driver’s next move when pre-selecting the next gear. So if an upshift gear has been pre-selected and the driver decides to overtake and a downshift is needed, the gearbox will try to predict that. 

VW may have been the first company to launch DCTs in big numbers with its DSG, but it wasn’t the first to get one running. Neither were Porsche or Audi with the deliciously named Porsche Doppelkupplungsgetriebe (PDK), which graced the 956 and 962 racing cars and Sport Quattro S1 rally car

No, the first working prototype DCT was developed in Leamington Spa by Automotive Products in 1980 and called the hot-shift automatic gearbox. The concept may have been hampered by snail-pace electronics, but the name was excellent. Conventional torque converter gearboxes are not that well suited to small engines, and especially weren’t back then, when power consumption from a torque converter was relatively high – and that’s what prompted the idea. 

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In terms of basic layout, modern DCTs are similar to AP’s brilliant hot-shift design. It had one dry clutch and one wet (running in oil). VW’s first family of DCTs were wet clutch transmissions capable of handling up to 258lb ft torque. The clutch packs – developed by BorgWarner with the trademark DualTronic – are concentric (one inside the other) to save space and the clutches could be smaller thanks to the lubrication. VW launched the seven-speed DSG for compact cars in 2008. Because the torque capacity would be less at 184lb ft, the clutches were dry to reduce drag, but slightly larger in diameter with thicker friction linings to combat wear, and had a design life of 186,000 miles. 

You’ve probably already figured out that the reason these mechatronic marvels happened at all is because they’re super-efficient, save fuel and reduce emissions. In theory, they should also deliver the ultimate driving experience, but maybe sometimes you just can’t beat a manual for thrills.

Wet behind the gears

The clutches in Volkswagen’s original six-speed DSG are ‘wet’, which means they run in oil to reduce wear. That means they can be smaller and concentric, packaged one inside the other in this neat unit.

Read more

Under the skin: the latest CVT gearbox technology​

Under the skin: the technology behind torque vectoring​

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Comments
22

13 May 2019

Teeth grindingly awful cvt? I've had a fair few cvt equiped cars and none have been as awful as you describe, cvt is often more economical and a lot more reliable and less complicated than dsg and as such is well suited to small cars, it too is fun using the manual override.

13 May 2019
si73 wrote:

Teeth grindingly awful cvt? I've had a fair few cvt equiped cars and none have been as awful as you describe, cvt is often more economical and a lot more reliable and less complicated than dsg and as such is well suited to small cars, it too is fun using the manual override.

i take it you never drove fast because CVT's sound AWFUL when under acceleration, well more to the point it makes the engine sound terrible as it just hold the revs away up somewhere in the rev range.

#IDONTPROOFREAD

13 May 2019

You only have to come off the throttle slightly for the revs to drop and if I did decide to drive quickly I had the paddle option which negated that continuous high revving sensation as the revs dropped with each pull of the paddle. However I never found it an issue if I left it in auto and accelerated hard to overtake, it never bothered me as it was how the system was designed to operate. Over 90% of my driving isnt flat out, and a cvt is superbly smooth and responsive through all of it.

13 May 2019
5cylinderT wrote:

i take it you never drove fast because CVT's sound AWFUL when under acceleration, well more to the point it makes the engine sound terrible as it just hold the revs away up somewhere in the rev range.

Cos thats the most efficient way of accelerating - if you want to accelerate fast who cares about the noise ? Thats chucking the baby out with the bath water.

XXXX just went POP.

13 May 2019

And what's wrong with having an engine sitting at constant revs, where it can develop maximum power (or maximum efficiency lower down in the range) all the time?  It's just that most people are not used to it, and our brains wrongly translate the constant drone as a lack of acceleration. 

If all cars had CVT transmission, we'd wonder what on earth was wrong with a conventional transmission car with it's engine constantly hunting in and out of the powerband!

That said, conventional belt drive CVT have very poor mechanical efficiency, and for that reason never quite deliver the promised performance or fuel consumption that they should be capable of. But Toyota's eCVT is a different proposition and one I believe should be applauded...

13 May 2019
LP in Brighton wrote:

And what's wrong with having an engine sitting at constant revs, where it can develop maximum power (or maximum efficiency lower down in the range) all the time?  It's just that most people are not used to it, and our brains wrongly translate the constant drone as a lack of acceleration. 

If all cars had CVT transmission, we'd wonder what on earth was wrong with a conventional transmission car with it's engine constantly hunting in and out of the powerband!

That said, conventional belt drive CVT have very poor mechanical efficiency, and for that reason never quite deliver the promised performance or fuel consumption that they should be capable of. But Toyota's eCVT is a different proposition and one I believe should be applauded...

Yes, CVTs are easily the best auto transmission.

XXXX just went POP.

13 May 2019

I find it quite incredible how an otherwise interesting article can fail to mention the reliability of VW DSG gearboxes, or rather some of them.

The original problem was as stated the common torque converter boxes not being suited to smaller engines, but it's those very DSG's that VAG fit to their smaller engines that have proven the most unreliable. The article makes specific mention of those dry clutch 7-speed boxes with a design life of 186,000 miles yet many have completely failed before they reached 8,600 miles!

Come off it, this isn't a serious article, it reads more like an advert.

Of course it's not just a VW issue, Ford suffers from twin clutch failures too, so much so that they've dropped their dual clutch setup and gone back to torque converter on many vehicles.

13 May 2019
scotty5 wrote:

I find it quite incredible how an otherwise interesting article can fail to mention the reliability of VW DSG gearboxes, or rather some of them.

I find this amazing too.

Another example of VW group's hastily developed engineering, which shows complete contempt for its customers, and significantly predates their similar attitudes with regard to defeat devices.

13 May 2019
scotty5 wrote:

 

The original problem was as stated the common torque converter boxes not being suited to smaller engines

Torque converters are not suited to ANY engine, theyre outdated ineffiecient sh*te that belongs in the trash can along with transverse leaf springs, neither has any place on any modern vehicle.

XXXX just went POP.

13 May 2019
typos1 wrote:

scotty5 wrote:

 

The original problem was as stated the common torque converter boxes not being suited to smaller engines

Torque converters are not suited to ANY engine, theyre outdated ineffiecient sh*te that belongs in the trash can along with transverse leaf springs, neither has any place on any modern vehicle.

 

Ah, perhaps a knee jerk reaction...if you care to find the reviews of the many iterations of the TC gearbox made by ZF, as used by many premium and non premium OEM's, over many generations of their world best selling models, you will find that your claim is just plain wrong. No need to vent your spleen in my direction, just because you are incorrect, just check on-line and fume in private.

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