Not a correction, it could be 100% the reason why they did it, but I am still having problems with the logic.

While the main reason for a DCT's existence is hard fast shifts under WOT without having to clutch or back off the throttle. At low throttle angles in auto mode I can go up through the gears & never feel it shift.

Most times I would not know what gear its in without looking at the indicator so I still wonder what is the benefit of the additional complexity & weight of adding a torque converter into the mix.

 

I think I read on TOV that the torque converter is only used to get away from a stop. After that it locks up to fully realize the benefits of the DCT.

 

^^ I think you are correct Colin...I remember hearing something to that effect that this would be the best of both worlds...or at least, that is the intent.

 

Sounds like a solution searching for a problem.

 

^^ I don't know. I've driven quite a few DCTs and they all suffer with 'jerkiness' or at least indecisiveness when slowly crawling over a speedbump or doing an urban crawl. It always reminds me of a centrifugal clutch. I think the difficulty is when the system has to balance going slowly with not stalling.

 

Have 25K miles on my DCT as a DD without the described problem showing up. Pass over 12 speed bumps 5 days a week picking my granddaughter up from school.

Would also seem odd that the $250,000+ supercar manufacturers would have such a problem & not employed a torque converter “fix” if it was necessary.

 

Not sure if I'd go as far to call it a problem, but it's certainly different than a regular automatic. Maybe a characteristic? [shrug]

 

I was going to add that since I noticed you're on a 335i. With more torque it could 'lug it' and help mitigate the feel/sound of the engine revving vs. clutch slipping. (BTW, a quick search of "BMW DCT jerky" yields pages of topics)

I was also going to add that the customer for a 335i is different than a 4 cylinder H/A product (and even here, there are complaints/comments). I'm thinking of all the varied clients we have for the TSX and could see lots of them complaining if they don't understand what is happening and why it's better.

 

Maybe intended use might dictate acceptance levels for shift feel. The DCT 7's are ZF's mostly running in high horsepower & torque applications while the Honda built DCT 8 is relatively weak with 200ftlbs max torque handling capacity.

This makes it unable to be used with the 3.5 V6. Is the DCT 7 in the RLX built with a torque converter?

 

Yeah, have seen those. When they are drilled down most are the result of trying to drive in one of the sport modes when traffic does not warrant it.

The base DCT has 6 performance modes controlled by stick position & sport button selection, the M3 has more, all of which increase the harshness of the shift (jerky) & the RPM the shift will take place at over each prior mode up to full manual mode - sport button engaged which shifts right now & very hard. Lots of people have real trouble with having to read the manual.

I think someone would have to work at getting a jerky result in auto/normal mode in any kind of heavy traffic or over speed bumps.

 

I prefer manual. I don't care if autos are faster and get "better" mpg. Manuals are more fun even in traffic.

The "better" mpg is bs in real world experience. My 06 6mt G coupe got 16.7 mpg. My current Q50 gets 13.6. (similar driving habits).

 

I think that my usage of the word "jerky" has led us astray. Lets redirect this to the feel/sound of the clutch slipping/engaging, primarily from a stop. Even if the driver gets a smooth getaway, there is (IMO) some effect that is noticeable as the computer engages the clutch. My concern is that for non-enthusiast drivers, this will be unfamiliar if they're only used to regular automatics. Especially if they've never driven a manual or understand the mechanics of the clutch etc.

 

The 9-speed ZF AT with torque converter may be more reliable in the long run compared to wet or dry DCT's. I'm no techie but it seems many can confirm this as TC's been around for decades.

I wonder why Honda took the approach of in-house building an 8-speed DCT (although its i-DCD for 1.5L hybrids are already mated to a 7-speed DCT) but then went with the 9-speed ZF for the V6.

 

I'm going to guess it has to do with the torque limits of the small clutches in a DCT gearbox.

 

I don't believe the TLX 3.5 will come anywhere near the torque limits of a standard ZF DCT. The RLX only generates 275ftlbs & I am running over 420ftlbs through mine, so there is plenty of margin in the 7DCT.

The Honda designed 8DCT does have low torque limits, about 200ftlbs, but its a function of Honda's chosen design application not of the basic technology.

I think they are making a mistake not using the 7 speed units across the line but as Colin said they are looking for very smooth shifts with the TC version. I would think the TLX will get the same power train as the RLX & have a normal DCT.

Honda Press release for the RLX:

"An all-new advanced 7-speed dual-clutch transmission (DCT) is standard on the Sport Hybrid—a first for Acura. Unlike a conventional automatic transmission, the DCT offers ultra-quick gear changes and eliminates the need for a torque converter, which significantly improves efficiency. It can operate in fully automatic mode, or can be shifted manually via steering wheel-mounted paddle shifters."

 

I've driven both a 2014 BMW 535i and 2014 BMW 328i both with the ZF 8 speed auto and they're the best automatic transmissions I've ever driven - quick shifting and smooth. I currently have a 2011 BMW 135i with the 7 speed DCT and while it does shift amazingly fast and acceleration is incredible, slow speed, stop and go performance is not nearly as smooth as the ZF auto.

I would expect the new TLX's ZF auto to be just as good, if not better. I'm very curious to see how well their new DCT will perform.

 

I believe the 7DCT for the RLX SH is different from a traditional DCT design in that the electric motor serves as the coupling between the engine and the transmission, thus eliminating the need for a torque converter to get smooth transitions by using the electric motor to take up the slack.

 

Not so sure about that. AFAIK the third motor is attached directly to only one of the DCT’s two input shafts. Since its attached to half of the DCT’s input shafts this would suggest it has no effect on smoothing the DCT’s output

My understanding was the third motor acted as a starter to get the engine running then immediately switched into generator mode to charge the battery & run accessories. It would only switch to power mode at WOT to aid acceleration, otherwise it was not part of the power generation train.

 

Smoothing would only take place in first gear when moving from a standstill or at low speed crawl situations, which is where most automated clutches struggle to engage smoothly. With the motor integrated into the transmission, it seems logical to use it to avoid any stutter while the DCT's clutch is engaging from a standing start or to disengage the DCT and use the electric motor to creep forward instead of slipping the clutch of the DCT.

Also according to Honda's press release, the electric motor is connected to the drive shaft via a clutch. That sounds more like output shaft rather than input, though it is not clear without an engineering diagram to scrutinize.

http://www.honda.com/newsandviews/ar...spx?id=7504-en

 

This is what I read:

"A 47-hp electric motor putting out 109 lb-ft of torque is integrated into the transaxle, although it’s not in the typical meat-of-the-sandwich location seen in most hybrids, where the motor sits between the engine and gearbox. Rather, it’s at the most outboard location and fixed to the odd-gear input. When the transmission is in an even gear, motor torque is routed through the odd shaft to the wheels. (Worth noting: This isn’t the gearbox that will go into the NSX. The RLX is a transverse application versus the supercar’s longitudinal layout.)"

Also its had some problems in Japan with 3 recalls so far, might be too complex.

 

Hmm....that's interesting that their information does not seem to quite match up exactly. Whatever the case, I guess we will see what the real deal is once the car hits the dealerships and we can check it out.