Inside Fiat's Dual Dry Clutch Transmission

Alfa Romeo MiTo DDCT shifter

In April, I reported the Fiat 500 will be getting a version of the new Dual Dry Clutch Transmission (DDCT). Here's more about this transmission.

The 6 speed Dual Dry Clutch C635 transmission debuted this spring in the B segment Alfa Romeo MiTo, with the C segment Alfa Giulietta following. This transmission will eventually show up in the next generation of B, C and D segment Chrysler products coming to showrooms next year. Just recently, Fiat announced the Fiat 500 will receive a smaller version of the Dual Dry Clutch Transmission , this time with seven speeds.

Questions

There are questions concerning this smaller DDCT as far as which model 500 will get it and when. This seven speed DD CT is a natural for the Abarth but it is not exactly clear if it will get it. Curiously, this sporty transmission will initially have a torque capacity up to 140lbs.ft. (190Nm). That is suitable for 500 models with TwinAir, 1.2 liter, 1.4 liter and 1.3 liter MultiJet engines, however, 500 Abarth has a torque rating of between 152lbs.ft. (206Nm) to 170lbs.ft (231Nm), so it is assumed that there will be some changes to allow it to handle the added torque of the turbocharged 1.4 liter Abarth engine.

The New C625 TCT


Or could there be a totally new DDCT for the Abarth? Tucked away in Fiat's Five Year presentation, I discovered a new transmission mentioned. It is called the C625 TCT (Twin Clutch Transmission) and is a DDCT type suitable for power levels between 148-184 lb.-ft. (200-250 Nm), exactly the torque range of the Abarth's 1.4 liter Turbo. There was no mention of this transmission during the presentation and not much is known about it, but, from what I have gathered in Italy, it is a smaller version of the C635 DDCT. We'll watch this one for you.

C625 TCT transmission listed, but not talked about

Another question is when will the 500 receive the DDCT? I mentioned in March there was talk in Italy that the US 500 will use the DDCT as the automatic transmission option and not the Dualogic semi-automatic. However, the smaller DDCT is not in production yet and the 500 is due out in 6 months. The question is will Fiat spend the money certifying the Dualogic for December and then latter next year, certify another transmission for the 500? Remember, each engine/trans combination needs to get certified by the EPA, a time consuming and EXPENSIVE operation.

We'll have to see how this all plays out, but here's what I think: My guess is the DDCT will show up in a US 500 at some point, but it might be in 2012, when a refreshed version of the 500 will make its appearance.

I can't see the 500 Abarth not having the DDCT. As far as time frame, the 500 Abarth is due out around fourth quarter 2011 and thats enough time to get it together for the transmission certification. So I wouldn't be surprised if the 500 Abarth would be the first 500 model to show up in the US with a Dual Dry Clutch Transmission (the C625 TCT).

What do you think? Feel free to post a comment below. In the meantime, let us explore Fiat's DDCT transmission as fitted to the Alfa Romeo Giulietta.

A look at the C635 DDCT

The C635 DDCT mounted to the 1.4liter Turbo of the Alfa Romeo MiTo

Click here to take you to a site that has a great short video on how a dual clutch transmission works.

The C635 DDCT has some notable features. With a torque rating of up to 260ft.lbs (350nm), it currently has the highest torque capacity of any dual dry clutch application on the market. It is also relatively light weight at 178.6lbs (81kg), complete with fluids.

Differential is mounted as close to powertrain centerline as possible

Special steps were taken to make the transmission as short and compact as possible. The center differential was moved closer to the engine. This allows it to fit multiple platforms, from sub-compact platform B cars to larger mid-sized D platforms. Center shaft distance is 197 mm, but there are versions from 181mm (181mm is the same dimension as the C510 transmission used in the 500 Abarth, making the C625 TCT a plausible assumption)

Shared components with manual version

The C635 TCT was developed alongside a manual version and uses some common elements such as the three-shaft layout, the casings, the synchronizers, and even the shift forks. This saves considerable manufacturing costs.

Dual Dry Clutch supplied by LuK GmbH

The C635 TCT uses the Dual Dry Clutch manufactured by LuK GmbH, the premier maker of this type of clutch.

The highlights of using a dual dry clutch is the elimination of the hydraulic support systems and the high efficiency of the dry clutch compared with that of a wet clutch. This enables significant savings in fuel consumption of more than ten percent when compared to the wet clutch and up to six percent in comparison to manual transmissions.

Hydraulic actuation module located in front

Below is the BorgWarner press release explaining their contribution to the C635. Interestingly, they mention three C635 variations, which matches up to a smaller unit for the regular 500, the Abarth's C625 TCT and the larger C635.

BorgWarner will supply the hydraulic actuation module for Fiat Powertrain Technologies' (FPT's) first dry dual-clutch transmission, one of three variants of the C635 family of six-speed gearboxes with 350 Nm maximum torque capacity, launching in late 2009.

Magneti Marelli and BorgWarner were assigned to the industrial development of FPT's innovative transmission control system, which employs a high pressure electrically-driven hydraulic pump and control solenoid valves to actuate the gear selection and engagement as well as the dry dual-clutch unit. Magneti Marelli supplies the control system to FPT, integrating BorgWarner's hydraulic actuation module into its own power and transmission control units. The transmission control strategies remain FPT's responsibility.

Characterized by compactness, speed and efficiency, the FPT transmission control system also uses BorgWarner's solenoid valves, employed for the last 10 years by Magneti Marelli and Fiat in their automated manual transmissions (AMTs).

Alfa Romeo TCT

Alfa Romeo introduced DDCT transmission in the MiTo and later in the just released Giulietta. Alfa Romeo calls this transmission the Twin Clutch Transmission (TCT). Here is Alfa Romeo's official press release on the TCT:

The innovative �Alfa TCT� - the latest automatic dual dry clutch 6-speed transmission - will be debuting in Geneva on the Alfa Romeo MiTo.

Developed and produced by FPT, Fiat Powertrain Technologies, this new device is part of a modern family of 6-speed gearboxes (C635) that was launched - in the mechanical version - on the 170 HP MiTo 1.4 MultiAir Turbo petrol.


Video of Alfa Romeo Giulietta introduction.

Now it's the turn of the �Alfa TCT� teamed with MultiAir engines with Start&Stop system fitted as standard: indeed, the Alfa Romeo MiTo is the first car on the market to combine these three innovative technologies. Available from next spring, visitors to the show will be able to admire a 135 HP MiTo 1.4 MultiAir Turbo petrol with �Alfa TCT� and gear levers incorporated into the steering wheel (optional).



Video of engine and transmission cross section (music warning)

The new device, conceptually, consists of two gearboxes in parallel, each with its own clutch, which allows the selection and engagement of the subsequent gear while the previous one is still engaged. The gear is therefore changed with a simple gradual switch of the corresponding clutches, guaranteeing continuous torque delivery and therefore traction. The result is a driving comfort and sporty feeling well above those offered by conventional automatic transmissions (with torque converter), as proven by greater speed of gear shift, the possibility of selecting between manual or automatic mode and a near-zero power loss during the gear change. In addition, the purchasing, servicing and running costs are limited, while fuel consumption is reduced, thanks also to the implementation of the Start&Stop system, up to 10% less than a traditional automatic hydraulic transmission with torque converter.



Specifically, the �Alfa TCT� features the largest number of interactions with the vehicle's systems available on the market. Indeed, its operation interacts with the steering wheel, the brake and accelerator controls, the Alfa DNA selector, the Start&Stop system, the ABS, the engine and the inclinometer (slope detector to engage the Hill Holder and disable Start&Stop on activation).

Other peculiar features of the new �Alfa TCT� are its flexibility of application, thanks to the compact size of its components, and the fact that it is a dual dry clutch (the type of clutch that guarantees the highest degree of efficiency in terms of fuel consumption among all automatic transmissions). If we compare "Dry" clutches with oil bath ("Wet") ones, we can safely say that the former dissipate energy only during the actual slipping phase of the gear change and on pick-up, whereas wet clutches, which always operate in an oil bath, introduce losses due to viscous friction such as those of conventional automatic transmissions even when they are not in operation.

What's more, they require forced cooling with oil and therefore continuous energy expenditure to drive the dedicated oil pump (absent in the case of "Dry" clutches). Moreover, a "Wet" automatic transmission requires approximately 4.8 litres more oil than the "Dry" version, again for reasons of clutch cooling (in this way, weight is added and losses due to splashing increase). When all these effects are added together, a �Alfa TCT� is found to be approximately 6% more efficient than the corresponding "Wet" one in terms of consumption. Last but not least, the advantages of the "Dry" clutch include the lower cost and the increased ease of installation.



Lastly, it should be remembered that the new �Alfa TCT� boasts a generous 23 public patents split into 3 areas: gearbox control, gearbox mechanics and gearbox actuator.

With thanks to: LuK GmbH & Co, BorgWarner Inc, dctfacts.com,
Fiat Group Press