How does a DCT transfer torque between clutches?

"AddictedToM3s - Drives a GC" (addictedtom3s)
06/13/2018 at 22:42 • Filed to: None

I’ve had that question on my mind that has been increasing in curiosity lately and this is just the place to ask I imagine. My understanding of a dual clutch transmission is there are two multi-plate clutch packs arranged concentrically. There is an output shaft going through each of them. One is hollow and that is connected to the larger clutch-pack and handles the odd gears while the smaller clutch pack is inside the hollow driveshaft and drives the even gears. From there, the engine and ECU are able to determine what the next gear is and serve up the next gear and clutch almost instantly (8ms is the VW shift time I’ve found on a Borg-Werner DSG system).

Based on some wikipedia and YouTube it looks like most DCTs are wet-packs meaning they are cooled using oil. That same oil is then used to create hydraulic pressure to sandwich the clutch pack together to actuate one of the clutch packs.

So here’s my question, how is that hydraulic pressure regulated? What is performing that hydraulic actuation in 8ms?

Here’s what I was able to find:

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http://ufdc.ufl.edu/UFE0046724/00001

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DISCUSSION (12)

Nibby > AddictedToM3s - Drives a GC
06/13/2018 at 23:06

there are little gnomes that do all the dirty work... they feed off each others’ tears

sony1492 > AddictedToM3s - Drives a GC
06/13/2018 at 23:20

Kinja'd!!!

What i gathered is it uses an electromagnet to open up a section of the system to existing hydraulic pressure or it powers up any number of small electric motors to supply hydraulic pressure when in the gear.

gogmorgo - rowing gears in a Grand Cherokee > AddictedToM3s - Drives a GC
06/13/2018 at 23:25

I can’t really answer your question.

But the way I’ve always understood it is that it’s effectively an automated manual. The difference though is that it can have two gears engaged at once. When shifting from 1st to 2nd, it would have both of them engaged, then just disengage clutch 1 and engage clutch 2.

I imagine the hydraulic system is much like that in a traditional automatic. You’ll have a gear-driven pump, and electronically actuated solenoids to send the pressurized fluid to various hydraulic “rams” to actuate everything.

Smashing gears together is quite quick. If you select 3rd while you’re in second, 3rd gear will get smashed in place as you select it, and then the only delay you would notice between gears is the time it takes to release one clutch and grab the other after the gear’s been engaged.

AddictedToM3s - Drives a GC > Nibby
06/13/2018 at 23:28

Not gonna lie, this is more tame than I anticipated from you

AddictedToM3s - Drives a GC > sony1492
06/13/2018 at 23:28

Precisely what I was looking for. Thanks!

AddictedToM3s - Drives a GC > gogmorgo - rowing gears in a Grand Cherokee
06/13/2018 at 23:29

This combined with Sony1492's response makes a lot of sense now.

Textured Soy Protein > AddictedToM3s - Drives a GC
06/13/2018 at 23:32

This link talks about the Ford PowerShift DCT which is a dry clutch DCT but it has two electrically actuated clutches. I think maybe each of them is on opposite sides of the flywheel? Not sure if that’s what these gifs are implying.

Kinja'd!!!

Nibby > AddictedToM3s - Drives a GC
06/13/2018 at 23:37

sometimes you take a night off

AddictedToM3s - Drives a GC > Textured Soy Protein
06/13/2018 at 23:39

Hmm that’s strange. The gifs look like they’re on the same side since you can see the blue and yellow on the same side. The K1 gif you’ll notice is in the grey portion that’s longer than the green portion in the K2 gif. Now my question is how does that not wear out the throw out bearing int he system? it looks like the levers being pressed in are what compresses the clutch pack so I would assume that means the throwout bearing is always active?

Future Heap Owner > AddictedToM3s - Drives a GC
06/14/2018 at 04:31

Nothing to add, just wanted to say thanks for that video! It really helped me figure out how the two input shafts mesh to the different sets of gears.

Future Heap Owner > AddictedToM3s - Drives a GC
06/14/2018 at 04:36

I think the very idea of a DCT implies that at least one of the clutches is always disengaged. They must either engineer around having a throwout bearing active all the time (is it just that the inactive clutch & gear shaft spin down to stationary very quickly, at which point the bearing isn’t rolling?), or really beef up the bearings to compensate.

gogmorgo - rowing gears in a Grand Cherokee > AddictedToM3s - Drives a GC
06/14/2018 at 09:57

Solenoids are electromagnets that in this case open and close valves.