how double clutch transmissions works?
In: 5
I’m assuming you’re talking about a dual-sequential transmission (DSG in VW speak), not the technique of dual clutching a conventional manual transmission. If you mean the latter, look at /u/prominently_hidden’s comment.
A DSG has two shafts. One has the odd gears (1-3-5) and the other has the evens (2-4-6). Each shaft has a clutch on the end that can connect to the engine driveshaft. Inside the transmission there are electronically controlled actuators that can engage/disengage individual gears and a computer that’s running the whole show.
When you’re sitting there in neutral both clutches are disengaged…the engine happily spins, the gears don’t do anything. The computer assumes you’re going to go to 1 next so it engages 1 on the odd shaft (but still doesn’t close the clutch).
When you want to go, 1 is already engaged so all it has to do is close the clutch on the odd shaft. If you continue to accelerate the computer assumes you’re going to need 2 next so it “pre-engages” 2 on the other shaft (which isn’t connected to anything right now so can shift on it’s own sweet time). When it comes time to shift it very quickly engages the even shaft clutch and releases the odd shaft clutch. Because the actual gear shifting already happened, it can do this really fast and, if the clutches are synchronized properly, with basically zero noticeable loss in power transmission. It repeats this pattern of pre-engaging the next gear then rapidly swapping clutches all the way up through the gears, 1-2-3-4-5-6, and then back down if you’re decelerating.
One in a while you’ll find that a DSG does a really slow shift when you were accelerating and suddenly decelerate (or vice versa)…that’s because you outsmarted the computer…it was planning ahead for one direction and you went the other way, so now it *can’t* just swap clutches. It takes it a bit of time to dis-engage the gear it was expecting and engage the other one, *then* do the clutch swap. It’s still pretty quick, comparable to a regular automatic shifting, but not nearly as fast as a planned shift.
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