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When you shift in a traditional manual transmission, the clutch is disengaged and a sleeve is shifted from one gear to another. The teeth of the sleeve must align with the teeth of the target gear. Because the gears are different ratios (and therefore traveling at different speeds), the sleeve has a synchronizer cone which is pressed up against the target gear to match its speed before the sleeve slides all the way over.

As I understand it, a dual-clutch transmission is basically two smaller manual transmissions: one for the odd gears and one for the even gears. There are two clutches and when one is engaged the other is disengaged. Therefore, only the even or only the odd gears are in motion at any given time (I think?). This gives the advantage that the transmission sleeve can be "loaded" onto the target gear before unloading it from the active gear, then the active clutch is switched and the target gear is now active.

(Apologies if my usage of terminology is incorrect. This is all new to me.)

Is it true that, in a dual-clutch transmission, the target gear is stationary when the sleeve is loaded? Does a DCT require synchronizer cones?

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Yes DCT transmissions have synchroniser mechanisms just like manual transmissions and they work the same.

As the shift fork and sleeve travel towards the gear to be engaged.. If there is a speed difference between the sleeve, synchroniser hub and gear, the sleeve is blocked by a 'blocker ring' to prevent further travel of the sleeve, the synchronizer ring creates friction to help match gear speeds. When the speeds between hubs & sleeves are synced the sleeve can then travel fully and engage with the engagement ring spine on the gear.

A transmissions floating gears are rotating all the time, they're NOT all mechanically locked to their shafts unless selected, but they will all rotate even if only due to the viscous friction between oil, shaft and gear.

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  • neat! so the "floating gears" may be in motion because when they're no longer engaged, they're allowed to "free-spin", e.g. keep any rotational momentum they had from when they were engaged and potentially (eventually) coast to a stop?
    – Woodrow Barlow
    Jun 15, 2017 at 15:01
  • Noo.. The floating gears are always rotating.. So they won't stop as they're always meshed with their associated mainshaft gear. They're just not directly selected (meaning that the shafts are locked/linked together via the synchronizer hub. The only gear that can actually stop rotating totally is reverse.
    – Orb
    Jun 15, 2017 at 18:10
  • Syncronizer aka gear brake.
    – Moab
    Jun 18, 2017 at 2:46

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