Talk:Double clutch
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[edit] input shaft speed vs. engine revolutions
Is it the same in this article's context? Because when I looked at other sites, I find that if I substitute input shaft speed with revs, the instructions become much clearer (its probably just me, though).
- Gearbox input shaft speed is not engine crank shaft speed. To prove it to yourself, play with the clutch (which couples engine output to gearbox input) and the throttle. ;)
- Paul Jakma
[edit] Article title
Does anyone have a reason why this article shouldn't be moved from "double declutch" to "double clutch"? I've never heard the term double declutch before, and from my experience, the term double clutch is quite common in industry and literature. Just for some credibility, I drive trucks for a living. If noone objects, I'll move this article over shortly. -Lommer | talk 23:25, 21 July 2005 (UTC)
[edit] Rev-matching?
What's the technique called where you rev the engine then let off the gas and as the revs come down you can shift without pressing the clutch pedal i.e. the gears just kind of slip into place? Or am I too dense to understand that this article already describes this technique? Thanks Ewlyahoocom 09:12, 30 July 2005 (UTC)
- That's clutchless shifting. You don't rev the engine, you just /very/ quickly close/open the throttle as you shift up - just enough so the revs only drop a small amount, leaving the gearbox without load through it (be it forward or reverse). This is really only feasible on sequential shift gearboxes for a human to do (ie motorcycle gearboxes and race-orientated car gearboxes) - normal car H pattern selector gearboxes would be tricky to do fast enough (never tried myself, so don't know ;)).
- On race machinery (bikes at least) the gear selector often is wired to an ignition kill circuit, so that as the rider starts shifting up the ignition automatically is briefly cut - the rider no longer has to manually shut/open the throttle, all they have to do is tap the selector.
- The 'rev the engine' thing you refer to is called "Heel and Toe" for cars, throttle-blipping is probably best term for motorcycles. It's done for down-shifts only. However, at least with modern race motorcycles (dont know about race cars), the practice is slowly dying out due to the advent of slipper-clutches - they're appearing even on production road-going sports bikes.
- Don't know about other people, but "Heel and Toe" is misnamed for me, should be "Ball and Side" - I use the ball of my foot to brake and the side edge of my foot to blip the throttle ;).
- Paul Jakma
[edit] Fuel efficiency
This article says that unsynchronized transmissions are more efficient than synchronized transmissions. Is this true? According to what my uncle Jim said, the earlier unsynchronized transmissions used a lot of gas. He said that the manual transmissions with the synchromesh are more efficient. —Gm1121983 16:36 13 April 2006
- I haven't seen synchros in person, but I'd assume this only has an effect while clutching (as opposed to an automatic transmition which really does waste enrgy all the time). If so, it's not very important. —Ben FrantzDale 02:30, 14 April 2006 (UTC)
[edit] Puzzled
OK, I confess I'm a bit stumped. It looks like double-clutching simply means "let the clutch out while in neutral" -- as opposed to my synchromesh transmission, where I match revs with the clutch pedal depressed. But if the only real difference is that a double-clutching transmission doesn't have syncronizers (and hence requires you to match revs fairly well), why does it matter if you're matching revs with the clutch pedal down, or with the clutch pedal up and the gearshift in neutral? Cheers.
- With a quck glance, this article appears not to give an answer. From reading various web pages, my sense is that there is a free-spinning shaft between the gearbox and the clutch, like so:
[engine]----||----[gears]---(wheels)
clutch ^ ^idler
- When you put the car in neutral but with the clutch engaged, the idler is spinning with the engine. If you have the car in gear but the clutch pressed, then the idler is spinning with the wheels. If you don't double clutch, the synchros get that idler spinning the right speed as you throw the shift lever. With double clutching, the idea is to use the engine to do the synchros' job, so you don't have to wait for them to do their thing. That is, when you let go of the pedal while in neutral, you are reconnecting the engine to this shaft and so can get it spinning the correct speed for when you throw it into gear. That's my rough understanding, anyway. —Ben FrantzDale 02:01, 22 May 2006 (UTC)
