Talk:Double clutch

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Contents 1 input shaft speed vs. engine revolutions 2 Article title 3 Rev-matching? 4 Fuel efficiency 5 Puzzled 6 Citation

[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)

I've always called it "double declutch", which is in fact more correct since the technique involves the disengaging of the clutch (ie depressing the pedal) twice. I suspect it may be "double clutch" in North America and "double declutch" in the British Empire.--Yeti Hunter 11:49, 12 June 2007 (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

The generally accepted term for this (in the US) is 'powershifting', and it's extremely damaging to your car. If I understand correctly (your point being to shift without depressing the clutch?), this is definetly -not- heel-toe technique, which is used to quickly control the throttle during cornering. (Allowing you to brake and accellerate with no time lost to move the foot.) As has been said, this should really only be done on a sequential shift vehicle such as a motorcycle, and even then it's a great way to screw up your tranny. Aspengrey 04:55, 11 September 2007 (UTC)

[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)

The main reason that this technique is more fuel effecient is that you don't waste engine power driving a synchro, which matches the RPMs of the transmission and the engine for you. (The synchro also introduces a lot of rotational torque) On a non-synchro transmission it simply isn't possible to shift while the RPMS are very different, so it's kind of a moot point. Aspengrey 04:55, 11 September 2007 (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)

The main advantage of actually double clutching rather than matching with the clutch in is that the engine will lose or gain RPMs faster while in neutral than just with the clutch depressed. Aspengrey 04:56, 11 September 2007 (UTC)

I find this article very unclear. It does not describe why the word "double" is used in the phrase. Further, the definition seems to allude to some extra action that may lead the novice reader to think that another action is involved and that it was this other action is why the word "double" is used in the phrase yet this appears not to be the case, maybe. Very unclear. Fraberj (talk) 03:07, 26 December 2007 (UTC)

The word "double" is used, presumably, because you press the clutch pedal twice. Hence, "double clutch", or the more accurate "double declutch" since the depressing of the clutch pedal actually disengages the clutch. Yeti Hunter (talk) 10:53, 26 December 2007 (UTC)

[edit] Citation

Ok, SERIOUSLY, does that first citation need to be there?! I mean, this is the definition of double-clutching, right there. Anyway, I added 'primarily' in case that was the persons beef, as this is a very useful technique even for syncromesh cars. Aspengrey 04:56, 11 September 2007 (UTC)

Strictly speaking, everything should be cited. However, according to WP:VERIFY, inline citations are only needed for statements that are controversial or likely to be challenged. I don't think any good-faith editor would challenge the lead sentence, therefore I reckon the cite request can be removed.--Yeti Hunter 09:52, 11 September 2007 (UTC)

Apparently the argument is that the term unsynchronized needs to be cited... but it's a link? Here's the edit: 19:07, 18 July 2007 StationNT5Bmedia (Talk | contribs) (3,623 bytes) (cite resource for term unsynchronized) (undo) Aspengrey 02:32, 12 September 2007 (UTC)

Because of your comment, and my adding 'primarily', I think we've cleared up StationNT5Bmedia's concers about the citations, so I'm removing the tag. Aspengrey 15:24, 12 September 2007 (UTC)