What is "Double Clutching"

kluivert

What is "Double Clutching".

And is it of any use on the road.

Alun

There's no such thing, but for a discussion of double de-clutching see here.

whippet

I believe it is a techniqe that was used on older sports cars. As far as I know it was where you would clutch in to take the car out of gear, clutch out with gear in neutral and then clutch in again to select new gear.

I have no idea why this was of use in older cars and would think it would have no use in modern cars.

I am totally open to correction on the above post.

aldy05

i used to have to do it from time to time on my 91 honda civic basically because if I put the clutch in and tried to change gears straight away it wouldnt go into gear, i was told double clutching is used if the gearbox is more worn and the selectors etc are not totally in line as the would be if it was new

maidhc

People do it with older non-synchromesh gearboxes, or where the synchro is cooked.

Don't do it unless you have a particular reason. Even non-synchro boxes are easy enough to use without doing it.

smash

according to Top Gear 2 nights ago where he discussed the tiptronic Audi TT with a double clutch..... If you're in say 2nd gear, there's a 2nd clutch with 3rd gear ready to go so you get a faster, smoother gear change...

Is this what you mean?

\m/_(>_<)_\m/

also used when car isn't revving enough in a gear... with the throttle fully down and revs not climbing fast enough, drop the clutch to increase the revs and away you go...

very handy when you want to lift a bike onto the back wheel without dropping a gear. wheeeeeeeeeeely

Pigeon Reaper

Older gearboxes needed this. Citroen came up with the solution so it is no longer needed unless the gearbox is knackered. sometimes people refer to matching the Rev's of the engine to the gears as double clutching. You can do this although use of the correct gears is better practice under normal driving conditions. Motorbikes blip the throttle with the clutch in to bring rev's up when changing down gears. This helps prevent rear wheel lockup but newer clutches are making this no longer needed.

SouperComputer

also used when car isn't revving enough in a gear... with the throttle fully down and revs not climbing fast enough, drop the clutch to increase the revs and away you go...

Thats slipping the clutch! Or, if it involves changing gear its called a powershift.

Double clutching is the incorrect wording for Double De-Clutching

Basically, you go through neutal as if it was a gear as you shift. Really only used with non-syncro streight cut gears. Nowadays, the only thing you are likely to achieve with double-declutching is premature failure of the release bearing.

A more modern, practical method is heel-toe.

maidhc

\m/_(>_<)_\m/ wrote:

also used when car isn't revving enough in a gear... with the throttle fully down and revs not climbing fast enough, drop the clutch to increase the revs and away you go...

Not exactly the best for the clutch!

Vegeta

\m/_(>_<)_\m/ wrote:

also used when car isn't revving enough in a gear... with the throttle fully down and revs not climbing fast enough, drop the clutch to increase the revs and away you go...

very handy when you want to lift a bike onto the back wheel without dropping a gear. wheeeeeeeeeeely

good for getting vtecs to kick in with a honda as well

\m/_(>_<)_\m/

maidhc wrote:

Not exactly the best for the clutch!

or the engine

AMurphy

steve06 wrote:

according to Top Gear 2 nights ago where he discussed the tiptronic Audi TT with a double clutch..... If you're in say 2nd gear, there's a 2nd clutch with 3rd gear ready to go so you get a faster, smoother gear change...

Is this what you mean?

That's a specific design of clutch, not the same I suspect.

Several pointed out it is used on non-synchro gearboxes. Correct. The main reason being to allow the driver adjust the speeds of the next engaging gear set to they do not grind. Remember the grinding gears one hears often from old cars, the reason is the gears are at different speeds, you can get the same effect by trying to engage reverse too rapidly on a modern car, as rev does not have synchro, no need.
So between gears, you let in the clutch and reved the engine to speed up the driven shaft and gears, (drag from the oil, etc would have slowed or stopped it quickly), then pressed the clutch again and as the shaft slowed, it would engage at the synch point, then you let the clutch in again.
also, most of these particular old boxes were not helical nor constant mesh unlike modern ones.
Old tractors tend to be that way also.

peasant

You know all about it when you drive an old 10 ton army truck with non syncronised gears down a hill and you want to shift down, to utilise engine breaking ....you'd better be a fast learner though

mrbungle

Dunno if this answers the OP's question :

Volkswagen and Audi's Direct Shift Gearbox (DSG)
From Aaron Gold,
Your Guide to Cars.
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What it is and how it works

The Direct Shift Gearbox (DSG), also known as the double-clutch gearbox, is a transmission developed by Audi and Volkswagen. What makes it special is that it can change gears faster than any other geared transmission. The DSG can be shifted either manually or automatically. It delivers more power and better control than a traditional automatic transmission and faster performance than a manual transmission.
The DSG is a development of the sequential manual transmission (SMT), which is essentially a fully-automated manual transmission with a computer-controlled clutch. Before we delve into the workings of the DSG, let's start with an explanation of the SMT.


SMT: The control of a manual with the ease of an automatic
Though it has appeared on a few passenger cars, the SMT is widely used in certain forms of racing and is featured on Ferrari's Enzo supercar.
Cars with SMTs have no clutch pedal; the clutch is automatically engaged. Most SMTs can be shifted automatically or manually, the latter using a shift lever or paddles on the steering wheel. The advantage to an SMT is that it uses a solid coupling, as opposed to a fluid coupling (torque converter) as used in a traditional automatic (including Tiptronic- or manumatic-style transmissions). As with a manual transmission, the SMT provides a direct connection between engine and transmission, allowing 100 of the engine's power to be transmitted to the wheels. The SMT provides more immediate response and ensures that the engine RPMs do not drop when the driver lifts off the accelerator (as happens with an automatic), giving her more precise control over power output.

SMTs can also perform matched-rev (our double-clutch) downshifts: When the driver downshifts, the SMT disengages the clutch, shifts to neutral, and re-engages the clutch. The SMT calculates what the engine RPMs will be in the next-lowest gear based on the current road speed, and revs the engine (and, since the clutch is engaged, the transmission) to that speed. It then disengages the clutch, shifts into the lower gear, and re-engages the clutch. The result is a smooth change with no jerk and no sudden deceleration.

SMTs have one major disadvantage, same as a manual: Power must be interrupted while the transmission changes gears.


DSG: An SMT without the lag
The DSG all but eliminates the lag inherent in SMTs. The DSG is essentially two 3-speed gearboxes with a pair of clutches. When the driver starts out, transmission #1 is in first gear and transmission #2 is in second. The clutch engages and the car starts out in first. When it's time to change gears, the DSG uses the clutches to swap transmissions. The #1 transmission immediately shifts to third gear. At the next change the DSG swaps transmissions again, and #2 shifts to fourth. The DSG's computerized controller calculates the next likely gearchange and shifts the "idle" transmission into that gear. The advantage is the speed of gearchanges: The DSG takes about 8 milliseconds to upshift. Compare that to the SMT in the Ferrari Enzo, which takes 150 ms to upshift. It's also significantly faster than a human: According to Audi, the A3 runs 0-60 in 6.9 seconds with a 6-speed manual and 6.7 seconds with the 6-speed DSG. Like the SMT, the DSG performs double-clutch downshifts and can skip gears (i.e. downshifting from 6th directly to 4th, 3rd, etc).

Driving with the DSG
The DSG uses a traditional P-R-N-D-S shift pattern. It can shift automatically in either normal (D) or Sport (S) modes. In Normal mode, the DSG shifts to the higher gears early in order to minimize engine noise and maximize fuel economy. In Sport mode the transmission holds the lower gears longer in order to keep the engine in its powerband. This is especially useful for turbocharged cars like Audi A3, VW GTI and VW Jetta GLI, since the turbocharger is only active at higher RPMs. Sport mode also provides more aggressive downshifts with slight accelerator pedal pressure.
Manual mode is engaged by either sliding the shift lever to the side or pulling one of the paddles on the steering wheel. Once in manual mode, shifts are made by moving the shifter fore and aft or using the paddles (which are marked " " and "-"). If manual mode was engaged with the paddles, pulling and holding the upshift paddle.