What is "Double (D) Clutching"?

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v0od0o

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In the army where my dad learnt it, it was sort of drive in any condition thing, he also learned how to change a flat tyre without using that ... errrm lever thing to lift up the car (I dunno its exact name in english) Also sort of do it urself army thing
So I think clutchless gear changes are not really for faster shifting, and I don't think you could shift faster without a clutch.
 

skorgu

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v0od0o maybe you mean a jack? How do you change a tire without a jack? That's one trick I'd like to know.

Also, remember that some track sluts will actually swap out their regular synchro gearboxes for non-synchro ones (I think they're called something like dogs tooth, not sure of the proper name), in which not only do you have to double-clutch if you shift normally, but you pretty much always do clutchless shifts. If you watch WRC drivers for example, they never touch the clutch except for starts/stops and really severe downshifts.

If you do it right (I've done it right twice, damn good feeling), the shifter just goes *snick* and you're in gear. I just wish I had a manual to practice on now, damn lazy Americans and their automatic transmissions...
 

v0od0o

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yes, jack exactly. They use any rocks they find in the desert, but the trick is to lift the car up and stabilize it on the rocks without damaging it from underneath
 

v0od0o

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lmao
I wouldn't wanna depend on that when I'm stranded in the desert with a flat tyre :p
 

smeghead

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Just a point about the WRC cars - they don't use the clutch, but then do you know how long a WRC gearbox lasts and costs?! They have fancy electronic devices, similar to F1, which cut the throttle and whack the car into the gear you select, then put the throttle back on, all in no time at all. Yes it's quick, but it destroys gearboxes at an alarming rate. A WRC is designed to run 600 miles and then need completely rebuilding - well the engine and transmission anyway.

You can of course change gear without the clutch, but the only way to do it without damaging the gearbox is to gently push the shifter until the revs are matched, when it gives up resistance and slides in. But all that feeling around takes time, and the revs have to be matched perfectly, which makes it nigh on impossible to do it properly on a reliable basis. Use a damn clutch!!! Is it really that big a problem in your lives?!?!?!

Sam
 

skorgu

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Yes, but... A modern WRC gearbox isn't really a manual transmission, it's a manual transmission with either an electronic or pneumatic system attached to it. Any rally car with a paddle shifter has it set up this way. Because the computers can, as you say, match revs perfectly and shift obscenely fast (40 msec), they're obviously better for racing.

Also, FIA regulations permit unlimited gearbox changes, even mid-stage, so reliability isn't an issue for WRC teams, and the gearbox techs had this in mind when they designed and built the boxes. Because of this, the WRC boxes tend to be fragile and easily worn, but light and fast. Road cars have different requirements, as most people wouldn't want to change their transmissions every 400km.

I wasn't actually referring to modern rally cars before, but I guess I didn't type that, did I? :) If you watch rally videos, especially from the 80s (Too Fast To Race, etc), you'll see that back then they used "real" manuals, and still sometimes did clutchless shifting, without computer and pneumatic assistance.

There really shouldn't be much feeling around for the shift once you get good at it, as it's really just a matter of knowing the revs. If you fiddle around and watch where your revs are when you feel that *snick*, you should have a good idea of when to do it. If you had a tach with a shift light, you'd just be able to, with practice of course, "know" when to shift. It's not any harder, conceptually, than using the clutch, its just a different set of skills. The time when the revs are matched isn't going to change around on you, especially if you get a good shift rythm going.

Also, non-WRC racers, who can't swap gearboxes mid-race due to rules or cash use dogsteeth boxes that don't have synchros and would have to be double-clutched to change gears at all if you didn't do clutchless shifting, and those usually last longer than synchro boxes, simply because the synchros are what usually wear out.
 

andyhui01

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I think it would be quite difficult to drive a full manual for rally... it would take loads and loads of practice. :wink:
Can someone explain what pneumatic system is... I kept seeing Mclaren having problems with it in F1 this season but never understood what it is.
 

skorgu

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Pneumatics is like hydraulics except with air instead of special fluid. You have a tube that doesn't flex a lot, and an air pump at one end, and at the other end you've got an attachment to whatever you want to move.

Its kind of like a bicycle's brake cables, the outside of the cable is attached to something that doesn't move, and a little piston inside the pneumatic tube is attached to what's getting moved.

I don't know exactly how the real systems work, but a simple one would be something like this:

In a manual tranny, you've got an H of gears, so you'd need at least two actuators.

So to get from first to second, the computer would send 1/2 power to the up/down actuator, bringing the gear lever to neutral, then send it to full power to bring it all the way down to 2nd. To get from 2-3, the pneumatics for the up/down go to 1/2 power and bring the lever to neutral, and then left-right pneumatics go to 1/3 and the lever slides to between 3/4, then the up down goes to 0 and it goes up to 3rd.

I'm certain the "real" system has nothing in common with this, but that's one way it could work. The good part about pneumatics is that they're pretty powerful and very fast, and you can get good control of where and how hard you're moving things. Also, air is light :)

I dunno if McLaren is using pneumatics for their transmission and/or their valve timings. A lot of race and prototype cars are using pneumatics to move the valves up/down in the engine so the computer can imitate cams of various sizes/profiles quickly.

Its kind of like VVTi or VTEC or whatever they're called, where you can have one cam setting when you're acellerating, another when you're braking, etc.

Pneumatics are used because they're fast, but as you said reliability is an issue.

And remember that SMGs are new features on rally cars, the Old School cars didn't even have engine computers! At one point, all-wheel drive was revolutionary :) Of course you couldn't drive a regular manual in a modern WRC race, but plenty of non-WRC rallies happen all the time with regular manuals. Group-N is the FIA's lower-end rally series, and a Group-N car is pretty easy to race all over the world. It has the same 2.0 litre restriction as WRC and also requires that all parts be on the same list, so all Group-N Imprezas, for example, are basically the same, so its more about the drivers than the cars. SMGs aren't to my knowledge currently homologated for Group-N, but I don't really know for sure.
 

bone

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there has been a rally driver on top gear (burns? after 5 mins they've just put him outside) and if i remeber correctly, he said they also used the flappy pedal gearboxes...
 

skorgu

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They (WRC cars) have paddles (actually, they have one big paddle in a ring around the steering column, in is up and out is down or something), but they're hooked up to an SMG, not a regular automatic. It looks the same from the driver's seat, but the mechanics are totally different. The Maserati Quattroporte has an SMG, hence everyone's bitching about how non-smooth it was, whereas most of the other paddles are automatics.

[Edit: which episode is that?]
 

andyhui01

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When James tested the Maserati... he complained that because the car has a SMG gearbox... and there is an option for you to put it to automatic for town driving and he said the shifting was horrible... it felt like a learning driver shifting for you and its on their first day :lol: . But paddles attached to automatics are usually really slow.. if you look at the DB9 and how long it takes for it to shift after the flick the paddle... I think its abt 3/4 of a second.
BTW... doesn't a M3 have SMG gearbox as well?... it also has an option to select how fast you want the gears to change
 

Mischief007

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If you guys want to watch some clutchless shifting watch the Australian V8 Supercar series. Watched it last weekend and drivers do clutchless shifting. It just amazes me. Oh and the racing was amazing :D
 

bone

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it was the 2002.11.10 episode
 

Wutputt

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skorgu said:
Yes, but... A modern WRC gearbox isn't really a manual transmission, it's a manual transmission with either an electronic or pneumatic system.
WRC's use a hydraulic system, not a pneumatic system.
On road cars automated manual transmissions, like the SMG, Selespeed, Easytronic, etc. use hydraulic or electric actuators. Most use hydraulics, only on small cars (Opel/Vauxhall Corsa Easytronic, Renault Twingo Quickshift, Toyota’s MMT ,etc.) electronic motors are used as actuators.

One of the main reasons why WRC's use hydraulics and not pneumatics is because with a pneumatic system, they have to install an extra air pump and air pressure reservoir. This adds extra weight. For an hydraulic system a lot of stuff is already available in a normal manual transmission: hydraulic fluid (oil), and sometimes oil coolers. Also oil is almost incompressible compared to oil.

VVT and VTEC-like systems also use hydraulics, cause oil pump, oil, etc. is already available on the engine.


skorgu said:
I dunno if McLaren is using pneumatics for their transmission and/or their valve timings. A lot of race and prototype cars are using pneumatics to move the valves up/down in the engine so the computer can imitate cams of various sizes/profiles quickly.
The actuators of the transmission are hydraulic, not pneumatic. It’s the same as with the WRC's ;)

And F1 engines don't use VVT systems, cause firstly there is no need for it. VVT systems on road cars are used to improve drivability (in low and mid rpm range) without compromising a lot of top end power at high revs. F1 engines run continuously at extremely high revs, and use therefore cams with a big opening angle. Drivability is no issue for F1 engines. Secondly those VVT systems would introduce extra weight and extra inertia in the rotating parts, and so reducing max rpm and thus max power.

The pneumatic failures on the McLaren are related to the valve 'springs'. An F1 car does not use normal valve springs like a road car. They use pneumatic springs (filled with nitrogen). At high rpm normal springs just are not stiff enough so the valves won't close properly anymore. Extremely stiff springs are no option, because tension loads on the cams would be too high. So F1 engines use pneumatic springs filled with nitrogen. They are stiff (and become stiffer when they are pressed) without adding too much load on the cams.
 
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