pourquoi une/des valve(s) ronde (s) ??

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TercelDriver

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en général un moteur devient plus perfomant a mesure qu'on augmente le nombre de valves.

Mais je me suis toujours demander pourquoi mettre des valves rondes ?? pourquoi pas faire une valve qui aurait la forme d'un demi-cercle ??

avec une valve on a une ouverture donné pour laisser entrer le mélange air/essence ou laisser sortir le gaz d'échappement (je sais que c pas la meme valve qui fait cette job la mais deux). avec deux valves, on agrandi l'ouverture et on laisse entrer plus de mélange air/essence. mais pourquoi pas faire un demi-cercle ?? ca pourrait etre encore plus efficace que de placer deux valves
 
comment est-ce que ça pourrait être plus efficace? tu veux dire couper tes valves en deux? mettre juste des demi valves? Ou mettre genre juste une valve gigantesque coupé en deux? moitié intake et moitié exhaust? J'ai de la misère à comprendre ce que tu veux dire.

faut pas que t'oublie que le but que ce soit rond c'est l'étanchéité sur le siège et le flow coulant puisqu'il n'y a pas de coin pointu. De plus, il y a une certaine limites à la grosseur de l'amener d'air qui se rend aux valves, trop gros, tu perd de la vélocité à bas régime
 
1- Une valve en demi-cercle serait pas étanche
2- La pression exercée sur la valve serait répartie inégalement donc la valve casserait
3- La pression exercée sur la valve agirait comme un bras de levier, je m'explique:

Vu que la valve n'aurait qu'un seul point d'appui (le côté rond) l'autre côté (le plat) serait porté à renfoncer dans son port ce qui ferait que le côté rond agirait comme un pivot et la valve crochirait.

4- Pourquoi faire une valve en demi-lune ? Pour les rapetisser ??? Tu vas en avoir besoin de plusieur pour égaler le flow d'une valve ronde. Alors pourquoi en faire en demi-lune ???
5- Un coin pointu = flow inégal = pas bon
 
The reason they are round is to disipate the heat better!
Also if there are any sharp edges it will create turbulence .
Fluid dynamics show that air flows better and faster in a round or roundish hole;)
If I go deeper in my explaination I'll have to kill you all!! :laugh:

Trust when I say they have tried thousands of shapes for valves;)

I know they are playing with oval valves in F1 and Nascar but havent heard of any gains as such :dunno:
 
tkm said:
I know they are playing with oval valves in F1 and Nascar but havent heard of any gains as such :dunno:
Click to expand...

you've pick my curiosity
i know their using pneumatic valves in F1 instead of camgears, it could have been related to the oval shaped valves, but if nascar teams use them too, i wonder what kind of gain they would have over the round shaped valve

maybe its in the head design ? they make the air spin faster or something ? maybe im wrong too.

anyway, cams, heads, valve, springs. etc, they're junk that break and cost alot for nothing :laugh:
 
D3rELiC said:
you've pick my curiosity
i know their using pneumatic valves in F1 instead of camgears, it could have been related to the oval shaped valves, but if nascar teams use them too, i wonder what kind of gain they would have over the round shaped valve

maybe its in the head design ? they make the air spin faster or something ? maybe im wrong too.

anyway, cams, heads, valve, springs. etc, they're junk that break and cost alot for nothing :laugh:
Click to expand...

hmm, i beleive the pneumatic on F1 are just to replace the springs, i beleive there is still a cam.
 
puma said:
hmm, i beleive the pneumatic on F1 are just to replace the springs, i beleive there is still a cam.
Click to expand...

i thought the valve control was completely controled by computer

but i might be wrong.
 
une autre raison est qu'une valve tourne sur elle meme pour un refroidissement uniforme et une usure unifomre aussi et il est vrai que la conduite offrant le moin de turbulence a un flow est celle circulaire
 
tkm said:
The reason they are round is to disipate the heat better!
Also if there are any sharp edges it will create turbulence .
Fluid dynamics show that air flows better and faster in a round or roundish hole;)
If I go deeper in my explaination I'll have to kill you all!! :laugh:

Trust when I say they have tried thousands of shapes for valves;)

I know they are playing with oval valves in F1 and Nascar but havent heard of any gains as such :dunno:
Click to expand...


Read my first line;)
Thats what I said as the starting quote!
 
D3rELiC said:
i thought the valve control was completely controled by computer

but i might be wrong.
Click to expand...
je pensais que les valves des F1 étaient controlées par des solenoids
 
clouter said:
je pensais que les valves des F1 étaient controlées par des solenoids
Click to expand...


Yes they are because valve springs above 14,000 rpm don't last and break so!

No valve spring would last 20,000 rpm.

This doesn't mean springs aren't reliable, just not at those rpm's;)
 
tkm said:
Yes they are because valve springs above 14,000 rpm don't last and break so!

No valve spring would last 20,000 rpm.

This doesn't mean springs aren't reliable, just not at those rpm's;)
Click to expand...
yeah that's what i had heard...

that at those rmps, they springs can't close the valve quickly enough
 
i thought the valve control was completely controled by computer

but i might be wrong.
Click to expand...

You still need some sort of actuation...Renault was working on an electrohydraulic system but I don't think they used it in a race environment yet. All the other engines use cams with a pneumatic return system.
 
merci pour vos réponses

les valves tournent sur elle-memes ?!? je le savais pas pantoute

je me doutais qu'un valve en demi-lune serait moins etanche mais je savais que la valve pourrait meme jusqu'a casser !!

en tk le fait de savoir que les valves tournent sur elle-même donne beaucoup moins de choix de forme c certain. qu'est-ce qui se passe en nascar ou en f1, les valves doivent s'accrocher partout lol !!
 
tkm said:
Yes they are because valve springs above 14,000 rpm don't last and break so!

No valve spring would last 20,000 rpm.

This doesn't mean springs aren't reliable, just not at those rpm's;)
Click to expand...

do you know if in F1 engine, they still have cams?

is it just the push back that is "pneumaticly" actuated?
 
puma said:
do you know if in F1 engine, they still have cams?

is it just the push back that is "pneumaticly" actuated?
Click to expand...


No cams all done by the solenoids.
They can increase or lower the power on those cars all by computer while they are driving around the track.
Basically the drivers are there for the gas pedal and the steering wheel!

That commercial for Hewlitt Packard is just about right when Montoya and Ralf are driving the cars remotely;)
 
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