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My brother's Renault has this and I have no idea what it does. However, he says it's so he can do 25MPH in 5th gear though I'm a little sceptical.
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To put simply, it allows camshaft timing to be adjusted according to revs.Ie overlap of inlet valve to exhaust.giving a a smoother power output..more power at lower revs..anyone correct if wrong?.
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Steve
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I believe I know exactly what it means, and was going to post an explanation. But then I thought "Better to keep your mouth shut and be thought a fool, than to open it and remove all doubt".
Steve has the advantage of being a mechanic and actually knowing what he is talking about.
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Err.Sorry Tom..I replied in simplistic manner.Apart from it can be achieved in several ways..please State what you was going to say..
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Steve
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Err.Sorry Tom..I replied in simplistic manner.Apart from it can be achieved in several ways..please State what you was going to say.. -- Steve
More or less what you said, but you explained it better than I could.
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Variable valve timing, or VVT, is a generic term for an automobile technology that allows the lift, duration, and timing (or all three) of the intake or exhaust valves (or both) to be changed while the engine is in operation.
See: encyclopedia.thefreedictionary.com/Variable%20valv...g
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I don't know the specific manufacturers' technologies, but the simplest method (well, the one I remember!), is where you have a cambelt/chain (say vertically) as usual, but with movable tensioners which slide (say horizontally) to give a longer or shorter run of belt/chain on one side, and vice-versa on the other.
F1 cars have electronically actuated valves, so making VVT work is a lot simpler to implement mechanically.
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Just a general reminder about this online automotive dictionary:
tinyurl.com/6ydxd
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F1 engines do not have electronically actuated valves, but they are operated pneumatically (removing the need for fragile valve springs), allowing them to run reliably at very high revs (up to 19000 rpm). Since the engines spend most of their time at high revs, there isn't a huge gain from VVC.
They have looked at electrmagnetic actuation but I think the main problem is the weight it adds to the top end of the engine.
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Surely, the pneumatic operation is electronically controlled?
Until we get piezo or similar technology, direct electronic actuation will not be viable. Altho superconductor technology, (with visions of associated cooling plants, or possible pit stops to top up with liquid helium?) may be an interim step. If weight distribution was the only issue with electromagnetic operation I would have thought we may have seen it for domestic use by now.
Just think of how the service departments would cope? A simple cambelt failure would just become a thing of the past.
pmh (was peter)
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No - all mechanical, via a device known as the camshaft !
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I meant electromagnetic valves, electronically controlled, it just came out wrong (hoonest!).
IIRC, the main limitation of using electromechanically/pneumatically operated valves in domestic cars is that it required a higher voltage system of 24 volts. Though thinking about it, I can't see why that would be a problem, just regulate everything else to 12v if needbe.
I'm not sure whether this post re Renault's engines is true www.honestjohn.co.uk/forum/post/index.htm?t=8951&m...e , though there is nothing on the F1 site rules®s section to suggest engines HAVE to have a camshaft, nor does it ban VVT.
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auto.howstuffworks.com/question229.htm
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Honda used to have some good pages on how their technological tour de force (VVTi) works, totally beyond me, but their petrol engines rev like crazy and develop daft amounts of bhp.
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The Japanese always had high-revving engines long before variable valve technology became widespread - even some of Yamaha and other motorcycle manufacturers' engines from many years ago used to peak at getting on for 20,000rpm...:-)
What's more they sounded as sweet as a nut and still do.
Here's how Honda brought their idea to fruit in 1989:
dwolsten.tripod.com/articles/jan89b.html
Some more links to the subject:
www.mr2sc.com/websites/articles/vvt.htm
dwolsten.tripod.com/articles/jan89b.html
www.ford.com/en/innovation/engineFuelTechnology/va...m
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What\'s for you won\'t pass you by
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Dont be mislead into thinking that variable valve timing is a new technology. I have a 1904 Japy Frere stationary (alcohol- hot tube ignition) engine that has variable exhaust valve timing. I think that it may have had the same set set up as early as 1897. It is used to control the speed from a centrifugal governor. This lets the exhaust sleeve valve open earlier if revs rise.
pmh (was peter)
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Should think spares for your Japy Bros. engine not too readily available Peter???
Have Merry Christmas and Prosperous New Year
Phil I
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Anyone know what happened to Desmodromic Valve Gear?..
Phil I
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it's always difficult to try and explain things like this and i agree with Tom Shaw's statement about Steve.o spot on and simple to understand dont think i could have managed that think i would have got lost in the explanation if you know what i mean...cheers ...keo
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