Variable Valve Timing

[Pixie]

Come back Charles Yale Knight - all is forgiven. Even the smoke ! (My two smokers may have competitors ).

Elimination of the poppet valve has been a Holy Grail of 4 stroke engine designers for more than a century. No-one has managed it yet (Though Mr Knight came close at one point)

All valves are the devil's work - abolish 'em altogether !

Aircraft engines had sleeve valves.The cylinder liners were moved to uncover fixed ports
http://www.classiccarclub.org/knightsleevevalvekb.htm
http://www.enginehistory.org/bristol_aquila.htm

[avrflr]

'infinite' variable valve timing would be the go as far as optimum performance, doing away with the camshaft would have to be the first improvement. Pnuematic valvetrain anyone? (Has to have a constant supply of pressuriesd air though!)

Formula one engines still have cams, only the valve spring is replaced by a cylinder filled with compressed nitrogen. (If air was used there is the potential for detonation....)

IMHO VVT isn't in the current crop of sportsbikes because they manage to fairly high specific power and a linear power curve using other, simpler and cheaper technologies. Like carefully designed inlets, airboxes, and a valve in the exhaust to help fill in the mid range flat spot you would otherwise get with a cam that delivers you 170hp/litre.

Of course, as the horsepower wars rage on, no doubt manufacturers will have to resort to more tricks like variable length inlet tracts and VVT to deliver more peak power without compromising civility.

[Motu]

As Ixion mentioned at the very begining of this thread - VVT is used to meet emmission standards,they have to meet those,power is just an added bonus.Bikes need to comply with few standards so any systems are basic and just marketing ploys.Electromagnetic valve actuation is not capable of high speed use at this stage,if ever,even a modern diesel revs too high for it.

[avrflr]

Motu, you seem so be saying that VVT is just about reducing emissions, which I would disagree with. I would say VVT (in any of it's forms) is simply a way of using a hotter cam and making it driveable. This applies to bikes as much as cars. Manufacturers just like to say that it reduces emissions because we all love the environment, don't we?

[Pixie]

As Ixion mentioned at the very begining of this thread - VVT is used to meet emmission standards,they have to meet those,power is just an added bonus.Bikes need to comply with few standards so any systems are basic and just marketing ploys.Electromagnetic valve actuation is not capable of high speed use at this stage,if ever,even a modern diesel revs too high for it.

Never say never.
http://www.grouplotus.com/mediactr/p...ad.php?pid=110

[Motu]

But that blurb says exactly nothing...although they do say electro hydraulic,which could be the answer.Solenoids can't opperate the valves fast enough,but if they opperate a hydraulic system that could be a way around it.Like a fuel injector,that's electronic control of a hydraulic system,and it works very well.

And I will defend my position of all engine advances in the last 30 years being driven by California Emmission regulations.The fact that combustion chamber design,camshaft profiles and electronic fuel injection and ign systems have offered a big increase in power is just the iceing on a rather messy cake.

[avrflr]

I hear what you're saying Motu, if oil was plentiful and nobody cared about pollution, to get more power manufacturers could just keep making bigger engines. For cars that is. Given that bikes need to be small, light, simple and cheap, a bigger engine might not be a good answer. So I think there are reasons bike manufacturers would look to things like combustion chamber design, cams, EFI, electronic ignition and VVT to pack more power in a small space without considering emissions.

[Ixion]

Why? (bike light and cheap I mean) Apart from aberrations like the NZ 250cc thing, it's still easier to just increase the engine size. Nothing beats cubes. Works for Harley. I don't see a massive rush of people buying things like the VTEC Honda fours. It's much cheaper just to have bigger holes than complicated whaddjamoogoos.

[SixPackBack]

Why? (bike light and cheap I mean) Apart from aberrations like the NZ 250cc thing, it's still easier to just increase the engine size. Nothing beats cubes. Works for Harley. I don't see a massive rush of people buying things like the VTEC Honda fours. It's much cheaper just to have bigger holes than complicated whaddjamoogoos.

Weight is the last thing you want to increase, reducing engine size whilst increasing performance produces superior motorcycles in every way.
Personally I can see Electronic linear actuators being the ultimate development for valve control...could be a while though.
Contemplate the advantages of controlling valve lift, opening and closing speed with continous adjustment, petrol engines would be so much closer to full torque at zero revs [a la electric mtr].

[SPman]

. Given that bikes need to be small, light, simple and cheap, a bigger engine might not be a good answer. .

Seems to have worked over the last 30 yrs..........

[avrflr]

OK I admit I am thinking more of the sports bike market (which forum is this again?). I don't really want a 190kg GSX-R2000 and I think the reason is obvious. I don't honestly need more power than I already have, if I used full throttle on the road much I wouldn't last long. A lighter bike on the other hand is always a good thing - better handling, less tyre wear, less fuel consumption, less emissions.

[Scouse]

yes your completely right OAB....I have no idea where twoseven is coming from... differing lenght inlet tracts [and diameter] change the flow of air at different RPM's by manipulating air speed to optimise burn and cyclinder fulling....even to the point that you can develop a supercharging effect at high RPM...

and this was about variable valve timing this thread I think...and honda's system on the vfr800 isn't real vtec...its a 4 valve per cyclinder head that only uses 2 valves up until a certain RPM and then employs the other two for high RPM running... but the varible valve timing yamaha are playing with alters valve lift and duration...so as to alter timing completely...so it can run high performance cam profile at high RPM for increased power over a middle of the road camshaft profile to suit drivability at all rpm like most bikes...while retaining low rpm and medium rpm performance aswell.... Expect one hell of a flat torque curve!!!!! and one very flexable motor....

Youv'e just disapointed me poo's Im not used to seeing such sensible posts coming form you

[Pixie]

But that blurb says exactly nothing...although they do say electro hydraulic,which could be the answer.Solenoids can't opperate the valves fast enough,but if they opperate a hydraulic system that could be a way around it.Like a fuel injector,that's electronic control of a hydraulic system,and it works very well.

And I will defend my position of all engine advances in the last 30 years being driven by California Emmission regulations.The fact that combustion chamber design,camshaft profiles and electronic fuel injection and ign systems have offered a big increase in power is just the iceing on a rather messy cake.

The blurb was dated 2003 and there have been pics of the test engine in the media,including bike media.
As you have noted it is electro-hydraulic,as there are solenoid valves fast enough for high speed engines.A fuel injector is a solenoid valve.
I'm sure we will see these around 2008.
Btw the unamed european manufacturer which signed up for the technology is Renault

[Motu]

The poppet valve is the stumbling block - like telescopic forks they are rude and crude,but work so well the high tech alternatives are a no show.I think electro/hydraulic control of some sort of window valve would be the go,kinda like rotary valves without the mechanical drive...

[Pixie]

The poppet valve is the stumbling block - like telescopic forks they are rude and crude,but work so well the high tech alternatives are a no show.I think electro/hydraulic control of some sort of window valve would be the go,kinda like rotary valves without the mechanical drive...

Poppet valves are easy to seal.Which is the problem with most other designs.

I was looking for a sleeve valve engine I saw in a model aircraft mag.Where the bore rotated around the piston and in the cylinder and the prop was attached to the rotating cylinder.
I found the website and it seems they are applying the technology to more than just models...

http://www.rcvengines.com/corporate/...ny_profile.htm
http://www.rcvengines.com/rcv120sp.htm
http://www.rcvengines.com/corporate/...plications.htm



* How it Works




The engine operates on a simple but elegant principle; the cylinder, incorporating the combustion chamber port, is rotated around a conventional piston and crank at 1/2 crank speed via a 2:1 gear reduction. A fixed timing ring completes this efficient rotating valve arrangement and removes the need for any complex overhead valves, cams or electronic servo cartridges. RCV have the following engine capacities in various stages of development:- 9.5cc, 10cc, 15cc, 20cc, 25cc, 33cc, 49cc, 90cc, 110cc, 125cc and 250cc.