I am intrigued by, but know little about, the high speed valve system used on current FI cars. I understand that they are powered using pneumatics and presumably this operation will also be desmodromic.
With engine peak rpm in the order of 13K plus the loads on the system will certainly be demanding.
Any background on the above would be welcome.
Julian Lindley
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Julian,
Pneumatics were first introduced as a replacement for conventional valve springs. In other words a normal rotating camshaft was opening the valves and air pressure pulling them shut. This avoided the dreaded valve spring "bounce" which was often the limiting factor in rpm. I don't think this qualifies as desmodrmic, as the cam itself was not linked to the valve to pull it shut mechanically (per Mercedes W156).
I belive that some current engines (Renault ?) have now dispensed with cams altogether, using electro-pneumatics to open and close the valves, but I have to admit that I haven't seen inside one, or even an exploded drawing, as secrets are so closely guarded nowadays. Such a system would, of course, give full control of valve duartion and timing to the electronics, a huge advantage. Current rpm targets are 18k to 20k !!!
I am amzed that more time has not gone into rotary, or sleve, valving, as this removes the reciprocating mass problem completely.
Regards, Adam
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Adam,
Thank you very much. I would love to see a sectioned drawing of the system but commercial security in F1 today makes that very unlikely.
What suprises me is the reciprocating frequency required using pneumatics. I guess a diaphragm rather than a piston would be used to obtain the response time.
I love the engineering inovation in F1, but find the racing rather boring now that commercial influences have changed it from sport to a lucrative business. Perhaps things will go full circle, as they often do when lessons have to be re learned.
Regards,
Julian Lindley
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Adam,
A great deal of time over many years has gone into researching the use of rotary valves in conventional engines but these introduce a whole new range of problems that are proving almost impossible to resolve. I think that rotary valves have now been written off by conventional engine manufacturers, and probably by the racing engine people as well.
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Surely current large capacity multi cylinder motorcycle engines have demonstrated the potential for high revs with conventional valves.
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Didnt see an answer to the following, so here goes:-
"
Surely current large capacity multi cylinder motorcycle engines have demonstrated the potential for high revs with conventional valves."
F1 engine cyclinder size is limited to 350cc if a 10 cyl engine, and 292cc if a 12 cyl (this is max no of cyls I understand to be currently allowed). As the designers are stuck with getting max power, the only way is to up the rated speed and reduce internal friction.
So by large capacity racing m/c engines, I assume we are talking about a 4 cyl 1000 cc machine, where cylinder size is 250cc. I understand these operate up to similar (14,000 rpm), and indeed use conventional valve actuation. The valves are smaller, and thus reciprocating forces less. Going to the 15000 to 17000 rpm that I believe F1 use, would present them with some interesting challnges.
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