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Why not make spinning valves?

  1. Aug 4, 2006 #1
    I was thinking about the valving system in a regular IC engine. The valves have huge springs on them and require a lot of force to open. The camshaft/lifter system makes for a lot of drag and lost horsepower. Instead of making the valves move up and down, why not make them spin? Imagine a a salt shaker with a turning lid. The lid turned to one side exposes holes for the salt to fall through, and turned to the other side closes the holes. I guess it's the same idea as a rotary valve. Why can't valves be shaped like half circles and have them spin open at the right time. It seems more efficient, but I can't really see any of the problems that would occur. Any thoughts?
     
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  3. Aug 4, 2006 #2

    FredGarvin

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    Only two things immediately come to mind:

    1) Complexity of the driving mechanism. The cam design now is very compact and easy to implement. How one would provide the motion to rotate the valves could be pretty tricky. In the end, would you really be saving anything?

    2) Valve design. Is it possible to get the same flow characteristics required of an intake or exhaust valve from a spherical or other type of valve that would suit the rotating idea? Possibly. It would definitely take some engineering work to get that worked out.
     
  4. Aug 4, 2006 #3

    NateTG

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    Actually people have made working engines that use sliding valves. IIRC sliding valves tend to have sealing issues compared to poppet valves.
     
  5. Aug 4, 2006 #4
    Rotary valves are nothing new. Some 2-stroke motors (boat motors) use them instead of reed valves. There isn't even an extra shaft. It is part of the crankshaft. Usually any reciprocating engine that revs to unusually high RPMs uses some sort of rotary valve because it is difficult to prevent a conventional valve from floating.
     
  6. Aug 4, 2006 #5
    The swirl issues relating to rotating valves would be an interesting study, depending on how the valves are set up. The difference in the end result would probably be almost nothing in that respect, but the nerd in me is intrigued by the idea. ;)
     
  7. Aug 4, 2006 #6

    turbo

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    Much of the friction/drag problems can be greatly reduced by using a Desmodromic valve actuator, in which cam followers on rocker arms positively open and close the valves, with no valve springs necessary. Ducatis featured this type of valve actuation for years. It practically eliminates valve float, and the valve position can be very tightly regulated, allowing longer valve throw without the risk of valve/piston collision.
     
  8. Aug 5, 2006 #7

    brewnog

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    Ooh that sounds like a lovely idea, I'd thought of it myself at some point but didn't know it had ever been put into practice. Why did Ducati stop using it? Was there a cam either side of the follower, or was the follower either side of the cam?
     
  9. Aug 7, 2006 #8

    turbo

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    Ducati may still employ this system on some bikes, or may plan to in the future - I don't know. Essentially, it involves timing a camshaft (With a chain or a belt) that has lobes designed to close and open every valve via the cam-followers. There is a bit of extra maintenance early-on, I believe as the bearing surfaces wear, but that should moderate with time.
     
  10. Aug 7, 2006 #9
    Desmodromic system is used on the high end Ducati bikes 2007 as it has for many years

    Rotary valves aka sleve valves have been used on cars but are a high wear item
    some [british] aircraft motors in ww2 used sleve valves

    in F-1 M-B used Desmodromic valves in 55-56 racer motors to very good results winning both years

    current 20,000 RPM F-1 motors use air pressure to close valves
     
  11. Aug 10, 2006 #10

    Mech_Engineer

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    In college one of the teams in my senior design class designed a sliding valave system for a Briggs & Stratton engine, and powered it with electric stepper-motors, making a fully-variable valving system. they were able to control the size of the valve opening and the time it opened. A very interesting design.
     
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