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Alternate exhaust valve lifting mechanisms

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  • #16
    RichR--I am trying to do this with only one shaft in the engine--the crankshaft. However, thank you for the sketch.---Brian
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • #17
      True, it adds a second shaft. But now both valves are incorporated into a single piece. I suspect it also requires less power to drive than push rods and springs.
      Location: Long Island, N.Y.

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      • #18
        The aspen rotary barrel valve springs to mind, but you put "sucessful" in there, and from what I've been reading of them, they didn't prove to be very durable a design. May be enough for a limited run engine and a talking point if so. They eliminate the poppets altogether by using a rotating barrel with the port machined into it. Reliability issues came from the barrel carboning up and seizing.

        Interesting modern take on it, apparently designed for serious use in f1 until the rules started to mandate poppet shaped valves explicitly.
        http://home.people.net.au/~mrbdesign...utoTechBRV.pdf
        Last edited by MrFluffy; 07-20-2014, 02:38 PM.

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        • #19
          Not suited for a make and break engine but bear with me:

          Fairbanks Morse made a line of valveless uni-flow opposed piston two cycle engines that used two crankshafts geared together offset 15 degrees.

          Look here, section D starting bottom of page 59:

          http://maritime.org/doc/fleetsub/diesel/chap3.htm

          With this you need scavange air. A functioning Roots blower would be a PITA to make so it worked efficiently on a small scale (<1"^3). I was thinking of a "displacer cyinder" a bit larger in displacement with a reed valve intake that discharged to the power cylinder intake port. Time the displacer so it develops significant pressure when the power cylinder port opens. Work it right and you can supercharge the engine.

          Maybe I'm all wet, but I submit one of the principle attractions of model engines is exposed moving parts working in novel motions of some complexity without pointless monkey-motion. Everything is to have an indespensible function without which the engine will not work.

          This little scheme of mine (gloating while rubbing hands and chortling fieindishly) might do just that.

          A second cylinder with opposed pistons? A compact reed valve sticking up? A tidy crossover pipe leading scavange air to the power cylinder intake? I got this mental picture...
          Last edited by Forrest Addy; 07-20-2014, 03:34 PM.

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          • #20
            OK, I have not thought this through at all and likely will not (because I am not all that smart about such stuff) but how about and additional crank journal(s) and connecting rod(s) with appropriate offsets and linkages to actuate the valves?

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            • #21
              How about a port plate indexed by a Geneva stop mechanism

              http://en.wikipedia.org/wiki/Geneva_drive

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              • #22
                As Mr Fluffy says, there's the Aspen rotary valve. There's also the Cross rotary valve.
                Location- Rugby, Warwickshire. UK

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                • #23
                  Thinking out loud here Brian..............how about a push rod mechanism which has excess clearance requiring a movable spacer to be in place for the valve to lift? The spacer could be pushed into place by pressure bled from the combustion chamber.

                  There would be no pressure to move the spacer during the inlet stroke so the exhaust valve would not lift during the compression stroke but pressure during the power stroke would move the spacer into position and cause the exhaust valve to lift during the exhaust stroke.

                  The spacer would drop out of position when the pressure of the push rod is removed at the end of the exhaust stroke.

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                  • #24
                    Originally posted by Forrest Addy View Post
                    How about a port plate indexed by a Geneva stop mechanism

                    http://en.wikipedia.org/wiki/Geneva_drive
                    There could be the usable lobes?
                    Gene

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                    • #25
                      How about the NSU Max valve actuation - driven by eccentrics?

                      See http://www.bsa-c15.org.uk/bikemuseum...c_assembly.gif
                      Bill

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                      • #26
                        Just go 2-cycle. All they have is flapper valves on the ports. No cam. Part of the timing is built into the piston though.

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                        • #27
                          There's also the Lanchester side valve arrangment for poppet valves..

                          http://commons.wikimedia.org/wiki/Fi..._actuation.jpg

                          It does have cams as shown,but I'm sure you could redesign it ,but keeping the general idea.

                          this site also has plenty of unusual engines

                          http://www.aqpl43.dsl.pipex.com/MUSE...usualICeng.htm

                          Rob
                          Last edited by MrSleepy; 07-20-2014, 05:22 PM.

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                          • #28
                            I think the idea that dp mentioned about the ball point pen mechanism may have some merit. Think about this:

                            The cam lobe is a part of the periphery of the crankshaft counterweight.

                            As the lobe comes around it moves a rocker arm that opens the exhaust valve. As the valve closes the ball pen clicker rotates to the "released" position. Next revolution the rocker moves as usual but does not open the valve. When the rocker returns to its relaxed position the clicker resets into the "active" and is ready to open the valve next time around. So the valve only operates every 2nd revolution of the crank.

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                            • #29
                              Now here is something you will find interesting. I have idled the afternoon away modelling the indexer mechanism designed by Philip Duclos for his Gearless engine. I have chosen this one primarily because I know it works. I have watched a half dozen Youtube videos of it. I'm not altogether sure that I will build it, or incorporate it into something of my own design yet, but modelling it gives me a much clearer understanding of how it works. This is activated by a single cam on the crankshaft acting on the roller wheel which shows up in the assembly at the end opposite the "swastica', and the "swastica" shaped part rotates 1/4 of a turn every time the cam comes around. The long part of the arm opposite the weird shaped part comes up every other time and pushed on the stem of the exhaust valve to operate it.

                              Brian Rupnow
                              Design engineer
                              Barrie, Ontario, Canada

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                              • #30
                                This is the really interesting part of the post. A solid model doesn't give you any real idea of size. Without anything to compare the model to, it could be smaller than a grain of rice, or bigger than an elephant. Part of the ridiculous fee $$$ that I pay each year for my Solidworks license gives me access to a databank of models created by other designers. Someone was kind enough to model a human hand. I downloaded it, and measured it to check for size against my own hand, and it is exactly to proper scale.So--to give you some idea of the actual size of this indexer mechanism, here it is, full size, held in the palm of an average man size hand!!!
                                Brian Rupnow
                                Design engineer
                                Barrie, Ontario, Canada

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