Different crank shaft system

Discussion in 'General Science & Technology' started by allmee, Jul 2, 2007.

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  1. allmee Registered Member

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    I have designed a new crank shaft system but can not post a pic. only 3 posts so far.Try (www . thescienceforum.com/viewtopic.php?t=7592&start=0&postdays=0&postorder=asc&highlight=)
     
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  3. phonetic stroking my banjo Registered Senior Member

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    (From allmee's link)

    Looks as though the teeth could wear relatively quickly, and the springs also.

    If you think about the number of times a minute this thing could be turning and the forces involved.

    Interesting idea. Could you explain a little more, in depth?

    edit - Will the crank push the piston back down, forcing the springs back down? Depending on the power of the springs, might it be slightly less efficient overall? What's the benefit of using the springs and how powerful a spring would you intend to use? What materials are all of the components made from?
     
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  5. Oli Heute der Enteteich... Registered Senior Member

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    Questions:

    what returns the piston to the lower position?
    what prevents the piston turning the crankshaft the wrong way as it returns?
    why teeth on both sides of the piston?
    when the teeth are not engaged (as in the left-hand diagram) what turns the crankshaft to get engagement started?
    when the teeth run clear of the piston's rack set what keeps the crankshaft turning?
     
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  7. Janus58 Valued Senior Member

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    From what I can see, it would be subject to jamming. Consider the compression stroke followed by the combustion stroke:

    The piston rises to compress the fuel air mixture. At the top of the stroke, the teeth on the shaft clear the teeth on the piston shaft. There will now be a downward force(from the compressed mixture) pushing down on the rod. The piston rod will start moving downward before the teeth on the shaft can move into position for the dowward stroke), the teeth won't mesh properly, and you'll get a jammed mechanism. Even if you can avoid this, even a slightly advanced ignition timing will cause the the same problem.

    Also, when you stop the engine, if at any time the crank shaft stops with its teeth pointing up, the piston will drop to the bottom of its stroke. When you try and start it up again the shaft turns, enages the teeth on the rod trying to push it down. But it will already be in its lowest position, and once again the whole engine jams. If the teeth stop at the bottom of the strokem the springs will push up on the rod, pushing it out of position for the teeth on the shaft
     
  8. allmee Registered Member

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    Sorry forgot to add the gears.
    http : //img146.imageshack.us/my.php?image=mcphersoncrankshaftsystvg9.jpg
     
  9. allmee Registered Member

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    A and B are front view and c is side view.
    The system has to be setup with the one pistons teeth all ways on the crank shaft (8 pistons one of the pistons teeth should be connected(teeth for piston 1 are at the right side of the crank shaft teeth for 2 are at the bottom 3 are at the left side and four are at the top)).
    c the gears should keep the pistons moveing at the same speed as the crank shaft.
     
  10. Janus58 Valued Senior Member

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    From looking at your images,(BTW, I had to edit URL you gave in order to see them.) This simply will not work.
    In your image C, going from left to right, you have piston 1 in its top postion, piston 2 in the bottom postion, piston 3 in top and piston 4 at bottom. Granted, in this arrangement, the pistons will go up and down in unison.
    But, from your above text, the pistons would have to go like this:

    Piston 1 halfway in its downward stroke.
    Piston 2 at the bottom of its stroke.
    Piston 3 halfway in its upward stroke.
    Piston 4 at the top of its stroke.

    There is no way that the gears between pistons can work with this staggering. With the gears, the pistons all have have to be at either the bottom or top of there strokes at the same time, as that is when the gears will reverse directions. The point being that all the pistons have to reverse direction at the same time.

    In the staggered positions, two of the pistons are ready to reverse direction while the other two are not. It is obvious that this will not work. There is no way to make the simple gear arrangement shown work with staggered pistons. (It might be possible to come up with some type of complicated gear-shift mechanism to make it work, but why design something complicated to do what a standard crank shaft does simply.)
     
  11. allmee Registered Member

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    http : //img242.imageshack.us/my.php?image=mcphersoncrankshaftsystwi2.jpg
    Still under 20 posts, sorry.
     
  12. phonetic stroking my banjo Registered Senior Member

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  13. hypewaders Save Changes Registered Senior Member

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    You may have the ideal testbed for a wonderful new oil filter (for catching all the broken and ground-up teeth) or a new alloy to keep the parts from cracking.

    Seriously though, consider the constantly changing and reversing velocity of the piston: Because piston velocity isn't constant, the intertial and harmonic stresses would be horrendous if you coupled the two so directly as this. Think about how the traditional crank/pushrod allows for a sinoid piston velocity curve to be coupled to constant crankshaft velocity. Think about the implications of connecting two rods and two differing crankshaft throws to a piston, and alternating between the two with every revolution- That is in effect what you have envisioned. Imagine what the experience of pedaling a "McPherson Crank" bicycle would feel like.

    And whatever you do, don't feel bad. Thought experiments are an excellent way to learn.
     
    Last edited: Jul 4, 2007
  14. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I tend to think the gears on piston not feasible also, but post 1 caused me to think briefly about how to better use the expanding combustion gas of the ICE. Why not have no piston tie rod, no crank shaft, no drive heavy train, but a “FREE FLOATING” piston, which only serves to keep the corrosive exhaust separate for the driven hydraulic fluid?

    Automatic transmission must not be too inefficient and as I understand them, they are basically hydraulic motor that is driven by hydraulic pump, which is driven by the crank shaft. (Their hydraulic motor section then drives the remainder of the drive train to rotate the wheels.) Could one not have a small pressure buffer reservoir (like used long ago on the hydraulic ram water pumps) to keep a nearly constant hydraulic pressure in the high pressure line? It seems to me that all that is required in the chamber on the opposite side of the piston from the combustion gases is a pair of simple “check valves.” One opens as the piston reaches the bottom of it travel, or sooner if the hydraulic fluid below the piston already exceeds the pressure in the buffer reservoir. The other opens as the piston is rising to allow the lower pressure hydraulic fluid (from the low pressure side of the hydraulic motor) to re-enter the chamber below the piston. Surely these valves are cheaper and more durable than those that open for the exhaust the combustion gas.

    I have not thought thru the pressures variations or much else, but there is a problem with the fact that the combustion gas pressure is much higher just after spark than as the piston nears bottom of its stroke, where as then the pressure in the hydraulic fluid below the piston is maximum. One possible solution is to inject the fuel during the entire down stroke of the piston under computer control to keep the combustion gas pressure constant, until exhaust time. Another possibility to consider is to have significant inertia in the free floating piston so it is oscillating between two “gas springs.”

    I expect this will not work, has already been thought of long ago. This is the reason why I have spent less time thinking about details than typing this. Anyone have comments, ideas?
     
    Last edited by a moderator: Jul 4, 2007
  15. Janus58 Valued Senior Member

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    Here's an operating 4 cylinder, 4-stroke engine with standard crankshaft.

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    Pay attention to the combustion stroke. The piston does not just get a downward force at the moment of ignition while the piston is near TDC, but also pushed down by the hot gasses left after ignition. As the piston moves down, the volume of the cylinder increases and the pressure from these gases drops, decreasing the force on the piston. Since less downward force is converted to torque while the piston is at the top then when it is lower, and there is more force when it is at the top then it is lower, this tends to even out the torque apllied to the crankshaft over the entire stroke.
    What you seem to think as a disadvantage in the standard crankshaft system, is actually an advantage.

    Your system would cause more variation of torque over the stroke, leading to more vibration and stress on the engine.
     
  16. hypewaders Save Changes Registered Senior Member

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    Thanks for posting that elegant .gif, Janus58. It's also an opportunity for you to contemplate the "wasted" energy of the lower connecting rod motion being handled by the crankshaft counterweights,allmee- since it was this challenge you have been looking at. If you study dynamic counterweights, you'll find that a great deal of interesting thought goes into their design. Isolating and balancing piston inertia is much harder to do than trapping the imbalances and vibration resulting from the lower-end motion around the crank throws.

    For even more food for thought, consider this: It may soon become practical to minimize those pesky reciprocating loads, greatly expand the torque band, reduce engine weight, and increase efficiency with the Quasiturbine configuration for internal combustion. This concept may enable better motors, compresssors, and pumps for many energy-conversion applications.

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    Last edited: Jul 4, 2007
  17. Janus58 Valued Senior Member

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    Your welcome. It's my pride and joy. It took quite a few lines of POV-Ray code to create it.
     
  18. hypewaders Save Changes Registered Senior Member

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    Now I'm really impressed- Nice work! The reflections on the tappets, and the vapor swirls are sweet artistic plays on cutaway visualization.

    Edit: As for me, well I just lamely cut-and-pasted the quasiturbine .gif:shrug: If you have the time and inclination, maybe you would consider offering a better rendering of that example to the people at quasiturbine.com
     
    Last edited: Jul 4, 2007
  19. hypewaders Save Changes Registered Senior Member

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    Billy T:

    Direct hydraulic conversion of piston motion is problematic, because of the mass, incompressibility, and friction of fluids. But carrying that notion over into similarly using gases on the back side of a piston, we arrive at the intriguing Stirling Engine.
     
  20. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Yes, that is why I suggested "small pressure buffer reservoir (like used long ago on the hydraulic ram water pumps)" as the only gas connected to a liquid hydrolic system. I think most gases, if run thru a compression/expansion cycle in the hydraulic pump / motor, would make too much heat (Lose too much energy). I guess you are too young to know much about how these resevoirs functioned with water pressure system. Perhaps you at least have heard of "water hamer" when flow is suddently stopped. Small gas presure buffer resevoirs are also used to solve this problem. Certainly water can be considered incompressible fluid also. As far as "friction of fluids" it can not be too bad - Recall I also mention in my post that automatic transmissions used fluid to tranfer all the energy from motor to the wheels.

    Did not go to you striling link, but recall they do do have a "recuperator" thru which the working fluid flows - something to do with keeping the isothermal legs of the cycle at constant temperperature but forget the details just now. Now that you mention it, there are some simularities to my vague suggestion and the sterling engine. Specificially if the fuel is injected at top of combustion cylinder (and burned) with not too much mixing with the already burnt gas to be exhasted following the power stroke, at the correct rate, it could operate at constant temperature heat input, just like the sterling eingine. I.e. both P and T of PV = nRT could be held constant during the power stoke if "n" is constanly increasing as the volume V increases. It would be sort of an ICE/Sterling and as it would be able to immediately turn on or change power levels it would surpass the main reasons why no cars run on sterling engines. (With their external heating you are too slow to get away at the stop light as the increased heating takes time to get thru the walls to the working fluid.) Some one ought to look at my vague idea more carefully.

    Summary: I agree with your notice of these problems but think they are not in them selves "show stoppers." In fact a more careful read of my post will show I conseider them already as well as other potential "dynamic presure problem" for which I mentioned two potential solutions.

    On your nice animated "quasiturbine" - is this not just a Wankel engine with rollers replacing the wiping blades?
     
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  21. hypewaders Save Changes Registered Senior Member

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    "Recall I also mention in my post that automatic transmissions used fluid to tranfer all the energy from motor to the wheels."

    Granted, but recall also that most transmissions "lock up" after shifting phases- that is, once engine and geartrain speeds are equal, the rotors and stators have equal velocity, and fluid drive stops. Friction losses resulting from pumping fluids are wasteful and problematic in terms of transmission overheating. That's why an automatic transmission mainly uses hydraulic drive as a clutch.

    "On your nice animated "quasiturbine" - is this not just a Wankel engine with rollers replacing the wiping blades?"

    No, you may recall that a Wankel uses a figure-8-shaped chamber wall, triangular rotor, rotor/stator synchronizer gears, and is less efficient than modern reciprocating engines. The quasiturbine (I'm not so fond of the name) has significantly different geometry, allowing much more efficient gas and thermal flow, greater simplicity, and even better balancing. quasiturbine.com is worth a look. It's what the Wankels wanted to be but aren't. Things get really interesting in the quasiturbine versions that exploit detonation, like a diesel- but beginning within those smaller chambers that conform to the bogeys.

    Here's a quasiturbine discussion/promotion group
     
    Last edited: Jul 4, 2007
  22. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Good point - I knew but forgot that fact. I guess a fluid system is to wasteful. Let me try again (with even less though (if that is possible):

    Make the piston have one end of high Curie temp feromagnetic material and a stationary "pick up" coil. The magnetic end of piston plunges in and out of the coil making electric power for electric motors. Probably two 180 out of phase pistons in a "one pushs the exhaust out of the other" linear arangement with dual permanent magnets (of opposite polarity) one entering the coil as the other leaves.
     
  23. hypewaders Save Changes Registered Senior Member

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    Now that's interesting. In the case of an internal-combustion electric generator, I like the idea because if a step can be skipped in energy conversion, so would the attendant losses be avoided, lower parts-count/materials/weight etc.

    There's also an interesting aspect of integrating electrics with the QT, because there's plenty of room right in the middle of the thing for an electric motor/generator.
     
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