Gear box question

Discussion in 'Inboards' started by Steve in SoCal, May 17, 2007.

  1. Steve in SoCal
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    Steve in SoCal Junior Member

    Alan,

    I am not following the inside bearings? The last part of your comment is how my idea works, one engine, with a two gear transmission to reverse rotation drive both engines.

    My idea is a simple way to divide power from one source to two propellers. A simple design is elegant and robust, with few moving parts there is little to go wrong. While I don't think too many people share my views on the merits of this, the concept intrigues me.

    I originally thought about using alternative power sources to drive a boat I am thinking about building. This concept would address the need to run at slow speeds for extended periods with two relatively high power engines. Instead of having both engines turning at very low power, use one engine to drive both props. The fuel saving alone is not much to speak of over a short time period and you would need a bow thruster to maneuver because both props are spinning at the same speed when the gear is engaged. That said; the run time on each engine is halved and a few gallons an hour over a hundred hours is still a few hundred gallons of fuel not used.

    Perhaps the boats that I am thinking about for this are just not used in the profile I mentioned. The idea is and was based on boats like sport fishers and express cruisers that have high power and use that power only a fraction of the time. I guess my fraction is much smaller than the norm.

    Steve
     
  2. StianM
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    StianM Senior Member

    So use CP proppelers. You will nead to have a cutom gear buildt for this annyway if this is really what your going for and having forward, reverse and neutral on the gear would just make it more complicated.

    You get some units like this to fitt on the propeler shaft eliminating anny extra in the gearbox for the CP propeller system[​IMG]
     
  3. alan white
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    alan white Senior Member

    Sorry-- I meant the prop shafts, that they be carried on robust inner bearings, to which universal joints on drive shafts carry to a more central point (the drive shafts converging at a narrow gearbox). The angle should not exceed 6 degrees. From there, there would be two more drive shafts splayed forward (appearing from the outside as if driving the prop shafts straight through), though power is rerouted within the box so that either one or both engines drive both prop shafts.
    This would require a substantial distance between engines and props, which is important, because universal joints work best at smaller angles due to accelleration forces (shaft speeding up and slowing down).
    From above, the setup would look like an X. The engine transmissions would not spin because the disengagement is within the central gearbox.
    This would provide the most efficient use of power. One or two sets of gears are in mesh (depending on using one or two engines). The system would be simple and reliable. Although not limiting engines to being axial to props, with U joints the axes should be within a half degree of parallel. Engines axes could be parallel with, but above or below prop to the 6 degree limit imposed by the four drive shafts. U-jointed drive shafts are very cheap to make up to length. The gearbox is very simple (rectangular box, 1/2" plate steel, thicker ends to accomodate bearings and seals) milled on two side by side axes perhaps six inches center to center.
    I do understand what you want, but don't know the distance between engines and props, which determines the feasability of the drive shafts at the limited angle allowed.

    Alan
     
  4. Steve in SoCal
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    Steve in SoCal Junior Member

    Stian,

    While that would work I am seeking a cost effective way to achieve the goal. If you throw enough money at something any idea is viable, I want to do this at a cost that allows me to build a boat not just a couple of engines sitting on wood pallets.

    Alan,

    I do understand drive angles and u-joints, the idea here is to make something that fits into a normal medium size boats engine room. We are both thinking along the same lines with a simple gear box, a set of to reverse rotation. I plan to keep the two engines completely separate for a number of reasons. My gear box uses two gears inboard that clutch into two pulleys. The output flanges on the existing transmissions would have a pulley between them and the prop shaft. These pulleys would have timing belts that connect the shafts and the combining transmission in between the two engines. The combining transmission would have a bit of elevation in relation to the output flanges and the belts would have a shallow V from the center to each flange and shaft. The center transmission would also have the same relative down angle as the output so the belts are running parallel from the combining transmission to the shafts. The gears that reverse the rotation would only turn when the combining transmission was engaged. The center pulleys would turn with each shaft regardless of power source, if a shaft turned the belt and pulleys on that shaft would move. The pulleys would be clutched to the gears so that each side would be completely disconnected from the other when un-coupled. The only drag on the system when it was not in use would the parasitic drag of the belts and pulleys. The center pulleys would be supported on two electric motor bearings rated for the speed and load of the system. The belts would require almost no maintenance and the gears would be in a sealed oil bath case. The only service items would be belt tension and inter-lock components.

    The inter-locking would consist of locking the dead engines transmission in neutral, de-rating the live engines power to maximum torque RPM and Maximum EGT. The inter-lock would not prevent the dead engine from starting so it could be run to warm up for a maneuver or change over without shutting down the active engine. The inter-lock would also cut out upon engine shut down so every time the engine or engines were stopped the system would revert to normal operations. I may try to do something like block the dead engines transmission controls when the system engages, this could be done with a solenoid easily.

    That is the nuts and bolts of the system and how it works.

    Steve
     
  5. alan white
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    alan white Senior Member

    So the gearbox would do what this one does. Not shown with reversing gears, but imagine them inside the box at the bottom. I forgot them. It would be more efficient to put the gearbox axial to one engine and avoid one belt, but probably not possible.
     

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  6. Steve in SoCal
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    Steve in SoCal Junior Member

    Hi Alan,

    I don't have any drawing to show but the idea is to use two gears to reverse the rotation from the shaft driving through the gears to the shaft being driven. It matters not what side is driven or if the shaft is driving forward or reverse. This is based on a counter rotating prop design, if both shaft turn the same way you would not need any gears only a central pulley assembly that clutched the two belts.

    If you take two gears; straight, helical whatever and mesh them turning one clock wise turns the other counter clock wise. The rest of the system works from the active engines control, ahead to go forward, astern to reverse and the belts just follow the transmission being powered. The shaft of the running engine is supplying power to the shaft and by way of the belts and combining gear to the other shaft at the same speed in the opposite direction. Put the engines transmission in reverse and everything reverses just as it would using both transmissions except; the power and RPM to both shafts is equal at all times when the combining gear is engaged.

    Steve
     
  7. alan white
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    alan white Senior Member

    Yeah, I know, Steve. I said I forgot them in the last coment (maybe you missed the edit where I added that), but they'd be at the bottom of the gearbox as the pic is oriented. They are two equal sized gears, in mesh, reversing. So imagine them as one with the output ends of the box shown.
    More important is the disengagement and re-engagement of one or both or either. I show two levers, each with two positions, and one is shown engaged. Thus engine one drives both props with the addition of the imagined reversing gears.
    End dogs, or end clutches are used, straight cut because they reverse sometimes. They slide on splined output shafts into and out of engagement.
    You also get a neutral out of this arrangement, excellent for anchoring in a tide race without turning the engine tranny outputs or belts.
    Either engine can turn two props. It's the simplest arrangement you could have. From all you've said, this is what you want.
    Easy to build, no synchronizer clutches, but match engine RPM to other before engagement (could even have a go-no go control-locking solonoid to prevent damage from mismatched shaft speeds run off the tachs).
     
  8. alan white
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    alan white Senior Member

    It is best to have the two gears in constant mesh (because they will wear together better) with end clutches dis/
    engaging instead. I assume you need two counter-rotating outputs from the gearbox, otherwise you cannot reverse the props.
    As I understand it, there are 4 belts involved. Two from engines to gearbox, and two from gearbox to props.
     
  9. Steve in SoCal
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    Steve in SoCal Junior Member

    Alan,

    You get the picture, I thought of using syncro rings on sliding shafts to the pulleys. Either a cam or electric actuator would shift the syncros into the gears to engage. The square dogs are the easiest to do but from afar say in the pilot house they may be hard to mesh with out a clank.

    I have be notified by somebody on another list that a Fedship had a system like this, and that the idea is hardly new. I did think I had re-invented the wheel just surprised that it is not more widely used.
     
  10. Steve in SoCal
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    Steve in SoCal Junior Member

    Alan,

    No two belts, a belt from each shaft to the central gear box. The gears are in constant mesh but, they only turn when clutched into the pulleys. The pulleys always turn when a shaft turns so if both engines are providing power, both belts and all pulleys turn, the pulleys at the center transmission are just spinning because the shaft the slides into them to join the two shaft are free. The type of dis-connect I am thinking of is a sliding shaft that is moved for and aft to engage a splined hub in the pulley. When both engines are used both belts are disconnected from the gear set and the gears remain meshed but do not move. The pulleys and belts are just along for the ride.

    Steve
     
  11. alan white
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    alan white Senior Member

    You mentioned you wanted to run both props from a single engine. This would mean the reversing gears would be active, their purpose being to reverse the second prop. You want to avoid synchronization of the engines however, when both are used, or at least not turn the reversing gears.
    Seems it would be just as simple to put a clutch behind each engine and not turn the belts at all when both engines are driving. What you would need would then be the type of engagement clutches shown in the drawing within a rubber bellows behind each engine.
    One part is splinedly affixed to the prop shaft, the other to the pulley, which freewheels on the same prop shaft. Now you've got it but you mentioned not wishing to spin the output of the idle engine. My guess is that speaking to the manufacturer would clear up that question. Otherwise, two more clutches would be needed.

    Alan
     
  12. alan white
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    alan white Senior Member

    A quick solution would be to run the two belts to a forshortened automotive differential and mount a disc brake on the (automotive) input of that. One belt would be maybe a foot and a half ahead of the other. This would be super simple and allow smooth and anxiety-free engagement. The differential would reverse the belts when the brake was engaged by hydraulic pressure. When released, the ring gear would be allowed to rotate. The power in the case of one engine driving would pass through the planetaries instead of two reversing gears (maybe five gears would be involved, but a heavy equipment differential designed for a lot of turning could handle the load.

    Alan
     
  13. Steve in SoCal
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    Steve in SoCal Junior Member

    Hi Alan,

    I don't have any drawing to show but the idea is to use two gears to reverse the rotation from the shaft driving through the gears to the shaft being driven. It matters not what side is driven or if the shaft is driving forward or reverse. This is based on a counter rotating prop design, if both shaft turn the same way you would not need any gears only a central pulley assembly that clutched the two belts.

    If you take two gears; straight, helical whatever and mesh them turning one clock wise turns the other counter clock wise. The rest of the system works from the active engines control, ahead to go forward, astern to reverse and the belts just follow the transmission being powered. The shaft of the running engine is supplying power to the shaft and by way of the belts and combining gear to the other shaft at the same speed in the opposite direction. Put the engines transmission in reverse and everything reverses just as it would using both transmissions except; the power and RPM to both shafts is equal at all times when the combining gear is engaged.

    Steve
     
  14. alan white
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    alan white Senior Member

    Yes, I know. You have asked for ideas on how to disengage either engine and have the remaining engine power both shafts. I know this has nothing to do with forward and reverse. Each engine has its own transmission already, and this system you're talking about begins where the output shaft of the engines is supplying power in forward and reverse. What I don't understand is what is already there now. How much of what is there is to remain?
    I mentioned (based on my understanding) that it seemed a better idea to declutch in a way that didn't effect the belts by putting the clutches on the prop shafts, so that even parasitic friction would be eliminated. Response?

    Alan
     

  15. Steve in SoCal
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    Steve in SoCal Junior Member

    Alan,

    I don't think I ever said what exact application it was on as this is more of a conceptual idea. The idea I am using is a couple of Cat 3406E and ZF single speed gear boxes with conventional shafts and props.

    The parasitic drag on the system would be the drag of the belts and free running pulleys. When the system is disengaged the pulleys on the shafts are spinning the center pulleys and idlers with only the bearing and belt drag. The gears are not turning and the pulleys are not driving any thing they are have no resistance other than the afore mentioned bearing and belt load. I may not have described the way I intend to drive the gears with enough detail.

    The gears have splined shafts that a sliding clutch dog rides on, when the dogs uncouple they are under cut so that neither the gear or the pulley cause them to turn. The gears don't rotate, the dogs don't rotate and the pulleys are basically idlers at this point. The dogs are outside of the gear case and if you could envision the entire combining transmission as modules coupled together. The gear box module is a sealed oil bath with the pulley section attached to the face of the gear box and the clutch assembly is positioned in front of that using spring return cylinders to move the dogs.

    Now as for the utilization of parts; I would keep everything intact and the only change to the as built driveline would be the pulleys and hubs that attach to the shafts at the marine transmission output flanges. The idea here is do no harm and keep all of the functionality of the standard drive. This would be a retro-fit on most boats and it would eliminate replacing or modifying anything. It would also allow standard repair and replacement parts to be used and any skilled tech would be able to service everything just like a standard boat. To replace a belt you would either have to have a spare on the shaft out of the way or break the flange loose but that is the only down side to repairs I can think of.

    In thinking of this I tried to make it as bullet proof and simple as I could. I have developed many aftermarket products for cars, over engineering and complex systems tend to have many weaknesses and pit falls that only come to light after they are in service. The belts use far less power than other methods of power transmission and chains and shafts can be down right dangerous in these sizes plus the belt drive very light weight. My goal is to make something that would offer a true benefit to users not just a different way to slice bread. It is not so outrageous that the average Joe sport fisherman couldn't see the value in it.

    Steve
     
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