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One for the engineers... OJ etc..

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One for the engineers... OJ etc..

I've been mulling something over recently about helicopters that have twin engines and how they'd be connected to a single rotor shaft. Likewise ships with multiple engines but one propellor.
Something struck me.. if one engine shuts down and they were both directly linked, the other engine would be jammed too making the second engine pointless. I've found plenty of articles on google where people have linked two car engines via flywheels for banger racing etc but again.. one engine goes pop (eg piston through the cylinder block) and the other engine is rendered useless too - making that pointless.
So I figured that there must be a way for two engine outputs to be combined into one output to the rotor shaft but still able to run independently and pick up the slack if one engine fails. Then I had a thought... car axles have differentials that take one input and provide two outputs - essentially the same process but in reverse!
So I've googled this for several days both web searches and image searches but the most I have found about using a differential in reverse to combine two engines is from LEGO users  Crazy I cannot find any reference to this actually being used in any real world application. This made me wonder if a differential would even be physically strong enough to be able to cope with the input from two engines and effectively double up the output.
As I can't seem to find any real reference to this technique being used by real engineers / machines other than Lego users, I am left wondering if it is really possible?
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gtowen
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Re: One for the engineers... OJ etc..

A patent has been registered for the idea
http://www.google.co.uk/patents/US4829850
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Re: One for the engineers... OJ etc..

Yes i noticed that yesterday but its not quite what i was referring to really as it's not used in helicopters, ships etc. Granted it is very similar but it goes on about using clutches, overspeed limiters etc.. the latter meaning little to me lol.
I just wanted to know if the ultra simple idea of using a differential in reverse was actually plausible and actually used in anything or if it is simply lego nerds being unreal  Undecided
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Re: One for the engineers... OJ etc..

Maybe I'm wrong but with large ship engines I believe a single piston can be taken out of service and worked on without the engine having to be turned off.
Or is it a case of multiple engines and I've misunderstood.
gtowen
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Re: One for the engineers... OJ etc..

@billnotben  .... That's a twin engined vessel where one engine can be locked to prevent it turning and then the vessel can proceed on the one engine while work done on the locked engine.
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Re: One for the engineers... OJ etc..

http://www.industry.siemens.com/drives/global/en/gear-units/application-specific-gear-units/ships/mu... but basically the easiest way is to solid connect the whole thing together as shown here http://www.finnoygear.no/en/en_tomotor.html with a clutch between the motors and the gearbox
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Re: One for the engineers... OJ etc..

Quote from: billnotben
Maybe I'm wrong but with large ship engines I believe a single piston can be taken out of service and worked on without the engine having to be turned off.
Or is it a case of multiple engines and I've misunderstood.

I seem to recall seeing something like this on Mighty Ships on Quest a while back. They locked one piston but left the rest of the engine going - I'm sure i made a post about it here on this forum at the time but was told something like this:
Quote from: gtowen
@billnotben  .... That's a twin engined vessel where one engine can be locked to prevent it turning and then the vessel can proceed on the one engine while work done on the locked engine.

I seem to recall hearing this before but I'm sure on the program i saw they were able to stop individual cylinders while the others continued operating. When you think about it, a V or W engine is simply multiple engine blocks joined together and sharing the same crank. In that case, why can't cylinders operate individually through some gearing system but remain part of one engine and thus be stoppable without affecting the rest of the engine?
@OJ Thanks for those links and they are indeed a bit of an eye opener however what i fail to see the point of is linking two engines with a solid link when one could go bang and then knock out the other - which makes redundancy... well.. redundant! To me that seems daft when you could have them both operating but not linked and then have one to fall back on if an engine fails. Twin engined helicopters work like this.
What I did find via google images however was these which kind of gets at what i'm talking about:
 
While both of these seem clever using one way bearings, clutches and the like, the first thing that stuck out is that you need both engines running at identical speeds in order to contribute anything. Either engine being a little sluggish with a solid link will slow the other down and put strain on one or both engines. If using one way clutches and one engine is slower it wouldn't really contribute anything would it?
Thats why I am asking about using a differential in reverse because if one engine were to run say 2-300rpm slower, its output into the differential would still (in theory) be combined into the output. Likewise it would (again in theory) allow one engine to stop and be locked and let the other pick up the slack with some electronic hocus pocus ECU stuff.
To me using a diff would make sense but like i say, i can't actually find any real world examples of it in use other than by lego users...
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gtowen
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Re: One for the engineers... OJ etc..

Quote
I seem to recall seeing something like this on Mighty Ships on Quest a while back. They locked one piston but left the rest of the engine going - I'm sure i made a post about it here on this forum at the time but was told something like this:

Assuming an 8 piston engine, if there is a problem with one unit it is possible to disable this unit and proceed under 7 piston/units. Depending on the problem this can be achieved in a number of ways. The simplest would be to "lift" the fuel pump so that it did not make contact with the camshaft and thus did not deliver fuel to that unit. The engine could then be run on 7 units.
It is supposedly possible to actually remove one piston and blocking the cylinder but I've never seen that done.
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Re: One for the engineers... OJ etc..

You can achieve a multi-engine configuration within compressed air systems driving one or more outputs, but this approach is probably not within the OP's enquiry.
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rongtw
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Re: One for the engineers... OJ etc..

if you have a 12 cyl engine i cannot see the possibility of removing one piston  ,, while the rest are running .
i think what it refers to is a multi engine configuration you stop one engine while one is not in use , while using the other 
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Re: One for the engineers... OJ etc..

Quote from: 7up
So I figured that there must be a way for two engine outputs to be combined into one output to the rotor shaft but still able to run independently and pick up the slack if one engine fails. Then I had a thought... car axles have differentials that take one input and provide two outputs - essentially the same process but in reverse!

The immediate problem I can see for that is that if only one engine is running then the output speed from the differential would be half the speed compared with when both engines are running.
Quote
If using one way clutches and one engine is slower it wouldn't really contribute anything would it?

The speed of most engines is rather load-dependent so the 'slower' engine would speed up if not contributing to the output load.  As long as both engines were working somewhere near expectation the speeds would soon match even though the contribution to the output load might not.
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