Geared Crankshafts in IC engines 2

[factsb4pride]

I have been working on a project to develop an IC engine that uses gears to translate reciprocating motion to rotary motion. I have heard many posts here, as well as information posted elsewhere, that says current gear technology is not strong enough to allow gear teeth to survive combustion pulses without damage or undue wear in the long run.

However, another member recently posted info in a thread about Neander motors, which has 2 counter-rotating "crankshafts" that are directly geared to one another. Then power is taken from one crank by a CHAIN drive to the tranny. So combustion pulses are definitely being transferred across the gear tooth faces and through the gear teeth. AND this is a diesel engine, NOT a gas motor, so the forces the gear tooth must handle are very high.

So I guess my question is, do current gear tooth profiles and fabrication materials allow for this now? Are objections to this design of engine based on current realities, or outdated facts and opinions?

Yes, I understand no current engines use this method (except the neander motor), and that it is not a common practice. But my question is: Is it a viable research path to take, and if not, why not. Please be specific.

 

[factsb4pride]

No, I got that point, but the research I have read completely disagrees with your statement that only torque loads are experienced by the gear teeth involved in the mesh in this application. Instantaneous combustion loads ARE experienced by the gear teeth, according to my sources. Please refer to the paper "A Critical Evaluation of the Geared Hypocyloid Mechanism for Internal Combustion Engine Application" by Beachley & Lenz. If you have verifiable sources that disagree with their conclusions, I would sincerely love to read them.

 

[BrianPetersen]

Explain why, if you replace that vibration-damped clutch basket with a lightweight "racing" clutch basket, that one of the consequences is that the gearbox eventually gets smashed up.

 

[factsb4pride]

My last post was confusing, as your initial statement I referred to was directed at a typical motorcycle setup, and I took it to refer to the cardan setup. Sorry if I went awry there.

I am also wondering about the role played by hydrodynamic bearings in absorbing at least part of the instantaneous combustion forces. The Neander motor has 2 piston pins and 2 "big end" hydrodynamic bearings for each piston, twice as many as normal. Does that play a part? The design I am working with employs a large hydrodynamic "big end" bearing between the piston and drive gear (unlike most concepts of this engine). Just a thought that occurred to me, I will do some reading, it may be nothing.

I am coming up with a couple more thoughts/concepts for discussion, but want to work through them first, and will post more later.

 

[factsb4pride]

Brian,
I am not disputing the ability of the springs in the clutch basket to absorb/smooth out instantaneous forces. I see the points you have made, and my pre-superbowl brain is rolling this all around.

Although I never suggested a vibration damper should be between the piston and gear in a cardan setup, your comment did make me think along another line. One which I came across in the intro of a patent application I read recently, as well as in the paper I mentioned a couple posts back:

Tangential gear tooth force is equal to the sin of crank angle times the gas load force. At TDC almost all of the loads are taken by the crankshaft bearings (on both the drive gear and crank mains), while at ~30 degrees ATDC (when cylinder pressures are highest) the loads are split evenly between the mesh teeth and the bearings. At 90 degrees ATDC, when the leverage is highest on the gear teeth, the cylinder pressure is well below its earlier peak, though what loads that do exist are almost all on the mesh at that point. This all adds up to the gear mesh not absorbing the peak gas loads alone, but spreading the loads to the bearings, and further to cylinder expansion/engine load.

Further, due to the inherent high contact ratio of internal ring gear & pinion sets, 2 teeth or more will be involved in the mesh at any point in time, further spreading the loads out and not concentrating them on a single tooth. This was mentioned as a main concern in the literature I read, but more recent gear research determined more than one tooth would be involved, which earlier studies had not taken into consideration.

Other than looking into the possible effect of hydrodynamic bearings, this is my current case to make up for the fact no "vibration damper" exists to smooth out/absorb instantaneous combustion pulses that pass through the drive gear in a cardan crank engine. I also think if you use a generous gear face width for drive pinion and ring gear, and lubricate well, it might be practical and durable.

 

[factsb4pride]

Hey Terry,
With regard to the engine you mentioned you had worked on: did it have a spring loaded "basket" or gear from the engine to the tranny? Like the neander motor does? Can you give any more details on that particular engine configuration?

If anyone has any example of engine directly absorbing dynamic combustion loads directly with gears, please post!

 

[factsb4pride]

Something else that occurred to me: the drive gear in rotary engines absorbs combustion pulses directly, as we have already mentioned in this thread. Does anyone have any numbers on the dynamic combustion loads created by a rotary engine on its rotor drive gear? I will be tracking down the reference Terry provided earlier on this.

 

[factsb4pride]

Okay, I found Terry's rotary engine reference online, and checked it out. The show the rotary engine stationary gear as being able to take up to 930kg of tangential gear tooth pressure in cases where only trailing sparkplugs are utilized.

They also mention the use of "spring pins" to mount the internal ring gear in the rotor. They mention the pins absorb gear shocks. Can anyone elaborate on this with specifics? I am unfamiliar with the use of "spring pins" to mount gears.

 

[dgallup]

I would expect "spring pins" to be something like this:

http://www.spirol.com/mkt/rs1.php?search=2

 

[factsb4pride]

No, that is not what they had illustrated in the book. More like a center pin, with 4 equally spaced, spring loaded side-pieces mounted at the base of the pin.

 

[factsb4pride]

Here is what I am referring to:

http://www.google.com/patents?id=hw...urce=gbs_overview_r&cad=0#v=onepage&q&f=false

Question is, could this method be used in a cardan style crank to mount the gears? The pins work by displacing very slightly as they absorb shock, but then recenter once again. The rotary engine is likely less sensitive to gear displacement than a hypocycloidal engine, but I will look into it anyway.

 

[tbuelna]

"With regard to the engine you mentioned you had worked on: did it have a spring loaded "basket" or gear from the engine to the tranny....

factsb4pride,

The engine was a single cylinder, opposed piston, uniflow two-stroke, displacing around 100 cubic inches. It was simply a dyno test rig, and thus there was no "tranny" involved. The max brake torque the engine produced was about 375 ft-lb.

As I noted, the engine had one cylinder, two pistons, four conrods, and four cranks. There was a pair of counter rotating cranks at each end of the engine, connected by a pair of phasing gears. The phasing gears were carburized & ground spur gears, with a face width of around 1". They were rigidly bolted to one end of the crank with several bolts, and were cantilevered. Torque was transmitted from the crank to the phasing gear solely through friction in the clamped joint. There were no splines or "springs". There was a compound idler gear in the gear train connecting the cranks at each end of the engine. The compound idler gear had slotted bolt holes, so that timing adjustments could be made between the cranks at each end of the engine.

Also, at the opposite end from the phasing gear of one crank in each pair, a 100 lb flywheel was attached. The large inertia flywheels helped give a more uniform crank angular velocity with the large single cylinder engine.

To answer your question, obviously a rigid gear drive can be made to work.

Regards,
Terry

 

[factsb4pride]

Well, the rotary engine paper Terry posted led me astray slightly. The "spring pins" used to mount rotor ring gears in rotary engines are really ordinary split pins, but with double pins, one inside the other. So ordinary split pins can be used for this application. I am curious/hopeful this will alleviate some of the loads from instantaneous piston forces.

Terry, I appreciate the details about the engine project you were involved with. I am still not sure that engine design represents a case where gear teeth are taking the full instantaneous piston forces. Since the engine was not running under load from your desription, and since the gears are all rotating at the same rpm, I remain unsure.

In a cardan application, one gear is stationary while one rotates and applies forces, they are not both rotating together at the same rpm when those instantaneous combustion forces are applied. Though I am sure it does not mitigate them entirely, I would think that co-rotation would tend to lower the loads on the gear teeth in the engine setup you described. Feel free to point out any problems you see with my reasoning here.

 

[factsb4pride]

As things are now, I am planning to utilize a ring gear/pinion pair that is 1/2 the pinion pitch diameter in width. That will hopefully be robust enough to withstand the combustion forces involved. I am planning to mount the ring gears with double split pins to mitigate peak combustion loads. Initially, I will be sticking with an involute gear tooth profile, in a spur gear configuration. Though if that proves problematic, I will look into alternate gear tooth profiles in more depth.

I wish the new metallic glass material that was discovered recently were available commercially now:

http://news.cnet.com/8301-17938_105-20028318-1.html

Gears made from this would likely have no problem surviving in this application.

I am honestly surpised and disappointed at how few public attempts have been made to construct an engine like this. Given the obvious advantages, one would think it would have been done quite a bit. And maybe it has, but the research was done privately/proprietarily, and then put away for whatever reason.

I am also considering utilizing a direct injection system that would employ multiple injection events during combustion. this might be able to more evenly spread out the loads across the cylinder expansion and subsequently reduce peak forces. I will be looking into this, just an idea at this point, so feel free to post sources and/or comments.

 

[MikeHalloran]

Just a comment about product development in general:

Inclusion of just one leading edge/ bleeding edge/ immature/ unknown/ unfamiliar technology in a project roughly doubles the risk that the project will die before completion.

Inclusion of two such technologies doubles the risk again, effectively dooming the project unless your pockets are very, very deep and you are very, very stubborn.



Mike Halloran
Pembroke Pines, FL, USA

 

[factsb4pride]

Thank you all.

 

[waross]

As I understand it, this is to improve efficiency by reducing side forces on the piston. Do some calculations on just doubling the length of the connecting rod in a conventional engine. Another advantage of this approach is the suitability for use in multiple cylinder engines.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[gruntguru]

Scotch yoke is a good option too - especially in an opposed config with 2 pistons and yoke all in one rigid part.

Engineering is the art of creating things you need, from things you can get.

 

[GregLocock]

Are there any PRODUCTION Scotch yoke engines, as opposed to fantasy engines like the Bourke?



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[gruntguru]

Not to my knowledge. On the other hand I don't know of any Hypocycloid crank engines either. Which would you back in a two-horse race to production?

Engineering is the art of creating things you need, from things you can get.

 

[BrianPetersen]

I would back a conventional crankshaft-and-conrod, myself. I just don't see the advantage of doing anything else outweighing the substantial disadvantages and uncertainties.