Geared Crankshafts in IC engines
Geared Crankshafts in IC engines
(OP)
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 Are objections to this design of engine based on current realities, or outdated facts and opinions?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.
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 Are objections to this design of engine based on current realities, or outdated facts and opinions?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.





RE: Geared Crankshafts in IC engines
Just a few examples: the Arial Square Four [SI], the Coventry Climax Flat 16 [SI], Junkers Jumo 205 [CI], Napier Deltic [CI], Napier Sabre [SI], Sulzer 12LDA28 [CI], and on and on.
PJGD
RE: Geared Crankshafts in IC engines
In my research I came across a paper written back in '88 titled "A Critical Evaluation of the Geared Hypocloid Mechanism for Internal Combustion Engine Application". The focus of this paper was engines using an internal ring gear and planetary gear with a ratio of 2:1 to translate reciprocating motion into rotary motion. One of its conclusions was that the tangential gear tooth loads were within an allowable range for the gear teeth to handle, but the tangential dynamic loads were right on the borderline of acceptance.
I have also seen many objections on this site over the years to engines that have gears receving direct combustion pulses and loads. So I thought I would just ask if there were still valid objections to them based on verifiable evidence, especially since viable engines are using them that are for sale today. And please understand my approach is not manufacturing costs, or any others, but simply whether or not current gear technology can handle that kind of service without undue wear or gear tooth damage.
RE: Geared Crankshafts in IC engines
Most transverse motorcycle engines use a direct gear drive from the crankshaft to the clutch basket, and that clutch basket has a set of springs between the actual gear and the clutch basket itself to allow some compliance. Same type of mechanism that car engines with manual clutches use to absorb some of the vibration between the crankshaft/flywheel and the transmission input shaft.
If you are using the gears directly in place of the crank and con-rod in some fashion, so that the piston loads are being transferred directly into the gear without any interposing rather-high-inertia flywheel, it might be a different story, though.
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
Another conclusion reached in the paper I mentioned previously was that a certain ratio of bore to stroke could be applied to geared "crankshafts", and they determined it was 3:4. The idea being that if the large internal ring gear was always kept a certain ratio larger than the bore, the subsequent combustion gas loads would never exceed the strength of the gear system, and more specifically, the individual gear teeth. Anyone have any thoughts on that?
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
The process of actually doing that engineering comprises a lot of calculations conducted with differing values of many of the possible parameters, and may include graphical layouts or their mathematical representations, and perhaps a few physical prototypes or test articles associated with experiments conducted to answer idle speculations or unresolved issues.
The process may include some of the 'bench racing' you are attempting, _after_ at least some of the calculations have been done, but the bench racing does not comprise the whole of the process.
You insult our education and experience with the phrase "outdated facts and opinions". I will refrain from a complementary slur.
It has been pointed out in a separate discussion that Watt's planetary linear to rotary converter was invented in order to get around a patent that covered the slider-crank. Both are now in the public domain, and have been analyzed to death, and can be used to make durable engines. Slider cranks dominate right now because they are much less expensive to manufacture. That is also a valid engineering constraint on a problem's solution space.
Mike Halloran
Pembroke Pines, FL, USA
RE: Geared Crankshafts in IC engines
Why add extra complication if it's not needed.
Regards
Pat
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RE: Geared Crankshafts in IC engines
The rotor gear is a light press fit and is located rotationally with spring pins (split roll pins). Interestingly, Mazda reduced gear loads by switching from nine pins to twelve.
RE: Geared Crankshafts in IC engines
The orbiting rotor connected to an output shaft by a 3:2 planetary gearset was the result of a kinematic transformation, which allowed the engine shell to remain stationary, greatly simplifying the fuel system, etc.
The output shaft geared to the rotor represented complexity added because it _was_ necessary.
Mike Halloran
Pembroke Pines, FL, USA
RE: Geared Crankshafts in IC engines
"Are objections to this design of engine based on current realities, or outdated facts and opinions?"
While I appreciate your input, no insult to anyone was written or intended on my part.
To others:
I have also analysed the use of gears in the mazda rotary engine, as well as others, and thus my question to the forum: Has gear technology reached the level where gears can directly absorb the kind of punishment that IC engines dish out, both gas and diesel? If the consensus is no on this forum, that is information worth knowing considering my current project at work.
Based on my research and calculations so far, the answer depends on how many gears are used to direct combustion pulses from a single cylinder to the rest of the drivetrain, what the ratio of bore to stroke is, crank throw length, and other factors as well, such as tooth profile design and gear module used. If an internal ring gear and pinion are used, and rotating forces are balanced out properly, the only loads the gears see are tangential in nature, and comprise the gas loads from the piston.
Please keep your input coming, appreciate it all!
RE: Geared Crankshafts in IC engines
If the gear mechanism is big enough, and the cylinder is small enough, and the revs are low enough, at some point the stresses will be OK.
You will have to analyse the forces involved in your proposed cylinder size, taking into account the peak cylinder pressure and the various inertial loads, find out how much torque is being applied to the gear (and along with that, how much force is being applied to every other part of the mechanism), and then size the gears accordingly and design the rest of the mechanism accordingly.
There is no substitute for crunching the numbers. No amount of us telling you whether it is okay or not will take the place of that!
RE: Geared Crankshafts in IC engines
I already stated my research has revealed a bore-to-stroke ratio of 3:4 has been proposed as a guideline to designing IC gear driven systems that employ internal ring gears. This relates directly to your comment that such systems can be designed effectively.
I am hopeful that some of you readers have real world experience you are willing to share on this topic. Hopefully with experimental data or supporting references...
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
A gear drive connecting two counter rotating crankshafts can be successfully designed. But as BrianPetersen points out, there are lots of issues to consider.
The gears must be designed to handle the peak instantaneous loads throughout an engine cycle, produced by all the cylinders. The gear loads must also take into account any dynamic loads due to crankshaft torsionals. Some teeth on the crank gears will have a shorter fatigue life than the rest, since they are the ones in mesh during periods of peak loads. And if the gears are fastened to the crankshaft, the gear face contacts should be de-rated for any mesh misalignments caused by crankshaft bending.
Finally, if you put any idlers in the gear train, be sure to use a lower tooth bending stress allowable for your idlers, since they will experience full reverse bending loads. Also take into account the fact that engine oil is not a particularly good gear lubricant.
Good luck.
Terry
RE: Geared Crankshafts in IC engines
@ Brian P: The 3:4 ratio I mentioned takes into account the factors you mention, including peak gas forces, and compression ratios. The idea being that the bigger the ring gear, with the number of gear teeth remaining constant, the more force the gear teeth can handle. Given those constraints, larger ring gears = larger geer teeth. If the ring gear and pinion always stay a certain ratio above cylinder bore diameter, the researchers (that came up with the ratio) claim it will always be able to handle the subsequent dynamic gear tooth loads. I encourage you to read the paper I posted earlier, as it goes into great detail about this topic. I also have another paper where the authors claim the pinion gear face width should be no less than one-third of the pinion gear diameter. So more than one research group has come up with guidelines for constructing this kind of mechanism.
@ tbuelna: I am very familiar with the concepts and points you posted, as I have been researching this topic for quite a while. Setting that aside, my goal here was to find people who could provide any real world experience, or experimental data, that I might have missed in my own research. I am well versed in the loads that gears must endure to achieve the stated goal in this application, I am simply trying to find gear technology that can accomodate those loads, or find people who can offer relevant input.
One thing I need to clarify: size does matter. Of course, just about any engineer worth his salt could design a hugely oversized gear set that would survive direct combustion forces. That is fairly obvious. I am talking about a practical application, not merely a thought exercise, so if I gave the wrong impression earlier on, I apologize.
The engine I am designing is intended for home electricity generation, and use as a hybrid generator. It will run at its most efficient rpm most of the time. Efficiency is more important a consideration than a broad torque band, or high end power output or high rpm. Some additional cost for gear sets (over and above what slider cranks would have called for) is allowable, but within reason. Just as the gear set sizes have some variability, but within reason.
As another poster pointed out, a lot of research has gone into this kind of concept over the last 40 years. The problem I see is that all people do is theorize about the topic, with few if any actual machines built, run, and/or tested tested. Ishida was one of those. I was hoping to come across the few exceptions in this forum, but that may not be a valid expectation.
RE: Geared Crankshafts in IC engines
"if the velocity profiles on each side are not too different from each other".
In the neander motor I mentioned earlier, the crank gears rotate together in the same direction at the same speed and loads. One is not stationary, while the other is in motion, they are both in motion equally at the same time. That would seem to shoot down my train of thought that the neander motor proves it can be done.
However, as near as I can tell the neander motor passes power to the transmission off a single crankshaft cog and through a chain. So the total combustion peak loads of the whole engine would be passed through that one chain cog. If that is possible, it seems it would be possible for a solid gear to absorb those same forces, especially on a single, per-cylinder basis.
RE: Geared Crankshafts in IC engines
A few thoughts:
1) If your engine is 4-stroke, you might be able to tune the engine to be efficient at twice the generator speed, and then drive the generator off the same gear as the camshaft. See SAE paper 700205 on the Teledyne Continental "Tiara" engine to see an example of this.
2) A good strategy might be to use the artifice of a "hunting" tooth in your gear mesh to distribute the wear from the pulse loading and any mesh errors across all the teeth.
3) I think that the rule of thumb is that you can expect to loose about 0.5% of transmitted power per gear mesh.
PJGD
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
While you haven't given exact details of your proposed "hypocycloid" gear crank drive, if it's something like the ones described in the link below then you will have one very big issue to consider. With a 4 stroke engine, I believe you will have load reversals at the gear mesh. Since involute gears need to have some amount of backlash to operate, the point of load reversal in the cycle will create very high impact loads on the gear teeth as the backlash is taken up.
Take a look here:
http
Hope that helps.
Terry
RE: Geared Crankshafts in IC engines
The goal is too reduce parasitic friction between piston and cylinder walls without adding TOO much complexity or weight or cost. SOME increase of those items is allowable, but within reason. The fact that most Stirling engine use hypocycloidal crank designs is encouraging, but the design requires modification for IC engines, which is what I am working on due to higher gas loads on the piston.
@tbuelna: The link didn't work that you posted, but I think it is the same paper I posted earlier in the thread.
The subject of gear backlash is covered in another paper. They conclude involute gears are the best to use, as long as backlash is kept very tight for the very reasons you mention.
https://oa
Is anyone aware of a gear tooth profile that has sliding AND rolling at the pitch diameter contact point? Seems "rolling only" contact between the involute gear teeth at that point reduces the lubrication layer of the oil on the gear teeth. I am also open to alternative gear tooth profile designs, if anyone has any to suggest that might work better than involute gear teeth in this application.
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
Unfortunately, the "hunting tooth" concept cannot be applied to applications where an exact 2:1 ratio is required. While I understand why it seemed a good idea, my research shows it is not viable here specifically. If it were, my task would be greatly simplified!
RE: Geared Crankshafts in IC engines
1. If possible, enough flywheel effect should be built into the "inner" rotating masses rather than in the composite crank as a whole or even externally so that the "inner" flywheel effect carrries through to minimize torque reversal effects on the teeth.
2. Gearsets should be arranged if possible to that marinally adjustable idlers can be used to lightly preload the mesh. Thermal expansion effects will need to be examined.
3. If possible, the application should be designed so that mounting arrangements provide a bit of compliance and so that peak loads tend to drive the teeth deeper into mesh, rather than apart.
4. Application of gear lubricant exactly at the point of maximum load might possibly be used to flood the teeth at that point to buffer peak loads.
5. If helical gears are chosen to prevent cogging effects, it may be beneficial to use the helical gears in opposite-handed pairs to create composite herringbone gears sets to elminate end thrust.
6. Gears need not be of constant thickness around their full circumference; it may be desirable to allow full thickness only at maximum load and or wear points and thin the remainder of the gear to optimize rotating mass or balances.
7. Because the gear set is phase-locked, it may likewise be desirable to use different tooth profiles or pitches at different parts of the pattern; e.g. large buttress teeth at max pressure, and smaller more closely spaced teeth at torque reversal. Yes; a machining nightmare, but maybe a point-by-point optimization that would allow the use of less expensive sintered or precision cast materials.
8. Consider direct cushioning of the peak gas loads... Maybe the rod big end bearing could float slightly in an oil cushion or an elastomeric insert to spread out the peak, or a bit of compliance could be built in to the rod itself.
Obviously, there are countless other possibilities that might even better facilitate a cost-effective design; when you are trying to find 'subtle', you don't want to avoid it's cousin 'outlandish'. They tend to hang around together.
RE: Geared Crankshafts in IC engines
factsb4pride,
The rotor phasing gear in a Mazda rotary has involute geometry. However, this gear's function is likely different from what you're proposing. The gearset in the Mazda rotary only serves to keep the rotor faces properly oriented as the rotor orbits within the housing. Thus the gear mesh is fairly lightly loaded without reversals. The combustion forces acting on the rotor faces are taken out thru the crankpin.
Terry
RE: Geared Crankshafts in IC engines
The gears in the rotary are more easily able to handle the loads presented to them due to the fact there is only a 3:1 drive gear ratio in a mazda rotary, while there is a 2:1 drive gear ratio in piston motors with a hypocycloidal crank system. So given equal volume combustion chambers, at peak combustion pressure the mazda rotary drive gear will see 33% LESS tangential gear tooth loading than a piston engine with a 2:1 drive gear ratio.
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
Regards
Pat
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RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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for site rules
RE: Geared Crankshafts in IC engines
With regards to phasing gear tooth loads in the Mazda rotary, you can find a good explanation in Kenichi Yamamoto's book "Rotary Engine". It's in chapter 3.3.2 (page 25). Figure 3.17 gives a max ring gear load of about 480kg at 8000 rpm and WOT (I'm assuming the load is referenced at the gear pitch line).
Hope that helps.
Terry
RE: Geared Crankshafts in IC engines
I will do some calculating and reading on the loads in the rotary engine drive gears and get back to you.
One thing I missed in the first paper I quoted: they suggest the face width of the gearing should be equal to the pinion pitch radius. This is different than the other paper I posted, which suggests the gearing width should be 1/3 the pinion gear radius.
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
I have to think about it some more yet though, every time I look at it I get mesmerised...
http://www.youtube.com/watch?v=JYlBe7VkC6k
BG
RE: Geared Crankshafts in IC engines
Should be scalable, but the gears get heavy.
I've built an equivalent linkage using timing pulleys with levers affixed. With timing pulleys and a timing belt, you also don't need an internal gear. You just arrange for a small pulley to orbit a big one, and put a lever on the small pulley. Works very nicely for light duty; I wouldn't attempt it in an engine.
Mike Halloran
Pembroke Pines, FL, USA
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
BG
RE: Geared Crankshafts in IC engines
My current design is a V4 configuration, utilizing zero counterweights, yet still providing a perfectly balanced engine.
RE: Geared Crankshafts in IC engines
just a thought, not sure about it at all.
RE: Geared Crankshafts in IC engines
I'll try a word picture.
Stationary timing belt pulley, size 2N.
Arm rotates around its center, length L.
Tip of arm carries another timing belt pulley, size N,
free to rotate relative to arm.
Second timing belt pulley carries another arm, same length as the primary one, typically more delicate.
A belt of appropriate length connects the two pulleys.
As the primary arm rotates around the larger pulley, the tip of the secondary arm moves in a straight line.
Mike Halloran
Pembroke Pines, FL, USA
RE: Geared Crankshafts in IC engines
If the neander motor can pass the diesel combustion pulses from 2 large cylinders through a single chain and crank sprocket, surely a similar type of chain could handle those same loads for a single cylinder in the configuration we are currently discussing. You could even have 2 chains per cylinder, one on each side of the mechanism, to further distribute the dynamic combustion loads that must be absorbed.
Anyone have any info on chain design and dynamic load capacities?
RE: Geared Crankshafts in IC engines
http://u
Motorcycle drive chains operate well outside these rating tables.
Keep in mind that chains and belts have some compliance to them which is not present with gears.
RE: Geared Crankshafts in IC engines
Power is sent to the tranny through the main crankshaft gears. Which is bad and good. Bad that chains have not been used in this application, which is supported by the post before this one. Good in that it illustrates that gears can transmit these kinds of loads.
I will be contacting neander directly to see if I can get more details from them.
Question: do internal ring gear & pinion sets with a 2:1 ratio have stronger gear-to-gear interaction than an external gear of the same size would have with another external gear half its diameter? It occurred to me that the pinion gear might "nestle" into the ring gear more so than regular external gears would, and subsequently engage more teeth at the same time in the process. The mazda rotary engine drive gears do this nicely, but with a 3:2 gear ratio. Would this effect also apply to 2:1 ring gear/pinion gear sets?
And if so, by what factor increase (or decrease) in dynamic load bearing strength over external gear sets?
RE: Geared Crankshafts in IC engines
I am now looking at alternatives to involute gear tooth profiles. Double circular arc gear designs are reported to have 1.5 to 4.5 times the load bearing capacity of involute gear teeth. So I am taking a look at them to see if they could make a direct gear drive viable. Involute gears were close to making the cut already, so if the gains in strength that are claimed for double arc circular gears are valid, then its very possible they will work out in a watt/cardan style gear drive for combustion engines.
I have numerous papers and studies I am reading about this, but if anyone has any recent info on this, please post.
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
This is encouraging to me in that it shows you can absorb diesel combustion loads with gear teeth, and perhaps that method can be used in alternative engine crank designs.
Additionally, I have been researching alternative gear tooth profiles, and believe that an improved form of W-N circular arc tooth profiles would offer additional strength and increased hertzian contact loads over a standard involute gear tooth profile.
No one has posted in awhile, so curious if anyone is still following this, or has anything to comment...
RE: Geared Crankshafts in IC engines
Thanks for the link to Neander Motors.
Coincidentally, a few years back, I worked on a diesel engine that had an identical crank and conrod arrangement. Except that this engine was an opposed piston two stroke instead of a four stroke, and it had four cranks instead of just two. So, besides having gears connecting each pair of adjacent cranks, it also had a geartrain connecting the cranks at opposite ends of the engine.
This engine was a very high firing pressure (3000 psi) single cylinder diesel. We did a few hundred hours of testing and never had trouble with the gears. The gears were all involute spur gears, made from case hardened 9310 and finish ground with a slight crown profile.
With regards to your question back on Jan. 11 about the load capacity of an internal ring and pinion versus two spur gears having the same ratio, the ring and pinion combination would tend to have better load capacity due to its greater contact ratio. Of course, there are also other practical considerations between the two choices, such as direction of input/output rotations and mounting requirements.
Hope that helps.
Terry
RE: Geared Crankshafts in IC engines
Appreciate your post! The setup you describe almost sounds like the research Achates has been engaged in. I am intrigued by your report of using case hardened gears with involute tooth profiles in an engine application as we have been discussing. That is the kind of info I am looking for here. Do you have any further info to share about that project, where I could perhaps take a look at a patent or further data? For example, in the engine you mention, did the same teeth in the mesh always take the combustion load pulses, or did different teeth do so with each combustion cycle?
Also, on Neander Motors website they have a cutaway of their engine that shows it also is using what appear (maybe) to be involute gears on the cranks meshing directly with the input gear of the tranny. I will attach it to this post. Those guys have created a real jewel of an engine!
Appreciate your comments as well about contact ratio being greater with ring gears & pinion than with 2 external gears. I have been unable to locate a formula to calculate those values with ring gears & pinions though, so if you have it, please post.
So it seems that it might be possible to build a cardan/watt style internal combustion engine, using either spark or compression ignition, based on Neander's motor and also the experiences of Terry. I am encouraged!!!
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
I looked at the cutaway picture of the Neander engine. If that picture is accurate those guys don't understand gear design.
If you look closely at that picture, you'll notice that the crank gear that meshes with the tranny input gear has the same face width as the other crank gear. If properly sized, this middle gear should have a much wider face width than the other crank gear for a couple of reasons.
First, the middle crank gear is an idler. So it's teeth are subject to reverse bending loads, and typically should have a wider face to equalize the bending fatigue life with its mating gears.
Second, the middle crank gear is subject to both combined crank gear loads where it meshes with the tranny input gear, while the outer crank gear only sees about half of that load.
Regards,
Terry
RE: Geared Crankshafts in IC engines
From my research, and as you pointed out, face width of the internal ring gear and pinion (or external gears such as the Neander Motor) should be the most easily adjustable variable to increase gear train strength in an engine application such as this. That is also assuming you use the largest tooth size that is practical, and don't get too carried away with cylinder bore size and subsequent gas loads. I would also incorporate an appropriate lubrication system.
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
The crank gears on the Neander engine don't have to deal with the full cylinder pressure. The kinetic energy transfers between the pistons and crankshafts without going through the gears. Since both crankshafts operate together but in opposite directions, both crankshafts accelerate and decelerate together, so the gears only have to transmit the net output torque to the clutch basket. Same as any other motorcycle engine.
RE: Geared Crankshafts in IC engines
This confused me at first as well, but if ANY of the crank gears are meshed with tranny gears, in that mesh gear teeth are handling direct combustion loads.
As far as the NVH thing, from what I had read I expected spur gears to generate too much NVH to be used in this application, but that may indeed be incorrect. No reviewer mentioned any objections to gear or tranny noise/vibration whatsoever in all of the Neander Motorcycle articles I have read (about a dozen).
RE: Geared Crankshafts in IC engines
This is what that clutch basket looks like from the backside ... the gear drives the basket itself through those springs, which take up all the shock loading ...
http
RE: Geared Crankshafts in IC engines
I guess my next question would be: how effectively does the clutch shock absorber react and absorb gear tooth bending stresses vs. gear tooth contact stresses? If the clutch can handle both those forces in a dynamic way, then I am unsure as to why a watt/cardan style combustion engine has not been pursued by anyone in the past. If the clutch can absorb all of those forces with no problem or side effects to the engine, why have so many researchers walked away from this type of crankshaft design, considering all its advantages?
RE: Geared Crankshafts in IC engines
The SPRINGS in that clutch basket take up the shock loads. The gear accelerates and decelerates with the crankshaft and only the average torque is transmitted to the clutch and that means - neglecting the inertia of the drive gear, which is small compared to the inertia of the crankshaft - only the average torque is handled by the gear teeth, NOT the instantaneous combustion loads.
If you use a Watt gear setup, you cannot have a vibration damper between the piston and the gears! The combustion load goes straight through to the gears and THEN to the inertia of the crankshaft.
Do you see the difference here?
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
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.
RE: Geared Crankshafts in IC engines
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.
RE: Geared Crankshafts in IC engines
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!
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
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.
RE: Geared Crankshafts in IC engines
http://www.spirol.com/mkt/rs1.php?search=2
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
ht
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.
RE: Geared Crankshafts in IC engines
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
RE: Geared Crankshafts in IC engines
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.
RE: Geared Crankshafts in IC engines
I wish the new metallic glass material that was discovered recently were available commercially now:
h
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.
RE: Geared Crankshafts in IC engines
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
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Geared Crankshafts in IC engines
Engineering is the art of creating things you need, from things you can get.
RE: Geared Crankshafts in IC engines
Cheers
Greg Locock
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RE: Geared Crankshafts in IC engines
Engineering is the art of creating things you need, from things you can get.
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
Looking to the future though, downsize, down-speed and boost is where it is at for pass-car, and specific ratings are rising for all engines. We are already at ~30 bar BMEP for production engines, and peak cylinder pressures are moving to 240 bar and beyond for HD truck engines. Given the imperative to reduce friction and parasitics, I think that solutions that will circumvent the piston side load issue will start to look attractive. Yes, there is still the piston ring friction issue at high cylinder pressures, but with better control of piston side-to-side and angular attitude issues, I suspect that better ring options become available.
I think that diverting some R&D resource to revisit some of these other motion translation mechanisms would be justified.
PJGD
RE: Geared Crankshafts in IC engines
RE: Geared Crankshafts in IC engines
The future trend in production auto engines will be continued downsizing with higher boost using a SI 4-stroke cycle. The high levels of boost with SI cycles are made possible by super accurate control of ignition, valvetrain and fuel systems. This allows the SI engine to run closer to its detonation limit more of the time.
As purely an academic proposition, factsb4pride's mechanism was an interesting topic. But from a practical standpoint, it doesn't seem to have merit. As the old saying goes, "A complex solution to a non-existent problem".
RE: Geared Crankshafts in IC engines
It is one thing to look at the efficiency of the engine as a separate entity, but in reality, the efficiency will be measured for the complete vehicle it is installed in, not just the efficiency of the engine.
Regards
Pat
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RE: Geared Crankshafts in IC engines
Why bother? A crankshaft works just fine.
RE: Geared Crankshafts in IC engines
Not that there is anything wrong with looking for new innovations, as without that there is no growth, but it reminds me a lot of the not-infrequent attempts to get rid of chained bicycle drive.