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 Are objections to this design of engine based on current realities, or outdated facts and opinions?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.

 

[PJGD]

Looking at where we are today and where we have come from in terms of engine technology history, I would back the crankshaft-and-conrod solution too. My next move might be to adopt the cross-head, but that makes for a rather tall engine.

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

 

[BrianPetersen]

As someone else noted ... long rods, and offsetting the crankshaft centerline relative to the cylinder centerline so that the power stroke occurs with the rod more vertical, both reduce piston side-load, and they do it without introducing any uncertainty or non-standard manufacturing practices, and both solutions are in production today.

 

[tbuelna]

As many posters noted, modern automotive production engines look like they do for a very good reason. It's the best compromise when all requirements are considered, especially costs. Piston skirt friction losses are not that significant. And making an engine's crank assembly more complex and costly just to reduce this small friction loss slightly is definitely not justified.

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".

 

[patprimmer]

Apart from cost, if the engine is heavier and/or bulkier the small efficiencies gained by reduced friction on the piston skirt will very quickly be lost when carting around a heavier engine or the aero losses if the cylinder head needs to be higher for the same bore and stroke.

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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[dicer]

Gears / a transmission = more losses

Why bother? A crankshaft works just fine.

 

[izzmus]

But it's the same system that's been in use since the 1800s. It is old therefore it is bad.

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.