Con rod - Can you work it out?

Just for the crack - have at it in the comments


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[timmyreconski]

Well my real stab at it is telling me the angle of each of the piston bores in the mechanism would result in it wanting to move in one direction on the downstroke and the opposite on the upstroke due to dynamics and the piston angles aligning with the linear motion of the rod at certain points during the strokes. It also seems like the piston will block the oil from entering the bores when the piston is bottomed out in the cylinder. This stopping of oil and the shifting of inertial forces on the pistons due to the changes in con rod angle seems to be how it works without too much complication. The differing bore sizes seems to be due to the fact that the compression and combustion forces work to want to lower the cog so the fighting of that wanting to happen means one bore should be larger, and then when the cog is already lowered, the forces to keep it lower are less in magnitude so a smaller bore gets the job done. I am a structural engineer so in my world nothing is supposed to move. When dynamics get thrown into it, I get a bit light-headed. That's my stab at it. Probably a lot wrong in my guess, but I tried. Keep up the videos. I really enjoy learning and understanding as much as I can.

[cncdaddio]

Engineering virgin: I'm not ready to work out engineering porn.

[arrindaley]

No idea if I'm correct but...I'm feeling like it doesn't use solenoids or anything like that to control oil into the pistons because I can't see a way to achieve it, I think it's sensing cylinder pressure at bdc on the power stroke. If there's enough cylinder pressure to overcome the difference in the hydraulics between the two cylinders then it reverts to low compression mode. The different size cylinders would isolate out the effect of differing oil pressures as the difference between the two cylinders is likely to stay constant. It's going to need valving to allow the small piston to link to larger piston at bdc allowing the decision to be made. At bdc inlet if there's enough vacuum to overcome the hydraulic bias then it can extend back to the high compression state.
If this is the case I like it because it is acting when variable compression is actually required on a cylinder by cylinder basis and not when a designer or ecu thinks it might need higher compression.

[onhawaii]

The only thing I can think about right now is that the check valve is operated by velocity so the one opens in higher RPM and the other in lower RPM.

[hellishgrin]

(I wrote this before seeing all of the video to keep track of some initial thoughts, so I may edit it to remove answered questions... I probably won’t)

Interesting, does it work on oil pressure, or is there a centrifugal aspect as well? But would a small turbo/supercharger not be easier and less costly? How do you think this effects performance in terms of rotational mass? I’d also be interested if there weren’t an easier way to achieve this in the head itself with some kind of secondary pressure chamber too, as opposed to the conn rod. Imagine a system that stores some of the pressurized exhaust gasses from the previous exhaust stroke before the valve opens and then adds it to the next compression stroke. Think the hot gasses would make it combust better/burn more efficient?

I wonder how a telescopic cylinder head would work? Just lower it like you would pushing a cork into a bottle, only less of a friction fit. Though I suppose that could lead to valve interference... So more valves then? Gaskets would be a pain for that as well.

Ultimate side note here. What if they made a piston with a hollow chamber in the center with a tube that fit into it on the head that acted as the exhaust port, kind of like how nitro 2 cycles just use a hole in the cylinder. Imagine one of those cushioned hydraulic rams, but in reverse.. It would just vent as it reached the bottom of the stroke and maybe need to draw less air because of some potentially remaining hot gases left above the tube. A weird cross between a 2c and a 4c, but would still run like a 4c as the tube would still have an exhaust valve.

All I know is that mechanics would hate it, lol..

[lionelg-]

G'day Matt. I'm fucking fascinated by your CAD drawings. They're insane!

I haven't descended through the comments, but it looks to me like by adjusting the position of the eccentric boss pin receiver, it adjusts how high the piston is, and can vary the stroke length, and therefore the displacement.

Less displacement to lower the compression, and fuel and air; more efficient.

I can't see the pistons in the conrod actuating at 10, 000+ RPM for such a delicate piece. You mentioned that these pistons are actuated, or have check valves. They're usually associated with a pressure release when it gets too high.

Perhaps the high pressure from hard acceleration, blows the valve from pushing down on the cylinder piston, causing the conrod pistons to move the eccentric boss receiver, and thus increasing the displacement and more air.

More air on same fuel; leaner, more complete combustion, more power when it's needed.

Cylinder head pressure reduces, oil from pump and high centrifugal forces, force oil back into the other conrod piston, and the eccentric boss receiver raises to lower the displacement.

Dunno? Hahaha

[flatbrimsickdope]

How do you control feed pressure for each individual piston at the rod journal? So each rod journal has 3 feeds? Solenoids? Dump valves? Plumbing?

[LorenziLéo]

I'm pretty sure it's all about oil pressure.

On idle it's quite low, and gets higher and higher the higher the rpm are.

The conrod journal (and the whole engine) gets different amount of pressures depending on that.

So, here comes different pistons sizes in the rod.

On the low oil pressure, you should get the high compression position, and in high pressure, low compression.

My guess is that the small piston gets filled quicker than the big one at low pressures, or at least than the oil inside the small cylinder is enough to withstand the compression and keep the high compression position despite the small leverage.

Higher pressures would overcome that and push the big one instead, with bigger leverage and more force/oil pressure.

I think that very precise pistons clearances/sealing are the key to make everything work properly, as the oil has to leak around the big one to be able to change compression positions.

My guess again is that there is enough pressure to seal the small piston at low rpms, but not enough to seal the big one.

When higher pressure comes, the big one seals and overcome the small one.

Am I in the good way?

[petrolheadJJ]

Oil pressure is directed to one or the other piston so the see saw can change positions. Higher or lower compression ratio. Piston acceleration/deceleration make the thing flip positions after the oil pressure is switched from one to the other piston.

[kckyscotland]

Looks like a mixture of variable valve timing and hydaulic valve lifter technology, varying the length of the stroke to alter the compression. Problem being through time there will be variations in wear across the cylinder bank causing horrendous imballances, and even more horrendous repair bills. Glad I'll be dead before they ram this shit down our throats.

[jamesbower]

Higher compression at lower loads and lower compression at higher loads. Very good for efficiency and boosted performance.

[pgtmr]

Oil pressure moves the tiny internal pistons, changing the effective length of the rod while in motion, changing directions as the crank rotates and delivers oil through crank passages to the other side of the rod. Less drag on the crank on the upstroke.

[eozdzfy]

And the pistons are operated by check valves that are controlled by ither boost pressure or the ecu thats reading off a map sensor or something along them lines as a guess

[JPMotorhead]

It’s controlled by oil pressure, either indirectly by rpm or a variable displacement/pressure oil pump.

Oil pump goes into low pressure mode and con rod responds by actuating the pistons for high compression. Both benefitting fuel efficiency.

Vise versa, oil pump goes into high pressure mode and con rod goes into low compression mode to support high boost/peak cyl. pressure.

[petrolheadJJ]

Bloody hell. Is there some pin locking the splined Seesaw thing in position?

[WillsStuff]

Are the two cylinder feeds from a single or two different sources from the crank?

[brianrhubbard]

With a cam free valve-train one could really put down some power with this piston design. Would make programming simpler also. Since the quill at the wrist pin looks to be mechanical also oil pressure will work but does the actuation happen at BDC?

[brianrhubbard]

I remember in college Toyota used the Atkinson stroke technology on their hybrid engines. I have never seen an eccentric wrist pin. It just makes sense. I would think that the piston skirt would clap or chatter during the actuation of the eccentric. The more I look at it I think your on to something.

[stephenward]

At low RPM it is in a high state of compression and as the RPM increases the pressure in the rod galleries decreases and the compression ratio drops?

[adrianaugustus]

Matt did you ever get round to doing the follow up videos? I agree, this is a fascinating bit of engineering - just checked out FEV website - thanks for sharing and making an awesome 3D model to demonstrate it. With that extra mass one might wonder how much benefit it brings (F=ma and all that) but compared to the reaction force F from the crankshaft the delta is likely insignificant.