F1 pankl conrod

[F1_eng]

"the conrod cap will always stretch more than the bolt, "filling up" any gap that will form"

I take it you mean this will occur during dynamic loading?
If so, it is certainly not true. Both components change in length during dynamic loading must be equal, until the joint separates.
You also seem to be implying that the bolt will be stiffer than the cap, again definetely not the case. If this were true, the bolt would be taking the majority of the alternating load.

You don't need a finite element model to calculate the axial stiffness of the con-rod bolted joint, just a simple hand calc.

There is absolutely no need to be investigating separation of the joint, the two bolts will be excerting a clamping force of much more than double the maximum inertia loading. I would put money on the fact that one of the bolts could provide enough clamping force.

Why don't you perform a calculation to eastimate the axial clamping force an M8 or M10 bolt produces when torqued up to a generic value or a percentage of yield. You would at least then have an appreciation of the joint clamping force and be clear in your own mind that it is not an issue.
If you want I can do a random calculation for an M8 or whatever size bolt's axial force.
Or you can attempt it yourself which would be more beneficial.

[PlatinumZealot]

"Filling the gap" was just an exaggeration to illustrate. I know there is no separation, just read all my posts in this thread. Riff-raff's point is valid, I was the one that said if the clamping force is high enough why the notch anyway, But thinking about about it, lowering the joint stiffness can allow you to use a lighter or softer bolt, so that is good.

I did my little hand calculations like in my little diagram above. But one dimensional calculations is not enough for this thing.

So, I have joined you guys in this bolt stretch thing, and thanks to Riff-raff it is now is now done and dusted. However, I think the design has more secrets like the slant cut.

[F1_eng]

I dont think I agree that the bolt stretching thing is done and dusted, what was the conclusion you guys came up with?

[riff_raff]

F1_eng,

My conclusion remains the same. The little semi-circular notch makes the cap section less stiff in compression. All other things being equal, this would result in greater axial deflection in the cap, for a given static preload force. However, if nothing is changed in the bolt, its axial preload strain should remain unchanged. The greater preload axial deflection within the less stiff grooved cap section is compensated for by an increased engagement of the bolt screw threads.

riff_raff

[F1_eng]

And do you now see that this grove is a way of tuning the stiffness ratios between bolt and cap which changes the bolt alternating force?

This is exactly what I said right from the start but I am still not sure people have understood the concept of the bolt alternating force and how it is influenced.

[mep]

I must agree with F1-eng.
After he called us stupid half rated engineers I took out a book and checked this stuff.
In fact it seems like it is possible to affect the screw force by the stiffness of the plates you are connecting. There is a nice diagram where you can see the effect. I just had not found the time to post it here.
The effect of the slot on the screw is really stunning and goes against your logical intuition.
However the thing is still not done.
New questions arise by this.

[ringo]

The same thing can be done with nut material, bolt material, cap material,
groving, using washers or even drilling a hole through it.

There can be more to it than stiffness. Why is it the newer rods don't have this groove?

[AvalineV8]

Guy's, This bolt discussion has been great. Sadly, my enthusiasm outweighs my technical ability, but I have been enthralled in the details of the design of the bolt and big end cap.
Looking forward to your thoughts on why the mating surfaces of the cap/rod are tapered?

Thanks...

[PlatinumZealot]

And do you now see that this grove is a way of tuning the stiffness ratios between bolt and cap which changes the bolt alternating force?

This is exactly what I said right from the start but I am still not sure people have understood the concept of the bolt alternating force and how it is influenced.

Considering the pre-loads are the same, the notch doesn't change the force in the bolt as compared to no notch (all tension is provided by the bolt). You said it again!

The difference with the notch is that now you can use a stiffer material for the connecting rod and get stiffness where you need it, and compliance where you need it. Additionally you may use a less stiff bolt, or less preload, or leave everything the same and get a larger margin of safety. Which I think you already know, but I am just rephrasing.

On the other hand I still think there might be something else to it as I said from way back when.

On the the alternating loads it is not the only reason to use a pre-loads. You can still use bolt preloads and soft flanges with steady forces. In fact most applications, fasteners, bearings and springs are preloaded.

[F1_eng]

"Considering the pre-loads are the same, the notch doesn't change the force in the bolt as compared to no notch (all tension is provided by the bolt). You said it again!"

Nobody is saying it changes any pre-load force. I am saying it changes the ratio of how much of the alternating force is taken up by the cap and bolt. This reduces the magnitude of the alternating force. As you increases the bolt mean stress, the allowable alternating range of stress decreases. Since you normaly tighten close to yield, you already know that the allowable alternating stress is going to be fairly small. Any reduction in the alternating force can have a large effect on the factor of safety, especially when working close to the yield point.

[PlatinumZealot]

That Is why I said assuming the same pre-load. So when you replied I thought you meant a dynamic change while the engine comes up to speed. But yes, the ratio of alternating force will change if you use a different pre-load.

[rrrocket]

Brian G: do you have the mass of this conrod available?

My guess is about 195 grams...

[Sayshina]

The V layout was the ideal shape for air ducting under car, and up around engine. The 4 pot will take a lot of work to get the same effect.

In what way does a V layout offer superior underbody aero performance to an inline 4? Assuming of course you don't lay the 4 over past where the near side v bank resides.

Also, rumor has it the 4's will be strictly vertical, by rule.

[TauToadmiester]

What is/was the bearing surface?

I assume a plain bearing but Honda used, when only a engine supplier (maybe when a car team as well), a bearing ingredient that was so delicate that a bare finger would destroy it, they had to apply it using special gloves and NEVER touch the surface, they later used it for some road cars as well (hard to believe).

This special surface ingredient held/suspended the oil (much better than normal plain bearing surface) to make a superior bearing surface, just wonder what is used today with highest technology?

Anyone know?

[riff_raff]

TauToadmiester,

With journal bearings, I don't really think having a surface coating that "held/suspended the oil" would be of benefit. Creating sufficient hydrodynamic oil film pressures in the bearing is not usually a problem. But keeping the bearing cool usually is, so the mass flow of oil through the bearing is critical.

Having accurate bearing/journal surfaces with minimal roughness helps maintain full oil films at high loads. Having crankshaft, conrod, and crankcase structures that don't deflect under mechanical loads or temperature variation is critical.

Journal bearings use several thin surface layers of various materials, and each material serves a specific function such as embedability, adhesion, or heat transfer. The shell backing material is usually a metal that has sufficient surface compressive fatigue strength for the bearing's oil film pressures. A shell material with good thermal conductivity is also desirable. And shell materials that have a CTE match with the journal and crankcase or conrod also helps.

riff_raff