Connecting rod design 2

[Aled87]

Hi,
I'm looking for a good book on connecting rod design, i.e. forces, fatigue stress, optimisation, etc. Does anyone know if there are any out there? some guidance would be appreciated

Many thanks,

 

[140Airpower]

dicer, I agree that the H-beam rods I've seen tend to be wider in plan form than any I-beams. This is probably necessary to make up for the low area moment of inertia (MOI or 2nd moment of inertia) of the H form compared to the I form with respect to the plane of rotation where the main bending moment exists. The other expedient for increasing strength in the plane of rotation is to increase the section -the amount of material and the weight. So, an H-beam will be heavier than an I-beam for the same strength in the plane of rotation. However, inline6 pointed out that the H-beam is lighter than the I-beam for the same strength in tension.
The H-beam rod obviously has other advantages not explained in this analysis otherwise it would not be the preferred design in so many areas of racing. From what I have read, it is only in F1 where H-beams are definitely not considered suitable.

 

[patprimmer]

If you look at F1 rods, they are neither true "I" or "H" beam. They are a complex composite design that requires considerably more machining. F1 budgets allow for a considerable cost for a small weight saving.

I still think the initial popularity with "H" beams was relative simplicity of machining from billet at the time they became popular.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[140Airpower]

Pat, I think that Fred Carrillo actually believed in the H-beam configuration. True, it is the cheapest shape to machine from billet or from a forged blank, assuming it is required that the rod be fully machined. I suspect he was influenced by Taylor's observation that the H-beam is inherently stress-free compared to an I-beam. It meant Carrillo could make the most reliable rods. A big advantage was that the kind of big-end you would want to use with the H-beam was naturally stronger than the way most rod big ends were being made.
I think that serendipitously they learned that the disadvantage of the H-beam (being not as strong as an I-beam) was not so important in practice. In any case, H-beam rods have been popular in high buck racing except for F1 since the days of the extreme rpm challenge.

BTW, although some F1 rods are weird, others are straightforward I-beams with added reinforcing ribs between the big-end bearing eye and the beam flanges. Back in the '80s, when rpms were not much higher than 12,000, many F1 engines used H-beam rods.

 

[Tmoose]

When it comes to current F1 engine design the only "what" I have access to is on the Internet. Not much incentive for a manufacturer to reveal all, or even very much there.
Even if I really knew "what" this year's F1 con rod looks like, I'm not real confident in my speculative powers about the "why" behind the design decisions without input from the designers. And even then, I'd want to compare their techno-confessions made when sober, drunk, and under the influence of truth serums.

Suzuki GSX R600 has been rated max power at 13,500 rpm or so for a few years.
At Suzuki.com Suzuki says this "The GSX-R600 engine revs to 15,500 rpm, the highest figure among production Suzuki bikes, and similar to racing machines."

http://www.suzukimotorcycles.com.au/bikes/road/supersport/2011/gsx-r600.html

They come with a 12 month limited warrantee.
Their rods reportedly look like this.

http://static.zigwheels.com/media/content/2011/Mar/main03_2011gsxr750-600_560x420.jpg

 

[140Airpower]

Tmoose, we have pictures of rods from the 17,000 - 20,000 rpm V10 era which show what worked then. Knowing F1, you are right that they would not have stopped development even with a 18,000 rpm limit, so today's rods could be different. However, the most recent photos we have are still valid for this rpm range. The discarding of the earlier H-beam and the comments of the F1 engine designers about not using H-beams are very instructive.

The Suzuki shows what can be done with steel valve springs. The rods look like "ordinary" I-beams.
The main bearings look small for lower friction, but looks like there is little pin overlap. This is an F1 characteristic.

 

[BrianGar]

Pat,
agreed. They cannot be called ''I'' beams as I mentioned before. A recent chat with Sauber guys in Paris led me to believe they call them A beams. Not for cross-section form, but the Elevation outline. The cross-section is a mishmash of different forms as you mentioned.
I sectioned a ti rod not so long ago to get a feel for material position. Ill post some pictures once I find all the bits.

Brian,

 

[140Airpower]

Brian, maybe you cannot call them I-beams, but Mario Illien called them I-beams. In the comparison of I-beam vs H-beam in F1, Illien said "not H". This is consistent with the photos of F1 rods that I have seen. Do you have any pictures that show what you are talking about or even a good detailed description would be good. Note that reinforcing the web of an I-beam with ribs and struts is common in many engineering uses of I-beams. It is not so common to reinforce the flanges with ribs as we have seen on the Cosworth and Ferrari rods.
"A-beam", if referring to a straight tapered rod, is not related to the beam cross section at all. There can be A formed H-beams, I-beams, X-beams, hollow-beams, etc. All F1 rods I've seen over many years are wide, tapered rods in either H or I beams. They all have a curved taper except for a BMW H-beam from the early '80s. There are a lot of straight-taper aftermarket rods.
I wonder if the Sauber guys have anything to do with Ferrari engine design? Can you ask them what are the engineering reasons F1 stopped using H-beam rods since H-beams are very popular in other elite classes of racing?

 

[BrianGar]

Im not calling them anything really. But what I am stating is they cannot be compared to ''I'' beams for engineering purposes, or depending on where the most mass lies in the rod because they bare no resemblance at all in either description.
Fair enough if you want to label them I's but thats just a terminology row then, and pointless.

I believe, and will settle on that they are a combined design, with some.

I will dig out the pictures in a week or two. They are on a dead drive that is currently with data recovery solutions in Dublin.
If they dont come out ok, Ill take more. Hopefully I still have all bits, as I gave a box of stuff/cutaways to a local school recently as learning tools.

peace,

Brian,

ps, Ill ask a few questions the next time Im with some engine guys,
pps, I dont think there is any 'best' design. The best design comes from thousands of euros, a lot of lads staring at screens, best materials, and a whole load of testing. The final shape is just a by-product of all the 'trimming'. Keep in mind too that all that has to tally with the working targets/endurance/lifespan in hand.

 

[140Airpower]

Brian, that would be great.

 

[dicer]

http://www.bmeltd.com/rods.htm

Here is an example of a nice con rod design.

Personally I can not understand the love affair with the H design. Who in a right mind would want 2 skinny edges with not much skin area as the beam? Does anyone know stress and strain anymore?

http://www.youtube.com/watch?v=uTpRfREYa9Q

This shows the dynamic bending moments setup in operation. And how many overhead crane systems use an H beam, ie the beam twisted 90 degress? I think H beam is a cool factor marketing tool.

And yes look at something like a GSXR motorcycle, just a good old I beam rod, not fancy at all. 13K rpms and very high power density.