HKS Kansai carbon driveshaft coming - lighter than current carbon drive shafts
 

http://www.kansaisv.co.jp/sp_info/im...007pic_3_8.jpg

No pricing, still in development (I checked again this morning)

Weight is claimed to be 4.2kg, which is at least 1kg lighter than the current carbon driveshafts available.

Will post when I know more.

would love to have a ds this light, but not looking to spend 2k on this type of part atm.

Still, I'm liking where they are going. Thanks for posting this

How do you know it'll be 2k?

3 letters...
H
K
S

+ Kansai.

http://www.kansaisv.co.jp/index.html

http://www.kansaisv.co.jp/demo_car/p...odel=democar_1

Everything put on the car is $$$.

-alex

Man thats pretty

Carbon prop shafts for S2000 costs about 390000~450000yen so I think price should be around there.

Finally a company uses the correct weave.

Why is this the correct weave and by inference the others incorrect weave?

This is interesting. As I've tried a cf shaft let me explain what I hope this shaft has difference wise. I had a DSS shaft great piece btw. Acceleration and lack of slop was fantastic. No vibration or drive ability issues per say. Only I'm very sensitive "hearing wise" when I'd get to around 70-85mph there would be an air like noise, super hard to explain. Again no vibes etc but to me it was so different it was strange. Now I spoke in great length to some folks that had same concern again only hearing and they had their custom with microballs of styrofoam so like an acoustical filler if you will inside the shaft. I wonder if this shaft comes with any sort of coustic filler???

My other concerns is their glue and what rpm they're balanced to and how their balanced. Good find though gonna sub for updates thanks!!

I'm not going to get to much into this but it is basically the angles of the threads and how they braid the threads. The only reason I think this is done better is from reading lots about carbon fiber and how to make it stronger in different directions. Other shafts I have seen use unidirectional weave which is awesome for body panels and random parts made from carbon fiber but not in a shaft that is receiving really only torque and no other stresses.

Sent from my HTCONE using Tapatalk

Carbon fiber is a lot like wood - it's not uniformly strong in all directions. It's much stronger along the grain/weave than it is perpendicular to it. For a shaft loaded in torsion (in other words, pretty much every driveshaft ever made), the maximum loads will be at a 45 degree angle to the shaft. So, for a carbon fiber part (or fiberglass), you want the fibers to be wound at a 45 degree angle for the best strength with the minimum amount of material. Since it can be loaded in either direction (acceleration or engine braking), you want fibers wound around it in both directions, at 45 degrees. You can see this in the shaft above.

For some reason (that I do not understand), many carbon driveshafts instead have the fibers wound very nearly circumferentially, at least at the surface of the driveshaft. This gives very little strength against a twisting load (but it would be great for a pressure vessel, like a composite scuba tank). They must have fibers in some other orientations internally as well, to give them the necessary strength, but even so, the fibers wound circumferentially at the surface are doing almost nothing aside from adding weight - for a driveshaft, you really want all of the fibers at or near 45 degrees (you could maybe make a case for varying the winding angle between perhaps 30 and 60 degrees in the various layers, but even that isn't really necessary).

This also probably explains why they can make it lighter than other CF driveshafts. They also could be using a higher grade carbon - all CF isn't created equal. A standard carbon fiber might have a modulus (stiffness) of around 230GPa and a strength of around 3.5GPa, while a high modulus carbon will have a similar strength and a modulus of around 550-600GPa (so it's 2 or 3 times stiffer, but not a lot stronger). A high strength carbon fiber on the other hand might have a modulus around 300GPa (only a bit stiffer than the basic stuff), but an ultimate strength of around 6GPa or even a bit more (so nearly twice as strong as the basic carbon fiber). Of course, the high stiffness and high strength carbon fibers are a lot more expensive than the ordinary carbon, but using them can significantly improve the strength and stiffness (or reduce the weight for the same strength and stiffness) compared to a component made with basic CF.

Sick looking CF DS, this will be easily $2k or higher like others said HKS Kansai


Sent from my iPhone using TapatalkfQ

Interesting info :w00t:

Could the circumferentially wound carbon be a safty measure, to hold the shaft together better at high rpms?

Only if their manufacturing process is awful. The centrifugal loads on a driveshaft are pretty small, and the 45 degree winding is still fairly strong in that direction. Even with the driveshaft spinning a bit over 12,000 rpm (which is the equivalent of redline in 6th in an AT car, even though they actually couldn't come close to pulling that off in reality), assuming a 3 inch diameter driveshaft, the load is only about 6000G at the outer diameter. This sounds like a lot, but it's only about the equivalent (assuming all the weight is concentrated around the outside) of the load that would be caused by pressurizing the driveshaft to around 100psi (based on some rough, back-of-the-envelope calculations). That's a pretty easy load for a CF tube (even one wound at 45 degrees) to handle. Far and away the biggest load on the driveshaft will be from the torque of the engine (especially clutch dumps/launches/jerky shifts), not from rotation.

You could maybe make a case that you would want some fibers oriented to maximize the driveshaft's bending stiffness, so you wouldn't set up any transverse vibration modes due to any slight eccentricities or asymmetries, but in that case, you'd actually want the fibers running more parallel to the driveshaft, not circumferentially.


(isn't engineering fun?)

Well I'd like to try another cf shaft hope there's more info on this one soon!!

What's being done about the carbon fiber / aluminum interface?

Hopefully something. CF/Aluminum makes a pretty gnarly galvanic couple. No bueno.

@chrisl - are you sure about the wrap on other driveshafts? I haven't seen any up close but in pics the most apparent thing to me is the imprint left by what looks like a shrink tape (or just plain tensioned plastic wrap) final overwrap done before cure to consolidate the wind. That would be nearly perpendicular to the shaft. I can't see the other driveshaft manufacturers being so dumb as to waste material (and therefore $$$) on an inefficient wrap pattern but maybe I'm missing something.


EDIT-http://www.rallysportdirect.com/cata...z1256_4_lg.jpg

If you look at the above pic you can pretty clearly see the carbon is running more closely to a 45* angle than the lines left in the surface by the manufacturing process would indicate. This is the PST. Arguably a less pretty wrap job, but probably nearly as functional.

Cheers
Nathan

I've only looked at 2 aftermarket CF driveshafts in person, and they definitely had the incorrect wrap. I can't say for sure if that's common or not though...

As for that one in your picture, it's kind of hard to tell. I don't really like the small voids visible in the surface layer, but they aren't a problem so long as there aren't any deeper within the composite. The fiber direction is also difficult to see, though it does look like it's somewhere between diagonal and longitudinal, which isn't a bad choice. It does look like the surface layer is entirely wrapped in one direction, instead of alternately in both directions, but again, that isn't too much of a problem so long as a layer just underneath is wrapped the other way.

correct weave?

http://throughtheroofnunderground.fi...r_weave_01.jpg

Thanks for the info. It looked to me like there was some fiber running in the opposite direction in the bottom left of the shaft in that pic, but it is hard to tell. Would be pretty easy to sort out in person.

The voids look typical of a wet wound shaft done without an exterior mold/shaped vacuum bag. Not likely to have a huge strength impact but as you say, they are less than ideal.

Nathan

Just to start off, this is NOT to start an argument and more to help people understand about carbon fiber and how it is used.

As chrisl stated carbon fiber strands are strong in tension, and weak in every other possible aspect(think of a rope). So to get the most strength from the fibers you want the fibers to be in tension. In any other direction all the loads are being taken up by the Resins that are used to hold the carbon together.

The interaction of the resin, the type of resin, and amount of resin has more to do with how a carbon fiber acts when loaded then just the carbon itself. Resin makes up between 35-50% of the material, and can have not only your basic components but also things like nano-carbon tunes and fillers to make it stronger or flexible. The better the resin for the application the more load the entire matrix(term used to describer carbon and resin sample) can hold in all directions but ultimately it will be the strongest in the direction that puts load on carbon in tension.

Carbon fiber is made in layers, a single layer is thin (1/4" thick piece of carbon fiber is anywhere between 75-150 layers) and each layer can be oriented in a different direction to give you the desired results. The worst way to use carbon fiber is to make it quasi-isotropic (making it the same in all directions), so manufactures will mix layers and put material in different directions depending on what properties they want from the material.

For this application the ideal placement of fiber direction is along the direction of load, which is around the shaft in the perpendicular direction. However due to the weak bond between the resin and fibers the shaft would simply sheer if all fibers were in that direction. Then if you put all fibers in the parallel direction there would be no sheer issues but you have load issues were the shaft is not able to take high loads with out bending. So it comes down to a fine balance of each different aspect.

Last but not least, unless you are the manufacture you do not know what the manufacture has done to the carbon, what carbon they use, what resin they use, and in which direction they have placed the carbon elements. Carbon fiber is typically 8-20 layers deep and each layer plays a critical part in how much load the matrix can take and in what direction. The automotive industry is driven by aesthetics, so everyone makes the outside of parts look shiny and pretty. But with carbon fiber its on the INSIDE that counts. And given that people buy majority of parts on how they look on the outside, many manufactures go out of their way to make outsides of parts look more impressive then 98% of the rest of the product. No carbon manufacture will simply come out and tell you what resin and carbon they use, what manufacturing technique, what carbon lay up, and the curing temperatures/pressure as that is the "secret sauce".

So the moral of the story is simple, you simply cant look at a true carbon fiber part and say if its "good" or "bad" with out running tests on it or getting the manufacture to tell you the recipe to their "sauce" on how they made it and so forth. Its like looking at a cut of raw steak and guessing the age of the cow and where the cow came from with out knowing all the details.


Kirill
RallySportDirect.com

I agree with most of what RallySport says above, with one exception. Namely, this:


(warning: engineering-speak incoming)

In a torsionally loaded shaft, the direction of load is not around the shaft in the perpendicular direction. Instead, as I mentioned above, the principal stresses are at a 45 degree angle to the shaft. In addition, CF typically has a compressive strength nearly as high as its tensile strength (admittedly with some exceptions, depending on the type and grade of the carbon fiber). As one of the principal stresses will be in tension and the other will be in compression, a shaft with windings at the surface layer that are at ~45 degrees in both directions is ideal, since the fiber direction will align with both principal stresses (which are the two directions in which there is no shear stress). The only time you want the carbon wrapped perpendicular to the tube is if the tube has to withstand a crushing or expanding load, such as a weight set on the side of the tube, or if the tube is part of a highly pressurized system.

In a brittle material (in other words, one which fails due to tensile, rather than shear stress), the failure mode will be a helical fracture surface, as can be seen if you twist a piece of chalk to failure. A carbon driveshaft is admittedly a bit more complicated than this due to the interaction of the resin with the fibers, but this is still the basic failure mode for most fiber-reinforced plastic composites (fiberglass and CF, along with a few other exotic ones). By orienting the fibers at 45 degrees (perpendicular to this failure surface), their usefulness is maximized.

Interestingly, after going back and looking at some of my engineering textbooks, I might have to take back what I said above about the voids in the surface of that driveshaft posted by SubieNate not being a big concern. A torsionally loaded shaft has the maximum stress at the surface, and surface imperfections can cause stress concentrations that significantly weaken the overall shaft. Admittedly, most of these driveshafts are probably manufactured with such a large safety factor that you would never get close to their failure point anyways, but surface imperfections do apparently have a larger influence on the failure of a shaft in torsion than I had remembered. The driveshaft in the OP does appear to be better made in that regard, as it appears to have a uniform, smooth surface finish with an equal number of fibers wrapped in each direction.

Sounds like we speak the same language ;)

You are correct, its been a couple years from when I had to deal with stresses in a shaft under torsion. :bonk:

We can go for quite some time going back and forth but I think most of what needed to be said has been cleared up.



If someone wants to learn a little more about composites and fall asleep here is a good way to get your toes wet and possibly get confused of how loads in composites interact.

This is posted by one of the pioneering research Universities that specializes in the composite industry research.

http://www.mech.utah.edu/~rusmeeha/l...omposites.html


Kirill
RallySportDirect.com

Any updates on this HKS Shaft? Will production model come with front protective cup that will mate in nicely as well to keep out debris? :iono::iono:

+1 would like to know as well.

Did these guys ever make this shaft for sales/production?

I don't see it listed as an available item anywhere. There are a couple other brands of JDM CF propshafts and they are in the $3500-$4500 range... I can't see it ever being worth it compared to something from the US vendors.

Curious if anyone has more info if this will be released?