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Discussion Starter · #221 ·
Re: (MeisterBrau)

Quote, originally posted by MeisterBrau »


What about changing the teeth so they make better contact? Would we feel comfortable doing this or do we need to make prototypes and test?

This is critical with a new part, but yes, we would need to test.
 

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Discussion Starter · #222 ·
Re: (FEO)

Quote, originally posted by FEO »
Alex ( & associated expert):

what is your opinion on a plasma coating like the one described above by ShortCircuit

price should also be considered....

dung < old OEM < Nitride-coated OEM < stainless < machined + plasma < machined+hardening < ??

(please fix/add my chain above)

I guess the question is, at what point is it overkill? this is not going into a 40 ton tank



Basically any coating will not have the same long term benefits of case hardening since it merely adds a hard shell over the soft core (think like an egg), this is what the nitride coating Volvo used does. Case hardening goes much deeper and penetrates almost the entire tooth on the gears so this would be the preferred method in this case.

With the stainless steel part, cost is the only real issue. SS costs more, but you would not need to treat it after machining, the case hardened part would take more labour and processing to complete but the material is cheaper.
 

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Re: (adykes)

Quote, originally posted by adykes »

With the stainless steel part, cost is the only real issue. SS costs more, but you would not need to treat it after machining, the case hardened part would take more labour and processing to complete but the material is cheaper.

What about brittleness and the possibility of catastrophic failure at high peak loads? Do we really think Volvo picked a soft metal just because it was cheaper? Ductility might be needed to some degree?

Also, if the teeth fit the same, a harder part makes it more likely that the angle gear input shaft would become stripped, right? Which is a much more expensive fix...
 

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Discussion Starter · #224 ·
Re: (MeisterBrau)

Quote, originally posted by MeisterBrau »


What about brittleness and the possibility of catastrophic failure at high peak loads? Do we really think Volvo picked a soft metal just because it was cheaper? Ductility might be needed to some degree?

We are discussing a stainless allow that has the appropriate ductility required. Not all stainless steel alloys are necessarily more brittle than what is used, allow selection is important.

Quote, originally posted by MeisterBrau »

Also, if the teeth fit the same, a harder part makes it more likely that the angle gear input shaft would become stripped, right? Which is a much more expensive fix...

As I keep saying, the new part will need to have a better fit. This is NOT a discussion of making an identical part, this is a discussion on how to IMPROVE the part and that has to components: materials and design.

The materials have been defined and the need for a design correction has been identified and needs to be measured with greater precision to have prototypes made. Chilled Man is our point man on the replacement part as he has access to input/output splines more readily than I do unless we want to try to convince IPD to join the party.
 

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Re: (adykes)

Given the measurements, I could possibly provide a 3D model (I'd have to sweet talk a couple of our designers, but I've got access to Pro/Engineer).
 

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Discussion Starter · #226 ·
It would be handy if we could get reliable moulds of the input/output shafts off a few cars, but that might be a tall order.
 

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Re: (adykes)

In all of VOLVO's infinite wisdom, don't you think VOLVO engineers are aware that these parts "fit" the way they do? And if they do, is it THAT MUCH of a burden for them to have redesigned that part and put it in production which would have had better teeth fit? Playing devil's advocate, I wonder out loud if the part needs to be designed this way while "cold", and "warms up" upon driving making these parts fit better together - and that was VOLVO's design criteria. Is it possible that these metals expand in such a way that the parts are, in fact, a perfect fit once "warmed-up" via driving xx miles?

This needs to be answered before we go ahead and attempt to improve the teeth-to-spline engagement/fit.
 

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Re: (Short Circuit)

the other thing is that somewhere is the cad file for this thing which would make things so much easier (i.e no reconstructing the gear cad model)
 

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Re: (98glt)

And what do you think the chances are of Volvo giving that up?

Slim None

Somewhere between the two!

Heck, they won't even acknowledge there's a problem or participate in this discussion
 

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Re: (Short Circuit)

Quote, originally posted by Short Circuit »
In all of VOLVO's infinite wisdom, don't you think VOLVO engineers are aware that these parts "fit" the way they do? And if they do, is it THAT MUCH of a burden for them to have redesigned that part and put it in production which would have had better teeth fit? Playing devil's advocate, I wonder out loud if the part needs to be designed this way while "cold", and "warms up" upon driving making these parts fit better together - and that was VOLVO's design criteria. Is it possible that these metals expand in such a way that the parts are, in fact, a perfect fit once "warmed-up" via driving xx miles?

This needs to be answered before we go ahead and attempt to improve the teeth-to-spline engagement/fit.
We think alike - I've been pondering the dynamics of this assembly as well. If the fit is too exact, without a coating to reduce friction, one might run into a problem separating the collar after extended usage - even more so than the current collar. Have no calcs to back this up but second the fitment concerns.
 

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Discussion Starter · #231 ·
Re: (ZenZone)

Quote, originally posted by ZenZone »

We think alike - I've been pondering the dynamics of this assembly as well. If the fit is too exact, without a coating to reduce friction, one might run into a problem separating the collar after extended usage - even more so than the current collar. Have no calcs to back this up but second the fitment concerns.

The problem removing the collar gear at present has nothing to do with the fit, it has to do with Volvo trying to solve the fitment problem by epoxying the collar in place.

With a case hardened part you don't need a coating, remember these parts do not need to have play in a perfect world, this is a spline connector not a gear in the traditional sense, grease as Volvo recommends is all that should be required. Remember that the fitment is the reason even the current part is failing, if the fit was better failure rates would be much lower even without changing the material.
 

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Re: (adykes)

Quote, originally posted by adykes »
With a case hardened part you don't need a coating, remember these parts do not need to have play in a perfect world, this is a spline connector not a gear in the traditional sense, grease as Volvo recommends is all that should be required.

Since it is case hardened and basically open air, expansion/contraction due to temperature differentials should not be a concern either. Looks like it's on to the angle gear assembly -

Thanks again http://********************/smile/emthup.gif
 

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Re: (adykes)

I'm trying to think of a good analogy to describe the whole 'poor fitment' issue, but can't... Why? Because who in their right mind would design a part that DOESN'T FIT PROPERLY?!?!?

Why on this green earth would you want a CAD file of a part that doesn't fit? What you could possibly use is the schematic of the parts that it fits INTO... and on that note, you can give the engineers the 'benefit of the doubt' and think that the collar gear was properly designed but the way it was manufactured caused the defect, so all bets are off


Again, my hat goes off to all of you folks contributing to the effort, as it is a truly amazing accomplishment. Find me another automotive forum that would take a solution like this to the extreme that this has gone. Bravo~!

... still trying to think of an analogy... cannot.
 

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Re: (98glt)

Quote, originally posted by 98glt »
the other thing is that somewhere is the cad file for this thing which would make things so much easier (i.e no reconstructing the gear cad model)

You don't need a 100% accurate cad model of the teeth for a shop to make a gear or spline, you specify the spline (or gear) by pitch, # of teeth, and fit quality. You can even schematically draw it by using dashed lines for the minor, major, and pitch diameters, instead of drawing teeth. And even if you had a 100% accurate CAD model, you can't just give that to any CNC shop and say "make this" as the teeth need to be generated using dedicated spline or gear hobbing equipment in order to meet the fit criteria. We just have to hope to high heaven that they used a standard spline.

If you guys need a CAD model and/or an engineering drawing, I'm an ME with SolidWorks on my home PC. I'd be willing to model/draw parts up for the community.

And if the choices are between 300 or 400 series stainless and 4140 steel, I'd say go with the 4140. It has up to 5x the tensile strength and 8x the yield strength. Which means it's both tougher and less mushy. I suspect that'll be the case with most stainless steels unless we get into real exotic alloys (or stuff that's so unmachinable that the cost skyrockets).

4140 with a nice nickel or chrome plating on it would be both very tough and highly corrosion resistant. I'd have to do a little more research to figure out which plating would be tougher. Also we could do a thin case hardening on it to maintain toughness at the core but give wear resistance. There are also semi-exotic film lubricants available that aren't expensive. Basically a micro thin paint that is tough enough to not come off, used to lubricate geartrains in environments where grease is not allowed, like the hot zone of nuke plants or nuclear submarines. It's good stuff, but I don't know how it would last in a contaminated environment.

I've been cruising the web looking for a steel with 350,000 psi tensile strength, and have found very little info. Not calling your data into question, but it appears to be a pretty exotic (and expensive) alloy if that's right. The highest "regular guy grade" steel is 260,000 psi. An oil quenched 4140 can hit 230,000 psi.

On the other hand, as was said over and over, the failure mode isn't breaking of the part, it's wear. Theoretically we should be able to improve the fit and coat/plate the part and get what we need out of it. Case hardening combined with thick chrome plating and an improved fit might solve the problems.

I do have a few questions and comments, as I'm completely inexperienced with this assembly:

Is this thing not able to be kept greased? Is it exposed to the environment or is it in a sealed chamber? Because a good packing of grease goes a long way to preventing wear and corrosion. Also, if it's not sealed, it might be a good idea to explore sealing options so that grease can stay packed and clean inside the assembly.

I'm wondering if the part is designed so sloppy because the angle gear case has too much tolerance on its mating to the transmission, and the spline needs to have a little tolerance for misalignment. I'd hope not, as that's a recipe for wear, but I was just thinking of cases where that might make sense. Does the assembly have dowel pins lining it up?

As far as thermal expansion, the steel in the temp ranges we're talking about will only expand a few thousandths of an inch at most, and most steels (even of wildly different alloys) have coefficients of thermal expansion so close that the difference between the parts' relative expansion rates will be negligible. It'll definitely be lower than the limits of manufacturing tolerance itself. So in my opinion that amount of slop is definitely not to compensate for thermal expansion, and that as long as we're sticking to steel on both parts, thermal expansion is a non issue.

There's been a lot of talk about fusible links and failure points. That failure point should be where the tires meet the road, and I can't imagine a designer doing anything different. That's a fairly predictable shear, or at least it should be. Of course, generated power is also a known, so all components should be able to handle said power with a factor of safety. I know this has already been debunked, but just wanted to throw that in there.

Anyway, let me know if I can be of any help. I don't even own an AWD car!
 

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Re: (LloydDobler)

Hasn't it been determined that the o6-07 gt has a very low failure rate? Does this gear fit with any greater tolerance than than the MT part?
 

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two quick points.

Xc90 V8 part is case hardened but the R MT part redesign has a nitride coating. Case hardening would prob have been better but nitriding allowed use of the same part with a coating and was a cheaper redesign???

Second prob. Failure seems due to wear due to fitment issue. Exacerbated but a soft material. Even with a harder part this is a problem. Too early to tell if redesign part fails in the same way.

how about comparing the spline design of the XC90 V8 part verses the MT nitrided or original. Is the fitment really different. Can it be copied in the planned redesigned R MT part?

My guy feeling though is that the material is the problem....splines deform under load due to soft surface which then starts the whole wear mechanism and eventually slip of the connection.

would volvo not have redesigned the fit of the part at the same time of launching the redesigned nitrided part?

Rear wheel Paul, dont be naive. Of course and engineer from volvo would not take part in a discussion like this openly and wave their "I work for volvo on this project".

only way would be to use a random login name and just happen to be very helpful and strongly suggesting a route that the redesigned part would take......
 

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Discussion Starter · #237 ·
We have not yet been able to find anyone with an XC90 V8 that has had this part fail, nor have we been able to find an 06-07 GT R owner who has had this part fail. All the new S80/V70/XC70 cars are likely still under warranty so we won't find any there. As such, we cannot tell whether the fitment is any better on those cars. Remember that the XC90 V8 part is very different, different diameter, number of splines, size of the mating area, etc.

My concern with fitment is that we have seen a small selection of collar gears and they all show that the input/output splines are of teh same dimensions, but what we do not know is what the variation in manufacturing is. Are they all very very close to the same size or not? We need to find this out, or just go forward with what we have and correct as we encounter a problem.

With the mass spectrometer you can approach a range of alloys but being exact is beyond the abilities of the instrument that was used. 4140 is fairly close in composition, but there are a few other elements present in the XC90 gear. According to the guys at BAE a well case hardened and then oil quenched 4140 that was machined in the annealed condition and harded afterwards would be quite close to the current part at the surface which is the important part. Case hardening is like an egg in a way, hard on the surface soft inside, but the hardened portion goes much deeper than a simple coating. According to the transmission guys at BAE a simple plating on the part would not correct the problem, especially if the fitment issue was not addressed, since the coatings are so thin it would just wear slightly slower, this is also evident with the nitrided replacement part that Volvo introduced sometime late 2006ish.

Corrosion is not a significant issue with this part. It is not "sealed" per se, but neither is it just out there in the open. It is in this bizare little area between the transmission and the angle gear where the two metal cases are bolted together and sit flush but without a seal. For the most part dirt and water are kept out but moisture I'm sure can get in as it is not sealed. The two used parts we tested had been in the cars for between 40,000 and 60,000 miles and showed corrosion consistent with a sealed environment. Be that as it may, it is still advisable to grease the part as per Volvo's instructions.

Misalignment could be a plausible excuse for the poor fitment, as could reducing any stress on the seals as a result of misalignment. Inspection of the wear patterns on these two collar gears indicates that there was not a noticeable misalignment of input/output shaft, but based only on this we cannot say with such a small sample size that this is representative of all AWD P2 cars. However, Volvo epoxied both sides of this part on a large number of Rs which is why some people / shops have had a hard time removing them (and they used it liberally) because they used epoxy, that would reduce the play and fill in the gaps at least temporarily which indicates that the alignment is most likely spot on for most cars, with the available evidence I do not think this is a significant concern for this application.
 

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Re: (casperl)

Quote, originally posted by casperl »
Rear wheel Paul, dont be naive. Of course and engineer from volvo would not take part in a discussion like this openly and wave their "I work for volvo on this project".

I'm not naive at all. I'm hoping to drive home the issue that Volvo has failed its owners wrt:

1. the design of the original;
2. service support; and
3. replacement parts.

I think we would all agree that a really good company would say:

"Yeah, we note the problem. We've learned a lot as a result of user-trials and failures in the field. We've made a part that is better (with before/after specifications for hardness, tensile strength, galling, corrosion resistance, etc.). This part is available for all older Volvo cars, with p/n as follows..."

This isn't an admission of guilt. It's an acknowledgment of documented problems. It's providing support to owners who are facing some expensive repairs and are worried that they'll have to repeat repairs in a few more years.

So I'm not naive. I'm just wishing that Volvo would show some leadership on this issue.
 

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Re: (RearWheelPaul)

Quote, originally posted by RearWheelPaul »
I'm not naive at all. I'm hoping to drive home the issue that Volvo has failed its owners wrt:

1. the design of the original;
2. service support; and
3. replacement parts.

I think we would all agree that a really good company would say:

"Yeah, we note the problem. We've learned a lot as a result of user-trials and failures in the field. We've made a part that is better (with before/after specifications for hardness, tensile strength, galling, corrosion resistance, etc.). This part is available for all older Volvo cars, with p/n as follows..."

This isn't an admission of guilt. It's an acknowledgment of documented problems. It's providing support to owners who are facing some expensive repairs and are worried that they'll have to repeat repairs in a few more years.

So I'm not naive. I'm just wishing that Volvo would show some leadership on this issue.

Paul, you need to understand that Volvo is only responsible for ensuring that the car and all parts last and function properly for the duration of the factory warranty. After that, we are all on our own. Extended warranties have nothing to do with this as they are independent. The fact that the standard warranty costs IIRC $2500 for this car tells you what the expected cost of repairs is between the end of the factory warranty and the extended one, minus whatever profit margin they have.

So Volvo may never make such a statement or apology or whatever you want to call it, simply because most Rs are just fine within the 50k miles of factory warranty.

It's like buying a tv. It comes with a 1 year warranty. If ~1%-2% of them burn up during that 1st year, call it a normal failure rate and fix under warranty, but when the tvs start burning up after that 1 year more and more...oh well, it's out of warranty. The tv manufacturer might even be happy that his 1 year tv lasted 5 years...
 

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Re: (S60R1)

As customers, you are treated only as well as you demand.

If folks are happy with the service life of the spline and gear, so be it.

BTW, we're not looking at a 1-2% failure rate, are we?
 
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