REM Polishing transmission gears and final drive? 1

[ads22]

Has anyone seen objective data re driveline loss reduction via the so-called "REM" micropolishing of transmission or final drive gears?

I've seen some claims that are kind of hard to believe, and wonder if anyone here has any actual data?

I'm rebuilding a fwd transaxle for road racing and considering this, but doubting that any really significant gains are to be had.

I can see durability gains from eliminating stress risers, but my power level is low enough that I don't foresee fatiguing the teeth. I can see possible significant reductions in a hypoid gearset, as I believe that that tooth pair type has significant sliding - but my R&P are simple helical gears.

Thanks in advance!

Al Seim

 

[TVP]

REM Chemicals has a number of publications on this subject, but if you are looking for some independent corroboration, both NASA and the US Army have evaluated superfinishing (or polishing or whatever name one wants to use). Use the following links for more information:

http://gltrs.grc.nasa.gov/reports/2005/TM-2005-213958.pdf

http://ammtiac.alionscience.com/pdf/AMPQ7_1.pdf

 

[TVP]

This is actually the NASA paper I was originally thinking of:

http://gltrs.grc.nasa.gov/reports/2000/TM-2000-210044.pdf

 

[ads22]

TVP -

Thanks!

I've contacted REM for their tech info.

An obvious fear re the REM data is that, given the large scatter of automotive dyno results, it is so easy to "cherry pick" an outstanding result. And no marketing department worth its salt would fail to do so, at least to some extent!

It will be interesting to see what they have to say, and if they can cite any independent testing.

Skimming the papers referenced in your links - they look quite convincing on the subject of fatigue life, but barely touch on the subject of power loss. There is one mention of a known 30% reduction in frictional loss, which is intriguing. But I have no idea how significant the frictional loss is in a typical helical gear application. I think that it is significant in a hypoid gear.

(It is interesting that the authors of the paper attribute part of the fatigue life increase to friction reduction, not just to removal of stress risers.)

Anyway, thanks again.

Al Seim

 

[TVP]

Keep in mind that friction = heat, and heat causes the carburized surface layer to soften over time, thus reducing strength. Due to the large contact stresses in any type of gear, friction is always a concern, especially for pitting fatigue. Bending fatigue is not so affected. This type of chemical finishing also improves the fatigue life of other highly loaded components, such as helical compression springs, just due to the reduction of surface roughness. I know of one application where a spring compressed completely to solid would fail around 100,000 cycles after conventional processing, but this was extended to greater than 400,000 cycles when super finished. I would definitely recommend it for improving performance.

 

[Fabrico]

It might be an improvement. But even if so, it is not likely to be one you can feel or point to. It is likely that your money and time would be better spent elsewhere.

 

[Tmoose]

SKF and FAG both predict "infinite" fatigue life in place of L10 calculated life for their ball and roller bearings below a certain contact stress >>IF<< some lubrication conditions can be met. One condition is that true ElastoHydroDynamic (EHD) operation be attained. One of the main requirements for EHD is sufficient lube viscosity for conditions.

Surface roughness undermines EHD (similar to hydroplaning) and would revert to the much shorter L10 predictions. Assignment or prediction of surface VS subsurface failures are not easy

 

[Lowlife]

The REM process known as Isotropic Super Finishining (ISF), has proven itself in the automotive racing industry already and is currently proving itself beneficial for helicopter transmissions as well.

As one of the folks working to implement this technology within the military helicopter community I can tell you "ISF'ing" your gears is the least inexpensive insurance policy you can buy. Navy data obtained two weeks ago shows used gears outperform new gears in terms of lower operating temperature, single tooth bending fatigue, pitting and scoring......all without any detrimental change in gear geometry. We are currently qualifying this for use on three exisiting aircraft and even the most pessimistic among our group have found NOTHING to complain or take exception with.

If you can find a cheaper, easier or less risky means by which to improve a gear...........let me know.......... because right now, ISF wins hands down!

 

[Fabrico]

Those among our group have found nothing to complain or take exception with.

 

[injunmike]

Has your group explored the added advantage of fuel efficiency from ISF Finishing? Also what type of testing did your group do? We have found increases in Hp and reduced gearbox temps.

 

[Lowlife]

Proprietary data exist showing an increase in fuel efficiency, which makes pretty good sense when you think about it. ISF reduces friction loss, allowing the drivetrain to operate more efficiently, thereby consuming less fuel.

 

[Philrock]

REM finishing may offer many advantages, however, even a 30% decrease in losses in a spur or helical gearset is not a large advantage. Helical gears with conventional finish are about 98% efficient, so losses are 2%. A 30% decrease in losses means losss will be 2% x (1 - .3) = 1.4%. Efficiency has increased from 98% to 98.6%. If input power is 200 h.p., output will increase from 196 h.p. to 197.2 h.p.

 

[GregLocock]

Losses in the differential are about 15%, that's what i'd be interested in sorting out.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[geesamand]

I take it that this superfinishing exceeds any finish obtainable by lapping? Or is it chosen because it doesn't involve much manual labor?

Dave

 

[swall]

Yes, it is a vibratory deburring type of process that uses chemical etching in addition to abrasive media. Dump your parts in the tub full of media, set the flow of the etchant, push a button and walk away.

 

[groundPork]

I had briefly spoken with a racing transmission engineer/designer at a trade show, and he had told me in some instances if the person performing the process is neglectful or inexperienced, it's possible for heat to build to the point of annealing the gear from the friction... anyone care to validate or contest this? It seems also to me that the ability to retain oil may be of concern in street driven vehicles... Anyone care to validate or contest this also?

 

[Fabrico]

I would tend to question the comparing of a FWD transaxle to most other setups, especially with all but the final drive being planetary. Differences among things such as shock load, impact, lubrication, deflection, etc., are quite significant.

 

[NickE]

groundPork- You would have to have a significant process problem. I've seen dry finishing get hot enought to soften polyurethane but any more thant 120F is not really easy to do. With the REM process its a water bath which easily keeps the temperature below 80F.

 

[ads22]

My fwd transaxle is a VW manual shift (020) gearbox, so all power transmission, including final drive, is via conventional helical gears on parallel shafts.

I'm convinced through reading that REM finishing does an excellent job in dramatically increasing fatigue life, and most probably significantly reduces loss in a typical hypoid (RWD) final drive.

What I'm not sure of is whether it would reduce loss measurably in an application like mine, ie all shallow angle parallel shaft helical gears, since friction loss is pretty small to start with.

Having said that, I've had several friends swear that they have seen ~2% gains on a chassis dyno using this. My problem is that I have trouble believing that chassis dynos, especially "casually used", repeat well enough to see a 2% gain - there are an awful lot of variables. A true transmission dyno would probably pick it up, but of course (??) the best test would be to use a transmission dyno but judge the results from trans temperature rise. But I've never heard of anyone doing that.

Al Seim

 

[GregLocock]

"But I've never heard of anyone doing that."

That's how Dana measure diff efficiency. I think there is an SAE paper on it


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.