Letter 37096

Cylinder wall / piston ring holy grail?  

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Hello All,

I work for a major semiconductor capital equipment company and have quite a few years of experience with PVD technologies. I am also a race car driver in need of an engine rebuild so I thought I would bring these 2 together to try and shake things up.

I have been researching cylinder wall / piston ring coatings and have seen some of the work done with Cr and DLC. My question to the board is, what is the holy grail of this relationship for reduction of friction in a car engine?

Any help would be appreciated.

Nick Littleton
semiconductor capital equipment - San Jose, CA, USA

We have a number of good coatings now, including chromium, and nickel-silicon carbide and other composites, and I suppose DLC. But the holy grail will be a coating which exhibits zero friction via a fundamental development in physics similar to the way the development of superconductivity eliminated electrical resistance. Whether it will be achieved by the atom-by-atom placement of a yet-to-be-designed molecule, or whether the surfaces will be "activated" at the contact points in a way analogous to how LEDs light up is something that only time will tell. Perhaps neither of the above, but something I can't yet even imagine.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

As far as friction reduction, a hard chrome and polished bore with molybdenum disulfide coated rings and Teflon coated piston skirt would have to be close to the ultimate. The drawbacks would be delayed ring seating and short life of the Teflon on the skirts. A better compromise would be plain iron bores, plateau honed, with low tension hard chrome plated rings and moly coated skirts. That's pretty much state of the art today.

Jeffrey Holmes, CEF - Spartanburg, SC, USA

Perhaps Holy Grail might be a little to far fetched. My intent is available coatings on the market. Has anyone seen any dyno results on coating various parts? I read about Bekaert / Sorevi coating cams with DLC for F1 / Le Mans / NASCAR. Was there a translation to HP gain in doing this? or is this just a longevity issue?

Also, in my world of PVD (semiconductors) we have many ways of coating sidewalls of vias at aspect ratios on order of 25:1 with very good uniformity using a flat target. Seems like coating a cylinder wall is the hard thing to do at the moment, maybe I can help, just need to know the right combo of materials for piston ring to cylinder wall using somewhat conventional motor oils?? (the Holy Grail).

Nick Littleton
- San Jose, CA, USA

Hi Nick,

I liked Jeff Holmes reply ... but doesn't the latest piston ring technology show that the rings on the piston are NOT all the same 'size'?

Have you consider ultra high pressure (l,000 psi) on the fuel lines on the premise that successful fireworks have the ingredients ground down to preferably 5 microns? Hence the ratio of ultra fine droplets to the air is enormous.
Technology used by an odour combating Company called ODERCHEM.

Freeman Newton - White Rock, B.C. Canada

Reduced friction is a good thing in that it can lead to increased net HP and lower temps, but...it's a marginal increase, and if lower friction comes at the expense of increased blow-by, then net HP might be down. And, of course, in a race car there is much more than just HP to consider in improving lap times.

If you're old enough to remember, Tazio Nuvolari often defeated the Silver Arrow Mercedes and Auto-Union teams which had twice the HP. His Alfa had better handling, less tire wear, and most importantly, Tazio behind the wheel.

If I were a race car driver, and I'm not, I'd opt for a state-of-the-art engine (APT in SoCal will be happy to provide one) and put my money and efforts into improving the driver.

Jeffrey Holmes, CEF - Spartanburg, South Carolina

That's the thing about racing, there are all kinda ways to win, yes, driving is one on the skills, but so is being smart and with engineering. My motor builder is one of the best on the west coast but the kicker is the motors cant be state of the art due to the rules. We are forced to 1960s technology, Holley carbs, Edelbrock intake, 305 2 bolt main block, etc, etc... The rules don't say anything about coatings hence my quest for HP thru reducing friction. I know the F1 guys are doing it, just trying to find out what they are doing? Anyone know an F1 engine builder that is willing to talk?

Nick Littleton
- San Jose, CA

Engine builders use DLC and many other common and proprietary coatings and platings in their engines. These coatings are used on much more than just the piston and cylinders. The types and combinations vary builder to builder and by car types. Coatings and plating are also used on suspension,exhaust, brakes and drive train parts.

Todd Osmolski Charlotte Plating, Inc. Charlotte, NC USA

Anything that you do that will give you a noticeable advantage will lead to an inspection, and if the judges determine that it is due to the surface conditioning of the engine internals, they will just outlaw it (remember the hemi?).

Sheldon Taylor    supply chain electronics Wake Forest, No. Carolina

Hello,
I too have worked in materials science for several years and have seen many things tried to gain HP,reduce time etc.
When a reduction in friction is obtained by what ever means this means less drag"simple as that"however keep in mind it takes a lot of hourses to drag around all that oil!
Ceramic and diamond hard thin films will help,no question about that as long as they are inert to the metals and oil etc.Internal Surfacing (ID hard thin film Coatings are available now)
Our company does not produce these coatings so Im unbiased when it comes who or what materials work best.I can assure you that when the deposition is done correctly(make no mistake!)you will meet at least some of your objectives that will lead you toward goals your now setting for yourself!(I have done some of the depositions for Indy Cars etc.I can not say here what formula I used however I can tell you IT DOES WORK!

William M. Turner Ph.D.
- New Smyrna Beach, FL, USA

Consider finding a near by public library that carries Society of Automotive Engineering technical papers. They are a good source of technical information. If not available, one can buy email downloads of technical papers directly from SAE.org. An additional source is patent literature. Some is free on the web and copies can be purchased from the government. Patents often contain lists of prior patents.

Marvin McConoughey
- Corvallis, Oregon, USA

I for one can tell you that DLC coatings in general, and the ones used by Bakaert/Sorevi in particular, do work. In a recent build of a FIA historic racing motor I had the opportunity to use several variations of Cavidur on items such as transmission gears and shafts, ring and pinion, piston skirts, flat tappet lifters, camshaft, valve stems, and piston pins.

At the time I did not use DLC on the rocker shaft but I would in a future rebuild. At present the rocker shaft is a 4340 thick wall hollow shaft, centerless ground, hardchrome plated and then final ground to size with a polished finish. This has a hardness of Rc65 and a Ra of 0.2. The shafts have a radial oil groove running to the bottom of the shaft (rocker arm boundary layer interface contact area) from the rocker arm feed supply hole, with an "X" groove to promote a larger oil distribution area. While there is pressure there no hydrodynamnic wedge effect is seen due to the oscillating nature of the interface. Likewise, because of the total "spill orifice clearance" of the 8 rocker arms, the amount of oil pressure actually generated at the rocker/shaft boundary layer interface is quite low. The rocker at the moment has a silicon-bronze insert. The largest problem I encountered was using DLC on small internal bores, such as a 15mm diameter rocker arm fulcrum bore. During the original developement of this engine, in the 1960s-1070s, needle bearing rockers were used. However, I believe that with DLC coatings a lower coefficient of friction could be achieved at the rocker/shaft interface. How much better it would be to the current hard chrome plated shaft/bronze bushed rocker arm I do not know.

Likewise, I would like to coat the inside of the ring grooves, and the piston rings, as well in a effort to provide a better seal at both the cylinder wall and the ring land.

The outcome of this initial work was that we had a motor that produced more than 2.2 HP per cubic inch at 8500 RPM (122HP/59.9Cu. in.). This may not seem like much, at least by modern pent roof combustion chamber standards, but for an engine designed in the 1960s using a 3 main bearing crankshaft I do not consider this a bad effort.

In discussing "parasitic losses" and possible improvements, this same car also had hybrid ball bearings (steel races with ceramic balls)in the entire drive train (gearbox/differential/wheel hubs etc). This made a significant difference in the horsepower lost via the drivetrain.

Paul Vanderheijden
Scuderia Topolino - Raleigh, NC