Molecular Mechanisms for Functions of Lubrication

[SkyPup]

Current State of the Art Science in Oil Additive Functional Chemisty:

One method commonly used to protect surfaces from wear involves the use of anti-wear additives. These additives are incorporated into lubricant packages and form surface films that protect the underlying material from the destructive forces applied under sliding conditions. The most widespread application of antiwear additives is in automobile engines, where the rubbing surfaces are almost exclusively composed of steel or cast iron. The most common antiwear additives used in engines are zinc dialkyldithiophosphates (ZDDPs), which have the chemical formula Zn[S2P(OR)2]2, where R is an alkyl group. ZDDPs have successfully been used for over 60 years, and to date no superior antiwear additive has been developed for use on steel.

The inability of ZDDP antiwear films to protect aluminum surfaces has been a major impediment to the mass production of automobiles that contain engines in which aluminum is the main component.

SOURCE:

Science, Vol 307, Issue 5715, 1612-1615 , 11 March 2005

http://www.sciencemag.org/cgi/content/full/307/5715/1612

 

[_RaT_]

Why would it be necessary to protect the aluminum engines? Even on aluminum engines, wear surfaces are some type of other metal. I can't imagine the bearings for the crank, rods, cam(s) etc, even the rings add enough weight to be enough of a factor that it would be necessary to go to a lighter material. On the otherhand, obviously weight is one of the most important criteria in determining the fuel appetite in todays vehicles. I looked at some mpg specifications on some SUV's like a BMW X5 and found that whether you used the I-6 or V8 with much more HP and displacement, your still getting about the same MPG.
Unfortunately the link would not let me in as I am qualified to view it. /forums/images/graemlins/smirk.gif

 

[SkyPup]

"The replacement of steel by aluminum is motivated by efforts to reduce vehicle weight as a means of improving fuel efficiency. For example, it has been estimated that a 10% reduction in vehicle weight can result in a 7% improvement in fuel economy. However, because of the inability of ZDDPs to adequately protect aluminum surfaces, automobile manufacturers have had to resort to engines composed of aluminum-based composite materials or to engine blocks that contain steel sleeves. These measures are costly and complicate engine fabrication."

 

[isucrazy]

Some overhead cam engines have NO cam bearings at all in alum. heads. The cam floats on a film of oil and nothing else between the steel cam and the alum. head. Im thinking this kind of engine would not bee possable with out some darn good slickem flowing around in there. things sure have changed, from cuttin up your belt to make new bearings to none at all.

 

[RobS]

RaT, lots of aluminum wear surfaces in just about any engine. Pistons have been aluminum for decades. Aluminum blocks and cylinder heads, some with inserts, some not /forums/images/graemlins/smile.gif

 

[_RaT_]

But the piston has steel rings that wear on a steel liner. The blocks typically are no more then a framework to structually support or contain the engine, no apparent wear points, Aluminum heads have valve seats, valve guides etc made of something other then aluminum.

I have seen where the OHC bearing surfaces are all aluminum, your right.

I thought the idea of using ceramic was floated around.

I can certainly see your point Skypup about adding the steel inserts complicating the engine building process. I think even more then reducing engine weight will be other reductions be it the frame, the transmission, well, just about everything is a candidate. The engine is perhaps the one componet short of the exahust system that has to be able to handle very large temperature swings and built accordingly.

 

[SkyPup]

My 1974 BMW Tii 2002 2.0 liter SOHC balanced and blueprinted 4 banger had an all aluminum head on a cast iron block and the cam bearing surface wore out @ 180,000 miles (8,000 rpm redline). Had to get a new head and sold it @ 350,000 and still going strong today.