variations and tolerances are not "the main culprit in bearing wear"...your inference, in using both words...variations AND tolerances inferred that you were defining them separately, and both of them being (incorrectly) the main culprit.
If you said clearances and tolerences, you would be defining two different things...but they are neither the main culprits in bearing wear either.
Bearings have a characteristic number (Sommerfeld) number (r/c)^2*u*N/P, where
r is the radius
C is the radial clearance
u is KV
N Rotational Speed
P is applied pressure to the bearing = Load/(length* diameter)
(take out the (r/c)^2 as a constant for a given design, and you get the number used on the Stribeck curve...funny that...and notice that the stribeck curve, nor the Sommerfeld mention "variations and tolerances").
These are for perfect bearings in proper alignment, with no shaft flex etc...
So MOFT, and the lack thereof are "the main culprit in bearing wear in real life, in this current universe, witht he laws of physics as they currently stand...in a made up universe, YMMV, but that's not here.
So if you want to increase MOFT - increase the So number.
* increase engine speed
* increase viscosity
* increase shaft diameter
* reduce radial clearances
* REDUCE P (+)
(+) You can reduce P by
* increasing shaft diameter (already included above)
* reducing the load on the bearing (no likely)
* increasing length.
The Japanese OEMs are using lower viscosity, by their own admission to reduce operating friction, for the purposes of fuel economy and/or CO2 emissions. And they are trying to do that while maintaining (to quote Honda) "acceptable wear".
So that pushes things to the left on both the So, and the Stribeck (based on So for journals)...oh, and BTW, the polymers aren't any "higher strength" than the substrates, they are softer, more embeddable, and less prone to
stop start boundary lubrication...well that's what Mahle say, and Federal Mogul don't call them higher strength then the substrate either...they claim that they las longer in stop start and hybrid.
So to get better MOFT, the OEMS are (per Honda papers, not adverts)
* reducing radial clearances
* increasing shaft diameters
* increasing bearing length
Which flies in the face of efficiency, but they have more to gain in piston/skirt than they lose in bearings...there WILL be a cost benefit payoff there.
The changes that Honda are stating come with problems...longer length and lower clearances mean that shaft alignment needs to be better maintained.
Greater journal diameter helps improve the stiffness (and alignment) of the shaft.
Blocks have to be stiffer, which is why we are seeing skirted blocks, crank bearing girdles, cross bolting, and strong alloy sumps.
re "variations and tolerances" being the main culprit in bearing were...it's bunk.
Look at the MOFT curves I show...pick a design point, then go a little to the left, and a little to the right...the effect is virtually NIL in MOFT.
