Originally Posted By: danielLD
The Japanese earlier this year announced they would start evaluating viscosities for the first time on the operating film thickness vs. just HTHS.
Have asked a few times for you to link us up to the statement...
As a degree qualified mechanical engineer with 25 years in power generation, 10 years specifically in turbines, including bearing design (these things seem important to you), you can't have one (film thickness) without the other (viscosity)...
MOFT is related to bearing design (diameter, length, clearance), and operational parameters (load and speed), and lubricant (viscosity).
Sommerfeld Number = (r/c)^2 x uN/P
r=shaft radius
c= radial clearance
u= viscosity
N= RPS
P= average film pressure (load/(2rl)), l being the bearing length.
For all else being constant (dimensions, load and speed), you get the following relationship.
Simple...it's laws of physics.
Now where I think that you are getting confused in the Japanese papers is that (most I've read is Honda), they are chasing lower viscosity oils...clearly, they are the main diver for the sub 20 grades.
However, they state that they are changing the bearing parameters to maintain MOFT in this low viscosity world.
They are:
* lengthening bearings (depreses the "P" component)
* reducing clearances (makes r/c bigger)
* stiffening bottom ends (allows for reduced clerances)
* coating (for when contact occurs becuase MOFT is too low).
My engineering assessment is that the are chasing the friction in the piston/skirt area, and have reached the limit of the bottom end, so to go lower in HTHS, they need to change the bottom end.
I think THAT's what you are picking up. and not understanding the engineering are giving it a spin that's not there.
But the statement that increasing HTHS increases part separation in any given design (like the OP's V-6) is an engineering fact.