Tribology vs. Engine bearing clearance
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MolaKule
Staff member
Did you mean to say, "Tribology OF Engine Bearing and Clearances?"
What did you find interesting or surprising about this article?
What did you find interesting or surprising about this article?
It's a superficial look at traditional iterative bearing design using proprietary software...rather than a half dozen iterations for every design point, and produces some very useful trends...the charts are applicable to the 2" bearing that they state, but the trends are worth paying attention to.
e.g.
Chart 6 gives two quite useful rules of thumb...
* that doubling rotational speed for a given design uses twice the oil (as I've stated before, bearings move their own oil. Oil pressure is there to provide oil for the bearing to use, not to push oil into/through the bearing)
* doubling the bearing clearance basically doubles the flow that the bearing utilises also.
Chart 7 shows the temperature rise for different clearances/speeds. This is demonstrative of the "work" that the engine has to do spinning the journal inside the bearing and shearing the oil...the average working temperature, and thus the bearing oil temperature is typically approximated by supply temperature plus half the rise...the part of the curve to the left needs to be read in conjunction with chart 6, as the smaller radial clearances result in smaller amounts of lubricant flow through the bearings, which means that the energy expended shearing the oil is on a smaller volume per unit time and provides greater heating...except for the extreme, and artificial left side, it would probably have only a minor impact on bulk oil temperatures, but in the oil being flung from the bearing, into an environment of hot blowby gasses could be significant in varnish production, not to mention the operational viscosity in the bearing.
Charts 4 and 5 demonstrate that if the bearing clearances are too large, the load is shared less equally around the loaded side of the bearing, and at lower speeds (2,000 RPM is not low, it's cruising speed, not off idle/stalled it letting the clutch out)...bearings too loose, and the journal is more like a high heeled shoe (poor analogy, but it works I think), and can cause material damage to the shell...spinning it faster reduces the effect.
THEN read charts 1 and 2, and you can see how the "high heel" effect, exaccerbated at low speeds, reduces the minimum oil film thickness.
(for interest, note also that 40 micro-inches is about a micron...compare that to available oil filter ratings/efficiencies)
Take the above charts into account, and you can see why revving engines with little high load/low speed requirement go loose.
Reverse it and see why the like of Honda are going tighter on clearances for street engines with lower viscosity oils.
Look at them all together, and you can recognise the futility in determining minimum oil film thickness from a pressure gauge on a supply line.
e.g.
Chart 6 gives two quite useful rules of thumb...
* that doubling rotational speed for a given design uses twice the oil (as I've stated before, bearings move their own oil. Oil pressure is there to provide oil for the bearing to use, not to push oil into/through the bearing)
* doubling the bearing clearance basically doubles the flow that the bearing utilises also.
Chart 7 shows the temperature rise for different clearances/speeds. This is demonstrative of the "work" that the engine has to do spinning the journal inside the bearing and shearing the oil...the average working temperature, and thus the bearing oil temperature is typically approximated by supply temperature plus half the rise...the part of the curve to the left needs to be read in conjunction with chart 6, as the smaller radial clearances result in smaller amounts of lubricant flow through the bearings, which means that the energy expended shearing the oil is on a smaller volume per unit time and provides greater heating...except for the extreme, and artificial left side, it would probably have only a minor impact on bulk oil temperatures, but in the oil being flung from the bearing, into an environment of hot blowby gasses could be significant in varnish production, not to mention the operational viscosity in the bearing.
Charts 4 and 5 demonstrate that if the bearing clearances are too large, the load is shared less equally around the loaded side of the bearing, and at lower speeds (2,000 RPM is not low, it's cruising speed, not off idle/stalled it letting the clutch out)...bearings too loose, and the journal is more like a high heeled shoe (poor analogy, but it works I think), and can cause material damage to the shell...spinning it faster reduces the effect.
THEN read charts 1 and 2, and you can see how the "high heel" effect, exaccerbated at low speeds, reduces the minimum oil film thickness.
(for interest, note also that 40 micro-inches is about a micron...compare that to available oil filter ratings/efficiencies)
Take the above charts into account, and you can see why revving engines with little high load/low speed requirement go loose.
Reverse it and see why the like of Honda are going tighter on clearances for street engines with lower viscosity oils.
Look at them all together, and you can recognise the futility in determining minimum oil film thickness from a pressure gauge on a supply line.
MolaKule
Staff member
I would have liked to have seen charts simulated with various viscosities of oil, and a description of the oil's additive components (assuming the simulation accounted for PI packages).
The author stuck with 5W50 throughout the article and I assume the oil had a 18.5 cSt value at 100C. It would have been instructive to see the viscosity at various temperatures at the pressures simulated since he stated the ENSIM software simulated the thermodynamic, dynamic, hydrodynamic, and mechanical parameters.
The author stuck with 5W50 throughout the article and I assume the oil had a 18.5 cSt value at 100C. It would have been instructive to see the viscosity at various temperatures at the pressures simulated since he stated the ENSIM software simulated the thermodynamic, dynamic, hydrodynamic, and mechanical parameters.
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Hello MolaKule-
Your suggested title is far more appropriate. I regret the error and stand corrected.
I’ve learned much from your myriad posts and the vast insights you’ve shared.
Merely a beginner at the study of the science and art of lubricants,
it’s striking how relatively minuscule changes in bearing clearances can affect dramatic changes in flow, temperatures, et cetera.
Stumbled across issues of Engine Professional, Machinery Lubrication and Race Engine Technology (amongst others) at our local machine shop.
A call to their respective publishers resulted in a subscription to each periodical.
Just a hobby and pastime for me, you and other BITOG experts have whet an appetite for continuing education. And so it goes.
Your suggested title is far more appropriate. I regret the error and stand corrected.
I’ve learned much from your myriad posts and the vast insights you’ve shared.
Merely a beginner at the study of the science and art of lubricants,
it’s striking how relatively minuscule changes in bearing clearances can affect dramatic changes in flow, temperatures, et cetera.
Stumbled across issues of Engine Professional, Machinery Lubrication and Race Engine Technology (amongst others) at our local machine shop.
A call to their respective publishers resulted in a subscription to each periodical.
Just a hobby and pastime for me, you and other BITOG experts have whet an appetite for continuing education. And so it goes.
MolaKule
Staff member
Sprinter, Thanks for the submitting the Engine Professional issue.
The article on Honing was interesting as well.
The article on Honing was interesting as well.
Originally Posted By: splinter
From Engine Professional
Pages 48-52...
http://www.aera.org/ep/EPQ3-2014/index.html
Thanks for the find
From Engine Professional
Pages 48-52...
http://www.aera.org/ep/EPQ3-2014/index.html
Thanks for the find
I'm going to download it too.
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