Originally Posted By: Shannow
Given that the paper is on "BIG END" beariings, and as we've already been over, BIG END bearings don't recieve "Pressure Lubrication" for a significant part of their rotation, maybe something "BIG END" related would have been pertinent to the topic, rather than wheeling out your constant stuff about pressurised bearing and oil flow.
In the paper you linked, there are plenty of graphs showing the relationship between big end bearing oil flow rate as a function of supply pressure in both types of oil passages designs discussed in the paper - V type passage design flowed better and had less aeration than the I type passage design, so again this is just another kind of design variable which can be added to the multiple variables that can effect pressurized bearing flow. But the fact is, no matter what the design of the oil delivery passage or the bearing itself, supplying pressured oil to the bearing will always result in the bearing flowing more oil volume.
Even though big end bearings don't receive constant oil flow throughout their entire 360 deg rotation (some worse than others as in the V and I passage design examples), they still get plenty of oil flow when pressurized adequately to ensure reliability. You did noticed what was said in the paper you linked below that if supply oil pressure was reduced too much the lubrication became inadequate, which could lead to bearing failure. These guys trying to cut back the oil volume supply on modern engines by using variable volume oil pumps could be walking a thin line on reliability if they get a bit too nuts trying to save some MPG.
The guys designing those old high output airplane engines didn't care about trying to cut down the oil pressure to some absolute minimum to try and save 1% in fuel consumption - there was no "CAFE" involved back in those days. They were going for reliability as the #1 design goal.
Back in the old days big end bearings on automobiles were not fed with pressurized oil, they used either oil squirters directed to the rod bearings ("splash" design) or a small scoop on the rod cap to help "ram" oil into the bearing (quasi-pressurized method). Those bearings still survived a decent amount of mileage because the demand on the bearings wasn't as great as it is today in modern engines. As the aviation article mentioned, not force feeding the bearings with oil would have caused them to over heat and fail, so clearly they knew the benefits of force feeding bearings.
Originally Posted By: Shannow
As I've said, the role of the lubrication system is to supply adequate volumes of oil at a pressure that gets it to the remotest part of the engine.
Guess that still goes along with your premise that if the oil inlet hole to the journal bearing is at only 1 ATM (0 gauge pressure) then it will have adequate lubrication. As clearly mentioned in the aviation article, that's wasn't the case with the crank pin bearings in high output aircraft piston engines used over the period 1915-1950. And it's not the case with many modern day engines with high specific power output.
Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Yeah, other changes in the bearing design variables can also help ... but so can increased oil pressure to increase flow and cooling, which mightbe a better option then changing the physical characteristics of the bearing depending on the exact situation. This is a good example of that. Are the blinders opening up any now?
"might" ???
Well clearly, with the war effort at their disposal, "might" didn't become "was", so they clearly found the alternative means described "to avoid the issues of excessive pressure" adequate (or even superior) to the simplistic logic of increasing pressure like hotrodders, (who aren't engine designers) do.
Well, it ended up being "was" because it clearly states that the only way to keep the bearings cool enough and not prevent failure in those high output engines was to force feed them with oil pressure. Good thing the engineers designing those war plane engines knew better than to try and make them work without an adequately pressurized oiling system in order to keep the bearings cool enough to prevent planes from dropping out of the sky. Hot rodders know more than you might think, and many are designers that come up with all kinds of ways to improve engine performance and reliability.
Originally Posted By: Shannow
edit...as an example, here's a paper with calculated and observed flows to a big end bearing with a couple of different crank drillings, demonstrating that sufficient pressure is required to overcome crankshaft dynamic forces and prevent cavitation in the part of the cycle where bearing supply ISN'T pressurised...
http://www.tytlabs.com/english/review/rev383epdf/e383_044suzuki.pdf
And yes, more pressure is clearly more flow and cooling...in this paper, pertinent to what happens in BIG END bearings, the topic of the thread.
Yeah, and the purpose of oil pressure is typically more than just "getting the oil to the bearing" so it can "draw" oil in from the gallery just to make up for side leakage as you keep mentioning. Start cutting back the oil pressure and you start causing aeration and a bearing temperature increase which could result in MOFT break down and eventually bearing failure.
Given that the paper is on "BIG END" beariings, and as we've already been over, BIG END bearings don't recieve "Pressure Lubrication" for a significant part of their rotation, maybe something "BIG END" related would have been pertinent to the topic, rather than wheeling out your constant stuff about pressurised bearing and oil flow.
In the paper you linked, there are plenty of graphs showing the relationship between big end bearing oil flow rate as a function of supply pressure in both types of oil passages designs discussed in the paper - V type passage design flowed better and had less aeration than the I type passage design, so again this is just another kind of design variable which can be added to the multiple variables that can effect pressurized bearing flow. But the fact is, no matter what the design of the oil delivery passage or the bearing itself, supplying pressured oil to the bearing will always result in the bearing flowing more oil volume.
Even though big end bearings don't receive constant oil flow throughout their entire 360 deg rotation (some worse than others as in the V and I passage design examples), they still get plenty of oil flow when pressurized adequately to ensure reliability. You did noticed what was said in the paper you linked below that if supply oil pressure was reduced too much the lubrication became inadequate, which could lead to bearing failure. These guys trying to cut back the oil volume supply on modern engines by using variable volume oil pumps could be walking a thin line on reliability if they get a bit too nuts trying to save some MPG.
The guys designing those old high output airplane engines didn't care about trying to cut down the oil pressure to some absolute minimum to try and save 1% in fuel consumption - there was no "CAFE" involved back in those days. They were going for reliability as the #1 design goal.
Back in the old days big end bearings on automobiles were not fed with pressurized oil, they used either oil squirters directed to the rod bearings ("splash" design) or a small scoop on the rod cap to help "ram" oil into the bearing (quasi-pressurized method). Those bearings still survived a decent amount of mileage because the demand on the bearings wasn't as great as it is today in modern engines. As the aviation article mentioned, not force feeding the bearings with oil would have caused them to over heat and fail, so clearly they knew the benefits of force feeding bearings.
Originally Posted By: Shannow
As I've said, the role of the lubrication system is to supply adequate volumes of oil at a pressure that gets it to the remotest part of the engine.
Guess that still goes along with your premise that if the oil inlet hole to the journal bearing is at only 1 ATM (0 gauge pressure) then it will have adequate lubrication. As clearly mentioned in the aviation article, that's wasn't the case with the crank pin bearings in high output aircraft piston engines used over the period 1915-1950. And it's not the case with many modern day engines with high specific power output.
Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Yeah, other changes in the bearing design variables can also help ... but so can increased oil pressure to increase flow and cooling, which mightbe a better option then changing the physical characteristics of the bearing depending on the exact situation. This is a good example of that. Are the blinders opening up any now?
"might" ???
Well clearly, with the war effort at their disposal, "might" didn't become "was", so they clearly found the alternative means described "to avoid the issues of excessive pressure" adequate (or even superior) to the simplistic logic of increasing pressure like hotrodders, (who aren't engine designers) do.
Well, it ended up being "was" because it clearly states that the only way to keep the bearings cool enough and not prevent failure in those high output engines was to force feed them with oil pressure. Good thing the engineers designing those war plane engines knew better than to try and make them work without an adequately pressurized oiling system in order to keep the bearings cool enough to prevent planes from dropping out of the sky. Hot rodders know more than you might think, and many are designers that come up with all kinds of ways to improve engine performance and reliability.
Originally Posted By: Shannow
edit...as an example, here's a paper with calculated and observed flows to a big end bearing with a couple of different crank drillings, demonstrating that sufficient pressure is required to overcome crankshaft dynamic forces and prevent cavitation in the part of the cycle where bearing supply ISN'T pressurised...
http://www.tytlabs.com/english/review/rev383epdf/e383_044suzuki.pdf
And yes, more pressure is clearly more flow and cooling...in this paper, pertinent to what happens in BIG END bearings, the topic of the thread.
Yeah, and the purpose of oil pressure is typically more than just "getting the oil to the bearing" so it can "draw" oil in from the gallery just to make up for side leakage as you keep mentioning. Start cutting back the oil pressure and you start causing aeration and a bearing temperature increase which could result in MOFT break down and eventually bearing failure.
