Couple of oiling system design papers

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A New Approach to Flow Network Analysis of an Engine Lubrication System


Has some pretty interesting commentary on designing and modelling chain tensioner squirters etc...plus a little bit on gallery filling from start...e.g. can see how in the test case, the pump slip increases when the oil gets really thin and takes longer to fill.
gallery%20filling.jpg



Engine Lubrication System Analysis and Oil Pump Design Optimization

Only get the first two pages on Springer,

More is available on Google Books, but sometimes Google boooks links don't work.

Has commentary on design points, like sufficient pressure at 1,000RPM to actuate cam phasors etc. Main gallery target pressure, and the setting of PRVs and redesigning to save energy.
 
hmm, seems like thin oil is actually worse to get "all parts lubricated" in short order?

Turbo cars tend to have higher oil pressures at idle compared to strictly NA cars, I've noticed.
 
Originally Posted By: Jetronic
hmm, seems like thin oil is actually worse to get "all parts lubricated" in short order?


Yeah, I tried to explain the concept of internal slip versus viscosity some time ago to a member who is a huge advocate of thin...

It's actually funny, in that the internal slip reduces the efficiency (clearly) and creates MORE heat in the oil that makes it through...it's not huge, but it's there.
 
Agree re "slip versus viscosity."

Why does their test engine take so long to reach 400 RPM?

That chart would be more interesting if it extended farther to the left (cold) side.
 
Originally Posted By: CR94
Agree re "slip versus viscosity."

Why does their test engine take so long to reach 400 RPM?

That chart would be more interesting if it extended farther to the left (cold) side.


I've been trying to find papers on that for ages...this is the first I've found that gives the details from 40C upwards, which demonstrates that there's diddly squat difference in the range (in that engine) spanning the 60 to 10cst range at least.

Extreme Left, I've found that the "W" basically offsets the pumpability issues off in that direction.

oil%20pressure%20temperature.jpg


Oil%20gallery%20fill%20and%20rocker%20time.jpg


Originally Posted By: BITOG lore
the heavier the oil the longer it takes to prime the bearings and ultimately reaching the farthest lubrication point in an engine.

The lighter the oil the faster the flow and better the lubrication.
 
Originally Posted By: BITOG lore
As long as the PD oil pump is not in pressure relief, then 100% of the pump's output goes through the engine. A well designed oiling system would give max oil volume flow through the engine with hot oil and never hit pump pressure relief, but come close at near red line RPM.


Originally Posted By: BITOG lore
The devil is in the details. No engineer worth his salt would council running the oil pump in relief at operating temperature.


Per the first paper...

Quote:
Accord-ing to our experience, the minimum value of 12-15% of oil pump flow rate should be passed through relief valve at maximum oil temperature and rated speed.


Never would you have zero (or less) design margin in something that you would expect to be in service for hundreds of thousands of miles, and possibly decades...there's ALWAYS margin designed in, even if it costs you 50W or so.

Especially as per the second paper, when the "worst case" design point (again for the test engine) is for 2.3bar (33psi), at 6,800RPM (1,000), while the normal operating point is far lower in terms of RPM and temperature, prompting novel relief designs, and variable displacement pumps....
 
More from the second, all quite self evident...

Quote:
Fihure 1 shows a typical minimum oil pressure curve to support the main and big end bearings. Usually the pump is sized to meet the low speed and hot oil condition. As an example, this engine required 1.0bar oil pressure to drive the VCT Unit at 1,000RPM. This oil pressure has to be achieved regardless of the oil temperature which according to the engine and vehicle test data can reach 140C in the worst case. Also the pump and bearings are designed to last for the whole engine life. The bearing clearance increase and pump performance degradation against the engine running time have to be considered in the model.


Quote:
More oil delivery to engine than what it requires will generate higher oil pressure than what te engine requires. The energy used to generate higher oil pressure is just wasted. There is a clear trend over the next 3 to 5 years to increase the use of variable flow oil pump.


Quote:
For example, if the pressure loss from the pump exit to the main gallery is 2.3 bar at 6,800RPM and 140C oil temperature, the PRV open pressure has to be set at >4.8bar when the minimum required gallery oil pressure is 2.5 bar.

However, at normal operating condition, say 2,000RPM and 100C oil temperature the pressure loss from the pump exit to the main gallery could be as little as 1.0b, That means the pressure setting catered for the condition of high speed and high oil temperature is a penalty for the lower speed and lower oil temperature.


Interesting, you could decrease the losses in the supply TO the mains, reducing the pump oil pressure requirement for the requirement of 2.5 bar at the main gallery (36.25psi @ 6,800RPM), but that would then penalise you on gallery filling from cold or after a hot-hot start.

Clearly a pump discharge pressure ISN'T the pressure requirement of the bearings, but that required to overcome all of the losses plus overcome the dynamics of a crank/big end, and maintain pressure to auxiliaries and squirters.
 
Originally Posted By: Shannow


Clearly a pump discharge pressure ISN'T the pressure requirement of the bearings, but that required to overcome all of the losses plus overcome the dynamics of a crank/big end, and maintain pressure to auxiliaries and squirters.


Exactly. I touched on this with my little diagram of the SBC in one of the other threads. The feed pressure isn't the requirement, but simply the artifact of getting the components furthest away from the pump what they need.
 
Originally Posted By: OVERKILL
Originally Posted By: Shannow

Clearly a pump discharge pressure ISN'T the pressure requirement of the bearings, but that required to overcome all of the losses plus overcome the dynamics of a crank/big end, and maintain pressure to auxiliaries and squirters.


Exactly. I touched on this with my little diagram of the SBC in one of the other threads. The feed pressure isn't the requirement, but simply the artifact of getting the components furthest away from the pump what they need.


I really doubt there is a 60 or 70 PSI pressure drop between the main oil gallery and the farthest away main bearing. But keep in mind that with a PD pump that all the volume must go someplace in the oiling system until the pressure relief valve starts to operate. And yes, the observed oil pressure is the artifact of how much volume the PD pump is putting through the system, and what the overall flow resistance is of the system as seen by the pump.
 
I'm starting to think that the oil pressure wasn't the problem in those domestic V8s, but instead the HTHS viscosity was too low.
Because we did not understand HTHS and MOFT, we added oil pressure instead of viscosity, thinking that was the solution.

There is a lot of flexing and harmonics going on in those old engines, which can change running bearing clearances.

In the case where the oil pump is operating at relief pressure, as it should at high rpm, then a thicker oil, not more pressure should be the solution to bearing problems.
 
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Originally Posted By: ZeeOSix
Originally Posted By: OVERKILL
Originally Posted By: Shannow

Clearly a pump discharge pressure ISN'T the pressure requirement of the bearings, but that required to overcome all of the losses plus overcome the dynamics of a crank/big end, and maintain pressure to auxiliaries and squirters.


Exactly. I touched on this with my little diagram of the SBC in one of the other threads. The feed pressure isn't the requirement, but simply the artifact of getting the components furthest away from the pump what they need.


I really doubt there is a 60 or 70 PSI pressure drop between the main oil gallery and the farthest away main bearing. But keep in mind that with a PD pump that all the volume must go someplace in the oiling system until the pressure relief valve starts to operate. And yes, the observed oil pressure is the artifact of how much volume the PD pump is putting through the system, and what the overall flow resistance is of the system as seen by the pump.


No, it was something like 15-20psi on the SBC IIRC. But it wasn't the main bearings that were the issue, it was the rod bearings, and the furthest ones from the pump. And of course as was just noted, mechanical flex and harmonics played as role as well, dynamically changing the scenario. It was also, as I noted in the other thread, an issue that presented at elevated RPM. I also cited a few examples of relief operation in that thread as I'm sure you recall.
 
Originally Posted By: userfriendly
I'm starting to think that the oil pressure wasn't the problem in those domestic V8s, but instead the HTHS viscosity was too low.
Because we did not understand HTHS and MOFT, we added oil pressure instead of viscosity, thinking that was the solution.

There is a lot of flexing and harmonics going on in those old engines, which can change running bearing clearances.


Could have been a number of factors all adding up in the same bad direction to cause bearing failure - proper film thickness is most essential. Once the film thickness goes away you get metal-to-metal contact and it opens the door to a bad news failure. Connecting rod bearings have a harsh life due to the high cyclic bearing loading as seen in Fig 6.

OVERKILL mentioned in another thread about modified SBC failures being resolved by a higher volume oil pump with a higher pressure relief setting. Guys were probably also running higher viscosity oil along with the HV pump. Force feeding the bearings with thicker oil helped maintain a safer oil film thickness to make up for any lacking in the oil quality back in those days. Just running a little thicker oil may be enough in some circumstances - the days of 20W-50 Castrol GTX. Tables 7 & 8 show the effect of how the viscosity changes the oil film thickness. This is why so many people get up in arms about running a xW-20 oil in high performance cars used for track days, etc where the engine is living in the high stress zone.

Originally Posted By: userfriendly
In the case where the oil pump is operating at relief pressure, as it should at high rpm, then a thicker oil, not more pressure should be the solution to bearing problems.


Only problem with just throwing a much thicker oil in an engine that lives near redline is that the thicker oil will make the pump hit pressure relief with less flow going to the engine - especially if the pump was already designed to be in pressure relief at high engine RPM. That's one main reason guys who used thicker oil in older modified V8s also ran a HV pump with increase relief pressure - so the flow at high RPM was maintained. Just increasing the relief pressure by shimming or replacing the relief spring might have sufficed on some engines.

Also, Tables 7 & 8 show that it's not a good thing to "lug" an engine at low RPM and high throttle openings (ie, floor it at low RPM, or two something heavy at low engine revs with high throttle opening) because the oil film thickness is lower at low bearing RPM - especially if the oil viscosity is really low. Most hi-pro engines can put out ton of torque at low RPM at WOT which means the rod bearings get very high loads when the oil film thickness is the lowest. It's much easier on the bearing to rev the engine higher then to lug it at large throttle openings.
 
The Figures and Tables I referenced above are in this link from the other thread: LINK
 
Z06, I'm guilty of your paragraph 1; HV oil pumps (sbc & bbc) and what I thought at the time, thick 15w40 engine oil.

I agree with your "lug", low speed & high load situation. In that case, I'm in the high viscosity camp, not exclusively the high oil pressure camp.
In addition for legacy , I will go extra clearance for flex and harmonics, with it thick oil, to deal with extra and changing bearing clearance.

Modern extreme in that direction, would be nitro methane, a late burning fuel, not un-like a double base gun powder.

Late burning.... heat releases 02 from the fuel. Un-like N0S, the O2 is contained in the fuel, not added with an "enrichment hydro-carbon fuel.
I'm going down this "top fuel" road to illustrate the need for "SAE 70" engine oil (no such grade) to handle the high load, not un-like the lug condition you mentioned.
Obviously, oil pressure would not compensate.
 
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