Effect of viscosity on hydrodynamic engine bearing

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix

In actual use at full operating temp (100 deg C), the difference in pump slip between running say a xW-20 vs a xW-30 or xW-40 in an IC engine isn't going to be enough to cause any oil flow/delivery issues. The delta in viscosity between those oils when fully hot isn't that drastic. Most pumps are over designed anyway, so any small increase in slip isn't going to make any difference impacting proper lubrication.


Exactly my point all along...

Pump only ever has to supply enough volume for the bearing's make-up requirements at the worst point, and operating point of the engine...the excess delivery is seen as "oil pressure".

Oil pressure may well be necessary when having to cool pistons, run actuators and the like...well at least that's per Honda's papers for street engines say as they reduce viscosity.


And along with that, the excess PD pump volume is also causing increased flow through the now "pressure fed" journal bearings due to the increased oil supply pressure. Journal bearings will also contribute to the overall flow resistance of the oiling system due to their tight clearance in conjunction with the PD pump trying to force more oil through the bearings than they would "naturally draw" while rotating. Basically saying he same thing, but with the pressure fed/more flow caveat. Definitely need oil pressure for such things as cooling jets, chain tensioners, variable cam timing actuators/phasers, etc.

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Typically the engine will be around the 2000 RPM range in high gear when just "cruising" down the highway to maintain highway speed. So in reality the HP savings is more like 25W (0.034 HP) with 0W-5 vs 10w30 and 70W (0.094 HP) between 0W-5 vs 10W-60 (which nobody uses anyway). That's using the 0.004" bearing clearance data points.




So if the required HP was at 18, then the power savings is realistically more like 0.034/18 = 2%

More accurately, the HP required to cruise at a constant 65 MPH on flat ground is more along the lines of 24.5 HP for a 3500 lb vehicle. 12.4 HP from wind resistance and 12.1 HP from rolling resistance. So in that case, the power savings would only be 0.034/24.5 = 0.14%.


Couple of quick questions...

How many road going engines have you seen with:
* 0.004" bearing clearances (mains or rods, doesn't really matter).; or
* only one bearing per engine ?

The latter would make it a fairly "uni"que design pardon the pun.

Go back here for catch-up.


If you applied my example to the 0.0004 bearing clearance data in that graph, the "gains" would be even less than for the 0.004 bearing, because the power loss deltas at 0.0004 clearance between the 3 different oil viscosities are even less.

 

[ZeeOSix]

Originally Posted By: userfriendly
Thanks Zee06; For some reason it seems that we have come full circle with this logical explanation;

https://en.wikipedia.org/wiki/False_equivalence or, "1cP = 1 cSt"


Yeah, as I said above, I was mistaken on that ... 1 cP = 1 cSt if the specific gravity is equal to 1 (ie, water).

 

[Shannow]

https://www.youtube.com/watch?v=6iaR3WO71j4

hint...engines have more than 1 bearing....

 

[Shannow]

Originally Posted By: ZeeOSix
If you applied my example to the 0.0004 bearing clearance data in that graph,


Do you have a different graph to the one that you linked to ?

That stopped an order of magnitude higher

 

[ZeeOSix]

Originally Posted By: Shannow
https://www.youtube.com/watch?v=6iaR3WO71j4

hint...engines have more than 1 bearing....


Ok, smart arse ... assume it's a 4 cylinder with 4 big end and 5 crank bearings.

If the car needs 24.5 HP to maintain 65 MPH, then the total savings would still only be (9 x 0.034)/24.5 = 1.25%.

Use the same example with the data on the 0.0004" bearing clearance, and it's less than 1%.

 

[ZeeOSix]

You still think journal bearings flow the same regardless of how much oil supply pressure is put on them?

 

[Shannow]

Originally Posted By: ZeeOSix
You still think journal bearings flow the same regardless of how much oil supply pressure is put on them?


Nope, you keep telling me that's my belief, in spite of me stating that it is NOT my beleif, and supplying you with the rotating shaft equations from Orlov demonstrating the relationship.

Why would you keep stating it when I've told you multiple, multiple times that it's not my belief, nor my position ?

Disingenuous in the very least...

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
You still think journal bearings flow the same regardless of how much oil supply pressure is put on them?


Nope, you keep telling me that's my belief, in spite of me stating that it is NOT my beleif, and supplying you with the rotating shaft equations from Orlov demonstrating the relationship.

Why would you keep stating it when I've told you multiple, multiple times that it's not my belief, nor my position ?

Disingenuous in the very least...


The reason I say it is because even after all the discussion in the other threads about journal bearing flow, and even after you once agreed that supply pressure does increase bearing flow after the Orlov discussions, you then go back to making statements like these below - which clearly says you still don't think force fed bearings flow more than not.

Originally Posted By: Shannow
The oil pump is only supplying oil to make up for the bearing's inherent side leakage, which is influenced by viscosity, RPM, speed, diameter, length, load, and diametrical clearance...it's not "flowing" oil through the bearings.


Originally Posted By: Shannow
Again, bearing parameters determine the oil make-up requirement...which is what the pump needs to supply, NOT jamming oil through it...

 

[Shannow]

Seriously ????

I'll type very very slowly, so try to keep up...

The bearings need the oil to be replenished due to side leakage.

That side leakage is replenished by the oil pump, which has to provide sufficient pressure to get eh oil to ALL of the places that it needs to be.

The oil pump supplies more volume than is necessary, as it has to allow for all likely states of engine wear, pump wear, viscosity loss in service, and operating temperatures.

The artifact of over-supply is oil pressure, and it's clearly higher when cold, as the side leakage is far less volumetrically.

Also, part of the design parameters are having sufficient pressure to operate hydraulics and supply squirters.

Those quotes that you keep using to defend YOUR position on what I'm saying demonstrate that you are trying to attribute to me a flawed belief system that I don't hold, as it helps "prove your point"...

Yes, higher pressure will always push more oil through them...but THAT isn't the design point, they are not designed to have oil "jammed through them" as you would posit.

Here's me quoting myself...I'll leave you to explain how when I state that the flow rate is linear with RPM, and cube root of pressure differential is denying that flow changes with pressure.

You've tried in those two quotes, and even to the casual observer, your push is irrational, because nowhere have I ever said that more pressure doesn't make more flow (*)

Originally Posted By: Shannow


Anyway...

So linear with RPM, cube root of absolute pressure (1 is atmospheric, and the "p" gauge pressure).


(*) because if I HAD made such a statement, you'd have quoted it.

 

[Shannow]

Originally Posted By: ZeeOSix
Ok, smart arse ... assume it's a 4 cylinder with 4 big end and 5 crank bearings.

If the car needs 24.5 HP to maintain 65 MPH, then the total savings would still only be (9 x 0.034)/24.5 = 1.25%.

Use the same example with the data on the 0.0004" bearing clearance, and it's less than 1%.


But that's ONLY the crank and bearings.

Remember, engines have other components, like pistons and rings, which are a significant source of friction.

Japanese passenger car engines are heading still further down the viscosity path, while improving block rigidity and increasing bearing sizes (more drag), as they are trying to get the piston assembly drag down, and keep bearings alive (wonder why they don't just supply more pressure ???)

OTR engine manufacturers are taking paths to reduce skirt drag like thermal barrier coatings to keep the mid stroke temperatures high (viscosity low), while keeping the viscosity in the bearings at a typical norm, so that they don't have to repackage the bottom end.

 

[ZeeOSix]

Originally Posted By: Shannow
Here's me quoting myself...I'll leave you to explain how when I state that the flow rate is linear with RPM, and cube root of pressure differential is denying that flow changes with pressure.


Yeah, seriously. If you agree that more oil is flowing through a journal bearing due to increased supply pressure then stop making statements like you do after all this was already discussed - and especially if you already claimed that you agreed it does.

Statement made 09/20/16
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4207115/Re:_Oil's_affect_on_motorcycle#Post4207115

Statement made 10/14/16
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4225160/Re:_All_evidence_supports_this#Post4225160

Right back to where you were before the Orlov discussion, almost a month later. Short memory?

But even after the Orlov discussion you keep going back to making statements that journal bearings only flow what they "naturally" want to due to rotation caused by side leakage, even in a pressurized oiling system. And you keep saying that pressure from the PD oil pump doesn't cause oil to flow through them - it's just there to ensure the galleries are full so the bearing can draw oil to make up for side leakage (only true for oil supplied at ATM pressure). You keep making those erroneous statements ... not me. So stop trying to justify that you agree when you still don't by making those same statements even after you claimed you agreed.

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Ok, smart arse ... assume it's a 4 cylinder with 4 big end and 5 crank bearings.

If the car needs 24.5 HP to maintain 65 MPH, then the total savings would still only be (9 x 0.034)/24.5 = 1.25%.

Use the same example with the data on the 0.0004" bearing clearance, and it's less than 1%.


But that's ONLY the crank and bearings.

Remember, engines have other components, like pistons and rings, which are a significant source of friction.

Japanese passenger car engines are heading still further down the viscosity path, while improving block rigidity and increasing bearing sizes (more drag), as they are trying to get the piston assembly drag down, and keep bearings alive (wonder why they don't just supply more pressure ???)

OTR engine manufacturers are taking paths to reduce skirt drag like thermal barrier coatings to keep the mid stroke temperatures high (viscosity low), while keeping the viscosity in the bearings at a typical norm, so that they don't have to repackage the bottom end.


Yes, it's a big engineering game to see who can squeeze that last few percent of fuel mileage out of these engines by cutting down on every sliver of friction. Car designers also need to work on better aerodynamics and less rolling resistance, which would net better fuel mileage gains than saving 1% in engine friction.

 

[Shannow]

OK,
Shannow's position is that the role of the oil pump is to supply oil to the bearing to make up for the natural side leakage. The oil pump provides PRESSURE to get the oil to the worst location (and then more to operated other equipment). They provide excess volume to allow for wear, and all operational conditions, which increases backpressure (oil pressure)....yes, it increases flow, always have agreed that it does, but that pressure is not the design element, it's an artifact of the overdesign.

Zee0Six...the bearings are designed such that they need to be pressure lubricated (oil jammed through them) to provide lubrication and cooling...oh, and they should never be operating in relief.

Note in none of the technical papers do they use your pressure fed concept when talking about bearing flows, the modelled flows are all the typical side leakage flows...why is that do you think ?

Design for "normal", and add a safety margin through pump capacity...it's pretty simple.

 

[ZeeOSix]

Originally Posted By: Shannow
OK,
Shannow's position is that the role of the oil pump is to supply oil to the bearing to make up for the natural side leakage. The oil pump provides PRESSURE to get the oil to the worst location (and then more to operated other equipment). They provide excess volume to allow for wear, and all operational conditions, which increases backpressure (oil pressure)....yes, it increases flow, always have agreed that it does, but that pressure is not the design element, it's an artifact of the overdesign.


Nope, you can't say that in red above when you clearly state in the quotes below that the pump doesn't cause flow through the bearings.

Originally Posted By: Shannow
The oil pump is only supplying oil to make up for the bearing's inherent side leakage, which is influenced by viscosity, RPM, speed, diameter, length, load, and diametrical clearance...it's not "flowing" oil through the bearings.


Originally Posted By: Shannow
Again, bearing parameters determine the oil make-up requirement...which is what the pump needs to supply, NOT jamming oil through it...


______________________________________________

Originally Posted By: Shannow
Zee0Six...the bearings are designed such that they need to be pressure lubricated (oil jammed through them) to provide lubrication and cooling...oh, and they should never be operating in relief.


Wrong ... I never stated that the bearings NEED a pressurized oil supply. I simply stated that the flow is increased in a pressureized system because you keep making statements that claim the pump does nothing but fill the galleries. Go dig up some quotes of mine in those other threads that clearly states (not reading between the lines) that I said journal bearings absolutely NEED pressurized oil to survive.

Originally Posted By: Shannow
Note in none of the technical papers do they use your pressure fed concept when talking about bearing flows, the modelled flows are all the typical side leakage flows...why is that do you think ?


In those other threads I posted quite a few references that talked about increased flow in a pressure fed bearing ... you just chose not to believe it. Here's a couple more for you.

"High-speed and close-clearance fluid-film bearings are difficult to cool. The flow rate through a journal bearing consists of a hydrodynamic portion and a hydrostatic portion. The hydrodynamic flow is proportional to RCw/2 multiplied by a constant which is a function of load or eccentricity e. Here, R = bearing radius, in., C = clearance, in. and w = journal speed, rpm. The hydrostatic flow is proportional to feed pressure and is also a function of feed groove shape, cube of oil-film thickness, and local viscosity."

 

[Shannow]

Seriously, you must have received a significant knock in secret agents school.

 

[ZeeOSix]

Originally Posted By: Shannow
Seriously, you must have received a significant knock in secret agents school.


LoL ... you must have a serious problem with reading comprehension ... even of your own writings. You agree on something, and then turn around and disagree with what you just agreed with.

Here's another classic that shows you do not believe oil supply pressure increases bearing flow. So how can you say above that "yes, it increases flow, always have agreed that it does".

Originally Posted By: Shannow
Again, the function of the oil pump is to provide oil to the bearings, it's not to force it through them.

Bearings draw off from the supply what they need, and the artifact of them needing less than the pump delivery is oil pressure.

No, you don't use pressure to pump the oil through ...

 

[userfriendly]

Is there a change in bearing flow dynamics from a crank bearing to a big end rod bearing that does not have a constant shear velocity?
It seems to me that the rod bearing travels in an elliptical orbit, starting and stopping at top and bottom dead center.
It looks like the oil feed hole on the rod journal follows the unloaded side of the bearing.

 

[d00df00d]

So, in sum: While pump delivery may affect flow rates through the bearings and generate oil pressure, that doesn't mean the purpose of an oil pump is to positively generate those flow rates and that pressure.

Shannow, is that a fair reading of what you're saying?

 

[Jetronic]

pump pressure affects flow rates through the unloaded side of the bearings anyway..