Oil's affect on motorcycle gear shift feel?

[ZeeOSix]

I was playing around with the bearing flow rate formula Shannow showed above that has both the RPM and oil supply pressure variables to see how the flow curves might look. I made an assumption for the "clearance ratio" and bearing diameter and length just so I could see how the RPM and supply variables effected the flow.

Flow increases from both RPM and supply pressure as can be seen in the graph below. The orange line is the flow with no added supply pressure - ie, the bearing was feed at 1 atmosphere (zero gauge pressure). The blue line is the same bearing with the oil supply pressure changing linearly from 30 PSI at 1000 RPM to 90 PSI at 7000 RPM - ie, the typical GM V8 type of oil pressure increase with engine RPM.

 

[Shannow]

Correlates pretty well with some engine data from Ricardo...with constant supply pressure

https://www.ricardo.com/Documents/Downloads/pdf/ringpak_comparison_of_predicted.pdf

Problem is, that as per the racing thread, that engines don't NEED all that volume at the high end, which is WHY you get the pressure curve that you do...it's not needed for addition cooling (the "If the regular flow is insufficient")...so the OEMs are going to variable displacement oil pumps, and here's the link I shared a few days ago.

http://www.melling.com/Portals/0/OE%20Pr...p%20systems.pdf

Clearly, the engine demand is NOT that of a constant volume PD pump with linear delivery flow rate, and the constant pressure rise.

Engine needs more volume per revolution at lower speeds, and oil requirement at higher speeds drops off...a bit like the bearing Q/Qo flow curves show eh ?

 

[ZeeOSix]

Originally Posted By: Shannow
Problem is, that as per the racing thread, that engines don't NEED all that volume at the high end, which is WHY you get the pressure curve that you do...it's not needed for addition cooling (the "If the regular flow is insufficient")...so the OEMs are going to variable displacement oil pumps, and here's the link I shared a few days ago.

Clearly, the engine demand is NOT that of a constant volume PD pump with linear delivery flow rate, and the constant pressure rise.

Engine needs more volume per revolution at lower speeds, and oil requirement at higher speeds drops off...a bit like the bearing Q/Qo flow curves show eh ?


That SAE paper about variable flow (aka: "energy savings" = "fuel savings") pump development, and clearly indicates the technology is driven by the car manufactures trying to save a small amount of wasted power driving a PD pump when the engine's oiling system might not need to be "force fed" as much oil as they currently are.

The required drive power difference between a PD pump and a variable flow pump can be seen in Figure 14 on page 6. The power difference at 6500 RPM is 920 W, which is a "whopping" 1.2 HP. And if this particular engine lives at more like 2500~3000 RPM (more realistic normal use RPM) the difference is only about 200W = 0.27 HP.

I agree that some engines may not need as much oil as the "old fashion" PD pump supplies to keep them from blowing up, but you would never see such a variable flow oil pump on any very high performance engine, and certainly not on that 2.4L V8 Honda F1 engine that revs to 18,000 RPM and has a sky high HP/liter output.

The car manufacturers are splitting hairs and trying to squeeze out another 0.05 MPG by complicating the oiling system.

 

[userfriendly]

If the above is true, increasing engine oil viscosity from SAE 30 to SAE 50 will not change oil pressure with an engine equipped with a variable volume and pressure pump.
Would engine "requirement" fall further below "flow delivered" on the graph with a thicker oil at the same supply pressure?

 

[ZeeOSix]

Originally Posted By: userfriendly
If the above is true, increasing engine oil viscosity from SAE 30 to SAE 50 will not change oil pressure with an engine equipped with a variable volume and pressure pump.
Would engine "requirement" fall further below "flow delivered" on the graph with a thicker oil at the same supply pressure?


If the oiling system was really purely pressure controlled, then using a thicker oil will reduce the volume of oil flowing through the journal bearings. The viscosity affects both the flow due to bearing RPM (ATM feed pressure flow), and the flow due to pressure feeding above atmospheric pressure (pressure fed flow).

But it sounds like some of these variable flow oil pumps are still PD types, it's just that the output volume is variable, and the pump still forces the reduced positive displacement volume like a traditional PD pump.

 

[Shannow]

Originally Posted By: ZeeOSix
But it sounds like some of these variable flow oil pumps are still PD types, it's just that the output volume is variable, and the pump still forces the reduced positive displacement volume like a traditional PD pump.

the one in the link (and every other one that I've seen) has a control mechanism like this

So basically they are an oversized PD pump, with volume control related to discharge pressure...that way they can deliver more oil at lower RPM, and reduce output at higher RPM.

so userfriendly's posit that more viscosity would be less flow is spot on.

Higher viscosity, less draw from things like bearings, increased backpressure (aka oil pressure), and the pump runs back to deliver less volume.

 

[ZeeOSix]

Originally Posted By: Shannow
so userfriendly's posit that more viscosity would be less flow is spot on.


Only if the pump was a purely pressure controlled device (ie, not a true PD design).

If it was a variable volume controlled PD pump, the supply pressure would just increase slightly with a higher viscosity oil and the PD feeding flow would remain the same - until of course the pump hit pressure relief or max volume output. But the bearing's "self feeding" flow factor (ATM flow factor) would decrease due to the increased viscosity.

 

[Shannow]

Look at the pic I posted.

It is BOTH positive displacement, and variable flow AND pressure controlled...well that's more than both.

 

[ZeeOSix]

I'll back up a bit. Based on the bearing flow equations, the oil viscosity affects both flow modes (ATM fed and pressure fed factors) regardless of what the bearing characteristic number is, or what the supply pressure is. Both curves as I plotted before will decrease if a higher viscosity oil is used in the calculations.

Originally Posted By: Shannow
Look at the pic I posted.

It is BOTH positive displacement, and variable flow AND pressure controlled...well that's more than both.


What I was trying to get at was if an oil pump was truly just controlling the supply pressure over the entire operating range, then using a thicker oil will result in less flow at the same pressure, whereas a true PD pump (even if a variable flow design) will still try to force its output volume through the system which will result in a higher oil supply pressure.

You either control the PD output volume or you control the supply pressure in the realm of operation below the relief pressure. The pressure control part of a true PD pump (variable flow or not) is there to only limit the maximum supply pressure.

 

[Shannow]

Originally Posted By: ZeeOSix
You either control the PD output volume or you control the supply pressure in the realm of operation below the relief pressure. The pressure control part of a true PD pump (variable flow or not) is there to only limit the maximum supply pressure.


Look at the picture that I posted...you can clearly see that the volume of the swept cavity (therefore the volume per revolution) is changed in response to pressure to keep the discharge pressure constant (or as constant as it can be)...pretty simple picture, not that hard to comprehend really....it's CONTROLLING pressure by varying flow rate.

Not a "relief" function...it's just not jamming flow through the bearings, simply because the bearings don't NEED to have oil jammed through them.

 

[ZeeOSix]

Originally Posted By: Shannow
Look at the picture that I posted...you can clearly see that the volume of the swept cavity (therefore the volume per revolution) is changed in response to pressure to keep the discharge pressure constant (or as constant as it can be)...pretty simple picture, not that hard to comprehend really....it's CONTROLLING pressure by varying flow rate.


Like I said in the other thread - there was no information in that write-up to indicate the pump is actually controlling the oil supply to a constant pressure. It's simply a variable flow PD pump that controls the output volume to give less volume output in the higher RPM range compared to a fixed output PD pump.

If you read that SAE paper again about the variable flow vane pump you showed above (Fig 4), they are saying the variable output pump controls the output volume of the pump, and doesn't even use a pressure relief of any kind. It is not controlling the supply pressure to a constant value - it's only controlling the output volume based on the demand they think the engine needs over its RPM range (ie, the flow demand graph). The oil pressure the engine sees at any given RPM is the result of the pump only controlling the output volume. If the pump output volume decreases, so does the supply pressure (with all other factors held constant).

If the supply pressure was actually held constant at all times like you think these variable flow pumps work, then the flow volume through the oiling system would be highly influenced by the oil viscosity as it changed temperature, and you would have much less flow at a constant supply pressure with thick cold oil than with hot thin oil. Not really a good way to supply oil to the engine. The variable flow pumps are still true PD pumps, they just vary the output volume independent of engine RPM.

 

[Ducman]

As stated quite correctly many times on this forum.
Pressure is a measure of resistance to flow.

With the shown Shannow's example of the rather clever variable displacement pump design.
It's to be assumed there is no pressure relief mechanism integrated into the pump design or assumedly into the lubrication circuit of the unit somewhere else.
It's the simplest form of a self regulating pressure system which automatically compensates for oil thinning, with the resistance to flow occurring at the crankshaft and or cam phasers(if fitted) being the only determining factor with absolutely no requirement for a separate pressure relief mechanism, by automatically varying pump displacement as required.
Brilliant really.
There's no indication that the variable displacement pump in the shown example supplies less oil volume than is required by the engine at higher RPM's.
The supply volume is dictated by demand and the variable pump volume is compensating for side leakage.
We must trust the engine manufacturer has done their homework as to the reliability of the engine assembly through their durability testing.

It's a good thing I don't have to worry about this issue as my Gm LS2 never goes over about 55 PSI(dead cold) or under about 45 PSI(stinking hot) anyway regardless of oil viscosity or temp. It's all good.

 

[Shannow]

Originally Posted By: ZeeOSix
I doubt the flow split percentage changes enough in all the elements comprising the oiling system to even matter or could even be measured. You have a reference white paper where it was proven that the flow spit is changing dramatically under different engine PRM (ie, varying oil pump volume/pressure outputs)?


Yep...all the same...

 

[Shannow]

Should have used this one...

yeah, exactly the same "flow percentage"

 

[BrocLuno]

Which is why, in my estimation, we'll see constant flow pumps driven electrically in the future. All loads not absolutely required to make an engine run, will be shifted to the electrical side like cooling fans are now ...

The parasitic loads will be ECU controlled and reduced to the minimum. The alternator will become the crucial component in these systems, even in non-hybrid applications. So maintenance will become more about maintaining electrical connections, conductivity, voltage loss, etc.

We see some MFG's talking 48v systems now. Aircraft and marine have been at 24v for a long time. We'll get there in short order for cars

But, what this all has to do with shift feel for motorcycles I don't have the foggiest

 

[ZeeOSix]

Originally Posted By: Shannow
Should have used this one...

yeah, exactly the same "flow percentage"

Another example of you not actually grasping what's being said. Look at the same graph where I have put vertical red lines at the various RPM points. The percentage of the total flow split between the components basically remains the same as RPM increases, except the crank pin does deviates somewhat in the high RPM end because it stays more linear and doesn't knee over like the other components do. The same is basically true for all practical purposes in the other graph you showed of required oil flow to each component.

I've said it before to help get you back on track - I'm not saying that each component gets the same exact split percentage of the total. Listen carefully, I'm saying the percentage split that each component gets of the total flow basically stays the same (whatever that split happens to be) as the RPM increases. And that is basically what you are seeing in this graph, except for the slight deviation of the crank pin flow.

 

[Shannow]

OK, so in order
* the percentage of total flow stays basically the same
* except the big end flow which is different.
* You are NOT saying that each component gets the same percentage split of the total; but
* You ARE saying that the percentage split that each component gets of the total stays basically the same.

* and the crankpin is different, but that's immaterial.

Clear as mud Chief.

 

[SlipperyPete]

Why don't you guys start a freakin' bearing lubrication thread? I'm surprised a mod hasn't deleted all of your off topic [censored] and banned you both.

 

[Shannow]

I started a thread on Honda's F1 engine here...

https://bobistheoilguy.com/forums/ubbthreads.php/topics/4211293/1

And he took to that one too...defacto bearing thread now.

 

[ZeeOSix]

Originally Posted By: Shannow
OK, so in order
* the percentage of total flow stays basically the same
* except the big end flow which is different.
* You are NOT saying that each component gets the same percentage split of the total; but
* You ARE saying that the percentage split that each component gets of the total stays basically the same.

* and the crankpin is different, but that's immaterial.

Clear as mud Chief.


It is clear if you can actually follow along and comprehend what's being said.

Actually, to be more accurate it's more along the lines of:
* the percentage split of total flow going to each individual engine components stays basically the same.