Oil's affect on motorcycle gear shift feel?

[ZeeOSix]

What do you think the whole purpose of a PD oil pump is on an engine? It's to FORCE FEED the bearings. Modern high HP engines have to have FORCE FED journal bearings to make them handle the load and heat and last way longer than if they were not pressure fed.

Where do you think all that oil volume goes that leaves the PD oil pump? Do you think it's just circulates around and around in empty oil galleries and never goes through all the bearings?

How in the world do you explain what was happening in the video I posted a few pages back of the NON RUNNING engine being pressure fed oil, and all that oil was dripping out of every crank, rod and camshaft bearing at a significant flow?

You are so fixated on NON PRESSURIZED journal bearings that you are totally blind to what's really going on in a modern IC engine with a pressurized oiling system. As my mechanical design handbook clearly shows, there is a difference on how oil flows through a PRESSURE FED vs non pressure fed (ie, fed at atmospheric pressure) journal bearing. Yet you fail to believe it, or to even dig out your handbook (if you even have any), or do some Google searching like I suggested on pressure fed bearings to school yourself. You won't listen to me, so maybe you'll listen to what information is out there that reflects exactly what I've been saying.

You are so locked in and blind to what atmospheric fed bearing are all about that you can't understand the difference between them and pressure fed bearings. This is now just a waste.

 

[ZeeOSix]

Originally Posted By: Shannow
Google
"oil pressure requirement automotive engine bearings", and see how many scientific hits you get...


Maybe you should Google it yourself ... and you'd find that the requirement is that they are pressure fed, which means lots of volume is forced through them, just as I've shown.

 

[ZeeOSix]

Here's a couple of Google search hits for "pressure fed journal bearings". Why can't you see the difference between non-pressure fed (the world you're stuck in) and pressure fed journal bearings (which you apparently don't even believe they exist). There is a ton of info supporting what the difference is.

http://www.mathworks.com/help/physmod/hy...w.mathworks.com
"The lubricant under pressure p is pumped into the circumferential groove at the center of the bearing."
As seen in this link also, the flow volume through the bearing is a function of the supplied oil pressure and viscosity, and of course the dimensional properties of the bearing itself.

https://www.highpowermedia.com/blog/3526/principles-of-journal-bearing-design
"Hydrodynamic lubrication does not depend upon the introduction of lubricant under pressure, but it does require an adequate supply of oil at all times. The oil film pressure is created by the moving surface dragging the lubricant into a wedge shaped zone at a sufficiently high velocity to create the pressure to separate the surfaces. Heat is generated within the bearing due to the work performed by shearing of the oil film as the journal rotates in the bearing. A pressure fed system is used to force greater oil flow through the bearing to improve cooling. Hydrodynamic lubrication is sometimes referred to as full film, fluid, or thick film lubrication."

 

[userfriendly]

If I took the oil pan off an engine and placed the oil pump pick-up in a remote supply, plumbed the pressure relief into a holding tank then bar'd the engine over by hand, for every revolution, an equal amount of oil would drip into a catch pan. Because of the low pressure and time allowed for leakage, that amount would equal the positive displacement of the pump.

If instead, I motored the engine with an electric motor capable of the peak rpm of the test engine, what would happen as the rpm increased?
I think the oil pressure would rise with rpm, as there would be less leakage time at the bearings. There would be more flow from metered orifices, such as piston coolers and valve train components as the pressure increased.

Unless the oil was thin enough to avoid operating the pump in relief (!), excess oil would flow into the holding tank.

Maybe an over simplification, but that is how I see it.

 

[ZeeOSix]

Originally Posted By: userfriendly
If I took the oil pan off an engine and placed the oil pump pick-up in a remote supply, plumbed the pressure relief into a holding tank then bar'd the engine over by hand, for every revolution, an equal amount of oil would drip into a catch pan. Because of the low pressure and time allowed for leakage, that amount would equal the positive displacement of the pump.

If instead, I motored the engine with an electric motor capable of the peak rpm of the test engine, what would happen as the rpm increased?
I think the oil pressure would rise with rpm, as there would be less leakage time at the bearings. There would be more flow from metered orifices, such as piston coolers and valve train components as the pressure increased.

Unless the oil was thin enough to avoid operating the pump in relief (!), excess oil would flow into the holding tank.

Maybe an over simplification, but that is how I see it.


There would also be more flow dripping from every journal bearing as the oil pressure was increased, until the PD pump hit its pressure relief setting. The video I posted of someone pre-oiling the engine shows exactly what's happening and what you are describing.

https://www.youtube.com/watch?v=iy_OmYl21hA

If there was no pump pressure relief, and you spun that PD pump until the pressure in the oil galleries was at 200 PSI, the journal bearings would be spewing oil like mad compared to if the pump was only spun up to make 10 PSI in the oil galleries. Keep in mind that the pump is PD and if not in pressure relief all volume leaving it must go somewhere throughout the oiling system.

The simplest concept in fluid flow is that the oiling system is pressure fed - fluids flow from a high pressure to a low pressure, and if pressure is increased so is flow volume.

 

[userfriendly]

If instead of a mechanically driven pd pump, an electric pump is hooked up and held to 80 psi for example, would oil flow increase proportionately to rpm?

On topic, the clutch on most motorcycles engages the transmission to the final drive, not the engine to the transmission.
I can shift all day long without using the clutch by creating back-lash with the throttle.
During that moment, I suspect there is no engine power or engine brake loading on the transmission gears.

 

[ZeeOSix]

Originally Posted By: userfriendly
If instead of a mechanically driven pd pump, an electric pump is hooked up and held to 80 psi for example, would oil flow increase proportionately to rpm?


The flow increases proportionally to the supply pressure - if all other variables are held constant.

See the flow equation for pressurized journal bearings. If the supply pressure "p" goes up, so does the flow "q" through the bearing.
http://www.mathworks.com/help/physmod/hy...w.mathworks.com

 

[ZeeOSix]

Originally Posted By: userfriendly
On topic, the clutch on most motorcycles engages the transmission to the final drive, not the engine to the transmission.
I can shift all day long without using the clutch by creating back-lash with the throttle.
During that moment, I suspect there is no engine power or engine brake loading on the transmission gears.


You can shift all day long on a motorcycle without using the clutch (and slightly taking the load off the gears by reducing throttle a bit) because the transmission is a "constant mesh" design. It does not use synchronizers like in a car manual transmission. You can actually shift a transmission with syncronizers too without a clutch if you know that exact way to do it - but it's a lot easier on a bike with the constant mesh transmission.

When the clutch on a bike is disengaged, if there is enough oil drag between the clutch plates then the main shaft will still turn when in neutral. The gear on the engine's crankshaft is spinning the outside clutch basket, and the oil drag between the clutch plates will cause the inner basket and the main shaft of the transmission that is connected to the basket to spin.

In neutral, the counter shaft (the shaft the counter shaft sproket is on) is not turning at all. So when you put the bike in 1st gear you get a gear that is turning on the main shaft to mate with a gear on the counter shaft that is not turning. The result is a nice "clunk" as the two gears engage.

 

[Shannow]

Originally Posted By: ZeeOSix
Originally Posted By: userfriendly
If instead of a mechanically driven pd pump, an electric pump is hooked up and held to 80 psi for example, would oil flow increase proportionately to rpm?


The flow increases proportionally to the supply pressure - if all other variables are held constant.


Except the question was with a constant supply pressure, what happens to flow rate as RPM increases...

You didn't answer that it, of course, increases with RPM...all else being equal of course.

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Originally Posted By: userfriendly
If instead of a mechanically driven pd pump, an electric pump is hooked up and held to 80 psi for example, would oil flow increase proportionately to rpm?


The flow increases proportionally to the supply pressure - if all other variables are held constant.


Except the question was with a constant supply pressure, what happens to flow rate as RPM increases...

You didn't answer that it, of course, increases with RPM...all else being equal of course.


Got ya ... so in order to determine how the oil flow rate (q) would change in a pressure fed bearing just due to changing RPM with the pressure (p) held at 80 PSI and all other parameters held constant, you would have to determine what the change in the relative eccentricity ratio would be as a function of RPM. Only the eccentricity ratio would change slightly in that case, which would make the pressure fed flow rate (q) change slightly. But the question is just how much of a change is it really over the RPM range?

Once the bearing starts rotating pretty good above an idle state, I doubt the eccentricity ratio changes by very much since the clearances in most journal bearings is very small to start with compared to the radius of the journal (e is going to be way smaller than r). You have any kind of info that shows the relationship of how the eccentricity (e) changes with bearing RPM?

Be interesting to run some numbers to see just how sensitive the eccentricity ratio is on the bearing's flow rate. Just by looking at the physical dimension relationship, the eccentricity ratio is going to be a very small number, especially when a number less than 1 is squared (e smaller than r makes the ratio way less than 1).

 

[ZeeOSix]

Just by looking at the physical dimension relationship of a journal bearing, the relative eccentricity ratio is going to be a very small number, especially when a number less than 1 is squared (e is always going to be much smaller than r - squaring that will make it even smaller). The correction term in parenthesis in the flow equation really doesn't make much of a difference at all to the bearing flow rate. The supply pressure is the main parameter that effects the flow rate (q). If the bearing journal happens to ride up concentric to the center of the bearing, then the eccentricity ratio becomes zero, and the small correction term in parenthesis disappears entirely.

Therefore, you can conclude that the flow rate through a pressure fed journal bearing is basically just a function of the supply pressure, and not much (if at all) from engine RPM.

 

[Shannow]

Originally Posted By: ZeeOSix
Therefore, you can conclude that the flow rate through a pressure fed journal bearing is basically just a function of the supply pressure, and not much (if at all) from engine RPM.


Nope, you can't...that matlab example is for laminar flow on long cylinders what the continuity of the Hagan Poisiuelle equations give...It completely ignores shaft rotation in and of it's first principals.

It is not using the dynamics of actual bearing operation, i.e. pressure increase into the load bearing area which is the primary driver of side leakage.

It suits your magically stopped shaft example, nd by relying on a magically stopped shaft, it automatically draws you into discounting the hydrodynamics of the bearing in the first place...which is what you have been trying to achieve for the last however long.

Because a stationary shaft with laminar end flows is NOT what happens in a bearing, pressure fed or otherwise.

If a gravity fed bearing (That's a supply pressure in and of itself) increases flow with RPM, then a pressure fed bearing does too.

 

[Silk]

Originally Posted By: ZeeOSix
You can shift all day long on a motorcycle without using the clutch (and slightly taking the load off the gears by reducing throttle a bit) because the transmission is a "constant mesh" design. It does not use synchronizers like in a car manual transmission.


Car and truck gearboxes are also constant mesh, it just that in a car trans the sliding dogs have syncromesh fitted. You can drive a truck all day without using the clutch too - some I've driven you couldn't use the clutch anyway.

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Therefore, you can conclude that the flow rate through a pressure fed journal bearing is basically just a function of the supply pressure, and not much (if at all) from engine RPM.


Nope, you can't...that matlab example is for laminar flow on long cylinders what the continuity of the Hagan Poisiuelle equations give...It completely ignores shaft rotation in and of it's first principals.

It is not using the dynamics of actual bearing operation, i.e. pressure increase into the load bearing area which is the primary driver of side leakage.

It suits your magically stopped shaft example, nd by relying on a magically stopped shaft, it automatically draws you into discounting the hydrodynamics of the bearing in the first place...which is what you have been trying to achieve for the last however long.

Because a stationary shaft with laminar end flows is NOT what happens in a bearing, pressure fed or otherwise.

If a gravity fed bearing (That's a supply pressure in and of itself) increases flow with RPM, then a pressure fed bearing does too.


After looking at some more info and doing a few bearing flow calculations, and looking at the flow dependence due to the bearing RPM, also assuming that the dynamic flow behaves the same even if the bearing is pressurized, then the total flow should be the summation of the gravity fed flow + pressure fed flow. I couldn't find a direct reference clarifying that's totally true, but logically that seems right. So I agree that the total flow is not totally pressure dependent when the bearing is rotating.

So the question is, which one dominates the flow? That all depends on all the exact bearing parameters involved, but in any case it's still true that pressurized bearings will always flow more oil than non-pressurized, even when they are rotating.

 

[ZeeOSix]

Originally Posted By: Silk
Originally Posted By: ZeeOSix
You can shift all day long on a motorcycle without using the clutch (and slightly taking the load off the gears by reducing throttle a bit) because the transmission is a "constant mesh" design. It does not use synchronizers like in a car manual transmission.


Car and truck gearboxes are also constant mesh, it just that in a car trans the sliding dogs have syncromesh fitted. You can drive a truck all day without using the clutch too - some I've driven you couldn't use the clutch anyway.


Yes, agreed that car and truck transmissions can also be shifted without the clutch if done correctly ... but seem to be a bit more tricky to do than on a motorcycle transmission. On many of the dirt bikes I've owned, the only time I would use the clutch was to start from a dead stop.

 

[Silk]

Motorcycle gearboxes are not engine speed, there is a primary reduction. Athough I can clutchless shift on my BMW, but it is a slow deliberate process like a truck...downshifts are easy and faster without the clutch.

 

[Shannow]

Originally Posted By: ZeeOSix
So the question is, which one dominates the flow? That all depends on all the exact bearing parameters involved, but in any case it's still true that pressurized bearings will always flow more oil than non-pressurized, even when they are rotating.

Had a post ready, but Windows 10 decided that it needed my machine more than I did.

I've got Shigley, it was a mandatory text, but in Imperial, so I also bought Orlov, "Fundamentals of Machine Design", as being Russian, it was (mostly) metric...still used calories, and RPM rather than Radians

It's still a good set of books, has lots of design inversion (e.g stationary shaft, spinning journal like a rotary radial engine isn't the same as a regular radial in therms of how bearing pressure profiles work etc.)...

Anyway...

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

 

[ZeeOSix]

^^^ Good find on flow and temperature rise equations that address both speed and supply pressure together in one equation. I don't see any viscosity term in the flow equation, so was that equation simplified for an example that already stated the oil viscosity? The "3.3x10^-3" term must be the viscosity defined somewhere earlier. Was there a more "raw" version of the equation shown earlier in the book?

 

[Shannow]

Yep, dimensional analysis shows that the formula isn't complete, by the values within the cube root.

It's a practical russian text that starts at the point of what sort of machining tolerances are available (remember it's the 70s), then has you check the sommerfeld and bearing characteristics for the range of tolerances within the design...for stability, basically if it's not stable, not worth bothering with (been there, fought that on a Generator drive end 21"OD, 19" length that was too close to the stability line, had to purposelt misalign, and choke the oil supply to get it to behave)...then picks the design point in the middle of those ranges as "constants" for the bearing.

 

[userfriendly]

Would oil temperature in addition to pressure affect the flow rate through a bearing (use a mono-grade to avoid VII influence)?
Zee mentioned that there might be a change in flow between a stationary and a rotating shaft, but would flow continue to increase with rpm?
The oil when cold would cause more fluid friction than when hot and create more heat in the process, but that would take shear, a product of rpm.