Does high oil pressure help film strength? Thinking of motors like the Ford Coyote V8 that runs on 5w20 and produces oil pressure of 20 to 25 psi per 1000 rpm - - about twice what used to be the norm of 10 psi per 1k rpm.
Does Oil Pressure Help Film Strength?
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Pressure too!
Ok, give speed on surface, give load, give viscosity and lower the pressure below minimum to see the big picture ... And you cant separate it from flow, since given the same clearance a bigger pressure translate, to bigger flow. Just blow a straw to see. The harder the pressure more liquid transported in a given time.
Am I wrong?
Ok, give speed on surface, give load, give viscosity and lower the pressure below minimum to see the big picture ... And you cant separate it from flow, since given the same clearance a bigger pressure translate, to bigger flow. Just blow a straw to see. The harder the pressure more liquid transported in a given time.
Am I wrong?
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Originally Posted By: Pontual
Pressure too!
Ok, give speed on surface, give load, give viscosity and lower the pressure to see the big picture ...
Oil pressure of a few tens of psi does nothing to the oil film thickness, where the pressures are hundreds of psi or more.
Unless in "lowering the pressure", you get to the point that there is insufficient supply to the bearings, then everything goes south...the absence of sufficient oil does not make pressure a variable in MOFT.
But in the presence of adequate oil supply, pressure in and of itself does nothing.
Pressure too!
Ok, give speed on surface, give load, give viscosity and lower the pressure to see the big picture ...
Oil pressure of a few tens of psi does nothing to the oil film thickness, where the pressures are hundreds of psi or more.
Unless in "lowering the pressure", you get to the point that there is insufficient supply to the bearings, then everything goes south...the absence of sufficient oil does not make pressure a variable in MOFT.
But in the presence of adequate oil supply, pressure in and of itself does nothing.
Originally Posted By: Pontual
And you cant separate it from flow, since given the same clearance a bigger pressure translate, to bigger flow. Just blow a straw to see. The harder the pressure more liquid transported in a given time.
Am I wrong?
sorry, you edited while I was posting.
Bearings take oil from the supply galleries, in sufficient quantity to make up for the side leakage that occurs.
The fact that the oil pump supplies more oil than they need is shown by the presence of oil pressure...pump supplies more volume than they need, and the backpressure rises.
It's not pushing more oil through like volume through a straw, the bearings take only what they need.
This pic was lifted from a paper where they separated a particular bearing from the oil galleries, and provided a constant supply pressure through a measuring device.
The HTHS changed the amount of oil that the bearing drew from the galleries all other things being equal.
The inverse of the experiment, and CATERHAM has proved it in his engine is that if reversed, the lower HTHS provides lower oil pressure than higher HTHS.
And you cant separate it from flow, since given the same clearance a bigger pressure translate, to bigger flow. Just blow a straw to see. The harder the pressure more liquid transported in a given time.
Am I wrong?
sorry, you edited while I was posting.
Bearings take oil from the supply galleries, in sufficient quantity to make up for the side leakage that occurs.
The fact that the oil pump supplies more oil than they need is shown by the presence of oil pressure...pump supplies more volume than they need, and the backpressure rises.
It's not pushing more oil through like volume through a straw, the bearings take only what they need.
This pic was lifted from a paper where they separated a particular bearing from the oil galleries, and provided a constant supply pressure through a measuring device.
The HTHS changed the amount of oil that the bearing drew from the galleries all other things being equal.
The inverse of the experiment, and CATERHAM has proved it in his engine is that if reversed, the lower HTHS provides lower oil pressure than higher HTHS.
Pressure can float a shaft though. I know you've talked about the turbine shaft jacking system that operates when the differential speed between the shaft and bearing is too slow to create an oil wedge.
A birthday cake today? Really?
A birthday cake today? Really?
Yep, oil injected at the point of maximum pressure CAN float a shaft, and as you say, turbine bearings often have jacking oil to get the parts apart to allow run-up.
But that's 3,000 psi oil, injected against the stationary load to do the lifting.
In the case of an engine, pressurised oil going in at the 12:00 position when the point of MOFT at 6:00 is going to do nothing (good or bbad).
Yep, except I didn't get a birthday cake this year...
But that's 3,000 psi oil, injected against the stationary load to do the lifting.
In the case of an engine, pressurised oil going in at the 12:00 position when the point of MOFT at 6:00 is going to do nothing (good or bbad).
Yep, except I didn't get a birthday cake this year...
Originally Posted By: Shannow
In the case of an engine, pressurised oil going in at the 12:00 position when the point of MOFT at 6:00 is going to do nothing (good or bbad).
Some bearings are grooved, so I wonder? A hundred psi gives about a hundred pounds lift at each journal. Many street engines have no more than 400 ft/lbs torque.
Just thinking out loud.
In the case of an engine, pressurised oil going in at the 12:00 position when the point of MOFT at 6:00 is going to do nothing (good or bbad).
Some bearings are grooved, so I wonder? A hundred psi gives about a hundred pounds lift at each journal. Many street engines have no more than 400 ft/lbs torque.
Just thinking out loud.
I'm thinking the shaft will tend to center. With bearings that are grooved all the way around with thick oil.
If you had full grooves, the pressure could be 360 degrees.
However equal pressure all round provides no nett force, so there's no "centering effect"
to achieve a hydrostatically centred bearing, you need three minimum injection points, and some bearing chambers to stop it flowing easily circumferentially.
However equal pressure all round provides no nett force, so there's no "centering effect"
to achieve a hydrostatically centred bearing, you need three minimum injection points, and some bearing chambers to stop it flowing easily circumferentially.
Originally Posted By: Shannow
If you had full grooves, the pressure could be 360 degrees.
However equal pressure all round provides no nett force, so there's no "centering effect"
to achieve a hydrostatically centred bearing, you need three minimum injection points, and some bearing chambers to stop it flowing easily circumferentially.
Thinking that's why oil pressure is so crucial-- to help provide the net effect. Creating the net effect of hydrostatic self centering to further aid what should be a natural distribution due to rotating assemblies. Just a thought.
If you had full grooves, the pressure could be 360 degrees.
However equal pressure all round provides no nett force, so there's no "centering effect"
to achieve a hydrostatically centred bearing, you need three minimum injection points, and some bearing chambers to stop it flowing easily circumferentially.
Thinking that's why oil pressure is so crucial-- to help provide the net effect. Creating the net effect of hydrostatic self centering to further aid what should be a natural distribution due to rotating assemblies. Just a thought.
Oil pressure, flow rate, and galley/orifice size is analagous to volts, amps, and resistance in an electric circuit.
This may help to visualize what's going on. We know more resistance at a given voltage results in less flow.
In this case, its somewhat more like amps (flow) is fixed at a given oil pump RPM, then the viscosity of the oil and galley sizes determine resistance to flow, which means volts (oil pressure) goes up to maintain that fixed amps (flow).
This may help to visualize what's going on. We know more resistance at a given voltage results in less flow.
In this case, its somewhat more like amps (flow) is fixed at a given oil pump RPM, then the viscosity of the oil and galley sizes determine resistance to flow, which means volts (oil pressure) goes up to maintain that fixed amps (flow).
I prefer to see pressure as voltage and flow as amperage. Thats the classic definition. Resistance could be the clearances... could see the bearings/journals as repelling magnets. But if you raise the voltage has no intensified reppel effect ?
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Well I hope your right, because the oil pressure is way down with 0W30 in my 3500 Duramax. More intake noise with the lighter engine oil which must mean the turbo is spooling up quicker. My pucker-point is around 3.4 HTHS with these engines. To go lower, perhaps 2.9, the oil would likely have to be VII free.
Oil pressure and piston cooling is another subject.
Oil pressure and piston cooling is another subject.
MolaKule
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Quote:
We know more resistance at a given voltage results in less flow.
No, more resistance in an electrical circuit results in less current flow "through" the resistance and more voltage drop "across" the resistance.
Quote:
In this case, its somewhat more like amps (flow) is fixed at a given oil pump RPM, then the viscosity of the oil and galley sizes determine resistance to flow, which means volts (oil pressure) goes up to maintain that fixed amps (flow).
In hydraulics yes, but not in electrical circuits.
We know more resistance at a given voltage results in less flow.
No, more resistance in an electrical circuit results in less current flow "through" the resistance and more voltage drop "across" the resistance.
Quote:
In this case, its somewhat more like amps (flow) is fixed at a given oil pump RPM, then the viscosity of the oil and galley sizes determine resistance to flow, which means volts (oil pressure) goes up to maintain that fixed amps (flow).
In hydraulics yes, but not in electrical circuits.
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you can have constant current power supplies, which obviously adjust the voltage to keep current stable
Yep, but a rather stronger pressure will fill the groove in time to push the caps out of the journals creating a competent wedge.
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