Yes, I see the "oil demand" graph, and you are correct that on that particular graph the demand drops off more in the higher RPM range. No real information given if that graph takes into account bearing temperature rise or not. If bearings are found to have a significant temperature rise with their design, then the flow could be increased more in the higher RPM range - which means the flow demand curve would not knee over as much as what's shown in the graph above. But in any case, yes ... the bearing's "demand" for oil flow drops off as RPM increases per the bearing "Sommerfeld Number".
The only benefit there might be to safely cutting supply volume to the bearings is to save 1% or less in oil pump input drive power as mentioned in the paper. Obviously "over feeding" the bearings isn't going to hurt, and like in the example of the Honda V8 F1 engine, is probably required for that engine to survive. As you saw in the F1 engine write-up, the total max flow is about 20 GPM (75L/min), and the flow vs RPM curve is almost a straight line. Also, the twin rotor PD pump system they use basically feeds the oiling system with a near linear output vs RPM. So the last thing on those engine designer's mind is cutting back the oil flow in the high RPM range of the engine - and for good reasons. Surely not to save 0.3 MPG.
Originally Posted By: Shannow
... remember too (again, as they keep dropping off your radar for whatever reason) the big ends too...they are clearly NOT pressure fed per your assertion).
So if you are referring to the "big ends" as the big ends of the piston rods, then they certainly are pressure fed oil. There are holes drilled in the crankshaft to bring oil under pressure right into the supply groove of the big end rod bearings. The "small ends" (ie, the piston wrist pin bearing) is not pressure fed, but instead either supplied oil by squirters or simply from the splashed oil getting up underneath the piston.
Originally Posted By: Shannow
Here's the general design that they follow to achieve the more volume at low RPM, less at high.
Basically they are oversized, and pressure controlled to a constant output pressure.
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.
The only benefit there might be to safely cutting supply volume to the bearings is to save 1% or less in oil pump input drive power as mentioned in the paper. Obviously "over feeding" the bearings isn't going to hurt, and like in the example of the Honda V8 F1 engine, is probably required for that engine to survive. As you saw in the F1 engine write-up, the total max flow is about 20 GPM (75L/min), and the flow vs RPM curve is almost a straight line. Also, the twin rotor PD pump system they use basically feeds the oiling system with a near linear output vs RPM. So the last thing on those engine designer's mind is cutting back the oil flow in the high RPM range of the engine - and for good reasons. Surely not to save 0.3 MPG.
Originally Posted By: Shannow
... remember too (again, as they keep dropping off your radar for whatever reason) the big ends too...they are clearly NOT pressure fed per your assertion).
So if you are referring to the "big ends" as the big ends of the piston rods, then they certainly are pressure fed oil. There are holes drilled in the crankshaft to bring oil under pressure right into the supply groove of the big end rod bearings. The "small ends" (ie, the piston wrist pin bearing) is not pressure fed, but instead either supplied oil by squirters or simply from the splashed oil getting up underneath the piston.
Originally Posted By: Shannow
Here's the general design that they follow to achieve the more volume at low RPM, less at high.
Basically they are oversized, and pressure controlled to a constant output pressure.
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.
