Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Originally Posted By: Shannow
But you posit that they are jamming a full pump's volume THROUGH that engine at every other point of the curve to keep temperatures (the extreme end of the bell curve) again under control ?
In a high performance engine application, that would fall into the displacement per revolution spec of the pump
if determined that bearing temperature control needed to be part of the pump design criteria. But it doesn't mean that the same oil pump would need to be in pressure relief at 70% of redline revs. Those variables are not mutually dependent.
See, you are now coming around to the "if" part, which was exactly what your Shigley excerpt stated...IF you need additional cooling supply more pressure, which you've taken as "always"...when nearly every engine paper I've offered starts with the short bearing approximation flow rate, i.e. independent of pressure, to determine the need for additional flow.
This is another example of you forming false viewpoints of what I've actually said. Bearing designers certainly do look at the oil film temperature rise in any bearing design exercise (pressurized or not), and I said they certainly could use oil supply pressure as a way to help control film temperature and ensure some safety margin in the MOFT ... mostly in high specific power engines (like discussed in the aviation article). Yes, it's an "IF" ... just like many other design exercises that address "ifs" in order come up with a proper solution. I've never said excess supply pressure is mandatory or an "always" in bearing design.
Here's a Tribology International paper (that I showed in another thread, but you purposely ignored) that discusses the two bearing oil flow factors (hydrodynamic flow, Qh and the feed pressure flow, Qp) which comprises the total bearing oil flow Q,leakage. See page marked 827.
http://web.iitd.ac.in/~hirani/rapid_perfromancce.pdf
It also specifically addresses the bearing temperature rise on pages marked 828-829. You can see in the temperature rise equation that Q,leakage (which contains Qp) is a factor in the denominator, so if Qp goes up, so does Q,leakage which also means the temperature rise goes down. So yeah, engines with PD pumps and pressurized oiling systems certainly do have the supply oil pressure considered in the bearing design. Again, the supply pressure required will be specific to the engine design as a total system, so there are many factors involved, but bearing oil film temperature certainly
could be a big factor in some engine designs.
Originally Posted By: Shannow
Given that the engine requires MORE per revolution flow at lower revs, with a static displacement pump, you can't escape it being in relief for a fairly significant amount of the time. Not sure what you'r 70% came from, means, or why you keep referencing it, but if it helps you, keep using it.
THAT is why they are going to variable displacement oil pumps...more flow/RPM down low, and less flow/RPM up top...where the engine needs less...per mellings
Most typical modern engines I've seen have the pump pressure relief valve set to around 75 ~ 90 PSI. Some high performance engines can be much more than that. How much time a pump spends in relief is based on the relief valve setting. You could make it go into relief at any point along the RPM range, or make it never go into relief. If it's such a waste to "over feed" the bearings with pressure, then why do most automakers still do it? And it's not because there is 70 PSI of pressure drop through the oil galleries in order to get 5~10 PSI at the inlet to the bearings - not nearly that much pressure drop due to gallery flow resistance.
Auto designers could have simply specified a softer relief spring in the current fixed PD pump design and make it shunt oil to the sump much sooner in the range that the bearings don't need as much flow (3500 RPM and higher in the graph example). But of course that wastes HP and heats up the oil, so designers have now come up with variable volume pumps in order to save a little bit of fuel mileage by cutting lost HP in the oil pump. CAFE is a "wonderful" thing . I think we are in agreement on all of that.
The 70% was just based on memory of a figure you once posted, and I've found the figure for this discussion. It's Figure 13 in the link below, which obviously you've used to refer technical information from in some of these threads, even though it's just another internet guy's hack on the subject matter.
http://www.audizine.com/forum/showthread...bleshooting-DIY
What I'm saying is the vehicles I've seen don't run around all day long with the oil pump in pressure relief starting at 43% of max RPM (3000 out of 7000 RPM in the Fig 13 example) with oil at full operating temperature. If that Figure 13 is actually for the 1.8T engine he's discussing, then the designers were a bit nuts with oil pump "design margin".
From another previous thread discussing oil pumps, this is more like it ... not the 60% going through the pressure relief valve like shown in Figure 13 above.
Quote:
According to our experience, the minimum value of 12-15% of oil pump flow rate should be passed through relief valve at maximum oil temperature and rated speed.
I have logged all kinds of oil pressure vs oil temp vs RPM (up to redline) on my Z06, and looking at the data the oil pressure started kneeing over noticeably at 5500 RPM, which is 85% of the 6500 redline. So it correlated very well with the statement above. Having the relief kick in 12~15% of max RPM gives plenty of design margin. Even if it went into relief at redline or almost into relief at redline, there is still plenty of design margin for wear because in the upper 60% of the RPM range the bearings don't need as much oil supply anyway (using the Mellings graph as example). Again, one size doesn't fit all in these oil pump discussion, so don't go splitting hairs.
Originally Posted By: Shannow
BASS asckwards...
Yes it was, and at least I'll admit to it, but at lease it's not as major of a misconception as thinking journal bearings don't flow additional oil above the hydrodynamic flow when the galleries are pressurized. If you want to keep digging up erroneous comments, I can find a couple dozen on your pressure fed bearing misconception in just the threads we've had discussions in. You seem you have changed your tune some on that premise, and I have changed my tune some on things in these discussions also ... so wouldn't you agree it's time to get off the merry-go-round ride.
