stepped oil passages 3

[Manifolddesigner]

Howdy all,
I understand that if you were to take pressure readings along the main bearings of an engine, each main would have less and less pressure coming from the oil pump.
In an effort to remedy this, has anybody ever tried a stepped oiling system?
In the HVAC systems and Foundry gating systems that I'm familiar with it is important to have one large runner w/ several gates coming off it. The runner starts out relatively large and gets smaller by the CSA of ea gate. This keeps the pressure the same at each gate.
These are relatively low pressure systems.

In an engine you must make sure the lowest pressure bearing never gets too low, you must make sure you're making enough at the front. This usually means way more pressure than you'd otherwise run.

Would a stepped oil galley allow the use of a smaller (less power to drive) oil pump?

Am I totally out in left field here?

Jason.

 

[ivymike]

the pressure drops in the direction of flow, and drops more quickly when the passage is smaller. If I understand what you're describing, it would make the pressure difference worse, not better.

 

[IceStationZebra]

The one thing a stepped layout would do is keep the velocities relatively the same at the expense of higher backpressure. With HVAC systems the pressure increase is relatively small and worth the money you can save in downsizing the ducting. I suspect that a certain velocity is desired to get the conditioned air to mix with the room air. I'm not really familiar with foundry gating, but I'm guessing that having a more consistent velocity across multiple molds helps keep them all filling in a similar and consistent manner.

The other thing to consider is that it would be impossible to design a perfect stepped oiling system. The step sizes necessary would depend on the oil pressure and viscosity, but both of these vary dramatically during an engine's operating cycle.

ISZ

 

[Manifolddesigner]

sorry ice no, I don't think that's right.
wrt hvac, it is definitely a constant pressure deal.

This foundry paper puts it in better perspective.

http://www.slideshare.net/corematerials/talat-lecture-3203-the-filling-of-castings

see pg. 14.

The fluid flow in the first gate of the non-stepped runner is actually reversed! the runner is taking metal in thru the gate instead of feeding it out.

Also ice-I said the main galley would reduce in CSA by the same CSA as each main feeder. E.g. 11/16"dia galley would be reduced to about 5/8 after the first main, and then reduced to 9/16 then 7/16 then finally 5/16.

JM

 

[ivymike]

well, regardless of what you hold to be true for HVAC and casting systems, that ain't the way it works in a lube system. A system with progressively smaller diameter in the direction of flow will have more pressure drop from end to end of the gallery than one with constant diameter.

 

[Lou Scannon]

From the standpoint of providing pump pressure with little/no loss equally to all main bearings, a large plenum would be in order. However, apart from space & weight issues, I see an issue with building oil pressure quickly upon startup. A lube prime pump that pressurizes the plenum prior to cranking would solve this, but this would not be accepted by the general automotive public, I think.
A stepped main gallery would have some merit if the starting size were somewhat larger than a typical constant diameter oil rifle, and stepped down from there as described in the OP.
I see a potential manufacturing cost issue here though, as well as a potential space/weight issue. Is there a known problem with oil pressure distribution that needs to be solved?
Another way to reduce inequality of pressure to the mains would be to supply oil from the pump to both ends of the main gallery. This, just possibly, is something you could rig up on your own, depending on the engine, as well as the level of engineering and effort you are willing to undertake, of course.

 

[Manifolddesigner]

Aweee crap. you're right hemi, starting would be an issue (even if it worked).

 

[patprimmer]

And it solves a problem that is not a problem.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[LionelHutz]

Ya, I always thought that you needed a larger passage to maintain a constant pressure in the passage.

A furnace duct is stepped down because as each outlet is tapped off the required airflow in the duct is reduced by the amount of flow that outlet requires. Once you reach the point where you don't need the huge duct to support the airflow requirements of the remaining outlets you might as well reduce the size of the duct. The ducts are sized to maintain the pressure throughout the length of the duct considering the number of outlets in use - each reducer do not re-booste the pressure. The flow is controlled by the round pipe runners to the outlets. Reducing the size is a simple case of economics and space reductions.

 

[Manifolddesigner]

Fire sprinklers are done the same way. I really have trouble beleiving they would go through the trouble of carrying 4 different sizes of pipe w/ associated reducers if they didn't have to.

I bring it up because it is a problem that something so simple can't be addressed. It just winds my engineering propeller really tight. In a race motor where every horsepower counts, running a slightly smaller oil pump or slightly smaller bearings could be the difference between 1st winner and 1st loser.
In an economy box, 1% economy or 1% more power could be the deciding factor to thousands of people in choosing a new car or meeting emissions standards for another 5 years w/o a complete redesign.

Mostly, it just winds my propeller.

 

[ivymike]

have you priced pipe lately? it costs more when it's bigger.

this idea that the downstream pressure is increased somehow by the step reductions in diameter is bogus... might want to review your fluids textbook.

http://www.engineersedge.com/fluid_flow/pressure_drop/pressure_drop.htm

 

[LionelHutz]

Am I totally out in left field here?

YES

 

[strokersix]

If you think about this the other way around meaning increased CSA upstream rather than reduced CSA downstream it makes a lot more sense.

Whether it's worth doing or not or causes some other problem are different questions.

 

[dicer]

Well I can tell this idea wasn't thought out via an engineer from the 1940's era.

 

[Tmoose]

Until into the 60s Chevy 4 main bearing sixes had different diameter main bearing journals incremented by about 0.03 inch . Almost 0.100 inch Smaller at the front, with different lengths to boot. I presume maybe to handle the torque, or maybe as a manufacturing convenience to machine all the bores at once with just an inch or so tool travel, although curiously the cam bearings are incremented in the opposite direction.

It could be argued that the rear main bearing load capacity was greater than the front or the middle ones

 

[Manifolddesigner]

I've often thought of stepped main bearings. However, my thoughts came to the conclusion that the vertical loads were fairly consistent and the main bearings needed to be about the same size, however, the torque through each main journal was carrying the load of all the previous bearings and the internal diameter could be stepped quite dramatically.

JM

 

[TyrannosaurusRX]

At least some Buick V6s used stepped main oil galleries.

When the Porsche 928 came out, they were noted for having a much larger than normal main oil gallery, which functioned more or less as a plenum.

Modern designs like the Ford Mod V8 or GM LS1 have a single modest diameter all the way through.

Most engines use somewhere around 3/8", with 1/2" cup plugs or 1/4 NPT pipe plugs to seal the ends. These sizes are common across most 4, 6, and 8 cylinder engines I've encountered. I suspect 3/8" is used more because the deep hole drills and equipment being common and (relatively) inexpensive than because of design considerations.

 

[BrianPetersen]

Regulated oil pressure relief valve setting = 75 psi (give or take)

Velocity pressure of the oil inside the gallery = maybe 1 psi if that?

It just isn't going to matter much.

 

[YvesLLewelyn]

Doesn't the "side-oiler" layout made famous in the mid-sixties by NASCAR engines get around any problems with pressure drop along the crankshaft? It may have been made famous by NASCAR but humble engines like the pushrod Jag engines of the 30's and 40's were also "side-oiler" and I suspect that there are plenty of other examples as well.