Electric Oil Pump??

[MiketheEngineer]

Just a crazy old Structural that likes to break things - and fix them.

If we believe all the oil advertising and engine mfgs, they say the worst engine wear happens during the first few seconds of startup due to lack of oil pressure.

Why not install an auxiliary electric oil pump that cycles for a few seconds before ignition and then shuts off once started. Seems simple and couldn't cost too much. Or am I just missing something here??

 

[thruthefence]

Lots of race cars do this. Here's a solution that doesn't used an electric pump, but a precharged accumulator. Captures oil at pressure at shut down, and releases it back into the oil gallery at start. (or when you have a transiet drop in oil pressure)

http://www.accusump.com/

 

[MikeHalloran]

It's called pre-oiling, and is often done for large industrial engines using an electric pump. ... which is also commonly run for a few minutes after shutdown to prevent oil coking and other nasty behaviors, and also used on a timed schedule to run crankcase oil through a heater to retard corrosion and maintain proper oil viscosity during idle periods.



Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

and the reason it isn't fitted to passenger cars is that /you/ don't want to pay for it, both in variable or fixed costs. It might extend the engine life from 200000 miles to 400000 miles. Nobody of any financial significance is interested in that. Cars are sold to the first buyer, so long as they make it to 100000 miles that is all that matters. Sorry about that.

Cheers

Greg Locock


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[patprimmer]

It still does not oil the rings and bores before start up.

A better system might be to incorporate a starting protocol into the ECU that delays start up until the oil has reached all bearings and to severely limit power until it has had time to splash onto the bores then somewhat limit power until a reasonable operating temperature (and therefore internal clearances) is reached. Oh that's right, they mostly already do the last one.

As Greg already implied. It solves a problem that really does not exist as most engines outlive the car they are in.

Regards
Pat
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[patprimmer]

Also some oils have a much stronger tendency to stay on the surfaces over time. Specifying and using such oils would help.

Regards
Pat
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[DanEE]

"A better system might be to incorporate a starting protocol into the ECU that delays start up until the oil has reached all bearings....."

The Toyota Prius does that...

Ignition and fuel is not applied until oil pressure is up..

And, there is sufficient range in the variable valve timing to delay closing of the intake valve to the point of serving as a compression release during the initial spin up of the engine.

 

[evelrod]

I agree that the major wear is at cold startup...intuitive.
I disagree that this "wear" is excessive in most street applications. It is not at all uncommon to have modern engines make 400,000 miles and still be serviceable. My son and I put over 385,000 on a '77 360 Dodge PU before we sold it and there were no problems in the engine dept.
My auto insurance agent has a MB that is at the 400k mark.

My point, is that this simply means that there is no incentive for OEM to do anything with pre oilers/after oilers/accusumps, etc.

For the uninitiated--- I use the Canton 3 qt. Accusump with an electric pressure (55psi in the Mini, 35psi in the Lotus) regulated solenoid and prior to any cold startup crank the engine over several times before turning on the ignition...simple...and...if the engine has been sitting around over the winter, I take out the plugs and crank it over for a bit before final startup. Again, simple.

Rod

 

[drwebb]

Furthermore, appreciate there's invisible technology in modern engine oils to ensure that they pump as fast as possible at cold start-up. For example, the GF-5 specification introduced new requirements to ensure cold-start pumpability is maintained during extended drain service. Such measures can reduce the need for or benefit of auxillary hardware.

 

[tbuelna]

I would argue that pre-oiling does not provide as much benefit as one would imagine. However, allowing the engine to idle and cool off before shut down would provide benefit, especially with a turbo engine.

Most of the sliding contacts in a recip piston engine (rings, wrist pins, valvetrain, etc.) are capable of operating safely for short periods with whatever entrained oil is present at start up. Most of these components normally operate with boundary type contacts and thus don't require much oil to be present.

As for the hydrodynamic contacts present in the main and rod bearings, these also do not require much oil flow at start up. The oil volume that must be present to produce the load supporting hydrodynamic film is extremely small (ie. a small drop). The normal operating oil flow required by journal bearings is based entirely on cooling requirements. And for the 2 or 3 seconds of light load, low speed operation at start-up before oil pressure is built up and flows begin, no real damage should be occurring to the bearings since they won't build up much heat.

Bearings are more likely to fail due to surface fatigue, corrosion, or contamination. Not "wear" at start up.

Regards,
Terry

 

[GregLocock]

Terry (or anyone) - what design compromises are made so as to allow the engine to start up with zero oil pressure?



Cheers

Greg Locock


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[MikeHalloran]

My last major project involved a zero-time rebuild of a pair of Waukesha natural gas engines for an oil rig in the Gulf of Mexico, where they are expected to provide electrical power for the whole rig for the next 30 years, given regular oil changes.

They have pre-oilers, as specified by the customer.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Pre 1920 most cars had zero oil pressure and quite a few carried that over to almost 1930 I think. The system was called splash feed, and that was with substantially inferior oils and bearing materials than are typical in modern engines.

I have also experienced engines that have run for several hour with an empty sump, so not even enough for real splash feed.

The role of oil pressure in my opinion is to provide enough flow to cool the bearings to allow the great increase in speed rather than load that modern engines utilise.

Not having oil pressure at start up therefore is no serious disadvantage so long as the surfaces are wet with oil and the time until pressure builds is short enough to prevent excessive heat build up. At low rpm and load this is a considerable time. Unfortunately once heat starts to build, clearances close down, then heat builds faster then clearances close down faster etc etc

The ECU restricting power output and speed significantly until oil pressure is obtained should solve any problems if they in fact existed.



Regards
Pat
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[evelrod]

I'm not sure I know of any specific compromises to mitigate wear on cold startup/zero oil pressure conditions. Interesting question.

As to the 'splash oiling' of early engines v bearing wear at startup...I think I have posted here a time or two that in Jan, 2000 I rebuilt my 1930 Ford engine with machining for modern bearing shells, counterweighted crank, solid valve guides w/Buick SS valves, etc. Well just last year the engine lost a head gasket and hydrauliced the #4 cylinder bending the OEM rod.

Fast foreword---New engine is in place with aftermarket rods, etc.---At teardown we inspected the bearing shells of rod and main with some 25,000 miles of use in a totally splash oil system...NO APPRECIABLE WEAR! in fact, the bearings still looked NEW.

Now what does that say about pre oiling? Not much. I simply cannot compare my Model A engine at ~4:1 CR with my Mini Cooper engine at 15.33:1 CR...Loading on the bearings at startup are vastly different.

Until someone can show me different, I'll stick to the system of oil accumulator/pre oiler that has proven effective for many years.

Rod

 

[tbuelna]

Terry (or anyone) - what design compromises are made so as to allow the engine to start up with zero oil pressure?

That's a good question. There's a few things I can think of that could be done, although I would not specifically classify them as "compromises".

For one, the ignition spark can be interrupted briefly when the engine first cranks over, as well as keeping the throttle fully closed (SI engines only). This will limit the max pressure loads on the crank and rod journals.

The layout of the lube circuit can also reduce (but not eliminate) the delay in oil flow to critical points like the crank and rod bearings. Most auto engines are wet sumps, and putting the pressure pump inlet at or below the oil level will promote rapid priming and minimize the delay getting oil flow going. The same goes for the way the filter bowl/housing is positioned, so that it remains full of oil during shut-down.

Another thing to consider is that no oil pressure at start-up does not mean there is no oil present at the bearings. There are drilled galleries between the crank journals that usually trap some oil at shut-down. When the crank rotates at start-up, this oil will be pushed out to the rod bearings.

As I noted in my previous post, journal bearing oil flows are entirely a function of cooling requirements. Creating a load supporting hydrodynamic oil film takes very little oil volume. Having full oil pressure feeding your crank's journal bearings provides no benefit for the few seconds at start-up, versus simply having some entrained oil present within the bearing gaps. The fluid pressures within the hydrodynamic oil film can be 20,000psi or more. The pressures are created through viscous effects in the oil itself, and not by the pressure of the 60psi oil circuit feed.

With regards to the original post, while an electric oil pump would not really help with perceived "wear" issues at start-up, it would have other benefits. The most important being the ability to vary flows independent of crank speed.

Hope that helps answer your question.
Terry