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#3390995 - 06/06/14 07:34 PM Why designers allow mixed lubrication regimes
Shannow Online   content


Registered: 12/12/02
Posts: 35953
Loc: Oz
Investigation into Power Losses in Automotive Bearings

Paper discusses the presence or otherwise of mixed/boundary lubrication in automotive journal bearings, and the resultant friction and power loss.

Has both computational and test bench (applied reciprocating load, variable speed), and compares SAE 40 and SAE 20 lubricants.

(Figure 3 supports one of Gokhan's assertions regarding viscosity/pressure.)

(Paper also supports my previous assertion that temperature rises in bearings of 20C are typical).

Quote:
As SAE20 oil has about half the viscosity of SAE40 (see
Figure 3), the operating conditions in the journal bearings are
distinctly different. The difference in viscosity affects the load carrying capacity of the journal bearing which is consequently reduced for lubrication with SAE20 and weak mixed lubrication occurs.

This can be seen in Figure 9 where the friction power losses due to hydrodynamic lubrication and due to metal-metal contact are shown separately for the test bearing. As only during a
short time of the load cycle metal-metal contact occurs, the load cycle averaged contribution of metal-metal contact to the total friction power losses appears rather low with 5 W despite that significant amounts of metal-metal contact occur for a short time of the load cycle.


If you look up the article, Fig9 shows are power consumption for the 40 weight oil of 600W, versus 500W for the 20...clearly a major reduction in frictional work, and a driver for economy.

Extrapolation from this is what the likes of Honda are showing, we are at the end of the diminishing returns with bearings, and any reduction in viscosity is leading to more mixed lubrication...so they are going thinner, while increasing their bearing projected areas, and reducing clearances...which increase drag, but also indicate that their gains are being made elsewhere (pistons, actual viscous pumping in galleries, dunno what else).

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#3391031 - 06/06/14 08:12 PM Re: Why designers allow mixed lubrication regimes [Re: Shannow]
d00df00d Offline


Registered: 10/20/05
Posts: 10660
Loc: PA
Interesting. Thanks for posting!
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#3391075 - 06/06/14 09:01 PM Re: Why designers allow mixed lubrication regimes [Re: Shannow]
Rand Offline


Registered: 08/20/03
Posts: 11640
Loc: NE,Ohio
thanks for posting something that isn't someones "personal theory"

And an excellent read.
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#3391112 - 06/06/14 09:44 PM Re: Why designers allow mixed lubrication regimes [Re: Shannow]
jrustles Offline


Registered: 02/24/13
Posts: 2035
Loc: Ontario, Canada
Thanks for posting. It's a nice recent paper too thumbsup
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#3391151 - 06/06/14 10:42 PM Re: Why designers allow mixed lubrication regimes [Re: Shannow]
FetchFar Offline


Registered: 10/17/13
Posts: 831
Loc: Colorado
shannow obviously didn't read the paper. His title here "Why designers allow mixed lubrication regimes" is misleading at best. The paper is not a design paper at all. Its theorists at a university investigating how to model mixed-boundary lubrication in journal bearings, a simulation modelling exercise. Thats all.

In the real world of engines, we know that Mazda, Toyota, Ford, Honda, GM, Subaru, and now BMW (LL-14) all specify 20 weights with great success.


Edited by FetchFar (06/06/14 10:47 PM)
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#3391153 - 06/06/14 10:45 PM Re: Why designers allow mixed lubrication regimes [Re: Shannow]
FetchFar Offline


Registered: 10/17/13
Posts: 831
Loc: Colorado
Originally Posted By: Shannow

Extrapolation from this is what the likes of Honda are showing, we are at the end of the diminishing returns with bearings, and any reduction in viscosity is leading to more mixed lubrication...so they are going thinner, while increasing their bearing projected areas, and reducing clearances...which increase drag, but also indicate that their gains are being made elsewhere (pistons, actual viscous pumping in galleries, dunno what else).


Really? "Extrapolation" from this paper? You mean your wild guess. Simulation modeling research, not design. Big difference.
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#3391379 - 06/07/14 10:03 AM Re: Why designers allow mixed lubrication regimes [Re: FetchFar]
MolaKule Offline


Registered: 06/05/02
Posts: 18046
Loc: Iowegia - USA
Originally Posted By: FetchFar
shannow obviously didn't read the paper. His title here "Why designers allow mixed lubrication regimes" is misleading at best. The paper is not a design paper at all. Its theorists at a university investigating how to model mixed-boundary lubrication in journal bearings, a simulation modelling exercise. Thats all.

In the real world of engines, we know that Mazda, Toyota, Ford, Honda, GM, Subaru, and now BMW (LL-14) all specify 20 weights with great success.


Simulations are only as good as to how well they correlate with experimental results.

IE, simulations can only be believed or trusted if the simulation results do not deviate too far from real world results.

I don't think mechanical component designers have any choice wrt lubrication regimes in machines with widely varying loads.
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#3391626 - 06/07/14 05:57 PM Re: Why designers allow mixed lubrication regimes [Re: FetchFar]
Shannow Online   content


Registered: 12/12/02
Posts: 35953
Loc: Oz
Originally Posted By: FetchFar
shannow obviously didn't read the paper. His title here "Why designers allow mixed lubrication regimes" is misleading at best. The paper is not a design paper at all. Its theorists at a university investigating how to model mixed-boundary lubrication in journal bearings, a simulation modelling exercise. Thats all.

In the real world of engines, we know that Mazda, Toyota, Ford, Honda, GM, Subaru, and now BMW (LL-14) all specify 20 weights with great success.


And they all do component by component simulations, mechanical and mathematical the determine just how far they can stretch the science.

e.g. Honda https://www.hondarandd.jp/point.php?pid=292&lang=en

Quote:
Proposal of New Bearing Simulation Rig Tester for High Efficiency Engine Bearing Development

To select bearing specifications for an engine using a bearing rig test, it is necessary to achieve sliding conditions that are near the actual operating conditions of the engine. A new bearing rig tester with low resonance and high rigidity permits high frequency excitation and has a mechanism to correct misalignment between the axle and the bearing. This rig tester can reproduce load fluctuations under the actual operating conditions of the engine. The test equipment makes it possible to clarify for the first time the mechanism that causes the difference in the break-in performance of lead alloy and aluminum alloy bearings. It was possible to evaluate the small end bearing fitted on an actual connecting rod, and the sliding characteristics caused by different surface treatment methods for the small end bearings. In addition, it was possible to measure the friction coefficient of the bearings with high repeatability, and efficiently evaluate the bearing material.


There's a whole lot more to machine design...as you (may) well understand, often you have to break machines down component to component to understand specific behaviours...the Honda rig goes further, in allowing the journal to tilt, and thus model crankshaft misalignment/flexibility.

It not just making a statement that I have a Stribeck number of 0.4...or is that 1...heck, or I don't even know what the loads are, but here's a number that I like.

As to my statement, it's not misleading.

the 20, in minor mixed lubrication had significantly lower friction than the 40, in both the test bench and the mathematical model...even 'though the 20 had some mixed lubrication.

Honda have said in their 16 papers that they are operating at times in mixed mode, but still have "adequate" durability...in the paper linked, on a motored L13 Honda engine (another test method commonly used to gain understanding of behaviours), the thing goes undergoes mixed lubrication conditions at 1,500 RPM...with out combustion pressure being added.

https://www.hondarandd.jp/point.php?pid=72&lang=en

You are so committed to proving others wrong, that you are losing sight of the ball.

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