Why is crankcase oil supplied to sleeve bearings?


by marellasunny
Tags: bearings
marellasunny
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#1
Jan19-13, 09:21 PM
P: 206
(Diagram attached)
Why is crankcase oil supplied to sleeve bearings in the connecting rod?Does the oil film act like in a journal bearing?

I was reading about compressors and there is a mechanism called a 'crosshead'(see diagram) that converts rotary to reciprocating motion. Its funny how oil is used instead of real bearings.
Attached Thumbnails
Crosshead_bearing.png  
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SteamKing
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#2
Jan19-13, 09:58 PM
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Bearings require lubrication or they will seize, thus destroying the engine.
marellasunny
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#3
Jan19-13, 10:17 PM
P: 206
but,there are no needle/round bearings in the crosshead.Its just oil flowing throw the crank pin that is taking-up all the rotation,which is what surprises me.
I would imagine the same lubricating mechanism in a IC engine for automobiles. Since there always exists the phenomenon of blow-by in IC engines,what is to ensure that the crank oil always reaches the pin in the first place?

OCR
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#4
Jan20-13, 03:11 AM
P: 108

Why is crankcase oil supplied to sleeve bearings?


Quote Quote by marellasunny View Post
there is a mechanism called a 'crosshead' that converts rotary to reciprocating motion.
marellasunny,

A crosshead is a mechanism used in large reciprocating engines and reciprocating compressors to eliminate sideways pressure on the piston, caused by the connecting rod.

http://en.wikipedia.org/wiki/Crosshead

http://marinediesels.info/2_stroke_e.../crosshead.htm

The connecting rod connects the piston to the crankshaft... the connecting rod is actually what converts the rotating motion of the crankshaft into linear motion (reciprocating motion).
Or, vice versa... linear into rotating motion.

http://en.wikipedia.org/wiki/Connecting_rod

http://en.wikipedia.org/wiki/Connect...ustion_engines

http://en.wikipedia.org/wiki/Connect...#Compound_rods

The bearings are 'real'... they're called plain bearings, or journal bearings, as opposed to rolling-element bearings.

http://en.wikipedia.org/wiki/Journal_bearing#Two-piece

http://en.wikipedia.org/wiki/Rolling-element_bearing

http://en.wikipedia.org/wiki/Bearing_%28mechanical%29

And, yes... they ride on a film of oil, supplied by the engine oil pump.

http://en.wikipedia.org/wiki/Plain_b...id_lubrication

http://en.wikipedia.org/wiki/Oil_pum...tion_engine%29



OCR
pantaz
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#5
Jan20-13, 03:01 PM
P: 586
Quote Quote by marellasunny View Post
but,there are no needle/round bearings in the crosshead.Its just oil flowing throw the crank pin that is taking-up all the rotation,which is what surprises me.
I would imagine the same lubricating mechanism in a IC engine for automobiles. Since there always exists the phenomenon of blow-by in IC engines,what is to ensure that the crank oil always reaches the pin in the first place?
Why do you think that "blow-by" would interfere with journal bearing lubrication?
marellasunny
marellasunny is offline
#6
Jan21-13, 08:30 AM
P: 206
the exhaust gases mix with the oil and make it more viscous than needed.
Now,the question is whether journal bearings would survive in such extreme conditions...why would engineers take the risk of the crosshead with a journal than the usual needle?
256bits
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#7
Jan26-13, 11:35 AM
P: 1,271
why would engineers take the risk of the crosshead with a journal than the usual needle?
What is the risk?
ae86drftr
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#8
Feb5-13, 01:03 AM
P: 1
I would imagine the load placed on the needle bearing would render it useless. The oil acts as a cushion to soften the impact as to prevent any damage from rod to crank


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