Red marquis: /* Air ventilation */

2010-05-08T19:43:29Z

Air ventilation

← Older revision		Revision as of 19:43, 8 May 2010
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	=== Air ventilation ===		=== Air ventilation ===
	During normal operation, a small amount of unburned fuel and exhaust gases escape around the [[piston ring]]s and enter the crankcase, referred to as "'''blow-by'''". <ref name="cartalk_sep99">[http://www.cartalk.com/content/columns/Archive/1999/September/08.html September 1999 question] on Car Talk</ref> If these gases remained in the crankcase and condensed, the oil would become more diluted over time, decreasing its ability to lubricate. Condensed water would also cause parts of the engine to rust. <ref>[http://www.cartalk.com/content/columns/Archive/2001/January/11.html January 2001 question] on Car Talk</ref> To counter this, a crankcase ventilation system exists to draw fresh air in from the [[air filter]] and expel the gases out the [[PCV valve]] into the [[intake manifold]]. In a non-turbo engine, the intake manifold is at a ~~[[manifold vacuum\|~~lower pressure]] than the crankcase, providing the suction to keep the ventilation system going. A [[Turbocharger\|turbo]] engine usually has a [[check valve]] somewhere in the tubing to avoid pressurizing the crankcase when the turbo produces [[Turbocharger#Boost threshold\|boost]].		During normal operation, a small amount of unburned fuel and exhaust gases escape around the [[piston ring]]s and enter the crankcase, referred to as "'''blow-by'''". <ref name="cartalk_sep99">[http://www.cartalk.com/content/columns/Archive/1999/September/08.html September 1999 question] on Car Talk</ref> If these gases remained in the crankcase and condensed, the oil would become more diluted over time, decreasing its ability to lubricate. Condensed water would also cause parts of the engine to rust. <ref>[http://www.cartalk.com/content/columns/Archive/2001/January/11.html January 2001 question] on Car Talk</ref> To counter this, a crankcase ventilation system exists to draw fresh air in from the air filter]and expel the gases out the PCV valve into the [[intake manifold]]. In a non-turbo engine, the intake manifold is at a lower pressure than the crankcase, providing the suction to keep the ventilation system going. A [[Turbocharger\|turbo]] engine usually has a check valve somewhere in the tubing to avoid pressurizing the crankcase when the turbo produces [[Turbocharger#Boost threshold\|boost]].

	If an engine is damaged or enters old age, gaps can form between the cylinder walls and pistons, resulting in larger amounts of blow-by than the crankcase ventilation system can handle. The gaps cause power loss, and ultimately mean that the engine needs to be rebuilt or replaced. <ref name="cartalk_sep99"/> Symptoms of excessive blow-by include oil being pushed up into the air filter, out the dipstick<ref>[http://cartalk.com/content/columns/Archive/2002/August/07.html August 2002 question] on Car Talk</ref>, or out the PCV valve.		If an engine is damaged or enters old age, gaps can form between the cylinder walls and pistons, resulting in larger amounts of blow-by than the crankcase ventilation system can handle. The gaps cause power loss, and ultimately mean that the engine needs to be rebuilt or replaced. <ref name="cartalk_sep99"/> Symptoms of excessive blow-by include oil being pushed up into the air filter, out the dipstick<ref>[http://cartalk.com/content/columns/Archive/2002/August/07.html August 2002 question] on Car Talk</ref>, or out the PCV valve.

Red marquis at 19:42, 8 May 2010

2010-05-08T19:42:45Z

New page

In an [[internal combustion engine]], the '''crankcase''' is the housing for the [[crankshaft]]. The enclosure forms the largest cavity in the engine and is located below the [[cylinder block]].

Besides protecting the crankshaft and [[connecting rod]]s from foreign objects, the crankcase serves other functions, depending on engine type.

== Two-stroke engines ==

In [[two-stroke cycle|two-stroke]] [[gasoline]] engines, the crankcase is sealed and is used as a pressurization chamber for the fuel/air mixture. As the piston rises, it pushes out exhaust gases and produces a partial vacuum in the crankcase which aspirates fuel and air. As the piston travels downward, the fuel/air charge is pushed from the crankcase and into the cylinder. <ref>[http://science.howstuffworks.com/two-stroke5.htm The Compression Stroke in Two-stroke Engines] at HowStuffWorks</ref>

Unlike four-stroke gasoline engines, the crankcase does not contain [[engine oil]] because it handles the fuel/air mixture. Instead, oil is mixed in with the fuel, and the mixture provides lubrication for the cylinder walls, crankshaft and [[connecting rod]] [[plain bearing|bearings]].

== Four-stroke engines ==

In a [[four-stroke cycle|four-stroke]] engine, the crankcase is filled mainly with air and oil, and is largely sealed off from the fuel/air mixture by the pistons.

=== Oil circulation ===
Oil circulation is kept separate from the fuel/air mixture, thereby preserving oil rather than burning it as happens in two-stroke engines. Oil moves from its reservoir, is pressurized by an [[oil pump]], and is pumped through the [[oil filter]] to remove grit. The oil is then squirted into the crankshaft and connecting rod bearings and onto the cylinder walls, and eventually drips off into the bottom of the crankcase. <ref> Image:4-Stroke-Engine.gif[http://auto.howstuffworks.com/engine6.htm How Car Engines Work] at HowStuffWorks</ref> In a [[wet sump]] system, oil remains in a reservoir at the bottom of the crankcase, referred to as the '''oil pan'''. In a [[dry sump]] system, oil is instead pumped to an external reservoir. <ref>[http://auto.howstuffworks.com/question331.htm Why do some engines use a dry sump oil system?] at HowStuffWorks</ref>

Even in a wet sump system, the crankshaft has minimal contact with the sump oil. Otherwise, the high-speed rotation of the crankshaft would cause the oil to froth, making it difficult for the oil pump to move the oil, which can starve the engine of lubrication. <ref>[http://www.cartalk.com/content/columns/Archive/1996/October/08.html October 1996 question] on Car Talk</ref> Small amounts of oil may splash onto the crankshaft during rough driving, referred to as windage. <ref>{{cite web|url=http://www.circletrack.com/techarticles/76818/|title=Oil Pans For Power|author=Jeff Huneycutt|publisher=Circle Track magazine|accessdate=2006-11-16}}</ref>

In a wet sump system, the main [[dipstick]] and oil filler cap connect to the crankcase.

=== Air ventilation ===
During normal operation, a small amount of unburned fuel and exhaust gases escape around the [[piston ring]]s and enter the crankcase, referred to as "'''blow-by'''". <ref name="cartalk_sep99">[http://www.cartalk.com/content/columns/Archive/1999/September/08.html September 1999 question] on Car Talk</ref> If these gases remained in the crankcase and condensed, the oil would become more diluted over time, decreasing its ability to lubricate. Condensed water would also cause parts of the engine to rust. <ref>[http://www.cartalk.com/content/columns/Archive/2001/January/11.html January 2001 question] on Car Talk</ref> To counter this, a crankcase ventilation system exists to draw fresh air in from the [[air filter]] and expel the gases out the [[PCV valve]] into the [[intake manifold]]. In a non-turbo engine, the intake manifold is at a [[manifold vacuum|lower pressure]] than the crankcase, providing the suction to keep the ventilation system going. A [[Turbocharger|turbo]] engine usually has a [[check valve]] somewhere in the tubing to avoid pressurizing the crankcase when the turbo produces [[Turbocharger#Boost threshold|boost]].

If an engine is damaged or enters old age, gaps can form between the cylinder walls and pistons, resulting in larger amounts of blow-by than the crankcase ventilation system can handle. The gaps cause power loss, and ultimately mean that the engine needs to be rebuilt or replaced. <ref name="cartalk_sep99"/> Symptoms of excessive blow-by include oil being pushed up into the air filter, out the dipstick<ref>[http://cartalk.com/content/columns/Archive/2002/August/07.html August 2002 question] on Car Talk</ref>, or out the PCV valve.

==Open crank engine==
Early internal combustion engines were of the "open crank" style, that is, there was no enclosed crankcase. The crankshaft, connecting rod, camshaft, gears, governor, etc. were all completely exposed and could be viewed in operation when the engine was running. This made for a messy environment as oil was thrown from the engine and could run on the ground. Another disadvantage was that dirt and dust could get on moving engine parts, causing excessive wear and possible malfunction of the engine. Frequent cleaning of the engine was required to keep it in normal working order.

[[Category:Engine technology]]
[[Category:Engine components]]

Crankcase - Revision history

Red marquis: /* Air ventilation */

Red marquis at 19:42, 8 May 2010