A crankcase is home to a crankshaft in an internal combustion reciprocating engine. The enclosures form the largest cavities in the machine and are located beneath the cylinder (s), which in a multicylinder engine are usually integrated into one or several cylinder blocks. Crankcases often become separate parts, but more often they are integral with the cylinder bank (s), forming a block of machines. However, the area around the crankshaft is still commonly referred to as crankcase. Crankcases and other basic engine structure components (eg cylinder, cylinder block, cylinder head, and integrated combination) are usually made of cast iron or cast aluminum through sand casting. Today the casting process is usually very automated, with some skilled workers to manage the casting of thousands of sections.
A crankcase often has an opening at the bottom where an oil pan is attached with a bolt connection. Some crankcase designs completely surround the main bearing crank journal, while many others only form half, with bearing lids forming the other. Some crankcase areas do not require the structural strength of the oil pan itself (in which case the oil pan is usually stamped from sheet steel), while other crankcase designs do (in this case the oil pot is casting in itself). Both crankcase and rigid cast oil pans often have reinforced ribs thrown into them, as well as bosses that are drilled and tapped to accept the installation of screws/screws for various other engine parts.
In addition to protecting the crankshaft and connecting the rod of a foreign object, the crankcase is functioning differently, depending on the machine type. This includes maintaining motor oil contained, usually hermetic or almost hermetic (and in hermetic, enabling oil to be pressurized); providing a rigid structure to join the machine to the transmission; and in some cases, even part of the vehicle framework (as in many agricultural tractors).
Video Crankcase
Two-step engine
Small engine and crankcase compression engine
A large number of small two-stroke engines use a closed crankcase as a compression chamber for their mix. This is very common such as gasoline or small gasoline engines for motorcycles, gensets and garden equipment. Both sides of the piston are used as work surfaces: the top side is the power piston, the lower side serves as the scavenging pump. As the piston rises, it pushes out the exhaust gas and produces a partial vacuum in the crankcase, which attracts fuel and air. As the piston moves down, the fuel charge/compressed air is pushed from the crankcase to the cylinder.
Unlike larger engines, crankcase does not contain engine oil because it handles fuel/air mixtures. In contrast, oil is mixed with fuel supply as petroleum, and this mixture provides lubrication for cylinder walls, crankshaft and connecting rod bearings. Using a ball or roller bearings for bearings in such machines is always more common than regular oil-treated bearings used for other machines, as it is easier to use this oil mist lubrication. These machines have been used in larger sizes for small cars. They were considered in the 1980s as a more fuel-efficient engine for larger cars, but the increased concern of engine emissions prevented their use: mixing lubricating oil into the engine intake mix provided high HC emissions and these problems were not addressed.
Small diesel engines can also use this type of compression crankcase. Such machines are still rare, compared to gasoline engines, but they are used for generators and industrial equipment and become available for diesel motorcycles.
Bigger two-step engine
The big two-step engine does not use crankcase compression, but a separate sponge or supercharger blower. Their crankcases are reserved for lubrication purposes and are comparable to four-step engines.
High-speed two-stroke diesel engines, such as those on boats, may have their crankcase as a separate chamber from a cylinder, or as an open crank. The piston rod is supported by a separate chapter title. The space between the piston rod and the chapter title, or the crosshead to the crankshaft, may be mostly open for maintenance access. Because they are large and their movements are slow, the pads can be individually made quite closed to catch and return the oil from the pads.
Maps Crankcase
Four-stroke engine
In a four-stroke engine, the crankcase is filled mainly with air and oil, and is largely covered from the fuel/air mixture by the piston.
Oil circulation
Oil circulation is kept separate from the fuel/air mixture, thus conserving oil rather than burning it as it does on two-stroke engines. Oil moves from its reservoir, pressurized by an oil pump, and pumped through an oil filter to remove sand. The oil is then sprayed onto the crankshaft and connects the rod bearings and into the cylinder wall, and finally drips to the bottom of the crankcase. In the wet sump system, the oil remains in the reservoir at the bottom of the crank case, referred to as oil pan . In a dry sump system, oil is pumped into an external reservoir.
Even in a wet sump system, the crankshaft has minimal contact with sump oil. Otherwise, a high speed spin crankshaft will cause foaming oil, making it difficult for oil pumps to move the oil, which can make the lubrication machine starve. A small amount of oil can spray onto the crankshaft during rough driving, called windage.
In the wet sump system, the main dipstick reaches to near the bottom of the crankcase. Oil filler cap covers the hole in the crankcase where oil can be added; usually located at the top of the rocker cover (or if two, which is closer to the front of the vehicle).
Air ventilation
During normal operation, a small amount of unburned fuel and exhaust out of the piston rings and into the crankcase, referred to as "bb> blow-by ". If these gases do not have a controlled escape mechanism, the gas-leaking joints will leak (because they "find their own way out"); Also, if the gas remains in the crankcase and condensed, the oil will become diluted and chemically degraded over time, lowering its ability to lubricate. Condensed water will also cause the engine parts to become rusty. To overcome this, engine vessel vent systems exist. In all modern vehicles, it consists of a channel to get the gas out of the crankcase, through an oil separator baffle, into the PCV valve, into the intake manifold. In a non-turbo engine, the intake manifold has a lower pressure than the crankcase, providing suction to keep the ventilation system running. The turbo engine usually has a valve somewhere in the tubing to avoid pressure on the crankcase when the turbo produces a boost.
If the engine breaks or enters old age, a gap can form between the cylinder and piston walls, resulting in a greater blow-by count that can be handled by crankcase systems. The gap causes loss of power, and ultimately means that the engine needs to be rebuilt or replaced. Excessive blow-by symptoms include oil being pushed into the air filter, exit the dipstick, or out of the PCV valve. In rare cases of serious piston or ring damage, metal sheets of oil filters may explode in the lining.
Crank engine is open
The starting machine is an "open-crank" style, that is, there is no closed crankcase. Crankshaft, connecting rod, camshaft, gears, governors, etc. Everything is completely open and can be seen during machine operation. This is made for a messy environment, because oil is thrown from the engine and can run on the ground. Another disadvantage is that dirt and dust can move parts of the machine, causing excessive wear and possible engine damage. Machine cleaning is often required to keep it functioning normally.
See also
- Machine tub tunnel
References
Source of the article : Wikipedia
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