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Conditions in which it operates piston extreme and characterized by high pressure, temperature and inertial loads. at least from steel. The pistons are made of two ways - by injection molding or by stamping called forged pistons .
Scheme piston engine
The piston is integral structural element , which is conventionally divided into head (some sources call it the bottom) and a skirt. The shape and design of the piston is largely determined by the type of engine , the shape of the combustion chamber and the combustion process occurring in it. Piston gasoline engine has a flat or near- flat surface of the head . It may be provided with grooves for the full valve opening . Pistons with direct fuel injection have a more complex shape. In the top of the piston diesel engine combustion chamber holds a certain form , which provides a nice twist and improves mixture formation .
Below the piston head run grooves for mounting piston rings. The piston skirt has a tapered or curved ( barrel ) form . Such a shape of the skirt of the piston compensates for thermal expansion during heating. When reaching the operating temperature of the engine piston takes a cylindrical shape. To reduce the friction losses on the piston side with a layer of antifriction material ( molybdenum disulfide, graphite) . In the piston skirt has holes with the tides ( the boss ) to secure the piston pin .
Piston cooling is carried out by the internal surface of a variety of ways :
oil mist in the cylinder;
oil splashing through the hole in the rod ;
oil splashes special nozzle ;
injection of oil into a special zone in the annular channel rings;
oil flow through the tubular coil in the piston crown .
Piston rings form a tight connection with the wall of the piston cylinder. They are made of cast iron modified . Piston rings are the main source of friction in the internal combustion engine. Friction losses in the rings reach to 25 % of mechanical loss in the engine.
The number and location of the rings depends upon the type and purpose of the engine . The most common scheme - two compression and one oil ring . Compression rings prevent breakthrough of gas from the combustion chamber into the crankcase . The first compression ring works in the most severe conditions. Therefore, a number of pistons of diesel and gasoline engines forced into the groove of the ring set steel insert that improves durability and allows to realize the maximum compression . Compression rings may have a trapezoidal , a barrel , a conical shape , some are performed with a cut ( notch ) .
Scraper ring removes the excess oil from the surface of the cylinder and prevents the ingress of oil into the combustion chamber . The ring has a plurality of drainage holes . Some designs have a spring ring expander .
Compound piston rod by means of a piston pin which has a tubular shape and is made of steel. There are several way to install the piston pin . The most popular so-called floating finger that has the ability to rotate in bosses and the piston rod head during operation. To prevent displacement of the finger he fixed retainer rings . Much less is applied rigidly fixed ends of the piston pin or rigid fastening pin into the piston rod head .
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