The Piston is one of the elements of the crank mechanism, which is based on the principle of operation of many internal combustion engines. In the above article describes the design and features of these components.
Piston — this is a detail that performs in the cylinder reciprocating motion and which convert into mechanical work of gas pressure change.
With the participation of these components realizes the thermodynamic process of the engine. As the piston — is one of the elements of the crank mechanism, it takes the pressure produced by the gases and transmits the force on the connecting rod. Besides, it provides sealing of the combustion chamber and branch of heat from it.
Piston — it trehlistna detail, i.e. its design includes three components that perform different functions, and two parts: the head, which unite the bottom sealing part and guide part, represented by the skirt.
Can have different shapes depending on many factors. For example, the configuration of the piston of the internal combustion engine is determined by the location of other structural components such as injectors, spark plugs, valves, combustion chamber shape, the peculiarities of the current processes, the overall design of the engine, etc. In any case, it determines the peculiarities of the functioning.
There are two main types of piston configuration: convex and concave. The first provides great strength, but deteriorates the configuration of the combustion chamber. When the concave shape of the bottom of the combustion chamber, on the contrary, has the best form, but more intensely delayed Nagar. Rarely (in two-stroke engines) meet the pistons with a bottom, represented by the projection of the reflector. This is necessary when scavenging for the directional movement of the combustion products. Parts of petrol engines usually have the bottom flat or nearly flat shapes. Sometimes they contain grooves to fully open the valves. The engines with direct injection pistons are characterized by a more complex configuration. Diesel engines, they differ in the presence of the combustion chamber in the bottom to ensure good turbulence and improves mixing.
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Most of the pistons unilateral, although there are bilateral options, which have two bottoms.
The distance between the groove of the first compression ring and the bottom is called the fire belt of the piston. It is very important the value of its height which is different for parts of different materials. In any case, the exit height of the fire ring beyond the minimum permissible values can lead to burnout of the piston and deformation of the seats of the upper compression ring.
Here are the oil and compression rings. The parts of the first type channels are through holes for receipt inside of the piston remote from the surface of the oil cylinder where it enters the sump. Some of them have a rim of corrosion resistant cast iron with a groove for the top compression ring.
Piston ring composed of cast iron, used to create a tight fit of the piston to the cylinder. Therefore, they are the source of greatest friction in the engine, the losses from which amount to 25% of the total amount of mechanical losses in the motor. The number and position of the rings depend on the type and purpose of the engine. Most often use 2 compression and 1 oil ring.
Compression ring perform the task of preventing the entry of gases into the crankcase from the combustion chamber. The greatest load comes on the first of them, so in some engines his groove reinforcing steel insert. The compression rings may be trapezoidal, conical, barrel-shaped. Some of them have a cutout.
Oil scraper ring serves to remove excess oil from the cylinder and prevents its getting into the combustion chamber. To this end, it has holes in it. Some variants have a spring expander.
Has a barrel shaped (curved) or conical shape to compensate for thermal expansion. There are two tide to the piston pin. In these areas the skirt has the greatest mass. In addition, there exhibits the greatest thermal deformation during heating. To reduce them use a variety of measures. At the bottom of the skirt may be a piston oil ring.
To transfer force from the piston or it is used most often crank or rod. The piston pin serves to connect the part with them. It consists of steel, has a tubular shape and can be installed in several ways. Most often used floating finger that can rotate in the process. To prevent displacement of the fixed retaining rings. Rigid link is used much less frequently. Stock in some cases performs the function of the sending device, replacing the piston skirt.
The engine Piston may consist of different materials. In any case, they must possess qualities such as highstrength, good conductivity, anti-friction properties, corrosion resistance and low linear expansion coefficient and density. For the production of pistons utilize aluminum alloys and cast iron.
Distinguished by high strength, wear resistance and low coefficient of linear expansion. The latter property provides the possibility of operation of such pistons with small gaps, and thus a good seal of the cylinder. However, due to the considerable specific weight of the cast iron parts are used only in those engines where the reciprocating moving masses have inertia forces up to the sixth part of the pressure forces on the bottom of the piston gases. In addition, due to the low thermal conductivity, the heating of the bottom of the cast iron parts in the process of operation of the engine reaches 350-450 °S, which is particularly undesirable for gasoline variants, as it leads to pre-ignition.
The material used for pistons most often. This is due to the small specific weight (aluminum parts easier to iron 30%), high thermal conductivity (3-4 times more than cast iron), ensuring the heating of the bottoms not more than 250 °C, what Provides opportunity zoomGovernance gradeAnd compression Provides betterE napolnenyE cylinderIn and High frictionMi properties. When aluminum is greater 2 times than that of cast iron, Coefficient of linear expansion that forces you to do large Periods with the walls of the cylinders, So The size of the pistons Aluminum less than cast ironA for the same cylinders. Those items AndHave less strength, especially when heated (at 300 °C, it reduces to 50-55%, while cast ironData — 10%).
In order To reduce the friction of the wall of the piston cover antifriction material, which is used as graphite and molybdenum disulfide.
As mentioned, in the process of operation of the engine the pistons can get up to about 250-450 °C. Therefore, it is necessary to take measures aimed at reducing heating and to compensation caused by thermal expansion of parts.
To use piston-cooling oil, which in various ways served inside them: create an oil mist in the cylinder, spray it through the hole in the connecting rod or injector is injected into an annular channel circulating in a tubular coil in the bottom of the piston.
To compensate For thermal deformations In areas of the tides Skirts Two sides Grind metal 0.5-1.5 mm in depth In the form of P - or T-shaped slots. This measure improves It Lubrication and Prevents tE from temperature deformations for scoring, so dataE the deepening of the called refrigerator. Their is used in combination with Conoco or barrel shape of the skirt. This compensates for her Linear expansion due to the fact that heating Skirt takes a cylindrical shape. In addition, use of compensatory inserts to the diameter of the piston have experienced limited thermalE expansionE in the plane of swing of the connecting rod. You can also isolate the rail from the top of the head subjected to the greatest heat. Finally, the walls of the skirt give a spring property by Applying oblique incision along its entire length.
The method of manufacturing the pistons are subdivided into cast and wrought (stamped). Details of the first type Apply mostE cars, and the replacement pistons to forged is used when tuning. Forged options are characterized by high strength and durability and less weight. Therefore, the installation of pistons of this type increases the reliability and performance of the engine. This is particularly important for motors operating in conditions of high loads, while for everyday use enough castings.
Piston — this is a multifunctional item. So it is used not only in engines. For example, there is the caliper piston brake system As it works in the same way. Also Crank mechanism used on some models of compressors, pumps and other equipment.
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Alin Trodden - author of the article, editor
"Hi, I'm Alin Trodden. I write texts, read books, and look for impressions. And I'm not bad at telling you about it. I am always happy to participate in interesting projects."
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