The piston is a detail of the engine of the car. The device, replacement, installation of the piston

The piston is one of the elements of the crank mechanism, on which the principle of operation of many internal combustion engines is based. In the above article, the design and features of these parts are considered.

Definition

The piston is a part that performs reciprocating movements in the cylinder and provides conversion of the gas pressure to mechanical work.

Appointment

With the participation of these parts, the thermodynamic process of the motor is realized. Since the piston is one of the elements of the crank mechanism, it perceives the pressure produced by the gases and transfers the force to the connecting rod. In addition, it ensures the sealing of the combustion chamber and the removal of heat from it.

Design

The piston is a three-part component, i.e. its design includes three components performing various functions, and two parts: a head into which the bottom and a sealing portion are combined, and a guide part represented by a skirt.

Bottom

Can have a different shape depending on many factors. For example, the configuration of the bottom of the pistons of the internal combustion engine is determined by the arrangement of other structural elements such as injectors, candles, valves, the shape of the combustion chamber, the peculiarities of the processes occurring in it, the general design of the engine, etc. In any case, it determines the features of functioning.

There are two main types of piston crown configuration: convex and concave. The first provides greater strength, but worsens the configuration of the combustion chamber. With the concave bottom of the bottom, the combustion chamber, on the other hand, has an optimal shape, but the deposit is more intensively deposited. Less often (in two-stroke engines) there are pistons with a bottom represented by a protrusion of the reflector. This is necessary when blowing for directional movement of combustion products. Parts of gasoline engines usually have a bottom flat or almost flat. Sometimes they have grooves for the full opening of the valves. In motors with direct injection, the pistons are characterized by a more complex configuration. In diesel engines, they are distinguished by the presence of a combustion chamber in the bottom, which provides good turbulence and improves the mixture formation.

Most pistons are one-sided, although there are also two-sided variants that have two bottoms.

The distance between the groove of the first compression ring and the bottom is called the piston fire belt. Very important is the value of its height, which is different for parts from different materials. In any case, the output of the height of the fire ring beyond the minimum allowable value may result in the piston burnout and deformation of the seat of the upper compression ring.

Sealing part

Here are oil-removal and compression rings. For the first type, the channels have through holes for the intake of the oil removed from the surface of the cylinder of the oil from where it enters the oil pan. Some of them have a rim of corrosion-resistant cast iron with a groove for the upper compression ring.

Piston rings, consisting of cast iron, serve to create a tight fit of the piston to the cylinder. Therefore, they are the source of the greatest friction in the motor, the loss of which is 25% of the total number of mechanical losses in the motor. The number and arrangement of the rings are determined by the type and purpose of the engine. The most commonly used are 2 compression rings and 1 oil ring.

Compression rings perform the task of preventing gases from entering the crankcase from the combustion chamber. The greatest load falls on the first of them, therefore in some engines its groove is strengthened with a steel insert. Compression rings can be trapezoidal, conical, barrel-shaped. Some of them have a cutout.

The oil removal ring serves to remove excess oil from the cylinder and prevents its entry into the combustion chamber. For this, there are holes in it. Some options have a spring expander.

Guide part (skirt)

Has a barrel-shaped (curvilinear) or cone-shaped shape to compensate for temperature expansion. There are two tides for the piston pin on it. In these areas, the skirt has the largest mass. In addition, the greatest temperature deformations are observed when heated. Various measures are used to reduce them. In the lower part of the skirt there can be an oil ring.

To transfer force from the piston or to it, the crank or rod is most often used. The piston pin serves to connect this part to them. It consists of steel, has a tubular shape and can be installed in several ways. The most commonly used floating finger, which can be rotated during operation. To prevent displacement, it is fixed with locking rings. Hard fixing is used much less often. The rod in some cases serves as a guide, replacing the piston skirt.

Materials

The engine piston may consist of various materials. In any case, they must have such qualities as high strength, good thermal conductivity, antifriction properties, corrosion resistance and low coefficient of linear expansion and density. Alloys of aluminum and cast iron are used for the production of pistons.

Cast iron

It is characterized by high strength, wear resistance and a low coefficient of linear expansion. The latter property ensures the operation of such pistons with small gaps, so that a good seal of the cylinder is achieved. However, due to the significant specific gravity, the cast iron parts are used only in those engines where the reciprocating masses have inertial forces that constitute not more than a sixth of the pressure forces on the bottom of the piston of gases. С, что особо нежелательно для карбюраторных вариантов, так как приводит к калильному зажиганию. In addition, due to low thermal conductivity, the heating of the bottom of the cast iron parts during the operation of the engine reaches 350-450 ° C, which is particularly undesirable for carburettor variants, since it leads to a glow ignition.

Aluminum

This material is used for pistons most often. предоставляет возможность увелич ения степен и сжатия и обеспечивает лучше е наполнени е цилиндро в, и высокими антифрикционны ми свойствами. This is due to the low specific gravity (aluminum parts are lighter than cast iron by 30%), high thermal conductivity (3-4 times greater than that of cast iron), which provides heating of the bottom to no more than 250 ° C, which makes it possible to increase the degrees and compressions and Provides a better filling of the cylinder , and high antifriction properties. коэффициент линейного расширения , что вынуждает делать большие промежутки со стенками цилиндров, то есть размеры поршней из алюминия меньше, чем из чугун а, для одинаковых цилиндров . In this case, aluminum has a factor of linear expansion 2 times larger than that of cast iron, which makes it necessary to make large gaps with the walls of the cylinders, that is, the dimensions of the pistons of aluminum are less than that of cast iron , for identical cylinders . и меют меньшую прочность, особенно в нагретом состоянии (при 300 °С она снижается на 50-55%, тогда как у чугун ных — на 10%). In addition, such details also show a lower strength, especially in the heated state (at 300 ° C it decreases by 50-55%, while in cast iron - by 10%).

To reduce the degree of friction, the walls of the pistons are coated with an antifriction material, which uses graphite and molybdenum disulphide.

Heat

As mentioned, pistons can be heated up to 250-450 ° C during engine operation . Therefore, it is necessary to take measures aimed at both reducing the heating and compensating for the temperature expansion of the parts caused by it.

For the cooling of the pistons, oil is used, which is fed into them in various ways: create an oil mist in the cylinder, spray it through the hole in the connecting rod or injector, inject into the annular channel, circulate along the tubular coil in the bottom of the piston.

на участках приливов юбки с двух сторон обтачивают металл на 0,5-1,5 мм в глубину в виде П- или Т-образных прорезей . To compensate for temperature deformations in tidal areas, skirts from both sides grind the metal 0.5-1.5 mm deep in the form of P- or T-shaped slits . ее смазывание и предотвращает появлени е от температурных деформаций задиров, поэтому данны е углубления называют холодильниками. Such a measure improves its lubrication and prevents the appearance of thermal deformations of scuffs, so these grooves are called refrigerators. используют в сочетании с конусо- или бочкообразной формой юбки. They are used in combination with a cone-shaped or barrel-shaped skirt. линейное расширение за счет того, что при нагреве юбка принимает цилиндрическую форму. This compensates for its linear expansion due to the fact that the skirt takes on a cylindrical shape when heated . , чтобы диаметр поршня испытывал ограниченное теплово е расширени е в плоскости качания шатуна. In addition, compensating inserts are used so that the piston diameter experiences a limited thermal expansion e in the rocking plane of the connecting rod. It is also possible to isolate the guide part from the head experiencing the greatest heating. нанесения косого разреза по всей ее длине. Finally, the walls of the skirt are given springing properties by applying an oblique cut along its entire length.

Production technology

By the way of making the pistons are divided into cast and forged (stamped). применяют на большинств е автомобилей, а замена поршней на кованые используется при тюнинге. Parts of the first type are used on most cars, and replacing the pistons with forged ones is used for tuning. Forged versions are characterized by increased strength and durability, as well as a smaller mass. Therefore, the installation of pistons of this type increases the reliability and performance of the engine. This is especially important for motors operating under conditions of high loads, while for daily operation there are enough cast parts.

Application

The piston is a multifunctional part. Therefore, it is used not only in engines. так как она функционирует аналогичным образом . For example, there is a brake caliper piston, because it functions in a similar way . кривошипно-шатунный механизм применяют на некоторых моделях компрессоров, насосов и прочем оборудовании. Also , the crank mechanism is used on some models of compressors, pumps and other equipment.