The piston occupies a central place in the process of converting fuel energy into thermal and mechanical energy. Let's talk about engine pistons, what they are and how they work.

What it is?

A piston is a cylindrical part that reciprocates inside an engine cylinder. Needed to change gas pressure into mechanical work, or vice versa - reciprocating movement into a change in pressure. Those. it transmits to the connecting rod the force arising from the gas pressure and ensures the flow of all cycles of the working cycle. It looks like an inverted glass and consists of a bottom, a head, a guide part (skirt).

Gasoline engines use flat-bottom pistons due to ease of manufacture and less heat during operation. Although some modern cars make special recesses for the valves. This is necessary so that when the timing belt breaks, the pistons and valves do not meet and do not entail a serious repair. The bottom of the diesel piston is made with a recess, which depends on the degree of mixture formation and the location of the valves and injectors. With this shape of the bottom, the air is better mixed with the fuel entering the cylinder.

The piston is exposed to high temperatures and pressures. It moves at high speed inside the cylinder. Therefore, initially for automobile engines they were cast from cast iron. With the development of technology, aluminum began to be used, because. it gave the following advantages: an increase in speed and power, less stress on parts, better heat transfer.

Since then, the power of the motors has increased many times. The temperature and pressure in the cylinders of modern automobile engines (especially diesel engines) have become such that aluminum has reached its limit of strength. Therefore, in recent years, such motors are equipped with steel pistons that can confidently withstand increased loads. They are lighter than aluminum due to thinner walls and lower compression height, i.e. distance from the bottom to the axis of the aluminum pin. And the steel pistons are not cast, but prefabricated.

Among other things, reducing the vertical dimensions of the piston with the same cylinder block makes it possible to lengthen the connecting rods. This will reduce the lateral loads in the piston-cylinder pair, which will positively affect fuel consumption and engine life. Or, without changing the connecting rods and crankshaft, you can shorten the cylinder block. Thus, we will lighten the engine.

What are the requirements?

• The piston, moving in the cylinder, allows the compressed gases, the product of fuel combustion, to expand and perform mechanical work. Therefore, it must be resistant to high temperature, gas pressure and reliably seal the cylinder bore.
• It must best meet the requirements of the friction pair in order to minimize mechanical losses and, as a result, wear.
• Experiencing loads from the combustion chamber and reaction from the connecting rod, it must withstand mechanical stress.
• When reciprocating at high speed, it should load the crank mechanism with inertial forces as little as possible.

Main purpose

Fuel, burning in the space above the piston, releases a huge amount of heat in each cycle of the engine. The temperature of the burnt gases reaches 2000 degrees. They will transfer only part of the energy to the moving parts of the motor, everything else in the form of heat will heat the engine. What remains, together with the exhaust gases, will fly into the pipe. Therefore, if we do not cool the piston, it will melt after a while. This is an important point for understanding the operating conditions of the piston group.

Once again, we repeat the well-known fact that the heat flow is directed from more heated bodies to less heated ones.

The most heated is the working fluid, or, in other words, the gases in the combustion chamber. It is quite clear that the heat will be transferred to the surrounding air - the coldest. Air, washing the radiator and engine housing, will cool the coolant, cylinder block and head housing. It remains to find a bridge through which the piston gives off its heat to the block and antifreeze. There are four ways for this.

So, the first path providing the most flow, are piston rings. Moreover, the first ring plays a major role, as it is located closer to the bottom. This is the shortest path to the coolant through the cylinder wall. The rings are simultaneously pressed against both the piston grooves and against the cylinder wall. They provide more than 50% of the heat flow.

The second way is less obvious. The second coolant in the engine is oil. Having access to the most heated places of the engine, oil mist carries away and gives to the oil pan a significant part of the heat from the hottest points. In the case of using oil nozzles that direct the jet to the inner surface of the piston bottom, the share of oil in heat exchange can reach 30 - 40%. It is clear that when loading the oil with the function of a coolant, we must take care to cool it down. Otherwise, overheated oil may lose its properties. Also, the higher the temperature of the oil, the less heat it can carry.

Third way. Part of the heat is taken away for heating by the fresh air-fuel mixture that enters the cylinder. The amount of fresh mixture and the amount of heat that it takes away depends on the mode of operation and the degree of opening of the throttle. It should be noted that the heat obtained during combustion is also proportional to the charge. Therefore, this cooling path is impulsive; it is fast and highly efficient due to the fact that the heat is taken from the side from which the piston is heated.

Due to its greater importance, close attention should be paid to the transfer of heat through the piston rings. It is clear that if we block this path, then it is unlikely that the engine will withstand any long forced regimes. The temperature will rise, the piston material will "float", and the engine will collapse.

Recall such a characteristic as compression. Let us imagine that the ring does not adhere along its entire length to the wall of the cylinder. Then the burnt gases, breaking through into the gap, will create a barrier that prevents the transfer of heat from the piston through the ring to the cylinder wall. This is the same as if you closed part of the radiator and deprived it of the ability to be cooled by air.

The picture is more terrible if the ring does not have close contact with the groove. In those places where gases have the opportunity to flow past the ring through the groove, the piston section is deprived of the opportunity to cool. As a result, burnout and chipping of the part adjacent to the leak.

How many rings do you need for a piston? From a mechanical point of view, the fewer rings, the better. The narrower they are, the lower the losses in the piston group. With a decrease in their number and height, the conditions for cooling the piston worsen, increasing the thermal resistance of the bottom - ring - cylinder wall. Therefore, the choice of design is always a compromise.

When we sit behind the wheel of a car, turn the key in the ignition and press the gas pedal, many very complex mechanisms begin to occur under the hood, which produce movement. All these mechanisms do not interest us at all, the main thing is that the car is moving. But when a breakdown occurs, we begin to puzzle over what the reason is and we have to master all the necessary information about the device and the functioning of each individual part. But in order not to waste time on this, when you don’t have this time, before you get behind the wheel, you should have a good understanding of the features of automotive parts.

In particular, today we will talk with you about the piston. After all, this detail is central in the process of processing fuel energy into thermal and mechanical energy. We will deal with you what a piston is, its purpose, the basic requirements for it and the features of its design.

1. Engine piston and its main characteristics

We certainly hope that experienced motorists do not need to explain for a long time what an engine piston is. However, if there are “beginners” among our readers, then especially for them we will explain that the piston is a car part that converts changes in the pressure of gas, vapor and liquid inside the engine into mechanical force. The piston has the shape of a cylinder, inside which reciprocating movements are constantly made, due to which a mechanical force is formed.

The duty of this part is very responsible and its effectiveness depends on how well he copes with it. In fact, it is the most complex part of the car, it is rather difficult for an unprepared mind to understand the features and contradictory properties of which. Few people know, but practically not a single automobile concern is engaged in the independent manufacture of pistons for their cars, but they order them specifically for their engines. Complicating the situation for ordinary motorists is the fact that today there are a large number of different shapes and sizes of pistons. Therefore, the maintenance and repair of this part can always be carried out in different ways.

What requirements must a reliable piston meet?

Since the piston is a rather complicated part, a great many requirements are set for it. Due to the complexity of production, there are not so many manufacturers of engine pistons, and this part costs quite a lot on the car market. And so, let's see what requirements a good piston must meet:

1. Moving inside the cylinder, it is the engine piston that provides the expansion of compressed gases, which are the product of fuel combustion. Thanks to this, gases can perform mechanical work - to drive all other mechanisms of the car. As a result, the main requirement for pistons is the ability to resist the high temperature at which all these processes take place, the high gas pressure and seal the cylinder bore well (otherwise it will not be able to influence the gas pressure).

2. The piston is not a single device, it works together with the cylinder and piston rings. Together these parts form a linear plain bearing. In this regard, the bearing must necessarily meet all the requirements and features of the friction pair. If all requirements are taken into account with the highest accuracy, then this will not only help to minimize mechanical losses during fuel combustion, but also the wear of all parts.

3. The piston is constantly under heavy loads, the strongest of which are the loads from the combustion chamber of the fuel and the reactions from it. Its design must necessarily take into account all these factors and withstand such a strong mechanical impact.

4. Despite the fact that the piston moves at a fairly high speed during operation, it should not heavily load the crank mechanism of the car with inertial forces, otherwise this can lead to breakage.

2. Appointment of pistons or their functional duties

We have repeatedly mentioned that the piston plays a very important role in the entire operation of an automobile engine. So, the main purpose of pistons is to:

- to receive gas pressure from the combustion chamber and transfer these pressures to the engine in the form of mechanical force;

Seal the engine cylinder cavity above the piston. Thus, it protects the entire automotive mechanism from blowing gases into the crater and from penetrating lubricating oil.

Moreover, the second function is more important, since it is thanks to this that the piston itself provides normal working conditions. Even about what technical condition the engine is located, experts draw a conclusion only after inspecting the piston group and checking its sealing ability. After all, if oil consumption exceeds 3% of fuel consumption (and this happens due to its burning when it enters the combustion chamber), then the entire car engine must be urgently sent for repair, or it can even be decommissioned. You can understand that something is wrong with your engine by looking at the smoke in the exhaust gases. But it's better not to let that happen.

Probably, reading that the piston and its elements work in conditions with very high temperatures, you are surprised how this device itself does not fail? We add to this that, in addition to difficult temperature conditions, the operation of the piston is constantly accompanied by cyclic, sharply changing loads. With all this, the elements of the described part do not even always have enough lubrication. But of course, all the designers and developers of pistons thought about this.

Firstly, they are designed taking into account the purpose and type of engine on which they will be installed (stationary, diesel, two-stroke, forced or transport), so only the most stable materials are used for this.

Secondly, there are several ways in which the cooling of this part is carried out. But first, a little about how and where heat (or even heat) flows from the combustion chamber. It escapes into the surrounding cold air, which flows around the radiator and engine, as well as the cylinder block. But in what ways does the piston give heat to the block and antifreeze?

1. through piston rings. The most important of these is the first, since it is located closest to the bottom of the piston. Since the rings are simultaneously pressed against both the piston grooves and the cylinder wall, about 50% of the total heat flow from the piston is given off due to them.

2. Thanks to the second "coolant", the role of which is performed by engine oil. Since the oil approaches the hottest parts of the engine, it is he who manages to carry a very large amount of heat from the most heated points into the crankcase. However, in order for the oil to be able to cool the pistons, it must also be cooled, otherwise it will have to be changed very soon.

3. Heat travels through the lugs to the pin, to the connecting rod, and to the oil. The less efficient way, however, and it plays its important role.

4. Oddly enough, but the fuel also helps to cool the piston and the engine as a whole. So, when a fresh mixture of fuel and air enters the combustion chamber, it draws quite a lot of heat onto itself, although then it gives it back in even larger quantities. However, the amount of the mixture and the heat it can absorb is directly related to how the car is running and how open the throttle is. The advantage of this path is that the mixture absorbs heat exactly from the side from which the piston heats up the most.

However, we got ahead of ourselves a little, because we started talking about the functioning of the piston, without fully understanding the design features of this part. This is what we will devote the next section to.

3. Piston design: everything the average car enthusiast needs to know about the part

In general, talking about the piston alone is like talking about bread, discussing only the properties of flour. It is more logical to get acquainted with the entire piston group of the engine, which is represented by such details:

- the piston itself;

Piston rings;

Piston pin.

This design of the piston group has been unchanged since the advent of the very first internal combustion engines. Therefore, this description will be common to almost all engines.

Naturally, the piston performs the most important functions, the design of which has not changed for 150 years. If you do not want to become a professional mechanic, then you only need to know about such important areas of the piston and their functional purposes:

1. Piston head. The surface of a part that directly faces the combustion chamber of an engine. With its profile, the bottom determines the lower surface of this very chamber. This form can depend on: the shape of the combustion chamber, on its volume, the features of the supply of fuel-air mass into it, on the location of the valves. There are cases when there is a recess on the bottom due to which the volume of the combustion chamber increases. But, since this is not desirable, then to reduce the volume of the chamber, it is necessary to use special displacers - a certain amount of metal located above the bottom plane.

2. "Heat (fire) belt." This term refers to the distance that runs from the bottom of the piston to its first ring. It is important to know that the smaller the distance from the bottom to the rings, the higher the thermal load will fall on these same elements, and the more they will wear out.

3. Sealing area. It's about about the grooves that are located on the side surface of the cylindrical piston. These grooves are a direct way to install the rings, which in turn allow the seal to move. Also, in the groove for the oil scraper ring, there must be a hole through which excess oil can be discharged into the internal cavity of the piston.

Another function of the sealing section is to remove part of the heat from the engine piston using, as we have already mentioned, piston rings. However, for effective heat dissipation, it is very important that the piston rings fit snugly into both the grooves and the cylinder surface. So, the end gap of the first compression ring should be about 0.045 to 0.070 mm, for the second - from 0.035 to 0.06 mm, and for the oil scraper - from 0.025 to 0.005 mm. But between the rings and grooves, the radial clearance indicator can be from 1.2 to 0.3 millimeters. But these indicators are not significant for the human eye, they can only be determined with the help of special equipment.

4. Piston head. This is a generalized section, which includes the bottom and the sealing part already described above.

5. Compression height of the piston. The distance that is calculated from the axis of the piston pin to the piston crown.

6. "Skirt". The bottom of the piston. Includes lugs with holes for the piston pin to fit into. The outer surface of this section is the supporting and guiding surface for the piston. Thanks to it, the correct ratio of the piston axis and the engine cylinder axis is ensured. An equally important role is played by the side surface of the "skirt", due to which the transverse forces that periodically occur in the piston group of the engine are transmitted to the cylinder. And especially in order to improve the workability of the surface of the skirt and reduce friction, it is coated with a special protective coating of tin (graphite and molybdenum disulfide can also be used as the basis of the coating. Or, instead of coating, grooves of a special profile can be applied to the skirt, which retain oil and create hydrodynamic force preventing contact with the cylinder walls.

How and from what: features of the manufacture of automotive pistons

It is clear that in order to perform such functions that the piston performs, a sufficiently “hardy” metal is required. However, it is far from steel. Pistons are made from aluminum alloys, to which silicon is always added. This is done in order to reduce the expansion coefficient under the influence of high temperatures and increase the wear resistance of the part.

However, for the manufacture of pistons, an alloy with a different percentage of silicon content can be used. For example, 13% silicon alloys are most often used for this purpose, which are called eutectic. There are alloys with a higher silicon content, which are called hypereutectic. And the higher this percentage, the higher the heat-conducting characteristics of the alloy. But this does not make such a material ideal for the manufacture of pistons.

The fact is that when cooled, such a material begins to release silicon grains, ranging in size from 0.5 to 1 millimeter. Obviously, such a process affects the casting and mechanical properties of both the material and the part that is made from it. For this reason, in addition to silicon, the following list of regulating additives is introduced into such alloys:

- manganese;

How is the main part of the automobile piston made? There are even two ways in which you can get the workpiece of this part. The first of these involves pouring a hot alloy into a special mold called a chill mold. This method is the most common. The second option for manufacturing a workpiece is hot stamping. But after machining the mold, the future piston is also subjected to various heat treatments, which makes it possible to increase the hardness of the metal, strength and wear resistance. Also, such procedures allow you to remove the residual stress in the metal.

Although the use of forged metal increases the strength of the part, they also have their drawbacks. Such products are usually made in the classic version with a high “skirt”, which makes them too heavy. Also, such products do not allow the use of thermocompensating rings or plates with them. Due to the increased weight of such a piston, its thermal deformation also increases, as a result, it is necessary to increase the size of the gap between the piston and the cylinder.

The consequences of this will not please the driver at all, since they are increased engine noise, rapid cylinder wear and high oil consumption. The use of forged pistons justifies itself only in cases where the car is regularly operated in the most extreme conditions.

To date, designers and physicists are making every effort to make the design of pistons as ideal and accurate as possible. In particular, the most important trends are directed to the following list:

- reducing the weight of the part;

The use of only “thin” rings on the piston;

Reducing the compression height of the piston;

Reducing piston pins and using only the shortest pistons in the piston design;

Improvement of protective coatings and their application on all surfaces of the part.

A similar achievement today can be seen on the T-shaped piston design of the latest generation. this design is called T-shaped precisely due to the external similarity of the part with the letter "T". The main difference between such pistons is the reduced height of the skirt and the area of ​​​​its guide part. Such pistons are made from a hypereutectic alloy, which contains a fairly large amount of silicon. And they are made mainly by hot stamping.

However, what kind of engine piston design will want to put on the car, its developers will depend on many factors. Such a decision is always preceded by a long period of calculations and analysis of the behavior of all units of the connecting rod and piston group under the influence of a new part. The calculation of all parts is carried out on their most limiting capabilities of their designs and the materials from which they are made. However, sadly, but in this case, the manufacturer will not overpay. He will choose the option that provides the necessary resource just “in time” and will not spend money on increasing it.

Be that as it may, but an ordinary motorist has to understand and operate what has already been installed on his car. We hope that our article has helped you to better understand how pistons function and what is the purpose of them. We wish you that you never have problems with this part, for which it is necessary to provide it with the correct operating conditions - do not “drive” too much and change the engine oil on time.

Most cars are forced to move by a piston internal combustion engine (abbreviated internal combustion engine) with crank mechanism. This design has become widespread due to the low cost and manufacturability of production, relatively small dimensions and weight.

According to the type of fuel used, internal combustion engines can be divided into gasoline and diesel. I must say that gasoline engines work great on. This division directly affects the design of the engine.

How does a piston internal combustion engine work?

The basis of its design is the cylinder block. This is a body cast from cast iron, aluminum or sometimes magnesium alloy. Most of the mechanisms and parts of other engine systems are attached specifically to the cylinder block, or located inside it.

Another major part of the engine is its head. It is located at the top of the cylinder block. The head also houses parts of the engine systems.

A pallet is attached to the cylinder block from below. If this part takes the load when the engine is running, it is often called the oil pan, or crankcase.

All engine systems

1. crank mechanism;
2. gas distribution mechanism;
3. supply system;
4. cooling system;
5. Lubrication system;
6. ignition system;
7. engine management system.

crank mechanism consists of piston, cylinder liner, connecting rod and crankshaft.

Crank mechanism:
1. Oil scraper ring expander. 2. Piston oil scraper ring. 3. Compression ring, third. 4. Compression ring, second. 5. Compression ring, top. 6. Piston. 7. Retaining ring. 8. Piston pin. 9. Connecting rod bushing. 10. Connecting rod. 11. Connecting rod cap. 12. Insert of the lower head of the connecting rod. 13. Connecting rod cap bolt, short. 14. Connecting rod cap bolt, long. 15. Drive gear. 16. Plug of the oil channel of the crankpin. 17. Crankshaft bearing shell, upper. 18. Gear ring. 19. Bolts. 20. Flywheel. 21. Pins. 22. Bolts. 23. Oil deflector, rear. 24. Crankshaft rear bearing cap. 25. Pins. 26. Thrust bearing half ring. 27. Crankshaft bearing shell, lower. 28. Counterweight of the crankshaft. 29. Screw. 30. Crankshaft bearing cap. 31. Coupling bolt. 32. A bolt of fastening of a cover of the bearing. 33. Crankshaft. 34. Counterweight, front. 35. Oil slinger, front. 36. Lock nut. 37. Pulley. 38. Bolts.

The piston is located inside the cylinder liner. With the help of a piston pin, it is connected to a connecting rod, the lower head of which is attached to the connecting rod journal of the crankshaft. The cylinder liner is a hole in the block, or a cast iron sleeve inserted into the block.

Cylinder liner with block

The cylinder liner is closed with a head on top. The crankshaft is also attached to the block at the bottom. The mechanism converts the rectilinear movement of the piston into the rotational movement of the crankshaft. The same rotation that ultimately makes the wheels of the car spin.

Gas distribution mechanism is responsible for supplying a mixture of fuel and air vapors to the space above the piston and removing combustion products through valves that open strictly at a certain point in time.

The power system is primarily responsible for the preparation of a combustible mixture of the desired composition. The devices of the system store the fuel, purify it, mix it with air in such a way as to ensure the preparation of a mixture of the desired composition and quantity. The system is also responsible for removing fuel combustion products from the engine.

During the operation of the engine, thermal energy is generated in an amount greater than the engine is able to convert into mechanical energy. Unfortunately, the so-called thermal efficiency of even the best examples of modern engines does not exceed 40%. Therefore, a large amount of "extra" heat has to be dissipated in the surrounding space. This is exactly what it does, removes heat and maintains a stable operating temperature of the engine.

Lubrication system . This is just the case: “If you don’t grease, you won’t go.” Internal combustion engines have a large number of friction units and so-called plain bearings: there is a hole, the shaft rotates in it. There will be no lubrication, the assembly will fail from friction and overheating.

Ignition system designed to set fire, strictly at a certain point in time, a mixture of fuel and air in the space above the piston. there is no such system. There, the fuel spontaneously ignites under certain conditions.

Video:

The engine management system, using an electronic control unit (ECU), controls the engine systems and coordinates their work. First of all, this is the preparation of a mixture of the desired composition and timely ignition of it in the engine cylinders.

In the engine device, the piston is a key element of the working process. The piston is made in the form of a metal hollow glass, located with a spherical bottom (piston head) up. The piston guide part, otherwise known as the skirt, has shallow grooves designed to hold the piston rings in them. The purpose of the piston rings is to ensure, firstly, the tightness of the above-piston space, where, during engine operation, the gasoline-air mixture is instantly burned and the resulting expanding gas could not, having rounded the skirt, rush under the piston. Secondly, the rings prevent the oil under the piston from entering the over-piston space. Thus, the rings in the piston act as seals. The lower (lower) piston ring is called the oil scraper ring, and the upper (upper) ring is called compression, that is, it provides a high degree of compression of the mixture.

When a fuel-air or fuel mixture enters the cylinder from a carburetor or injector, it is compressed by the piston as it moves up and ignited by an electric discharge from the spark plug (in a diesel engine, the mixture self-ignites due to sudden compression). The resulting combustion gases have a much larger volume than the original fuel mixture, and, expanding, sharply push the piston down. Thus, the thermal energy of the fuel is converted into a reciprocating (up and down) movement of the piston in the cylinder.

Next, you need to convert this movement into rotation of the shaft. This happens as follows: inside the piston skirt there is a finger on which the upper part of the connecting rod is fixed, the latter is pivotally fixed on the crankshaft crank. The crankshaft rotates freely on support bearings that are located in the crankcase of an internal combustion engine. When the piston moves, the connecting rod begins to rotate the crankshaft, from which the torque is transmitted to the transmission and - further through the gear system - to the drive wheels.

Engine specifications. Engine specifications When moving up and down, the piston has two positions, which are called dead points. Top dead center (TDC) is the moment of maximum lifting of the head and the entire piston up, after which it begins to move down; bottom dead center (BDC) - the lowest position of the piston, after which the direction vector changes and the piston rushes up. The distance between TDC and BDC is called the piston stroke, the volume of the upper part of the cylinder with the piston at TDC forms the combustion chamber, and the maximum cylinder volume with the piston at BDC is called the total volume of the cylinder. The difference between the total volume and the volume of the combustion chamber is called the working volume of the cylinder.
The total working volume of all cylinders of an internal combustion engine is indicated in the technical characteristics of the engine, expressed in liters, therefore, in everyday life it is called the engine displacement. The second most important characteristic of any internal combustion engine is the compression ratio (SS), defined as the quotient of dividing the total volume by the volume of the combustion chamber. For carburetor engines, SS varies from 6 to 14, for diesel engines - from 16 to 30. It is this indicator, along with engine size, that determines its power, efficiency and completeness of combustion of the fuel-air mixture, which affects the toxicity of emissions during engine operation. .
Engine power has a binary designation - in horsepower (hp) and in kilowatts (kW). To convert units to one another, a coefficient of 0.735 is applied, that is, 1 hp. = 0.735 kW.
The duty cycle of a four-stroke internal combustion engine is determined by two revolutions of the crankshaft - half a turn per stroke, corresponding to one stroke of the piston. If the engine is single-cylinder, then unevenness is observed in its operation: a sharp acceleration of the piston stroke during the explosive combustion of the mixture and slowing it down as it approaches BDC and further. In order to stop this unevenness, a massive flywheel disk with a large inertia is installed on the shaft outside the motor housing, due to which the moment of rotation of the shaft in time becomes more stable.

The principle of operation of the internal combustion engine
A modern car, most of all, is driven by an internal combustion engine. There are many such engines. They differ in volume, number of cylinders, power, rotation speed, fuel used (diesel, gasoline and gas internal combustion engines). But, in principle, the device of the internal combustion engine, it seems.
How does an engine work and why is it called a four-stroke internal combustion engine? I understand about internal combustion. Fuel burns inside the engine. And why 4 cycles of the engine, what is it? Indeed, there are two-stroke engines. But on cars they are used extremely rarely.
A four-stroke engine is called because its work can be divided into four parts equal in time. The piston will pass through the cylinder four times - twice up and twice down. The stroke begins when the piston is at its lowest or highest point. For motorists-mechanics, this is called top dead center (TDC) and bottom dead center (BDC).
First stroke - intake stroke

The first stroke, also known as intake, starts at TDC (top dead center). Moving down, the piston sucks the air-fuel mixture into the cylinder. The operation of this stroke occurs with the intake valve open. By the way, there are many engines with multiple intake valves. Their number, size, time spent in the open state can significantly affect engine power. There are engines in which, depending on the pressure on the gas pedal, there is a forced increase in the time the intake valves are open. This is done to increase the amount of fuel taken in, which, once ignited, increases engine power. The car, in this case, can accelerate much faster.

The second stroke is the compression stroke

The next stroke of the engine is the compression stroke. After the piston reaches its lowest point, it begins to rise, thereby compressing the mixture that entered the cylinder on the intake stroke. The fuel mixture is compressed to the volume of the combustion chamber. What kind of camera is this? The free space between the top of the piston and the top of the cylinder when the piston is at top dead center is called the combustion chamber. The valves are completely closed during this stroke of the engine. The tighter they are closed, the better the compression is. Great importance has, in this case, the condition of the piston, cylinder, piston rings. If there are large gaps, then good compression will not work, and, accordingly, the power of such an engine will be much lower. Compression can be checked with a special device. By the magnitude of the compression, one can draw a conclusion about the degree of engine wear.

Third cycle - working stroke

The third cycle is a working one, it starts from TDC. It is called a worker for a reason. After all, it is in this cycle that an action occurs that makes the car move. At this point, the ignition system comes into play. Why is this system so called? Yes, because it is responsible for igniting the fuel mixture compressed in the cylinder in the combustion chamber. It works very simply - the candle of the system gives a spark. In fairness, it is worth noting that the spark is given out on the spark plug a few degrees before the piston reaches the top point. These degrees, in a modern engine, are automatically regulated by the "brains" of the car.
After the fuel ignites, an explosion occurs - it sharply increases in volume, forcing the piston to move down. The valves in this stroke of the engine, as in the previous one, are in the closed state.

The fourth measure is the release measure

The fourth stroke of the engine, the last one is exhaust. Having reached the bottom point, after the working stroke, the exhaust valve begins to open in the engine. There may be several such valves, as well as intake valves. Moving up, the piston removes exhaust gases from the cylinder through this valve - it ventilates it. The degree of compression in the cylinders, the complete removal of exhaust gases and the required amount of intake air-fuel mixture depend on the precise operation of the valves.

After the fourth measure, it is the turn of the first. The process is repeated cyclically. And due to what does the rotation occur - the operation of the internal combustion engine all 4 strokes, which causes the piston to rise and fall in the compression, exhaust and intake strokes? The fact is that not all the energy received in the working cycle is directed to the movement of the car. Part of the energy is used to spin the flywheel. And he, under the influence of inertia, turns the crankshaft of the engine, moving the piston during the period of "non-working" cycles.

Gas distribution mechanism

The gas distribution mechanism (GRM) is designed for fuel injection and exhaust gases in internal combustion engines. The gas distribution mechanism itself is divided into a lower valve, when the camshaft is in the cylinder block, and an upper valve. The overhead valve mechanism implies that the camshaft is located in the cylinder head (cylinder head). There are also alternative gas distribution mechanisms, such as a sleeve timing system, a desmodromic system, and a variable phase mechanism.
For two-stroke engines, the gas distribution mechanism is carried out using intake and exhaust ports in the cylinder. For four-stroke engines, the most common overhead valve system, which will be discussed below.

Timing device
In the upper part of the cylinder block is the cylinder head (cylinder head) with the camshaft, valves, pushers or rocker arms located on it. The camshaft drive pulley is moved out of the cylinder head. To prevent the leakage of engine oil from under the valve cover, an oil seal is installed on the camshaft neck. The valve cover itself is mounted on an oil-petrol-resistant gasket. The timing belt or chain is worn on the camshaft pulley and is driven by the crankshaft gear. Tension rollers are used to tension the belt, tension “shoes” are used for the chain. Typically, the timing belt drives the water cooling pump, the intermediate shaft for the ignition system and the high pressure pump drive of the injection pump (for diesel versions).
On the opposite side of the camshaft, a vacuum booster, power steering or car alternator can be driven by direct transmission or by means of a belt.

The camshaft is an axle with cams machined on it. The cams are located along the shaft so that during rotation, in contact with the valve lifters, they are pressed exactly in accordance with the engine's operating cycles.
There are engines with two camshafts (DOHC) and a large number of valves. As in the first case, the pulleys are driven by a single timing belt and chain. Each camshaft closes one type of intake or exhaust valve.
The valve is pressed by a rocker (early versions of engines) or a pusher. There are two types of pushers. The first is pushers, where the gap is regulated by shims, the second is hydraulic pushers. The hydraulic pusher softens the blow to the valve due to the oil that is in it. Adjustment of the gap between the cam and the top of the pusher is not required.

The principle of operation of the timing

The entire gas distribution process is reduced to the synchronous rotation of the crankshaft and camshaft. As well as opening the intake and exhaust valves at a certain position of the pistons.
To accurately position the camshaft relative to the crankshaft, alignment marks are used. Before putting on the timing belt, the marks are combined and fixed. Then the belt is put on, the pulleys are “released”, after which the belt is tensioned by the tension rollers.
When the valve is opened with a rocker arm, the following happens: the camshaft "runs" on the rocker arm, which presses the valve, after passing through the cam, the valve closes under the action of the spring. The valves in this case are arranged in a v-shape.
If pushers are used in the engine, then the camshaft is located directly above the pushers, during rotation, pressing its cams on them. The advantage of such timing is low noise, low price, maintainability.
In a chain engine, the entire gas distribution process is the same, only when assembling the mechanism, the chain is put on the shaft together with the pulley.

crank mechanism

Crank mechanism (hereinafter abbreviated as KShM) is an engine mechanism. The main purpose of the crankshaft is to convert the reciprocating movements of a cylindrical piston into rotational movements of the crankshaft in an internal combustion engine and vice versa.

KShM device
Piston

The piston has the form of a cylinder made of aluminum alloys. The main function of this part is to convert the change in gas pressure into mechanical work, or vice versa - pressurization due to reciprocating motion.
The piston is a bottom, head and skirt folded together, which perform completely different functions. The piston head of a flat, concave or convex shape contains a combustion chamber. The head has cut grooves where the piston rings (compression and oil scraper) are placed. Compression rings prevent gas breakthrough into the engine crankcase, and piston oil scraper rings help remove excess oil on the inner walls of the cylinder. There are two bosses in the skirt, which provide the placement of the piston pin connecting the piston to the connecting rod.

A stamped or forged steel (rarely titanium) connecting rod has swivel joints. The main role of the connecting rod is to transfer the piston force to the crankshaft. The design of the connecting rod assumes the presence of an upper and lower head, as well as a rod with an I-section. The upper head and bosses contain a rotating ("floating") piston pin, while the lower head is collapsible, thus allowing for a close connection with the shaft journal. The modern technology of controlled splitting of the lower head makes it possible to ensure high precision of the connection of its parts.

The flywheel is mounted on the end of the crankshaft. Today, dual-mass flywheels are widely used, having the form of two elastically interconnected discs. The flywheel ring gear is directly involved in starting the engine through the starter.

Block and cylinder head

The cylinder block and cylinder head are cast iron (rarely aluminum alloys). The cylinder block has cooling jackets, beds for crankshaft and camshaft bearings, as well as attachment points for instruments and assemblies. The cylinder itself acts as a guide for the pistons. The cylinder head contains a combustion chamber, inlet-outlet channels, special threaded holes for spark plugs, bushings and pressed seats. The tightness of the connection of the cylinder block with the head is provided with a gasket. In addition, the cylinder head is closed with a stamped cover, and between them, as a rule, an oil-resistant rubber gasket is installed.

In general, the piston, cylinder liner and connecting rod form the cylinder or cylinder-piston group of the crank mechanism. Modern engines can have up to 16 or more cylinders.

The piston occupies a central place in the process of converting the chemical energy of the fuel into thermal and mechanical energy. Let's talk about pistons of an internal combustion engine, what it is and the main purpose in the work.

WHAT IS AN ENGINE PISTON?

Engine piston- this is a cylindrical part that reciprocates inside the cylinder and serves to convert a change in the pressure of a gas, vapor or liquid into mechanical work, or vice versa - a reciprocating movement into a change in pressure. Initially, pistons for automotive internal combustion engines were cast from cast iron. With the development of technology, aluminum began to be used, because. it gave the following advantages: an increase in speed and power, less stress on parts, better heat transfer.

Since then, engine power has increased many times over, the temperature and pressure in the cylinders of modern automobile engines (especially diesel engines) have become such that aluminum has reached its limit of strength. Therefore, in recent years, such motors are equipped with steel pistons that can confidently withstand increased loads. They are lighter than aluminum due to thinner walls and lower compression height, i.e. distance from the bottom to the axis of the aluminum pin. And the steel pistons are not cast, but prefabricated.
Among other things, reducing the vertical dimensions of the piston with the same cylinder block makes it possible to lengthen the connecting rods. This will reduce lateral loads in the piston-cylinder pair, which will positively affect fuel consumption and engine life. Or, without changing the connecting rods and crankshaft, you can shorten the cylinder block and thus lighten the engine

The piston performs a number of important functions:

• ensures the transfer of mechanical forces to the connecting rod;
• is responsible for sealing the fuel combustion chamber;
• ensures timely removal of excess heat from the combustion chamber

The work of the piston takes place in difficult and in many ways dangerous conditions - at elevated temperatures and increased loads, therefore it is especially important that pistons for engines are distinguished by efficiency, reliability and wear resistance. That is why light but heavy-duty materials are used for their production - heat-resistant aluminum or steel alloys. Pistons are made by two methods - casting or stamping.

Extreme conditions dictate piston material

The piston is operated under extreme conditions, the characteristic features of which are high: pressure, inertial loads and temperatures. That is why the main requirements for materials for its manufacture include:

• high mechanical strength;
• good thermal conductivity;
• low density;
• insignificant coefficient of linear expansion, antifriction properties;
• good corrosion resistance.

The required parameters correspond to special aluminum alloys, which are distinguished by strength, heat resistance and lightness. Less commonly, gray cast irons and steel alloys are used in the manufacture of pistons.
Pistons can be:

• cast;
• forged.

In the first version, they are made by injection molding. Forged ones are made by stamping from an aluminum alloy with a small addition of silicon (on average, about 15%), which significantly increases their strength and reduces the degree of expansion of the piston in the operating temperature range.

Piston design

The engine piston has a fairly simple design, which consists of the following parts:

1. ICE piston head
2. piston pin
3. Retaining ring
4. Boss
5. connecting rod
6. Steel insert
7. Compression ring one
8. Second compression ring
9. Oil scraper ring

The design features of the piston in most cases depend on the type of engine, the shape of its combustion chamber and the type of fuel that is used.

Bottom

The bottom can have a different shape depending on the functions it performs - flat, concave and convex. The concave shape of the bottom provides more efficient operation of the combustion chamber, however, this contributes to more deposits during the combustion of fuel. The convex shape of the bottom improves the performance of the piston, but at the same time reduces the efficiency of the combustion process of the fuel mixture in the chamber.

Piston rings

Below the bottom are special grooves (grooves) for installing piston rings. The distance from the bottom to the first compression ring is called the firing zone.

Piston rings are responsible for reliable connection cylinder and piston. They provide reliable tightness due to a snug fit to the cylinder walls, which is accompanied by an intense friction process. Engine oil is used to reduce friction. Piston rings are made from cast iron.

The number of piston rings that can be installed in a piston depends on the type of engine used and its purpose. Often systems with one oil scraper ring and two compression rings (first and second) are installed.

PISTON TYPES

In internal combustion engines, two types of pistons are used, which differ in their design - one-piece and composite.

One-piece parts are made by casting followed by machining. In the process of casting, a blank is created from metal, which is given the general shape of the part. Further, on metalworking machines, working surfaces are processed in the resulting workpiece, grooves are cut for rings, technological holes and recesses are made.

In the composite elements, the head and the skirt are separated, and they are assembled into a single structure during installation on the engine. Moreover, the assembly in one piece is carried out by connecting the piston to the connecting rod. For this, in addition to the holes for the piston pin in the skirt, there are special lugs on the head.

The advantage of composite pistons is the possibility of combining materials of manufacture, which increases the performance of the part.

Removal of excess heat from the piston

In addition to significant mechanical stresses, the piston is also subjected to the negative effects of extremely high temperatures. Heat is removed from the piston group:

• cooling system from the cylinder walls;
• the internal cavity of the piston, then - the piston pin and connecting rod, as well as the oil circulating in the lubrication system;
• partially cold air-fuel mixture supplied to the cylinders.

From the inner surface of the piston, its cooling is carried out using:

Oil scraper ring and compression rings

The oil scraper ring ensures the timely removal of excess oil from the inner walls of the cylinder, and the compression rings prevent gases from entering the crankcase.

The compression ring, located first, receives most of the inertial loads during piston operation.

To reduce loads in many engines, a steel insert is installed in the annular groove, which increases the strength and degree of compression of the ring. Compression type rings can be made in the form of a trapezoid, barrel, cone, with a cutout.

The oil scraper ring in most cases is equipped with many holes for oil drainage, sometimes with a spring expander.

piston pin

This is a tubular part that is responsible for the reliable connection of the piston to the connecting rod. Made from steel alloy. When installing the piston pin in the bosses, it is tightly fixed with special retaining rings.

The piston, piston pin and rings together form the so-called engine piston group.

Skirt

The guide part of the piston device, which can be made in the form of a cone or barrel. The piston skirt is equipped with two bosses for connection with the piston pin.

To reduce friction losses, a thin layer of an antifriction agent is applied to the surface of the skirt (often graphite or molybdenum disulfide is used). The lower part of the skirt is equipped with an oil scraper ring.

A mandatory process for the operation of a piston device is its cooling, which can be carried out by the following methods:

• spraying oil through the holes in the connecting rod or nozzle;
• the movement of oil along the coil in the piston head;
• supplying oil to the area of ​​the rings through the annular channel;
• oil mist

Sealing part

The sealing part and the bottom are connected in the form of a piston head. In this part of the device there are piston rings - oil scraper and compression. The channels for the rings have small holes through which the used oil enters the piston and then flows into the crankcase.

In general, the piston of an internal combustion engine is one of the most heavily loaded parts, which is subjected to strong dynamic and at the same time thermal effects. This imposes increased requirements both on the materials used in the production of pistons and on the quality of their manufacture.