What is the piston made of? Engine piston - almost everything about it. What is a car internal combustion engine piston

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?

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.

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

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

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.

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.

Most cars are forced to move by a piston internal combustion engine (abbreviated internal combustion engine) with a 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.

The piston is one of the most significant elements in the conversion of the chemical energy of the fuel into thermal energy, and then into mechanical energy, both literally and figuratively. Motor performance largely depends on how well the piston performs its tasks. This determines the efficiency and, more importantly, the reliability of the motor. This parameter takes on special significance when it comes to car modifications in tuning salons, or sports applications. Designers always collide with the problem of using special pistons when power increases. The piston can be considered one of the most complex motor parts due to its many functions and rather contradictory properties. This is eminently confirmed by the fact that very few car builders make pistons for their engines using only their own strength.

In most cases, they resort to the services of firms specializing in this matter. There is a huge amount of mystery and conjecture about pistons, which creates a variety of sizes and shapes of this part. In the relevant section of our site you can find an article. It is technically difficult, almost impossible, to manufacture a piston under standard conditions of mechanical engineering in tuning companies, so most companies refuse to deal with this business. In addition, the production of such complex parts by the piece can be burdensome from a financial point of view. Intuitively tuners understand that improved engines must have improved pistons.

Piston device

Let's take a closer look at what requirements are usually placed on pistons, and how they are generally arranged.

• The piston, firstly, moves in the cylinder, which allows mechanical work to be performed by expanding the combustion products of the fuel, that is, compressed gases

From this we can conclude that it must resist the pressure of gases, have heat resistance and seal the cylinder bore.

• Secondly, the piston must meet the requirements of the friction pair so that mechanical losses and wear are minimal.
• Thirdly, it must withstand the reaction of the connecting rod and the mechanical impact from the combustion chamber.
• Fourthly, the piston must minimally load the crank mechanism with inertial forces, making reciprocating movements at high speed.

It turns out that all the problems associated with this significant part of the engine can be divided into two categories:

1. These are mechanical processes.
2. Thermal processes, and the first is much more extensive than the second. Categories have a fairly close relationship. Let's take a closer look at the first one.

As you know, fuel burns in a non-piston space, and at the same time it releases a very large amount of heat during each cycle of engine operation. The temperature of already burned gases is on average 2000 degrees. Part of the energy will go to the moving parts of the motor, and the rest will heat the engine. The energy that remains in the end will fly into the pipe along with the treated gases. According to the laws of physics, two bodies can transfer heat to each other until their temperatures are completely equal. Accordingly, if the piston is not periodically cooled, after a while it will simply melt. This is a very significant moment for understanding the principles of operation of the entire piston group.

This is especially important when the motor is boosted. With an increase in engine power, the amount of heat generated in the combustion chamber per one time unit automatically increases. Of course, we see very infrequently melted pistons, however, temperature is always mentioned in any of their problems, just like speed is present in any accident. Of course, the blame here lies with the driver, but no one would have been hurt if the car had stood still. The fact is that high temperatures degrade the characteristics of all materials. A load of 100 degrees will cause elastic deformation, a load of 300 degrees will completely deform the product, and a load of 450 degrees will deform it. For this reason, either materials must be used that can withstand severe stress from high temperatures, or measures must be taken to prevent the piston from rising in temperature. Usually both are done. However, the design of the piston must be such that in the right places there is a certain amount of metal that is able to withstand destruction.

The course of general physics confirms the fact that the heat flow is directed to less heated bodies from more heated ones. Thus, we have the opportunity to see how temperatures are distributed over the piston during its operation, and to determine the significant design points that affect its temperature, in other words, to understand how cooling occurs. We know that the working fluid, that is, the gases in the combustion chamber, heats up more than all the parts. It is quite clear that in the end the heat will be transferred to the air that surrounds the car - the coldest, but under certain circumstances infinitely warm. Washing the engine housing and radiator, the air cools the cylinder block, coolant and head housing. We just have to find a bridge across which the piston gives off its heat to the antifreeze and block. There are four ways to do this. In terms of their contribution, they are completely different, but it is necessary to mention each of them, since they are of lesser or greater importance depending on the design of the engine.

First way

These are the piston rings, it provides the most flow. Since the first ring is located closer to the bottom, it is it that plays the main role. This is the shortest way to the coolant through the cylinder wall. At the same time, the rings are pressed against the cylinder walls and piston grooves. They provide more than half of the total heat flow.

Second way

It is not so obvious, but it is difficult to underestimate it. The second liquid for engine cooling is oil. Despite its poor circulation and relatively small volume, oil mist has access to the hottest parts of the motor. It carries away a significant part of the heat from the hottest spots, and gives it to the oil pan. In this section of our site you can find an article about. When using oil nozzles, which direct the jet to the inner surface of the piston crown, the proportion of oil in heat exchange often reaches 30 - 40 percent. Of course, if we load the oil more than the degree of function of the coolant, it will need to be cooled. Overheated oil will not only lose its properties, but can also lead to bearing failure. And the higher the temperature of the oil, the less it will be able to transfer heat through itself.

third way

Through the big bosses into the finger, then into the connecting rod, and only then into the oil. This method is not so interesting, because on the way there are significant thermal resistances in the form of steel parts and gaps, which have a low resistance coefficient and a significant length.

Fourth way

Not related to coolant or oil. Part of the heat is taken away by the fresh air-fuel mixture entering the cylinder after the intake stroke. The amount of heat that this mixture will take depends on the degree of throttle opening and the mode of operation. It should be noted that the heat that is generated during combustion is also proportional to the charge. It can be said that this cooling path is fast, impulsive, highly efficient, proportional to subsequent heating, due to the fact that heat is taken from the same side from which the piston is heated.

You should also talk about the standard technique that is used when setting up sports-type motors. The fact is that the heat capacity of a mixture is largely determined by its composition. Often, to normalize the operation of the motor, you need quite a bit, by 5 - 10 degrees, to lower the internal temperature. This is achieved by slightly enriching the mixture. Moreover, this fact does not affect the combustion process in any way, and the temperature decreases. The detonation threshold is pushed back, the glow ignition disappears. In this case, a little richer is better than a little poorer. Motors that run on methanol make much less demands on the cooling system due to the heat of conversion, which is 3 times greater than that of gasoline.

Close attention should be paid to the process of heat transfer through the piston rings due to its greater importance. It is quite clear that if this path is blocked for any reason, the engine will no longer withstand long forced modes. The temperature will become very high, the piston will begin to melt, and the engine will collapse. Now let's remember such a characteristic as a procession, which, it would seem, does not affect heat transfer in any way. If a person has come across a used car, he must clearly understand what it is. This is a very significant parameter that any car owner who cares about the condition of the engine of his car wants to know about. Compression indirectly indicates the degree of density of the piston group. This is a very important parameter if we consider it from the point of view of heat transfer.

Let's imagine a situation where the ring does not adhere to the cylinder wall along its entire length. In this case, the burnt gases will create a barrier that will interfere with the transfer of heat through the ring to the cylinder wall, starting from the piston, when they break through into the slot. This is equivalent to covering up part of the car's radiator so that it doesn't have a chance to cool with air.

If the ring does not have close contact with the groove, we will see an even more terrible picture. In those places where the gases have the opportunity to flow through the groove past the ring, the piston section simply loses the opportunity to cool down, falling into a kind of heat bag. As a result, we get chipping and burnout of the part of the fire belt, which is adjacent to the leak. It is for this reason that so much attention is paid to groove wear and ring cylinder geometry. And the main reason is not the deterioration of energy. After all, a small amount of gases that break into the crankcase does not carry enough energy in itself to affect the pressure loss in the stroke of the power stroke and, accordingly, the loss of engine torque. Especially when it comes to high-speed motor. Much more damage to the engine is caused by low density in terms of loss of reliability and rigidity and local thermal overloads. It is for this reason that pistons restored by re-sleeving the block or replacing rings break very quickly, which are already out of order. That is why, first of all, in sports engines, a cylinder that has less compression is destroyed.

Here, apparently, we should touch on the issue that is necessarily discussed in the manufacture of special pistons for tuning or sports applications. How many rings will the new piston have? How thick are these rings? From the point of view of mechanics, it is better when there are few rings. The narrower they are, the less losses will be in the piston group. However, with a decrease in the thickness and height of the rings, the conditions for cooling the piston will worsen, and the thermal resistance will increase. Therefore, when choosing a design, you always have to compromise. The rigidity of the frames increases with the speed of the motor. In this section of our site you can find an article about. The rapidity of the processes reduces the requirements for compaction. Mechanical losses increase with speed, and they must be reduced, otherwise everything that was converted earlier into mechanical power simply will not reach the wheels. Meanwhile, the amount of heat generated becomes larger, so the cooling bridge must be expanded. From this we get that the rings should be both narrow and wide. Two are needed for speed, and three for piston cooling efficiency. The designer must find the optimal solution to this problem. The results of his work will show the balance of the engine.

Today, engineers who work in large research centers and manufacturing companies have a huge amount of empirical material, on the basis of which they create calculation methods that make it possible to predict the field of characteristics and temperatures of a particular product with very high accuracy. This is available to very, very few tuning companies. This article does not specifically mention many of the values ​​of specific quantities that would encourage some readers to pick up calculators. To do thermal calculations on the fingers is not at all promising and absolutely useless to anyone. This article reveals that side of the processes occurring in the engine, which is very rarely considered, but always implied. I just wanted to reveal the necessity and importance of the effect of heat on the overall efficiency of the engine. As for the mechanical part of this issue, we will talk about it in detail next time.

In the crank mechanism, the piston performs several functions, including the perception of gas pressure and the transfer of forces to the connecting rod, the sealing of the combustion chamber and the removal of heat from it. The piston is the most characteristic part of an internal combustion engine. it is with its help that the thermodynamic process of the engine is realized.

The conditions under which the piston operates are extreme and are characterized by high pressure, temperature and inertial loads. Therefore, pistons on modern engines are made of light, durable and heat-resistant material - aluminum alloy, less often steel. Pistons are made in two ways - injection molding or stamping, the so-called. forged pistons.

The piston is a one-piece structural element, which is conditionally divided into a head (in some sources it is called a 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 that takes place in it. The piston of a gasoline engine has a flat or close to flat head surface. Grooves can be made in it to fully open the valves. The pistons of engines with direct fuel injection have a more complex shape. The combustion chamber of a certain shape is made in the piston head of a diesel engine, which provides good swirl and improves mixture formation.

Below the piston head, grooves are made for installing piston rings. Piston skirt has a conical or curvilinear ( barrel-shaped) shape. This shape of the skirt compensates for the thermal expansion of the piston when heated. When the operating temperature of the engine is reached, the piston assumes a cylindrical shape. To reduce friction losses, a layer of antifriction material is applied to the side surface of the piston ( molybdenum disulfide, graphite). In the piston skirt there are holes with tides ( bosses) for attaching the piston pin.

Piston cooling carried out from the side of the inner surface in various ways:

1. oil mist in the cylinder;
2. splashing oil through a hole in the connecting rod;
3. spraying oil with a special nozzle;
4. oil injection into a special annular channel in the zone of the rings;
5. oil circulation through a tubular coil in the piston head.

Piston rings form a tight connection between the piston and the cylinder walls. They are made from modified cast iron. Piston rings are the main source of friction in an internal combustion engine. Friction losses in the rings reach up to 25% of all mechanical losses in the engine.

The number and arrangement of rings depends on the type and purpose of the engine. The most common scheme is two compression and one oil scraper ring. Compression rings prevent the breakthrough of gases from the combustion chamber into the crankcase. The first compression ring works in the most severe conditions. Therefore, on the pistons of diesel and a number of forced gasoline engines, a steel insert is installed in the ring groove, which increases strength and allows for the maximum compression ratio. Compression rings can have a trapezoidal, barrel-shaped, conical shape, some are made with a cut (cut).

Oil scraper ring removes excess oil from the surface of the cylinder and prevents oil from entering the combustion chamber. The ring has many drainage holes. Some ring designs have a spring expander.

The connection of the piston to the connecting rod is carried out using a piston pin, which has a tubular shape and is made of steel. There are several ways to install the piston pin. The most popular so-called. floating finger, which has the ability to rotate in the bosses and piston head of the connecting rod during operation. To prevent displacement of the finger, it is fixed with retaining rings. Much less often, rigid fastening of the ends of the pin in the piston or rigid fastening of the pin in the piston head of the connecting rod is used.

The piston, piston rings and piston pin are known as the piston group.

Definition.

piston engine- one of the variants of the internal combustion engine, which works by converting the internal energy of the burning fuel into the mechanical work of the translational movement of the piston. The piston is set in motion by the expansion of the working fluid in the cylinder.

The crank mechanism converts the translational motion of the piston into rotational motion of the crankshaft.

The working cycle of the engine consists of a sequence of cycles of one-sided translational piston strokes. Subdivided engines with two and four cycles of work.

The principle of operation of two-stroke and four-stroke piston engines.

Number of cylinders in piston engines may vary depending on the design (from 1 to 24). The volume of the engine is considered to be equal to the sum of the volumes of all cylinders, the capacity of which is found by the product of the cross section and the piston stroke.

IN piston engines different designs, the process of fuel ignition occurs in different ways:

Electric spark discharge, which is formed on spark plugs. Such engines can run on both gasoline and other types of fuel (natural gas).

Compression of the working body:

IN diesel engines, running on diesel fuel or gas (with 5% addition of diesel fuel), air is compressed, and when the piston reaches the point of maximum compression, fuel is injected, which ignites from contact with heated air.

Compression model engines. The fuel supply in them is exactly the same as in gasoline engines. Therefore, for their operation, a special fuel composition (with impurities of air and diethyl ether) is required, as well as precise adjustment of the compression ratio. Compressor engines have found their distribution in the aircraft and automotive industries.

glow engines. The principle of their operation is in many respects similar to the engines of the compression model, however, it was not without a design feature. The role of ignition in them is performed by a glow plug, the glow of which is maintained by the energy of the fuel burning on the previous cycle. The composition of the fuel is also special, based on methanol, nitromethane and castor oil. Such engines are used both on cars and on airplanes.

calorific engines. In these engines, ignition occurs when fuel comes into contact with hot parts of the engine (usually the piston crown). Open-hearth gas is used as fuel. They are used as drive motors in rolling mills.

Fuel types used in piston engines:

Liquid fuel– diesel fuel, gasoline, alcohols, biodiesel;

gases– natural and biological gases, liquefied gases, hydrogen, gaseous products of oil cracking;

Produced in a gas generator from coal, peat and wood, carbon monoxide is also used as a fuel.

Operation of piston engines.

Engine cycles described in detail in technical thermodynamics. Different cyclograms are described by different thermodynamic cycles: Otto, Diesel, Atkinson or Miller and Trinkler.

Causes of piston engine failures.

piston engine efficiency.

The maximum efficiency that could be obtained on piston engine is 60%, i.e. slightly less than half of the burning fuel is spent on heating engine parts, and also comes out with the heat of the exhaust gases. In this connection, it is necessary to equip the engines with cooling systems.

Classification of cooling systems:

Air CO- they give off heat to the air due to the ribbed outer surface of the cylinders. Are the
more on weak engines (tens of hp), or on powerful aircraft engines that are cooled by a fast air flow.

Liquid CO- a liquid (water, antifreeze or oil) is used as a coolant, which is pumped through the cooling jacket (channels in the walls of the cylinder block) and enters the cooling radiator, in which it is cooled by air flows, natural or from fans. Rarely, sodium metal is also used as a coolant, which is melted by the heat of a warming engine.

Application.

Piston engines, due to their power range (1 watt - 75,000 kW), have gained great popularity not only in the automotive industry, but also in the aircraft industry and shipbuilding. They are also used to drive military, agricultural and construction equipment, electric generators, water pumps, chainsaws and other machines, both mobile and stationary.