The engine is the heart. How much does this word mean today. Not a single device works without an engine, the engine gives life to any unit. In this article, we will consider what an engine is, what types there are, how a car engine works.
The main task of any engine is to turn fuel into motion. One way to achieve this is by burning fuel inside the engine. Hence the name internal combustion engine.
But apart from ICE it is necessary to distinguish between an external combustion engine. An example is the steam engine of a ship, when its fuel (wood, coal) is burned outside the engine, generating steam, which is the driving force. An external combustion engine is not as efficient as an internal one.
To date, the internal combustion engine, which is equipped with all cars, has become widespread. Despite the fact that the efficiency of internal combustion engines is not close to 100%, the best scientists and engineers are working to bring it to perfection.
By type of engine are divided:
Gasoline: can be both carburetor and injection, an injection system is used.
Diesel: they work on the basis of diesel fuel, which is sprayed under pressure into the combustion chamber by a fuel injector.
Gas: work on the basis of liquefied or compressed gas produced from the processing of coal, peat, wood.
So, let's move on to the filling of the motor.
The main mechanism is the cylinder block, which is also part of the mechanism body. The block consists of various channels inside itself, which serves to circulate the coolant, reducing the temperature of the mechanism, popularly called the cooling jacket.
Pistons are located inside the cylinder block, their number depends on the specific engine. Compression rings are put on the piston in the upper part, and oil scraper rings in the lower part. Compression rings serve to create tightness during compression for ignition, and oil scraper rings to take lubricating fluid from the cylinder block wall and prevent oil from entering the combustion chamber.
Crank mechanism: transmits torque from the piston to the crankshaft. It consists of pistons, cylinders, heads, piston pins, connecting rods, crankcase, crankshaft.
Engine operation algorithm quite simple: the fuel is sprayed by a nozzle in the combustion chamber, where it mixes with air and, under the influence of a spark, the resulting mixture ignites.
The resulting gases push the piston down and the torque is transferred to the crankshaft, which transmits the rotation of the transmission. With the help of a gear mechanism, the wheels move.
If we create an uninterrupted cycle of ignition of a combustible mixture for a certain amount of time, we will get a primitive engine.
Modern engines rely on a four-stroke combustion cycle to convert fuel into propulsion. Sometimes such a cycle is called in honor of the German scientist Otto Nikolaus, who created in 1867 a cycle consisting of such cycles: intake, compression, combustion, removal of combustion products.
Description and purpose of systems:
Power system: doses the resulting mixture of air and fuel and supplies it to the combustion chambers - engine cylinders. In the carburetor version, it consists of a carburetor, an air filter, an inlet pipe, a flange, a fuel pump with a sump, a gas tank, and a fuel line.
Gas distribution system: balances the processes of intake of a combustible mixture and exhaust gases. Consists of gears, camshaft, spring, pusher, valve.
: designed to supply current to the contact of the candle to ignite the working mixture.
: protects the motor from overheating by circulating and cooling the liquid.
: supplies lubricating fluid to rubbing parts to minimize friction and wear.
This article discusses the concept of the engine, its types, description and purpose of individual systems, the cycle and its cycles.
Many engineers are working to minimize engine displacement and significantly increase power while reducing fuel consumption. The novelties of the automotive industry once again confirm the rationality of design developments.
At present, the internal combustion engine is the main type of automobile engine. An internal combustion engine (abbreviated name - ICE) is a heat engine that converts the chemical energy of fuel into mechanical work.
There are the following main types of internal combustion engines: piston, rotary piston and gas turbine. Of the presented types of engines, the most common is a piston internal combustion engine, so the device and the principle of operation are considered using its example.
Virtues piston internal combustion engine, which ensured its wide application, are: autonomy, versatility (combination with various consumers), low cost, compactness, low weight, the ability to quickly start, multi-fuel.
However, internal combustion engines have a number of significant shortcomings, which include: high noise level, high crankshaft speed, exhaust gas toxicity, low resource, low efficiency.
Depending on the type of fuel used, gasoline and diesel engines are distinguished. Alternative fuels used in internal combustion engines are natural gas, alcohol fuels - methanol and ethanol, hydrogen.
From the point of view of ecology, the hydrogen engine is promising, because. does not create harmful emissions. Along with internal combustion engines, hydrogen is used to create electrical energy in the fuel cells of cars.
Internal combustion engine device
A piston internal combustion engine includes a housing, two mechanisms (crank and gas distribution) and a number of systems (inlet, fuel, ignition, lubrication, cooling, exhaust and control system).
The engine housing integrates the cylinder block and the cylinder head. The crank mechanism converts the reciprocating motion of the piston into rotational motion of the crankshaft. The gas distribution mechanism ensures the timely supply of air or a fuel-air mixture to the cylinders and the release of exhaust gases.
The engine management system provides electronic control of the internal combustion engine systems.
The operation of the internal combustion engine
The principle of operation of the internal combustion engine is based on the effect of thermal expansion of gases that occurs during the combustion of the fuel-air mixture and ensures the movement of the piston in the cylinder.
The operation of a piston internal combustion engine is carried out cyclically. Each work cycle occurs in two revolutions of the crankshaft and includes four cycles (four-stroke engine): intake, compression, power stroke and exhaust.
During the intake and power strokes, the piston moves down, while the compression and exhaust strokes move up. The operating cycles in each of the engine cylinders do not coincide in phase, which ensures uniform operation of the internal combustion engine. In some designs of internal combustion engines, the operating cycle is implemented in two cycles - compression and power stroke (two-stroke engine).
On the intake stroke the intake and fuel systems provide the formation of a fuel-air mixture. Depending on the design, the mixture is formed in the intake manifold (central and multipoint injection of gasoline engines) or directly in the combustion chamber (direct injection of gasoline engines, injection of diesel engines). When the intake valves of the gas distribution mechanism are opened, air or a fuel-air mixture is supplied into the combustion chamber due to the vacuum that occurs when the piston moves down.
On the compression stroke The intake valves close and the air-fuel mixture is compressed in the engine cylinders.
Stroke stroke accompanied by ignition of the fuel-air mixture (forced or self-ignition). As a result of ignition, a large amount of gases is formed, which put pressure on the piston and force it to move down. The movement of the piston through the crank mechanism is converted into rotational movement of the crankshaft, which is then used to propel the car.
On tact release the exhaust valves of the gas distribution mechanism open, and the exhaust gases are removed from the cylinders to the exhaust system, where they are cleaned, cooled and noise is reduced. The gases are then released into the atmosphere.
The considered principle of operation of the internal combustion engine makes it possible to understand why the internal combustion engine has a low efficiency - about 40%. At a particular moment in time, as a rule, useful work is performed in only one cylinder, while in the rest - providing cycles: intake, compression, exhaust.
The vast majority of cars use oil derivatives as fuel for engines. When these substances are burned, gases are released. In a confined space, they create pressure. A complex mechanism perceives these loads and transforms them first into translational motion, and then into rotational. This is the principle of operation of the internal combustion engine. Further, the rotation is already transmitted to the drive wheels.
piston engine
What is the advantage of such a mechanism? What gave a new principle of operation of the internal combustion engine? Currently, they are equipped not only with cars, but also with agricultural and loading vehicles, train locomotives, motorcycles, mopeds, and scooters. Engines of this type are installed on military equipment: tanks, armored personnel carriers, helicopters, boats. You can also think of chainsaws, mowers, motor pumps, generator substations and other mobile equipment that uses diesel fuel, gasoline or a gas mixture for operation.
Before the invention of the principle of internal combustion, fuel, more often solid (coal, firewood), was burned in a separate chamber. For this, a boiler was used that heated the water. Steam was used as the primary source of driving force. Such mechanisms were massive and overall. They were equipped with locomotives of steam locomotives and ships. The invention of the internal combustion engine made it possible to significantly reduce the dimensions of mechanisms.
System
When the engine is running, a number of cyclical processes constantly occur. They must be stable and take place within a strictly defined period of time. This condition ensures the smooth operation of all systems.
Diesel engines do not pre-treat the fuel. The fuel supply system delivers it from the tank and it is supplied at high pressure to the cylinders. Gasoline is pre-mixed with air along the way.
The principle of operation of an internal combustion engine is such that the ignition system ignites this mixture, and the crank mechanism receives, transforms and transfers the energy of gases to the transmission. The gas distribution system releases combustion products from the cylinders and takes them out of the vehicle. At the same time, the sound of the exhaust is reduced.
The lubrication system provides the possibility of rotation of moving parts. However, the rubbing surfaces heat up. The cooling system ensures that the temperature does not go beyond the permissible values. Although all processes occur automatically, they still need to be monitored. This is provided by the control system. It transmits data to the control panel in the driver's cab.
A fairly complex mechanism should have a body. The main components and assemblies are mounted in it. Additional equipment for systems that ensure its normal operation is located nearby and mounted on removable mounts.
The crank mechanism is located in the cylinder block. The main load from the burnt fuel gases is transferred to the piston. It is connected by a connecting rod to the crankshaft, which converts translational motion into rotational motion.
Also in the block is a cylinder. A piston moves along its inner plane. Grooves are cut into it, in which o-rings are placed. This is necessary to minimize the gap between the planes and create compression.
The cylinder head is attached to the top of the body. A gas distribution mechanism is mounted in it. It consists of a shaft with eccentrics, rocker arms and valves. Their alternate opening and closing ensure the inlet of fuel into the cylinder and then the release of spent combustion products.
The pallet of the cylinder block is mounted to the bottom of the housing. Oil flows there after it lubricates the rubbing joints of parts of assemblies and mechanisms. Inside the engine there are still channels through which the coolant circulates.
The principle of operation of the internal combustion engine
The essence of the process is the transformation of one type of energy into another. This occurs when fuel is burned in the closed space of an engine cylinder. The gases released during this expand, and excess pressure is created inside the working space. It is received by the piston. He can move up and down. The piston is connected to the crankshaft by means of a connecting rod. In fact, these are the main parts of the crank mechanism - the main unit responsible for converting the chemical energy of the fuel into rotational movement of the shaft.
The principle of operation of the internal combustion engine is based on the alternate cycle change. When the piston moves downward, work is done - the crankshaft rotates at a certain angle. A massive flywheel is fixed at one end. Having received acceleration, it continues to move by inertia, and this still turns the crankshaft. The connecting rod is now pushing the piston up. He takes up the working position and is again ready to take on the energy of the ignited fuel.
Peculiarities
The principle of operation of the internal combustion engine of passenger cars is most often based on the conversion of the energy of combustible gasoline. Trucks, tractors and special vehicles are mainly equipped with diesel engines. LPG can also be used as fuel. Diesel engines do not have an ignition system. The ignition of the fuel occurs from the pressure created in the working chamber of the cylinder.
The working cycle can be carried out in one or two revolutions of the crankshaft. In the first case, there are four cycles: fuel inlet and ignition, power stroke, compression, exhaust gases. A two-stroke internal combustion engine performs a complete cycle in one revolution of the crankshaft. At the same time, fuel is admitted and compressed in one cycle, and ignition, power stroke and exhaust gases are released in the second cycle. The role of the gas distribution mechanism in engines of this type is played by a piston. Moving up and down, it alternately opens the fuel inlet and exhaust ports.
In addition to piston internal combustion engines, there are also turbine, jet and combined internal combustion engines. The conversion of fuel energy in them into the forward motion of the vehicle is carried out according to other principles. The design of the engine and auxiliary systems is also significantly different.
Losses
Despite the fact that the internal combustion engine is reliable and stable, its efficiency is not high enough, as it might seem at first glance. In mathematical terms, the efficiency of an internal combustion engine is on average 30-45%. This suggests that most of the energy of the combustible fuel is wasted.
The efficiency of the best gasoline engines can be only 30%. And only massive economical diesel engines, which have many additional mechanisms and systems, can effectively convert up to 45% of fuel energy in terms of power and useful work.
The design of the internal combustion engine cannot eliminate losses. Part of the fuel does not have time to burn and leaves with the exhaust gases. Another article of losses is the energy consumption to overcome various types of resistance during friction of the mating surfaces of parts of assemblies and mechanisms. And another part of it is spent on actuating the engine systems that ensure its normal and uninterrupted operation.
An internal combustion engine (ICE) is an engine in which the combustion of fuel occurs directly inside the working chamber. It is these units that are widely used in the automotive industry, providing the conversion of thermal energy from fuel combustion into mechanical force.
The method for implementing the working cycle can take place in one cycle, or in two cycles. Therefore, two-stroke and four-stroke internal combustion engines are distinguished. The stroke is the piston stroke between two dead centers, with the crankshaft rotated 180 degrees.
Principle of operation
The principles of operation of each type of engine are somewhat different. In a two-stroke motor, in one revolution, the work cycle is completed in two stages - due to compression and expansion. There are no valves in such a device, and the piston performs their function. Its movement ensures the opening and closing of purge windows.
The working process in a four-stroke engine occurs in four stages. At the same time, processes such as intake at the first stage and release at the fourth stage, respectively, are added to compression and expansion.
The main difference between such motors is excellent gas exchange mechanisms, i.e. fuel supply to the cylinders and exhaust gases. The design of four-stroke units includes a gas distribution mechanism that ensures the opening and closing of valves at certain points in time. In two-stroke engines, the cylinders are emptied and filled during the compression and expansion strokes.
Video: Device and how an internal combustion engine works
General ICE device
According to the type of thermal energy conversion, all engines can be divided into the following types:
- Piston. In such units, fuel combustion occurs in cylinders, and due to the reciprocating movement of the piston, due to the crank mechanism, thermal energy is converted into mechanical energy;
- Rotary piston. Energy is converted by rotating a rotor with a special profile due to working gases;
- Gas turbine. In such engines, the energy conversion is provided by a rotor with wedge-shaped blades.
The most popular and in demand among all types of units is a piston internal combustion engine, due to its versatility, ability to quickly start and the ability to work with various types of fuel.
The general device of the internal combustion engine includes the body of the unit, as well as two types of mechanisms - crank and gas distribution. In addition, it contains a number of systems - power, ignition, start-up, cooling and lubrication. All of these systems consist of certain units and mechanisms, as well as the necessary communication elements.
Important! Only thanks to the coordinated performance of their functions by mechanisms and systems, the uninterrupted operation of the internal combustion engine is ensured.
crank mechanism
The cyclic translational motion of the piston, described by it when moving in the cylinder, must be converted into rotational motion of the crankshaft. It is this action that is provided thanks to the crank mechanism (KShM).
The design of such a mechanism includes moving components - pistons, piston rings, fingers, connecting rods, flywheel and crankshaft. The KShM also includes fixed elements - a cylinder block and a gasket, a cylinder head, cylinders, a crankcase, a pallet. In addition, the device includes various fasteners, mounting and connecting rod bearings.
Gas distribution mechanism
Thanks to the gas distribution mechanism (GRM), timely supply of air or fuel-air mixture to the cylinders, depending on the type of internal combustion engine, as well as the release of exhaust gases into the exhaust system.
Interesting! Thanks to the timely opening or closing of the timing valves, the uninterrupted operation of the mechanism is ensured.
The timing structure includes the following components and mechanisms:
- camshaft. Cast iron or steel element that opens or closes valves.
- Pushers. They provide the transfer of forces to the valves from the cams.
- intake and exhaust valves. Contribute to the supply of the mixture into the chamber, and also remove exhaust gases. Depending on the diameter of the head, inlet and outlet valves are distinguished. In addition, the intake valve head is chrome-plated, and the exhaust valve head is made of heat-resistant steel.
- Rods. Due to which there is a transfer of force from the pushers to the rods.
- Timing drive, which provides the opening and closing of valves, by transferring the rotation of the crankshaft to the camshaft. As a drive, both a belt and a timing chain, as well as a gear train, can be used.
Supply system
The structure of this system includes such devices as fuel storage elements, air cleaning devices, fuel cleaning and supply units, as well as devices for preparing the fuel mixture.
The internal combustion engine batteries are:
- Fuel tank and fuel lines;
- Fuel filter and pump;
- Air filter;
- Carburetor, mono injection or injector, depending on the device of the power system.
Interesting! In injector power systems, the operation of fuel injectors is regulated by an electronic device - a control unit, the design of which includes various control sensors.
The main functions of the fuel system are:
- Fuel supply from the tank;
- Fuel filtration;
- The formation of a combustible mixture;
- Supply of the mixture to the cylinders.
Fuel systems differ depending on the type of fuel used: in diesel units, injection into the chamber occurs at high pressure, for which a high-pressure fuel pump is used.
Ignition system
The main function of this system is to supply a spark to the spark plugs at a certain point in time. There are three main types of ignition systems:
- Contact. The creation of impulses occurs at the moment of breaking the contacts.
- Contactless. The control pulses are generated by a transistor control device.
- The microprocessor ignition system is controlled by an electronic device.
The main elements of the system are:
- Power supply;
- Ignition switch;
- Storage device;
- Spark plug;
- Distribution system;
- High voltage wire.
The principle of operation of this system is based on the accumulation of voltage with low characteristics by the ignition coil and its transformation into high voltage. After the accumulated energy is transferred to the spark plugs, and the spark formed at the required time ignites the fuel-air mixture.
Start
The main components of the internal combustion engine start-up system are:
- Starter;
- Accumulator battery;
- Ignition switch.
This system provides a convenient, reliable and quick engine start, regardless of the operating conditions of the car.
Cooling
The functioning of systems and mechanisms of internal combustion engines without organizing the removal of excess heat is not possible, since their operation is associated with an increased temperature regime. The main purpose of the cooling system is to reduce the temperature of the working elements of the motor.
Interesting! If the car is equipped with an automatic transmission, then the cooling system is also involved in organizing the cooling of the transmission fluid.
There are two main types of internal combustion engine cooling systems:
- liquid;
- Air.
In addition to the main functions, the cooling system is responsible for:
- The operation of the heating, ventilation and air conditioning system;
- Oil cooling in the lubrication system;
- Cooling gases in the exhaust system.
The most common is a liquid cooling system, which is facilitated by uniform and efficient cooling of components and mechanisms, as well as a low noise level during operation.
Important elements of the cooling system are:
- Liquid radiator;
- Oil radiator;
- Heat exchanger;
- Fan;
- Centrifugal pump;
- Expansion tank;
- Thermostat.
An important consumable material, due to which cooling is provided, is the working fluid - antifreeze.
Lubrication system
The operation of the mechanisms and components of the internal combustion engine takes place under conditions of constant friction of the elements. This adversely affects their condition, causing wear and reducing the performance of the unit. It is to prevent such negative phenomena that a lubrication system is included in the design of the internal combustion engine. It is combined, i.e. engine oil is mixed with fuel.
The main elements of the ICE lubrication system are:
- Oil filter and pump;
- Pallet;
- Fence;
- Circuits providing oil supply to the elements.
With the help of an oil pump, oil is supplied to the filter, and then it is distributed between the lubrication units and channels. This process occurs constantly, and thanks to the presence of special sensors, the pressure in the system is monitored.
tuning
To improve the performance of the engine, its modernization and increase in torque, a procedure such as tuning is used. The main types of tuning are:
- Cylinder boring, which contributes to an increase in the combustion chamber of the fuel, which somewhat increases the power capabilities of the unit.
- Turbine installation, which provides an increase in engine power and efficiency;
- Chip tuning - an increase in performance by changing the operation of the electronic part of the control unit.
- Installation of nitrous oxide, which contributes to a significant increase in engine power.
As a rule, tuning is carried out only if the components and mechanisms of the power unit are in full working order and must be carried out by qualified car service masters.
For the smooth and efficient operation of the internal combustion engine, you should pay attention to any changes and timely diagnose and repair equipment.
| You can ask your questions on the topic of the presented article by leaving your comment at the bottom of the page. You will be answered by the Deputy General Director of the Mustang Driving School for Academic Affairs Higher school teacher, candidate of technical sciences Kuznetsov Yury Alexandrovich |
Part 1. ENGINE AND ITS MECHANISMS
The engine is a source of mechanical energy.
The vast majority of vehicles use an internal combustion engine.
An internal combustion engine is a device in which the chemical energy of a fuel is converted into useful mechanical work.
Automotive internal combustion engines are classified:
By type of fuel used:
Light liquid (gas, gasoline),
Heavy liquid (diesel fuel).
Gasoline engines
Petrol carburetor.Fuel-air mixturebeing prepared in carburetor or in the intake manifold using spray nozzles (mechanical or electric), then the mixture is fed into the cylinder, compressed, and then ignited using a spark that jumps between the electrodes candles .
Petrol injectionMixing occurs by injecting gasoline into the intake manifold or directly into the cylinder using spray nozzles. nozzles ( injector ov). There are systems of single-point and distributed injection of various mechanical and electronic systems. In mechanical injection systems, fuel is dosed by a plunger-lever mechanism with the possibility of electronic adjustment of the mixture composition. In electronic systems, mixture formation is carried out under the control of an electronic control unit (ECU) by injection that controls electric gasoline valves.
gas engines
The engine burns hydrocarbons in the gaseous state as fuel. Most often, gas engines run on propane, but there are others that run on associated (petroleum), liquefied, blast furnace, generator and other types of gaseous fuels.
The fundamental difference between gas engines and gasoline and diesel engines is a higher compression ratio. The use of gas makes it possible to avoid excessive wear of parts, since the processes of combustion of the air-fuel mixture occur more correctly due to the initial (gaseous) state of the fuel. Also, gas engines are more economical, since gas is cheaper than oil and easier to extract.
The undoubted advantages of gas engines include safety and smokelessness of the exhaust.
By themselves, gas engines are rarely mass-produced, most often they appear after the conversion of traditional internal combustion engines, by equipping them with special gas equipment.
Diesel engines
Special diesel fuel is injected at a certain point (before reaching top dead center) into the cylinder at high pressure through an injector. The combustible mixture is formed directly in the cylinder as fuel is injected. The movement of the piston into the cylinder causes heating and subsequent ignition of the air-fuel mixture. Diesel engines are low speed and are characterized by high torque on the engine shaft. An additional advantage of the diesel engine is that, unlike positive ignition engines, it does not need electricity to operate (in automotive diesel engines, the electrical system is used only for starting), and, as a result, it is less afraid of water.
According to the method of ignition:
From a spark (gasoline),
From compression (diesel).
According to the number and arrangement of cylinders:
inline,
Opposite,
V - figurative,
VR - figurative,
W - figurative.
inline engine
This engine has been known since the very beginning of automotive engine building. The cylinders are arranged in one row perpendicular to the crankshaft.
Dignity:simplicity of design
Flaw:with a large number of cylinders, a very long unit is obtained, which cannot be positioned transversely relative to the longitudinal axis of the vehicle.
boxer engine
Horizontally opposed engines have a lower overall height than in-line or V-engines, which lowers the center of gravity of the entire vehicle. Light weight, compact design and symmetrical layout reduces the vehicle's yaw moment.
V-engine
To reduce the length of the engines, in this engine the cylinders are arranged at an angle of 60 to 120 degrees, with the longitudinal axis of the cylinders passing through the longitudinal axis of the crankshaft.
Dignity:relatively short engine
Flaws:the engine is relatively wide, has two separate heads of the block, increased manufacturing cost, too large a displacement.
VR engines
In search of a compromise solution for the performance of engines for passenger cars of the middle class, they came up with the creation of VR engines. Six cylinders at 150 degrees form a relatively narrow and generally short engine. In addition, such an engine has only one block head.
W-motors
In the W-family engines, two rows of cylinders in VR-version are connected in one engine.
The cylinders of each row are placed at an angle of 150 to one another, and the rows of cylinders themselves are located at an angle of 720.
A standard car engine consists of two mechanisms and five systems.
Engine mechanisms
Crank mechanism,
Gas distribution mechanism.
Engine systems
Cooling system,
Lubrication system,
Supply system,
ignition system,
System of release of the fulfilled gases.
crank mechanism
The crank mechanism is designed to convert the reciprocating motion of the piston in the cylinder into the rotational motion of the engine crankshaft.
The crank mechanism consists of:
Cylinder block with crankcase,
cylinder heads,
engine oil pan,
Pistons with rings and fingers,
Shatunov,
crankshaft,
Flywheel.
Cylinder block
It is a one-piece cast part that combines the engine cylinders. On the cylinder block there are bearing surfaces for installing the crankshaft, the cylinder head is usually attached to the upper part of the block, the lower part is part of the crankcase. Thus, the cylinder block is the basis of the engine, on which the rest of the parts are hung.
Cast as a rule - from cast iron, less often - aluminum.
Blocks made from these materials are by no means equivalent in their properties.
So, the cast-iron block is the most rigid, which means that, other things being equal, it withstands the highest degree of forcing and is the least sensitive to overheating. The heat capacity of cast iron is about half that of aluminum, which means that an engine with a cast iron block warms up to operating temperature faster. However, cast iron is very heavy (2.7 times heavier than aluminum), prone to corrosion, and its thermal conductivity is about 4 times lower than that of aluminum, so the engine with a cast iron crankcase has a more intense cooling system.
Aluminum cylinder blocks are lighter and cooler better, but in this case there is a problem with the material from which the cylinder walls are made directly. If the pistons of an engine with such a block are made of cast iron or steel, then they will wear out the aluminum cylinder walls very quickly. If the pistons are made of soft aluminum, then they will simply “grab” with the walls, and the engine will instantly jam.
Cylinders in an engine block can either be part of the cylinder block casting or be separate replacement bushings that can be "wet" or "dry". In addition to the forming part of the engine, the cylinder block has additional functions, such as the basis of the lubrication system - through the holes in the cylinder block, oil under pressure is supplied to the lubrication points, and in liquid-cooled engines, the base of the cooling system - through similar holes, the liquid circulates through the cylinder block.
The walls of the inner cavity of the cylinder also serve as guides for the piston when it moves between extreme positions. Therefore, the length of the generatrices of the cylinder is predetermined by the magnitude of the piston stroke.
The cylinder operates under conditions of variable pressures in the over-piston cavity. Its inner walls are in contact with the flame and hot gases heated to a temperature of 1500-2500°C. In addition, the average sliding speed of a piston set along the cylinder walls in automobile engines reaches 12–15 m/s with insufficient lubrication. Therefore, the material used for the manufacture of cylinders must have high mechanical strength, and the wall structure itself must have increased rigidity. Cylinder walls must resist scuffing with limited lubrication and have an overall high resistance to other possible types of wear.
In accordance with these requirements, pearlitic gray cast iron with small additions of alloying elements (nickel, chromium, etc.) is used as the main material for cylinders. High-alloy cast iron, steel, magnesium and aluminum alloys are also used.
cylinder head
It is the second most important and largest component of the engine. Combustion chambers, valves and cylinder candles are located in the head, and a camshaft with cams rotates on bearings in it. Just like in the cylinder block, there are water and oil channels and cavities in its head. The head is attached to the cylinder block and, when the engine is running, forms a single whole with the block.
Engine oil pan
It closes the crankcase from below (cast as a single unit with the cylinder block) and is used as an oil reservoir and protects engine parts from contamination. At the bottom of the sump there is a plug for draining engine oil. The pan is bolted to the crankcase. A gasket is installed between them to prevent oil leakage.
Piston
A piston is a cylindrical part that performs a reciprocating motion 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 motion into a change in pressure.
The piston is divided into three parts that perform different functions:
Bottom,
sealing part,
Guide part (skirt).
The shape of the bottom depends on the function performed by the piston. For example, in internal combustion engines, the shape depends on the location of the spark plugs, injectors, valves, engine design, and other factors. With a concave shape of the bottom, the most rational combustion chamber is formed, but soot is deposited more intensively in it. With a convex bottom, the strength of the piston increases, but the shape of the combustion chamber deteriorates.
The bottom and the sealing part form the piston head. Compression and oil scraper rings are located in the sealing part of the piston.
The distance from the bottom of the piston to the groove of the first compression ring is called the firing zone of the piston. Depending on the material from which the piston is made, the fire belt has a minimum allowable height, a decrease in which can lead to burnout of the piston along the outer wall, as well as destruction of the seat of the upper compression ring.
The sealing functions performed by the piston group are of great importance for the normal operation of piston engines. The technical condition of the engine is judged by the sealing ability of the piston group. For example, in automobile engines it is not allowed that oil consumption due to its waste due to excessive penetration (suction) into the combustion chamber exceeds 3% of fuel consumption.
The piston skirt (tronk) is its guiding part when moving in the cylinder and has two tides (lugs) for installing the piston pin. To reduce the temperature stresses of the piston on both sides, where the bosses are located, from the surface of the skirt, metal is removed to a depth of 0.5-1.5 mm. These recesses, which improve the lubrication of the piston in the cylinder and prevent the formation of scuffing from temperature deformations, are called "refrigerators". An oil scraper ring can also be located at the bottom of the skirt.
For the manufacture of pistons, gray cast irons and aluminum alloys are used.
Cast iron
Advantages:Cast iron pistons are strong and wear resistant.
Due to their low coefficient of linear expansion, they can operate with relatively small gaps, providing good cylinder sealing.
Flaws:Cast iron has a fairly large specific gravity. In this regard, the scope of cast-iron pistons is limited to relatively low-speed engines, in which the inertia forces of the reciprocating masses do not exceed one sixth of the gas pressure force on the piston bottom.
Cast iron has a low thermal conductivity, so the heating of the bottom of cast iron pistons reaches 350–400 °C. Such heating is undesirable, especially in carburetor engines, since it causes glow ignition.
Aluminum
The vast majority of modern car engines have aluminum pistons.
Advantages:
Low weight (at least 30% less compared to cast iron);
High thermal conductivity (3-4 times higher than the thermal conductivity of cast iron), which ensures the heating of the piston crown no more than 250 ° C, which contributes to better filling of the cylinders and allows you to increase the compression ratio in gasoline engines;
Good anti-friction properties.
connecting rod
A connecting rod is a part that connects piston (throughpiston pin) and crankpincrankshaft. Serves to transmit reciprocating movements from the piston to the crankshaft. For less wear of the connecting rod journals of the crankshaft, aspecial liners that have an anti-friction coating.
Crankshaft
The crankshaft is a complex-shaped part with necks for fastening connecting rods , from which it perceives efforts and converts them into torque .
Crankshafts are made of carbon, chromium-manganese, chromium-nickel-molybdenum, and other steels, as well as special high-strength cast irons.
The main elements of the crankshaft
root neck- shaft support, lying in the main bearing located in crankcase engine.
Connecting rod journal- a support with which the shaft is connected to connecting rods (there are oil channels for lubrication of connecting rod bearings).
Cheeks- connect the main and connecting rod necks.
Front shaft output (toe) - part of the shaft on which it is attached gear or pulley power take-off for drivegas distribution mechanism (GRM)and various auxiliary units, systems and assemblies.
Rear output shaft (shank) - part of the shaft connected to flywheel or massive gear selection of the main part of the power.
Counterweights- provide unloading of the main bearings from the centrifugal inertia forces of the first order of the unbalanced masses of the crank and the lower part of the connecting rod.
Flywheel
Massive disc with a toothed rim. The ring gear is necessary to start the engine (the starter gear engages with the flywheel gear and spins the engine shaft). The flywheel also serves to reduce uneven rotation of the crankshaft.
Gas distribution mechanism
Designed for the timely intake of a combustible mixture into the cylinders and the release of exhaust gases.
The main parts of the gas distribution mechanism are:
Camshaft,
Inlet and outlet valves.
Camshaft
According to the location of the camshaft, engines are distinguished:
With camshaft located in cylinder block (Cam-in-Block);
With a camshaft located in the cylinder head (Cam-in-Head).
In modern automotive engines, it is usually located at the top of the block head cylinders and connected to pulley or toothed sprocket crankshaft belt or timing chain, respectively, and rotates at half the frequency than the latter (on 4-stroke engines).
An integral part of the camshaft are its cams , the number of which corresponds to the number of intake and exhaust valves engine. Thus, each valve corresponds to an individual cam, which opens the valve by running on the valve lifter lever. When the cam "runs away" from the lever, the valve closes under the action of a powerful return spring.
Engines with an in-line configuration of cylinders and one pair of valves per cylinder usually have one camshaft (in the case of four valves per cylinder, two), while V-shaped and opposed engines have either one in the collapse of the block, or two, one for each half-block ( in each block head). Engines with 3 valves per cylinder (most commonly two intake and one exhaust) typically have one camshaft per head, while those with 4 valves per cylinder (two intake and 2 exhaust) have 2 camshafts per head.
Modern engines sometimes have valve timing systems, that is, mechanisms that allow you to rotate the camshaft relative to the drive sprocket, thereby changing the moment of opening and closing (phase) of the valves, which makes it possible to more efficiently fill the cylinders with the working mixture at different speeds.
valve
The valve consists of a flat head and a stem connected by a smooth transition. To better fill the cylinders with a combustible mixture, the diameter of the head of the intake valves is made much larger than the diameter of the exhaust. Since the valves operate at high temperatures, they are made of high quality steels. Inlet valves are made of chromium steel, exhaust valves are made of heat-resistant steel, since the latter come into contact with combustible exhaust gases and heat up to 600 - 800 0 C. The high heating temperature of the valves necessitates the installation of special inserts made of heat-resistant cast iron in the cylinder head, which are called seats.
The principle of the engine
Basic concepts
Top dead center - the highest position of the piston in the cylinder.
bottom dead center - the lowest position of the piston in the cylinder.
piston stroke- the distance that the piston travels from one dead center to another.
The combustion chamber- the space between the cylinder head and the piston when it is at top dead center.
Cylinder displacement - the space released by the piston when it moves from top dead center to bottom dead center.
Engine displacement - the sum of the working volumes of all engine cylinders. It is expressed in liters, which is why it is often called the displacement of the engine.
Full cylinder volume - the sum of the volume of the combustion chamber and the working volume of the cylinder.
Compression ratio- shows how many times the total volume of the cylinder is greater than the volume of the combustion chamber.
Compressionpressure in the cylinder at the end of the compression stroke.
Tact- the process (part of the working cycle) that occurs in the cylinder in one stroke of the piston.
Engine duty cycle
1st stroke - inlet. When the piston moves down in the cylinder, a vacuum is formed, under the action of which a combustible mixture (fuel-air mixture) enters the cylinder through the open intake valve.
2nd measure - compression . The piston moves up under the action of the crankshaft and the connecting rod. Both valves are closed and the combustible mixture is compressed.
3rd cycle - working stroke . At the end of the compression stroke, the combustible mixture ignites (from compression in a diesel engine, from a spark plug in a gasoline engine). Under the pressure of expanding gases, the piston moves down and drives the crankshaft through the connecting rod.
4th measure - release . The piston moves up and the exhaust gases exit through the opened exhaust valve.
