The engine cooling system serves to maintain the normal thermal operation of engines by intensively removing heat from hot engine parts and transferring this heat to the environment.

The removed heat consists of a part of the heat released in the engine cylinders, which is not converted into work and is not carried away with the exhaust gases, and from the heat of the friction work that occurs during the movement of engine parts.

Most of the heat is removed to the environment by the cooling system, a smaller part - by the lubrication system and directly from the outer surfaces of the engine.

Forced heat removal is necessary because at high temperatures of gases in the engine cylinders (during the combustion process 1800–2400 °C, the average gas temperature for the operating cycle at full load is 600–1000 °C), natural heat transfer to the environment is insufficient.

Violation of proper heat dissipation causes deterioration of lubrication of rubbing surfaces, oil burnout and overheating of engine parts. The latter leads to a sharp drop in the strength of the material of the parts and even their burning (for example, exhaust valves). When the engine is severely overheated, the normal clearances between its parts are violated, which usually leads to increased wear, seizing, and even breakdown. Overheating of the engine is also harmful because it causes a decrease in the filling factor, and in gasoline engines, in addition, detonation combustion and self-ignition of the working mixture.

Excessive cooling of the engine is also undesirable, since it entails the condensation of fuel particles on the cylinder walls, deterioration of mixture formation and flammability of the working mixture, a decrease in its combustion rate and, as a result, a decrease in engine power and efficiency.

Classification of cooling systems

In automobile and tractor engines, depending on the working fluid, systems are used liquid and air cooling. The most widely used liquid cooling.

With liquid cooling, the liquid circulating in the engine cooling system takes heat from the cylinder walls and combustion chambers and then transfers this heat to the environment using a radiator.

According to the principle of heat removal to the environment, cooling systems can be closed and open (flowing).

Liquid cooling systems of autotractor engines have a closed cooling system, i.e. a constant amount of liquid circulates in the system. In a flow-through cooling system, the heated liquid, after passing through it, is released into the environment, and a new one is taken in to be fed into the engine. The use of such systems is limited to marine and stationary engines.

Air cooling systems are open. The cooling air after passing through the cooling system is discharged into the environment.

The classification of cooling systems is shown in fig. 3.1.

According to the method of circulating the liquid of the cooling system, there can be:

forced in which circulation is provided by a special pump located on the engine (or in the power plant), or pressure, under which the liquid is supplied to the power plant from the external environment;

thermosiphon, in which the circulation of the liquid occurs due to the difference in gravitational forces resulting from the different density of the liquid heated near the surfaces of engine parts and cooled in the cooler;

combined, in which the most heated parts (cylinder heads, pistons) are forced to cool, and cylinder blocks - according to the thermosyphon principle .

Rice. 3.1. Classification of cooling systems

Liquid cooling systems can be open or closed.

open systems- systems that communicate with the environment using a vapor tube.

Most automotive and tractor engines currently use closed systems cooling, i.e., systems separated from the environment by a steam-air valve installed in the radiator cap.

The pressure and, accordingly, the permissible temperature of the coolant (100–105 °С) in these systems are higher than in open systems (90–95 °С), as a result of which the difference between the temperatures of the liquid and the air sucked through the radiator and the heat transfer of the radiator increase. This allows you to reduce the size of the radiator and the power consumption for driving the fan and water pump. In closed systems, there is almost no evaporation of water through the steam outlet pipe and its boiling when the engine is running in high mountain conditions.

Liquid cooling system

On fig. 3.2 shows a diagram of a liquid cooling system with forced circulation of the coolant.

Cylinder Block Cooling Jacket 2 and block heads 3, the radiator and pipes are filled with coolant through the filler neck. The liquid washes the walls of the cylinders and combustion chambers of a running engine and, heating up, cools them. Centrifugal pump 1 pumps liquid into the cylinder block jacket, from which the heated liquid enters the block head jacket and then is forced out into the radiator through the upper pipe. The liquid cooled in the radiator returns to the pump through the lower pipe.

Rice. 3.2. Liquid cooling system diagram

Fluid circulation depending on the thermal state of the engine is changed using a thermostat 4. When the coolant temperature is below 70–75 °C, the main thermostat valve is closed. In this case, the liquid does not enter the radiator 5 , but circulates along a small circuit through a branch pipe 6, which contributes to the rapid heating of the engine to the optimum thermal regime. When the temperature-sensitive element of the thermostat is heated to 70-75 ° C, the main valve of the thermostat begins to open and let water into the radiator, where it is cooled. The thermostat opens completely at 83–90 °C. From this point on, water circulates through the radiator, i.e., large circuit. The temperature regime of the engine is also regulated with the help of rotary shutters, by changing the air flow created by the fan 7 and passing through the radiator.

In recent years, the most effective and rational way to automatically control the temperature regime of the engine is to change the performance of the fan itself.

Elements of the fluid system

Thermostat designed to provide automatic control of the coolant temperature during engine operation.

To quickly warm up the engine when it is started, a thermostat is installed in the outlet pipe of the cylinder head jacket. It maintains the desired temperature of the coolant by changing the intensity of its circulation through the radiator.

On fig. 3.3 shows a bellows-type thermostat. It consists of a body 2, corrugated cylinder (bellows), valve 1 and a stem connecting the bellows to the valve . The bellows is made of thin brass and is filled with a volatile liquid (eg ether or a mixture of ethyl alcohol and water). Windows located in the thermostat housing 3 depending on the temperature of the coolant, they can either remain open or be closed valves .

When the temperature of the coolant washing the bellows is below 70 ° C, the valve 1 closed and windows 3 open. As a result, the coolant does not enter the radiator, but circulates inside the engine jacket. When the temperature of the coolant rises above 70 ° C, the bellows, under the vapor pressure of the liquid evaporating in it, lengthens and begins to open the valve 1 and gradually cover the windows with valves 3. At a coolant temperature above 80-85 ° C, the valve 1 fully opens, the windows are completely closed, as a result of which all the coolant circulates through the radiator. Currently, this type of thermostats is used very rarely.

Rice. 3.3. Bellows thermostat

Now engines are equipped with thermostats in which the damper 1 opens with the expansion of a solid filler - ceresin (Fig. 3.4). This substance expands when the temperature rises and opens the damper 1 , ensuring the flow of coolant to the radiator.

Rice. 3.4. Solid fill thermostat

Radiator is a heat dissipating device designed to transfer the heat of the coolant to the surrounding air.

The radiators of automobile and tractor engines consist of upper and lower tanks connected to each other by a large number of thin tubes.

To enhance the transfer of heat from the coolant to the air, the fluid flow in the radiator is directed through a series of narrow tubes or channels blown by air. Radiators are made of materials that conduct and give off heat well (brass and aluminum).

Depending on the design of the cooling grille, radiators are divided into tubular, plate and honeycomb.

At present, the most widespread tubular radiators. The cooling grid of such radiators (Fig. 3.5a) consists of vertical tubes of oval or round cross section passing through a series of thin horizontal plates and soldered to the upper and lower radiator reservoirs. The presence of plates improves heat transfer and increases the rigidity of the radiator. Tubes of oval (flat) section are preferable, since with the same jet cross section, their cooling surface is larger than the cooling surface of round tubes; in addition, when water freezes in the radiator, flat tubes do not break, but only change the shape of the cross section.

Rice. 3.5. Radiators

AT plate radiators the cooling grid (Fig. 3.5b) is designed so that the coolant circulates in space , formed by each pair of plates soldered together at the edges. The upper and lower ends of the plates are also soldered into the holes of the upper and lower radiator reservoirs. The air cooling the radiator is sucked by the fan through the passages between the soldered plates. To increase the cooling surface, the plates are usually made wavy. Lamellar radiators have a larger cooling surface than tubular ones, but due to a number of disadvantages (rapid contamination, a large number of soldered seams, the need for more thorough maintenance), they are used relatively rarely.

Cellular radiator refers to radiators with air tubes (Fig. 3.5c). In the honeycomb radiator grill, air passes through horizontal, circular tubes, which are washed from the outside with water or coolant. To make it possible to solder the ends of the tubes, their edges are flared so that in cross section they have the shape of a regular hexagon.

The advantage of honeycomb radiators is a larger cooling surface than in other types of radiators. Due to a number of disadvantages, most of which are the same as those of plate radiators, honeycomb radiators are extremely rare today.

A steam valve is installed in the radiator filler cap 2 and air valve 1 , which serve to maintain the pressure within the specified limits (Fig. 3.6).

Rice. 3.6. Radiator cap

Water pump circulates the coolant in the system. As a rule, small-sized single-stage low-pressure centrifugal pumps with a capacity of up to 13 m 3 /h, which create a pressure of 0.05–0.2 MPa, are installed in cooling systems. Such pumps are structurally simple, reliable and provide high performance (Fig. 3.7).

The casing and the impeller of the pumps are cast from magnesium and aluminum alloys, the impeller, in addition, from plastics. In water pumps of automobile engines, semi-closed impellers are usually used, that is, impellers with one disk.

The impellers of centrifugal water pumps are often mounted on the same shaft as the fan. In this case, the pump is installed in the upper front of the engine, it is driven from the crankshaft using a V-belt drive.

Rice. 3.7. Water pump

Belt drive can also be used when installing a centrifugal pump separately from the fan. In some engines of trucks and tractors, the water pump is driven from the crankshaft by a gear transmission. The shaft of a centrifugal water pump is usually mounted on rolling bearings and equipped with simple or self-adjusting seals to seal the working surface.

Fan in liquid cooling systems, they are installed to create an artificial air flow passing through the radiator. Fans of automobile and tractor engines are divided into two types: a) with blades stamped from sheet steel attached to the hub; b) with blades that are cast in one piece with the hub.

The number of fan blades varies between four and six. Increasing the number of blades above six is ​​impractical, since the performance of the fan increases very slightly. Fan blades can be made flat and convex.

The cooling system of an internal combustion engine is designed to remove excess heat from engine parts and assemblies. In fact, this system is bad for your pocket. Approximately one third of the heat obtained from the combustion of precious fuel has to be dissipated in the environment. But such is the structure of a modern internal combustion engine. The ideal would be an engine that can operate without removing heat to the environment, and turn all of it into useful work. But the materials used in modern engine building cannot withstand such temperatures. Therefore, at least two main, basic parts of the engine - the cylinder block and the block head - have to be additionally cooled. At the dawn of the automotive industry, two cooling systems appeared and competed for a long time: liquid and air. But the air cooling system gradually lost ground and is now used mainly on very small motor vehicle engines and low power generator sets. Therefore, let's take a closer look at the liquid cooling system.

Cooling system device

The cooling system of a modern automobile engine includes an engine cooling jacket, a coolant pump, a thermostat, connecting hoses, and a radiator with a fan. The heater heat exchanger is connected to the cooling system. In some engines, the coolant is also used to heat the throttle assembly. Also, in engines with a pressurization system, coolant is supplied to liquid-air intercoolers or to the turbocharger itself to reduce its temperature.

The cooling system works quite simply. After starting a cold engine, the coolant begins to circulate in a small circle with the help of a pump. It passes through the cooling jacket of the block and cylinder head of the engine and returns to the pump through the bypass (bypass) pipes. In parallel (on the vast majority of modern cars), the liquid constantly circulates through the heater heat exchanger. As soon as the temperature reaches the set value, usually around 80-90 ˚С, the thermostat starts to open. Its main valve directs the flow to the radiator, where the liquid is cooled by the oncoming air flow. If there is not enough airflow, then the cooling system fan comes into operation, in most cases it has an electric drive. The movement of liquid in all other nodes of the cooling system continues. Often the exception is the bypass channel, but it does not close on all vehicles.

The schemes of cooling systems in recent years have become very similar to each other. But two fundamental differences remain. The first is the location of the thermostat before and after the radiator (in the direction of the liquid). The second difference is the use of a pressurized circulating expansion tank, or an unpressurized expansion tank, which is a simple reserve volume.

Using the example of three schemes of cooling systems, we will show the difference between these options.

Components

Shirt head and cylinder block are channels cast in an aluminum or cast iron product. The channels are sealed, and the joint between the block and the cylinder head is sealed with a gasket.

coolant pump bladed, centrifugal type. Driven by either a timing belt or an accessory drive belt.

Thermostat is an automatic valve that operates when a certain temperature is reached. It opens, and part of the hot liquid is discharged into the radiator, where it cools. Recently, electronic control of this simple device has been used. The coolant began to be heated with a special heating element for earlier opening of the thermostat if necessary.

Fluid change and flush

If you didn’t have to replace any node in the cooling system earlier, then the instructions recommend changing antifreeze at least every 5–10 years. If you did not have to add water to the system from a canister, and even worse - from a roadside ditch, then when changing the fluid, the system can not be flushed.

But if the car has seen a lot in its lifetime, then when replacing the fluid it is useful to produce. Having opened the system in several places, you can thoroughly rinse it with a jet of water from a hose. Or just drain the old liquid and pour clean, boiled water. Start the engine and warm up to operating temperature. After waiting until the system cools down, so as not to burn yourself, drain the water. Then blow air through the system and fill in fresh antifreeze.

Flushing the cooling system is usually started in two cases: when the engine overheats (this manifests itself primarily in the summer) and when the stove stops heating in winter. In the first case, the reason lies in the radiator tubes overgrown with dirt from the outside and clogged from the inside. In the second, the problem is that the heater radiator tubes are clogged with deposits. Therefore, during a planned fluid change and when replacing components of the cooling system, do not miss the opportunity to thoroughly flush all the components.

Tell us what kind of cooling system problems you encountered. And wish you a hot heater in winter and good cooling in summer.

Reliable and trouble-free operation of the internal combustion engine (internal combustion engine) cannot be carried out without a cooling system. It is convenient to present its basic principles of operation in the form of a diagram of the engine cooling system. The main purpose of the system is to remove excess heat from the engine and. An additional function is the heating of the car with the interior heater stove. The device and the principle of operation shown in the diagram are approximately the same for different types of cars.

Scheme, elements of the cooling system and their work

The main elements that make up the engine cooling system circuit are found and are similar in different types of engines: injection, diesel and carburetor.

General scheme of the liquid engine cooling system

Liquid cooling of the motor makes it possible to equally take heat from all components and parts of the engine, regardless of the degree of thermal load. A water-cooled engine generates less noise than an air-cooled engine and has a faster warm-up rate at start-up.

The engine cooling system contains the following parts and elements:

• cooling jacket (water jacket);
• radiator;
• fan;
• liquid pump (pump);
• expansion tank;
• connecting pipes and drain taps;
• interior heater.

• The cooling jacket (“water jacket”) is considered to be the cavities that communicate between the double walls in those places where the removal of excess heat is most needed.
• Radiator. Designed to dissipate heat into the surrounding atmosphere. It structurally consists of many curved tubes with additional ribs to increase heat transfer.
• The fan, which is activated by an electromagnetic, less often by a hydraulic clutch, when the coolant temperature sensor is triggered, increases the air flow on the car. Fans with a “classic” (always on) belt drive are rare these days, mostly on older cars.
• The centrifugal liquid pump (pump) in the cooling system provides a constant circulation of the coolant. The pump drive is most often implemented using a belt or gear. Turbocharged engines with direct fuel injection are usually equipped with an additional pump.
• Thermostat - the main unit that regulates the flow of coolant, is usually installed between the radiator inlet pipe and the "water jacket", structurally made in the form of a bimetallic or electronic valve. The purpose of the thermostat is to maintain the specified operating temperature range of the coolant in all engine operating modes.
• The heater radiator is very similar to the smaller cooling system radiator and is located in the passenger compartment. The fundamental difference is that the heater radiator transfers heat to the passenger compartment, and the cooling system radiator to the environment.

Principle of operation

The principle of operation of liquid cooling of the engine is as follows: the cylinders are surrounded by a “water jacket” of coolant, which takes away excess heat and transfers it to the radiator, from where it is transferred to the atmosphere. The liquid, continuously circulating, ensures the optimum temperature of the engine.

The principle of operation of the engine cooling system

Coolants - antifreeze, antifreeze and water - during operation form sediment and scale, disrupting the normal operation of the entire system.

Water is not chemically pure in principle (with the exception of distilled water) - it contains impurities, salts and all kinds of aggressive compounds. At elevated temperatures, they precipitate and form scale.

Unlike water, antifreezes do not create scale, but decompose during operation, and the decay products adversely affect the operation of mechanisms: corrosion deposits and layers of organic substances appear on the internal surfaces of metal elements.

In addition, various foreign contaminants such as oil, detergents or dust can enter the cooling system. They can also get in, used for emergency repair of damage in radiators.

All these contaminants are deposited on the internal surfaces of components and assemblies. They are characterized by poor thermal conductivity and clog thin tubes and radiator cells, disrupting the efficient operation of the cooling system, which leads to engine overheating.

Video on how motor cooling works, the principle of operation and malfunctions

Something else useful for you:

flushing

Flushing the engine cooling system is a process that many drivers often neglect, which sooner or later can cause fatal consequences.

Signs it's time to flush

1. If the arrow of the temperature gauge is not in the middle, but tends to the red zone while driving;
2. It is cold in the cabin, the heating stove does not provide sufficient temperature;
3. Radiator fan turns on too often

It is impossible to flush the cooling system with plain water, since contaminants are concentrated in the system, which are not removed even by water heated to high temperatures.

Scale is removed with acid, and fats and organic compounds are removed exclusively with alkali, but both compositions cannot be poured into the radiator at the same time, since they are mutually neutralized according to the laws of chemistry. Manufacturers of flushing products, trying to solve this problem, have created a number of products that can be roughly divided into:

• alkaline;
• acid;
• neutral;
• two-component.

The first two are too aggressive and are almost never used in their pure form, as they are dangerous for the cooling system and require neutralization after use. Less common are two-component types of cleaners containing both solutions - alkaline and acidic, which are poured alternately.

The greatest demand is for neutral cleaners that do not contain strong alkalis and acids. These products have varying degrees of effectiveness and can be used both for prevention and for major flushing of the engine cooling system from severe contamination.

Flushing the cooling system

Flushing the cooling system

1. Antifreeze, antifreeze or water is drained. Before this, you need to start the engine for a couple of minutes.
2. Fill the system with water and cleaner.
3. Turn on the engine for 5-30 minutes (depending on the brand of cleaner) and turn on the interior heating.
4. After the time indicated in the instructions, the engine must be turned off.
5. Drain the used cleaner.
6. Rinse with water or a special compound.
7. Top up with fresh coolant.

Flushing the cooling system is simple and affordable: even inexperienced car owners can perform them. This operation significantly extends the engine life and maintains its performance at a high level.

Faults

There are a number of the most common malfunctions in the engine cooling system:

1. Airing the engine cooling system: remove the air lock.
2. Insufficient pump performance: replace the pump. Select a pump with a maximum impeller height.
3. Faulty thermostat: eliminated by replacing with a new device.
4. Low performance of the coolant radiator: flushing the old one or replacing the standard one with a model with higher heat dissipation qualities.
5. Insufficient performance level of the main fan: Install a new fan with a higher performance.

Video - identifying malfunctions of the cooling system in a car service

Regular care, timely replacement of the coolant guarantees long-term operation of the car as a whole.

The cooling system is designed to cool engine parts that are heated as a result of its operation. On modern cars, the cooling system, in addition to the main function, performs a number of other functions, including:

Depending on the method of cooling, the following types of cooling systems are distinguished: liquid (closed type), air (open type) and combined. In a liquid-cooled system, heat is removed from the heated parts of the engine by the fluid flow. The air system uses air flow for cooling. The combined system combines liquid and air systems.

On cars, the most common liquid cooling system. This system provides uniform and efficient cooling, and also has a lower noise level. Therefore, the device and principle of operation of the cooling system are considered on the example of a liquid cooling system.

The design of the cooling system of gasoline and diesel engines are similar. The engine cooling system includes many elements, including a coolant radiator, an oil cooler, a heater heat exchanger, a radiator fan, a centrifugal pump, as well as an expansion tank and a thermostat. The engine cooling jacket is included in the cooling system circuit. Control elements are used to regulate the operation of the system.

The radiator is designed to cool the heated coolant with air flow. To increase heat transfer, the radiator has a special tubular device.

Along with the main radiator, an oil cooler and an exhaust gas recirculation cooler can be installed in the cooling system. The oil cooler serves to cool the oil in the lubrication system.

The exhaust gas recirculation cooler cools the exhaust gases, thereby reducing the combustion temperature of the fuel-air mixture and the formation of nitrogen oxides. The exhaust gas cooler is operated by an additional coolant circulation pump included in the cooling system.

The heater heat exchanger performs the opposite function of the cooling system radiator. The heat exchanger heats the air passing through it. For efficient operation, the heater heat exchanger is installed directly at the outlet of the heated coolant from the engine.

To compensate for the change in coolant volume due to temperature, an expansion tank is installed in the system. Filling the system with coolant is usually done through the expansion tank.

Coolant circulation in the system is provided by a centrifugal pump. In everyday life, a centrifugal pump is called pomp. The centrifugal pump can have a different drive: gear, belt, etc. On some engines equipped with a turbocharger, an additional coolant circulation pump is installed to cool the charge air and the turbocharger, connected by the engine control unit.

The thermostat is designed to regulate the amount of coolant passing through the radiator, which ensures the optimum temperature in the system. The thermostat is installed in the pipe between the radiator and the "cooling jacket" of the engine.

On powerful engines, an electrically heated thermostat is installed, which provides two-stage control of the coolant temperature. To do this, the design of the thermostat provides for three operating positions: closed, partially open and fully open. When the engine is fully loaded, the thermostat is electrically heated to fully open it. In this case, the temperature of the coolant is reduced to 90 ° C, the tendency of the engine to detonate decreases. In other cases, the coolant temperature is maintained within 105°C.

The radiator fan serves to increase the intensity of cooling of the liquid in the radiator. The fan can have a different drive:

• mechanical ( permanent connection to the engine crankshaft);
• electric ( controlled electric motor);
• hydraulic ( fluid coupling).

The most widespread is the electric drive of the fan, which provides ample opportunities for regulation.

Typical cooling system controls are a coolant temperature sensor, an electronic control unit and various actuators.

The coolant temperature sensor captures the value of the controlled parameter and converts it into an electrical signal. To expand the functions of the cooling system (exhaust gas cooling in the exhaust gas recirculation system, fan control, etc.), an additional coolant temperature sensor is installed at the radiator outlet.

The signals from the sensor are received by the electronic control unit and converted into control actions on the actuators. As a rule, an engine control unit with the corresponding software installed is used.

The following actuators can be used in the operation of the control system: thermostat heater, auxiliary coolant pump relay, radiator fan control unit, engine cooling after shutdown relay.

The principle of operation of the cooling system

The operation of the cooling system is provided by the engine management system. In modern engines, the operation algorithm is implemented on the basis of a mathematical model that takes into account various parameters (coolant temperature, oil temperature, outside temperature, etc.) and sets the optimal switching conditions and operating time of structural elements.

The coolant in the system has forced circulation, which is provided by a centrifugal pump. The movement of fluid is carried out through the "cooling jacket" of the engine. In this case, the engine is cooled and the coolant is heated. The direction of fluid movement in the "cooling jacket" can be longitudinal (from the first cylinder to the last) or transverse (from the exhaust manifold to the intake).

Depending on the temperature, the liquid circulates in a small or large circle. When starting the engine, the engine itself and the coolant in it are cold. To speed up the engine warm-up, the coolant moves in a small circle, bypassing the radiator. The thermostat is closed.

As the coolant heats up, the thermostat opens and the coolant moves in a large circle - through the radiator. The heated liquid passes through the radiator, where it is cooled by the oncoming air flow. If necessary, the liquid is cooled by air flow from the fan.

After cooling, the liquid again enters the "cooling jacket" of the engine. During the operation of the engine, the cycle of movement of the coolant is repeated many times.

On turbocharged vehicles, a dual-circuit cooling system can be used, in which one circuit is responsible for cooling the engine, the other for cooling the charge air.

Cooling system- this is a set of devices that provide forced removal of heat from heating parts of the engine.

The need for cooling systems for modern engines is due to the fact that the natural heat dissipation by the outer surfaces of the engine and heat removal to the circulating engine oil do not provide the optimal temperature regime for the engine and some of its systems. Engine overheating is associated with a deterioration in the process of filling the cylinders with a fresh charge, oil burning, an increase in friction losses, and even piston seizure. On gasoline engines, there is also a danger of glow ignition (not from a spark plug, but due to the high temperature of the combustion chamber).

The cooling system should ensure automatic maintenance of the optimal thermal regime of the engine at all speed and load modes of its operation at an ambient temperature of -45 ... +45 ° С, rapid warm-up of the engine to operating temperature, minimum power consumption for actuating system units, low weight and small overall dimensions, operational reliability, determined by the service life, simplicity and ease of maintenance and repair.

Air and liquid cooling systems are used on modern wheeled and tracked vehicles.

When using an air cooling system (Fig. a), heat from the head and cylinder block is transferred directly to the air blowing them. Through the air jacket formed by the casing 3, the cooling air is driven by the fan 2, driven by the crankshaft using a belt drive. To improve heat dissipation, cylinders 5 and their heads are equipped with ribs 4. The intensity of cooling is regulated by special air dampers 6, controlled automatically by air thermostats.

Most modern engines have a liquid cooling system (fig. b). The system includes cooling jackets 11 and 13, respectively, of the head and cylinder block, radiator 18, upper 8 and lower 16 connecting pipes with hoses 7 and 15, liquid pump 14, distribution pipe 72, thermostat 9, expansion (compensation) tank 10 and fan 77 Coolant (water or antifreeze - non-freezing liquid) is in the cooling jacket, radiator and pipes.

Rice. Schemes of air (a) and liquid (b) engine cooling systems:
1 - belt drive; 2, 17 - fans; 3 - casing; 4 - ribs of the cylinder; 5 - cylinder; 6 - air damper; 7, 15 - hoses; 8, 16 - upper and lower connecting pipes; 9 - thermostat; 10 - expansion tank; 77, - cooling jackets for the head and cylinder block; 12 - distribution pipe; 14 - liquid pump; 18 - radiator

When the engine is running, a crankshaft-driven fluid pump circulates coolant through the system. Through the distribution pipe 12, the liquid is first directed to the most heated parts (cylinders, block head), cools them and enters the radiator 18 through the pipe 8. In the radiator, the liquid flow branches through the tubes into thin streams and is cooled by air blown through the radiator. The cooled liquid from the lower tank of the radiator through pipe 16 and hose 15 again enters the liquid pump. The flow of air through the radiator is usually created by a fan 77 driven by a crankshaft or a special electric motor. On some tracked vehicles, an ejection device is used to ensure air flow. The principle of operation of this device is to use the energy of exhaust gases flowing at high speed from the exhaust pipe and entraining air.

Regulates the circulation of liquid in the radiator, maintaining the optimum temperature of the engine, thermostat 9. The higher the temperature of the liquid in the jacket, the more open the thermostat valve and more liquid enters the radiator. At a low engine temperature (for example, immediately after it is started), the thermostat valve is closed, and the liquid is not directed to the radiator (through a large circulation circle), but immediately into the pump intake cavity (in a small circle). This ensures that the engine warms up quickly after starting. The intensity of cooling is also regulated by means of shutters installed at the inlet or outlet of the air path. The greater the degree of closing of the blinds, the less air passes through the radiator and the worse the cooling of the liquid.

In the expansion tank 10, located above the radiator, there is a supply of liquid to compensate for its loss in the circuit due to evaporation and leaks. In the upper cavity of the expansion tank, the steam formed in the system is often removed from the upper radiator manifold and cooling jacket.

Liquid cooling has the following advantages compared to air cooling: easier engine start-up at low ambient temperatures, more uniform engine cooling, the possibility of using block cylinder structures, simplification of the layout and the possibility

insulation of the air path, less noise from the engine and lower mechanical stresses in its parts. However, the liquid cooling system has a number of disadvantages, such as a more complex engine and system design, the need for coolant and more frequent oil changes, the risk of fluid leakage and freezing, increased corrosive wear, significant fuel consumption, more complex maintenance and repair , as well as (in some cases) increased sensitivity to changes in ambient temperature.

Liquid pump 14 (see Fig. b) circulates the coolant in the system. Centrifugal vane pumps are commonly used, but gear and piston pumps are sometimes used. The thermostat 9 can be one- and two-valve with a liquid thermo-force element or an element containing a solid filler (ceresin). In any case, the material for the thermal force element must have a very high coefficient of volumetric expansion, so that when heated, the thermostatic valve stem can move a fairly large distance.

In practice, all engines of liquid-cooled ground vehicles are equipped with so-called closed cooling systems, which do not have a permanent connection with the atmosphere. In this case, excess pressure is formed in the system, which leads to an increase in the boiling point of the liquid (up to 105 ... 110 ° C), an increase in cooling efficiency and a decrease in losses, as well as a decrease in the likelihood of air and steam bubbles appearing in the liquid flow.

Maintaining the necessary overpressure in the system and providing access to atmospheric air during rarefaction is carried out using a double vapor-air valve, which is installed at the highest point of the liquid system (usually in the filler cap of the expansion tank or radiator). The steam valve opens, allowing excess steam to escape into the atmosphere, if the pressure in the system exceeds atmospheric pressure by 20 ... 60 kPa. The air valve opens when the pressure in the system decreases by 1 ... 4 kPa compared to atmospheric pressure (after the engine is stopped, the coolant cools down and its volume decreases). The pressure drops at which the valves open are provided by the selection of the parameters of the valve springs.

In a liquid ventilated cooling system, the heatsink is circulated by airflow generated by a fan. Depending on the mutual arrangement of the radiator and the fan, the following types of fans can be used: axial, centrifugal and combined, creating both axial and radial air flows. Axial fans are installed in front of the radiator or behind it in a special air supply duct. Air is supplied to the centrifugal fan along the axis of its rotation, and removed - along the radius (or vice versa). When the radiator is located in front of the fan (in the suction area), the air flow in the radiator is more uniform, and the air temperature is not increased due to its mixing by the fan. When the radiator is located behind the fan (in the discharge area), the air flow in the radiator is turbulent, which increases the cooling intensity.

On heavy wheeled and tracked vehicles, the fan is usually driven by the engine crankshaft. Cardan, belt and gear (cylindrical and bevel) transmissions can be used. In order to reduce dynamic loads on the fan in its drive from the crankshaft, unloading and damping devices in the form of torsion rollers, rubber, friction and viscous couplings, as well as fluid couplings are often used. To drive the fan of relatively low-power engines, special electric motors are widely used, which are powered from the onboard electrical system. This, as a rule, reduces the mass of the power plant and simplifies its layout. In addition, the use of an electric motor to drive the fan allows you to adjust the frequency of its rotation, and hence the intensity of cooling. If the coolant temperature is low, the fan may switch off automatically.

Radiators connect the air and liquid paths of the cooling system with each other. The purpose of radiators is to transfer heat from the coolant to atmospheric air. The main parts of the radiator are the inlet and outlet manifolds, as well as the core (cooling grid). The core is made of copper, brass or aluminum alloys. According to the type of core, the following types of radiators are distinguished: tubular, tubular-lamellar, tubular-tape, lamellar and honeycomb.

In the cooling systems of wheeled and tracked vehicles, tubular-lamellar and tubular-tape radiators are most widely used. They are rigid, durable, manufacturable and have high thermal efficiency. The tubes of such radiators have, as a rule, a flat-oval section. Tubular-lamellar radiators can also consist of round or oval tubes. Sometimes flat-oval tubes are placed at an angle of 10 ... 15 ° to the air flow, which contributes to the turbulence (swirl) of the air and increases the heat transfer of the radiator. Plates (tapes) can be smooth or corrugated, with pyramidal protrusions or bent notches. The corrugation of the plates, the application of notches and protrusions increase the cooling surface and provide a turbulent flow of air between the tubes.

Rice. Grilles of tubular-lamellar (a) and tubular-tape (b) radiators