Why did the car run?

An engine is a machine that converts heat energy generated by fuel combustion into mechanical energy. In each conversion process, it has to go through four strokes of air intake, compression, expansion and exhaust, which is a working cycle.

The main moving part in the engine is the piston, which moves around itself; And reciprocating motion. When the piston moves back and forth in the above four strokes to complete a working cycle, it is called a four-stroke engine. A two-stroke engine completes a cycle after two strokes. An engine that uses gasoline as fuel is called an oiler gasoline engine. It first mixes gasoline and air in a carburetor and sends them to a cylinder, and generates power after the above-mentioned journey. Where gasoline is directly injected into the cylinder or intake pipe and then mixed with air to form a mixed gas, it is called a direct injection gasoline engine after the above stroke. Diesel engines fueled by diesel oil are generally called compression ignition diesel engines. Diesel oil is directly injected into cylinders by fuel injection pumps, mixed with compressed air, and automatically combusted at high temperature and high pressure to generate power. Under the requirement of energy shortage and environmental protection all over the world, engines using natural gas, liquefied petroleum gas and other clean fuels have appeared. But its working principle is similar.

Let's talk about each trip in detail.

If the mixture meets Mars, it will easily explode. In an automobile engine, it is the force generated by this explosion that pushes the piston in the cylinder from the highest position to the lowest position. The distance the piston moves from top to bottom is called stroke. In the first stroke (see figure 2a), the piston is pulled down by the crankshaft through the connecting rod, and the mixed gas enters the top of the cylinder piston through the intake valve. The second stroke is called the compression stroke (see figure 2b), when both the intake valve and the exhaust valve are closed. The piston moves upward until the inhaled mixture is pulled down by the crankshaft again. The third stroke is called the power stroke (see figure 2c). At this time, the two valves are still in the closed state, and the high-voltage electricity supplied by the distributor causes the spark plug in the combustion chamber to generate sparks, ignite the mixed gas, and generate explosive force to push the piston to move downward. At this time, the cylinder is full of hot smoke. When the piston rises again, the exhaust valve opens. These thick smoke are pushed out of the cylinder combustion chamber by the piston and enter the exhaust pipe. This is the last stroke, which is called the exhaust path (see Figure 2d). After that, the engine starts the first stroke of the next working cycle and works endlessly.

In order to further understand the working condition of the engine, it is necessary to introduce the functions of its components as follows:

Cylinder block and cylinder head

Among the engine components, the cylinder block (see Figure 3) is the heaviest and largest. It is the basic component that assembles all the mechanisms and systems of the engine into a whole. There are several cylindrical hollow cylinders in the cylinder body, which are the space for the piston to move, and are called cylinders. When there are several empty cylinders, there are several cylinders. A general four-cylinder engine is called a four-cylinder engine. Of course, there are more, such as 6 cylinders, 8 cylinders and even 12 cylinders. The more cylinders, the greater the power of the engine. However, if the piston is in complete contact with the cylinder in the cylinder, its motion resistance is still not small. In order to reduce the contact area, several piston rings are put on the piston. Let the piston ring contact with the cylinder wall, greatly reducing the resistance of piston movement. Generally, there is more than one piston ring on the piston, including gas ring and oil ring.

Because the surface of the cylinder is often in contact with high-temperature and high-pressure combustion gas, the piston moves back and forth at high speed on it, so the material of the cylinder must be resistant to high temperature, wear and corrosion. In order to meet these requirements, high-quality alloy cast iron containing a small amount of alloying elements such as nickel, molybdenum, chromium and phosphorus is usually used and honed to obtain a working surface with high roughness, shape and dimensional accuracy.

But if the cylinder body is made of all the above-mentioned high-quality materials, it will be too expensive. Because except for these working faces, the rest of the cylinder body has no such high requirements. Therefore, flexible and detachable working surfaces, namely cylinder liners, are widely used in engines. It can be made of high-quality materials, and the cylinder block can be cast by ordinary cast iron or light alloy. Cylinder liners are divided into dry sleeves and wet sleeves according to whether they contact cooling water or not. The latter has the advantages of convenient casting, easy disassembly and assembly and good cooling effect. Disadvantages are poor rigidity and easy water leakage.

There is a cylinder head covering the cylinder barrel at the upper part of the cylinder block (see Figure 3). Its main function is to seal the upper part of the cylinder block and form a combustion chamber with the piston top and cylinder barrel. Generally made of gray cast iron or alloy cast iron and aluminum alloy, containing water jacket. Screw together with the cylinder block through bolts. For sealing, a layer of cylinder gasket is usually added between them. On the cylinder head, each cylinder has its own intake valve, exhaust valve, spark plug seat hole or injector seat hole and valve guide hole. There are many cylinder heads. Different engines have different cylinder heads, and some are divided into several cylinders. The advantage of the former is that it can shorten the overall length of the engine. Disadvantages are poor rigidity, easy deformation when heated, affecting sealing, and need to be replaced as a whole after damage. The shape of combustion chamber composed of cylinder head has great influence on the engine work. Therefore, its basic requirements are: compact structure, small cooling surface, so that the mixture can produce vortex before combustion. Its purpose is to reduce the heat loss, shorten the flame diffusion distance, improve the combustion speed, ensure the timely and sufficient combustion, so as to obtain the maximum power and reduce the harmful substances contained in the waste gas. Generally speaking, a water-cooled engine has an integrally cast bent crankcase at the lower part of the cylinder block. Its interior is the space for crankshaft movement. The crankshaft is suspended directly below the crankcase. There is also a plate-like part in the lower part of the crankcase, called the oil pan (see Figure 4). Mainly used for storing engine oil and sealing crankcase. The oil pump is located in the oil pan. The oil pan is also equipped with a baffle to prevent the oil from shaking too much. A magnetic oil drain plug is installed at the bottom to absorb the metal chips in the engine oil. On one side of the oil pan, there is also a dipstick to check the oil amount in the oil pan.

Crankshaft piston connecting rod group

The main moving parts in the engine are crankshaft, piston and connecting rod. It consists of crankshaft, piston, piston ring, piston pin, connecting rod and flywheel.

(1) crankshaft

This is a shaft with several bends (Figure 1). The number of cranks depends on how many cylinders the engine has and their arrangement. If connecting rods are connected with cranks, the number of cranks is equal to the number of cylinders. If two connecting rods are connected by a crank, the number of cranks is half of the number of cylinders.

Crankshaft requires impact resistance and wear resistance. Generally, it is forged with medium carbon steel or medium carbon alloy steel, and also cast with ductile iron.

Figure 1 shows the crankshaft with flywheel. The main journal located in the center of rotation is connected with the crankcase through the bearing bushing. The journal that is not in the center of rotation is called connecting rod journal or crank pin, and it is connected with connecting rod through connecting rod bearing bush and bolt.

Because the crankshaft rotates at high speed, it is necessary to constantly lubricate the friction surface with engine oil. Therefore, oil passages are drilled in the crankshaft body of the main journal of the crankshaft and the connecting rod journal, so that oil can pass through these oil passages and lubricate these parts.

Because the shape of the crankshaft is very irregular, it will shake when it rotates. Experts call this phenomenon imbalance. If the artificial cotton develops when the engine is working, it will not only produce a lot of noise, but also greatly shorten the life of the parts. The main causes of imbalance are the irregular centrifugal force and centrifugal moment generated when the crankshaft rotates, and the inertia force of the piston reciprocating motion. For engines with different cylinder numbers, these forces and moments exist or do not exist. Therefore, it is necessary to set a balance block according to the specific structure to balance. Some balance weights are integrated with the crankshaft, and some are fixed on the crankshaft by bolts.

We know that once a wheel with a large mass turns, it will keep turning without resistance. Therefore, a flywheel made of gray cast iron or nodular cast iron and cast steel is installed at the rear end of the crankshaft. It is a disk with great inertia and wide and thick edges. Its main function is to store the kinetic energy given by the engine, overcome the resistance of crankshaft connecting rod movement, overcome short-term overload, and ensure the engine to output uniform torque and speed. In addition, it is also the transmission part of the friction clutch, so it needs to be balanced with the crankshaft.

(2) Piston

It is like an inverted cup, the bottom of which is upward, forming a part of the combustion chamber. There is a round hole in the cup wall, through which the piston pin can pass. The connecting rod passes through the cup mouth and is connected with the piston through the piston pin. Its main function is to transfer the explosive force generated by the combustion of mixed gas to the connecting rod through the piston pin, thus pushing the crank of the crankshaft to rotate (Figure 2).

The working conditions of the piston are very bad. The top of the piston is in contact with high-temperature gas, and bears the impact caused by high-speed reciprocating motion and the high pressure caused by inertia force. All parts of the piston are subjected to the comprehensive force and moment of tension, pressure and bending, and the heating is uneven. Therefore, the piston is required to have small mass, small thermal expansion, good heat transfer and wear resistance. The piston made of aluminum alloy has both the above properties and is the first choice for the piston of the former automobile.

The basic structure of piston can be divided into three parts: top, head and skirt.

The piston top is divided into flat top and concave top, and the surface is as smooth as possible. The head of the piston has several annular grooves with rectangular cross section for accommodating various piston rings, and the bottom of the annular grooves is drilled with many radial holes, so that the oil scraped from the cylinder wall can flow to the oil pan through these holes. The piston head bears and transmits the explosive force after the combustion of the mixed gas; Can conduct the heat generated by the combustion of the mixed gas; A combustion chamber forming part with the piston ring. The skirt of the piston refers to the good part from the piston ring groove to the cup mouth. Its main function is that the piston plays a guiding role in the reciprocating motion in the cylinder to bear the lateral pressure given to it by the cylinder wall.

When the piston works in the cylinder, the heating stress is very uneven, which will bring uneven deformation, so the gap between the piston and the cylinder wall is large or small, and there is also the possibility of air leakage and scratching the surface of the cylinder wall. In severe cases, it will jam and damage the piston.

In order to make the piston have a uniform gap with the cylinder wall at normal working temperature, although the cylinder itself is still cylindrical, the piston is made into an oval shape, so that the piston can expand into a similar cylinder when working. Therefore, under normal circumstances, the piston is generally conical or oval with a small upper diameter and a large lower diameter.

Of course, if you pay attention, you will also find that some piston skirts have longitudinal and transverse grooves. The main purpose of opening the transverse groove is to prevent heat from transferring from the top of the piston to the skirt, so as to force the skirt not to expand too much. If it is located horizontally in the oil ring groove, it can also play the role of oil hole. The function of the longitudinal groove is to obtain the minimum clearance with the cylinder wall when assembling the piston in cold state; In the hot state, the piston will not get stuck in the cylinder. The direction of the longitudinal groove is not parallel to the piston movement direction, and the inclined groove can prevent the piston from scratching the cylinder wall.

(3) Piston ring

The piston must be closely matched with the cylinder wall, and embedding the piston ring in the piston is the measure to solve this problem. Piston rings are divided into gas rings and oil rings. The former prevents the combustion mixture from escaping into the crankcase. The latter is prevented from being made of alloy cast iron, with inclined openings and elasticity. When it is sleeved on the piston, it has the characteristics of extending outward and clinging to the cylinder wall. If the sealing state is damaged and air leaks, the engine will lose some power, the loss of fuel and engine oil will increase, and serious carbon deposition will appear on the piston and combustion chamber surface, causing environmental pollution.

Generally, the piston is equipped with 2 ~ 3 gas rings and 1 ~ 2 oil rings. Under the requirement of ensuring sealing, try to reduce the number of rings. Although there are several gas rings, the requirements for each gas ring are not the same. The first gas ring is closest to the top. Because it is close to the combustion chamber and works in the environment with the highest temperature and pressure and the most difficult lubrication, porous chromium is generally plated on its working surface, which not only improves the surface hardness, but also stores a small amount of engine oil, improves the lubrication conditions and prolongs the service life. Other gas rings are generally only tinned or phosphatized. Because the working temperature of the first gas ring is high, its gap is also large. When installing each piston ring on the piston, its respective notches must be staggered, which is beneficial to the sealing of the cylinder.

(4) Piston pin

It is the connecting piece between the piston and the small end of the connecting rod (see Figure 2), which plays the role of transmitting the force of the piston locust to the connecting rod. Because it bears periodic impact force at high temperature and its lubrication condition is poor, it requires sufficient rigidity, strength and wear resistance. In order to reduce inertia, it is generally made into a hollow cylinder to reduce mass. Piston pin is generally made of low carbon steel, and its surface is carburized and then honed and polished to improve its surface hardness and overall toughness. The piston pin is floating when it is installed in the piston pin hole and the connecting rod small head hole. When the engine is working, it can rotate slowly around its main shaft in the pin seat hole to obtain more uniform wear. In order to prevent the piston pin from moving along the spindle direction, the snap ring in the piston pin hole is embedded in the groove of the pin seat for limiting.

(5) Connecting rod

(Figure 4) It connects the piston pin at the upper end with the crankshaft at the lower end, which can convert the reciprocating motion of the piston into the rotary motion of the crankshaft. Just like the movement of your thighs when you ride a bike. Connecting rods are generally made of medium carbon steel or alloy steel by forging, machining and heat treatment. Because the connecting rod bears periodic changes of compression, tension and bending when working, it is required to be as small as possible and have sufficient stiffness and strength. Insufficient rigidity, large holes are not round, and poor lubrication will burn the bearing bush. Bending of the rod will lead to air leakage and oil leakage in the cylinder.

The connecting rod head is generally composed of two semicircular blocks, one is the lower end of the connecting rod head, and the other is called the connecting rod cover, which is screwed together by connecting rod bolts (Figure 5). These two parts are machined (drilled) together. The surface of the big end hole has a high smoothness so as to closely fit the bearing bushing, and the surface is also milled with grooves and small oil holes for positioning the bearing bushing.

The working conditions of connecting rod bolts are the same as those of connecting rods. Generally made of high-quality alloy steel or high-quality carbon steel, forged or cold heading. When installing the big end of the connecting rod, the connecting rod bolt must be tightened according to the torque specified by the manufacturer, and measures should be taken to prevent it from loosening itself.

Connecting rod bearing bush is made in half like connecting rod big head. The bearing base is a thin steel plate, and the inner surface is cast with a wear-reducing gold layer such as Babbitt. Reducing gold during running-in period can reduce friction, accelerate running-in period and maintain oil film.

The surface of the bearing bush matched with the big end of the connecting rod and the connecting rod cover should have a very high smoothness. Half of the bearing bushing is not semicircular before loading. When it is loaded, the bearing bush can cling to the wall of the large hole due to pressure (interference). In order to prevent the bearing bush from rotating or axially displacing during operation, the stamping positioning bosses on the bearing bush are respectively embedded into the grooves of the big head and the connecting rod cover. There are oil grooves on the inner surface of the bearing bushing to ensure good lubrication.

We know that the more mixed gas enters the cylinder combustion chamber, the more heat is released during combustion, and the more explosive it is. For a specific engine, the total volume of its combustion chamber is certain. In order to fill the combustion chamber with more mixed gas, the pressure of mixed gas must be high and the temperature must be low. However, because the mixture can only enter the cylinder through the intake pipe, it will inevitably produce resistance in the flow process and reduce the inflation pressure; In addition, it is difficult to meet this requirement 100% because the high temperature exhaust gas in the cylinder and the high temperature of the adjacent components after the last cycle heated the mixed gas that just entered the cylinder. Engine designers generally start with improving the structure to reduce the intake and exhaust resistance, the opening and duration of intake and exhaust valves, and keep sufficient intake and exhaust volume as much as possible. Valves are very important parts in the engine, and they must be opened or closed at accurate time. According to the arrangement of valves, it can be divided into top type and side type. According to the number of valves in each cylinder, there are two valves, four valves and even more.

The most common valve configuration is overhead. Its intake valve and exhaust valve are hung on the cylinder head, with the big head at the bottom and the small head at the top. The valve train ensures the timely opening and closing of each valve.

As mentioned above, in order to open and close the valve at accurate time, there must be a valve mechanism.

3. Air valve

The valve mechanism consists of camshaft, tappet, push rod, rocker arm, rocker arm shaft, valve spring and valve guide.

Camshafts (Figure 1) are arranged at the lower, side and top of the engine. Modern engines are usually overhead and located on the cylinder head. The camshaft directly drives the valve through the rocker arm, which saves a large set of reciprocating parts such as tappets and pushrods, which is very suitable for high-speed generators, but it also brings difficulties to the transmission shaft. Because the camshaft is on the cylinder head, the disassembly and assembly of the cylinder head is more troublesome, and the arrangement of injectors is also more difficult. The other overhead type is that the amplitude wheel of camshaft directly drives the valve. The advantages of this form are not only simple mechanism, small inertia and low requirements for camshaft, so it is widely used in new cars.

So what drives the camshaft to rotate? Most of the earliest cars were driven by timing gears (see figure 1). When the crankshaft rotates, the camshaft is driven by a pair of gears at its front end, and sometimes an intermediate gear (idler) is added. In order to reduce the transmission noise and make the meshing smooth, the timing gear is mostly bakelite, which is helical. In overhead valve drive mechanism, chain drive or belt drive is often used. The matrix of the belt is neoprene with glass fiber or nylon fabric sandwiched in the middle. It has been widely used in recent years because of its high strength, low noise, light weight and low price.

Usually, the engine has only one intake valve and one exhaust valve per cylinder. In order to improve the inflation efficiency, multi-valve technology is often used now, for example, each cylinder has four valves. This multi-valve structure is particularly beneficial for engines with direct fuel injection. The fuel injector is arranged in the center of the combustion chamber, the ignition and combustion path is uniform, and the opening of each valve can be reduced appropriately.

When four valves are used in each cylinder, there are two valve arrangements: one is a mixed row of intake valves and exhaust valves; The other is that the intake valve and the exhaust valve are arranged in a row respectively. All valves in the former are driven by a camshaft through a T-shaped rod, but the working conditions and effects are not good because of the different positions of the valves in the intake port, while the latter has great shortcomings, but it needs to be equipped with two camshafts. Whenever the word DOHC appears, it refers to the overhead double camshaft. In recent years, most engines have adopted this form. Of course, it is not uncommon for each cylinder to have more than four valves. The main purpose is to improve the charging efficiency.

4. Vaporizer

In order to make the car work continuously, it is necessary to continuously supply oil and gas to the engine, not only to supply it, but also to mix it properly, and the exhaust gas should be discharged smoothly after combustion. For this reason, the fuel needs to be stored in the fuel tank, and there must be an oil pump and pipeline to send the fuel in the fuel tank to the engine. In order to prevent the fuel from being polluted, it needs to be filtered by a filter. The outside air contains dust, and the air sent to the engine needs to be filtered by the air filter. How to mix clean air with fuel as required requires an indispensable part, that is, carburetor (Figure 2).

The carburetor must do two things: first, it must vaporize the fuel; The second is to mix vaporized fuel oil with a certain proportion of air to form mixed gas.

The outside air enters the carburetor after being filtered, and the air intake is controlled by changing the position of the choke valve. Air rushes through the throat in the carburetor to generate suction, which sucks the fuel out of the float chamber through the nozzle and atomizes the fuel. Atomized fuel and air are mixed together and sucked by the cylinder through the intake manifold. The intake of mixed gas is controlled by the accelerator pedal, which is controlled by the accelerator located in the carburetor. The amount of oil pumped into the float chamber by the gasoline pump is controlled by the float in the float chamber. The float rises and falls with the amount of oil in the float chamber. When the float chamber is filled with steam oil, the float floats up and blocks the oil inlet with its needle valve. The driver changes the engine speed by controlling the throttle opening, which is the working principle of a simple carburetor (Figure 3). The concentration of the mixture becomes thicker with the increase of the throttle.

The working conditions of the automobile engine should often change in a large range, such as before the automobile starts and before the green light at the intersection, when the engine is idling, the load is zero, the throttle opening is the smallest and the speed is the lowest; When the car climbs the hill with full load, the throttle is fully open, but the speed is not high; When driving on a flat road, the throttle does not need to be fully opened, the engine discharge load is moderate, and the speed and speed are moderate; When driving on expressway, the engine may be at full load and the speed will reach the maximum. Under so many complicated working conditions, the requirements for mixed gas cannot be the same. For example, under idle speed and small load, the former requires that the mixture must be very rich, while the latter requires that the concentration gradually become thinner; Under medium load, in order to save fuel, carburetor is required to supply mixture with minimum fuel consumption; Under full load, carburetor is required to provide rich mixture to make the engine emit maximum power. In addition, if the car is cold-started, the mixture is required to be rich; When accelerating, when the throttle suddenly opens wide, the carburetor needs to provide additional fuel. To sum up, under normal working conditions, the carburetor is required to supply a mixture from rich to lean with the increase of load at medium and low load, and the mixture is required to be from lean to rich at full load. According to the above requirements, it is impossible to meet the requirements only by the above simple carburetor.

In order to meet these requirements, modern carburetor is equipped with a series of mixture concentration compensation devices. Such as main oil supply pump, idle system, economizer, acceleration system and starting system. In order to ensure that the carburetor can supply proper concentration of mixed gas under different working conditions of gasoline engine.

Although the carburetor is small, with so many systems integrated inside, the structure becomes complicated. The seed ensures that the carburetor can work normally, so its regular maintenance is very important. The main disadvantage of using carburetor is that cylinder inflation and mixture distribution are not ideal, which affects the improvement of engine power and economy and is not conducive to meeting emission requirements. In recent years, in order to meet the requirements of environmental protection, countries have adopted direct fuel injection instead of carburetor. The advantages of direct injection are high inflation efficiency, high output power, uniform distribution of mixed gas, providing mixed gas with the best composition according to the change of working conditions, and low fuel consumption. The disadvantage is that it is difficult to arrange on the cylinder head and the manufacturing cost is high. According to the injection position, it can be divided into in-cylinder injection and intake pipe injection, and according to the control system, it can be divided into mechanical injection and electronic injection (EFI).

Since 1960s, electronically controlled gasoline injection system has been gradually adopted by car engines produced in Europe and America. In order to meet the requirements of automobile emission regulations, China has begun to steadily promote EFI vehicles. In the EFI system, there is an adjusting device, which can accurately control the composition of the mixed gas, and then install a three-way catalyst to greatly reduce the harmful components in the exhaust gas.

The basic principle of EFI system is that the collected information is fed back to the microcomputer for processing through sensors located in various parts, and it sends instructions to control the air-fuel ratio in the mixture, so that the supplied mixture can meet the needs of various engine working conditions. For example, the computer judges and calculates the basis of fuel injection according to the information collected by the air flow sensor, the engine speed, even the position of the throttle, the temperature of cooling water and the temperature of air, determines the opening time of each injector, and sends instructions to the injectors for fuel injection.

Each sensor receives different information at different parts: for example, the ignition coil of the distributor receives the information of the number of revolutions of the starter; The air flow sensor receives the information of the intake air flow; Startup and shutdown to receive startup information; Throttle opening information of throttle switch; The cooling water temperature sensor receives water temperature information, and the air temperature sensor receives air temperature information. This information is fed back to the computer through the circuit.

Besides the computer, the most important component in the EFI system is the fuel injector. Generally, the engine has only one injector per cylinder, which is located above the intake valve. The fuel is atomized by the fuel injector and then mixed with the air entering the cylinder from the intake pipe.

In order to meet the requirements of exhaust emission regulations, some automobile EFI systems are equipped with mixed gas regulation systems. It mainly uses an oxygen sensor in the trachea to feed back the lean or rich information of the mixed gas to the computer. According to this information, the computer re-instructs the fuel injector to obtain the correct fuel injection quantity.

The new generation engine integrates gasoline injection system and ignition system, which embodies the optimal control of mixture composition and ignition time and greatly improves the performance of the engine. The above introduction is multi-point injection. Because the injection mode is staged injection, the four injectors of a four-cylinder engine are injected separately, and each cylinder is injected once every revolution of the crankshaft.

In addition, there are single-point injection systems, also known as throttle body injection systems. On a multi-cylinder engine, there is only one injector, which is installed above the throttle body, injects oil in the intake pipe, mixes it with air, and then distributes it to each cylinder through the intake pipe. Single point injection is also controlled by computer. Although the performance is slightly poor (low injection pressure), it has the advantages of simple structure, low cost, reliable work and convenient maintenance due to the small number of injectors used. Other parts are basically the same as multi-point injection.

Cooling and lubrication

When the car is traveling at a speed of 50 km/h, each piston in the engine cylinder moves up and down 6000 times per minute. The combustion of mixed gas in the combustion chamber will produce high temperature and high pressure combustion gas (about 800-2000℃). Therefore, the cylinder must be cooled, otherwise the moving parts in the cylinder will be damaged due to thermal expansion, the mechanical strength will be reduced, and the lubrication will be ineffective and stuck. Of course, excessive cooling will also lead to reduced cylinder expansion, abnormal combustion, decreased power, increased fuel consumption and poor lubrication. The purpose of installing a cooling system on a car is to keep the engine working at a proper temperature.

At present, water cooling is widely used to cool automobile engines. The heat of high-temperature parts of the engine is conducted to the cooling water in the surrounding water jacket through the cylinder liner and cylinder head, and then the heat absorbed by the cooling water is radiated to the outside atmosphere. When the engine is working normally, the water temperature in the water jacket should be kept at about 80 ~ 90℃.

At present, the forced circulating water cooling system is widely used in automobile engines (Figure 1). There are water jackets in the engine cylinder head and cylinder block. The water pump sucks cooling water from the outside of the machine and pressurizes it, so that the cooling water flows in the water jacket and takes away the heat of the adjacent components. After the cooling water absorbs heat, the temperature rises and enters the radiator (water tank) in front of the car. Due to the advance of the car and the suction of the fan, the cold air from outside passes through the radiator, taking away the heat of the cooling water in the radiator and sending it into the atmosphere. After cooling, the cold water in the radiator enters the water jacket again under the action of the water pump. This cycle continuously cools the high-temperature parts of the engine.

In order to ensure that the engine works in the most suitable temperature range under different loads, speeds and seasons, some cars are also equipped with shutters, thermostats and fan clutches.

When the car is moving forward, the radiator is located at the front end (rear end) of the car in the windward direction. There are two water storage chambers at the upper and lower ends, which are connected by many thin cooling pipes. Most cooling pipes adopt flat circular cross-section. In order to strengthen the cooling effect, many metal fins are arranged on the jacket of the cooling pipe to increase the cooling area and the stiffness and strength of the radiator itself. The component consisting of cooling pipe and heat sink is called radiator core. The above structure is called tubular radiator core (Figure 2).

Another widely used radiator core is the tube-belt radiator core (Figure 3), which is formed by alternately welding corrugated radiator belts and cooling pipes. There are small fins on the heat dissipation belt to disturb the airflow, thus improving the heat dissipation energy: force. This form is widely used because of its good heat dissipation effect, easy manufacture and light weight. The disadvantage is that the structural strength is not as good as that of tube.

The requirement of radiator core is that the material used has good thermal conductivity, and brass sheet is generally used. In order to save copper, aluminum radiator core is promising. At present, it is mostly used in advanced cars and racing cars.