How many parts does an automobile engine consist of?

The engine block is the skeleton of the engine and the installation foundation of various mechanisms and systems of the engine. The main parts of the engine are all installed inside and outside and bear various loads. Therefore, the car body must have sufficient strength and rigidity. Engine cylinder block is mainly composed of cylinder block, crankcase, cylinder head and cylinder gasket. 1. Cylinder block (Figure 2- 1) The cylinder block and upper crankcase of a water-cooled engine are often cast as a whole, which is called cylinder block-crankcase or cylinder block. The cylinder block is usually made of gray cast iron. The cylindrical cavity in the upper part of the cylinder block is called the cylinder, the lower part is the crankcase supporting the crankshaft, and its inner cavity is the space for the crankshaft to move. Many reinforcing ribs, cooling water jackets and lubricating oil passages are cast in the cylinder block. The cylinder block should have sufficient strength and rigidity. According to the different installation plane positions of the cylinder block and the oil pan, the cylinder block is usually divided into the following three forms. (Figure 2-2) (1) The general cylinder block is characterized in that the installation plane of the oil pan is at the same height as the rotation center of the crankshaft. The advantages of this cylinder block are small height, light weight, compact structure, convenient processing and convenient disassembly and assembly of crankshaft; But its disadvantages are poor rigidity and strength. (2) The gantry cylinder block is characterized in that the installation plane of the oil pan is lower than the rotation center of the crankshaft. Its advantages are good strength and rigidity, and it can bear large mechanical load. But its disadvantages are poor manufacturability, heavy structure and difficult processing. (3) Tunnel cylinder block The crankshaft main bearing hole of this cylinder block is integral with rolling bearings. The main bearing hole is large, and the crankshaft is loaded from the back of the cylinder block. Its advantages are compact structure, good rigidity and strength, but its disadvantages are high machining accuracy, poor manufacturability and inconvenient disassembly and assembly of crankshaft. In order to make the inner surface of the cylinder work normally at high temperature, it is necessary to properly cool the cylinder and cylinder head. There are two cooling methods, one is water cooling and the other is air cooling (Figure 2-3). Cooling water jackets are processed around the cylinder and cylinder head of water-cooled engine, and the cylinder block and cylinder head are communicated with each other. The cooling water continuously circulates in the water jacket, taking away some heat and cooling the cylinder and cylinder head. Modern cars basically use water-cooled multi-cylinder engines. For a multi-cylinder engine, the arrangement of cylinders determines the overall size and structural characteristics of the engine, and also affects the stiffness and strength of the engine block, which is related to the overall layout of the automobile. According to the different cylinder arrangement, the cylinder block can also be divided into three types: single row, V-shaped and opposite (Figure 2-4). (1) The cylinders of an in-line engine are generally arranged longitudinally. The single exhaust cylinder block is simple in structure and easy to process, but the length and height of the engine are large. Generally, engines with less than six cylinders are mostly single-row engines. For example, Jetta, Fukang and Hongqi cars all use this kind of in-line cylinder block. Some cars tilt the engine at an angle to reduce the height of the engine. (2) V-shaped cylinders are arranged in two rows, and the included angle between the center lines of the two rows of cylinders is γ < 180, which is called V-shaped engine. Compared with the in-line engine, the V-type engine shortens the length and height of the engine block, increases the rigidity of the engine block and reduces the weight of the engine, but increases the width of the engine, which is complicated in shape and difficult to process. Generally used for engines with more than 8 cylinders, and 6-cylinder engines also adopt this form. (3) Opposed cylinders are arranged in two rows, and the left and right cylinders are on the same horizontal plane, that is, the included angle between the center lines of the left and right cylinders is γ = 180, which is called opposition. It is characterized by small height and convenient overall layout, which is beneficial to air cooling. This kind of cylinder is seldom used. A cylinder that directly drills holes in the cylinder block is called an integral cylinder. The integral cylinder has good strength and rigidity and can bear a large load. This kind of cylinder requires high materials and costs. If the cylinder is manufactured as a separate cylindrical part (i.e., cylinder liner) and then installed in the cylinder block. In this way, the cylinder liner is made of wear-resistant high-quality materials, and the cylinder block can be made of low-priced general materials, thus reducing the manufacturing cost. At the same time, the cylinder liner can be taken out of the cylinder block, which is convenient for maintenance and replacement and can greatly prolong the service life of the cylinder block. There are two types of cylinder liners: dry cylinder liners and wet cylinder liners (Figure 2-5). The characteristic of dry cylinder liner is that after the cylinder liner is put into the cylinder block, its outer wall is not in direct contact with cooling water, but in direct contact with the cylinder block wall. The wall thickness is relatively thin, generally 1 ~ 3 mm, which has the advantages of integral cylinder block, good strength and rigidity, but complicated processing, inconvenient disassembly and assembly, and poor heat dissipation. The characteristic of wet cylinder liner is that after the cylinder liner is put into the cylinder block, its outer wall is in direct contact with cooling water, and the cylinder liner is only in contact with the cylinder block up and down, and the wall thickness is generally 5 ~ 9mm. Good heat dissipation, uniform cooling and easy processing. Usually, only the inner surface needs to be finished, and the outer surface in contact with water does not need to be machined, so it is convenient to disassemble and assemble. However, its strength and stiffness are not as good as dry cylinder liner, which is easy to cause water leakage. Some measures should be taken to prevent leakage. 2. The lower part of the crankcase cylinder block used to install the crankshaft is called the crankcase, and the crankcase is divided into an upper crankcase and a lower crankcase. The upper crankcase is integrated with the cylinder block, and the lower crankcase is used to store lubricating oil and seal the upper crankcase, so it is also called the oil pan diagram (Figure 2-6). The oil pan bears little force and is generally stamped from thin steel plate. Its shape depends on the overall layout of the engine and the oil capacity. An oil stabilizing baffle is installed in the oil pan to prevent the oil level from fluctuating too much when the car bumps. There is also an oil drain plug at the bottom of the oil pan. A permanent magnet is usually installed on the oil drain plug to absorb the metal chips in the lubricating oil and reduce the wear of the engine. The gasket is installed between the joint surfaces of the upper crankcase and the lower crankcase to prevent the lubricating oil from leaking. 3. Cylinder head (Figure 2-7) The cylinder head is installed on the cylinder block to seal the cylinder from the top to form a combustion chamber. It is often in contact with high temperature and high pressure gas, so it bears great thermal load and mechanical load. A cooling water jacket is arranged in the cylinder head of the water-cooled engine, and the cooling water hole at the lower end face of the cylinder head is communicated with the cooling water hole of the cylinder block. Circulating water is used to cool high-temperature components such as combustion chambers. The cylinder head is also equipped with intake and exhaust valve seats, valve guide holes for installing intake and exhaust valves, and intake and exhaust passages. The cylinder head of gasoline engine has holes for installing spark plugs, and the cylinder head of diesel engine has holes for installing fuel injectors. There are also camshaft bearing holes on the cylinder head of overhead camshaft engines for installing camshafts. Figure 2-7 Cylinder heads are generally made of gray cast iron or alloy cast iron. Aluminum alloy has good thermal conductivity, which is beneficial to improve compression ratio. Therefore, in recent years, aluminum alloy cylinder heads have been used more and more. The cylinder head is an integral part of the combustion chamber, and the shape of the combustion chamber has a great influence on the work of the engine. Because of the different combustion modes of gasoline engine and diesel engine, the parts of cylinder head that make up the combustion chamber are also very different. The combustion chamber of gasoline engine is mainly on the cylinder head, and the combustion chamber of diesel engine is mainly in the pit at the top of piston. Only the combustion chamber of gasoline engine is introduced here, and the combustion chamber of diesel engine is introduced in the diesel supply system. Three common forms of combustion chamber of gasoline engine (Figure 2-8). (1) hemispherical combustion chamber The hemispherical combustion chamber is compact in structure, and the spark plug is arranged in the center of the combustion chamber, so the flame stroke is short, so the combustion rate is high, the heat dissipation is low, and the thermal efficiency is high. The structure of this combustion chamber also allows the valves to be arranged in two rows, and the diameter of the air inlet is larger, so the charging efficiency is higher. Although the valve train has become more complicated, it is beneficial to exhaust purification and is widely used in automobile engines. (2) Wedge combustion chamber Wedge combustion chamber has simple and compact structure, small heat dissipation area and small heat loss, which can ensure the mixture to form a good vortex motion in the compression stroke, which is beneficial to improve the mixing quality of the mixture, with small intake resistance and improved charging efficiency. The valves are arranged in a row, which makes the valve train simple, but the spark plug is placed at the height of the wedge-shaped combustion chamber, and the flame propagation distance is longer. This type of combustion chamber is used in Cherokee automobile engines. (3) Basin combustion chamber Basin combustion chamber, the cylinder head has good manufacturability and low manufacturing cost, but because the valve diameter is easily limited, the intake and exhaust effect is worse than that of hemispherical combustion chamber. Jetta engine and Audi engine use basin combustion chamber. 4. Cylinder gasket (Figure 2-9) The cylinder gasket is installed between the cylinder head and the cylinder block to ensure the sealing of the contact surface between the cylinder head and the cylinder block and prevent air leakage, water leakage and oil leakage. The material of the cylinder gasket should have certain elasticity, which can compensate the unevenness of the joint surface and ensure sealing. At the same time, it should have good heat resistance and pressure resistance, and it will not burn or deform under high temperature and high pressure. At present, the cylinder gasket with copper cotton structure is widely used. Because there are three layers of copper skin at the flanging of copper skin-cotton cylinder pad, it is not easy to deform when pressed compared with asbestos. Some engines also use cylinder pads made of asbestos with woven steel mesh or perforated steel plate as the skeleton and asbestos and rubber adhesive pressed on both sides. When installing the cylinder gasket, first check the quality and integrity of the cylinder gasket, and all the holes in the cylinder gasket should be aligned with the holes in the cylinder block. Secondly, the cylinder head bolts should be installed in strict accordance with the requirements of the manual. When tightening the cylinder head bolts, they must be expanded symmetrically from the center to the periphery for 2 ~ 3 times, and finally tightened to the specified torque.