Basic structure of an internal combustion engine

The engine block forms the framework of the engine and serves as the foundation for installing various mechanisms and systems. All major components and accessories of the engine are mounted inside and outside the engine block, which also bears various loads. Therefore, the engine block must have sufficient strength and rigidity. The engine block assembly is mainly composed of components such as the cylinder block, cylinder liner, cylinder head, and cylinder gasket.
Cylinder Block
In water-cooled engines, the cylinder block and the upper part of the crankcase are usually cast together, called the cylinder block-crankcase, also known as the cylinder block. The cylinder block is generally made of gray cast iron. The cylindrical cavity in the upper part of the cylinder block is called the cylinder, and the lower part is the crankcase that supports the crankshaft. The inner cavity is the working space of the crankshaft. Many reinforcing ribs, cooling water jackets, and lubricating oil passages are cast inside the cylinder block.
The cylinder block should have sufficient strength and rigidity. According to the different positions of the cylinder block and the mounting plane of the oil pan, the cylinder block is usually divided into the following three forms.
1. Ordinary cylinder block: Its characteristic is that the mounting plane of the oil pan is at the same height as the center of rotation of the crankshaft. The advantages of this type of cylinder block are its small height, light weight, compact structure, easy machining, and convenient crankshaft assembly and disassembly; the disadvantages are its poor rigidity and strength.
2. Gantry-type cylinder block: Its characteristic is that the oil pan mounting plane is lower than the center of rotation of the crankshaft. Its advantages are good strength and rigidity, and it can withstand large mechanical loads; however, its disadvantages are poor processability, heavy structure, and difficult machining.
3. Tunnel-type cylinder block: The crankshaft main bearing holes of this type of cylinder block are integral and use rolling bearings. The main bearing holes are larger, and the crankshaft is installed from the rear of the cylinder block. Its advantages are compact structure, good rigidity and strength; the disadvantages are high processing precision requirements, poor machinability, and inconvenient crankshaft assembly and disassembly.
In order to ensure that the inner surface of the cylinder works normally at high temperatures, the cylinder and cylinder head must be properly cooled. There are two cooling methods: water cooling and air cooling. Water-cooled engines have cooling water jackets machined around the cylinder and inside the cylinder head, and the cooling water jackets of the cylinder block and cylinder head are connected. The cooling water circulates continuously in the water jacket, taking away some heat and cooling the cylinder and cylinder head.
Crankcase
The lower part of the cylinder block where the crankshaft is installed is called the crankcase, which is divided into the upper crankcase and the lower crankcase. The upper crankcase is integrated with the cylinder block, while the lower crankcase is used to store lubricating oil and seal the upper crankcase, so it is also called the oil pan. The oil pan is subjected to very little stress and is generally made of thin steel sheet by stamping. Its shape depends on the overall layout of the engine and the oil capacity. A stable oil baffle is installed on the oil pan to prevent excessive fluctuation of the oil level when the car is shaking. The bottom of the oil pan is also equipped with a drain plug, which usually has a permanent magnet to adsorb metal chips in the lubricating oil, reducing engine wear. A gasket is installed between the upper and lower mating surfaces of the crankcase to prevent lubricating oil leakage.
Cylinder Head
The cylinder head is installed on top of the cylinder block, sealing the cylinder from the top and forming the combustion chamber. It is frequently in contact with high-temperature and high-pressure gases, so it bears enormous thermal and mechanical loads. The interior of the cylinder head of a water-cooled engine is equipped with a cooling water jacket, and the cooling water holes on the lower end face of the cylinder head communicate with the cooling water holes on the cylinder block. Circulating water is used to cool high-temperature components such as the combustion chamber.