The cylinder block of the water-cooled engine and the upper crankcase are often integrally molded, called a cylinder block, a crankcase, which may also be called a cylinder block. The cylinder block is generally cast from gray cast iron. The cylindrical cavity in the upper part of the cylinder block is called a cylinder, and the lower part is a crankcase supporting the crankshaft. The inner cavity is a space for crankshaft movement. A plurality of reinforcing ribs, a cooling water jacket and a lubricating oil passage are cast inside the cylinder block.
The cylinder block should have sufficient strength and rigidity. According to the position of the cylinder block and the oil pan mounting plane, the cylinder block is usually divided into the following three forms.
1. General cylinder block: It is characterized in that the oil pan mounting plane and the crankshaft rotation center are at the same height. The advantage of the cylinder block is that the height of the cylinder body is small, the weight is light, the structure is compact, the processing is convenient, and the crankshaft is easy to disassemble; but the disadvantage is that the rigidity and the strength are poor.
2. Gantry cylinder block: It is characterized in that the oil pan installation plane is lower than the rotation center of the crankshaft.
Its advantages are good strength and stiffness, and can withstand large mechanical loads; but its shortcomings are poor processability, heavy structure and difficult processing.
3. Tunnel type cylinder block: The main bearing hole of this type of cylinder block crankshaft is integral, adopting rolling bearing, the main bearing hole is large, and the crankshaft is loaded from the rear of the cylinder block. The advantages are compact structure, good rigidity and strength, but the disadvantages are high processing precision, poor processability, and inconvenient cranking.
In order to enable the inner surface of the cylinder to operate normally at high temperatures, the cylinder and cylinder head must be properly cooled. There are two cooling methods, one is water cooling and the other is air cooling. A cooling water jacket is arranged around the cylinder of the water-cooled engine and in the cylinder head, and the cylinder block and the cylinder head cooling water jacket are connected, and the cooling water continuously circulates in the water jacket to take away part of the heat to cool the cylinder and the cylinder head.