Overview of cylinder head
The cylinder head is installed on the top of the cylinder block, sealing the cylinder from above and forming a combustion chamber. It is often in contact with high-temperature and high-pressure gas, so it bears a large thermal load and mechanical load. A cooling water jacket is made inside the cylinder head of the water-cooled engine, and the cooling water holes on the lower end surface of the cylinder head communicate with the cooling water holes of the cylinder block. Use circulating water to cool high temperature parts such as combustion chamber.
The cylinder head is also equipped with inlet and exhaust valve seats and valve guide holes for installing inlet and exhaust valves, as well as intake and exhaust channels. The cylinder head of the gasoline engine has holes for installing spark plugs, while the cylinder head of the diesel engine has holes for installing injectors. A camshaft bearing hole is also machined on the cylinder head of the overhead camshaft engine to install the camshaft.
The cylinder head is generally made of gray cast iron or alloy cast iron. The aluminum alloy has good thermal conductivity, which is beneficial to improve the compression ratio.
The cylinder head is an integral part of the combustion chamber. The shape of the combustion chamber has a great influence on the operation of the engine. Due to the different combustion modes of gasoline engines and diesel engines, the parts of the cylinder head that make up the combustion chamber differ greatly. The combustion chamber of the gasoline engine is mainly on the cylinder head, while the combustion chamber of the diesel engine is mainly in the pit on the top of the piston.
Processing technology of cylinder head
The engine cylinder head is one of the most critical parts in the engine. Its precision requirements are high, the processing technology is complex, and the quality of the processing directly affects the overall performance and quality of the engine. Therefore, the processing of the engine cylinder head is particularly important. The key parts of the valve seat ring and The processing of catheter holes is even more important.
The engine inlet and exhaust valve seats are important working parts to control the gas intake and exhaust discharge. During the working process, they will be subjected to the erosion of the airflow and the impact friction of the valve at high temperature. The working conditions are very bad: during normal operation, The valve seat ring is under a high temperature of (600~800) ℃ for a long time. High-temperature gas corrosion and parts deformation will cause the valve duct and seat cone to be damaged more severely, resulting in inadequate sealing of the valve. A large amount of energy is discharged with the discharge of high-temperature gas Wasted in vain, which greatly reduces the power of the engine. Therefore, the valve seat ring and the duct hole should have good high temperature wear resistance, corrosion resistance, heat transfer and high temperature strength, high temperature creep resistance, and a coefficient of thermal expansion matching the cylinder head. At the same time, if the center of the valve deviates too much from the center of the valve seat ring when the engine is working, the engine power and fuel consumption will increase, and at the same time, the wear of the valve and the duct hole will be accelerated. Therefore, the machining accuracy of the valve seat ring and the duct hole, especially the runout of the valve cone working cone facing the duct hole, stipulates strict tolerance limits.
The general requirements for the machining accuracy of the valve seat ring and the duct hole of the engine cylinder head are: the tolerance of the coaxiality of the gasoline engine is (0.015 ~ 0.025) mm; while the diesel engine is only (0.01 ~ 0.015) mm, and the cone runout is ( 0.03～0.05) mm, the hole accuracy grade is generally H7 grade. [