When the valve is working, if a slow rotary motion can be generated, the circumferential temperature distribution of the valve head can be relatively uniform, thereby reducing the thermal deformation of the valve head. At the same time, when the valve rotates, it produces a slight friction on the sealing cone surface, which can remove the deposit on the cone surface.
1. Working conditions of the valve
The working conditions of the valve are very bad. First of all, the valve is directly in contact with the high-temperature gas, which is severely heated, and the heat dissipation is difficult, so the valve temperature is high. Secondly, the valve is subjected to the action of the gas force and the valve spring force, and the inertial force of the moving member of the valve train causes the valve to be impacted when it is seated. Third, the valve opens and closes at a very high speed under poor lubrication conditions and reciprocates at high speed in the valve guide. In addition, the valve is corroded by contact with corrosive gases in the high temperature gas.
2, valve material
Intake valves are generally made of medium carbon alloy steel, such as chrome steel, chrome molybdenum steel and nickel chrome steel. The exhaust valve is made of heat-resistant alloy steel, such as silicon chrome steel, silicon chromium molybdenum steel, silicon chromium manganese steel.
3. Valve structure
The intake and exhaust valves of the automobile engine are all mushroom-shaped valves, which are composed of a valve head and a valve stem. The top surface of the valve has a shape such as a flat top, a concave top and a convex top. At present, the most widely used flat-top valve is simple in structure, convenient in manufacture, small in heat-receiving area, and can be used in both intake and exhaust valves.
The valve is sealed by a cone between the valve seat and the valve seat. The angle between the valve cone and the top surface of the valve is called the valve cone angle. The valve cone angles of the intake and exhaust valves are generally 45°, and only a few engines have an intake valve cone angle of 30°.
Part of the heat received by the valve head is transmitted to the cylinder head through the valve seat; the other part is also transmitted to the cylinder head through the valve stem and the valve guide, and is finally carried away by the coolant in the cylinder cover water jacket. In order to enhance heat transfer, the sealing cone of the valve and valve seat must be tightly fitted. For this reason, the two must be paired and ground, and they cannot be interchanged after grinding. The valve stem has high machining accuracy and low roughness, and maintains a small clearance gap with the valve guide to reduce wear and provide good guiding and heat dissipation. The shape of the end of the valve is determined by the way the upper valve spring seat is fixed. The upper valve spring seat is fixed by a valve lock clip which is divided into two halves and has a tapered outer surface. The utility model has the advantages of simple structure, reliable work and convenient disassembly and assembly, and thus has been widely used. The inner surface of the valve lock clip has various shapes, and correspondingly, the valve tail end also has various types of valve lock clamping grooves. The use of a medium air door valve on some highly reinforced engines is designed to reduce valve mass and reduce inertia of valve motion. In order to reduce the temperature of the exhaust valve and enhance the heat dissipation capability of the exhaust valve, sodium cooling valves are used on many automobile engines. This valve is filled with half of the metal sodium in the hollow valve stem. Because sodium has a melting point of 97.8 ° C and a boiling point of 880 ° C, when the valve is working, sodium becomes liquid, violently shaking up and down in the valve stem, continuously absorbing heat from the valve head and transmitting it to the valve stem, and then The valve guide is transmitted to the cylinder head to cool the valve head.
