Working conditions are very bad valve. First of all, a valve in direct contact with the hot gas, severe heat, the heat is difficult, so high temperature valve. Secondly, the valve and the valve receiving gas force acting spring force, and the impact due to the inertia force of the valve means so that movement of the valve seating member. Third, the valve opening and closing a very high speed in a case where lubrication conditions are very poor high speed and reciprocates within the valve guide. Further, since the contact with the gas valve in the hot gas corrosion and corrosive.
1. The valve train describes a valve
First, the valve
1. The operating conditions of the valve
is very bad working conditions the valve. First of all, a valve in direct contact with the hot gas, severe heat, the heat is difficult, so high temperature valve. Secondly, the valve and the valve receiving gas force acting spring force, and the impact due to the inertia force of the valve means so that movement of the valve seating member. Third, the valve opening and closing a very high speed in a case where lubrication conditions are very poor high speed and reciprocates within the valve guide. Further, since the contact with the gas valve in the hot gas corrosion and corrosive.
2, the valve material
of the intake valve is generally used for producing carbon steel, such as chromium steel, chromium molybdenum steel and nickel-chromium steel. The exhaust heat-resistant alloy steel, chromium steel such as silicon, silicon-chromium-molybdenum steel, silicon-chromium-manganese steel and the like.
3. The valve construction
automotive engine intake and exhaust valves are poppet valve, a valve head and a valve stem made of two parts. The valve has a flattened top surface, a concave and convex roof top shape. Currently the most widely flattened valve is simple in structure, easy to manufacture, small heating area, intake and exhaust valves can be used.
between the valve and valve seat or seal against the tapered valve seat. Angle between the top surface of the valve cone and the valve cone angle referred to as the valve. Intake, exhaust valve cone angle are generally 45 °, the taper angle of the intake valve and only a small number of the engine is 30 °
of the valve head receiving a portion of the heat transmitted to the valve seat of the cylinder head; the other part by the valve stem and valve guide are also transmitted to the cylinder head, the cylinder head are eventually coolant water jacket away. To enhance heat transfer, tapered sealing valve and valve seat must be closely bonded. To this end, both to be paired grinding, after grinding are not interchangeable. The valve stem has a high machining accuracy and low roughness valve guide with the gap kept small, to reduce wear and play a good guiding and cooling effect. The shape of the trailing end of the valve depends on the fixation of the valve spring seat. And split in half using the tapered outer surface of the air lock folder on the valve spring seat is fixed, the structure is simple, reliable, easy accessibility, it is widely used. Air lock folder inner surface of a variety of shapes, a corresponding valve trailing end have a range of different shapes of air lock clip groove. Using the air valve door lever in certain highly enhanced engine, aimed at reducing the mass and inertial forces on the valve to reduce the valve motion. In order to reduce the temperature of the exhaust valves, enhance the cooling capacity of the exhaust valve, the valve using a sodium-cooled engines in many cars. Such a valve is filled half of the sodium metal in the hollow valve stem. Because the melting point of sodium is 97.8 deg.] C, a boiling point of 880 deg.] C, so work on the valve, into the liquid sodium, the intense shaking up and down in the valve stem, the valve continue to absorb heat from the head portion and to the valve stem, and then passed to the cylinder head valve guide, the valve head is cooled.
4. The number of valves per cylinder
Usually the engine has two valves per cylinder, i.e. one intake valve and one exhaust valve. An intake valve head diameter than the large percentage of the exhaust valves 15 to 30 percentage of the object is to increase intakeBy cross-sectional area, reducing the intake resistance and increase the intake air amount. Any number of intake and exhaust valves are the same, the intake valve is better than the exhaust valve head diameter large. Two valves per cylinder engine, also known as two-valve engine. Modern high-performance automobile engine commonly used three, four, five valves per cylinder, four-valve engine which most especially in number.
two four-valve engine intake valves per cylinder, two exhaust valves. Its outstanding advantage is broken by a large area of the valve, intake and exhaust sufficiently increase the intake air amount, the engine torque and power increase. Followed by four valves per cylinder, each valve head diameter is small, the quality of each valve is reduced, inertia force is reduced, help increase the engine speed. Finally, use of four-valve engine with a combustion chamber shaped canopy, the spark plug is arranged at the center of the combustion chamber, the combustion beneficial.
2. The valve seat and the valve train seat
relative to the cylinder head and the valve cone, said bonded portion of the valve seat. High temperature valve seat, and subjected to high frequency impact load, easy to wear. Thus, most of the cast aluminum cylinder head and a cylinder head are inlaid valve seat by a powder metallurgy alloy or austenitic cast iron or steel. The cylinder head valve seat insert can extend the life of the cylinder head. There are also some cast iron cylinder head without valve seat inserts, directly to the cylinder head machined valve seat.
3. The valve train valve guide
is a function of the valve guide movement of the valve guide, the valve to ensure that linearly reciprocates in the valve and valve seat or valve seat properly bonded. Furthermore, the valve stem will be receiving heat transmitted to the cylinder head part. Higher operating temperature of the valve guide, and poor lubrication conditions, work against splashed with oil to lubricate the valve mechanism of the valve stem and valve guide bore. Valve guide made from gray cast iron, ductile iron or iron-based powder metallurgy. After a certain interference pressed into the valve guide bore cylinder head valve guide, the valve guide hole and then fine hinge to ensure proper clearance fit with the valve stem of the valve guides.
4. The valve train valve spring
function of the valve spring is able to close with the valve seat or valve seat bonded when guarantee valve closure, and to overcome generating valve means when the valve is opened the inertial force causes the drive member is always controlled by the cam without departing from each other.
of the valve spring is generally cylindrical coil spring pitch and the like. When the operating frequency is equal to the valve spring with its natural vibration frequency or an integer multiple of, the valve spring will resonate. When will the destruction of the resonance valve timing, the valve rebound and shock occurs, even the springBroken. To prevent the resonance, the structural measures can be taken:
1) on the double valve spring diesel and gasoline engines widely used in high performance mounting each valve two different diameters, the rotation in the opposite, outer spring. Due to the different natural frequencies of the two springs, one spring when resonance occurs, the other spring can play a role in damping. Dual valve spring can reduce the height of the valve spring, and when a broken spring, other spring can still maintain the valve operating. Rotation in the opposite spring, coil spring can be prevented from breaking another spring snaps into the circle can not be operated or damaged.
2) The valve spring variable pitch certain high performance gasoline engines using variable pitch single valve spring. Variable pitch spring not constant natural frequency, thereby avoiding resonance.
3) The stiffness and the natural frequency of the spring along the axial direction of the tapered conical valve spring of the valve spring is changed, thus eliminating the possibility of resonance.