Introduction of The Valve Train

Engine gas distribution mechanism is in accordance with the engine in each cylinder work cycle and ignition sequence requirements, time to open and close the cylinder intake and exhaust valves, so that the fresh combustible mixture or air to enter the cylinder in time, the exhaust gas from the cylinder in time to discharge. In the compression and work stroke, close the valve to ensure the sealing of the combustion chamber.

Requirements of The Valve Train

The requirements of the valve train parts are structural parameters and form is conducive to reduce the intake and exhaust resistance, and into, exhaust valve opening moment and the continuation of the opening time is more appropriate, so that the intake and exhaust are as full as possible to get a larger power torque and emission performance.

Fresh mixture or air filled with the degree of cylinder, with inflation efficiency to indicate. The higher the filling efficiency, indicating that the fresh air into the cylinder or combustible mixture of gas quality, the greater the heat of combustion mixture may be issued, the greater the engine power. For a certain volume of the engine, the quality and the end of the air intake T and P. The lower the T and P of the air intake, the greater the quality of the air intake, the higher the efficiency of inflation.

But because of the intake system resistance to the gas caused by the end of the cylinder pressure drop, and because of the residual high temperature exhaust gas in the last cycle, so that the end of the gas temperature, the actual quality of the gas into the total less than in the general state of the full cylinder gas quality. In other words, the inflation efficiency is always less than 1. Generally 0.8~0.9.

Layout type

Valve overhead type

Valve overhead type is one of the most widely used gas distribution mechanism type. Intake and exhaust valves are upside down on the cylinder head. Valve group includes valve, valve guide, valve seat, spring seat, valve spring, locking plate and other parts; valve transmission group generally consists of rocker arm, rocker arm shaft, push rod, tappet, camshaft and timing gear. When the working cycle of the cylinder requires the valve to be opened for air change, the crankshaft drives the camshaft to rotate through the transmission mechanism (such as timing gear), so that the cam projection on the camshaft pushes the rocker arm through the tappet, push rod and adjusting screw, and the other end of the rocker arm pushes the valve downward, while further compressing the spring. When the apex of the cam projection turns over the tappet, the thrust on the tappet is gradually reduced, and the valve opening is gradually reduced under the action of the spring tension until it is finally closed. During the compression and work stroke, the valve closes tightly under the action of the spring tension.

Camshaft arrangement type

Under camshaft type air distribution mechanism: The camshaft is installed in the crankcase and is driven by the crankshaft directly by meshing the camshaft timing gear with the crankshaft timing gear. The valve transmission group includes all the above parts, and its application is the most widespread.
Mid-camshaft distribution mechanism: The camshaft is located in the upper part of the cylinder block. In order to reduce the mass of reciprocating motion of valve transmission mechanism, for high speed engines, the position of camshaft can be moved to the upper part of the cylinder block, and the rocker arm is driven directly by the camshaft through the tappet and the push rod is omitted. The crankshaft and camshaft are far away from the centerline of the distribution mechanism, and an intermediate gear is generally added in the middle.
Camshaft top-mounted air distribution mechanism: The camshaft is arranged on the cylinder head. The camshaft drives the valve directly through the rocker arm, without tappet and push rod, so the mass of reciprocating motion is greatly reduced, and the requirement for camshaft and valve spring is the lowest, so it is suitable for high speed reinforced engine.

Camshaft drive method

The camshaft is driven by the crankshaft to rotate, and they can be driven by timing gears, timing chains or timing belts. For each completed work cycle of a four-stroke engine, the crankshaft rotates twice and the intake and exhaust valves of each cylinder open once, i.e. the camshaft turns only once, so the ratio of crankshaft to camshaft is 2:1.