The valve failure of high-speed diesel engine usually shows as follows: disc falling off, rod fracture, surfacing layer falling off, ablation, warping deformation, cone wear and serious carbon deposition. Poor working conditions, poor combustion, cooling water treatment and preheating, over speed and overload operation may lead to early fatigue damage of diesel engine valves. The matching of diesel valve and valve mechanism plays a decisive role in the function and service life of the valve. The mechanical stress of the valve mainly comes from the driving force of the valve train, the inertia force of the parts and the maximum combustion pressure of the diesel engine. The design parameters of the valve train, the geometric position and dynamic performance of the driving machinery may increase the valve stress and lead to the failure of the diesel engine valve.

气门盘部设计不合理，工作时可能在杆部与盘部过渡区产生交变应力，超出气门材料的屈服考虑到吸气作用，进气门直径要比排气门直径大15% ~20%。在增压发动机中，进、排气门盘部直径比接近1:1;气门盘部密封锥角有30°和45°两种，较大锥角可以提高气门盘部边缘的刚度，保证气门锥面与阀座密封良好，因此，大多数气门设计都采用45°锥面角。实践证明，45°锥面角不但密封良好，而且能够满足气门座圈的耐磨性要求。

The design of valve disc part is unreasonable. During operation, alternating stress may be generated in the transition zone between rod part and disc part, exceeding the yield of valve material. Considering the suction effect, the diameter of inlet valve is 15% - 20% larger than that of exhaust valve. In supercharged engine, the diameter ratio of intake and exhaust valve disc is close to 1:1; There are two kinds of valve disc sealing cone angles: 30 ° and 45 °. A larger cone angle can improve the stiffness of the edge of the valve disc and ensure good sealing between the valve cone and the valve seat. Therefore, most valve designs adopt 45 ° cone angle. Practice has proved that the 45 ° cone angle not only has good sealing, but also can meet the wear resistance requirements of valve seat ring.

气门颈部过渡锥角β和过渡半径R的大小对气流有很大的影响，锥角β应保证气流的圆滑过渡，但更重要的是能够保证气门颈部表面各处的应力分布均匀。一般来说，排气门的过渡锥角β及过渡半径R比进气门的要大些。

Transition cone angle of valve neck β And the transition radius r have a great influence on the air flow, cone angle β The smooth transition of air flow shall be ensured, but more importantly, the stress distribution on the surface of valve neck shall be uniform. Generally speaking, the transition cone angle of exhaust valve β And the transition radius R is larger than that of the inlet valve.

R尺寸-一般为气门盘外圆D的0.2~0.5倍;β值一般为15°~30°。另外在均布压力作用下，气门盘的变形主要发生在盘外缘，在气门盘部厚度一定的情况下，气门盘的刚性主要取决于β和R的大小。

R dimension - generally 0.2 ~ 0.5 times of valve disc outer circle D; β The value is generally 15 ° ~ 30 °. In addition, under the action of uniform pressure, the deformation of the valve disc mainly occurs at the outer edge of the valve disc. When the thickness of the valve disc is certain, the rigidity of the valve disc mainly depends on β And r.

为便于加工，进、排气门的长度尺寸在设计中一般保持-致。对于采用双金属摩擦焊接的排气门，应保证焊缝处避免高温燃气的直接冲刷与腐蚀，设计中一般使气门在大升程时，杆部焊缝处保留在气门导管里面。大量试验证明，进气门大升程取(0.26 ~0.28 )d，排气门大升程取(0.3~0. 35)d时，换气效果佳。

In order to facilitate processing, the length dimension of inlet and exhaust valves is generally maintained in the design. For the exhaust valve with bimetallic friction welding, the direct erosion and corrosion of high-temperature gas shall be avoided at the weld. In the design, generally, when the valve is at the maximum lift, the weld at the rod shall be retained in the valve guide. A large number of tests show that when the maximum lift of inlet valve is (0.26 ~ 0.28) D and that of exhaust valve is (0.3 ~ 0.35) d, the ventilation effect is the best.

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