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.

氣門盤部設(shè)計不合理，工作時可能在桿部與盤部過渡區(qū)產(chǎn)生交變應(yīng)力，超出氣門材料的屈服考慮到吸氣作用，進(jìn)氣門直徑要比排氣門直徑大15% ~20%。在增壓發(fā)動機中，進(jìn)、排氣門盤部直徑比接近1:1;氣門盤部密封錐角有30°和45°兩種，較大錐角可以提高氣門盤部邊緣的剛度，保證氣門錐面與閥座密封良好，因此，大多數(shù)氣門設(shè)計都采用45°錐面角。實踐證明，45°錐面角不但密封良好，而且能夠滿足氣門座圈的耐磨性要求。

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.

氣門頸部過渡錐角β和過渡半徑R的大小對氣流有很大的影響，錐角β應(yīng)保證氣流的圓滑過渡，但更重要的是能夠保證氣門頸部表面各處的應(yīng)力分布均勻。一般來說，排氣門的過渡錐角β及過渡半徑R比進(jìn)氣門的要大些。

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-一般為氣門盤外圓D的0.2~0.5倍;β值一般為15°~30°。另外在均布壓力作用下，氣門盤的變形主要發(fā)生在盤外緣，在氣門盤部厚度一定的情況下，氣門盤的剛性主要取決于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.

為便于加工，進(jìn)、排氣門的長度尺寸在設(shè)計中一般保持-致。對于采用雙金屬摩擦焊接的排氣門，應(yīng)保證焊縫處避免高溫燃?xì)獾闹苯記_刷與腐蝕，設(shè)計中一般使氣門在大升程時，桿部焊縫處保留在氣門導(dǎo)管里面。大量試驗證明，進(jìn)氣門大升程取(0.26 ~0.28 )d，排氣門大升程取(0.3~0. 35)d時，換氣效果佳。

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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