附 錄 Crankshaft design requirements and working conditions Crankshaft is in constant cyclical changes in the gas pressure, reciprocating and rotating motion of the inertial force and the quality of their work under the joint action of the moment, so that both the torsion and bending the crankshaft, resulting in fatigue, stress state； internal imbalance of the engine crankshaft also withstand bending moment and shear force； not taken measures to make the crankshaft torsional vibration damping effect may also be a large amplitude torsional elastic torque. These loads are cross degeneration, may cause fatigue failure of the crankshaft. Practice shows that the bending has a decisive role in bending fatigue failure is the main failure modes. Therefore, the structural strength of the crankshaft bending fatigue strength is the focus, the crankshaft is designed to be committed to improving the fatigue strength of the crankshaft. Crankshaft complex shape, stress concentration is very serious, especially in the connecting rod journal and the crank arm of the fillet and lubricants at the stress concentration near the exit hole is particularly prominent. Common crankshaft fracture, fatigue crack begins with fillet and the hole place. Figure 7-1 shows the crankshaft bending fatigue and fatigue failure of the reverse situation. Root bending fatigue cracks in the surface of the fillet from the journal at the development of the crank, the crank is basically broken into 450； torsion fatigue damage is usually bad from the machining start hole edge, about 450 cut into the crank pin. Therefore, in the design of the crankshaft, pay special attention to finding ways to ease stress concentration, strengthen the stress concentration. Crankshaft journal at a very high ratio of pressure to a large relative velocity of sliding friction in the bearings in place. The bearings in the actual operation conditions changed conditions does not always guarantee a liquid friction, especially when the oil is not clean, the journal was a strong abrasive wear surface, making the actual life of the crankshaft greatly reduced. Therefore, the design, to wear to the friction surface, and the appropriate material bearing a good match. Crank in the crankshaft is the central link, the stiffness is very important. If the crankshaft bending stiffness, then the possible occurrence of more severe bending, the piston rod and bearing deterioration in working conditions greatly affect the reliability of these parts work and durability, even the crankcase is too large and the local stress cracking. Crankshafts torsional stiffness is poor, the working speed range may be a strong torsional vibration. Ranging from noise, such as transmission gear on the crank to accelerate the wear； while in the crankshaft fracture. Therefore, the design should ensure it has the highest possible bending stiffness and torsional stiffness. As the crankshaft by the power complex, geometric cross-section shape is rather special, in the design, has yet to reflect the objective reality of a theoretical formula for Universal. Therefore, the current design of the crankshaft design relies mainly on experience. 曲軸的工作條件和設(shè)計要求 曲軸是在不斷周期性變化的氣體壓力、往復(fù)和旋轉(zhuǎn)運動質(zhì)量的慣性力以及它們的力矩共同作用下工作的，從而使曲軸既扭轉(zhuǎn)又彎曲，產(chǎn)生疲勞應(yīng)力狀態(tài)；對內(nèi)不平衡的發(fā) 動機曲軸還承受內(nèi)彎矩和剪力；未采取扭轉(zhuǎn)振動減振措施使曲軸還可能作用著幅值較大的扭轉(zhuǎn)振動彈性力矩。這些載荷都是交變性的，可能引起曲軸疲勞失效。實踐表明，彎曲載荷具有決定性作用，彎曲疲勞失效是主要破壞形式。因此曲軸結(jié)構(gòu)強度的研究重點是彎曲疲勞強度，曲軸設(shè)計上要致力于提高曲軸的疲勞強度。 曲軸形狀復(fù)雜，應(yīng)力集中現(xiàn)象相當(dāng)嚴(yán)重，特別在連桿軸頸與曲柄臂的過渡圓角處和潤滑油孔出口附近的應(yīng)力集中尤為突出。通常的曲軸斷裂、疲勞裂紋都始于過渡圓角和油孔處。圖 7-1 表明了曲軸彎曲疲勞破壞和扭轉(zhuǎn)疲勞破壞的情況。彎曲疲勞裂縫從軸頸根 部表面的圓角處發(fā)展到曲柄上，基本上成 450 折斷曲柄；扭轉(zhuǎn)疲勞破壞通常是從機械加工不良的油孔邊緣開始，約成 450 剪斷曲柄銷。所以，在設(shè)計曲軸時，要特別注意設(shè)法緩和應(yīng)力集中現(xiàn)象，強化應(yīng)力集中部位。 曲軸各軸頸在很高的比壓下，以很大的相對速度在軸承中發(fā)生滑動摩擦。這些軸承在實際變工況運轉(zhuǎn)條件下并不總能保證為液體摩擦，尤其當(dāng)潤滑油不潔凈時，軸頸表面遭到強烈的磨料磨損，使得曲軸的實際使用壽命大大降低。所以，設(shè)計時，要使其各摩擦表面耐磨，并匹配好適當(dāng)材料的軸瓦。 曲軸是曲柄連桿機構(gòu)中的中心環(huán)節(jié)，其剛度亦很重要。如果曲軸 彎曲剛度不足，則可能發(fā)生較劇烈的彎曲振動，使活塞連桿和軸承