外文翻译汽车差速器.doc

Failure analysis of an automobile differential pinion shaftAbstractDifferential is used to decrease the speed and to provide moment increase for transmitting the movement coming from the engine to the wheels by turning it according to the suitable angle in vehicles and to provide that inner and outer wheels turn differently. Pinion gear and shaft at the entrance are manufactured as a single part whereas they are in different forms according to automobile types. Mirror gear which will work with this gear should become familiar before the assembly. In case of any breakdown, they should be changed as a pair. Generally, in these systems there are wear damages in gears. The gear inspected in this study has damage as a form of shaft fracture.In this study, failure analysis of the differential pinion shaft is carried out. Mechanical characteristics of the material are obtained first. Then, the microstructure and chemical compositions are determined. Some fractographic studies are carried out to asses the fatigue and fracture conditions.Keywords: Differential; Fracture; Power transfer; Pinion shaft1. IntroductionThe final-drive gears may be directly or indirectly driven from the output gearing of the gearbox. Directly driven final drives are used when the engine and transmission units are combined together to form an integral construction. Indirectly driven final drives are used at the rear of the vehicle being either sprung and attached to the body structure or unsprung and incorporated in the rear-axle casing. The final-drive gears are used in the transmission system for the following reasons 1:(a) to redirect the drive from the gearbox or propeller shaft through 90° and,(b) to provide a permanent gear reduction between the engine and the driving road-wheels.In vehicles, differential is the main part which transmits the movement coming from the engine to the wheels. On a smooth road, the movement comes to both wheels evenly. The inner wheel should turn less and the outer wheel should turn more to do the turning without lateral slipping and being flung. Differential, which is generally placed in the middle part of the rear bridge, consists of pinion gear, mirror gear,differential box, two axle gear and two pinion spider gears.A schematic illustration of a differential is given in Fig. 1. The technical drawing of the fractured pinion shaft is also given in Fig. 2. Fig. 3 shows the photograph of the fractured pinion shaft and the fracture section is indicated.In differentials, mirror and pinion gear are made to get used to each other during manufacturing and the same serial number is given. Both of them are changed on condition that there are any problems. In these systems, the common damage is the wear of gears 24. In this study, the pinion shaft of the differential of aminibus has been inspected. The minibus is a diesel vehicle driven at the rear axle and has a passenger capacity of 15 people. Maximum engine power is 90/4000 HP/rpm, and maximum torque is 205/1600 Nm/rpm. Its transmission box has manual system (5 forward, 1 back). The damage was caused by stopping and starting the minibus at a traffic lights. In this differential, entrance shaft which carries the pinion gear was broken. Various studies have been made to determine the type and possible reasons of the damage.These are: studies carried out to determine the material of the shaft; studies carried out to determine the micro-structure; studies related to the fracture surface.There is a closer photograph of the fractured surfaces and fracture area in Fig. 4. The fracture was caused by taking out circular mark gear seen in the middle of surfaces.Fig. 1. Schematic of the analysed differential.Fig. 2. Technical drawing of the analysed pinion shaftFig. 3. The picture of the undamaged differential pinion analysed in the studyFig. 4. Photographs of failed shaft2. Experimental procedure Specimens extracted from the shaft were subjected to various tests including hardness tests and metallographic and scanning electron microscopy as well as the determination of chemical composition. All tests were carried out at room temperature.2.1. Chemical and metallurgical analysis Chemical analysis of the fractured differential material was carried out using a spectrometer. The chemical composition of the material is given in Table 1. Chemical composition shows that the material is a low alloy carburising steel of the AISI 8620 type.Hardenability of this steel is very low because of low carbon proportion. Therefore, surface area becomes hard and highly enduring, and inner areas becomes tough by increasing carbon proportion on the surface area with cementation operation. This is the kind of steel which is generally used in mechanical parts subjected do torsion and bending. High resistance is obtained on the surface and high fatigue endurance value can be obtained with compressive residual stress by making the surface harder 57.In which alloy elements distribute themselves in carbon steels depends primarily on the compound- and carbide-forming tendencies of each element. Nickel dissolves in the a ferrite of the steel since it has less tendency to form carbides than iron. Silicon combines to a limited extent with the oxygen present in the steel to form nonmetallic inclusions but otherwise dissolves in the ferrite. Most of the manganese added to carbon steels dissolves in the ferrite. Chromium, which has a somewhat stronger carbide-forming tendency than iron, partitions between the ferrite and carbide phases. The distribution of chromium depends on the amount of carbon present and if other stronger carbide-forming elements such as titanium and columbium are absent. Tungsten and molybdenum combine with carbon to form carbides if there is sufficient carbon present and if other stronger carbide-forming elements such as titanium and columbium are absent. Manganese and nickel lower the eutectoid temperature 8.Preliminary micro structural examination of the failed differential material is shown in Fig. 5. It can be seen that the material has a mixed structure in which some ferrite exist probably as a result of slow cooling and high Si content. High Si content in this type of steel improves the heat treatment susceptibility as well as an improvement of yield strength and maximum stress without any reduction of ductility 9. If the microstructure cannot be inverted to martensite by quenching, a reduction of fatigue limit is observed.Table 1 Chemical analysis of the pinion gear material (wt%)Fe C Si Mn P S Cr Mo Ni 96.92 0.235 0.252 0.786 0.044 0.016 0.481 0.151 0.517 and fracture surfaces.Fig. 5. Micro structure of the material (200·).There are areas with carbon phase in Fig. 5(a). There is the transition boundary of carburisation in Fig. 5(b) and (c) shows the matrix region without carburisation. As far as it is seen in these photographs, the piece was first carburised, then the quenching operation was done and than tempered. This situation can be understood from blind martensite plates.2.2. Hardness testsThe hardness measurements are carried out by a MetTest-HT type computer integrated hardness tester. The load is 1471 N. The medium hardness value of the interior regions is obtained as 43 HRC. Micro hardness measurements have been made to determine the chance of hardness values along the cross-section because of the hardening of surface area due to carburisation. The results of Vickers hardness measurement under a load of 4.903 N are illustrated in Table 2.2.3. Inspection of the fractureThe direct observations of the piece with fractured surfaces and SEM analyses are given in this chapter. The crack started because of a possible problem in the bottom of notch caused the shaft to be broken completely. The crack started on the outer part, after some time it continued beyond the centre and there was only a little part left. And this part was broken statically during sudden starting of the vehicle at the traffic lights. As a characteristic of the fatigue fracture, there are two regions in the fractured surface. These are a smooth surface created by crack propagation and a rough surface created by sudden fracture. These two regions can be seen clearly for the entire problem as in Fig. 4. The fatigue crack propagation region covers more than 80% of the cross-section.Table 2 Micro hardness values Distance from surface (lm) 50 100 200 400 CenterValues HV (4903N) 588 410 293 286 263Fig.Fig. 6. SEM image of the fracture surface showing the ductile shear.Fig. 7. SEM image of the fracture surface showing the beach marks of the fatigue crack propagation.Shaft works under the effect of bending, torsion and axial forces which affect repeatedly depending on the usage place. There is a sharp fillet at level on the fractured section. For this reason, stress concentration factors of the area have been determined. Kt = 2.4 value (for bending and tension) and Kt = 1.9 value (for torsion) have been acquired according to calculations. These are quite high values for areas exposed to combined loading.These observations and analysis show that the piece was broken under the influence of torsion with low nominal stresses and medium stress concentration 10.The scanning electron microscopy shows that the fracture has taken place in a ductile manner (Fig. 6). There are some shear lips in the crack propagation region which is a glue of the plastic shear deformations. Fig. 7 shows the beach marks of the fatigue crack propagation. The distance between any two lines is nearly 133 nm.3. ConclusionsA failed differential pinion shaft is analysed in this study. The pinion shaft is produced from AISI 8620 low carbon carburising steel which had a carburising, quenching and tempering heat treatment process. Mechanical properties, micro structural properties, chemical compositions and fractographic analyses are carried out to determine the possible fracture reasons of the component. As a conclusion, the following statements can be drawn: The fracture has taken place at a region having a high stress concentration by a fatigue procedure under a combined bending, torsion and axial stresses having highly reversible nature. The crack of the fracture is initiated probably at a material defect region at the critical location. The fracture is taken place in a ductile manner. Possible later failures may easily be prevented by reducing the stress concentration at the critical location.AcknowledgementThe author is very indebted to Prof. S. Tasgetiren for his advice and recommendations during the study.H. Bayrakceken / Engineering Failure Analysis 13 (2006) 14221428References1 Heisler H. Vehicle and engine technology. 2nd ed. London: SAE International; 1999.2 Makevet E, Roman I. Failure analysis of a final drive transmission in off-road vehicles. Eng Failure Anal 2002;9:57992.3 Orhan S, Aktu¨rk N. Determination of physical faults in gearbox through vibration analysis. J Fac Eng Arch Gazi University2003;18(3):97106.4 Tasgetiren S, Aslantas K, Ucun I. Effect of press-fitting pressure on the fatigue damages of root in spur gears. Technol Res: EJMT2004;2:219.5 Nanawarea GK, Pableb MJ. Failures of rear axle shafts of 575 DI tractors. Eng Failure Anal 2003;10:71924.6 Aslantas K, Tasgetiren S. A study of spur gear pitting formation and life prediction. Wear 2004;257:116775.7 Savas V, O¨ zek C. Investigation of the distribution of temperature on a shaft with respect to the deflection. Technol Res: EJMT2005;1:338.8 Smith FW. Principles of materials science and engineering. 3rd ed. USA: McGraw-Hill Series; 1996. p. 51718.9 ASM metal handbook, vol. 1. Properties and selection, irons, steels, and high performance alloys; 1991.10 Voort GFV. Visual examination and light microscopy. ASM handbook metallography and microstructures. Materials Park(OH): ASM International; 1991. p. 10065.汽车差速器小齿轮轴的失效分析摘要差速器的作用是根据车辆合适的角度, 通过将运动转向, 为运动传输减速或者提供瞬间加速, 这个运动来自引擎, 到车轮去, 使内外车轮转动不同。开口处的游星齿轮和轮轴是作为单一零件的，但是根据车辆型号有不同的形状。和这个齿轮一起工作的镜面齿轮应该在组装前就磨合好。一旦发生故障，它们应该成对更换。一般来说，在这些系统中齿轮都存在磨损损坏。本文中检查的齿轮损坏具体说是轮轴断裂。本研究进行了差速器小齿轮轴的失效分析。首先，取得材料的机械特点，然后确定其微观结构和化学成分，还要做一些显微镜观察研究来评估其疲劳和破损状况。关键词：差速器; 破损；动力分配装置；小齿轮轴简介最终传动齿轮可能直接或间接地由齿轮箱的输出齿轮驱动。当引擎和传输设备结合在一起，形成统一结构时，就需要使用直接驱动的最终传动齿轮。间接驱动最终传动齿轮或者借助一些装置附在汽车后端，或者并入后桥壳。最终驱动齿轮由于如下原因被使用在传输系统中：(a)为了使齿轮箱或者传动轴的动力90°转向(b)为了提供引擎和驱动轮之间永久的齿轮减速。在汽车中，差速器是将运动从引擎传输到车轮的主要部件。在平坦的道路上，运动会平均分配给两个轮子。内侧车轮应该程度小一些, 外侧车轮转向程度应该大一些, 这样转弯才不会侧滑。差速器通常置于后桥中部，由游星齿轮、镜面齿轮、差速器箱、轴齿轮和两个游星蜘蛛齿轮构成。图表一是差速器的示意图，图表二是断裂的小齿轮轴的技术图解，图表三是断裂的小齿轮轴的图片，表示出了断裂部分。在差速器里，人们生产时将镜面和流星齿轮制作得相互适应，并且使用相同的序列号。出现问题的话，二者都要更换。在这些系统中，常见的损伤是齿轮磨损。本研究检查了一辆小型巴士的差速器小齿轮轴。该小型巴士是后轴驱动的柴油汽车，可搭载15名乘客。发动机最大功率是 ，最大扭转力是 。传动箱里有手动系统 (5个向前，一个向后)。损伤是由巴士在交通灯出停止和启动引起的。在差速器中，驱动流星齿轮的输入轴断裂。人们做了各种各样的研究来确定这种损伤的类型和可能的原因。它们是:确定轮轴材料的研究确定微观结构的研究与断裂面相关的研究图四是断裂表面和断裂区域的近距离照片。这个断裂是将表面中心的圆形标记齿轮取走形成的。镜面齿轮行星齿轮齿轮轴十字销太阳轮半轴图1 进行分析的差速器的图解图2 进行分析的小齿轮轴的技术图解失效十字部分图3 研究中进行分析的完好小齿轮轴的图片静态断裂区域裂纹扩展区域图4 失效轮轴的照片实验步骤从轮轴中取得的样本要接受各种各样的测试，包括硬度测试，金相和扫描电子显微镜以及化学成分的确定。左右测试均在室温下进行。化学和冶金分析断裂差速器材料的化学分析是使用光谱仪完成的。该材料的化学成分如表一所示。化学成分显示该材料是美国钢铁协会8620型的一种低合金碳化钢。这种钢的淬硬性很低，因为碳含量比例较低。因而，需要通过渗碳处理增加表面区域的碳比例，使表面区域变得坚硬，非常耐用，内部区域变得坚韧。这种钢一般用在需要扭转和弯曲的机械部件中。通过使表面变硬，用残余应力使表面获得高阻力性，获得高疲劳承受值。合金元素怎样掺入碳钢主要取决于每种元素的化合倾向和形成碳化物的倾向。镍溶解于钢的铁酸盐，因为它比铁更不容易形成碳化物。硅与钢中的氧在一定程度上结合形成非金属内含物，不然的话则溶于铁酸盐。铬比铁更容易形成碳化物一些，会在铁酸盐和碳化物阶段之间分解。掺入铬取决于碳含量以及是否没有钛、钶这样更易形成碳化物的元素存在。如果有足够的碳并且没有钛、钶这样更易形成碳化物的元素存在，钨和钼可以和碳形成碳化物。锰和镍可以降低共析混合物的温度。失效差速器材料的初步微观检验如图五所示。可以看出这种材料有一种复合结构，由于缓慢冷却和较高的硅含量，该结构中很可能存在铁酸盐。这种钢中的高硅含量可以提高受热敏感性还有提高屈服强度和最大压力，而不降低延展性。如果微观结构不能通过冷淬转化为马氏体, 就可以观察到疲劳极限降低。表1流星齿轮材料的化学分析扩散区域过渡区域渗碳区域图5 该材料的微观结构图5（a）中有处于碳阶段的区域。图五(b)中有渗碳的过渡边缘，(c)显示了未渗碳的基质区域，而后进行冷淬操作，接着再回火。这种情形可以从不易观察到的马氏体片来理解。22 硬度测试硬度测试时通过MetTest-HT型计算机集成硬度测试器进行的。其负荷为14N。内部区域的平均硬度值为43HRC，并进行了微观硬度测试，以确定渗碳引起的表面的硬化带来的横截面硬度值的变化。在4.903N的负荷量下，维式硬度计硬度测试的结果如表2所示。2.3 断裂处的检查本章给出了表面断裂的轮轴的直接观察结果和扫描式电子显微镜分析结果。刻痕底部可能的问题导致出现裂缝，使整个轮轴完全断裂。裂缝在外部开始，过一段时间断裂范围越过中心部分，只剩一小部分没有断裂。而这一部分也会在车辆在交通灯处突然启动时静止断裂。在断裂表面有两个区域，这是疲劳断裂的一个特点。有一个裂缝扩大引起的光滑表面和一个突然断裂引起的粗糙表面。这两个区域可以在图4的问题中清楚地看到。疲劳裂缝扩大区域占横截面的80%。表2微观硬度值图6 显示出断裂表面韧性剪切带的扫描式电子显微镜图像图7 显示疲劳裂缝扩散海滩纹的断裂表面的扫描电子显微镜图像轮轴在弯曲、扭转、轴向力的作用下工作，弯曲、扭转、轴线力不断影响依赖使用区域。在断裂部分有一个锋利的薄片, 这样就可以确定该区域的压力集中因素。根据计算，得知弯曲和压力的Kt值为2.4，扭转的Kt值为1.9。对于承受组合负荷的区域这些数值是相当高的。这些观察和分析显示，轮轴在很少压力，中等压力集中的情况下，受扭转影响而断裂。扫描电子显微镜显示，断裂是延展的状态下发生的（图6）。在裂缝扩散区域有一些切变裂痕，切变裂痕总是伴随切变形发生。图7 显示了疲劳裂缝扩散的海滩纹。任何两条纹之间都在133纳米左右。3.结论本文分析了失效的差速器小齿轮轴。小齿轮轴是用美国钢铁协会8620低碳渗碳钢生产的，这种钢经过渗碳、冷淬和回火热处理过程。进行了机械性质、微观结构性质、化学成分和金属断面的显微镜观察分析，以确定小齿轮轴可能的断裂原因。 可以得出以下结论：1、 断裂发生在有高压力集中的区域，这些高压力集中是由弯曲、扭转以及高度2、 可反转轴向力共同作用下的疲劳过程引起的。3、 断裂的裂缝很有可能是关键位置的材料瑕疵部位开始的。4、断裂是在延展状态下发生的。5、减少关键位置的压力集中可能很容易的避免之后可能的失效。AcknowledgementThe author is very indebted to Prof. S. Tasgetiren for his advi