【作者】 朱振林；

【导师】 刘宏伟； 苏学军；

【作者基本信息】 吉林大学 ， 车辆工程， 2010， 硕士

【摘要】 面对石油资源日益枯竭和人们对能源需求不断增加的矛盾,如何保证传统燃料客车最大限度的节能,是当前阶段各生产企业追求的重要指标。在客车发展过程中,由于国内客车以前无专用底盘,多是采用货车底盘进行改装而成。对发动机进、排气、冷却系统的设计匹配与验证基本上是采用经验设计和试验场试验及市场用户实地运行,根据市场反馈的问题再进行改进,改进速度慢,没有必要的试验办法和试验数据来反映发动机工作时的真实情况,从而不能得到有效的改进和提高,致使发动机使用工况差、油耗居高不下。近几年,随着客车技术的发展及国外客车技术的进入以及国家对能源的政策导向,越来越多的制造业将能耗指标作为产品的主要性能要求,因此,过去的思路和方法已不能满足当前形势发展的需要,如何对发动机外围附件进行合理的设计与匹配,如何采集发动机进气系统相关真实数据,并在理论的指导下进行部件的优化设计,确保发动机达最佳工作状态,成为客车底盘发动机附件匹配设计的重点。本文以中通客车LCK6122D2车型选配的发动机附件为研究对象,对发动机的进气系统、排气系统、冷却系统进行选配并优化试验,力求使发动机得到理想的性能发挥,最终达到发动机的使用要求。发动机附件对发动机性能的正常发挥起着至关重要的作用,由于发动机实际工况非常复杂,所以对发动机附件的工作要求较高,而在发动机附件匹配过程中,理论计算的方法很难充分体现发动机运行的各种工况。在发动机附件匹配设计时,首先根据发动机的要求对发动机附件进行初步选择和设计,并根据经验进行结构选择与初步计算,部分部件借助于试验进行检测,但由于条件所限,各附件在进行实际检测时不可能完全模拟发动机的实际使用工况,所以,整机厂对各附件装机后的匹配试验至关重要。本文根据相关标准及发动机要求,制定了合适的试验方案,对发动机附件中的空气滤清器、中冷器、散热器等重要部件的性能数据进行提取,通过试验数据的分析验证附件匹配合理性。本文采用负荷拖车牵引试验法,对发动机各附件的输出结果进行提取,然后对测试数据进行分析。负荷拖车牵引试验法是以刚性连接的方式与试验车辆连接,试验车以合适的档位、油门保持到底状态牵引负荷拖车全速行驶,通过调整负荷拖车的状态来调整试验负荷,使发动机分别以最大功率和最大扭矩及最佳经济运行转速三种状态运转。试验时全程监测连续记录发动机出水温度、发动机机油温度及试验环境温度,直至发动机出水温度和机油温度在连续3min内的变化稳定在1℃以内时,即认为达到发动机热平衡状态。本文对最大功率和最大扭矩及最佳经济运行转速下三个状态点的发动机各附件运行数据进行提取后发现了问题点:中冷器阻力偏出合格范围。中冷器的阻力太大,会影响进气密度,进而影响发动机性能,必须进行改进。在发动机各附件中,中冷器的性能参数由于受制造水平和设计水平的制约,比较难以达到设计要求,虽然生产厂商在根据主机厂提供的参数作成产品后进行过相应的风洞实验,对中冷器的进出口温度和压力进行了测试,但其试验环境很难与实际工况吻合,所以本文对中冷器进行了改进分析、仿真计算和试验验证,之后重点对改进后的中冷器采用CFD即计算流体力学进行分析,得出了计算仿真和试验数据较一致的结论,从而验证了试验仿真结果的可靠。通过附件选取、试验验证、CFD仿真分析及试验,总结出了中冷器设计与开发的相关流程方法。主要研究内容和结论总结如下:1、发动机附件的作用和匹配设计要求。发动机附件对发动机性能的正常发挥起着至关重要的作用,首先对发动机各附件的作用进行了阐述,结合工作实践,明确了发动机各附件的匹配设计要求。2、LCK6122D2型客车的发动机附件匹配设计。按照提出的发动机附件匹配设计要求,对LCK6122D2型客车的发动机附件进行了具体的匹配设计。3、发动机附件性能参数测量与分析。试验是对理论设计的有效验证,从试验中可以发现设计中存在的问题及下一步改进工作的方向。本文采用负荷拖车牵引试验法,对发动机各附件的输出结果进行测量,然后对测试数据进行分析,得出了改进的方向并进行了改进。4、重点对中冷器进行了建模,采用CFD(计算流体力学)软件对中冷器的结构进行了分析,找出不合理元素并进行优化,用优化后的结构进行试验,试验结果达到设计要求,从而得出了实际设计过程中中冷器的设计技巧,总结出了中冷器设计的相关流程方法:1)在实际设计过程中进行中冷器匹配时,首先对中冷器的设计参数进行提取,然后根据参数的要求进行结构设计,对产品进行风洞实验,对设计结构进行验证。2)由于发动机在大进气流量的满负荷条件下,要获得足够低的温度,因此,在具体设计时,对中冷器应按满负荷条件下设计。一般我们用最大功率点的条件去设计,用最大扭矩点去校核。3)对于冷却能力合乎要求,而压力降超标的结构进行分析时,要对中冷器及连接管路的具体结构进行分析,原因可能是:发动机进出气管弯曲太多,流道太长;气室设计不合理;进出气管直径太小,进出气管口截面变化太激烈,管子全部为软管等,采用CFD技术对中冷器进行流场分析,可以有效给出解决方案。4)在最大功率点,由于进气流量大,中冷器内部压力降容易超标,在最大扭矩点,由于冷风流量较小,中冷器散热性能难以达到要求,而冷却能力的改善和压降的降低两者没有明确的换算公式,只能应用试验手段来进行确认。5)冷却效果的好坏除发动机附件本身的性能外,还取决于冷却空气流通渠道的设计好坏,所以,在设计冷却空气流道时:ⅰ、确保中冷器的迎风面积:对于侧面进风的结构,侧仓门的进风孔面积应不低于散热器芯体迎风面积的80%,最好大于散热器芯部的正面面积。ⅱ、确保发动机仓和进风室仓进行隔离,两仓之间采取必要的隔热措施。ⅲ、将中冷器和散热器叠放在一起时的间隙用适当的材料予以消除。ⅳ、尽量使风扇护风罩内部结构圆滑,为保证空气流通效率,应使风扇叶和散热器芯体保持一定距离,一般取80-130mm;同时使风扇和护风罩之间距离尽量小,一般取5-15mm。ⅴ、为保证冷却空气的流速,应使冷却风扇对发动机输出有一定的传动比。一般是:发动机曲轴和冷却风扇之间转速传动比为1~1.2。ⅵ、在不影响总体效果的前提下,尽量加大风扇后部气流出口,以使气流顺利导出。ⅶ、为防止发动机下部热源返流至进气口处,应对发动机下部和散热器下部加装隔热板。更多还原

【Abstract】 With facing the conflict of the lack of petroleum resource and the people`s increasing requirement for energy sources , the important index for enterprises of present stage is to assure how to save the energy resource maximum for traditional fuel. During the development of bus, domestic bus mostly adopt modified truck chassis, because of there is no special bus chassis at that time. Regarding the design matching and testing for engine air intake and exhaust/cooling system, mostly through experience design and tested by testing factory as well as the operation in market by clients, and make modification based on the feedback from the market, and the modification speed is very slowly, there is no good testing method and testing data to reflect the real working condition of engine, and that can not get effective modification and improvement, and result in bad working condition of engine and high fuel consumption.In recently years, along with the development of bus technology and the introduction of overseas bus technology, more and more manufacturer take index of energy consumption as the main performance requirements for the products, so the old opinions and method can not meet the requirement for present development, in this case how to design and match the engine accessories, how to get the real data of engine air intake system and optimize it by the instruction of theory, to assure the best working condition of engine, will become the emphasis during the matching design for the accessories of bus chassis engine.This text take Zhongtong Bus LCK6122D2 engine accessories as the reach object, and design and match for engine air intake parts, exhaust parts , cooling system parts and take optimization test, try to make engine reach the best performance , and meet the use requirements for engine. Engine accessories play an important role for the performance of engine, during the matching design for engine accessories, because of the complicated engine real working condition, so it will have higher requirement for engine accessories, but during the process of matching of engine accessories, the theory calculation can not fully reflect all kinds of working condition of engine. So that during the matching of engine accessories, firstly we make the initial selection and design for engine accessories, and carrying configuration selection and initial calculation based on our experience, and some parts were tested with the support of trial. But because of the limit of condition, it can not completely simulate all kinds of engine working condition, so it is very important for engine factory to test engine accessories for the matching situation. According to the relative standard and the requirement for the engine, and make suitable testing plan, to get the performance data of key parts of air cleaner, inter–cooler, radiator etc, and by analyzing the data to find the unsuitable accessories, by analyzing the data to validate the matching reasonableness of such accessories.Trial is efficiency verification for the theory design, we can find the potential problem of design and the direction for the next modification.This text adopt load trailer towing test method, to get the output result for engine accessories, then analyze the data to find the un-matching accessories. Load trailer towing full load driving test is to connect the testing vehicle by rigid connection, the testing vehicle tow the loaded trailer by full speed with the suitable gear and fully opened throttle valve.By adjusting the condition of load trailer to adjust testing load, to make sure the engine running under three condition separately of Max. speed, Max. torque and best economic operation, at the same time to make the vehicle driving by full load. During the test, to survey and note down the engine water temperature, engine oil temperature and test environment temperature, until the change of the engine water and oil temperature within 1℃in continuous 3 min, it will be regarded as to reach engine thermal equilibrium state. This test get the data under three condition point of Max. speed, Max. torque, best economic operation, and find the problems: inter cooler resistance is beyond the qualified range, if the inter cooler resistance is too big it will effect the air intake density, further more will effect engine performance, and it must to be modified.Based on design experience and this testing result, among engine accessories, the inter cooler is difficult to reach the design requirement because of the limit of manufacture level and design level, though the manufacturer carry the relevant wind tunnel test based on the parameter provided by the engine plant, and test the air intake and outlet temperature as well as the pressure, but the testing environment is hard to accord with the real working condition, in this case this text carry checking calculation after make some modification to inter cooler, then mainly analyze the modified inter cooler by using CFD ( calculate fluid mechanics), and get the conclusion that the calculation simulation is nearly accord with the testing result, thereby test and verify the test simulation result is reliable.Through selection of accessories , testing and verify, CFD simulation analysis and test, and get the conclusion of inter cooler design and development process method, the main research contains and conclusion are as follows:1、The role of engine accessories and the requirement for matching. Engine accessories play an important role for the engine performance, firstly make explanation for the role of engine accessories and combine with working practice, make clear the matching design requirements for each engine accessories.2、The matching design for LCK6122D2. According to the engine accessories matching requirement to carry the matching design for LCK6122D2 engine accessories.3、Engine accessories performance parameter measurement and analysis. Testing is the effective verification for theory design, from the test we can find the present problems and make the modification direction. This text adopt load trailer towing testing method, and test the output result of engine accessories, then make analysis for the testing data, get the modification direction and carry the modification at the same time.4、Mainly carry the modeling analysis for inter cooler, adopt CFD software to analyze the construction of inter cooler and find the unreasonable factors and make the optimization, and test the optimized construction, and the test result reach the requirement of design, thereby get the design tactics for inter cooler during the process of real design, and get the conclusion of inter cooler design process method.1)When match the intercooler during the process of design, firstly should get the design parameter of inter cooler, and then make the structural design based on the requirement of parameter, carry the wind tunnel test, and verify the designed structure.2)Because of the engine need to get enough low temperature under the full load condition with big air suction flow, in this case inter cooler should be designed under full load condition, normally we design it based on the Max. power condition and to verify by Max. torque.3)To analyze the structure of which the cooling capacity is qualified but the fall of pressure exceed standard, we should analyze the structure of inter cooler and its connection pipes, the reasons probable are: too many curves for engine air intake and air exit pipes, pipes too long; unreasonable design for air chamber; too small diameter of air intake and air exit pipe, section of air intake and air outlet change too sharp, all are soft pipes etc, to analyze inter cooler by adopting CFD , and can provide effective solution.4)At the Max.power point, inter cooler inside pressure drop is easy to exceed standard because of the big air suction flow, because of the cool air flow is small, inter cooler heat dispersion can not reach the requirements, while the improvement for cooling capacity and the reduction of pressure drop have no specific formula, can only using testing method to verify.5)The cooling effect depends on the design of cooling air flow pipes except the performance of engine accessories itself, so when design the cooling air pipes, we should:ⅰ、To assure the windward area of inter cooler, and the side air intake structure , side luggage door air inlet should not be less than windward of core.ⅱ、To assure that the partition between engine compartment and air intake chamber , and should take heat insulation method.ⅲ、Using suitable material to eliminate the clearance between inter cooler and radiator when these two put together.ⅳ、To assure the internal structure of fan cover smooth, to assure a kind of distance between fan leaf and radiator core, generally 80-130mm, at the same time to assure the as short distance as can between fan and fan cover, generally 5-15mm. ⅴ、To assure the cooling air flow speed, should keep fixed transmission ratio between cooling fan and engine output. Generally:The transmission ratio between engine crankshaft and cooling fan : 1~1.2ⅵ、To enlarge the air outlet at the back of fan without effect the overall performance.ⅶ、To stop the heat air return the air inlet, should install insulation panel under engine bottom and radiator botoom.更多还原