轻型货车(5+1)挡变速器设计(直接操纵、全部采用同步器换挡)【含UG三维图纸、说明书】
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含UG三维图纸、说明书
轻型货车5+1挡变速器设计直接操纵
全部采用同步器换挡
全部采用同步器换挡
货车变速器设计5+1
变速器设计含
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载货汽车变速器
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毕业设计(论 文)任务书课题名称 轻型货车(5+1)挡变速器设计 (直接操纵、全部采用同步器换挡) 系 别 汽车工程系专 业 班 级 学 号 姓 名 指导教师 年 02月 13日教研室主任 年 02月 13日系 主 任 年 02 月 13日 年2月13日一、课题的主要内容和基本要求:参数:发动机: =220; 车速:=90 ;额定转速:n= 3200 RPM; 车轮滚动半径:R01= 0.366 m ;汽车总质量:4490 Kg ;爬坡度:30 ;主减速比:i0= 5.83 ;要求:采用中间轴式、全同步器换挡。本次设计要求:对各挡齿轮的接触强度、弯曲应力及轴的强度、刚度进行校核计算。设计工作量:1、集资料、进行方案论证、结构分析,确定合理的结构方案。2、选择正确的参数,对变速器的强度及刚度进行校核计算。3、三维建模,变速器结构图;绘CAD图(A1)一张。4、设计中的计算要求编程,上机计算,打印程序、结果。5、英译中大于5000字符(折合中文约大于3000字)。 6、设计说明书应包括:目录、中、英文摘要、设计说明、方案论证、计算过程、结论、毕业设计完成情况的自我评价及其它说明。要求大于1.2万字。二、进度计划与应完成的工作:第四周:进行方案论证。第五、六周:齿轮设计与校核(含编程计算)及各轴传动方案确定与各轴的定位。第七、八周:轴尺寸的确定,轴承、花鍵的选择,轴及花鍵的校核,同步器的设计。第九、十、十一、十二周:完成三维设计数模及设计图纸。第十三、十四周:整理完成说明书;进行外文翻译;检查图纸及设计说明书,订正错误。为答辩做好充分准备。三、完成期限:2012、05、18四、主要参考文献、资料:汽车构造、汽车理论、汽车设计、机械零件、材料力学,现代汽车设计手册、机械零件设计手册、汽车底盘图册 毕业设计(论文)说明书课题名称:轻型货车(5+1)挡变速器设计(直接操纵、全部采用同步器换挡)系 别: 汽车与交通学院 专 业:班 级:学 号:姓 名:指导教师:年 5 月 18 日摘 要本次轻型货车变速器的设计,主要目的是检验大学四年的学习成果。文中阐述了变速器的功用与设计要求,对该变速器进行了了大量的调查研究,并进行了初步的方案论证,根据设计要求选用中间轴式五档变速器,其优点:最高挡采用直接挡,传递扭矩效率高,齿轮和轴承磨损小,噪音小。中间轴采用旋转式,中间轴上的全部斜齿轮的螺旋方向一律取为右旋,第一、第二轴上的斜齿轮取左旋。五个前进挡和倒挡均采用锁环式惯性同步器换挡,保证迅速、省力、无冲击、无噪音换挡,与操作熟练程度无关,从而提高了加速性、经济性和行驶安全性。根据轻型货车的要求,操纵机构选用直接操纵。本文说明并论证了变速器主要参数的确定,齿轮几何参数的计算、列表、齿轮材料的选择、齿轮的强度计算、强度校核,轴的设计及强度刚度校核,轴的材料选择,轴承的选择,花键的选择以及简单介绍了变速器的拆装顺序和对本次设计做出总结。关键词:轻型货车;变速器设计;中间轴式;倒挡ABSTRACTThe design of this light truck transmission, the main purpose is to test the results of four years of study in the university. This design explained the function of the function and design requirements, had the transmission a large number of surveys and studies, and conducted a preliminary studies program. According to the design requirement to choose a intermediate bearing type five gear transmission and its advantages are: the high grade adopts the direct, it is high in efficiency to transmit the torsion , the wearing and tearing of gears and axles is light .the intermediate shaft with rotary, The middle of all the helical gear shaft be taken as the right-hand screw direction, the first and second helical gear to take left. The five gears and reverse gear all use lock ring type inertia synchronizer shifted gears and ensure rapid, labor-saving, non-impact, noise-free transmission ,and operation of proficiency has nothing to do so as to enhance the cars acceleration economy and road safety. According to the design requirements of the light truck ,the manipulation agencies use direct control. Noted and demonstrated that the transmission parameters, the calculations and the list of gear geometry parameters ,the gear material selection ,gear strength and strength check, the design of the shaft and stiffness and strength check ,shaft material selection, bearing selection, spline options .And briefly introduce the transmission disassembly sequence, as well as a summary of this design.KEY WORD: light truck;transmission design;intermediate bearing type;the reverse gear shaft 毕业设计(论文)附件资料课题名称:轻型货车(5+1)挡变速器设计(直接操纵、全部采用同步器换挡) 系 别: 汽车与交通学院 专 业:班 级:学 号:姓 名:指导教师:目 录第1章 外文翻译11.1中文译文11.1.1设计构思11.1.2历史21.2英文原文41.2.1 Designs51.2.2 History5第2章 方案论证82.1变速器的类型选择82.1.1结构工艺性82.1.2变速器的径向尺寸92.1.3变速器齿轮的寿命92.1.4变速器的传动效率92.2倒挡的型式及布置方案92.3换挡的结构型式及齿轮的安排112.3.1换挡的结构型式112.3.2齿轮的安排1115第1章 外文翻译1.1中文译文运动型多用途车运动型多用途车是一款装有轻型货车地盘的与旅行车相同的在市场上交易的交通工具。它常常装备有四轮驱动,是为了拥有越野能力以及符合其他的一些要求或者是在崎岖路面行驶的能力。并不是所有的四轮驱动的车辆都叫做SUV。SUV是包括具有拖拉性能的搭载乘客的敞篷小型载货汽车以及具有货运空间的小型货车或者加大的轿车。由于SUV被考虑成为轻型载货汽车和轻运货车共同享用一个技术平台,在美国政策和能源保护法以及空气洁净法令这两部法律条例下,与乘用车相比较它们被管理得比较松。从2004年开始,美国环境保护局(EPA)开始像其他车辆一样严格控制SUV的尾气排放标准。这个条款并不是适用于所有的国家地区。在北美之外的其他地区“越野车辆”,“四轮驱动”仅仅是用牌子来形容像“吉普”、“兰德路华”这样子的车。然而,并不是所有的具有四轮驱动能力的乘用车就是SUV。越野车主要是为了越野使用而设计的一大类车辆。然而,SUV的特征并不是为了普通大众和媒体而设计制造的。尽管一些SUV拥有越野的能力,但是它们通常仅仅是扮演次要的角色,而且,这些SUV通常没有在两轮驱动与四轮驱动高速档的传动装置的和四轮驱动低速档传动装置的能力。当汽车生产商出售SUV时,利用广告和给SUV命名的方式来宣传SUV高超的技艺时,越来越多的SUV在道路上和城市地区行驶。SUV在90年代末和本世纪初大受欢迎,但是由于油价的上涨和经济的衰退SUV的销售额开始下降。传统的卡车底盘的SUV逐步的被交叉型的SUV代替。交叉型的SUV是一类使用更轻的汽车质量和更好的燃油效率的汽车平台,作为对运动型多用途车的许多苛刻要求的回复。1.1.1设计构思尽管SUV的设计构思多样化,但是它拥有历史上中型乘用车的与轻型货车相似的框架车身和底盘。早期的SUV主要是双门型的和汽车顶部能够移动的。然而,根据消费者的需求,SUV市场向着四门型发展。到2002年所有的全双门型的SUV已经被市场淘汰。只有吉普牧马人保留了全双门型,尽管它仍然加入了四车门的变形体。全双门型SUV大部分都是遗留模型,并且后的设计流程,双门型SUV的销售额不能够保证它的从新设计。在2010年,随着路虎览胜和美人奴的发布,双门型的SUV的销售有所增强,尽管这两款车都是单片式车身汽车。大部分的SUV都设计有发动机室、结合乘客与货物的载货舱以及专用的汽车车尾行李箱,如旅行车的车身。大部分的中等运动型多用途车和全尺寸的SUV都有三排的座位,以及在最后一排座位后面的载货区。货物栅栏通常调整到使其适应载货区以便在突发事件突然减速或者碰撞事件时用来保护无抵押货物以免被损坏。尽管SUV的设计多样化,传统意义上的SUV是一种与轻型卡车拥有类似的框架和底盘的中型客运车类,大多数的SUV配备发送机舱,并兼具客运与货运的车厢,并没有专门一个专门的主干机构,例如旅行车的车体。许多的中型和全尺寸的SUV拥有三排座位以及在最后一排后面直接拥有货物区域。SUV以高离地间隙、方方正正的车体以及高H点著称。由于这种车身的高重心,可以使这种车型更容易翻转。SUV的车体最近变得更有空气动力,但是这种绝对形的尺寸和重量能保持小的耗油量。1.1.2历史1)起源最早的长轴距货车式SUV是雪弗兰的Carryall 郊区(1935),嘎斯-61(1938),威利斯吉普旅行车(1948),Pobeda M-72(嘎斯-M20/1955),其中俄罗斯的引用信贷肯能是SUV的第一个现代的SUV,国际收割机Travelall(1953),兰德路华(路虎)系列二109(1958)以及国际收割机考特80(1961)。其次是更加“现代”的吉普瓦贡尔(1963),国际收割机童军二(1971),福特野马(1966),丰田陆地巡航舰FJ-55(1968),雪弗兰开拓者/GMC Jimmy(1969),以及兰德路华(路虎)Range Rover(1970)。这实际术语“运动型多用途车”直到二十世纪八十年代才收到人们的欢迎。许多这样子的汽车在旅行车的年代被推向市场。根据在福特汽车博物馆的运输馆长Robert Casey的介绍,现代理解这个术语吉普的切诺基才是真正的运动型多用途车。这是向市区的家庭推出用来代替传统汽车的一款SUV(尤其是旅行车,在那时候相当受欢迎的一类车型)。这款吉普的切诺基拥有四轮驱动系统在一个相当容易操作的尺寸的空间里(与全尺寸的瓦格尼相比较),以及豪华舒适的内部装饰,就相当于一辆旅行车。拥有引进的更豪华的车型和更加强大的4.0排量的发动机,尽管汽油的价格上涨,切诺基的销售额还是增加了,并且这个术语“运动型多用途车”首次被国家的出版社使用。成功的来临使紧凑型的吉普-切诺基汽车改变了卡车的行业。在二十世纪七十年代公司燃油经济性标准(CAPE)被批准通过,这是用来控制乘用车的燃油性的。汽车制造商通过销售SUV这种车辆来逃避这个标准。在过去的25年里SUV在诚实里得到了普及特别是在过去的十年里。因此,现代的SUV拥有豪华车的特点,并且一些交叉车模型还采用了降低悬架的高度以便使其适应道路的行驶。Keith Bradsher解释说为了增加SUV的生产销售,AMC汽车公司对美国环境保护局(EPA)进行了游说,让其在SUV的生产上放弃美国空气清洁法。随后美国环境保护局指定AMC公司的紧凑型的切诺基汽车就是一款轻型卡车,该公司能够向每一个司机出售这款车。AMC公司新型车型的成功影响了官方对立法的制定,导致了SUV的热潮,而当时其他的汽车生产商通过向市场推广他们自己的车型回应切诺基抢走他们常规汽车的销售额。2)普及在二十世纪末和二十一世纪初SUV在美国、加拿大、和澳大利亚大受欢迎。美国的汽车制造商每销售一辆SUV就可以赚到10000美元的利润,而他们只是失去了在销售小型汽车的几百美元的利润。例如:每销售一辆福特Excursion就可以净赚18000美元,而当他们销售一辆福克斯时他们却没有亏损除非买方选择选项,这就导致了底特律的三大汽车制造商主要集中于生产SUV.小型汽车的销售主要靠价格便宜和符合联邦的平均燃用经济性标准来吸引年轻的买者。在美国和加拿大的相对比较高工资的汽车工会(汽车工人联合会(UAW)和加拿大汽车工人工会(CAW),与低工资的在属于美国工会的公司,像日本丰田公司,使美国汽车生产商制造小型汽车没有利润可赚。例如:在阿灵顿,德克萨斯州的美国通用汽车公司生产后轮驱动的汽车,比如雪弗兰-随想曲、别克-路尊、凯迪拉克- Fleetwood Brougham被转换成卡车和SUV产品,终止了全尺寸家庭旅行车的生产和全面终止生产全尺寸车。由于美国三大汽车公司战略决策的改变,许多长时间运行的汽车比如:Ford Taurus、Buick Century和Pontiac Grand Pix在产品的特点和外观上(更倚重的快速的销售而不是优惠折扣价的刺激手段)将竞争对手远远的平抛在了后面,有些已经被停止使用。高速公路保险协会的汽车碰撞试验表露SUV探险者碰撞福特福克斯的伤害程度。购买者主要是被SUV大的车身空间、较高的悬架高度和感知的安全性。全尺寸的SUV常常提供有自己的产品特征,比如:三排座椅有效的代替了全尺寸旅行车和小型货车。货车常常被看成是过时的。此外,全尺寸SUV比传统的汽车拥有较大的牵引能力,并且能够拖拉拖车或者旅行拖车和船。增加了汽车的离地净高度在下大雪的时候可以很好的行驶。正是二十世纪九十年代低的燃油价格很好的促进了运营成本的降低。SUV的外观真正的说明了它们的普及,尤其是在女性之间,她们在美国构成了SUV一半以上的拥有者。在美国SUV是女性选择的最受欢迎的汽车之一。社会科学家通过大受欢迎的民间传说比如都市传奇来举例说明为什么市场能够利用SUV提供的力量和安全感觉吸引人们的眼球。比如:流行的故事包括母亲通过与持械抢劫者斗争来拯救家庭和其他通过夺取越野汽车的事件。在澳大利亚,SUV销售额的增加是因为SUV比轿车有更加低的进口税,这样与其他相同类型的箱式进口轿车先比他们花费更少的钱就可以买到SUV。然而,这间隙将会逐渐的减小,在2010年汽车的进口关税降低了5%已经和SUV相称。由于原油价格的提高和经济的衰退,在2000中期年代SUV和其他轻型货车的销售额开始下降。在2008年的6月美国通用公司宣布计划建立四个卡车和SUV的工厂,包括Oshawa Truck Assembly。由于紧随而来的燃油价格的提高,公司将会减少大型车辆的引进。在二十世纪中后期公司的经营模式主要集中于SUV和轻型卡车,以生产燃油经济的紧凑型车型和中型车因销售额的下降而被底特律三大汽车制造商责备。与他们的竞争者日本汽车公司相比这三大巨头是比较慢才能适应生产小型汽车去适应生产发展的要求,这是由于这些不能够转变的生产设备,使其对生产小型车没有利润。1.2英文原文Sport utility vehicleA sport utility vehicle (SUV) is a generic marketing term for a vehicle similar to a station wagon, but built on a light-truck chassis. It is usually equipped with four-wheel drive for on- or off-road ability, and with some pretension or ability to be used as an off-road vehicle. Not all four-wheel-drive vehicles are termed as SUV. Some SUVs include the towing capacity of a pickup truck with the passenger-carrying space of a minivan or large sedan. Since SUVs are considered light trucks and often share the same platform with pick-up trucks, they were regulated less strictly than passenger cars under the two laws in the United States, the Energy Policy and Conservation Act for fuel economy, and the Clean Air Act for emissions. Starting in 2004, the United States Environmental Protection Agency (EPA) began to hold sport utility vehicles to the same tailpipe emissions standards as cars.The term is not used in all countries, and outside North America the terms off-road vehicle, four-wheel drive or four-by-four (abbreviated to 4WD or 4x4) or simply use of the brand name to describe the vehicle like Jeep or Land Rover are more common. However, not all SUVs have four-wheel drive capabilities. Conversely, not all four-wheel-drive passenger vehicles are SUVs. Off-road vehicle is a broad class of vehicles, built primarily for off-road use. However, this distinction is often not made by the general public and the media. Although some SUVs have off-road capabilities, they often play only a secondary role, and SUVs often do not have the ability to switch among two-wheel and four-wheel-drive high gearing and four-wheel-drive low gearing. While auto makers tout an SUVs off-road prowess with advertising and naming, the daily use of SUVs is largely on paved roads and in urban areas.Popular in the late-1990s and early-2000s, SUVs sales have since declined due to high oil prices and a declining economy. The traditional truck-based SUV is gradually being supplanted by the crossover SUV, which uses an automobile platform for lighter weight and better fuel efficiency, as a response to much of the criticism of sport utility vehicles.1.2.1 DesignsAlthough designs vary, SUVs have historically been mid-size passenger vehicles with a body-on-frame chassis similar to that found on light trucks. Early SUVs were mostly two-door models, and were available with removable tops. However, consumer demand pushed the SUV market towards four doors, by 2002 all full-size two-door SUVs were gone from the market. Only the Jeep Wrangler remained as a two-door SUV, although it was also joined by a four-door variant. Two-door SUVs were mostly carry-over models, and their sales were not viable enough to warrant a redesign at the end of their design cycle. Two-door SUV models increased in the 2010s with the release of the Range Rover Evoque and the Nissan Murano convertible, although both vehicles are unibody.Most SUVs are designed with an engine compartment, a combined passenger and cargo compartment, and no dedicated trunk such as in a station wagon body. Most mid-size and full-size SUVs have three rows of seats with a cargo area directly behind the last row of seats. Cargo barriers are often fitted to the cargo area to protect the vehicles occupants from injury from unsecured cargo in the event of sudden deceleration or collision.SUVs are known for high ground clearance, upright, boxy body, and high H-point. This can make them more likely to roll over due to their high center of gravity. Bodies of SUVs have recently become more aerodynamic, but the sheer size and weight keeps their fuel economy poor.1.2.2 History1)OriginsEarly SUVs were descendants from commercial and military vehicles such as the World War II Jeep nd Land Rover. SUVs have been popular for many years with rural buyers due to their off-road capabilities.The earliest examples of longer-wheelbase wagon-type SUVs were the Chevrolet Carryall Suburban (1935, RWD only), GAZ-61 (1938, 4x4), Willys Jeep Wagon (1948), Pobeda M-72 (GAZ-M20/1955), which Russian references credit as possibly being the first modern SUV (with unitary body rather than body-on-frame), International Harvester Travelall (1953), Land Rover Series II 109 (1958), and the International Harvester Scout 80 (1961). These were followed by the more modern Jeep Wagoneer (1963), International Harvester Scout II (1971), Ford Bronco (1966), Toyota Land Cruiser FJ-55 (1968), the Chevrolet Blazer / GMC Jimmy (1969), and the Land Rover Range Rover (1970). The actual term sport utility vehicle did not come into wide popular usage until the late 1980s; many of these vehicles were marketed during their era as station wagons.According to the transportation curator at the Henry Ford Museum, Robert Casey, the Jeep Cherokee (XJ) was the first true sport utility vehicle in the modern understanding of the term. Marketed to urban families as a substitute for a traditional car (and especially station wagons, which were still fairly popular at the time), the Chrerokee had four-wheel drive in a more manageable size (compared to the full-size Wagoneer), as well as a plush interior resembling a station wagon. With the introduction of more luxurious models and a much more powerful 4-liter engine, sales of the Cherokee increased even higher as the price of gasoline fell, and the term sport utility vehicle began to be used in the national press for the first time. The advent and immediate success of AMC/Jeeps compact four-door Cherokee turned the truck industry upside down. The corporate average fuel economy (CAFE) standard was ratified in the 1970s to regulate the fuel economy of passenger vehicles. Car manufacturers evaded the regulation by selling SUVs as work vehicles. The popularity of SUV increased among urban drivers in the last 25 years, and particularly in the last decade. Consequently, modern SUVs are available with luxury vehicle features, and some crossover models adopt lower ride heights to accommodate on-road driving.Keith Bradsher explained the rise of the SUV with American Motors (AMC) lobbying the United States Environmental Protection Agency (EPA) for a waiver of the United States Clean Air Act. The EPA subsequently designated AMCs compact Cherokee as a light truck, and the company marketed the vehicle to everyday drivers. AMCs effort to affect rulemaking changing the official definition of their new model then led to the SUV boom when other auto makers marketed their own models in response to the Cherokee taking sales from their regular cars. 2)PopularitySUVs became popular in the United States, Canada, and Australia in the 1990s and early-2000s. U.S. automakers could enjoy profit margins of $10,000 per SUV, while losing a few hundred dollars on a compact car. For example, the Ford Excursion could net the company $18,000, while they could not break even with the Ford Focus unless the buyer chose options, leading Detroits big three automakers to focus on SUVs over small cars.Small cars were sold mainly to attract young buyers with inexpensive options and to increase their fleet average fuel economies to meet federal standards. The relatively high wages of unionized auto workers in the U.S. and Canada (members of the UAW and CAW, respectively), compared to the low wages of non-union workers at non-U.S. companies like Toyota, made it unprofitable for the U.S. auto makers to build small cars. For example, the General Motors factory in Arlington, Texas where rear-wheel-drive cars were built, such as the Chevrolet Caprice, Buick Roadmaster, and Cadillac Fleetwood Brougham was converted to truck and SUV production, putting an end to full-size family station wagon and overall terminating production of rear-wheel drive full-size cars. Due to the shift in the Big Threes strategy, many long-running cars like the Ford Taurus, Buick Century and Pontiac Grand Prix fell behind their Japanese competitors in features and image (relying more on fleet sales instead of retail and/or heavy incentive discounts); some were discontinued. Buyers were drawn to SUVs large cabins, higher ride height, and perceived safety. Full-size SUVs often offered features such as three-row seating, to effectively replace full-size station wagons and minivans. Wagons were seen as old-fashioned. Additionally, full-size SUVs have greater towing capabilities than conventional cars, and can haul trailers, travel trailers (caravans) and boats. Increased ground clearance is useful in climates with heavy snowfall. The very low oil prices of the 1990s helped to keep down running costs. The SUVs image of utility may partly explain its popularity, not least among some women, who constitute more than half of SUV drivers in the U.S. The SUV was one of the most popular choices of vehicle for female drivers in the U.S. Social scientists have drawn on popular folklore such as urban legends to illustrate how marketers have been able to capitalize on the feelings of strength and security offered by SUVs. Popular tales include narratives where mothers save the family from armed robbery and other incidents by taking the automobile off road, for example.In Australia, SUV sales were helped by the fact that SUVs had much lower import duty than passengers cars did, so that they cost less than similarly equipped imported sedans. However, this gap was gradually narrowed, and in January 2010 the import duty on cars was lowered to match the 5percent duty on SUVs. Sales of SUVs and other light trucks fell in the mid-2000s because of high oil prices and declining economy. In June 2008, General Motors announced plans to close four truck and SUV plants, including the Oshawa Truck Assembly. The company cited decreased sales of large vehicles in the wake of rising fuel prices. The business model of focusing on SUVs and light trucks, at the expense of more fuel-efficient compact and midsized cars, is blamed for declining sales and profits among Detroits Big Three automakers since the mid-late 2000s. The Big Three were slower to adapt than their Japanese rivals in producing small cars to meet growing demand due to inflexible manufacturing facilities, which made it unprofitable to build small cars. 第2章 方案论证2.1变速器的类型选择现代汽车多采用三轴式变速器,而发动机前置前轮驱动的轿车,若变速器的传动比小,则采用二轴式变速器。如图1-1和1-2分别为两轴式和三轴式变速器的示意图。在设计时,究竟采用哪一种方案,除了汽车总布置的要求外,主要考虑以下四个方面:图2-1 两轴式变速器示意图图2-2 三轴式变速器示意图2.1.1结构工艺性两轴式变速器输出轴与主减速器主动齿轮做成一体,当发动机纵置时,主减速器可用螺旋圆锥齿轮或双曲面齿轮,而发动机横置时用圆柱齿轮,因而简化了制造工艺。2.1.2变速器的径向尺寸两轴式变速器的前进挡均为一堆齿轮副,而三轴式变速器则有两队齿轮副。因此,对于相同的传动比要求,三轴式变速器的径向尺寸可以比两轴式变速器小得多。2.1.3变速器齿轮的寿命 两轴式变速器的低档齿轮副大小相差悬殊,小齿轮工作循环次数比大齿轮要高得多,因此,小齿轮工作寿命比大齿轮要短。三轴式变速器的各前进档均为常啮合齿轮传动,大小齿轮的径向尺寸相差较小,因此寿命比较接近。在直接档时,齿轮只是空转,不影响齿轮寿命。2.1.4变速器的传动效率两轴式变速器,虽然可以有等于1的传动比,但是仍要有一对齿轮传动,因而有功率损失。而三轴式变速器,可以将输入轴和输出轴直接相连,得到直接档,因而传动效率高,磨损小,噪声也较小。 轿车,尤其是微型汽车,采用两轴式变速器比较多,这样可将变速器和主传动器组成一个整体,使传动系的结构紧凑,汽车得到较大的有效空间,便于汽车的总体布置。因此,近年来在欧洲的轿车中采用得比较多。而中、重型载货汽车则多采用三轴式变速器。这次设计的变速器是轻型货车使用,所以采用三轴式变速器2.2倒挡的型式及布置方案与前进挡位比较,倒挡使用率不高,而且都是在停车状态下实现换挡,故多数方案均采用直齿滑动齿轮方式换倒挡。为实现倒档传动,有些方案利用在中间轴和第二轴上的齿轮传动路线中加入一个中间传动齿轮的方案;也有利用两个联体齿轮的方案。前者虽然结构简单,但是中间传动齿轮的轮齿是在最不利的正、负交替对称变化的弯曲应力状态下工作;而后者是在较为有利的单向循环弯曲应力状态下工作,并使倒档传动比略有增加。也有少数变速器采用结构复杂和使成本增加的啮合套或同步器方案换入倒档。常见的倒挡结构方案有以下几种:方案1.(如图2-3a)所示)在前进档的传动路线中,加入一个传动,使结构简单,但齿轮处于正负交替对称变化的弯曲应力状态下工作。此方案广泛用于轿车和轻型货车的四档全同步器式变速器中。方案2.(如图2-3b)所示)此方案的优点是换倒挡时利用了中间轴上
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