轻型货车变速器设计-三轴式四档【三维UG模型】【含CAD图纸、说明书】【QX系列】
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2012届毕业设计说明书一、课题的主要内容和基本要求参数:发动机最大扭矩(N.m):210.9; 一档传动比:5.568 ; 主减速器减速比:6.142要求:采用中间轴式、全同步器换档。本次设计要求:对各档齿轮的接触强度、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以及为将来的工作打下坚实的基础。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,根据设计要求决定选用了三轴式四档变速器,中间轴采用旋转式,倒档的换档方式采用倒档轴上滑动齿轮换档,其他档位采用同步器换档,根据轻型货车的要求,操纵机构选用远距离操纵。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,轴的材料选择和校核,轴承的选择,花键的选择。并简单介绍了变速器的拆装顺序,以及对本次设计做出总结。整个毕业设计历时两个多月,在老师的悉心指导和同学的热心帮助下得以顺利完成。最后感谢在毕业设计期间给予我帮助的老师和同学。本次设计,计算机三维建模,变速器结构图及绘CAD图(A1)一张1张,翻译外文资料一份,编写MATLAB程序3份,以及编辑说明书一份。关键词:轻型货车 变速器 设计 三轴式 倒档轴ABSTRACTThe design of this light truck transmission, the main purpose is to test the results of four years of study in the university and lay a solid foundation for the future work.This design explained the function of the transmission 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 three-axis 4th speed transmission and the rotation middle shaft, the reverse stall used to shift the gear on the reverse gear shaft, the other stalls used Synchronizer shift, according to the design requirements of the light truck,the manipulation agencies use remote control. Describe and demonstrate the determination of main parameters of transmission, gear geometric parameters of the calculation, the list, the choice of gear materials, gear strength calculation, strength check, shaft stiffness and strength check of the design, material selection and check of the shaft, bearings choice, the choice of spline. And briefly describes the transmission of the disassembly order, and make a summary of this design. Graduation took the whole two months, the guidance of teachers and students enthusiastic assistance been completed successfully.Finally thanks to the teachers and classmates who give me much help during the graduation design.This design, three-dimensional computer modeling, CAD drawing transmission structure, and Figure (A1) a 1, a translation of foreign language data, the preparation of 3 copies of MATLAB programs, and editing a manual.KEY WORDS: light truck, transmission, design, three-axis, the reverse gear shaft广西科技大学(筹)2012届毕业设计说明书第1章 外文翻译1中文翻译:变速器所有变速箱技术中,手动变速器的效益最高,输出功率可达到输入功率的96%,但并不是所有的人都能驾驭手动变速箱,也不是所有人愿意用它。因为用手动变速器需要踩离合器,这是在交通繁忙的时候很不舒服,驾驶员容易疲劳,而由扭矩中断导致的“点头”效应也会使乘客很难受。由驾驶员操纵离合器而产生的扭矩中断是手动变速器主要的缺点。在换档加速时,驾驶员都必须通过松开油门并踩下离合器来使扭矩中断,完成整个过程大概需要一秒,但在这段时间里车辆会暂时停止加速,速度也会降低。与此截然不同的是自动变速箱,到目前为止现代汽车自动变速器是汽车上最复杂的元件。它是一种可以自己换挡的变速器。力矩转换器或流体联合器被用来代替手动离合器连接发动机。汽车上变后轮驱动或前轮驱动是车辆自动变速器的两种基本类型。在一个后轮驱动的速器通常放在发动机后面凸起后长板旁边气体踏板下方的位置。驾驶杆连接变速器后端,最终驾驶的准确位置在后轴,用操纵力控制后轮。发动机的动力简单连续的在这个系统中循环,在通过变速器时改变力矩,通过传动轴后在主减速器分流到两后轮。在前轮驱动汽车中,变速器常常兼有最终驱动叫做变速驱动桥。前轮驱动汽车通常在发动机的后下方安装有横向变速驱动桥。前桥直接连接在发动机的变速驱动桥上为前轮提供动力,动力从发动机出发转过一个大链条后经180转变传给变速器。从而,将主动力通过变速器后分流传到驱动轴再送到两前轮。也有一些其他方式的前轮驱动车辆,车架前方代替另一边的其他系统驱动四轮,但在这儿仅对其中的两个系统进行说明。相对于前轮驱动来说最流行的是后轮驱动,在发动机上连接一个输出轴,将改变后的力矩传给后驱动轮。这个系统是探寻前后轴实施改进的新的节能动力平衡装置。另一个驱动系统是把所有的驱动零件都按在后轮上。这种排列方式发动机通常后置。现代自动变速器由许多的部件和系统组成,它们有行星齿轮组、液压系统、密封圈和密封衬垫、变矩器、油压调节器、调制器、节气门拉线、电子控制装置等,经精心设计运转协调,其中的电子控制装置经历了多年的发展,已经以巧妙的形式溶入了许多人性化的设计。汽车上的行星齿轮主要用在两个地方,一是驱动桥减速器、二是自动变速器。很多网友都想知道,行星齿轮有什么功能,为什么汽车少不了它。我们熟知的齿轮绝大部分都是转动轴线固定的齿轮。例如机械式钟表,上面所有的齿轮尽管都在做转动,但是它们的转动中心(与圆心位置重合)往往通过轴承安装在机壳上,因此,它们的转动轴都是相对机壳固定的,因而也被称为定轴齿轮。 轴线固定的齿轮传动原理很简单,在一对互相啮合的齿轮中,有一个齿轮作为主动轮,动力从它那里传入,另一个齿轮作为从动轮,动力从它往外输出。也有的齿轮仅作为中转站,一边与主动轮啮合,另一边与从动轮啮合,动力从它那里通过。在包含行星齿轮的齿轮系统中,情形就不同了。由于存在行星架,也就是说,可以有三条转动轴允许动力输入/输出,还可以用离合器或制动器之类的手段,在需要的时候限制其中一条轴的转动,剩下两条轴进行传动,这样一来,互相啮合的齿轮之间的关系就可以有多种组合:动力从其中一个太阳轮输入,从另外一个太阳轮输出,行星架通过刹车机构刹死;动力从其中一个太阳轮输入,从行星架输出,另外一个太阳轮刹死;动力从行星架输入,从其中一个太阳轮输出,另外一个太阳轮刹死;两股动力分别从两个太阳轮输入,合成后从行星架输出;两股动力分别从行星架和其中一个太阳轮输入,合成后从另外一个太阳轮输出;动力从其中一个太阳轮输入,从另外一个太阳轮和行星架分两路输出;动力从行星架输入,分两路从两个太阳轮输出。由于采用了变矩器,这种变速器的换档质量不错但效率相对较差虽然目前有所改进。因此,目前进行了许多研究,试图发现传统变速器的有效的代替方案。主要的技术还是无级变速器(CVT)、双离合变速(DCT)和手自一体(AMT)变速器。它们在不同的方面优于传统的行星齿轮式自动变速器。无级变速器采用带、链或锥盘滚轮来产生无限多种速比,与传统自动变速器相比其效率和成本都有所改善。之所以有这些优点,是因为它结构简单,这种变速器的零部件很少,通常只有一根橡胶或金属传动带、一个液压作用的驱动带轮、一个机械扭矩感应式驱动带轮、一些微处理器和传感器等。这种变速器的工作原理是改变两个主带轮表面之间的距离,带轮上挂传动带的地方开了V形槽,一侧的带轮沿轴向固定,另一侧的带轮可在液压的作用下移动。在驱动轮后,液压缸可增加或减少带轮两侧之间的距离,这样会使传动带在带轮侧壁上的位置上下变动,变动的方式取决于驾驶情况。这样就会使变速比改变。锥盘滚轮型变速器的工作原理与此类似但用的是驱动盘和动力滚轮。CVT(无极)变速器的特点对技术人员最具有吸引力。因为这样没有档位,CVT可使发动机保持在最佳的功率范围内。这样可以使效率提高并在相同的油耗下增加行驶里程。CVT可将发动机工作曲线上的每一点转变为其本身工作曲线上相应的点。这种变速器最受日本汽车制造商青睐,并且日本变速器生产商JACTO是主要生产者,但在欧美国家,情况就有所不同。尽管奥迪和其它一些制造商在一些车型上推出了CVT,但在这方面他们追赶的步伐仍然很缓慢。DCT实际上是将两台手动变速器合在一起,换档过程是通过两台变速器的离合器之间的相互切换来实现的。这种变速器的换档质量和传统的自动变速器相同,但由于系统会发生滑动、液体阻力和液压损失,其效率和加速性只比传统行星齿轮自动变速器稍有提高,开发控制系统的成本也很高。“最近在传统自动变速器技术上所取得的进展,使开发和生产CVT或DCT的呼声有所降低。”变速器生产企业Zeroshift公司的执行总裁比尔马丁说,“由于成本过高,有些汽车厂已经取消了DCT项目。”AMT是成本最低的自动变速器技术,AMT用执行器来代替传统的离合器踏板和换档杆,这种变速器保留了手动变速器的高效率和加速性能,但某些型号的变速器换档质量不高,扭矩中断和“点头”效应仍是主要的缺点。那么什么是最好的代替方案?变速器方面的新技术是层出不穷的,但Zeroshift公司声称其变速器的效率优于手动变速器,提高失去驾驶的燃油经济性,同时,其换档效率可以和改进后的自动变速器相媲美。Zeroshift公司采用的是一种改进版的AMT技术,这种技术用先进的犬牙啮合系统代替同步器。犬牙啮合技术许多年前就已经在赛车运动中采用,目的是为了加快换档速度。传统的犬牙式变速器并不适合在公路上,因为驱动环或犬牙之间的空隙很大,会产生后坐由扭矩突然转向而产生的一种不舒适的窜动。Zeroshift公司通过增加第二套驱动犬牙来解决这一问题,这种技术还使每组犬牙只能传递两种相反方向扭矩中的一种。“通过对两套犬牙的啮合和分离,可在上一个档位没有分离的情况下换入新的档位。”马丁说,“换档质量超过采用现代化的6档变速器的豪华轿车。”换档可在瞬间完成,而扭矩不发生中断,而且这种方法既可用于升档又可用于降档。“在使用传统的AMT变速器时,由于需要关闭并重新打开油门,换档过程中排放会达到高峰,而通过这种无过渡的换档方式可以消除这种现象。”马丁说,“这样还能降低燃油消耗。”“尽管在技术上变速器领域还比较新,但公司称已经引起了欧美各大汽车制造商的注意,最大的吸引力在于其成本比DCT低”,马丁说。由于可以保留大部分手动变速器的结构,这种变速器的成本和复杂性都不会高于传统的AMT变速箱。控制系统的成本也会大大降低,这对试图减少排放和削减成本的工程师来说是个好消息。“大部分制造商都来参观过,”马丁说,“有些公司马上就和我们签合同,另一些未作决定,拒绝的一个都没有。”这再清楚不过的表明了汽车制造商现在正在将动力系统开发的重点转移到变速箱上。Zeroshift公司的变速系统是怎样工作的呢?它的硬件部分包括两套犬牙,安装在两个独立的犬牙环上并受其驱动,两套犬牙有一个共同的盖,盖和一个花键轴相连。每个犬牙都有特殊的轮廓。在一侧是用于啮合的直角面。这些直角面是沿对角线相对的,这样的犬牙在对某一个档位具有驱动功能的同时,对另一个档位具有超越传动的功能。啮合面有轻微的后向锥度,以保证犬牙能在加载时锁定在啮合齿轮上。相对角上有一个斜坡,可在新档位啮合后将犬牙从前一个档位推离。在空档时,两个犬牙环处于变速比的中间位置。选一档时,犬牙会发生移动并和犬牙啮合面发生啮合。犬牙通过与换档执行器相连的换档拨叉驱动。驱动犬牙将一档齿轮与输出轴锁定在一起,将扭矩从齿轮传递到输出轴。一档的超越传动犬牙也会移动并将齿轮以相反的方向和输出轴锁定。这样可以在油门关闭且发动机倒拖时将扭矩从齿轮传递到输出轴。这样就消除了犬牙啮合式变速器常见的后坐现象。在加大油门换档时,一档齿轮的超越传动犬牙卸载后和二档齿轮啮合。然后换入二档时,前一个驱动环卸载。如果犬牙之间不能完全啮合,即实现两个犬牙面之间的啮合,由于相对速度差的存在,二档齿轮会打开一个啮合缺口。在犬牙抵住啮合面后,在拨叉和执行器的共同作用下,储存的能量会将犬牙送入缺口内。此时,一档超越传动犬牙成为二档的驱动犬牙。在换入二档后,一档的驱动犬牙随即卸载。这时候,这些犬牙不再受其固定面固定,可以被执行器或犬牙上的斜面推离档位。2 外文原文:TRANSMISSIONOf all transmission technologies, the manual gearbox is the most efficient; around 96 per cent of the energy that is put in comes out of the other end. But not everyone can drive one or wants to. Because you have to dip the clutch pedal, it is less comfortable to drive in heavy traffic. It makes the driver tired and the torque interruptions head-nod effect on passengers can be wearing. The drivers clutch control and corresponding torque interruptions are also the manuals weak point. When accelerating up through the gearbox, each up-shift requires the driver to cut the torque momentarily by lifting the gas pedal and dipping the clutch. It may just take a second to complete the operation, but during this time the vehicle is losing speed and acceleration. At the opposite end of the spectrum is the traditional automatic. The modern transmission is by far, the most complicated mechanical component in todays automobile. It is a type of transmission that shifts itself .A fluid coupling or torque converter is used instead of a manually operated clutch to connect the transmission to the engine. There are two basic types of automatic transmissions based on whetherthe vehicle is rear wheel drive . On a rear wheel drive car , the transmission is usually mounted to the back of the engine and is located under the hump in the center of the floorboard alongside the gas pedal position . A drive shaft connects the rear of the transmission to the final drive which is located in the rear axle and is used to send power to the rear wheel. Power flow on this system is simple and straight forward going from the engine, through the torque converter , then through the transmission and driver shaft until it reaches the final driver where it is split and sent to the two rear wheel . On a front wheel drive car, the transmission is usually combined .With the final drive to from what is called a transaxle. The engine on a front wheel driver car is usually mounted sideways in the car with the transaxle tucked under it on the side of the engine facing the rear of the car. Front axles are connected directly to the transaxle and provide power to the front wheels. In this example, power flows from the engine through the torque converter to a large chain that sends the power through a 180 degree turn to the transmission that is along side the engine. From there,The power is routed through the transmission to the final drive where it is split and sent to the two front wheels through the drive axles. There are a number of other arrangements including front drive vehicles where the engine is mounted front to back instead of sideways and there are other systems that drive all four wheels but the two systems described here are by far the most popular. A must less popular rear drive arrangement has the transmission mounted to the final drive at the rear and is connected by a drive shaft to the torque converter which is still mounted on the engine. This system is found on the new corvette and is used in order to balance the weight evenly between the front and rear wheels for improved performance and handling. Another rear drive system mounts everything, the engine, transmission and final drive in the rear. This rear engine arrangement is popular on the Porsche. The modern automatic transmission consists of many components and systems that are designed to work together in a symphony of planetary gear sets, the hydraulic system, seals and gaskets, the torque converter, the governor and the modulator or throttle cable and computer consider being an art form. On the automobile planet gear mainly uses in two places, one is the driving axle reduction gear, two is the automatic transmission. Very many net friends all want to know that, the planet gear has any function, why automobile must have it. We knew very well the gear major part all rotates the spool thread fixed gear. For example mechanical type clock and watch, above all gears although all in make the rotation, but their rotation center (with center of a circle position superposition) often installs through the bearing on the cabinet, therefore, their rotating axis all is the relative cabinet fixed, thus also is called dead axle gear.Has must have surely moves, the corresponding place, some kind of not that manner knows very well is called planet gear the gear, their rotation spool thread is not fixed, but is installs the support which may rotate in (blue color) on (in chart black part is shell, yellow expression bearing). The planet gear (green) besides can look like the dead axle gear such to revolve own rotating axis (B-B) to rotate, their rotating axis also (is called planet) along with the blue color support to circle other gears the spool thread (A-A) to rotate. Circles oneself spool thread the rotation to be called rotation, circles other gear spool threads the rotation to be called revolution, looks like in solar system planet such, therefore acquires fame.The spool thread fixed gear drive principle is very simple, meshes mutually in a pair in the gear, some gear takes the driving pulley, the power spreads from its there, another gear takes the driven wheel, the power outputs from it toward outside. Also some gears only take the stopover station, at the same time meshes with the driving pulley, one side meshes in addition with the driven wheel, the power passes from its there.In contains the planet gear in the gear system, the situation was different. Because has the planet frame, in other words, may have three rotating axes permissions power input/Output, but also may use the coupling or the brake and so on method. in needs time limits axis the rotation, is left over two axes to carry on the transmission, as the matter stands, meshes mutually between the gear relations may have the many kinds of combinations: The power from sun gear input, outputs from other sun gear, the planet put through brake mechanism has checked dies; Power from sun gear input, from planet output, moreover a sun gear ecks dies; The power from a planet input, outputs from sun gear, moreover a sun gear checks dies; Two powers separately from two sun gears inputs, after synthesis from planet output; Two powers separately from the planet and sun gear input, after the synthesis output from other sun gear; The power from sun gear input, divides two groups outputs from other sun gear and the planet frame; The power from a planet input, divides two groups to output from two sun gears;Its shift quality is good thanks to its torque converter, but efficiency is relatively poor despite recent advances. Because of this, a lot of the current research is trying to find an efficient alternative to the conventional automatic. The main technologies are continuously variable transmissions (CVTs); dual clutch transmissions (DCTs) and automated manual transmission (AMTs).They all offer different benefits over the conventional planetary automatic. The CVT uses a belt chain or torodial shaped dish drive to vary an infinite number of gear ratios. It has improved efficiency and cost when compared to conventional automatics. Its advantage comes from its simplicity. It consists of very few components;usually a rubber or metal-link belt;a hydraulically operated driving pulley, a mechanical torque-sensing driving pulley, microprocessors and some sensors. The transmission works by varying the distance between the face of the two main pulleys. The pulleys have Vshaped grooves in which the connecting the belt rides. One side of the pulley is fixed axially; the other side moves, actuated by hydraulics. When actuated, the cylinder can increase or reduce the amount of space between the two sides of the pulley. This allows the belt to ride lower or higher along the walls of the pulley, depending on driving conditions. This changes the gear ratio. A torodial-type design works in a similar way but runs an discs and power- rollers The step less nature of its design is CVTs biggest draw for automotive engineers .Because of this, a CVT can work to keep the engine in its optimum power range, thereby increasing efficiency and mileage. A CVT can convert every point on the equines operating curve to a corresponding point on its own operating curve. The transmission is most popular with Japanese carmakers and Japanese supplier JATCO is a major producer. But in the US and Europe driving styles are different. Uptake has been slow despite Audi and other manufacturers having Offered CVT operations on their ranges. The DCT is, in effect, two manual gearboxes coupled together. Gear shifts are made by switching from one clutch on one gearbox to another clutch on the other. The shift quality is equal to a conventional automatic, but slip, fluid drag and hydraulic losses in the system result in only slightly improved efficiency and acceleration over the conventional planetary automatic. Developing the control strategy is costly too. Resent advances in conventional automatic technology have weakened the argument to develop and set up production for CVT or DCT, says Bill Martin, managing director of transmission firm Zeroshift Some carmakers have cancelled DCT projects because of the cost. The cheapest way to build an automatic is with an AMT. AMTs use actuators to replace the clutch pedal and gear stick of a conventional manual. They keep the high efficiency and acceleration of a manual gearbox, but the shift quality on some models is lacking. Torque interruptions and the head-nod effect are the most common complaint. SO what is the alternative? There are always new ideas in transmissions, but Zeroshift says that its technology has efficiency benefits over a manual, delivering fuel economy improvements to city driving. Shift quality can also be equal to that of a refined automatic.Zeroshifts approach is an upgrade to the AMT. The synchromesh is replaced with an advanced dog engagement system.Dog engagement has been used for many years in motor sport to allow fast shifts. Conventional dog Boxes are unsuitable for road use as the large spaces between the drive lugs or dogs create backlash, an uncomfortable shunt caused by the sudden change in torque direction. Zeroshifts technology solves this problem by adding a second set of drive dogs. It has also made each of The two sets of dogs only capable of transmitting torque in one or other opposing directions.” By controlling the engagement and disengagement of the two sets you can shift into the new gear before disengaging the previous gear, says Martin The shift quality is smoother than a typical modern six-speed automatic luxury carThe shift is instant and the torque is not interrupted. This philosophy is used for both up and down shifts.In conventional AMT there is an emissions spike during a shift due to the need to back off and reintroduce throttle, this is eliminated by going seamless, says Martin.” This also reduces fuel consumption. “ It is a relative newcomer to the transmission sector, but the firm says that it is already attracting the attention of major European and US carmakers. The big draw is as a low-cost alternative to DCT, says Martin. Because the manual gearbox architecture is largely maintained, production costs and complexity are not greater than for a conventional AMT. Development of tile controls side is also considerably cheaper. Music to the ears of engineers trying to cut emissions and costs.Most of the carmakers have seen the system at least once, says Martin Some signed us up immediately some have said not yet. None have said no. That may be the clearest sign yet that when it comes to power train developments, carmaker are starting to focus on the transmission.How zeroshift works? The hardware consists of two sets of bullets mounted and actuate on two independent bullet rings. Both set of bullets run on the common hub, which is attached to the shaft with splints.Each bullet has a special profile. On one side they have an angled face for engagement. These are diagonally opposed, allowing the bullet to have a drive function for one gear and an overrun function for the other gear. The engagement faces taper backwards slightly to ensure the bullet latches onto the engaged under load.The opposite corners have a ramp, which pushes the bullet out of the previous gear once the new gear has been engaged.In neutral both bullet rings are positioned midway between the ratios. To select first gear, the bullets are moved into mesh with the engagement dogs. The bullets are actuated via shift forks connected to the shift actuators.第2章 变速器的方案论证2.1 变速器类型选择及传动方案设计变速器的种类很多,按其传动比变化方式不同可以分为有级式、无级式和综合式三种。有级式变速器根据前进挡数的不同,可以分为三、四、五挡和多挡变速器;而按其轴中心线的位置又分为固定轴线式、螺旋轴线(行星齿轮)式和综合式。其中,固定式变速器应用较广泛,又可分为两轴式,三轴式和多轴式变速器。现代汽车大多都采用三轴式变速器。对发动机前置前轮驱动的轿车,如变速器传动比小,则常采用两轴式变速器。以下是两轴式和三轴式变速器的传动方案。要采用哪一种方案,除了汽车总布置的要求外,主要考虑以下四个方面: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对齿轮副,而三轴式变速器则有两对齿轮副。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挡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挡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。在直接挡时,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,得到直接挡,因而传动效率高,磨损小,噪声也较小。 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,采用三轴式变速器。2.2变速器传动机构的分析根据第一节所述,采用中间轴式变速器,在各挡数相同的条件下,各变速器的差别主要在常啮合齿轮对数,换挡方案和倒挡传动方案。2.2.1 换挡结构形式的选择目前,汽车上的机械式变速器的换挡结构形式有直齿滑动齿轮、啮合套和同步器换挡三种。1)滑动齿轮换挡通常是采用滑动直齿轮换挡,但也有采用滑动斜齿轮换挡的。滑动直齿轮换挡的优点是结构简单、紧凑、容易制造。缺点是换挡时齿端面承受很大的冲击会导致齿轮过早损坏,并且直齿轮工作噪声大,所以这种换挡方式一般仅用在一挡和倒挡上。2)啮合套换挡用啮合套换挡,可以将结构为某传动比的一对齿轮,制造成常啮合的斜齿轮。用啮合套换挡,因同时承受换挡冲击载荷的接合齿齿数多,而轮齿又不参与换挡,因此它们都不会过早损坏,但是不能消除换挡冲击,所以仍要求驾驶员有熟练的操作技术。此外,因增设了啮合套和常啮合齿轮,使变速器的轴向尺寸和旋转部分的总惯量增大。因此,这种换挡方法目前只在某些要求不高的挡位及重型货车变速器上使用。这是因为重型货车挡位间的公比较小,要求换挡手感强,而且在这种车型上又不宜使用同步器(寿命太短,维修不便)。3)同步器换挡现在大多数汽车的变速器都采用同步器换挡。使用同步器能保证迅速、无冲击、无噪声换挡,与操作技术熟练程度无关,从而提高了汽车的加速性、经济性和行驶安全性。同上述两种换挡方法相比,虽然它有结构复杂、制造精度要求高、轴向尺寸大、同步环使用寿命短等缺点,但仍然得到广泛应用。近年来,由于同步器广泛使用,寿命问题已得到基本解决。上述三种换挡方案,可同时用在同一变速器中的不同挡位上,一般倒挡和一挡采用结构较简单的滑动直齿轮或啮合套的形式,对于常用的高挡位则采用同步器或啮合套。本次设计方案五个前进挡和倒挡均采用同步器换挡。2.2.2倒挡的形式及布置方案倒挡使用率不高,常采用直齿滑动齿轮方案换入倒挡。为实现传动有些利用在前进挡的传动路线中,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。图2-1倒挡结构方案常见的倒挡结构方案有以下几种:方案1.(如图2-1a)所示)在前进挡的传动路线中,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挡全同步器式变速器中。方案2.(如图2-1b)所示)此方案的优点是可以利用中间轴上一挡齿轮,因而缩短了中间轴的长度,但换挡时两对齿轮必须同时啮合,致使换挡困难。某些轻型货车四挡变速器采用此方案。方案3.(如图2-1c)所示)此方案能获得较大的倒挡传动比,突出的缺点是换挡程序不合理。方案4.(如图2-1d)所示)此方案针对前者的缺点作了修改,因而经常在货车变速器中使用。方案5.(如图2-1e)所示)此方案中,将中间轴上一挡和倒挡齿轮做成一体其齿体、宽加大,因而缩短了一些长度。方案6.(如图2-1f)所示)此方案中,采用了全部齿轮副均为常啮合齿轮,换挡方便。方案7.(如图2-1g)所示)为了充分利用空间,缩短变速器轴向长度,有些货车采用此方案,其缺点是一挡和倒挡得各用一根变速器拨叉轴,使变速器上盖中的操纵机构复杂一些,一般3、4、5、6、7这五种方案用于五挡变速器。综合考虑,本次设计采用一挡和倒挡共用一个同步器换挡。2.3 变速器操纵机构方案分析2.3.1变速器操纵机构的功用变速器操纵机构的功用是保证各挡齿轮、啮合套或同步器移动规定的距离,以获得要求的挡位,而且又不允许同时挂入两个挡位。2.3.2 设计变速器操纵机构时,应该满足的基本要求:1、要有锁止装置,包括自锁、互锁和倒挡锁;2、要使换挡动作轻便、省力,以减轻驾驶员的疲劳强度;3、应使驾驶员得到必要的手感。2.3.3换挡位置设计操纵机构首先要确定换挡位置。换挡位置的确定主要从换挡方便考虑。为此应该注意以下三点:1、按换挡次序来排列 ;2、将常用挡位放在中间位置,其它挡位放在两边;3、为了避免误挂倒挡,往往将倒挡安排在最靠边的位置,有时于1挡组成一排。2.4 齿轮形式的分析确定斜齿圆柱齿轮虽然工作时有轴向力且加工复杂些,但仍以其运转平稳噪声低寿命长的突出优点得到变速器的普遍采用。本次设计一档和倒挡采用直齿轮,其它各挡均采用斜齿轮。2.5 齿轮副安排的分析确定各齿轮副的相对安排位置,对于整个变速器的结构布置有很大的影响。各挡位置的安排,应考虑以下四个方面的要求:2.5.1 整车总布置根据整车的总布置,对变速器输入轴与输出轴的相对位置和变速器的轮廓形状以及换挡机构提出要求。比如说是该车是采用发动机前置前驱动还是发动机前置后驱动等等,这些问题都牵连着变速器的设计方案。2.5.2 驾驶员的使用习惯人们习惯于按挡的高低顺序,由左到右或由右到左排列来换挡,如下图b和c。值得注意的是倒挡,虽然它是平常换挡序列之外的一个特殊挡位,然而却是决定序列组合方案的重要环节。例如在四挡变速器中采用的基本序列组合方案有三种,见图2.2。其中b和c是倒挡与序列不结合的方案,即挂挡时,需先换位再挂倒挡。倒挡与序列结合与不结合两者比较,前者在结构上可省去一个拨叉和一根变速滑杆,后者如布置适当,则可使变速器的轴向长度缩短。按习惯,倒挡最好与序列不结合。否则,从安全考虑,将倒挡与一挡放在一起较好。根据以上的要求,本次设计的挡位布置方案如图2.2所示:图 2-2 挡位布置方案2.5.3 提高平均传动效率为提高平均传动效率,在三轴式变速器中,普遍采用具有直接挡的传动方案,并尽可能地将使用时间最多的挡位实际成直接挡。2.5.4改善齿轮受载状况各挡齿轮在变速器中的位置安排,应考虑齿轮的受载状况。承受载荷大的低挡齿轮,一般安置在离轴承较近的地方,以减小轴的变形,使齿轮的重叠系数不致下降过多。变速器齿轮主要是因接触应力过高而造成表面点蚀损坏,因此将高挡齿轮安排在离两支承较远处较好。该处因轴的变形而引起齿轮的偏转角较小,故齿轮的偏载也小。本次设计传动方案如图2.4所示传动路线:挡:一轴12中间轴566和9间的同步器二轴输出
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