汽车悬架系统设计前后钢板弹簧悬架设计
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机电工程学院
毕业设计外文资料翻译
设计题目: ZY1160货车底盘总体及悬架设计
译文题目: 汽车工程学:汽车纵向动力学
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正文:外文资料译文 附 件:外文资料原文
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正文:(选自《汽车工程学:汽车纵向动力学》P123--132)
变速器
图3-67显示双速行星齿轮作为后置组的二轴传动。
图3-67 9速商用车变速器装双速行星齿轮的后部安装组
在三轴传动中,16个不同的齿轮可以以相对较低的生产费用从四级的变速器中获得主传动。图3-68是一个有16个齿轮的例子。图3-69所描绘的是三轴变速器换档图。
分流部分 四齿轮零件与反向齿轮 范围组
商用车的三组传动
齿轮
图 3-69 三组传动的设计与功率
导阀位置
后置组
主要组
前置组
3.4.2机械无级变速器
在对比了目前使用的机械传动的汽车。机械无级变速器,也被称为无级变速器,根据它们的原理,其具有一定的优势。功率特性如图3- 70所示。基于连续变量的转矩转换,达到的功率曲线(图3-70b)代表转换器的性能。其调整到不同的驱动条件,可以达到传动区域(图3-70c),该无级变速器只要求满足发动机特性曲线(图3-70a)。除了起始区,这需要额外的离合器(要有足够的传动比),其全部需求可以以 [3-33] 的方式所呈现。
转换范围
离合器范围(起动)
无级变速器转换特性
变压器输出的曲线
变压器特性曲线
发动机特性曲线
变压器输出速度
变压器输出转矩
速度比
发动机转速
转矩比
发动机扭矩
由于无级变速器允许自由选择发动机参数(扭矩和转速),内燃机的操作可以基于不同的标准来优化。当发动机在图象上显示整个发动机的性能的最佳点,这是曲线相对于功率的参数化,也叫“控制曲线”,图3-71显示的优化准则的“噪音”,“燃料消耗”和“驾驶动态”的控制线。
噪声
转矩
驾驶动态
速度
不同的优化标准的控制线
控制曲线
燃料消耗
当只有一条控制线,使用相对简单的机械控制传输操作,绘制曲线是一个很好的办法。在这种情况下,可以实现控制线对应的需求以及需求的驱动程序。这就意味着,无级变速器可以完全被实现为自动变速器。
机械无级变速器,传动比的变化是通过改变应用的力的半径来实现。转矩由摩擦传递。基于转矩传动机械无级变速器的类型可分为:
1)带式传动
2)间距传动
3.4.2.1带式传动
在带式传动中,使用皮带、带或链的强制传输来实现,这是一套适合于磁盘轮对之间的传动。通过改变不同的轮上的滚动半径,传输率可以是改变的。因此,磁盘轮对的调节机制也被称为变速器。对于力传递,到目前为止,不同的皮带,带和链的概念已经提出。图3-72显示目前使用的动力传动系统。
现代皮带传动中的动力传动
橡胶带用于皮带式变速传动在50年代由Van doorne,荷兰人所发明,通过改变扭矩(210 N•m)和效率,尤其是通过改变无级变速器钢链连接电流,可以使传输显著提高。传动元件,又称推力连杆带,包括约三百钢段,在两边的钢带包(带大小0.1mm)传到远处。
相反的推力连接带,由PIV-Antriebe Werner Reimers KG制造的变速器,一个链的拉载用于传力。单链连接的封装连接到彼此的压缩部分。在压缩部件和盘轮的接触区域中发生摩擦。通过设计适当的U形金属卡子从外部链条导引,该卡子钩环带金属夹,通常用于链传动,当链路开始与磁盘车轮接触,多多少少可以通过适当设计的链避免。
为了保持离心载荷在U波段尽可能低。Gates Rubber,美国人,开发了由芳纶纤维增强的橡胶带的动力系统。为了提高横向承载能力,橡胶带具有一个集成的金属结构。在钢-钢摩擦副进行油润滑,是没有必要的。这考虑到一个开放的传输设计与较低的重量。
Kumm Industries,美国人,提出的第四个传输系统对比前带传输在图3-72所示,其中传力元件夹在两锥盘对之间,Kumm的无级变速器包括橡胶带这也是由凯夫拉(盖茨开发)和运行在每个磁盘端螺栓进行加固。螺栓可在螺旋形槽内移动。这里不需要润滑。
3.4.2.2间距传动
由于汽车的发展,一次又一次进行间距变速器的设计、制造和测试,但是没有成功。图3-73描绘间距传力的一些基本形式。
变速器上的力传递形式
通过改变力的作用点,即有效的间距半径,可以使传动比发生变化。除摩擦系数外,倾斜的压力也决定了可转换的力。
间距传输的发展可以归因于新的高摩擦润滑油,相比传统的润滑油有近两倍大的间距,使机构之间进行力传递。
对于机动车辆中的应用,使输入和输出轴之间的位置牢固最合适的方法,这可以使用在旋转对称体形式的中间链路来实现 。
3.4.3液压无级变速器
传输,在该系统中利用不可压缩的流体转移,可以根据功能的类型来分类:
1)液力传动
2)静液压传动
3.4.3.1液力传动
在液力传动,扭矩传递的发生根据佛廷格原理采用两旋转叶片、泵和涡轮盘。与液力离合器形成对比(3.3章),液力传动还包括定子转矩支撑,支撑在壳体[ 3-34 ]。
结果: MTur = MPump + MSt ( 3-51 )
MTur------水轮机轮转矩
MPump---泵轮转矩;
MSt--------定子转矩。
图3-74显示了液力传动(特立劳格帝亚转换器)的结构细节,伴随着叶片的原理和流动条件下nA/ nE = 0.7,这在现在还被使用。
泵
自由轮
定子
圆周速度
定子
出口
涡轮
入口
泵
相对速度
绝对速度
特立劳格帝亚转换器的原理
定子
涡轮
泵
流动方向
涡轮
工作流体,通常是油,通过泵轮相连的发动机,然后转移到涡轮机轮,它在其中被减慢加速。在这样做时,它将远处的能量到传输输出。另外一个重定向, 或多或少的延迟,导致扭矩加强。如果在泵和涡轮之间的速度差大,这加强就大。当v = 0时,这意味着一个牢牢制动涡轮机,所述扭矩转化率达到其最大值。随着涡轮转速增加,扭矩转换降到几乎线性的一个1:1的扭矩比(连接点)。
在这个例子中,在转速比、最佳操作点出现在约nA/ nE = 0.7,无冲击损失。如果速度比的进一步增加,则流体从定子流向后面直到速比约nA/ nE = 0.9(连接点)和定子不产生任何变形了,这意味着它不吸收扭矩,为了避免这种转矩恶化,再进一步增加速度比,定子与单向离合器变速器壳体,它可以运行,不传递扭矩,速度比为上面的连接点。在这个区域,特立劳格帝亚转换器作为一个离合器。
图3-75显示,在一个理想的方式,转矩和效率平均速度比。
摩擦损失
损失影响
转矩比
效率
离合器
转换器
特立劳格帝亚转换器的特性
速度比
此外,图片显示效率的粗糙特征的影响损失(流量和叶片方向之间没有联系)和摩擦损失(流体和壁面之间的摩擦)。
特立劳格帝亚转换器和发动机之间进行如下传动:
在连接点上,在泵轮输入的流量比是独立在传输的输出,因为该定子,这是在静止状态。重要的K值[式(3-18)],因此泵的特性曲线是不变的。在这种情况下,泵特性曲线,如果可能的话,应位于最佳的发动机效率的区域内。以上的耦合点,当定子和涡轮机轮作为一个“共同的”涡轮轮旋转,同样的原理,在液力离合器,变得适用。在那里,泵特性曲线移动的速度比nA/nE。从图3-76,因此我们发现只有图中的一部分可以通过发动机的扭矩和特立劳格帝亚器特性的相互作用。输出扭矩,这显示在图3-76,因此产生。
内燃机和特立劳格帝亚变换器之间的相互作用(来源:米奇可,“车辆动力学”)
传输输出速度
不适用区域
发动机转矩
效率
满负荷
部分负荷
效率
部分负荷
满负荷
理想的牵引力曲线
适用
转矩比
转速比
发动机转速
泵的特性曲线
发动机全负荷特性曲线
相比于理想的转矩特性的转矩要求和提供的转矩之间仍然比较大的差异。这意味着可达到的转换区(开始转换约2.0-2.5),并在高扭矩比低效率不足以其唯一的工作如在机动车辆的变矩器。特立劳格帝亚转换器与这样的传输加强联合。除了对需求曲线的有利途径,这可能是这里的特立劳格帝亚变换器的优点成为明显的只有采用组合台阶变速器。其优点包括紧凑,良好的散热性超过液压流体,自由的磨损在很大程度上,在功能作为一个扭转振动阻尼器。
3.4.3.2静液压传动
泵或发动机的双排量机器的液压传动系统使内燃机的转速与负荷无关。通过将液压机、液压机的轴向活塞泵或发动机的速度移动,在任一方向上的负速度可以设置为零和最大值之间。因此,在静液传动装置,既不启动离合器也没有离合器齿轮集所需的向后驾驶。具有这种特性的变速器称为IVT(无级变速器)。图3-77显示了这种传动的转换特性。它基本上相当于以前的机械式无级变速器[ 35 ]原理。
无级变速器转换器特性
发动机特性曲线
发动机转矩
变压器输出速度
变压器输出区域
变压器特性曲线
转换范围
超压阀限制
理论曲线
变压器输出转矩
转速比
转矩比
发动机转速
这里的缺点是,每两个液压机需要传送整个驱动力,因此他们的尺寸必须相对较大。这有一个显着效果的传输效率(负)。静液压传输的缺点包括不利的特定输出功率。它们的高生产成本和噪音,因此,这种传输将不再被使用了。这种变速器通常用于建筑和农业机械,部分是高技术传输的组件,其中一个机械部件负责提高效率。
3.4.4自动变速器(AT)
存在不同的可能性,实现自动变速器。在这样做时,主要使用以下概念:
1)行星变速器与液力变矩器。
2)手自一体变速器。
3)机械式无级变速器。
3.4.4.1带式缠绕式液力变矩器
最普遍的组合是一个由特立劳格帝亚转换器转移力矩传动,已经证明,单独特立劳格帝亚转换器不能提供一个充分的传递图(图3-76)。图3-78显示转矩特性可采用后置式阶梯传输来实现。
传输输出速度
传输输出转矩
自动变速器传送图(来源:米奇克;“车辆动力学”)
齿轮
常数
性能曲线
齿轮
齿轮
图3-79显示了轿车的三速自动变速器。
轿车三速自动变速器
附件:(Automotive Engineering Ⅰ:longitudinal dynamics of vehicles P123-132)
Fig.3-67 Shows a two-group transmission with two-speed planetary train as a rearmounted gound .
In a three-group transmission .up to 16 different gear levels can be obtained from a four-speed main transmission at a relatively low constructional expense. An example with 16 gears is shown in Fig.3-68.
The shifting diagram of this three-group transmission is depicted in Fig.3-69.
3 .4 .2 Mechanical continuously variable transmissions
In contrast to mechanical stepped transmissions so far used ire motor vehicles, mechanical continuous variable transmissions. Also called CVTs , have certain advantages based on their principle. The power characteristic is shown in Fig.3 -70. As a result of the continuous variable torque conversion. The achieved power curve (Fig.3-70b) represents the converter characteristic curare. In order to produce a delivery map (Fig.3-70c) which adjusts to different driving conditions,the CVT only requires a supply characteristic line (Fig.3-70a) from the engine. Except for the starting area , which requires an additional clutch (for a sufficient range of transmission ratios ), the entire demand map can be covered in this way [3-33].
Since the CVT allows .a free selection of the engine parameters (the torque and the speed)the operation of the combustion engine can be optimised based on different criteria. When the optimum points on the engine map are combined over the entire performance area of the engine,a curve which is parameterised with respect to power,also called the“control line”,results.Fig.3-71 shows the control lines for the optimisation criteria“noise”,“fuel consumption”,and“driving dynamics".
When realising only one control line for transmission operation using a relatively simple mechanical control ,the drawn-in curve represents a good compromise. in this case,control lines that correspond to demand as well as the drivers needs , can be realized . This already implies that continuously variable transmissions can exclusively be realised as automatic transmissions.
In mechanical CVTs,the variation of transmission ratio is achieved by varying the radius of the point of application forces. The torque is transferred by friction. Based on the type of torque transmission mechanical CVTs can be classified into:
1)Belt wrap transmission
2)Pitch transmission
3. 4. 2. 1 Belt wrap transmission
In Belt wrap transmissions,force transmission is achieved using belts,bands or chains, which are farce-fit clamped between disk pairs. By varying the rolling radii on the disks,the transmission ratio can be varied infinitely. As a result, the disk pairs along with the accompanying adjusting mechanism are also called variators. For force transmission, so far different belt,band and chain concepts have been proposed. Fig .3-72 shows the currently used force transmission systems.
In contrast to rubber belts used in variomatic transmissions in the 50s by Van Doorne,Holland,the transferable torque (up to 210 N·m) and efficiency,in particular,were significantly improved by changing over to steel-link bands in current CVTs,The transmission element,also called the thrust link band due to the kind of loading,consists of approx. three hundred steel segments that are held together on both sides by steel band packages(band size fl.1mm)piled onto each other.
In contrast to the thrust link band,in transmissions manufactured by PIV-Antriebe Werner Reimers KG,a chain loaded by tension is used for force transmission. The single chain link packages are connected to each other by cradle compression parts. Force transmission takes place by friction in the contact areas of the cradle compression parts and the disk wheels. U-shaped metallic clips that enclose the shackle bandage from the outside take over chain guide,The whistle,otherwise typical for chain drives,which occurs when the link comes into contact with the disk wheels,can be more or less avoided by an appropriately designed chain.
In order to keep the centrifugal load on a U-band as low as possible .Gates Rubber. USA, developed a rubber belt called power-trac which is reinforced by Kevlar fibers. In order to increase the transversal loading capacity, the rubber band is provided with an integrated metallic structure. Oil lubrication .as required in steel-steel friction pairings,is not necessary. This allows for an open transmission design associated with lower weight.
Kumm Industries,USA,proposes the fourth transmission system shown in Fig.3-72.In contrast to former Belt wrap transmissions,in which the force transmission element is clamped between two conical disk pairs,the Kumm CVT includes a rubber band which is also reinforced by Kevlar (Gates-development)and runs at each disk end on studs. The studs can be shifted in spirally-shaped grooves. No lubrication is required here as well.
3.4.2. 2 Pitch transmission
Since the development of automobiles,pitch transmissions have been designed, manufactured and tested over and over again,however with no lasting success. Fig.3-73 depicts some basic forms of pitch body force transmission.
The continuous variable change of the transmission ratio takes place under load by varying the point of action of the force,i.e. the effective pitch body radius. Apart from friction coefficient,the pressure force of the pitch bodies also determines the transferable force.
A renewed interest in pitch transmissions can be attributed to the development of new high-friction lubricants which enable nearly twice as large the force transmission between pitch bodies when compared to conventional lubricants.
For application in motor vehicles,only concepts which enable a firm position between the input and the output shafts can be used. This can be achieved using an intermediate link in the form of a rotationally symmetrical body.
3.4.3 Hydraulic continuously variable transmissions
Transmissions,in which power is transferred by an incompressible fluid,can be
classified, according to the type of function,into:
1) Hydrodynamic transmission
2) Hydrostatic transmission
3.4.3.1 Hydrodynamic transmission
In hydrodynamic transmissions,the transmission of torque takes place according to Foettinger principle using two rotating blade wheels,the pump and the turbine wheel. In contrast to hydrodynamic clutches(Chapter 3.3),the hydrodynamic transmission additionally includes a stator as torque support,that props up at the housing[3-34].
As a result: MTur = MPump + MSt ( 3 -51)
Where MTur -turbine wheel torque
MPump - pump wheel torque;
MSt - stator torque.
Fig.3-74 shows the constructional details of a hydrodynamic transmission( Trilok converter )which is exclusively used today,with the accompanying blade principle and flow conditions for nA/nE=0. 7.
The working fluid,which is generally oil,is accelerated by the pump wheel linked to the engine and then transferred to the turbine wheel where it is slowed down. While doing so,it gives away its energy to the transmission output. An additional redirection,
more or less without delay,leads to torque reinforcement. This reinforcement is high if the speed difference between the pump and the turbine is high. With v=0,implying a firmly braked turbine,the torque conversion reaches its maximum value. With increasing turbine speeds,the torque conversion drops almost linearly to a torque ratio of 1:1 (coupling point) .
In this example,at the indicated speed ratio,an optimal operation point appears at approx. nA/nE=0.7,without impact loss. If the speed ratio increases further,then the stator is increasingly streamed from behind until at a speed ratio of approx. nA/nE=0.9 (coupling point)and the stator does not produce any deflection anymore,meaning that it does not absorb a reaction torque,In order to avoid this torque deterioration at a further increased speed ratio,the stator is connected with the transmission housing by a one-way clutch so that it can run along,without torque transmission,at speed ratios above the coupling point. In this region,the trilok converter operates as a clutch.
Fig.3-75 shows,in an idealised way,the torque-and efficiency course aver the speed ratio.
Moreover the picture shows the rough characterisitcs of efficiency,the impact losses(no correspondence between flow and blade direction)and the friction losses(friction between fluid and walls)。
The interaction between a trilok converter and the combustion engine proceeds as follows:
Up to the coupling point,the flow ratios at the pump wheel input are independent of the ones at the transmission output because of the stator,which is at standstill. The important k-factor [Eq. (3-18)] and thus the pump characteristic curve are constant. in this case,the pump characteristic curve,if possible,should be located within the area of optimum engine efficiency. Above the coupling point,when the stator- and the turbine wheels rotate as a“common”turbine wheel,the same principle,as in the hydrodynamic clutch,becomes applicable. There, the pump characteristic curve moves in relation to the speed ratio nA/nE. From Fig.3-76,we thus notice that only a part of the engine map can be used through the interaction of the engine torque and the trilok converter characteristic. The output torque which is indicated in Fig.3-76,thus results.
Compared to the ideal torque characteristic there are still relatively large differences between the torque demanded and the torque supplied. This means that the attainable conversion area (starting conversion approx. 2.0-2.5) and the poor efficiency at high torque ratios are not sufficient for its exclusive employment as a torque converter in the motor vehicle. Trilok converters are thus combined with stepped transmissions. Apart from the favourable approach towards the demand characteristic curve, which is possible here, the advantages of the trilok converter thus become obvious only when used combination with stepped transmissions. The advantages include compactness,good heat dissipation over the hydraulic fluid,the fact that it is free of wear to a large extent and also in its function as a torsional vibration damper。
3.4.3.2 Hydrostatic transmission
Hydrostatic transmissions with two displacement machines working as a pump or as an engine enable a variation of the combustion engine speed independent of load. By shifting the hydraulic machines,e .g. axial piston pump or engine,the negative velocity of flow can be set between zero and the maximum value in either direction. Thus,in hydrostatic transmissions,neither starting clutches nor gear clusters are required for backwards driving. Transmissions having such characteristics are called IVT’s (Infinitely Variable Transmissions).Fig.3-77 shows the conversion characteristic of such a transmission. It essentially corresponds to the principle of the previously mechanical CVT [ 3-35].
The disadvantage here is that each of the two hydraulic machines has to transfer the entire driving power and thus they have to be dimensioned correspondingly large. This has a significant effect (negative) on the transmission efficiency. Further disadvantages of hydrostatic transmissions include the unfavorable specific power output,their high production costs and the noise development. Therefore such transmissions shall not be dealt with anymore. Such transmissions are often used in construction and agricultural machinery,partly as components of hi-tech transmissions in which a mechanical component is responsible for improving the efficiency.
3 .4 .4 Automatic transmissions(AT)
There exist different possibilities to realise automatic transmissions. In doing so,the following concepts are mostly used:
1) Planetary transmission with a hydrodynamic converter.
2) Automated manual transmission.
3) Mechanical CVT.
3.4.4. 1 Belt wrap transmission with a hydrodynamic converter
The most widespread combination is the one consisting of a trilok converter arid a power-shifted planetary transmission,It has already been explained that the trilok converter alone doesn’t provide a sufficient delivery map(Fig.3-76). Fig.3-78 shows the torque characteristic which can be achieved using a rear-mounted stepped transmission.
Fig .3-79 shows the example of a passenger car three-speed automatic transmission.
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