车辆动态分析装载机与悬浮轴

1、长春工业大学 赵敌车辆动态分析装载机与悬浮轴文摘i轮式装载机是一种工程机械主要用来在较短的距离移动未加工的材料。因为车辆的设计没有车轮悬架,轮式装载机司机暴露于高水平的全身振动中严重影响司机的舒适性。提出了本文的工作就是为轮式装载机添加一个轴悬挂,以减少振动和提高处理质量。而悬浮轴潜力巨大提高乘坐舒适性和性能,他们也必然影响到车辆动态行为，在许多方面不同于乘用车或其他道路车辆:轮式装载机有大螺距惯性质量,相比的轴载荷与加载条件相差很大,对车辆使用一个铰接框架转向系统而不是方向盘。这些问题都必须考虑在轮式装载机悬挂设计过程中。悬浮轴上的影响是通过振动模拟一个多体轮式装载机模型和无轴悬挂来分析的。

2、来自仿真结果表明,udinal和垂直加速度的去处以及水平加速度大大降低轴支撑,但这对侧向加速度减小的较小。通过减少了轧辊刚度侧向加速度可以进一步减少,尽管这可能不可行,因为操纵稳定性要求。俯仰振荡的车辆也被研究过,因为这是已知对乘坐舒适性有很大影响的。一个分析模型用于研究前后悬架特征在俯仰响应的轮式装载机上的效果表明一个更强硬的后方悬架是有利于减少倾斜,但用更硬的前悬架是可以达到类似的效应的。与多体仿真结果相比,显示相同的分析预测趋势。通过一个包含在线性表示一个液压气动悬挂在模型中,同时还发现,有利的动态行为可以维持，当车辆加载时可以利用悬架刚度与轴负载增加这一事实。当高速度时，铰接式车辆可能

3、出现横向振荡称为“蛇行”驱动。悬浮轴的影响在这些振荡进行分析使用多体仿真模型的轮式装载机使用一个等效辊刚度悬架模型。它是利用辊运动的簧上质量有一个略不稳定影响的蜿蜒振荡。这个效果更加显著,如果身体转动频率接近的曲线运动的频率,虽然这个损失在稳定性方面可以通过增加等效刚度或阻尼的转向系统来弥补。现有的车辆动力学理论一起和设计规则,研究报告这个工作中提供了一个对轮式装载机设计的特殊视角。 1介绍1.1背景建筑机械,有时被称为工程车辆或挖土机,基本上是一个类的自航机械用于土木工程。在本论文的工作关注的是一个特殊类施工机械、轮式装载机。这车本来是一个类型配备固定的拖拉机,前安装升降手臂由油缸来实现。与

4、气体车辆设计不同轮式装载机主要用于运输,它的建立没有任何轴悬挂。前面轮子是直接连接到车辆的身体,并且后轴是允许摆动在纵轴,从而允许所有车轮保持接触地面。一个示例的一个中型轮式装载机如图1所示。装载机主要用于建设或表面开采原油，在较短的距离移动材料,但因为属于多功能性的机器他们也常用于托盘搬运、木材加载和类似的任务.在出现第一个特制的轮式装载机大约50年前,对于提高效率、安全性和可操作性的车辆人们已经付出了很大努力。然而,对于控制振动或操作稳定方面重视不足。传统上,装载机已被视为机器而不是车辆所以驾驶动力学被认为是不太重要。然而,自需要提高工作效能和操作者的舒适度不断增长,未来需求为隔振和高速运

5、输能力将需要悬挂系统,允许安全而舒适的驾驶在一个范围的操作条件.这意味着在设计的装载机时车辆动态因素正在成为越来越重要的。由于原始汽车设计和粗糙的表面被应用于轮式装载机上,轮式装载机司机经常暴露于高水平的全身振动。在短期的角度来看这些振动会影响操作者消极,导致司机疲劳。长期暴露于低频率振动也被证明能增加背部疼痛的风险,也被认为是导致各种内脏器官疾病的原因之一.因此,全身振动可以被认为是一个主要的职业危害对于挖土机操作者这也已经成为了各种立法的重点如欧洲振动指令。因为轮式装载机没有任何轴支撑,主要隔离从地面激振动是通过轮胎。挖土机轮胎通常是大的和软的,因此通过地面粗糙度滤来吸收振动和冲击.从理论

6、上讲,轮胎可以被人为抑制高度虽然这将对振动实际上是非常不切实际的。据线图表示,轮胎会吸收大约五到十倍的振动能量为了充分保护操作员来自地面感应振动。这将大大影响轮胎的滚动阻力,因此车辆的能源消耗也会增加。此外,较大的能量吸收会导致高热力和机械应力在轮胎的材料上,这将加速磨损。很明显,轮胎设计增加振动隔离很快就会冲突经济和环境方面的考虑。驾驶室和座椅悬架也能减少操作员振动水平。驾驶室通常安装在橡胶元素上,有时加上一个集成的油箱,从而提供振动隔离通过弹性和粘性阻尼。更精致的驾驶室悬架也存在,驾驶室是安装在一个暂停的副框架上的。高端的司机座位通常设计用液压或气动阻尼器来缓冲司机从振动和冲击。主要限制的

7、阀座和驾驶室悬架有少量的悬挂行程可用来实现的。因为这些限制,刚度系数的灵活的元素需要足够高,以避免影响在大量加载时悬挂,因此,本征频率的驾驶室或座椅悬架一般是高于提供隔振在低频率范围的。此外,驾驶室和阀座主要是减少振动悬架的垂直方向。这可能缓解由活跃的系统5,尽管潜在的先进技术是座位车辆动态分析装载机与悬浮轴仍然还不清楚。还应指出的是,振动隔离的座位通常是减少操作员的姿势不足。此外驾驶室和座椅悬架,更大的装载机通常装有升降臂悬挂系统质量和惯性分离的升降手臂在车身上。铲斗和提升臂被孤立，车辆通过气体弹簧进入起重液压从而在某种程度上俯仰和垂直振荡,主要是对于一个加载车辆。考更大的振动隔离,可以提供

8、全轮悬挂轮式装载机。这将意味着灵活的连接车轮车身通过弹簧和阻尼器,就如几乎所有的公路车辆和大多数越野车车辆一样。轴悬挂有更大的潜力来提高驾驶的舒适性因为可用悬挂行程比较大,也有可能减轻振动在横向和纵向方向的方式通过乘驾驶室和座椅悬架无论如何是不能实现的。除了减少司机接触振动、轴悬架也可以提高装载机的工作效率。一个挖土机通常根据效率来定义体积,可以用一个指定的时间,工作性能直接关系到最大的实际车辆的速度。这个速度是目前很大程度上受限于操作员能够承受振动能力,因此屏蔽来自操作符震动会在实践中增加实现车辆速度。一个轴悬挂对减少轮载荷的波动也起作用,从而提高处理质量和操纵稳定性以很高的速度。因此悬浮轴

9、不仅对于驾驶的舒适性是有益的也为车辆的效率有益。包括暂停轮轮轴在内,很大一部分车辆的质量将振荡在轴支撑而不是简单的轮胎的灵活性。这显然会影响到车辆的驾驶性能，自然,增加了车辆的复杂性也将增加总成本和维护需求,这是一个重要的考虑因素。悬浮轴有时被用在特定的工程车辆,主要是越野的转储卡车可以使用橡胶弹簧或液压气动作为悬挂元素。农业拖拉机、暂停前轮轴越来越普遍和一些模型特性也是用后桥悬挂,应用程序装载机不常见,只能局限于军事模型它们配备悬浮轴来保证高速驾驶,从而允许快速部署和增加战斗生存能力。因为之前的信息关于轮式装载机悬挂设计有限,评估目前的设计方法的适用性,以及开发新的方法论,还要求为轮式装载机

10、悬架设计提供必要的知识。1.2 目标和研究问题本文的目的是为轮式装载机加载悬浮轴提供一种方法论为轮式装载机加载悬浮轴。这包括车辆动态行为的分析车辆,以及这种行为将受到影响,通过增加悬挂。总之,研究问题可以被制定为:潜在的好处和增加悬挂轮装载机的问题是什么,考虑到汽车特定的车辆动态性能了吗?选定的研究方法是使用不同复杂性的仿真模型系统地研究车辆的动态行为。分析方法用于预测的基本特征,并提供输入更多准确的模拟。这个方法需要足够的车辆动态模型和客观的驾驶和操作舒适性的评定。因此,工作中的一个重要部分是也调查需要什么造型工具模拟研究的装载机。 图2:剖开立体图的现代轮式装载机现代轮式装载机铰接式拖拉机

11、后置式发动机基本上是用前置升降实现的,当车轮车轴不悬浮,后桥通常是安装在一个旋转接头上允许车轮接触在不平坦的地面上,尽管一些模型由一个联合中心完成这一联合,然而它也允许接合和转动位移。当研究车辆动态行为的轮式装载机,一些重要的特征要明确:车辆质量:现代装载机范围在质量,从2 000 - 3 000公斤紧凑机器非常大矿业装载机总质量超过200 000公斤。多数的车辆范围在10 000 - 000公斤。因此,一个平均大小的轮式装载机相当于一辆重型卡车的总质量。然而,完整的车子的重量只有两个车轴支撑。这意味着悬挂组件必须强大到足以维持车辆轴的加载,这是远非道路车辆的重量可比的。车辆轴距是相对较短的,

12、特别是影响俯仰动力学。同时,大型车辆质量和越野车的使用意味着专业轮胎也要被使用,它可能会有不同于乘用车轮胎的特性。轴载荷变化:最大负荷的轮式装载机通常是大约60%的卸下车重。与一辆卡车或其他货运车辆不同,这个负载由前轴进行加载,意味着不仅质量增加的同时,重心转移前移。通常,前轴上的负载会增加约三到四倍当车辆装载时,而后桥载荷减小大约三分之二的静态轴重的卸载。这也影响了车辆的俯仰转动惯量。因此,轮式装载机悬架必须能够处理这种大范围的轴负载。同时,当举升时重心将向上移.虽然这与驾驶和控制无关，然而在高速驾驶时举升臂通常放在下面较低的位置,它仍然是静态稳定和短周期加载应该注意的重要事项。装载机通常配

13、备铰接框架操纵。这意味着车辆分离在锋面和后框架,连接着垂直转动关节。获得的转向角是通过改变相对角前方及后方之间在偏航平面,而不是引导车轮上的阿克曼操纵车辆。这个操纵装置的优势是转弯半径小和一个更健壮的设计,但它也有缺点那就是是降低静态稳定转弯的时候在停滞的重心是在位移的外侧。与阿克曼转向相比,铰接框架转向有几方面不同。数学公式的车辆动力学是平面更加复杂和灵活的转向系统这可能导致在高速开车时不稳定。复杂的动力:一个客运车辆可以通过一个单一的刚体模型描述的相当好,动力学的重型车辆是更复杂的。这主要因为车辆由几种重型零件和灵活的元素组成各自的固有频率都在同一数量级这将作为整个车辆的刚体频率。类似的条

14、件也存在重型卡车上面,制定简单的和准确的模型更加困难,因为一些车辆零件导致低频车辆振动。虽然简化模型可以用于初步设计考虑,一个更加精炼的振动分析需要加入更多的车辆零部件不仅仅是车辆的身体。从上面的清单可以看到,轮式装载机拥有一定数量的独特的属性,这些属性使它有别于之前动态分析的车辆。这些属性都必须解决以提供有用的信息输入来设计轮式装载机轴悬挂。上面列出的这个特点也有助于得出哪些方法是适合轮装载机建模和分析的。车辆动态行为的评估3.1乘坐舒适性评估通常,术语“试驾质量”是用来描述车辆的振动频率的范围约0 - 25 Hz。更高的频率扰动被称为“噪声”。另一个区别是与触觉和视觉质量的振动联系在一起的

15、,而噪音代表听觉振动。车辆上的低频振动通常是由表面起伏引起的。振动由车辆本身引起的,如动力传动系统或发动机振动,通常是更高的频率,因此有关噪声而不是乘坐舒适性。噪声的考虑通常对于任何更大的程度上轴悬挂设计是没有影响的,因此聚焦在这个论文的主要是在乘坐质量上。除了影响操作者的舒适度,干扰振动也可能对乘坐健康有影响。作为健康的影响是长期的需要很长时间才能暴露出来的。量化这种影响比纯操作者的舒适度是更加困难。冲突的情况也可能存在于改善舒适性不一定意味着健康状况的改善效果不重要,反之亦然。这进一步复杂化了汽车乘坐振动的评价。乘坐舒适性评价方法一般分为两类,定义为主观或客观。主观的方法包括问卷调查、采访

16、或其他测试旨在评估司机的印象，这通常需要经过训练的测试车手,要求能够对车辆改动产生细微差距和对重复的结果和辨别。使用客观的方法可测量参数,最常见的加速度,用来估计舒适水平。这提供了一种直观的方式来预测舒适性,但是它还要求客观评价来估计有意义的主观印象.特别是越野车辆,那里的振动光谱可能差别很大与公路车辆相比。因此当解释客观测量舒适性需要考虑。建立强健的而且具有代表性的客观舒适性措施仍然是一个研究的主题和没有全世界的相互关系，在客观的措施于感觉舒适之间，虽然一些协议已经在特定的测试情形被显示。其它显示表明在一离开道路驾驶情节时客观的舒适措施与主观的印象互是有关连的.一项相似的研究被曼斯菲尔德和白

17、路易斯在一条粗糙的道路上的使用垂直的加速一辆道路车辆来估计乘坐舒适性进行了。3.1.1 标准一些标准已经为乘坐震动做出了客观评估被计划。仍然需要非常大的讨论，这些标准发现大量的使用能为乘坐评估提供一个好出发点。ISO 2631 国际标准组织标准的 2631个现行的评估的架构表明人类对不同的情节全部身体对震动的回应。给震动评估的一般指导方针是建立在标准的第一个部份， ISO 2631-1是当前作为车辆震动测量最广泛地使用用方法。标准包括周期性，任意和短暂的震动从 0.5-80赫兹之间，周期中与一延长至 0.1个赫兹被认为为晕车评估。被用的基本的测定单位是加速度，是在操作员在车辆位子表面、地板或椅

18、背接口中测量的。权衡的频率适用于标准的加速，因为在确定的频率震动被视为更重要的。权衡位子震动的曲线在图 4 被显示.垂直加速使用 Wk 重量，当 Wd的时候作为侧部和纵观的轴。可以看出垂直振动在1赫兹被认为是更高的频率,而横向和纵向振动是最接近于1赫兹。权重因素Wf用于晕车评价,这只在垂直方向才有。这对于车辆动态研究是不那么重要的因为为驾驶的频率通常高于考虑运动病态频率的影响。然而,它可以指出,晕动病的影响越来越重要在大约0.3赫兹,这意味着任何车辆悬挂应该这样设计：即驾驶频率至少高于0.3赫兹。测量得到的振动激烈性方根(RMS)总和的加权加速度时间历程返回单个值,定义为,在这里,T是测量周期

19、的持续时间。注意,ISO 2631 - 1使用既表示加速度时间历程也表示RMS值。单位为是.ISO 2631 - 1提供的指导方针根据测量的目的的不同在一些方面也是不同的。对于舒适性评价,加速度是可以测量的在所有的方向和速度的矢量加权加速度作为最后的舒适性尺度的衡量标准。角加速度也可以包括,被视为具有相同的效果,尽管这只是对乘坐的人有效果。平移加速度也可能适用于站立和休息的人。如果要估计健康的影响,与标准的建议相反,每个轴是单独评估,还包括一个额外的权重因子为1.4的横向和纵向方向,因为在这些方向的运动被认为是更危险的。角加速度是建议不要被包括。此外,健康效应评价主要对于坐人是有效的。作为IS

20、O 2631 - 1振动评估根据测量的目的不同的使用方法也不同,客观的结果可以在几个方面解读。这必须考虑如果研究结果用作输入到汽车设计过程中,对健康或安舒适性方面进行改善其影响可能导致在其他方面减少。例如,如果以距加速度减少为代价增加版本提卡加速度,这可能提高目标运行舒适感,但也可能导致更少的有利的动态行为与对健康的影响以为健康评价不考虑俯仰运动。ISO 2631 - 1标准一个经常被提到的缺点是对瞬变和冲击缺乏可靠的方法。作为标准使用RMS值来确定振动激烈性,孤立的瞬变不会对总价值产生影响如果测量周期很长。对于路边的车辆,这是一个明确的限制，运营商可能遇到这样的车辆冲击和瞬态远远超出道路汽车

21、司机。对乘坐舒适性评价,它已经表明,一个运行的均方根平均使用1 s窗口长度它与来自孤立冲击的主观印象紧密相关。然而,健康的影响仅仅通过RMS只值来说明不够的。最新ISO 2631标准的一部分,ISO 2631 - 5,一直专门开发解决这个缺陷。而不是仅仅使用加速度值,ISO 2631 - 5包括一个力学模型在回应座位来计算腰椎的加速度。评估健康影响,加速度是翻译成一个等效压缩应力用兆帕表达出来，作为一个健康效应测量。初步测试表明,这种方法似乎可以更精确地检测冲击比ISO 2631 - 1。然而,应用程序和可用性的标准仍然是有限。验证数据对于机械模型包含基于一个相当狭窄的选择测试对象(主要是健康

22、男性年龄在20到30岁),这意味着精度不能保证为个人,这个配置文件不匹配。标准也也在立法后被制定。这意味着新旧标准可能产生冲突,应该用于认证的目的虽然新方法实际上可能产生更多的相关结果。其它标准许多其他国家标准振动评价也存在。两个例子是英国BS 6841和德国VDI 2057,它相当类似ISO 2631 - 1标准。另一种方法是美国平均吸收功率(AAP),它使用一个不同的方法关注振动能量接收的人的身体在一段时间内。虽然这些国家标准仍然使用在某种程度上,但是ISO 2631 - 1还是是最常用的方法。3.1.2其他舒适性评价方法现有标准对于驾驶舒适性和健康评估已经被使用很长时间了并且经验表明,合

23、理的相关性与主观印象也被发现。因此,标准化的测量可以被认为是一个很好的起点工程预算即使结果需要被谨慎对待。最大的可能是在处理不确定性的影响和冲击隔离瞬变。基于目前的研究,已经提出了一些替代方法为了处理这个缺点。 Vehicle dynamic analysis ofwheel loaders with suspended axles iAbstract The wheel loader is a type of engineering ve hicle used primarily to move crude material over shorter distances. As the ve

24、hicle is designed without wheel suspension, wheel loader drivers are exposed to high levels of whole body vibration which influences ride comfort negatively. The work presented in this thesis has the aim to investigate the potential in adding an axle suspension to a wheel loader in order to reduce v

25、ibrations and increase handling quality. While suspended axles have great potential for improving ride comfort and performance, they will also necessarily affect the vehicle dynamic behaviour which is different in many aspects from that of passenger cars or other road vehicles: the wheel loader has

26、a large pitch inertia compared to its mass, the axle loads vary considerably with loading condition, and the vehicle uses an articulated frame steering system rather than wheel steerin g. These issues must all be considered in the design process for a wheel loader suspension. The effects of suspende

27、d axles on ride vibrations are analysed by simulating a multibody wheel loader model with and without axle suspension. Results from the simulations show that longit udinal and vertical acceleration levels are greatly reduced with axle suspension, but that the decrease in lateral acceleration is smal

28、ler. By reducing the roll stiffness lateral accelerations can be further reduced, although this may not be feasible because of requirements on handling stability. The pitching oscillation of the vehicle has also been studied as this is known to have a large influence on ride comfort. An analytical m

29、odel is used to study the effect of front and rear suspension characteristics on the pitching response of the wheel loader, showing that a stiffer rear suspension is favourable for reducing pitching but also that a similar effect is attainable with a stiffer front suspension. Results are compared to

30、 multibody simulations which show the same trend as anal ytical predictions. By including a linear is representation of a hydropneumatic suspension in the models, it is also shown that favourable dynamic behaviour can be maintained when the vehicle is loaded by utilising the fact that suspension sti

31、ffness is increasing with axle load. Articulated vehicles may exhibit lateral oscillations known as snaking when driven at high speed. The effect of suspended axles on these oscillations are analysed using a multibody simulation model of a wheel loader with an equivalent roll stiffness suspension mo

32、del. It is found that the roll motion of the sprung mass has a slightly destabilising effect on the snaking oscillations. This effect is more pronounced if the body roll frequency is close to the frequency of the snaking motion, although this loss in stability can be compensated for by increasing th

33、e equivalent stiffness or damping of the steering system. Together with existing vehicle dynamic theory and design rules, the studies reported in this work provide an insight into the specific issues related to suspension design for wheel loaders. 1 Introduction 1.1 Background Construction machines,

34、 sometimes referred to as engineering vehicles or earth movers, are basically a class of self-propelled machines designed for use in civil engineering. The work in this thesis concerns a special class of construction machines, the wheeled loader. This vehicle is essentially a type of tractor equippe

35、d with permanently attached, front mounted lifting arms operated by hydraulic cylinders. Unlike vehicles designed primarily for transport, the wheel loader is built without any axle suspension. The front wheels are attached directly to the vehicle body, and the rear axle is allowed to oscillate arou

36、nd the longitudinal axis, thus allowing all wheels to maintain contact with the ground. An example of a medium sized wheel loader is shown in figure 1. Wheel loaders are mainly used in construction or surface mining for moving crude material over shorter distances, but because of the versatility of

37、the machines they are also commonly used for pallet handling, timber loading and similar tasks. Since the advent of the first purpose-built wheel loader about 50 years ago, considerable effort has been made to improve the efficiency, safety and operability of the vehicle. However, less attention has

38、 been given to issues like ride vibrations or handling stability. Traditionally, wheel loaders have been seen as machines more than vehicles and so the driving dynamics have been considered less important. However, since the demands for increased task performance and operator comfort are continuousl

39、y growing, future requirements for vibration isolation and high speed transport capacity will call for suspension systems that allow safe and comfortable travel under a range of operating conditions. This means that vehicle dynamic considerations are becoming increasingly important in the design of

40、wheel loaders. As a consequence of the primitive vehicle design and the rough surfaces where wheel loaders are usually operated, wheel loader drivers are often exposed to high levels of whole body vibration. In short-term perspective these vibrations will affect operator comfort negatively and cause

41、 driver fatigue. Long term exposure to low frequency vibrations has been shown to increase the risk for lower back pain , and is also believed to be the cause of various internal organ disorders. Thus, whole-body vibration can be considered a major occupational hazard for earth mover operators and h

42、ave been the focus of various legislations such as the European Vibration Directive . As the wheel loader does not have any axle suspension, primary isolation from ground induced vibrations is provided by the tyres. Earth mover tyres are typically large and soft, thus filtering out and absorbing som

43、e of the vibrations and shocks caused by ground roughness. Theoretically, tyres could be engineered to dampen higher amounts of vibration although this would in reality be highly impractical. According to Lines etal 3, tyres would have to absorb about five to ten times more vibration energy in order

44、 to fully protect the operator from ground induced vibrations. This would greatly affect the rolling resistance of the tyre and hence the energy consumption of the vehicle would increase as well. Furthermore, the larger energy absorption would lead to high thermal and mechanical stress in the tyre m

45、aterial, which would accelerate wear. It is obvious that tyre design for increased vibration isolation would soon conflict with economic and environmental considerations. Cab and seat suspensions also function to reduce operator vibration levels. The cab is usually mounted on rubber elements, someti

46、mes combined with an integrated oil volume, thus providing vibration isolation through flexibility and viscous damping. More refined cab suspensions also exist where the cab is mounted on a suspended subframe 4. High-end driver seats are commonly designed with hydraulic or pneumatic dampers to cushi

47、on the driver from vibrations and shocks. The main limitation of seat and cab suspensions is the small amount of suspension stroke available. Because of these lim itations, the stiffness coefficien t of the flexible elements needs to be high enough to avoid impacts with suspension ends at large tran

48、sient loads, and therefore the eigenfrequency of the cab or seat suspension is generally too high to provide vibration isolation in the lower frequency range. Furthermore, cab and seat suspensions mainly reduce vibrations in the vertical direction. This could possibly be alleviated by active systems

49、 5, although the potential of advanced seat technology is Vehicle dynamic analysis of wheel loaders with suspended axles still unclear. It should also be noted that the vibration isolation of the seat is often reduced by inadequate operator posture . In addition to cab and seat suspensions, larger w

50、heel loaders are commonly fitted with a lifting arm suspension system to decouple the mass and inertia of the lifting arms from the vehicle body. The bucket and lifting arms are isolated from the vehicle by means of gas springs incorporated in the lifting hydraulics and thereby pitching and vertical

51、 oscillations to some extent, mainly for a loaded vehicle. Considerably greater vibration isolation can be provided by designing the wheel loader with full wheel suspension. This would mean flexibly attaching the wheels to the vehicle body by means of springs and dampers, as on virtually all road ve

52、hicles and on most offroad vehicles. Axle suspensions have greater potential for improved ride comfort as the available suspension travel is larger, and also have the potential to alleviate vibrations in the lateral and longitudinal directions in ways not possible by cab and seat suspensions. Apart

53、from reducing driver exposure to vibrations, axle suspensions could also improve the task performance of the loader. As the efficiency of an earth mover is usually defined by the volume of material that can be transported in a specified time, the working performance is directly related to the maximu

54、m practical velocity of the vehicle. This velocity is currently limited to a large extent by the operators ability to withstand vibrations and therefore shielding the operator from vibrations will in practice increase the attainable vehicle speed. An axle suspension also functions to reduce wheel lo

55、ad fluctuations, thus improving handling quality and manoeuvring stability at high speeds. Therefore suspended axles are not only beneficial for driver comfort but also for the performance of the vehicle. . With the inclusion of suspended wheel axles, a large part of the vehicle mass will be oscilla

56、ting on the axle suspension rather than simply the tyre flexibility. This will clearly have an impact on the driving dynamics of the vehicle. Naturally, the increased complexity of the vehicle will also add to overall cost and maintenance needs, which is not an unimportant consideration. Suspended a

57、xles have been used on certain engineering vehicles for some time, mainly off-highway dump trucks which utilise rubber springs or hydropneumatic struts as suspension elements. On agricultural tractors, suspended front axles are becoming increasingly common and some models feature rear axle suspensio

58、n as well 6. Applications to loader vehicles are less common and have mainly been limited to military models that are equipped with suspended axles to enable high speed road travel, thereby allowing rapid deployment and increased combat survivability 7, 8. Since previous information regarding wheel

59、loader suspension design is limited, a review of the applicability of current design methods, as well as the development of new methodology, is required to provide the necessary knowledge for wheel loader suspension design. 1.2 Objective and research question The objective of this thesis is to provi

60、de a methodology for the development of wheel loaders with suspended axles. This includes analysing the vehicle dynamic behaviour of the vehicle, and how this behaviour will be affected by the addition of a suspension. In summary, the research question can be formulated as: What are the potential be