某货车车架轻量化设计【三维CATIA】【含9张CAD图纸、说明书】【QX系列】
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本科毕业论文(设计)中期检查报告论文题目 某货车车架轻量化设计 1论文工作是否按开题报告预定的内容及进度安排进行论文工作按照开题报告预定内容进行,车架设计、建模、有限元静力分析已基本完成,下一步准备进行动态分析,为最后的轻量化设计做准备。2目前已完成的研究工作及结果(1)参照载重汽车相关参数进行车架设计;(2)建立车架结构的实体模型; (3)对车架结构进行静力分析; 车架弯曲(满载)工况,车架扭转工况3后期拟完成的研究工作及进度安排(1)拟完成的研究工作: 动态分析:包括模态分析和瞬态响应分析; 车架轻量化设计。(2)进度安排: 第十三周进行相关英文资料的翻译; 第十四周进行动态分析; 第十五周到十六周进行轻量化设计; 第十七到十八周撰写说明书并准备答辩。4存在的困难与问题(1)在软件运用方面还有些不熟练;(2)多像老师和同学请教。5如期完成全部论文工作的可能性论文工作进展顺利,预计能够如期地完成论文工作。中期报告检查组意见:(以下空46行文字) 组长(签字): 年 月 日(此行置于页面底部)- 6 - 本科毕业论文(设计)开 题 报 告论文题目 某货车车架轻量化设计 - 1 -1课题研究的目的和意义汽车问世百余年来,特别是从汽车产品的大批量生产及汽车工业的大发展以来,汽车为世界经济的大发展、为人类进入现代生活产生了无法估量的巨大影响。今天,在发达国家,汽车的普及已经达到很高的程度,在美国平均每个家庭拥有各种汽车2、3辆;虽然中国的汽车人均拥有量远低于发达国家水平,但是由于中国巨大的市场和国际汽车工业对中国汽车工业的影响,中国汽车工业经过50年的风雨历程,已形成一个比较完整的工业体系。任何问题都有两面性,汽车工业的发展为人们带入现代生活的同时也带来了许多问题12,例如,一、能源问题,每年汽车的石油消耗量保持在近100亿桶,并每年以一定的速度增加,而世界石油资源只能开采几十年,煤炭资源也只够开采一百来年,人类面临着严重的能源危机,节能环保成为工业领域不可避免的课题,汽车工业同样不可避免。二、环境问题,汽车每年向大气排放大约几亿吨的有害气体,占大气污染物的60以上,被认为大气污染的“头号杀手”。汽车尾气中C02、CO、HC是大气污染的主要有害气体,特别是C02温室效应近年来倾向日趋明显。汽车作为现代化社会大工业的产物,在推动人类文明向前跃进并给人类生活带来了便捷舒适的同时,对大自然生态环境的恶化也有着难以推卸的责任。目前世界汽车的保有量超过6亿辆,每年新生产的各种汽车约3500万辆,汽车每年的石油消耗量约占世界每年石油产量的一半以上。随着人们对环境保护的日益重视,以缓解石油资源紧缺所带来的能源危机,节能环保技术越来越多为广大汽车公司所采用,车辆轻量化是降低能量消耗的有效措施之一,资料表明,车重减轻10%,燃油消耗可降低6%-8%3。普遍认为客车、货车的车架骨架质量占整车质量的60%,对于专用车,车架所占的质量比例则更大,因此减小车架质量可为车辆轻量化提供最大的潜力。轻量化还可以减少原材料的消耗,降低车辆的生产成本。本课题就是在上述背景下提出的,目的在于研究载货车车架结构使之受力合理,等强度及等寿命设计。对重型车的车架进行以减轻自重为目标的结构优化,提出车架的轻量化方案,在保证承载能力的前提下有效降低质量,一定程度上起到节能的作用。最终达到保证载货车在性能和功能不受影响或有所提高的情况下,减轻载货车车架质量。2国内外研究现状受到能源和环境保护的压力,世界汽车工业很早就开始了轻量化的研究。虽然应用轻金属、现代复合材料是现代车辆轻量化研究的热点之一,但是这些新材料应用在主要承载部件上的成本较高,因此在短时间内很难普及4。另一方面,车辆的传统材料钢材,由于其强度高、成本低、工艺成熟,并且是最适于回收循环利用的材料,因此利用钢材实现轻量化的可能性备受关注。1994年,国际钢铁协会成立了由来自全世界18个国家的35个钢铁生产企业组成的ULSAB(Ultra-Light Steel Auto Body)项目组,其目的是在保持性能和不提高成本的同时,有效降低钢制车身的质量。ULSAB项目于1998年5月完成,其成果是显著的。ULSAB试制的车身总质量比对比车的平均值降低25%,同时扭转刚度提高80%,弯曲刚度提高52%,一阶模态频率提高58%,满足碰撞安全性要求,同时成本比对比车身造价降低15%5。从1997年5月启动的ULSAC (Ultra-Light Steel Auto Closures)、ULSAS(Ultra-Light Steel Auto Suspension)和1999年1月启动的ULSAB_AVC(AdvancedVehicle Concepts)为ULSAB的后续项目,也在轻量化研究上取得很大成68。除了以上提到的国际上著名的四个轻量化项目外,全世界范围内对基于结构优化的轻量化技术也进行了大量的研究。韩国汉阳大学J.K.Shin、K.H.Lee、S.I.Song和G.J.Park应用ULSAB的设计理念和组合钢板的工艺,对轿车前车门内板进行了结构优化,成功地使前车门内板的质量减重8.72%,此技术己在韩国一家汽车企业中得到应用9。通用汽车公司的R.R.MAYER、密西根大学的N.KIKUCHI和R.A.SCOTT应用拓扑优化技术以碰撞过程中最大吸收能量为目标对零件进行优化设计。此技术已应用到一款轿车的后围结构上10。瑞典Linkoping University的P.O.Marklund和L.Nilsson从碰撞安全性角度对轿车B柱进行了减重研究。研究以B柱变形过程中的最大速度为约束变量,以B柱各段的厚度为优化变量,以质量为优化目标,实现在不降低安全性能的条件下减重25%11。美国航天航空局兰利研究中心的J.Sobieszczanski Sobieski和SGI公司的S.Kodiyalam以及福特汽车公司车辆安全部门的R.Y.Yang共同进行了轿车的BIP(Body In Prime)基于NVH(噪声、振动、稳定性)和碰撞安全性要求下的轻量化研究,实现了在不降低性能的条件下减重15Kg12。从上面的文献中,可知国外的汽车结构轻量化研究主要可分为四类:(1) 提出先进的设计理念,发展先进的制造工艺并通过尺寸参数优化而得到新的轻量结构;(2) 将拓扑优化和形状优化引入到结构轻量化过程中;(3) 利用硬件优势,大量考虑动态过程(如碰撞、振动过程)中的各种约束,对尺寸参数进行优化而得到轻量结构,主要强调安全性;(4) 提出和应用新的现代优化算法,并引入到结构轻量化过程中、国内对基于结构优化的车辆轻量化研究开展也很多,在车架的轻量化方面,吉林工业大学的黄金陵曾经在对影响车架结构强度和刚度的因素进行理论分析的基础上,运用惩罚函数法得到了汽车车架各梁截面参数的最佳值13。河北工学院的冯国胜曾经在有限元分析的基础上,采用复合形法和罚函数法对汽车车架结构参数进行了实例优化计算14。此外,国内对轿车和客车的结构轻量化做了大量的研究1518。由国内外的研究现状可以看出,目前国内外对车辆的轻量化都主要集中在车身上,对车架的轻量化研究也集中在对轿车和客车的研究,真正将轻量化应用到重型车和专用车结构方面的还相当少。对于车架占据绝大部分质量的专用车辆来说,减小其车架质量可为车辆轻量化提供最大的潜力挖掘空间。依据国内外研究现状,目前对轿车和客车骨架应用有限元法进行静力分析和模态分析,并在此基础上对结构进行分析和改进己是常用的技术手段,但对于一些需求量相对较少,产量不高的重型车和专用车,有限元技术还没有得到广泛使用。本文将有限元法引入重型专用车的设计、分析和结构优化工作中,既解决企业设计生产过程中的实际问题,也有较高的应用价值。3. 本课题的研究内容及技术方案本文的研究对象为EQ1290W载重汽车车架,论文的任务侧重于对车架的结构有限元分析,完成其轻量化设计研究。主要内容包括:1. 车架设计 参照EQ1290W载重汽车相关参数进行车架设计;2. 车架有限元建模先在CATIA中建立其三维几何模型,在此基础上利用ANSYS建立其有限元模型及边界条件;3. 典型工况下车架静态分析根据实际车架受力情况对车架进行加载,分析各种工况下车架的静态强度和刚度,对静态性能进行评估;4. 车架质量的优化设计在满足强度和刚度的前提下,使其质量尽可能小,并做优化后的结构分析,检验方案的可行性;4. 本设计的特色ANSYS是大型的通用有限元软件,其功能强大,可靠性好,具有强大的结构分析能力和优化设计模块,因而被国外大多数汽车公司所采用。本文将基于ANSYS建立车架结构的实体单元模型,对汽车车架结构进行静力的研究。首先,对ANSYS进行了简要的介绍,为车架结构进行有限元分析做好准备工作;其次,以某重型载货汽车车架结构为研究对象,利用ANSYS建立了车架结构有限元的实体单元模型,对车架建模过程进行了研究;再次,对车架结构的静态特性进行深入研究,对车架进行性能分析评价;最后,建立车架结构简单的梁单元优化模型,以车架纵梁截面尺寸作为设计变量,以车架总体积为设计目标,运用ANSYS优化模块对车架结构的轻量化设计进行有益的尝试。5. 进度安排第1周至第3周:搜集资料,写开题报告;第4周至第7周:确定车架的基本结构;第8周至第10周:建立车架的三维实体模型;第11周至第16周:轻量化设计;第17周:撰写说明书;第18周:准备答辩。6. 参考文献1靳福来,汽车轻量化技术现状,汽车技术,1995,7:56582华润兰,论汽车轻量化,汽车工程,1994,209(6):3753833 B.Honf., G.Bremana, Light-weight Body-current Status and Future Challengers, Chenises-German Ultra-Light Symposium, Beijing, 2001, (9):2012074 冯美斌,汽车轻量化技术中新材料的发展及应用,汽车工程,2006,28(3):213220 5 Ultra-Light Steel Auto Body Final Report, Porsche Engineering Services, Inc. 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-汽车设计-车架设计车架是汽车最基本的台架,所有的悬架和转向连接部件都安装在车架上面。如果汽车车架柔性过大,会使汽车既无法转向,也无法进行正常操纵。而如果汽车车架结构刚性过大,又会引起不必要的震动传递给驾驶员和乘客的座舱室。汽车车架和悬架的结构设计不仅决定了汽车噪声大小和震动的幅度强度,而且也将影响到汽车的质量和车辆的正常操纵。汽车制造厂商们在他们生产的汽车上都使用了几种不同的车架结构。其中,整个七十年代最常使用的是壳体和大梁的分体结构。目前它仍然在大型货车、小吨位货车和卡车上应用着。在汽车壳体和大梁的分体结构里,发动机、传动装置、传动齿轮和车壳都是通过绝缘装置固定在车身大梁上。车架内部的绝缘装置是人造橡胶缓冲垫,能够阻止道路不平和发动机工作引起的噪音和震动传到驾驶员和乘客的座舱里。第二种是汽车车架的单体结构。这种设计到目前为止在现代汽车上是最常用。单体车架按所需的强度来分,设计有轻型结构。在这种汽车结构中大梁作为车架的一部分被直接焊接到壳体上。底盘的重量增加了大梁的强度。传动齿轮和传动装置经由大而软的人造橡胶绝缘垫安装在单体车架上。绝缘垫减弱了噪声的传动和震动。若绝缘垫太软,将会引起传动齿轮和传动装置位移。这种位移称为柔量,它会影响到汽车的操纵性能和控制性能。若绝缘垫太硬,则不能起到应有的隔绝噪音和减小震动的作用。汽车制造厂商们精心地设计绝缘垫,把它们装置在汽车适当的地方,以降低噪声,缓冲震动的传送,使汽车便于驾驶,驾驶员和乘客乘坐舒适。绝缘垫的性能随使用年限发生变化,当汽车变旧时原先的性能也随之改变。第三种结构是把前两种结构的主要特点结合在一起。它在汽车前舱使用了短车梁,在汽车后舱使用了单体车架。单体部分刚性很大,而短的车梁增强了绝缘作用。汽车制造厂家们在汽车上选择那种生产成本低而同时又符合对噪音震动,驾驶操纵性能要求很高的车架结构。老式的大型的车辆、货车、和卡车通常使用壳体和大梁的分体结构。较新的,较小型的车辆通常使用单体结构的车架。动力传动系统动力传动系统包括从发动机直到驱动轮的所有部件。联动装置和后驱动装置传送着来自发动机的扭矩。其它部件则把部件与部件相互连接起来。加速时发动机的扭矩和制动时的扭矩则加载在悬架部位上。修理悬架时,很可能需要拆卸传动系统的各零部件来进行修理。悬架移动时产生的噪音可能来源于传动系统的零部件。下边叙述一些不同的传动装置系统的基本知识,在进行悬架修理时可供参考。使用前轮驱动的传动系统经常将联动装置和后轮传动装置结合成一个装置。这个对中置和后置发动机的汽车也是很适用的。这个装置称为转换轴。它为两端各带有一个万向节的短半轴,把转换轴和车轮连接起来。这些轴当悬梁移动和转向时把动力从后传动装置传送到车轮上。后传动装置里的差速器分流输入的动力,每个驱动轮上各分一半。这就使驱动轮在转弯时会以不同的速度转动。在前置发动机后轮驱动的汽车里,联动装置位于驾驶坐舱的前底板下。传动轴被用来把发动机动力传送到后桥上。传动轴每端各有一个万向节。当悬架移动时,万向节通过变化着的传动系统的角度传送动力。驱动轮上带有独立悬架的汽车中有一个牢固地附加在车身大梁或发动机上的后传动装置。在加速时该装置在悬架部位上会产生动力,并不产生扭矩。如果刹车装置安装在车舱内,卡钳装到大梁上而不是悬架上,那么刹车装置也不会在悬架上产生扭矩。仅用于控制加速和减速扭矩的悬架与必须同时控制悬架力和扭矩的悬架在汽车设计上是完全不相同的。悬架系统悬架包括弹簧,避震器和控制连杆装置。它必须能够足以支撑车身自重和负载。悬架也应能够承受发动机和制动对它的反作用力。悬架系统最重要的作用是使轮胎与路面接触的时间尽可能的长。在支撑车体和负载时,甚至在高低不平的道路上行驶时更加应如此。这四个轮胎的胎面是车与路面相接触的唯一的部位。发动机全部输出的动力,转向力和制动力都通过与路面相接触的轮胎的胎面起作用。每当轮胎不与路面接触或汽车开始打滑时,汽车的控制力(动力、转向力、制动力)就会减弱甚至丧失。车体是靠弹簧支撑着,弹簧可分为螺旋型、钢板型、扭棒型和充气型。螺旋型弹簧是现代汽车中应用最为广泛的类型。螺旋型、扭棒型和充气型弹簧都需要用连杆和连杆臂以使车轮就位。钢板弹簧提供了对车体的横向和纵向控制,以防止汽车车轮在行驶时不必要的位移,它们通常用在载重货车和卡车上。悬架系统是随着客运汽车的发展而变化和改进着。豪华轿车,特种车辆,小型汽车和轻型卡车的设计目的是截然不同的。现代轮胎的改进不断地改善了车辆的操作性能,它的改进是与避震器,转向系统和悬架控制装置一起同步改进的。现代汽车在各种操纵条件下都需要轮胎与路面接触,以便安全、正确地控制并行驶汽车。要想要最大限度的安全驾车,要牢记这四个轮胎必须在任何时间都与路面相接触。同时需要考虑汽车操纵的灵活性,轮胎的抗耐磨性,汽车驾驶的舒适性和行车的安全性,以达到汽车的有效控制。悬架系统分为前悬架和后悬架。前悬架的设计已得到了飞速发展。从较为粗糙的硬轴结构发展到了现代的轻型、高强度、支撑型独立悬架结构,并由于增加了连杆装置而使汽车的性能得到了改善。悬架结构的改进是随着路况的改善和驾驶员的需要而进行改进的。大多数前置发动机,后轮驱动的汽车都采用一个简单的从属性后悬架。但后轮驱动的独立悬架结构复杂得多,而且成本极高,因而只用于少数客车上。对于前置发动机前轮驱动的车辆,通过把传动装置移至前部,后悬架仅用来调节驾驶控制力和刹车时的反作用。这就导致了简化的非独立的悬架机构,半独立的悬架机构和独立的后悬架机构的应用,后者大量应用于新型车辆的结构设计上。转向系统汽车驾驶员通过对转向齿轮的控制汽车前轮的方向。现代的转向齿轮有两个主要的部分组成,转向杆和齿轮组。转向杆有一个被支撑的轴,它把驾驶员的方向盘与齿轮组连在了一起。齿轮组可将汽车驾驶员的转向力增大,以带动转向连杆装置。后轮驱动汽车的前轮在一个心轴上转动。心轴是转向节的一部分。该转向节与带有球接头的前悬横梁相互连接。球接头在前悬架上下移动时可以进行转向。前轮驱动的汽车的轮毂在转向节里的轴承内的空心轴短轴杆上传动。汽车方向盘控制转向齿轮装置。它依次通过转向连杆装置使转向节开始移动。现在使用两种转向齿轮的结构,即齿轮齿条式结构以及循环球式结构。现代汽车设计了对速度敏感的转向结构。因此当汽车慢速行驶时需要较大的力才能使汽车转向。于是在很多汽车上装备了助力转向装置。由于助力转向装置起了主要作用,所以转向比降低了,这样就能够轻微转动方向盘使得汽车转向。助力转向齿轮类似于标准的转向齿轮。它有承压面,液体压力加在其上,以增加汽车驾驶员的转向力。齿轮齿条式转向结构和循环球齿轮结构都有了动力辅助装置。转向齿轮的动力是由发动机从动泵提供的。该泵使动力转向液体流过一个由阀体控制的系统。该控制阀能感知汽车驾驶员的转向力。把液体压力加到转向系统的承压面上。该液体压力承接了一些使汽车转向的力。现在汽车的转向杆有很多个部件组成。它被用来分散、抵消汽车碰撞力以保护驾驶员的切身安全。在有些汽车上转向杆还可以倾斜和伸缩来调节方向盘的位置使驾驶员感觉更加舒适。为了减少驾驶员汽车被盗的机会,还安装有一个转向齿轮的保险锁。很多汽车还有一个变速器保险锁。因为处在驾驶员很容易触及的范围内,所以转向杆上还可以带有变速器换挡控制滑杆,转向信号开关,前大灯和变光开关,刮水器开关,紧急闪烁器开关和速度控制器。制动系统使用中的制动器应能起到制动住车辆的作用。制动器能使汽车滑行时能防止行驶速度过快,在斜坡上制动时能将汽车停在适当的位置上。汽车刹车的设计应使驾驶员能调节制动力以控制汽车。汽车的控制不仅受悬架和转向系统影响,而且也受汽车刹车影响。制动系统的故障可导致汽车刹车时车轮滑脱。要修理悬梁系统,也可能需要将制动系统的部件拆卸开。为此本文将讨论制动系统。制动系统应给予汽车驾驶员提供均匀平稳的制动力。刹车板上所需的力不应太大,而使车轮不至于被瞬间刹死。为满足这些汽车刹车的要求,对于汽车制动已有了最低限度的刹车标准。驾驶员通过机械装置、真空和液压装置控制制动力。制动力是随着附加在汽车刹车板上的踏板力的增加而增加的。这个力通过制动系统的传递以把固定的汽车刹车片推压到转动的制动器表面上。当它把动能(运动的能量)转化为热能(热)时,就使汽车减速。制动量的最大值就产生于车轮被瞬间闸死而引起的轮胎在路面上滑动之前。所以制动量的最大值取决于轮胎和路面之间的附着力。当轮胎在道路上滑动时,制动效果减弱,汽车的方向控制可能就不起作用了。前刹车总成的固定构件安装在前悬架的转向节上,在后部,它们被安装在后桥壳或后心轴总成上,铸铁刹车鼓或车盘随车轮一起转动。汽车的制动盘刹车时:汽车制动盘刹车有随车轮一起转动的圆盘。它通常被称为汽车刹车转子。在固定的卡钳里的液压控制的活塞被用来把汽车的刹车片加在转子的汽车刹车表面上。汽车刹车片和转子之间的摩擦力的大小会减慢或阻止车轮的转动。固定的卡钳壳体使垫圈被压在转动的汽车刹车盘上,使之不能转动。汽车制动盘刹车垫圈的运动与刹车转子的表面垂直,这样会使它们卡在转子上减慢汽车的车轮运动。卡钳压的力与驾驶员加在汽车刹车板上的力成正比。汽车制动鼓刹车:汽车制动鼓刹车使用带有摩擦片的固定的内胀式刹车块。他们被安装在转动的汽车刹车鼓内侧。汽车刹车鼓紧箍在轮胎总成和毂总成或轮轴法兰之间。当汽车刹车块的直径膨胀至使汽车刹车片与汽车刹车表面相接触时,汽车刹车块就减慢了汽车刹车鼓的转动。它是由液压操纵的汽车刹车分泵来完成的。来自刹车总泵的流体压力被施加到汽车刹车分泵上,使刹车分泵膨胀起来。汽车刹车分泵的膨胀使刹车块通过机械连杆进行移动,把汽车刹车片压到转动的刹车鼓上。当汽车刹车鼓的转动速度减慢时,就起到了制动作用。英文资料部分Automobile Design-Frame DesignsThe vehicle frame is the basic platform to which all suspension and steering linkage parts attach. A vehicle will neither steer nor handle well if the frame is too flexible. A rigid frame structure may pass unnecessary vibrations into the passenger compartment. The frame and suspension design will affect the ride quality, handling, and durability, as well as the levels of both noise and vibration.Manufacturers use several different types of construction on their vehicles. Of these, separate body and frame construction was the most common through the 1970s. It is still used in large vans, pickups, and trucks. In this type of construction, the engine, drive line, running gear, and body mount to the frame through insulators. Insulators are synthetic rubber pads that keep road and engine noise and vibration from going into the passenger compartment.A second type of construction is the unitized body. This, design is by far the most popular in modern vehicles. The unitized design has a lightweight structure with the required strength. Tn this type of construction, the frame is welded into the body as part of the body structure. Body panels add strength to the frame pieces. The running gear and drive line are mounted to the unitized body through large, soft synthetic rubber insulators. The insulators minimize the transfer of noise and vibration. If the insulators are too soft, they will allow too much running gear and drive line movement. This movement, called compliance, affects vehicle handling and control. If the insulators are too hard, they will not insulate noise and vibration as they should. The manufacturer carefully designs the insulators and puts them where they will be in a vehicle with low noise and vibration transmission that still has proper handling and feel. Insulator properties change with age, changing original characteristics as the vehicle becomes older.A third type of construction combines the features of the first and second types. It uses a stub frame from the bulkhead forward and a unitized body from the bulkhead back. The unitized part is very rigid, while the stub frame provides a place for good insulation.Manufacturers select the type of construction .that is most economical to build, while providing the noise, vibration, and ride and handling characteristics they want in the vehicle. Large older vehicles, vans, and trucks generally use separate body and frame construction. The newer, smaller vehicles generally use unitized construction.Drive LinesThe drive line includes all the parts from the and final drive carry the torque from the engine, the other. The engine torque during acceleration and the torque during braking place loads on the suspension parts.During suspension repair, it may be essary to disassemble parts of the drive line. Noises produced when the suspension moves may originate from drive line parts. A basic understanding of different drive line assemblies is presented here to give you a working knowledge so that you can do suspension repair.Drive lines with front-wheel drive often combine the transmission and the final drive into one assembly. This is also true of mid-and rear-engine vehicles. The assembly is called a transaxle, Short half-shafts with universal joints at each end connect between the transaxle and the wheels. These shafts carry power from the final drive to the wheels even when the suspension moves and steers.A differential in the final drive splits incoming power, sending half to each drive wheel. This allows the drive wheels to turn at different speeds while rounding corners. The transmission Other parts form the link from one part to while cornering.In front-engine, rear-wheel drive vehicles, the transmission is located under the front floor of the passenger compartment. A drive shaft is used to carry engine power to the rear axle. The drive shaft has a universal joint at each end. It carries power through the changing drive line angles as the suspension moves.A vehicle with independent suspension at the drive wheels has the final drive attached rigidly to the vehicle frame or the engine. This drive arrangement produces forces, without any torques, on the suspension parts during acceleration. If the brakes are mounted inboard so the caliper mounts to a frame piece and not to a suspension, the brake will also not produce a torque on the suspension. A suspension designed to handle only acceleration and braking torques can be designed differently than one that must handle both suspension forces and torques.Suspension SystemsThe suspension includes springs, shock absorbers, and control linkages. It must be strong enough to support the vehicle body and load. The suspension must also resist engine and brake reactions. The most important job of the suspension is to keep the tires in contact with the road as much of the time as possible. This is done while supporting the vehicle and its load, even while traveling over rough roads. The four tire footprints are the only place the vehicle touches the road. All of the engine power, steering, and braking forces operate through the tire-to-road footprints. Control of the vehicle ( power, steering and braking) is reduced or lost any time a tire does not stay on the road or when skidding begins.The vehicle body is supported by springs. The springs can be of the coil, leaf, torsion bar, or pneumatic type. Coil springs are the most popular design used in the modern automobile. Coil, torsion bar, and pneumatic springs all require links and arms to hold the wheel in position. Leaf springs provide lateral and longitudinal control to prevent unwanted wheel motions. They are commonly found on vans and trucks.Suspension systems have been changed and refined as the passenger automobile has developed. Design objectives differ between luxury sedans, performance vehicles, small compact vehicles, and light trucks. Tire improvements, along with improvements in shock absorbers, steering systems, and suspension control devices, have continually upgraded vehicle handling characteristics.Tire-to-road contact is needed for safe, positive vehicle control under all operating conditions. Keep in mind that all four tires must stay in contact with the road at all times for maximum vehicle control. Compromises are made in handling response, tire wear, driver comfort, and ride harshness to achieve positive vehicle control.Suspension systems are divided into front suspension and rear suspension.Front suspension designs have developed from relatively rugged solid-axle designs to the modern lightweight, high-strength , strut-type independent designs. These have been upgraded with added linkage. Suspension design improvements have followed improvements in roadways and driver expectations.Most front-engine, rear-wheel-drive vehicles use a simple dependent rear suspension .Rear-wheel-drive independent suspension is much more complex and expensive. As a result, it is only used on a few passenger vehicles.To front-engine, front-wheel-drive vehicles by moving the drive train to the front, only ride control and braking reactions are controlled by the rear suspension. This has led to the use of simplified dependent suspension , semi-independent suspension and independent rear suspension. The latter is used in a larger number of new vehicle designs.Steering SystemsThe driver controls the direction of the front wheels of the vehicle through the steering gear. Modern steering gears have two major units* a steering column and a gear unit. Tin-steering column has a supported shaft that connects the drivers steering wheel to the gem unit. The gear unit multiplies the drivers steering effort to move the steering linkage.The front wheels of rear-wheel-drive vehicles rotate on a spindle. The spindle is part ol the steering knuckle . The knuckle is connected to the front suspension members with ball joints. The ball joints allow for steering as the suspension moves up and down. The wheel hubs on front-wheel-drive vehicles rotate on hollow axle stub shafts inside bearings within the steering knuckles.The steering wheel controls the steering gear assembly. This, in turn, moves the knuckle through the steering linkage. Two steering gear designs are in use today, the rack and pinion and recirculating ball.vehicles are designed with responsive steering. As a result, more effort is needed to steer the vehicle when it is moving slowly. Power steering supplies this effort on many vehicles.With power steering doing most of the work, steering ratios are decreased so that the vehicle can be steered with small steering wheel movements. The power steering gear is similar to the standard steering gear. It includes surfaces upon which fluid pressure is applied to aid the drivers steering effort. Both rack and pinion and recirculating ball gears may have power assist.Power for the steering gear is provided by an engine-driven pump. The pump forces power steering fluid through a system controlled by a valve. This control valve can sense the drivers steering effort. It puts fluid pressure against a pressure surface in the steering system. This fluid pressure takes over some of the effort needed to steer the vehicle.The steering column in the modern vehicle has many parts. It is designed to collapse or fold in a vehicle collision to protect the driver. In some installations, it may be tilted and telescoped to adjust the position of the steering wheel for the comfort of the driver. To reduce the chance of theft, it also has a steering gear lock. On many vehicles, it has a transmission lock. Because it is within easy reach of the driver, the steering column may carry the transmission shift control lever, turn signal switch, headlight and dimmer switches, wiper switch, emergency flasher switch, and speed control.Brake SystemsService brakes must be able to stop the vehicle, prevent excess speed when coasting, and hold the vehicle in position while it is stopped on grades. They are designed so the driver can adjust the braking effort to maintain vehicle control. Vehicle control is influenced by brakes as well as the suspension and steering systems. Faults in the brake system can lead to wheel pull during braking. To repair suspension systems, parts of the brake system may require disassembly. For these reasons, the brake system will be discussed briefly in this text.The brake system must provide smooth stopping power that can be controlled by the driver. The force required on the brake pedal must not be so high that the wheels cannot be locked. To meet these braking requirements, minimum braking standards have been set for vehicle brakes.The driver controls the braking force through mechanical, vacuum, and hydraulic mechanisms. The amount of braking increases as more force is placed on the brake pedal. This force is transferred through the brake system to push stationary brake linings against the rotating brake surface. This slows the vehicle as it turns kinetic energy (energy of motion) into thermal energy (heat). Maximum braking occurs just before the wheels lock to cause the tires to slide on the road surface. Maximum braking, therefore, depends on the adhesion between the tire and the road surface. When the tire slides on the road, braking effect is reduced and directional control of the vehicle may be lost.The stationary parts of the front brake assemblies are mounted on the steering knuckle of the front suspension. In the rear, they are mounted on the axle housing or the rear spindle assembly. The cast-iron brake drum or disc rotates with the wheel .Disc Brake. Disc brakes have discs that rotate with the wheel . The brake disc is usually called a brake rotor. A hydraulically operated piston in a stationary caliper is used to force the lining of the brake pad against the braking surface of the rotor. The friction between the lining and rotor is used to slow or stop wheel rotation. The stationary caliper housing keeps the pads from rotating when they are being forced against the rotating brake disc.Disc brake pads move perpendicular to the face of the brake rotor. In this way, they clamp on the rotor to slow the vehicle motion. The clamping force is proportional to the force the driver puts on the brake pedal.Drum Brakes. Drum brakes use stationary, internal expanding brake shoes with linings. They are mounted inside a rotating brake drum. The brake drum is fastened between the wheel-tire assembly and the hub assembly or the axle flange. The brake shoes slow drum rotation when the diameter of the shoes is expanded to bring the lining in contact with the brake surface. This is done by a hydraulically operated wheel cylinder. Fluid pressure from the master cylinder is forced into the wheel cylinders, expanding them. The expansion of the wheel cylinder moves the brake shoe through mechanical linkage to press the-linings against the rotating brake drum. This provides braking action as it slows the rotation of the drum.
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