轻型商用车制动器设计(含6张CAD图纸)
轻型商用车制动器设计(含6张CAD图纸),轻型,商用,制动器,设计,CAD,图纸
河南理工大学万方科技学院本科毕业设计(论文)开题报告题目名称轻型商用车制动器设计学生姓名王奎专业班级08机制3班学号0828070005一、选题的目的和意义1.1引言汽车制动系统是汽车的一个重要组成部分,他直接影响汽车的安全性。据有关资料介绍,在由于汽车本身造成的交通事故中,制动系统故障引起的事故占事故总量的45%。虽然每万辆车造成的死亡率呈下降趋势,但每10万人口死亡率却呈上升趋势。表1-1 2010全年由于制动系统故障造成的交通事故及损失情况故障原因事故次数(次)死亡人数受伤人数直接经济损失(元)制动失效46631023425638645167制动不良76332656544739413006在2010年11月召开的全国公安交通管理工作会议透露的最新统计数字,2010年前10个月,全国共发生交通事故379,200起,死亡80,339人。表1-1列举了2010全年由于制动系统故障造成的交通事故及损失情况。据最新统计,2011年全国涉及人员伤亡的道路交通事故210812起,共造成62387人死亡,虽然略有所下降,但在货车发生的交通事故中,除去排在第一位的违章驾驶以外,由于车辆机械故障而引起的交通事故仍就是最主要的原因,而在各种车辆机械故障中,制动系统失效占有相当高的比例。可见,汽车制动系统结构设计的好坏对于行车安全方面的重要性。1.2 汽车制动系统的概述汽车制动系统是汽车上用以使外界(主要是路面)在汽车某些部分(主要是车轮)施加一定的力,从而对其进行一定程度的强制制动的一系列专门装置,即是指为了在技术上保证汽车的安全行驶,提高汽车的平均速度等,而在汽车上安装制动装置专门用来制动的制动机构。对汽车起制动作用的只能是作用在汽车上且方向与汽车行驶方向相反的外力,而这些外力的大小都是随机的、不可控制的,因此汽车上必须装设一系列专门装置以实现上述功能,以便驾驶员能根据道路和交通等情况,借以使外界在汽车上某些部分施加一定的力,对汽车进行一定程度的强制制动。这种可控制的对汽车进行制动的外力,统称为制动力。这样的一系列专门装置即称为汽车制动系统。制动系统的一般工作原理是,利用与车身(或车架)相连的非旋转元件和与车轮(或传动轴)相连的旋转元件之间的相互摩擦来阻止车轮的转动或转动的趋势,以达到车辆减速,或直至停车的目的。1.3 汽车制动系统的类型、组成及功用1.3.1 制动系统的类型(1)按制动系统的作用分类行车制动系统使正在行使中的汽车减速或在最短的距离内停车的一套专门装置。驻车制动系统使停止的汽车驻留在原地不动的一套装置。应急系统在行车制动系失效的情况下,保证汽车仍能实现减速或停车的一套装置。辅助制动系统在汽车长下坡时用以稳定车速的一套装置。(2)按制动操纵能源分类人力制动系统以驾驶员的肢体作为唯一的制动能源的制动系统。动力制动系统完全靠由发动机的动力转化而成的气压或液压形式的势能进行制动的系统。伺服制动系统兼用人力和发动机动力进行制动的制动系统。(3)按照制动能量的传输方式,制动系又可分为机械式、液压式、气压式和电磁式等。同时采用两种以上方式的制动系,可称为组合式制动系。1.3.2 制动系统的组成任何制动系都具有以下四个基本组成部分:(1)供能装置包括供给、调节制动所需能量以及改善传能介质状态的各种部件。其中,产生制动能量的部位称为制动能源。(2)控制装置包括产生制动动作和控制制动效果的各种部件。(3)传动装置包括将制动能量传输到制动器的各个部件。(4)制动器产生阻碍车辆的运动或运动趋势的力的部件,其中也包括辅助制动系中的缓速装置。1.3.3 制动系的功用使行驶中的汽车按照驾驶员的要求进行强制减速甚至停车;使已停驶的汽车在各种道路条件下(包括在坡道上)稳定驻车;使下坡行驶的汽车速度保持稳定。 1.4 总结 从汽车诞生时起,汽车制动系统就在车辆安全方面扮演着至关重要的角色,特别是近年来,随着车辆技术的进步和汽车行驶速度的提高,这种重要性体现得越来越明显。伴随着节能型和清洁型能源汽车的研究开发,汽车动力系统发生了很大的改变,出现了很多新的结构型式和功能形式,新型动力系统的出现也要求制动系统结构型式和功能形式发生相应的改变。但最终目的始终是为了使高速行驶的汽车减速或在最短的距离内停车。如果该系统不能正常工作,车上的驾驶员和乘客将受到车祸的危害,所以分析和研究汽车制动系统具有极其重要的意义。在种类汽车制动系统中,制动器是汽车制动系中用以产生阻止车辆运动或运动趋势的力的部件。只有了解了其基本结构,清楚了其工作原理,分析出可能会出现的失效形式,才能准确的找出是什么原因引起的制动系统故障,从而才能对存在安全隐患的地方进行改良,只有这样才能完善制动系统,避免故障的再次发生。所以,对汽车制动系统设计的研究是十分有必要的,且有着深刻的意义。二、国内外研究综述由于汽车制动系统在车辆安全方面占据着显著的地位,众多的汽车工程师在改进汽车制动性能的研究中倾注了大量的心血。目前关于汽车制动的研究主要集中在制动控制方面,包括制动控制的理论和方法,以及采用新的技术。2.1 制动控制系统的历史最原始的制动控制只是驾驶员操纵一组简单的机械装置向制动器施加作用力,这时的车辆的质量比较小,速度比较低,机械制动虽已满足车辆制动的需要,但随着汽车自质量的增加,助力装置对机械制动器来说已显得十分必要。这时,开始出现真空助力装置。1932年生产的质量为2860kg的凯迪拉克V16车四轮采用直径419.1mm的鼓式制动器,并有制动踏板控制的真空助力装置。林肯公司也于1932年推出V12轿车,该车采用通过四根软索控制真空加力器的鼓式制动器。随着科学技术的发展及汽车工业的发展,尤其是军用车辆及军用技术的发展,车辆制动有了新的突破,液压制动是继机械制动后的又一重大革新。Duesenberg Eight车率先使用了轿车液压制动器。克莱斯勒的四轮液压制动器于1924年问世。通用和福特分别于1934年和1939年采用了液压制动技术。到20世纪50年代,液压助力制动器才成为现实。20世纪80年代后期,随着电子技术的发展,世界汽车技术领域最显著的成就就是防抱制动系统(ABS)的实用和推广。ABS集微电子技术、精密加工技术、液压控制技术为一体,是机电一体化的高技术产品。它的安装大大提高了汽车的主动安全性和操纵性。防抱装置一般包括三部分:传感器、控制器(电子计算机)与压力调节器。传感器接受运动参数,如车轮角速度、角加速度、车速等传送给控制装置,控制装置进行计算并与规定的数值进行比较后,给压力调节器发出指令。1936年,博世公司申请一项电液控制的ABS装置专利促进了防抱制动系统在汽车上的应用。1969年的福特使用了真空助力的ABS制动器;1971年,克莱斯勒车采用了四轮电子控制的ABS装置。这些早期的ABS装置性能有限,可靠性不够理想,且成本高。1979年,默本茨推出了一种性能可靠、带有独立液压助力器的全数字电子系统控制的ABS制动装置。1985年美国开发出带有数字显示微处理器、复合主缸、液压制动助力器、电磁阀及执行器“一体化”的ABS防抱装置。随着大规模集成电路和超大规模集成电路技术的出现,以及电子信息处理技术的高速发展,ABS以成为性能可靠、成本日趋下降的具有广泛应用前景的成熟产品。1992年ABS的世界年产量已超过1000万辆份,世界汽车ABS的装用率已超过20%。一些国家和地区(如欧洲、日本、美国等)已制定法规,使ABS成为汽车的标准设备。2.2 制动控制系统的现状当考虑基本的制动功能量,液压操纵仍然是最可靠、最经济的方法。即使增加了防抱制动(ABS)功能后,传统的“油液制动系统”仍然占有优势地位。但是就复杂性和经济性而言,增加的牵引力控制、车辆稳定性控制和一些正在考虑用于“智能汽车”的新技术使基本的制动器显得微不足道。传统的制动控制系统只做一样事情,即均匀分配油液压力。当制动踏板踏下时,主缸就将等量的油液送到通往每个制动器的管路,并通过一个比例阀使前后平衡。而ABS或其他一种制动干预系统则按照每个制动器的需要时对油液压力进行调节。目前,车辆防抱制动控制系统(ABS)已发展成为成熟的产品,并在各种车辆上得到了广泛的应用,但是这些产品基本都是基于车轮加、减速门限及参考滑移率方法设计的。方法虽然简单实用,但是其调试比较困难,不同的车辆需要不同的匹配技术,在许多不同的道路上加以验证;从理论上来说,整个控制过程车轮滑移率不是保持在最佳滑移率上,并未达到最佳的制动效果。另外,由于编制逻辑门限ABS有许多局限性,所以近年来在ABS的基础上发展了车辆动力学控制系统(VDC)。结合动力学控制的最佳ABS是以滑移率为控制目标的ABS,它是以连续量控制形式,使制动过程中保持最佳的、稳定的滑移率,理论上是一种理想的ABS控制系统。滑移率控制的难点在于确定各种路况下的最佳滑移率,另一个难点是车辆速度的测量问题,它应是低成本可靠的技术,并最终能发展成为使用的产品。对以滑移率为目标的ABS而言,控制精度并不是十分突出的问题,并且达到高精度的控制也比较困难;因为路面及车辆运动状态的变化很大,多种干扰影响较大,所以重要的问题在于控制的稳定性,即系统鲁棒性,应保持在各种条件下不失控。防抱系统要求高可靠性,否则会导致人身伤亡及车辆损坏。因此,发展鲁棒性的ABS控制系统成为关键。现在,多种鲁棒控制系统应用到ABS的控制逻辑中来。除传统的逻辑门限方法是以比较为目的外,增益调度PID控制、变结构控制和模糊控制是常用的鲁棒控制系统,是目前所采用的以滑移率为目标的连续控制系统。模糊控制法是基于经验规则的控制,与系统的模型无关,具有很好的鲁棒性和控制规则的灵活性,但调整控制参数比较困难,无理论而言,基本上是靠试凑的方法。然而对大多数基于目标值的控制而言,控制规律有一定的规律。另外,也有采用其它的控制方法,如基于状态空门及线性反馈理论的方法,模糊神经网络控制系统等。各种控制方法并不是单独应用在汽车上,通常是几种控制方法组合起来实施。如可以将模糊控制和PID结合起来,兼顾模糊控制的鲁棒性和PID控制的高精度,能达到很好的控制效果。车轮的驱动打滑与制动抱死是很类似的问题。在汽车起动或加速时,因驱动力过大而使驱动轮高速旋转、超过摩擦极限而引起打滑。此时,车轮同样不具有足够的侧向力来保持车辆的稳定,车轮切向力也减少,影响加速性能。由此看出,防止车轮打滑与抱死都是要控制汽车的滑移率,所以在ABS的基础上发展了驱动防滑系统(ASR)。ASR是ABS的逻辑和功能扩展。ABS在增加了ASR功能后,主要的变化是在电子控制单元中增加了驱动防滑逻辑系统,来监测驱动轮的转速。ASR大多借用ABS的硬件,两者共存一体,发展成为ABS/ASR系统。目前,ABS/ASR已在欧洲新载货车中普遍使用,并且欧共体法规EEC/71/320已强制性规定在总质量大于3.5t的某些载货车上使用,重型车是首先装用的。然而ABS/ASR只是解决了紧急制动时附着系数的利用,并可获得较短的制动距离及制动方向稳定性,但是它不能解决制动系统中的所有缺陷。因此ABS/ASR功能,同时可进行制动强度的控制。ABS只有在极端情况下(车轮完全抱死)才会控制制动,在部分制动时,电子制动使可控制单个制动缸压力,因此反应时间缩短,确保在任一瞬间得到正确的制动压力。近几年电子技术及计算机控制技术的飞速发展为EBS的发展带来了机遇。德国自20世纪80年代以来率先发展了ABS/ASR系统并投入市场,在EBS的研究与发展过程中走到了世界的前列。德国博世公司在1993年与斯堪尼公司联合首次在Scania牵引车及挂车上装用了EBS。然而EBS是全新的系统,它有很大的潜力,必将给现在及将来的制动系统带来革命性的变革。2.3 制动控制系统的发展今天,ABS/ASR已经成为欧美和日本等发达国家汽车的标准设备。车辆制动控制系统的发展主要是控制技术的发展。一方面是扩大控制范围、增加控制功能;另一方面是采用优化控制理论,实施伺服控制和高精度控制。在第一方面,ABS功能的扩充除ASR外,同时把悬架和转向控制扩展进来,使ABS不仅仅是防抱死系统,而成为更综合的车辆控制系统。制动器开发厂商还提出了未来将ABS/TCS和VDC与智能化运输系统一体化运用的构想。随着电子控制传动、悬架系统及转向装置的发展,将产生电子控制系统之间的联系网络,从而产生一些新的功能,如:采用电子控制的离合器可大大提高汽车静止启动的效率;在制动过程中,通过输入一个驱动命令给电子悬架系统,能防止车辆的俯仰。在第二个方面,一些智能控制技术如神经网络控制技术是现在比较新的控制技术,已经有人将其应用在汽车的制动控制系统中。ABS/ASR并不能解决汽车制动中的所有问题。因此由ABS/ASR进一步发展演变成电子控制制动系统(EBS),这将是控制系统发展的一个重要的方向。但是EBS要想在实际中应用开来,并不是一个简单的问题。除技术外,系统的成本和相关的法规是其投入应用的关键。经过了一百多年的发展,汽车制动系统的形式已经基本固定下来。随着电子,特别是大规模、超大规模集成电路的发展,汽车制动系统的形式也将发生变化。如凯西-海斯(K-H)公司在一辆实验车上安装了一种电-液(EH)制动系统,该系统彻底改变了制动器的操作机理。通过采用4个比例阀和电力电子控制装置,K-H公司的EBM就能考虑到基本制动、ABS、牵引力控制、巡航控制制动干预等情况,而不需另外增加任何一种附加装置。EBM系统潜在的优点是比标准制动器能更加有效地分配基本制动力,从而使制动距离缩短5%。一种完全无油液、完全的电路制动BBW(Brake-By-Wire)的开发使传统的液压制动装置成为历史。2.4 全电路制动(BBW)BBW是未来制动控制系统的发展方向。全电制动不同于传统的制动系统,因为其传递的是电,而不是液压油或压缩空气,可以省略许多管路和传感器,缩短制动反应时间。全电制动的结构如下图所示。其主要包含以下部分:电制动器。其结构和液压制动器基本类似,有盘式和鼓式两种,作动器是电动机;电制动控制单元(ECU)。接收制动踏板发出的信号,控制制动器制动;接收驻车制动信号,控制驻车制动;接收车轮传感器信号,识别车轮是否抱死、打滑等,控制车轮制动力,实现防抱死和驱动防滑。由于各种控制系统如卫星定位、导航系统,自动变速系统,无级转向系统,悬架系统等的控制系统与制动控制系统高度集成,所以ECU还得兼顾这些系统的控制;轮速传感器。准确、可靠、及时地获得车轮的速度;线束。给系统传递能源和电控制信号;电源。为整个电制动系统提供能源。与其他系统共用。可以是各种电源,也包括再生能源。从结构上可以看出这种全电路制动系统具有其他传统制动控制系统无法比拟的优点:整个制动系统结构简单,省去了传统制动系统中的制动油箱、制动主缸、助力装置。液压阀、复杂的管路系统等部件,使整车质量降低;制动响应时间短,提高制动性能;无制动液,维护简单;系统总成制造、装配、测试简单快捷,制动分总成为模块化结构;采用电线连接,系统耐久性能良好;易于改进,稍加改进就可以增加各种电控制功能。全电制动控制系统是一个全新的系统,给制动控制系统带来了巨大的变革,为将来的车辆智能控制提供条件。但是,要想全面推广,还有不少问题需要解决:首先是驱动能源问题。采用全电路制动控制系统,需要较多的能源,一个盘式制动器大约需要1kW的驱动能量。目前车辆12V电力系统提供不了这么大的能量,因此,将来车辆动力系统采用高压电,加大能源供应,可以满足制动能量要求,同时需要解决高电压带来的安全问题。其次是控制系统失效处理。全电制动控制系统面临的一个难题是制动失效的处理。因为不存在独立的主动备用制动系统,因此需要一个备用系统保证制动安全,不论是ECU元件失效,传感器失效还是制动器本身、线束失效,都能保证制动的基本性能。实现全电制动控制的一个关键技术是系统失效时的信息交流协议,如TTP/C。系统一旦出现故障,立即发出信息,确保信息传递符合法规最适合的方法是多重通道分时区(TDMA),它可以保证不出现不可预测的信息滞后。TTP/C协议是根据TDMA制定的。第三是抗干扰处理。车辆在运行过程中会有各种干扰信号,如何消除这些干扰信号造成的影响,目前存在多种抗干扰控制系统,基本上分为两种:即对称式和非对称式抗干扰控制系统。对称式抗干扰控制系统是用两个相同的CPU和同样的计算程序处理制动信号。非对称式抗干扰控制系统是用两个不同的CPU和不一样的计算程序处理制动信号。两种方法各有优缺点。另外,电制动控制系统的软件和硬件如何实现模块化,以适应不同种类的车型需要;如何实现底盘的模块化,是一个重要的难题。只有将制动、转向、悬架、导航等系统综合考虑进来,从算法上模块化,建立数据总线系统,才能以最低的成本获得最好的控制系统。电制动控制系统首先用在混合动力制动系统车辆上,采用液压制动和电制动两种制动系统。这种混合制动系统是全电制动系统的过渡方案。由于两套制动系统共存,使结构复杂,成本偏高。随着技术的进步,上述的各种问题会逐步得到解决,全电制动控制系统会真正代替传统的以液压为主的制动控制系统。图3是这种全电制动控制系统的配置方案。2.5 结论综上所述,现代汽车制动控制技术正朝着电子制动控制方向发展。全电制动控制因其巨大的优越性,将取代传统的以液压为主的传统制动控制系统。同时,随着其他汽车电子技术特别是超大规模集成电路的发展,电子元件的成本及尺寸不断下降。汽车电子制动控制系统将与其他汽车电子系统如汽车电子悬架系统、汽车主动式方向摆动稳定系统、电子导航系统、无人驾驶系统等融合在一起成为综合的汽车电子控制系统,未来的汽车中就不存在孤立的制动控制系统,各种控制单元集中在一个ECU中,并将逐渐代替常规的控制系统,实现车辆控制的智能化。但是,汽车制动控制技术的发展受整个汽车工业发展的制约。有一个巨大的汽车现有及潜在的市场的吸引,各种先进的电子技术、生物技术、信息技术以及各种智能技术才不断应用到汽车制动控制系统中来。同时需要各种国际及国内的相关法规的健全,这样装备新的制动技术的汽车就会真正应用到汽车的批量生产中。三、毕业设计(论文)所用的主要技术与方法:3.1 形式确定通常,汽车所用制动器一般都采用摩擦式的,也就是阻止汽车运动的制动力矩来源于固定元件和旋转工作表面之间的摩擦。主要是盘式制动器和鼓式制动器两种形式。鼓式制动器的选用:鼓式制动器是靠制动块在制动轮上压紧产生摩擦来实现刹车的。鼓式制动器的形式有很多种,如领从蹄式制动器、单向双领蹄式制动器、双向双领蹄式制动器、单向自增力式制动器、双向自增力式制动器、凸轮式制动器、楔式制动器。它们都各有利弊,其中领从蹄式制动器发展较早,且其效能和效能稳定性在各式制动器中均居于中游;前进、倒退行驶的制动效果不变;便于附装驻车制动驱动机构;易于调整蹄片与制动鼓之间的间隙;且有结构简单,成本低等优点。但领从蹄式制动器也有两蹄片的压力不等(在两制动蹄上的摩擦衬片面积相等的条件下),因而两蹄片磨损不均匀、寿命不同的缺点。此外,因只有一个轮缸,两制动蹄必须在同一驱动回路下工作。因此,本设计采用由定位销定位的一个自由度的非平衡式的领从蹄式制动器。盘式制动器的选用:盘式制动器又叫做碟式制动器,一般是由液压控制,主要的部件有制动盘、制动钳、固定器,制动轮缸等组成。按摩擦副中固定元件的结构不同,盘式制动器分为钳盘式和全盘式两类。全盘式制动器的固定摩擦元件和旋转元件均为圆盘形,制动时各盘摩擦表面全部接触。用得较多的是多片全盘式制动器,以便获得较大的制动力。但这种制动器的散热性能较差,故多为油冷式,结构较复杂。钳盘式制动器按制动钳的结构型式又可分为固定钳盘式制动器和浮钳盘式制动器。定钳盘式制动器的制动钳固定安装在车桥上,既不能旋转,也不能沿着制动盘轴线方向移动,因此必须在制动盘的两侧都 安装制动块的促动装置,以便于将两侧的制动块分别压向制动盘。定钳盘式制动器在制动钳体上有两个液压油缸,其中各装有一个活塞。当压力油液进入两个油缸活塞外腔时,推动两个活塞向内将位于制动盘两侧的制动块总成压紧到制动盘上,从而将车轮制动。当放松制动踏板使油液压力减小时,回位弹簧又将两制动块总成及活塞推离制动盘。这种型式也称为对置活塞式或浮动活塞式。定钳盘式制动器的缺点就是:(1)制动盘的两侧各有液压缸,使制动钳的结构复杂。(2)液压缸分装于制动盘的两侧,制动液必须跨越制动盘的钳内油道或者外部的油管。(3)热负荷较大,液压缸和跨越制动盘的钳内制动管路或者是外部油管内的制动液容易气化。(4)若想兼用于驻车制动装置,则必须要添加一个机械促动的驻车制动钳。由于上述的种种原因,定钳盘式制动装置已经很难适应现代轿车的发展趋势,也逐渐的在70年代以后让位于浮钳盘式制动器。 浮钳盘式制动器只在制动盘的一侧装油缸,结构简单,造价低廉,易于布置,结构尺寸紧凑,可以将制动器进一步移近轮毂,同一组制动块可兼用于行车和驻车制动,在兼行车和驻车制动的情况下不需要加设驻车制动钳,只需要在行车制动钳液压缸的附近加装一些用于推动液压缸活塞的驻车制动机械传动零件即可。浮动钳由于没有跨越制动盘的油道或油管,减少了受热机会,单侧油缸又位于盘的内侧,受车轮遮蔽较少使冷却条件较好。另外,单侧油缸的活塞比两侧油缸的活塞要长,也增大了油缸的散热面积,因此制动液温度比用固定钳时低3050,气化的可能性较小。但由于制动钳体是浮动的,必须设法减少滑动处或摆动中心处的摩擦、磨损和噪声。因此本设计采用浮钳盘式制动器小结:本设计以轻型商用车为例,据了解其在制动过程中,由于惯性的作用,前轮的负荷通常占汽车全部负荷的70%80%,因此前轮制动力要比后轮大。经过对不同制动器优缺点的比较,从经济与实用的角度出发,根据车型、车辆所要满足的制动性能、国家或行业标准,及制动器本身的结构和性能特点,参考同类型车制动器设计,确定制动器的类型为前盘后鼓式制动器,即前轮盘式制动,后轮鼓式制动。II型 X型 HI型 LL型 HH型图3-1 液压分路系统形式3.2 制动管路的确定为了提高制动工作的可靠性,应采用分路系统,即全车的所有行车制动器的液压或气压管路分为两个或更多的相互独立的回路,其中一个回路失效后,仍可利用其他完好的回路起制动作用。 双轴汽车的双回路制动系统有以下常见的物种分路形式(如图3-1所示):(1) 一轴对一轴(II)型,前轴制动器与后桥制动器各用一个回路。(2) 交叉型(X),前轴的一侧车轮制动器与后桥的对策车轮制动器同属一个回路。(3) 一周半对半轴(HI)型,两侧前制动器的板书轮缸和全部后制动器轮缸属于一个回路,其余的前轮缸则属另一回路。(4) 半轴一轮对半轴一轮(LL)型,两个回路分别对两侧前轮制动器的半数轮缸和一个后轮制动器起作用。(5) 双半轴对双半轴(HH)型,每个回路均只对每个前、后制动器的半数轮缸起作用。II型管路布置较为简单,可与传统的但轮岗鼓式制动器配合使用,成本较低,目前在各类汽车特别是商用车商用得最广泛,所以采用II型制动管路。3.3 制动驱动机构的结构型式选择根据动力源的不同,制动驱动机构可分为简单制动,动力制动,伺服制动。(1) 简单制动单靠驾驶员施加的踏板力或手柄力作为制动力源,故亦称人力制动。有机械式和液压式两种。机械式结构简单,造价低廉,工作可靠,但机械效率低,因此仅用于中小型汽车的驻车制动装置中。液压式曾广泛用于轿车,轻型及以下的货车和部分中型货车上,但由于其操纵较沉重,不能适应现代汽车提高操纵轻便性的要求,故当前仅用于微型汽车上,在轿车和轻型汽车上己极少采用。(2) 动力制动有气压制动,气顶液式制动,全液压制动。气压制动是动力制动最常见型式,由于可获得较大的制动驱动力,且主车与被拖的挂车以及汽车列车之间制动驱动系统的连接结构简单,因此被广泛用于总质量8t以上的载货汽车,越野车和客车上。气顶液式制动系统结构复杂,质量大,造价高,故主要用于重型汽车上,一部分总质量为9t-11t的中型汽车上也有所采用。全液压制动结构复杂,精密件多,对系统的密封性要求也较高,故并未得到广泛应用,目前仅用于某些高级轿车,大型客车以及少数的重型矿用自卸汽车上。(3) 伺服制动系统分真空伺服制动系统、气压伺服制动系统、液压伺服制动。真空伺服制动是利用发动机进气管中节气门后的真空度作动力源。一般的柴油车若采用伺服制动系统时,则需要专门的真空源由发动机驱动的真空泵或喷吸器构成。气压伺服制动是由发动机驱动的空气压缩机提供压缩空气作为动力源,伺服气压一般0.6MPA0.7MPA。气压伺服制动系统的组成部分比真空伺服复杂的多。真空伺服制动用于总质量在1.1t1.35t以上的轿车及装载质量在6t以下的轻中型载货汽车上,而气压伺服制动系统则广泛用于装载质量为6t12t的中重型载货汽车以及少数高级轿车上。液压伺服制动系统是以发动机驱动液压油泵产生的高压油液为伺服能源,且基本上均为助力式的。由于这种制动系统的工作压力很高,因此可大大地减小伺服机构的尺寸,且制动反应快,但对零部件的加工精密度和密封性能要求很高。其仅用于高级轿车。通过以上对各种制动驱动机构结构型式的比较分析,衡量其优缺点,及其适用的车型最后选定液压伺服制动系统为本次设计的制动驱动机构。3.4 部件型式的确定(1) 制动主缸:制动主缸由灰铸铁制造,也可以用低碳钢冷挤成型;活塞可用灰铸铁,铝合金或中碳钢制造。主缸的作用是将驾驶员踩到制动踏板上的压力传递到四个车轮的制动器以使汽车停车。主缸将驾驶员在踏板上的机械压力转变为液压力,在车轮制动器处液压力转变为机械力。主缸利用液体不可压缩原理,将驾驶员的踏板运动传送到车轮制动器。主缸由储液罐和主缸体构成。储液罐提供处缸工作的制动液。现在的所有储液罐都是分体设计,即两个独立的活塞有两个独立的储液区域。分体设计分别为前轮和后轮,或一个前轮一个后轮的液压系统供液,以防一个液压系统失效影响另一个液压系统。本设计采用双体设计的液压主缸,即双腔液压主缸。(2) 制动轮缸:后轮鼓式制动器制动轮缸是液压活塞式制动蹄张开机构,其机构简单,在车轮制动器中布置方便。轮缸的缸体由灰铸铁HT250制成,其缸筒为通孔,需搪磨,活塞由铝合金制造,活塞外端压有钢制的开槽顶块,以支承插入槽中的制动蹄腹板的橡胶密封圈或靠在活塞内端面处的橡胶皮碗密封。(3) 制动鼓:制动鼓的材料与摩擦衬片的材料相匹配,应能保证具有高的摩擦系数并使工作表面磨损均匀故我选用由钢板冲压成型的辐板与铸铁鼓筒部分铸、成一体的组合式制动鼓。制动蹄选用T形钢辗压成的制动蹄。制动底板是除制动鼓外制动器各零件的安装基体,应保证各安装零件相互间的正确位置,制动底板承受着制动器工作时的制动反力矩,故应有足够的刚度,为此我选用具有凹凸起伏形状的钢板冲压成型的制动底板。摩擦材料采用模压。材料,它是以石棉纤维为主并与树胶粘结剂,调整摩擦性能的填充剂与噪声消除剂等混合后,在高温下模压成型的。模压材料的挠性较差故应安衬片或衬块规格模压,其优点是可以选用各种不同的聚合树脂配料,使衬片或衬块具有不同的摩擦性能和其他性能。综合以上特点总结出制动鼓选材应该有足够的强度,刚度和热容量,与摩擦衬片材料相配合,又应当有较高的摩擦因数。3.5 总结根据课题内容、任务要求,深入了解汽车制动系统的构造及工作原理;并收集相关车辆制动系统设计资料;参考现有研究成果,并进行深入的学习和分析,借鉴经验;同时学习有关汽车零部件设计准则;计算和确定主要尺寸,绘制部件装配图和总图,通过自己的研究分析;发挥自己的设计能力并通过试验最终确定制动系统设计方案,绘制全部零件工作图,编写说明书。同时,将设计过程中发现的遗漏部分及时作补充。所用技术:在这次设计中将采用机械图形设计软件AutoCAD2008 进行绘图,并参考相关设计和专业书籍,进行设计。四、主要参考文献与资料获得情况4.1 主要参考文献如下:1程国华.汽车制动系统发展漫谈J :汽车运用.2003年第6期2朱育权.制动盘(鼓)研究现状与发展趋势J :西安工业学院学报 20013张海清.非石棉盘式制动器的发展现状J :汽车技术.1993(6)4张国强.车辆制动系统的发展现状及趋势浅析J .农业与技术 20095王望予.汽车设计.北京:机械工业出版社M.20066刘惟信.汽车制动系统的结构分析与设计计算北京M:清华大学出版社,20047方泳龙.汽车制动理论与设计M.北京:国防工业出版社,20058余志生.汽车理论.北京:机械工业出版社M.2006年9陈家瑞.汽车构造(下),机械工业出版社M.2005年8月,第四版10朱旬、金海东.轿车制动主缸结构浅析J :汽车研究与开发.1999 年第 2 期11陈步童.微型汽车制动系统常见故障诊断与检修J :无锡职业技术学院学报.2003.4期12张涛,王燕玲.汽车制动性能与测试J .仪器仪表学报 .2002 13张建俊、汽车检测技术M .北京:高等教育出版社 .20034.2 资料获取情况如下:从学校图书馆借阅相关图书;从网上搜索相关资料,例如在学校图书馆网页上下载相关文献或期刊;在设计过程中遇到难题时向指导老师和专业老师请教;五、毕业设计(论文)进度安排: 时 间 内 容3.10-3.15 熟悉课题,收集和整理资料3.16-3.23 毕业实习,调研3.24-4.06 提出研究方案,准备开题4.07-4.13 制动器参数初步计算 4.14-4.20 制动器参数计算4.21-4.27 强度校核计算4.28-5.04 制动性能分析及编程5.05-5.11 绘制装配草图、绘制装配图5.12-5.18 中期检查、绘制零件图5.19-5.25 完善图纸5.26-6.01 写设计计算说明书6.02-6.08 审阅图纸6.09-6.10 准备答辩六、指导教师审批意见指导教师: (签名)年 月 日 河南理工大学万方科技学院毕 业 设 计(论 文)附 录I中 英 文 文 献 翻 译姓 名: 王 奎 所在院系: 机械与动力工程系 专业班级: 机械设计08-3班 学 号: 0828070005 指导教师: 赵 武 原文标题: Automobile Brake System2012 年 5 月 25 日Automobile Brake SystemThe braking system is the most important system in cars. If the brakes fail, the result can be disastrous. Brakes are actually energy conversion devices, which convert the kinetic energy (momentum) of the vehicle into thermal energy (heat).When stepping on the brakes, the driver commands a stopping force ten times as powerful as the force that puts the car in motion. The braking system can exert thousands of pounds of pressure on each of the four brakes.Two complete independent braking systems are used on the car. They are the service brake and the parking brake.The service brake acts to slow, stop, or hold the vehicle during normal driving. They are foot-operated by the driver depressing and releasing the brake pedal. The primary purpose of the brake is to hold the vehicle stationary while it is unattended. The parking brake is mechanically operated by when a separate parking brake foot pedal or hand lever is set.The brake system is composed of the following basic components: the “master cylinder” which is located under the hood, and is directly connected to the brake pedal, converts driver foots mechanical pressure into hydraulic pressure. Steel “brake lines” and flexible “brake hoses” connect the master cylinder to the “slave cylinders” located at each wheel. Brake fluid, specially designed to work in extreme conditions, fills the system. “Shoes” and “pads” are pushed by the slave cylinders to contact the “drums” and “rotors” thus causing drag, which (hopefully) slows the car.The typical brake system consists of disk brakes in front and either disk or drum brakes in the rear connected by a system of tubes and hoses that link the brake at each wheel to the master cylinder .Basically, all car brakes are friction brakes. When the driver applies the brake, the control device forces brake shoes, or pads, against the rotating brake drum or disks at wheel. Friction between the shoes or pads and the drums or disks then slows or stops the wheel so that the car is braked.In most modern brake systems, there is a fluid-filled cylinder, called master cylinder, which contains two separate sections, there is a piston in each section and both pistons are connected to a brake pedal in the drivers compartment. When the brake is pushed down, brake fluid is sent from the master cylinder to the wheels.At the wheels, the fluid pushes shoes, or pads, against revolving drums or disks. The friction between the stationary shoes, or pads, and the revolving drums or disks slows and stops them. This slows or stops the revolving wheels, which, in turn, slow or stop the car.The brake fluid reservoir is on top of the master cylinder. Most cars today have a transparent r reservoir so that you can see the level without opening the cover. The brake fluid level will drop slightly as the brake pads wear. This is a normal condition and no cause for concern. If the level drops noticeably over ashort period of time or goes down to about two thirds full, have your brakes checked as soon as possible. Keep the reservoir covered except for the amount of time you need to fill it and never leave a cam of brake fluid uncovered. Brake fluid must maintain a very high boiling point. Exposure to air will cause the fluid to absorb moisture which will lower that boiling point.The brake fluid travels from the master cylinder to the wheels through a series of steel tubes and reinforced rubber hoses. Rubber hoses are only used in places that require flexibility, such as at the front wheels, which move up and down as well as steer. The rest of the system uses non-corrosive seamless steel tubing with special fittings at all attachment points. If a steel line requires a repair, the best procedure is to replace the compete line. If this is not practical, a line can be repaired using special splice fittings that are made for brake system repair. You must never use copper tubing to repair a brake system. They are dangerous and illegal.Drum brakes, it consists of the brake drum, an expander, pull back springs, a stationary back plate, two shoes with friction linings, and anchor pins. The stationary back plate is secured to the flange of the axle housing or to the steering knuckle. The brake drum is mounted on the wheel hub. There is a clearance between the inner surface of the drum and the shoe lining. To apply brakes, the driver pushes pedal, the expander expands the shoes and presses them to the drum. Friction between the brake drum and the friction linings brakes the wheels and the vehicle stops. To release brakes, the driver release the pedal, the pull back spring retracts the shoes thus permitting free rotation of the wheels.Disk brakes, it has a metal disk instead of a drum. A flat shoe, or disk-brake pad, is located on each side of the disk. The shoes squeeze the rotatin g disk to stop the car. Fluid from the master cylinder forces the pistons to move in, toward the disk. This action pushes the friction pads tightly against the disk. The friction between the shoes and disk slows and stops it. This provides the braking action. Pistons are made of either plastic or metal. There are three general types of disk brakes. They are the floating-caliper type, the fixed-caliper type, and the sliding-caliper type. Floating-caliper and sliding-caliper disk brakes use a single piston. Fixed-caliper disk brakes have either two or four pistons.Brakes - what do they do?Brakes are designed to slow down your vehicle but probably not by the means that you think. The common misconception is that brakes squeeze against a drum or disc, and the pressure of the squeezing action is what slows you down. This in fact is only part of the equation. Brakes are essentially a mechanism to change energy types. When youre travelling at speed, your vehicle has kinetic energy. When you apply the brakes, the pads or shoes that press against the brake drum or rotor convert that energy into thermal energy via friction. The cooling of the brakes dissipates the heat and the vehicle slows down. Its the First Law of Thermodynamics, sometimes known as the law of conservation of energy. This states that energy cannot be created nor destroyed, it can only be converted from one form to another. In the case of brakes, it is converted from kinetic energy to thermal energy. Angular force. Because of the configuration of the brake pads and rotor in a disc brake, the location of the point of contact where the friction is generated also provides a mechanical moment to resist the turning motion of the rotor. Thermodynamics, brake fade and drilled rotors.If you ride a motorbike or drive a race car, youre probably familiar with the term brake fade, used to describe what happens to brakes when they get too hot. A good example is coming down a mountain pass using your brakes rather than your engine to slow you down. As you start to come down the pass, the brakes on your vehicle heat up, slowing you down. But if you keep using them, the rotors or drums stay hot and get no chance to cool off. At some point they cant absorb any more heat so the brake pads heat up instead. In every brake pad there is the friction material that is held together with some sort of resin and once this starts to get too hot, the resin starts to vapourise, forming a gas. Because the gas cant stay between the pad and the rotor, it forms a thin layer between the two whilst trying to escape. The pads lose contact with the rotor, reducing the amount of friction and voila. Complete brake fade. The typical remedy for this would be to get the vehicle to a stop and wait for a few minutes. As the brake components cool down, their ability to absorb heat returns and the next time you use the brakes, they seem to work just fine. This type of brake fade was more common in older vehicles. Newer vehicles tend to have less outgassing from the brake pad compounds but they still suffer brake fade. So why? Its still to do with the pads getting too hot. With newer brake pad compounds, the pads transfer heat into the calipers once the rotors are too hot, and the brake fluid starts to boil forming bubbles in it. Because air is compressible (brake fluid isnt) when you step on the brakes, the air bubbles compress instead of the fluid transferring the motion to the brake calipers. Voila. Modern brake fade. So how do the engineers design brakes to reduce or eliminate brake fade? For older vehicles, you give that vapourised gas somewhere to go. For newer vehicles, you find some way to cool the rotors off more effectively. Either way you end up with cross-drilled or grooved brake rotors. While grooving the surface may reduce the specific heat capacity of the rotor, its effect is negligible in the grand scheme of things. However, under heavy braking once everything is hot and the resin is vapourising, the grooves give the gas somewhere to go, so the pad can continue to contact the rotor, allowing you to stop. The whole understanding of the conversion of energy is critical in understanding how and why brakes do what they do, and why they are designed the way they are. If youve ever watched Formula 1 racing, youll see the front wheels have huge scoops inside the wheel pointing to the front (see the picture above). This is to duct air to the brake components to help them cool off because in F1 racing, the brakes are used viciously every few seconds and spend a lot of their time trying to stay hot. Without some form of cooling assistance, the brakes would be fine for the first few corners but then would fade and become near useless by half way around the track. Rotor technology.If a brake rotor was a single cast chunk of steel, it would have terrible heat dissipation properties and leave nowhere for the vapourised gas to go. Because of this, brake rotors are typically modified with all manner of extra design features to help them cool down as quickly as possible as well as dissapate any gas from between the pads and rotors. The diagram here shows some examples of rotor types with the various modification that can be done to them to help them create more friction, disperse more heat more quickly, and ventilate gas. From left to right. 1: Basic brake rotor. 2: Grooved rotor - the grooves give more bite and thus more friction as they pass between the brake pads They also allow gas to vent from between the pads and the rotor. 3: Grooved, drilled rotor - the drilled holes again give more bite, but also allow air currents (eddies) to blow through the brake disc to assist cooling and ventilating gas. 4: Dual ventilated rotors - same as before but now with two rotors instead of one, and with vanes in between them to generate a vortex which will cool the rotors even further whilst trying to actually suck any gas away from the pads. An important note about drilled rotors: Drilled rotors are typically only found (and to be used on) race cars. The drilling weakens the rotors and typically results in microfractures to the rotor. On race cars this isnt a problem - the brakes are changed after each race or weekend. But on a road car, this can eventually lead to brake rotor failure - not what you want. I only mention this because of a lot of performance suppliers will supply you with drilled rotors for street cars without mentioning this little fact. Big rotors.How does all this apply to bigger brake rotors - a common sports car upgrade? Sports cars and race bikes typically have much bigger discs or rotors than your average family car. A bigger rotor has more material in it so it can absorb more heat. More material also means a larger surface area for the pads to generate friction with, and better heat dissipation. Larger rotors also put the point of contact with the pads further away from the axle of rotation. This provides a larger mechanical advantage to resist the turning of the rotor itself. To best illustrate how this works, imagine a spinning steel disc on an axle in front of you. If you clamped your thumbs either side of the disc close to the middle, your thumbs would heat up very quickly and youd need to push pretty hard to generate the friction required to slow the disc down. Now imagine doing the same thing but clamping your thumbs together close to the outer rim of the disc. The disc will stop spinning much more quickly and your thumbs wont get as hot. That, in a nutshell explains the whole principle behind why bigger rotors = better stopping power.The different types of brake.All brakes work by friction. Friction causes heat which is part of the kinetic energy conversion process. How they create friction is down to the various designs. Bicycle wheel brakesI thought Id cover these because theyre about the most basic type of functioning brake that you can see, watch working, and understand. The construction is very simple and out-in-the-open. A pair of rubber blocks are attached to a pair of calipers which are pivoted on the frame. When you pull the brake cable, the pads are pressed against the side or inner edge of the bicycle wheel rim. The rubber creates friction, which creates heat, which is the transfer of kinetic energy that slows you down. Theres only really two types of bicycle brake - those on which each brake shoe shares the same pivot point, and those with two pivot points. If you can look at a bicycle brake and not understand whats going on, the rest of this page is going to cause you a bit of a headache. Drum brakes - single leading edgeThe next, more complicated type of brake is a drum brake. The concept here is simple. Two semicircular brake shoes sit inside a spinning drum which is attached to the wheel. When you apply the brakes, the shoes are expanded outwards to press against the inside of the drum. This creates friction, which creates heat, which transfers kinetic energy, which slows you down. The example below shows a simple model. The actuator in this case is the blue elliptical object. As that is twisted, it forces against the brake shoes and in turn forces them to expand outwards. The return spring is what pulls the shoes back away from the surface of the brake drum when the brakes are released. See the later section for more information on actuator types. The single leading edge refers to the number of parts of the brake shoe which actually contact the spinning drum. Because the brake shoe pivots at one end, simple geometry means that the entire brake pad cannot contact the brake drum. The leading edge is the term given to the part of the brake pad which does contact the drum, and in the case of a single leading edge system, its the part of the pad closest to the actuator. This diagram (right) shows what happens as the brakes are applied. The shoes are pressed outwards and the part of the brake pad which first contacts the drum is the leading edge. The action of the drum spinning actually helps to draw the brake pad outwards because of friction, which causes the brakes to bite. The trailing edge of the brake shoe makes virtually no contact with the drum at all. This simple geometry explains why its really difficult to stop a vehicle rolling backwards if its equipped only with single leading edge drum brakes. As the drum spins backwards, the leading edge of the shoe becomes the trailing edge and thus doesnt bite. Drum brakes - double leading edgeThe drawbacks of the single leading edge style of drum brake can be eliminated by adding a second return spring and turning the pivot point into a second actuator. Now when the brakes are applied, the shoes are pressed outwards at two points. So each brake pad now has one leading and one trailing edge. Because there are two brake shoes, there are two brake pads, which means there are two leading edges. Hence the name double leading edge. Disc brakesSome background. Disc brakes were invented in 1902 and patented by Birmingham car maker Frederick William Lanchester. His original design had two discs which pressed against each other to generate friction and slow his car down. It wasnt until 1949 that disc brakes appeared on a production car though. The obscure American car builder Crosley made a vehicle called the Hotshot which used the more familiar brake rotor and calipers that we all know and love today. His original design was a bit crap though - the brakes lasted less than a year each. Finally in 1954 Citron launched the way-ahead-of-its-time DS which had the first modern incarnation of disc brakes along with other nifty stuff like self-levelling suspension, semi-automatic gearbox, active headlights and composite body panels. (all things which were re-introduced as new by car makers in the 90s). Disc brakes are an order of magnitude better at stopping vehicles than drum brakes, which is why youll find disc brakes on the front of almost every car and motorbike built today. Sportier vehicles with higher speeds need better brakes to slow them down, so youll likely see disc brakes on the rear of those too.The brake system assemblies are actuated by mechanical, hydraulic or pneumatic devices. The mechanical leverage is used in the parking brakes fitted in all automobile. When the brake pedal is depressed, the rod pushes the piston of brake master cylinder which presses the fluid. The fluid flows through the pipelines to the power brake unit and then to the wheel cylinder. The fluid pressure expands the cylinder pistons thus pressing the shoes to the drum or disk. If the pedal is released, the piston returns to the initialposition, the pull back springs retract the shoes, the fluid is forced back to the master cylinder and braking ceases.The primary purpose of the parking brake is to hold the vehicle stationary while it is unattended. The parking brake is mechanically operated by the driver when a separate parking braking hand lever is set. The hand brake is normally used when the car has already stopped. A lever is pulled and the rear brakes are approached and locked in the “on” position. The car may now be left without fear of its rolling away. When the driver wants to move the car again, he must press a button before the lever can be released. The hand brake must also be able to stop the car in the event of the foot brake failing. For this reason, it is separate from the foot brake uses cable or rods instead of the hydraulic system.Anti-lock Brake SystemAnti-lock brake systems make braking safer and more convenient, Anti-lock brake systems modulate brake system hydraulic pressure to prevent the brakes from locking and the tires from skidding on slippery pavement or during a panic stop.Anti-lock brake systems have been used on aircraft for years, and some domestic car were offered with an early form of anti-lock braking in late 1990s. Recently, several automakers have introduced more sophisticated anti-lock system. Investigations in Europe, where anti-lock brakin g systems have been available for a decade, have led one manufacture to state that the number of traffic accidents could be reduced by seven and a half percent if all cars had anti-lock brakes. So some sources predict that all cars will offer anti-lock brakes to improve the safety of the car. Anti-lock systems modulate brake application force several times per second to hold the tires at a controlled amount of slip; all systems accomplish this in basically the same way. One or more speed sensors generate alternating current signal whose frequency increases with the wheel rotational speed. An electronic control unit continuously monitors these signals and if the frequency of a signal drops too rapidly indicating that a wheel is about to lock, the control un
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