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吉利微型车转向系设计
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微型车
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设计
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中文译文汽车电动助力转向系统的研究随着汽车电子技术的迅猛发展,人们对汽车转向操纵性能的要求也日益提高。汽车转向系统已从传统机械转向、液压助力转向(Hydraulic Power Steering ,简称HPS) 电控液压助力转向( Electric Hydraulic Power Steering , 简称EHPS) , 发展到电动助力转向系统(Electric Power Steering ,简称EPS) ,最终还将过渡到线控转向系统(Steer By Wire ,简称SBW)。机械转向系统是指以驾驶员的体力作为转向能源,其中所有传力件都是机械的,汽车的转向运动是由驾驶员操纵方向盘,通过转向器和一系列的杆件传递到转向车轮而实现的。机械转向系由转向操纵机构、转向器和转向传动机械3大部分组成。通常根据机械式转向器形式可以分为:齿轮齿条式、循环球式、蜗杆滚轮式、蜗杆指销式。应用最广的两种是齿轮齿条式和循环球式(用于需要较大的转向力时) 。在循环球式转向器中,输入转向圈与输出的转向摇臂摆角是成正比的;在齿轮齿条式转向器中,输入转向圈数与输出的齿条位移是成正比的。循环球式转向器由于是滚动摩擦形式,因而正传动效率很高,操作方便且使用寿命长,而且承载能力强,故广泛应用于载货汽车上。齿轮齿条式转向器与循环球式相比,最大特点是刚性大,结构紧凑重量轻,且成本低。由于这种方式容易由车轮将反作用力传至转向盘,所以具有对路面状态反应灵敏的优点,但同时也容易产生打手和摆振等现象,且其承载效率相对较弱,故主要应用于小汽车及轻型货车上,目前大部分低端轿车采用的就是齿轮齿条式机械转向系统。随着车辆载重的增加以及人们对车辆操纵性能要求的提高,简单的机械式转向系统已经无法满足需要,动力转向系统应运而生,它能在驾驶员转动方向盘的同时提供助力,动力转向系统分为液压转向系统和电动转向系统2种。其中液压转向系统是目前使用最为广泛的转向系统。液压转向系统在机械系统的基础上增加了液压系统,包括液压泵、V 形带轮、油管、供油装置、助力装置和控制阀。它借助于汽车发动机的动力驱动液压泵、空气压缩机和发电机等,以液力、气力或电力增大驾驶员操纵前轮转向的力量,使驾驶员可以轻便灵活地操纵汽车转向,减轻了劳动强度,提高了行驶安全性。液压助力转向系统从发明到现在已经有了大约半个世纪的历史,可以说是一种较为完善的系统,由于其工作可靠、技术成熟至今仍被广泛应用。它由液压泵作为动力源,经油管道控制阀向动力液压缸供油,通过活塞杆带动转向机构动作,可通过改变缸径及油压的大小来改变助力的大小,由此达到转向助力的作用。传统液压式动力转向系统一般按液流的形式可以分为:常流式和常压式2 种类型,也可根据控制阀形式分为转阀式和滑阀式。随着液压动力转向系统在汽车上的日益普及,人们对操作时的轻便性和路感的要求也日益提高,然而液压动力转向系统却存在许多的缺点: 由于其本身的结构决定了其无法保证车辆在任何工况下转动转向盘时,都有较理想的操纵稳定性,即无法同时保证低速时的转向轻便性和高速时的操纵稳定性; 汽车的转向特性受驾驶员驾驶技术的影响严重; 转向传动比固定,使汽车转向响应特性随车速、侧向加速度等变化而变化,驾驶员必须提前针对汽车转向特性幅值和相位的变化进行一定的操作补偿,从而控制汽车按其意愿行驶。这样增加了驾驶员的操纵负担,也使汽车转向行驶中存在不安全隐患;而此后出现了电控液压助力系统,它在传统的液压动力转向系统的基础上增加速度传感器,使汽车能够随着车速的变化自动调节操纵力的大小,在一定程度上缓和了传统的液压转向系统存在的问题。目前我国生产的商用车和轿车上采用的大多是电控液压助力转向系统,它是比较成熟和应用广泛的转向系统。尽管电控液压助力装置从一定程度上缓解了传统的液压转向中轻便性和路感之间的矛盾,然而它还是没有从根本上解决HPS 系统存在的不足,随着汽车微电子技术的发展,汽车燃油节能的要求以及全球性倡导环保,其在布置、安装、密封性、操纵灵敏度、能量消耗、磨损与噪声等方面的不足已越来越明显,转向系统向着电动助力转向系统发展。电动助力转向系统是现在汽车转向系统的发展方向,其工作原理是:EPS 系统的ECU 对来自转向盘转矩传感器和车速传感器的信号进行分析处理后,控制电机产生适当的助力转矩,协助驾驶员完成转向操作。近几年来,随着电子技术的发展,大幅度降低EPS的成本已成为可能,日本的大发汽车公司、三菱汽车公司、本田汽车公司、美国的Delphi 汽车系统公司、TRW公司及德国的ZF 公司都相继研制出EPS。Mercedes2Benz 和Siemens Automotive 两大公司共同投资6500万英镑用于开发EPS ,目标是到2002 年装车,年产300 万套,成为全球EPS 制造商。到目前为止,EPS 系统在轻微型轿车、厢式车上得到广泛的应用,并且每年以300 万台的速度发展。.转向是一个专业术语,适用于采集部件,联系等,其中允许一艘(舰船)或汽车(轿车)按照预期的方向行驶. 一个例外的情况是铁路运输由路轨组合在一起铁路道岔提供转向功能。许多现代轿车使用齿轮齿条式转向器,在方向盘末端有转动齿轮;该齿轮带动齿条移动,它是一种线性的齿轮紧密配合,从一边到一边。这种运动把转矩通过转向横拉杆和一种叫做转向节臂的短形臂传递给转向轮的主销。以前的设计往往采用循环球式转向器,而这种转向器仍然应用在卡车和多用途车辆。这是一种老式的螺母和齿扇设计，该转向管柱转动大螺丝(蜗轮),它与一个齿扇齿轮啮合,当蜗轮转动时，齿扇也随之转动，一个安装在齿扇轴上且与转向联动有关的摇臂带动转向节臂 ,从而使车轮转动. 循环球式转向器通过安装滚珠减少螺母和螺杆之间的摩擦;两根导管和螺母内的螺旋管状通道组合成两条各自独立的封闭的钢球“流到”。齿轮齿条式转向器设计具有很大程度的反馈和直接转向路感;它也通常不会有任何反弹,或呆滞。缺点是,它是不可调的,因此当它磨损唯一的解决办法更换。循环球式转向器的优点是机械优势,因此,它被使用在较大较重的车辆,而齿轮齿条式原本仅限于较小和较轻;由于几乎普遍采用动力转向系统,不过,这已不再是一个重要的优势,导致越来越多地在新型汽车应用齿轮齿条式转向器。 循环球式转向器设计在中心也有明显的冲击,或死点。凡一分钟交替方向盘出不来并不移动转向机构;这是很容易可调螺杆的端部来减少磨损,但它并不能完全消除或机制开始磨损很快。 这项设计目前仍在使用中,在卡车和其他大型车辆,也应用于迅速转向,路感与稳健性,可维护性,和机械的优势相比不太重要的场合。 较小程度的反馈,这样的设计也有时是一种优点;当前轮碰撞时，使用齿轮齿条转向的司机只有自己的大拇指受伤,造成方向盘揭开一边突然(因为驾驶教练告诉学生把自己的大拇指在前面的方向盘,而非放在左右的内边缘).这种效果在像卡车一样的重型汽车更为明显;循环球式转向防止这种程度的反馈,只是因为它可以在正常情况下防止可取反馈。 转向连锁连接转向器和车轮通常符合一个阿克曼转向几何的变化,它交代了一个事实:当转向是,内轮转过的半径比外轮小得多，因此适合驾驶的直路,是不适合曲折。由于车辆已成为较重而改用前轮驱动,为了扭转方向盘，通常的,主要的是体力。为了解决这一问题,汽车业发展的动力转向系统。 有两种类型的助力转向系统-液压和电气/电子。 T还有一种液压-电动混合系统。液压助力转向系统(hps)利用油压供应的一个发动机驱动泵,以协助将方向盘转转动。 电动助力转向系统(EPS)方式,是较有效率的液压助力转向系统,由于电动助力转向汽车只需要提供协助时,方向盘被转动,而液压泵必须不断运行。 在EPS的帮助下是很容易调节车型,最高车速,甚至驾驶的喜好。 另外一个好处是,通过泄漏和处置动力转向液消除对环境构成危险 。A动力转向的分支是速度可调转向而转向是大量辅助以低速行驶,稍微协助高速。 汽车制造商认为,当要停车时驾驶人可能需要做出大量转向投入，但当时高速行驶时则不然。第一辆有这特点的汽车,是雪铁龙与其diravi，虽然改变了现代汽车转向系统资金的投入，但它改变了定心凸轮的压力，使得方向盘尽力去回到原来的位置。现代速度可调式动力转向系统,当速度增长时减少了活塞的压力 ,给予更直接的感受。这一特点在所有新车正逐渐成为司空见惯。 四轮转向(或全轮转向)是一种系统,当高速行驶时能增加车辆稳定型，而在低速行驶时可以减小转弯半径。大多数的四轮转向系统,后轮转向通过单片机和驱动器实现。 后轮一般不能反过来,有几个系统,包括Delphi的quadrasteer，该系统在本田的生产前线，当前轮低速时，允许后轮在相反方向转向。这使得车辆转弯半径较小,有时应用于大型卡车车辆及挂车。 电子动力转向系统图1电子动力转向系统的工作原理电子动力转向系统是通过一个电动机来驱动动力方向盘液压泵或直接驱动转向联动装置。电子动力转向的功能由于不依赖于发动机转速，所以能节省能源电子动力转向系统是这样运行的传统的动力方向盘系统使用一条引擎辅助传送带驾驶泵浦，提供操作在动力方向盘齿轮或作动器的一个活塞协助司机的被加压的流体。在电动液压的指点，一个电子动力方向盘概念使用一台电动机驾驶的一个高效率泵浦。 泵浦速度是由一个电控制器调控的变化泵浦压力和流程，提供被剪裁的指点努力为不同的驾驶的情况。 泵浦可以跑在低速或关闭提供节能在大多时间在多数世界市场上)直向前的驾驶期间(直接电指点使用一台电动机附加指点机架通过齿轮机构(没有泵浦或流体)。 各种各样的马达类型和齿轮驱动是可能的。 微处理器控制指点动力学和司机努力。 输入包括车速和指点、轮子扭矩，角位和转动率。工作运行时的具体细节：A “指点传感器”位于它进入传动箱住房的输入轴。 指点传感器实际上是在一个的二个传感器： 那“扭矩的传感器”转换指点扭矩输入和它的方向成电压信号，并且那“自转的传感器”转换转动速度和方向成电压信号。 分享同一套住房的“接口”电路转换从扭矩传感器和自转传感器的信号成控制电子学可能处理的信号。从指点传感器的输入由那微处理器的控制单元消化也监测从车速传感器的输入。 传感器输入然后被比较确定多少机械化根据一张被预编程序的“力量地图”需要在控制单元的记忆。 控制单元然后派出适当的命令对然后供给电动机以潮流的“电源装置”。 马达推挤机架在右边或左根据哪个方式电压流动(扭转潮流扭转方向马达旋转)。 增加潮流对马达增加功率协助。系统有三种操作方式： 左边或右边机械化提供以回应从指点扭矩和自转传感器的输入的输入的“正常”控制方式; 被用于在完成轮以后协助指点回归的“回归”控制方式; 并且改变与车速改进路感受和挫伤佣金的“更加潮湿的”控制方式。如果方向盘被转动，并且举行在充分锁位置和指点协助到达最大值，控制单元使潮流降低到电动机防止也许损坏马达的超载情况。 控制单元也被设计保护马达以防止电压浪涌免受一个有毛病的交流发电机或充电的问题。电子转向控制单位有能力在自我诊断的缺点通过监测系统输入和产品和电动机的激励电流上。 如果问题发生，控制单元通过开动在电源装置的一个故障自动保险的中转关闭系统。 这消灭所有机械化，造成系统恢复回到手工指点。 破折号EPS警告灯也被阐明警告司机。 要诊断问题，技术员跳服务检查连接器的终端并且读出问题代码。 图 2电子动力方向盘机制当前发明与提供的供给动力的援助一电子功率驱动器马达关连给车操纵机构。根据当前发明的一个方面，那里为提供供给动力的援助提供一个电子功率驱动器机制给有车的操纵机构一名手动地可旋转的成员为操作操纵机构、传动机构包括可行扭矩的传感器感觉手动地被申请于可旋转的成员的扭矩，一个电子功率驱动器马达操纵着被连接到可旋转的成员和安排控制主驱动电动机自转速度和方向以回应从扭矩传感器收到的信号的控制器，扭矩传感器包括为与可旋转的成员的连接适应的传感器轴形成引伸因此，以便扭矩通过前述传感器轴被传送，当时 可旋转的成员被转动，并且应变仪在导致的信号传感器轴手动地登上表示通过前述轴被传送的相当数量扭矩。 图3传感器轴不旋转更好地登上在一个轴向末端在第一名联结成员和不旋转地登上在它的相反轴向末端在第二名联结成员，第一和第二名联结成员相互允诺允许有限的自转之间连接，以便在一个被预先决定的极限之下的扭矩由仅传感器轴传送，并且，以便在前述被预先决定的极限之上的扭矩通过第一和第二名联结成员被传送。更适宜地安排第一和第二名联结成员作为操纵的连接的第一和第二个部分的一座桥梁互相的旋转式成员。合适的传感器轴是通常在多数的长方形横断面它的长度中。应变仪包括一个或更多的适应地看见了谐振器绑到传感器轴上。好的马达操纵的被连接到可旋转的成员通过传动器。马达更好地包括一个工具箱和同心地被安排相对可旋转的成员。当前发明的Various方面此后将描述，关于伴随的图画， ：图1是一个车操纵机构的一个图表看法包括一个电子功率驱动器机制根据当前发明，图 2是说明在图显示的传动机构的各种各样的组分的之间流程图互作用1上，图 3是一个轴截面通过在图显示的传动机构1，图4上是一张截面图被采取沿着线IV-IV在表3，图5是在图显示的输入推进联结的一张更加详细的分解图3上，和图 6是显示在表3.的传动器的一张更加详细的分解图。 图1的最初Referring，那里显示一个车操纵机构10操纵的被连接到一个对易操纵的路轮子12。这个显示的操纵机构包括一个齿条和齿轮汇编14被连接到路轮子12通过联接15。 鸟翼末端(没显示)汇编14可旋转地驾驶一名手动地可旋转的成员以驾驶杆18的形式哪些由方向盘19手动地转动。这个驾驶杆18包括包括一台电主驱动电动机的一个电力的传动机构30 (没显示在驾驶的鸟翼末端图1)上以回应在驾驶杆18的扭矩装货为了为机械人员提供力量援助，当转动方向盘19时。如概要地被说明在表2，电力的传动机构包括测量驾驶杆申请的扭矩18，当驾驶鸟翼末端时并且提供信号给控制器40的扭矩传感器20。 控制器40被连接到主驱动电动机50并且控制电流被提供给马达50控制马达50和它的自转的方向扭矩引起的相当数量。马达50 操纵的更适宜地被连接到驾驶杆18通过工具箱60，更适宜地一个周转齿轮箱子和传动器70。 在一定条件下传动器70在正常运行时更适宜地永久地接合并且是有效的隔绝从马达50的驱动使鸟翼末端通过传动机构30手动地被驾驶。 这是使机制的安全特点起作用在试图的马达50情形下驾驶太快速的驾驶杆并且/或者在错误的方向或在案件 电动机和工具箱占领了。扭矩传感器20更适宜地是一个汇编包括在扭矩应用达到的传感器轴登上应变仪能够准确测量张力在一个被预先决定的范围之内的一个短的传感器轴。被测量扭矩的被预先决定的范围是0-lONm; 更好是关于l-5Nm。被测量的扭矩的范围更好地对应于大约0-1000微指令，并且传感器轴的建筑更好被选择这样5Nm扭矩比在轴的2导致较少的转弯，少于1 。好的应变仪是锯谐振器，在WO91/13832被描述的一台适当的锯谐振器。 类似在图显示的那WO91/13832 3上更好地运用配置，二看见谐振器被安排在对轴轴的45和在90对互相。谐振器经营与在200-400 MHz之间共鸣频率和被安排导致信号到控制器1 MHz 40 500 KHz根据传感器轴的自转方向的自我调节。 因此，当传感器轴不被扭转的归结于缺乏扭矩时，它导致一个1 MHz信号。当它导致在1.0到1.5 MHz之间的一个信号的传感器轴在一个方向被扭转。 当传感器轴在相反方向时被扭转它导致在1.0到0.5 MHz之间的一个信号。 因而同样传感器能导致信号表示程度扭矩并且传感器轴的自转的方向。好的马达扭矩引起的相当数量以回应在0-10Nm之间被测量的扭矩是0-40Nm，并且为在l-5Nm之间被测量的扭矩是0-25Nm。反馈电路提供自我调节，借以马达使用的电流由控制器40测量并且比较保证马达在正确方向运行并且提供期望功率协助。 控制器更好地行动使被测量的扭矩降低到零和如此控制马达增加它的扭矩产品减少被测量的扭矩。 (没显示)更适宜地提供车速传感器哪些寄发一个信号表示车速到控制器。 控制器使用这个信号修改程度力量协助提供以回应被测量的扭矩。将提供在低车速最大力量协助的，因而，并且将提供高车速极小的力量协助。更适宜地是逻辑顺序器有一个现场可编程序的门数组例如XC 4005如Xilinx供应这个控制器。 这样控制器不依靠软件和，因此能更起作用可靠地在汽车车环境里。 被想象也许使用有逻辑的序列一个现场可编程序的列阵。 一个电力传动机构10的A具体建筑在表3.被说明。电子动力转向系统（英文简称EPS）， 与液压动力转向系统（HPS）相比，EPS具有很多优点。即EPS的优势在于：1）效率高。HPS效率很低，一般为60%70%；而EPS与电机连接，效率高，有的可高达90%以上。2）耗能少。汽车在实际行驶过程中，处于转向的时间约占行驶时间的5%，对于HPS系统，发动机运转时，油泵始终处于工作状态，油液一直在管路中循环，从而使汽车燃油消耗率增加4%6%；而EPS仅在需要时供能，使汽车的燃油消耗率仅增加0.5%左右。 3）“路感“好。由于EPS内部采用刚性连接，系统的滞后特性可以通过软件加以控制，且可以根据驾驶员的操作习惯进行调整。4）回正性好。EPS结构简单内部阻力小，回正性好，从而可得到最佳的转向回正特性，改善汽车操纵稳定性。5）对环境污染少。HPS液压回路中有液压软管和接头，存在油液泄露问题，而且液压软管不可回收，对环境有有一定污染；而EPS对环境几乎没有污染。6）可以独立于发动机工作。EPS以电池为动力元件，只要电池电量充足，不论发动机出于何种状态，都可以产生助力作用。7）应有范围广。8）装配性好易于布置。现在，动力转向系统已成为一些轿车的标准设置，全世界约有一半的轿车采用动力转向。随着汽车电子技术的发展，目前一些轿车已经使用电动助力转向器，使汽车的经济性、动力性和机动性都有所提高。电动助力转向装置是汽车上一种新的助力转向系统装置,近年来在国内外发展迅速,由于它采用了可编程电子控制装置,在带来灵活性的同时也存在着安全隐患.在分析这种产品特殊性的基础上,笔者结合电子控制装置的特点,指出了事关安全性的因素,提出了处理安全性的措施,并讨论了几个事关安全性的具体问题.研究结果表明:现有标准不能够满足电动助力转向装置安全性的需要;并提出了对电动助力转向装置进行安全性测评的思想.研究工作对电动助力转向装置的开发以及评价具有参考意义。英文原文The auto electric power steering system research Along with automobile electronic technology swift and violent development, the people also day by day enhance to the motor turning handling quality request. The motor turning system hanged, the hydraulic pressure boost from the traditional machinery changes (Hydraulic Power Steering, is called HPS), the electrically controlled hydraulic pressure boost changes (Electronic Hydraulic Power Steering, is called EHPS), develops the electrically operated boost steering system (Electronic Power Steering, is called EPS), finally also will transit to the line controls the steering system (Steer By Wire, will be called SBW).The machinery steering system is refers by pilots physical strength achievement changes the energy, in which all power transmission all is mechanical, the automobile changes the movement is operates the steering wheel by the pilot, transmits through the diverter and a series of members changes the wheel to realize. The mechanical steering system by changes the control mechanism, the diverter and major part changes the gearing 3 to be composed.Usually may divide into according to the mechanical diverter form: The gear rack type, follows round the world -like, the worm bearing adjuster hoop type, the worm bearing adjuster refers sells the type. Is the gear rack type and follows using the broadest two kinds round the world -like (uses in needing time big steering force).In follows round the world -like in the diverter, the input changes the circle and the output steering arm pivot angle is proportional; In the gear rack type diverter, the input changes the turn and the output rack displacement is proportional. Follows round the world -like the diverter because is the rolling friction form, thus the transmission efficiency is very high, the ease of operation also the service life are long, moreover bearing capacity, therefore widely applies on the truck. The gear rack type diverter with follows round the world -like compares, the most major characteristic is the rigidity is big, the structure compact weight is light, also the cost is low. Because this way passes on easily by the wheel the reacting force to the steering wheel, therefore has to the pavement behavior response keen merit, but simultaneously also easy to have phenomena and so on goon and oscillation, also its load bearing efficiency relative weak, therefore mainly applies on the compact car and the pickup truck, at present the majority of low end passenger vehicle uses is the gear rack type machinery steering system. Along with the vehicles carrying capacity increase as well as the people to the vehicles handling quality request enhancement, the simple mechanical type steering system were already unable to meet the needs, the power steering system arise at the historic moment, it could rotate the steering wheel while the pilot to provide the boost, the power steering system divides into the hydraulic pressure steering system and the electrically operated steering system 2kinds.Hydraulic pressure steering system is at present uses the most widespread steering system.The hydraulic pressure steering system increased the hydraulic system in the mechanical system foundation, including hydraulic pump, V shape band pulley, drill tubing, feed installment, boost installment and control valve. It with the aid of in the motor car engine power actuation hydraulic pump, the air compressor and the generator and so on, by the fluid strength, the physical strength or the electric power increases the pilot to operate the strength which the front wheel changes, enables the pilot to be possible nimbly to operate motor turning facilely, reduced the labor intensity, enhanced the travel security.The hydraulic pressure boost steering system from invented already had about half century history to the present, might say was one kind of more perfect system, because its work reliable, the technology mature still widely is applied until now. It takes the power supply by the hydraulic pump, after oil pipe-line control valves to power hydraulic cylinder feed, through the connecting rod impetus rotation gear movement, may changes the boost through the change cylinder bore and the flowing tubing head pressure size the size, from this achieved changes the boost the function. The traditional hydraulic pressure type power steering system may divide into generally according to the liquid flow form: Ordinary flow type and atmospheric pressure type 2 kind of types, also may divide into according to the control valve form transfers the valve type and the slide-valve type.Along with hydraulic pressure power steering system on automobile daily popularization, the people to operates when the portability and the road feeling request also day by day enhance, however the hydraulic pressure power steering system has many shortcomings actually: Because its itself structure had decided it is unable to guarantee vehicles rotates the steering wheel when any operating mode, all has the ideal operation stability, namely is unable simultaneously to guarantee time the low speed changes the portability and the high speed time operation stability;The automobile changes the characteristic to drive the pilot technical the influence to be serious; The steering ratio is fixed, causes the motor turning response characteristic along with changes and so on vehicle speed, transverse acceleration to change, the pilot must aim at the motor turning characteristic peak-to-peak value and the phase change ahead of time carries on certain operation compensation, thus controls the automobile according to its wish travel. Like this increased pilots operation burden, also causes in the motor turning travel not to have the security hidden danger; But hereafter appeared the electrically controlled hydraulic booster system, it increases the velocity generator in the traditional hydraulic pressure power steering system foundation, enables the automobile along with the vehicle speed change automatic control force size, has to a certain extent relaxed the traditional hydraulic pressure steering system existence question.At present our country produces on the commercial vehicle and the passenger vehicle uses mostly is the electrically controlled hydraulic pressure boost steering system, it is quite mature and the application widespread steering system. Although the electrically controlled hydraulic servo alleviated the traditional hydraulic pressure from certain degree to change between the portability and the road feeling contradiction, however it did not have fundamentally to solve the HPS system existence insufficiency, along with automobile microelectronic technology development, automobile fuel oil energy conservation request as well as global initiative environmental protection, it in aspect and so on arrangement, installment, leak-proof quality, control sensitivity, energy consumption, attrition and noise insufficiencies already more and more obvious, the steering system turned towards the electrically operated boost steering system development.The electrically operated boost steering system is the present motor turning system development direction, its principle of work is: EPS system ECU after comes from the steering wheel torque sensor and the vehicle speed sensor signal carries on analysis processing, controls the electrical machinery to have the suitable boost torque, assists the pilot to complete changes the operation. In the last few years, along with the electronic technology development, reduces EPS the cost to become large scale possibly, Japan sends the car company, Mitsubishi Car company, this field car company, USs Delphi automobile system company, TRW Corporation and Germanys ZF Corporation greatly all one after another develops EPS.Mercedes2Benz Siemens Automotive Two big companies invested 65,000,000 pounds to use in developing EPS, the goal are together load a car to 2002, yearly produce 300 ten thousand sets, became the global EPS manufacturer. So far, the EPS system in the slight passenger vehicle, on the theater box type vehicle obtains the widespread application, and every year by 300 ten thousand speed development.Steering is the term applied to the collection of components, linkages, etc. which allow for a vessel (ship, boat) or vehicle (car) to follow the desired course. An exception is the case of rail transport by which rail tracks combined together with railroad switches provide the steering function.The most conventional steering arrangement is to turn the front wheels using a handoperated steering wheel which is positioned in front of the driver, via the steering column, which may contain universal joints to allow it to deviate somewhat from a straight line. Other arrangements are sometimes found on different types of vehicles, for example, a tiller or rearwheel steering. Tracked vehicles such as tanks usually employ differential steering that is, the tracks are made to move at different speeds or even in opposite directions to bring about a change of course.Many modern cars use rack and pinion steering mechanisms, where the steering wheel turns the pinion gear; the pinion moves the rack, which is a sort of linear gear which meshes with the pinion, from side to side. This motion applies steering torque to the kingpins of the steered wheels via tie rods and a short lever arm called the steering arm.Older designs often use the recirculating ball mechanism, which is still found on trucks and utility vehicles. This is a variation on the older worm and sector design; the steering column turns a large screw (the worm gear) which meshes with a sector of a gear, causing it to rotate about its axis as the worm gear is turned; an arm attached to the axis of the sector moves the pitman arm, which is connected to the steering linkage and thus steers the wheels. The recirculating ball version of this apparatus reduces the considerable friction by placing large ball bearings between the teeth of the worm and those of the screw; at either end of the apparatus the balls exit from between the two pieces into a channel internal to the box which connects them with the other end of the apparatus, thus they are recirculated.The rack and pinion design has the advantages of a large degree of feedback and direct steering feel; it also does not normally have any backlash, or slack. A disadvantage is that it is not adjustable, so that when it does wear and develop lash, the only cure is replacement.The recirculating ball mechanism has the advantage of a much greater mechanical advantage, so that it was found on larger, heavier vehicles while the rack and pinion was originally limited to smaller and lighter ones; due to the almost universal adoption of power steering, however, this is no longer an important advantage, leading to the increasing use of rack and pinion on newer cars. The recirculating ball design also has a perceptible lash, or dead spot on center, where a minute turn of the steering wheel in either direction does not move the steering apparatus; this is easily adjustable via a screw on the end of the steering box to account for wear, but it cannot be entirely eliminated or the mechanism begins to wear very rapidly. This design is still in use in trucks and other large vehicles, where rapidity of steering and direct feel are less important than robustness, maintainability, and mechanical advantage. The much smaller degree of feedback with this design can also sometimes be an advantage; drivers of vehicles with rack and pinion steering can have their thumbs broken when a front wheel hits a bump, causing the steering wheel to kick to one side suddenly (leading to driving instructors telling students to keep their thumbs on the front of the steering wheel, rather than wrapping around the inside of the rim). This effect is even stronger with a heavy vehicle like a truck; recirculating ball steering prevents this degree of feedback, just as it prevents desirable feedback under normal circumstances.The steering linkage connecting the steering box and the wheels usually conforms to a variation of Ackermann steering geometry, to account for the fact that in a turn, the inner wheel is actually traveling a path of smaller radius than the outer wheel, so that the degree of toe suitable for driving in a straight path is not suitable for turns.As vehicles have become heavier and switched to front wheel drive, the effort to turn the steering wheel manually has increased - often to the point where major physical exertion is required. To alleviate this, auto makers have developed power steering systems. There are two types of power steering systemshydraulic and electric/electronic. There is also a hydraulic-electric hybrid system possible.A hydraulic power steering (HPS) uses hydraulic pressure supplied by an engine-driven pump to assist the motion of turning the steering wheel. Electric power steering (EPS) is more efficient than the hydraulic power steering, since the electric power steering motor only needs to provide assist when the steering wheel is turned, whereas the hydraulic pump must run constantly. In EPS the assist level is easily tunable to the vehicle type, road speed, and even driver preference. An added benefit is the elimination of environmental hazard posed by leakage and disposal of hydraulic power steering fluid.An outgrowth of power steering is speed adjustable steering, where the steering is heavily assisted at low speed and lightly assisted at high speed. The auto makers perceive that motorists might need to make large steering inputs while manoeuvering for parking, but not while traveling at high speed. The first vehicle with this feature was the Citron SM with its Diravi layout, although rather than altering the amount of assistance as in modern power steering systems, it altered the pressure on a centring cam which made the steering wheel try to spring back to the straight-ahead position. Modern speed-adjustable power steering systems reduce the pressure fed to the ram as the speed increases, giving a more direct feel. This feature is gradually becoming commonplace across all new vehicles.Four-wheel steering (or all wheel steering) is a system employed by some vehicles to increase vehicle stability while maneuvering at high speed, or to decrease turning radius at low speed.In most four-wheel steering systems, the rear wheels are steered by a computer and actuators. The rear wheels generally cannot turn as far as the Alternatively, several systems, including Delphis Quadrasteer and the system in Hondas Prelude line, allow for the rear wheels to be steered in the opposite direction as the front wheels during low speeds. This allows the vehicle to turn in a significantly smaller radius sometimes critical for large trucks or vehicles with trailers. An exception is the case of rail transport by which rail tracks combined together with railroad switches provide the steering function.Many modern cars use steering mechanisms, where the steering wheel turns the pinion gear; the pinion moves the rack, which is a sort of linear gear which meshes with the pinion, from side to side.mechanism, which is still found on trucks and utility vehicles.This is a variation on the older and thus steers the wheels.The recirculating ball version of this apparatus reduces the considerable friction by placing large ball bearings between the teeth of the worm and those of the screw; at either end of the apparatus the balls exit from between the two pieces into a channel internal to the box which connects them with the other end of the apparatus, thus they are recirThe rack and pinion design has the advantages of a large degree of feedback and direct steering feel; it also does not normally have any , or slack.culated.A disadvantage is that it is not adjustable, so that when it does wear and develop lash, the only cure is replacement.The recirculating ball mechanism has the advantage of a much greater , however, this is no longer an important advantage, leading to the increasing use of rack and pinion on newer cars.to account for wear, but it cannot be entirely eliminated or the mechanism begins to wear very rapidly.This design is still in use in trucks and other large vehicles, where rapidity of steering and direct feel are less important than robustness, maintainability, and mechanical advantage.The much smaller degree of feedback with this design can also sometimes be an advantage; drivers of vehicles with rack and pinion steering can have their thumbs broken when a front wheel hits a bump, causing the steering wheel to kick to one side suddenly (leading to driving instructors telling students to keep their thumbs on the front of the steering wheel, rather than wrapping around the inside of the rim). This effect is even stronger with a heavy vehicle like a truck; recirculating ball steering prevents this degree of feedback, just as it prevents desirable feedback under normal circumstances.As vehicles have become heavier and switched to front wheel drive , the effort to turn the steering wheel manually has increased - often to the point where major physical exertion is required.There are two types of power steering systemshydraulic and electric/electronic.here is also a hydraulic-electric hybrid system possible.A hydraulic power steering (HPS) uses hydraulic pressure supplied by an engine-driven pump to assist the motion of turning the stElectric power steering (EPS) is more efficient than the hydraulic power steering, since the electric power steering motor only needs to provide assist when the steering wheel is turned, whereas the hydraulic pump must run constantly.eering wheel.In EPS the assist level is easily tunable to the vehicle type, road speed, and even driver preference.An added benefit is the elimination of environmental hazard posed by leakage and disposal of hydraulic power steering fluid.n outgrowth of power steering is speed adjustable steering, where the steering is heavily assisted at low speed and lightly assisted at high speed.The auto makers perceive that motorists might need to make large steering inputs while manoeuvering for parking, but not while traveling at high speed.The first vehicle with this feature was the Citron SM with its Diravi layout, although rather than altering the amount of assistance as in modern power steering systems, it altered the pressure on a centring cam which made the steering wheel try to spring back to the straight-ahead position.Modern speed-adjustable power steering systems reduce the pressure fed to the ram as the speed increases, The rear wheels giving a more direct feel.This feature is gradually becoming commonplace across all new vehicles.In most four-wheel steering systems, the rear wheels are steered by a computer and actuators.generally cannot turn as far as the Alternatively, several systems, including Delphis Quadrasteer and the system in Hondas Prelude line, allow for the rear wheels to be steered in the opposite direction as the front wheels during low speeds.This allows the vehicle to turn in a significantly smaller radius sometimes critical for large trucks or vehicles with trailers.Electronic power steering system What it isElectrically powered steering uses an electric motor to drive either the power steering hydraulic pump or the steering linkage directly. The power steering function is therefore independent of engine speed, resulting in significant energy savings.How it works :Conventional power steering systems use an engine accessory belt to drive the pump, providing pressurized fluid that operates a piston in the power steering gear or actuator to assist the driver.In electro-hydraulic steering, one electrically powered steering concept uses a high efficiency pump driven by an electric motor. Pump speed is regulated by an electric controller to vary pump pressure and flow, providing steering efforts tailored for different driving situations. The pump can be run at low speed or shut off to provide energy savings during straight ahead driving (which is most of the time in most world markets). Direct electric steering uses an electric motor attached to the steering rack via a gear mechanism (no pump or fluid). A variety of motor types and gear drives is possible. A microprocessor controls steering dynamics and driver effort. Inputs include vehicle speed and steering, wheel torque, angular position and turning rate. Working In Detail:A steering sensor is located on the input shaft where it enters the gearbox housing. The steering sensor is actually two sensors in one: a torque sensor that converts steering torque input and its direction into voltage signals, and a rotation sensor that converts the rotation speed and direction into voltage signals. An interface circuit that shares the same housing converts the signals from the torque sensor and rotation sensor into signals the control electronics can process. Inputs from the steering sensor are digested by a microprocessor control unit that also monitors input from the vehicles speed sensor. The sensor inputs are then compared to determine how much power assist is required according to a preprogrammed force map in the control units memory. The control unit then sends out the appropriate command to the power unit which then supplies the electric motor with current. The motor pushes the rack to the right or left depending on which way the voltage flows (reversing the current reverses the direction the motor spins). Increasing the current to the motor increases the amount of power assist.The system has three operating modes: a normal control mode in which left or right power assist is provided in response to input from the steering torque and rotation sensors inputs; a return control mode which is used to assist steering return after completing a turn; and a damper control mode that changes with vehicle speed to improve road feel and dampen kickback.If the steering wheel is turned and held in the full-lock position and steering assist reaches a maximum, the control unit reduces current to the electric motor to prevent an overload situation that might damage the motor. The control unit is also designed to protect the motor against voltage surges from a faulty alternator or charging problem.The electronic steering control unit is capable of self-diagnosing faults by monitoring the systems inputs and outputs, and the driving current of the electric motor. If a problem occurs, the control unit turns the system off by actuating a fail-safe relay in the power unit. This eliminates all power assist, causing the system to revert back to manual steering. A dash EPS warning light is also illuminated to alert the driver. To diagnose the problem, a technician jumps the terminals on the service check connector and reads out the trouble codes. Electric power steering systems promise weight reduction, fuel savings and package flexibility, at no cost penalty.Europes high fuel prices and smaller vehicles make a fertile testbed for electric steering, a technology that promises automakers weight savings and fuel economy gains. And in a short time, electric steering will make it to the U.S., too. Its just just a matter of time, says Aly Badawy, director of research and development for Delphi Saginaw Steering Systems in Saginaw, Mich. The issue was cost and thats behind us now. By 2002 here in the U.S. the cost of electric power steering will absolutely be a wash over hydraulic.Today, electric and hybrid-powered vehicles (EV), including Toyotas Prius and GMs EV-1, are the perfect domain for electric steering. But by 2010, a TRW Inc. internal study estimates that one out of every three cars produced in the world will be equipped with some form of electrically-assisted steering. The Cleveland-based supplier claims its new steering systems could improve fuel economy by up to 2 mpg, while enhancing handling. There are true bottom-line benefits as well for automakers by reducing overall costs and decreasing assembly time, since theres no need for pumps, hoses and fluids.Another claimed advantage is shortened development time. For instance, a Delphi group developed E-TUNE, a ride-and-handling software package that can be run off a laptop computer. They can take that computer and plug it in, attach it to the controller and change all the handling parameters - effort level, returnability, damping - on the fly, Badawy says. It used to take months. Delphi has one OEM customer that should start low-volume production in 99.Electric steering units are normally placed in one of three positions: column-drive, pinion-drive and rack-drive. Which system will become the norm is still unclear. Short term, OEMs will choose the steering system that is easiest to integrate into an existing platform. Obviously, greater potential comes from designing the system into an all-new platform.We have all three designs under consideration, says Dr. Herman Strecker, group vice president of steering systems division at ZF in Schwaebisch Gmuend, Germany. Its up to the market and OEMs which version finally will be used and manufactured.The large manufacturers have all grabbed hold of what they consider a core technology, explains James Handysides, TRW vice president, electrically assisted steering in Sterling Heights, Mich. His company offers a portfolio of electric steering systems (hybrid electric, rack-, pinion-, and column-drive). TRW originally concentrated on what it still believes is the purest engineering solution for electric steering-the rack-drive system. The system is sometimes refered to as direct drive or ball/nut drive.Still, this winter TRW hedged its bet, forming a joint venture with LucasVarity. The British supplier received $50 million in exchange for its electric column-drive steering technology and as sets. Initial production of the column and pinion drive electric steering systems is expected to begin in Birmingham, England, in 2000.What we lack is the credibility in the steering market, says Brendan Conner, managing director, TRW/LucasVarity Electric Steering Ltd. The combination with TRW provides us with a good opportunity for us to bridge that gap. LucasVarity currently has experimental systems on 11 different vehicle types, mostly European. TRW is currently supplying its EAS systems for Ford and Chrysler EVs in North America and for GMs new Opel Astra.In 1995, according to Delphi, traditional hydraulic power steering systems were on 7596 of all vehicles sold globally. That 37-million vehicle pool consumes about 10 million gallons in hydraulic fluid that could be superfluous, if electric steering really takes off.The present invention relates to an electrically powered drive mechamsm for providing powered assistance to a vehicle steering mechanism. According to one aspect of the present invention, there is provided an electrically powered driven mechanism for providing powered assistance to a vehicle steering mechanism having a manually rotatable member for operating the steering mechanism, the drive mechanism including a torque sensor operable to sense torque being manually applied to the rotatable member, an electrically powered drive motor drivingly connected to the rotatable member and a controller which is arranged to control the speed and direction of rotation of the drive motor in response to signals received from the torque sensor, the torque sensor including a sensor shaft adapted for connection to the rotatable member to form an extension thereof so that torque is transmitted through said sensor shaft when the rotatable member is manually rotated and a strain gauge mounted on the sensor shaft for producing a signal indicative of the amount of torque being transmitted through said shaft.Preferably the sensor shaft is non-rotatably mounted at one axial end in a first coupling member and is non-rotatably mounted at its opposite axial end in a second coupling member, the first and second coupling members being inter-engaged to permit limited rotation therebetween so that torque under a predetermined limit is transmitted by the sensor shaft only and so that torque above said predetermined limit is transmitted through the first and second coupling members.The first and second coupling members are preferably arranged to act as a bridge for drivingly connecting first and second portions of the rotating member to one another.Preferably the sensor shaft is of generally rectangular cross-section throughout the majority of its length.Preferably the strain gauge includes one or more SAW resonators secured to the sensor shaft.Preferably the motor is drivingly connected to the rotatable member via a clutch.Preferably the motor includes a gear box and is concentrically arranged relative to the rotatable member.Various aspects of the present invention will hereafter be described, with reference to the accompanying drawings, in which :Figure 1 is a diagrammatic view of a vehicle steering mechanism including an electrically powered drive mechanism according to the present invention,Figure 2 is a flow diagram illustrating interaction between various components of the drive mechanism shown in Figure 1 ,Figure 3 is an axial section through the drive mechanism shown in Figure 1, Figure 4 is a sectional view taken along lines IV-IV in Figure 3,Figure 5 is a more detailed exploded view of the input drives coupling shown in Figure 3, andFigure 6 is a more detailed exploded view of the clutch showing in Figure 3. Referring initially to Figure 1 , there is shown a vehicle steering mechanism 10 drivingly connected to a pair of steerable road wheels The steering mechanism 10 shown includes a rack and pinion assembly 14 connected to the road wheels 12 via joints 15. The pinion(not shown) of assembly 14 is rotatably driven by a manually rotatable member in the form of a steering column 18 which is manually rotated by a steering wheel 19.The steering column 18 includes an electric powered drive mechanism 30 which includes an electric drive motor (not shown in Figure 1) for driving the pinion in response to torque loadings in the steering column 18 in order to provide power assistance for the operative when rotating the steering wheel 19.As schematically illustrated in Figure 2, the electric powered drive mechanism includes a torque sensor20 which measures the torque applied by the steering column 18 when driving the pinion and supplies a signal to a controller 40. The controller 40 is connected to a drive motor 50 and controls the electric current supplied to the motor 50 to control the amount of torque generated by the motor 50 and the direction of its rotation.The motor 50 is drivingly connected to the steering column 18 preferably via a gear box 60, preferably an epicyclic gear box, and a clutch 70. The clutch 70 is preferably permanently engaged during normal operation and is operative under certain conditions to isolate drive from the motor 50 to enable the pinion to be driven manually through the drive mechanism 30. This is a safety feature to enable the mechanism to function in the event of the motor 50 attempting to drive the steering column too fast and/or in the wrong direction or in the case where the motor and/or gear box have seized.The torque sensor 20 is preferably an assembly including a short sensor shaft on which is mounted a strain gauge capable of accurately measuring strain in the sensor shaft brought about by the application of torque within a predetermined range.Preferably the predetermined range of torque which is measured is 0-lONm; more preferably is about l-5Nm.Preferably the range of measured torque corresponds to about 0-1000 microstrain and the construction of the sensor shaft is chosen such that a torque of 5Nm will result in a twist of less than 2 in the shaft, more preferably less than 1 .Preferably the strain gauge is a SAW resonator, a suitable SAW resonator being described in WO91/13832. Preferably a configuration similar to that shown in Figure 3 of WO91/13832 is utilised wherein twoSAW resonators are arranged at 45 to the shaft axis and at 90 to one another.Preferably the resonators operate with a resonance frequency of between 200-400 MHz and are arranged to produce a signal to the controller 40 of 1 MHz 500 KHz depending upon the direction of rotation of the sensor shaft. Thus, when
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