关节式自动上下料机械手设计【三自由度 圆柱坐标式液压驱动】【三菱PLC】

喜欢这套资料就充值下载吧。资源目录里展示的都可在线预览哦。下载后都有，请放心下载，文件全都包含在内，图纸为CAD格式可编辑，有疑问咨询QQ:414951605 或 1304139763p 毕业设计（论文）档案袋内组成部分 一、毕业设计（论文）册内容与装订顺序： l 封面：论文题目不得超过20个字，要简练、准确，可分为两行。 l 内容 1、毕业设计（论文）任务书；任务书由指导教师填写，经所在系部审查签字后生效。 2、毕业设计（论文）开题报告； 3、毕业设计（论文）学生申请答辩表与指导教师毕业设计（论文）评审表； 4、毕业设计（论文）评阅人评审表； 5、毕业设计（论文）答辩表； 6、毕业设计（论文）答辩记录表； 7、毕业设计（论文）成绩评定总表； 8、论文： (1)中文题目与作者； (2)英文题目与作者； (3)中文内容摘要和关键词； (4)英文内容摘要和关键词； (5)目录； (6)正文； (7)致谢； (8)参考文献及引用资料目录； (9)附录； (10)实验数据表、有关图纸(大于3#图幅时单独装订)； l 封底。 二、英文资料翻译册内容与装订顺序： l 封面； l 内容 1、英文原文； 2、中文翻译； 3、阅读书目； l 封底。 1 毕业设计（论文）任务书 系 部 机械工程系 指导教师 王海涛 职 称 副教授 学生姓名 郭嘉文 专业班级 05机制本（2） 学 号 0515011202 设计题目 关节式自动上下料机械手设计（PLC控制） 设 计 内 容 目 标 和 要 求 （设计内容目标和要求、设计进度等） 内容:了解关节式机械手的基本结构和设计方法，学习PLC控制的有关内容，利用PLC的梯形图编写程序，掌握液压系统的设计，学会查找资料，利用资料解决问题。 要求： 1． 完成关节式机械手的整体装配图； 2． 完成液压系统原理图； 3． 完成PLC外部接线图； 4． 完成PLC梯形图编程，运行程序通过； 5． 完成相关英文翻译一篇； 6． 撰写设计说明书，要求字迹工整。 指导教师签名： 年 月 日 系 部审 核 此表由指导教师填写 由所在系部审核 2-1 毕业设计（论文）学生开题报告 课题名称 关节式自动上下料机械手设计（PLC控制） 课题来源 生产实践 课题类型 AX 指导教师 王海涛（副教授） 学生姓名 郭嘉文 学 号 0515011202 专业班级 05机制2班 本课题的研究现状、研究目的及意义 工业机械手是人类创造的一种机器,更是人类创造的一项伟大奇迹,其研究、开发和设计是从二十世纪中叶开始的.我国的工业机械手是从80年代"七五"科技攻关开始起步,在国家的支持下,通过"七五","八五"科技攻关,目前已经基本掌握了机械手操作机的设计制造技术,控制系统硬件和软件设计技术,运动学和轨迹规划技术,生产了部分机器人关键元器件，开发出喷漆，孤焊，点焊，装配，搬运等机器人，其中有130多台喷漆机器人在二十余家企业的近30条自动喷漆生产线（站）上获得规模应用，孤焊机器人已经应用在汽车制造厂的焊装线上。但总的看来，我国的工业机械手技术及其工程应用的水平和国外比还有一定距离。如：可靠性低于国外产品，机械手应用工程起步较晚，应用领域窄，生产线系统技术与国外比有差距。影响我国机械手发展的关键平台因素就是其软件，硬件和机械结构。目前工业机械手仍大量应用在制造业，其中汽车工业占第一位（占28.9%），电器制造业第二位（占16.4%），化工第三位（占11.7%）。发达国家汽车行业机械手应用占总保有量百分比为23.4%～53%，年产每万辆汽车所拥有的机械手数为（包括整车和零部件）：日本88.0台，德国64.0台，法国32.2台，英国26.9台，美国33.8台，意大利48.0台 世界工业机械手的数目虽然每年在递增，但市场是波浪式向前发展的。在新世纪的曙光下人们追求更舒适的工作条件，恶劣危险的劳动环境都需要用机器人代替人工。随着机器人应用的深化和渗透，工业机械手在汽车行业中还在不断开辟着新用途。机械手的发展也已经由最初的液压，气压控制开始向人工智能化转变，并且随着电子技术的发展和科技的不断进步，这项技术将日益完善。 上料机械手与卸料机械手相比，其中上料机械手中的移动式搬运上料机械手适用于各种棒料，工件的自动搬运及上下料工作。例如铝型材挤压成型铝棒料的搬运及高温材料的自动上料作业，最大抓取棒料直径达180mm，最大抓握重量可达30公斤，最大行走距离为1200mm。根据作业要求及载荷情况，机械手各关节运动速度可调。移动式搬运上料机械手主要由手爪，小臂，大臂，手臂回转机构，小车行走机构，液压泵站电器控制系统组成，同时具有高温棒料启动疏料装置及用于安全防护用的光电保护系统。整个机械手及液压系统均集中设置在行走小车上，结构紧凑。电气控制系统采用OMRON可编程控制器，各种作业的实现可以通过编程实现。 2-2 本课题的研究内容 工业机器人系统由三大部分六个子系统组成。 三大部分是：机械部分，传感部分，控制部分。六个子系统是：驱动系统，机械结构系统，感受系统，机器人—环境交互系统，人机交互系统，控制系等等。 该机械手为机床上下料机械手，圆柱体工件约30千克，要求下料之后马上上料,一次完成上下料两步骤。 动作顺序：加工工位等候--机械手臂下降--手爪收拢夹紧已加工好的工件--手臂上升--手臂回转至卸料工位--手臂下降--（手腕回转）手爪松开工件--手臂上升--回转至加工工位--手臂下降--手爪松开工件--手臂上升至等待工位等候。机械手的动作全部采用液压驱动，PLC控制。 一、机械手驱动系统的选择： 设计机械手时,选择哪一类驱动系统,要根据机械手的用途,作业要求,机械手的性能规范,控制功能,维护的复杂程度,运行的功耗,性能与价格比以及现有条件等综合因素加以考虑.在注意各类驱动系统特点的基础上,综合上述各因素,充分论证其合理性,可行性,经济性以及可靠性后进行最终的选择。按动力源的不同机器人又分为:电气驱动、液压驱动、气动驱动三种。液压驱动的特点是功率大，气动驱动存在冲击力大，精度难以控制等缺点，而电气驱动具有控制方便、J性能好等优点。（综合考虑本机械手采用液压驱动） 二、机械手结构设计： 机械结构是物料抓取机械手最终的执行机构，是机器人赖以实现各种运动的实体，机械结构的布局、类型、传动方式以及驱动系统的设计直接关系着机器人的工作性能。 机械结构按坐标形式主要有直角坐标型、球坐标型、圆柱坐标型、SCARA型和关节型等。 直角坐标型机器人操作臂的优点是结构简单、刚度高，三个关节的运动相互独立，其间没有祸合，不影响末端手爪的姿态，不产生奇异状态，运动和控制都比较简单;缺点是占地面积大，动作范围小，操作灵活性差。 球坐标机器人和圆柱坐标机器人占地面积小，工作空间较大，在空间中的定位也比较直观，但是它们的移动关节不容易防护，极坐标型机器人也存在移动关节不易防护的问题，它们多用于一些特殊的作业环境。 SCARA型机器人的主要特点是结构轻便，响应快，最适用于在垂直方向完成零件的装配作业。 关节型机器人操作臂的优点是结构紧凑，占地面积小，动作灵活，在作业空间内手臂的干涉最小，工作空间大;缺点是进行控制时计算量比较大，确定末端执行部件的位姿不直观。 针对该上下料机械手，为了使它具有一定的操作灵活性和较好的使用性能，在结构设计上采用圆柱坐标型。整个机器人系统设计为四个自由度。 自由度的分布情况为：机身的升降和回转，手臂的伸缩，手腕的回转。 三、手部的结构设计： 手部就是与物件接触的部件。由于与物件接触的形式不同，可分为夹持式和吸附式手部。为了使机械手的通用性更强，把机械手的手部结构设计成可更换结构，当被夹持工件是圆柱刀柄时，使用夹持式手部;当该机械手做其他用途，被夹持工件是板料时，可使用气流负压式吸盘。（本课题工件为圆柱体工件，所以手部采用夹持式） 2-3 具体设计内容和要求 一、设计内容： 1．了解关节式机械手的基本结构和设计方法 2．械手手部结构和运动机构的结构设计 3．机械手驱动系统的设计 4．学习PLC控制的有关内容，利用PLC的梯形图编写程序 5．绘制零件图和装配图，设计说明书一份 二、设计要求： 1．完成关节式机械手的整体装配图 2．完成液压系统原理图 3．完成PLC外部接线图 4．完成PLC梯形图编程，运行程序通过 5．完成相关英文翻译一篇 6．撰写设计说明书，要求字迹工整 本课题研究的实施方案、进度安排 一、实施方案： 通过生产厂房中的实际观察，以及利用网络或图书馆参阅有关关节式上下料机械手的资料，根据已有的标准规格和设计要求，在老师的指导下进行合理的设计。 二、进度安排： 1）3月20-31日，主要进行毕业设计的准备工作，熟悉题目，收集资料，明确研究目的和任务； 2）4月1-25日，设计方案的确定，设计参数和尺寸的计算和分析； 3）4月26-5月15日，绘制机械手各部分图纸（手爪图、手腕图、手臂图和它们的组合图）； 4）5月16-5月27日，收尾完善，编写毕业设计论文，准备毕业设计答辩； 5）5月28-6月5日，毕业答辩。 3 毕业设计（论文）学生申请答辩表 课 题 名 称 关节式自动上下料机械手设计（PLC控制） 指导教师（职称） 王海涛（副教授） 申 请 理 由 申请毕业 学生所在系部 机械工程系 专业班级 05机制（本）2 学号 0515011202 学生签名： 日期： 毕业设计（论文）指导教师评审表 序号 评分项目（理工科、管理类） 评分项目(文科) 满分 评分 1 工作量 外文翻译 15 2 文献阅读与外文翻译 文献阅读与文献综述 10 3 技术水平与实际能力 创新能力与学术水平 25 4 研究成果基础理论与专业知识 论证能力 25 5 文字表达 文字表达 10 6 学习态度与规范要求 学习态度与规范要求 15 总 分 100 评 语 （是否同意参加答辩） 指导教师签名： 另附《毕业设计（论文）指导记录册》 年 月 日 4 毕业设计（论文）评阅人评审表 学生姓名 郭嘉文 专业班级 05机制（本）2 学号 0515011202 设计（论文）题目 关节式自动上下料机械手设计（PLC控制） 评阅人 评阅人职称 序号 评分项目（理工科、管理类） 评分项目(文科) 满分 评分 1 工作量 外文翻译 15 2 文献阅读与外文翻译 文献阅读与文献综述 10 3 技术水平与实际能力 创新能力与学术水平 25 4 研究成果基础理论与专业知识 论证能力 25 5 文字表达 文字表达 10 6 学习态度与规范要求 学习态度与规范要求 15 总 分 100 评 语 评阅人签名： 年 月 日 5 毕业设计（论文）答辩表 学生姓名 郭嘉文 专业班级 05机制（本）2 学号 0515011202 设计（论文）题目 关节式自动上下料机械手设计（PLC控制） 序号 评审项目 指 标 满分 评分 1 报告内容 思路清新；语言表达准确，概念清楚，论点正确；实验方法科学，分析归纳合理；结论有应用价值。 40 2 报告过程 准备工作充分,时间符合要求。 10 3 创 新 对前人工作有改进或突破，或有独特见解。 10 4 答 辩 回答问题有理论依据，基本概念清楚。主要问题回答准确，深入。 40 总 分 100 答 辩 组 评 语 答辩组组长（签字）： 年 月 日 答 辩 委 员 会 意 见 答辩委员会负责人（签字）： 年 月 日 6-1 毕业设计（论文）答辩记录表 学生姓名 郭嘉文 专业班级 05机制（本）2 学号 0515011202 设计（论文）题目 关节式自动上下料机械手设计（PLC控制） 答辩时间 答辩地点 答辩委员会名单 问题1 提问人： 问题： 回答（要点）： 问题2 提问人： 问题： 回答（要点）： 问题3 提问人： 问题： 回答（要点）： 记录人签名 问题4 提问人： 问题： 回答（要点）： 问题5 提问人： 问题： 回答（要点）： 问题6 提问人： 问题： 回答（要点）： 问题7 提问人： 问题： 回答（要点）： 问题8 提问人： 问题： 回答（要点）： 记录人签名 6-2 7 毕业设计（论文）成绩评定总表 学生姓名： 郭 嘉 文 专业班级： 05机制（本）2 毕业设计（论文）题目：关节式自动上下料机械手设计（PLC控制） 成绩类别 成绩评定 Ⅰ指导教师评定成绩 Ⅱ评阅人评定成绩 Ⅲ答辩组评定成绩 总评成绩 Ⅰ×40%+Ⅱ×20%+Ⅲ×40% 评定等级 注：成绩评定由指导教师、评阅教师和答辩组分别给分(以百分记)，最后按“优(90--100)”、“良(80--89)”、“中(70--79)”、“及格(60--69)”、“不及格(60以下)”评定等级。其中， 指导教师评定成绩占40%，评阅人评定成绩占20%，答辩组评定成绩占40%。 1The Effect of a Viscous Coupling Used as a Front-Wheel Drive Limited-Slip Differential on Vehicle Traction and Handling1 ABCTRACTThe viscous coupling is known mainly as a driveline component in four wheel drive vehicles. Developments in recent years, however, point toward the probability that this device will become a major player in mainstream front-wheel drive application. Production application in European and Japanese front-wheel drive cars have demonstrated that viscous couplings provide substantial improvements not only in traction on slippery surfaces but also in handing and stability even under normal driving conditions.This paper presents a serious of proving ground tests which investigate the effects of a viscous coupling in a front-wheel drive vehicle on traction and handing. Testing demonstrates substantial traction improvements while only slightly influencing steering torque. Factors affecting this steering torque in front-wheel drive vehicles during straight line driving are described. Key vehicle design parameters are identified which greatly influence the compatibility of limited-slip differentials in front-wheel drive vehicles.Cornering tests show the influence of the viscous coupling on the self steering behavior of a front-wheel drive vehicle. Further testing demonstrates that a vehicle with a viscous limited-slip differential exhibits an improved stability under acceleration and throttle-off maneuvers during cornering.2 THE VISCOUS COUPLINGThe viscous coupling is a well known component in drivetrains. In this paper only a short summary of its basic function and principle shall be given.The viscous coupling operates according to the principle of fluid friction, and is thus dependent on speed difference. As shown in Figure 1 the viscous coupling has slip controlling properties in contrast to torque sensing systems.This means that the drive torque which is transmitted to the front wheels is automatically controlled in the sense of an optimized torque distribution.In a front-wheel drive vehicle the viscous coupling can be installed inside the differential or externally on an intermediate shaft. The external solution is shown in Figure 2.This layout has some significant advantages over the internal solution. First, 2there is usually enough space available in the area of the intermediate shaft to provide the required viscous characteristic. This is in contrast to the limited space left in todays front-axle differentials. Further, only minimal modification to the differential carrier and transmission case is required. In-house production of differentials is thus only slightly affected. Introduction as an option can be made easily especially when the shaft and the viscous unit is supplied as a complete unit. Finally, the intermediate shaft makes it possible to provide for sideshafts of equal length with transversely installed engines which is important to reduce torque steer (shown later in section 4).This special design also gives a good possibility for significant weight and cost reductions of the viscous unit. GKN Viscodrive is developing a low weight and cost viscous coupling. By using only two standardized outer diameters, standardized plates, plastic hubs and extruded material for the housing which can easily be cut to different lengths, it is possible to utilize a wide range of viscous characteristics. An example of this development is shown in Figure 3.3 TRACTION EFFECTSAs a torque balancing device, an open differential provides equal tractive effort to both driving wheels. It allows each wheel to rotate at different speeds during cornering without torsional wind-up. These characteristics, however, can be disadvantageous when adhesion variations between the left and right sides of the road surface (split-) limits the torque transmitted for both wheels to that which can be supported by the low- wheel.With a viscous limited-slip differential, it is possible to utilize the higher adhesion potential of the wheel on the high-surface. This is schematically shown in Figure 4.When for example, the maximum transmittable torque for one wheel is exceeded on a split-surface or during cornering with high lateral acceleration, a speed difference between the two driving wheels occurs. The resulting self-locking torque in the viscous coupling resists any further increase in speed difference and transmits the appropriate torque to the wheel with the better traction potential.It can be seen in Figure 4 that the difference in the tractive forces results in a yawing moment which tries to turn the vehicle in to the low-side, To keep the vehicle in a straight line the driver has to compensate this with opposite steering input. Though the fluid-friction principle of the viscous coupling and the resulting soft 3transition from open to locking action, this is easily possible, The appropriate results obtained from vehicle tests are shown in Figure 5.Reported are the average steering-wheel torque Ts and the average corrective opposite steering input required to maintain a straight course during acceleration on a split-track with an open and a viscous differential. The differences between the values with the open differential and those with the viscous coupling are relatively large in comparison to each other. However, they are small in absolute terms. Subjectively, the steering influence is nearly unnoticeable. The torque steer is also influenced by several kinematic parameters which will be explained in the next section of this paper.4 FACTORS AFFECTING STEERING TORQUEAs shown in Figure 6 the tractive forces lead to an increase in the toe-in response per wheel. For differing tractive forces, Which appear when accelerating on split-with limited-slip differentials, the toe-in response changes per wheel are also different.Unfortunately, this effect leads to an undesirable turn-in response to the low-side, i.e. the same yaw direction as caused by the difference in the tractive forces.Reduced toe-in elasticity is thus an essential requirement for the successful front-axle application of a viscous limited-slip differential as well as any other type of limited-slip differential.Generally the following equations apply to the driving forces on a wheelVTFF With Tractive ForceTF Vertical Wheel LoadVF Utilized Adhesion CoefficientThese driving forces result in steering torque at each wheel via the wheel disturbance level arm “e” and a steering torque difference between the wheels given by the equation:=eTloHhiHFFecosWhere Steering Torque DifferenceeT e=Wheel Disturbance Level Arm King Pin Angle4 hi=high-side subscript lo=low-side subscriptIn the case of front-wheel drive vehicles with open differentials, Ts is almost unnoticeable, since the torque bias () is no more than 1.35.loHhiTFF/For applications with limited-slip differentials, however, the influence is significant. Thus the wheel disturbance lever arm e should be as small as possible. Differing wheel loads also lead to an increase in Te so the difference should also be as small as possible.When torque is transmitted by an articulated CV-Joint, on the drive side (subscript 1) and the driven side (subscript 2),differing secondary moments are produced that must have a reaction in a vertical plane relative to the plane of articulation. The magnitude and direction of the secondary moments (M) are calculated as follows (see Figure 8):Drive side M1 =vvTTtan/)2/tan(2Driven side M2 =vvTTtan/)2/tan(2With T2 =dynTrF =TsystemJoTfint, 2Where Vertical Articulation Anglev Resulting Articulation Angle Dynamic Wheel Radiusdynr Average Torque LossTThe component acts around the king-pin axis (see figure 7) as a cos2Msteering torque per wheel and as a steering torque difference between the wheels as follows:)tan/2/tan()sin/2/tan(cos22liwhiwTTTTT where Steering Torque DifferenceT WWheel side subscriptIt is therefore apparent that not only differing driving torque but also differing 5articulations caused by various driveshaft lengths are also a factor. Referring to the moment-polygon in Figure 7, the rotational direction of M2 or respectively change, Tdepending on the position of the wheel-center to the gearbox output.For the normal position of the halfshaft shown in Figure 7(wheel-center below the gearbox output joint) the secondary moments work in the same rotational direction as the driving forces. For a modified suspension layout (wheel-center above gearbox output joint, i.e. negative) the secondary moments counteract the moments caused vby the driving forces. Thus for good compatibility of the front axle with a limited-slip differential, the design requires: 1) vertical bending angles which are centered around or negative () with same values of on both left and right sides; and 2) 0v0vvsideshafts of equal length.The influence of the secondary moments on the steering is not only limited to the direct reactions described above. Indirect reactions from the connection shaft between the wheel-side and the gearbox-side joint can also arise, as shown below:Figure 9: Indirect Reactions Generated by Halfshaft Articulation in the Vertical PlaneFor transmission of torque without loss and both of the secondary vdvwmoments acting on the connection shaft compensate each other. In reality (with torque loss), however, a secondary moment difference appears: WDDWMMM12With TTTWD22The secondary moment difference is:DWMVWWVWWVDVDWTTDTwTTtan/2/tansin/tan22/2For reasons of simplification it apply that and to VVWVDTTTWDgiveVVVDWTMtan/1sin/12/tan requires opposing reaction forces on both joints where DWM. Due to the joint disturbance lever arm f, a further steering torque LMFDWDW/also acts around the king-pin axis:LfMTDWf/cos6loloDWhihiDWfLMLMfT/cosWhere Steering Torque per WheelfT Steering Torque DifferencefT Joint Disturbance Leverf Connection shaft (halfshaft) LengthLFor small values of f, which should be ideally zero, is of minor influence.fT5EFFECT ON CORNERINGViscous couplings also provide a self-locking torque when cornering, due to speed differences between the driving wheels. During steady state cornering, as shown in figure 10, the slower inside wheel tends to be additionally driven through the viscous coupling by the outside wheel.Figure 10: Tractive forces for a front-wheel drive vehicle during steady state cornering The difference between the Tractive forces Dfr and Dfl results in a yaw moment MCOG, which has to be compensated by a higher lateral force, and hence a larger slip angle af at the front axle. Thus the influence of a viscous coupling in a front-wheel drive vehicle on self-steering tends towards an understeering characteristic. This behavior is totally consistent with the handling bias of modern vehicles which all under steer during steady state cornering maneuvers. Appropriate test results are shown in figure 11.Figure 11: comparison between vehicles fitted with an open differential and viscous coupling during steady state cornering.The asymmetric distribution of the tractive forces during cornering as shown in figure 10 improves also the straight-line running. Every deviation from the straight-line position causes the wheels to roll on slightly different radii. The difference between the driving forces and the resulting yaw moment tries to restore the vehicle to straight-line running again (see figure 10).Although these directional deviations result in only small differences in wheel travel radii, the rotational differences especially at high speeds are large enough for a viscous coupling front differential to bring improvements in straight-line running.High powered front-wheel drive vehicles fitted with open differentials often spin 7their inside wheels when accelerating out of tight corners in low gear. In vehicles fitted with limited-slip viscous differentials, this spinning is limited and the torque generated by the speed difference between the wheels provides additional tractive effort for the outside driving wheel. this is shown in figure 12Figure 12: tractive forces for a front-wheel drive vehicle with viscous limited-slip differential during acceleration in a bend The acceleration capacity is thus improved, particularly when turning or accelerating out of a T-junction maneuver ( i.e. accelerating from a stopped position at a “T” intersection-right or left turn ).Figures 13 and 14 show the results of acceleration tests during steady state cornering with an open differential and with viscous limited-slip differential .Figure 13: acceleration characteristics for a front-wheel drive vehicle with an open differential on wet asphalt at a radius of 40m (fixed steering wheel angle throughout test).Figure 14: Acceleration Characteristics for a Front-Wheel Drive Vehicle with Viscous Coupling on Wet Asphalt at a Radius of 40m (Fixed steering wheel angle throughout test)The vehicle with an open differential achieves an average acceleration of 2.0 while the2/smvehicle with the viscous coupling reaches an average of 2.3 (limited by 2/smengine-power). In these tests, the maximum speed difference, caused by spinning of the inside driven wheel was reduced from 240 rpm with open differential to 100 rpm with the viscous coupling.During acceleration in a bend, front-wheel drive vehicles in general tend to understeer more than when running at a steady speed. The reason for this is the reduction of the potential to transmit lateral forces at the front-tires due to weight transfer to the rear wheels and increased longitudinal forces at the driving wheels. In an open loop control-circle-test this can be seen in the drop of the yawing speed (yaw rate) after starting to accelerate (Time 0 in Figure 13 and 14). It can also be taken from Figure 13 and Figure 14 that the yaw rate of the vehicle with the open differential falls-off more rapidly than for the vehicle with the viscous coupling starting to accelerate. Approximately 2 seconds after starting to accelerate, however, the yaw rate fall-off gradient of the viscous-coupled vehicle increases more than at the 8vehicle with open differential.The vehicle with the limited slip front differential thus has a more stable initial reaction under accelerating during cornering than the vehicle with the open differential, reducing its understeer. This is due to the higher slip at the inside driving wheel causing an increase in driving force through the viscous coupling to the outside wheel, which is illustrated in Figure 12. the imbalance in the front wheel tractive forces results in a yaw moment acting in direction of the turn, countering the CSDMundersteer.When the adhesion limits of the driving wheels are exceed, the vehicle with the viscous coupling understeers more noticeably than the vehicle with the open differential (here, 2 seconds after starting to accelerate). On very low friction surfaces, such as snow or ice, stronger understeer is to be expected when accelerating in a curve with a limited slip differential because the driving wheels-connected through the viscous coupling-can be made to spin more easily (power-under-steering). This characteristic can, however, be easily controlied by the driver or by an automatic throttle modulating traction control system. Under these conditions a much easier to control than a rear-wheel drive car. Which can exhibit power-oversteering when accelerating during cornering. All things, considered, the advantage through the stabilized acceleration behavior of a viscous coupling equipped vehicle during acceleration the small disadvantage on slippery surfaces.Throttle-off reactions during cornering, caused by releasing the accelerator suddenly, usually result in a front-wheel drive vehicle turning into the turn (throttle-off oversteering ). High-powered modeles which can reach high lateral accelerations show the heaviest reactions. This throttle-off reaction has several causes such as kinematic influence, or as the vehicle attempting to travel on a smaller cornering radius with reducing speed. The essential reason, however, is the dynamic weight transfer from the rear to the front axle, which results in reduced slip-angles on the front and increased slip-angles on the rear wheels. Because the rear wheels are not transmitting driving torque, the influence on the rear axle in this case is greater than that of the front axle. The driving forces on the front wheels before throttle-off (see Figure 10) become over running or braking forces afterwards, which is illustrated for the viscous equipped vehicle in Figure 15.Figure 15:Baraking Forces for a Front-Wheel Drive Vehicle with Viscous 9Limited-Slip Differential Immediately after a Throttle-off Maneuver While CorneringAs the inner wheel continued to turn more slowly than the outer wheel, the viscous coupling provides the outer wheel with the larger braking force . The force fBdifference between the front-wheels applied around the center of gravity of the vehicle causes a yaw moment that counteracts the normal turn-in reaction.GCM0When cornering behavior during a throttle-off maneuver is compared for vehicles with open differentials and viscous couplings, as shown in Figure 16 and 17, the speed difference between the two driving wheels is reduced with a viscous differential.Figure 16: Throttle-off Characteristics for a Front-Wheel Drive Vehicle with an open Differential on Wet Asphalt at a Radius of 40m (Open Loop)Figure 17:Throttle-off Characteristics for a Front-Wheel Drive Vehicle with Viscous Coupling on Wet Asphalt at a Radius of 40m (Open Loop)The yawing speed (yaw rate), and the relative yawing angle (in addition to the yaw angle which the vehicle would have maintained in case of continued steady state cornering) show a pronounced increase after throttle-off (Time=0 seconds in Figure 14 and 15) with the open differential. Both the sudden increase of the yaw rate after throttle-off and also the increase of the relative yaw angle are significantly reduced in the vehicle equipped with a viscous limited-slip differential.A normal driver os a front-wheel drive vehicle is usually only accustomed to neutral and understeering vehicle handing behavior, the driver can then be surprised by sudden and forceful oversteering reaction after an abrupt release of the throttle, for example in a bend with decreasing radius. This vehicle reaction is further worsened if the driver over-corrects for the situation. Accidents where cars leave the road to the inner side of the curve is proof of this occurrence. Hence the viscous coupling improves the throttle-off behavior while remaining controllable, predictable, and safer for an average driver.6. EFFECT ON BRAKING The viscous coupling in a front-wheel drive vehicle without ABS (anti-lock braking system) has only a very small influence on the braking behavior on split- surfaces. Hence the front-wheels are connected partially via the front-wheel on the low- side is slightly higher than in an vehicle with an open differential. On the other side ,the brake pressure to lock the front-wheel on the high- side is slightly lower. 10These differences can be measured in an instrumented test vehicle but are hardly noticeable in a subjective assessment. The locking sequence of front and rear axle is not influenced by the viscous coupling.Most ABS offered today have individual control of each front wheel. Electronic ABS in front-wheel drive vehicles must allow for the considerable differences in effective wheel inertia between braking with the clutch engaged and disengaged.Partial coupling of the front wheels through the viscous unit does not therefore compromise the action of the ABS - a fact that has been confirmed by numerous tests and by several independent car manufacturers. The one theoretical exception to this occurs on a split-surface if a yaw moment build-up delay or Yaw Moment Reduction(YMR) is included in the ABS control unit. Figure 18 shows typical brake pressure sequences, with and without YMR.figure 18: brake pressure build-up characteristics for t