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技术案例丨奥迪Q3怠速及低速行驶时抖动!
2020-03-25 11:27:58 点击:868
培训与技术中心的任贺新老师接到一台奥迪Q3,客户反映车辆怠速及低速行驶时,车辆抖动,在其他地方很难找到原因,一起来看看任老师是如何一步步解决问题的。
任老师检查发现,车辆在怠速和转速在1000-1200转之间时,明显感觉车辆晃动。
原因分析
车辆抖动一定有抖动源,传导后到达车身,继而让驾乘人员感受到。
所以故障点有可能出现在发动机、传导路径、动力总成和车身之间的缓冲装置——这也是我们排除故障的总思路。
下面逐一分析:1、发动机工作不良,某个或多个气缸存在偶发性失火。就像四个人抬桌子,忽然一个人不使力气了,桌子肯定会不稳。
2、发动机或变速箱的某个旋转部件工作失衡,例如平衡轴位置不正确,飞轮动态不平衡或者双离合器不平衡等。
3、动力总成至车身的缓冲装置工作不良,例如发动机支撑漏油损坏,变速箱支撑损坏等。
故障排查
第一步 首先检查发动机是否存在失火,发动机电脑没有故障码存储,读取每1000转失火数据,怠速时1-4缸失火次数均为0。轻点油门至1000转/分钟左右,感觉车身明显晃动时,稳住油门踏板再次读取失火数据,发现不定缸有少量失火(一般在5次以下)。任老师分析,这种失火不能说明发动机燃烧不良,发动机电脑通过曲轴位置传感器的信号分析曲轴加速度,再根据加速度推断各个气缸的燃烧质量,如果发动机存在明显的振动,也可能会引起曲轴转速的波动,导致发动机电脑误检测失火。维修不能只靠经验,需要有数据支持才能科学分析,科学施策。
查看过数据流之后,任老师为了进一步分析发动机工作状况,将WPS 500压力传感器插入排气管。

测量发动机怠速工况的排气脉动如下:

A通道(蓝色):排气脉动B通道(红色):1缸点火波形这台四缸车排气脉动非常均匀,说明发动机工作正常,燃烧良好。现在发动机失火这一原因排除。第二步
我们使用PICO示波器继续排查传导路径、动力总成和车身的缓冲装置。

PICO示波器是一款综合故障分析设备,可以测量压力(如缸压,进/排气压力,汽油压力等),测量振动量和频率,测量噪音(如发动机内部异响,底盘部件异响等),还可测量电压以及电流。我们现在用示波器测量这台车的震动量和频率,这样能更好地帮助我们查找振动源。
车主在驾驶时感觉到抖动,那么我们就将示波器的传感器吸附在驾驶员座椅导轨上。

(测量座椅导轨震动数据)
测量发动机转速在1000转左右时的振动:

一般振幅超过20mg,人的身体就能感受到明显的振动了。
此时进一步确定故障原因:
1某个与曲轴相同转速的部件失衡或者不圆,例如飞轮,双离合器等。
2缓冲装置工作不良,例如发动机支撑损坏,无法缓冲来自发动机的振动。
第三步
根据由简到繁的原则,先检查怠速状态下发动机的抖动。

(测量发动机震动数据)

怠速时发动机一阶振动(E1)的幅值为94mg,二阶振动(E2)的幅值为158mg,这个振动是否正常?我们找了一辆同款无故障的车进行对比,示波器测取不同位置的震动数据。

(测量翼子板震动数据)

直列四缸发动机能够平衡一阶振动,但存在较大的二阶振动,这是它自身结构特点导致的。该车是直列四缸发动机,产生的二阶振动相对较小,不用使用平衡轴,而是用发动机支撑(俗称脚垫)缓冲二阶振动。在二阶振动阶段,故障车与正常车辆数据对比能看出发动机到副驾侧翼子板的震动数据下降明显,说明发动机支撑(脚垫)缓冲性能良好,无故障。经过示波器的测量与对比,我们开始重考虑故障点在动力传导路径上,如发动机或变速箱的某个旋转部件工作失衡,也就是刚才分析的飞轮,双离合器等。以曲轴相同转速旋转的部件,最容易出现问题的是双质量飞轮,双质量飞轮与双离合器之间的连接关系如下:

这款车采用双质量飞轮,飞轮和内齿圈之间有弹簧,内齿圈跟双离合器的外齿轮啮合,次级质量是双离合器。针对此故障,拆解车辆,抬下变速箱,检查部件。
发现该车双质量飞轮的自由间隙将近1CM,而且用手就可以扭动,明显工作不正常。至此,找到故障点。中鑫之宝始终以严谨的态度探究故障原因,科学诊断。16年汽车维保经验,以综合技术为依托、研发各类维保专项,标准化工艺流程,具备中高端及超豪华汽车品牌综合维保能力,并已开启全方位服务。
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