燃油表故障检修一例

无颜 · 发表于 2012-9-15 22:43:44

有一辆96款日产风度轿车，故障症状是开小灯时燃油表指针往下走，而且走得比E(低点）还低。

故障诊断：对于这起故障，在检修燃油表之前，首先检查燃油箱里存储的燃油数量，结果油箱里大约还有l0L左右的燃油。该车的燃油表是指针式的，将点火开关置于0N位置，指针大约指在10L的位置上，指针所指位置与油箱内所剩燃油数量相一致。反复操作钥匙点火开关，每次指针都在相同的位置上，似乎没有什么异常。可此时用户反映，白天没有什么不好，到了晚上一开小灯，指在1／3左右的指针，开始往下来，一直到超过E90。

指针式燃油表的四个励磁线圈在空间上两两相差90度。燃油箱中的中心量规的电阻值随燃油量变化而变化。由于中心量规电阻值的变化，四个线圈的励磁量产生变化，磁力推动燃油表转子旋转一个适当的角度。当磁力消失之后(即点火开关关闭)，因为转子在硅油里，所以指针就停在那个位置上。

利用电路图为基础分析，燃油中心量规电阻值变到最小值时，燃油表指针应该升到F位置(最高)，因为此时线圈里的电流最大。然而实际情况是燃油表指针降到比E更低的位置，而中心量规的电阻值应该比E位置时的电阻值大，这一点非常可疑。

实际测量电阻值，F位置是6欧姆，E位置是80欧姆，并没有异常，这样一来，应该只与开小灯有关，而与燃油中心量规无关。因此在A点测量励磁线圈电压，对点火开关和小灯开关的各种组合状态的实测电压值如表所示。从此表上可以看得出来，本来应该与小灯开关毫无关系的A点电压，在油箱里有10L油时应该为4V，但是小灯开关一合，A点电压就莫明其妙地升高了。

不顾燃油中心量规电阻值毫无变化这一事实，A点电压升高是什么原因呢？电源电压升高以乎不能成立，因为即使断开点火开关，A点电压还高。从某一处接入电源的可能性极大，于是在仪表板部位检修照明灯，却没发现什么问题。

此外，有可能产生问题的部位，就是从驾驶座到油箱这一段导线。把万用表接在A点，沿着导线束的走向从燃油箱到构架不断地敲击导线束，在构架的斜坡上敲击时“啪”的一声，万用表电压降了下来。故障在驾驶座下面的发动机室附近。慎重检查导线束，突然冒出了白烟，马上就发现了故障部位。原来是导线夹子与导线束摩擦，把导线的绝缘皮磨破了。为此，A点电压上升，通常电流是从燃油表流向A点的，现在则相反，电流是从A点流入线圈的。由于磁力荷接地，线圈里的反向电流更大，因此指针继续往下来。

总结此故障，不管汽油车还是柴油车，都要装导线束夹子，构造其实都一样。但是柴油车振动比汽油车大，碰到此类故障时，更应该作为重点考虑。

kyakg · 发表于 2012-9-16 05:12:20

创意哦！楼主高人啊谢

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lgjqm · 发表于 2012-9-16 08:26:20

大家有什么好看法都说一下吧

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ansqingt · 发表于 2012-9-16 11:09:18

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