更正 | 关于发动机 wrap fault 的说明

经过一位朋友的提醒，纠正之前关于发动机 wrap fault 的说明错误。

参考资料：

CFM56-7B TRAINING MANUAL

FAULT DETECTION & ANNUNCIATION

CTC-219 Level 4

注意一定要 Level 4 的才有，Level 3 里没有 wrap fault 的相关说明。

↑ Level 3 里面没有 

以下是手册里的详细说明：

Wraparound

The EEC uses a current-driver-wraparound test to check correct operation of the torque motors, solenoid drivers,output databuses and certain relays.

To check the integrity of the circuits, the EEC outputs a calculated current and compares it to the sensed return current (wraparound).

To check the integrity of the circuits, the EEC outputs a calculated current and compares it to the sensed return current (wraparound).

Control current out-of-range

The EEC checks the integrity of the FMV, VSV, VBV,HPTA CC, LPTA CC and TBV torque-motor and solenoid circuits, using the current-driver-wraparound test.

If there is a difference between the output and return current, it must exceed a defined value for a specific time interval in order for a fault to be declared.

If this kind of fault is declared, a ‘CONTROL CURRENT IS OUT OF RANGE’ message is generated.

On a transition of channel selection state from standby to active, the EEC clears all wraparound faults and sets the fault-delay timers to zero.

↑ 手册里还列举了3种故障情况

Demand and position signals disagree

The EEC checks if the sensed (measured) actuator position agrees with the demanded position.

A fault message is generated if :

- The absolute value of the difference between the demand and valid position is greater than 5%.

and,

- There is not a wrap fault on the local channel.

and,

- N2 is greater that 3181 rpm (22% N2).

and,

- The channel is active.

and,

- The fault persists for more that 4.8 seconds (11.5 seconds for HPTA CC).

↑ 图中与TM相连的红色线路部分

VBV和VSV类似：

总结如下：

LPTACC, HPTACC, TBV，VBV，VSV，FMV，是通过HMU里的EHSV（electro-hydraulic servo valve）来进行控制的。EEC 通过TM（torque-motor）电流输入来控制EHSV，并且只有当前控制通道才会提供输入，另一个备用通道输入是断开的。

EEC监控TM的输入和输出电流，正常情况下输入和输出电流是相同的。如果输入和输出差异达到设定值且持续一定时间，EEC将设置一个wrap故障。

所以，wrap故障EEC记录的代码为Control Current Out of Range，通常是到EHSV的控制输入线路故障或者EHSV电气故障。

wrap故障监控的是输入控制电路，而不是反馈电路，HMU里 EHSV 反馈电路的故障通常是 Demand and Position Signals Disagree。而另一个Position Signal is Out of Range 故障，指的是LPTACCV, HPTACCV, TBV，VBV，VSV，FMV 的位置反馈信号。

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完