The fault diagnosis of modern units can be
divided into preliminary diagnosis and in-depth diagnosis according to the
depth of their diagnosis. The initial diagnosis is based on the fault
phenomenon and determines the approximate range of the cause of the fault.
In-depth diagnosis is based on the results of the initial diagnosis to analyze
and find the cause of the failure until the specific part of the fault is
found.
Modern unit fault diagnosis can be divided
into: intuitive diagnosis, self-diagnosis system diagnosis, simple instrument
diagnosis and special instrument diagnosis.
1) Intuitive diagnosis Intuitive
diagnosis is to diagnose, understand, grasp, and smell the characteristics of
the unit through the sensory organs of the human body, and then analyze and
judge the characteristics of the fault phenomenon. The direct diagnosis method
varies greatly depending on the experience of the diagnostician and the
familiarity with the crew. Experienced diagnostic experts can use the intuitive
diagnostic method to diagnose most of the faults that may occur in the unit,
including initial diagnosis and accurate determination of specific faults. The
main contents of the intuitive diagnosis are: Look, that is, visual inspection.
The purpose is to understand the system type and model of the electronic control
(electrical adjustment) unit, and to eliminate some general causes of failure
before entering more detailed testing and diagnosis. Such as the unit model,
electronic control system type, manufacturing company, production date, etc.
are very helpful in judging the fault. Remove the air filter, check for dirt,
debris or other contaminants around the filter element, and replace if
necessary, because the air filter blockage will affect the accuracy of the air
volume detection. Inspect the vacuum hose for aging, cracking or squeezing, and
check that the vacuum hose passes through the way and the fittings are good.
Check the connection status of the harness of the control system, such as
whether the sensor or the electrical appliance of the actuator is good, whether
the connection between the harness is loose or disconnected, whether the wire
is worn or short-circuited between wires, and whether the plug and socket of
the electrical connector are corroded. Wait. Check each sensor and actuator for
obvious damage. If it is possible to operate the unit and check for leaks at
the intake and exhaust manifolds. In order to quickly find the source of the
fault, it is first necessary to understand the situation and conditions of the
fault, how it occurred, and whether it has been overhauled and other
information related to the fault. To this end, we must carefully listen to the
description of the fault phenomenon by the crew members. Although the
description of the user may be misinterpreted or incomplete, it may be contradictory,
but it is often possible to raise the key to the problem. The best practice is
to think about the following initial diagnosis after listening to the user's
initial opinion, then ask some relevant questions to help determine or deny the
results of the initial diagnosis, and carefully record and form a fault with
the diagnostic test results. Basis. Listening, mainly listening to the sound of
the crew working, whether there is knocking, whether there is knocking, whether
there is stall, whether there are abnormalities in different working noise of
different parts. This requires long-term experience accumulation to accurately
judge. The test is mainly based on the aforementioned inspection, and the
targeted test machine is used to determine the fault asynchronously.
2) Using the unit self-diagnosis
system to diagnose the unit fault self-diagnosis system can self-diagnose the
system fault. It is a simple and quick diagnosis method in the current unit
diagnosis, but the scope of the diagnosis is far from the actual use.
Troubleshooting requirements. It is often the case that the unit is not
operating normally and is not related to the electronic control system. On the
other hand, due to the limitations of the unit self-diagnosis system, it is
impossible to design a self-diagnostic system to diagnose all possible faults.
Therefore, the visual diagnosis method is mainly used for inspection and
judgment. Work is irreplaceable for any system at any time.
3) Using simple instrument
diagnosis Using simple instrument diagnosis is to use a multimeter and an
oscilloscope as general-purpose instruments to diagnose the fault of the
electronic control (electrical adjustment) unit, because each component of the
electronic control (electrical adjustment) has a certain resistance value.
Range, output voltage range and output waveform during operation. Therefore,
use a multimeter to measure the resistance and output voltage of the component,
use an oscilloscope to test the output voltage waveform when the component is
working, and measure the continuity with a multimeter to judge whether the
component or the line is normal. This method is characterized by simple
diagnostic methods and low equipment costs. It is mainly used for fault
diagnosis of electronic control (electrical adjustment) systems and electrical
devices, so this method can be used to make in-depth judgments on faults. The
disadvantage is that the operator has higher requirements. When using a simple
instrument, the operator must have a fairly detailed understanding of the
system structure and the line connection to obtain a satisfactory diagnosis.
4) Diagnostics with dedicated
diagnostic instruments Unit-specific diagnostic instruments are divided into:
desktop computer analyzers, portable computer analyzers and pocket computer
analyzers. Among the fault analysis of the unit's electronic control
(electrical adjustment) system, the most widely used is the portable computer
analyzer. In general, modern units have fault detection software, which greatly
improves the diagnostic efficiency of the unit's electronic control (electrical
adjustment) system. But the cost of analyzers and analysis software is high.
5) Failure Symptom Simulation Test
Method The most difficult situation in fault diagnosis is faulty, but there are
no obvious signs of failure. In this case, a thorough failure analysis must be
performed and then the conditions and environment that are the same or similar to
the unit failure are simulated. Regardless of the rich experience of the
maintenance personnel and the proficiency of the technology, if the conclusion
of the failure is not verified, some important aspects will be ignored in the
maintenance. For example, some of the problems that occur in the cold state of
the unit cannot be diagnosed in the hot state. Commonly used vibration method,
heating method, water shower method, full load method, etc.
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