Types, failure modes and inspection methods of automotive wiring harnesses
The automotive wiring harness is the network main body of the automobile circuit, and there is no automobile circuit without the wiring harness. In the automotive wiring harness, the most important component is the wire.
Wires carry current into and out of electrical components, and most wires are copper. The cross-sectional area of the wire used in the car determines the amount of current it allows to pass.
Each circuit on a car has its own circuit number, and each wire has its own color. Wires can be either solid or striped
Types of wiring harnesses
Ordinary wire
The ordinary wire is usually made from multiple strands of thin copper wire. The multi-strand form has good bending resistance and is not easy to break due to repeated vibration.
Ordinary conductors consist of two parts: a copper core and an outer insulating material.
The insulating material usually uses PVC material, which has the following advantages:
① Will not melt under high current
② No open flame
③ Lightweight
shielded wire
The main function of shielded wires is to prevent electromagnetic interference. If the signal wiring harness is close to high current or high voltage wiring harnesses or components, the signal wires will be subject to electromagnetic interference and cause signal misalignment.
The shielded conductor is wrapped with aluminum foil or mesh wire harness for grounding. Electromagnetic wave interference is eliminated by direct grounding.
Factors Affecting Wire Resistance
Temperature
The effect of temperature on various materials varies. For example, the resistance of copper and steel increases with temperature. For some materials, the resistance of the material decreases with temperature. When making wire resistance measurements, we must disconnect the wire under test from the circuit. open.
Cross-sectional area
The larger the cross-sectional area of the wire, the more electrons can pass through in the same amount of time. The thinner the wire, the harder it is for current to flow
The higher the resistance of the wire. The resistance decreases as the diameter of the wire increases. When replacing a wire harness, a wire harness of the same wire diameter must be used. If a thinner wire harness is used, the resistance of the wire increases, the resistance increases, the power dissipated by the wire increases, and the wire harness overheats or melts
Length
As the wire length increases, the resistance increases because the electrons have to pass through more atoms. Electrons traveling through shorter wires encounter fewer atoms and therefore have less resistance
Rust
Corrosion in the circuit also affects the resistance, and the resistance will increase after the rust occurs
wire inspection
The inspection of the wire requires the use of the multimeter’s electrical barrier to measuring the resistance of the wire. The specific operation method is as follows:
First, disconnect the wire under test from the circuit;
Then select the appropriate range of the multimeter, and the needle of the multimeter is in contact with the wire.
If the resistance exceeds the standard value, it is necessary to check whether the grounding of the wire and the plug are virtual. connection status.
Connector
The structure of the connector
The car plug is mainly composed of pins, shells, and accessories. The structure is shown in the figure below.
Classification of connectors
Classification by connecting parts:
There are two types of plugs: wire and wire plugs, and wire and component plugs.
Wire and wire plug means that both ends of the plug are connected to the wire harness, and the plug plays the role of connection.
Wire and component plugs refer to the plugs where the wiring harness is connected to certain components.
Classification according to the structure of the plug:
Plugs can be divided into male plugs and female plugs according to structural characteristics. Male plugs are mainly based on pins. The female plug is mainly a spring leaf.
Failure Modes of Connectors
Common forms of plug failures include dirty plugs, pins falling off, and loose plugs.
① Dirty plug If the plug is dirty or corroded, it is easy to cause a short circuit between the pins of the plug.
② Pins fall off Damage to the pin clips on the plug shell may easily cause the pins of the plug to fall off, and the contact of the plug will be poor after the pins fall off.
③ Loose plug If the fixing clip on the plug shell is damaged, it will easily cause the plug to become loose, which will affect the work of electrical components.
Inspection of connectors
① Visual inspection
● Check for oxidation, which may cause poor connections to the internal terminals of the plug;
● Check pins and terminals for damage;
● Check that it is properly inserted into the connector;
● Check that the wires are properly connected to the pins or terminals;
● Check the pins and terminals especially carefully.
② Plug measurement
● Connect a multimeter between the ends of the wires to measure the resistance;
● if the plugs are making good contact and there are no open circuits, the multimeter should read about 0.
③ Check for loose plug pins
Check whether the wires on the plug are loose. If found, it needs to be repaired in time.
The above is the analysis and introduction of the types of automobile wiring harnesses, failure modes, and inspection methods.
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