Water Leakage of T&C Failure Mode of Wire Harness System Series

2021-05-13 11:40 Jeff Hu
This article is the last one in the "T&C Failure Series."
For water leakage, expected results usually have the following points:
#Terminal rust
#Voltage drop increase
#Circuit is not connected
Analysis of potential failure causes: (Note: The sealing plug mentioned in this article refers to signal wire seal, single-wire sealing plug unless otherwise specified.)
 1. The wire does not match the sealing plug. There are usually two situations:
One is that the diameter of the sealing plug and the wire exceeds the matching range of the sealing plug. This is generally caused by the carelessness of the product engineer, which is still easy to identify.
The second is that although the wire diameter of the wire is within the matching range of the sealing plug, it is not the wire gauge specified by the sealing plug. Everyone knows that the cables of different national standards have their core parameters and external parameters. Above, there are differences. For example, the connector requires a German standard wire, and the wiring harness factory does not have this specification of German common wire now. If it is replaced by a Japanese standard of approximate wire diameter, there may be a hidden danger of water leakage in the future. Although this problem is rare, there is still a specific chance of a problem, and it is more concealed. When the wire used is not the standard wire specified by the connector, please be careful, and the authorities must verify it. Of course, we do not recommend such an operation method, and it is best to use it under the required wire. But the current situation is that mixing is still quite common.
2. Incorrect selection of sealing plugs
This is also a mismatch; like the point above, this is the time to test the essential quality of product engineers. Usually, the connectors of significant manufacturers will be given the matching sealing plug material number. As long as you are careful, there will be no mistakes. Of course, another situation in which the wiring harness factory chooses other sealing plugs to substitute the original parts without authorization from cost considerations. Since this phenomenon has not been verified, the probability of problems in the next life cycle of this phenomenon is not tiny. But, because our vehicles usually have a warranty period of only two or three years, many of the later problems are not reported to the supplier for the claim processing. Many people believe that there is no problem, so they are not very concerned. That's it.
3. Unqualified terminal crimping
This is a common problem in water leakage, and it includes two aspects:
A. When crimping, the terminal pierces the sealing plug. This is well understood. Once the neck of the sealing plug is punctured, there is a possibility of water leakage, although the sealing effect is based on the annular skirt of the sealing plug; and it has the effect of pulling the sealing plug when the terminal is inserted into the connector. , It will exacerbate the damage.
B. When crimping, the terminal covers the sealing plug into an irregular shape. When crimping, the terminal package to the sealing plug is generally required to be round, allowing the sealing plug to fit the wire and the connector hole and; otherwise, there is a potential for water leakage.
4. The sealing plug is broken
The third point above also mentioned the problem of damage due to the puncture of the terminal during crimping. Besides, several situations may cause the sealing plug to break:
A. The sealing plug is scratched
This problem generally occurs at the rails of the automatic crimping machine; especially the made rails; another risky process is handling. Both places must be protected.
B. Damaged during assembly
Everyone knows that most of the sealing plugs are made of oil. This is for lubrication and makes it easier to insert the terminals into the connector during assembly. Yet, if some sealing plugs have low oil content, or the wiring harness factory has been placed in the buffer area for too long after crimping, causing a part of the oil to evaporate, then implanting the connector later, the terminal pulls the neck of the sealing plug The resistance will increase when the element enters the connector hole. The neck of the sealing plug will be broken when no additional tools are used. If you find that the sealing plug of the same wire diameter of the same connector has been implanted in the correct locking position, the height of the sealing plug is high; then you should beware of this problem.
5. The connector is subjected to excessive vibration
In a watery environment, when the connector is subjected to more excellent vibration than it can withstand, water leakage is a matter.
A. Real vehicle vibration is more significant than standard
On some domestic engines, under specific frequencies, the actual vibration value is greater than the value in the specification. Now, the connector is flooded, which is reasonable.
B. The connector is used in the wrong place
We all know that each connector has its vibration level, which is one of the inherent properties of the connection. If a connector with a low vibration level is used in a place with a high vibration level, the time may not be too long. After a long time, the problem is exposed.
6. Wire siphon
For this reason, some colleagues may be unfamiliar. Everyone should know the principle of siphoning, so I will go into more details here. This reason usually means that the sealing plug of the connector, including the wire and the sealing of the connector mating surface, is not a problem on the vehicle. Still, the water enters the male and female connector through the gap between the core wires of the wire. Cavities, which in turn leads to problems with the terminals. This problem is usually caused by improper handling of the waterproofing on the other end of the wire. Now that we know where the root of the problem is, it is not difficult to solve it.
7. Harness design issues
A. The tape winding size is inappropriate
We emphasize this problem. If the tape is not wound too close to the connector, the wire will pull on the terminal, thereby compressing the sealing plug and causing water leakage. This problem cannot be underestimated. Water leakage is only a terrible consequence of it.
B. The first fixed point on the wiring harness closest to the connector is too far away from the connector
This problem, in essence, is caused by vibration. Because the fixed point is far away, the force applied to the terminal (mass of the wire * vibration acceleration) is greater, and the compression on the sealing plug is also more significant. , So that water leakage becomes a possibility.
C. The bending angle of the wire at the end of the connector is too large
The reason for this is actually like reason 7.
A. The essence is that the wire gives the terminal stress, especially the multi-hole connector. This stress is likely to be very large. The difference from reason 3 is that the tape winding affects only the terminals on both sides of the connector, and the wire at the connector tail is bent. If the folding angle is too large, all the airports are affected, and the influence is even more significant.
But, this point is more challenging to solve. So, at the beginning of the design, it must be considered in the 3D wiring design. Once the prototype cars are out, it will be difficult to change them.