A brief discussion on the selection of low-voltage wire harness wrapping materials
Feb 01, 2024
Common failure problem types
1.1 Problems with water seepage in wiring harnesses
After a certain model underwent an intensive rain test, water seeped from the right front door glass lift switch wiring harness branch and the speaker wiring harness branch, as shown in the figure.
1) Cause of the problem.
After the actual car was exposed to rain again, it was found that the water seepage path was as follows: water dropped onto the velvet tape on the trunk of the rearview mirror branch. The water seeped through the velvet tape and entered the indoor right front door glass lift switch wiring harness and speaker wiring harness branch, collecting at the low point of the wiring harness, forming water droplets, as shown in the picture.
2) Solutions.
Based on the identified water seepage path, and by comparing the water absorption properties of flannel tape and PVC tape, the optimization measures are as follows: change the main branch in the wet area to PVC tape, and optimize the wrapping material of the right front door glass lift switch wiring harness and speaker wiring harness branch in the indoor dry area to PVC tape combined with local sponge noise reduction protection. Through repeated rain verification, the water seepage problem has been resolved, and the inspection beam branches are all dry.
1.2 Problems with abnormal noise in the wiring harness
During the road test of a certain model for abnormal noise evaluation on twisting roads, concave manhole covers, raised manhole covers, cobbled roads, gravel roads, etc., a slight knocking sound was heard on the left side of the rear door (near the driver's side). The abnormal sound disappears on non-bumpy road sections. The details are shown in the figure.
1) Cause of the problem.
The fault was first reproduced by simulating the real vehicle condition. That is, with the back door open, the sheet metal at the rear end was tapped by hand, and the location of the abnormal sound was initially traced to near the left taillight (Figure 4). Next, the elimination method was used to remove interfering parts, such as the interior panels and taillights, one by one. Finally, it was determined that the abnormal noise was caused by the knock between the trunk section of the tailgate wiring harness and the sheet metal.
2) Solutions.
Based on the contact between the back door wiring harness trunk and the back door sheet metal internal reinforcement plate on bumpy roads, the contact area of the back door wiring harness trunk was optimized by wrapping it with sponge tape on the outside. After multiple verifications on bumpy roads, the problem of the abnormal knocking noise was resolved.
1.3 Wiring harness wear problems
After dismantling a certain trial model and checking the wiring harness status, it was found that there were white indentations on the PVC tape at the contact point between the assembled floor wiring harness trunk and the sheet metal. The details are shown in the figure.
1) Cause of the problem.
The backbone of the floor wiring harness passes through the double-layer overlap edge of the body sheet metal. Although PVC tape adheres well, it is easily stretched and deformed, which leads to white indentations after contact with the sheet metal.
2) Solutions.
Based on the characteristics of PVC and the surrounding environment of the wiring harness layout, the wrapping material at the contact point between the backbone wiring harness and the sheet metal lap edge was changed from PVC tape to duct tape for protection, thus solving the wire harness wear problem.
1.4 Wiring harness temperature resistance issues
After a temperature field test on a certain model, the wiring harness status was checked, and it was found that the ESC branch of the front cabin wiring harness was adhering to the PVC tape near the exhaust area on the firewall, as shown in Figure.
1) Cause of the problem.
The ESC branch of the front cabin wiring harness is located near the engine exhaust heat shield. Temperature field tests were conducted under the most severe low-speed immersion conditions. The maximum temperature in this area reached 112°C, which exceeds the temperature resistance value of PVC tape, causing the PVC tape to adhere due to hot melt.
2) Solutions.
Based on the characteristics of PVC and the surrounding environment of the wiring harness layout, the PVC tape at the ESC branch of the front cabin wiring harness was replaced with aluminum foil fiberglass cloth. This solution effectively addressed the issue of hot melt adhesion of the PVC tape.
Characteristics and selection principles of wrapping materials
Since problems such as water seepage and abnormal noise often occur in actual vehicle use due to improper selection of low-voltage wire harness wrapping materials, analyzing the selection process for these materials is crucial. This analysis should consider both the characteristics of low-voltage wire harness wrapping materials and the principles for selecting the appropriate materials. Therefore, this section will analyze the materials from two key aspects: their characteristics and their selection criteria.
2.1 Characteristics of low-voltage wire harness wrapping materials
1,Tapes
Tapes are soft materials composed of a base and an adhesive. The base material may include PVC, PE, PET, aluminum foil fiberglass cloth, and others. The adhesives typically used are rubber-based or acrylic-based.
2,Corrugated Pipes
Corrugated pipes are heated and extruded from materials such as PA (nylon 6), PE (polyethylene), PP (polypropylene), and other polymers. The structure of these pipes resembles waves, making them flexible and durable.
3,Casing Type
A flexible type of pipe, often made of PVC or other materials, is used for encasing wires to provide protection against external damage.
4,Sponge Strips
Wire harness sponge tape is an effective protection material for wire harnesses. It consists of a flannel base layer combined with a sponge layer, and it is coated with a specially formulated pressure-sensitive adhesive that ensures strong attachment without damaging the wire harness.
Low-voltage wire harness wrapping materials exhibit varying properties such as temperature resistance, wear resistance, and noise reduction. These properties must be carefully considered when selecting materials for specific applications. To facilitate this, a performance list of commonly used wrapping materials for wire harnesses is shown in Table.
2.2 Principles for selecting wrapping materials
The vehicle environment is the basis for selecting wrapping materials. The requirements for wire harness wrapping materials can be summarized into four main characteristics: moisture resistance, noise reduction, wear resistance, and temperature resistance, as shown in Figures 7 and 8 (picture cited from tesa tape introduction).
Wrapping materials are used to bundle and protect the wire harness, which is the item being protected. Based on the environmental requirements of the vehicle-such as moisture resistance, noise reduction, wear resistance, and temperature resistance-the selection principles for wrapping materials are analyzed. This analysis guides the selection of wire harness wrapping materials, as shown in Table.
03 Summary
By analyzing the wiring harness issues that occurred in actual vehicles, the causes of the problems were identified through observed phenomena, and the issues were ultimately resolved. Since wrapping materials can affect the performance and cost of low-voltage wire harnesses, the selection of these materials was further analyzed to clarify the types, functions, and selection criteria for each material. This analysis aims to simplify the process of selecting low-voltage wire harness wrapping materials, improving the performance of wire harnesses while further reducing their design costs.
