Factors affecting current transmission in automotive connectors

Factors affecting current transmission in automotive connectors

1) Low terminal retention force. The terminal retention force measures the reliability of the terminal hanging in the sheath. According to the latest automotive standard QC/T1067.1-2017, terminals of different specifications need to meet different retention requirements. Low terminal retention can lead to a decrease in the reliability of the terminal's connection in the sheath. Especially during the movement of the vehicle body, the terminal is subjected to increased traction from the wiring harness. If the terminal retention force is small, the terminal will detach from the sheath, leading to connector transmission failure. The standard for terminal retention force is shown in Table 1

Therefore, when designing and selecting connectors, attention should be paid to the retention force of the connector as an important performance indicator.

2) The effective insertion depth is less than 11) mm. Effective insertion depth refers to the length of the plug part of the plug terminal that exceeds the contact point of the plug terminal, excluding the size of the plug crimping, provided that the connector is fully assembled in place. According to the latest standard QC/T1067.1-2017 in the automotive industry, the effective insertion depth of terminals is required to be at least 1-2017mm.

During the process of vehicle body movement, the schematic diagram of current I transmission between connectors also decreases over time. If the insertion depth is too small, once the effective insertion depth of the plug terminal becomes 0, the contact effect between the socket terminal spring and the plug contact point will decrease, leading to an increase in contact resistance at the contact point, an increase in temperature rise, and a series of serious consequences such as connector erosion.

3) Coating oxidation at terminal contact points. The main purpose of adding coating to connector terminals is to increase their corrosion resistance and oxidation resistance. After adding coatings, the corrosion resistance of the terminals is enhanced, which can meet the requirements of complex vehicle environments. At present, the coating used for mainstream connectors in the market is mostly tin plating, and gold and silver plating are also used in a small range. After the coating on the terminal contact point is damaged, the contact point will quickly oxidize, resulting in a high resistance of the oxide layer. Directly leading to a rapid increase in contact point resistance, the terminal temperature also increases accordingly. At the same time, the increase in temperature increases the resistance value of the resistor, forming a vicious cycle that ultimately leads to current transmission failure and severe erosion.

Therefore, the coating quality of terminals is also a key indicator, and the current coating acceptance standard is conducted through salt spray testing. According to the instructions. GB/T2423.17 (Neutral Salt Spray Test) standard requires that the sample should meet the requirement of 96h.

4) Socket terminal spring fault. Figure 3 shows the structural schematic diagram of the socket terminal spring. The current transmission effect of plug terminals and socket terminals is directly related to the positive voltage provided by the socket terminal to the plug terminal. A high positive voltage improves the electrical contact effect between terminals, while a low positive voltage reduces the electrical contact effect. The function of the socket terminal spring is to provide continuous positive pressure for the plug terminal, but the long-term stress deformation of the spring will cause local fatigue of the arc R at the root of the spring, causing the material to change from elastic deformation to plastic deformation, resulting in a decrease in material elasticity, a decrease in positive pressure, and ultimately affecting the current transmission effect. As is well known, the larger the root arc, the smaller the deformation per unit area. Therefore, while meeting the requirements for terminal insertion force, try to increase the value of root arc R as much as possible to reduce the incidence of plastic deformation.

5) The crimping wire does not match the terminal specifications. Due to the limitations of different terminal structures, even terminals of the same specification have varying current carrying capacity. Therefore, the prerequisite for selecting a terminal is to first confirm its current carrying capacity. Exceeding the current carrying capacity of the terminal itself can lead to faults such as terminal ablation. Therefore, in the process of selecting terminals, it is recommended to reduce the risk of use based on the principle of 80% of the terminal's current carrying capacity.

6) The crimping resistance is high. Crimping resistance refers to the resistance generated by terminals and wires during the crimping process. The resistance value is mainly influenced by the quality of the pressure connection. Therefore, during the crimping process, it is necessary to ensure that the tension of the terminal and the crimping section are qualified, and eliminate the hidden dangers of defect points.