Cause analysis of pin back of automobile wiring harness terminal

Terminal withdrawal is a more common form of failure for harness connectors. Terminal withdrawal refers to the fact that after the connector is assembled, the terminal is abnormally separated from the sheath, so that the function of the connector is lost. The reasons for the formation of this type of failure generally include three aspects: ①the retaining force of the terminal seals in the sheath is unqualified; ②interference in the insertion; ③product application problems. This article analyzes the terminal withdrawal of the connector and proposes solutions based on these three reasons.

1. Retaining force of the terminal in the jacket is not acceptable

The holding force of the terminal in the sheath refers to the force required to separate the terminal from the sheath in the axial direction. In order to avoid the phenomenon of terminal withdrawal, the performance test standard of the connector strictly stipulates the holding force of the terminal in the sheath: ①the holding force of the connector with a size not greater than 2.8 is greater than 40N; ②The holding force of the connector is greater than 60N. In practice, many terminal withdrawals occur because the holding force does not meet the requirements. In general, the reasons for the failure of the terminal's retaining force in the sheath are: structural design issues and material selection issues.

1.1 Structural design issues

The structural design problem mainly refers to the design of the connecting structure of the terminal and the sheath. This hook structure is generally an elastic structure, which is divided into an elastic structure on the sheath and an elastic structure on the terminal.

1.1.1 Elastic structure on the sheath

The sheath adopts an elastic structure. The elastic structure required for the assembly of the terminal and the sheath is designed on the sheath. During the assembly of the connector cavity terminal plug and the sheath, a force is applied through the sheath spring (the elastic structure designed on the sheath) Deformation to achieve the assembly of the terminal and the sheath. After the terminal and the sheath are assembled in place, the sheath tongue is restored to its original state due to the release of force. The cooperation of the sheath spring tongue and the hanging structure designed on the terminal ensures the effective positioning of the sheath on the terminal. The shear strength of the sheath tongue determines the retention force of the terminal in the sheath. The design clearance between the terminal and the sheath should be able to ensure that the shear area calculated under extreme conditions can withstand the yield shear stress greater than the required terminal retention force in the sheath.

1.1.2 Flexible structure on terminals

The use of an elastic structure on the terminal refers to designing the elastic structure required for the terminal and sheath assembly on the terminal. During the terminal and sheath assembly process, the terminal spring tongue (the elastic structure designed on the terminal) is deformed by force to achieve Terminal and sheath assembly. After the terminal and the sheath are assembled in place, the terminal spring tongue is restored to its original state due to the release of force. The cooperation of the terminal spring tongue and the hanging structure designed on the sheath guarantees the effective positioning of the terminal by the sheath. The yield strength of the terminal spring tongue determines the retention force of the terminal in the sheath. In practice, it should be ensured that under extreme conditions, the terminal tongue and the hanging platform structure designed on the sheath have a complete cooperation.

Connector Terminal Seal

1.2 Material selection issues

1.2.1 Sheath material selection

Common materials for automotive connector seal jackets are: polyamide (commonly known as nylon), polybutylene terephthalate (PBT), ABS, etc. For the sheath tongue structure, the toughness of the material is generally considered, and the size of the tongue structure is designed according to the allowable yield shear stress of the material that meets the toughness requirements. It should be emphasized that the allowable yield shear stress of the material should be calculated according to the allowable values of the material after the test of high temperature aging, temperature-humidity cycle, and chemical liquid corrosion that the connector may have.

1.2.2 Terminal material selection

Common materials for connector terminals are: copper, brass, bronze. According to their hardness, they can be divided into three states: soft, semi-rigid and hard. Of these three materials, copper is less commonly used, and is generally used for grounded hole or fork joints. Brass and bronze are more commonly used. Brass has better conductivity than bronze, and bronze has better hardness and elasticity than brass. When using the terminal spring tongue structure, bronze should generally be used. The use of brass materials often results in insufficient retention.