Crimp Internal Contacts (RS / wire) of Connector

This article introduces 7 internal contact structures of connectors to wiring harness engineers.
1. Double helix and wire spring contact structure
Amphenol’s contact structure solution for high-current connectors in motor control, motor drive and other parts of electric vehicles and hybrid vehicles adopts a double helix structure (Figure 1), with a contact area of 65%. It has low insertion and extraction force and high reliability, the working voltage can reach 630 V, the rated current is 455 A, it has a relatively high overload capacity, and the mechanical life is more than 500 times. It is one of the popular internal contact structures currently used in the field of high-voltage connections for electric vehicles. The wire spring contact system used by Rosenberger (Figure 2) can achieve more than 40 contact points, has high current carrying capacity, saves space, and has low contact resistance and plug-in force.

Flexible high-voltage plug

Figure 1. Double helix and wire spring contacts for connectors

New cylindrical crown spring contact

Figure 2. Wire spring contact structure of connector

2. Porous wear-resistant structure of the connector
We developed a porous and wear-resistant inner contact ring for high-voltage connectors for electric vehicles, including a porous elastic inner contact ring (Figure 3) and surface coating. The porous elastic contact ring is a highly elastic copper-nickel-silicon alloy open tube with a wall thickness of 0.5 mm, an inner diameter of 8 mm, and a length of 19 mm. The tube is arc-shaped and has a concave center with an inner diameter of 5 mm. The tube wall is staggered and evenly distributed with holes with a diameter of 1.5 mm. There is a seam along the axis of the tube, and the seam width is controlled within 0.5 mm. The surface coating is one of AgCu, AgSb, AgPd, and AuAg alloys, with a thickness of 0.5~2.0μs. The Cu content in AgCu alloy coating is 1%~2%. The Sb content in AgSb alloy coating is 1.5%~2.5%. The content of Pd in AgPd alloy coating is 8%~10%; the content of Ag in AuAg alloy coating is 30%~40%. Alloy coatings can be obtained by electroplating or magnetron sputtering.
The contact has a simple structure, reliable performance and a wide range of applications, and can effectively promote the application of high-voltage connectors. In this article, the porous wear-resistant elastic inner contact ring realizes mesh linear contact with the plug, has low contact resistance, and meets the contact resistance requirements of the LV215 high-voltage connector. The AgCu, AgSb, AgPd, and AuAg alloy coatings used instead of the pure Ag or pure Au coating of the inner contact ring improve the wear resistance of the inner contact structure. When the Cu content in the AgCu alloy coating is 1% to 2%, the wear resistance is 3 to 5 times higher than that of silver. When the Sb content in the AgSb alloy coating is 1.5%~2.5%, the wear resistance is 10~12 times higher than that of silver. When the Pd content in the AgPd alloy coating is 8% to 10%, the wear resistance is 5 to 10 times higher than that of pure silver. When the Ag content in the AuAg alloy coating is 30% to 40%, the wear resistance is 8 to 10 times higher than that of pure gold.

3. Elastic jack contacts
The elastic socket contact (Figure 4) consists of a sheath, an elastic piece and a socket. The elastic contact piece is made of an elastic wire or an elastic strip and is bent into a shape including a circular arc contact part and a hook-shaped fixing part. Arranged evenly on the circumference of the jack, the arc-shaped contact parts are suspended toward the center of the jack to form a sliding fulcrum, and an inner contact jack is formed in the radial direction of the jack. This structure has the advantages of simple structure, low insertion and extraction force and large carrying capacity.

contact points of leaf spring contact structure

Figure 3, porous wear-resistant contact structure

Contact elastic internal contact structure
Recently we have developed a contact-type elastic internal contact structure for high-voltage connectors for electric vehicles [4], which includes an elastic contact ring (Figure 5), a cylindrical contact head and a socket body. The elastic contact ring is fixed in the socket body and then butts with the cylindrical contact head. The elastic contact ring is an open tube structure. There are arc-shaped protrusions evenly distributed on the inside of the open tube structure, and the elastic contact ring is provided with seams along the direction of the tube axis. The diameter of the open tube of the elastic contact ring is 3~16 mm, the radius of the arc-shaped protrusion is 0.5~1 mm, and the height of the arc-shaped protrusion is 0.2~0.5 mm.

Array bump cut out contacts for connectors

Figure 4, Resilient jack contacts for connectors

The structure is simple to process and has reliable performance. The multi-contact elastic contact structure has low contact resistance and can meet the contact resistance requirements of LV215 high-voltage connector.
Multiple arrays of bumps are set on the inner wall of the laser-hollowed connecting tube (Figure 6), which can stably obtain multi-contact positive pressure and ensure the reliability of contact.

Multi-contact resilient contact rings for connectors

Figure 5, Multi-contact resilient contact rings for connectors

Resilient jack contacts for connectors

Figure 6, Array bump cut out contacts for connectors

Contacts of leaf spring contact structure
Leaf spring contact structure (Figure 7). The structure includes a C-shaped or ring-shaped main body part and a number of reeds formed on the main body. The reed is provided with a contact piece facing the axis of the main body, and the reed is provided in at least two rows along the axial direction of the main body. The two adjacent rows are offset in the axial direction to achieve better elasticity and resistance to plugging and unplugging.
New cylindrical crown spring contact
A new type of cylindrical crown spring was designed [7], which includes an upper end band and a lower end band arranged at both ends of the cylindrical crown spring, and several reeds arranged between the upper end band and the lower end band. Each reed has a contact portion extending axially toward the cylindrical crown spring (Fig. 8). This technical solution has more contact points, which can effectively reduce contact resistance, and the inward protrusions of the reed are divided into multiple layers. During the pin insertion process, the layers can be in contact with the pins, effectively reducing the insertion and extraction force of the pins.

porous wear-resistant contact structure

Figure 7, contact points of leaf spring contact structure

Wire spring contact structure of connector

Figure 8, New cylindrical crown spring contact
Regardless of the above contact structure, secondary contact is formed through an intermediate intermediary, not direct contact between the plug and socket, which increases the risk. The elastic high-voltage plug we developed (Figure 9) (patent has been accepted). The linear elastic contact piece at the contact end of the plug can directly form linear contact with the socket to ensure good contact of the plug and socket without the need for intermediaries such as crown springs. The stainless steel annular opening linear elastic piece is embedded under the linear elastic contact piece, which improves the fatigue resistance of the linear contact elastic piece and extends the service life. Silver-nickel, silver-nickel nanographite sheets, or silver-nickel carbon nanotube composite coatings are used instead of conventional silver or gold coatings to improve the hardness and wear resistance of the coating. The number of plugging and unplugging of high-voltage terminals has been increased. On the basis of the high-voltage petal socket, the surface of the plug is made into a tooth-shaped thread. It also achieves linear contact between plugs and sockets without the need for intermediate media to ensure the reliability of high-voltage connector contact.

Double helix and wire spring contacts for connectors

Figure 9, Flexible high-voltage plug

Conclusion
In short, there are two trends in the structural design of high-voltage connectors. One is to change from the original low-pressure surface contact to the line contact of a double helix curve structure, a line spring structure, a porous wear-resistant structure, a leaf spring contact structure, and an elastic jack structure under high pressure to increase the contact area. Reduce contact resistance and increase current carrying capacity. The other uses a multi-contact contact ring, a hollow connecting tube with an array of bumps, and a new cylindrical crown spring to directly realize point contact to reduce contact resistance and improve current carrying capacity. The elastic high-voltage plug can directly form linear contact with the socket without the need for intermediaries such as crown springs.