Analysis on crimping performance of high-voltage wire harness terminals of electric vehicles
With the rapid development of new energy vehicle industry, new energy harness has gained development opportunities. The difference between high voltage harness and low voltage harness is that the high voltage terminal is easy to generate heat due to the large current, which leads to the decline of the mechanical strength of the terminal and the insulation performance of the harness, and at the same time causes the conductor oxidation to further aggravate the heat and other problems.
The high voltage terminal crimping needs to consider both the reliability of crimping and the low temperature rise at the crimping point. This paper mainly introduces the influence of cold crimping on terminals.
Crimping uses crimping equipment and molds to connect wires and terminals through the crimping process. High frequency welding is to use high frequency welding machine to weld wires and terminals together. Resistance welding is to use special resistance welding equipment to connect wires and terminals together.
Simple operation, convenient use and maintenance, low manufacturing cost, high operation efficiency, suitable for mass production.
The wiring harness and terminal with high current passing rate and low resistance requirements after connecting wires and terminals are not satisfied. The common crimping method of large square high-voltage terminals is shown in the figure, which is hexagonal enclosed terminal.
The advantages of ordinary crimping are obvious, but how to make ordinary crimping develop its advantages and avoid its disadvantages, and how to reduce the crimping resistance as much as possible is particularly important. Reducing resistance means reducing heating, reducing product temperature rise, and making product life and quality more excellent.
Hazards of terminal heating
After the terminal heats up, it is easy to oxidize itself and the contact surface of the conductor, forming an oxide layer film, which increases the contact resistance. The increasing speed doubles with the increase of temperature, further increasing the temperature rise speed of the terminal, which may cause a fire in serious cases. At the same time, the elastic element of the contact structure will be annealed, the contact pressure will be reduced, and the contact resistance will be further increased. In addition, heating will make the insulation layer of the wire connecting the terminal aging and brittle, causing the insulation performance to decline. There is a risk of fire caused by electric leakage and overheating.
As shown in the figure, the high-voltage harness has three heat sources.
Conductor: the conductor itself has resistance. The smaller the cross-sectional area, the higher the resistance, and the resistance will cause heating.
Terminal crimping: insufficient compression ratio will make the conductor loose, resulting in large resistance and easy heating. Excessive crimping is easy to reduce the sectional area, and insufficient current carrying capacity causes heating.
Male and female terminal mating contact: poor terminal contact, or serious heating caused by terminal contact surface oxidation.
Method of reducing terminal temperature rise
Reduce contact resistance:Use materials with low resistivity. Common high-voltage terminals are H62, H65 copper or high conductivity copper. For products larger than 125 A, it is recommended to use high conductivity copper with low resistivity. Reduce the contact resistance of the conductor. The terminal and conductor shall be compacted as far as possible to reduce the crimping resistance. Increase the cross-sectional area of the conductor and reduce the temperature rise of the conductor.
Increase conductor heat dissipation area:Forced cooling, air cooling, water cooling and other measures can be used. Reasonably arrange conductors and harnesses with large current, and try to arrange them in the space easy for heat dissipation to facilitate natural heat dissipation.