The Composition and Application of EV HV Connecting cables

Traditional new energy vehicle wiring harnesses are composed of wires and plastic wire troughs. Because plastic trunking has poor heat dissipation, high-voltage wire bundles require larger gauge wires to reduce the impact of heat. In addition, changing and developing a new wire trough protection mold design is costly and the production cycle is long. So we saw the tube shielding wire harness solution, the representative of which is Sumitomo high-voltage wire harness.
With the rapid development of new energy vehicles in recent years. Its high-voltage electrical components, such as motors, inverters and high-voltage batteries, are also constantly developed and improved. The high-voltage wiring harnesses connecting them are also constantly developing and improving. The vehicle is in urgent need of high-voltage wiring harnesses to reduce costs, weight and layout space.

Unshielded cable facilitates connector design

Figure 1 shows the timeline for mass production of high-voltage wire harness products. In 1999, our company began large-scale production of high-voltage wiring harness products for Honda INSIGHT. The first comprehensive development of high-voltage wiring harness parts, such as wires, terminals and connectors, began in 2001 for the Toyota ESTIMA hybrid vehicle. In terms of terminals, two types of bolt-type molded and plug-type connectors have been developed based on the technical requirements of the connection interface. Electromagnetic shielding started with individually shielded cables, then introduced integral braided wire harness shielding for the Toyota Prius in 2003, and introduced the first tube shielding technology for the Honda CIVICHYBRID in 2005. The maximum temperature requirement for high-voltage wire harnesses has also changed from the original 120°C to 150°C.

Tubular shielded high voltage wire harness

Figure 2 shows the application of high-voltage wiring harness products in HEV models. On the right, the wiring harness assembly is shown, secured using wire troughs. In the lower left corner is the motor wiring harness. The terminals are bolted and shielded overall.

In order to prevent high-voltage wiring harnesses from causing interference to low-voltage wiring harnesses, radios, etc., electromagnetic shielding is particularly important for high-voltage wiring harnesses. In addition, most of the high-voltage wiring harnesses of new energy vehicles are routed on the chassis, and mechanical protection performance is also particularly important for high-voltage wiring harnesses.
The left side of Figure 3 shows the individually shielded high-voltage wire harness. Each wire is covered with a copper braided shield, with the overall shielding scheme on the right. There is no separate braided shield outside the cable, but overall shielding on the outside of multiple high-voltage cables. The 2003 Toyota Prius used an overall shielded high-voltage wire harness design to simplify the wire harness structure and reduce the number of necessary components, thereby reducing the cost of the overall high-voltage wire harness system. Figure 4 shows the use of protective sleeves and injection molded wire troughs on the outside of the two design options for mechanical protection.

A high-voltage wire harness with excellent heat dissipation performance

The disadvantages of the above high-voltage wiring harness design scheme are as follows:
1. Low thermal conductivity: due to low thermal conductivity caused by protective sleeves and injection molded wire troughs, the axial thermal conductivity of the wire harness is low;
2. As a result of this low heat transfer, the size of the wires increases, resulting in an increase in the weight and cost of the high-voltage harness;
3. Mechanical protection structure (wire trough): If the layout of the high-voltage wire harness changes, the shape and structure of the wire trough also need to be changed, which increases the cost and lengthens the development cycle.
In order to eliminate these shortcomings, YAXUN developed a tubular shielded high-voltage wire harness, which installs unshielded high-voltage wire harnesses into aluminum alloy tubes. Aluminum alloy steel pipe effectively combines electromagnetic shielding and mechanical protection, as shown in Figure 5.

The conductors of a shielded high-voltage wiring harness are covered with a copper braided shield

Compared with the previously mentioned solutions of individual shielding and overall shielding using protective sleeves and injection molded wire ducts, it has the following advantages:
1. The high heat transfer of aluminum alloy materials can reduce the conductor specifications of the wire harness;
2. Reduce the weight of the overall high-voltage wiring harness system;
3. The arrangement and installation of high-voltage wire harnesses are easier and more flexible.
This solution has been used in Honda INSIGHT (2009), CR-Z and Fit Hybrid (2010), and FREED Hybrid (2011).
Through experiments, the heat dissipation capabilities of high-voltage wire harnesses protected by aluminum alloy tubes and those protected by standard polypropylene plastic tubes were compared. Experiments have shown that aluminum alloy pipes have better heat dissipation capabilities than standard polypropylene plastic pipes.
The test setup is shown in Figure 6. Both components are placed on top of a heating system that generates high temperatures of approximately 350°C. Figure 7 shows the measured surface temperature measurements. Aluminum alloy tubes have good thermal conductivity and their axial heat transfer performance is much better than plastic protectors.

This excellent heat dissipation performance can reduce the conductor specifications of high-voltage cables and reduce the temperature resistance level of the cables. These two aspects can effectively reduce the cost of high-voltage cables.
In addition, due to this design, the high-voltage cable is changed from a shielded cable to an unshielded cable, eliminating the need for the cable outer sheath and injection molded protective trunking, and the weight can be reduced by about 18%. As high-voltage cables are changed from shielded cables to unshielded cables, the design of high-voltage connectors becomes simpler.

Since aluminum alloy steel pipes have good formability, high-voltage wire harnesses using aluminum alloy steel pipes are more conducive to installation during manufacturing.

The wiring harness assembly is fixed with wire trough

The high-voltage wire harness using aluminum alloy steel pipe has good rigidity and does not sag, and the distance between its fixed points can be set farther. Due to its high flexibility, it is difficult to ensure the ground clearance of traditional high-voltage wire harnesses when placed on the chassis.

When the design of high-voltage wire harnesses using injection molded wire ducts is changed, the mold needs to be re-opened or the mold needs to be modified. The use of aluminum alloy steel pipes only requires bending, which greatly shortens the development cycle of high-voltage wire harnesses.

Another most important performance is the electromagnetic shielding performance. Figure 16 Test method for electromagnetic shielding performance.

High-voltage wiring harness parts used in automobiles

Judging from the test results, the 0.8MHz individually shielded cable high-voltage wire harness has better shielding performance. Higher than 0.8MHz, high-voltage wire harnesses using aluminum alloy pipes have better electromagnetic shielding performance.

Because aluminum alloy steel pipes are used and arranged under the chassis of the vehicle, anti-corrosion performance testing is essential. Figure 18 shows that the pipeline after the gravel impact test and the wiring harness assembly after the salt spray test meet the requirements of the salt spray test.

Summary: Aluminum alloy tubular shielded high-voltage wire harness optimizes the high-voltage wire harness starting from the protective structure and materials. All aspects of high-voltage wire harness weight, cost, development cycle and manufacturing convenience have been improved.