The move to electric vehicles presents many opportunities for engineers to reexamine, innovate and optimize their approach to every application within a vehicle — right down to the materials used to protect EV-specific components.
Cross-linked polyolefin (XLPO) offers a compelling set of advantages over silicone as an insulating material for cables used in certain high-voltage applications in EVs. The right XLPO compound is tougher than silicone and more resistant to tears, cuts and abrasions. It allows for more flexibility while potentially lowering overall costs. In addition, XLPO is not affected by the same supply chain constraints that affect silicone, which is dependent on the availability of silicon that is also used in microchips.
Multiple forms of resistance
The most dramatic difference between XLPO and silicone is in abrasion resistance. Abrasion can obviously be a key factor in a vehicle, with wires packed tightly with other components inside a chassis that is often on the move. XLPO demonstrated 16 times the abrasion resistance of silicone in recent standard tests that used a belt sander with metal in the belt to grind against the material.
In addition, XLPO has 2.5 times the tear resistance of silicone, as measured by a tensile test machine that stretches the material and records the force it takes to break it. XLPO also exhibits four times the cut resistance of silicone, resisting the force of a blade applied to it. Such stresses are less of a factor in a well-designed vehicle, but these measures reflect the material’s toughness.
Because silicone has poor abrasion resistance, manufacturers often use tape or other coverings to protect it; however, this reduces the flexibility of the harness assembly, making it more difficult to route it through the tight confines of a vehicle’s body. With XLPO, engineers can avoid that step and take advantage of the material’s inherent flexibility. This makes it easier to install wiring harnesses in vehicles, a largely manual process.
Silicone retains an advantage in its temperature rating of 180° C, compared with XLPO’s rating of 150° C. But that higher rating is not always necessary to meet OEM requirements. In fact, most high-voltage applications throughout an EV will be satisfied with the 150° C rating.
Those high-voltage applications are growing as EVs become more sophisticated. Under current requirements, XLPO could perform well within a battery pack, insulating the busbars that are commonly used there instead of cables. Typically, those busbars use a nylon-based insulation and require only a 125° C rating. Future requirements, however, could call for much higher temperature ratings, and Aptiv is at the forefront of developing appropriate materials to meet those needs.
Engineers should consider the potential of a material that stands up well to abrasion while retaining much-needed flexibility and a robust temperature rating. While the costs of XLPO and silicone are similar, XLPO is less likely to require additional coverings – resulting in cost avoidance through fewer assembly steps, less labor and less materials. As EVs become more prevalent, this kind of innovation presents a unique opportunity.