Three-way vent valve A three-way vent valve has three unique functions: a battery case leak-check mechanism, and passive and active venting to supply overpressure relief for the vehicle’s battery pack. Unlike traditional testing methods, where a valve is left off to conduct leak testing and then replaced, the three-way vent allows testing through the valve, so the entire battery pack is tested while fully assembled. Some solutions require several breathing valves on the battery pack casing, which must be masked off before testing, but the three-in-one design meets all flow requirements and overpressure relief with just one valve, so no masking is needed. The battery case leak-check feature eliminates the need to install the vent valve as the final step of the battery assembly process, which is standard in today’s EV architectures. It is also more thorough than traditional methods, as it includes testing the sealing surface of the vent itself when the battery vent valve is already assembled. A custom tool actuates the leakcheck mechanism on the assembly lines, allowing for testing through pressurisation or a vacuum, which ensures a proper seal to improve safety. Sealed battery enclosures must compensate for temperature and pressure changes, and they keep water and dirt outside the pack. The vent prevents the enclosure from exceeding a pressure that would cause catastrophic failure during a thermal runaway event, when gases and heat are generated quickly. A battery thermal runaway situation can occur when individual cells inside the unit fail through physical impact or a short circuit. This is where the rising temperatures and pressures released by cells exceed the venting capability of low-flow breathing vents. The battery vent valve can be precisely designed to meet specific opening pressures and optimise venting. Developers can specify low opening pressures in contrast to the conventional, burst-valve technology commonly used today, and a low-flow breathing mode that allows air to move through porous material to normalise pressure during regular operation. The battery vent valve can be assembled through a robust, quickconnect feature or by a screwed-on, metal-to-metal connection, which gives developers flexibility while ensuring a sturdy connection that stays in place. A hydrophobic membrane always allows the passage of air in and out of the battery case, but it will not allow liquids or dirt to enter. Also, the valve is made of materials that meet a UL94 V-0 rating, a standard set by United Laboratories for testing plastics and rubber for flammability. Meeting a V-0 rating is the most stringent rating and means the materials can withstand a vertical flame test, which is required by most customers. This porous membrane maintains the pressure within the battery case at atmospheric pressure. To meet the ISO standard for ingress protection, all sealing mechanisms within the valve must not allow the passage of debris or water. To maintain the ability to contain debris within a battery case in the event of thermal runaway, the three-in-one valve can include a metal mesh. Tape sealing Keeping the battery pack sealed from external elements is key to an EV’s performance and longevity. Seals range from foam-in-place gasketing and Focus | Battery sealing May/June 2024 | E-Mobility Engineering 40 A three-way vent improves test times (Image courtesy of Eaton)
RkJQdWJsaXNoZXIy MjI2Mzk4