Detroit — As the auto industry prepares for the growth of electric vehicle production, suppliers are setting themselves up to provide the technical parts needed to make sure EVs function safely.
Auto supplier Eaton Corp. created a single-stage vent valve for EV batteries that acts as an overpressure release in the event of a thermal runaway situation. The valve is resealable, allowing for full functionality testing compared with conventional burst-valve technology and allows Eaton's customers to specify low opening pressures.
Usually, an EV battery either has two valves, or a single valve with two functions, Jens Buhlinger, sales growth manager at Eaton, told Plastics News.
One function is "passive venting," Buhlinger said. "Usually that's done through a membrane, a material that lets gas pass through it … during normal operations … because this is a sealed enclosure and inside the battery during charging, heat is generated, but also when you drive your vehicle to altitudes the pressure changes inside the battery so you need to equalize the pressure."
In the case of a physical impact, he said, "the membrane needs to be strong enough that it's not destroyed when something like that happens."
"If you have a resealing functionality, it will go up quickly, release the air that is compressed during that event and reseal. You don't have to design around that.
"In the case of a thermal event, an overpressure will rupture the membrane, and that opens a bigger flow path, which is then used to release the gas," he said. "If you have a membrane that bursts, you can only use that product once. … The valve is not usable anymore because the membrane is not intact.
"Our part can be used several times," Buhlinger said.
Eaton's single-stage overpressure relief valve has no membrane, uses a stainless steel spring and an over-molded rubber seal inside two injection molded parts. The company declined to comment on the exact materials in the injection molded parts. It sits in the battery housing, which could be a plastic, aluminum or aluminum-steel compound enclosure, he said. "This whole structure is a sealed enclosure; you have to protect the battery from anything getting into [it]."
The product is "simple and robust," with a quick-connect feature so it's easy for customers to install, he said. "It's screwed in, it sits very tight and [makes] a certain sounds that you understand the product is in place and it's clicked in."
Because the product is an overpressure relief valve, it "is a safety-critical part," he said. "If you have a one-time product, you cannot test each and every component that leaves your manufacturing line. You obviously design it to open and rupture at the requirements that you define together with the vehicle or battery manufacturer. But you cannot guarantee that every single part is tested to open at the defined pressure because you cannot test it."
Because the valve can be fully tested, Buhlinger said, it has "higher reliability."
Also in the case of a thermal event, if the battery's valve starts "to vent early … you have less risk of thermal runaway spilling over to other cells," he said. "The lower you define your opening pressure, the earlier you start to vent the battery in case of a thermal runaway.
"We can adjust to different opening pressures the OEMs want to have by changing the spring while keeping all the components common," he said, adding that keeping the parts the same despite opening pressures makes the product cost-effective for customers. "I think that's something we will help to standardize the products that are on the market," Buhlinger said.