Plastic valve Diavent: A small part with great responsibility

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Plastic valve Diavent: A small part with great responsibility-valve

In 2020 more electric cars were sold worldwide than ever. Larger ranges thanks to powerful batteries should help to continue this trend. In order to guarantee the safety of the drives, the supplier company Freudenberg Sealing Technologies created a product that combines two functions in itself: the pressure equalization in normal operation and the emergency gas emergency.

Who takes the product, a plastic part called Diavent, which may find it inconspicuous. With a diameter of only 55 millimeters and a height of 16 millimeters, it is not excessively large. But what seems so unspectacular, it has in the truest sense of the word in itself. The clou of the product attached to the battery case from electric cars is in its inner life. Nonwoven elements ensure that the lithium-ion batteries are not only appropriately ventilated and vented, but also protected against moisture. And in case of emergencies, an elastic sealing lip helps to quickly dissipate large gas volumes and then completely seal the battery case again.

“The interest of our customers at Diavent is very large, which will show not last four serial orders. We therefore set Diavent to the right topic for our future portfolio.”- Tanja Heislitz, Technical Director E-Mobility at Freudenberg Sealing Technologies

Lithium-ion batteries are the heart of electric cars. The metal or plastic housing is intended to protect the cells placed therein from dust, moisture and oils. There are two trends to observe: to increase the range of the E-cars, the energy density of the battery cells is resistant. In addition, the cells in the battery case are always arranged narrower, to obtain “dead volume” as little as possible.

At the same time, the housings are becoming more and more thin, thin-walled and thus pressure-sensitive. So that the housing is not deformed on pass roads or between a cold start and high speed on the highway, it requires efficient pressure equalization. So far, this took over a porous PTFE film. However, it reacts sensitive to destructive mechanical influences and impurities by particles or oils. This can affect the air permeability and ultimately the pressure equalization function in normal operation.

In the cases of batteries can develop a sudden gas or great heat under accident conditions. These are released, for example, by the destruction of cells in an accident, by foreign bodies entering the cell, or short circuits. Then pressure and heat must escape quickly, otherwise the housing threatens to burst. A danger to the vehicle and its occupants.

Therefore, each battery requires a 100 percent reliable emergency gas. So far, this was only possible by breaking a rupture disk with corresponding pressure differences from a pin. Although this principle is the acute danger, but at the expense of further: The battery case remains permanently open after activation of the rupture disk. Ambient air can be acceded to the interior of the battery, which can result in uncontrollable thermal reactions. In addition, moisture can penetrate, which complicates the safe transport of the damaged battery. In addition, toxic products can get to the outside.

Two make one: Diavent

According to Freudenberg Sealing Technologies, Diavent is the right answer to these weaknesses. It manages both normal operation such as emergency degassing and makes the PTFE foil superfluous as well as rupture slices. In control mode, the valve ensures a constant pressure compensation. Breathable non-woven layers integrated in it enable the desired air exchange of around 16 liters per minute, as the supplier communicates. At the same time, the pressure equalization layer after a filter prevents the penetration of water and dirt.

With a stuffing gasification comes the second function of the Diavent into the game. A shield valve reacts from a certain pressure difference between the interior of the battery and the atmosphere. From then, the valve opens and leaves at a differential pressure of 300 millibar 15 liters of gas per second to escape on laterally attached openings. But that’s not enough: has the gas leaked, the elastic sealing lip spring back and closes the battery as before waterproof.

Plastic valve Diavent: A small part with great responsibility-valveFreudenberg Sealing Technologies

In addition, it uses the emergency gas function to reduce short-term pressure peaks. As soon as they are inserted, the screen valve opens, takes pressure from the system and immediately closes again. The conventional solution with rupture discs then remained open, although no serious emergency.

But how does Freudenberg Sealing Technologies specialist for sealing solutions to bring such a product to market? “We experience a transformation in the vehicle industry for electromobility. That is, the manufacturers will continue to need seals from us, “says Tanja Heislitz, Technical Director E-Mobility at Freudenberg Sealing Technologies. “However, material developments for the safety of the battery electrical vehicle play an increasingly important role.”Because security would not be guaranteed, then the growing interest of consumers would cool to the alternative drive. “Security decides on the success of electromobility and we make the electromobility with our Diavent safer”, it brings Heissitz to the point.

Innovating Together as an innovation base

Anyway, Freudenberg Sealing Technologies had the best conditions for the Diavent development according to its own statement. “We have exceptional competence in material development. She is our DNA. And she was also the key to the success of Diavent, “says Heislitz. So the sealing lip consists of a special silicone elastomer. Its stiffness can set the elastomer experts exactly that it reacts reliably at pre-defined pressure ratios and thus makes the way for emergency gas, then but also closes automatically again.

In addition, within the Freudenberg Group, the Performance Materials business unit contributes the know-how for powerful nonwovens. “Diavent is the perfect slip of the Freudenberg-Claim, Innovating Together ‘. We have shown that we have good ideas in the new segment and can implement them in reality. So we have acquired credibility quickly, “Heislitz is convinced.

Between the impetus of the Diavent development and serial maturity were just four years. A very short period of such innovation. The market requires for ever shorter development cycles. Idea of the Diavent was among other things. Peter Kritzer, Senior Application Manager E-Mobility. He recognized early the potential of such a component and gave valuable denschings. With Christian Kleinke, Christopher Schafer and Roman Duke, three developers made themselves the conception of a prototype. And that in parallel to the day-to-day business.

“This shows that we do not proliferate long, but just do it,” underlines Heissitz. Together with key customers, Freudenberg Sealing Technologies finally developed the pressure compensation element for series production. The advantages are obvious: Diavent increase the safety of the battery significantly. It is more robust than the previous solutions. It can be easily attached to the housing. And it helps to save costs because it combines two functions in a component.

Strong customer focus, strong demand

Since each vehicle manufacturer sets for its models to different batteries, however, any other requirements for Diavent has. “In the automotive sector, we almost exclusively produce products that have been adapted to the needs of customers,” says Tanja Heislitz. The functionality remains unchanged, but different thick housing walls make modifications necessary. In addition, varies how the element is attached to the housing. The most demanded are fittings. But also releasable such as non-releasable bayonet solutions are possible. “We put together with our customers and develop the solution that fits you. This is our top priority, “emphasizes Heislitz the customer-centered approach. “Only in this way, our innovations meet their purpose: to take the applians in a certain area their greatest pain.”

Since 2020, first manufacturer Diavent have in series use. About Abt, which equips the E-Caddy and the E-transporter of Volkswagen with it. In addition, the Chinese vehicle manufacturer Bjev uses Diavent. Even an Indian vehicle manufacturer as well as a battery manufacturer rely on it.

Meanwhile, Freudenberg Sealing Technologies Diavent has developed further, as more and more efficient batteries in an emergency is more and more gas volume. Diavent HighFlow can deliver up to 120 liters per second with a differential pressure of 500 millibar. In normal operation, it exchanges 10 liters of air per minute. The modification had to be made again under great time pressure. “We have optimized the angle of the sealing lip and integrated additional exhaust air channels. What sounds simple, required many simulations and revisions, “says Heislitz. The demand is also great here and some users intend to attach several of the new pressure compensation elements to the battery case.

Pressure compensation elements also for fuel cells and e-motors

The further development of the Diavent is not limited to use in batteries. With Diavent Light, Freudenberg Sealing Technologies has currently launched a modification on the market, which should help fuel cells and e-engines to handle the prevailing ambient pressure. Since no emergency gas is needed in both cases, Diavent Light has only the pressure-regulating function, which is no less important.

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