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Boost car electronics safety with ventilation techniques

Posted: 23 Feb 2015     Print Version  Bookmark and Share

Keywords:hybrid and electric vehicles  expanded polytetrafluoroethylene  ePTFE  IP  battery housing 

Cars are becoming increasingly electrified. With electronic components taking over more and more essential vehicle functions, it is becoming increasingly important that they be able to function reliably over the vehicle's entire service life – despite exposure to enormous variations in temperature and harsh environmental conditions. Electronics in hybrid and electric vehicles in particular present automotive manufacturers and suppliers with new technological hurdles – problems they can solve only with the help of efficient pressure equalisation and ventilation components. The most effective solution is a membrane that allows the electronics housing to "breathe" while protecting it from dirt and liquids.

Equipping electronics for extreme conditions
Whether on the underbody of the car or under the hood, electronic components such as engines, control units, sensors, compressors or pumps are exposed to extreme variations in temperature and must be protected from dirt or liquids getting in. At the very least, they should be protected in line with the IP6k9k standard. Electronics housings that meet this standard offer reliable protection against dust particles, brief immersion and jets of steam.

Electronic components in vehicles are exposed to major fluctuations between the operating temperature and the cooler ambient temperature. When the vehicle is in use, the components become very hot; when confronted with something such as cold road spray, they are then subjected to rapid cooling. This generates a great deal of negative pressure in the electronics housings, sucking in air from the outside through the seals. Over time, this unwanted pressure equalisation puts such stress on the seals that dirt particles and liquids get in, corroding the electronics and potentially shortening the component's service life.

A particular challenge: protecting electronics in electric and hybrid vehicles
Because of their extremely high operating temperatures and the above-average size of their electronics housings, hybrid and electric vehicles present automotive manufacturers and suppliers with an even greater challenge when it comes to the issue of temperature and pressure equalisation. When hybrid or electric vehicles are in operation, significant power dissipation heats up their sensitive high-performance components to a far greater extent than it would the electronics in a vehicle with a combustion engine.

To protect the electronics from damage caused by extreme temperature fluctuations and keep them in the optimal temperature range, manufacturers most often turn to liquid cooling. However, this still carries the danger of condensation forming at the coldest point in the housing – corroding and possibly even destroying the electronics.

Figure 1: Humidity creates challenges to batteries and electronics packages in vehicles.

These high-performance electronics must also be protected against the pressure spikes that occur due to the difference between the internal and external temperatures. In large battery housings, these pressure variations reach an extent where they are almost insurmountable without effective temperature and pressure equalisation solutions. Even small differences in temperature can exert enough pressure on large housings to deform them.

Example: pressure equalisation in a high-voltage battery housing
The following example demonstrates this phenomenon using the pressure changes observed in an electric battery with a volume of 150 l measuring 100 cm x 50 cm x 30 cm. Let us assume that the volume of free air within the housing is 50 l. In the 30-minute journey from Innsbruck (570 m above sea level) to the Brenner Pass (1370 m above sea level), the electric vehicle will have gained 800 m in altitude. In an electric battery with no ventilation, this leads to a positive pressure of 90 mbar, a difference that cannot be equalised even over a 15-minute break at a service station and that puts constant pressure on the seals (figure 2). This 90 mbar of positive pressure is equivalent to around 450kg acting on a surface of 0.5 m2. No housing built using lightweight engineering techniques will be able to withstand that sort of force in the long term. And while the seals are designed to cope with high levels of stress, this sort of extreme strain will eventually lead to a porous and inadequate seal for the housing.

Figure 2: Pressure difference caused by altitude change in a battery (50l free volume); ride from Brenner pass (1.370m above sea level) to Innsbruck (570m) plus 15 mins of break in Innsbruck. Red: unventilated; green: ventilated.

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