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Extend lifetime of automotive electronic components

Posted: 18 Aug 2014     Print Version  Bookmark and Share

Keywords:electronic components  pressure differential  inverter  venting solution  PTFE 

Nowadays, electronic components are playing a vital role in vehicles. It is therefore all the more important that sensitive electronics function reliably despite the extreme temperature differences and rough environmental conditions they have to withstand during a drive. The most effective solution is a membrane that protects electronic housings against contamination and fluids and provides air exchange and pressure equalisation at the same time.

All electronic components whether part of compressors, pumps, motors, control units or sensors for increasingly popular active security systems are subjected to huge temperature fluctuations throughout their service life. These can arise when the components housing heats up in operation and then comes into contact with cold spray from the road or at the carwash. These fluctuations in temperature can cause a significant vacuum to develop inside the electronics housing. The resulting pressure differential can be so strong that the seals and sealing components protecting the sensitive electronics can be seriously compromised, letting in dirt particles and liquids that can corrode the component and shorten its service life. Damaged or defective components usually have to be replaced, leading to high warranty and repair costs for automakers and their suppliers.

Higher challenges in electric and hybrid vehicles
One major challenge facing the automotive industry is the thermal management of high-performance electronics and batteries in electric vehicles, since these components need to operate in a certain temperature range in order to achieve optimum performance. They get very hot when running and need to be cooled using fluids. This can cause such huge temperature differentials within the electronic unit itself that condensate can form at the coldest point in the housing, which can lead to corrosion or cause a short circuit. For large battery housings, this problem can be so extensive that it is difficult to solve without effective measures to equalise temperature and pressure. Given the housings size, even minor temperature differentials can put enough pressure on the housing to cause deformation. In certain circumstances, driving a car out of a warm garage into the cold winter air can produce an interior vacuum that exerts a negative pressure of 500kg per square metre. Lightweight housings are scarcely able to withstand such pressure.

Figure 1: Pressure over times in vented vs unvented housing.

Membranes provide air and pressure equalisation
OEMs generally deal with these problems in one of three ways. The first option is to pot the electronic components. While this solution creates a perfectly sealed system, the unit ends up significantly heavier and cannot be reopened and repaired if it fails. Another way to achieve a hermetically sealed system is to use high-quality seals and thicker housing walls. The drawback of this system, however, is that it makes components more expensive and unnecessarily heavy.

A common and much more sensible solution is to incorporate a membrane that equalises the air inside the housing while at the same time preventing the ingress of liquids and dirt particles (figure 1).

The graph shows the continuous buildup of negative pressure within a hermetically sealed housing. In unvented housings, as little as 7 kPa of pressure can be enough to cause seals to fail after several temperature cycles. Vented housings equalise pressure and avoid seal leakage.

Use case: Vacuum in an inverter housing in the car wash
The following example explains the pressure conditions in an inverter housing during a drive through the car wash: Assuming that the inverters dimensions are 40 cm x 20 cm x 20 cm, which is equivalent to 16 l, the housing contains 4 l free air volume. While driving the inverter operates at a temperature around 70 C. The underbody of the vehicle is sprinkled with 8 to 10 C cold water in the car wash. Within only a few minutes the inverter is cooled down to about 40 C. Without a venting solution this temperature difference leads to an vacuum of 90 mbar. With every drive through the car wash this vacuum stresses the seals and leads to leaks in the long term. Oils, cleaning agents and other liquids can penetrate into the housing and threaten to damage or even destroy the sensitive electronics inside.

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