Introduction: Automotive electrification is steadily moving forward. Whether using a conventional internal combustion engine or an electric power system, it is essential to protect sensitive electronic components during the life of the vehicle. Hybrids and electric vehicles face new technical challenges, and automakers and suppliers are only expected to meet these challenges with high-efficiency pressure equalization and waterproof and breathable components.
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Automotive electronic components are susceptible to harsh environmental conditions. Whether mounted under the chassis or in the engine compartment, electronic components such as motors, control units, sensors, compressors or electronic components in pumps are subject to extreme temperature fluctuations and must be protected against Intrusion of dirt or liquid. The degree of protection to meet the most basic requirements is IP6k9k, which ensures that the electronics housing is protected from dust particles, short-term immersion and steam.
Electronic components in automobiles with internal combustion engines and in vehicles with hybrid electric motors or electric motors face a common challenge: there is a difference between their operating temperature and the lower external ambient temperature. Parts heat up during vehicle operation, and if they come into contact with lower temperature roads that splash or wash water, their temperatures drop rapidly. This situation creates an extreme vacuum effect in the outer casing of the electronic component, causing air to enter the component through the seal. Over time, this poor pressure equalization creates stress in the seal and seal assembly, causing ingress of dirt particles and liquids, corrosive to electronic components and shortening their service life. Low-viscosity liquids and cleaners can exacerbate this risk of intrusion when used in vehicles.
Special challenges for electric and hybrid vehicles
The electronic components of hybrid and electric vehicles are subject to more harsh environmental conditions. Extremely high operating temperatures and larger electronic component housings make it more difficult for automakers and suppliers to balance temperature and pressure. Sensitive electronic components of the powertrain, such as electric motors, high-performance electronic components, chargers, start-stop generators, etc., must withstand extremely high temperature and differential pressures.
The reason is that the heat generated during operation affects these sensitive high-performance electronic components more than they affect the electronic components of traditional internal combustion engines. To prevent these high-performance electronic components from being damaged by extreme temperature fluctuations and allowing them to operate within the optimum temperature range, they are usually cooled with liquid. However, this method is also risky, it will form condensation at the lowest temperature in the outer casing, corroding electronic components, causing it to malfunction prematurely. On the other hand, sudden changes in temperature caused by contact with low-temperature sputtered water or car wash water while the vehicle is running can also damage electronic equipment.
Case Study: Equilibrium Pressure in Inverters and High Voltage Battery Enclosures
The following example demonstrates this by changing the pressure in the AC inverter housing while cleaning the vehicle. The inverter converts the DC output from the battery to AC for use by the motor. The object of the calculation is a casing measuring 40 cm x 20 cm x 20 cm (equivalent to a volume of 16 liters). In this example, one-quarter of the interior space of the enclosure is empty, that is, the enclosure contains 4 liters of free-flowing air. The temperature of the inverter can reach 70 °C during vehicle operation. When washing the car, cold water with a temperature of 8 ° C to 10 ° C will be sprayed to the bottom of the car, allowing the inverter to cool to 40 ° C in five minutes, as shown in Figure 1.
In a housing that does not utilize a waterproof, breathable product, this temperature difference can cause a vacuum of about 90 mbar. Whenever the vehicle passes over an area where cold water is accumulated, such a vacuum is formed, and the vacuum exerts a great stress on the seal ring, and after a certain period of time, the seal ring will leak. The consequence is that detergents, oils, chemicals and water enter the inverter casing and cause damage to sensitive electronic components. The addition of waterproof and breathable products ensures that the vacuum effect is quickly balanced and that sudden changes in pressure can be eliminated. The pressure in the outer casing of the waterproof and breathable product returns to ambient pressure in just six minutes.
For volume reasons, high-voltage batteries for hybrid or electric vehicles require a more efficient solution to equalize the pressure. The best way to do this is to use a waterproof and breathable solution with extremely high air permeability. Since the battery is only in contact with sputtered water rather than high pressure water, it does not require the same level of protection as the components inside the engine hood.
In this example, the battery casing has a size of 100 cm x 50 cm x 30 cm and a volume of 150 liters, of which the free air volume is 50 liters. In the 30-minute drive from Innsbruck (750 meters above sea level) to the Brenner Pass (1370 meters above sea level), the elevation of the electric car climbs up to 800 meters. In batteries that are not waterproof and ventilated, this condition produces a positive pressure of 90 mbar. Even after 15 minutes of waiting at the Yamaguchi rest station, the pressure is not evenly balanced, which causes permanent stress on the seal. A positive pressure of 90 mbar is equivalent to a pressure of about 450 kg acting on a surface of 0.5 m2, and the lightweight casing cannot withstand such pressure for a long time. Although the seal is designed to handle high loads, this extreme stress eventually causes it to fail, rendering the enclosure unsealed.
More dangerous than the positive pressure created in the outer casing when going up the mountain is the 90 mbar vacuum formed when going downhill. In order to equalize this degree of vacuum, air enters the outer casing through the affected sealing ring, bringing dirt particles and liquids therein, thereby forming condensation inside the outer casing, thereby causing damage. In the case of a waterproof and ventilated product, only about 15 mbar insignificant vacuum is generated, so that the sealing ring is not overloaded, and the pressure difference can be completely equalized in the 15-minute parking rest time, such as Figure 2 shows.
Breathable membrane technology for air and pressure equalization in hybrid and electric vehicles
To achieve pressure equalization and to ensure that motors, power electronics and high-voltage batteries remain reliable over their lifetime, waterproof and breathable solutions with vented membranes are required. Breathable membrane technology allows air exchange in a closed enclosure and also prevents the ingress of liquids and dirt particles. As seen in the previous high voltage battery example, for a particular application, the amount of gas permeability and water permeability are two fundamental parameters that determine the performance of the gas permeable membrane. The amount of air permeability refers to the amount of air passing through the gas permeable membrane at a given time and a given pressure difference. The amount of time required to equalize the differential pressure can be determined by the amount of gas. Permeability refers to the minimum hydrostatic pressure that a gas permeable membrane must withstand before it leaks. However, the amount of gas and water pressure are not the only variables: temperature resistance and chemical resistance are also important parameters of the gas permeable membrane module. Breathable film suppliers must choose the best combination of properties for the breathable film based on the specific waterproof and breathable application. For large battery cases that require a large amount of air to enter and exit quickly, and the degree of protection does not need to be too high, a gas permeable membrane can be used to obtain a higher gas permeability. The electronic component housing installed in the engine compartment needs to constantly cope with temperature peaks, so a high temperature resistant gas permeable membrane should generally be used. Because the challenges associated with specific applications vary, automotive manufacturers and suppliers should work closely with gas permeable membrane manufacturers to develop the most technically and economically viable solutions.
Automotive ventilation products in hybrid and electric vehicles
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