Batteries in quarantine

More and more vehicle manufacturers are launching electric cars on the market – and testing these in crash tests beforehand. This is not without risk, which is why vehicle safety tests with e-cars require a special procedure and additional safety measures. IAV’s crash facilities in Gifhorn and Ingolstadt are staffed and technically prepared for all eventualities – including decay tank and insulated forklift truck.

In conventional vehicles, crash tests follow a relatively simple script: The car is disassembled for the purpose of installing sensors and cameras. After mechanical and electrical preparation, the dummies take their place inside. Now the climax: At ten to 80 kilometers per hour, the test vehicle crashes into an obstacle. A photo analysis on the crash plate provides initial findings on the damage. More details emerge later when the car is disassembled for further analyses. So far, everything is a well-practiced routine – there is hardly any danger for the team in the crash hall.

Electric cars with their high-voltage (HV) systems are fundamentally changing the tests. ” Without properly designed safety precautions, people’s lives are at risk here.

«Future demands on the range of high-voltage vehicles are leading to the use of higher and higher voltages. While voltages of around 48 volts were the norm for the first hybrid vehicles, today there are voltages of up to 800 volts in battery-electric vehicles. In the future, even more than 1,000 volts can be expected.»

Dr. Burkhard Scholz — IAV Fahrzeugsicherheit GmbH

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High-voltage system first switch to inactive

Before a crash test, the vehicle is fitted with the sensors with the HV system switched off. In addition, voltage and temperature are measured at the battery. The next step is the commissioning of the software, which is particularly complex because of the new wiring system architectures. “All the components have to work because everything is connected to everything else,” says Florian Mayr from IAV Fahrzeugsicherheit GmbH. “Even the exterior mirror has to work, otherwise nothing works.” Once the software is updated, the e-vehicle is metrologically prepared. After this, itmrolls onto the crash track, always accompanied by a specially trained electrician. Now the crash can take place.

Not only the preparation, but also the phase after the crash differs significantly from tests with conventional cars. “We have to quarantine the vehicle for at least ten minutes, because a battery fire does not happen suddenly,” says Scholz. “During this process, there are always two firefighters in protective suits standing by. They are equipped with thermal imaging cameras and gas detectors.”In an emergency, they use a forklift truck with insulated tines to tow the car to a pool of water, where it only poses little danger still to its surroundings in the event of a fire. “Burning battery modules cannot be extinguished. However, the waste heat causes other modules to be destroyed,” Mayr explains. “In the past, this has led to complete vehicles burning down.”

Intensive staff training

After the quarantine, an electrician checks whether the HV voltage is switched off and the body is voltage-free. Only after this are the test results documented. However, this is not the end of the complex procedure: A second quarantine may follow for 24 hours in a special garage. “Because problems with the battery can still occur,” Mayr explains. “This is why, depending on the situation, we use battery monitoring to measure whether the temperature or voltage is behaving conspicuously.” If this is the case, the battery monitoring system sends a message to the emergency call system, leaving enough time for countermeasures. Should the car be used for further tests – up to five crashes per vehicle are possible – the next tests are prepared. To do this, the IAV experts will have to get the cooling system going so that the battery can be charged, among others.

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“E-vehicles pose a manageable safety risk during testing,” Scholz sums up. “But as with all new topics, we have to take a lot of precautions with the procedures and train our personnel intensively.” The qualification takes place internally and externally at TÜV and is oriented to the qualification levels stipulated by the German Statutory Accident Insurance .

In Ingolstadt alone, IAV runs ten tests a week and around 400 a year – and the trend is rising. The company operates one of the most modern crash facilities in Europe there and can support customers in any crash phase with e-mobility. “We have trained employees at all levels,” Scholz emphasizes. “Thanks in no small part to our employees and our modern infrastructure and measurement technology, there has never been a major accident to date.”

The article appeared in automotion 02/2021, IAV’s automotive engineering trade magazine. Here you can order the automotion free of charge.

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