Using leak testing in the mass manufacturing of electric vehicles is relatively new, since the transportation industry is accustomed to testing internal combustion engines and turbojets. The drive away from fossil fuels and CO2 emissions has driven the development of new technologies. These new devices present new challenges for production-line leak testing. Testing for leaks in one submarine electric motor or battery system per year, versus leak testing thousands of vehicle motors per day, requires very different testing solutions.
e-Mobility is not for toys and prototypes anymore
e-Vehicles can range from an electric-assisted bicycle, a fully electric motorbike or scooter, a fully electric car or hybrid vehicle, to small electric drones and even large aircraft. ATEQ, with its technical focus and culture of innovation, has found new ways to test these components for mass manufacturing.
The first basic component of every battery is a cell. A battery is a collection of cells. To keep the weight low, battery cells are frequently packaged in flexible pouches. ATEQ has developed a leak test method (patent pending) for testing these pouch cells using ionised air technology. It allows for the testing of pouches, even without evaporating solvent.
The ionised air test can provide a leak test result for the whole pouch and it can also be used to locate the leak’s location in the cell. For metallic body cells, ATEQ also has a test method that detects the evaporation of the solvent. Each battery cell has a semi-permeable membrane that separates the battery’s positive and negative sides. This cell is flow tested prior to assembly to make sure the air flows through the membrane within the designated specifications and that there is not an unexpected hole in the membrane.
Cells can be packaged together in a module with a protective envelope for easy handling. At this stage, the module housing is generally not leak-tight but sometimes a pressure decay leak test is used to test the module housing. Since a group of cells does not reach full charge if the cells are not at an identical charge level, ATEQ has developed a module balancer to even out the charging level of cells during the manufacturing or maintenance process. The cells or modules are packaged together in leak-tight protective housings to protect them against dust, water and mud splashing. Whether it’s the 12 V battery of a classical internal combustion engine vehicle, a small bicycle’s rechargeable battery or a fully electric vehicle-sized battery, the leak tests all function similarly.
These battery housings and covers are tested for leaks separately before the cells/modules are mounted inside. If the housing is plastic, a differential pressure decay test with noise cancellation technology can be used to test for overall leaks in battery covers. If there is a desire to locate the defect in the cover, an ionised air leak test can be used. If the cover or tray is metal, only pressure decay technology with noise cancellation can be used. To locate leaks on a metal cover, a forming gas (H2N2) leak detection and localisation with ATEQ’s H6000 portable gas-sensitive detector is the solution. ATEQ also proposes to automate this test with a smart holding robot.
Once the battery cells and modules are assembled in the housing, a final leak test needs to be performed. It can be done using pressure decay or air mass flow technology, with very low pressure drop sensors to quickly measure leaks. ATEQ’s patent-pending Differential Noise Cancelling (DNC) technology blocks out background conditions from the leak reading. The housing typically has a semi-permeable membrane that enables the air pressure to equalise with atmospheric and temperature changes. This semi-permeable membrane lets air through, but not water.
ATEQ has an air flow tester to test the breathing patch to ensure it is not double-stacked and that it has not been poked or punctured. The tester can also perform a wet test which puts air over water to detect smaller defects at the sub-assembly level. Some batteries have a check valve instead of a breathing patch to relieve the pressure generated by any gases produced during charging. This check valve is tested with air pressure to look for openings, ‘cracking’ pressure and flow using an ATEQ ERD leak tester.
Some large battery housings can be equipped with a liquid cooling circuit, which is itself tested for leaks with an air tester. For large battery failure analysis, a forming gas sniffer can be used to locate leaks, since air leak tests cannot show leak locations. Gas sniffer leak tests are also useful for troubleshooting potential leaks in a fixture.
The disadvantage of using a tracer gas leak test on large batteries is that the tracer gas can take a lot of time to mix with the atmospheric air inside a battery if there is no tracer gas current across the battery. It is recommended to fully evacuate the atmospheric air from the battery tray or cover prior to pressurising it with tracer gas, since the tray/cover cannot sustain much vacuum. It is also recommended to monitor the tracer gas concentration on multiple sealed openings in the battery to verify that the tracer gas has reached every corner of the battery.
Based on ATEQ’s experience with aviation battery testers, the company can make custom battery testers that charge and discharge an entire battery.
Fuelling the charge
A fuel cell creates chemical energy by combining hydrogen, or any other combustible gas, with oxygen from the air and turning it into electricity for the vehicle.
The fuel-side components are typically tested for leaks with a mix of 5% H2 (hydrogen) and 95% N2 (nitrogen) – known as forming gas. Contrary to pure hydrogen, forming gas is not flammable, and it helps detect defect areas that hydrogen could flow through. The air side is typically tested for leaks with an air pressure decay or mass flow instrument. The fuel cell’s semi-permeable membrane should be tested for air flow, and the vehicle’s cooling system is leak tested with an air tester.
The upstream fuel storage and delivery systems are also tested for leaks, with air or forming gas, depending on the application. The electric motors that operate the wheels are in leak-tight housings that protect the motor against splashing water. A motor housing made of plastic can be tested using ionised air when it is not mounted. If the housing is metal, or fully assembled, it can be tested with air. The motor coil wires are coated with an insulating ‘varnish’. At times, this gets cracked, mainly where the wires are bent. ATEQ has developed a test to detect this defect using ionised air technology.
The latest electric vehicles also come with automated driving assistance that uses sensors to sense the environment. Whether they are cameras, lidar or something else, the sensors are in leak-tight housings since they are exposed to the elements. ATEQ also tests the TPMS (tyre pressure monitoring system) sensors, during wheel and vehicle assembly and for maintenance level. An air leak test is generally preferred to test these sealed sensors.
At times, a car battery cannot sustain a fast enough injection of electrical charge, so the energy has to be stored in a large capacitor to protect the battery. ATEQ has an instrument designed to safely discharge these capacitors before servicing the vehicle.
Electric doesn’t just mean batteries
In addition to the new electric vehicle leak testing applications, it is important to remember that many of the traditional automotive air leak testing applications still exist within an EV, such as brake systems, headlights, taillights, ABS and central computer electronics, steering components and air conditioning systems.
With the accelerating shift toward electric, hybrid electric, plug-in electric, and fuel cell technologies, OEMs must introduce new models to the market quicker than ever to stay competitive. However, this means that vehicle makers will face many new challenges during the manufacturing process, such as the increasing complexity of new vehicles, new technologies not yet fully mastered, and the increased pressure to achieve the highest level of quality to avoid security risks and vehicle recalls.
To address these new challenges, ATEQ offers leak, flow, battery and TPMS testing instruments to ensure the quality testing of numerous components throughout the electric vehicle manufacturing process.
ATEQ application engineers are familiar with existing electric vehicle leak test applications. They also have the capabilities to design a new leak testing solution for an application that has never been leak tested before, backed by hundreds of experienced professionals who are trained in leak testing technologies. With offices and engineers all over the world, ATEQ is able to provide local assistance in developing the perfect quality testing solution for your application.
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