51 E-Mobility Engineering | July/August 2026 winding, assembly and impregnation processes, new laser stripping and brazing, increased rotor balancing accuracy, new high-capacity ovens, stator laser welding and complete stator quality control, covering dimensional, electrical and leak testing. These boost YASA’s capability to create complete motor sets while improving repeatability and reliability, and introduce more flexibility by eliminating bottlenecks in the component supply chain. Cooling The elements for cooling the motors to ensure a stable thermal environment are a major challenge for the production process. Heat losses during operation cause the temperature inside the electric motor to rise, which reduces the performance of the machine due to temperature-dependent material properties. In addition, the output is often deliberately reduced for a certain period of time to protect the components. “We use direct oil cooling. One way is to use a carbon fibre tube in the air gap so you are sealing the stator and oil can flow in the winding slots. This tube needs to be very thin otherwise you increase the air gap,” says Meister at AVL. “A new patent we have applied for removes the carbon fibre tube and we close off the stator slots directly so the air gap remains unchanged. It’s an additional manufacturing process step but this increases the permanent power. The ratio of permanent power to peak power increases significantly from 3:1 [33%] or 2:1 [50%], and we achieve over 70%. “For example, in a heavy-duty truck application, if you want to maintain a constant speed going uphill you need 70–80% of peak power. With a ratio of 2:1 you need a huge machine. With this new e-motor you can reduce the size significantly and you gain back the investment in inserting additional components,” he continues. Hyperdrives in Germany is working with RWTH Aachen University on a twoyear project to develop processes for producing hollow conductors in motors for cooling. “The thermal design of electric motors – especially if their compactness and performance are to be maintained – is one of the current challenges in the production of electric mobility,” says Prof Kampker. “Production-related qualification of the hairpin stator process chain for the processing of rectangular hollow conductors for use in traction drives.” Hollow conductors allow for direct cooling of the motor, where indirect cooling methods have been used until now. The outer cross-section and cavity can be of different shapes such as rectangular, circular or other types. In the case of direct cooling with the help of hollow conductors, a cooling medium flows through the conductors and thus dissipates the heat generated in the active part of the winding. “Therefore, hollow conductors offer significant potential for increasing the efficiency and performance of electric drive machines,” says Till Backes, project manager at PEM. End-of-line testing For end-of-line testing, a fingerprint of a known good machine is compared with the produced machine. This covers the complete NVH behaviour and the forces acting on the motor. “We have dedicated sensors based on piezoelectric technology where we fix the sensor on the baseplate fixture, the motor is attached to the sensor, and we measure dynamically the reaction forces and torque of the motor in a 30 second acceleration”, says Alban Hemery, department manager for E-Motor Test Systems. “It takes 1 to 2 minutes to attach the stator and run the test. In the past, the machines were fully connected with a load and the testing time was about five minutes. “The other element is the software and control. There is a lot of flexibility and the switching frequencies of the inverters are going up and that can trade-off NVH and efficiency and the integration into the vehicle. NVH is an issue when you increase the speed. Now, with centralised architectures, there can be limited control on the inverter and the control moves to the centralised compute.” An end-of-line e-motor test cell (Image: AVL)
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