Parameter Study on Bending of Rectangular Copper Hollow Wire for the Use in Hairpin Stator Electric Traction Motors

Within the disruptive change of the automotive industry towards electric drives, it is necessary to continuously work on the development of product and process technologies for future electric drive trains. Besides the winding technology, the cooling of electric motors is a central field of research. Rising temperatures due to loss mechanisms fundamentally limit the performance capability of an electric motor. By directly cooling the active part of the stator winding the heat transfer gets more efficient, losses in the motor are reduced and power limits are enhanced. Using hollow copper wire and pumping a cooling liquid through the cavity represents one solution to the application of direct cooling. The combination of hairpin winding and hollow conductors thus offers great potential in the field of electric traction motors. A challenge in the application of hollow conductors is the bending of the wire so that the cavity retains its form and pressure loss is kept at a minimum. Therefore, in this work hollow wire is investigated for its bending properties and its behavior during bending. The influence of different bending angles on the characteristics of the hollow wire is evaluated and compared to the unprocessed wire. The results from the tests are held against results for different cross sections and shapes of hollow wires.