Failure Analysis of Random Vibration and an Effective Solution for Three-Phase Busbar of Flat Wire Motor Applied in Electric Vehicles

As flat wire motors have gained prominence in electric vehicles, the design of three-phase busbars, which are the weakest parts inside the motors, has become critical. The factors contributing to failure during random vibration experiment in design verification (DV) are analyzed using microfracture morphology and simulation analysis calibrated by using the modal test. It indicates that the primary cause of vibration failure is that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\sigma $ </tex-math></inline-formula> stress in solder joints of W-phase surpasses material yield strength in the original scheme. A proposed scheme involving coating on solder joints is presented to solve the problem of vibration failure quickly, effectively, and reliably. The analysis shows that the measures targeted at the solder joints can significantly reduce their <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\sigma $ </tex-math></inline-formula> stress. The coating scheme can reduce the stress from 349.9 to 92.1 MPa and the clamping scheme reduces it to 172.2 MPa. The proposed scheme has been validated through vibration and powered thermal cycling endurance (PTCE) experiments. The influences of structural size and the impregnation of winding ends on the stress of busbars are analyzed using simulation. The research also shows that the hardening length of soft copper bar and the impregnation of winding end have a significant impact on the stress of busbars.