Article Journal of Vibration and Control 2020, Vol. 0(0) 1–9 © The Author(s) 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1077546320937634 journals.sagepub.com/home/jvc Reducing the vibration of bearing units of electric vehicle asynchronous traction motors Vasiliy Migal 1 , Anatoliy Lebedev 1 , Mykhailo Shuliak 1 , Evgeniy Kalinin 1 , Shchasiana Arhun 2  and Vladimir Korohodskyi 2  Abstract The impact of the accuracy class of bearings, rotational speed, load, clearances, and fits on the vibration levels of electric motor bearing units is investigated. The ways to reduce the vibrations of mechanical origin are offered. The boundary vibration levels of asynchronous motors limited by vibration levels of 40 dB at a frequency of 5 Hz and 80 dB at a frequency of 10,000 Hz are determined. The effect of increasing the rotational speed and load on the vibration levels of bearing units has been determined, and reserves for reducing vibration while ensuring the optimum bearing preload on the shaft journal have been identified. It is established that the clearance between the cap and the bearing when it is fixed in the housing (primer) does not ensure the unambiguity of the bearing unit assembly, which results in a large variation in vibration levels compared with rigid and elastic fixation. The results of this research can be applied to all types of traction electric motors. Keywords Electric car, asynchronous traction motors, vibration level, bearing, bearing unit, electric motor vibration class, vibrodiagnostic 1. Introduction Traction electric motors (EMs) of vehicles operate in a wide range of rotational frequencies, in varying load conditions, frequent stops and starts, and in difficult road conditions. The specified conditions result in an increase in vibration loads of EMs and, accordingly, to a decrease in reliability and service life of the latter. Therefore, vibration levels are the main criterion for assessing the quality of EMs; on the basis of which design and production defects are determined, and during opera- tion, their malfunctions. Reducing the vibration levels of EMs makes it possible to increase their reliability, dura- bility, service life, reduce the harmful effects on humans and the environment, and reduce the cost of car maintenance. The main weak link in the mechanical system of asynchronous EMs is in bearing units. They transmit the total force effects from rotating machine parts and them- selves present the sources of the periodic and nonperiodic dynamic and vibration effects occurrence. Electric vehicles appear to be one of the viable solutions in face of the growing concerns for environmental pro- tection and the fast rate of depletion of the world’ s fuel oil supplies. Electric vehicles can become a viable alternative to the internal combustion engine provided that they are able to meet certain reliability, safety, performance, and cost criteria (Nanda and Kar, 2006; Sendek-Matysiak, 2019). Mechanical losses in asynchronous EMs primarily oc- cur because of friction in the bearing assemblies, and in direct current (DC) motors and additionally, when brushes with slip rings are sliding. About 40–60% of all early EMs failures are caused by bearings (Farfan-Cabrera, 2019). Most bearing failures result from improper or insufficient lubrication (Walther and Holub, 2014). Consequently, rotor bearings and brushes/slip rings can be considered as critical tribological elements in EMs that should be optimized in the future (Farfan-Cabrera, 2019). 1 Kharkiv Petro Vasylenko National Technical University of Agriculture, Ukraine 2 Kharkiv National Automobile and Highway University (KhNAHU), Ukraine Received: 17 April 2020; accepted: 5 June 2020 Corresponding author: Shchasiana Arhun, Vehicle Electronics Department, Kharkiv National Automobile and Highway University, 25, Yaroslav Mudryi Street, Kharkiv 61002, Ukraine. Email: shasyana@gmail.com