Rheometer-Based Cogging and Hysteresis Torque and Iron Loss Determination of Sub-Fractional Horsepower Motors

Stefan Leitner*, Georg Krenn, Hannes Grübler, Annette Muetze

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Accurately measuring the cogging torque, hysteresis torque, and iron losses of permanent magnet (PM) motors is a challenging task. This is especially true for sub-fractional horsepower (SFHP) variants used, e.g., in auxiliary drives for automotive fan and pump applications. Their cogging torque and hysteresis torque peak values are often in the sub-milli-Newton meter range, causing conventional measuring methods and devices to fail as especially friction impedes the measurement significantly. Moreover, their iron losses are hard to determine and usually merely estimated in the literature. This article presents an unconventional rheometer-based method to determine both 1) the cogging torque and hysteresis torque of SFHP PM motors and 2) their iron losses by evaluating the observed offset torque. Two SFHP outer-rotor PM motor topologies for fan applications are analyzed, i.e., a claw-pole motor and a salient-pole motor. The results show that, with the proposed setup, settings, and evaluation, a rheometer can successfully be used to determine the cogging torque and hysteresis torque waveforms in the sub-milli-Newton meter range and the iron losses of SFHP motors, both with excellent accuracy.

Original languageEnglish
Article number9079654
Pages (from-to)3679-3690
Number of pages12
JournalIEEE Transactions on Industry Applications
Issue number4
Publication statusPublished - 1 Jul 2020


  • Brushless motor
  • claw-pole motor
  • cogging torque
  • eddy current torque
  • hysteresis torque
  • iron loss measurement
  • permanent magnet (PM) motors
  • rheometer
  • salient-pole motor
  • sub-fractional horsepower (SFHP)
  • torque measurement

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Control and Systems Engineering
  • Industrial and Manufacturing Engineering

Fields of Expertise

  • Mobility & Production


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