Permanent Magnet Direct Current Motor Thermal Simulation to Predict Its Temperature Rise during Eaton Automotive Rear Axle Differential Operation

Eaton’s automotive rear axle differential is used in vehicles to improve stability while experiencing variable road conditions. It adjusts the power ratio between wheels to reduce wheel spin and add understeer. A Permanent Magnet Direct Current (PMDC) motor is used to develop hydraulic pressure, which is converted into a bias torque across the axle.

Heat generated in a PMDC motor during transient operation can affect its torque output due to changes in current. The variation in motor torque can impact the rate at which hydraulic pressure is developed. Because of this, the differential performance can be affected. A three-dimensional (3D) transient numerical simulation methodology has been developed to predict temperature rise at critical PMDC motor locations when subjected to a transient duty cycle. Heat load required for simulation is calculated using motor current and efficiency curve, thereby eliminating multi-physics simulation. Two modeling approaches, Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD), are described with their advantages and limitations. Model predictions agree with literature findings and correlated with test data with 21°C deviation.