Finite Element Analysis and Optimal Design of DC Brush Motor for Automotive Engine Start Applications

The purpose of this paper is to study the DC brush motor used in automobile engines. In the research, the diesel generator starting motor of the 4-pole 21-slot internal structure is used as the reference object prototype. The finite element magnetic circuit analysis software, RMxprt and Maxwell 2D by ANSYS, are used to modeling and analyze the transient magnetic field characteristics in a parametric manner. The electrical and magnetic characteristics including induced electromotive force, armature current, electromagnetic torque, rated speed, magnetic flux density and magnetic field distribution of the magnetic circuit are discussed. With the geometric dimensions of the reference motor, different stator and rotor core materials, the finite element analysis software RMxprt is used to quickly establish a DC brushed motor model. The results of the RMxprt were analyzed by two-dimensional finite element analysis software Maxwell 2D. Two improvement schemes are proposed to optimize the pole core. One is to cut the pole core into two parts, using different materials as the pole core, which can reduce the magnetic saturation phenomenon at the tip of the pole core. The second way is digging holes in the front pole tip forced the magnetic distribution toward to the rear pole tip for improving the magnetic saturation phenomenon. In the paper, the optimal design of the hole in the front pole of the pole core was selected. The stator structure was optimized by the Taguchi algorithm for maximum output power. At the rated speed of 3,400 rpm, the output torque after the reducer was 73.44 N-m, the output power can be as high as 7.69 kW, verified the feasibility of the improvement strategy.