Improvement of the transmission efficiency in electric vehicles by using double staggered helical gears with shortened teeth

Abstract

The application of double staggered helical gears with shortened teeth is proposed to increase the efficiency of gear reducers applied in electric vehicles. The staggered helical gears are designed with short addendum and dedendum as well as a phase angle between their two parts. Reduction of power losses is achieved by avoiding contact between tooth surfaces where the sliding velocities are larger, since the meshing occurs in areas close to the pitch circle during a longer period of the cycle of meshing. The calculation of the efficiency is based on the application of the finite element method through two algorithms for post-processing the obtained results. The first one is based on the use of tangential forces and sliding velocities to compute the power losses along the cycle of meshing. The second one is based on the determination of the input and output powers through the torques and velocities at the pinion and gear reference nodes of the finite element model. A constant friction coefficient is being considered between the contacting tooth surfaces for all the geometries. Several two-stage gear transmissions are analyzed and compared, considering standard helical gears and their counterpart double staggered helical gears with shortened teeth, different facewidth-to-module ratios, and different helix angles. The results show an improvement in the efficiency about 1.8 percentile points among the compared geometries.