Higher Quality Internal Gears
By Dwight Smith, VP, Mitsubishi Heavy Industries America

Automotive gear manufacturers have implemented significant improvements in external planetary gear manufacturing yielding quieter gears. In addition, process stability has increased due to the post-heat treatment finishing processes employed. Beyond planetary pinions and sun gears, external transfer and final drive gears are commonly ground or honed, or in some cases, ground and honed. Add to this the widespread use of low pressure or vacuum carburizing, the current bill of process for automotive gears bears little resemblance to the hob and shave pre-heat treat processes of 20 years ago. As hybrid and electric vehicles are developed and brought to market, the demand for quieter gears continues to rise. In planetary gear systems, the internal ring gear is the final frontier for improvement to meet the requirement for quieter transmissions. This article explains various complete solutions for cutting and finishing internal ring gears.