Injection molded asymmetric spur gear — development and preliminary performance evaluation

Abstract

Innovative gear designs are essential to meet the increasing demands of high load carrying capacity, high endurance, low cost, long life, and high speeds in automobile, aerospace, and wind turbine industries. Conventional gears are having symmetric teeth; however most of the applications necessitate power/motion transmission in one direction. This unidirectional transmission leads to the design of asymmetric teeth in a gear. Extensive research work on design and optimization and asymmetric gear tooth profile for improved bending and contact strength has been attempted. However, very little experimental investigation has been attempted and no work has been attempted in the experimental investigation of asymmetric polymeric gears. In this work, unreinforced polypropylene material is injection molded for the asymmetric spur gears. Gears are molded to the size of 3 mm module, 18 number of teeth and having pressure angle of 34° and 20° at drive and coast side respectively. To examine surface durability and the kinematic characteristics of asymmetric gear, a gear test rig is developed in the laboratory with permanent magnet direct current motor and powder clutch dynamometer as driving and power absorption unit with necessary inline torque sensors and non contact temperature sensor. Preliminary transmission efficiency and surface temperature of test gears promises wide scope for asymmetric composite gears in motion transmission application. Due to the increase in pressure angle at drive side of gear tooth, relative sliding velocity found to decrease and hence asymmetric gear exhibit superior gear pair efficiency and less surface temperature.