The paper describes a comprehensive study of a novel external spur gear design with physical separation between sliding and rolling motions in the contact point of meshing gears. The sliding motion is accommodated by shear deformation of a thin-layered rubber-metal laminate allowing very high compression loads. Kinematic conditions of such "composite" gear system were studied analytically. The mathematical concept and kinematics of the novel external spur gear was fully developed and optimized for better suitability of the concept for engineering application of the gear in the power transmission. Closed form solutions were obtained for two different shapes of the composite tooth core, and were optimized for a gear pair used in the final stage of a helicopter rotor transmission. Static FE stress analyses was also performed, using the finite element approach for complex meshing conditions involving interaction of metal and elastomeric (rubber) materials. The results obtained for the composite gear system compare beneficially to the conventional involute gears. The displacement of the tooth core can be reduced by 25%, because of the load distribution by rubber--metal laminate which leads to the reduced transmission error and sequentially decreases noise and vibration of the power transmission. The contact forces in the tooth core can be reduced by 60%, which relaxes the requirements for the contact strength and costly annealing of the gear. A working prototype was built and tested for the analyzed model, and has shown a good correlation of the strain data as well as kinematics.
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