Fundamental development of hypocycloidal gear transmissions

Abstract

The objective of this research is to push the Electro-Mechanical (EM) actuator technology forward and make it capable of meeting increasingly demanding requirements by improving gear transmission technology which has the most significant effects on actuator performance. The research presents in-depth parametric design and analysis of the Hypocycloidal Gear Transmission (HGT) and its circular-arc tooth profile. This unique combination is claimed to provide exceptional advantages including very high torque to weight/volume ratio, quiet and smooth operation under load, almost zero lost motion and backlash, very high efficiency, and insensitiveness to the manufacturing errors. Careful parametric design of the highly conformal, convex-concave circular-arc tooth profile and its tip relief can further enhance the performance of the HGT by dramatically improving the Hertz contact property, and maximizing the contact ratio. This high contact ratio leads to ideal load distribution and gradual pickup/release of the vii load (minimization of tooth-to-tooth impact). One of the key deliverables of this research is to provide a parametric design guideline for the HGT employing the circular-arc teeth. Several analyses were performed to establish the claimed advantages. In the tooth meshing analysis, clearances/interferences and kinematics of the contacts were analyzed for understanding of the contact characteristics of the HGT. Parametric decision based on this analysis also provided an exceptionally low pressure angle for one of the prototype HGTs. In the loaded tooth contact analysis, real contact ratio under tooth deformation and load sharing factor were analyzed for demonstration of an effective ‘self-protecting’ feature, which made the HGT suitable for extremely heavy load applications. In the efficiency analysis, friction power losses in the prototype HGTs were evaluated to verify the claimed high efficiency. Finally, effects of manufacturing errors on the contact properties were analyzed for visualization of the error-insensitiveness of the HGT. This report successfully proves that the HGT is a promising architecture for use in EM actuators. Sponsored by Navy and DOE, two EM actuator prototypes which employ the HGT as a key component have been built, and set up for performance tests. The design and analysis of these prototype HGTs have been fully documented in this report.