| Difficulties in increasing the lifespan and precision and reducing the noise of synchronous belt have become the bottleneck problems in the application and development of synchronous belt. Double helical synchronous belt is among the hottest research topics in the belt-transmission field after the straight- and helical-toothed synchronous belts. The tooth arrangement of double helical synchronous belts is superior to that of straight- and helical-toothed synchronous belts in terms of the mechanism of meshing transmission, and is the key to solving the bottleneck problems for a technological break-through.Difference exists in the mechanisms of complete and incomplete meshing regions between double helical synchronous belt and pulley. This study aimed at improving the performance of transmission system by optimizing tooth profiles of both belt and pulley with different(complete and incomplete) meshing mechanisms. Built on recent advancements as well as the theory of coordinated conjugate meshing with high-order contact, the current study further developed a new normal-plane tooth profile model of double helical synchronous belt with arc-shaped teeth, which are characterized by a minimal backlash during transmission, coordinated tooth profiles, high contact strength at tooth surface, and an infinitely-small order-3contact backlash. Utilizing conformal mapping with complex function based on plane elasticity mechanics, normal-plane tooth profile parameters and a mathematic model for calculating the relationship between load and stresses teeth of asynchronous belt were established. The effects of variables related to tooth profile on tooth stress was studied, which reveal their coupling relationships and patterns among parameters. Major parameters that affect tooth stress were identified. A model of the three-dimensional finite element analysis of belt-pulley or rigid-flexible coupling was established. The influence of helical angle, backlash, and pulley structure on the stresses and deformation of belt tooth and the reinforcing layer and their relationships were studied with important determinant parameters identified. A three-dimensional model for digital simulation of meshing transmission was established for the double helical synchronous belts with new profile in the complete and incomplete meshing regions. The effects of interference of tooth profile, pitch difference and double-helix’s angle and other related variables on meshing transmission performance were investigated. The relationship between tooth profile and related variables was revealed. Transmission’s structure and parameters related to tooth profiles were optimized.Research on key technologies for manufacturing double helical synchronous belt and pulley with new profile was initiated. Based on the characteristics of mold and the shape of the double helical tooth’s surfaces, tools for molding pulley and cutting belt teeth with double enveloping system were designed. Meshing boundaries, undercutting limit line, instantaneous contact line, secondary contact line and the formation of enveloping curve of the tooth profile during surface enveloping were characterized. The authors had not only identified the causes of vibration and shaking in the cutting and shaving process but also developed a method to reduce vibration and shaking. Sample belts and pulleys had been produced.Magnitudes in transmission errors, noise, and tooth fatigue wear were compared between the new double helical synchronous belt and the straight-toothed belt with identical transverse tooth profile. A model for assessing the dynamic transmission error of the new double helical synchronous belt with some characteristics of climbing tooth was established. The effects of belt’s width, helical angle, and the number of pulley’s teeth on transmission error were investigated. The mechanisms whereby the new double helical synchronous belt had high transmission precision were revealed: the reducing the helical angel was the key to reduce transmission error. Transmission error became minimal when the helical angel is an integer. The authors collected, analyzed and compared data about noise and fatigue wear in experimental investigations and found that transmission with double helical synchronous belt was steadier with less vibration and noise(the maximum noise was 11 d B under resonance conditions), compared with straight toothed synchronous belt. Compared with data from the literature, the new double helical synchronous belt reported here was better with a certain degree in reducing transmission noise. After 263 and 233 hours of running for the new double helical synchronous belt and the straight-toothed belt, respectively, examination under the optical microscope showed that fatigue wear of teeth ate posterior-lateral view was lighter in the new double helical synchronous belt compared with the straight-toothed belt. The locations and degree of wear are consistent with that predicted by theories developed in this project. These results demonstrated the superiority of the double helical synchronous belt with new profile compared with the straight-toothed belt by design. |
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