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There is a growing and prevalent trend in the power transmission field of high-performance polymers replacing metallic materials given the strict light-weight requirement. Polymer gears exhibit a low elasticity modulus, high-temperature sensitivity, and increased geometric design flexibility, presenting technical challenges to the straightforward application of metallic design methods to polymer gear systems. This study is centred on the development of a high-power-density polymer gear transmission system for the accessory unit of a gas turbine engine, utilising an adaptive NSGA-III algorithm and surrogate sub-models. A comprehensive assessment indicator for the operating performance of the transmission system is suggested, encompassing gear strength, bearing temperature, and shaft torsional stiffness. The model made it possible to simultaneously optimise forty-six structural parameters, including gear tooth module, web thickness, and bearing clearance. In contrast to the original steel design scheme, the optimised polymer gear transmission system indicated a 49% reduction in weight and a 1.96-fold increase in power density. This presents a method for substituting steel with polymers for effective power transmission.

With the increasing requirements of power density，load capacity and service life of gear transmission for aviation，wind power and other equipment，gear contact fatigue failure has become an important bottleneck limiting the service performance and reliability of modern gear equipment，and the material microstructure characteristics determine the fatigue performance of gear and other service parts. Through the surveys of the current related research situation both at home and abroad，the main microstructure features of gear materials such as retained austenite，carbide，grain size and their influence on the contact fatigue performance of gears are introduced. The reported numerical simulations of gear contact fatigue based on microstructure modeling and micromechanics constitutive model are summarized to describe the microscopic mechanical behavior of in gear contact fatigue，and to improve the understanding of the key characteristics and mechanism of gear fatigue. The various contact fatigue failure forms of gears occurred in the engineering practice are expounded in detail，and the main factors affecting the contact fatigue failure of gears，the induced microstructure evolution and degradation of mechanical properties，as well as the potential mechanisms of the gear contact fatigue failure，are analyzed. This review aims to provide the further understanding of the relationship between microstructure evolution characteristics and mechanical property degradation during the service process of gears，as well as the internal mechanism of contact fatigue failure，and providing the reference for anti-fatigue design and manufacturing method of high-performance gears.

Planetary roller screw mechanism (PRSM) is a novel high-performance linear transmission device. The non-uniformity of load distribution over PRSM threads is a vital problem severely affecting its load-carrying capacity and service performance. This work aims to develop a PRSM load distribution improvement approach with good manufacturability and general applicability. A roller taper modification method for load distribution optimization is proposed based on the deformation compatibility and force equilibrium, then the roller grinding experiment is carried out. Finally, the effects of external load and thread number on load sharing optimization are analyzed to examine the applicability. The results show that the maximum reduction in load sharing coefficient reaches 31.4% after roller taper modification under the case studied. The taper modification of roller threads could be rapidly implemented by only adjusting the roller grinding angle. The roller grinding experiment results agree well with the theoretical values, and the maximum error is no more than 2 μm. As the external load and thread number change, the improvement approach still works well. The proposed method has been verified by comparisons with finite element simulations and available references. This work can provide theoretical guidance for the optimal design of PRSM and has good engineering application prospects.

To investigate the influence of the manufacturing parameters on mesh behaviors for harmonic gear drive, the mathematical model of slotting the circular spline was established using kinematic method based on the tooth profile of the circular spline. Considering the circular runout errors from the machine tool and slotting cutter, the influences of two kinds of circular runout errors on the transmission error for harmonic gear drive were analyzed. Then, the influences of the slotting cutter teeth number and the slotting cycles of the circular spline on the transmission error were discussed. Two circular splines were machined by two types of slotting cutters with different teeth number to verify the theoretical analysis. Results show that the influence of the machine tool's circular runout error on the transmission error is more significant than that of the slotting cutter's circular runout error. For the slotting of the circular spline with one circle, the transmission error is the smallest when the tooth number of the slotting cutter is one third of that of the circular spline. For the slotting of the circular spline with two or three circles, the transmission error is the smallest when the tooth number of the slotting cutter is two thirds of that of the circular spline. However, the transmission error of harmonic gear is the largest when the tooth number of the slotting cutter is half of that of the circular spline.

Based on the spatial position relationship of spiral bevel gear, mathematical model and mesh model applied with finite element analysis (FEA) approach has been established. The influence of axial position errors of pinion and wheel, offset error, and shaft angle error on the meshing characteristics has been investigated. A method has been proposed to compensate the gear assembly errors by the axial displacement of the pinion and wheel, and the correctness of this method verified by numerical examples. The performed results indicate that the existence of assembly errors can cause contact pattern on the tooth surface to deviate from its design position, resulting in poor meshing quality and having a certain impact on transmission error (TE) and peak-to-peak transmission error (PPTE). The pinion and wheel's axial positioning errors can be offset by each other, whereas the offset error and shaft angle error can be mitigated by the interplay between the axial positioning of the pinion and wheel. By compensating for assembly errors with axial displacement, the position of the contact pattern can be precisely controlled, and TE will not significant changes. [ABSTRACT FROM AUTHOR]