The convective heat transfer coefficient of different tooth surfaces and the friction heat flux were identified based on the theory of tribology, heat transfer, and gear meshing theory. A more accurate parametric model of finite element thermal analysis of a single tooth was established by using APDL and the more accurate bulk temperature field of the gear was obtained. The factors that affect the bulk temperature field of gears were also analyzed, and the influence mechanism of each factor was carried out. The results show that high-pressure angle and tooth profile modification cannot only effectively reduce the bulk temperature of the gear, but also benefits the distribution of the bulk temperature. Long-addendum gear is beneficial to the distribution of the bulk temperature. The bulk temperature is proportional to the initial temperature of the lubricating oil. The variations of the equivalent curvature radius, the stiffness and the load sharing ratio of the meshing point are the ultimate cause of the change of the bulk temperature. The results of this paper can provide a more accurate and practical method for obtaining the bulk temperature of the gear, and it also can provide a theoretical basis and method to improve the thermal behavior of gears.

The two-parallel shaft gear transmission system is the most widely used system among the multi-stage gear transmission systems. The dynamic characteristics analysis of the two-parallel shaft gear transmission system is of great significance for nonlinear behavior research and noise control of gear transmission systems. This paper establishes a dynamic model and equations for the two-parallel shaft gear transmission system. According to the solution to the dynamic equations, the effects are studied of parameters such as speed, damping, modulus, and precision on the dynamic characteristics of the system. The results provide the basis for reducing vibration and noise control in multi-stage gear transmission systems.

Gear drives are widely used in mechanical driving devices, and the heating problem of gear has been paid much attention. The tooth surface temperature field of spur/helical gear is compared and thermal characteristic of spur/helical gear is studied in this paper. The calculation formula of frictional heat flux and convective heat transfer coefficient, which considers different surfaces of gear tooth, is derived. The frictional heat flux of the helical gear is different from that of the spur gear, and the calculation method is different. The finite element parametric model for thermal analysis is built and it realizes the automatic parametric modeling, loading, and generation of temperature field by ANSYS parametric design language (APDL) program. The influence of different parameters on gear temperature rise is analyzed and the distribution of the three-dimensional (3D) temperature field of spur/helical is obtained. The simulation analysis and experiment are compared to validate the accuracy of thermal analysis results. The research result reveals the distribution law of the 3D temperature field of spur/helical gear transmission at different working parameters. It provides theoretical guidance for gear antiscuffing capability and gear optimization design.

This paper presents a modified NSGA-II algorithm based on the spatial density (SD) operator, combined with computer graphics-based surface parameterisation methods and computational fluid dynamics (CFD) simulations. This was done to optimise the multi-objective aerodynamic design of a centrifugal impeller for a 100-kW vehicle-mounted fuel cell and improve the multi-conditions aerodynamic performance of the centrifugal impeller of the vehicle-mounted fuel cell (FC). The optimisation objectives are to maximise the isentropic efficiency of the rated and common operating conditions. The optimisation results showed that the efficiency of rated working conditions had an increase of 1.29%, mass flow increase of 8.8%, pressure ratio increase of 0.74% and comprehensive margin increase of 6.2%. The efficiency of common working conditions had an increase of 1.2%, mass flow increase of 9.1%, pressure ratio increase of 0.24% and comprehensive margin increase of 10%. The optimisation effect is obvious under the premise of satisfying the constraints, which proves the optimisation method’s engineering effectiveness and provides technical support and methodological research for the multi-objective aerodynamic design optimisation of centrifugal impellers for vehicle-mounted FCs.