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The gear-rotor system is a core transmission component in fields such as railway and aerospace. As one of the key internal motivating factors of the system, the time-varying meshing stiffness directly affects its vibration and operational stability. Hertzian contact stiffness, as the core dynamic component of the time-varying meshing stiffness, exhibits load-dependent nonlinear characteristics due to the dynamic variation of meshing force, yet this characteristic has been neglected in most studies. Therefore, it is of great significance to establish a calculation model considering the dynamic Hertzian contact stiffness and explore its influence on the system for improving the accuracy of the dynamic investigation of the gear-rotor system.

As one of the most vital energy conversation systems, the safe operation of wind turbines is very important; however, weak fault and time-varying speed may challenge the conventional monitoring strategies. Thus, an entropy-aided meshing-order modulation method is proposed for detecting the optimal frequency band, which contains the weak fault-related information. Specifically, the variable rotational frequency trend is first identified and extracted based on the time–frequency representation of the raw signal by constructing a novel scaling-basis local reassigning chirplet transform (SLRCT). A new entropy-aided meshing-order modulation (EMOM) indicator is then constructed to locate the most sensitive modulation frequency area according to the extracted fine speed trend with the help of order tracking technique. Finally, the raw vibration signal is bandpass filtered via the corresponding optimal frequency band with the highest EMOM indicator. The order components resulting from the weak fault can be highlighted to accomplish weak fault detection. The effectiveness of the proposed EMOM analysis-based method has been tested using the experimental data of three different gear fault types of different fault levels from a planetary test rig.

Aiming at the limitations of the existing hydraulic pumps, a new type of bidirectional water-hydraulic internal ball gear pump using concave-convex ball teeth meshing to transfer power is proposed. In this paper, the principle of internal gear pump is utilized to establish the model of internal ball gear pump, and its mechanical properties and dynamic meshing characteristics are numerically investigated by using the finite element method. The results show that (a) the concave-convex ball gears run smoothly without any interference, and (b) increasing the number of gear rows can effectively reduce the maximum stress and meshing impact under a given load and speed. This study provides a basis for the development of high-performance ball gear pumps.

Rack rail vehicles show strong capability of mountain climbing and have become a popular transportation mode for mountain areas in recent years. Therefore, this paper investigated on the dynamic performance of rack rail vehicle through simulation of a multibody dynamic model. Firstly, a multibody dynamic model of rack rail vehicle considering both the wheel/rail interaction and the gear-rack meshing was developed in the SIMPACK software platform. A rack rail with a large slope of 250‰ was taken into consideration in the proposed study. Subsequently, the gear-rack meshing dynamics in terms of the meshing stiffness and the meshing force in both circumferential- and radial- directions were investigated. Moreover, two types of driving modes were compared to illustrate the effects of driving mode on the wheel/rail interaction and the gear-rack meshing. The results show that due to the gear-rack meshing the meshing stiffness and the meshing force are subject to the periodical variations and the gear-rack meshing can significantly affect the wheel/rail interaction, especially in the presence of track irregularities. The driving mode that the gear wheel is installed on the wheelset axle through a hollow shaft is considered as a more practical design for the rack vehicle.

This paper introduces a novel gear drive characterized by high transmission efficiency. The gear incorporates cubic curves with corresponding tangents defining the normal section tooth profile. The generation principle of this new gear drive is thoroughly established. Utilizing gear meshing theory, key parameters such as the relative motion velocity, normal vector, and meshing equation are derived. Subsequently, the fundamental principle of the conjugate curve is formulated. The methodology for generating the tooth profile is also explored. An efficiency test was conducted on the gear, and the results demonstrate a superior transmission efficiency relative to that of traditional involute gears.

Aiming to address the issues associated with the over-positioning structure and the demanding manufacturing and assembly precision requirements of rotate vector (RV) reducer, a novel 2 K-H internal meshing planetary gear reducer, accompanied by a new involute-cycloid tooth profile curve, is proposed. To enhance the load carrying capacity and dynamic characteristics of the proposed reducer, a method for profile and lead modification of the working gear is proposed. Firstly, the mathematical equations of the tooth surface considering modification are derived and geometric model of the modified gear pair is also reconstructed. Then, loaded tooth contact analysis is employed to quantitatively evaluate the influence of four individual modification strategies—drum profile modification, line profile modification, drum lead modification, and line lead modification—as well as their comprehensive modification, on contact pattern, contact stress, and transmission error. Finally, the influence of different shaft angle errors on the meshing behavior of modified gear pair has been carried out. The results demonstrate that, in comparison with drum and line modifications applied individually to the profile or lead, the contact pattern area and contact stress distribution of comprehensive modified gear are significantly improved. During both meshing-in and out stages, the maximum contact stresses of the gear pair are reduced from 711.83 to295.75 MPa before modification to 242.57 MPa and 132.21 MPa after modification, reducing by 65.92 and 55.29%, respectively. Compared with the unmodified case, the contact stress and transmission error of the comprehensive-modified gear pair exhibits reduced sensitivity to the shaft angle errors, effectively mitigating meshing shocks and ensuring smoother gear transmission.

The gear system is a common mechanical transmission device that transmits power and motion through the continuous interaction of conjugate tooth surfaces. It is widely used in new energy vehicles, industrial machinery, aerospace, and other fields. When gears transmit power, the tooth surfaces inevitably undergo wear, and this wear occurs throughout the entire operation process. Stiffness, as an important indicator of gear performance, is crucial for accurately calculating the meshing stiffness after wear. This paper intends to model and calculate the wear of helical gear tooth surfaces, and calculate the meshing stiffness after wear based on the improved flexibility matrix. This provides a theoretical reference for the research on gear wear faults.

The microscopic topography of tooth surface affects the nonlinear dynamic characteristics of the gear system. However, few studies have fully taken into account the effects of microscopic topography on time-varying meshing stiffness (TVMS) and backlash in gear dynamics. In this context, this study derives TVMS and time-varying backlash with fractal characteristics based on fractal theory and introduced them into a 6-DOF nonlinear dynamic model. With various nonlinear dynamics analysis tools, the dynamic characteristics of the gear system under different fractal parameters are investigated. The results indicate that the increase in the fractal dimension or the decrease in the characteristic scale coefficient leads to a smoother tooth surface, larger TVMS, and smaller amplitude of backlash. The effect of fractal dimension is more sensitive than characteristic scale coefficient. Furthermore, in the low-speed region, the increase in fractal dimension has a positive effect on the dynamic response of the system and can reduce the amplitude of dynamic transmission error. In the high-speed region, the opposite is true. It is worth pointing out that the influence of fractal dimension on gear dynamic characteristics is nonlinear. Considering the machining cost and dynamic response of gear, the fractal dimension of 1.5 is the best choice. The influence of characteristic scale coefficient on system dynamics is similar to that of fractal dimension, but the intensity is much weaker.

Teeth disengagement or back-side teeth engagement induced by backlash reduces the transmission quality and dynamic performance of gear systems, and the accurate interpretation of multi-state meshing behavior can provide guidance for structural optimization and performance evaluation. Therefore, the multi-state meshing behavior of the gear system is elaborated. A new nonlinear dynamic model of a spur gear system with five-state meshing behavior is established based on the time-varying backlash and contact ratio. The time-varying meshing stiffness and time-varying backlash considering the elastic contact of gear teeth, gear temperature rise and lubrication are included in the model. The five-state meshing behavior is clearly characterized by constructing five Poincaré maps, and its generation mechanism is revealed using dynamic meshing force time history, teeth relative displacement time history and phase portrait. The bifurcation and evolution of five-state meshing behavior are analyzed under the effects of load factor, meshing frequency and error coefficient. The results show that the mutation in the direction of dynamic meshing force leads to teeth disengaging and back-side single- or double-tooth contact, forming multi-state meshing behavior. Bifurcation caused by parameter changes greatly affects the evolution of five-state meshing behavior, particularly grazing bifurcation can decrease the number of teeth disengagement. Chaotic behavior or trajectory expansion inspires multi-state meshing vibration of the system. Previous gear system models could not reveal these phenomena due to ignoring the multi-state meshing behavior.

Face gear assemblies transfer motion between intersecting axes using a cylindrical pinion paired with a face gear. Tooth surface modification is a common way to increase the contact area ratio, reduce maximum contact stress, and improve the reliability of face gear drives. Currently, modification methods focus on individual manufacturing processes for the cylindrical and face gears, without considering their interaction during meshing. This leads to unclear mapping between surface modification and meshing performance, making it hard to control the contact area. To tackle this issue, this paper presents a method for topologically modifying the cylindrical gear tooth surface, taking into account both meshing performance and extensive contact areas. First, the contact lines on both gears’ tooth surfaces are determined. A mathematical model for topological modification is created based on the cylindrical gear’s theoretical tooth surface, focusing on the contact trajectory and direction. The modification amount is applied to the cylindrical gear’s tooth surface to achieve the topologically corrected gear. Finally, a finite element method is used to compare the traditional and proposed modification methods. Results show that the new method increases the contact area ratio by 40% and 50% and reduces the maximum contact stress by 26% and 10%, respectively, compared to the traditional method.