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The fault of transmission system seriously affects the life of robot joints, so it is urgent to study the crack of the displacement wheel set. Firstly, the tooth profile equation of the modified gear is established, and the time-varying mesh stiffness (TVMS) is obtained. Secondly, the multi-degree-of-freedom electromechanical coupling dynamic equation is established. Finally, the vibration displacement under steady state, start-up and shock conditions is analyzed. The results show that: (a)The positive displacement can increase TVMS, while negative displacement is the opposite. (b) The appearance of cracks accelerates the damage to two adjacent teeth. (c) The decrease of TVMS increases with the increase of crack depth. (d) The crack causes the gear pair to generate vibration shock, and the vibration displacement increases significantly in the case of broken teeth. (e) Statistical analysis of the vibration displacement reveals that the root means square value can detect early cracks, and the kurtosis index can predict life. (f) Cracks have a large effect on the transient process at start-up and shock, but the effect of cracks is weakened during no-load steady-state operation. [ABSTRACT FROM AUTHOR]

Due to the complex structure of the planetary gear train, the influence of early fault on the dynamic characteristics of the planetary gear train is complex and changeable. This paper proposes a time-varying meshing stiffness (TVMS) calculation model of internal meshing considering the coupling effect between teeth; and a multi-tooth coupling stiffness calculation model of the planetary gear train. The Archard equation is used to calculate the wear depth; moreover, the potential energy method calculated The TVMS of the planetary gear train under the wear state. The wear fault will cause the TVMS of the gear to decrease. In the two-stage planetary gear train, the TVMS of the first-stage sun-planet gear decreases more obviously. In addition, there is a specific coupling effect between the sun, ring, and planetary gear. The influence of the wear fault on the two-stage planetary gear train is analyzed by calculating the synthetic stiffness considering the meshing phase difference. The results show that under the same wear fault condition, the more teeth involved in meshing, the more significant the decrease in coupling stiffness. [ABSTRACT FROM AUTHOR]

Strategy of Speed disturbance is used to stabilize an unstable periodic orbits which embedded in the chaotic attractor of chaos in nonlinear torsional vibration model of a planetary gear set. The small speed disturbance control strategy is used for the system that the differential equations are unknown and the allowance of speed disturbance is very small and the optimal parameter control method is used to calculate the speed disturbance in the control procedure. A new method called large parameter perturbation is used for the system that the differential equations are known and the allowance of speed disturbance is relatively big,and the speed is still selected as control parameter. Both the two method control the chaos of planetary gear set to periodic motion state successfully.

A bending-torsional nonlinear dynamics model of the spur gear pair with 6-DOF is established and the dimensionless dynamics equations are derived.The tooth surface friction,time-varying stiffness,gear backlashes as well as gear mesh errors are considered in this model.Based on the location of the contact line,the mathematical expressions of the tooth surface friction and the friction torque are both derived.The effects of tooth surface friction on the dynamic behaviors of the system are studied.The results show that the tooth surface friction can increase the vibration of the system,and the effect is more obvious on the vibration in the perpendicular direction to the meshing line.The degree of the chaotic motion of the system can be reduced by the tooth surface friction,and the bifurcation of the system becomes blurred at the high meshing frequency and chaotic motion appears earlier by the tooth surface friction.

With the objective of reducing windage power losses (WPL) in herringbone gears, WPL experiments involving the use of a shroud are conducted. Based on computational fluid dynamics (CFD), a herringbone gear numerical model is established. Based on the renormalization group (RNG) k–ε two-equation turbulence model and dynamic mesh technique, the features of flow field distribution around the gear; mechanism of reduction of WPL; shroud installation distance, coverage, and installation position; and influence law of WPL are analyzed. The CFD and experimental results, which exhibit good consistency, are used to infer the WPL behavior with respect to the input parameters. [ABSTRACT FROM AUTHOR]

The planetary gear transmission with double moduli and pressure angles gearing is proposed for meeting the low weight high reliability requires. A dynamic differential equation of the NGW planetary gear train system with double and pressure angles is established. The 4-Order Runge-Kutta numerical integration method is used to solve the equations from which the result of the dynamic response is got. The dynamic load coefficients are formulated and are compared with those of the normal gear train．The double modulus planetary gear transmission is designed and manufactured. The experiment of operating and vibration are carried out and provides.

During the actual operation of gears, phenomena such as friction and cracking occur. Based on the energy method, a time-varying mesh stiffness solution model of the gear pair is established, and a dynamics model of the gear transmission system is built, and the sensitivity of the vibration signal and its response is analysed using wavelet transform as well as statistical indicators. The results show that cracks promote the effect of friction on the mesh stiffness as they enter the mesh. Friction will make the vibration displacement increase, and crack will cause vibration displacement to produce vibration shock, the wavelet diagram at the crack will become bright, kurtosis is the most effective indicator to determine the crack damage, which provides a theoretical basis to study the dynamic characteristics of friction and crack under actual working conditions and vibration and noise reduction. [ABSTRACT FROM AUTHOR]

Based on computational fluid dynamics, a two-phase flow model was established to calculate the churning power loss of the spiral bevel gears under splash lubrication. The error between the simulation results and experiment results is only 7.04%. Taking a certain helicopter as an example, the churning power loss of the intermediate gearbox is ∼2.6051 kW, accounting for ∼1.93% of the input power. Besides, the motion mechanisms of free flow, ejection flow and splashing flow of the spiral bevel gear were investigated. The influences of the rotational speed and oil immersion depth on the churning power loss were analysed. The rotational speed and oil immersion depth of the intermediate gearbox should be in the range of 3000–5000 r/min and 17–26 mm, respectively, which can ensure sufficient lubrication and low churning power loss. [ABSTRACT FROM AUTHOR]

In this study, we propose a computational fluid dynamics (CFD)-based method to study the lubrication and temperature characteristics of an intermediate gearbox with splash lubrication. A volume of fluid (VOF) multiphase model was used to track the interface between oil and air. A multiple reference frame (MRF) model was adopted to accurately simulate the movement characteristics of the gears, bearings, and the surrounding flow field. The thermal-fluid coupling computational model of an intermediate gearbox with splash lubrication was then established. Combined with experimental results, we verified that the lubricating oil temperature was below the limit requirement (<110 °C). The numerical results revealed that large amounts of lubricating oil were splashed onto the tooth surfaces near the gear meshing area. A large convective heat transfer coefficient corresponds to a low gear tooth surface temperature. The tooth surface temperature of the driving gear is higher than that of the driven gear. The distribution law of oil volume fraction of the bearing roller was jointly affected by the roller rotation direction and gravity. The convective heat transfer coefficient of the roller wall was largely related to the lubrication environment of the roller, including the oil distribution inside the bearing cavity and the flow rate. [ABSTRACT FROM AUTHOR]

To investigate the influence of the groove shape of friction disks on the wear of a friction clutch friction pair, a wear calculation model that considers the actual sliding distance between the friction clutch friction pair is presented based on the Archard adhesive wear model. The wear of three different groove-shaped friction pairs was calculated and analyzed. The wear test was carried out on the SAE#2 testing rig to obtain the actual wear amount and verify the accuracy and validity of the mathematical model. The results show that, among the three types of grooves, the friction disks with waffle grooves were the most prone to wear, followed by three-way parallel grooves. The wear performance of the two-way parallel grooves was the best, and the wear from one-time engagement can better reflect the change in the dynamic engagement of the friction pair. With the increase in the engagement time, the increase of the wear amount decreases. [ABSTRACT FROM AUTHOR]

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