Chaosheng Song

Effect of tooth profile modification on lubrication performance of a cycloid drive

A numerical study on contact performance of a cycloid drive lubricated with the grease is conducted. The effect of the tooth profile modification on lubrication performance is emphasized. Four profile modification methods are proposed and their influences on the length of the line of action, the pressure and the film thickness are compared. Results show that at a certain manufacturing accuracy, the lubrication performance of the one with a combined modification is better than the performance of the ones with single modification. The combined negative equidistant and negative radial-moving scheme has the best lubrication performance while the single negative radial-moving modification scheme has the worst lubrication performance among the selected schemes. Effect of the amount of the radial-moving modification and the amount of the combined negative equidistant with negative radial-moving modification are studied and results show that as the modification value increases, the length of LOA, the load-carrying capacity, and the film thickness decrease, which represents a worse lubrication performance. After modification, the lubrication performance of the engaging tooth pair would deteriorate. The higher the manufacturing precision, the smaller the amount of the modification, the better the lubrication performance.

Influence of lubrication starvation and surface waviness on the oil film stiffness of elastohydrodynamic lubrication line contact

Stiffness properties of interfacial engineering surfaces are of great importance to the dynamic performance of relevant mechanical systems. Normal contact stiffness and oil film stiffness of line contact problems are studied in this work analytically and numerically. The Hertzian contact theory and the Yang–Sun method are applied to predict the contact stiffness, while the empirical elastohydrodynamic lubrication (EHL) film thickness method and the complete numerical EHL model are used to predict the oil film stiffness. The numerical model mainly consists of the Reynolds equation; the film thickness equation, in which the regular surface roughness is taken into consideration; the force balance equation; and the viscosity-pressure equation. The effects of the normal load, rolling speed, regular surface waviness, and starved lubrication level on the oil film stiffness are investigated.

Study on Starved Lubrication Performance of a Cycloid Drive

ABSTRACT The lubrication performance of cycloid drives affects the dynamic characteristics, mechanical efficiency, and contact fatigue behavior. Starved lubrication performance of a cycloid gear drive is studied using a numerical thermo-starved elastohydrodynamic lubrication model. The parameter of the inlet oil film thickness is chosen to represent the starvation degree. Effects of the inlet film thickness on the central film thickness, friction coefficient, frictional power loss, starting position of the effective film thickness, and lubrication efficiency are investigated. The optimum inlet film thickness is defined and is calculated under different rolling–sliding ratios, speeds, and loads. Finally, the optimum inlet film thickness during the meshing process of a cycloid drive is calculated.

Concave modifications of tooth surfaces of beveloid gears with crossed axes

The mathematical models of the beveloid gear surfaces with different scenarios of combinations of profile concave modification and lead crowning are derived. Four schemes of modifications were proposed for beveloid gears with crossed axes. Tooth contact analysis is developed to study the influences of different schemes of concave modifications on the mesh behaviors including film thickness, transmission errors, contact ratio, root stresses, and contact patterns. Comparison of the contact characteristics of a beveloid gear drive with and without concave modifications is conducted. The results show that all the concave modification schemes can increase the area of contact patterns and decrease the maximum value of contact stresses, while the minimum film thickness can be increased. For the scheme i.e. the pinion with profile crowning modification and gear with profile concave modification, the contact ratio increases firstly then decreases to a relative lower value. Also, the root stresses are increased obviously. For the scheme for pinion without modification and gear with lead concave modification and the scheme for both pinion and gear with lead concave modification, the transmission errors are decreased slightly. The scheme for the pinion with combined crowning modification and gear with combined concave modification shows the largest improvement for the mesh behaviors in terms of the transmission errors and contact patterns where an almost contact condition can be found for the crossed beveloid gear pair.

A numerical study on the contact fatigue life of a coated gear pair under EHL

Purpose Coatings are widely employed in gears to keep interface from wearing excessively. The purpose of this paper is to study the effect of coating properties and working conditions on the pressure, the shear traction, stresses as well as the fatigue life of spur gear. Design/methodology/approach A numerical contact fatigue life model of a coated spur gear pair under elastohydrodynamic lubrication (EHL) is developed based on the characteristics of gear geometry and kinematics, lubrication conditions and material properties. Frequency response functions and the discrete convolute and fast Fourier transform (DC-FFT) algorithm are applied to obtain elastic deformation and stress. Mutil-axial fatigue criteria are used to evaluate the contact fatigue life based upon the predicted time-varying stress fields of coated bodies. Findings The maximum Mises stress decreases while the fatigue life increases as the coating modulus decreases. A thinner coating leads to a longer life and a smaller maximum Mises stress ...

Effect of the Shape of Inlet Oil-Supply Layer on Starved Lubrication Performance of a Cycloid Drive

The lubrication performances of cycloid drives affect the dynamic characteristics, the mechanical efficiency and the contact fatigue behavior of the system. To maintain tranmission precision it is required to minimum the times of disassebly, hence grease lubrication is often applied where starvation might occur in service. Starved lubrication performance of a cycloid gear drive is studied using a numerical finte line starved-elastohydrodynamic lubrication model. The parameter of the inlet oil film thickness is chosen to represent the starved status. Effects of the inlet film thickness on the centralfilm thickness, the friction coefficient and the frictional power loss are investigated. In addition, effects of different shape of inlet oil-supply layer in the same starved degree on lubrication performance are studied. Under the same inlet oil supply volume, the convex type profile would present a better oil film within the nominal contact zone compared with other four different shapes of the inlet film supply.Copyright

On-line vibration monitoring and diagnosing of a multi-megawatt wind turbine gearbox

A wind turbine gearbox is always working under transient and variable load conditions, and its vibration characteristics have a great influence on the reliability and life-span of the whole wind turbine. In this work a remote on-line vibration monitoring system is built to monitor the working performance of a multi-megawatt wind turbine gearbox. The wind turbine gearbox is tested using this system and thus obtains acceleration signals at critical testing points on the case. The resulting vibration signals are analyzed with a comprehensive way including the time domain method, frequency domain method, time-frequency method and wavelet transform method. Furthermore, this paper summarizes the vibration characteristics of the wind turbine gearbox operating in the wind field. This work is believed to be useful for the evaluation of the working performance of the system.

Coupled Tooth Contact Analysis of Intersected Beveloid Gears for Marine Transmissions

Beveloid gears are widely applied in fields like ships, automobiles and industrial precision transmissions. In this paper, the formulas of the beveloid gear tooth surface used in marine transmissions were derived and a mesh model for the intersected beveloid gear pair was setup. Then loaded tooth contact analysis was performed using the finite element method considering the coupling of the assembly errors and the elastic deformation of tooth surface. Through the analysis, the influences of assembly errors on contact patterns, mesh force and tooth surface deformations were investigated. In a further step, the tooth profile modifications were performed to alleviate the edge contact and a subsequent major improvement of the mesh condition was obtained. Finally, loaded tooth contact experiments for marine gearboxes with small shaft angle were conducted. The tested results showed good correlation with the computed results. This work may provide some value for the practical design aiming at improved contact characteristics of the beveloid gears with intersected axes.© 2013 ASME