Caichao Zhu

Mixed Lubricated Line Contact Analysis for Spur Gears using a Deterministic Model

The unified approach based upon the Reduced Reynolds technique is applied to develop a deterministic transient mixed lubrication line contact model. This model is used in spur gear applications to comprehensively show effects of roughness, working conditions, i.e., rotational speeds and loads on pressure ripples and severity of asperity contacts. Results show effects of the speed, the load, as well as the RMS value are coupled which makes it difficult to evaluate lubrication states by only considering one variable. Considering the Ree-Eyring non-Newtonian behavior could alleviate pressure ripples significantly, compared with the Newtonian fluid assumption. Small RMS values of surfaces, which could be achieved by superfinish techniques, would be desirable when evaluating gear tooth surface contact performances.

Spur Gear Lubrication Analysis with Dynamic Loads

A thermal elastohydrodynamic lubrication line contact model, which could handle ultra-thin-film conditions, was developed to study effects of speed on the lubrication performance of a spur gear pair. Dynamic loads were calculated using a classic mass-spring model. They effect of speed on lubrication performance was studied comprehensively through its direct influence on lubrication and indirect influence by affecting dynamic loads of the gear pair. The effect of dynamic loads on film thickness, pressure distribution, and temperature field were studied. It was concluded that a comprehensive model combining a lubricated contact analysis and a dynamic analysis for a gear system is required for a reasonable performance evaluation.

Parametric studies of spur gear lubrication performance considering dynamic loads

Effects of friction excitation and gear backlash on spur gear lubrication performance, i.e. minimum film thickness, maximum pressure, etc. are investigated by considering the dynamic loads due to excitations of mesh stiffness, friction between gear tooth, and backlash. Dynamic loads are obtained using a semi-definite two-degree-of-freedom lumped-parameter model. Reduced Reynolds technique is applied to develop a lubrication model capable of dealing with any potential ‘asperity contacts.’ Varying spur gear geometry parameters and the Ree–Eyring fluid behavior are taken into account. Results show that friction excitation has a very limited influence on the dynamic load and hence on the lubrication performance. Backlash affects the dynamic load significantly but has a limited influence on the minimum film thickness. Maximum pressure increases with the value of backlash due to the direct relationship of pressure and load.

Effect of flexible pin on the dynamic behaviors of wind turbine planetary gear drives

Flexible pins eliminate the need for straddle mounting, and therefore enable the maximum possible number of planets to be used for any particular epicyclic ratio of power transmission systems. Having more planet gears will significantly increase the input torque density. In this type of design, the pin stiffness and position tolerances are important parameters as they affect the dynamic performances significantly. The present study addresses this issue by modeling, the design of double cantilevered flexible pin, and analyzing the contributions of pin stiffness and misalignment applying the lumped parameter approach. The proposed model formulates the coupled lateral-torsional dynamic response of a planetary spur gear, including the effects of mesh stiffness and phasing as a function of pin error. The resultant equations of motion are applied to examine the effects of pin stiffness and position errors on the natural modes and structural dynamic response. The effects of pin stiffness on deviation of the tooth contact forces of the sun-planet and ring-planet gear pairs are analyzed to understand the relationship between mesh characteristic and input speed variations. The calculated supporting forces of the planet gear are examined to understand the load sharing characteristic due to pin errors, pin stiffness and input load of the power transmission system.

A thermal finite line contact EHL model of a helical gear pair

A thermal finite line contact elastohydrodynamic lubrication (EHL) model is developed to study lubricated contact performance of a helical gear pair. Three typical engagement positions during a meshing cycle, i.e. the engage-in position, the engage-out position and the pitch point position are chosen to show effect of load, speed, and addendum modification on pressure distribution, film profile, temperature field, etc. Results show temperature rise increases as the load or the speed goes up. The temperature distribution when the gear pair engaging around the pitch point behaves like a V-shape with higher values at the end parts. For the case with a standard center distance, proper addendum modification, i.e., negative modification for the bigger gear and positive modification for the small gear is good for improving lubrication performance and the service life of the helical gear drive.

Parametric Analysis of Gear Mesh and Dynamic Response of Loaded Helical Beveloid Transmission With Small Shaft Angle

A synthesized gear mesh and dynamic model assuming line contact that is derived from a set of manufacturing parameters is formulated for analyzing the beveloid gear mesh-coupling mechanism. Using the proposed model, the effect of the dominant geometry design parameter that is the crossed angle between the first principal directions of the tooth surface curvatures (FPD-angle) on gear mesh characteristic and dynamic response is investigated. Also, the analysis of the gear mesh characteristic and dynamic response subject to torque load variation is performed. It is shown that the dynamic transmission error and dynamic mesh force worsen as the geometry FPD-angle increases for a specific torque load level. Furthermore, even though higher torque load can produce larger contact area, which is desirable, it also increases the gear mesh stiffness and transmission error that tend to aggravate dynamic response.

Effects of Working Conditions on TEHL Performance of a Helical Gear Pair With Non-Newtonian Fluids

A thermal elastohydrodynamic lubrication (TEHL) finite line contact model is developed for a helical gear pair lubricated with an Eyring fluid or a power-law fluid in order to investigate the effects of the working conditions. A lubrication analysis within a meshing period shows that the differences between the Eyring and Newtonian solutions mainly lie in the film temperature and the shear stress. For the power-law fluid, the power index n has a significant effect on the film thickness. The effects of load and speed on lubrication performance along the line of action are discussed.

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.

A Micro-TEHL Finite Line Contact Model for a Helical Gear Pair

A micro-TEHL finite line contact model for a helical gear pair is developed by considering sinusoidal waviness on tooth surfaces. Effects of working conditions, the amplitude, and the wavelength of the waviness roughness on the lubrication performance are studied. Results show that surface roughness has a significant influence on the pressure, the temperature, and so forth. The pressure within the nominal contact zone for a rough-surface case fluctuates around the smooth-surface solution. For the working conditions studied, at local area within the contact zone, the maximum pressure may be 50% higher than the smooth-surface result. The film contraction at the outlet zone becomes more remarkable. The film temperature also fluctuates regularly. As the amplitude of the roughness increases, the local pressure within the nominal contact zone increases while the minimum film thickness decreases. As the wavelength of the roughness decreases, the local pressure and the temperature within the nominal contact zone increase while the film thickness decreases. Effect of wavelength on the lubrication performance is more evident along the rolling speed direction than along the contact line direction.

Investigation on the effect of coating properties on lubrication of a coated spur gear pair

A thermal elastohydrodynamic lubrication model is proposed for a coated gear pair in which the influence coefficients for the elastic deformation and the subsurface stress components are obtained through the frequency response functions. The generalized Reynolds equation is utilized to represent the non-Newtonian effect. Energy equations of the contacting solids and the oil film are derived and solved based upon the marching method. The discrete convolute, fast Fourier transform method is used for fast calculation of the tooth surface displacement and the stress components underneath the surface. Variations of the slide-to-roll ratio, rolling speed, and the tooth load during gear meshing are considered and the film squeeze effect is taken into account. Effects of the coating thickness on the tribological performance, i.e. the film thickness, the pressure, the frictional behavior as well as the stress components are investigated under both the smooth and rough surface assumptions. Effects of the root mean square value of the tooth surface roughness on the pressure and stresses are discussed.