Huaiju Liu

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.

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.

Effect of Thermal Properties of a Coated Elastohydrodynamic Lubrication Line Contact Under Various Slide-to-Roll Ratios

A numerical thermal elastohydrodynamic lubrication (EHL) model is developed for coated line contacts by considering both the mechanical properties and the thermal properties of the coating and the substrate. The temperature fields within the oil film and within the solids are solved by deriving the energy equations for the solids and the oil film. Heat continuity conditions are satisfied at the interfaces between the solids and the oil film, and the coating/substrate interfaces. Effects of the slide-to-roll ratio (SR), the thermal conductivities of the coating bodies, and the oil film on temperature fields are studied. [DOI: 10.1115/1.4036078]

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.

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