Junyang Li

Accelerated life testing of harmonic driver in space lubrication

For mechanical moving components in space applications, the accelerated life test for the verification of reliability is very important. Since traditional methods of the accelerated life test for liquid lubrication have some limitations, a new method is proposed in this paper, in which the harmonic driver is used as the object of study. First, the life test of a harmonic driver is performed in vacuum. The results show that the adhesive wear caused by asperity contact at the wave generator–flexspline interfaces is the crucial factor governing the life of harmonic driver. To clarify the lubricant film behavior at the wave generator–flexspline interface, a mixed lubrication analysis is conducted. Furthermore, the scheme of the accelerated life test is discussed. The speed and load are selected as the acceleration stresses of the test, while the load supported by asperity contact is defined as the characteristic quantity of the life and used to select acceleration factors. Finally, accelerated life tests under different working conditions are conducted to validate the results of the theoretical analysis.

Effect of surface topography associated with arbitrary velocity direction on the lubrication film thickness in elliptical contacts

Purpose The purpose of this study is to describe and observe the effect of surface topography associated with arbitrary directions of rolling and sliding velocities on the performance of lubricating films in elliptical contacts. Design/methodology/approach The most recently published mixed elastohydrodynamic (EHL) model by Pu and Zhu is used. Three different machined rough surfaces are discussed and the correlated inclined angle of surface velocity varies from 0° to 90° in the analyzed cases. These cases are carried out in a wide range of speeds (five orders of magnitude) while the simulated lubrication condition covers full-film and mixed EHL down to the boundary lubrication. Findings The results indicate that the variation of the average film thickness corresponding to different entrainment angles is distinct from those without considering surface roughness. In addition, the surface topography appears to have an immense effect on the lubrication film thickness in the exceptive situation. Originality/value This paper has not been published previously. Surface roughness has attracted much attention for many years owing to the significant influence on lubricating property. However, previous studies mainly focus on the counterformal contact with the same direction between surface velocity and principal axis of the contact zone. Little attention has been paid to the specific condition with the arbitrary direction of rolling and sliding velocities found in hypoid gears and worm, and some other components. The purpose of this study is to describe and observe the effect of surface topography associated with arbitrary directions of rolling and sliding velocities on the performance of lubricating films in elliptical contacts based on the most recently published mixed EHL model by Pu and Zhu.

Micro-bottom shape effects on the misaligned herringbone grooved axial piston bearing with a new parallel algorithm

This paper presents a group of elastic Hydrodynamic lubrication (EHL) analyses to evaluate the effects of micro-bottom shape on the performance of misaligned herringbone grooved axial piston bearing. Due to the time-consuming elastic Hydrodynamic lubrication (EHL) tasks introduced in herringbone grooves, complex bottom shape, rotation combined axial movement, and misalignments require high-speed computation. So a new parallel elastic Hydrodynamic lubrication (EHL) numerical algorithm is proposed, which exhibits higher computing speed than the normal successive over relaxation (SOR) method. The results suggest the bottom shapes of herringbone grooves significantly affect the lubrication performance of misaligned herringbone grooved axial piston bearing. Rectangle and left triangle bottom shapes involve a micro-step bearing effect which can significantly improve the lubrication performance, comparing to semiellipse, isosceles triangle, and right triangle bottom shapes.

Study on the stiffness and damping coefficients of water-lubricated rubber bearings with multiple grooves:

By considering the effects of multiple grooves, rubber deformation, and actual boundary conditions, the steady elastohydrodynamic lubrication mathematical model and the dynamic Reynolds equation of water-lubricated rubber bearings are presented. The Reynolds equation is solved numerically by the finite difference method, and the stiffness and damping coefficients are calculated from the real and imaginary parts of the integrated pressure. Analysis results suggest that angular velocity, eccentricity ratio, groove configuration, and radial clearance have significant effects on the steady state and dynamic stiffness as well as damping characteristics, which also help in designing proper structure parameters of water-lubricated rubber bearings to obtain better dynamic performance.

Innovation design and experiment research on the N–N type planetary gear apparatus with small tooth number difference

The three high-performance indicators (low retrace tolerance, long life and low vibration) of N–N type planetary gear apparatus with small tooth number difference (abbrev “N–N–PGA”) are hardly achieved simultaneously until recently. At present, the root cause analysis (RCA) and TRIZ are considered to be comprehensive and systematic new theories for technological innovation, which provides a new way to figure out the conundrum existed in the N–N–PGA. In the present study, the “root cause” of the problem is proposed with the RCA approach and two contradictions existed in the N–N–PGA have been revealed: Harmful side effect and stability of composition; harmful side effect and durability of a moving object. Besides, two reasonable principles (“Dynamicity” and “Composite materials”) for the N–N–PGA design recommended by the TRIZ method are used to eliminate these contradictions. In addition, a prototype of the obtained new type N–N–PGA design is developed for experimental testing. The obtained result demonstrates the capability of the above method for obtaining low retrace tolerance, long life, and low vibration.