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The paper aims to present a new friction modifier (mixture of zinc and copper oleates) proper for industrial running-in of repaired engines.

The method of comparison was used for testing the offered friction modifier, a market product “Renom Engine” and a blank sample of motor oil as an etalon. Running-in time has been established. The mechanical losses change and the relevant coefficients have been determined. Data of the bearings wear have been included.

The benefit of the metal oleates and Renom Engine usage as friction modifiers has been proved. Time for industrial cold running-in of repaired engines decreases by around 20 per cent when friction modifiers are used in comparison with the etalon oil. The coefficient of the mechanical losses reduction at running-in with friction modifiers is higher than the coefficient for the etalon oil. The higher coefficient values indicate that the running-in of the working surfaces occurs more intensively and for a shorter period of time. Lower wear of the bearings is combined with smaller roughness of the friction surface, which secures higher quality of the surfaces run-in with the friction modifiers and greater capacity by around 30 per cent.

This study introduces a new friction modifier for industrial running-in of repaired engines. It would be of interest to the customers and manufacturers of oil additives.

The purpose of this paper is to study the tribological effect of zinc borate ultrafine powder (ZBUP) oil additive on the running-in quality.

The running-in quality was assessed by friction coefficient and surface topography. Fractal parameters including fractal dimension, the width of multifractal, the multifractal difference, multifractal parameters, phase trajectory and correlation dimension were used to extract the nonlinear characteristics of surface topography and friction coefficient.

When the ZBUP additive was added, the convergence degree of the phase trajectory and the stability of the running in were higher than that of base oil. It indicates that the ZBUP additive can improve the running-in quality of sliding bearing. Besides, the ZBUP additive can shorten the running-in time. A boundary protective film, which has good friction-reducing and anti-wear effects, was generated on the surface when the ZBUP additive was added.

The results have a great significance to improve the running-in quality and prolong the service life of the sliding bearing.

During running-in, the change in the honed cylinder liner surface alters the performance and efficiency of the piston ring-pack system. The present paper, thus, aims to investigate the surface topography and wear and friction evolution of a cylinder liner surface during the running-in tests on a reciprocating ring–liner tribometer under a mixed lubrication regime. After an initial period of rapid wear termed “running-in wear”, a relatively long-term steady-state surface topography can emerge. A numerical model is developed to predict the frictional performance of a piston ring-pack system at the initial and steady-state stages.

The liner surfaces are produced by slide honing (SH) and plateau honing (PH). The bearing area parameter (Rk family), commonly used in the automotive industry, is used to quantitatively characterize the surface topography change during the running-in process. A wear volume-sensitive surface roughness parameter, Rktot, is used to show the wear evolution.

The experimental results show that a slide-honed surface leads to reduced wear, and it reduces the costly running-in period compared to the plateau-honed surface. The simulation results show that running-in is a beneficial wear process that leads to a reduced friction mean effective pressure at the steady-state.

To simulate the mixed lubrication performance of a ring–liner system with non-Gaussian roughness, a one-dimensional homogenized mixed lubrication model was established. The real surface topography instead of its statistical properties is taken into account.

The purpose of this paper is to study the real-time change of surface roughness at different small regions of piston rings during running-in process. Meanwhile, the effects of real-time change of the rough surface topography on the lubrication and friction of piston rings are investigated.

An uneven wear model has been developed to research the running-in behavior at the different small regions of piston rings. The model is verified by comparing the simulation results with the experimental results on a reciprocating friction and wear test rig.

This research shows that the wear process of piston ring surface is uneven during running-in. At most time of the operating cycle except the vicinity of top dead center and bottom dead center, the minimum oil film thickness ratio increases while the friction force and power loss decrease after the running-in period.

Through this research, the running-in behavior of piston rings is investigated in detail. The interaction between the running-in and the lubrication and friction of piston rings is understood more deeply.

This paper aims to explore the influence of applied pressure on the tribological properties of the friction component in a wet multi-disc clutch during the running-in process.

The running-in evolutionary was explored in terms of global friction performance. The variation of friction torque and mean COF of the initial 300 engagement cycles was obtained by full-scale tests. Finally, an optical microscope was used to detect the wear characteristics of friction surfaces.

The applied pressure showed a significant influence on the tribological behaviors of wet clutches during the running-in process. The mean COF decreased and then increases with the increase of the applied pressure. A higher applied pressure contributed to more asperity summits being sheared, thus resulting in a smoother surface. Considering a suitable wore performance, properly applied pressure is necessary.

The results provide theoretical guidance for selecting the optimal applied pressure in the running-in of wet clutches.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2022-0256/

The purpose of this paper is to study the correlation between the dynamic features of the running-in attractor and the wear particle group, so as to characterize the running-in attractor by means of the wear particle group.

Wear particles are collected in phased wear experiments, and their dynamic features are investigated by the equivalent mean chord length L. Then, the correlation between the equivalent mean chord length L and the correlation dimension D of the running-in attractor is studied.

In the wear process, the equivalent means chord length L first decreases, then remains steady, and finally increases, this process agrees with the increase, stabilization and decrease of the correlation dimension D. Therefore, the wear particle group has a dynamic nature, which characterizes the formation, stabilization, and disappearance of a running-in attractor. Consequently, the dynamic characteristics and evolution of a running-in attractor can be revealed by the wear particle group.

The intrinsic relationship between the wear particle group and the running-in attractor is proved, and this is advantageous for further revealing the dynamic features of the running-in attractor and identifying the wear states.

This paper aims to investigate the mechanism of spur gears running-in and to solve the lubrication problems of teeth running-in.

The elastohydrodynamic lubrication (EHL) model considering solid particles was established by applying multi-grid and multiple-grid integration methods to the numerical solution.

In the region where debris settle, transient pressure increases sharply, and a noticeable increase in the running-in load causes a remarkable increase in both the centre and maximum pressures and a slight increase in the minimum film thickness. Roughness wavelength makes a considerable difference to the minimum film thickness at double-to-single tooth transient. A considerable increase in rotation velocity can cause a remarkable reduction in both the centre and maximum pressures but an amazing increase in the minimum film thickness. The effects of roughness amplitude on the maximum pressure are considerably distinct.

Research on EHL of spur gears in the running-in process considering solid particles, surface roughness and time-variant effect is meaningful to practical gears running-in. Thermal effect can be included in the next study.

The analysis results can be applied to predict and improve lubrication performance of the meshing teeth.

The aim is to reduce gears’ manufacture and running-in costs and improve economic performance.

The EHL model that considers solid particles was established. The Reynolds equation was deduced taking the effects of solid particles into account. The EHL of spur gears running-in was investigated considering the time-variant effect, surface roughness, running-in load and rotation speed.

SINCE THE INTRODUCTION of the hypoid gear as the right‐angled drive in automotive rear axles there has been a constant demand for specialised lubricants, particularly for running‐in purposes. Requirements are gradually and constantly becoming more severe and standards of performance adequate 5 or 10 years ago may be marginal today and unacceptable in the future.

This study aims to reconstruct the frictional vibration signal from noise and characterize the running-in process by frictional vibration.

There is a strong correlation between tangential frictional vibration and normal frictional vibration. On this basis, a new frictional vibration reconstruction method combining cross-correlation analysis with ensemble empirical mode decomposition (EEMD) was proposed. Moreover, the concept of information entropy of friction vibration is introduced to characterize the running-in process.

Compared with the wavelet packet method, the tangential friction vibration and the normal friction vibration reconstructed by the method presented in this paper have a stronger correlation. More importantly, during the running-in process, the information entropy of friction vibration gradually decreases until the equilibrium point is reached, which is the same as the changing trend of friction coefficient, indicating that the information entropy of friction vibration can be used to characterize the running-in process.

The study reveals that the application EEMD method is an appropriate approach to reconstruct frictional vibration and the information entropy of friction vibration represents the running-in process. Based on these results, a condition monitoring system can be established to automatically evaluate the running-in state of mechanical parts.

The EEMD method was applied to reconstruct the frictional vibration. Furthermore, the information entropy of friction vibration was used to analysis the running-in process.

The purpose of this work is to comprehensively reveal the spatial distribution and evolution features of a running-in attractor.

The friction coefficient signals extracted from wear experiments are reconstructed. A projected matrix is obtained based on the reconstructed matrix. Then the approach of three-dimensional (3D) histogram of phase points is proposed, which is used to intuitively characterize the complex properties of the running-in attractor.

The space occupied by the running-in attractor gradually contracts, then stabilizes and finally expands; the maximum of phase points number in a certain bin initially decreases, then keeps stable and finally increases rapidly; yet the percentage of bins number storing phase points shows an inverse variation tendency. Consequently, 3D histogram evolves from a nonuniform state to a uniform state then returns back to the nonuniform state, which indicates the evolution rule of “formation, stabilization and disappearance” of the running-in attractor.

Characterization on the features of the running-in attractor can provide valuable information about friction systems and their dynamic behaviors.