The cylinder block/valve plate interface in the axial piston pump has been proven to be easily worn out, which will increase power loss and reduce its efficiency. The valve plate surface is required to be manufactured with low viscous friction and wear. Multi-scale micro-texture has been proven to improve surface tribological properties. However, there are few types of research in the effect of surface topography on the tribological performance of multi-scale micro-textured surfaces. The purpose of this study is to explore how the multi-scale micro-texture on H62 brass affects its sliding friction behavior on 38CrMoAl. Based on micro-milling and wet micro-blasting, the multi-scale micro-textured surface was manufactured on H62 brass. The wet micro-blasting was applied in the H62 brass after the surface micro-texturing. The surface topography of multi-scale micro-textured samples processed by three abrasive grit sizes accompanied by two processing times was comprehensively measured in terms of height, feature, functional, and functional volume parameters. The tribological performance of multi-scale micro-textured H62 brass was characterized by disk-on-disk frictional experiments. Through analyzing the relationship between surface morphology and tribological properties, the anti-friction mechanism of the multi-scale micro-textured surface was analyzed from the perspective of 3D surface roughness parameters. The friction coefficient of the multi-scale micro-textured surface processed by the combination of micro-milling and wet micro-blasting decreased with the increasing grit size and micro-blasting time.

Cylinder bore honing is a finishing process that generates a crosshatch pattern with alternate valleys and plateaus responsible for enhancing lubrication and preventing gas and oil leakage in the engine cylinder bore. The required functional surface in the cylinder bore is generated by a sequential honing process and is characterized by R k roughness parameters (R k , R vk , R pk , M r1 , M r2 ). Predicting the desired surface roughness relies primarily on two techniques: (i) analytical models (AM) and (ii) machine learning (ML) models. Both of these techniques offer certain advantages and limitations. AM's are interpretable as they indicate distinct mapping relation between input variables and honed surface texture. However, AM's are usually based on simplified assumptions to ensure the traceability of multiple variables. Consequently, their prediction accuracy is adversely impacted when these assumptions are not satisfied. However, ML models accurately predict the surface texture but their prediction mechanism is challenging to interpret. Furthermore, the ML models' performance relies heavily on the representativeness of data employed in developing them. Thus, either prediction accuracy or model interpretability suffers when AM and ML models are implemented independently. This study proposes a hybrid model framework to incorporate the benefits of AM and ML simultaneously. In the hybrid model, an artificial neural network (ANN) compensates the AM by correcting its error. This retains the physical understanding built into the model while simultaneously enhancing the prediction accuracy. The proposed approach resulted in a hybrid model that significantly improved the prediction accuracy of the AM and additionally provided superior performance compared to independent ANN.

The dimensional accuracy of engine cylinder bore at multiscale has a tremendous influence on engine performances including friction power loss, vibration, leak tightness between piston and cylinder, and wear resistance. Tremendous researches were devoted to predict the dimensional accuracies of the honed cylinder by means of analytical, experimental, and numerical simulation methods. The dimensional quality of the honed cylinder bore was usually determined by establishing the relationship between honing parameters and dimensional accuracies of the honed cylinder bore. However, most researches predicted dimensional accuracy at macroscale or surface texture at microscale, respectively. Few efforts were devoted to predict the dimensional quality of honed cylinder bore at both macroscale and microscale levels simultaneously. To explore a new understanding of the honing mechanism of the cylinder bore, a multiscale model is proposed to predict the dimensional accuracy and surface texture of cylinder bore generated from the honing process at the macroscale and microscale simultaneously. The model aims to integrate both microscale factors including honing stone abrasives distribution, abrasive wear process, previous cylinder surface topography, and macroscale factors including cylinder geometric features and honing head motion trajectory into a multiscale analytical analysis. A force matching method is adopted in the multiscale predictive model to determine the feed depth in the honing of the cylinder bore. Thus, the proposed multiscale analytical model possesses an excellent capacity to simultaneously predict the roundness and cylindricity of the honed cylinder bore, as well as the surface texture/roughness of the honed cylinder bore in terms of Abbott-Firestone curve. The simulated results also revealed that the material removal process is closely related to the initial shape deviations of the cylinder bore, which cannot be corrected, compensated, or eliminated by the subsequent honing process given the deviations are associated with wavelengths higher than 27 mm under the given honing condition.

Fretting is a damaging phenomenon, generally observed when a mating pair is subjected to a small amplitude of oscillatory motion. The contact behavior in fretting is governed by a complex interaction between mechanical properties of mating pair, contact geometry, and loading conditions. In most of the practical applications, dissimilar materials are chosen for a contacting pair with one of the materials having superior material properties than other so as to replace the worn-out or unfit component during the maintenance. In the literature, many researchers have studied the effect of dissimilar materials on fretting behavior but mainly in the context of hardness. As experimental methodology has been adopted in these studies, the effect of dissimilar material properties has been reported in terms of global variables like wear volume or fretting fatigue life, but its influence on underlying local contact tractions could not be studied. In the present work, a two-dimensional finite element analysis has been carried out for a cylinder-on-plate configuration. The effect of dissimilar materials for the mating pair has been studied by modeling elastic–plastic behavior for combinations of three different materials, namely, SS 304, ASTM A302-B, and aluminum. The validation of the finite element model is carried out by comparing the results of elastic analysis with the analytical solutions available in the literature. The pertinent contact parameters in the context of fretting wear, namely, contact pressure, contact slip, and contact stresses are extracted. A frictional dissipation energy density-based approach is used for the qualitative comparison of the fretting damage for different cases and validated with the literature data.

As the road transport accounts between 15%–18% of worldwide CO 2 emissions, the automotive sector has a deep commitment to mitigate global warming. Consequently, stricter regulations have been adopted by the European Union and worldwide to reduce that big impact. Approximately, 10% of the energy generated by fuel combustion in the engine is destined to the auxiliaries components activation and the movement of mechanical elements with relative motion between themselves. A reduction on that figure or alternatively a mechanical efficiency improvement can be directly translated on target alignment. The aim of this work is developing a model to predict the mechanical and friction losses and its distribution in a four-stroke direct injection-diesel engine and simulating different strategies, which increment the engine efficiency. A 1D model has been developed and fitted in gt-suite based on the experimental results of a 1.6-L diesel engine. Additionally, a description of the tribological performance has been realized in different parts of the engine where friction is present. Finally, the engine friction maps have been broken down in order to quantify the friction losses produced in the piston ring assembly, crankshaft bearings, and valvetrain.

Sequential honing process is usually implemented in engine cylinder bore processing to obtain the cross-hatched surface texture with excellent function to balance lubricant storage capacities and supporting performance. Many researches have devoted to correlating honed surface quality of cylinder bore with honing process parameters by means of experiments or simulations. Quite a few efforts have addressed the effect of sequential multiple steps on the surface texture in the honing of engine cylinder bore. However, these researches cannot provide an explicit and analytical methodology to predict honed surface texture efficiently and accurately. This paper presents an analytical and explicit methodology to incorporate a proposed microscale abrasive model into the analytical simulation process of sequential honing. The proposed abrasive model synthetically considers the shape, size, posture, and position of abrasives randomly distributed in honing stone, which is incorporated into honing head motions in terms of rotation, oscillation, and feeding. The kinematics of honing head is calculated by space–time discretization to capture the interaction between honing stones and cylinder bore surface. The above procedure acts as each single step for the sequential honing processes. This study investigates the sequential honing of two stages including semi-finish honing and plateau honing at different feeding speeds by applying the abrasive model with different abrasive sizes. The formation of cross-hatched surface texture was successfully achieved sequentially by semi-finish honing and plateaus honing. Then, the Abbott-Firestone curve of the honed surface can be obtained to analyze the influences of abrasive size and honing time of two stages on the surface roughness. Correctness of surface roughness predicted by the model is verified by comparing with a group of experiment measurements in terms of Abbott-Firestone Curve. Most errors of all the predicted R k roughness family roughness parameters in the two honing stages are less than 15%. Based on the model, simulations are done to analyze the influences of abrasive size and honing duration time of two stages on the surface roughness. The result shows that the larger abrasive used in finish honing leads to the decrease in the material portions M r 1 , M r 2 and the increase in the reduced valley depth R vk . The longer plateau honing duration time is preferred to produce the larger M r 1 , M r 2 , and the smaller R vk .

This work investigates the effect of convexity position of ring barrel surface on the wear properties and scuffing resistance of the Cr–Al 2 O 3 coated piston rings against with the CuNiCr cast iron cylinder liner. The scuffed surface morphology and elements distribution as well as the oil film edge were analyzed to explore the influencing mechanism of the convexity position on the scuffing resistance. The results show that the convexity offset rate on the barrel surface of the ring has no noticeable influence on both friction coefficient and wear loss near the dead points, but a suitable convexity position will result in the improved scuffing resistance. The shape of the barrel face not only affects the worn area on the ring, but also determines the oil film wedge and pressure distribution, consequently influences the scuffing resistance.

The tribological performance of a compression ring-cylinder liner system (CRCL) is numerically studied. A thermal-mixed lubrication model is developed for the lubrication analysis of the CRCL with consideration of the cylinder liner deformation. An oil transport model coupled with a mass conservation cavitation algorithm is employed to predict the oil consumption and the transition between the fully flooded lubrication condition and starved lubrication condition. On this basis, the effects of the oil supply and cylinder liner deformation on the frictional characteristics are investigated under cold and warm engine conditions. The results show that the cylinder liner deformation and oil supply have great influence on the tribological performance of the CRCL. Better tribological performance and lower oil consumption can be obtained by reasonably controlling the oil supply.

Despite the importance of precise evaluation of wear volume losses from cylinders, several factors make the investigation of large surface areas from cylinder bores a hard issue. Topography analysis has been widely used to quantify wear in cylinders but no method was found in the literature for the quantification of wear volume losses considering the whole stroke length of cylinder bores. In this work, three-dimensional (3D) measurements were taken from a gasoline engine tested in dynamometer for 625 h and wear volume profiles were obtained for all cylinders. The results from the proposed method showed good agreement with both the variation of the core height and the visual analysis from stereo images.

In this paper, a profile design of surface texture was applied for improving the tribological performance of piston ring–cylinder pair. The design of texture pattern was implemented by numerous textures of different depths in sliding speed direction to imitate the outline of barrel-shaped ring. The thickness and pressure distribution of oil film were obtained through a joint solution of modified Reynolds equation and other governing equations for textured surface. The results indicate that the novel texture pattern has the best overall performance in oil film thickness and friction force compared with normal surface textures, and the average friction power is 10.04% and 16.85% less than normal surface textures and barrel-shaped ring in the whole working cycle. Extra microhydrodynamic lubrication can be observed in the middle region of textured piston ring through the pressure distribution of oil film. At last, the experiment was conducted in a motored test rig and exhibited up to 3% reduction in friction power.

To enhance the friction property of Al–Si alloy cylinder liner in running-in period, MoS 2 coatings were electrodeposited on the chemical-etched surface of cylinder liner. The friction coefficient decreased by 15% comparing with the original honed surface, indicating the better friction property. This is because the synergistic action between solid lubricant and etched surface. MoS 2 coatings prevent the direct contact between silicon particles and piston ring during friction. At top dead center, the oil film was thinnest and even was broken during the reciprocate friction. When oil film was invalidated, MoS 2 coatings undertook lubrication. Then, MoS 2 coatings were depleted, and advantage of etched surface became apparent.

This work presents a finite element study of a two-dimensional (2D) plane strain fretting model of a half cylinder in contact with a flat block under oscillatory tangential loading. The two bodies are deformable and are set to the same material properties (specifically steel), however, because the results are normalized, they can characterize a range of contact scales (micro to macro), and are applicable for ductile material pairs that behave in an elastic-perfectly plastic manner. Different coefficients of friction (COFs) are used in the interface. This work finds that the edges of the contacting areas experience large von Mises stresses along with significant residual plastic strains, while pileup could also appear there when the COFs are sufficiently large. In addition, junction growth is investigated, showing a magnitude that increases with the COF, while the rate of growth stabilization decreases with the COF. The fretting loop (caused by the tangential force during the fretting motion) for the initial few cycles of loading is generated, and it compares well with reported experimental results. The effects of boundary conditions are also discussed where a prestressed compressed block is found to improve (i.e., reduce) the magnitude of the plastic strain compared to an unstressed block.

The status of the lubricating oil transport in the piston skirt-cylinder liner has important influence on the lubrication of piston assembly frictional pair, the consumption of lubricating oil, the emission, and the performance degradation of lubrication oil. In this paper, based on the model of piston secondary motion, fluid lubrication and lubricating oil flow, the status of the lubricating oil transport between the piston skirt and the cylinder liner on different engine operating condition is calculated, and the quantity of lubricating oil retained on the surface of cylinder liner is mainly analyzed when the piston skirt moves from the top dead center to the bottom dead center. The results show that the variation of the quantity of retained lubricating oil is almost same in the corresponding stroke on different engine operating condition; the quantity of retained lubricating oil is dissimilar at different moment and is equal in principle at the piston top and bottom dead center. The quantity of lubricating oil retention is dissimilar at different moment in the intake stroke or expansion stroke, but the quantity of lubricating oil retention is equal in principle at the top and bottom dead center on different engine operating condition. When the engine is on the same load condition, as the engine rotational speed increasing, the quantity of retained lubricating oil is decreased in the whole intake stroke and the middle and later parts of expansion stroke, but the quantity of retained lubricating oil is increased in the front part of expansion stroke. When the engine is on the same rotational speed condition, the quantity of retained lubricating oil increases with the increasing engine load in the front part of expansion stroke, it does not vary with the engine load in principle in the middle and later part of expansion stroke, the variation that the quantity of retained lubricating oil varies with the engine load is dissimilar in the intake stroke on different engine rotational speed condition.

Hydraulic cylinders are generally used as power take-off (PTO) mechanisms in wave energy converters (WECs). The dynamic behavior of its PTO force, which integrates friction and pressure forces, is a difficult constraint to include in an analytical or in a numerical model. In this paper, the PTO force characteristics of a hydraulic cylinder are experimentally and numerically investigated under different magnitudes of controlled excitation force. In order to characterize the dynamic behaviors of PTO force, the displacement, acceleration, and pressure in the cylinder chamber for given excitation forces are measured. The pressure force is calculated using the measured value of the pressure, and the friction force is calculated based on the equation of motion using measured values of the pressure, excitation force, and acceleration of the piston. Experimental results show clearly a strong nonlinear force–velocity characteristics, including stochastic and hysteretic behaviors. To model the hysteretic behavior, the modified LuGre model is used for the friction force and a new approach is proposed for the pressure force. To model the stochastic behavior of the friction and pressure forces, the spectral representation method is used. The systematically comparison between measured and simulated results shows that the numerical model captures most of dynamic behaviors of PTO force.

Different profile structures were designed for a high-power engine piston, and engine tests were carried out to analyze and compare the influences of the widest point position and contraction rate on the skirt wear property. The results show that the lower position of the widest point will cause poor guidance, and at the same time the rapid radial reduction in both the upper and lower parts will increase the swing angles and the kinetic energy; the uniformity of wear loads can be improved effectively by increasing the height of the widest point and the width of the maximum diameter region; the degree of wear of the skirt can be considered through a comparison of the outer diameter variation.

Ball piston is an essential design element in eccentric ball piston pump. The objective of this paper is to investigate the dynamic force and lubrication characteristics of the ball piston. In this study, a tribodynamic model of the ball piston is proposed. The model couples the elastohydrodynamic lubrication model of ball–ring pair and the elastohydrodynamic model of ball–cylinder pair with the dynamic model of the ball piston. The interaction between tribological behavior and dynamic performance and the effects of centrifugation and structural deformation of the ball piston are considered. The pressure distributions and film profiles of the ball–ring pair and ball–cylinder pair are calculated. The dynamic normal contact forces and friction forces are analyzed. The friction torque loss and mechanical efficiency of the whole pump are obtained by combing the tribodynamic model of the ball piston with a simplified friction torque model of cylinder-valve shaft pair. A test bench is established for validating the simulation results. The results show that the normal contact force of the ball–ring pair waves in each stroke, and in discharge stroke, the contact force is much bigger than that in suction stoke because of loading force, while the friction force changes very little for the ball sliding in the outer ring. Comparing with the average friction force of the ball–ring pair, the average friction force of the ball–cylinder pair is small, which reflects that the ball–ring pair is more prone to wear. For the ball–ring friction pair, when the load increases, the secondary contact pressure peak appears, the profile of film presents a horseshoe shape, and the classical shrinkage appears at the outlet of contact region. For the ball–cylinder pair, the film pits and the contact pressure jumps at the entrance of contact region for the heavy load and the high shear stain of film. In addition, the friction torque presents a nonlinear growth trend with the increasing working pressure

A starved lubrication experiment and analytical model have been developed to investigate the friction condition transition (FCT) at the interface between a piston ring and a cylinder liner with the piston ring reciprocating liner test rig. To obtain a solution for the friction condition transition, phase space trajectories are used to extract the transient features of the friction force. The trajectories have three typical patterns for starved lubrication conditions. The irregular friction force of different strokes is classified based on the trajectories. When the projection of the trajectories in the phase space enters into the third pattern variation, this indicates the onset and progression of scuffing. The autocorrelation analysis of the wear surface topography at the stroke end validates the characterization method.

A theoretical and computational framework for the analysis of fully transient, thermomechanically coupled, frictional rolling contact based on an arbitrary Lagrangian–Eulerian (ALE) kinematical description is presented. In particular, a computationally efficient methodology for mixed control between the ALE referential velocities and their corresponding driving forces is developed and discussed in depth. Numerical examples involving two-dimensional (2D) cylinder–plate rolling contact are presented, covering a range of transient, thermomechanically coupled rolling contact phenomena, taking place on a broad range of time scales. Here, particular points of emphasis include dynamical effects in the vicinity of the contact region and the time scales on which mechanical and thermal mechanisms operate.

Minimization of parasitic losses in the internal combustion (IC) engine is essential for improved fuel efficiency and reduced emissions. Surface texturing has emerged as a method palliating these losses in instances where thin lubricant films lead to mixed or boundary regimes of lubrication. Such thin films are prevalent in contact of compression ring to cylinder liner at piston motion reversals because of momentary cessation of entraining motion. The paper provides combined solution of Reynolds equation, boundary interactions, and a gas flow model to predict the tribological conditions, particularly at piston reversals. This model is then validated against measurements using a floating liner for determination of in situ friction of an engine under motored condition. Very good agreement is obtained. The validated model is then used to ascertain the effect of surface texturing of the liner surface during reversals. Therefore, the paper is a combined study of numerical predictions and the effect of surface texturing. The predictions show that some marginal gains in engine performance can be expected with laser textured chevron features of shallow depth under certain operating conditions.

A comprehensive numerical model is developed using Lagrangian finite element (FE) formulation for investigating the steady-state viscoelastic (VE) rolling contact response. Schapery's nonlinear viscoelastic (NVE) model is adopted to simulate the VE behavior. The model accounts for large displacements and rotations. A spatially dependent incremental form of the VE constitutive equations is derived. The dependence on the history of the strain rate is expressed in terms of the spatial variation of the strain. The Lagrange multiplier approach is employed. The classical Coulomb's friction law is used. The developed model is verified and its applicability is demonstrated.