Piston Skirt Friction Research Articles

Research on Friction and Wear Behaviors of Different Solid Lubricant Coatings on Aluminum-Based Piston Skirts

Abstract Stringent requirements in emissions drive the application of low-carbon fuel engines, which result in prominent friction and lubrication problems in the cylinder. Solid coating technology is an effective way to enhance the tribological performance of tribo-pairs and has great potential to solve friction and lubricant problems. In this work, graphite, molybdenum disulfide (MoS2), and tungsten disulfide (WS2) solid lubricant coatings were prepared on aluminum-based piston skirts, respectively. The friction and wear behaviors of three coatings were investigated using a self-designed piston skirt friction and wear apparatus. The chemical products generated on the worn surfaces were analyzed, and the combined effect of lubricating oil and solid lubricant coatings was confirmed. The results show that the solid coatings can effectively enhance the friction and wear characteristics of piston skirt-cylinder liner tribosystem, and WS2 coating has the best anti-friction and wear-resistant performance among the three coatings.

Reduction of Piston Skirt Friction Using the Micro-scale Patterned Surface

Reduction of Piston Skirt Friction Using the Micro-scale Patterned Surface

Investigation of Friction and Wear Behavior of Cast Aluminum Alloy Piston Skirt with Graphite Coating Using a Designed Piston Skirt Test Apparatus.

A piston skirt friction and wear apparatus that simulates the contact and the relative motion of piston and cylinder liner in a real engine has been designed and constructed. With this apparatus, the friction and wear behavior of a cast aluminum alloy piston with a graphite coating under different loads was studied, and the effectiveness of the apparatus was confirmed. The total wear of the piston skirt was higher under a higher load, and the upper part of the skirt surface (around the height of the piston pin) was worn more severely. The wear mechanisms were studied and, based on the test results and surface analyses, three main wear modes were believed to occur in the wear process of the piston skirt: abrasive, adhesive, and fatigue wear. The effects of skirt profile design, coating, and surface texturing on the friction and wear behavior of the piston skirt can be investigated well using the proposed apparatus, which can truly reflect actual working conditions and is useful to improve the tribological performances of piston skirts.

An experimental and theoretical investigation on the effects of piston clearance and oil viscosity on Cranktrain friction

In this paper, the effects of clearance between piston and cylinder and oil viscosity index on the friction of area between the piston and cylinder of an internal combustion (IC) engine were investigated experimentally and theoretically. To this end, two values of 33 and 66 µm for the piston clearance, and two types of engine oil namely SAE10W40 and SAE20W50 were considered. To carry out the experiments, the engine was run under motored condition. The experiments were implemented at different oil temperatures and engine speeds. Based on the experimental results, although reduction in the piston clearance and the use of 20W50 oil caused an increase in the friction, but the effects of these two parameters became less with an increase in oil temperature and engine speed. The experimental results showed that the effect of clearance on the friction was more noticeable for low speeds. The maximum influence of the piston clearance decrease on the friction was 16% with the use of 20W50 oil at 1000 r/min when the oil temperature was 35 °C. The minimum influence of the piston clearance on the friction was 0.5% when the oil temperature was 90 °C and the engine speed was set on 6000 r/min. The theoretical results showed that the most contribution of the friction of piston/ring/cylinder assembly belonged to the piston skirt. Moreover, the effect of the piston skirt on the friction at high speeds was more than that of the piston rings. The friction value of the piston rings was not significantly altered by changing the engine speed, but it was considerably changed by the oil temperature variation. Whereas the piston skirt friction had an increasing trend with the speed rise, the change in the engine oil temperature, especially for low temperatures, had no significant effect on the piston skirt friction.

Study of Break-In Process and its Effects on Piston Skirt Lubrication in Internal Combustion Engines

The piston skirt is one of the main contributors to the total mechanical loss in internal combustion engines. Usually, the skirt friction experiences a rapid change during the break-in period largely due to the wear of the machine marks or roughness against soft coatings. It is thus important to consider the effect of the change of the roughness for a realistic prediction of the piston skirt friction and system optimization. In this work, an existing model of piston skirt lubrication was improved with the consideration of a breaking in process for the most commonly used triangle machine marks. A new set of flow factors in the averaged Reynolds equation were analytically derived for the trapezoid shape formed after wear of the original triangle shape. A new asperity contact model was developed for the trapezoid shape. The calculation results reflect the trend of friction mean effective pressure (FMEP) during break-in in an engine test and showed quantitative agreement under the same amount of wear.

Piston skirt friction loss and dynamic analyses based on FEM method

PurposeThe analysis carried out in this study can provide guidance for manufacturers and researchers to design a piston for the development of engines.Design/methodology/approachRunning conditions for pistons have become very severe because of the high combustion pressure and increase in piston temperature in the past 10 years. The precision of the model has a great effect on the power transmission, vibration noise emission. In this paper, the model was established with lubrication and dynamic governing equations, which were solved using finite element method coupled with Runge–Kutta method. A piston of an inline six-cylinder engine was studied, and some structural parameters were used to investigate its effect on the friction loss with lubrication and dynamic motion theory.FindingsBased on the analyses, the effect of the friction load at the oil groove and thermal deformation of piston skirt were added to the model, and some useful information about the friction loss and dynamic characteristics were compared.Originality/valueAll the results will provide guidance for the development of the piston and reduction in the friction loss and wear.

Analysis of the Influences of Piston Crankshaft Offset on Piston Secondary Movements

This paper takes dynamics analysis on the piston and the dynamic lubrication theory on the skirt and the ring of piston as the basis. Using AVL Glide software, through the establishment of the analysis model of the piston secondary movements, this study focuses on the effects of the crankshaft bias on piston secondary movements’ characteristics. This paper takes 5 different offsets, by comparing the piston lateral displacement, transverse movement speed, transverse acceleration, swinging angle, swing angular velocity and angular acceleration, finds out the relationships between crank offset value and the piston “slap”, piston impact energy and piston skirt friction loss, thus, provides the basis for the design of internal combustion engines.

Technique to determine instantaneous piston skirt friction during piston slap

The intermittent transient contact of the piston skirt and cylinder liner is related to the secondary motion of the piston. The instantaneous piston secondary motion measured using laser displacement sensors can indicate whether the piston skirt is in contact with the cylinder liner. The force of the impacting piston skirt on the cylinder liner can be calculated using the equation of motion, which allows the piston skirt friction force to be distinguished from the total friction force and friction torque. The results showed that the piston skirt friction force contributes as much as 44% of the overall piston assembly friction force.

Practical challenges in determining piston ring friction

Practical challenges from both experiment and calculation sides were discussed for determining two piece twin land oil control ring friction. A floating liner engine was used for twin land oil control ring study. Effects of floating liner engine system dynamics and piston skirt friction were addressed and methods to mitigate them were discussed. A deterministic twin land oil control ring model was used for ring friction calculation. Variation of the surface roughness at different spots of the liner and its effects on both hydrodynamic and boundary lubrication predictions were discussed. A multi-point correlation method was introduced to address surface variation effects on the twin land oil control ring model. Ring land width variation between two lands as well as along the circumference and its effects on calculation were shown, and methods to address it were discussed. By taking all these necessary steps in both experiments and calculations, this study shows that a reasonable match can be achieved between the measured and calculated friction, which covers all three lubrication regimes. This study lays a foundation for realistically predicting the friction of piston rings in internal combustion engines.

Coupled Analysis of Piston Mechanism and Lubrication (Numerical Calculation of Piston Skirt Friction)

In this study, we have developed a coupled analysis method of piston dynamics and lubrication. The kinematic motion and structural vibration are calculated by the flexible multibody dynamics theory developed in the former study. The mixed lubrication film between the piston skirt and the cylinder bore is numerically modeled as a force element. The hydrodynamic pressure and the friction force in fluid lubrication region on this interface are solved by a finite difference method. The contact pressure and the friction force by solid contact are calculated by the statistic asperity contact model. This mixed lubrication model is validated by a reciprocating friction tester. Then, we apply this method to the estimation of the friction force measured by a floating liner type friction tester at firing condition, and clarify the contributions of hydrodynamic and solid contact on the friction force.

複リンク式高膨張比内燃機関の熱効率(熱工学,内燃機関,動力など)

Research has been conducted on an extended expansion engine, using a multiple-linkage system to increase thermal efficiency of internal combustion engines. A four-jointed linkage was attached between the connecting rod and the crank pin of a conventional piston-crank system. The end of the linkage rotates at half the speed of the crankshaft, resulting in piston strokes unequal length in each revolution. The length of the expansion stroke is greater than that of the compression stroke, thereby providing an extended expansion cycle, so called Atkinson cycle. An air-cooled single-cylinder engine equipped with this mechanism was constructed and its thermal efficiency was compared in tests against a conventional engine which has same maxmum power. The brake performance of both engines was measured, displaying 2.7 to 3.5% increase of brake efficiency under high-load operation. Measurements of drive loss during motoring operation showed that the friction of this engine is approximately the same as that of a conventional engine, due to the reduction of the piston skirt friction during expansion stroke. The maximum inclination angle of connecting rod of this linkage system during expansion stroke is small, so the side force of piston skirt is smaller than that of the conventional piston-crank system.

Analysis of piston assembly friction using the indicated mean effective pressure experimental method to validate mathematical models

The piston assembly friction is experimentally measured using the indicated mean effective pressure with detailed accuracy. The experimental results are compared with a relatively less complex piston assembly friction model typical of those used in industry, predicting the individual performance of compression rings, the oil control ring, and the piston skirt. The validation is carried out under fired conditions on a single-cylinder gasoline engine. The experimental results for an SAE 0W20 lubricant without a friction modifier were compared with the predictions. The predicted results correlate very well with the measurements, especially at higher lubricant inlet temperatures. The piston skirt friction was predicted using a simple concentric piston—cylinder model and a more realistic but computationally intensive method incorporating the piston's secondary motion. The results clearly indicate that a relatively less complex model can give realistic results under real engine conditions.

214 ガソリンエンジンにおけるピストンスカート部のフリクション低減に関する研究(熱力学3)

214 ガソリンエンジンにおけるピストンスカート部のフリクション低減に関する研究(熱力学3)

Analysis of Piston Skirt Friction in a Gasoline Engine

In order to reduce the friction of the piston system, it is important to understand the friction and lubrication at the skirt and ring. In gasoline engines, the friction of the skirt is often equal to or larger than that of the ring pack, then the reduction of the friction at the skirt is indispensable. In this study, the piston skirt friction was measured by the floating liner engine which consists of independent measuring devices for skirt and ring pack friction. In addition, the skirt friction was calculated by a simulation model considered surface roughness, boundary lubrication, skirt profile and skirt stiffness. The calculated skirt friction compared with experimental data measured by floating liner method. As a result, the calculated skirt friction showed good agreement with the measured results, thus it was confirmed that the calculation accuracy of the skirt friction was sufficient. Furthermore, calculations of the skirt friction were carried out to clarify the influence of friction factors. It was also found that the skirt friction was affected by the skirt stiffness, skirt profile and skirt bearing area at the case of gasoline engines.

2228 ピストン隙間減少時のピストン摩擦力とその改善に関する研究

Piston frictional force by using floating liner method and piston slap motion were measured in a single-cylinder DI diesel engine. Various piston skirt clearance were tested to evaluated the effect on the piston skirt friction. As a result, it was found that reduced piston clearance produces high frictional force around the top dead centers (TDC) because disappearance the clearance at upper part of the skirt. Both strut piston and resin coating piston were experimented to reduce frictinal force at TDC. Large effects of friction reduction in both method were also demonstrated in this paper.

A comprehensive study of the friction and dynamic motion of the piston assembly

A mixed lubrication model based on a two-dimensional average Reynolds equation is presented in this paper. It is developed for use in conjunction with a piston secondary motion analysis. The motion has been studied and the effects of structure parameters and different profiles of piston skirts on the motion are also investigated. The friction force and power loss consisting of piston skirt friction and the friction of the piston ring pack are also given.

An Automotive Piston Lubrication Model

An analytical study of the dynamics of a piston in a reciprocating engine was conducted. The analysis, which incorporates a hydrodynamic lubrication model, was applied to a V-8 automotive spark ignition engine. The variation of piston transverse position and rotation with crank angle, and the piston-skirt frictional power loss were calculated for different wrist pin locations, piston-to-cylinder clearances, and lubricant viscosities. The results obtained indicate that piston motion is strongly affected by the location of the wrist pin and that piston-skirt friction is increased significantly if the wrist pin is at an unfavorable position. In addition, piston dynamics were found to be sensitive to piston-cylinder bore clearance and lubricant viscosity, underscoring their importance in engine design. Presented at the 37th Annual Meeting in Cincinnati, Ohio, May 10–13, 1982