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Abstract Lubricated full-floating pin bearings are being more and more widely used in the industrial products because of the advantages in terms of lubrication, scuffing resistance and durability. The present study develops a numerical model for the lubricated full-floating pin bearings in multibody mechanical systems by embedding the hydrodynamic lubrication and solid contact forces in the revolute joint clearance. The modified Coulomb law is employed to deal with the numerical difficulties caused by the pin stick-slip motion, while the MEBDF approach is applied to a high computation efficiency. An application example in a gasoline engine is then used to demonstrate the validity of the proposed model and reveal the friction reducing and anti-wear mechanisms for such pin bearings. Highlights • A numerical model for the lubricated full-floating pin bearing is developed. • Modified Coulomb law is employed to deal with the numerical instability. • The MEBDF approach is applied to a high computational efficiency. • Friction reducing and anti-wear mechanisms are investigated. [ABSTRACT FROM AUTHOR]

Robust and accurate measurement techniques are essential to studying the piston-assembly friction of Internal Combustion (IC) engines. Based on the instantaneous Indicated Mean Effective Pressure (IMEP) method, this paper develops an improved measurement technique to evaluate the piston-assembly friction in engines. Wireless telemetry technology is employed in the measurement of connecting rod axial force, which greatly minimizes the engine modifications and enhances the measurement stability compared to the conventional wired way. The measurement system, which is composed of computer, data acquisition system, sampling trigger apparatus and sensors, is exploited with special attention given to the sampling synchronization of signal channels including cylinder pressure, connecting rod force and crank angle position. Engineering implementations are carried out on a four-stroke gasoline engine under motored condition. The measurement results are compared with numerical results from a newly developed numerical coupling model system, and it shows that the two agree well. In addition, the piston-assembly friction under different engine speeds and inlet lubricant temperatures are also measured, and analyses indicate that these results are in good correlation with the well-known Stribeck curve. This improved measurement technique provides an accurate and reliable option for the friction evaluation of piston-assembly components in engine designs. [ABSTRACT FROM AUTHOR]

Fuel economy improvement of the Internal Combustion (IC) engine is prompted by the broad promulgation of more stringent vehicle emission regulations. Friction loss during the engine start-up is a longstanding issue because of the high frictional dissipation under cold-start and the heavy wear within warm-start. This study presents a numerical cycle-by-cycle investigation into the piston tribo-dynamics characteristics and friction loss during the Spark Ignition (SI) engine cold- and warm-start based on a coupled piston tribo-dynamics model system. The model system consists of the piston skirt-liner mixed lubrication model and the piston-rod-crank mechanism multibody dynamics model. Thermal distortion of the piston and the liner, and the lubricant viscosity-temperature property are accurately incorporated into the corresponding engine start-up conditions. Analyses and comparisons between the cold- and warm-start are carried out in terms of tribology and dynamics. Results show that frictional energy dissipated by the cold-start is 72% higher than the warm-start, which primarily due to viscous shearing of lubricant oil. At low engine speed, the tight clearance under warm-start results in a lower level of slap noise excitation than under cold-start. It is also found that the low oil viscosity of warm-start leads to a high risk of catastrophic scuffing and seizure failure near the FTDC of the first ignition cycle. In the light of the above analysis, a piston profile optimization scheme is proposed and its influence on piston scuffing resistance and energy efficiency enhancement is assessed. The evaluations indicate that almost half of friction consumption can be reduced for the engine warm-start if the thermal intricacies are properly factored in the piston design. [ABSTRACT FROM AUTHOR]

The machining micro-grooves on the piston skirt surface are very common in internal combustion engines. To accurately investigate the influence of the grooves on piston tribodynamic performance, a coupling model of piston skirt-liner lubrication and crank-rod-piston multibody dynamics is built in this study. The lubrication model is solved by the Finite Element Method with deterministic treatment of the grooves. The multibody dynamics equations are formulated with Lagrange multipliers and constraint Jacobian matrix in the form of Differential Algebraic Equations (DAEs). The MEBDF approach is applied to a high efficient time integration of the DAEs. Based on the above model, the influences of grooves and some groove parameters on piston skirt-liner lubrication as well as piston slap are studied and revealed. [ABSTRACT FROM AUTHOR]

• A model couples piston skirt-liner system and floating pin assembly is developed. • Tribo-dynamic interaction mechanisms between the two friction pairs are revealed. • Effects of design parameters including piston pin clearance and offset are probed. • Friction torque on pin visibly affects piston tribo-dynamic behavior near the FTDC. • Piston is more sensitive to pin offset than pin assembly in tribo-dynamic behavior. Piston Skirt-Liner (PSL) system and Piston Pin Bearing (PPB), two key friction pairs in piston-assembly, interact with each other via impact and friction when transmitting the combustion load to crank train. Literature reporting such an interaction behavior in terms of tribology and dynamics is still rare, due to the complexity in a systematic modeling way. This paper proposed an efficient numerical model that fully couples these two friction pairs to investigate tribo-dynamic interactions between them. The model is built by coupling Reynolds-based mixed lubrication models for the friction pairs with Lagrange multibody motion equations for the piston-connecting rod-crank mechanism. Coupling effects between the piston skirt-liner system and the pin assembly are explored by comparing the cases contain the two friction pairs and one of them. Based on the above analyses, some design parameters including pin assembly clearance and pin offset, are further studied to disclose their influences on the tribo-dynamic performance of these two friction pairs. This work has a guiding significance for the systematic design of piston-assembly aiming to improve the dynamic property, economical efficiency and environmental-friendliness of engines. [ABSTRACT FROM AUTHOR]