Abstract
The friction pair of piston rings and cylinder liner is one of the most important friction couplings in an internal combustion engine. It influences engine efficiency and service life. Under the excitation of piston slaps, the dynamic deformation of cylinder liner is close to the surface roughness magnitudes, which can affect the friction and lubrication performance between the piston rings and cylinder assemblies. To investigate the potential influences of structural deformations to tribological behaviours of cylinder assemblies, the dynamic deformation of the inner surface due to pistons slaps is obtained by dynamic simulations, and then coupled into an improved lubrication model. Different from the traditional lubrication model which takes the pressure stress factor and shear stress factor to be constant, the model proposed in this paper calculated these factors in real time using numerical integration to achieve a more realistic simulation. Based on the improved piston rings and cylinder liner lubrication model, the minimum oil film thickness and friction force curves are obtained for an entire work cycle. It shows that the friction force obtained from the improved model manifests clear oscillations in each stoke, which is different from the smoothed profiles predicted traditionally. Moreover, the average amplitude of the friction forces also shows clear reduction.
Highlights
Parasitic losses account for nearly 20% of an internal combustion (IC) engine’s total losses.As one of the primary sources of friction in the engine, the compression rings are responsible for 4%to 5% of all losses in a typical diesel engine [1]
There are two ways in which the dynamic deformation affects the lubrication behaviours between the piston rings and liners: one is that the deformation of the surface morphology directly changes the distribution of lubricating oil film, changing the asperity friction; the other is that the deformation may cause changes in shear properties, i.e., shear stress factors, of lubricating oil, resulting in viscous friction changes
In order to study the differences in influences of models aredynamic proposed, which only considers the effect of the oil film surface deformations on the oil film distribution anddynamic oil shear deformation properties, twoon improved distribution named model
Summary
Parasitic losses account for nearly 20% of an internal combustion (IC) engine’s total losses. Ma et al [10] studied the impacts of liner distortion on the friction forces between the piston rings and cylinder liners. Meng et al [12] further indicated that the vibration of the cylinder liner can result in oscillations in the dynamic and tribological performances of the piston assembly, especially in the power stroke of an IC engine Their studies have shown that the vibration-induced friction reduction is closely related to the engine’s running speed, structural stiffness, and damping characteristics, and the mass of the cylinder structure. To investigate the effect of surface finish on piston ring-pack performance, Jeffrey Jocsak [15] proposed an integral calculation method of stress factors that makes it possible to consider the influence of non-Gaussian surface morphology on viscous friction forces.
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