Takayuki Arai

Numerical Simulation of Piston Ring in Mixed Lubrication—A Nonaxisymmetrical Analysis

The assumption of axisymmetry, employed by most of studies on piston ring lubrication, probably gives a too idealistic model for the real situation. A theoretical model for a nonaxisymmetrical analysis of piston ring lubrication has been established in the present study. When a piston ring with an arbitrary free shape is fitted into the cylinder bore, the determination of ring deflection and contact load has been modeled mathematically as a Linear Complementary Problem (LCP). By combining LCP solution with lubrication analysis, the film thickness and contact load distribution over the circumference are obtained, leading to a more realistic simulation for piston ring lubrication

A Numerical Analysis for Piston Skirts in Mixed Lubrication—Part I: Basic Modeling

This paper presents a mathematical model for piston skirls in mixed lubrication. It lakes into account the effects of surface waviness, roughness, piston skirl surface profile, bulk elastic deformation and thermal distortion of both piston skirls and cylinder bore on piston motion, lubrication and friction. The corresponding computer program developed can be used to calculate the entire piston trajectory and the hydrodynamic and contact friction forces as functions of crack angle under engine running conditions

A Numerical Analysis for Piston Skirts in Mixed Lubrication: Part II—Deformation Considerations

This paper presents a mathematical model for piston skirts in mixed lubrication. It takes into account the effects of surface waviness, roughness, piston skirt surface profile, bulk elastic deformation and thermal distortion of both piton skirts and cylinder bore on piton motion, lubrication and friction. The corresponding computer program developed can be used to calculate the entire piston trajectory and the hydrodynamic and contact friction forces as functions of crank angle under engine running conditions. Complete distributions of the oil film thickness and elastic deformation as well as the hydrodynamic and contact pressures can also be given at any crank angle if needed

A Study of a Variable Compression Ratio System with a Multi-Link Mechanism

This paper presents a variable compression ratio (VCR) system that has a new piston-crankshaft mechanism with multiple links. This multi-link mechanism varies the piston position at top dead center (TDC), making it possible to change the compression ratio of the engine continuously. Previous attempts have been made to achieve variable compression ratio with this type of method, but it was difficult to avoid various undesirable effects such as an increase in the engine size, substantial weight increases, increased engine block vibration due to a worsening of piston acceleration characteristics and increased friction resulting from a larger number of sliding parts. At the stage of developing the basic design of the multi-link geometry, emphasis was placed on selection of a suitable link geometry and optimization of the detailed dimensions with the aim of essentially resolving these previous issues. As a result of the studies conducted at that stage, a VCR link geometry was found that optimally resolves these various issues. Besides achieving the desired VCR capability, this VCR system also provides several new and additional benefits including: (1) a reduction of second-order vibration by making the piston stroke resemble simple harmonic motion (similar to second-order balancer function); (2) lower piston friction loss as a result of reducing the piston-side thrust load in the expansion stroke; and (3) a compact package that can be housed in the crankcase of existing engines. The basic characteristics of a prototype VCR engine that incorporates these new benefits are described on the basis of a theoretical analysis and experimental results obtained in tests conducted with the prototype engine.

A study on engine bearing performance using EHL analysis and experimental analysis

Abstract In order to efficiently improve engine bearing durability, we investigated the feasibility of predicting the durability of actual engine bearings by means of hydrodynamic lubrication computations. This paper describes a method of predicting the amount of actual engine bearing wear based on the results of a numerical analysis (EHL analysis) which takes into account the pressure dependence of lubricant viscosity and the elastic deformation of the bearing housing. The wear shape predicted by this method serves as input data for the EHL analysis calculations. The results show that variations in bearing performance caused by wear are substantial. Analyses that incorporate wear shape data make it possible to examine durability under conditions that more closely approximate actual conditions.