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To help ensure that engine components are as reliable as customers need them to be, we have thus far evaluated them by establishing development target values based on market requirements, having engineers design parts to meet these requirements, then performing durability tests. These durability requirements are calculated to provide a margin of safety for use in the marketplace. However, depending on the part, these evaluation criteria can be overly aggressive against how it is used in the market, having led to a decrease in development efficiency as engine systems become more advanced. Therefore, in this study, we focused on the subject of high-cycle fatigue, which affects numerous components and is highly scalable, and built up a process for estimating the life span of components that would enable us to conduct appropriate evaluations that reflect how parts are truly used in the market.

The piston and piston ring are used in a severe contact environment in engine durability tests, which causes severe wear to the piston ring groove, leading to significant development costs for countermeasures. Conventionally, in order to ensure functional feasibility through wear on the piston top ring groove (hereinafter “ring groove”), only functional evaluations through actual engine durability testing were performed, and there was an issue in determining the limit value for the actual amount of wear itself. Because of this, the mechanism that may cause wear on the ring groove was clarified through past research, but this resulted in judgment criteria with some leeway from the perspective of functional assurance. To establish judgment criteria, it was necessary to understand both functional effect from ring groove wear and the mechanism behind it.

Recent trends to downsize engines have resulted in lighter weight and greater compactness. At the same time, however, power density has increased due to the addition of turbocharger and other such means to supplement engine power and torque, and this has increased the thermal and mechanical load. In this kind of environment, corrosion of the copper alloy bushing (piston pin bushing) that is press-fitted in the small end of the connecting rod becomes an issue. The material used in automobile bearings, of which the bushing is a typical example, is known to undergo sulfidation corrosion through reaction with an extreme-pressure additive Zinc Dialkyldithiophosphate (ZnDTP) in the lubricating oil. However, that reaction path has not been clarified. The purpose of the present research, therefore, is to clarify the reaction path of ZnDTP and copper in an actual engine environment.

During engine durability tests (peak power, constant engine speed) conducted in the development process, it has been the case that excessive wear has occurred to the upper surfaces of the piston top ring grooves, despite the fact that contact pressure due to combustion pressure has been low. This has resulted in considerable increases in development man-hours. The research discussed in this paper therefore set out to conduct a factor analysis of wear on the upper surfaces of piston top ring grooves in order to elucidate the wear mechanism in petrol engine for passenger car. This paper will discuss the test method employed in the factor analysis and the mechanism of wear demonstrated by the analysis. First, the form of the wear was analyzed, and rig test methods able to reproduce wear were developed. With regard to the form of wear, both sliding and impact modes were observed. Sensitivity analyses for each form of wear were conducted using rig tests.

The purpose of this research was to predict the amount of wear on exhaust valve seats in durability testing of gasoline engines. Through the rig wear test, a prediction formula was constructed with multiple factors as variables. In the rig test, the wear rate was measured in some cases where a number of factors of valve seat wear were within a certain range. Through these tests, sensitivity for each factor was determined from the measured wear data, and then a prediction formula for calculating the amount of wear was constructed with high sensitivity factors. Combining the wear amount calculation formula with the operation mode of the actual engine, the wear amount in that mode can be calculated. The calculated wear amount showed a high correlation with the wear amount measured in bench tests and the wear amount measured in vehicle tests.

In order to simulate the valve behavior of an engine that uses a hydraulic lash adjuster (HLA), it is necessary to accurately reproduce the dynamic characteristics of the HLA in the model. Formerly, the model used values from drawings and values based on past experiences, and did not reflect actual driving conditions such as oil properties, leaked oil quantity, or oil aeration rate. We therefore developed a technique to reproduce HLA unit dynamic characteristics in a high-accuracy simulation. This representation was made possible using a unit excitation test to quantify the HLA unit dynamic characteristics in four categories: HLA stiffness, load response delay of the plunger, sinking displacement after relaxation, and lissajous curve of load vs. displacement. The effectiveness of this model calibration technique was confirmed through comparison of unit dynamic characteristics in a unit excitation test and a calibrated simulation.

To accurately simulate valve behavior in an engine employing a Hydraulic Lash Adjuster (HLA), it is necessary to reflect in the simulation model the dynamic characteristics of the HLA when feeding aerated engine oil. Traditionally HLA behavior was measured by agitating oil to aerate it inside an actual engine. With this technique, however, the aeration rate cannot be controlled to allow an examination of the relationship between aeration rate and HLA behavior. This study aims to establish a technique for obtaining HLA dynamic characteristics when oil contains air. We created an aeration device that allows free control of the oil aeration rate and, by applying excitation input to the plunger, revealed the relationship between oil aeration rate and the changes in HLA stiffness. Because of the small clearance between the HLA plunger and its housing, it is difficult for air to escape from low-temperature oil inside the HLA high-pressure chamber, which greatly affects HLA behavior.