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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.