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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.

One of the phenomena accompanying the lightweight/compact/high power output feature of engines is the cylinder bore deformation, which may readily cause increased oil consumption, gas leakage, unusual wear, scuffing, etc.. The authors have had experiences that piston rings had generated contact failure during engine operation (1)*. Such deformation is generated as a combination of the static deformation due to head bolt tightening, crankshaft installation, etc., and the deformation by the operating factors; thermal load and combustion pressure. Countermeasure of design have been made for the former (2)*, and prediction of the deformation during actual operating have been tried using FEM analysis, etc. for the latter (3)*. Therefore, the accurate measurement result have been required strongly, for a long time. But it could not be realized in the past.

Achieving a multi-cylinder engine with excellent noise/vibration character sties and low friction at the main bearings requires an optimal design not only for the crankshaft construction but also for the bearing support system of the cylinder block. To accomplish that, it is necessary to understand crankshaft system behavior and the bearing load distribution for each of the main bearings. Crankshaft system behavior has traditionally been evaluated experimentally because of the difficulty in performing calculations to predict resonance behavior over the entire engine speed range. A coupled crankshaft-block analysis method has been developed to calculate crankshaft system behavior by treating vibration and lubrication in a systematic manner. This method has the feature that the coupled behavior of the crankshaft and the cylinder block is analyzed by means of main bearing lubrication calculations. This paper presents the results obtained with this method.