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Axial engines (sometimes known as barrel or Z-crank engines) are a type of reciprocating engine with pistons arranged around an output shaft with their axes parallel to the shaft. Barrel refers to the cylindrical shape of the cylinder group (result of the pistons being spaced evenly around the central crankshaft and aligned parallel to the crankshaft axis) whilst the Z-crank alludes to the shape of the crankshaft. The key advantage of the axial design is that the cylinders are arranged in parallel around the output/crank shaft rather than at 90 degrees as in crankshaft engines. As a result, it is a very compact, cylindrical engine, allowing variation in compression ratio of the engine while running. In a swashplate engine the piston rods stay parallel with the shaft, and piston side-forces that cause excessive wear can be eliminated almost completely. The small-end bearing of a traditional connecting rod, one of the most problematic bearings in a traditional engine, is eliminated. An alternate design, the Rand cam engine, replaces the plate with a sine-shaped cam. It can be derived as either a cam engine or swashplate or wobble-plate engine. A wobble-plate is similar to a swashplate, in that the pistons press down on the plate in sequence, forcing it to nutate around its center. This motion can be simulated by placing a Compact Disc on a ball bearing at its centre and pressing down at progressive places around its circumference. The difference is that while a wobble plate nutates, a swash-plate rotates. Axial engines are challenging to make practicable at typical engine operating speeds. ==History== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Axial engine」の詳細全文を読む スポンサード リンク
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