| 摘要 |
PURPOSE:To raise the thermal efficiency of an engine as well as to aim at improvement in fuel consumption and/or output by installing the outer piston fitted slidably in the axial direction and an oil passage interconnecting an upper fluid chamber to a working fluid chamber, on the circumference of an inner piston. CONSTITUTION:When high combustion pressure acts on the top of an outer piston 21, pressure oil in an upper fluid chamber 31 acts on a pressure receiving part of a spool valve 26 via a third oil passage 37. With this action, the spool valve 26 moves in the specified direction in a moment, closing a second oil passage 36. Consequently, the pressure oil inside the upper fluid chamber 31 is discharged to the outside quickly and simultaneously the outer piston 21 quickly goes down. Thus, responsiveness in variable control from a high compression ratio state to a low compression ratio is improved.
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