JPS6424131A - Compression ratio variable device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the responsiveness in the changeover of compression ratio by fitting, an inner piston connected to a connecting rod via a piston pin fitted with a spool valve, to the inside of an outer piston and changing over the spool valve through the oil pressure in an upper liquid chamber so as to rapidly discharge pressurized oil. CONSTITUTION:An inner piston 29 connected to a connecting rod 24 via a piston pin provided with an oil chamber 25 and a spool valve 26 therein is fitted slidably in the vertical direction to the inside of an outer piston 21. Thus, an upper liquid chamber 31 and annular-type lower liquid chamber 32 are formed on the upper surface 29a of the inner piston 29 and on the space between the upper surface of an annular part 22 and the lower surface of the inner piston 29, respectively. The spool valve 26 is leftwardly moved by leading the pressurized oil in the upper liquid chamber 31 to an operative liquid chamber 47 via a pressure passage 37 and check valve 39. Therefore, it is possible to changeover a supply passage 35 for supplying pressurized oil from a main passage 34 inside the connecting rod 24 to the upper liquid chamber 31 and a discharge passage 35 for discharging pressurized oil inside the upper liquid chamber 31 to the external at the time of closing the supply passage 35.