for crank angles engine speeds ne intake manifold pressures pb throttle angles and the like according to the above mentioned embodiment the engine 1 may need to change to the high compression ratio based on sensor signals for the crank angle the engine speed the intake manifold pressure and the throttle angle supplied to the ecu 51 in such case the ecu 51 sends a signal to change the selector valve 50 to the high compression ratio position in fig5 and select the branch channel 47 a vertical movement of the piston 6 applies a load on the lever arm 25 from the flexing portion k of the connecting rod 13 via the control rod 21 a load is applied to the lever arm 25 to rotate it counterclockwise in vain because the check valve 49 prevents movement of the hydraulic fluid from the right hydraulic chamber 43 to the left hydraulic chamber 44 let us assume that a load is applied to rotate the lever arm 25 clockwise the check valve 49 permits movement of the hydraulic fluid from the left hydraulic chamber 44 to the right hydraulic chamber 43 consequently the piston section 35 of the hydraulic control cylinder 27 moves to the left by pushing the hydraulic fluid out of the left hydraulic chamber 44 to the right hydraulic chamber 43 this allows clockwise rotation of.