Patent ID: 8360031

Claim:
A variable compression ratio device having a piston, a crankshaft, a connecting rod including a small end portion rotatably connected to the piston and a large end portion rotatably connected to the crankshaft and converting reciprocative motion of the piston to rotary motion of the crankshaft, comprising: a piston pin that passes through the small end portion of the connecting rod and fixed thereto; a receiving hole formed inside the piston and rotatably receiving the piston pin therein, wherein the receiving hole includes a convex portion and a concave portion along an interior circumference thereof; at least a variable pin slidably coupled to an exterior circumference of the piston pin and slidably coupled to the interior circumference of the receiving hole, wherein the at least a variable pin has a protrusion at an exterior circumference thereof; and an oil supply passage selectively supplying oil to apply hydraulic pressure to the at least a variable pin so as to slidably move the at least a variable pin along the piston pin, wherein the protrusion of the at least a variable pin is selectively coupled to the convex portion or the concave portion of the receiving hole to change a distance between an upper surface of the piston and a center axis of the piston pin.