Patent ID: 7412950

Claim:
A valve operation device of an internal combustion engine, comprising: a camshaft which interlockingly rotates around a crankshaft of the internal combustion engine; a valve operation cam pivotally supported on the camshaft to open and close an engine valve that comprises one of an intake valve and an exhaust valve; a driving cam which integrally rotates with the camshaft; an interlocking mechanism through which the driving cam rocks the valve operation cam around the camshaft; and a driving mechanism which rocks the interlocking mechanism around the camshaft, wherein the driving cam includes a base circle portion having a sectional shape of a circular arc, and a cam swelled portion having a sectional shape in which a radius from a center different from a center of the base circle portion increases and decreases in a rotation direction of the camshaft, opening and closing of the engine valve start at a damping portion of the valve operation cam, and the driving mechanism rocks the valve operation cam around the camshaft via the interlocking mechanism to control an opening timing and a closing timing of the engine valve, and the cam swelled portion of the driving cam has a constant velocity portion at which a lift velocity, which is a ratio of a change in a height of the cam swelled portion with respect to a change in a rotational angle of the camshaft, is constant, and the constant velocity portion is provided over an angular width that includes at least the opening timing in a most advanced angle position of the opening timing of the engine valve and the opening timing in a most retarded angle position of the opening timing of the engine valve.