Valve timing adjustment apparatus for internal combustion engine

A valve timing adjustment apparatus for an internal combustion engine, the valve timing adjustment apparatus comprising:

• a housing defining a space with a latchet plate operatively associated with a crankshaft;
• a rotor having a plurality of vanes configured to rotate relative to the housing within a predetermined angle range by a pressure of a working fluid, the rotor disposed in the housing to operate with a camshaft;
• and
• an anti-rotation mechanism configured to inhibit or prevent a positional change between the rotor and the housing by inhibiting or preventing relative rotation of the rotor to the housing,
• wherein the anti-rotation mechanism includes:
• a plurality of locking grooves formed on the ratchet plate with different depths and connected to each other;
• and
• a locking pin member comprising:
• an outer pin elastically disposed in a fitting hole formed in at least one vane of the plurality of vanes, and
• an inner pin elastically disposed inside the outer pin, and configured to lock the rotor to the housing when the outer pin and the inner pin are sequentially fitted in the plurality of locking grooves.