Variable valve timing apparatus for internal combustion engine

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

• a variable valve timing mechanism that changes a valve timing of at least one of an intake valve or an exhaust valve by changing a relative rotation phase of a camshaft with respect to a crankshaft;
• and
• a lock mechanism that fixes the valve timing at an intermediate angle between a most advanced angle and a most retarded angle,
• wherein the variable valve timing mechanism includes i) a first rotating body and a second rotating body that are rotating bodies that rotate about the same rotational axis, the first rotating body being drivingly connected to the crankshaft and having a plurality of housing chambers surrounding the rotational axis, and the second rotating body being drivingly connected to the camshaft and having a plurality of vanes that extend in a radial direction of the rotational axis and are arranged in the housing chambers, one vane being housed in each housing chamber;
• ii) an advance chamber formed on one side of the vane in each housing chamber and a retard chamber formed on the other side of the vane in each housing chamber, the advance chambers and the retard chambers serving as hydraulic pressure chambers into which hydraulic fluid is supplied from an oil pump;
• iii) a discharge passage that extends from each of the hydraulic pressure chambers on the rotational axis side and discharges hydraulic fluid from the hydraulic pressure chambers;
• and iv) an opening mechanism that communicates the hydraulic pressure chambers with an ambient air space to open the hydraulic pressure chambers to ambient air at least when the first rotating body and the second rotating body have stopped rotating,
• and wherein the opening mechanism places at least one of the hydraulic pressure chambers that is communicated with the discharge passage in a position vertically higher than the rotational axis when the first rotating body and the second rotating body have stopped rotating at a given phase, and from which hydraulic fluid is discharged into the discharge passage, in a state constantly open to ambient air regardless of the phase at which the first rotating body and the second rotating body have stopped.