Variable valve timing mechanism

A variable valve timing mechanism including a housing configured to rotate in conjunction with a crankshaft of an engine, a rotor that is provided coaxially with the housing to be rotatable relative to the housing and is configured to rotate in conjunction with a camshaft, an advance oil chamber that oil is to enter to rotate the rotor to an advance side, a retard oil chamber that the oil is to enter to rotate the rotor to a retard side, the advance oil chamber and the retard oil chamber being defined by the housing and the rotor, and a controller configured to control supply and discharge of the oil to and from the advance oil chamber and the retard oil chamber, the variable valve timing mechanism being configured to vary a valve timing by controlling the supply and discharge of the oil to and from the advance oil chamber and the retard oil chamber depending on an operation state of the engine to rotationally adjust a phase difference between the housing and the rotor, the variable valve timing mechanism comprising:

• a detent valve comprising a spool having one end coupled to a detent oil passage through which a hydraulic pressure is to be supplied, and having another end provided with an urging member configured to apply an urging force in a direction opposite to a direction of a pressing force of the hydraulic pressure, the spool being configured to slide in an axial direction according to a balance between the pressing force of the hydraulic pressure that is applied to one end surface and the urging force of the urging member that is applied to another end surface to switch oil passages to move the rotor to a predetermined lock position or to allow the rotor to rotate;
• and
• a foreign matter discharge oil passage that makes communication between an outside and the detent oil passage through which the hydraulic pressure is to be supplied to the one end surface of the spool constituting the detent valve, wherein
• the urging force of the urging member constituting the detent valve is set such that
• when the hydraulic pressure applied to the one end surface of the spool constituting the detent valve is lower than a first predetermined hydraulic pressure, the detent valve switches the oil passages to move the rotor to the predetermined lock position and interrupts communication between the detent oil passage and the foreign matter discharge oil passage,
• when the hydraulic pressure applied to the one end surface of the spool constituting the detent valve is equal to or higher than the first predetermined hydraulic pressure and lower than a second predetermined hydraulic pressure, the detent valve switches the oil passages to allow the rotor to rotate and interrupts the communication between the detent oil passage and the foreign matter discharge oil passage, and
• when the hydraulic pressure applied to the one end surface of the spool constituting the detent valve is equal to or higher than the second predetermined hydraulic pressure, the detent valve switches the oil passages to allow the rotor to rotate and causes the detent oil passage and the foreign matter discharge oil passage to communicate with each other.