Conventionally, a fluid pressure type valve timing control apparatus is known, which controls a valve timing of an intake valve by a pressure of hydraulic fluid. Generally, the valve timing control apparatus is equipped with a housing rotor and a vane rotor which are rotated with a crankshaft and a camshaft of an internal combustion engine, respectively. The rotation phase between the rotors is changed when the vane rotor receives the pressure of hydraulic fluid in the housing rotor. The valve timing is adjusted by the change in the rotation phase.
JP 4161356 B describes such a valve timing control apparatus, in which the rotation phase is locked at a middle phase which is on the advance side from the most retard phase when the internal combustion engine is started. In this case, the timing closing an intake valve can be made early as much as possible, so a real compression ratio in a cylinder can be made high. Therefore, the temperature of gas in the cylinder is raised by heat produced by the compression, and the fuel evaporation is promoted. For example, under low temperature environment, the engine startability can be secured after the engine is left for a long time in the stop state.
However, the high compression ratio in the cylinder may cause knocking when the internal combustion engine is started under comparatively high temperature environment such as normal temperature.
Moreover, in case where the internal combustion engine is applied to an idling stop system or a hybrid system, when the engine is restarted, pre-ignition may be generated. Also, when the engine is restarted immediately after the engine is stopped by ignition-off, pre-ignition may be generated. The pre-ignition means a self-ignition before ignition when the temperature of gas in the cylinder becomes too much high at the time of compression. Moreover, if the variation in the cranking rotation is increased by a large reaction force of the compression, unpleasant vibration or noise is generated.
JP 2002-256910 A describes a fluid pressure type valve timing control apparatus, in which the lock phase is selected between a retard phase and a middle phase at the time of starting the internal combustion engine. The retard phase is set for closing an intake valve later than a timing at which the piston in a cylinder reaches a bottom dead center. The middle phase is on the advance side from the retard phase. Such a selection makes it possible to suitably start the engine based on the temperature of the engine (hereafter may be referred to engine temperature).
However, in JP 2002-256910 A, at the time of starting the engine under high temperature environment, the pressure of hydraulic fluid is applied to the vane rotor in the housing rotor, such that the retard phase is selected by the control in the rotation phase not by the lock of the rotation phase. Therefore, in case where the pressure of hydraulic fluid is low when the engine is started, the vane rotor is rotated on the advance side relative to the housing rotor by the variation torque applied from the camshaft, so the rotation phase is easily shifted from the retard phase.
Moreover, in JP 2002-256910 A, because the variation torque changes the rotation phase to the middle phase at the time of starting the engine under low temperature environment, the hydraulic fluid which gives pressure to the vane rotor in the housing rotor is drained. As a result, since the hydraulic fluid which gives pressure to a lock member is also drained, the lock member may move to an unlock position, so the lock at the middle phase may become difficult.