Previously, there is known a variable valve timing apparatus, which advances or retards opening timing and closing timing of an intake valve or an exhaust valve of an internal combustion engine through use of an oil pressure.
This type of variable valve timing apparatus includes a variable timing device, an oil pressure supply device, a phase sensing device, and a control device, which will be described hereinafter.
The variable timing device rotates vanes toward an advancing side or a retarding side through use of the oil pressure to advance or retard the opening timing and closing timing of the valve.
The oil pressure supply device includes a supply port, a valve element and an electromagnetic solenoid. The oil pressure is supplied to the variable timing device through the supply port. The valve element increase or decreases an opening degree of the supply port. The electromagnetic solenoid drives the valve element. The electric power supply to the electromagnetic solenoid is controlled to increase or decrease the opening degree of the supply port to adjust the supply of the oil pressure.
The phase sensing device senses a phase, which indicates a degree of advancing or a degree of retarding of the opening timing and closing timing of the intake valve or the exhaust valve.
The control device computes a target value of the phase based on an operational state of the internal combustion engine and controls the electric power supply to the electromagnetic solenoid based on a result of comparison between a sensed value of the phase, which is obtained from the phase sensing device, and the target value of the phase.
There would be a case where foreign objects, such as metal particles, are contained in the oil. Therefore, for example, at the time of closing the supply port, the foreign object may possibly be introduced into and caught in a gap between the supply port and the valve element to disable complete closing of the supply port with the valve element. In such a case, the oil pressure is continuously supplied to the variable timing device, and thereby a difference between the target value of the phase and the sensed value of the phase is disadvantageously increased.
In view of the above point, there is a known technique of that the supply port is opened for a small amount, which does not have a substantial influence on the operation of the internal combustion engine, so that the foreign object is removed from the gap.
However, there is a possibility of that the small opening degree does not allow removal of the foreign object.
Thus, it is conceivable to increase the opening degree of the supply port to an extent that allows reliable removal of the foreign object.
However, when the opening degree of the supply port is increased, the oil pressure is rapidly supplied to the variable timing device. Therefore, the phase is changed within a short period of time to possibly increase a possibility of an unexpected sudden increase in a rotational speed of the internal combustion engine.
Therefore, it is desirable to have a structure that can reliably remove the foreign object while limiting the unexpected sudden increase in the rotational speed of the internal combustion engine.
JP2001-234768A discloses a structure that can limit occurrence of the unexpected sudden increase in the rotational speed of the internal combustion engine even when the opening degree of the supply port is increased for the purpose of removing the foreign object.
Specifically, in the variable valve timing apparatus of JP2001-234768A, a lock pin is engaged with a vane to limit a change in the phase. The engagement of the lock pin is controlled by supplying the oil pressure from a separate oil pressure supply device, which is different from the oil pressure supply device that supplies the oil pressure to the variable timing device.
Therefore, in the variable valve timing apparatus of JP2001-234768A, the opening degree of the supply port can be increased while limiting the change in the phase even during the operation of the internal combustion engine. Thus, the foreign object can be reliably removed while limiting the unexpected sudden increase in the rotational speed of the internal combustion engine.
However, the variable valve timing apparatus of JP2001-234768A additionally requires the lock pin and the oil pressure supply device for the lock pin. Furthermore, a control mode for controlling the oil pressure supply device is required. Therefore, the structure of the variable valve timing apparatus becomes complicated.