Control system for engine

1. A control system for an engine, the control system including a hydraulically-operated variable valve timing mechanism, a variable oil pump, and a hydraulic-pressure control valve, the hydraulically-operated variable valve timing mechanism having advance-side and retard-side operation chambers that are formed by a housing for rotating in cooperation with a crankshaft of the engine and a vane body for integrally rotating with a camshaft, and change a phase angle of the camshaft with respect to the crankshaft by supplying hydraulic pressure, and a locking mechanism including a locking member, the locking mechanism unlocking, by supplying hydraulic pressure, the locking member to fix the phase angle of the camshaft with respect to the crankshaft, the variable oil pump supplying, via a hydraulic-pressure path, oil to hydraulically-operated devices including the variable valve timing mechanism of the engine, the hydraulic-pressure control valve controlling the hydraulic pressure to be supplied to the locking mechanism and the advance-side and retard-side operation chambers, the control system comprising:

a hydraulic-pressure sensor for detecting the hydraulic pressure within the hydraulic-pressure path; and

a pump control device for performing a target hydraulic-pressure control for controlling an oil discharge amount of the variable oil pump to control the hydraulic pressure that is to be detected by the hydraulic-pressure sensor to be a target hydraulic pressure set according to an operating state of the engine,

wherein during a change of the operating state of the engine in a specific operation of the engine in which the locking member of the locking mechanism is in a locked state, while an unlocking operation of the locking member is performed, the pump control device performs, instead of the target hydraulic-pressure control, a discharge amount restricting control for restricting the oil discharge amount of the variable oil pump to control the hydraulic pressure that is to be detected by the hydraulic-pressure sensor up to and including an upper-limit hydraulic-pressure value, the upper-limit hydraulic-pressure value being an upper limit for the unlocking operation of the locking member to be performed.

2. The control system of claim 1 , further comprising a cam angle sensor for detecting a rotational phase of the camshaft,

wherein when an engine load is increased in the change of the operating state of the engine during the specific operation of the engine, while the unlocking operation of the locking member of the locking mechanism is performed, the pump control device determines, based on detection information from the cam angle sensor, whether the unlocking operation of the locking member is completed, and until the unlocking operation of the locking member is determined to be completed, the pump control device performs the discharge amount restricting control instead of the target hydraulic-pressure control.

3. The control system of claim 2 , wherein the hydraulically-operated devices further include a hydraulically-operated valve stopping mechanism for performing a reduced-cylinder operation of the engine by supplying hydraulic pressure to suspend one or more of cylinders of the engine, the one or more of the cylinders being less than all the cylinders, and

wherein in the reduced-cylinder operation of the engine, the pump control device performs the target hydraulic-pressure control to control the hydraulic pressure that is to be detected by the hydraulic-pressure sensor to be a target hydraulic pressure higher than a required hydraulic pressure of the valve stopping mechanism.

4. The control system of claim 1 , wherein when an engine load is increased in the change of the operating state of the engine during the specific operation of the engine, the pump control device performs the discharge amount restricting control instead of the target hydraulic-pressure control for a predetermined period of time from a start of the unlocking operation of the locking member of the locking mechanism.

5. The control system of claim 4 , wherein the hydraulically-operated devices include a hydraulically-operated valve stopping mechanism for performing a reduced-cylinder operation of the engine by supplying hydraulic pressure to suspend one or more of cylinders of the engine, the one or more of the cylinders being less than all the cylinders, and

wherein in the reduced-cylinder operation of the engine, the pump control device performs the target hydraulic-pressure control to control the hydraulic pressure that is to be detected by the hydraulic-pressure sensor to be a target hydraulic pressure higher than a required hydraulic pressure of the valve stopping mechanism.

6. The control system of claim 1 , wherein the hydraulically-operated devices further include a hydraulically-operated valve stopping mechanism for performing a reduced-cylinder operation of the engine by supplying the hydraulic pressure to suspend one or more of cylinders of the engine, the one or more of the cylinders being less than all the cylinders, and

wherein in the reduced-cylinder operation of the engine, the pump control device performs the target hydraulic-pressure control to control the hydraulic pressure that is to be detected by the hydraulic-pressure sensor to be a target hydraulic pressure higher than a required hydraulic pressure of the valve stopping mechanism.