Variable valve timing control apparatus for internal combustion engine

A variable valve timing control apparatus comprising:

• a hydraulic type of variable valve timing apparatus controllable for adjusting a valve timing of an internal combustion engine by adjusting a VCT phase of a camshaft of said engine with respect to a crankshaft of said engine, and comprising a lock pin movable between a protruding position whereby said VCT phase is locked at an intermediate lock phase located within an adjustment range of said VCT phase and a retracted position whereby said VCT phase is released from said locked condition,
• an oil pressure control apparatus controllable for selectively supplying oil to an advancement chamber of said variable valve timing apparatus for advancing said VCT phase and to a retardation chamber of said variable valve timing apparatus for retarding said VCT phase, and controllable for supplying oil to a lock release chamber of said variable valve timing apparatus for driving said lock pin to said protruding position and for releasing said oil from said lock release chamber for driving said lock pin to said retracted position,
• locking control circuitry responsive to a locking command for controlling said oil pressure control apparatus to drive said lock pin to said protruding position, for locking said VCT phase at said intermediate lock phase,
• lock release control circuitry responsive to a lock release command for effecting a lock release operation by controlling said oil pressure control apparatus to drive said lock pin to said retracted position, and
• phase control circuitry configured to determine a post-release target value of VCT phase to be applied in feedback control of said VCT phase following completion of said lock release operation, and configured to execute said feedback control;
• wherein said variable valve timing apparatus is configured for enabling communication between said retardation chamber and said advancement chamber and thereby enabling oil to pass between said retardation chamber and said advancement chamber, when said lock pin is displaced from said retracted position by more than a predetermined amount, and wherein when said lock release command is issued,
• during a predetermined reverse-direction drive interval, reverse-direction drive control is executed whereby said oil pressure control apparatus is controlled to urge said lock pin towards said protruding position while oil is selectively supplied to said advancement chamber and retardation chamber for driving said VCT phase in a direction that is opposite to a direction for changing from said intermediate lock phase to said post release target value of VCT phase, and
• feedback control of said VCT phase based on said post-release target value of VCT phase is initiated immediately following said reverse-direction drive interval, while said lock pin continues to be urged towards said protruding position.

A variable valve timing control apparatus comprising

• a hydraulic type of variable valve timing apparatus controllable for adjusting a valve timing of an internal combustion engine by adjusting a variable cam timing phase (abbreviated herein to VCT phase) of a camshaft of said engine, and comprising a lock pin movable by oil pressure, within a lock release chamber, between a protruding position whereby said VCT phase is held in a locked condition and a retracted position whereby said VCT phase is released from said locked condition,
• an oil pressure control apparatus controllable for selectively supplying oil to an advancement chamber and to a retardation chamber of said variable valve timing apparatus, to respectively advance and retard said VCT phase, and for supplying oil to said lock release chamber, and
• locking control circuitry responsive to a locking command for controlling said oil pressure control apparatus to selectively set said lock pin to said retracted position and said protruding position;
• wherein:
• said variable valve timing apparatus is configured for enabling communication between said retardation chamber and said advancement chamber and thereby enabling oil to pass between said retardation chamber and said advancement chamber, when said lock pin becomes set at said protruding position, and
• said lock control circuitry is configured to control said oil pressure control apparatus for supplying oil to a predetermined one of said advancement chamber and said retardation chamber during each of periodically repeated oil fill intervals while said locked condition continues, for thereby maintaining each of said advancement chamber and said retardation chamber filled with oil during said locked condition.