Patent ID: 8464672

Claim:
A variable valve timing control apparatus comprising: a hydraulic type of variable valve timing apparatus operable 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 between a fully protruding position whereby said VCT phase is held in a locked condition at an intermediate lock phase that is within a range of adjustment 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 varying a difference between respective oil pressures within an advancement chamber and to a retardation chamber of said variable valve timing apparatus, for selectively advancing and retarding said VCT phase, and controllable for varying an oil pressure within a lock control chamber of said variable valve timing apparatus, for selectively urging said lock pin towards said retracted position and towards said fully protruding position, and wherein said variable valve timing apparatus is configured for establishing communication between said advancement chamber and said retardation chamber, enabling oil to pass between said advancement chamber and retardation chamber, when said lock pin is displaced from said retracted position towards said fully protruding position by at least a predetermined amount, and for isolating said advancement chamber from said retardation chamber when said lock pin is set at said retracted position, and said variable valve timing control apparatus comprises lock control circuitry configured to be responsive to a locking command for: during an oil fill interval of predetermined duration, controlling said oil pressure control apparatus to supply oil to a predetermined one if said advancement chamber and said retardation chamber for thereby adjusting said VCT phase to successively reduce a difference between said VCT phase and said intermediate lock phase, while controlling said oil pressure control apparatus to displace said lock pin from said retracted position and urge said lock pin towards said fully protruding position, to thereby establish communication between said retardation chamber and said advancement chamber; immediately subsequent to said oil fill interval, controlling said oil pressure control apparatus to establish a lock hold state in which supplying of oil to each of said advancement chamber and said retardation chamber is terminated or substantially restricted, while urging said lock pin towards said fully protruding position; and measuring a duration of said lock hold state, and judging that said locked condition has been attained when said duration attains a predetermined value.