Patent Document ID: 8457864
Application ID: 12839585
Patent Flag: 1

Claim One:
1. A variable valve timing control apparatus for an internal combustion engine having a crankshaft and a camshaft, the variable valve timing control apparatus comprising: a hydraulic variable valve timing unit configured to adjust valve timing by changing a variable cam timing (VCT) phase that is a rotational phase of the camshaft relative to the crankshaft; an oil pressure control device configured to control oil pressure that actuates the variable valve timing unit; VCT phase control means for feed-back controlling a VCT control amount of the oil pressure control device such that an actual VCT phase becomes a target VCT phase, wherein: the variable valve timing unit is configured to have a plurality of control ranges of the VCT phase, each of which has a different control characteristic; and an ambiguity range is a predetermined range defined around a boundary between the plurality of control ranges and has a control characteristic that is difficult to be identified; and hold control amount learning means for learning a hold control amount for each of the plurality of control ranges when a predetermined hold control amount learning execution condition is satisfied, the hold control amount being required to control the oil pressure control device to maintain the actual VCT phase, wherein: when the target VCT phase is positioned away from the ambiguity range, the VCT phase control means computes the VCT control amount by using the hold control amount learning value of one of the plurality of control ranges, in which the target VCT phase is positioned; when the target VCT phase is positioned in the ambiguity range, if a difference between the actual VCT phase and the target VCT phase is stably equal to or greater than a predetermined value, the VCT phase control means executes a VCT control amount computation process, in which one of the following is performed: the VCT phase control means switches the hold control amount learning value of one of the plurality of control ranges, which is presently used in computation of the VCT control amount, into the hold control amount learning value for the other one of the plurality of control ranges such that the hold control amount learning value for the other one of the plurality of control ranges is used in the computation of the VCT control amount, the other one of the plurality of control ranges being positioned adjacent to the ambiguity range; and the VCT phase control means corrects the VCT control amount based on a difference between the hold control amount learning values of two of the plurality of control ranges, which are positioned adjacent to the ambiguity range.