Patent ID: 7938088

Claim:
A variable valve timing system that changes opening/closing timing of at least one of an intake valve and an exhaust valve provided in an engine, comprising: a changing mechanism that is structured to change the opening/closing timing of the intake valve or the exhaust valve by an amount of change corresponding to an operation amount of an actuator that is driven in a control mode selected from among multiple control modes; a control unit that prepares operation commands for the actuator based on a current value of the opening/closing timing, and that prepares a pulsed operation command signal which indicates, among the prepared operation commands, at least both which operating direction the actuator should be operated and the selected control mode; and a drive control unit that receives the pulsed operation command signal from the control unit, and that controls the actuator in accordance with the operation commands prepared by the control unit, wherein the control unit sets a duty ratio of the pulsed operation command signal to a predetermined value assigned to a corresponding one of multiple combinations of the operating direction and the selected control mode, the multiple combinations being assigned with different predetermined values; and the predetermined values assigned to the corresponding multiple combinations of the multiple control modes and one of the operating directions are higher than a boundary value, and the predetermined values assigned to the corresponding multiple combinations of the multiple control modes and the other operating direction are lower than the boundary value; and among the predetermined values corresponding to each of the operating directions, a difference between the boundary value and the predetermined value, which is assigned to one of the control modes is larger than a difference between the boundary value and the predetermined value, which is assigned to another one of the control modes in which a rate of change in the opening/closing timing is lower than that in the one of the control modes.