Patent ID: 7909008
Filing Date: 2011-03-22
Classification: F01L,F02D,Y02T

Abstract:
1. 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 by changing a rotational phase difference between a camshaft that drives the valve of which the opening closing timing is changed and a crankshaft in a direction, which is determined based on whether a rotational speed of an electric motor, used as an actuator, relative to a rotational speed of the camshaft takes a positive value or a negative value, and at a rate that is determined based on a degree of the rotational speed of the electric motor relative to the rotational speed of the camshaft, when the engine is operating; and a stop-time phase control unit that sets a control mode for the opening/closing timing after a command to stop the engine is issued, wherein the stop-time phase control unit includes a mode changeover condition setting unit that sets a mode changeover condition based on a rotational speed of the electric motor, and a mode changeover determination unit that determines whether the mode changeover condition is satisfied based on a status of control over the opening/closing timing, and the mode changeover determination unit sets the control mode to a first mode in which the electric motor is rotated at a highest possible speed in a current operating state and in a direction in which the opening/closing timing is changed toward a target opening/closing timing that should be achieved when the engine is stopped after the command to stop the engine is issued until the mode changeover condition is satisfied, and the mode changeover determination unit sets the control mode to a second mode in which a feedback control for setting a rotational speed command for the electric motor based on a deviation of the current opening/closing timing from the target opening/closing timing is executed after the mode changeover condition is satisfied.