Patent ID: 7424872

Claim:
A failure diagnostic apparatus for a variable valve mechanism that detects a valve characteristic value, which is at least one of a valve lift amount and a valve working angle of an internal combustion engine, by using a sensor, and that adjusts the valve characteristic value, comprising: a failure diagnostic device which determines whether the valve characteristic value is in a refuge running performable region, which is set in a range where the valve characteristic value can be adjusted by the variable valve mechanism, and performs a failure diagnosis for the variable valve mechanism when it is determined that the valve characteristic value is in the refuge running performable region; and a valve state maintaining device which performs maintaining control for maintaining the valve characteristic value at a value in the refuge running performable region, when the failure diagnostic device determines that a failure has occurred in the variable valve mechanism, the variable valve mechanism includes a control shaft; a control shaft position adjusting mechanism and an actuator which drives the control shaft via the control shaft position adjusting mechanism in order to adjust the valve characteristic value, the variable valve mechanism includes a spiral cam which serves as the control shaft position adjusting mechanism, and moves the control shaft in an axial direction by rotating the spiral cam using the actuator, thereby adjusting the valve characteristic value of the internal combustion engine, the refuge running performable region is a region in which the valve characteristic value is a maximum value, the spiral cam has an arc-shaped surface, whose axis is a rotational axis of the spiral cam, in a cam surface corresponding to the refuge running performable region.