Abnormality determination apparatus and abnormality determination method for valve characteristics change mechanism

An abnormality determination apparatus that determines whether or not a valve characteristics change mechanism is operating normally, in an internal combustion engine that includes the valve characteristics change mechanism that changes a maximum lift amount and a lift duration of an engine valve continuously in correspondence with a position of a control shaft, an actuator that drives the control shaft in an axial direction, and a drive amount detector that detects a drive amount of the actuator, wherein the maximum lift amount and the lift duration of the engine valve are changed by controlling the actuator such that the drive amount approaches a target drive amount, the abnormality determination apparatus comprising:

• a shaft position detection sensor that outputs, as a shaft position detection value, a signal whose magnitude changes stepwise by a predetermined amount in correspondence with the position of the control shaft in the axial direction, wherein
• the abnormality determination apparatus stores in advance, as a determination reference value, the drive amount at the time when the shaft position detection value, which changes stepwise, changes by one step, and
• the abnormality determination apparatus performs normality determination to indicate that the valve characteristics change mechanism is operating normally if the drive amount at the time when the shaft position detection value changes along with driving of the actuator is equal to the determination reference value, and performs abnormality determination to indicate that an abnormality is occurring in the valve characteristics change mechanism if the drive amount at the time when the shaft position detection value changes is not equal to the determination reference value.