Patent ID: 8474790

Claim:
A valve drive apparatus comprising: a shaft that rotates integrally with a valve; an electric motor that generates a rotational torque upon energization of the electric motor; a speed reducing mechanism that includes a final gear, which applies the rotational torque to the shaft; and a valve opening degree sensor that includes: a magnet that is rotated integrally with the shaft; and a magnetic sensing device that is provided to a stationary member and senses a change in a magnetic flux supplied from the magnet, wherein: a sensed result of the valve opening degree sensor is changeable between high and low; the valve opening degree sensor senses a change in the valve opening degree from a valve close side to a valve open side when the sensed result indicates one of a change from the low to the high and a change from the high to the low only at a valve open sensing degree that is passed at time of rotating the valve from a full close degree to a full open degree of the valve; the valve opening degree sensor senses a change in the valve opening degree from the valve open side to the valve close side when the sensed result indicates the other one of the change from the low to the high and the change from the high to the low only at a valve close sensing degree that is passed at time of rotating the valve from the full open degree to the full close degree of the valve; the final gear and the magnet are separately joined to the shaft; the valve drive apparatus includes a means for limiting a rotational range of the final gear between a full open position and a full close position; a positional relationship between the final gear and the magnet is set such that the final gear and the magnet contact with each other in a rotational direction when the final gear is rotated in a state where a connection between the shaft and a final gear support portion, through which the final gear is installed to the shaft, is damaged; the final gear and the magnet are arranged to satisfy at least one of θa>Θ-θswo and θb>θswc, where: θa denotes a valve open side clearance that is a circumferential gap angle circumferentially measured between the magnet and an open side end part of the final gear, which is an end part of the final gear in a valve opening direction; θb denotes a valve close side clearance that is a circumferential gap angle circumferentially measured between the magnet and a close side end part of the final gear, which is an end part of the final gear in a valve closing direction; Θ denotes the full open degree; θswo denotes the valve open sensing degree; and θswc denotes the valve close sensing degree; and the valve drive apparatus includes a means for determining a failure of the valve in a case where a change in an open/close state of the valve is not sensed with the valve opening degree sensor at time of driving the final gear from the valve close side to the valve open side or from the valve open side to the valve close side.