Patent ID: 7516656

Claim:
A motor-operated valve diagnostic method for diagnosing a motor-operated valve comprising a valve disc for opening and closing a given passage, a worm rotatably driven by motor power, a link mechanism which opens and closes the valve disc with the rotational driving force transmitted from the worm, and a spring cartridge containing disc springs which expand or compress in response to reaction force acting axially on the worm from the link mechanism, said method comprising: calibrating a torque curve representing elastic characteristics of the spring cartridge based on a load including at least a preload of the spring cartridge, diagnosing the motor-operated valve based on the torque curve thus calibrated, detecting a condition of compression of the spring cartridge resulting from the reaction force as axial displacement of the worm, detecting a given physical quantity corresponding to the preload of the spring cartridge, and detecting the preload of the spring cartridge based on the given physical quantity.