Patent ID: 7739923

Claim:
A torque measuring method for a motor-operated valve comprising a valve driving mechanism operable to open and close the valve, an axially extending and axially displaceable worm operatively connected to the valve driving mechanism to operate the valve driving mechanism by driving of the motor, and a spring cartridge having a plurality of axially arranged belleville springs applied with a preload so that the belleville springs operate as a unit, said spring cartridge being disposed coaxially with the worm for compression by axial displacement of the worm, so that a torque proportional to a compression of the belleville springs is applied to the driving mechanism upon an axial displacement of the worm, said method comprising the steps of: (a) obtaining basic data representing a relationship between reference amounts of compression of the belleville springs of the spring cartridge and corresponding reference torques exerted by the reference amounts of compression; (b) measuring an axial displacement of the worm or the spring cartridge and acquiring, from the thus obtained axial displacement of the worm or the spring cartridge, a real amount of compression of the belleville springs in which an influence of a play in the axial direction of the spring cartridge has been removed; and (c) substituting said real amount of compression of the belleville springs for the reference amount of compression of the belleville springs of said basic data to acquire a real torque corresponding to said real amount of compression, wherein step (b) comprises: measuring a first initial value representing a distance in the axial direction between a measuring point on the spring cartridge side and a reference point when the spring cartridge is located at a first initial position at which the spring cartridge has stopped moving when the valve is operated in the valve opening direction; measuring a second initial value representing a distance in the axial direction between said measuring point and said reference point when the spring cartridge is located at a second initial position at which the spring cartridge has stopped moving when the valve is operated in the valve closing direction; measuring a first measured value representing a distance in the axial direction between said measuring point and said reference point when the valve closing operation is conducted; measuring a second measured value representing a distance in the axial direction between said measuring point and said reference point when the valve opening operation is conducted; and detecting the direction of the operation of the valve and acquiring said real amount of compression of the belleville springs, said real amount of compression equals an absolute value of a difference between said first measured value and said second initial value when the valve closing operation is conducted or an absolute value of a difference between said second measured value and said first initial value when the valve opening operation is conducted.