Abnormality determination device and abnormality determination method of lock up clutch

An abnormality determination device of a lock up clutch, the abnormality determination device comprising:

• a controller configured to set the lock up clutch in a torque converter at an engaged state or a disengaged state, the torque converter being provided in an automatic transmission of a vehicle, the engaged state including permitting linkage between a rotating member on input side and a rotating member on output side in the torque converter, and the disengaged state including interrupting the linkage between the rotating member on the input side and the rotating member on the output side;
• and
• a determining unit configured to determine presence or absence of an abnormality in the lock up clutch, the abnormality corresponding to a situation that the lock up clutch is stuck in the engaged state,
• the determining unit being configured to determine,
• on a condition that deceleration of the vehicle on travel with the lock up clutch in the engaged state causes a control signal to be outputted from the controller, the control signal causing the lock up clutch to make a transition to the disengaged state,
• the presence or the absence of the abnormality in the lock up clutch, on a basis of a determination result as to whether or not a difference in number of rotations is equal to or larger than a first threshold, the first threshold varying with a rate of deceleration of the vehicle, the difference in the number of rotations being a difference between number of engine rotations and number of turbine rotations, the number of engine rotations being number of rotations of an engine that transmits rotation to the rotating member on the input side, and the number of turbine rotations being number of rotations of the rotating member on the output side.