Friction engagement element control system and method of controlling friction engagement element

A friction engagement element control system, comprising:

• a friction engagement element including friction plates, which are an input-side friction plate, an output-side friction plate, and an actuation system configured to engage the input-side friction plate with the output-side friction plate with a pushing force, the friction plates having a negative slope characteristic in which a friction coefficient thereof decreases as a rotational difference between the friction plates increases;
• a rotational difference sensor configured to detect the rotational difference of the friction engagement element;
• a filter configured to divide a variation in the rotational difference detected by the rotational difference sensor into a high-frequency component that is a vibration component and other low-frequency components;
• and
• a controller configured to control the pushing force of the friction engagement element only for the vibration component of the rotational difference so that the negative slope characteristic becomes a positive slope characteristic in which a frictional force of the friction engagement element decreases as the rotational difference decreases, when engaging the friction engagement element.