Control system of vehicle including automatic transmission

A control system of a vehicle, comprising:

• an automatic transmission provided with a first friction engagement element able to change between an engaged state and a disengaged state, the first friction engagement element including:
• a plurality of friction plates;
• a piston movable between an engaged position at which the plurality of friction plates are engaged and a disengaged position at which the plurality of friction plates are disengaged;
• an engaging hydraulic pressure chamber configured to apply a hydraulic pressure to the piston to set the piston at the engaged position;
• and
• a disengaging hydraulic pressure chamber configured to apply a hydraulic pressure to the piston to set the piston at the disengaged position;
• a first hydraulic pressure control valve configured to adjust the hydraulic pressure applied to the engaging hydraulic pressure chamber of the first friction engagement element;
• a second hydraulic pressure control valve configured to adjust the hydraulic pressure applied to the disengaging hydraulic pressure chamber of the first friction engagement element;
• and
• a controller configured to control the first and second hydraulic pressure control valves to change the first friction engagement element between the engaged state and the disengaged state,
• wherein, when changing the first friction engagement element from the engaged state to the disengaged state, the controller performs:
• a first control in which the first hydraulic pressure control valve is controlled to raise the hydraulic pressure applied to the engaging hydraulic pressure chamber;
• a second control in which after the first control the second hydraulic pressure control valve is controlled to raise the hydraulic pressure applied to the disengaging hydraulic pressure chamber;
• and
• a third control in which after the second control the first hydraulic pressure control valve is controlled to reduce the hydraulic pressure applied to the engaging hydraulic pressure chamber.