Control apparatus for 4WD vehicle

A control apparatus for a four wheel drive vehicle, the four wheel drive vehicle including:

• main driving wheels;
• auxiliary driving wheels;
• a driving force source that outputs a power to the main driving wheels;
• a driving force transmission shaft having a driving force source end operatively connected to the driving force source and an opposite auxiliary driving wheels end operatively connected to the auxiliary driving wheels, the driving force transmission shaft configured to transmit a part of the power that the driving force source transmits to the main driving wheels to the auxiliary driving wheels during four wheel drive traveling, the driving force transmission shaft is part of a power transmission path between the driving force source and the auxiliary driving wheels;
• a first disconnection mechanism disposed on the driving force source end of the driving force transmission shaft;
• and
• a second disconnection mechanism disposed on the auxiliary driving wheels end of the driving force transmission shaft, the first disconnection mechanism and the second disconnection mechanism being configured to move between an engaged position and a released position, in the engaged position the first disconnection mechanism and the second disconnection mechanism connect the power transmission path between the driving force source and the auxiliary driving wheels and in the released position the first disconnection mechanism and the second disconnection mechanism disconnect the power transmission path between the driving force source and the auxiliary driving wheels;
• the control apparatus comprising:
• an electronic control unit configured to:
• (i) control one of the first disconnection mechanism and the second disconnection mechanism to be in the engaged position and then control the other one of the first disconnection mechanism and the second disconnection mechanism to be in the engaged position when a disconnect state is canceled, the disconnect state being a state where both the first disconnection mechanism and the second disconnection mechanism are in the released position;
• and
• (ii) set, when the disconnect state is canceled, an increasing gradient of a rotation speed of the driving force transmission shaft in accordance with a condition that the electronic control unit determines to cancel the disconnect state.