Four-wheel drive vehicle

A four-wheel drive vehicle comprising:

• main drive wheels and auxiliary drive wheels;
• a drive power source including an engine and a vehicle-drive rotating machine;
• a drive-power distribution device including (i) a drive-power distribution clutch configured to distribute a drive power from the drive power source to the main drive wheels and the auxiliary drive wheels, with a drive-power distribution ratio that is a ratio of distribution of the drive power between the auxiliary drive wheels and the main drive wheels, (ii) a worm-drive electric motor that is provided apart from the vehicle-drive rotating machine, (iii) a gear mechanism including (iii-1) a worm provided on a shaft of the worm-drive electric motor and (iii-2) a worm wheel meshing with the worm and (iv) a conversion mechanism configured to cause a pressing force to be generated in the drive-power distribution clutch by converting a rotary motion of the worm-drive electric motor into a linear motion in a direction of an axis of the drive-power distribution clutch;
• and
• a control apparatus configured to control rotation of the worm-drive electric motor such that the drive-power distribution ratio becomes a target distribution ratio value,
• wherein the control apparatus is configured, when changing the drive-power distribution ratio to the target distribution ratio value, to set an electric-current command value that is proportional to power provided for driving and rotating the worm-drive electric motor, such that the electric-current command value is set depending on whether the drive power from the engine is being transmitted to the drive-power distribution device or not, and
• wherein the control apparatus is configured, in a drive-power transmitted state in which the drive power from the engine is being transmitted to the drive-power distribution device, to execute a command-value reduction control operation for causing the worm-drive electric motor to be driven and rotated, with the electric-current command value being set to a value smaller than in a drive-power non-transmitted state in which the drive power from the engine is not being transmitted to the drive-power distribution device.