Clutch control device for 4-wheel drive vehicle

A clutch control device for a four-wheel drive vehicle having a pair of main drive wheels and a pair of auxiliary drive wheels which are selectively connected to a drive source, the clutch control device comprising:

• a dog clutch operatively disposed in a transmission path between the main drive wheels and the auxiliary drive wheels to separate a system for transmitting drive force to the auxiliary drive wheels from a system for transmitting drive force to the main drive wheels by releasing the dog clutch;
• a friction clutch operatively disposed in a transmission path between the main drive wheels and the auxiliary drive wheels to allocate a portion of the drive force from the drive source to the auxiliary drive wheels in accordance with a clutch engagement capacity of the friction clutch;
• and
• a clutch controller operatively coupled to the dog clutch and the friction clutch to selectively carry out an engagement and disengagement control of the dog clutch and an engagement and disengagement control of the friction clutch,
• the clutch controller, in response to a request to engage the dog clutch, being programmed to first control an engagement of the friction clutch, monitor a change gradient of a clutch differential rotation speed of the dog clutch while controlling the engagement of the friction clutch, and start an engagement of the dog clutch upon determining that the gradient of the clutch differential rotation speed is no longer decreasing, the clutch controller monitoring a change gradient of the clutch differential rotation speed of the dog clutch by calculating a difference between an output rotational speed and an input rotational speed of the dog clutch.