Patent ID: 8521381

Claim:
A power transfer device including a stepped automatic transmission mounted on a vehicle to transfer power from a power source to an axle using changeable shift speeds, comprising: a fluid transmission apparatus including an input-side fluid transmission element connected to the power source, an output-side fluid transmission element connected to an input shaft of the automatic transmission, and a lock-up clutch that engages and disengages the input-side fluid transmission element and the output-side fluid transmission element; an engagement force adjustment unit that adjusts an engagement force of the lock-up clutch; a target slip speed setting unit that sets, after a kickdown condition, that is, a downshift of the automatic transmission is to be performed in response to a predetermined request for a large drive force, is satisfied, a target slip speed to a predetermined value larger than a non-shifting-time value before a rotational speed of the power source exceeds a post-shifting input shaft speed which is a rotational speed of the input shaft after the downshift, and setting the target slip speed so as to decrease toward the non-shifting-time value along with lapse of time after the rotational speed of the power source exceeds the post-shifting input shaft speed, wherein the target slip speed is a target value of a slip speed which is a difference between the rotational speed of the power source and the rotational speed of the input shaft, and the non-shifting-time value is a value that is set when no shifting of the automatic transmission is performed; and a control unit that controls the engagement force adjustment unit such that the slip speed becomes the set target slip speed, wherein after the rotational speed of the power source exceeds the post-shifting input shaft speed, the target slip speed setting unit sets the target slip speed to a smaller one of the predetermined value and a value obtained by adding to the input shaft speed difference, the larger of a second predetermined value smaller than the predetermined value and a non-shifting-time target slip speed, wherein the input shaft speed difference is a difference between the rotational speed of the input shaft and the post-shifting input shaft speed, and the target slip speed setting unit sets the target slip speed so as to decrease at a predetermined change rate along with lapse of time after the rotational speed of the input shaft reaches the post-shifting input shaft speed.