The power transmission device and a control method thereof

A power output apparatus (20) of the present invention includes a clutch motor (30), an assist motor (40), and a controller (80) for controlling the clutch motor (30) and the assist motor (40). The clutch motor (30) includes an outer rotor (32) linked with a crankshaft (56) of a gasoline engine (50) and an inner rotor (34) connecting with a drive shaft (22). The assist motor (40) includes a rotor (42) connecting with the drive shaft (22). When the residual capacity of a battery (94) is less than an allowable minimum value, a control CPU (90) of the controller (80) controls a first driving circuit (91) to enable the clutch motor (30) to carry out the power operation and apply a first torque to the drive shaft (22) in the direction of rotation of the drive shaft (22). The control CPU (90) concurrently controls a second driving circuit (92) to enable the assist motor (40) to carry out the regenerative operation and apply a second torque to the drive shaft (22) in the reverse of the rotation of the drive shaft (22). The second torque is substantially equal in magnitude but opposite in direction to the first torque. The electric power regenerated by the assist motor (40) is supplied to the battery (94) to supplement the electric power of the battery (94). The power output apparatus (20) of the invention can thus make the torque output to the drive shaft (22) approximately equal to zero.