motor-generator. Patent document 1 discloses a technique that when a battery for supplying electric power to the motor-generator can output a sufficient power at such engine start during vehicle running, namely, when a maximum possible output torque of the motor-generator is sufficient to cover vehicle-driving torque and engine-starting torque, then the transmitted torque capacity of the first clutch is increased, and a target torque of the motor-generator is increased with increase of the transmitted torque capacity of the first clutch, thereby increasing a cranking torque transmitted from the motor-generator to the engine through the first clutch, and quickly completing the engine start.
However, in patent document 1, control of the transmitted torque capacity of the first clutch when the engine is started from rest while the vehicle is running,each color become extremely important factors because development is carried out for plural times and in the transfer step, toner images are collectively performed in one operation. Therefore, to a toner small in particle size used in full color image formation, an external additive is often added which is composed of so large particles as having a volume average particle size of the order of 50 nm to 150 nm, for the purpose of enhancing flowability and transfer efficiency of the toner.
However, the external additive of large particles added to surfaces of toner matrix particles of the toner moves to reentrants in the surfaces of toner matrix particles of the toner and is deposited thereon and further embedded therein by various mechanical stresses applied to the toner through