1. Field of the Invention
The present invention relates to a rotor shaft used for a rotor of a dynamo-electric machine.
2. Description of the Related Art
In a dynamo-electric machine such as a motor, a generator and a motor generator used for a hybrid vehicle, an electric vehicle and the like, a rotor having a magnetic body is rotatably disposed on an inner peripheral side portion of a stator having a field winding. The rotor includes a rotor shaft and the magnetic body mounted on the rotor shaft.
As shown in FIG. 6, a rotor shaft 93 is formed by connecting an inner peripheral side portion 931 and an outer peripheral side portion 933 with each other through a flange 932, and the rotor shaft 93 is integrally formed by forging or the like.
However, if the product is increased in size, it becomes difficult to form the product integrally using the above method. Hence, if the rotor shaft is divided radially into an inner shaft and an outer shaft, the rotor shaft can be produced easily. In Japanese Patent Application Laid-open No. 2007-166863 for example, the inner shaft is shrink-fitted into the outer shaft, and both the shafts are fastened to each other to form the rotor shaft.
When the divided structure is employed as described above, however, it has been a problem at which position the rotor shaft is divided. In the case where the dividing position is not appropriate, a fastening strength between the inner shaft and the outer shaft is not sufficiently secured, and if a large torque is applied to the rotor shaft in its rotating direction (circumferential direction), the fastened state between the inner shaft and the outer shaft is loosened in some cases.
For this reason, it is desired to realize a rotor shaft of the divided structure having such a sufficient fastening strength that can withstand a large rotation torque, and a dividing position for realizing the rotor shaft has been studied.