Conventionally, as described in Patent Document 1: Japanese Unexamined Laid-open Patent Application Publication No. 2006-191782 which is hereinafter referred to when describing the conventional art, as an electric motor used as a driving source for various electric vehicles including electric motorcycles or for various electric devices, an electric rotating machine equipped with a rotor having permanent magnets and configured to rotate about a rotation axis and a stator having stator windings and facing the rotor via a gap in a radial direction of the rotor is widely known.
In recent years, a small and high-performance electric motor as a driving source for use in various electric vehicles including electric motorcycles has been desired. In electric motors of this kind, if the operational range from a high torque low speed revolution speed range to a low torque high speed revolution speed range is wide, a driving force required for a vehicle operation can be obtained without using a transmission which is normally required for a vehicle with an internal combustion engine.
Due to characteristics of an electric motor, however, an electric motor has a problem that although a high torque can be generated in a low revolution speed range, the upper limit of the revolution speed will be limited in a high revolution speed range. That is, in an electric motor, although a high torque can be generated in a low revolution speed range, as the revolution speed increases, the induced voltage (i.e., back electromotive force), which is to be generated at the stator winding arranged on the stator by magnetic flux of the permanent magnet provided at the rotor, increases. When the revolution speed increases and reaches a certain speed, the induced voltage induced at the stator winding becomes equal to the applied voltage of the electric motor, preventing the electric current flow in the stator winding. This in turn prevents a further increase of the revolution speed. To solve this problem, it is performed, for example, to decrease the induced voltage (i.e., back electromotive force) by performing a field weakening control.
The field weakening control, however, requires an additional electrical power to negate the induced voltage. Therefore, in the case of a product having an electric motor used in a state in which an electric power is supplied from the outside, the increased power consumption does not result in a shortened drivable time. However, in the case of a product, such as, an electric motorcycle driven by a battery mounted thereon, since the battery capacity is limited, the electric current supplied to negate the induced voltage induced in the stator winding causes increased electric power consumption, resulting in a shortened drivable time. For this reason, it is requested to decrease the power consumption as much as possible.
The present inventors proposed a new stator structure capable of eliminating the need for a conventional field weakening control which induces additional power consumption. In this proposal, a tooth portion of a stator on which a winding is arranged is divided into at least two divided tooth portions in a relatively movable manner so that the relative movement thereof changes the flow of magnetic flux to decrease the flux linkage of the stator winding at the time of a high revolution speed. According to this proposal, since the flux linkage of the stator winding at the time of a high revolution speed can be adjusted by a physical means, the electrical power conventionally required for the field weakening control can be decreased or eliminated, which enabled to provide an electric rotating machine capable of decreasing power consumption.
In such an electric rotating machine having the aforementioned structure, it is desired to further enlarge the operational range from a high torque low revolution speed range to a low torque high revolution speed range.