1. Field of the Invention
The present invention relates to a rotary electrical machine capable of obtaining a high output power by rotating a rotating magnetic field at a speed different from a rotating speed of a rotor.
2. Background Art
In a conventional rotating-field type rotary electrical machine such as generator for vehicle or synchronous generator, rotating speed of the magnetic field is equal to the rotating speed of the rotor. The rotating-field type rotary electrical machine requires any slip ring and any brush in order to feed an electric current to a field coil, and the machine cannot be completely maintenance free. A maintenance free rotary electrical machine without slip ring and brush is an inductor-rotating type rotary electrical machine. In the inductor-rotating type rotary electrical machine, an armature and a field coil are fixed, an inductor is disposed between the armature and the field coil, and a rotating magnetic field is brought to the armature by rotating the inductor.
For example, the Japanese Patent Publication (unexamined) No. 15929/1995 discloses an art relating to the mentioned inductor-rotating type rotary electrical machine. In this known art, an inductor serving as a rotor rotates in an air gap formed between a field of a stator magnetized in axial direction and an armature of the same stator, thereby a rotating magnetic field is given to the armature. In such a structure, the slip ring and the brush are not required and the machine is free from maintenance, however, the rotating speed of the rotating field is equal to the rotating speed of the rotor as a matter of course.
In order to obtain a sufficient output power with a small-sized rotary electrical machine, in the case of a generator, for example, it is necessary to increase the rotating speed of the rotor and increase the winding number of the armature coil as compared with a prime mover. Taking the case of a generator for a vehicle as an example, in the rotary electrical machine of a wide normal rotating range, increasing a speed-increasing ratio of the rotor to the prime mover requires that the machine has strength enough to withstand centrifugal force, and there exists a limit in increasing the speed-increasing ratio. As long as the rotary electrical machine is not large-sized, increase in winding number of the armature coil brings about increase in copper loss of the armature coil, and consequently, the temperature rises remarkably, and it is difficult to increase the output power with a small-sized rotary electrical machine.
The present invention was made to solve the above-discussed problems and has an object of obtaining a rotary electrical machine capable of obtaining a sufficient output power, without increasing any speed of a rotor itself and without increasing any winding number of an armature coil, by rotating a rotating magnetic field at a speed different from a rotating speed of a rotor in a case where the rotary electrical machine is used as a generator.
According to the invention, a rotary electrical machine includes an armature forming a stator, a field forming the stator with the armature, a rotor that rotates facing the armature and the field, a first coil that is disposed at a portion facing the field of the rotor and generates an electric power by means of a magnetic field produced by the field, and a second coil that is disposed at a portion facing the armature of the rotor, supplied with an electric current from the first coil, and brings a magnetic field to the armature. As a result of such arrangement, it is possible to obtain a rotating magnetic field of a rotating speed different from the rotating speed of the rotor from the second coil and use the rotary electrical machine as a generator of high output power or as an electric motor of high torque.