The present application is based on and claims priority from Japanese Patent Applications 2000-327290 filed Oct. 26, 2000 and 2001-13360 filed Jan. 22, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rotary electric machine that has a plurality of permanent magnet main poles and a plurality of auxiliary poles disposed between neighboring main poles.
2. Description of the Related Art
As a prior art, JP-A-2000-261989 or EP1035629A2, which corresponds to the former publication, discloses a DC motor.
This DC motor has a plurality of circumferentially disposed main poles, a plurality of auxiliary poles each of which is disposed between neighboring two of the main poles and a plurality of magnet fixing members for fixing the main poles and the auxiliary poles.
As shown in FIGS. 9A and 9B of EP1035629A2, the magnet fixing member is formed from a U-bent elastic metal plate that has opposite side walls, between which an auxiliary-pole space is formed to hold an auxiliary pole. The opposite side walls are bent inwardly to be opposed to each other at edges thereof, and axial ends of the bent edges are separated from the side walls to form elastic retaining members.
The auxiliary pole is inserted into the auxiliary-pole space of the magnet fixing member after an elastic retaining member is opened inwardly in a radial direction. The auxiliary pole is restricted to shift in axial directions by a stopper that is formed at an end of the elastic retaining member. The auxiliary pole is also supported in the radial direction both by cutout pieces cut from an upper wall surface of the magnet fixing member at radially outside surface and by the bent edge at the inner periphery thereof.
The elastic retaining member of the bent edge is slightly curled upward at the end thereof from the bent edge when the auxiliary pole is not inserted in the auxiliary pole space. Therefore, when the auxiliary pole is inserted into the auxiliary pole space, the elastic retaining member and the bent edge are brought into the same plane so that the elastic retaining member provides spring force. Accordingly, the auxiliary pole is prevented from shifting in the radial directions when the outside surface of the auxiliary pole is supported by the cutout pieces.
The elastic retaining member has to have a suitable length to open radially inward when the auxiliary pole is inserted in the axial direction. Accordingly, the spring force of the elastic retaining member is too small to prevent the auxiliary pole from shifting in the radial directions while the auxiliary pole is disposed in the auxiliary pole space.
The auxiliary pole may shift in the radial direction due to vibration of the armature during rotation and armature reaction, and the elastic retaining member may bend inward, thereby to interfere with the armature.
The shifting of the auxiliary pole gives such excessive stress on the elastic retaining member that the elastic retaining member may be cut off.
JP-B2-57-12380 discloses a rotary electric machine of this kind. In this rotary electric machine, an auxiliary pole is disposed between two neighboring main poles so that a pair of circumferentially opposite pole surfaces of the auxiliary pole can have the same polarities as the polarities of the armature-side of neighboring main poles. Thus, leakage magnetic flux between the main poles are controlled to increase effective magnetic flux supplied to the armature via air gap. Therefore, the output power of the rotary electric machine can be increased without increasing the size of the rotary electric machine. In other words, the size of the rotary electric machine can be reduced without reducing the output power thereof.
While the rotary electric machine is operating, current flows in the armature. As a result, a magnetic flux distribution is formed due to armature reaction. The magnetic flux distribution forms triangular curves, which have a peak between the neighboring main poles or at the auxiliary pole, as shown in FIG. 9. The amount of the magnetic flux at the auxiliary poles is larger than the amount of the magnetic flux at the main pole. In other words, the auxiliary poles are more affected by the armature reaction than the main poles. The auxiliary poles are affected and demagnetized by the magnetic flux of the armature reaction that is different in direction from the magnetic flux of itself. If the armature reaction is too large, the auxiliary poles are irreversibly demagnetized, and the flux density thereof will not return to the initial magnetic flux density after the armature reaction is removed. As a result, the auxiliary poles will not effectively control the leakage flux between the main poles, resulting in lowering the output power of the rotary electric machine.
The present invention has been made in view of the above circumstances, and an object of the invention is to provide an improved rotary electric machine in which elastic retaining members from being cut off or from deforming badly.
According to a main feature of the invention, a magnet fixing member is comprised of a U-bent elastic metal plate having a pair of circumferentially opposite walls that provides an auxiliary pole space for holding an auxiliary pole therein, the opposite walls are respectively bent inward at edges thereof in circumferentially opposite directions to be opposed to each other, the bent edges are separated at the axial ends to form an elastic retaining member that can elastically deform in radial directions and has an elastic projection at a portion thereof, and the auxiliary pole is inserted into the auxiliary pole space after opening the elastic retaining member radially inward in an axial direction so as to be held radially outward by the elastic retaining member.
Therefore, the auxiliary pole in the auxiliary pole space is biased radially outward by the elastic projection to be fixed tightly. Accordingly, the load applied to the elastic retaining member can be made small so that shift due to the vibration while the armature is rotating and armature reaction can be prevented.
In the rotary electric machine according to another feature of the invention, the elastic projection comprises a convex portion of the bent edge.
In the rotary electric machine according another feature of the invention, the magnet fixing member has a plurality of outside supporting portions for supporting the auxiliary pole that is biased radially outward by the elastic projection.
Therefore, the auxiliary pole can be supported at the outer periphery thereof by a plurality of portions. The auxiliary pole can be more fixedly and stably supported by the plurality of portions than by the surface of the magnet fixing member.
In the rotary electric machine according another feature of the invention, the magnet fixing member has a base wall that faces radially outer surface of the auxiliary pole, and the outside supporting portion is formed from a portion that is cut and bent radially inward from the base wall.
Therefore, the outside supporting portions can be formed easily, and the number of the outside supporting portions can be easily changed.
In the rotary electric machine according to another feature of the invention, the elastic retaining member is formed at opposite axial ends of the bent edge and has a stopper for retaining an axial end surface of the auxiliary pole.
Therefore, the auxiliary pole can be prevented from shifting in the axial directions so that the auxiliary pole can be fixed more stably.
Another object of the invention is to provide a reliable rotary electric machine that will prevent the auxiliary poles from being demagnetized and maintain the leakage flux control function of the auxiliary poles to prevent lowering the output power by suitable selection of the magnetic characteristics of the auxiliary poles.
In a rotary electric machine according to another main feature of the invention, coercive force of auxiliary poles is set to a value that is high enough to prevent the auxiliary poles from being irreversibly demagnetized by a maximum armature reaction of said rotary electric machine. Therefore, the irreversible demagnetization of the auxiliary pole can be prevented so that the auxiliary poles can effectively suppress magnetic leakage among the main poles. Accordingly, the output power of the rotary electric machine can be maintained for long time.
Particularly, according to another feature of the invention, the coercive force of the auxiliary poles is set larger than the coercive force of the main poles, so that the main poles can employ less expensive material than the auxiliary poles. As a result, the rotary electric machine can have a stable magnetic leakage suppressing function of the main poles without increasing production cost.
In the rotary electric machine according to another feature of the invention, remnant magnetic flux density of the auxiliary poles is set so that remnant magnetic flux density after the auxiliary poles is irreversibly demagnetized by a maximum armature reaction of the rotary electric machine is still higher than a predetermined value. Therefore, even after the auxiliary poles are demagnetized due to the maximum armature reaction of the rotary electric machine in operation, the auxiliary poles maintain a magnetic flux density that can sufficiently suppress the magnetic leakage of the main poles so that the output power of the rotary electric machine can be stably maintained.
In particular, according to another feature of the invention, the magnetic flux density of the auxiliary pole is set lower than that of the main pole. Therefore, the main poles can use less expensive material than the auxiliary poles, so that the rotary electric machine can have auxiliary poles that effectively suppress the magnetic leakage of the main poles without increasing cost thereof.
In the rotary electric machine according to another feature of the invention, the maximum armature reaction of the rotary electric machine is caused by locked-rotor current flowing while the rotary electric machine is being started. Generally, the maximum armature current is locked-rotor current flowing while the rotary electric machine is started. Therefore, the function of the auxiliary poles is prevented from lowering due to the maximum armature reaction of the rotary electric machine in operation.