Abstract:
A brushless peripheral-rotor electric motor comprises a stator assembly, having an axis, a stator plate holder, fixed on the axis, at least one stator plate assembly, mounted on the stator plate holder, and electric coils, would around the plates of the stator plate assembly; and a rotor assembly, having a casing, a rotor magnet retainer assembly, placed inside of the casing, and at least one permanent magnet, mounted on plates of the rotor magnet retainer assembly; wherein the stator plate assembly and/or the rotor magnet retainer assembly have plates which are stacked on top of each other and which are each divided into at least two sectors, saving production cost.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electric motor, particularly to an electric motor in which rotor and stator plates divided in several sections are substituted for a conventional rotor and stator plates in single pieces. Thereby cost of molding and waste material are greatly reduced and unused material of other processes is usable, resulting in a significant cost advantage.  
         [0003]     2. Description of Related Art  
         [0004]     In conventional art, brushless peripheral-rotor motors, in which rotors-are placed outside stators, are widely used in hubs of electric vehicles and washing machines. Motors of this type have inner stators with a plurality of electric coils connected with power. During operation as an electric generator, a rotating external magnetic field results in the generation of electric curent. In each motor of this type, the rotor has a larger diameter than the stator and is provided with a plurality of permanent magnets. Usually, the rotor is made of a curved rotor plate in which the stator is inserted. Various ways of placing the permanent magnets in the rotor are used, which are mainly decided by cost. Right positions of the permanent magnets in the rotor plate are important for proper functioning of the motor.  
         [0005]     There are mainly two conventional methods of making rotors. In the first, a rotor body is made in a single piece on a lathe, with inner peripheral grooves being cut out. Into each of the inner peripheral grooves a permanent magnet is laid. Since cutting of the inner peripheral grooves and automatic inserting of the permanent magnets is difficult, the permanent magnets are usually glued to an inner periphery of the rotor body. This method, however, is expensive and often results in errors of production. Furthermore, since the permanent magnets are glued to metal, magnetic flux is reduced by some degree. In the second method, rotor plates are produced by punching. Using silicon steel leads to better magnetic properties and a higher magnetic flux. Several rotor plates are inserted in a casing. By the rotor having several plates, cutting grooves is facilitated and working is easy. Choosing appropriate shapes for the rotor plates results in good magnetic properties and high effectivity in conjunction with the stator coils. However, since the rotor plates have relatively large diameters, large punching machines are required, and punching produces large quantities of waste material, leading to high cost of production.  
       SUMMARY OF THE INVENTION  
       [0006]     It is the object of the present invention to provide an electric motor which is easy to produce and which is manufactured at low cost and with little waste material.  
         [0007]     The electric motor of the present invention has a stator and a rotor, both of which have plates that are divided into several sectors. The sectors are made by punching at high precision and automatically assembled, facilitating automatic inserting of permanent magnets.  
         [0008]     The present invention can be more fully understood by reference to the following description and accompanying drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0009]     As shown in  FIGS. 1 and 2 , the electric motor of the present invention has a rotor that surrounds a stator, working as a motor or as an electricity generator. The following explanation takes a motor used in a hub of an electric vehicle or in a washing machine as an example. The electric motor of the present invention comprises: A stator assembly  10 , having coils  15 ; and a rotor assembly  20 , having permanent magnets  21 . The rotor assembly  20  is made of a plurality of rotor plates stacked on top of each other, and the stator assembly  10  is made of a plurality of stator plates stacked on top of each other. The rotor plates and the stator plates are each divided into a plurality of sectors, resulting in easy manufacturing at low cost. In the following, a detailed explanation is given.  
         [0010]     The stator assembly  10  has a stator axis  11  with two ends that are fastened to a stator frame  12 . A stator plate holder  13  is by a bolt  131  fixed to the stator axis  11 , being made of material that allows for effective dissipation of heat, like aluminum. Moreover, cooling by gas or liquid is possible to dissipate heat generated in the stator assembly  10  during operation. The stator holder  13  carries a stator plate assembly  14 . Electric coils  15  are wound on plates of the stator plate assembly  14  and on opposite sides fixed thereon. The plates of the stator plate assembly  14  are fastened by bolts  16  or screws on fastening plates  17  on the stator plate holder  13 . The electric coils  15  are supplied with electric currents through holes  111  in the stator axis  11 . Electric current flowing through the electric coils  15  generates a radially oriented magnetic field, which interacts with the magnetic field of the permanent magnets  21 . Gaps are left between the electric coils  15  and the permanent magnets  21 , so that the permanent magnets  21  are able to move unhindered by the stator plate assembly  14 .  
         [0011]     The rotor group  20  comprises the permanent magnets  21 , a rotor plate assembly  22 , and a casing  23 . The permanent magnets  21  are mounted on a lower seide of the rotor plate assembly  22 , and the rotor plate assembly  22  is fitted into the casing  23 , forming an integral body. The casing  23  has two sides that are mounted on a shaft  231 , allowing the rotor assembly freely to rotate on the stator axis  11 . A brake drum  24  is attached to an opposite side of the rotor assembly  20 , having a brake (not shown) for stopping a rotating movement of the rotor assembly  20 .  
         [0012]     In the interaction between the stator assembly  10  and the rotor assembly  20 , the permanent magnets  21  are driven by the rotating magnetic field generated by the electric coils  15 . On the other hand, if the casing  23  is rotated against the stator assembly  10 , the rotating magnetic field of the permanent magnets  21  generates an electric current in the electric coils  15 .  
         [0013]     Referring to  FIGS. 3-6 , the rotor plate assembly  22  comprises a plurality of plates stacked on top of each other. Each plate of the rotor plate assembly  22  consists of at least two rotor plate sectors  221 . Each rotor plate sector  221  has two edges connecting to a neighboring rotor plate sector  221 , on which a hook  222  and a groove  223  are respectively placed. Connecting the hooks  222  and grooves  223  forms a plate, and stacking plates on top of each other forms the rotor plate assembly  22 . Each of the rotor plate sectors  221  has positioning projections  224  of circular, square or other suitable shapes and positioning depressions  224   a  at an opposite side, allowing to stack plates on each other, so that the rotor plate assembly  22  has a predetermined thickness. Furthermore, each of the rotor plate sectors  221  has a lower side in which holding grooves  225  for accommodating the permanent magnets  21  are cut. The rotor plate sectors  221  are manufactured by punching, using silicon steel as material for favorable magnetic properties.  
         [0014]     For each of the rotor plate sectors  221 , the hook  222  and a groove  223  are of any suitable shape. As shown in  FIGS. 7   a - 7   d , in various embodiments of the present invention, hooks  222   a  and grooves  223   a  of zigzagging shapes, hooks  222   b  and grooves  223   b  of embossed shapes, hooks  222   c  and grooves  223   c  of linear shapes, or hooks  222   d  and grooves  223   d  of waving shapes are used. Furthermore, as shown in  FIGS. 7   e  and  7   f , a rotor plate sector  221   e  accommodates one permanent magnet  21 , or a rotor plate sector  221   f  accommodates several permanent magnets  21 .  
         [0015]     Referring to  FIGS. 6, 8  and  9 , the electric coils  15  have a number of magentic poles that is equal to the number of magnetic poles of the permanent magnets  21  or that differs therefrom, so that a field difference results. Each of the electric coils  15  is separately wound on a plate of the stator plate assembly  14 . The stator plate assembly  14  has plates that are made of silicon steel with good magnetic properties and are preferably stacked on each other. Each plate of the stator plate assembly  14  consists of at least two stator plate sectors  141 . Each stator plate sector  141  has two edges connecting to a neighboring stator plate sector  141 , on which a hook  142  and a groove  143  are respectively placed, allowing to fasten neighboring stator plate sectors  141  to each other. Each of the stator plate sectors  141  has positioning projections  144  of circular, square or other suitable shapes and positioning depressions  144   a  at an opposite side, allowing to stack plates on each other, so that the stator plate assembly  14  has a predetermined thickness. Each of the stator plate sectors  141  on the edges thereof has seats  145 ,  146  for accommodating one of the electric coils  15 .  
         [0016]     Furthermore, each of the stator plate sectors  141  has a fixing hole  147 , allowing a bolt or a screw to be led through for fastening the stator plate assembly  14  on the stator plate holder  13 .  
         [0017]     Referring to  FIG. 10 , in another embodiment of the present invention, a rotor plate assembly  22   a  (permanent magnet seat) is made of elongated shape for use in a linear motor, so that a magnetic bearing of low production cost is formed. Furthermore, the permanent magnets  21  are disposable in a moving part as a well as a fixed part of the motor. In the latter case, rotor plate sectors  221   a  are fixed by bolts or screws.  
         [0018]     To summarize, the present invention has a stator plate assembly and a rotor plate assembly having single plates which are further divided into sectors. Production thereof by punching is fast and allows for precise and easy accommodating of permanent magnets. Furthermore, waste material during production is minimized, even waste material from other production processes is usable, so that costs are greatly reduced.  
         [0019]     While the invention has been described with reference to preferred embodiments thereof, it is to be understood that modifications or variations may be easily made without departing from the spirit of this invention which is defined by the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a front view of the electric motor of the present invention.  
         [0021]      FIG. 2  is a top view of the electric motor of the present invention.  
         [0022]      FIGS. 3   a  and  3   b  are front and side views of one of the rotor plate sectors of the present invention.  
         [0023]      FIG. 4  is a front view of the rotor plate assembly of the present invention.  
         [0024]      FIG. 5  is a cross-sectional view taken along line  5 - 5  of  FIG. 4 .  
         [0025]      FIG. 6  is a partial sectional view of one of the rotor plate sectors and one of the stator plate sectors of the present invention.  
         [0026]      FIGS. 7   a - 7   f  are front views of the present invention in other embodiments.  
         [0027]      FIGS. 8   a  and  8   b  are front and side views of one of the stator plate sectors of the present invention.  
         [0028]      FIG. 9  is a front view of the stator plate assembly of the present invention.  
         [0029]      FIG. 10  is a front view of the rotor plate assembly of the present invention in another embodiment.