CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation application of U.S. patent application Ser. No. 11/034,662 filed on Jan. 12, 2005.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric motor, particularly to an brushless peripheral-rotor electric hub 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.
2. Description of Related Art
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 current. 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. Accurate positions of the permanent magnets in the rotor plate are important for proper functioning of the motor.
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
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.
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 are automatically assembled, facilitating automatic inserting of permanent magnets.
The present invention can be more fully understood by reference to the following description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of the electric motor of the present invention.
FIG. 2 is a top view of the electric motor of the present invention.
FIGS. 3a and 3b are front and side views of one of the rotor plate sectors of the present invention.
FIG. 4 is a front view of the rotor plate assembly of the present invention.
FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 4.
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.
FIGS. 7a-7f are front views of the present invention in other embodiments.
FIGS. 8a and 8b are front and side views of one of the stator plate sectors of the present invention.
FIG. 9 is a front view of the stator plate assembly of the present invention.
FIG. 10 is a front view of the rotor plate assembly of the present invention in another embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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 1 of the present invention comprises: A stator assembly 10, having electric 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.
The stator assembly 10 has a stator axle 11 with two ends that are fastened to a stator frame 12. A stator plate sector holder 13 is by a bolt 131 fixed to the stator axle 11, and is 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 plate sector holder 13 carries a stator sector assembly 14. Electric coils 15 are wound on plates of the stator sector assembly 14 and on opposite sides fixed thereon. The plates of the stator sector assembly 14 are fastened by bolts 16 or screws on fastening plates 17 on the stator plate sector holder 13. The electric coils 15 are supplied with electric currents through holes 111 in the stator axle 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 sector assembly 14.
The rotor assembly 20 comprises the permanent magnets 21, a rotor magnet retainer assembly 22, and a casing 23. The permanent magnets 21 are mounted on the inward surface of the rotor magnet retainer assembly 22, and the rotor magnet retainer 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 axle 11. A brake drum 24 is attached to an opposite side of the rotor assembly 20, having a brake shoe (not shown) for stopping a rotating movement of the rotor assembly 20.
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.
Referring to FIGS. 3-6, the rotor magnet retainer assembly 22 comprises a plurality of plates stacked on top of each other. Each plate of the rotor magnet retainer 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 protrusions 222 and recesses 223 forms a plate, and stacking plates on top of each other forms the rotor magnet retainer assembly 22. Each of the rotor plate sectors 221 has positioning elongated alignment ridges 224 composed of circular, square or other suitable shapes and positioning alignment valleys 224a at an opposite side, allowing to stack plates on each other, so that the rotor magnet retainer assembly 22 has a predetermined thickness. Furthermore, each of the rotor plate sectors 221 has a inner side in which holding recesses 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.
For each of the rotor plate sectors 221, the protrusions 222 and a recess 223 are of any suitable shape. As shown in FIGS. 7a-7d, in various embodiments of the present invention, protrusions 222a and recesses 223a of zigzagging shapes, protrusions 222b and recesses 223b of embossed shapes, protrusions 222c and recesses 223c of linear shapes, or protrusions 222d and recesses 223d of waving shapes are used. Furthermore, as shown in FIGS. 7e and 7f, a rotor plate sector 221e accommodates one permanent magnet 21, or a rotor plate sector 221f accommodates several permanent magnets 21.
Referring to FIGS. 6, 8 and 9, the electric coils 15 have a number of magnetic poles that is selected to be compatible with the number of magnetic poles of the permanent magnets 21, so that a field difference results. Each of the electric coils 15 is separately wound on a sector of the stator plate assembly 14. The stator sector 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 sector 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 protrusions and a recesses 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 144a 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.
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.
Referring to FIG. 10, in another embodiment of the present invention, a rotor magnet retainer assembly 22a (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 221a are fixed by bolts or screws.
To summarize, the present invention has a stator plate assembly and a rotor magnet retainer 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.
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.