Abstract:
A stator structure comprising at least one first magnetic conductive plate and at least one second magnetic conductive plate, each magnetic conductive plate having a plurality of radial arms and pole tooth provided on ends of the radial arms, wherein the pole teeth of the first and second magnetic conductive plates have different shapes.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is based on, and claims priority from, Taiwan Application Serial Number 93118063, filed Jun. 23, 2004, the disclosure of which is hereby incorporated by reference herein in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     (a) Field of the Invention  
         [0003]     The present invention relates to a stator structure of a motor and, more particularly, to a stator structure easy to create starting offset for the motor.  
         [0004]     (b) Description of the Related Art  
         [0005]     In conventional designs for direct current brushless electric motors, starting offset must be created to eliminate the dead angle and thus to provide sufficient starting torque for all relative orientations between the stator and the rotor of the motor.  
         [0006]     An conventional way of creating the starting offset is to have silicon steel sheets that constitute a stator structure be applied with uneven magnetic force. Referring to  FIG. 1 , one of the opposite sides of the pole tooth  104  is cut at its periphery to form a tangential plane, so that the gap D, measured from the tangential plane to the rotor  102 , is larger than the gap d, measured from the side surface of the pole tooth  104  without the tangential plane, to result in different values of magnetic resistance. Accordingly, the starting offset is introduced by the asymmetry of the pole tooth  104 . Except the formation of the tangential plane shown in  FIG. 2A , in conventional method the asymmetry of the pole tooth  104  may be achieved by the formation of cambers with different curvatures at two sides, as in  FIG. 2B , or the formation of a step portion at one side, as in  FIG. 2C .  
         [0007]     However, according to the conventional methods given above, the interval between the stator and the rotor are thus enlarged to lower the magnetic flux therebetween (the magnetic flux is in inverse proportion to the square of the distance) so that the torque of the motor is decreased. Also, the asymmetry of the pole tooth  104  is liable to be ill-formed to result in an inaccurate starting offset.  
         [0008]     Further, when the starting offset is needs to be adapted to a different rotational sped, load, or threshold voltage, the silicon steel sheet must be replaced with a new one having a different interval between the stator and the rotor. This is costly and time-wasting.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     In view of this, an object of the invention is to provide a stator structure easy to create starting offset for a motor.  
         [0010]     According to the invention, a stator structure includes a stack of at least one first magnetic conductive plate and at least one second magnetic conductive plate. Each magnetic conductive plate has a plurality of radial arms and pole teeth provided on ends of the radial arms, and each pole tooth has a first and a second side portions substantially symmetrical to each other with respect to the radial arm. The second magnetic conductive plate is identical with the first one except the first side portion of the second magnetic conductive plate is formed with a cut, and the first and second magnetic conductive plates are stacked in a manner that the magnetic center of a rotor in relation to each pole tooth is closer to the second side portion than the first one. The magnetic conductive plates may be silicon steel sheets.  
         [0011]     Through the design of the invention, since all the magnetic conductive plates have identical radii R, from center to the outer periphery, the stator structure formed of a stack of them can keep the same small gap apart from the rotor to have larger torque and improved efficiency. Further, since the two sets of the magnetic conductive plates are pre-designed to have the mere difference of the cut, when the offset angle θ is needed to be adapt to a different rotational speed, load or threshold voltages, the adjustment of the offset angle θ accompanied by the alternation to the magnetic action area is easy to be achieved only by varying the respective numbers of the first and second magnetic conductive plates in a stack. Thereby, the magnetic conductive plate is not needed to be replaced with a new one to change the starting offset, and thus the manufacture cost and labor time are considerably reduced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  and  FIG. 2  show schematic views illustrating conventional ways of creating starting offset for a motor.  
         [0013]      FIG. 3A  and  FIG. 3B  show schematic views illustrating two different sets of silicon steel sheets that together constitute the stator structure of the invention.  
         [0014]      FIG. 4  illustrates a stator structure according to an embodiment of the invention.  
         [0015]      FIG. 5  shows a cross-section of the stator structure cut along A-A line in  FIG.4 .  
         [0016]      FIG. 6A  and  FIG. 6B  illustrate stack modifications of the magnetic conductive plates.  
         [0017]      FIG. 7  shows a schematic diagram illustrating another embodiment of the invention.  
         [0018]      FIG. 8  shows a schematic diagram illustrating another embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]      FIG. 3A  and  FIG. 3B  show schematic views illustrating two different sets of silicon steel sheets that together constitute the stator structure of the invention. The stator structure of the invention is a stack of magnetic conductive plates such as two different sets of silicon steel sheets. Referring to  FIG. 3A , the first silicon steel sheet  10  is provided with an opening  12  at its central location and radial arms  14  surrounding the opening  12  and extending outwardly and radially from the center to allow a coil (not shown) to be wrapped thereon. Each radial arm  14  is provided with a pole tooth  16  at its end, spanning tangential to the extending direction of the radial arm  14 . The outer periphery  18  of the pole tooth  16  constitutes the magnetic action surface of the stator structure interacted with a rotor (not shown).  
         [0020]     The second silicon steel sheet  20 , provided with an opening  22  and four radial arms  24  having their respective pole teeth  26 , is identical with the first silicon steel sheet  20  in shape as well as the radius R from center to the outer periphery. The pole teeth  16  of the first silicon steel sheet  10  and the pole teeth  26  of the second silicon steel sheet  20  have different shape or magnetic action area. For example, the shape or magnetic action area of a side portion  26   a  of the first silicon steel sheet  20  is different from a side portions  26   b  of the first silicon steel sheet  20 . The side portion  26   a  has at least one cut, notch or through hole. The section of the cut, notch or through hole is parallel to the extending direction of the radial arm.  
         [0021]     In this embodiment, the section of the cut is parallel to the extending direction of the radial arm  24 . Also, the dimension of the cut is not limited and is determined according to the actual demand. Further, the numbers of the radial arms  14  and  24 , though exemplified as four units, is not limited and is selected by the pole number of the motor.  
         [0022]      FIG. 4  illustrates a stator structure  30  composed of a stack of the first silicon steel sheet  10  and the second silicon steel sheet  20 .  
         [0023]     Referring to  FIG. 4 , two second silicon steel sheets  20  having cuts are stacked on two silicon steel sheets  10  without cuts, and further a coil  34  is wrapped on their radial arms, with their outer peripheries  38  being aligned to each other to constitute a magnetic action surface interacted with a rotor.  
         [0024]      FIG. 5  shows a cross-section of the stator structure  30  cut along A-A line in  FIG.4 . Referring to  FIG. 4  and  FIG. 5 , when the magnetic action surface is divided into two parts along the center line P of one of the pole tooth, the magnetic action area of the left part I is smaller than that of the right part II because of the formation of the cut. Hence, the magnetic center of the rotor in relation to each pole tooth is closer to right part II (the half part without the cut) to reach magnetic force balance, thus forming an offset angle θ as indicated in  FIG. 4 .  
         [0025]     Through the design of the invention, since all the silicon steel sheets have identical radii R, from center to the outer periphery  18 , the stator structure formed of a stack of them can keep the same small gap apart from the rotor to have larger torque and improved efficiency.  
         [0026]     Further, since the two sets of the silicon steel sheets are pre-designed to have the mere difference of the cut, when the offset angle θ is needed to be adapt to a different rotational speed, load or threshold voltages, the adjustment of the offset angle θ accompanied by the alternation to the magnetic action area is easy to be achieved only by varying the respective numbers of the first and second silicon steel sheets in a stack. Thereby, the offset angle of the stator structure can be charged without re-molding, and thus the manufacture cost and labor time are considerably reduced.  
         [0027]     Further, referring to  FIG.5 , since the second silicon steel sheets  20  are stacked above the first magnetic conductive plates  10 , the lower half part of the stator structure has a downward magnetic pressure applied on the rotor to obviate the axial vibration of the motor.  
         [0028]     According to the invention, the respective numbers and stack style of the two sets of silicon steel sheets are not limited, and they are only to create different magnetic action area with respect to two half parts divided along the center line P of a radial arm. For example, the silicon steel sheet  20  having cuts may be stacked to be adjacent to one another, as in  FIG. 6A , or the first and the second silicon steel sheet may be alternately stacked, as in  FIG. 6B .  
         [0029]      FIG. 7  shows a schematic diagram illustrating another embodiment of the invention. Referring to  FIG. 3A  and  FIG. 7 , in this embodiment, the stator structure is a stack of silicon steel sheet  10  and silicon steel sheet  40 . The two sets of the silicon steel sheet  10 ,  40  are equally provided with identical openings  12 ,  42 , radial arms  14 ,  44 , and pole teeth  16 ,  46 , as in the afore said embodiment, except one side portion of the silicon steel sheet  40  is notched out to form a step portion  48 . Hence, the adjustment of the offset angle θ accompanied by the alternation to the magnetic action area is also easy to be achieved only by varying the respective numbers of the silicon steel sheets  10 ,  40 .  
         [0030]     Alternatively, as shown in  FIG. 8 , a silicon steel sheet  50  is provided with an opening  52 , radial arms  54  and pool tooth  56 . The pool tooth  56  may be dug on its outer periphery to form at least one through hole  58  at its one side to alter the magnetic action area.  
         [0031]     Hence, according to the invention, simply as all the pole teeth maintain identical lengths from their outer periphery to the center of the magnetically conductive sheet, at least one set of the magnetically conductive sheets may be provided with cuts, notches, or through holes to alter the magnetic action area, and the adjustment of the offset angle θ accompanied by the alternation to the magnetic action area is also easy to be achieved.  
         [0032]     While the invention has been recited by way of examples and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.