Abstract:
A stater of an electrical machine has a cross section, a longitudinal extension, a jacket surface, a plurality of winding holders configured so that at least one of the winding holders for receiving a field winding has a larger winding width than another of the winding holders.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention is directed to a stator of an electrical machine, an electrical machine, and a power tool. 
         [0002]    Electrical machines that are composed of a stator and a rotor, and that may be operated using alternating current or direct current, are also referred to as universal motors. Electric motors of this type are often used in household appliances and power tools, they may be powered by an alternating-current system, and a rectifier may also be used. 
         [0003]    Increasingly greater energy densities are being required specifically of power tools, e.g., of angle grinders, since customers continually demand ever-smaller tools. The reduction in tool size should not necessarily require that the power also be reduced. Instead, reduced tool size should make it possible to increase the power. Basic limiting geometric conditions often makes this impossible, however. 
         [0004]    With small angle grinders, for example, the electric motor is located directly in the user&#39;s grip region. The diameter of the electric motor is therefore particularly significant in this region, since it directly affects the diameter of the grip. Angle grinders typically have a further property that influences the grip shape and diameter, however. The tool is set into operation by actuating a pushbutton, and the switch-on motion takes place via a sliding switch that passes by the electric motor, in the rear region of the tool, in order to actuate an electrical switch that is located there inside the tool housing. To this end, the field core of the electric motor has a flat region in the axial direction on both sides of the field core. The housing in the grip region therefore encloses the electric motor, a sliding switch, and possibly an air gap between the electric motor and the housing, to ensure adequate cooling. 
         [0005]    If the sliding switch is moved too closely to the field core, i.e., the laminated iron core, there is a risk that the field windings of the sliding switch could become jammed due to accumulation of dirt or deformation due to high temperature, thereby impairing or blocking the switch-on function—and, primarily, the switch-off function—of the device. 
         [0006]    For this reason, two-pieced fields, i.e., a longitudinally divided field core with two core halves, have been provided, in the case of which the field core is separated in the pole separation. The field winding may be inserted in the core halves very easily and accurately, as a premanufactured coil or by winding the coil directly in place. The core halves are placed on top of each other before installation, and they are installed together with the motor housing. The two-pieced core is typically flat on the sides and makes it possible to obtain a much greater distance between the sliding switch and the field core than is possible with a one-pieced design. In the one-pieced design, the field core is composed of only one laminated core. The width of the field winding is greater than it is with a one-pieced field, however, with the disadvantage of higher losses in the field winding as compared with the one-pieced design. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to a stator of an electrical machine, in particular of a universal motor, with a cross section, a longitudinal extension, and a jacket surface. 
         [0008]    It is provided that at least one winding holder for receiving a field winding has a larger winding width than does another winding holder. 
         [0009]    Basically, the stator may be used in electric motors or in generators. They are used particularly advantagously in universal motors for household devices and power tools. The stator may be designed with a one-pieced configuration with a field core, that is composed of a single laminated core, or it may have a two-pieced or multiple-pieced design, with which the field core is therefore composed of two or more laminated cores. The field core may even be composed of solid material or sintered material instead of laminated iron. 
         [0010]    Advantageously, the winding holder with the larger winding width may be provided on one side of the cross section, and a winding holder with a smaller winding width may be provided on the opposite side of the cross section. 
         [0011]    Advantageously, due to the asymmetrical location of the winding widths of the field windings in one of the halves of the stator, a favorable geometry results for a one-pieced design of a field core, which results in a relative short winding length due to a relatively small winding width of the field winding, which, in turn, results in low ohmic resistance and, therefore, low electrical losses in the field winding, which is usually made of copper. This results in favorable efficiency with a correspondingly favorable, high energy density for an electrical machine, especially since it is not necessary to provide open space for installation in a motor housing. Instead, the stator may optimally fill a motor housing on this side and make optimal use of its installation space. As such, a relatively great deal of iron is available on this side for the electromagnetic effects of the electrical machine and/or the electric motor. 
         [0012]    The asymmetrical placement of the winding widths on the opposite side of the stator cross section with the larger winding width also results in a desired open space when installed in a housing, which open space may be used for any type of component, e.g., for accommodating a sliding switch, for guiding lines, etc. The inner diameter of the stator in which a rotor may be accommodated remains unchanged. The large, flat region of the jacket surface of the field core on this side of the stator results in an advantageous synergy based on the installation space in a housing. Despite the increased winding width on this side of the stator, a favorable energy overall results for the electrical machine in which the inventive stator is inserted. 
         [0013]    A flat section may be formed in the jacket surface, in parallel with the longitudinal extension, and at that point of the cross section on which the winding holder with the larger winding width is located. The flat section makes it possible to create a large open space when the stator is accommodated in a housing, in particular a cylindrical or at least partially cylindrical housing, e.g., in a grip part of an angle grinder. 
         [0014]    Advantageously, the wall of the stator may be designed thinner in the region of the larger winding width than it is in the region of the smaller winding width. As a result, free space outside of the stator may be attained on this side of the stator when the stator is inserted in a housing. 
         [0015]    A favorable installation of field windings is possible when an axial division of the stator into two halves may be provided, in which case the at least one flat section is located entirely in one half. The windings may be prefabricated and inserted in the freely accessible interior of the stator halves, or they may be wound directly in the winding holders. 
         [0016]    According to a further aspect of the present invention, an electrical machine, in particular a universal motor, with a stator that has a cross section, a longitudinal extension, and a jacket surface, and a rotor, which interacts with the stator are provided, with which at least one winding holder—that is provided for receiving a field winding—has a larger winding width than does another winding holder. The electrical machine offers a high energy density while providing a relatively great deal of installation space between the stator and the housing. Large winding widths and large winding heads with a correspondingly greater winding length are necessary in only one part of the stator, while, in another part of the stator, a smaller winding length results in lower ohmic losses. 
         [0017]    A flat section may be formed in the jacket surface, in parallel with the longitudinal extension, and at that point of the cross section on which the winding holder with the larger winding width is located. A large open space is provided between the flat section and a housing that encloses the stator, which may accommodate components such as a sliding switch, electrical lines, capacitors, coils, electronics printed circuit boards, resistors, signal lines, optical waveguides, coolant lines, and the like. 
         [0018]    Advantageously, the jacket surface may be designed to fit inside a cylindrical motor housing for this purpose. 
         [0019]    According to a further aspect of the present invention, a power tool, in particular an angle grinder, with an electric motor located inside a housing, with a stator that has a cross section, a longitudinal extension and a jacket surface, and a rotor are provided, with which at least one winding holder—that is provided for receiving a field winding—has a larger winding width than does another winding holder. 
         [0020]    Advantageously, a flat section may be formed in the jacket surface, in parallel with the longitudinal extension, and at that point of the cross section on which the winding holder with the larger winding width is located. There is a great deal of open space available in the region of the flat section. 
         [0021]    A recess for guiding a sliding element and/or an electrical supply line and/or a signal line and/or a fluid line may be formed in the flat section. 
         [0022]    Further advantages result from the description of the drawing, below. Exemplary embodiments of the present invention are shown in the drawing. One skilled in the art will also advantageously consider the features disclosed in the drawing, the description and the claims individually and combine them to form further reasonable combinations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a preferred power tool in the form of an angle grinder; 
           [0024]      FIG. 2  shows a cross section of the grip part of the angle grinder in  FIG. 1 ; and 
           [0025]      FIG. 3  shows a top view of a cross section of the grip part in  FIGS. 1 and 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Elements that are the same or similar are labelled with the same reference numerals in the figures. 
         [0027]    To explain the present invention,  FIG. 1  shows a preferred power tool  10  designed as an angle grinder. Power tool  10 , which is designed as an angle grinder, includes a grip part  14 , in the front section of which—that points toward an insertion tool  16 —a motor housing  18  is located. A handle  12  extends outwardly, transversely to grip part  14 . During handling, a user holds handle  12  with one hand, holds grip part  14  with the other hand, and guides power tool  10 —which is designed as an angle grinder—with insertion tool  16  over a work piece to be machined. The diameter of grip part  14  is therefore advantageously limited to a magnitude such that the user may hold grip part  14  with one hand and securely guide it. 
         [0028]      FIG. 2  shows a cross section of grip part  14  of the angle grinder in  FIG. 1 . An electric motor  30  designed as a universal motor is inserted in motor housing  18 , the longitudinal axis of which lies in the longitudinal direction of grip part  14 . An upper and a lower winding head of a field coil  32  are shown, which extend axially out of a stator  50  of electric motor  30 . A flat section  60  on a jacket surface  58  of stator  50  is shown. 
         [0029]    A sliding switch  20  is located above flat section  60 , which is actuated via a pushbutton  22  that is accessible to the user from the outside, and which is slid backward toward a switch  24  located inside grip part  14 . 
         [0030]    The diameter of stator  50  and the distance between sliding switch  20  and stator  50  essentially determine the diameter of grip part  14 . 
         [0031]    The details of preferred stator  50  and preferred electric motor  30 , which is designed as a universal motor, are shown in a top view in  FIG. 3 , and in a cross section  54  of grip part  14  in  FIGS. 1 and 2 . Stator  50  includes, e.g., two pole shoes, which serve as winding holders  36 ,  38 . 
         [0032]    A rotor  40 , which is designed as an internal rotor, is located inside stator  50 . Stator  50  and rotor  40  are located inside a preferably cylindrical or nearly cylindrical motor housing  18 , which encloses a jacket surface  58  of stator  50  as closely as possible. The air gap between motor housing  18  and jacket surface  58  serves to air-cool electric motor  30 . The axial extension of rotor  40 , stator  50 , and motor housing  16  is indicated by longitudinal extension  56 , which is drawn as an axis in the top view. 
         [0033]    Stator  50  has an asymmetrical cross section. Cross section of stator  50  is divided into two sides  62  and  64 , based on a separating line  68 , which is shown as a dashed line. Side  64  shown on the right in the figure includes a winding holder  38  with pole horns  38   a,    38   b,  around which a field winding  34  is located, and which has a relatively small winding width X 1 . Field winding  34  is located, as is typical, in a slot between pole horn  38   a  and  38   b  and inside of stator  50 . Jacket surface  58  of stator  50  is flattened slightly symmetrically to winding holder  38 . 
         [0034]    If stator  50 —in the embodiment shown, with pole horns  38   a,    38   b  on side  64 —were designed with mirror symmetry around separating line  68 , this would correspond to a typical one-pieced design of a stator with a single laminated core as the field core. 
         [0035]    The asymmetrical design of stator  50  is shown clearly via a winding holder  36  with pole horns  36   a,    36   b  on opposite side  62  of cross section  54 , which requires a much greater winding width X 3  than on opposite side  64 . Pole horns  36   a,    36   b  extend more closely to separating line  68  than do pole horns  38   a,    38   b,  so that field winding  32  also extends more closely to separating line  68  than do pole horns  38   a,    38   b  of field winding  34 . Windings  32 ,  34  are electrically connected with each other in the typical manner, so that rotor  40  will rotate when current is applied to windings  32 ,  34 . Despite the asymmetrical design of stator  50 , the pole axes, which form the center of winding holders  36 ,  38 , are symmetrical to each other, and the interconnection angle on the other side is 180°, as measured between the pole axes in the center of winding holders  36 ,  38 . 
         [0036]    Jacket surface  58  of stator  50  has a flat section  60  on side  62 , which creates an open space  66  between jacket surface  58  and motor housing  18 , in which sliding switch  20  may be moved at a sufficient distance away from stator  50 . A dimension X 2 , which represents the distance between flat section  60  and the small gap on side  64 , is designed to be asymmetrical around separating line  68 . Pole horns  36   a,    36   b  of pole halves (winding holder  36 ) with the larger winding width X 3  are designed to be shorter in length than pole homes  38   a,    38   b  of the pole halves (winding holder  38 ) with the smaller winding width X 1 . 
         [0037]    If stator  50  in this embodiment would be symmetrical around separating line  68  on side  62 , the embodiment would correspond to that of a two-pieced field core with pronounced flat sections on the side and a large winding width. 
         [0038]    Stator  50  has—in the region of flat section  60  and, therefore, in the region of the larger winding width X 3  on the pole axis in the center of winding holder  36 —a thinner wall thickness  72 , while wall thickness  74  on the pole axis of winding holder  38  is greater in the region of smaller winding width X 1 . 
         [0039]    As an option, stator  50  may be divided axially into two halves  76 ,  78 , as indicated using dashed lines on diametrically opposed separating points  70 . Flat section  60  is located entirely in one half  76 . In this case, field windings  32 ,  34  may be placed in each half  76 ,  78 , and halves  76 ,  78  may be joined together. Halves  76 ,  78 —with field windings  32 ,  34  installed—are then inserted in motor housing  18 . Windings  32 ,  34  may be electrically connected with each other before or after they are inserted in motor housing  18 . 
         [0040]    The preferred embodiment of stator  50 , in combination with a cylindrical or nearly cylindrical housing  18 , and in combination with a sliding switch  20 , results in optimal use of the installation space in housing  18  and an advantageously small diameter of grip part  14  with a high power output, in particular with a universal motor that is installed in a hand-held power tool  10 . 
         [0041]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
         [0042]    While the invention has been illustrated and described as embodied in a stator of an electrical machine, electrical machine, and power tool, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
         [0043]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.