Abstract:
An electric hand tool is described that includes a machine housing ( 1 ) with an electric motor ( 12 ) accommodated in the machine housing ( 11 ) for driving a tool ( 13 ), and a fan wheel ( 21 ) accommodated in the machine housing ( 11 ) for generating a cooling air current that flows through the machine housing ( 11 ), which said fan wheel creates a suction space ( 22 ) and a pressure space ( 23 ) on opposite sides when it rotates. To increase the performance of the electric hand tool with longer idle periods for the machine components, purposeful cooling is carried out by providing means for generating an additional air current, which said means are configured such that the additional air current flows to machine components that are located outside of or in a low-flow region of the cooling air current.

Description:
BACKGROUND INFORMATION  
         [0001]    The present invention is directed to an electric hand tool as recited in the preamble of claim  1 .  
           [0002]    With an electric hand tool of this type (DE 196 00 339 C1), fan guide vanes are located on either side of a fan wheel that is mounted on the motor shaft between the electric motor and gearbox, in order to improve the cooling of the electric motor and a gearbox that is located between the electric motor and a drive spindel for a tool, which said fan guide vanes cool the electric motor and the gearbox separately and independently of one another via corresponding air ducts.  
           [0003]    With an electric hand tool having an impact mechanism (DE 100 30 962 C2), an annular channel with an opening on the outside is formed in the impact region of the snap die, which said opening is connected to the suction side of a ventilation system of the electric motor. The dust that is produced in the abrasive process of removing material, which said material also penetrates the working area of the snap die, is suctioned away from this area through the annular channel by the vacuum generated by the ventilation system.  
         ADVANTAGES OF THE INVENTION  
         [0004]    The electric hand tool according to the invention having the features of claim  1  has the advantage that greater performance and longer idle periods for the machine components and the electric hand tool as a whole can be obtained by purposefully cooling machine components that are subject to warming and are not ventilated at all or inadequately by the cooling air current that is generated by the fan wheel, which is preferably driven by the electric motor, by means of the additional air current that is diverted from the cooling air current or injected additionally from the outside. In contrast to the known electric hand tools, no dead air space regions develop, in which components are not cooled. The improved cooling can increase the performance of the electric hand tool with the same housing cross-section, or the housing cross-section can be reduced in size in the region of the electric motor while retaining the same performance. No additional production costs are incurred, since the means for the additional air current can be designed such that they can be produced at the same time as the machine housing or fan wheel.  
           [0005]    Advantageous further developments and improvements of the electric hand tool described in claim  1  are made possible by the measures listed in the further claims.  
           [0006]    According to an advantageous embodiment of the invention, the electric motor has a motor winding with winding heads that project outward on at least one end face of the electric motor, and the fan wheel is located with axial clearance in front of the end face of the drive motor and is configured such that the suction space is located directly in front of the end face of the drive motor on which the winding heads are carried. The means for generating the additional air current have air inlets that lead into the suction space. The fan wheel can be configured as an axial, diagonal or radial fan wheel. This structural configuration has the advantage that additional air is supplied through the air inlets that lead into the suction space, which said air inlets reach the “dead air space regions”, inside the suction space, where the winding heads are located. Said dead air space regions are produced because the cooling air current that is drawn in by the fan wheel flows substantially through the working air gap between the rotor and stator and into the suction space and, from there, it is blown over the fan wheel vanes into the pressure space without reaching the winding heads of the motor winding that are located toward the outside relative to the working air gap.  
           [0007]    According to an advantageous embodiment of the invention, the air inlets are openings that are configured in the wall of the machine housing at or near the end face of the electric motor. With this configuration of the air inlets, the amount of air in the cooling air current that is flowing into the suction space is increased by the amount of air drawn in from the outside through the openings. At the same time, air is directed in purposeful and efficient fashion past the winding heads without any noteworthy additional costs being incurred.  
           [0008]    According to an advantageous embodiment of the invention, the air inlets are openings in a dividing wall that separates the pressure space from the suction space, which said openings are preferably located with the greatest radial clearance possible from the axis of the fan wheel. The dividing wall can be fixed in position, and it can be part of the machine housing or part of the fan wheel, and it can rotate with said fan wheel. By means of this “internal injection”, a portion of the air flowing into the pressure space is directed, as additional air, from the pressure space back into the suction space. It is thereby directed past the winding heads to be cooled without requiring any additional components or production costs. By making the openings larger or smaller, the amount of air flowing back into the suction space can be controlled very well. Openings to the outside, as used in the case of “external injection” described hereinabove, are eliminated, which also rules out an additional contamination risk.  
           [0009]    According to an alternative embodiment of the invention, the means for generating the additional air current have air guide elements that divert a sub-current, as the additional air current, from the cooling air current to the machine components that are poorly ventilated by the cooling air current. Although this does not increase the cooling air current, the cooling air current is divided into branches such that purposeful and efficient cooling of individual machine components is obtained. The additional costs required to produce and install the air guide elements is minimal.  
           [0010]    According to an advantageous embodiment of the invention, the means for generating the additional air current have at least one air duct guided in the machine housing; one end of the duct is located in the cooling air stream, and the other end of the duct is located at or near the machine component. This has the advantage that machine components, such as electrical, electronic or mechanical components that are not located directly in the vicinity of the cooling air stream that is flowing through the machine, are cooled well and therefore have a longer service life and can be designed smaller in size. This reduces structural volume and lowers the costs to fabricate the components. At the same time, greater structural and design-oriented freedom is obtained in terms of configuring the electric hand tool, since components that work fine without cooling no longer need to be located in the immediate vicinity of the cooling air current. Instead, they can be placed anywhere, due to the air duct according to the invention. Preferably, the air duct is positioned such that the duct inlet is close to the machine component to be ventilated, e.g., the on/off switch for the electric motor, and the duct outlet leads into the suction space of the fan wheel.  
           [0011]    According to a preferred embodiment of the invention, the at least one air duct is integrated directly in the plastic wall of the machine housing. As a result, no additional production costs for the air duct would be incurred, since said air duct can be formed when the machine housing is produced.  
           [0012]    According to an advantageous embodiment of the invention, the electric motor, which is designed as a commutator motor, e.g., a universal motor, has a commutator with commutator brushes. The means for generating the additional air current have air turbulence-generating elements that encircle the periphery of the commutator and are configured such that the additional air current they generate flows across the commutator surface. The air turbulence-generating elements can be located on the commutator itself, or they can be the fan wheel vanes of an axial fan wheel that is joined with the commutator in torsion-proof fashion, e.g., it is mounted together with the commutator on the driven shaft of the electric motor in torsion-proof fashion. Said structural features increase the overall amount of cooling air that flows through the machine housing, and permits optimum flow of cooling air onto the commutator and commutator brushes. With commutator motors having a short structural shape, the axial fan wheel is designed as a plastic disk that is mounted in torsion-proof fashion on the driven shaft of the drive motor, on the periphery of which said plastic disk the fan wheel vanes are equidistantly located as small, bent segments. The advantage of this is that, due to the plastic disk, a sufficiently large creepage distance is retained between the pivot bearing and the commutator, despite the short structural shape.  
           [0013]    According to an advantageous embodiment of the invention, the brush cartridges for holding and guiding the commutator brushes are equipped with cooling ribs, through which the air current generated by the axial fan wheel flows. The large surface area of the cooling ribs ensures substantially improved heat dissipation at the brush cartridges and the commutator brushes, which permits in longer idle periods for the commutator brushes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0014]    The invention is described in greater detail in the description below with reference to the embodiments shown in the drawing.  
         [0015]    [0015]FIG. 1 is a schematic representation of a section of a longitudinal cross-section of an electric hand tool,  
         [0016]    [0016]FIG. 2 is the same depiction as in FIG. 1, according to a further embodiment,  
         [0017]    [0017]FIG. 3 is a view in the direction III in FIG. 2 of a structural configuration of a fan wheel in the electric hand tool according to FIG. 2, depicted with perspective,  
         [0018]    FIGS.  4  show the same depiction as in FIG. 1, in accordance to a third and  5  and fourth embodiment,  
         [0019]    [0019]FIG. 6 is a schematic representation of a longitudinal section of an electric hand tool according to a further embodiment,  
         [0020]    [0020]FIG. 7 shows a section of an enlarged section of a portion of a wall of the machine housing of an electric hand tool that has been modified relative to FIG. 6,  
         [0021]    [0021]FIG. 8 is an enlarged, perspective view of the commutator of the electric motor in the electric hand tool according to FIG. 6, and  
         [0022]    [0022]FIG. 9 is an enlarged, perspective view of a brush cartridge of the electric motor in the electric hand tool according to FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0023]    The electric hand tool, e.g., an electric hand-held drill, shown in FIG. 1 in a sectional view and in FIG. 6 in a complete view, includes, in known fashion, a machine housing  11 , in which an electric motor  12  for a tool  13 , e.g., a drill bit, is accommodated. As depicted in FIG. 6 in principle only, tool  13  is clamped in a tool receptacle  14 , e.g., a drill chuck, which is mounted in torsion-proof fashion on a drive spindle, which is driven by a gearbox (not shown in FIG. 4) by driven shaft  15  of electric motor  12  depicted here as a commutator motor, as an example.  
         [0024]    As shown in FIGS. 1 and 6, electric motor  12  includes a stator  30  with stator or field winding  31  (FIG. 1) and a rotor  32  that is mounted in torsion-proof fashion on driven shaft  15 , which said rotor is concentrically surrounded by stator  30 , with an air gap  33  between said rotor and said stator. Field winding  31  is inserted in known fashion in axial grooves in stator  30  and projects via winding heads  311  out of said stator on both end faces of stator  30 . A rotor winding that is inserted in rotor  32 , but is not shown in FIGS. 1 and 6, is connected to the commutator bars of a commutator  37  that is mounted in torsion-proof fashion on driven shaft  15 . At least two commutator brushes  38  serve to conduct current to the rotor winding, each of which said commutator brushes is accommodated in axially displaceable fashion in a brush cartridge  38 , and each of which is pressed radially against the commutator bars of commutator  37  using spring pressure. Brush cartridges  38  are fixed in position on a brush holder located in machine housing  11 . An on/off switch  17  is located in an easily accessible location in a handle  16  that is integrally formed on machine housing  11 , for switching electric motor  12  on and off (FIG. 6).  
         [0025]    The electric hand tool is air-cooled and includes a fan that is configured as an axial or radial fan, for cooling electric motor  12  and gearbox, which said fan draws in air through air inlet slits  18  that are formed in the rear region of machine housing  11 , and blows air out through air outlet openings  19  that are formed in the front region of machine housing  11 . For this purpose, a fan wheel  21  is mounted—downstream of the air current and directly behind electric motor  12 —on driven shaft  15  in torsion-proof fashion, so that fan wheel  21  is positioned between electric motor  12  and gearbox on the side furthest from commutator  37 . When fan wheel  21  rotates, it produces a suction space  22  on its side closest to drive motor  12 , and a pressure space  23  on its other side, which is furthest from said drive motor, which said pressure space is connected with air outlet openings  19 . As a result, as indicated by the flow arrows in FIGS. 1 and 6, air is drawn in from the environment through air inlet openings  18  and through annular gap  33  in electric motor  12 , whereby the air absorbs heat produced in electric motor  12 .  
         [0026]    Finally, the warmed air is blown back out into the environment through air outlet openings  19 .  
         [0027]    Due to the high internal air resistance of the electric hand tool and the high flow speed of the air inside air gap  33 , a sufficient amount of cooling air does not always reach components to be cooled, e.g., winding heads  311  of field winding  31  that are shown on the left side of FIG. 1 and which are located downstream from the cooling air current, so that said cooling air can carry away enough heat from here. In order to eliminate this inadequacy, air inlets that lead into suction space  22  are provided in embodiments of the electric hand tool depicted in FIGS. 1 and 2 in order to generate an additional air current. Due to the position of the air inlets, the additional air is directed into suction space  22  such that the additional air flows past winding heads  311  in suction space  22 , where it absorbs a sufficient amount of heat from winding heads  311 . In the embodiment of the electric hand tool according to FIG. 1, said air inlets are slit-shaped air inlet openings  24  that are formed in the wall of machine housing  11  within the region of suction space  22 . Air inlet openings  24  are preferably distributed evenly around the periphery of machine housing  11  and are located in the immediate vicinity of the end face of electric motor  12  or its stator  30 . As the air flow arrows drawn in FIG. 1 show, when fan wheel  21  rotates, the cooling air current as well as additional air from the environment flows through air inlet openings  24 , over winding heads  311 , and into suction space  22 . Said additional air effectively cools winding heads  311  and, therefore, field winding  31 , and increases the amount of cooling air in suction space  22 .  
         [0028]    In the embodiment of an electric hand tool shown in a sectional view in FIG. 2, the air inlets are passages  25  that are formed in a portion of fan wheel  21 , which said portion divides suction space  22  from pressure space  23 . As the air flow arrows drawn in FIG. 2 show, when fan wheel  21  rotates, a portion of the air from pressure space  23  does not flow through air outlet openings  19 . Instead, the vacuum in suction space  22  causes said portion of air to flow through passages  25  into suction space  22 . Since passages  25  are located close to the outer edge of fan wheel  21 , the additional air drawn from pressure space  23  flows over winding heads  311 , and is then guided by fan wheel  21  back into pressure space  23 .  
         [0029]    Fan wheel  21 , which is shown in a sectional view of a longitudinal cross-section in FIG. 2 as a schematic representation, is shown in FIG. 3 in a top view with perspective in a real embodiment as a radial fan wheel. When fan wheel  21  is mounted on driven shaft  15 , the top-view side in FIG. 3 faces electric motor  12 . Fan wheel  21  includes an annular cover plate  26  that borders suction area  22 , a base plate  27 —that has axial clearance from said cover plate—with a central hub  271  for sliding onto driven shaft  15 , and radially oriented fan vanes  28  that are located between cover plate  26  and base plate  27 . Passages  25  are located in cover plate  26  in the form of circular holes  251 ,  252 . For example, holes  251  having the larger diameter are located on an outer perimeter, and holes  252  having the smaller diameter are located on a concentric, inner perimeter having a smaller diameter. The size of the holes and the distance between them are purposefully selected in order to prevent an undesired reduction in the efficiency of the radial fan caused by the injection of an excessive volume of air from pressure space  23  into suction space  22 . Locating holes  251  having the larger diameter on the outer perimeter is advantageous because the greater portion of the air injected into suction space  22  flows in the region of winding heads  311  of field winding  31 . Passages  25  can have any cross-sectional shape. For example, said passages can be configured as slits.  
         [0030]    With the embodiment of the electric hand tool that is shown as a sectional view in FIG. 4, fan wheel  21  is modified such that cover plate  26  with passages  25  is eliminated, and the dividing wall function of cover plate  26  is now performed by a dividing wall  40  that is fixed in position, which said dividing wall is part of machine housing  11 . Passages  25  are located in dividing wall  40  in the same manner as described hereinabove in conjunction with cover plate  26 . Dividing wall  40 , which is configured as a hollow cylinder having the shape of a pagoda, can be designed integral with machine housing  11 , or it can be mounted, as a separate structural component, on the wall of machine housing  11 .  
         [0031]    With the embodiment of the electric hand tool shown in FIG. 5, the air inlets in the suction space are eliminated in order to increase the size of the cooling air mass in suction space  22  and, instead, the additional current that flows onto winding heads  311  branches off from the cooling air current. For this purpose, at least one air guide element  40  is located in suction space  22  such that a sub-current of the cooling air current that flows in through air gap  33  between stator  30  and rotor  32  into suction space  22  branches off such that it forms the additional air current that flows onto winding heads  311 . Radial fan wheel  21  is configured as described in connection with FIG. 2, but cover plate  26  does not contain passages. Of course, fan wheel  21  can also be configured as shown in FIG. 4. Fixed dividing wall  40 , which would then be required, does not have passages in this case, either.  
         [0032]    In order to also cool components in the electric hand tool that cannot be positioned in the cooling air current that forms between air inlet slits  18  and air outlet openings  19 , such as electrical on/off switch  17  installed in handle  16  as shown in FIG. 6, special air ducts are provided in machine housing  11 , with which air is drawn in over the electrical, electronic or mechanical components to be cooled, such as on/off switch  17 . An air duct  34  of this type is shown in FIG. 6. Said air duct extends along the inner wall of machine housing  11  and has a duct inlet  35 , which is located in the region of on/off switch  17 , and a duct outlet  36 , which leads into suction space  22 . When fan wheel  21  rotates, the vacuum that is generated in suction space  22  causes air to be drawn in at duct inlet  35 , which said air flows in from the outside due to installation tolerances of on/off switch  17  in housing  11 . Said air flows over on/off switch  17  and past it. After it absorbs heat at on/off switch  17 , said air is drawn into air duct  34 . Advantageously, air duct  34  is integrated in the wall of machine housing  11 , as shown in FIG. 7. Machine housing  11 , which is formed via injection molding of plastic, is joined in a plane of symmetry that passes through the longitudinal axis of the electric hand tool. To integrate air duct  34  in machine housing  11 , one half  341  or  342  of air duct  34  is configured in each housing shell  111  and  112 . When the two housing shells  111  and  112  are joined, the two duct halves  341 ,  342  combine to form air duct  34 , as shown in a sectional view in FIG. 7 for the region of handle  16 .  
         [0033]    In addition to air duct  34 , which was described as an example, for ventilating and cooling electrical on/off switch  17 , further air ducts having a similar configuration may be guided to other electrical or electronic or mechanical components inside machine housing  11 . It is advantageous, for example, with an electric hand tool that is designed as a battery pack-operated machine, to guide an air duct to the battery pack and thereby passively cool the battery pack. The cooling effect of air ducts  24  is independent of whether fan wheel  21  works using “external air injection” (FIG. 1) or “internal air injection” (FIG. 2), or whether injection of this type is eliminated altogether. In the case of “external air injection” according to FIG. 1, air ducts  34  can be utilized instead of or in addition to air inlet openings  24  to draw in additional air from the outside.  
         [0034]    Commutator  37  of electric motor  12  is a machine component of the electric hand tool that is subjected to high levels of thermal stress. In order to improve the cooling of commutator  37  and commutator brushes  38  that ride on commutator  37 , air turbulence-generating elements  42  are located on commutator  37 , which rotate with commutator  37 . Said air turbulence-generating elements  42  can be mounted directly on commutator  37 . In the embodiment of commutator  37  shown in FIG. 8, fan vanes  43  of an axial fan wheel  44  are air turbulence-generating elements  42 , which said axial fan wheel is mounted together with commutator  37  on driven shaft  15  of electric motor  12 . Axial fan wheel  44  is located between a pivot bearing  45  of driven shaft  15 —which said pivot bearing is accommodated in machine housing  11 —and commutator  37 , that is, on the end face of commutator  37  that is furthest from rotor  32 . Axial fan wheel  44  is preferably configured as a plastic disk  46  that is mounted on driven shaft  15  in torsion-proof fashion, with fan vanes  43  formed by bent axial segments mounted on the periphery of said plastic disk. The advantage of this is that, due to plastic disk  46 , a sufficiently large creepage distance is retained between pivot bearing  45  and commutator  37 , despite a short structural shape of electric motor  12 . When driven shaft  15  rotates, fan vanes  43  generate an air current in addition to the cooling air current that is generated by fan wheel  21 , which said additional air current flows across the surface of commutator  37  and commutator brushes  38  and increases the amount of air in the cooling air current.  
         [0035]    To enhance the cooling of commutator brushes  38 , brush cartridges  39  are equipped with cooling ribs  47 , through which the additional air current flows. Since the surface area of brush cartridges  39  is greatly increased by cooling ribs  47 , the dissipation of heat from commutator brushes  38 —which are held axially inward in displaceable fashion—is markedly improved.  
         [0036]    The invention is not limited to the embodiments described hereinabove. For example, in the embodiment shown in FIG. 1, fan wheel  21  can be configured such that its pressure space is located in front of the end face of electric motor  12  on which winding heads  311  are mounted. In this case as well, an additional air current would be drawn over winding heads  311  through openings that are equivalent to air inlet openings  24  in the wall of machine housing  11 , and would provide better cooling of winding heads  311 . Likewise, air ducts  34  in machine housing  11  can be positioned such that their duct inlet is located in pressure space  23  formed by fan wheel  21 , and their duct outlet is located at the machine component  17  to be cooled.