Abstract:
A hand power tool that is driven via an electric motor ( 20 ), the electric motor ( 20 ) having a commutator ( 28 ) which is formed of disklike annular segments or laminations ( 32 ), is made more secure against contact spark development by providing that at least one of the laminations ( 32 ) has at least one central recess ( 42, 44, 46 ).

Description:
BACKGROUND OF THE INVENTION 
   The invention is based on a hand power tool. 
   From European Patent Disclosure EP 350 855, a commutator for a universal motor is known, of the kind also provided for hand power tools. Its laminations have the outer contour of a low rectangle whose short sides have U-shaped openings into which an annular armature that bundles the laminations together in ringlike fashion can be placed. The laminations are also shaped in the form of bars and, at the operating speed of approximately 3000 rpm of the electric motor that carries the commutator, they are subjected to relatively strong forces that bend the individual laminations outward and cause the commutator, on its outside oriented toward the carbon brushes, not to have a flat, cylindrical contour but rather to have the tendency of having a curved convex contour. As a result, the contact area between the arched outside of the commutator and the flat carbon brushes is reduced considerably, resulting in increased spark development between the carbon brushes and the commutator; both the commutator and the carbon brushes suffer considerable wear or damage from the high temperatures in the arc. 
   In known commutators of hand power tool motors, the attempt has been made to counteract their deformation at high rpm by means of annular armatures, which keep the annularly bundled laminations that form the commutator prestressed radially inward. This arrangement has had only partial success, and despite the provisions described the known commutators are only inadequately secured against deformation and are relatively complicated and expensive to produce and install. 
   SUMMARY OF THE INVENTION 
   The present invention has the advantage that even at extremely high rpm the commutator does not become perceptibly performed and consequences assures a low-spark contact with the carbon brushes. As a result, wear of both the carbon brushes and the commutator is slight, and the service life of the applicable electrical motor is prolonged. Its efficiency is improved, since more electrical power is converted into work and less into heat. Furthermore, because of the lesser amount of arcing, interference in the radio wave range is less, and interference suppression for the hand power tool is simplified or can be dispensed with. 
   Because the commutator lamination has at least one central recess, it forms a bar profile that is dimensionally stable and that because of the high radial acceleration presents high resistance to deformation or bending in response to deformation forces oriented transversely to the longitudinal axis and that because of the reduction in mass is exposed to lesser forces of deformation than commutator laminations known before now. 
   Because the recess extends centrally transversely through the lamination, the lamination packet bundled annularly relative to the commutator forms an annular conduit through which cooling air can be passed, or which can be engaged by a further annular armature, which prestresses the laminations radially inward at the center so that at high rpm they can be deformed radially outward only slightly. 
   Because the recess is punched, and a thin residual wall remains, the structure of the material comprising the lamination is strengthened and the dimensional stability is improved because of the profile formation. 
   Because the recess is designed as a windowlike opening through which the lamination reaches completely, a mass-reducing annular conduit is formed in the commutator; compared to previous embodiments, this enables a better distribution of the adhesive or compacting compound for holding the commutator together. 
   Because a recess extends longitudinally through the barlike lamination, the lamination is lighter than a solid lamination and is at least equally dimensionally stable. Because of the lesser mass of each lamination, lesser mass forces are operative, so that at high radial acceleration, the deformation of the laminations or of the commutator is less. 
   Because the central transverse recess is oval or is an ovally contoured, for instance octagonal, polygon, the corresponding lamination forms an especially dimensionally stable profile. 
   Because the lamination has additional, open transverse recesses on both ends, the end regions of the laminations can have a tendency to deform radially outward more markedly than solid laminations. This serves to counteract arching outward of the middle region of the lamination, so that the lamination remains flat in the region of contact with the carbon brushes. The end regions have a cross section that increases from the outside inward and thus have increasing bending strength, so that their radial deformation outward caused by centrifugal force is reduced. Moreover, the compacting compound or the adhesive can become better distributed in the region of the voids. 
   Because the ends of the barlike laminations form a fan blade, an additional cooling air flow is generated around the commutator or through it and, because of better cooling, markedly improves the efficiency of the electric motor equipped with the commutator of the invention. 
   Because a cooling air flow is passed through the recess, the individual laminations and thus the entire commutator can be cooled. This precludes a heat buildup and overheating of the electric motor. 
   Because a prestressable annular armature reaches through the central transverse recess, the deformation of the laminations at high radial acceleration can be counteracted. 
   Because the transverse recesses form everted features toward one side of each lamination, the laminations in the annular composite structure form an especially stable structure that is secure against deformation. 
   Because the laminations are provided with fan blades on their outer ends acting as contact lugs, the cooling of the motor in the commutator region is improved. 

   
     DRAWINGS 
     The invention is described in further detail below in terms of an exemplary embodiment in conjunction with the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1 , a longitudinal section through a hand power tool with a universal motor; 
       FIG. 2 , the three-dimensional longitudinal section through a commutator; 
       FIG. 3 , a cross section through a collector of the invention; 
       FIG. 4 , a further longitudinal section through a collector of the invention; and 
       FIG. 5 , a single lamination of the commutator. 
       FIG. 6 , a different variant of a single lamination; and 
       FIG. 7 , a further variant of a single of the commutator. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a longitudinal section through a hand power tool  10 , designed as an eccentric wiper, whose stepped-cylindrical housing  12  has a vertically extending longitudinal axis  13  from which a main handle  14  extends essentially vertically radially outward, and an extra handle  18  extends in the opposite direction, that is, toward the front. On the underside of the main handle  14 , there is a button  16  of a switch, not identified by reference numeral, that is provided for turning the hand power tool drive  10  on and off. 
   Centrally in the housing  20  or relative to the longitudinal axis  13 , an electric motor  20  is provided, whose stator  22  is embraced without play by the housing  12  and fixed, and whose central rotor  24  comprises a central rotor shaft  25  that is equipped with radially outward-extending rotor blades. The rotor blades  26  are penetrated by an electrical wire winding, not identified by reference numeral, which is electrically connected to a commutator  28  in a known manner. The commutator  28  is seated on the upper end of the rotor  24  on the rotor shaft  25 , whose end is in turn rotatably supported in a bearing  29  structurally connected to the housing. The commutator  28  is contacted electrically on diametrically opposite sides by two carbon brushes  30 , which are braced, prestressed radially inward by means of springs  31 , on the commutator  28 . 
   The commutator  28  is composed of many laminations  32  joined together to form a ring. The laminations are spaced apart from one another by an electrical insulation  43  that forms a small interstice. Toward the bottom in the viewing direction, the rotor shaft  25  continues in the form of a drive shaft  36 , where it drives a fan and a wiper plate  38  to rotate. 
     FIG. 2  shows a variant of a commutator  28  of the invention in the form an enlarged detail. Its structure becomes clear as a result and is based on a central supporting cylinder  41 , which is embraced by a tubular insulation layer  43 , around which an annular packet of elongated, narrow laminations  32  of V-shaped cross section is composed. Each lamination  32  changes into a hook  50  bent outward at a right angle, which serves as a contact lug for connection to the electrical leads, not identified by reference numeral, of the rotor winding. Each of the low, elongated laminations  32 , adjacent to the next lamination  32 , has a radially flat electrical insulation layer  34 . On both ends, each lamination  32  has groovelike peripheral recesses  48 , through which a prestressable annular armature  40  reaches that keeps each individual lamination  32  prestressed radially inward against the support tube  41 . As a result, at least the ends of the commutator laminations  32  are prevented from becoming detached radially outward from the support cylinder  41  or insulation layer  43  at operating speed in response to the high radial acceleration at approximately 30000 rpm. 
   Through a central recess  42  and a trapezoidal design of the outer ends  45  of the laminations, each individual lamination  32  is given a shape which reinforces its middle and end regions in such a way that they do not arch radially outward perceptibly even at extremely high rpm of the rotor. As a result, even at extremely high rpm, the lamination  32  remains level or straight on the outside, so that optimal electrical contact with the straight contact faces of the carbon brushes  30  is assured, and no convex longitudinal arching motions cause linear contact and hence increased spark development. 
     FIG. 3  shows a cross section through the commutator  28 ; its laminations  32  of V-shaped cross section can be seen as they are made into a packet to form an annular structure, and the vertical insulation layer  34  and the hooks  50  on the side of the rotor can also be seen. The hooks  50  are provided with additional, fan-bladelike, punch-indented surfaces for cooling. All laminations  32  are provided with longitudinal recesses  44 ,  46 , which extend through the entire lamination and lend it further-improved dimensional stability and reduce its mass. 
     FIG. 4  shows a longitudinal section through a further exemplary embodiment of a commutator  280 , whose support tube  410  is provided with undercut grooves  411  which are engaged by a tubular insulation layer  430  so that it is firmly held, and this layer in turn supports an annular packet of laminations  32 , with hooks  50  acting as contact lugs and with a central recess  42 . These laminations  32  are potted with the insulation layer  43  and are firmly held by their entrance into the peripheral recesses  48 . 
   On their outer ends, the laminations  32  have fan blades  52  for improving the motor cooling in the region of the commutator. 
     FIG. 5  shows the detail of a lamination  32 , its V-shaped cross section, and its peripheral recesses  48  and central recess  42 , as well as longitudinal recesses  44 ,  46 . Moreover, the side faces have impressed angular indentations, which further reinforce the structure of the lamination  32  and improve a form-locking connection with the respective insulation layer  34 . 
     FIGS. 5 ,  6  each show one exemplary embodiment of a lamination with trapezoidal outer ends in the region  45 ; the transversely extending central recess  42  forms an approximate hexagon, and located between it and the peripheral recesses  48  are further transversely extending, small triangular openings  55 . Triangular notches  60  are also made in the lower long edge, diametrically opposite webs  66  of material. 
     FIG. 7  shows a lamination  3200 , which substantially matches that of  FIG. 5 , with the distinction of having a hook  50 , acting as a contact lug, with a fan blade  52  and on the other outer end a further fan blade  52  for improving the cooling in the commutator region.