Abstract:
The invention relates to a handheld machine tool, in particular a hammer drill and/or chipping hammer. The tool has an impacting unit which has at least one impacting pin and a guide unit which is provided for guiding the impacting pin. It is proposed that the guide unit is formed from at least two different materials.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2008/065376 filed on Nov. 12, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on a handheld power tool. 
     2. Description of the Prior Art 
     A handheld power tool formed by a rotary and/or chisel hammer and having a striking unit is already known. The striking unit has a striking pin and a guide unit that is provided for guiding the striking pin. 
     ADVANTAGES AND SUMMARY OF THE INVENTION 
     The invention is based on a handheld power tool, in particular a rotary and/or chisel hammer, having a striking unit which has at least one striking pin and a guide unit that is provided for guiding the striking pin. 
     It is proposed that the guide unit be formed of at least two different materials. In this connection, the term “provided” should be understood in particular to mean especially equipped and/or especially designed. Moreover, “two different materials” should be understood to mean in particular two materials that differ from one another in terms of at least one material property. The striking pin is provided for transmitting an impact pulse, preferably from a striking element of the striking unit, to a tool during operation of the handheld power tool. The striking unit can be formed by a mechanical striking unit or especially advantageously by a pneumatic striking unit. Preferably, the striking unit has a hammer tube, in which the striking pin is supported. The guide unit is provided in particular for guiding the striking pin inside the hammer tube and to that end is disposed in a middle region of the striking pin that preferably has a larger cross-sectional area than a cross-sectional area in peripheral regions disposed along a length of the striking pin. 
     By means of the embodiment according to the invention, support and/or guidance of the striking pin inside the striking unit or hammer tube can advantageously be attained with an effective guidance property that remains as constant as possible even at high operating temperatures. Especially advantageously, a material of the guide unit that is in direct contact with the striking pin is formed by a temperature-resistant material, which over a wide temperature range has a virtually constant, only slightly varying guidance property. Furthermore, an especially lightweight, weight-saving guide unit can be realized if at least one material of the guide unit is formed by a lightweight material. 
     It is also proposed that the guide unit has at least one guide element, which is formed by a metal; as a result, in addition to temperature dissipation by the guide element, an advantageous stability of the guide unit can also be attained. In a further feature of the invention, an embodiment of the guide element by a further temperature-resistant or heat-resistant material, such as a Teflon material and/or other materials that appear appropriate to one skilled in the art is conceivable at any time. 
     It is also proposed that the guide element is formed by a sheet-metal component, as a result of which the guide unit can be made especially economically. Especially advantageously in this respect, the guide element is formed by a deep-drawn sheet-metal component, which can be made economically in a deep-drawing process. Alternatively, the guide element can also be produced by a turning process and/or other processes that appear appropriate to one skilled in the art. 
     Especially advantageously in this respect, the guide element is formed at least in part by a sheet-metal sleeve, so that uniform stability of the guide unit around the striking pin in a circumferential direction of the striking pin can be attained. Moreover, an advantageous introduction of force per unit of surface area can be attained by means of the sheet-metal sleeve during a B impact or recoil impetus by the striking pin on the guide unit. 
     It is additionally proposed that the guide element have at least in part a guide face for guiding the striking pin, as a result of which an advantageous guidance of the striking pin, which in particular reduces wear, can be attained in a structurally simple manner. 
     In an advantageous refinement of the invention, it is proposed that the guide unit has at least one further component, which is formed by a damping mechanism. As a result, besides guidance by the guide element, advantageous impact damping by the guide element can be attained, and it is thus possible and economical to dispense with additional components, such as a separate damping unit. 
     It is also proposed that the damping mechanism is formed by an elastomer, as a result of which a shape of the damping mechanism can be adapted in a structurally simple way to an installation space available inside the guide unit. Moreover, by means of the elastomer, additional components for fixation and/or support of the guide element inside the guide unit can be dispensed with, especially if the guide element is disposed at least partly on the elastomer. In this connection, the term “elastomer” should be understood to mean in particular a fixed-shape and at the same time elastically deformable material, such as a plastic comprising random and preferably wide-mesh cross-linked molecule chains that make a rubber-elastic property of the elastomer possible. Preferably, the elastomer is intended to deform in response to an exertion of force, such as a tensile and/or compressive stress, and after the exertion of force ceases, the elastomer returns to its original shape again. 
     Further components, installation space, assembly effort, and costs can also advantageously be saved if the guide element is embodied as at least partially in one piece with the damping mechanism. In this connection, the term “in one piece” should in particular be understood to mean formed in one part and/or from one cast and/or as one component. Preferably, the guide element can be embodied in one piece with the damping mechanism by means of a vulcanizing process and/or other processes or methods that appear appropriate to one skilled in the art. 
     In an advantageous refinement of the invention, it is proposed that the guide element rests at least partially on a radially inward-facing surface of the damping means. In this connection, “radially inward-facing surface” should be understood to mean in particular a face of the damping mechanism that faces inward along a radial direction that extends essentially perpendicular to a force flow direction of the striking unit and/or parallel to a diameter of the guide element. In this way, unwanted overheating of the damping mechanism can advantageously be prevented, and furthermore, during operation of the handheld power tool and particularly in an impact mode of operation, can be supported in a way that damps vibration or impact. 
     It is furthermore proposed that the guide unit has at least one bracing element for bracing in at least one direction on a hammer tube, as a result of which an advantageous dissipation of force via the guide unit or the bracing element to the hammer tube can be attained, and moreover, an advantageous guidance position of the guide unit or guide element inside the striking unit can be maintained. 
     Still further components, installation space, assembly effort and costs can advantageously be saved if the guide element and the bracing element are embodied as at least partially in one piece. Moreover, a structurally simple and in particular space-saving bracing of the guide unit or guide element on the hammer tube can be attained in this way. 
     It is also provided that the bracing element extends outward in a radial direction on the guide element, as a result of which a structurally simple bracing of the guide unit or guide element can be achieved. 
    
    
     
       BREIF DESCRIPTION OF THE DRAWINGS 
       Further advantages will become apparent from the ensuing description of the drawings. In the drawings, one exemplary embodiment of the invention is shown. The drawings, description and claims include numerous characteristics in combination. One skilled in the art will expediently consider the characteristics individually as well and put them together to make useful further combinations. 
         FIG. 1  shows a handheld power tool of the invention in a schematic view; and 
         FIG. 2  shows a striking unit with a guide unit of the handheld power tool, in a schematic view. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In  FIG. 1 , a handheld power tool  10  formed by a rotary hammer is schematically shown. The handheld power tool  10  includes a housing  48  and, in a front region  50 , a tool holder  52  for receiving a tool. On a side  54  facing away from the front region  50 , the handheld power tool  10  has a main handle  56  for actuation of the handheld power tool  10  and for transmitting force from a user to the handheld power tool  10 . For generating a driving torque, the handheld power tool  10  has a drive unit  58 , shown only schematically in  FIG. 1 . The driving torque of the drive unit  58  is transmitted, via a gear system, not shown in detail, of the handheld power tool  10 , to a striking unit  12  and/or to a rotating power takeoff means formed by a hammer tube  44  ( FIG. 2 ). 
     In  FIG. 2 , the striking unit  12  of the handheld power tool  10  of  FIG. 1  is shown in further detail in a schematic sectional view. The striking unit  12  includes the hammer tube  44 , a striking pin  14 , and a guide unit  16 . The guide unit  16  and the striking pin  14  are disposed inside the hammer tube  44 . Furthermore, in operation of the handheld power tool  10  or in a impact mode of operation, the striking pin  14  is provided for transmitting an impact pulse from a striking element  60  of the striking unit  12  to a tool. To that end, the striking pin  14  is disposed in an axial direction  62 ,  64  between the striking element  60  and the tool. The axial direction  62 ,  64  is essentially parallel to a main extension direction  66  of the hammer tube  44 . The hammer tube  44  is furthermore provided for driving the tool to rotate. In the impact mode of operation, for generating the impact pulse, the striking element  60  is driven pneumatically by a piston, not shown in further detail, to execute a reciprocating motion in the axial direction  62 ,  64 . 
     The guide unit  16  is provided for guiding the striking pin  14  and to that end is disposed around the striking pin  14  in a middle region  68 . In this middle region  68 , the striking pin  14  has a larger diameter  70  than a diameter  72  in end regions  74 ,  76  of the striking pin  14  that are disposed in the axial direction  62 ,  64 . The guide unit  16  is furthermore formed of two different materials  18 ,  20 . For that purpose, the guide unit  16  has a guide element  22  and a further component  32 , which is formed by a damping means  34 ; the guide element  22  is formed by the material  18  which is a metal, and the damping means  34  is formed by the material  20  which is an elastomer  36 . The guide element  22  is formed by a sheet-metal sleeve  28 , which is a thin-walled sheet-metal component  26 . The sheet-metal sleeve  28  furthermore forms a reception region  104  for the striking pin  14 . The guide element  22  and the damping means  34  are furthermore embodied in one piece with one another by means of a vulcanizing process. In an alternative embodiment of the invention, it is moreover also conceivable for the guide element  22  and the damping means  34  to form two components embodied separately from one another. 
     The guide element  22  rests on a surface  38  of the damping means  34  oriented inward in a radial direction  46 . The guide element  22  or sheet-metal sleeve  28  also has a surface  78  oriented inward in the radial direction  46  and facing away from the damping means  34 , which surface is provided by a guide face  30  for guiding the striking pin  14 . The guide face  30  of the sheet-metal sleeve  28  is adapted to an outer contour of the middle region  68  of the striking pin  14 . For that purpose, the sheet-metal sleeve  28 , or the reception region  104  for receiving the striking pin  14 , is tapered with a conically tapering portion  82  in the axial direction  64  from a reception region  80  for the tool in a direction of the striking element  60  on which region  82  the striking pin  14  in a impact mode of operation rests, when a tool is located in or has been introduced into the tool holder. An end region  90 , oriented toward the striking element  60 , of the sheet-metal sleeve  28  in the axial direction  64  is formed cylindrically with a constant diameter  92 , and the end region  90  rests on the end region  76  of the striking pin  14 . 
     The guide unit  16  furthermore has a bracing element  40 , which is provided for bracing the guide unit  16  or guide element  22  in the axial direction  62  of the striking element  60  in a direction  42  of the reception region  80  for the tool. The bracing element  40  is embodied in one piece with the sheet-metal sleeve  28  and is disposed on an end region  84  of the sheet-metal sleeve  28  oriented toward the reception region  80  for the tool. From the sheet-metal sleeve  28 , the bracing element  40  extends outward in the radial direction  46  and is braced or disposed with a radially outward-oriented region on the hammer tube  44 . In the axial direction  62  from the striking element  60  in the direction  42  of the reception region  80  for the tool, the bracing element  40  is disposed between the damping means  34  and an idling ring  86 . The idling ring  86  is formed of steel. In an idling mode, in which the gear unit is in a impact mode of operation but in which no pressure is exerted on the tool by a workpiece, the striking pin  14  rests (not shown in  FIG. 2 ) on the idling ring  86  in an end position oriented toward the reception region  80  for the tool, so that wear of components of the striking unit  12  in the idling mode is advantageously reduced. 
     The damping means  34  is embodied in the shape of an O-ring in an end region  88  that faces away from the reception region  80  for the tool and is oriented toward the striking element  60 . As a result, in an idling mode, the striking element  60  in an idling position can be retained on the damping means  34 . The O-ring-like end region  88  of the damping means  34 , in a impact mode of operation of the handheld power tool  10 , rests on the end region  76 , oriented toward the striking element  60 , of the striking pin  14 . 
     In the axial direction  64  from the reception region  80  for the tool in a direction of the striking element  60 , the damping means  34  together with the guide element  22  is secured by a sleeve  94  and a snap ring  96  against motion or shifting in the axial direction  64 . The sleeve  94  rests on a curved surface  98  of the damping means  34  that faces outward in the radial direction  46  and toward the striking element  60  in the axial direction  64 . Furthermore, the sleeve  94  rests on the hammer tube  44  on an end region  102  facing away from the striking element  60 . The snap ring  96  is disposed on the hammer tube  44  and thus fixes the sleeve  94  and the damping means  34  in the axial direction  64 . The damping means  34  furthermore has an undulating contour on a radially outward-oriented surface  100  resting on the hammer tube  44 , so that a damping effect of the damping means  34  in the impact mode of operation of the handheld power tool  10  is amplified. 
     The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.