Abstract:
The handheld power tool ( 1 ) has a tool socket ( 2 ) to hold a tool ( 4 ) on a working axis ( 11 ) as well as a striking mechanism ( 6 ) with a striker ( 14 ) that is moved periodically back and forth along the working axis ( 11 ). The striking mechanism ( 6 ) is secured in a tool housing ( 20 ). A handle ( 9 ) is attached to the tool housing ( 20 ) by means of a damper ( 21 ). The damper ( 21 ) has a surface ( 25 ) that is joined to the tool housing ( 20 ) as well as a surface ( 24 ) that is joined to the handle. A block ( 27 ) made of a porous elastomer is arranged so as to be in contact with the tool surface ( 25 ) and with the handle surface ( 26 ). An air-filled cavity ( 30 ) is provided inside the block ( 27 ) between the tool surface ( 25 ) and the handle surface ( 24 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a handheld power tool, as is known, for example, from German patent application DE 1020 1004 0094 A1. 
       SUMMARY OF THE INVENTION 
       [0002]    The handheld power tool according to the invention has a tool socket to hold a tool on a working axis as well as a striking mechanism with a striker that is moved periodically back and forth along the working axis. The striking mechanism is secured in a tool housing. A handle is attached to the tool housing by means of a damper. The damper has a surface that is joined to the tool housing as well as a surface that is joined to the handle. A block made of a porous elastomer is arranged so as to be in contact with the tool surface and with the handle surface. An air-filled cavity is provided inside the block between the tool surface and the handle surface. 
         [0003]    The cavities inside the porous elastomer bring about an increasing stiffness of the damper as the user applies greater contact force. The stiffness can be very easily adapted to the envisaged characteristics. The cavities in the block prove to be sufficiently sturdy under continuous stress, especially vis-à-vis abrasion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The description below explains the invention on the basis of embodiments and figures provided by way of an example. The figures show the following: 
           [0005]      FIG. 1 : a hammer drill; 
           [0006]      FIG. 2 : a sectional view through a handle decoupling element of the hammer drill in plane II; 
           [0007]      FIG. 3 : a sectional view through a handle decoupling element of a hammer drill in plane II. 
       
    
    
       [0008]    Unless otherwise indicated, the same or functionally identical elements are designated in the figures by the same reference numerals. 
       DETAILED DESCRIPTION 
       [0009]      FIG. 1  schematically shows a hammer drill  1  as an example of a hand-held chiseling power tool. The hammer drill  1  has a tool socket  2  into which an shank end  3  of a tool, for example, a drill bit  4 , can be inserted. The primary drive of the hammer drill  1  is in the form of a motor  5  that drives a striking mechanism  6  and a driven shaft  7 . A battery pack  8  or a mains line supplies the motor  5  with power. The user can guide the hammer drill  1  by means of a handle  9  and can start up the hammer drill  1  by means of a system switch  10 . During operation, the hammer drill  1  continuously rotates the drill bit  4  around the working axis  11  and, in this process, it can cause the drill bit  4  to strike into a substrate in the striking direction  12  along the working axis  11 . 
         [0010]    The striking mechanism  6  is a pneumatic striking mechanism  6 . An exciter piston  13  and a striker  14  are installed movably along the working axis  11  in a guide tube  15  in the striking mechanism  6 . The exciter piston  13  is coupled to the motor  5  via an eccentric  16  and it is forced to execute a periodical, linear movement. A connecting link  17  connects the eccentric  16  to the exciter piston  13 . A pneumatic spring that is formed by a pneumatic chamber  18  between the exciter piston  13  and the striker  14  couples a movement of the striker  14  to the movement of the exciter piston  13 . The striker  14  can strike a rear end of the drill bit  4  directly, or it can transfer some of its pulse to the drill bit  4  indirectly via an essentially stationary intermediate striker  19 . The striking mechanism  6  and preferably the additional drive components are arranged inside a tool housing  20 . 
         [0011]    A recoil of the pneumatic striking mechanism  6  is transferred via the tool housing  20  onto the handle  9 . The handle  9  is suspended on the tool housing  20  by means of a damper  21  in order to reduce the peak load of the recoil. The damper  21  is depicted in a sectional view in  FIG. 2 . The damper  21  has a stamp  22  that is rigidly attached to the handle  9 . The stamp  22  is situated in a cage  23  that is rigidly attached to the tool housing  20 . The stamp  22  can be moved in the cage  23  along the working axis  11 . The stamp  22  has a stamp surface  24  which faces in the striking direction  12  and which is located opposite from a stop surface  25  of the cage  23  facing counter to the striking direction  12 . The two surfaces  24 ,  25  are preferably flat or, if they are bent, they have the same curvature. The stamp surface  24  is essentially uniform along its entire surface area all the way to the stop surface  25  at a distance  26 . 
         [0012]    The damper  21  has a porous elastomer element  27  arranged between the stamp  22  and the cage  23 . In the striking direction  12 , the porous elastomer element  27  transmits a force from the handle  9  to the tool housing  20 . The porous elastomer element  27  has a buffer section  28  that is in contact with the stamp surface  24  and the opposite stop surface  25 . The dimensions of the buffer section  28  perpendicular to the working axis  11  are the same as the corresponding dimensions of the stamp surface  24  that is attached here, for instance, to the handle  9 . The outer surface of the porous elastomer element  27  that faces in the striking direction  12  preferably rests flush and completely against the stop surface  25 , at least in the buffer section  28 . By the same token, the outer surface of the buffer section  28  that faces counter to the striking direction  12  preferably rests flush and completely against the stamp surface  24 . The porous elastomer element  27 , especially the buffer section  28 , is compressed when the user exerts pressure onto the handle  9  in the striking direction  12 . In addition to the contact force, the vibrations of the hammer drill  1  also act dynamically on the porous elastomer element  27 . Since the construction of the buffer section  28  is such that it is continuously in contact with the stamp surface  24  and with the stop surface  25 , it is effectively prevented that the buffer section  28  moves parallel to the stamp surface  24  and to the stop surface  25  in case of dynamic load changes. Especially in view of the dusty working environment of the hammer drill  1 , the porous elastomer element  27  suffers a great deal of wear and tear, particularly in the case of an elastomer element  27  that is rubber-free and open-pored, as is preferred for the damping. The outer surfaces of the porous elastomer element  27  that perpendicularly face the working axis  11  are preferably surrounded by an air gap  29 . This air gap  29  is dimensioned sufficiently for the porous elastomer element  27  not to touch the sides of the cage  23  or of another housing due to compression or due to the contact force being exerted by the user. The porous elastomer element  27  preferably has a prismatic structure. Along one axis, here, for instance, along the handle axis, the porous elastomer element  27  has a constant cross section ( FIG. 2 ). Therefore, the porous elastomer element  27  can be cut out of a cube using a water-jet saw. 
         [0013]    The porous elastomer element  27  shown has, for instance, two air-filled cavities  30 . The cavities  30  are arranged inside the buffer section  28 , that is to say, between the stamp surface  24  and the stop surface  25 . In this context, the cavities  30  are located inside the buffer section  28  in that they are not open towards the stamp surface  24  or the stop surface  25 . The cavity  30  is closed along the working axis  11 . The cavity  30  can be open in a direction perpendicular to the working axis  11 . The cavities  30  shown by way of an example have a cylindrical shape with an elliptical cross section that extends through the entire porous elastomer element  27 . Here, the axes of the cavities  30  are shown by way of an example as being parallel to the handle axis. The largest dimension  31  of the cavity  30  along the working axis  11 , here the smaller half-axis of the ellipse, amounts to between 20% and 50% of the distance  26  between the stamp surface  24  and the stop surface  25 , in other words, the axial outer dimension of the buffer section  28 . The axial dimensions of the porous elastomer element  27  should be determined without external force being applied onto the damper  21 , especially without any contact force being exerted onto the handle  9  by the user. When the handle  9  is pushed in the striking direction  12 , the cavities  30  are compressed to an increasing degree, until the opposite inner surfaces  32 ,  33  of the cavity  30  come to rest against each other completely. As a result, the stiffness of buffer section  28  increases due to the growing contact force until the cavity  30  is closed. The damper  21 , which is soft at a low holding force, only transmits very few vibrations when the user holds the handle  9  loosely. As the contact force increases, more vibrations are transmitted in principle, but the arm of the user also accounts for a natural damping. The latter effect undergoes saturation, which is why beyond a medium level of holding force, any further increase in the stiffness is ergonomically disadvantageous. 
         [0014]    The cavity  30  preferably has a cross section that remains constant along one axis. The axis is perpendicular to or slanted with respect to the working axis  11 . The cross section of the cavity  30  is closed annularly. The cross section has a dimension  31  along the working axis  11  and a dimension  34  perpendicular to the working axis  11 . The dimension  34  perpendicular to the working axis  11  is preferably at least twice as large as the dimension  31  along the working axis  11 . The opposite inner surfaces  32 ,  33  can touch each other, especially the points that were originally furthest away along the working axis, without this causing crack formation in the porous elastomer element  27  during the dynamic loads. 
         [0015]      FIG. 3  illustrates the elastomer element  27  with cavities  130  that are configured differently. The cavity  35  has a drop-shaped cross section. An inner surface  36  that faces the cage  23  as well as an opposite inner surface  37  that faces the stamp  22  are essentially flat and converge to form a tip. The two inner surfaces  36 ,  37  are appropriately inclined relative to each other by an angle between 30° and 90°. Opposite from the tip, the two flat inner surfaces  36 ,  37  are connected by a semi-cylindrical inner surface. The axis of the drop shape, that is to say, leading from the tip to the semi-cylinder, runs perpendicular to the working axis  11 . The width  38  of the drop, that is to say, its dimension  34  along the working axis  11 , is preferably between 20% and 50% of the distance  26  between the stamp surface  24  and the stop surface  25 . The length  39  of the drop, that is to say, along its axis through the tip, is greater than the width  38 , preferably at least twice as large.