Abstract:
The invention relates to a striking mechanism of a handheld electric power tool, in particular a percussion drill and/or percussion hammer, having a hammer cylinder, a piston mounted with a guide section inside the hammer cylinder in a longitudinally displaceable manner, and a piston outer guide on which a guide area of the piston is guided in a longitudinally displaceable manner. A piston end located outside the hammer cylinder comprises an overlap for overlapping an end area of the hammer cylinder, and the guide area at least partially belongs to the overlap or is affixed there.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2007/061597 filed on Oct. 29, 2007. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a striking mechanism of an electric handheld power tool, in particular a rotary and/or percussion hammer. 
     Description of the Prior Art 
     An impact mechanism with a hammer tube, a piston, and an external piston guide is known, for example, for percussion hammers. The impact mechanism drives a tool, for example a chisel, abruptly forward in a periodically repeating fashion. In order to produce a corresponding impulse, the piston that an electric motor moves in reciprocating fashion moves—at least partially—in the hammer tube and drives a striking element, which is likewise guided by the hammer tube, via an air cushion situated between the piston and the striking element. The moving striking mass of the striking element transmits an impulse when it strikes against a tool element. The tool element in this case can be the tool itself, part of a tool holder, or an impact pin situated between the tool and the striking element. The preferably cylindrical piston is supported in a longitudinally movable fashion in the hammer tube by means of a guide section and is driven by the drive unit of the impact mechanism, for example by means of a connecting rod. Since the guide region of the piston is situated outside the hammer tube in every position of the reciprocating motion, the impact mechanism has an external piston guide likewise situated outside the hammer tube. Consequently, on the one hand, the piston is guided in a longitudinally movable fashion in the hammer tube by means of a guide section and on the other hand, is guided in a longitudinally movable fashion by means of an external piston guide that is situated, viewed from the tool, behind the hammer tube in the longitudinal direction of the hammer tube. The usual overall length of an impact mechanism with a cylindrical piston is composed of the overall length of the impact mechanism, the air cushion, the piston, and the associated connecting rod or other piston drive element. This overall length cannot be easily reduced without influencing the function of the impact mechanism. 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     According to one proposal, in the impact mechanism according to the invention, a piston end situated outside the hammer tube has an overlap end for overlapping an end region of the hammer tube; in addition, the guide region is at least partly a component of the overlap end or is fastened to it. In this case, the guide region is at least partially situated on the outer circumference of the overlap end. Because the piston end protruding from the hammer tube has an overlap end for overlapping an end region of the hammer tube and the guide region is at least partly a component of the overlap end or is fastened to it, the external piston guide can be—at least partially—situated in a longitudinal section of the impact mechanism that coincides with the hammer tube. In the longitudinal direction, this yields an “overlap region” of the external piston guide with the hammer tube. This “shifting” of the external piston guide in the direction toward the hammer tube makes it possible to reduce the overall length of the impact mechanism and therefore of the electric handheld power tool as a whole without limiting the length of the external piston guide. It is consequently possible to produce the shortest possible impact mechanism while at the same time maintaining the largest possible guide surface between the external piston guide and the guide region. In particular, the impact mechanism here includes the piston drive unit. This piston drive unit is preferably part of an overall drive unit that drives the tool in all of the movements that the electric handheld power tool allows. 
     According to another proposal, a piston drive element that belongs to a piston drive unit is at least partially a component of the overlap end or is fastened to it. For example, the piston drive element is a connecting rod that is fastened to the overlap end, for example by means of a cotter pin, and is used by the piston drive unit to drive the piston in an oscillating, reciprocating fashion. Because of the embodiment of the piston drive element at the overlap end, the piston drive unit engages the overlap end of the piston laterally, thus advantageously achieving a particularly short overall length of the impact mechanism. 
     According to one advantageous proposal, the piston drive unit has an eccentric mechanism that cooperates with the piston drive element to produce the movement of the piston. In particular, the eccentric mechanism is equipped with a crank. The cooperation of the crank with the piston drive element converts a rotary motion of the piston drive unit into the oscillating reciprocation of the piston. 
     According to another advantageous proposal, the piston drive element is embodied in the form of a sliding block guide. The sliding block guide is advantageously composed of two opposing ribs between which a groove is embodied. The ribs here are preferably of one piece with the overlap end. The sliding block guide is advantageously situated essentially perpendicular to the movement direction of the piston. 
     According to another proposal, the eccentric mechanism has an eccentric protrusion that engages in the sliding block guide. The engagement of the eccentric protrusion in the sliding block guide converts the initial rotary motion of the piston drive unit into the oscillating reciprocation of the piston. 
     According to a proposal in a modification of the invention, the overlap end with the piston end constitutes an overlap sleeve or at least an overlap arm. The embodiment of the overlap end in the form of an overlap sleeve in this case offers the advantage that this sleeve has a large area for the embodiment or attachment of the guide region and/or the piston drive element. By contrast, an overlap end embodied in the form of at least one overlap arm has the advantage of requiring less material. The embodiment of the overlap end in the form of at least one overlap arm also has the advantage that it can be embodied so that other elements of the electric handheld power tool—in particular drive elements—can be situated in the vicinity of the end of the hammer tube. 
     According to an advantageous proposal, the piston is embodied in the form of a hollow piston with a cavity. The embodiment of the piston as a hollow piston saves material and also makes available additional space into which additional components of the electric handheld power tool can be built. This makes it possible to further reduce the overall length of the electric handheld power tool. In connection with the impact mechanism according to the invention, a “hollow piston” is also understood to be a hollow piston whose cavity is formed by the piston and its overlap arms. 
     According to another advantageous proposal, the cavity of the hollow piston has an access opening that is situated at the end remote from the hammer tube. For example, a part of the piston drive unit or another element of the electric handheld power tool protrudes through the access opening into the cavity of the hollow piston. In connection with the impact mechanism according to the invention, the term “hollow piston” is not limited to a pot piston, which is known in the context of impact mechanisms and simultaneously accommodates the striking element in order to guide the latter. 
     The invention also relates to an electric handheld power tool, in particular a rotary and/or percussion hammer equipped with the above-mentioned impact mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in greater detail below in conjunction with the drawings. 
         FIG. 1  shows a first exemplary embodiment of the invention and 
         FIG. 2  shows a second exemplary embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a schematic side view of part of an electric handheld power tool  1  embodied in the form of a percussion hammer  2 . The percussion hammer  2  has an impact mechanism  5  situated in a middle section  3  of a housing  4 . Between the impact mechanism  5  and a handle  6  at the end  7  of the housing, there is a drive unit  8 , which has an electric motor  9 , and a two-stage transmission  10  equipped with a first transmission stage  11  and a second transmission stage  12 . The impact mechanism  5  is essentially composed of a hammer tube  13  with a longitudinal axis  14 , a striking element  15  supported in the hammer tube  13 , and a piston  17  situated in the end region  16  of the hammer tube  13 . Between the striking element  15  and the piston  17  in the hammer tube  13 , there is an air cushion  18  via which the piston  17  drives the striking element  15 . Oriented toward the striking element  15 , the piston  17  has an end surface  19 , which is adjoined by a guide section  20  of the piston  17 . The guide section  20  has a circumference surface  21  that faces an inner surface  22  of the hammer tube  13 . In its circumference surface  21  in the guide section  20 , the piston  17  has an annular groove  23  that contains an  0 -ring  24  for producing a seal between the piston  17  and the inner surface  22  of the hammer tube  13 . The guide section  20  of the piston  17  is axially adjoined by an inner piston  25  that extends to a piston end  26  of the piston  17  and has a smaller diameter than the piston  17  in the guide section  20 . The piston end  26  has an overlap end  27  that partially overlaps the inner piston  25 . The overlap end  27  and the piston end  26  combine to form an overlap sleeve  28 , which likewise encompasses the end region  16  of the hammer tube  13  when slid inward into a position in which the piston  17  is situated completely inside the hammer tube  13 , except for the piston end  26 . The circumference surface of the overlap sleeve  28  constitutes a guide region  29  that cooperates with an inner surface  30  of an external piston guide  31 . The external piston guide  31  is situated outside the hammer tube  13  and encompasses the end region  16  of the hammer tube  13  in a section A and also encompasses an axial region B adjoining the end region  16  that adjoins the end region  16  of the hammer tube  13 . The external piston guide  31  has a C-shaped contour in a section with a cutting surface perpendicular to the longitudinal axis  14 , with which it circumferentially encompasses the overlap sleeve  28 , with one circumference region left out. In this circumference region, the outside  32  of the overlap end  27  has a sliding block guide  33  arranged perpendicular to the longitudinal axis  14  of the hammer tube  13 . The sliding block guide  33  is a piston drive element  34  and is composed of two opposing ribs  35 ,  35 ′, which are of one piece with the overlap sleeve  28  in the exemplary embodiment shown. A groove  36  is formed between the ribs  35 ,  35 ′. 
     The drive unit  8  includes the electric motor  9  and the two-stage transmission  10  with the first transmission stage  11  and the second transmission stage  12 . It is part of the impact mechanism  13 . The electric motor  9  has an output shaft  37  that is situated parallel to a rotatably supported shaft  38  of the first transmission stage  11 . The first transmission stage  11  is composed of the shaft  38  that is supported by two roller bearings spaced apart from each other and on which two transmission gears  39 ,  40 , each provided with a gearing, are situated spaced apart from each other and fixed for co-rotation with the shaft  38 . The transmission gear  40  here has a smaller diameter than the transmission gear  39 . The free end  41  of the output shaft  37  is provided with a gearing that meshes with a spur gearing of the transmission gear  39 . 
     The second transmission stage  12  is essentially composed of a rotatably supported shaft  42 , which is supported by two roller bearings spaced apart from each other. A transmission gear  43  and an eccentric wheel  44  are mounted on the shaft  42  and fixed for co-rotation with the shaft  42 . The transmission gear  43  of the second transmission stage  10  meshes with the transmission gear  40  of the first transmission stage  11 . The eccentric wheel  44  has a pin-shaped eccentric protrusion  45  that is situated eccentric to the longitudinal axis of the shaft  42  and engages in the groove  36  of the sliding block guide  33 . The part of the drive unit  8  shown is consequently a piston drive unit  46  that converts the rotary motion of the shaft  42  into an oscillating reciprocation of the piston  17  by means of an eccentric mechanism  47 . 
     The impact mechanism according to the invention functions as follows: in order to reduce the overall length L of the impact mechanism  5 , which includes the hammer tube  13 , the piston  17  supported in a longitudinally movable fashion in the hammer tube  13  by means of its guide section  20 , and the external piston guide  31  along which the guide region  29  of the piston  17  is guided in a longitudinally movable fashion, the piston end  26  situated outside the hammer tube  13  is provided with the overlap end  27 . The guide region  29  comprises part of the overlap end  27 . The arrangement of the guide region  29  at the overlap end  27  makes it possible to shift the position of the external piston guide  31  in the direction toward the hammer tube  13  in comparison to an impact mechanism not according to the invention, which has a piston without an overlap end and has a guide region  29  with a guidance area of the same magnitude. This shifting makes it possible to produce an axial section A (“overlap region”) in which the external piston guide  31  encompasses the end region  16  of the hammer tube  13 . This reduces the overall length L of the impact mechanism  5  by the length  1  of the section A, which constitutes the reduction in the length by which the external piston guide  31  protrudes axially beyond the end region  16  of the hammer tube  13 . 
     The overall length L can also be further reduced by the fact that the eccentric protrusion  45  of the eccentric mechanism  47  engages in the piston drive element  34  embodied in the form of a sliding block guide  33  in the region of the overlap end  27 . 
     Since the electric handheld power tool  1  in  FIG. 2  essentially corresponds to the one in  FIG. 1 , only the differences will be discussed below. The piston  17  of the impact mechanism  5  shown in  FIG. 2  is embodied in the form of a hollow piston  48  that has an access opening  49  situated at the end remote from the hammer tube  13 . The piston drive unit  46  is situated in the resulting cavity  50  of the hollow piston  48 . This piston drive unit  46  is composed of the electric motor  9  with its output shaft  37  to which the eccentric wheel  44  is fixed for co-rotation. The eccentric protrusion  45  of the eccentric wheel  44  in this case engages in a sliding block guide  33  situated on the inner surface  51  of an overlap arm  52 . The overlap arm  52  also supports an overlap end  27  with a guide region  29  for guiding the piston  17 . With this arrangement, the overall length L of the impact mechanism  5  and therefore also the overall length of the electric handheld power tool  1  is reduced even further since the piston drive unit  46  composed of the electric motor  9  and the eccentric wheel  44  with the eccentric protrusion  45  is situated in the cavity  50  of the hollow piston  48 . 
     The foregoing relates to the preferred exemplary embodiments 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.