BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a percussion hammer and/or drill hammer that is equipped with a safety coupling. 
         [0003]    2. Description of the Related Art 
         [0004]    In particular during drilling, in percussion and/or drill hammers (called “hammers” for brevity hereinafter) there is the danger that the drill or drill bit will become lodged upon impact in the stone that is being worked, which can result in a significant increase in the effective torques in the hammer, causing damage to the drive train. Moreover, the torques must be manually supported by the operator, so that in heavier devices a sudden blocking of the drilling tool can result in the hammer being torn from the operator&#39;s hand. For this reason, in known hammers a safety coupling is built into the torque flow, which interrupts the torque flow acting in the device when a predetermined boundary torque value is exceeded. In this way, an excessive torque that may occur will no longer have a damaging effect on the drive or on the operator. 
         [0005]    In its many different technical realizations, the safety coupling can be situated at various locations inside the device in the flow of force or torque, in particular in the flow of torque between a drive of the hammer (e.g. an electric motor or internal combustion engine) and a tool holder that holds the tool. Installation locations situated between a crankshaft belonging to the drive and a drill shaft that accepts the tool holder or is connected before the tool holder have turned out to be particularly suitable. 
         [0006]    Safety couplings can be constructed in many different ways. In practice, what are known as latch or claw safety couplings have turned out to be particularly advantageous that are situated in the area of the drive shaft or of a percussion mechanism tube belonging to a percussion mechanism of the hammer. Standardly, a toothed drive wheel attached to the drill shaft or to the percussion mechanism tube and provided with latches or claws on its front side is pressed by an engaging spring against a collar that is also provided with latches and that is connected integrally to the percussion mechanism tube or the drill shaft. Safety couplings of this sort can be manufactured economically and are robust and durable, because when actuated the rotational speeds are low, and at the location of installation there is a large diameter and sufficient space for generous dimensioning. 
         [0007]      FIG. 8  shows a section through a typical drill hammer, as is for example known from DE 101 45 464 A1. The torque of an electric motor  1  that acts as a drive is transmitted via a multiplicity of toothed wheels and a crankshaft  2  to a main shaft  3 , and is finally transmitted via additional toothed wheels to a drill shaft  4  that holds a tool holder  5 , in which a drill and/or chisel tool (not shown) can be inserted. 
         [0008]    In main shaft  3  there is integrated a safety coupling  6  that has a toothed disk  8  supported by a spring  7 . When a prespecified boundary torque value is exceeded, there arises at the teeth of toothed disk  8  axial forces that are large enough to press toothed disk  8  back against the action of spring  7 . This results in an interruption of the torque flow, so that danger to the operator of the hammer, e.g. given a blocking of the drill tool during drilling, is avoided. 
         [0009]    From DE 42 15 288 A1, a drill hammer is known that has a safety coupling in which the toothed drive wheel situated on the safety coupling must be displaced axially against the action of a spring in order to bring it out of engagement with its paired mating gear, and thus to interrupt the torque flow. As long as the hammer is new, this is unproblematic. However, in older devices there is the danger that after longer periods of use, due to wear the toothed drive wheel will run together with the toothed mating gear in such a way that the drive wheel can no longer be axially displaced. If this has happened, a desired response of the safety coupling when the boundary torque value is exceeded is no longer ensured. 
         [0010]    In addition, drill hammers can often be switched between a plurality of operating modes. Besides a pure drilling mode (with the percussion mechanism switched off) and a drill hammer operation (drilling and chiseling), a pure chiseling operation is also possible in which the tool is not rotationally driven. In known hammers, the chisel is then however freely rotatable in an uncontrolled fashion, which can be disadvantageous when guiding the device as a whole. 
       OBJECT OF THE INVENTION 
       [0011]    The present invention is based on the object of indicating a percussion and/or drill hammer having a safety coupling that is improved with respect to its resistance to wear, reliability, and functionality. 
         [0012]    According to the present invention, this object is achieved by a percussion and/or drill hammer as recited in patent claim  1 . Advantageous constructions of the present invention are defined in the dependent claims. 
         [0013]    The percussion and/or drill hammer according to the present invention is equipped with a safety coupling that has a toothed drive wheel capable of being driven by the drive with the torque, a sealing ring situated axially to the toothed drive wheel and via which the torque can be guided, and a latch device situated between the toothed drive wheel and the sealing ring. In a normal operating state, the latch device ensures a flow of torque between the toothed drive wheel and the sealing ring. In an overload state, in which a torque exceeding a prespecified boundary torque value is introduced into the safety coupling, the latch device interrupts the torque flow between the toothed drive wheel and the sealing ring. 
         [0014]    The axial situation of the toothed drive wheel and the sealing ring with the latch device situated axially between them makes it possible to realize the safety coupling in such a way that at least the axial position of the toothed drive wheel need not be modified even in the overload state. Rather, the latch device takes over the function of interrupting the torque flow, through axial displacement. 
         [0015]    The toothed drive wheel can remain at all times in its intended axial position, and can thus mesh with its allocated mating gear even in case of overload. The problems that occur in the prior art of a mutual running together of the toothed drive wheel and the mating gear, and the resulting limited reliability of the safety coupling, are avoided in this way. 
         [0016]    Particularly advantageously, it can be ensured that the axial position of the toothed drive wheel need not be modified if at least a part of the latch device is capable of axial movement relative to the sealing ring and/or relative to the toothed drive wheel. This makes possible for example a realization in which only the latch device, or a part thereof, executes an axial movement, e.g. in the overload state, while the other components of the safety coupling remain in their axial position. 
         [0017]    Preferably, the axial position of the toothed drive wheel and/or of the sealing ring is fixed in at least one axial direction. A movement of the toothed drive wheel or of the sealing ring in the opposite axial direction can be permissible under some circumstances, but should then be possible only against the action of a spring. This enables various constructions of the safety coupling. 
         [0018]    It is particularly advantageous if the toothed drive wheel and the sealing ring are situated on a base sleeve. This design of the safety coupling enables a compact construction in which the safety coupling can be preassembled before being installed in the hammer. 
         [0019]    In a particularly advantageous specific embodiment of the present invention, the toothed drive wheel is mounted on the base sleeve so as to be capable of rotation, while the sealing ring is fastened to the base sleeve or is fashioned in one piece with the base sleeve. 
         [0020]    In another specific embodiment of the present invention, this design can be reversed, so that the sealing ring is mounted on the base sleeve so as to be capable of rotation, while the toothed drive wheel is fixedly attached to the base sleeve. Finally, a variant is also possible in which both the toothed drive wheel and also the sealing ring are rotatably mounted on the base sleeve. 
         [0021]    In a particularly advantageous specific embodiment of the present invention, the latch device has a latch ring situated between the toothed drive wheel and the sealing ring. The latch ring is rotationally fixed relative to the sealing ring, and is capable of being axially displaced against the action of a spring device. The toothed drive wheel and the latch ring have a mutually engaging latch toothing via which the torque that is to be transmitted by the safety coupling is conducted. In the normal operating state, the latch ring is pressed axially against the toothed drive wheel by the spring device, so that the latch toothings engage with one another. In the overload state, the latch ring is pushed in the direction of the sealing ring axially against the action of the spring device, so that the latch toothings of the latch ring and the toothed drive wheel disengage from one another. 
         [0022]    In a particularly advantageous construction of the present invention, the latch toothings each have beveled side edges (viewed in the circumferential direction) via which the torque to be transmitted by the safety coupling is transmitted. Through the beveled side edges, an axial force directed against the action of the spring device is constantly produced on the latch ring. If in the overload state the effective torque exceeds the prespecified boundary torque value, the axial force becomes large enough that it axially pushes the latch ring in the direction of the sealing ring, against the action of the spring device, so that the latch toothings disengage from one another. 
         [0023]    In a particularly advantageous construction of the present invention, the sealing ring and the latch ring each have entraining claws that constantly engage with one another. In this way, the sealing ring and the latch ring are rotationally fixed to one another in the circumferential direction. In contrast, in the axial direction the latch ring is capable of being moved relative to the sealing ring. The entraining claws can be constructed in a stable fashion, so that they also reliably transmit the torque when the latch ring is in its position furthest from the sealing ring. 
         [0024]    Preferably, the toothed drive wheel is axially mounted or supported at least on a side of the base sleeve facing away from the latch claws. In this way, an expensive separate mounting of the toothed drive wheel can be avoided. An axial mounting on the side of the latch claws, in contrast, is not required, because on this side the toothed drive wheel is constantly supported by the latch ring and the spring device acting behind it. 
         [0025]    Another specific embodiment of the present invention presents a kinematic reversal of the above-described specific embodiment. According to this embodiment, the latch ring situated between the toothed drive wheel and the sealing ring is rotationally fixed relative to the toothed drive wheel, and is capable of axial displacement relative to the toothed drive wheel, against the action of a spring device. In contrast to the above-described specific embodiment, the latch toothings are not formed between the toothed drive wheel and the latch ring, but rather between the sealing ring and the latch ring. Accordingly, the sealing ring has a latch toothing on a front side facing the latch ring, while the latch ring has a latch toothing that fits the latch toothing of the sealing ring on a side facing the sealing ring. Via the spring device, the latch ring is supported not against the sealing ring, but against the toothed drive wheel. In the normal operating state, the latch ring is pressed against the sealing ring in such a way that the latch toothings engage with one another. In contrast, in the overload state the latch ring is axially displaced in the direction of the toothed drive wheel, so that the latch toothings disengage. 
         [0026]    In another advantageous construction of the present invention, the base sleeve is an integral component of the drill shaft or is a part of a percussion mechanism tube. This means that the base sleeve need not necessarily be a separate additional component. Rather, it is possible to construct the toothed drive wheel, the sealing ring, and the latch device on an already-present component in the hammer, in particular the drill shaft, the percussion mechanism tube, or another shaft situated in the torque flow. However, a separate base sleeve has the advantage of a particularly simple preassembly outside the hammer. 
         [0027]    It is particularly advantageous that the safety coupling can be completely preassembled and then pushed with its base sleeve onto a bearer sleeve so as to be capable of rotational movement. The bearer sleeve can be a part of a drill shaft and/or a part of a percussion mechanism or percussion mechanism tube. In principle, the safety coupling according to the present invention can be used in any kind of percussion and/or drill hammer, so that the bearer sleeve can be used at a suitable location. 
         [0028]    In a particularly advantageous construction of the present invention, on the bearer sleeve there is provided an axially displaceable switching ring with which the flow of torque from the safety coupling to the bearer sleeve can be created or interrupted. The switching ring is used to preset various operating states of the hammer, as is explained in more detail below. 
         [0029]    The switching ring is preferably connected in rotationally fixed fashion to the bearer sleeve, and has on one side switching claws to which there are allocated oppositely situated switching claws provided on a rear side of the sealing ring. Thus, the switching claws of the switching ring can be brought into engagement with the switching claws of the sealing ring, so that the flow of torque can be transmitted from the sealing ring via the switching claws to the switching ring, and from the switching ring to the bearer sleeve. 
         [0030]    In a particularly preferred specific embodiment of the present invention, the switching ring can be displaced at least between a drilling position in which the switching claws of the switching ring are engaged with the switching claws of the sealing ring, and a free rotation position in which the switching claws are not engaged. In the drilling position, of course, impacts from the percussion mechanism provided in the hammer can also be exerted on the tool, so that the term “drilling position” also includes a “drilling/chiseling position.” In contrast, in the free rotation position no drilling torque is transmitted to the tool. Rather, the tool is then capable of unhindered rotation relative to the hammer, for example if the operator correspondingly pivots the hammer. The free rotation position is standardly used before chiseling in order to bring a chisel cutting edge into a suitable angular rotational position relative to the hammer housing. 
         [0031]    In a particularly advantageous construction of the present invention, the switching ring is also capable of being moved into a fixing position (chiseling position) in which fixing claws that are attached to the switching ring on a rear side opposite the front side are brought into engagement with oppositely situated fixing claws provided on a fixing ring that is fixedly attached to the housing. Thus, in the fixing position the switching ring, and consequently also the bearer sleeve, are fixed relative to the hammer housing. A rotation of the bearer sleeve or of the drill shaft, and thus of the tool, relative to the hammer is then not possible. The fixing position is used by the operator during pure chiseling work (without drilling). 
         [0032]    These and other advantages and features of the present invention are explained in more detail below in relation to an example, with the aid of the accompanying Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  shows a section through a safety coupling according to the present invention for a percussion and/or drill hammer; 
           [0034]      FIG. 2  shows a perspectival exploded view of the safety coupling of  FIG. 1 ; 
           [0035]      FIG. 3  shows the exploded view of  FIG. 2  from a different perspective; 
           [0036]      FIG. 4  shows a section having a safety coupling built onto a percussion mechanism tube; 
           [0037]      FIG. 5  shows an external view of  FIG. 4 ; 
           [0038]      FIG. 6  shows a perspective exploded view of  FIGS. 4 and 5 ; 
           [0039]      FIG. 7  shows a section through another specific embodiment of the safety coupling according to the present invention; and 
           [0040]      FIG. 8  shows a section through a percussion and/or drill hammer according to the prior art. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0041]      FIGS. 1 to 3  show a safety coupling according to the present invention in sectional or exploded view. 
         [0042]    On a base sleeve  20 , a toothed drive wheel  21  is situated that is supported with its smooth sliding surface  22  against a corresponding collar  23  of base sleeve  20 . Toothed drive wheel  21  can rotate freely relative to base sleeve  20  and meshes with a mating gear (not shown), from which the drive torque of a drive (not shown) is introduced. On a side  24  situated opposite sliding surface  22 , toothed drive wheel  21  has a plurality of radially offset latch claws  25  of a latch toothing  26  (see  FIG. 2 ). 
         [0043]    On the end of base sleeve  20  situated opposite collar  23 , a sealing ring  27  is fixedly placed, for example by a press-fit seating. Of course, sealing ring  27  can also be fastened to base sleeve  20  in some other way, e.g. by screwing, or can be fashioned in one piece with the sleeve. 
         [0044]    Between sealing ring  27  and toothed drive wheel  21 , there is situated a latch ring  28  that is capable of axial displacement and that is pressed axially against toothed drive wheel  21  by a plurality of springs  29  that are supported against sealing ring  27 . Latch ring  28  bears a plurality of entraining claws  30  that extend axially and that engage in corresponding grooves  31  between allocated entraining claws  32  of sealing ring  27 . Correspondingly, it is possible for latch ring  28  to be displaced axially by springs  29 , or against the action of springs  29 , entraining claws  30  of latch ring  28  remaining at all times engaged with entraining claws  32  of sealing ring  27 , so that a torque can be transmitted. 
         [0045]    Latch ring  28  has on a side facing toothed drive wheel  21  a plurality of latch claws  33  that form a latch toothing  34 . Latch toothing  26  of toothed drive wheel  21  and latch toothing  34  of latch ring  28  are fashioned such that latch claws  25  and latch claws  33  are able to engage in one another in at least one particular relative rotational position of toothed drive wheel  21  and latch ring  28 . Individual latch claws  25  or  33  can have different or asymmetrical widths in the circumferential direction (angular extensions), so that latch claws  25 ,  33  can latch into one another less frequently than would be possible in principle based on the number of intermediate spaces between latch claws  25 ,  33 . This prevents rattling of the safety coupling and reduces wear in the case of overload. On the other hand, the increased number of latch claws  25 ,  33  results in a plurality of latch locations, so that the torque can be reliably transmitted. 
         [0046]    Latch claws  25 ,  33  each have beveled side edges  35  via which the force or torque flow is guided between toothed drive wheel  21  and latch ring  28 . Due to their oblique position, side edges  35  each also produce axial forces that push toothed drive wheel  21  and latch ring  28  away from one another. Because toothed drive wheel  21  is supported against collar  23 , however, it cannot move axially, but rather always remains in the desired axial position, in which it meshes with the mating gear (not shown). In contrast, latch ring  28  is capable of axial displacement, as shown above. 
         [0047]    When the torque introduced into toothed drive wheel  21  exceeds a particular boundary value (boundary torque), the axial forces caused by beveled side edges  35  become large enough that latch ring  28  is pressed back in the direction of sealing ring  27 , against the action of spring  29 . This causes latch toothings  26  and  34  to disengage, so that further transmission of the torque is prevented. The safety coupling is then in the overload state, and fulfills its intended function of protecting the drive train and the operator manually holding the hammer. Accordingly, in the overload state latch ring  28  is pressed by beveled lateral edges  35  against sealing ring  27  in such a way that latch toothings  26  and  34  disengage. Springs  29 , however, continuously press latch ring  28  back in order to bring it into engagement with latch toothing  26  of toothed drive wheel  21 . If the torque to be transmitted is still greater than the boundary torque value, latch ring  28  is again subjected to an increased axial force that again presses it back against sealing ring  27 . Correspondingly, the safety coupling in the case of overload will rattle until the operator interrupts the operation of the hammer. 
         [0048]    In the specific embodiment shown in  FIGS. 1 to 3 , springs  29  are largely placed in bores  36  that are essentially formed in entraining claws  32  of sealing ring  27 . Alternatively, however, it is also possible for springs  29  to be placed in corresponding bores in entraining claws  30  of latch ring  28 . This would even enable an enlargement of the axial width of latch ring  28 , which would improve its axial gliding properties on base sleeve  20 . 
         [0049]    The safety coupling shown in  FIGS. 1 to 3  represents a self-sufficient assembly that can be preassembled outside the hammer. The assembly can then easily be installed in the hammer as a unified component. 
         [0050]      FIGS. 4 ,  5 , and  6  show the safety coupling in the installed state, i.e., pushed onto a bearer sleeve  40 .  FIG. 4  shows a section. In  FIG. 5 , a side view corresponding to the section of  FIG. 4  is shown, while  FIG. 6  shows the system in a perspective exploded view. 
         [0051]    Bearer sleeve  40  can be part of a drill shaft. In the example shown in  FIGS. 4 to 6 , bearer sleeve  40  is a percussion mechanism tube inside which a known pneumatic spring hammer mechanism (not shown in the Figures) is situated. Pneumatic spring hammer mechanisms are based on the principle that a drive piston that is capable of axial back-and-forth movement, e.g. driven by a crankshaft, drives an impact piston situated in front of the drive piston back and forth via an air spring. The impact piston in turn cyclically transmits its impact energy to a tool. Because pneumatic spring hammer mechanisms of this sort are known in many realizations, a more detailed description is not necessary here. 
         [0052]    If bearer sleeve  40  is fashioned as a drill shaft, it can accept a complete hammer mechanism, in particular including a hammer mechanism tube, or else can itself form the hammer mechanism tube or housing, as shown in  FIGS. 4 to 6 . 
         [0053]    In the specific embodiment shown in  FIGS. 4 to 6 , it is necessary for the hammer mechanism tube to take over the function of a drill shaft, and correspondingly to execute an entrained rotation in order to transmit the torque. 
         [0054]    For this purpose, on bearer sleeve  40  there is situated a switching ring  41  that is capable of axial displacement and that is connected in rotationally fixed fashion to bearer sleeve  40  via wedges  42 . Switching ring  41  acts to create or interrupt the flow of torque from the safety coupling to bearer sleeve  40 . On a front side of switching ring  41 , switching claws  43  are provided to which there are allocated oppositely situated switching claws  44  that are situated on a rear side of sealing ring  27 . Switching claws  44  are also clearly visible in  FIGS. 1 to 3 . 
         [0055]    In the position of switching ring  41  shown in  FIGS. 4 and 5 , switching ring  41  assumes what is called a drilling position, in which switching claws  43  of switching ring  41  engage with switching claws  44  of sealing ring  27 , so that the torque introduced via toothed drive wheel  21  can be transmitted to bearer sleeve  40  via sealing ring  27 , switching ring  41 , and wedge toothing  42 . From bearer sleeve  40 , the torque is transmitted in a known manner (not shown) to a tool (also not shown). 
         [0056]    If, in contrast, switching ring  41  is displaced axially on bearer sleeve  40  in such a way that switching claws  43 ,  44  disengage, what is known as a free rotational position is achieved, in which no torque is introduced to bearer sleeve  40 . Rather, bearer sleeve  40  can rotate freely together with switching ring  41 . 
         [0057]    Finally, another fixing ring  45  is provided that is fastened to a housing (not shown) of the hammer. On fixing ring  45 , fixing claws  46  are fashioned on the front side, to which fixing claws  48  are allocated that are oppositely situated on a rear side  47  of switching ring  41 . Switching ring  41  is correspondingly able to be displaced into a fixing position (not shown in the Figures) in which fixing claws  48  of switching ring  41  engage with fixing claws  46  of fixing ring  45 . In this fixing position, no torque is introduced to bearer sleeve  40  by the drive. However, bearer sleeve  40  cannot rotate freely, because its position relative to the housing is fixed. 
         [0058]    The axial displacement of switching ring  41  takes place with the aid of a switching lever  49  that is accessible from the outside by the operator, and which for example can also be realized as a rotary switch, as is shown in particular in  FIG. 6 . The rotational position of switching lever  49  is transmitted via a switching cam  50  and a known switching spring  51  to a switching fork  52  that engages in a circumferential groove  43  in the outer area of switching ring  41 . Through switching spring  51 , it is possible in particular for an axial force to be exerted on switching claws  43 , if for example switching claws  43  of switching ring  41  are situated over switching claws  44  of sealing ring  27 , so that when there is further rotation of switching ring  41  relative to sealing ring  27 , switching claws  43  can finally move into engagement. For the operator, this means increased ease of operation, because the operator can use switching lever  49  to preselect the desired operating mode, and to place the device automatically into the desired operating mode via the spring pre-tension of switching spring  41 . 
         [0059]      FIG. 7  shows another specific embodiment of the safety coupling according to the present invention in a sectional view. 
         [0060]    Because the safety coupling corresponds in its design to the safety coupling shown in  FIG. 1 , for simplicity identical reference characters are used. However, differing from the safety coupling of  FIG. 1 , here toothed drive wheel  21  is attached fixedly to base sleeve  20 . In contrast, sealing ring  27  is capable of radial rotation on base sleeve  20 . It is supported axially against collar  23 , and the action of springs  29  secures the axial position of sealing ring  27  against collar  23 . Springs  29  are in turn supported via latch ring  28  against toothed drive wheel  21 , which is fastened on base sleeve  20 . 
         [0061]    The further functioning of the safety coupling, in particular the latch device having latch ring  28  and springs  29 , corresponds to the design explained above with reference to  FIGS. 1 to 3 , so that repetition here is not necessary. 
         [0062]    In another specific embodiment of the present invention (not shown), both toothed drive wheel  21  and sealing ring  27  can be situated on base sleeve  20  so as to be capable of free rotation; here one collar  23 , as shown in  FIGS. 1 and 7 , must be provided for each of elements  21 ,  27 . Springs  29 , together with latch ring  28 , ensure that both latch ring  27  and toothed drive wheel  21  are pressed against their respectively allocated collar  23 , so that the respective axial position is ensured. 
         [0063]    Although the safety couplings shown in the Figures each have a base sleeve  20 , for the realization of the present invention it is not required to provide such a base sleeve  20 . Rather, it is also possible to construct toothed drive wheel  21 , sealing ring  27 , and the latch device comprising latch ring  28  and springs  29  at a suitable location, e.g. on the drill shaft, without an additional base sleeve  20 .
A safety coupling in a percussion hammer and/or drill hammer, comprising a basic sleeve, a driven toothed wheel that is rotatably mounted on the basic sleeve and can be driven by a drive unit, a closing ring which is fastened to the basic sleeve, and a locking ring located between the driven toothed wheel and the closing ring. Said locking ring is fixed in a torsion-proof manner relative to the closing ring while being movable relative to the closing ring in an axial direction, counter to the effect of a spring mechanism. The locking ring is axially displaced while the driven toothed wheel remains in the axial position thereof when a threshold torque is exceeded.