Abstract:
The invention is based on a power tool having a beater mechanism ( 14 ) and a coupling device ( 12, 100 ), which can be engaged and disengaged in order to make and break a drive connection ( 16, 102 ) of the beater mechanism ( 14 ). 
     It is proposed that the coupling device ( 12, 100 ) has a synchronizing device ( 18, 112 ), with a detent mechanism ( 20, 110 ) which transmits a drive moment and which in a synchronizing operation has at least two corresponding detent elements ( 22, 24, 108 ), at least one of the detent elements ( 22 ) being movable about its detent position upon an overlooking moment, counter to the spring force of a spring element ( 26, 116 ).

Description:
BACKGROUND OF THE INVENTION 
   The invention is based on a drill- and/or chipping hammer. 
   Drill- and/or chipping hammers with pneumatic beater mechanisms are known that can be activated and deactivated via a mechanical friction coupling. If the drill- and/or chipping hammer is pressed with a tool against a machining surface, a tool holder that holds the tool is guided, in the direction of a user, into a housing of the drill- and/or chipping hammer. In the process, conical friction faces of the friction coupling come into contact, and the pneumatic beater mechanism is driven via a nonpositive engagement. During operation, with an axially movable piston guided in a cylinder, the beater mechanism generates a cushion of compressed air, which accelerates a beater in the axial direction against an impact bolt. The beater strikes the impact bolt, which thereby experiences a pulse. 
   If the drill- and/or chipping hammer with the tool is lifted from the machining surface, the frictional faces of the friction coupling are disconnected by a so-called idling spring, and the drive connection of the beater mechanism is broken. 
   SUMMARY OF THE INVENTION 
   The invention is based on a power tool having a beater mechanism and a coupling device, which can be engaged and disengaged in order to make and break a drive connection of the beater mechanism. 
   It is proposed that the coupling device has a synchronizing device, with a detent mechanism which transmits a drive moment and which in a synchronizing operation has at least two corresponding detent elements, at least one of the detent elements being movable about its detent position upon an overlooking moment, counter to a spring force of a spring element. With the detent mechanism, by means of an unlockable positive engagement, an advantageous synchronizing device can be created which at even a slight coupling force is capable of transmitting a relatively high torque. Because only slight coupling forces are required, an especially comfortable power tool can be achieved, which can be guided into its working position with only slight force on the part of the user. 
   As a result of the unlockable positive engagement, synchronization can advantageously be achieved over a short distance, and the synchronization is largely independent of the viscosity of a lubricant used in the coupling device. A damped engagement is also attainable with the synchronizing device, and a coupling device with little wear can be achieved. 
   Advantageously, the detent element that is movable counter to a spring force is formed by a roller body, and the detent element, corresponding to the detent element embodied as a roller body, is formed by a recess. The roller body can be formed for instance by a ball, roller, barrel, and so forth. The detent elements can roll in the overlooking process, and the wear can be reduced. The recess can be especially adapted to the rolling of the roller body, and uniform, low-wear synchronization can be achieved. If roller bodies embodied as rollers are used, then large transmission surface areas can be achieved, and in comparison with balls, greater torques can be transmitted, while conversely, with balls, a rolling motion in more than two directions can advantageously be achieved and canting can be avoided. Fundamentally, however, still other detent elements that appear useful to one skilled in the art can also be used, such as sliding blocks and the like. 
   In a first feature of the invention, it is proposed that the detent element embodied as a roller body is movable out of its detent position counter to an annular spring. A simple, space-saving construction with only one spring element can be achieved. The annular spring can be embodied in various ways, for instance as a single spring with a means of securing against rotation, a single spring without a means for securing against rotation and with a suitably embodied slot, which despite the tensed spring prevents the detent elements embodied as roller bodies from escaping, or as a spring packet, as a result of which a high spring force with low spring tension can advantageously be achieved. 
   If the detent element, at the onset of the synchronizing operation, is displaced along a conical face counter to the annular spring, then with a small axial force, a high radial force and thus a high synchronizing force can be attained. The conical face and/or the detent element with the annular spring can be embodied so that it is axially movably supported. With the conical face, a boost in the axial force can be attained, specifically because a greater axial motion with a lesser axial force can be converted into a lesser radial motion with a greater radial force. Moreover, the detent element embodied as a roller body can be guided into the detent element embodied as a recess with a continuous motion, and a uniform acceleration and advantageous engagement can be attained. Preferably, the detent element embodied as a recess has a dome-shaped cross-sectional area. 
   Advantageously, the conical face is formed onto one end of a component that is displaceable axially and fixed against relative rotation on a drivable shaft, and a detent element embodied as a recess extends into the conical face. The synchronizing device can be realized in a space-saving, structurally simple manner, with only a few additional components. 
   In a further feature of the invention, it is proposed that at the onset of the synchronizing operation, the detent element is guidable radially outward along the conical face. An existing installation space radially outward can advantageously be utilized, and a large, low-tolerance spring can be used. In principle, however, it is also conceivable to dispose the detent elements radially outside an annular spring and to embody them as movable radially inward counter to the annular spring. 
   If a component that transmits a pulse of the beater mechanism is connected to the displaceable component via a connection, which transmits a force in the pulse direction, then the pulse for attaining the idling position can be utilized, and a restoring spring or idling spring can be reinforced in its action. Advantageously, the restoring spring can be embodied smaller than in a conventional engagement coupling, and a low user force and a high degree of comfort can be attained. 
   It is also proposed that a root inner circle of at least two detent elements embodied as recesses has the same diameter as a root inner circle of the detent elements embodied as roller bodies, in an idling position. At a standstill, the roller bodies can be guided unhindered, without loading the spring, into the recesses, and simple engagement and disengagement can be achieved. Moreover and in particular, it can be attained that the annular spring is not under load while the tool is in a working position. 
   In a second feature of the invention, it is proposed that the detent element is formed by a ball, which is braced on a conical ring that is displaceable on a drivable shaft axially counter to a spring. The spring can take on the function of a synchronizing spring and an idling spring, so that additional components, installation space, weight and expense can be saved. With the conical ring, a boost is attainable with which a slight axial force can be converted into a strong radial force and a strong synchronizing force. 
   If the conical ring, once the drive connection is made, is axially fixed by a stop, the detent element can be used to establish a positive-engagement connection, and additional positive-engagement elements can be dispensed with. 
   It is also proposed that the detent element embodied as a ball is braced radially inward on the displaceable conical ring and can be brought radially outward into operative connection with the corresponding detent element as a recess. Existing installation space in the radial direction outward can advantageously be utilized. In principle, however, it is also conceivable for the detent elements to be braced radially outward on an axially displaceable conical ring. 
   If the detent element is supported in one part of a drive element, in particular a drive bearing, of the beater mechanism, then existing components can be used, and additional components, installation space and expense can be saved. 
   If the coupling device has positive-engagement elements, which after the synchronizing operation come into engagement next to the detent mechanism, then the detent mechanism can be relieved during operation, and the wear on the detent elements can be reduced. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages will become apparent from the ensuing drawing description. In the drawings, exemplary embodiments of the invention are shown. The drawings, descriptions 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. 
     Shown are: 
       FIG. 1 , a fragmentary section through a drill- and/or chipping hammer; 
       FIG. 2 , a coupling device of the drill- and/or chipping hammer of  FIG. 1 , in an idling position; 
       FIG. 3 , the coupling device of  FIG. 2  during a synchronizing operation; 
       FIG. 4 , the coupling device of  FIG. 2  in a percussion drilling position; 
       FIG. 5 , a coupling element of the coupling device of  FIG. 2 , seen obliquely from above; 
       FIG. 6 , a fragmentary section through a drill- and/or chipping hammer with an alternative coupling device; 
       FIG. 7 , the coupling device of  FIG. 6  in an idling position; 
       FIG. 8 , the coupling device of  FIG. 6  during a synchronizing operation; 
       FIG. 9 , the coupling device of  FIG. 6  in a percussion drilling position; 
       FIG. 10 , a coupling element of the coupling device of  FIG. 6  seen in the axial direction; and 
       FIG. 11 , a coupling device that is an alternative to  FIG. 6 , with additional positive-engagement elements. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a fragmentary section through a drill- and/or chipping hammer, with an electric motor, not shown in further detail, that is disposed in a housing  10  and has a drive shaft  52 . Formed onto the drive shaft  52  is a pinion, which meshes with a fixed wheel  118  disposed on a shaft  30  that extends parallel to the drive shaft  52 . The shaft  30 , on a side toward a tool holder  54 , has a formed-on gear wheel  56 , by way of which the shaft  30  meshes with a gear wheel  58  disposed on a hammer tube  60 . The gear wheel  58  is supported rotatably on the hammer tube  60  and is connected, via roller bodies of an overlock coupling  62 , to a detent disk  64  that is disposed in a manner fixed against relative rotation on the hammer tube  60 . The hammer tube  60  is in turn connected in a manner fixed against relative rotation to the tool holder  54 . 
   A beater mechanism  14  is rotatably supported with a drive bearing  74  on the shaft  30 . Also supported on the shaft  30  is a coupling device  12 , which can be engaged and disengaged to make and break a drive connection  16  of the beater mechanism  14 . On the side of the gear wheel  56  remote from the tool holder  54 , the coupling device  12  has a first coupling element  32 , supported on the shaft  30  axially displaceably but in a manner fixed against relative rotation. The first coupling element  32 , on its end toward the tool holder  54 , has a set of internal teeth, with which the first coupling element  32  is guided in a manner fixed against relative rotation but axially displaceably on the gear wheel  56 . On an end remote from the tool holder  54 , one part of a synchronizing device  18 , specifically a conical face  28 , whose diameter increases in the direction of the tool holder  54 , is formed onto an outer circumference of the first coupling element  32  ( FIGS. 1–5 ). Instead of a conical face, still other faces that appear useful to one skilled in the art may also be formed on, such as convex and/or concave faces, whose diameters preferably increase in the direction of the tool holder. The synchronizing behavior can advantageously be varied by means of how the face is embodied. 
   Originating in the conical face  28  are detent elements  24 , embodied as recesses and extending in the direction of the tool holder  54 , of a detent mechanism  20  of the synchronizing device  18  ( FIGS. 1 and 5 ). The detent elements  24  embodied as recesses have a domelike cross-sectional area. To achieve gentle engagement, the transitions in the circumferential direction to the recesses are rounded in the region of the conical face  28  ( FIG. 5 ). 
   The first coupling element  32  protrudes, with its end remote from the tool holder  54 , into a second, corresponding coupling element  44 , which furthermore forms one part of the drive bearing  74  of the beater mechanism  14 . In the second coupling element  44 , detent elements  22  of the detent mechanism  20  that are embodied as balls are supported in a plurality of radially extending bores distributed over the circumference. In an idling position of the drill- and/or chipping hammer, the detent elements  22  embodied as balls protrude radially inward with one part, past an inner circumference of the second coupling element  44 , and in the process are braced radially inward, each on a respective formed-on collar in the bores. The detent elements  22  embodied as balls form a root inner circle  36 , which has the same diameter as a root inner circle  34  of the detent elements  24  embodied as recesses ( FIGS. 1–4 ). Moreover, the number of balls matches the number of recesses, so that the first and second coupling elements  32 ,  44 , at a standstill of the drill- and/or chipping hammer, can be joined without force. 
   The detent elements  22  embodied as balls are surrounded radially outward by an annular spring  26 . The synchronization behavior can be adjusted, in particular via the design of the detent elements  24  embodied as recesses and via the annular spring  26 .  FIGS. 2–4  show a process of engaging the coupling device  12 . If the drill- and/or chipping hammer is pressed against a machining surface by a tool not shown further here, a reaction force is transmitted from the tool holder  54  to the detent disk  64 , via a securing ring  38 , the hammer tube  60 , and a securing ring  40 , and from the detent disk  64  to the first coupling element  32 , via a positive-engagement connection  76 , and in particular, the components  32 ,  54 ,  60 ,  64  are thrust farther into the housing  10 . An annular groove  70  is formed onto an outer circumference of the detent disk  64 , and this groove is engaged by a collar  72  formed onto the first coupling element  32 . The annular groove  70  and the collar  72  form the positive-engagement connection  76  in the axial direction between the detent disk  64  and the first coupling element  32  ( FIG. 1 ). 
   Via the detent disk  64  and via the connection  76 , the first coupling element  32  is thrust into the second coupling element  44 , counter to an idling spring  68 . The idling spring  68 , embodied as a helical compression spring, is disposed on the shaft  30  and is braced, by its end remote from the tool holder  54 , on the shaft  30  via a bracing ring  78  and a securing ring  42  secured in an annular groove of the shaft  30 . With its end toward the tool holder  54 , the idling spring  68  protrudes axially into an annular recess between the first coupling element  32  and the shaft  30  and acts with a compressive force in the direction of the tool holder  54  on a stop formed onto the first coupling element  32 . 
   The detent elements  22  embodied as balls are displaced radially outward counter to the annular spring  26  along the conical face  28 , at the onset of the synchronizing operation ( FIGS. 2 and 3 ). In the process, the detent elements  22  embodied as balls come into operative contact with the detent elements  24  embodied as recesses. An unlockable positive engagement is attained, because the detent elements  22  embodied as balls, during the synchronizing operation, can become unlocked radially outward at an overlooking moment from their detent positions, specifically from the detent elements  24  embodied as recesses, counter to the annular spring  26  ( FIG. 3 ). The first coupling element  32 , via the unlockable positive engagement, accelerates the second coupling element  44 , and beyond the conical face  28 , a maximum torque of the detent mechanism  20  is attained. 
   After a synchronization of the first and second coupling elements  32 ,  44 , clawlike positive-engagement elements  48 , formed onto the first coupling element  32  and extending axially in the direction toward the second coupling element  44 , come into engagement with correspondingly embodied clawlike positive-engagement elements  50 , which are formed onto the second coupling element  44  and extend axially in the direction toward the first coupling element  32 . The detent mechanism  20  is bridged, and the beater mechanism  14  is driven via the positive-engagement elements  48 ,  50  ( FIG. 4 ). If the drive moment exceeds an allowable value during operation, the gear wheel  58  is deflected counter to an overlock spring  66  in the axial direction toward the tool holder  54 , and the drive connection of the tool with the electric motor is broken.  FIGS. 1 and 4  show the drill- and/or chipping hammer and the coupling device  12  in a percussion drilling position. 
   When the drill- and/or chipping hammer is lifted from the machining surface, the first detent element  32 , via the connection  76 ; the detent disk  64 , via the securing ring  40 ; the hammer tube  60 ; and the tool holder  54 , via the securing ring  38 , are all are displaced axially into their outset position in the direction of the machining surface by the spring  68 . The idling spring  68  is reinforced in its mode of operation here by an idling stop of a beater  80 , guided in the hammer tube  60 ; specifically, a pulse of the beater  80  is transmitted to the first coupling element  32 , via a snap die  46 , the tool holder  54 , the hammer tube  60 , the detent disk  64 , and the connection  76 . 
   In  FIGS. 6–10 , a further exemplary embodiment with an alternative coupling device  100  is shown. Components remaining essentially the same are all identified by the same reference numerals. Moreover, for characteristics and functions that remain the same, reference may be made to the description of the exemplary embodiment in  FIGS. 1–5 . 
   A beater mechanism  14  is rotatably supported by a drive bearing  74  on a shaft  30 . Also supported on the shaft  30  is a coupling device  100 , which can be engaged and disengaged in order to make and break a drive connection  102  of the beater mechanism  14 . The coupling device  100 , on a side of a gear wheel  56  remote from a tool holder  54 , has a first coupling element  104  that is axially displaceable on the shaft  30  and is supported thereon in a manner fixed against relative rotation. The first coupling element  104 , on its end toward the tool holder  54 , has a set of internal teeth, with which the first coupling element  104  is guided on the gear wheel  56  axially displaceably and in a manner fixed against relative rotation ( FIG. 6 ). 
   A sleeve  106  is formed onto the first coupling element  104 , on its side remote from the tool holder  54 , and fits over a second, corresponding coupling element  122 . The second coupling element  122  forms one part of the drive bearing  74  of the beater mechanism  14 . 
   The sleeve  106 , on its inside circumference, has detent elements  108 , embodied as recesses, of a detent mechanism  110  of a synchronizing device  112 . The detent elements  108  extend obliquely radially outward toward one end remote from the tool holder  54  and have a decreasing depth, and in a final region before the end remote from the tool holder  54 , the sleeve  106  has an inside diameter corresponding to a root circle  126  of the detent elements  108  ( FIG. 10 ). The detent elements  108  have a domelike cross-sectional area. 
   Radially inside the sleeve  106 , a conical ring  114  is supported on the shaft  30 , in a manner fixed against relative rotation and displaceably in the axial direction. The conical ring  114  is displaceable counter to a spring  116  on a side toward the tool holder  54 . In the direction opposite the tool holder  54 , the conical ring  114  is braced on the shaft  30  via a securing ring  120  secured in an annular groove of the shaft  30 . The spring  115  is formed by a helical compression spring, which has an increasing diameter in the direction of the tool holder  54  and is disposed between the first coupling element  104  and the conical ring  114 . With its end toward the tool holder  54 , the spring  116  is braced in an annular recess on a collar of the first coupling element  104 . On its end remote from the tool holder  54 , the spring  166  is braced on the conical ring  114  ( FIGS. 6–10 ). The synchronization behavior can be adjusted by way of the choice of the spring  116 , by way of a conical angle of the conical ring  114 , and by way of the detent elements embodied as recesses, and in particular by way of a transition to the recesses. 
   In the second coupling element  122 , detent elements  22  embodied as balls in the detent mechanism  110  are supported in a plurality of bores extending radially and distributed over the circumference. The detent elements  22  embodied as balls protrude with one part radially inward beyond an inside circumference of the second coupling element  122  and in the process are braced on the inside on the conical ring  114  that is displaceable counter to the spring  116  ( FIGS. 6–9 ). 
   In  FIG. 7 , the coupling device  100  is shown in the disengaged state. If the drill- and/or chipping hammer is pressed against a machining surface by a tool, not shown in detail here, a reaction force is transmitted from the tool holder  54  to the detent disk  64 , via a securing ring  38 , the hammer tube  60 , and a securing ring  40 , and from the detent disk  64  to the first coupling element  104  via a positive-engagement connection  76 ; in particular, the components  54 ,  60 ,  64  and  104  are thrust farther into the housing  10 . An annular groove  70  is formed onto an outer circumference of the detent disk  64 , and this groove is engaged by a collar  72  that is formed onto the first coupling element  104 . The annular groove  70  and the collar  72  form the positive-engagement connection  76  in the axial direction between the detent disk  64  and the first coupling element  104 . 
   The first coupling element  104  is displaced counter to the spring  116  via the second coupling element  122 . The spring  116  is prestressed and transmits the axial motion of the first coupling element  104 , with a compressive force, onto the conical ring  114 . The detent elements  22  embodied as balls are forced radially outward by the conical ring  114  against the sleeve  106  of the first coupling element  104  ( FIG. 8 ). 
   Because of the axial motion of the first coupling element  104  in the direction of the beater mechanism  14 , the detent elements  22  embodied as balls come into operative contact with the detent elements  108 , embodied as recesses, of the first coupling element  104 . An unlockable positive engagement is attained, because the detent elements  22  embodied as balls, during the synchronizing operation, can become unlocked radially outward at an overlooking moment from their detent positions, specifically from the detent elements  108  embodied as recesses, counter to the conical ring  114 , and the conical ring  114  can be displaced counter to the spring  116  in the direction of the tool holder  54 . The first coupling element  104 , via the unlockable positive engagement, accelerates the second coupling element  122  ( FIG. 8 ). 
   Once the drive connection  102  has been made, the conical ring  114  is fixed axially in the direction of the tool holder  54  by means of a stop  124  of the first coupling element  104  ( FIGS. 6 and 9 ). The detent elements  22  embodied as balls are braced radially inward on the axially fixed conical ring  114  and are securely compartmented in the corresponding detent elements  108  embodied as recesses. As a result of the stop  124 , unlocking of the detent elements  22  is avoided, and the detent elements  22 ,  108  form a positive-engagement connection between the first and second coupling elements  104 ,  122 . If the drive moment exceeds an allowable value during operation, the gear wheel  58  is deflected in the axial direction toward the tool holder  54  counter to an overlock spring  66 , and the drive connection is broken. 
     FIGS. 6 and 9  show the drill- and/or chipping hammer and the coupling device  112  in a percussion drilling position. When the drill- and/or chipping hammer is lifted from the machining surface, the first coupling element  104 , via the connection  76 ; the detent disk  64 , via the securing ring  40 ; the hammer tube  60 ; and the tool holder  54 , via the securing ring  38 , are all are displaced axially into their outset position in the direction of the machining surface by the spring  116 . In the process, the spring  116  is reinforced in its mode of operation by an idling stop of a beater  80  guided in the hammer tube  60 ; specifically, a pulse of the beater  80  is transmitted to the first coupling element  104  via a snap die  46 , the tool holder  54 , the hammer tube  60 , and the detent disk  64 , and the connection  76 . 
     FIG. 11  shows a variant of the coupling device  100  of  FIG. 7 . After a synchronization of the first and second coupling elements  104 ,  122 , clawlike positive-engagement elements  128  formed onto the first coupling element  104  and extending axially in the direction of the second coupling element  122  come into engagement with correspondingly embodied clawlike positive-engagement elements  130  that are formed onto the second coupling element  122  and extend axially in the direction toward the first coupling element  104 . The detent mechanism  110  is bridged, and the beater mechanism  14  is driven via the positive-engagement elements  128 ,  130 . 
   
     
       
             
           
             
             
           
         
             
                 
             
             
               List of Reference Numerals 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               10 
               Housing 
             
             
               12 
               Coupling device 
             
             
               14 
               Beater mechanism 
             
             
               16 
               Drive connection 
             
             
               18 
               Synchronizing device 
             
             
               20 
               Detent mechanism 
             
             
               22 
               Detent element 
             
             
               24 
               Detent element 
             
             
               26 
               Annular spring 
             
             
               28 
               Conical face 
             
             
               30 
               Shaft 
             
             
               32 
               Coupling element 
             
             
               34 
               Root inner circle 
             
             
               36 
               Root inner circle 
             
             
               38 
               Securing ring 
             
             
               40 
               Securing ring 
             
             
               42 
               Securing ring 
             
             
               44 
               Coupling element 
             
             
               46 
               Snap die 
             
             
               48 
               Positive-engagement element 
             
             
               50 
               Positive-engagement element 
             
             
               52 
               Drive shaft 
             
             
               54 
               Tool holder 
             
             
               56 
               Gear wheel 
             
             
               58 
               Gear wheel 
             
             
               60 
               Hammer tube 
             
             
               62 
               Overlock coupling 
             
             
               64 
               Detent disk 
             
             
               66 
               Overlock spring 
             
             
               68 
               Idling spring 
             
             
               70 
               Annular groove 
             
             
               72 
               Collar 
             
             
               74 
               Drive bearing 
             
             
               76 
               Connection 
             
             
               78 
               Bracing ring 
             
             
               80 
               Beater 
             
             
               100 
               Coupling device 
             
             
               102 
               Drive connection 
             
             
               104 
               Coupling element 
             
             
               106 
               Sleeve 
             
             
               108 
               Detent element 
             
             
               110 
               Detent mechanism 
             
             
               112 
               Synchronizing device 
             
             
               114 
               Conical ring 
             
             
               116 
               Spring 
             
             
               118 
               Fixed wheel 
             
             
               120 
               Securing ring 
             
             
               122 
               Coupling element 
             
             
               124 
               Stop 
             
             
               126 
               Root circle 
             
             
               128 
               Positive-engagement element 
             
             
               130 
               Positive-engagement element