Abstract:
A pneumatic percussion mechanism for a hand-held power tool includes a percussion piston ( 23 ) displaceable in a guide tube ( 21 ) for applying impacts to an anvil ( 24 ), a driving member ( 22 ) reciprocating in the guide tube ( 21 ) for driving the percussion piston, and an air spring ( 25 ) for transmitting a driving torque from the driving member ( 22 ) to the percussion piston ( 23 ) and directly switchable on and off by the anvil ( 24 ).

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a pneumatic percussion mechanism for a hand-held power tool such as, e.g., a chisel or combination hammer and including a guide tube, an anvil, a percussion piston displaceable in the guide tube for applying impacts to the anvil, a driving member reciprocating in the guide tube for driving the percussion piston and an air spring for transmitting a driving torque from the driving member to the percussion piston and switchable between active and passive conditions. 
   2. Description of the Prior Art 
   German Publication DE 43 10 835 A1 discloses a hand-held, electrically driven rotary-percussion or percussion hammer having a motor-driven percussion mechanism arranged in the tool housing. The percussion mechanism includes a driving member, such as a driving piston displaceable in a guide tube and reciprocated with a rod actuatable by the motor. The driving member drives, via an air cushion or an air spring a percussion piston likewise displaceable in the guide tube and applying, through an anvil, blows or impacts to a working tool received in the power tool chuck. The anvil is formed, at its end remote from the working tool, with a pot-shaped section, in the pot space of which the percussion piston is partially received. A seal, which is provided between the pot-shaped anvil and the guide tube seals the percussion mechanism against release of the lubricant outwardly. The air spring is controlled by a sleeve displaceable over the guide tube and which opens or closes aeration bores in the guide tube. The sleeve is controlled indirectly by the anvil. The drawback of the above-described percussion mechanism consists in that several components are needed for controlling the air spring. Therefore, the costs associated with manufacturing and assembly of the percussion mechanism are elevated. 
   Accordingly, an object of the present invention is to provide a percussion mechanism in which the foregoing drawback of the known mechanism is eliminated, and in which the air spring can be controlled in a simple way. 
   Another object of the present invention is a hand-held power tool with a percussion mechanism having a simply controlled air spring. 
   SUMMARY OF THE INVENTION 
   These and other objects of the present invention, which will become apparent hereinafter, are achieved by controlling the air spring directly with the anvil. 
   The use of the anvil for switching the air spring on or off significantly simplifies the control of the air spring and reduces the constructional space occupied by the percussion mechanism. The weight of the power tool and the manufacturing costs are likewise reduced due to the reduction in the number of parts necessary for affecting the air spring control. 
   Advantageously, the anvil forms a closing body of an air spring controlling valve, which represents a constructively simple solution of the direct control of the air spring with the anvil. 
   It is advantageous, when the anvil is formed as a pot-shaped member having a pot section provided with a valve section that forms the closing body. This measure permits to reduce the length of the anvil despite its large mass, and permits to realize the air spring control, using the pot section of the anvil. 
   It is further advantageous when there is provided a first seal located between the guide tube and the valve section. The first seal forms, together with the valve section, the air-spring controlling valve. For switching the air spring on, the seal seals the space, which is located between the driving member, e.g., driving piston, and the percussion piston, against one or a plurality of aeration openings which, e.g., are formed in the guide tube. 
   Advantageously, the guide tube has a drive section having a first inner diameter in which the driving member is displaceable, and an anvil section adjoining the drive section in which the pot section of the anvil is received and which has a second inner diameter. This provides for displacement of the percussion piston in the pot section of the anvil and in the drive section of the guide tube. 
   It is further advantageous when the first seal is arranged on an inner surface of the anvil section of the guide tube adjacent to a transition area between the anvil section and the drive section. Thereby, switching of the air spring on is only achieved at almost complete displacement of the anvil up to the stop or up to the transition area between the anvil and the drive section and, thus, when the working tool is completely pressed against a workpiece. At the same time, at a weak pressure of the working tool against the workpiece, a reduced impact force is provided because the anvil, which acts as a closing body of the air spring controlling valve, opens it only for a short time or only partially. 
   It is also advantageous when the pot section has an interior pot space in which the percussion piston can completely be received, or its axial length is at least as large as the axial length of the percussion piston. Therefore, at an open valve or the switched-off air spring, the percussion piston cannot be drawn in the direction of the driving piston, and the percussion mechanism is reliably disabled in absence of a press-on force. 
   Advantageously, the pot space has a diameter that corresponds to the first inner diameter of the drive section of the guide tube. Thereby, the percussion piston can reciprocate between the pot space and the drive section of the guide tube during operation of the percussion mechanism when the air spring is switched on. 
   According to a further advantageous embodiment of the invention, the anvil has an axially extending, elongate extension over which the annular percussion piston is axially displaceable, and which has, at its end adjacent to the driving member, a valve section that forms the closing body that cooperates with an annular portion of the driving member which encloses an aeration opening. This also permits to reduce the length of the anvil despite its large mass, providing simultaneously for control of the air spring with the elongate bar-shaped extension of the anvil. 
   Advantageously, in the embodiment described immediately above, the first seal of the valve is located between the valve section of the anvil and the annular portion of the driving member. The first seal seals the space between the driving member and percussion piston relative to the aeration opening of the valve, which is provided in the annular portion of the driving member, for switching the air spring on. 
   In a constructively advantageous embodiment, the first seal is provided on the annular portion of the drive member radially inwardly of the annular portion. 
   The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings show: 
       FIG. 1  a side view of a hand-held power tool with a pneumatic percussion mechanism; 
       FIG. 2  a cross-sectional view of a section of the hand-held power tool according to mark II in  FIG. 1  at an increased in comparison with  FIG. 1 , scale and in a condition of the power tool in which the power tool is pressed against a workpiece; 
       FIG. 3  a cross-sectional view of the section of the power tool shown in  FIG. 2 , in a condition of the power tool when it is not pressed against a workpiece; and 
       FIG. 4  a cross-sectional view similar to that of  FIG. 2  of another embodiment of a hand-held tool according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A hand-held power tool  10  according to the present invention, which is formed as a rotary-percussion combination hammer shown in  FIG. 1 , includes a housing  11  and located in the housing  11 , a percussion mechanism  20  acting on a working tool  15  received in a chuck  14 , a drive gear  13  and a motor  12 . A driven shaft  16  connects the percussion mechanism  20  with the drive gear  13  that transmits a rotational movement of the motor  12  to the percussion mechanism  20 . 
     FIGS. 2-3  show the percussion mechanism  20  in detail. The percussion mechanism  20  includes a guide tube  21  in which a driving member  22 , which is formed as a driving piston, reciprocates. In order to facilitate the assembly of the percussion mechanism, the guide tube  21  can be formed of two or more parts. For producing a reciprocating movement of the driving member  22 , a rod  29 , which is pivotally supported on the driving member  22 , connects the driving member  22  with an eccentric  17  mounted on the output shaft  16  of the drive gear  13 . A pot-shaped anvil  24  is axially displaceably supported in the guide tube  21 . A percussion piston  23  is displaceable in a pot space  34  of the pot-shaped anvil  24 . The percussion piston  23  and the pot space  34  are so dimensioned that the percussion piston  23  can be completely received in the pot space  34 , as shown in  FIG. 2 . 
   At its end remote from the percussion piston  23 , the anvil  24  has an impact end  30  that can transmit impacts or blows to the working tool  15  inserted in the chuck  14 . 
   Between the driving member  22  and the percussion piston  23 , there is located an air spring  25  that can be switched on and off. To this end, the anvil  24  forms with its valve section  36  remote from its impact end  30 , and a first seal  27 , which is located between the guide tube  21  and valve section  36 , a valve  26 . The valve section  36  of the anvil  24  functions as a closing body of the valve  26 . In the guide tube  21 , there is further provided aeration openings  35  through which, at the open valve  26 , air from the space between the driving member  22  and the percussion piston  23 , can escape in the space outside of the guide tube  21  (see  FIG. 3 ). The diameter D T  of the pot space  34  corresponds to the inner diameter D I1  of the drive section  21   a  of the guide tube  21  in which the driving piston  22  is located. Thus, during the operation of the percussion mechanism  20 , at active or switched-on air spring  25 , the percussion piston  23  can be displaced into the drive section  21   a  of the guide tube  21 . An anvil section  21   b  of the guide tube  21 , remote from the drive section  21   a , has a greater inner diameter D I2  than the drive section  21   a  so that the pot section  39  of the anvil  24  can be received in the guide tube  21 , provided the diameter D T  of the pot space  34  is equal to the inner diameter D I1  of the section  21   a  of the guide tube  21 . 
   On the percussion piston  23 , there is provided at least one circumferential second seal  28  for sealing against the inner surface of the pot section  29  of the anvil  24  or against the inner surface of the drive section  21   a  of the guide tube  21 . The driving member  22  also has at least one annular third seal  37  that seals the driving member  22  against the inner surface of the drive section  21   a  of the guide tube  21 . For aeration of the space between an end of the percussion piston  23 , adjacent to the impact and  30  of the anvil  24 , and the anvil  24 , two aeration bores  32  are formed in the end region of the pot section  39  adjacent to the impact end  30 . The aeration bores  32  communicate with the aeration openings  31  in the guide tube  21 . 
     FIG. 2  shows, as discussed above, the power tool  10 , shown in  FIG. 1 , in its operational condition in which the working tool  15 , which is received in the chuck  14 , is pressed against a workpiece (not shown). The anvil  24  is located in a position in which it extends farthest into the guide tube  21  in the direction of the driving member  22 . In this position of the anvil  24 , the valve  26  is closed because the valve section  36  of the anvil  24  sealingly abuts the first seal  27 , and the space between the driving member  22  and the percussion piston  23  does not communicate with the aeration openings  35  (see  FIG. 3 ). The air spring  25  is active or is switched on, and the percussion mechanism  20  works normally. 
     FIG. 3  shows, as it has already mentioned above, the power tool in a condition in which it is not pressed with the working tool  15 , which is secured in the chuck  14 , against a workpiece. The anvil  24  is in its end position adjacent to the working tool  15 . In this position of the anvil  24 , the valve  26  is open, as the valve section  36  of the anvil  24  is spaced from the first seal  27 . As a result, the space between the driving member  22  and the percussion piston  23  communicates with the aeration openings  35 . The air spring  25 , which is located between the driving member  22  and the percussion piston  23  is inactive or is switched off. The percussion mechanism  20  produces an empty impact because the percussion piston  23  cannot be displaced and cannot apply an impact to the working tool. 
     FIG. 4  shows a further embodiment of the inventive percussion mechanism  20  of the hand-held power tool  10  shown in  FIG. 1 . As in the embodiment of the percussion mechanism  20  shown in  FIGS. 2-3 , the percussion mechanism  20  includes a guide tube  21  in which a driving member  22 , which is formed as a driving piston, reciprocates. For producing a reciprocating movement of the driving member  22 , a rod  29 , which is pivotally supported on the driving member  22 , connects the driving member  22  with an eccentric  17  mounted on the output shaft  16  of the drive gear  13 . An anvil  24  is axially displaceably supported in the guide tube  21 . The anvil  24  has an elongate bar-shaped extension  40  that has, at its end region adjacent to the driving member  22 , a valve section  36  of the valve  26  and which forms a closing body of the valve  26 . The percussion piston  23  is formed as an annular member and is axially displaceably supported on the extension  40 , engaging the cylindrical surface of the extension  40  with an annular seal  38  located in an annular groove formed in the inner surface of the percussion piston  23 . On the outer circumference of the percussion piston  23 , there is arranged a further circumferential seal  38  that seals the percussion piston  23  against the inner wall of the guide tube  21 . The driving member  22  has an annular section  22   a  likewise with inner and outer circumferential seals  27  and  37 . Further, the inwardly located seals  27  and  28  of the driving member  22  an the percussion piston  23  would be referred to, respectively, as first and second seal, and the outwardly located seals  37 ,  38  of the driving member  22  and the percussion piston  23 , respectively, will be referred to as third and fourth seals. The annular opening of the driving member  22  functions as an aeration opening  35  and cooperates with the valve section  36  of the anvil  24 . The valve section  36  of the anvil  24  forms, together with the first seal  27 , the valve  26 . 
     FIG. 4  shows the anvil  24  in a first position (continuous lines) in which it is displaced in the guide tube  21  farthest in the direction of the driving member  22  because the power tool  10  ( FIG. 1 ) is pressed with the working tool  15  against a workpiece (not shown). In this position of the anvil  24 , the valve  26  is closed as the valve section  36  tightly abuts the first seal  27  provided in the aeration opening  35  in the driving member  22 , closing the aeration opening  35 . The air spring  25 , which is located between the percussion piston  23  and the driving member  22 , is active or switched on, and the percussion mechanism  20  functions normally. 
   In  FIG. 4 , the anvil  24  is also shown (with dash lines) in its end position, adjacent to the chuck, in which the hand-held power tool  10  is not pressed against a workpiece. In this position of the anvil  24 , the valve  26  is open as the valve section  36  of the anvil  24  is spaced from the first seal  27 , and the aeration opening  35  in the driving member  22  is open, so that the space between the driving member  22  and the percussion mechanism  23  communicates with the opening  35 . The air spring  25  between the driving member  22  and the percussion member  23  in inactive or is switched off. The percussion mechanism  20  produces an empty impact because the percussion piston  23  cannot be displaced and cannot impact the working tool which is received in the chuck. 
   For the description of elements with reference numerals not mentioned in the description of  FIG. 4 , reference should be made to the description of  FIGS. 1-3 . 
   Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.