Patent Publication Number: US-2016221172-A1

Title: Hand-held Power Tool

Description:
This application claims the priority of International Application No. PCT/EP2014/070294, filed Sep. 24, 2014, and European Patent Document No. 13187206.1, filed Oct. 3, 2013, the disclosures of which are expressly incorporated by reference herein. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to a hand-held power tool, in particular a hammer drill with a pneumatic percussive mechanism. 
     As known from DE 102008054976 A1, among other prior art publications, the percussive mechanism includes a driving piston. The driving piston is coupled by means of a cross pin and a connecting rod to a cam gear or an equivalent rotary drive system. The cross pin fixes the connecting rod on its eye in the driving piston. The cross pin is inserted through a radial boring in the cylindrical surface of the driving piston. A sealing ring to seal the pneumatic chamber of the percussion mechanism is inserted into the cylindrical surface. 
     The sealing ring is subject to significant wear and must be replaced as part of servicing. The service intervals are determined by, among other things, the useful life of the sealing ring. 
     The hand-held power tool according to the invention has a drive system and a pneumatic percussion mechanism. The percussion mechanism contains a beater that moves on a working axis, a driving piston that is connected to the drive system by means of a connecting rod and a pneumatic chamber that couples a movement of the hammer to the driving piston. The connecting rod can swivel around a swiveling axis, preferably with a pin that is suspended in the driving piston. A sealing ring encompasses, in a plane, a cylindrical surface of the driving piston. The swiveling axis lies in the plane defined by the sealing ring. The pin and the sealing ring preferably overlap completely or partly along the working axis or the swiveling axis is located at an offset with respect to the plane in the percussion direction. The plane is perpendicular to the working axis, parallel to the end face of the driving piston and runs through the center of the sealing ring. The location of the swiveling axis and of the driving end of the connecting rod on opposite sides of the sealing ring is favorable for wear. 
     The driving piston preferably has a cylindrical surface that is completely closed or closed. at least in the vicinity of the pin. In particular, there are no borings in the cylindrical surface. 
     In one configuration of the invention, the pin is fixed in the driving piston with a turn-lock fastener. With regard to the turn-lock fastener, in particular a bayonet fastener, it has been found to be advantageous to locate the swiveling axis inside the sealing ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a hammer drill; 
         FIG. 2  shows a driving piston in longitudinal section in the plane II-II; 
         FIG. 3  shows the driving piston in cross section in the plane III-III; 
         FIG. 4  shows the driving piston in longitudinal section in the plane IV-IV; 
         FIG. 5  shows a driving piston in longitudinal section in the plane V-V; 
         FIG. 6  shows the driving piston in cross section in the plane VI-VI; 
         FIG. 7  shows the driving piston in longitudinal section in the plane VII-VII; 
         FIG. 8  shows the driving piston in longitudinal section in the plane VIII-VIII; 
         FIG. 9  shows a driving piston in longitudinal section in the plane IX-IX; and 
         FIG. 10  shows the driving piston in longitudinal section in the plane X-X. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Unless indicated otherwise, in the drawings identical elements or elements with identical functions are identified by identical reference numbers. 
       FIG. 1  is a schematic illustration of a hammer drill  1  using the example of a chiseling hand-held. machine tool. The hammer drill  1  has a tool holder  2  into which one shaft end  3  of a tool, e.g., one end of the drill  4 , can be inserted. The primary drive system of the hammer drill  1  is formed by a motor  5  that drives a percussion mechanism  6  and an output shaft  7 . A battery pack  8  or a power cord supplies the motor  5  with current. A user can guide the hammer drill  1  by means of a hand grip  9  and can initiate the operation of the hammer drill  1  by means of a system switch  10 . In operation, the hammer drill  1  rotates the drill  4  continuously around a working axis  11  and the drill  4  can thereby drill into a substrate in the percussion direction  12  along the working axis  11 . 
     The percussion mechanism  6  is a pneumatic percussion mechanism  6 . A driving piston  13  and a beater  14  are movably guided in a guide tube  15  in the percussion mechanism  6  along the working axis  11 . The driving piston  13  is coupled to the motor  5  by means of a cam  16  and is forced to execute a periodic linear motion. A connecting rod  17  connects the cam  16  with the driving piston  13 . A pneumatic spring formed by a pneumatic chamber  18  between the driving piston  13  and the beater  14  couples a movement of the beater  14  to the movement of the driving piston  13 . The heater  14  can strike a rear end of the drill  4  directly or indirectly transmit a portion of its pulse to the drill  4  by means of an intermediate beater  19  that is essentially static. The percussion mechanism  6  and preferably the other drive components are located inside a machine housing  20 . 
       FIG. 2  shows the driving piston  13  in a longitudinal section in the plane II-II;  FIG. 3  shows the driving piston  13  in a cross-section in the plane III-III;  FIG. 4  is a longitudinal section in the plane IV-IV. The driving piston  13  has a hollow cylindrical base body  21  that is closed on one end surface  22 . The end surface  22  faces the heater  14  and compresses and decompresses the pneumatic spring in the pneumatic chamber  18 . A cylindrical surface  23  of the base body  21  slides along the inside wall of the guide tube  15 . An annular groove  24  is machined into the cylindrical surface  23  near the end surface  22 . A sealing ring  25  is inserted into the groove  24 . The sealing ring  25  is in contact with the guide tube  15  and provides an airtight seal of the pneumatic chamber  18 . 
     The connecting rod  17  is suspended on a pin  26  in the driving piston  13 . The pin  26 , which can be cylindrical, for example, defines a swiveling axis  27  around which the connecting rod  17  can swivel. The connecting rod  17  has an eye at  28  into which the pin  26  is inserted. The connecting rod  17  projects essentially radially from the pin  26 . The pin  26  is fastened perpendicular to the axis  11 . in the driving piston  13 . 
     The swiveling axis  27  of the pin  26  lies in a plane  29  with the sealing ring  25 . The swiveling axis  27  therefore runs through the sealing ring  25 . The eye  28  of the connecting rod  17  is close to or in the center of gravity of the sealing ring  25 . 
     The offset, along the axis  11 , of the swiveling axis  27  from the center of gravity is less than one half the width, measured along the axis  11 , of the sealing ring  25 . Torques acting between the connecting rod  17  and the sealing ring  25  can thereby be advantageously minimized to enhance the sealing property and the service life of the sealing ring. 
     The pin  26  lies completely inside the driving piston  13  and the driving piston  13 , in the vicinity of the pin  26 , has a completely closed cylindrical surface  23 . The pin  26  is fastened in the driving piston  13  by a turn-lock fastener, such as a bayonet fastener, for example. The pin  26  can be inserted in an angular orientation into the hollow cylindrical base body  21 . A length  30  of the pin  26  is smaller than the radially interior dimension  31  of the base body  21  in this first angular orientation. The base body  21  has a radially projecting web  32  which, in another, second angular orientation, reduces the internal dimension  33  to less than the length  30  of the pin  26 . The web  32  is provided at the axial height of the sealing ring  25  with a groove  34  that runs parallel to the circumferential direction  35 . The width, i.e., the dimension along the axis  11 , of the groove  34  is approximately equal to the diameter of the pin  26 . The pin  26  can be rotated into the second angular orientation, wherein its ends  36  projecting beyond the eye  28  are introduced into the groove  34 . The flanks  37 ,  38  of the groove  34  that run perpendicular to the axis  11  chuck the pin  26 . The groove  34  can be provided with a barb  39  that prevents the pin  26  from rotating hack into the first angular orientation. Preferably the groove  34  is closed in a peripheral direction  35  by a flank  40  that runs parallel to the axis  11 , as a result of which a rotation beyond the second angular orientation is prevented. 
     During assembly, the connecting rod  17  is first pre-installed with its eye  28  on the pin  26 , before the pin  26  is inserted into the driving piston  13  and secured. by rotating it. 
       FIGS. 5 to 7  show a variant of the driving piston  13 . The driving piston  13  has a hollow cylindrical base body  21  that is closed, on one end surface  22 . The sealing ring  25  encompasses the closed cylindrical surface  23  of the base body  21 . The cylindrical pin  26  defines the swiveling axis  27  around which the connecting rod  17  is suspended so that it can swivel. The swiveling axis  27  lies in a plane  29  with the sealing ring  25 . 
     The pin  26  is fastened by means of a turn-lock fastener in the driving piston  13 . The pin  26  is chucked between the end surface  22  of the driving piston  13  and two radially inward projecting webs  41 . A plate  42  bridges the axial distance between the webs  41  in the pin  26 . The plate  42  has two radially projecting fingers  43  that are in contact with the two radially inward projecting webs  41  of the base body  21 . The plate  42  has a semi-cylindrical recess  44  that is in contact with the pin  26 . The pin  26  is also in contact, on an annular flank  45  perpendicular to the axis  11 , with the end surface  22 . Stops  46  with a flank  40  pointing in the peripheral direction  35  project along the axis  11  from the flank  45 . 
       FIGS. 9 and 10  illustrate an additional driving piston  47 . The driving piston  47  is connected to a connecting rod  50 . The driving piston  47  has a protuberance  48  on its inside opposite the end surface  22 . The protuberance  48  has the form of a cylindrical segment. The surface  49  of the protuberance  48  has a. constant radius of curvature. The radius of curvature is preferably greater than the distance of the protuberance from the end surface  22 . Accordingly, the axis  53  is offset in the percussion direction  12  outside the driving piston  13 . The surface  49  preferably lies inside the sealing ring  25 , i.e., the sealing ring  25  and the surface  49  overlap along the working axis  11 . The plane  29  defined by the sealing ring  25  preferably intersects the convex surface  49 . The connecting rod  50  has one end shaped into a shell  51 . The shell  51  has a concave surface, the radius of curvature of which is equal to that of the protuberance  48 . The shell  51  lies on the protuberance  48  and by swiveling around the axis  53  can slide along the protuberance  48 . The shell  51  transmits thrust forces along the percussion direction  12  into the driving piston  47 . 
     The shell  51  is held in the driving piston  47  by means of a snap connection. The snap connection contains, for example, two or more swiveling tongues  52  that project radially into the interior of the driving piston  13 . When the connecting rod  50  is installed, the tongues  52  are in contact against a side of the shell  51  facing opposite to the percussion direction  12 .