Abstract:
A pile hammer includes a cylinder, a piston displaceably guided in the cylinder, and a striker displaceably guided in the cylinder. The striker is disposed underneath the piston in the operating position of the pile hammer. A combustion chamber is delimited axially by a face surface of the striker that lies in the interior of the cylinder and by a face surface of the piston. Using at least one fuel feed device a predetermined amount of fuel can be introduced into the combustion chamber during each work cycle. The piston has a cavity that is filled, at least in part, with a movable filler.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicant claims priority under 35 U.S.C. §119 of European Application No. 14162394.2 filed Mar. 28, 2014, the disclosure of which is incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a pile hammer comprising a cylinder, a piston displaceably guided in the cylinder, and a striker displaceably guided in the cylinder. 
         [0004]    2. Description of the Related Art 
         [0005]    With pile-driving concrete pillars, the problem regularly exists that the low maximally permissible pressure and tension stresses in the pillar require special measures to prevent damage to the concrete pillars. For this purpose, a damping package is disposed between the workpiece of the pile-driver and the pillar, in order to counteract damage to the concrete pillar. 
         [0006]    It is a disadvantage of the known arrangement that a damping package must be affixed before pile-driving every concrete pillar, thereby increasing the effort and expenditure. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention wishes to provide a remedy for this situation. The invention is based on the task of making available a pile hammer that allows pile-driving concrete pillars, without the requirement of an additional damping package. According to the invention, this task is accomplished by means of a pile hammer including a cylinder, a piston displaceably guided in the cylinder, and a striker displaceably guided in the cylinder. The striker is disposed underneath the piston in the operating position of the pile hammer. A combustion chamber is delimited axially by a face surface of the striker that lies in the interior of the cylinder and by a face surface of the piston. Using at least one fuel feed device, a predetermined amount of fuel can be introduced into the combustion chamber. The piston has a cavity that is filled, at least in part, with a second filler that is different from the piston material. 
         [0008]    With the invention, a pile hammer is made available that allows pile-driving concrete pillars, without the requirement of an additional damping package. By configuring the piston to have a cavity that is filled at least in part with a movable filler, damping of the impact is achieved. As a result, damage to the concrete pillar is counteracted without the requirement of an additional damping package. 
         [0009]    In a further development of the invention, the cavity of the piston is closed off by way of a lid releasably connected with the piston. In this way, the introduction of different fillers is made possible, in contrast to non-releasable attachment—which is also possible—by means of welding, for example, thereby making it possible to adjust different damping, depending on the material of the pillar to be pile-driven. Preferably, the filler is formed by a bulk material or a liquid. In particular, quartz sand or also metal blasting media, particularly steel or aluminum blasting media, are used here as bulk materials. Suitable liquids are oil or water, for example. 
         [0010]    In a further development of the invention, the filler is formed from particles having an essentially round geometry. In this way, a low settling time of the material is achieved, thereby bringing about an optimal damping progression. 
         [0011]    In a further embodiment of the invention, a projection for engagement of a disengagement device is disposed on the piston at its end opposite the combustion chamber. In this way, the lifting groove of the cylinder can be eliminated, because the lifting procedure takes place entirely outside of the cylinder. 
         [0012]    In a further embodiment of the invention, an encapsulation hood is provided, which can be set onto a concrete pillar and has an opening for the striker to pass through. Alternatively, the encapsulation hood can also be configured so that it can be attached to the cylinder of the pile hammer. In this way, sound-absorbing mantling of the impact surface is brought about, thereby bringing about a reduction in the noise emissions. Because the impact of the striker on the pillar represents a main sound source, a significant reduction in the noise level during the pile-driving process is thereby brought about. It is advantageous to dispose at least one sound-absorption element on the encapsulation hood, surrounding the passage opening. More or less homogeneous or fibrous materials are particularly suitable as sound-absorption elements, the thickness of which is defined through the lower frequency at which almost complete absorption of the impacting sound waves can still be achieved. A corresponding absorption can also be achieved by means of the placement of a suitable flow resistance, for example in the form of a nonwoven fiber fabric, which is stretched onto a perforated metal sheet having a perforation in the form of holes or slits, for example, which perforation is sufficiently large and distributed as uniformly as possible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. 
           [0014]    In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
           [0015]      FIG. 1  is a schematic representation of a pile hammer in the form of a diesel pile driver; 
           [0016]      FIG. 2  is a representation of the piston of the pile hammer from  FIG. 1 ; 
           [0017]      FIG. 3  is a schematic representation of the placement of an encapsulation hood between pile hammer and concrete pillar; and 
           [0018]      FIG. 4  is a schematic representation of the upper segment of the pile hammer from  FIG. 1 , with the disengagement apparatus disposed on it. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    Referring now in detail to the drawings, the pile hammer shown in  FIG. 1  selected as an exemplary embodiment comprises a cylinder  1  that is open on both sides, and regularly can have a length of 3 to 8 meters and a diameter of 0.2 to 1.5 meters. A piston  2  is displaceably disposed in the cylinder  1 . A striker  3  coaxial to the piston  2  engages into the open lower end of the cylinder  1 , in displaceable manner. A ring-shaped bearing unit  9  is attached at the lower end of the cylinder  1 , in which unit a central shaft section  31  of the striker  3  is guided in tight and displaceable manner. Central shaft section  31  has an outside diameter that is reduced as compared with the inside diameter of the cylinder  1 . The pile hammer is mounted so as to be vertically displaceable along a leader, by way of guide jaws  13  disposed on the cylinder  1 . 
         [0020]    A striker plate  32  that lies below the cylinder  1  is formed onto the lower end of the shaft section  31 , the lower convex delimitation surface  33  of which plate, directed outward, interacts with the upper end of a concrete pillar  8  shown in  FIG. 3  to be pile-driven during operation. 
         [0021]    A piston section  34  having multiple circumferential sealing rings, spaced apart from one another axially, which run on the inner mantle surface  11  of the cylinder  1 , is formed onto the upper end of the shaft section  31  of the striker  3 . A combustion chamber  12  is delimited by the top of the piston section  34  of the striker  3 , together with the underside of the piston  2  as well as the inner mantle surface  11  of the cylinder  1 . The face surface of the striker  3  that faces the combustion chamber  12  of the cylinder  1  is ground to be planar with a flat fuel bowl  30 . 
         [0022]    A damping ring  91  is disposed between the striker plate  32  of the striker  3  and the bearing unit  9  of the cylinder  1 . A further damping ring  92  is disposed adjacent to the bearing unit  9 , between the top of the bearing unit  9  and the underside of the piston section  34  of the striker  3 . 
         [0023]    A lower working end  23  of the piston  2 , provided with circumferential sealing rings  93  spaced apart from one another axially, runs in the interior of the cylinder  1 , above the striker  3 . The lower free face surface  21  of the piston  2 , which is ground to be planar, is set off by means of a radially circumferential step. 
         [0024]    A mass section  22  that extends into the upper section of the cylinder  1  and has a cavity  24  ( FIG. 2 ) on the inside is formed onto the lower working end  23  of the piston  2 . The cavity  24  is closed off with a lid  25  shown in  FIGS. 2 and 4  on its end of the piston  2  that lies opposite the face surface  21 . In the exemplary embodiment, the lid  25  is attached to the piston  2  by way of screws  251 . The lid  25  is provided with a threaded bore  252  in its center. The threaded bore  252  serves for engagement of a screw anchor—not shown—for handling of the lid  25 . A projection  26  is formed onto the piston  2  on the end side, running circumferentially on the outside, in the region of the lid  25 . The projection  26  serves for accommodating the hooks  71  of a disengagement apparatus  7 . In the exemplary embodiment, the cavity  24  of the piston  2  is filled with quartz sand. 
         [0025]    An injection apparatus  4  is disposed on the circumference wall of the cylinder  1 , which apparatus comprises a fuel pump  41  that is connected with the injection nozzle  42  by way of a line  43 . The inlet of the fuel pump  41  is supplied with diesel oil by way of a fuel tank  5 . 
         [0026]    The fuel pump  41 , connected with the fuel tank  5  by way of the line  43 , has a biased pump lever  44  that projects into the interior of the cylinder  1 , by way of which lever the pump is driven as the dropping piston  2  moves past it. The injection nozzle  42  is configured and oriented in such a manner that the fuel emitted is sprayed approximately onto the center of the face surface of the striker  3  in an essentially cohesive stream. 
         [0027]    Furthermore, a lubricant dispenser  51  is disposed on the cylinder  1 , which dispenser is connected with lubricant nozzles distributed in the circumference direction of the cylinder  1 . The lubricant is dispensed between the piston  2  and the inner mantle surface  11  of the cylinder  1  by means of the lubricant nozzles. 
         [0028]    In  FIG. 3 , use of the pile hammer with an encapsulation hood  6  is shown. The encapsulation hood  6  is configured essentially as a hollow cylinder and has a ring-shaped sound absorption element  61  on its end facing the pile hammer, which element delimits the passage opening  62 . Below the sound absorption element  61 , a pillar accommodation  63  is disposed in the encapsulation hood  6 , which accommodation is provided with an elastomer layer  64  on its side facing the pillar  8 . The encapsulation hood  6  serves to reduce the sound emissions during impact of the striker  3 . 
         [0029]    The pile hammer described above works as follows: In the starting state, the piston  2  is raised into an upper position by way of a disengagement apparatus  7 . For this purpose, the hook  71  of the disengagement apparatus  7  engages into the projection  26  of the piston  2  and the piston  2  is subsequently pulled upward by way of the hook  71 , which hook is connected with a cable winch  72  for this purpose. After disengagement of the hook  71 , the piston  2  falls downward under the effect of gravity, closes the working connectors  16 , and activates the pump lever  44  of the injection apparatus  4  with its face surface  21 , thereby causing the injection nozzle  42  to spray fuel onto the fuel bowl  30  of the striker  3 . Here, an ignitable mixture of fuel droplets and air is formed by means of impact atomization. 
         [0030]    When the piston  2  impacts the striker  3 , a force directed downward is exerted by the striker  3 , and, by way of the striker  3 , on the concrete pillar  8 , which force drives the concrete pillar  8  further into the ground. Because of the quartz sand introduced into the cavity  24  of the piston  2 , the impulse of the piston is damped, thereby counteracting damage to the concrete pillar during impact. In this connection, the sound emitted during impact of the piston  2  on the striker  3 , and, by way of the striker  3 , onto the concrete pillar  8 , is reduced by means of the encapsulation hood  6 . 
         [0031]    During the subsequent upward movement of the piston  2 , triggered by the explosion-like combustion of the fuel, the piston  2  releases the working connectors  16  again, thereby causing the combustion gases to relax and to flow away by way of the working connectors  16 . The piston  2  is now accelerated further upward, drawing fresh air in through the working connectors  16 , until it has reached its upper end position and the work cycle, as described, is repeated. 
         [0032]    Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.