Patent Publication Number: US-2007107920-A1

Title: Motor driven drilling hammer

Description:
This application claims Paris Convention priority of EP 05 024 979.6 filed Nov. 16, 2005 the complete disclosure of which is hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      The invention concerns a motor-driven drilling hammer with a percussion and rotary drive, and a drill sleeve which is disposed in a housing.  
      One problem of drilling hammers is that the percussion drive causes strong vibrations transferred from the percussion mechanism to the housing and handle components. It has been proposed to provide a demolition hammer with a spring/mass system, wherein the oscillations caused by the axially operating percussion drive are damped by a mass which is pretensioned on both sides by springs.  
      It is the underlying purpose of the present invention to effectively reduce vibrations in drilling hammers.  
     SUMMARY OF THE INVENTION  
      This object is achieved with a drilling hammer of the above-mentioned type in that the drill sleeve is connected on its outer periphery to a spring means of an elastomeric material which has a wall thickness of 1 to 10 mm, wherein the spring means has a damping mass which can be displaced in the peripheral and longitudinal directions of the drill sleeve relative thereto due to the elasticity of the spring means, thereby effecting damping to reduce vibrations.  
      In the inventive drilling hammer, the damping mass may oscillate in a translatory and also rotary direction. The spring/mass system is thereby designed, such that oscillation of the damping mass in the translatory and rotary directions is, in each case, counter-phased to the oscillations of the drill sleeve, such that these oscillating frequencies are cancelled or effectively damped. This reduces the overall oscillation excitation of the drilling hammer by these two main components. In accordance with the invention, it has turned out that, especially for small and medium-sized drilling hammers, the vibrations at the handle are primarily generated by the percussion and rotary forces acting on the tool. Since the percussion and rotational speed of drilling hammers remain largely constant during operation, the oscillations can advantageously be damped to reduce vibrations. The inventive design reduces vibrations in a highly effective fashion, since translatory and also rotary oscillations can be damped.  
      The inventive arrangement of the damping mass permits cancelling of at least two dominant excitation frequencies by one single mass. The design of the spring/mass system depends on the geometry and weight of the damping mass, and the geometry and design of the elastomeric spring means. In order to reduce e.g. the damping frequency, the elastomeric mass may be thicker or the weight of the damping mass may be increased. This must be achieved in each case through suitable design of the spring/mass system in correspondence with the frequencies to be damped, which are generated during operation of the drilling hammer.  
      With particular advantage, the elastomeric material may continuously surround the drill sleeve in the peripheral direction, and be substantially cylindrical. This produces a very load-resistant connection between the damping mass and the drill sleeve, which is also largely insensitive to shearing loads. In certain cases, it may also be advantageous to segment the elastomeric material, i.e. to provide several bordering or spaced-apart segments of elastomeric material on the outer periphery of the drill sleeve or to provide the elastomeric material with perforations, recesses or openings in a radial, tangential or axial direction.  
      For the use of small and medium-sized drilling hammers, a wall thickness of the elastomeric material of 4 to 8 mm has proven to be advantageous. In one further preferred embodiment, the elastomeric material has an axial extension in the longitudinal direction of the drill sleeve of 5 to 20 mm.  
      The damping mass may moreover advantageously be substantially cylindrical. This yields a symmetric mass distribution which is uniform and continuous in the peripheral direction around the drill sleeve, which is suitable in view of vibration damping. The axial extension of the damping mass may advantageously also be 5 to 20 mm. It is preferably 3 to 8 times its wall thickness.  
      The damping mass/spring system is moreover advantageously designed to damp vibrations of between 30 and 100 Hz. For smaller drilling hammers, the oscillations to be cancelled are preferentially between 70 and 80 Hz.  
      Further features, details and advantages of the invention can be extracted from the enclosed claims, the drawing and the following description of a preferred embodiment of the inventive drilling hammer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       FIG. 1  shows a sectional view of a relevant region of a drilling hammer; and  
       FIG. 2  shows a perspective view of the drilling hammer according to  FIG. 1 , illustrating the rotary drive of the drill sleeve. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The figures show a region  2  comprising the drive components of an inventive drilling hammer. A region comprising the electromotor and a handle region of the drilling hammer are not shown. A main drive shaft extends through the indicated rotary duct  4  into the region  2  and drives a shaft  6  (in a manner not shown). The shaft  6  has a wobble plate arrangement  8  (best shown in  FIG. 2 ) which drives a percussion mechanism  10  of the drilling hammer, and a toothed wheel  12  (only shown in  FIG. 2 ) which rotates a drill sleeve  14 .  
      The percussion mechanism  10  has a sleeve  18 , which defines a cylindrical chamber  16  and can be moved, i.e. axially reciprocated, by the wobble plate arrangement  8  in the longitudinal direction  20  of the drill sleeve  14 . The sleeve  18  is disposed inside the drill sleeve  14 , concentrically thereto, and can be axially moved relative thereto. A free flight body is provided as beater  22  within the cylindrical chamber  16 , which forms a pneumatic spring  24  together with the sleeve  18 . When the sleeve  18  is accelerated to the left in  FIG. 1  by the wobble plate arrangement  8 , the beater  22  initially remains in its position due to its inertial mass, thereby forming an underpressure within the cylindrical chamber  16 , which then causes delayed acceleration of the beater  22 . When the sleeve  18  is moved again to the right in  FIG. 1 , the cylindrical chamber and the air contained therein are compressed, in particular to between  10  and  20  bar, which greatly accelerates the beater  22  towards the right and towards an intermediate piston  26 . The impact surface  28  of the beater  22 , facing the intermediate piston  26 , strikes the intermediate piston  26  and is thereby immediately stopped, wherein the momentum is transferred to the intermediate piston  26  which subsequently strikes a tool, a drill or chisel, transferring a further momentum (percussion or hammer operation). When the intermediate piston  26  rebounds to the left in  FIG. 1 , it strikes the drill sleeve  14  via an intermediate elastomeric ring  30 , thereby generating vibrations which are transferred to the housing of the device and which are experienced by the user as being unpleasant.  
      A spring means  32  of an elastomeric material  34  is provided on the outer periphery  31  of the drill sleeve  14 . In the example shown, the spring means  32  or the elastomeric material  34  continuously surround the outer periphery  30  of the drill sleeve  15  in the peripheral direction. It is substantially cylindrical and has a wall thickness of between 1 and 10, in particular, 4 and 8 mm. A damping mass  36  which also has a cylindrical basic geometry, is provided radially outside on the elastomeric material  34 , and in the example shown, concentrically to the drill sleeve  14 . The damping mass  36  can be deflected in a resilient fashion relative to the drill sleeve  14  by the spring means  32  of elastomeric material in an axial, longitudinal direction  20  as well as in a peripheral direction. The connection between the damping mass  36  and the drill sleeve  14  basically provides six degrees of freedom due to the elastomeric material  34 . The damping mass/spring system is designed such that, due to the resilient deflectable arrangement of the damping mass  36 , the damping mass  36  can oscillate in a translatory and rotary direction with a respective phase which is opposite to that of the excitation oscillations acting on the drill sleeve, to thereby damp, cancel, or provide effective reduction of vibration. This eliminates two main components of the overall oscillation excitation of the drilling hammer.