Patent Publication Number: US-2002000325-A1

Title: Hand-held hammer drill

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The invention relates to a hand-held hammer drill for drilling holes, cutting slots for receiving cables, or the like in concrete, stone or similar materials.  
       [0003] 2. Description of the Related Art  
       [0004] For machining concrete, stone or similar materials, impact drilling machines and hammer drills with a rotating tool spindle are used in which, for example, a drill bit, in particular, with a hard metal chisel tip, is used. By means of a hammer mechanism the tool spindle is caused to perform an oscillating longitudinal movement so that the chisel tip of the inserted drill bit chisels pieces from the brittle material to be machined. As a result of the rotational movement of the tool spindle and of the drill bit in connection with a groove extending spirally about the drill bit, the material pieces that have been chiseled out are transported away so that a hole results. In so-called impact drilling machines, the oscillating impact action of the tool spindle is caused, for example, by an axial cam disc. The transmittable impact energy and the corresponding drilling efficiency depend to a great extent on the pressing force or contact pressure of the impact drilling machine against the material to be drilled which force must be applied by the operator. A high drilling efficiency requires thus a high force application by the operator which can result in an undesirable, quick fatigue.  
       [0005] Hammer drills with a pneumatically driven hammer mechanism are also known in which the oscillating hammer action of the tool spindle is caused by application of an oscillating air pressure. Such hammer drills require only a minimal pressing force but because of the pneumatic drive in connection with the space and weight limitations of a hand-held device, only a limited impact energy results. At times, this limitation can result in an unsatisfactory drilling efficiency, especially for very hard materials to be machined or a large number of holes to be drilled.  
       SUMMARY OF THE INVENTION  
       [0006] It is an object of the present invention to develop a hand-held hammer drill such that its handling is facilitated.  
       [0007] In accordance with the present invention, this is achieved in that the hand-held hammer drill comprises a tool spindle, which is rotatable about a rotational axis and is oscillatingly movable in the direction of the rotational axis in the longitudinal direction of the tool spindle and is configured for receiving a drill, a chisel or the like. The hammer drill comprises a housing with an electrical drive motor arranged therein for realizing the rotational movement of the tool spindle and with a hammer mechanism for generating the oscillating longitudinal movement of the tool spindle, wherein the hammer mechanism is hydraulically driven and the hydraulic pressure is generated by a hydraulic pump arranged in the housing.  
       [0008] Accordingly, the present invention suggests to drive the hammer mechanism of the hammer drill hydraulically and to provide the hydraulic pressure within the device. With this configuration, a hammer drill of a comfortable size with significantly increased specific impact or hammer energy is provided, while a large size and unreliable drive hydraulic supply lines are eliminated. In this connection, the hammer mechanism together with the hydraulic drive, relative to the obtainable impact or hammer energy, can be lightweight and compact so that an operator can easily perform even difficult tasks such as, for example, overhead drilling or the like, with reduced physical stress. It is preferred in this context to embody the tool spindle and the hammer mechanism separate from one another wherein both have a contact surface. The contact surfaces face one another and can be brought into contact with one another. Accordingly, the operator can press the hammer drill with the clamped drill bit with reduced pressing force against the material to be drilled. In the hammer mechanism, which operates independently from the tool spindle, the impact energy is built up and is then transmitted via the contact surfaces, according to the principle of a hammer, onto the tool spindle or the drill bit and thus onto the workpiece. This provides at the same time a high drilling efficiency with reduced force expenditure of the operator. The hammer mechanism is preferably embodied as a system comprised of a cylinder and a push rod with a piston guided in the cylinder, and, in particular, the hammer mechanism is arranged aligned with the axis of the tool spindle. Accordingly, while avoiding force deflections and energy losses, a direct transmission of the hammer or impact energy from the push rod onto the tool spindle is ensured. In a preferred embodiment of the invention, the piston can be loaded with hydraulic pressure on both ends in the hammer action direction as well as in the opposite return direction. Accordingly, the push rod performs a return movement even without applying pressing force, and this also results in a relief for the operator.  
       [0009] In an advantageous embodiment, the piston has an effective piston surface area in the return direction which is smaller than the effective piston surface area in the hammer action direction. Preferably, the active piston surface area active in the return movement direction is approximately 10% of the effective piston surface area in the hammer action direction. This realizes, on the one hand, a high push rod speed in the hammer action direction and thus a high impact energy. On the other hand, the return of the piston together with the push rod is realized with a reduced force so that a reduced vibration load results. Moreover, a simple control of the hammer mechanism can be achieved in that the piston surface area effective in the return direction is continuously loaded with a high hydraulic pressure. A suitable control device then must only control the pressure acting in the hammer action direction in that the corresponding piston surface area is alternatingly loaded with high and low hydraulic pressures. When a high pressure is applied, the force acting in the hammer action direction is greater, because of the larger effective piston surface area, than the hydraulic force acting in the return direction. When switching from high hydraulic pressure to low hydraulic pressure, the total force acting in the return direction is greater in the case of a suitable piston surface area ratio, so that the piston together with the push rod is returned. For controlling the hammer mechanism, it is thus only required to provide a simple control valve which acts on the hammer action side of the piston so that the constructive and manufacturing technological expenditure can be maintained at a low level.  
       [0010] Expediently, a hydraulic circuit is provided in the hammer drive which comprises a low-pressure part, a high pressure part, and a hydraulic pump arranged therebetween, which generates, especially continuously, high hydraulic pressure in the high pressure part. Accordingly, a suitable pressure potential is permanently available which can be supplied, as needed, with a suitable control device and with minimal losses to the hammer mechanism. The hydraulic pump is advantageously a gear pump so that a simple configuration with a high efficiency is provided. In an expedient further development, the hydraulic pump is driven by the drive motor of the hammer drive. Accordingly, an additional drive can be eliminated, and this is space-saving and cost-saving. In particular, in connection with a hammer mechanism and rotary drive that can be switched on and off as desired, the required power is thus available immediately for both devices, separately or in combination. Advantageously, in the low-pressure part a low-pressure storage chamber for storing hydraulic oil is provided which is divided, in particular, by means of a diaphragm, into a hydraulic chamber filled with hydraulic oil and into a compensation chamber. Accordingly, a hydraulic oil reservoir is available with which, for example, oil losses can be compensated and into which the leakage oil can be returned. By means of the diaphragm, the hydraulic circuit is sealed so that a position-independent working is possible with the hammer drill. By loading the compensation chamber with atmospheric pressure, a substantially constant supply pressure can be achieved in the low-pressure part via the elastic diaphragm. In an analogous manner, in the high pressure part a high pressure storage chamber is provided which is also preferably divided by a diaphragm into a hydraulic chamber and into a compensation chamber. The compensation chamber of the high pressure storage chamber has a pressure of approximately 16 to 18 bar and thus of approximately half the operating pressure of the high pressure part of approximately 34 bar. The filling medium is expediently nitrogen. By means of the high pressure storage chamber, pressure peaks in the high pressure part can be smoothed which can be caused by the hydraulic pump or by the feedback of the hammer mechanism. This ensures an approximately uniform and defined working pressure.  
       [0011] As a control means for the hammer mechanism a control valve has been found to be expedient which is hydraulically actuated. Accordingly, while eliminating a complex mechanical connection of the control valve to the hammer mechanism and while taking advantage of the already present hydraulic circuit, an effective control of the hammer mechanism with minimal constructive and manufacturing technological expenditure can be obtained. In an expedient configuration of the control valve, it is connected to a control line and is configured such that, as a function of the pressure in the control line, it can be switched back and forth between a hammer action position and a return position. The presence of a single control line further simplifies the configuration.  
       [0012] For controlling the control valve, in particular, by means of a single control line, the piston of the hammer mechanism has also correlated therewith a control function. For this purpose, it is provided at its periphery with an annular recess which forms an annular control chamber together with the cylinder. The control chamber is connected with the low-pressure part of the hydraulic circuit so that a low hydraulic pressure is continuously present in the control chamber. The control chamber divides the piston into a hammer action piston and a control piston. In the wall of the cylinder a high pressure opening and a low-pressure opening are provided which are staggered in the axial direction relative to one another. They can be alternatingly covered by the control piston. The high pressure opening and the low-pressure opening are connected with the control line. As a result of the oscillating movement of the push rod together with the control piston and the thus resulting alternating coverage of the high pressure opening and low-pressure opening, an oscillating loading of the control line with high or low hydraulic pressure is realized so that the control valve can be switched back and forth in a simple way between both positions. In this connection, the control piston and the high pressure opening and low-pressure opening are aligned relative to one another such that the movement of the push rod in its return direction can be hydraulically braked or decelerated so that the vibration level of the hammer mechanism and thus of the entire hammer drill is reduced. For a further reduction of the vibration level an anti-vibration device is provided which is active in the hammer action direction and which is embodied, in particular, as a vibration damper with a counter oscillator-suspended from a spring element. With a corresponding adjustment of the spring strength of the spring element and the mass of the counter oscillator, an effective vibration damping action can be provided with simple means.  
       [0013] In an advantageous embodiment of the invention, the rotary drive of the tool spindle and the hammer mechanism can be switched on and off independently of one another. With this measure, it is possible, for example, to operate the hammer drill with rotating tool spindle without hammer action, which can be used, for example, for drilling sensitive tile or the like. Also, with the rotary drive of the tool spindle switched off, the hammer mechanism can be operated alone so that the hammer drive can be used, for example, as an electric chisel for cutting slots for placing cable, tubing or the like. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0014] In the drawing:  
     [0015]FIG. 1 is a schematic overview representation of a hydraulic hammer drill with all the essential components;  
     [0016]FIG. 2 is a schematic illustration of the hydraulic circuit and the hammer mechanism of the hammer drill according to FIG. 1, showing the hammer mechanism in contact with the tool spindle, respectively, the tool;  
     [0017]FIG. 3 shows a detail of the illustration according to FIG. 2 with the push rod in the return movement;  
     [0018]FIG. 4 is an illustration according to FIG. 3 with the control valve being switched for braking the push rod;  
     [0019]FIG. 5 is a representation of the arrangement according to FIG. 3 at the beginning of the hammer action movement of the push rod;  
     [0020]FIG. 6 is an illustration of the arrangement according to FIG. 3 with the push rod shortly before impacting on the tool spindle and with the control valve shown shortly before switching into the position for generating the return movement. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0021]FIG. 1 shows in a schematic overview illustration the hydraulic hammer drill according to the invention. In a housing  43  (only schematically illustrated) an electrical drive motor  3  is arranged which is configured to drive a tool spindle  1 , rotatable about a rotational axis  2 , by means of a first gear stage  44 , a shaft  46 , and a second gear stage  45 . The rotary drive of the tool spindle  1  is, for example, switched off by a longitudinal movement of the shaft  46  in the direction of arrow  55  and can be switched on again by a movement in the opposite direction.  
     [0022] The tool spindle  1  can be longitudinally moved in the direction of the rotational axis  2 , wherein the longitudinal movement is oscillatingly and is actuated by means of a hydraulically driven hammer mechanism  4 . The hammer mechanism  4  can be switched on and off independent of the rotary drive of the tool spindle  1 . The tool spindle  1  and the hammer mechanism  4  can be connected with one another so that the oscillating movement of the hammer mechanism  4  can be directly transmitted onto the tool spindle  1 . In the illustrated embodiment, the two components are embodied separate from one another. Each has a contact surface  5 ,  6  which are facing one another and with which they can be brought into contact with one another. The hammer mechanism  4  comprises a cylinder  7  in which a push rod  8  with a piston  9  is guided. The piston  9  is loadable by means of a control valve  28  on both ends with hydraulic pressure wherein the hydraulic pressure, depending on the position of the control valve  28 , acts in the hammer action direction  10 , indicated by the arrow  10 , or in the return direction  11 , indicated by the arrow  11 . An embodiment of the hammer mechanism  4  can be expedient in which the hydraulic pressure acts only in the hammer action direction  10  and a return movement of the push rod  8  is realized by the contact pressure of a tool clamped in the tool spindle  1 .  
     [0023] For driving the hammer mechanism  4 , a hydraulic circuit  14  with a low-pressure part  15  and a high-pressure part  16  is provided between which a hydraulic pump  17  in the form of a gear pump  18  is arranged. The hydraulic pump  17  arranged in the housing  43  can be driven separately by its own motor; but in the illustrated embodiment it is advantageously driven by the electric drive motor  3  by means of the first gear stage  44 . For storing and returning hydraulic oil, a low-pressure storage chamber  19  is provided in the low-pressure part  15  which is divided by a diaphragm  20  into by a hydraulic chamber  21  and a compensation chamber  22 . The compensation chamber  22  is filled with air and has pressure compensation openings  52  as a result of which it can be loaded with atmospheric pressure. The atmospheric pressure is transmitted via the elastic diaphragm  20  onto the hydraulic chamber  21  as a result of which atmospheric pressure is present in the low-pressure part  15 .  
     [0024] Analogously, a high-pressure storage chamber  23  is provided in the high-pressure part  16  which is divided by a diaphragm  24  into a hydraulic chamber  25  and a compensation chamber  27 . The compensation chamber  27  can be filled via a valve  42  with gas, wherein the gas may be compressed air. In the illustrated embodiment the compensation chamber  27  is filled with nitrogen at a pressure of approximately 16 to 18 bar, wherein the pressure in the compensation chamber  27  determines the static hydraulic pressure within the high-pressure part  16  via the elastic diaphragm  24  when the hydraulic pump  17  is not active. The hydraulic pump  17  provides during operation an operating pressure in the high-pressure part  16  of approximately 34 bar.  
     [0025] For reducing the vibration level resulting from the oscillating movement of the push rod  8  and of the tool spindle  1 , an anti-vibration device  38  which is active in the hammer action direction  10  is provided at the side of the drive motor  3  facing away from the tool spindle  1 . The anti-vibration device  38  can be in the form of an elastic suspension of the hammer mechanism  4 , a suitable arrangement of impact damping means or the like; in the illustrated embodiment it is provided in the form of an adjusted vibration damper  39  with a spring element  40 , connected to the housing  43 , and a counter oscillator  41  suspended on the spring element  40 . The tool spindle  1 , the hammer mechanism  4 , and the anti-vibration device  38  are approximately aligned with one another on a common axis.  
     [0026]FIG. 2 shows in a schematic detail the hammer mechanism  4  and the hydraulic circuit  14  of the hammer drill according to FIG. 1. The push rod  8  and the tool spindle  1  are contacting one another via their two contact surfaces  5 ,  6  so that the push rod  8  can transmit its impact energy onto the tool spindle  1 . The piston  9  has peripherally an annular recess  32  which together with the piston  7  provides an annular control chamber  33 . The control chamber  33  is permanently connected via a low-pressure line  47  with the low-pressure part  15  of the hydraulic circuit  14 . As a result of the annular recess  32 , the piston  9  is divided into a hammer action piston  34  and a control piston  35 . Together with the cylinder  7 , the hammer action piston  34  provides at its end face a hammer action chamber  49  which is connected by means of a hammer action line  51  with the control valve  28 . Moreover, the cylinder  7 , together with the control piston  35  and the push rod  8 , forms an annular return chamber  48  at the side facing the tool spindle  1 . The annular return chamber  48  is continuously connected by means of a high-pressure line  50  with the high-pressure part  16  and the high-pressure storage chamber  23 . The hydraulic pressure in the high-pressure part  16  generates via the effective piston surface area  13  on the control piston  35  a force component onto the push rod  8  in the return direction  11  (FIG. 1). The effective piston surface area  13  is approximately 10% of the effective piston surface area  12  acting in the opposite direction on the hammer action piston  34  by which the push rod  8  is moved in the hammer action direction  10  (FIG. 1) when a corresponding pressure in the hammer action chamber  49  is present. The push rod  8  can be formed as a continuous or unitary part extending through the cylinder  7  as a result of which, via the two effective piston surface areas  12 ,  13  (see FIG. 2- 6 ) acting in both directions, the movement speed of the push rod  8  is approximately identical in both directions.  
     [0027] A high-pressure opening  36  and a low-pressure opening  37  are arranged at the periphery of the cylinder  7  in the area of the control piston  35  and are connected with the control line  29 . They are covered alternatingly by the control piston  35 . According to FIG. 2, the high-pressure opening  36  is covered by the control piston  35 , while the low-pressure opening  37  is open. Accordingly, the control line  29  is connected with the control chamber  33  so that the hydraulic pressure of the low-pressure part  15  of the hydraulic circuit  14  is present therein. The control valve  28  is connected with the control line  29  and configured such that, as a function of the pressure present in the control line  29 , it can be switched back and forth between two switching positions. According to FIG. 2, low hydraulic pressure is present in the control line  29  so that the control valve  28  is switched into the return position  31 . In this return position  31 , the hammer action chamber  49  is connected via the hammer action line  51  with the low-pressure part  51 . The force component resulting from the high hydraulic pressure in the return chamber  48  and acting onto the piston surface area  13  is greater than the force component which results from the hydraulic pressure present in the hammer action chamber  49  and acting on the piston surface area  12 . As a result, starting from the position of the push rod  8  according to FIG. 2, movement of the push rod  8  in the return direction  11  (FIG. 1) begins.  
     [0028] In FIG. 3 a detail of the arrangement according to FIG. 2 is illustrated wherein the push rod  8  is illustrated at a later point in time during its movement in the return direction  11 . The low-pressure opening  37  in this state is covered by the control piston  35  while the high-pressure opening  36  begins to open. The control valve  29  is still in the return position  31 , while, as a result of the beginning opening of the high-pressure opening  36 , the high hydraulic pressure of the return chamber  48  begins to build in the control line  29 .  
     [0029] According to FIG. 4, the high-pressure opening  36  is now completely released by the control piston  35  so that in the control line  29  the high hydraulic pressure of the return chamber  48  is now present. As a result, the control valve  28  is switched into its hammer action position  30  in which the hammer action chamber  49  is connected via the hammer action line  51  with the high-pressure part  16 . As a result of the inertia force of the push rod  8 , it continues to perform a movement in the return direction  11  which is braked in a controlled fashion by the high pressure in the hammer action chamber  49 . As a result of the inertia force of the push rod  8 , hydraulic oil is displaced in the direction of arrow  53  from the hammer action chamber  49  via the hammer action line  51  against the pressure that is present.  
     [0030]FIG. 5 shows the push rod  8  in the braked rest position at its point of reversal facing away from the tool spindle  1 . The control valve  28  is still in the hammer action position  30  so that in the hammer action chamber  49  a high hydraulic pressure is present. However, no volume flow of hydraulic oil through the hammer action line  51  takes place. In this state, the hydraulic pump  17  conveys according to FIG. 1 a volume flow into the high-pressure storage chamber  23 . As a result of the identical high hydraulic pressure in the return chamber  48  and in the hammer action chamber  49  in connection with the differently sized piston surface areas  12 ,  13 , a very fast, high energy movement of the push rod  8  in the hammer action direction  10 , described in more detail in connection with FIG. 6, takes place.  
     [0031] According to FIG. 6, the push rod  8  is accelerated with high speed in the hammer action direction  10  and is shown shortly before the impact of its contact surface  6  on the contact surface  5  of the tool spindle  1 . In the illustrated position, the high-pressure opening  36  is covered by the control piston  35 . High pressure is still present in the control line  29 . The control valve  28  is still in the hammer action position  30 . The low-pressure opening  37  begins to open by movement of the control piston  35  so that the pressure in the control line  29  can be relieved via the control chamber  33  and the low-pressure line  47 . As a result of this, the control valve  28  shortly thereafter is switched into the return position  31  illustrated in FIG. 2. Approximately at the same time, the two contact surfaces  5 ,  6  will then impact on one another so that, because of the fast movement of the push rod  8  in the hammer action direction  10 , the resulting impact energy is transmitted onto the tool spindle  1 . Subsequent thereto, the movement steps of the push rod  8 , which have been illustrated chronologically in FIGS.  2  to  6 , will be carried out, as a result of which an oscillating movement of the push rod  8  as well as of the tool spindle  1  in the direction of the axis of rotation  2  is generated. The hammer mechanism  4  can be configured to be switchable, for example, in that the control valve  28  is secured in the position illustrated in FIG. 6. In the hammer action line  51  a permanent high-pressure remains which continuously forces the push rod  8  with its contact surface  6  against the contact surface  5  of the tool spindle. When releasing the control valve  28 , the hammer action will again start. A further possibility of switching off the hammer mechanism  4  is provided when locking the control valve  28  in the position illustrated in FIG. 3.  
     [0032] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.