Abstract:
A drilling and/or percussive hammer comprises a handle and a hammer housing, which can move relative to the handle and inside of which, among other things, a pneumatic spring percussive mechanism is housed. The pneumatic spring of the pneumatic spring percussive mechanism can be ventilated via a no-load operation duct that is opened and closed by a valve. The valve can be opened and closed according to a pressing force acting upon the handle. A delay device controls the valve during closing so that the valve reaches the position corresponding to the detected pressing force only with a time delay. This causes a smooth transition from the no-load operation to the percussive operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drilling and/or percussive hammer having no-load operation control according to the preamble of patent claim  1 . 
     2. Description of the Related Art 
     Such a drilling and/or percussive hammer (hereinafter simply called “hammer”) having an application pressure-dependent no-load operation control is known from DE 101 45 464 A1. There, the hammer has a no-load channel for connecting a hollow space, formed between a drive piston and a percussion piston in a pneumatic spring percussion mechanism, to the surrounding environment, said channel being capable of being opened and closed by a valve. In the flow of force between the grip point of the handle and the hammer housing, there is situated an acquisition device for acquiring an application force that can be applied to the handle by the operator. The valve can be controlled dependent on the acquired application force. 
     The resulting advantages are described in detail in DE 101 45 464 A1. In particular, in this way it is possible for the operator to place the hammer at first gently onto the stone that is to be worked, even if the motor is already activated, and therefore has an increased rotational speed. In this state, the percussion mechanism is still in no-load operation, even if the drive piston in the percussion mechanism is already moved back and forth. The valve is not actuated, with closing of the no-load channel, until the application force is increased by the operator, whereupon an air spring can form in the hollow space between the drive piston and the percussion piston. In this way, percussion operation begins. 
     The hammer described in DE 101 45 464 A1 has proved its usefulness in practice. However, it has turned out that the design described there can be further improved. In particular, due to the fact that during the transition from no-load operation to percussion operation the hammer carries out certain intrinsic movements due to the actuation of the pneumatic spring percussion mechanism and the oscillations that arise therefrom, so that the hammer housing moves relative to the handle held by the operator, it is possible for the valve to close prematurely, so that in the end percussion operation begins suddenly, in a manner that is not anticipated by the operator. 
     OBJECT OF THE INVENTION 
     The object of the present invention is to improve a hammer of the general type described in such a way that a soft application of the hammer can be achieved through a relatively slow transition from no-load operation to percussion operation. 
     The solution of this problem according to the present invention is indicated in patent claim  1 . Advantageous developments of the present invention are defined in the dependent claims. 
     A drilling and/or percussive hammer according to the present invention (simply called “hammer” below) has a valve with which a hollow space situated in the pneumatic spring percussion mechanism and fashioned in order to accommodate an air spring can be brought into connection with the surrounding environment via a no-load channel. The valve is used to open the no-load channel in no-load operation and to close the no-load channel in percussion operation. In addition, an acquisition device is provided for the acquisition of a control quantity that distinguishes between percussion operation and no-load operation. The valve is capable of being opened and closed dependent on the control quantity, and for this purpose assumes a position corresponding to the control quantity. For this purpose, it can be useful to define a boundary value upon the overshooting or undershooting of which the position corresponding to percussion operation or to no-load operation is assumed. 
     According to the present invention, a delay device is provided via which during closing the valve can be controlled in such a way that it reaches the position corresponding to the acquired control quantity with a time delay. 
     As stated above, the closing of the no-load channel by the valve brings about a transition of the pneumatic spring percussion mechanism from no-load operation to percussion operation, because an air spring can then form in the hollow space between the drive piston and the percussion piston. The delay device brings it about that even when the hammer is applied abruptly, or even if there is an increase in the acquired application pressure due to an undesired or unpredictable intrinsic movement of the hammer housing, there nonetheless does not take place an immediate closing of the no-load channel by the valve, corresponding in this case to the increased application pressure. Rather, the valve changes its position in a manner that extends over time, independent of such short-term effects, and assumes the position corresponding to the acquired control quantity only after a certain period of time has elapsed. This has the result that the transition from no-load operation to percussion operation takes place in a relatively gentle manner that can be anticipated by the operator. 
     Advantageously, in contrast, during opening the valve can be controlled in such a way that it essentially immediately reaches a position that corresponds to one of the acquired control quantities, e.g. the application pressure. The opening of the no-load channel is necessary during the transition from percussion operation to no-load operation, and is achieved by lifting the hammer at the handle, and thus by reducing the application pressure. In this case, it is desirable for the hammer to go into no-load operation immediately, i.e. without a time delay, in order to avoid undesired vibrations of the hammer. Correspondingly, the valve should enable an opening of the no-load channel and ventilation of the air spring as immediately as possible. 
     For the closing, in contrast, in a particularly advantageous specific embodiment of the present invention the time delay, i.e. the period of time during which the valve is closed, is dimensioned such that it extends over a span of time of several impact cycles, each comprising a back-and-forth movement of the drive piston. For this purpose, it is useful if the valve changes its position essentially continuously during the span of time defined by the time delay, i.e. closes the no-load channel smoothly, in order to achieve the desired smooth transition from no-load operation to percussion operation. 
     As a control quantity, and thus as a criterion for distinguishing between no-load operation and percussion operation, various quantities are suitable, which can be evaluated alternatively or also in combined fashion. 
     Thus, for example as a control quantity the position of a tool that is acted on by the hammer and/or the position of the percussion piston and/or of a rivet header (intermediate piston) can be taken into account. If, in no-load operation, the hammer is lifted off the stone that is to be worked, the shaft of the tool slides somewhat out of the tool mount of the hammer, thus reaching a forward (relative to the work direction) position. Correspondingly, the rivet header and the percussion piston can also slide forward into a position that can never be reached in percussion operation. The acquisition device is preferably then fashioned so that it is capable of recognizing this forward position and evaluating it as a criterion for no-load operation. 
     In another specific embodiment of the present invention, as a control quantity the position of an actuating element that controls a drive of the drive piston and that can be manipulated by the operator is used. The actuating element can be for example a gas handle or gas lever in a pressurized air hammer, capable of being moved between an open position and a closed position. The term “actuating element” can also refer to a gas pedal for an internal combustion engine, or to an operating button for an electric motor. 
     In a particularly advantageous specific embodiment of the present invention, the application force that can be applied by the operator is evaluated as a control quantity. For this purpose, in the flow of force between a grip point of a handle at which the operator grips or applies pressure to the hammer and a hammer housing in which at least the pneumatic spring percussion mechanism, but generally also the drive, is housed, there is situated an acquisition device for the acquisition of a pressure force that is applied to the handle by the operator and that acts as a control quantity. The valve can be opened and closed dependent on the acquired application force, and in each case the valve assumes a predefined position corresponding to the application force. In particular when a specified boundary value for the application force is exceeded, the valve moves into the closed position, so that the percussion operation of the pneumatic spring percussion mechanism can begin. If, in contrast, the boundary value is undershot, the valve opens the no-load channel, so that the air spring in the percussion mechanism is ventilated and percussion operation is interrupted. 
     According to the present invention, via the delay device the valve can be controlled during closing in such a way that it reaches the position corresponding to the acquired application force with a time delay. 
     In a particularly advantageous specific embodiment of the present invention, the handle at which the operator applies the application force is capable of being moved relative to the hammer housing. The delay device brings it about that the relative movement between the hammer housing and the handle does not result immediately in an immediate closing of the no-load channel, but rather results in a slow change in the cross-section of the no-load channel, i.e., a temporally delayed reduction and finally closing of the no-load channel. 
     Here, between the handle and the hammer housing there can be provided a spring system associated with the acquisition device in order to provide the handle with a pre-tension, with a prespecified spring force, relative to the hammer housing. The displacement of the handle relative to the hammer housing is then essentially proportional to the force applied by the operator. 
     In a particularly advantageous specific embodiment of the present invention, an axially movable sleeve is provided that forms a control element of the valve, and whose axial position is capable of being modified dependent on the application force. The design of this sleeve corresponds to that of a sleeve known from DE 101 45 464 A1. However, according to the present invention the sleeve is connected to the handle only in an axial direction, in such a way (e.g. with a positive fit) that a reduction of the application force on the part of the operator brings about an immediate and proportional change in the position of the valve. 
     Differing from DE 101 45 464 A1, in the present invention the sleeve is connected to the handle in the other, oppositely oriented axial direction not with a positive fit, but rather is coupled thereto in such a way that an increase in the application force, and a concomitant shifting of the handle relative to the hammer housing, brings about, via the delay device, a temporally delayed or temporally extended shifting of the sleeve. Here, “temporally delayed” or “extended” shifting is to be understood as meaning that the sleeve moves with a speed that is essentially lower than the relative speed between the handle and the hammer housing. 
     In a particularly advantageous specific embodiment of the present invention, the drive piston has a hollow construction, and the impact piston is capable of movement in the drive piston. In a cylindrical wall of the drive piston, at least one opening is provided that, depending on the axial position of the drive piston, can form a part of the no-load channel. The drive piston is surrounded by a percussion mechanism tube in which at least one radial opening, allocated to the opening in the wall of the drive piston, is provided, which likewise forms a part of the no-load channel. The percussion mechanism tube in turn is surrounded by the above-described sleeve, which has a radial opening allocated to the radial opening of the percussion mechanism tube. 
     According to the present invention, the sleeve is capable of being axially displaced on the percussion mechanism tube against the action of a spring device in such a way that in order to open the valve the radial opening of the sleeve is capable of being moved over the radial opening of the percussion mechanism tube, while in order to close the valve the sleeve covers the radial opening of the percussion mechanism tube. Here, the spring device presses the sleeve into the closed position, so that in order to open the valve the sleeve has to be displaced against the action of the spring device. 
     In a particularly advantageous manner, the delay device has a hollow space, formed between the sleeve and the percussion mechanism tube, whose volume changes dependent on the relative position of the percussion mechanism tube and the sleeve. The hollow space is essentially sealed off from its surrounding environment, and is continuously connected to the surrounding environment only via a defined delay opening. The delay opening is dimensioned such that it ensures a prespecified air volume stream that depends essentially on the pressure difference between the hollow space and the surrounding environment. 
     In addition, the hollow space can have a non-return valve that provides an additional opening via which an excess air pressure existing in the hollow space can be dismantled as needed. In contrast, air cannot flow into the hollow space via the non-return valve. 
     Particularly advantageously, when the operator increases the application force the valve is moved in such a way that the volume of the hollow space is enlarged by the action of the spring device and the movement of the sleeve, while the speed of movement of the sleeve is defined or limited by the prespecified air volume stream via the delay opening. In particular, the movement speed is lower than the relative speed, brought about by the application force, between the handle and the hammer housing. The sleeve can thus move only relatively slowly into the target position determined by the applied force. Because the sleeve acts as a control element for the valve, the valve also reaches its prespecified end position, defined by the applied force, with a time delay, this position essentially bringing about a completely closed position of the no-load channel. 
     Thus, a gentle closing of the no-load channel is ensured, so that inside the pneumatic spring percussion mechanism the air spring is built up only slowly, thus achieving the desired soft startup of the hammer. 
     In contrast, when the hammer is lifted, a more rapid transition from percussion operation to no-load operation is desirable. The vibration decoupling device moves the handle, now relieved of stress (mostly through the spring action), into its defined initial or rest position. The sleeve coupled to the handle then moves in such a way that the volume of the hollow space between the sleeve and the percussion mechanism tube is reduced, so that an increased air pressure arises in the hollow space. At least a part of the air situated in the hollow space can flow out via the non-return valve. Another, though generally smaller, part will also flow out of the hollow space via the delay opening. In any case, in this way it is possible for the speed of movement of the sleeve to correspond essentially to the relative speed, caused by the vibration decoupling device, between the handle and the hammer housing. This is also ensured in that when this direction of movement takes place there is a positive coupling between the sleeve and the handle. 
     In another specific embodiment of the present invention, the acquisition device has a sensor for the acquisition of a state in which the handle is pressed against, the hammer housing against the action of the spring system, and in order to produce a corresponding pressure signal. The valve can have a valve element that can be controlled mechanically, electrically, electromechanically, or electromagnetically. The pressure signal can be supplied to a control device that correspondingly controls the valve element for the opening and closing of the valve, the closing of the valve being extended over a particular span of time. The control device this ensures that the closing of the valve, i.e. the transition from no-load operation to percussion operation, does not take place suddenly, over a very short span of time, but rather takes place over a longer, prespecified span of time. In this way, the same effects can be achieved as in the purely mechanical solution described above. 
     Preferably, the sensor is fashioned as a proximity sensor or as a force measurement sensor. 
     In addition, it can be advantageous if a position sensor is provided in order to acquire the position of the hammer in space relative to a horizontal plane and in order to produce a corresponding position signal that can be supplied to the control device. The control device then controls the valve element using the evaluation of the pressure signal and of the position signal. Here, a deviation of the position of the hammer from the horizontal plane can be taken into account in such a way that the resulting pressure signal is subjected to a correction, taking into account the effective weights of the handle, of the hammer housing, and of the components contained therein, as well as of a tool. 
     Insofar as the position of the tool, of the percussion piston, and/or of the rivet header is evaluated as a control quantity, it is advantageous if a forward position (relative to a working direction) of the tool, of the rivet header, and/or of the percussion piston is used as a criterion for no-load operation, while a position situated further to the rear (relative to the forward position) is used as a criterion for percussion operation. In no-load operation, the tool (chisel), the rivet header and the percussion piston slide somewhat out of the hammer, thus reaching a no-load position that can never be reached during percussion operation. Thus, the position of the tool, of the rivet header, and of the percussion piston is a suitable criterion for distinguishing no-load operation from percussion operation. 
     In a particularly simple embodiment, the acquisition device includes a device for determining the position of the tool, of the rivet header, and/or of the percussion piston at least two points, one of which can be allocated to no-load operation while the other can be allocated to percussion operation. Correspondingly, it is not necessary to acquire each arbitrary position of the tool, of the rivet header, or of the percussion piston and to provide an uninterrupted, continuous monitoring. Rather, it is sufficient to determine whether the relative components have crossed a boundary between no-load operation and percussion operation. This can be realized in a particularly simple manner if the position of the components is acquired at the two points that are separated by the imaginary boundary. 
     In another specific embodiment of the present invention, a no-load position of the actuating element for the drive (e.g. gas handle) is used as a criterion for no-load operation, while an operating position of the actuating element is used as a criterion for percussion operation. In this way, the position of the actuating element, e.g. in a pneumatic air hammer, is easily evaluated in order to permit the inference of no-load and percussion operation. 
     It is particularly advantageous if the acquisition device has a sensor for acquiring the control quantity and for producing a control signal, and the valve has a valve element that can be controlled mechanically, electrically, electromechanically, or electromagnetically. The control signal can then be supplied to a control unit that correspondingly controls the valve element for the opening and closing of the valve, the closing of the valve being extended over a particular span of time in the provided manner. In this way, independent of the largely purely mechanical solution described above, a mechatronic, electrical, or electronic variant can also be realized. 
     Because the closing of the valve can be controlled electronically, the electronics can also be used to define the time span required for the closing. Here, the acquisition device can also determine whether the operator is at first pressing only lightly on the hammer, and thus not yet calling for full impact power. With the aid of the control electronics, it is then possible to maintain intermediate states when opening and closing the valve as long as the operator is manipulating the hammer in the corresponding manner, e.g. is pressing on it. 
     These and additional advantages and features of the present invention are explained in more detail below with the aid of the accompanying Figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  shows a partial section through a drilling and/or percussive hammer according to the present invention in no-load operation; 
         FIG. 1   b  shows a detail enlargement of  FIG. 1   a;    
         FIG. 1   c  shows another detail enlargement of  FIG. 1   a;    
         FIG. 2   a  shows a partial section, corresponding to  FIG. 1   a , of the drilling and/or percussive hammer in the impact position; 
         FIG. 2   b  shows a detail enlargement of  FIG. 2   a;    
         FIG. 2   c  shows another detail enlargement of  FIG. 2   a ; and 
         FIG. 3  shows a section through another specific embodiment of a drilling and/or percussive hammer according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1   a  shows a drilling and/or percussive hammer, designated “hammer,” having a hammer housing  1  and a handle cover  2  that surrounds large parts of hammer housing  1 . 
     The term “hammer housing”  1  groups together a plurality of assemblies of the hammer, namely in particular a drive (not shown), a wobble finger mechanism  3  driven by the drive, and a pneumatic spring percussion mechanism  4 . In pneumatic spring percussion mechanism  4 , a drive piston  5  is set into axial back-and-forth motion by wobble finger mechanism  3 , causing a percussion piston  6 , also capable of back-and-forth motion in a hollow recess of drive piston  5 , to be driven back and forth via an air spring formed in a hollow space  7 . Percussion piston  6  in turn cyclically strikes the inserted end of a tool  8  (in  FIG. 1   a , this is a breaking chisel) that is held by a tool holding fixture  9 . 
     Hammer housing  1  accommodates at least some of the above-named components and is standardly made of metal. It is surrounded in essential parts by handle cover  2 , which is connected to hammer housing  1  via a known vibration decoupling device (not shown), e.g. via rubber cushions. Handle cover  2  can be made of plastic and can extend forward into the area of tool holding fixture  9 . 
     On handle cover  2  there is provided a handle  10  having a grip point  11  at which the operator can hold the handle and press it against the stone that is to be worked. 
     In a front area of handle cover  2 , another handle  12  is additionally provided that the operator can grasp with his other hand in a known manner for the better guiding of the hammer. 
     As described above, handle cover  2  surrounds essential parts of hammer housing  1 . Of course, variants are also possible in which handle cover  2  surrounds only a part of the hammer housing, in particular the rear part of hammer housing  1 , oriented towards handle  10 . Likewise, it is possible for handle cover  2  not to surround hammer housing  1  at all, but rather to be held behind hammer housing  1  by the vibration decoupling device. The term “handle cover” is therefore not to be interpreted as meaning that hammer housing  1  must be enclosed by this component. 
     The vibration decoupling device situated between handle cover  2  and hammer housing  1  is used to keep the impacts and vibrations that occur during the production of impacts by pneumatic spring percussion mechanism  4 , and during the working of the stone, away from handle cover  2  and thus away from handle  10 , in order to expose the operator to the damaging vibrations as little as possible. The vibration decoupling device ensures that handle cover  2  is capable of movement relative to hammer housing  1 . As can be seen immediately, for this purpose handle  10  can be pressed against hammer housing  1  by the operator in such a way that handle cover  2  is moved forward over hammer housing  1 , in the direction of tool  8 . 
     DE 101 45 464 A1 specifies that when a particular application force is applied, it is ensured that pneumatic spring percussion mechanism  4  changes from a no-load operating mode, in which hollow space  7  is connected to the surrounding environment and the air spring situated therein is ventilated, to a percussion operating mode, in which hollow space  7  is insulated from the surrounding environment so that the air spring can form in the desired manner. 
     For the acquisition of the application pressure that can be applied to handle  10  or to grip point  11  by the operator, an acquisition device is provided. In the specific embodiment shown in the Figures, the acquisition device consists in that the application force against the action of a spring device in the vibration decoupling device brings about a certain displacement of handle cover  2  relative to hammer housing  1 . Since the spring characteristic of the vibration decoupling device is known, it can reliably be inferred that a particular application force will also bring about a particular displacement. In this way, it is also possible for the displacement to be limited by a stop, a force being required to reach the stop that corresponds to a minimum required application force for percussion operation. 
       FIGS. 1   a  to  1   c  show the hammer in the no-load position when hollow space  7  is connected to its surrounding environment, i.e. is ventilated. The precise construction can be better seen in detail enlargements  1   b  and  1   c.    
     In a cylindrical wall of drive piston  5 , an opening  13  is provided in the form of a longitudinal slot. Drive piston  5  is guided radially by a percussion mechanism tube  14  that has a radial opening  15  that corresponds to opening  13  of drive piston  5 . 
     Percussion mechanism tube  14  is surrounded by a sleeve  16  in whose wall there is fashioned a radial opening  17  that corresponds to radial opening  15  of percussion mechanism tube  14 . As can be seen in  FIGS. 1   b  and  1   c , opening  13  and radial openings  15  and  17  are aligned with one another in such a way that they form a no-load channel via which hollow space  7  is brought into connection with the environment surrounding pneumatic spring percussion mechanism  5 . Correspondingly, when there is an axial movement of drive piston  3  no air spring can form in hollow space  7 , so that percussion piston  6  does not tend to follow the movement of drive piston  5 . Pneumatic spring percussion mechanism  4  then also runs in no-load operation when drive piston  5  moves back-and-forth due to the action of the drive. 
     Sleeve  16  is capable of being displaced on percussion mechanism tube  14  against the action of a spring  18  so that radial opening  17  can either, in no-load operation, be situated over radial opening  15 , or, as is explained below on the basis of  FIGS. 2   b  and  2   c , can be displaced in percussion operation in such a way that radial opening  17  is no longer situated over radial opening  15 , so that radial opening  15  is closed by sleeve  16 . Correspondingly, sleeve  16  represents a valve for the no-load channel. 
     The axial position of sleeve  16  is determined on the one hand by the action of spring  18 . On the other hand, sleeve  16  is supported at an end surface by a pin  19  that is in turn held by handle cover  2 . 
       FIGS. 2   a  to  2   c  show the same drilling hammer, but this time in a percussion position, in which the operator applies a force against handle  10 , so that handle cover  2  is displaced forward, in the direction of tool  8  relative to hammer housing  1 . 
     A comparison of  FIGS. 1   a  and  1   b  to  FIGS. 2   a  and  2   b  illustrates the effect on the position of sleeve  16 . 
     In the no-load position according to  FIGS. 1   a  and  1   b , the operator applies no force, or only a slight force, to handle  10 . In some circumstances, he may even lift the hammer up by handle  10 . The vibration decoupling device (not shown) ensures that handle cover  2  will assume the no-load position (initial position or idle position) shown in  FIG. 1   a  relative to hammer housing  1 . In this way, pin  19  presses sleeve  16  against the action of spring  18  into the position that can be seen in particular in  FIG. 1   b , so that the no-load channel is opened and the air spring in hollow space  7  is ventilated. The action of spring  18  is outweighed by the stronger force action of the vibration decoupling device. 
     If, in contrast, the operator applies a force to handle  10 , and handle cover  2  is correspondingly displaced forward, pin  19  fastened to handle cover  2  also travels forward. At first the end-side support of sleeve  16  is missing, so that sleeve  16  is also pressed forward due to the action of spring  18 , as can be seen in particular in  FIG. 2   b . Here, a hollow space  20  forms between percussion mechanism tube  14  and sleeve  16 , in particular between their end surfaces. Because hollow space  20  is essentially sealed off from the surrounding environment, a partial vacuum arises in the space due to the action of spring  18 . The vacuum in hollow space  20  can be dismantled only via a delay opening  21  fashioned in the end surface of sleeve  16 , via which air flows into hollow space  20 . Given a corresponding dimensioning of delay opening  21 , this means that sleeve  16  can move only relatively slowly from the no-load position shown in  FIG. 1   b  into the percussion position shown in  FIG. 2   b . Correspondingly, radial opening  17  also moves only slowly away from radial opening  15 , so that the no-load channel is closed slowly. This means that the transition from no-load operation to percussion operation takes place very gently, in a manner that can easily be anticipated and controlled by the operator. 
     Pin  19  can thus move away from sleeve  16  given a correspondingly rapid and forceful application of pressure to handle cover  2  by the operator. The operator then defines only the end position that can be reached by sleeve  16 , after which it has moved with a time delay in the direction of pin  19 . The time delay, i.e. the slowed axial movement of sleeve  16 , can be preselected in a suitable manner via the dimensioning of delay opening  21 . 
     The present invention thus indicates a delay device that consists essentially of spring  18 , hollow space  20 , and delay opening  21 . 
     After the work is finished, i.e. the hammer has been lifted from the stone being worked or the application force is no longer applied, in contrast a transition from percussion operation to no-load operation that is as fast as possible is desirable in order to protect the operator from undesirable vibrations. For this purpose, radial opening  17  must again be moved over radial opening  15  in order to open the no-load channel. Because here the air in hollow space  20  would form an air spring that would work against this movement, it is necessary for the supply of air in hollow space  20  to be able to be dismantled very quickly. For this purpose, a non-return valve  22  is provided that covers an opening  23  situated under it. For example, non-return valve  22  can be a rubber ring that is set into a peripheral groove and that covers a plurality of openings  23  distributed on the periphery. When the air pressure inside hollow space  20  is increased, the rubber ring of non-return valve  22  is lifted up, so that the air can escape very quickly via openings  23 . In this way, a rapid transition to no-load operation is ensured. 
     The above-described delay device has the effect that a relative movement between the non-cushioned hammer mass (essentially hammer housing  1  with the components contained therein) and the cushioned hammer mass (essentially handle cover  2  or handle  10 ) does not result immediately in an instantaneous change of the cross-sections in the no-load channel, but rather brings about a deliberate time delay or temporal extension. Using such a device, depending on the force applied by the operator the hammer can be held arbitrarily long in a state of reduced impact strength with the full number of hammer impacts. Thus, the operator can keep the drive at full rotational speed so that the percussion mechanism operates with the normal operating frequency without exerting strong impacts on tool  8 . However, when there is a sudden, rapid pressing of the hammer against the stone to be worked, the percussion mechanism will not make the transition to percussion operation equally quickly, but rather, due to the delay device, will require a few impact cycles before the full impact strength is reached. 
     The above example represents only one specific embodiment of the present invention. Of course, additional embodiments of the present invention are also possible. In particular, the increasing of the application force can also be acquired by an electric or electronic acquisition device that communicates a corresponding signal to a control device that controls a valve for the opening and closing of the no-load channel. 
     Here, the position of the hammer can also be taken into account, because the application force to be applied by the operator varies considerably dependent on the position of the hammer. Thus, the operator has to, apply a greater force when working horizontally or when working overhead than when working downward, because in the former cases the weight of the hammer also has to be supported. The resulting application forces and the corresponding consequences for the change between no-load operation and percussion operation can be evaluated or set by the control device in a suitable manner. 
       FIG. 3  shows a section through another specific embodiment of the drilling hammer according to the present invention that is based on the representation according to FIG. 4 from DE 101 45 464 A1. In DE 101 45 464 A1, with reference to this Figure a hammer is described in which a recognition of the force applied by the operator at the handle, and a resulting influencing of the position of the valve that controls the connection of hollow space  7  to the surrounding environment, takes place mechatronically. 
     For this purpose, a valve element  25  is set into a very short no-load channel. Here, the no-load channel is made up only of a recess  26  in percussion mechanism tube  14  and a connecting channel  27  in which valve element  25  is placed. Valve element  25  has in its interior a through-hole, and can be rotated by an actuating element not shown in the Figure. In  FIG. 3 , valve element  25  is rotated into a position in which the through-hole is not situated in the no-load channel, so that the connection between hollow space  7  and the surrounding environment of the pneumatic spring percussion mechanism is interrupted. However, valve element  25  can be rotated by 90° into a position in which the through-hole opens the no-load channel and creates the connection between hollow space  7  and the surrounding environment. 
     Handle  10  is fastened so as to be capable of movement relative to hammer housing  1 , against the action of spring systems  28 . The relative position between handle  10  and hammer housing  1  is acquired using a proximity sensor  29 . Proximity sensor  29  can be designed so that it is able to distinguish only binary states, namely percussion operation and no-load operation, or, alternatively, with the aid of a suitable proximity sensor it is possible to acquire the precise position of handle  10  relative to hammer housing  1  and to evaluate it correspondingly. Instead of proximity sensor  29  it is also possible to situate a suitable force measuring sensor, e.g. inside spring systems  28  or also independently of spring systems, that acquires the force applied by the operator. In addition, it is possible to use a touch-sensitive force measuring sensor in handle  10  itself to directly acquire the force applied to grip point  11  by the operator. 
     Proximity sensor  29  produces a pressure signal that corresponds to the application force, whether it be binary or proportional to the application force, and communicates it to a control device  30 . If control device  30  recognizes that the operator is pressing on the hammer in such a way that a transition from no-load operation to percussion operation is desired, control device  30  controls the valve actuating element (not shown) in order to rotate valve element  25  into the position shown in  FIG. 3 . When the hammer is lifted, and the application force is correspondingly relaxed, the reverse process is introduced. 
     In particular when valve element  25  is rotated into the percussion position in order to close no-load channel  27 , according to the present invention a certain time delay is to be achieved. This means that control device  30  includes the delay device, and controls the valve actuating element in such a way that the desired temporally extended transition can be achieved. 
     In other specific embodiments of the present invention, quantities other than the force applied by the operator can be evaluated as the control quantity. These include in particular the position of tool  8 , the position of percussion piston  6 , or the position of a rivet header (not shown in the Figures) that acts as an intermediate piston between percussion piston  6  and tool  8 . Here, it is not required to acquire the position precisely in each case. The essential thing is to determine a change of the position between the percussion position and the no-load position, and to determine therefrom whether the hammer is in no-load operation or in percussion operation. Thus, it is also not necessary for the position to be determined exactly. Rather, it is sufficient if the location of the relevant component whose position is to be determined is acquired within a certain range.