Abstract:
A hand-held power tool, in particular a rotary hammer, is indicated that includes a machine housing ( 10 ) with a tool fitting ( 12 ) integrated therein, the tool fitting ( 12 ) being rotatably drivable in a first mode and being non-rotatably fixable on the machine housing ( 10 ) in a second mode, and that includes a duty-type switch ( 20 ) with a coupling element ( 21 ) capable of being displaced to activate the modes, and an actuating element ( 22 ) that induces its displacement. To prevent maloperation and resultant damage to the machine when the operator switches between modes, the actuating element is designed as an electrical actuator ( 23 ), preferably as an electromagnet ( 25 ) controlled by an electronic control unit ( 24 ) (FIG.  1 ).

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
   The invention described and claimed hereinbelow is also described in German Patent Application DE 102004012433.7 filed on Mar. 13, 2004. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
   BACKGROUND OF THE INVENTION 
   The present invention is directed to a hand-held power tool, in particular a rotary hammer. 
   With a known hand-held power tool designed as a rotary/chisel hammer, the tool fitting is fixedly connected with a rotary or drive sleeve that is drivable in a rotatory manner by a driven wheel of a drive transmission situated on the rotary sleeve. The tool held in the tool fitting in an axially limited, displaceable manner is acted upon in the axial direction by an impact mechanism that impacts the shank end of the tool in a pulsed manner via a ram or a beatpiece. The hand-held power tool is selectively operable in the “impact drilling” mode or the “chiseling” mode. The tool is acted upon by the impact mechanism in both modes. In the “impact drilling” mode, in which an impact drill is inserted in the tool fitting, the tool fitting and, therefore, the tool are driven in a rotatory manner. In the “chiseling” mode, in which a chiseling tool is inserted in the tool fitting, the tool fitting is non-rotatably fixed to the mounting housing, and the chiseling tool only makes a hammering motion via the action of the impact mechanism. A duty-type switch is used to switch between modes, the switch including a manually operated rotary knob and an engaging fork capable of being displaced by the rotary knob. A coupling ring is installed on the engaging fork, the coupling ring fixedly coupling the rotary sleeve with the driven wheel of the drive transmission in a first displacement position and, in a second displacement position, fixedly joining the rotary sleeve with the machine housing. In an intermediate position, the coupling ring engages with neither the driven wheel nor the machine housing, so that the rotary sleeve and, therefore, the tool fitting, are free to rotate without being driven. 
   In the case of hand-held power tools with a rotating tool, operator errors, work piece faults or destruction of the tool can cause forces to act on the hand-held power tool that the operator is unable to control and, under certain circumstances, can result in injury to the operator. 
   In the case of a known hand-held power tool with a rotating tool (EP 0 771 619 B1), a system is installed with which uncontrolled jamming is detected and the resultant rotational motion of the machine housing is braked and limited. The system includes a sensor that detects the movement quantity that characterizes the special dimensions of the hand-held power tool as a whole, e.g., acceleration, rotational speed, or rotational travel of the machine housing, an operator that generates a control signal when a predefined threshold value of the movement quantity supplied by the sensor is reached or exceeded, and an actuator that interrupts the drive for the rotating tool based on the control signal from the operator. The actuator is designed as a separating clutch in the drive train of the tool and/or as a switch for turning off the drive motor and/or as a clutch for abruptly connecting the drive train with the machine housing. 
   SUMMARY OF THE INVENTION 
   The hand-held power tool according to the invention, has the advantage that, by replacing the method of switching modes from the use of a manual rotary knob to the use of an electronically controlled actuator, a switching-over between modes that is independent of the operator is carried out that rules out switching over during operation and thereby reduces maloperation and component wear, resulting in a longer service life of the machine overall. In the simplest case, the mode is preselected by the operator using a button located on the machine housing. In a more luxurious design, the modes are set automatically in that a sensor senses the type of tool inserted in the tool fitting and sends a corresponding characteristic signal to the electronic control unit, which sets the associated mode. In the latter case, an increased safety aspect results, since the risk of accidents is prevented, specifically accidents that are caused by the hand-held power tool being set in a mode that does not match the machining tool inserted in the tool fitting, e.g., the “impact drilling” mode with a chiseling tool inserted in the tool fitting. 
   Due to the measures listed in the further claims, advantageous further developments and improvements of the hand-held power tool described in Claim  1  are made possible. 
   According to an advantageous embodiment of the present invention, a manually operated, electric switch for turning the machine on and off is located on the machine housing, the electric switch being designed as a “deadman&#39;s switch” to provide an additional level of safety to the operator during drilling, i.e., in the “impact drilling” mode when the tool is rotating, it must be held manually in its closed position against the force of a reset spring. When the switch is released, the circuit is opened and the machine comes to a standstill. Since a “deadman&#39;s switch” of this type is not required in the “chiseling” mode with a tool fitting fixed to the machine housing, according to an advantageous embodiment of the present invention, an electromagnet controlled by the control device is assigned to the electric switch, the magnetic force of the electromagnet being greater than the spring force of the reset spring. The control unit is designed such that it provides an excitation current to the electromagnet in the mode with a non-rotating tool, the excitation current holding the electric switch in the closed position even when the operator is not actuating the switch. 
   According to an advantageous embodiment of the present invention, the electric switch is configured such that it can be manually lifted away from the energized electromagnet to be moved to its open position, so that the machine can also be turned off at any time during exclusively impact operation. Since the power supply to the electromagnet is also interrupted when the electric switch is opened, the electric switch must be closed before power can be resupplied to the electromagnet. 
   In a further embodiment of the present invention, the electronic signal for switching between modes can also be used to activate the booster function—which is known per se—in the hand-held power tool. A booster function of this type adjusts the electric drive motor after the switchover to the exclusively impact mode. 
   According to an advantageous embodiment of the present invention, a sensor connected to the control unit for detecting a tool jam in the mode with a rotating tool fitting is located on the machine housing, and the control unit is configured such that it de-energizes the electric motor when a sensor signal is received and triggers the actuator to switch to the mode with a tool fitting installed on the machine housing, or to allow the tool fitting to freewheel. Due to this design feature, a safety feature for an uncontrolled jam is easily integrated in the hand-held power tool that utilizes existing components and requires no additional hardware except for the sensor to detect the jam. By triggering the actuator accordingly, it is possible to fix the drive sleeve that starts the tool rotating to the machine housing or to allow it to rotate freely without being driven. 
   The present invention is described in greater detail below with reference to an exemplary embodiment shown in the drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  Shows a schematized side view of a hand-held power tool, with some sections exposed, 
       FIG. 2  Shows an enlarged illustration of section  11  in  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The hand-held power tool shown schematized in a side view in  FIG. 1  is designed as a rotary hammer that is selectively operable in a “impact drilling” mode or a “chiseling” mode. The hand-held power tool includes a machine housing  10  with an integrally-moulded bow handle  11  for holding the machine. A tool fitting  12  is integrated in machine housing  10  on the end of machine housing  10  opposite bow handle  11 , into which said tool fitting  12  a replaceable tool  13  is insertable such that it is non-rotatable and displaceable in an axially limited manner. In the impact drilling mode, tool  13  is an impact drill. In the hammering or chiseling mode, it is a chiseling tool. Although not shown, tool fitting  12  is fixedly coupled to a drive sleeve  14  that is rotatably supported in machine housing  10 , drive sleeve  14  being drivable in a rotatory manner by an electric motor  19 , shown here in a schematized view, via toothed gearing  15  configured here as bevel gearing. Toothed gearing  15  includes a driven wheel  16  that is rotatably mounted on drive sleeve  14  and a pinion  17  that meshes with driven wheel  16 . Pinion  17  is non-rotatably situated on driven shaft  18 , which is driven either directly or via an intermediate gearing  43  by electric motor  19 . Although not shown, an impact mechanism is also driven by electric motor  19 , which strikes the end face of tool  13  retained in tool fitting  12  via an impact piston guided in an axially displaceable manner in drive sleeve  14 , and rams or beatpieces, with an intermediate air cushion. An example of the design of the impact mechanism is described in DE 28 20 128 A1. 
   A duty-type switch  20  is provided for setting the duty types or modes, duty-type switch  20  including an axially displaceable coupling element  21  and an actuating element  22  that induces the displacement. Coupling element  21  is designed such that, in a first displacement setting, it fixedly couples driven wheel  16  of toothed gearing  15  with drive sleeve  14  and, in a second displacement setting, non-rotatably fixes drive sleeve  14  to machine housing  10 . To this end, actuating element  22  includes an electrical actuator  23  and an electronic control unit  24  that controls actuator  23 . In the exemplary embodiment in  FIG. 1 , electrical actuator  23  is designed as an electromagnet  25 . As an alternative, electrical actuator  23  can also be an electrical servomotor. Coupling element  21  actuated by actuator  23  includes an engaging fork  26  and an intermediate ring  27  with inner toothing  271  fastened to engaging fork  26  ( FIG. 2 ). When electromagnet  25  is energized, engaging fork  26  is displaceable against the force of a reset spring  28 . Reset spring  28  designed as a compression spring in this case bears against engaging fork  26  on one side and against a support  29  fixed to machine housing  10  on the other side. Holder  29  encloses drive sleeve  14  via an integrally-moulded retaining sleeve  291 . On its end section facing driven wheel  16 , retaining sleeve  291  includes an outer annular toothed section  30 . On its end section facing holder  29 , driven wheel  16  includes an outer gear rim  31 , the tooth spacing of which matches the tooth spacing of toothed section  30  on retaining sleeve  291 . Between retaining sleeve  291  and driven wheel  16 , a toothed wheel  32  with outer toothing is non-rotatably situated on drive sleeve  14 , the tooth spacing of which also matches the tooth spacing of toothed section  30  and gear rim  31 . Toothed wheel  32 , via its end face, abuts retaining sleeve  291  and driven wheel  16  and has an axial width that is slightly greater than the axial width of intermediate ring  27 . Intermediate ring  27  engages via its inner toothing  271  in outer toothing of toothed wheel  32  and, depending on the displacement, can also engage with gear rim  31  on driven wheel  16  or with toothed section  30  of retaining sleeve  291 . In the first-mentioned displacement position of intermediate ring  27  that it assumes via action of reset spring  28  when electromagnet  25  is not energized, driven wheel  16  is non-rotatably connected via intermediate ring  27  with toothed wheel  32 , so that driven wheel  16  is non-rotatably connected with drive sleeve  14 . In the second displacement position, in which intermediate ring  27  is moved against the force of reset spring  28  via displacement of engaging fork  26  when full current is supplied to electromagnet  25 , toothed wheel  32  is fixedly connected with toothed section  30 , so that drive sleeve  14 —on which toothed wheel  32  is non-rotatably mounted—is held on holder  29  in a non-rotatable manner. In the first displacement position of intermediate ring  27 , the hand-held power tool operates in the “impact drilling” mode, in which the rotary drive and the impact mechanism are both active, and in the second displacement position of intermediate ring  27 , the hand-held power tool operates in the “chiseling” mode, in which tool  13  is driven only by the impact mechanism. 
   Duty-type switch  20  also includes a button  33  located on machine housing  10 , with which the operator can manually preselect the desired mode. Button  33  is connected to control unit  24  via a connecting line  34  indicated in  FIG. 1  with dashed lines. The line that connects control unit  24  with electromagnet  25  is labelled  35 . 
   An electric switch  36  is used to turn electric motor  19  of hand-held power tool on and off, the electric switch being supplied with current in this case, as is control unit  24 , by a rechargeable battery  44 . Electric switch  36  can be actuated manually using a flip switch  37  and, in fact, in a manner such that when flip switch  37  is pressed, switch  36  is closed and, when flip switch  37  is released, switch  36  opens. Flip switch  37  is reset using a compression spring  38 . Electric switch  36  is designed as a “deadman&#39;s switch” as a safety feature for the operator so that the drive of hand-held power tool can be switched off by releasing flip switch  37 . 
   When electric switch  36  is closed, power is also supplied to control unit  24 . The preselect signal supplied by button  33  for the desired mode of the hand-held power tool is processed in control unit  24  and, depending on the specification, either energizes or de-energizes electromagnet  25 . If the “chiseling” mode was preselected, electromagnet  25  is energized, and it moves engaging fork  26  with intermediate ring  27  against the force of reset spring  28  into the displacement position shown in  FIGS. 1 and 2 , in which intermediate ring  27  non-rotatably fixes drive sleeve  14  to retaining sleeve  291 . When the electric motor is switched on, it only drives the impact mechanism, while driven wheel  16 —which was also set into rotation by electric motor  19 —rotates freely on drive sleeve  14 . If the “impact drilling” mode was preselected, electromagnet  25  is de-energized by control unit  24 , and reset spring  28  pushes engaging fork  26  with intermediate ring  27  in  FIGS. 1 and 2  to the right until inner toothing  271  of intermediate ring  27  engages in gear rim  31  on driven wheel  16 . Driven wheel  16  is now non-rotatably connected via intermediate ring  27  and gear rim  32  with drive sleeve  14 , and tool  13  is now also driven rotatively via drive sleeve  14  and tool fitting  12 . 
   Since the “deadman&#39;s” function of electric switch  36  is not required—nor is it desired—in the “chiseling” mode, for safety reasons, an electromagnet  39  is assigned to electric switch  36 , electromagnet  39  being connected to control unit  24  by a connecting line  40 . Electromagnet  39  is designed such that, when energized, it produces a magnetic force that is greater than the reset force of compression spring  38 . If the “chiseling” mode was preselected using button  33 , control unit  24  initiates the energization of electromagnet  39 , which holds electric switch  36  in the closed position against the force of compression spring  38 , even when flip switch  37  of electric switch  36  is released. To also allow the impact mechanism to be brought to a standstill at any time in the “chiseling” mode, flip switch  37  is designed in the manner of a rectangular lever with a long lever arm  371  and a short lever arm  372 . If the operator, using a finger, presses long lever arm  71  of flip switch  37 , electric switch  36  is moved into its closed position, in which it is held in the “chiseling” mode by energized electromagnet  39 . If the operator presses short lever arm  372 , electric switch  36  is returned to its open position against the magnetic force of electromagnet  39 , and the current supply to electric motor  19  is interrupted. 
   In a further embodiment of the hand-held power tool, the electronic switchover between modes is not carried out via preselection by the operator, but rather automatically, depending on the type of tool  13  inserted in tool fitting  12 . To this end, a sensor  41  is installed in tool fitting  12 , which detects the presence of a tool  13  in tool fitting  12  and the type of tool  13 , i.e., it determines whether it is an impact drill or a chiseling tool. Sensor  41  is connected to electronic control unit  24  via connecting line  42 . Button  33  with connecting line  34  is not provided. If electric switch  36  of the hand-held power tool is now closed, sensor  41  outputs a tool-classification signal to control unit  24 . If the classification signal is characteristic for a chiseling tool, electronic control unit  24  initiates energization of electromagnet  25 , and the “chiseling” mode is set in the drive setting, i.e., electric motor  19  drives only the impact mechanism. If the classification signal supplied by sensor  41  to control unit  24  is characteristic for an impact drilling tool, control unit  24  does not initiate energization of electromagnet  25 . Reset spring  28  serves to set the “impact drilling” mode in the drive system. Electromotor  19  drives the impact mechanism and drive sleeve  14 . 
   As shown schematically in  FIG. 1 , the power-supply connection of electromotor  19  to rechargeable battery  44  takes place via switch contact  451  of an electromagnetic relay  45  situated in the connecting line  46  of electromotor  19  and rechargeable battery  44 . Relay  45  is triggered by control unit  24 . Relay  45  is energized and relay contact  451  remains closed for as long as electric switch  36  remains closed. Duty-type switch  20  is also used to equip the hand-held power tool with a safety feature in case of an uncontrolled jam. A jam occurs when, due to an operator error or a work piece fault, the rotating tool is braked extremely or stops altogether and, as a result, intense rotation of the housing of the hand-held power tool is triggered, which can result in injury to the operator. To this end, a sensor  47  is located in machine housing  10  that senses when a tool is jammed and outputs an appropriate output signal to control unit  24  via connecting line  48 . To this end, the sensor detects a movement quantity of machine housing  10 , e.g., its acceleration or speed or a path of rotation. This movement quantity is compared with a predefined threshold in control unit  24 . If the sensor signal reaches or exceeds this threshold, control unit  24  de-energizes relay  45 , so that relay contact  451  opens and electric motor  19  is turned off. Control unit  24  also triggers energization of electromagnet  25 . Energized electromagnet  25  displaces engaging fork  26  against the force of reset spring  28  until intermediate ring  27 —and its inner toothing  271  connected with it—disengage from gear rim  31  on driven wheel  16 , so that driven wheel  16  rotates freely on drive sleeve  14  and the drive train that rotates tool  13  is interrupted. By way of a corresponding level of energization of electromagnet  25 , intermediate ring  27  is either displaced until its inner toothing  271  engages with toothed section  30  on retaining sleeve  291  and therefore non-rotatably fixes drive sleeve  14  via toothed wheel  32  to machine housing  10 , or it is displaced only so far that inner toothing  271  meshes only with toothed wheel  32 . In the latter case, drive sleeve  14  and, therefore, tool fitting  12 , remain free to rotate without being driven.