Abstract:
A machine tool braking apparatus, in particular a hand-held machine tool braking apparatus, of a portable machine tool, includes at least one mechanical braking unit that has at least one movably mounted braking element and includes at least one output unit that has at least one output element. The braking unit includes at least one actuating element that is intended to move the braking element, at least in one operating state, at least substantially perpendicular to an axis of rotation of the output element.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2012/051922, filed on Feb. 6, 2012, which claims the benefit of priority to Serial No. DE 10 2011 005 809.5, filed on Mar. 18, 2011 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     There is already known from DE 195 10 291 C2 a power-tool braking device of a portable power tool that has a mechanical braking unit and an output unit. In that case, the braking unit comprises a movably mounted braking element, and the output unit comprises an output element. 
     SUMMARY 
     The disclosure is based on a power-tool braking device, in particular a hand-held power-tool braking device, of a portable power tool, comprising at least one mechanical braking unit, which has at least one movably mounted braking element, and comprising at least one output unit, which has at least one output element. 
     It is proposed that the braking unit have at least one actuating element, which is provided to move the braking element, at least in one operating state, at least substantially perpendicularly in relation to a rotation axis of the output element. Particularly preferably, the braking unit is provided to brake, upon switch-off of the portable power tool, a rotational motion resulting from mass moments of inertia of an output shaft of the output unit, in particular of a spindle, and/or of a working tool mounted on the output shaft. A “portable power tool” is to be understood here to mean, in particular, a power tool, in particular a hand-held power tool, that can be transported by an operator without the use of a transport machine. The portable power tool has, in particular, a mass of less than 50 kg, preferably less than 20 kg, and particularly preferably less than 10 kg. The expression “mechanical braking unit” is intended here to define, in particular, a braking unit provided to put braking elements of the braking unit into a braking position and/or into a release position, as a result of a moment of inertia and/or as a result of a drive moment, in particular decoupled from a magnetic force. A “braking position” is to be understood here to mean, in particular, a position of the braking element in which at least a braking force is exerted upon a moving component in order to reduce a speed of the moving component, in particular by at least more than 50%, preferably by at least more than 65%, and particularly preferably by at least more than 80%, at least in one operating state. The term “release position” is intended here to define, in particular, a position of the braking element in which an action of the braking force upon the moving component to reduce the speed is at least substantially prevented. 
     The mechanical braking unit is preferably provided to brake the component, starting from a working speed, in a period, in particular, greater than 0.1 s, preferably greater than 0.5 s, and particularly preferably less than 3 s, in particular to a speed that is less than 50% of the working speed, preferably less than 20% of the working speed, and particularly preferably to a speed of 0 m/s. The braking element in this case has at least one brake lining, which is fixed to the braking element. The brake lining may be fixed to the braking element by means of a form-fitting, force-fitting and/or materially bonded connection, such as, for example, an adhesive connection, a riveted connection, a screwed connection or a connection produced by means of a sintering operation or by means of an injection molding method, etc. The brake lining in this case may be realized as a sintered brake lining, as an organic brake lining, as a brake lining made of carbon, as a brake lining made of ceramic, or as another brake lining considered appropriate by persons skilled in the art. Advantageously, the braking element is mounted so as to be movable relative to an output shaft of the output unit, in particular a spindle, in particular mounted so as to be rotatable about a rotation axis of the output shaft, by an angle greater than 2°, preferably greater than 5°, and particularly preferably less than 45°. The expression “mounted so as to be movable” is intended here to define, in particular, a mounting of the braking element, wherein the braking element, in particular decoupled from an elastic deformation of the braking element, has a capability to move along at least a travel distance greater than 1 mm, preferably greater than 10 mm, and particularly preferably greater than 50 mm, and/or a capability to move about at least one axis by an angle greater than 5°, preferably greater than 20°, and particularly preferably less than 45°. Particularly preferably, the braking element is mounted so as to be movable, at least, relative to the actuating element. 
     An “output unit” is to be understood here to mean, in particular, a unit that can be driven by means of a drive unit of the portable power tool and that transmits forces and/or torques, generated by the drive unit, to a working tool. Preferably, the output element of the output unit is realized as a gearwheel. Particularly preferably, the output element is realized as a ring gear. It is also conceivable, however, for the output element to be of another design, considered appropriate by persons skilled in the art, such as, for example, being designed as a shaft, etc. The output unit is preferably realized as a bevel gear transmission. A “bevel gear transmission” is to be understood here to mean, in particular, a transmission having an output shaft disposed with an angular offset relative to an input shaft, the rotation axes of the input shaft and output shaft preferably having a common point of intersection. “Disposed with an angular offset” is to be understood here to mean, in particular, a disposition of an axis relative to a further axis, in particular of two intersecting axes, wherein the two axes enclose an angle other than 180°. Preferably, when the output unit, realized as a bevel gear transmission, is in an assembled state, a rotation axis of the input shaft and a rotation axis of the output shaft enclose an angle of 90°. An “input shaft” is to be understood here to mean, in particular, a shaft that introduces forces and/or torques into the output unit realized as a bevel gear transmission. An “output shaft” is to be understood here to mean, in particular, a shaft, in particular a spindle of the output unit, that transmits forces and/or torques to, for example, a working tool that is connected to the output shaft in a rotationally fixed manner. “Rotationally fixed” is to be understood to mean, in particular, a connection that transmits a torque and/or a rotational motion at least substantially without change. “Transmit at least substantially without change” is to be understood here to mean, in particular, a transmission of forces and/or torques, from one component to a further component, that is complete apart from a loss resulting from friction and/or tolerances. “Substantially perpendicularly” is to be understood here to mean, in particular, an alignment of a direction relative to a reference direction, the direction and the relative direction, in particular as viewed in one plane, enclosing an angle of 90° and the angle having a maximum deviation of, in particular, less than 8°, advantageously less than 5°, and particularly advantageously less than 2°. The design of the power-tool braking device according to the disclosure enables a braking force for braking a moving component, in particular the output-unit output shaft, realized as a spindle, to be generated through simple design means. Advantageously, therefore, a rotational motion resulting from moments of mass inertia of a tool can be braked upon switch-off of the portable power tool. 
     Furthermore, it is proposed that the actuating element, at least in one operating state, act in combination, in a form-fitting manner, with a release element of the braking element. Preferably, the release element is provided, by acting in combination with the actuating element, to hold the braking element in a release position and/or in a braking position, and/or to move the braking element into a release position and/or into a braking position, in particular on a motion path defined by the combined action of the actuating element and the release element. Preferably, the release element and the actuating element engage mutually, at least in one operating state. Particularly preferably, the actuating element in this case is realized as a hook-shaped extension, which is provided to act in combination, in a form-fitting manner, with the release element, which is realized so as to correspond to the hook-shaped extension. In an alternative design of the power-tool braking device, the actuating element engages in the release element, at least in one operating state. It is also conceivable, however, for the release element to engage in the actuating element, at least in one operating state. Preferably, the release element is integral with the braking element. “Integral with” is to be understood to mean, in particular, connected at least in a materially bonded manner, for example by a welding process, an adhesive bonding process, an injection process and/or by another process considered appropriate by persons skilled in the art, and/or, advantageously, formed in one piece, such as, for example, by being produced from a casting and/or by being produced in a single- or multi-component injection process and, advantageously, from a single blank. It is also conceivable, however, for the release element to be connected to the braking element by means of a form-fitting and/or force-fitting connection. Advantageously, it is possible to achieve reliable holding of the braking element in a release position in which action of a braking force is prevented. 
     Preferably, the actuating element is connected to the output element in a rotationally fixed manner. Preferably, the actuating element is integral with the output element. In an alternative design, the actuating element is connected to the output element in a rotationally fixed manner by means of a screwed connection. It is also conceivable, however, for the actuating element to be connected to the output element by means of another form-fitting, force-fitting and/or materially bonded connection, considered appropriate by persons skilled in the art, such as, for example, an adhesive connection, a riveted connection, a screwed connection or a connection produced by means of a sintering operation or by means of an injection molding method, etc. A motion of the braking element by means of the actuating element, in dependence on a motion of the output element, can be achieved through simple design means. Advantageously, therefore, in the case of an interruption of a transmission of torque to the output element, a relative motion of the output element, relative to an output shaft of the output unit, in particular a spindle, can be used to move the braking element. Advantageously, it is possible to dispense with electrical and/or electronic components for moving the braking element. 
     Further, it is proposed that the braking unit have at least one driver element, on which the braking element is pivotally mounted. Preferably, the driver element is connected in a rotationally fixed manner to an output shaft of the output unit, in particular to a spindle. Thus, the driver element, together with the output shaft, is preferably mounted so as to be movable relative to the output element. The braking element is advantageously realized as a brake lever, which, at one end, is pivotally mounted on the driver element. By means of a spring element of the braking unit, the braking element can be biased, relative to the driver element, in the direction of a release position and/or in the direction of a braking position. The spring element in this case may be realized as a compression spring, as a tension spring, as a torsion spring, as a leaf spring, as a strip spring, or as another spring element considered appropriate by persons skilled in the art. Through simple design means, a centrifugal force can be used to move the braking element into a braking position and/or into a release position of the braking element. 
     Advantageously, the braking unit has at least one counter-braking element, which at least partially surrounds the braking element along a circumferential direction, as viewed in a plane running perpendicularly in relation to the rotation axis of the output element. Particularly preferably, the counter-braking element is provided, by acting in combination with the braking element, to convert an energy of motion, in particular an energy of motion of the spindle moving relative to the counter-braking element, and/or an energy of motion of the braking element moving relative to the counter-braking element, into a thermal energy. In this case, for the purpose of generating a braking force that counteracts a rotational motion of the spindle, the braking element and the counter-braking element are brought into direct contact with each other. The counter-braking element in this case may be composed of sintered bronze, steel, nitrided steel, aluminum or another surface-treated steel and/or metal. The mechanical braking unit is therefore preferably realized as a frictional brake. By means of combined action of the braking element and the counter-braking element, a braking force can be achieved through simple design means. 
     Preferably, the counter-braking element is realized as a brake drum. Particularly preferably, the brake drum is of a cylindrical shape, in particular on a side of the brake drum that faces toward the braking element. It is also conceivable, however, for the brake drum to be of another shape, considered appropriate by persons skilled in the art, such as, for example, conical, contra-conical, concave, convex, etc. Further, it is also conceivable for the brake drum to be of a perforated design and/or, on the side of the brake drum that faces toward the braking element, to have recesses, in the form of flutes or the like, which are provided to guide, for example, a lubricant away from a contact surface between the braking element and the brake drum. The brake drum, in particular the side of the brake drum that faces toward the braking element, extends, as viewed in the plane running perpendicularly in relation to the rotation axis of the output element, by 360° along the circumferential direction. Particularly preferably, the brake drum is disposed, fixed to the housing, in a bearing flange and/or in a transmission housing of the output unit. Advantageously, the brake drum is connected to the bearing flange and/or to the transmission housing by means of a force-fitting, form-fitting and/or materially bonded connection. It is likewise conceivable for a design of the bearing flange and/or of the transmission housing with the brake drum to be realized from, for example, a single casting. The bearing flange and/or the transmission housing can be produced from a metal, a metal alloy and/or a plastic. Preferably, the bearing flange and or the transmission housing is/are realized as a metal casting. Advantageously, a mechanical braking unit that is realized as a frictional brake can be constituted. 
     It is additionally proposed that the braking unit comprise at least one cam mechanism, which has at least one cam member provided to act in combination with the actuating element for the purpose of moving the braking element. A “cam mechanism” is to be understood here to mean, in particular, a mechanism that, as a result of a motion of the actuating element and as a result of acting in combination with the cam member, operates a component that, as a result, executes a motion defined by the combined action of the actuating element and the cam member. Preferably, the cam member is realized as a control recess. A “control recess” is to be understood here to mean, in particular, a material relief in which the actuating element engages for the purpose of generating a motion, wherein the actuating element and the control recess are movable, in particular relative to each other. By means of the cam mechanism, a defined motion path of the braking element can be achieved, in the case of a motion from a release position and/or from a braking position, through simple design means. 
     Preferably, the cam member is disposed on the braking element. Particularly preferably, in the alternative design of the power-tool braking device, the braking element is integral with the driver element. The braking element in this case, advantageously, by means of an elastic portion of the driver element and/or by means of a film hinge etc. that is integral with the braking element and the driver element, is mounted such that it can be pivoted relative to the driver element. Advantageously, a compact power-tool braking device can be achieved. 
     In a further alternative design, it is conceivable for the braking unit to be realized as a mountable module. The expression “mountable module” is intended here to define, in particular, an assembly of a unit whereby a plurality of components are pre-mounted and the unit can be mounted as a whole in a complete system, in particular in the portable power tool. The mountable module preferably has at least one fastening element, which is provided to detachably connect the mountable module to the complete system. Advantageously, the mountable module can be demounted from the complete system, in particular, with fewer than 10 fastening elements, preferably with fewer than 8 fastening elements, and particularly preferably with fewer than 5 fastening elements. Particularly preferably, the fastening elements are realized as screws. It is also conceivable, however, for the fastening elements to be realized as other elements, considered appropriate by persons skilled in the art, such as, for example, as quick-action clamping elements, fastening elements that can be actuated without tools, etc. Preferably, at least one function of the mountable module can be realized when demounted from the complete system. Particularly preferably, the mountable module can be demounted by an end user. The mountable module is therefore realized as an exchangeable unit, which can be replaced by a further mountable module, such as, for example, in the case of a defect of the mountable module or an expansion of function and/or change of function of the complete system. The design of the braking unit as a mountable module makes it possible, advantageously, to achieve a wide spectrum of application of the power-tool braking device. Moreover, integration into already existing portable power tools can be achieved through simple design means. Furthermore, advantageously, production costs can be kept low as a result. 
     The disclosure is additionally based on a portable power tool, in particular a portable hand-held power tool, having a power-tool braking device according to the disclosure, in particular having a hand-held power-tool braking device. The portable power tool in this case may be realized as an angle grinder, a drill, a hand-held circular saw, a chipping hammer and/or a hammer drill, etc. Advantageously, a safety function can be achieved for an operator of the portable power tool. 
     The power-tool braking device according to the disclosure and/or the portable power tool according to the disclosure in this case is/are not intended to be limited to the application and embodiment described above. In particular, the power-tool braking device according to the disclosure and/or the portable power tool according to the disclosure, for the purpose of implementing a functioning mode described herein, can have a number of individual elements, components and units that differs from a number stated herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages are given by the following description of the drawings. The drawings show exemplary embodiments of the disclosure. The drawings, the description and the claims contain numerous features in combination. Persons skilled in the art will also expediently consider the features individually and combine them to create appropriate further combinations. 
       In the drawings: 
         FIG. 1  shows a power tool according to the disclosure having a power-tool braking device according to the disclosure, in a schematic representation, 
         FIG. 2  shows a sectional view of a transmission housing, of the portable power tool according to the disclosure and of the power-tool braking device according to the disclosure, that has been demounted from a motor housing of the portable power tool according to the disclosure, in a schematic representation, 
         FIG. 3  shows a further sectional view of the transmission housing and of the power-tool braking device according to the disclosure, in a non-braked state, in a schematic representation, 
         FIG. 4  shows a further sectional view of the transmission housing and of the power-tool braking device according to the disclosure, in a braked state, in a schematic representation, 
         FIG. 5  shows a detail view of a braking unit of the power-tool braking device according to the disclosure, in a schematic representation, 
         FIG. 6  shows a detail view of a mounting plate of the braking unit of the power-tool braking device according to the disclosure, in a schematic representation, 
         FIG. 7  shows a detail view of a driver element of the braking unit having, disposed thereon, braking elements of the braking unit of the power-tool braking device according to the disclosure, in a schematic representation, 
         FIG. 8  shows a sectional view of an alternative embodiment of a power-tool braking device according to the disclosure, in a schematic representation, 
         FIG. 9  shows a detail view of an alternative output element of an alternative output unit of an alternative power-tool braking device according to the disclosure, in a schematic representation, 
         FIG. 10  shows a detail view of a further alternative embodiment of a power-tool braking device according to the disclosure, in a schematic representation, and 
         FIG. 11  shows a detail view of an output element of the alternative power-tool braking device, in a schematic representation. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a portable power tool  12   a , realized as an angle grinder  52   a , having a power-tool braking device  10   a . The angle grinder  52   a  comprises a protective hood unit  54   a , a power-tool housing  56   a  and a main handle  58   a . From the power-tool housing  56   a , the main handle  58   a  extends out, on a side  62   a  of the power-tool housing  56   a  that faces away from a working tool  60   a , in a direction that faces away from the power-tool housing  56   a  and that runs at least substantially parallelwise in relation to a direction of main extent  64   a  of the angle grinder  52   a . The working tool  60   a  in this case is realized as an abrasive disc. It is also conceivable, however, for the working tool  60   a  to be realized as a parting or polishing disc. The power-tool housing  56   a  comprises a motor housing  66   a , for accommodating a drive unit  68   a  of the angle grinder  52   a , and a transmission housing  70   a , for accommodating an output unit  22   a  of the power-tool braking device  10   a . The drive unit  68   a  is provided to drive the working tool  60   a  in rotation, via the output unit  22   a . The output unit  22   a  is connected to the drive unit  68   a , via a drive element  88   a  of the drive unit  68   a  that can be driven in rotation in a manner already known to persons skilled in the art. The drive element  88   a  is realized as a pinion gear, which is connected in a rotationally fixed manner to an armature shaft  90   a  of the drive unit  68   a  ( FIG. 2 ). An ancillary handle  72   a  is disposed on the transmission housing  70   a . The ancillary handle  72   a  extends transversely in relation to the direction of main extent  64   a  of the angle grinder  52   a.    
     The power-tool braking device  10   a  is disposed on the transmission housing  70   a  of the angle grinder  52   a  ( FIG. 2 ). A portion of the power-tool braking device  10   a  extends into the transmission housing  70   a . A portion of the power-tool braking device  10   a  is therefore enclosed by the transmission housing  70   a . The power-tool braking device  10   a  comprises a mechanical braking unit  14   a , which has three movably mounted braking elements  16   a ,  18   a ,  20   a  ( FIG. 3 ), and comprises the output unit  22   a , which has an output element  24   a . The output element  24   a  is realized as a ring gear. The output element  24   a  realized as a ring gear is disposed, by means of clearance fit, on a rotatably mounted output shaft of the output unit  22   a , which output shaft is realized as a spindle  80   a . The output unit  22   a  additionally comprises a bearing flange  82   a  and, disposed in the bearing flange  82   a , a bearing element  84   a  for carrying the spindle  80   a . The bearing flange  82   a  is detachably connected to the transmission housing  70   a  by means of fastening elements (not represented in greater detail here) of the output unit  22   a . Moreover, the working tool  60   a  can be connected to the spindle  80   a  in a rotationally fixed manner by means of a fastening element (not represented in greater detail here), for the purpose of performing work on a workpiece. When the angle grinder  52   a  is in operation, therefore, the working tool  60   a  can be driven in rotation. The power-tool braking device  10   a  additionally has a run-off safety unit  86   a , which is provided to prevent the working tool  60   a , and/or the fastening element for fastening the working tool  60   a , from running off the spindle  80   a  when the power-tool braking device  10   a  is in a braking mode. The run-off safety unit  86   a  in this case is realized as a receiving flange, which is connected to the spindle  80   a  in a rotationally fixed manner by means of a form-fit. It is also conceivable, however, for the run-off safety unit  86   a  to be connected to the spindle  80   a  in a rotationally fixed manner by means of other types of connection considered appropriate by persons skilled in the art. 
     The braking elements  16   a ,  18   a ,  20   a  of the braking unit  14   a  are each realized as brake levers ( FIG. 3 ). In this case, the braking elements  16   a ,  18   a ,  20   a  are disposed in the bearing flange  82   a  of the output unit  22   a . The braking elements  16   a ,  18   a ,  20   a  are disposed around the spindle  80   a , being evenly distributed along a circumferential direction  44   a . The circumferential direction  44   a  runs in a plane that extends perpendicularly in relation to a rotation axis  32   a  of the output element  24   a  realized as a ring gear. Each two of the three braking elements  16   a ,  18   a ,  20   a  that are disposed in series along the circumferential direction  44   a  are disposed at an equal distance from each other along the circumferential direction  44   a . Moreover, the braking elements  16   a ,  18   a ,  20   a  each have a brake lining  74   a ,  76   a ,  78   a . The brake linings  74   a ,  76   a ,  78   a , as viewed along a direction running substantially perpendicularly in relation to the rotation axis  32   a , are disposed on a side of the respective braking element  16   a ,  18   a ,  20   a  that faces away from the spindle  80   a . The brake linings  74   a ,  76   a ,  78   a  in this case are connected to the respective braking element  16   a ,  18   a ,  20   a  by means of a form-fitting, force-fitting and/or materially bonded connection, in a manner already known to persons skilled in the art. In addition, the brake linings  74   a ,  76   a ,  78   a , along the circumferential direction  44   a  and contrary to the circumferential direction  44   a , in each case bear against a stop (not represented in greater detail here) of the respective braking element  16   a ,  18   a ,  20   a , for the purpose of reliably transmitting shear forces and/or thrust forces. 
     The braking unit  14   a  additionally has three actuating elements  26   a ,  28   a ,  30   a  ( FIG. 3 ), which are provided to move the braking elements  16   a ,  18   a ,  20   a , at least in one operating state, at least substantially perpendicularly in relation to the rotation axis  32   a  of the output element  24   a  realized as a ring gear. In this case, respectively one of the actuating elements  26   a ,  28   a ,  30   a  is assigned to respectively one of the braking elements  16   a ,  18   a ,  20   a . The actuating elements  26   a ,  28   a ,  30   a  are connected in a rotationally fixed manner to the output element  24   a  realized as a ring gear. The output element  24   a  has three recesses  92   a ,  94   a  (only two are represented in  FIG. 5 ), realized as threaded bores, which are provided to receive fastening elements  98   a ,  100   a  of the braking unit  14   a , (only two are represented in  FIG. 5 ), which are realized as screws, for fastening a mounting plate  104   a  of the braking unit  14   a . The mounting plate  104   a  in this case has three recesses  96   a ,  140   a ,  142   a , in which the fastening elements  98   a ,  100   a  are disposed when in a mounted state. The actuating elements  26   a ,  28   a ,  30   a  are integral with the mounting plate  104   a  ( FIG. 6 ). Moreover, when in a mounted state, the actuating elements  26   a ,  28   a ,  30   a , as viewed along the circumferential direction  44   a , are disposed uniformly along the circumferential direction  44   a , on the mounting plate  104   a . The mounting plate  104   a , when in a mounted state, is disposed on a side of the output element  24   a  that faces away from a toothing  106   a  of the output element  24   a  realized as a ring gear. 
     For the purpose of moving the braking elements  16   a ,  18   a ,  20   a  by means of the actuating elements  26   a ,  28   a ,  30   a , the braking elements  16   a ,  18   a ,  20   a  have a respective operating element  34   a ,  36   a ,  38   a . The operating elements  34   a ,  36   a ,  38   a , as viewed along the direction running perpendicularly in relation to the rotation axis  32   a  of the output element  24   a , are each disposed on a side of the braking elements  16   a ,  18   a ,  20   a  that faces toward the spindle  80   a  and faces toward the respective actuating element  26   a ,  28   a ,  30   a . The actuating elements  26   a ,  28   a ,  30   a  have a hook-shaped configuration, for the purpose of working in combination with the operating elements  34   a ,  36   a ,  38   a  in a form-fitting manner. The operating elements  34   a ,  36   a ,  38   a  in this case have a hook-shaped configuration that corresponds to the hook-shaped configuration of the actuating elements  26   a ,  28   a ,  30   a . The actuating elements  26   a ,  28   a ,  30   a  and the operating elements  34   a ,  36   a ,  38   a  therefore engage mutually, at least in one operating state. 
     In addition, the braking unit  14   a  has a driver element  40   a , on which the braking elements  16   a ,  18   a ,  20   a  are pivotally mounted ( FIG. 7 ). The driver element  40   a , when in a mounted state, is connected to the spindle  80   a  in a rotationally fixed manner. For the purpose of mounting the braking elements  16   a ,  18   a ,  20   a , the driver element  40   a  has three bearing extensions  108   a ,  110   a ,  112   a , which extend along the direction running perpendicularly in relation to the rotation axis  32  of the output element  24   a . The bearing extensions  108   a ,  110   a ,  112   a  are disposed, uniformly distributed along the circumferential direction  44   a , on the driver element  40   a . In addition, the bearing extensions  108   a ,  110   a ,  112   a  each have a recess for receiving a bearing element  114   a ,  116   a ,  118   a  of the braking unit  14   a . The bearing elements  114   a ,  116   a ,  118   a  are realized as pins. For the purpose of pivotally mounting the braking elements  16   a ,  18   a ,  20   a , the bearing elements  114   a ,  116   a ,  118   a  realized as pins engage in recesses of the braking elements  16   a ,  18   a ,  20   a . The recesses of the braking elements  16   a ,  18   a ,  20   a  are disposed in bearing lugs  120   a ,  122   a ,  124   a  of the braking elements  16   a ,  18   a ,  20   a . The bearing lugs  120   a ,  122   a ,  124   a  each have two portions in which there is disposed a respective recess of the braking elements  16   a ,  18   a ,  20   a . In this case, the bearing extensions  108   a ,  110   a ,  112   a , when in a mounted state, as viewed along the rotation axis  32   a  of the output element  24   a , are each disposed between two portions of the bearing lugs  120   a ,  122   a ,  124   a . The bearing elements  114   a ,  116   a ,  118   a  realized as pins, as viewed along the rotation axis  32   a  of the output element  24   a , therefore extend through the recesses of the braking elements  16   a ,  18   a ,  20   a  that are disposed in the portions of the bearing lugs  120   a ,  122   a ,  124   a , and through the recesses of the bearing extensions  108   a ,  110   a ,  112   a . The bearing lugs  120   a ,  122   a ,  124   a  are each disposed at an end of the braking elements  16   a ,  18   a ,  20   a . The braking elements  16   a ,  18   a ,  20   a , at least in one operating state, can therefore each execute a pivoting motion about a longitudinal axis of the respective bearing element  114   a ,  116   a ,  118   a , which longitudinal axis runs at least substantially parallelwise in relation to the rotation axis  32   a  of the output element  24   a.    
     Furthermore, the braking unit  14   a  has a counter-braking element  42   a  ( FIG. 3 ), which surrounds the braking elements  16   a ,  18   a ,  20   a  along the circumferential direction  44   a , as viewed in the plane running perpendicularly in relation to the rotation axis  32   a  of the output element  24   a . The counter-braking element  42   a  in this case is realized as a brake drum. In this case, the counter-braking element  42   a  is fixed in the bearing flange  82   a  of the output unit  22   a  by means of a form-fitting connection. For this purpose, the counter-braking element  42   a  has a multiplicity of form-fit elements  126   a ,  128   a . The form-fit elements  126   a ,  128   a  are realized as extensions that, as viewed along the perpendicularly in relation to the rotation axis  32   a  of the output element  24   a , are disposed on a side of the counter-braking element  42   a  that faces away from the braking elements  16   a ,  18   a ,  20   a . For the purpose of fixing the counter-braking element  42   a , the form-fit elements  126   a ,  128   a , when in a mounted state, engage in connecting recesses  130   a ,  132   a  of the bearing flange  82   a . It is also conceivable, however, for the counter-braking element  42   a  to be connected to the bearing flange  82   a  by means of another type of connection considered appropriate by persons skilled in the art, such as, for example, by means of a force-fitting and/or form-fitting connection. It is conceivable in this case for the counter-braking element  42   a  to be connected to the bearing flange  82   a  by means of, for example, a press fit and/or by means of an injection molding method. 
     When the angle grinder  52   a  is put into operation, the output element  24   a  realized as a ring gear is driven by means of the drive element  88   a  of the drive unit  68   a , which drive element is realized as a pinion gear. The output element  24   a  in this case first moves relative to the driver element  40   a  that is connected to the spindle  80   a  in a rotationally fixed manner, until the actuating elements  26   a ,  28   a ,  30   a  come into engagement with the operating elements  34   a ,  36   a ,  38   a , and the braking elements  16   a ,  18   a ,  20   a  consequently move, along the direction running perpendicularly in relation to the rotation direction  32   a  of the output element  24   a , in the direction of the spindle  80   a , into the release position of the braking elements  16   a ,  18   a ,  20   a  ( FIG. 3 ). As a result of this, the braking elements  16   a ,  18   a ,  20   a  are moved away from the counter-braking element  42   a . In addition, the actuating element  26   a ,  28   a ,  30   a , owing to the motion relative to the driver element  40   a , along the circumferential direction  44   a , come to bear against sides of the bearing extensions  108   a ,  110   a ,  112   a  that face toward the actuating elements  26   a ,  28   a ,  30   a  along the circumferential direction  44   a . As soon as the actuating elements  26   a ,  28   a ,  30   a  bear against the sides of the bearing extensions  108   a ,  110   a ,  112   a  that face toward the actuating elements  26   a ,  28   a ,  30   a  along the circumferential direction  44   a , and the braking elements  16   a ,  18   a ,  20   a  have been moved away from the counter-braking element  42   a , the braking elements  16   a ,  18   a ,  20   a  are in the release position. When the braking elements  16   a ,  18   a ,  20   a  are in the release position, direct contact between the braking elements  16   a ,  18   a ,  20   a  and the counter-braking element  42   a  is prevented ( FIG. 3 ). As a result of the actuating elements  26   a ,  28   a ,  30   a  bearing against the bearing extensions  108   a ,  110   a ,  112   a , and as a result of the actuating elements  16   a ,  18   a ,  20   a  engaging in the operating elements  34   a ,  36   a ,  38   a , the rotational motion of the output element  24   a  is transmitted to the driver element  40   a , and consequently to the spindle  80   a . The output element  24   a , the driver element  40   a , the braking elements  16   a ,  18   a ,  20   a  disposed on the driver element  40   a , and the spindle  80   a  rotate jointly about the rotation axis  32   a  of the output element  24   a . Consequently, the braking elements  16   a ,  18   a ,  20   a  rotate relative to the counter-braking element  42   a . Owing to the combined action of the output element  24   a , driver element  40   a  and spindle  80   a , the working tool  60   a , which is connected to the spindle  80   a  in a rotationally fixed manner, is driven in rotation. Work can thus be performed on a workpiece by means of the working tool  60   a.    
     Upon switch-off of the angle grinder  52   a , the drive element  88   a , realized as a pinion gear, is braked. The working tool  60   a , which is fastened on the spindle  80   a , continues to rotate because of a mass inertia. Consequently, the spindle  80   a  likewise continues to be rotated about the rotation axis  32   a . The drive element  88   a  brakes the output element  24   a  that is realized as a ring gear. The output element  24   a  is rotated about the rotation axis  32   a , relative to the driver element  40   a , until, as a result of the relative motion, the actuating elements  26   a ,  28   a ,  30   a  strike against sides of the bearing extensions  108   a ,  110   a ,  112   a  that face toward the actuating elements  26   a ,  28   a ,  30   a , contrary to the circumferential direction  44   a  ( FIG. 4 ). During the relative motion of the output element  24   a  and driver element  40   a , the actuating elements  26   a ,  28   a ,  30   a  become disengaged from the operating elements  36   a ,  38   a ,  40   a . As a result of a centrifugal force, the braking elements  16   a ,  18   a ,  20   a  are moved, by means of the pivoted mounting, along the direction running perpendicularly in relation to the rotation direction  32   a , in the direction of the counter-braking element  42   a . It is additionally conceivable for the actuating elements  26   a ,  28   a ,  30   a  to assist a motion of the braking elements  16   a ,  18   a ,  20   a  in the direction of the counter-braking element  42   a  by means of ramp-type inclined surfaces that act in combination with the operating elements  34   a ,  36   a ,  38   a . As a result of the motion of the braking elements  16   a ,  18   a ,  20   a  in the direction of the counter-braking element  42   a , the brake linings  74   a ,  76   a ,  78   a  come into contact with the side of the counter-braking element  42   a  that faces toward the braking elements  16   a ,  18   a ,  20   a . As a result of this, by means of a friction between the brake linings  74   a ,  76   a ,  78   a  and the counter-braking element  42   a , a braking force is generated, for braking the spindle  80   a  and, consequently, the working tool  60   a . The braking elements  16   a ,  18   a ,  20   a  are therefore in the braking position ( FIG. 4 ). Owing to the fact that they are pivotally mounted, and owing to a frictional force that generates the braking force, the braking elements  16   a ,  18   a ,  20   a  become wedged between the driver element  40   a  and the counter-braking element  42   a . The frictional force in this case seeks to pivot the braking elements  16   a ,  18   a ,  20   a  further in the direction of the counter-braking element  42   a , relative to the driver element  40   a . However, this further pivoting motion is prevented, as far as possible, by means of the direct contact between the brake linings  74   a ,  76   a ,  78   a  and the counter-braking element  42   a . Consequently, the spindle  80   a , and the working tool  60   a , are braked to a standstill. When the angle grinder  52   a  is put into operation again, the combined action of the actuating elements  26   a ,  28   a ,  30   a  and operating elements  34   a ,  36   a ,  38   a  results in the braking elements  16   a ,  18   a ,  20   a  being reliably brought out of the braking position and into the release position. 
     The braking unit  14   a , together with the output unit  22   a , is realized as a mountable module  102   a  ( FIG. 5 ). The mountable module  102   a  thus constitutes the power-tool braking device  10   a . The mountable module  102   a  comprises four fastening elements (not represented here), realized as screws. The screws are provided for detachably connecting the mountable module  102   a  to the transmission housing  70   a . If necessary, an operator can demount the mountable module  102   a  from the transmission housing  70   a . The angle grinder  52   a  and the power-tool braking device  10   a  thus constitute a power-tool system. The power-tool system may comprise a further mountable module. The further mountable module may comprise, for example, an output unit realized as a bevel gear transmission. The further mountable module could be mounted on the transmission housing  70   a  by the operator, for example, as an alternative to the mountable module  102   a . An operator therefore has the possibility of equipping the angle grinder  52   a  with the mountable module  102   a  that comprises the braking unit  14   a  and the output unit  22   a , or with the further mountable module that comprises an output unit. For an application in which the angle grinder  52   a  is to be operated separately from the power-tool braking device  10   a , an operator can replace the mountable module  102   a  by the further mountable module of the power-tool system. For this purpose, the operator merely demounts the mountable module  102   a  from the transmission housing  70   a  and mounts the further mountable module on the transmission housing  70   a.    
     Alternative exemplary embodiments are represented in  FIGS. 8 to 11 . Components, features and functions that remain substantially the same are denoted by essentially the same references. To differentiate the exemplary embodiments, the letters a to c are appended to the references of the exemplary embodiments. The description that follows is limited essentially to the differences in respect of the first exemplary embodiment, described in  FIGS. 1 to 7 , and reference may be made to the description of the first exemplary embodiment in  FIGS. 1 to 7  in respect of components, features and functions that remain the same. 
       FIG. 8  shows an alternative power-tool braking device  10   b , which can be mounted on a transmission housing of an angle grinder (not represented in greater detail here) that is realized in a manner similar to the angle grinder  52   a  described in the description of  FIGS. 1 to 7 . The power-tool braking device  10   b  comprises a braking unit  14   b  and an output unit  22   b . The braking unit  14   b  and the output unit  22   b  are of a structure that is at least substantially similar to that of the braking unit  14   a  and output unit  22   a  described in the description of  FIGS. 1 to 7 . The braking unit  14   b  thus has three movably mounted braking elements  16   b ,  18   b  (only two are represented in  FIG. 8 ), and the output unit  22   b  has an output element  24   b . The braking unit  14   b  additionally has three actuating elements  26   b ,  28   b ,  30   b  ( FIG. 9 ), which are provided to move the braking elements  16   b ,  18   b , at least in one operating state, at least substantially perpendicularly in relation to a rotation axis  32   b  of the output element  24   b . The actuating elements  26   b ,  28   b ,  30   b  are integral with the output element  24   b  realized as a ring gear. Furthermore, the braking unit  14   b  has a counter-braking element  42   b , which is realized as a brake drum. The counter-braking element  42   b  is fixed, by means of a press fit, in a bearing flange  82   b  of the output unit  22   b . Reference may be made to the description of  FIGS. 1 to 7  in respect of a mode of functioning of the braking unit  14   b  and of the output unit  22   b.    
       FIG. 10  shows a further alternative power-tool braking device  10   c , which can be mounted on a transmission housing of an angle grinder (not represented in greater detail here) that is realized in a manner similar to the angle grinder  52   a  described in the description of  FIGS. 1 to 7 . The power-tool braking device  10   c  comprises a braking unit  14   c  and an output unit  22 . The output unit  22   c  is of a structure that is at least substantially similar to that of the output unit  22   a  described in the description of  FIGS. 1 to 7 . The output unit  22   c  thus has an output element  24   c  realized as a ring gear. The output element  24   c  realized as a ring gear is disposed, by means of a clearance fit, on an output shaft of the output unit  22   c , which output shaft is rotatably mounted and realized as a spindle  80   c.    
     The braking unit  14   c  has three movably mounted braking elements  16   c ,  18   c ,  20   c . Furthermore, the braking unit  14   c  has a counter-braking element  42   c , realized as a brake drum. The counter-braking element  42   c  is fixed, by means of a press fit, in a bearing flange  82   c  of the output unit  22   c . In addition, the braking unit  14   c  has three actuating elements  26   c ,  28   c ,  30   c , which are provided to move the braking elements  16   c ,  18   c ,  20   c , at least in one operating state, at least substantially perpendicularly in relation to a rotation axis  32   c  of the output element  24   c . For this purpose, the braking unit  14   c  has a cam mechanism, which has three cam members  46   c ,  48   c ,  50   c , which are provided to act in combination with the actuating elements  26   c ,  28   c ,  30   c  for the purpose of moving the braking elements  16   c ,  18   c ,  20   c . The cam members  46   c ,  48   c ,  50   c  are disposed on the braking elements  16   c ,  18   c ,  20   c . The cam members  46   c ,  48   c ,  50   c  are realized as cam-ways. The cam-ways in this case are constituted by control recesses made in the braking elements  16   c ,  18   c ,  20   c . It is also conceivable for the cam members  46   c ,  48   c ,  50   c  to be of another design, considered appropriate by persons skilled in the art, such as, for example, rib-type extensions, etc. The cam members  46   c ,  48   c ,  50   c  thus constitute operating elements  34   c ,  36   c ,  38   c  of the braking elements  16   c ,  18   c ,  20   c . The actuating elements  26   c ,  28   c ,  30   c  engage in the cam members  46   c ,  48   c ,  50   c . In addition, the actuating elements  26   c ,  28   c ,  30   c  are integral with the output element  24   c . The actuating elements  26   c ,  28   c ,  30   c  in this case are realized in the form of pins, and extend away from the output element  24   c  ( FIG. 11 ), on a side that faces away from a toothing  106   c  of the output element  24   c , along a direction running at least substantially parallelwise in relation to the rotation axis  32   c  of the output element  24   c.    
     The braking elements  16   c ,  18   c ,  20   c  are integral with a driver element  40   c  of the braking unit  14   c . The driver element  40   c  is connected to the spindle  80   c  of the output unit  22   c  in a rotationally fixed manner. By means of an elastic portion  134   c ,  136   c ,  138   c  of the driver element  40   c , the braking elements  16   c ,  18   c ,  20   c  are each mounted such that they can be pivoted relative to a region of the driver element  40   c  that is in direct contact with the spindle  80   c . It is also conceivable, however, for the braking elements  16   c ,  18   c ,  20   c  to be connected to each other by means of a film hinge and/or another articulated connection considered appropriate by persons skilled in the art. In addition, by means of the elastic portions  134   c ,  136   c ,  138   c , the braking elements  16   c ,  18   c ,  20   c  are connected in a materially bonded manner to the region of the driver element  40   c  that is in direct contact with the spindle  80   c.    
     Owing to the fact that the actuating elements  26   c ,  28   c ,  30   c  engage in the cam members  46   c ,  48   c ,  50   c , the fact that the braking elements  16   c ,  18   c ,  20   c  are pivotally mounted by means of the elastic portions  134   c ,  136   c ,  138   c , and owing to a relative motion of the output element  24   c  and driver element  40   c , the braking elements  16   c ,  18   c ,  20   c  are moved, in a manner substantially similar to that of the braking elements  16   a ,  18   a ,  20   a  described in the description of  FIGS. 1 to 7 , in the direction of a counter-braking element  42   c  of the braking unit  14   c , into a braking position, and/or in the direction of the spindle  80   c , into a release position.