Abstract:
A shaft locking device for a motor-driven, hand-guided work tool spindle has a driven member fixedly connected thereto, a freewheel with locking members, a ring fixedly connected to the housing and engaged by the locking members in both rotating directions, a drive member coaxially arranged to the spindle with unlocking members cooperating with locking members releasing when the driving member is engaged, thereby releasing the driven member from the ring. Drive member cams are spatially separated from unlocking members wherein they penetrate the locking member. Driven members have catch openings such that both drive and driven members also have torque-transmitting catch surfaces for a motor-driven action of the spindle so that the catch surfaces have a larger distance from one another in a neutral position of the drive member than between the unlocking members and the locking members.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a shaft locking device for the spindle of a motor-driven, hand-guided work tool. 
   A shaft locking device of the aforementioned kind is described in U.S. Pat. No. 3,243,023 which comprises a drive member with four unlocking elements for the locking members of a freewheel and where the unlocking elements are simultaneously designed as cams for engaging a driven member. The torque-transmitting surfaces of the cams and the driven member are designed to be very small in this solution and they are, therefore, subject to wear. 
   It is an object of the invention to create a shaft locking device for the spindle of a motor-driven, hand-held work tool that has a long service life. 
   SUMMARY OF THE INVENTION 
   Due to the spacial separation of unlocking elements and cams, there is space for sufficiently dimensioned torque-transmitting drive surfaces which are practically not subject to any wear. 
   Because of the one-piece design of the spindle and its penetration of the drive member and the driven member, it has a simple design and a stable support. This support of the spindle in connection with a loosely dimensioned support of the drive member on the spindle contributes to the long service life and the efficiency of the work tool, particularly if the drive member is embodied as a toothed wheel. When its teeth are made of plastic, there are noise-related advantages. 
   Because the axial cams penetrate the catch openings, the entire torque transferring drive surfaces are always active, even in the event of axial mounting deviations of the spindle. 
   Because of the positioning of the unlocking members and of the cams, manufacturing advantages exist for turning and milling the drive member. The cams can axially or radially penetrate or extend into the catch openings. 
   The deep-drawing or extruding of the driven member offers also advantages in regard to manufacturing the cams for the locking members and to flattening of the hub. The driven member can also be embodied as a thick disc which is preferably made of sintered steel. This realizes a particularly low wear and safe operation of the shaft locking device. The number of the locking members depends on the magnitude of the operational load. 
   The fixedly driven closing ring serves to limit the axial movement of the locking members of the free wheel and, thereby, its noise development. This is particularly important with hammer devices. In the case of different length ratios, the fixedly driven closing ring can be substituted by a standardized disc and, in the event that no hammer device is present, it can even be left out. 
   Advantageously, the cam surfaces of the cams are radially aligned with the drive surfaces of the catch openings. This provides favorable torque transmission and wear conditions. 
   A particularly torsionally strong connection between the driven member and the spindle is achieved when the driven member is positive-lockingly connected to the spindle. 
   Advantageously, the driven member is force-lockingly connected to the spindle. This can be achieved by a press fit, for example. Thereby, a slip-clutch-like slip between the driven member and the spindle is possible on an extreme load acting on the spindle so that a destruction due to breaking-stress can be avoided. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     More features can be taken from the further claims. The drawings schematically illustrate the embodiments of the invention which are described in the following. It is shown in: 
       FIG. 1  a longitudinal section of the shaft locking device, 
       FIG. 2  a cross-section of the shaft locking device, 
       FIG. 3  a longitudinal section of another shaft locking device, 
       FIG. 4  a cross-section of another shaft locking device, 
       FIG. 5  a longitudinal section of a preferred further embodiment of the shaft locking device, 
       FIG. 6  a cross-section of the preferred further embodiment of the shaft locking device. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2  show a spindle  1  with a thread  29  for the drill chuck and a ball bearing  2  as well as a drive member  3  and a driven member  4 . 
   The interior ring of the ball bearing  2  is axially supported on a shoulder  6  of the spindle  1  by a locking ring  5 . A second bearing provided at the driving end of the spindle  1  is not illustrated. 
   The driving member  3  consists of a toothed wheel  7  that has an end gearing and is supported on the spindle  1 . The toothed wheel  7  is axially fixed with axial play by a further locking ring  8  and a shoulder  9  of the spindle  1 . For noise-related reasons, the gearing can be comprised of plastic. At the end face of the toothed wheel  7  facing the driven member  4 , three unlocking members  10  and three axial cams  11  are arranged in pairs concentrically with respect to one another. The three pairs each have a common center line  12 , and neighboring center lines  12  are provided at equal spacings. 
   The driving member  3  can also be embodied as a planetary gearing and be provided with a two-position gear box. 
   The driven member  4  is provided with a deep-drawn, pot-shaped sheet metal member  13 , whose hub  14  is fixedly connected to the spindle  1  by two flattened portions  15 . The hub  14  can also be fixedly connected to the spindle  1  by a press fit or other kind of frictional connection or by positive locking. In the wall  16  of the sheet metal member  13  facing the drive member  3 , three catch openings  30  embodied as ring segments  17  are provided which are radially engaged with rotary play by the three axial cams  11  of the toothed wheel  7 . The cam surfaces  18  and drive surfaces  19  of the sheet metal member  13 , which face one another in the direction of rotation, are radially aligned and are positioned opposite one another with a clearance. 
   The sheet metal member  13  is provided with an outer ring-shaped wall  20  having an outer shape that is embodied as cams  21  for the locking members  22 . The locking members  22  are positioned as pairs in the area between the catch openings  30  and are arranged between the outer wall  20  and a ring  23  fixedly attached to the housing. The locking members  22  are being pressed apart by spring elements  24  (for example, metal or plastic springs) and are held in a clamping position on the cams  21 . The cams  21 , the locking members  22 , and the ring  23  attached to the housing together form a freewheel  28 . The number of the locking member pairs is dependent on the operational torque to be expected. 
   The unlocking members  10  embrace the outer, ring-shaped wall  20  of the metal member  13  at a spacing. They are provided at their end faces  25  facing the locking members  22  a shaped surface matching the locking members  22 . The distance between the shaped surface and the locking members  22  is smaller than the one between the cam surfaces  18  and the drive surfaces  19 . 
   The ring  23 , fixedly attached to the non-represented housing of the work tool, is positive-lockingly connected, for example, by a toothed ring  26 . 
   The sheet metal member  13  is provided at the side facing away from the driven member  4  with a closing member  27  that is fixedly connected to the spindle  1  and limits the axial movement of the locking members  22  and, thereby, the resulting noise development. This is particularly important with hammer devices. If this is missing, the closing member  27  can be eliminated. 
     FIGS. 3 and 4  illustrate another version of the shaft locking device. The same parts carry the same designation as in  FIGS. 1 and 2 , analogous parts carry a designation extended by an “a”. 
   In this version, differently designed cams  11   a  of a differently designed toothed wheel  7   a  of a differently designed drive member  3   a  engage with play corresponding radial recesses  17   a  of an extruded member  13   a  belonging to a differently designed driven member  4   a . This extruded member  13   a  is fixedly connected to a different spindle  1   a.    
   At the circumference of the extruded member  13   a , between the radial recesses  17   a , cams  21  (according to  FIGS. 1 and 2 ) are provided that can be connected by locking members  22  to the ring  23  fixedly attached to the housing. The locking members  22  are held axially by a closing member  27   a  that is connected to the differently designed cams  11   a.    
   The torque of the drive motor is transmitted by differently designed cam surfaces  18   a  to differently designed drive surfaces  19   a  of the extruded member  13   a.    
   Differently designed unlocking members  10   a  embrace the extruded member  13   a  at a spacing. The distance between the differently designed end surfaces  25   a  of the differently designed unlocking members  10   a  facing the locking members  22  and the locking members  22  is smaller than between the differently designed cam surfaces  18   a  and the differently designed drive surfaces  19   a  of the extruded member  13   a.    
     FIGS. 5 and 6  illustrate another preferred embodiment of the shaft clamping device. The same parts carry the same designation as in  FIGS. 1 and 2 , analogous parts carry a designation extended by a “b”. 
   In this embodiment, the cams  11   b  of a different toothed wheel  7   b  are similarly designed as the cams  11   a  shown in  FIGS. 4 , whereby differently designed cam surfaces  18   b  of the cams  1   b  are approximately radially aligned with different drive surfaces  19   b  of the catch opening  30 . These are embodied as differently designed radial recesses  17   b . The cams  11   b  project radially and axially with a play into the corresponding recesses  17   b  of a differently designed driven member  4   b  which is embodied as a thick disc  13   b . The driven member  4   b  is provided with a different hub  14   b  which is fixedly and force-lockingly connected to a different spindle  1   b  by press fit. 
   At the circumference of the disc  13   b  dovetailed cams  21  according to  FIGS. 1 to 4  are provided between the radial recesses  17   b . The cams  21  can be connected to the ring  23 , fixedly attached to the housing, by locking members  22 . The locking members  22  are held axially by a differently designed closing member  27   b  which is fixedly connected to the spindle  1   b.    
   The torque of the drive motor is transmitted by different cam surfaces  18   b  to different drive surfaces  19   b  of the disc  13   b.    
   Different unlocking elements  10   b  embrace the disc  13   b  at a spacing. The distance to the end surfaces  25  of the unlocking members  10   b  facing the locking members  22  is smaller than between the different cam surfaces  18   b  and the different drive surfaces  19   b  of the disc  13   b . In this embodiment, the locking members  22  rest against the corresponding ends  25  of the different unlocking members  10   b , due to the spring action of the spring element  24  arranged between them. 
   The illustrated shaft locking devices operate as follows: 
   On operation of the motor, the toothed wheel  7 ,  7   a ,  7   b  is rotated on the spindle  1 ,  1   a ,  1   b . Thereby, first, the first locking elements  22  as viewed in the direction of rotation are shifted into the recess of the cams  21  by the unlocking members  10 ,  10   a ,  10   b  and are thereby unlocked. Only then, the cam surfaces  18 ,  18   a ,  18   b  engage the drive surfaces  19 ,  19   a ,  19   b  of the driven member  4 ,  4   a ,  4   b  whereby also the second locking member  22  and, thereby, the freewheel  28  as an entity are unlocked. The spindle  1 ,  1   a ,  1   b , together with the drive member  3 ,  3   a ,  3   b  and the driven member  4 ,  4   a ,  4   b , can now freely rotate and transmit torque. 
   When the drive of the spindle  1 ,  1   a ,  1   b  rests, the axial cams  11 ,  11   a ,  11   b  and the unlocking members  10 ,  10   a ,  10   b  are positioned in neutral position without any contact to the driven member  4 ,  4   a ,  4   b  and the locking members  22 . The latter are held in a locking position by the spring elements  24 . On rotating the spindle  1 ,  1   a ,  1   b  by hand, one of the locking members  22  is engaged in the direction of the locking position and the other one in the unlocking direction, respectively, whereby the locking members  22  switch their function when the direction of rotation is changed. In this manner, a firm rotation connection to the housing of the work tool is always present when the spindle  1 ,  1   a ,  1   b  is rotated manually. This situation can be utilized for opening or closing, or screwing on and off the drill chuck with one hand. Thereby, a double bush drill chuck is not required which is expensive and has to be handled with both hands. Another advantage of the shaft locking device is that a screw can be manually screwed in and out by using the work tool as an effective screw driver. 
   The specification incorporates by reference the entire disclosure of German priority document 297 15 257.2 of Aug. 26, 1997, as well as of International Application PCT/EP98/05432 of Aug. 26, 1998. 
   The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.