Abstract:
A hand machine tool includes a tool retainer that retains a tool, a motor that drives the tool retainer in a rotary motion, and a torque-controlled sliding clutch that is connected in a drivetrain between the motor and the tool retainer. The sliding clutch includes a first clutch disk, a second clutch disk, a spring and a controlling unit which can be activated manually. The second clutch disk is arranged displaceably alongside an axis limited by a stop in the direction toward the first clutch disk. Force is applied to the second clutch disk by the spring alongside the axis in the direction toward the first clutch disk. The manually activated controlling unit variably sets an axial distance between the first clutch disk and the stop, with which an engagement depth of the first clutch disk with the second clutch disk can be defined.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to German Patent Application No. DE 10 2011 080 800.0, filed Aug. 11, 2011, which is hereby incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     Some embodiments of the present invention relate to a hand machine tool and, in particular, to an electric screw driver. 
     BRIEF SUMMARY OF THE INVENTION 
     The hand machine tool according to some embodiments includes a tool retainer that retains a tool, a motor that drives the tool retainer in a rotary motion, and a torque-controlled sliding clutch that is connected in a drivetrain between the motor and the tool retainer. The sliding clutch includes a first clutch disk, a second clutch disk, a spring, and a controlling unit which can be activated manually. The second clutch disk is displaceably arranged alongside an axis limited by a stop in a direction toward the first clutch disk. Force is applied to the second clutch disk by the spring alongside the axis in the direction toward the first clutch disk. The manually activated controlling unit variably sets an axial distance between the first clutch disk and the stop, with which an engagement depth of the first clutch disk with the second clutch disk can be defined. 
     In some embodiments, the spring keeps the two clutch disks engaged by default. The stop maintains a distance between the second clutch disk and the first clutch disk. Consequently, the engagement depth of the second clutch disk with the first clutch disk is limited by the stop. If a torque applied to the sliding clutch exceeds a critical limit, the second clutch disk is deflected alongside the axis against the effect of the spring to the point where the two clutch disks are fully disengaged and the torque transmission is interrupted. The limiting value can be set with the engagement depth, which is defined by the relative position of the first clutch disk compared to the stop. As a result, the controlling unit enables the user to set a desired triggering torque. 
     According to one embodiment, the first clutch disk has cams and the second clutch disk has cams. The clutch disks are engaged with each other via the cams. Each of the cams of at least one of the two clutch disks has a convexly curved top, wherein the radius of curvature of the top increases toward the summit. The cam has a concave base starting from a bottom, for example, having a negative curvature. In some embodiments, a flat side is connected to the base, followed by the convex top with the positive curvature. Alternatively, the convex top can be connected directly to the concave base. The sequence of the structures of a cam is viewed along a circumferential direction and at a constant distance to the axis. The top describes the entire area of a cam with a convex shape. The curvature of the top decreases from the base toward the direction of the summit or peak of the top. Although the grooves can be disadvantageous for other models of a sliding clutch due to their larger widths, they have proven advantageous in the presented configurations according to some embodiments. The decreasing curvature enables a robust setting of a low engagement depth and hence a low limit for triggering the sliding clutch. The mechanism is in particular robust against tolerances associated with the manufacture and installation of the sliding clutch. Setting high limits with a deep engagement depth is equally possible in some embodiments. 
     Some embodiments provide that the top includes of a first section and a second section on an ascending side to the summit and the first section includes a first radius of curvature and the second section includes a second radius of curvature in which the first radius of curvature is lower than the second radius of curvature. In some embodiments, the top is designed with two different radii of curvature (e.g., exactly two different radii of curvature). On the descending side, the radius of curvature can decrease again from the larger second radius of curvature to the first radius of curvature. The first radius of curvature is, for example, lower by at least 20% than the second radius of curvature. The second radius of curvature can be between 0.9 and 1.2 times as high as a height of the cam. The height of the cam refers to the maximum dimension of the cam alongside the axis, for example, from the start of the base to the summit of the top. 
     According to some embodiments, the second clutch disk is arranged movably on a shaft (e.g., an intermediate shaft), and the first clutch disk and the second clutch disk are arranged movably alongside the axis relative to the shaft. 
     The first clutch disk rests on an additional stop formed by the controlling mechanism displaceable alongside the axis toward a direction facing away from the second clutch disk. The two clutch disks are limited in their axial motion in the same direction by two separate stops. The other stop is displaceable relative to the first stop and the distance between them defines the engagement depth of the two clutch disks. 
     According to some embodiments, the second clutch disk is interlocked with the shaft for transmitting a torque and the first clutch disk is interlocked with an additional shaft for transmitting a torque in which the first clutch disk is displaceable relative to an additional shaft. The additional shaft is, for example, a spindle which retains a tool or is connected with the tool retainer. An axial mobility of the first clutch disk relative to the other shaft can, for example, be achieved with an interconnected claw clutch. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows an electric screw driver. 
         FIG. 2  shows a drivetrain of the electric screw driver. 
         FIG. 3  shows a clutch disk. 
         FIG. 4  shows a clutch disk. 
         FIG. 5  shows a drivetrain of an electric screw driver. 
         FIG. 6  shows a drivetrain of an electric screw driver. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an exemplary electric screw driver  1  which drives a tool  2 , or example, a screw bit, around a working axis  3  in a rotary motion when in operation. A tool retainer  4  for a tool  2  is arranged on a case  5  and is pivotal around the working axis  3 . The tool retainer  4  is coupled with an electric motor  7  via a drivetrain  6 . The electric motor rotates in response to the operation of a system button  8 . A user can start the electric screw driver  1  by means of the system button  8  and guide it by means of a handle  9  provided on the case  5 . 
       FIG. 2  illustrates a design of the drivetrain  6  with an adjustable sliding clutch  10 , which interrupts a transmission of a torque if an applied torque exceeds a limiting value. The limiting values can be set by a user by means of a slide  11 . The sliding clutch  10  engages with a countershaft  12  on the side of the drivetrain and with an output spindle  13  on the output side, which are both coaxial to the working axis  3 . The countershaft  12  is arranged axially stationary in the case  5 . The countershaft  12  is, for example, driven with a transmission  14 , here illustrated with two pinions as an example, which is connected torque-resistant with the electric motor  7 . The output spindle  13  is provided with the tool retainer  4  on a frontal end. The illustrated design of the drivetrain  6  is exemplary and may contain additional transducing or power-interrupting components in other embodiments. 
     The slide clutch  10  includes a clutch disk  15  on the drive side, a clutch disk  16  on the output side and a pull-back spring  17 . The clutch disk  15  on the drive side is arranged axially moveable on the countershaft  12 . The clutch disk  15  on the drive side can approach the clutch disk  16  on the output side alongside the working axis  3  in the engagement direction  18  or distance itself from the clutch disk  16  on the output side in the release direction  19  (e.g., in the opposite direction of the engagement direction  18 ). The pull-back spring  17  acts on the clutch disk  15  on the drive side in the engagement direction  18 , pushing it toward the clutch disk  16  on the output side in the engagement direction  18 . In a basic position of the slide clutch  10 , for example, without applied torque, the clutch disk  15  on the drive side is as close to the clutch disk  16  on the output side as possible. In the basic position, the clutch disks  15 ,  16 —designed, for example, in the form of cam rings—are engaged, whereby the clutch disk  15  on the drive side transmits an applied torque to the clutch disk  16  on the output side. One shape of the cam rings is designed in such a way that a force acting in the release direction  19  is exerted onto the clutch disk  15  on the drive side if a torque is applied. If the applied torque exceeds the limiting value, then the force is sufficiently released at the clutch disk  15  on the drive side against the force of the pull-back spring  17  in the release direction  19  to the point where the cam rings are completely disengaged. 
     A first stop  20  limits a movement of the clutch disk  15  on the drive side toward the engagement direction  18  in that the clutch disk  15  on the drive side comes to rest on this first stop  20  in the engagement direction  18 . The first stop  20  is arranged alongside an axial line between the clutch disk  15  on the drive side and the clutch disk  16  on the output side. The first stop  20  is axially stationary relative to the case  5  and the countershaft  12 . Consequently, the first stop  20  determines the relative axial position of the clutch disk  15  on the drive side compared to the clutch disk  16  on the output side in the basic position. In  FIG. 2 , the clutch disk  15  on the drive side has at least one radially protruding peg  21 , which engages with an axially running longitudinal groove  22  in the countershaft  12 . The longitudinal groove  22  is closed on one end of the groove  23  in the engagement direction  18 . The end of the groove  23  forms the first stop  20  and the peg  21  forms an interlock for the torsionally rigid coupling of the clutch disk  15  on the drive side with the countershaft  12  for the transmission of a torque. The interlock can include a plurality of longitudinal grooves  22  and pegs  21 . The first stop  20  can alternatively or additionally be formed with a ring  24  placed onto the countershaft  12 . The ring  24  is placed onto an end of the countershaft  12  pointing into the engagement direction  18 . 
     The clutch disk  16  on the output side is arranged movable relative to the countershaft  12 . Referring to  FIG. 2 , the clutch disk  16  on the output side is axially arranged movably on the output spindle  13 . A second stop  25  limits the motion of the clutch disk  16  on the output side in the engagement direction  18 . The directions are always quoted with respect to the motion of the clutch disk  15  on the drive side. If a torque is applied, the clutch disk  16  on the output side touches the second stop  25 . The shape of the grooves results in a partial conversion of the torque into a force acting on the clutch disk  16  on the output side in the engagement direction  18 . An optional spring  26  can be provided to retain the clutch disk  16  on the output side on the second stop  25 . The spring  26  acts on the clutch disk  16  on the output side in the engagement direction  18  and is braced, for example, on the countershaft  12 . 
     The second stop  25  is connected with the slide  11 . The slide  11  has a runner  27  which is, for example, placed onto the case  5  and can be rotated relative to the case  5 . The runner is provided for the user to grasp. A thread  28  on the runner  27  oriented alongside the working axis  3  engages with a corresponding thread  29  of the case  5 . When the runner  27  is turned, the runner  27  is displaced relative to the case  29  and the countershaft  12  alongside the working axis  3 . The second stop  25  is a ring protruding inward formed on the runner  27 . 
     The clutch disk  16  on the drive side has, for example, one or a plurality of pegs  30  pointing inward, which engage with grooves  31  in the output spindle  13  for transmitting a torque. 
     The first stop  20  and the second stop  25  define an axial distance between the clutch disk  15  on the drive side and the clutch disk  16  on the output side and hence a depth  32  of engagement in the basic position. Starting from the basic position, the engagement depth  32  corresponds to the deflection of the clutch disk  15  on the drive side in the release direction  19  which releases the sliding clutch  10 . The torque used to release the sliding clutch  10  increases with increasing engagement depth  32 , amongst other things, because of the spring power of the pull-back spring  17  increasing progressively as a result of the deflection. The user can set the limiting value for the transmitted torque by axially displacing the second stop  25 . 
       FIG. 3  shows an exemplary clutch disk  40  on the drive side in a perspective representation, with a view of a frontal area  41  pointing toward the engagement direction  19 .  FIG. 4  shows a section of an unrolled profile of the clutch disk  40  in which the cut out section is indicated as cylindrical area IV-IV in  FIG. 3 . The clutch disk  40  has a plurality of cams  42  (e.g., uniform cams) on the frontal area  41 . A clutch disk on the output side can be provided with identical cams as those of the clutch disk  40  on the drive side. The cams  42  are arranged successively in the circumferential direction  43  around the working axis  3 . Arranged successively in the circumferential direction  43 , the cam  42  has a front base  44 , a flank  45  rising in the engagement direction  19 , a top  46 , a flank  47  sloping down in the engagement direction  19  and a back base  48 . The clutch disk  40  can include a flat bottom  49  between two successive cams  42 . 
     During an engagement of the clutch disk  40  on the drive side with the clutch disk on the output side, the respective rising flanks  45  extensively rest on each other. The rising flank  45  and the falling flank  47  are flat for this purpose according to some embodiments. An incline of the flanks  45 ,  47  relative to the working axis  3  ranges, for example, between 45 degrees and 70 degrees. The incline defines the conversion of the applied torque into an axially acting force. The flank  45  covers a ratio of 20% to 30% of a height  50  of the cam  42 . The slide  11  makes it possible to define the engagement depth  32 . If the engagement depth  32  is deeper, the rising flanks  45  of the two clutch disks are completely resting on each other across the entire height. 
     In some embodiments, the base  44  has a negative curvature with a constant radius of curvature from the bottom  49  to the flank  45 . A transition from the bottom  49  to the base  44  is smooth, i.e., provided with a gradually rising incline without any jumps. Similarly, a transition between the base  44  and the flank  45  is smooth. In some embodiments, a radius of curvature of the base  44  is considerably smaller than the height  50  of the cam  42 , e.g., smaller than 40% of the height  50 . The ratio of the base  44  on the height  50  of the cam  42  can therefore be kept low. 
     The top  46  has a continuous positive curvature, which includes at least two radii of curvature in the rise from the rising flank  45  to a summit  51  of the top  46 . The flank  45  transitions smoothly into a first section  52  of the top  46 . The first section  52  has a first radius of curvature  53  and transitions smoothly into a second section  54  with a second radius of curvature  55 . The summit  51  of the top  46  is located in the second section  54 . The exemplary top  46  is symmetrical to the summit  51 , and a third section  56  with a radius of curvature identical to the first radius of curvature  53  is connected to the second section  54 . 
     The first radius of curvature  53  is lower than the second radius of curvature  55 , in some embodiments by at least 20%, and by at most 60% lower than the second radius of curvature  55 . The first section  52  has the strongest local curvature (lowest radius of curvature) between the flat flank  45  and the summit  51  of the cam  42 . A length, measured in the unrolling direction, of the cam  42  is 20% to 40% longer because the middle second section  54  is less curved than a cam whose top is designed with a cylindrical top and the second radius of curvature. A ratio of height  50  of the cam  42  and the second radius of curvature  55  is within the range of 0.5 and 0.75. The first radius of curvature  53  is nearly identical to the height  50 , their ratio ranging between 0.9 and 1.2, for example. The top  46  has a ratio of more than 50% of the height  50  of the cam  42 . A point of transition  57  from the first area  52  to the second area  54  is located at about 90% to 95% of the height  50  of the cam  42 . If the user sets the slide  11  to a minimum torque, the second clutch disk only engages with the first clutch disk to the point of transition  57 , while the first section  54  remains untouched. 
       FIG. 5  shows an additional embodiment of the drivetrain  6 . The clutch disk  15  on the drive side is designed essentially identical to the previous embodiment and arranged axially movable and interlocking in the direction of rotation on the countershaft  12 . A clutch disk  60  on the drive side is arranged axially movable on the countershaft  12  and can rotate freely relative to the countershaft  12 . The clutch disk  15  on the drive side and the clutch disk  60  on the output side are engaged by means of cams  42 , as described above. The axial distance between the clutch disk  15  on the drive side and the clutch disk  60  on the output side in the basic position is defined for the clutch disk  60  on the drive side by the stop  25  positioned by the slide  11 . 
     The spindle  13  is axially moveable relative to the countershaft  12 . A spring  62  between the spindle  13  and the countershaft  12  keeps them at a distance in the basic position. The spindle  13  includes axially protruding claws  63  in the direction toward the countershaft  12 . The claws are able to engage with corresponding claws  64  on the clutch disk  60  on the output side. The claw clutch formed with the claws  63 ,  64  can be part of a mechanical activation of the spindle  13 . In some embodiments, the engagement only takes place when a user pushes the spindle  13  against the countershaft  12 . 
       FIG. 6  shows an additional embodiment of a drivetrain  70 . The drivetrain  70  has a motor-activated pinion  71  and a countershaft  72  which are coupled by way of a torque-controlled clutch  73 . The pinion  71  is arranged pivotally on the countershaft  72 . A drive pinion (not illustrated) combs with the pinion  71 . The pinion  71  includes cams  76  on its frontal side  75  pointing in the direction  74  toward the tool retainer  4  and designed as clutch disk on the drive side. The pinion  71  is stationary inside the case  5  alongside the working axis  3 . A clutch disk  77  on the output side engaging with the clutch disk on the drive side is axially movably arranged on the countershaft  72 . Cams  76  of the clutch disk  71  on the drive side and cams  78  of the clutch disk  77  on the output side can be designed identical to the cams of the embodiments described above. The clutch disk  77  on the drive side is torsionally rigidly coupled with the countershaft  72  via internal interlocking  79 . 
     A pull-back spring  80  pushes the movable clutch disk  77  on the drive side toward the clutch disk  71  on the output side in the readjustment direction  81 , in order to keep it engaged in a basic position. The pull-back spring  80  is braced on a ring  82  against the readjustment direction  81 . The ring  82  is mounted on the countershaft  72  axially stationary. In some embodiments, the ring  82  turns together with the countershaft  72 , in order to prevent a torsion of the pull-back spring  80 . In the basic position, the clutch disk  77  on the drive side rests on a stop  83  in the readjustment direction  81 . The stop is axially connected rigidly with a runner  84  surrounding the clutch disk  77  on the output side. The stop  83  is realized, for example, with a spring ring, which overlaps with the clutch disk  77  on the output side in radial direction. A distance  85  of the stop  83  from the clutch disk  71  on the drive side defines how far the cams  76 ,  78  are allowed to engage maximally with each other, for example, in the basic position. The runner  84  and hence the stop  83  can be displaced at different settings alongside the working axis  3  relative to the countershaft  72  and the clutch disk  71  on the drive side. A helicoidally connecting link  86  on a set collar  87 , which the user can grasp, engages with the runner  84  and defines its axial position relative to the case  5 . 
     An output shaft  88  is axially moveable relative to the countershaft  72  and engages with the countershaft  72  via a claw clutch  89 . The ring  82  mounted on the countershaft is designed as a part of the claw clutch  89 . Alternatively, the driveshaft  87  can be connected rigidly with the countershaft  72 .