Abstract:
A screwdriver is disclosed, comprising a removable depth stop which selectably either, when equipped with the depth stop, allows noiseless shutoff or, with the depth stop removed, allows torque-dependent shutoff, without any chattering occurring when the machine continues to run. To this end, an adjustable torque-dependent release clutch is combined with an entrainment clutch of known type, which is additionally preceded by a disconnect clutch, a locking means being provided in order to hold a throwout ring, which forms one of the two elements of the disconnect clutch, in a predetermined position under load. In this way, noiseless operation is ensured after release, both when working with the depth stop and in the case of torque-dependent shutoff, with the depth stop removed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a power-driven screwdriver comprising: 
     a housing on which a depth stop can be fastened; 
     a tool drive shaft, displaceable relative to the depth stop in the direction of its rotation axis, on which a tool receptacle is held; 
     a drive shaft; 
     a drive gear, received in rotatable and axially displaceable fashion on the drive shaft, which is motor-driven; 
     an intermediate ring that is mounted rotatably on the drive shaft and has a first side facing toward the drive gear, and a second side; 
     a cam ring that is mounted rotatably on the tool drive shaft and has a first side facing toward the intermediate ring, and a second side; 
     first cam elements on the drive gear that coact with associated second cam elements on the first side of the intermediate ring in order to form a first cam clutch; 
     third cam elements on the second side of the intermediate ring that coact with associated cam elements on the cam ring in order to form a second cam clutch; 
     first catch elements on the intermediate ring that coact with associated second catch elements on the cam ring and form, together with the third and fourth cam elements, an entrainment clutch; and 
     a first spring element for noiseless disconnection upon release of the release clutch. 
     A screwdriver with depth stop of this kind is known from U.S. Pat. No. 4,655,103, the disclosure of which is fully incorporated by reference. 
     With the known screwdriver, a screw can be driven into a surface to a driving depth preset with a depth stop. When the depth stop encounters the surface, this initiates shutoff of a clutch with which a largely noiseless shutoff is accomplished. A motor-driven drive gear, which together with an idler gear arranged in axially movable fashion forms a first cam clutch, is provided for this purpose. The idler gear coacts, on its other side facing the tool carrier, with a further clutch element, the oblique cam surfaces of the associated elements forming a second cam clutch. In addition, catch elements in the form of straight, axially parallel flanks, by way of which, when a certain baseline torque occurs, the clutch element joined to the tool receptacle is entrained by the intermediate clutch element, are provided on the idler gear and on the second clutch element. In addition, a compression spring by way of which the idler gear is preloaded in the direction toward the tool receptacle is arranged between the drive gear and the idler gear. 
     In operation, first the depth stop is set to the desired driving depth and then the tool carrier with its tool is placed onto, for example, a screw that is to be driven in, and pressed down. As a result, all three clutch elements come into engagement with one another, so that initially the torque is transferred from the drive gear to the tool carrier as the screwdriving operation begins. As a result of the torque occurring during the screwdriving operation, the idler gear and the clutch element joined to the tool receptacle are pushed slightly apart until the straight catch flanks come into engagement with one another and positive entrainment is guaranteed. When the depth stop encounters the surface, the tool carrier with the tool receptacle and the screw move even further until the latter is completely driven in. The cam elements of the first cam clutch then slide apart, assisted by the compression spring, until it releases. Because the torque has now decreased to zero, the idler gear is pressed by the compression spring against the second clutch element that is joined to the tool receptacle, so that the drive gear can continue to rotate freely without touching the idler gear. A “noiseless” shutoff is thus accomplished. 
     Also known are various screwdrivers which provide for a disconnection of the drive train by means of a shutoff system as soon as a preset torque is reached (cf., for example, EP 0 239 670 B1). 
     It is also known, in the case of a screw machine tool, to implement selectably a switchover capability between a shutoff by way of a depth stop and a shutoff by way of a preset torque (EP 0 401 548 B1). If this screwdriver is used for shutoff with a depth stop, the construction and operation then correspond in principle to the aforementioned U.S. Pat. No. 4,655,103. 
     By way of a spring-loaded coupling ring that is activated via pins upon removal of the depth stop and that covers the intermediate ring and the second clutch element facing the tool drive shaft, the intermediate clutch element and the second clutch element are pressed toward one another, when the depth stop has been removed, under the action of the spring, and are positively joined to one another via a spline set, so that these two elements act like a single clutch element even when acted upon by torque. What therefore results in this position, in combination with the oblique cam surfaces of the drive gear, is a cam clutch that releases at a torque that is preset by way of a corresponding adjustment mechanism. 
     Even after release, however, this clutch continues to run and “chatter.” 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a power-driven screwdriver with depth stop in which selectably either a shutoff via depth stop or a torque-dependent shutoff is provided for, and in either case no chattering of the shutoff clutch occurs. 
     This and other objects are achieved according to the present invention in a screwdriver of the type cited initially, in that 
     a throwout ring, which is mounted on the tool drive shaft against a resistance, is provided; 
     the first spring element is arranged between the cam ring and the throwout ring in order to preload the cam ring in the direction toward the drive gear; 
     a second spring element, supported on the housing side, is provided on the side of the drive gear facing away from the first cam elements; 
     first claw elements, which coact with second claw elements on the throwout ring in order to form a disconnect clutch, are provided on the second side of the cam ring. 
     The object of the invention is completely achieved in this fashion. 
     Both when a depth stop is used and when the depth stop has been removed, at the completion of a screwdriving operation a disconnection of the drive shaft from the tool drive shaft is accomplished, thus ensuring that no chattering occurs even if the drive motor continues to run. 
     In a preferred embodiment of the invention, the throwout ring is fastened on the tool drive shaft nonrotatably and in axially displaceable fashion toward the resistance. In addition, a locking means is provided in order to hold the throwout ring in a position slid forward axially toward the tool receptacle when the throwout ring shifts axially toward the tool receptacle during operation under load, and to disengage the throwout ring again after release of the disconnect clutch and subsequent pressure release. 
     According to a development of the invention, an axial stop against which is supported a third spring element, against which the throwout ring can be axially displaced toward the tool receptacle, is provided on the tool drive shaft. 
     With this kind of arrangement of a spring element, disengagement of the locking means that is locked in the slid-forward position can easily be achieved after release of the disconnect clutch and subsequent pressure release. 
     According to a further embodiment of the invention, the first spring element is clamped between the cam ring and an axial stop of the tool drive shaft. 
     This type of arrangement of the first spring element enhances the function of the entrainment clutch. 
     In a further preferred embodiment of the invention, the tool drive shaft is guided in axially displaceable fashion on the drive shaft with one end. 
     This simplifies mounting of the tool drive shaft. 
     In a preferred development of the invention, the locking means is configured as a ball catch that is lockable by way of a fourth spring element that is arranged between the tool drive shaft and the drive shaft. 
     This makes it possible to utilize the relative motion between the tool drive shaft and drive shaft to easily immobilize the throwout ring in a position that is axially slid forward toward the tool receptacle. 
     In an additional development of this embodiment, the locking means has axial guide lands on the tool drive shaft that coact with associated grooves on the throwout ring in order to guide the latter. 
     In an additional development of this embodiment, the axial guide lands are configured as lands, projecting outward from the tool drive shaft, whose first, tool-side, axial end serves to support the third spring element on its side facing toward the throwout ring, and whose second end, facing toward the throwout ring, serves to support the first spring element. 
     The construction, and the installation of the locking means and of the associated spring elements on the tool drive shaft, can thereby be simplified. 
     It is preferred in this context if a plurality of balls, which can be acted upon via a central ball by the fourth spring element in order to lock the throwout ring, are movably guided in transverse bores of the tool drive shaft. 
     In an additional development of this embodiment, the tool drive shaft has on the side toward the drive shaft a central bore in which the drive shaft is axially displaceably guided with a first end. 
     In this context, a blind hole in which a first end of the fourth spring element is received can be provided at the first end of the drive shaft, a second end of the fourth spring element resting against the central ball that is guided in axially displaceable fashion in the bore. 
     These features guarantee reliable operation of the locking means, and at the same time ensure a simplified design. 
     In an additional development of the invention, the second spring element is configured as a cup spring that is supported between the drive gear and an axial stop on the side of the drive gear facing away from the tool receptacle. 
     Configuring the second spring element as a cup spring makes it possible to achieve a relatively large spring force with a spring element of small physical size, so as thereby to ensure a large adjustment range for the release torque in the case of torque shutoff. 
     In a preferred development of the invention, the depth stop is mounted removably on the housing. 
     Although the depth stop could also be made nonfunctional in other ways, this is a particularly simple way of allowing a changeover between shutoff via depth stop and torque shutoff. 
     In an additional development of the invention, an adjusting sleeve is provided for axial adjustment of the intermediate ring toward the drive gear. 
     It is thereby possible to modify the release torque of the release clutch in simple fashion by modifying the overlap between the cam elements of the intermediate ring and of the drive gear. 
     For this purpose, in an additional development of this embodiment, a snap ring, which is fastened rotatably with respect to the housing and can be snap-locked in various angular positions, is fastened on the adjusting sleeve in axially displaceable fashion and nonrotatably with respect thereto. 
     It is thereby possible to achieve, in simple fashion, a simple axial adjustment of the adjusting sleeve with respect to the housing, together with snap-locking in various angular positions, if the adjusting sleeve is joined to the housing via threads. 
     In a preferred development of the invention, the catch elements on the cam ring and on the intermediate ring are configured as straight flanks, extending in the axial direction, at the outer end of the third and fourth cam elements. 
     It is thereby possible to achieve, with simple means, a positive entrainment for power transfer from the intermediate ring to the cam ring. Other connections would, however, theoretically also be conceivable, for example the use on one of the two rings of curved surfaces on which, for example, a transverse pin on the other of the two rings is guided. 
     In an advantageous development of the invention, the spring elements are coordinated with one another in such a way that after a shutoff of the screwdriver and subsequent pressure release, the locking means is unlocked again and pushed back into its starting position. 
     In a further embodiment of the invention, the first and second claw elements are furthermore configured as claws having straight surfaces running in the axial direction, or as cams having oblique surfaces that are more steeply sloped, with respect to the axial direction, than the first through fourth cam elements. 
     These features allow a simple configuration and manufacture of the relevant cam elements, catch elements, and claw elements. 
     In a further embodiment of the invention, the first, second, third, and fourth cam elements are configured as oblique cam surfaces, the slope of the first and second cam elements being greater than the slope of the third and fourth cam elements so as to guarantee, under load, that the cam ring is first displaced toward the throwout ring before, at greater torque, any displacement of the drive gear occurs. 
     Reliable operation in combination with simple manufacture and assembly can be achieved with a configuration of this kind. 
     It is understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the context of the present invention. 
    
    
     SHORT DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention are evident from the following description of preferred exemplary embodiments, referring to the drawings, in which: 
     FIG. 1 shows a partial longitudinal section through a screwdriver according to the present invention; 
     FIGS.  2   a-   2   d  show schematic representations of the operation of the screwdriver according to the present invention with the use of torque shutoff, in a greatly simplified manner of representation, in which: 
     FIG.  2   a  shows the screwdriver being manually placed and pressed onto a screw; 
     FIG.  2   b  shows the position established, during the screwdriving operation, as a consequence of a certain baseline torque; 
     FIG.  2   c  shows release of the release clutch when the preset torque is reached; 
     FIG.  2   d  shows the release of the disconnect clutch that occurs as a result of the decreased torque, thus allowing continued rotation without chattering; 
     FIGS.  3   a-   3   d  show schematic representations of the screwdriver according to the present invention with the use of the depth stop, in a greatly simplified representation, in which: 
     FIG.  3   a  shows the screwdriver being placed on a screw; 
     FIG.  3   b  shows the position established, during the screwdriving operation, as a consequence of the baseline torque; 
     FIG.  3   c  shows the depth stop encountering the surface into which the screw is to be driven; and 
     FIG.  3   d  shows the response of the disconnect clutch, thus allowing continued rotation without chattering. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a screwdriver according to the present invention is labeled in its entirety with the number  10 . 
     Screwdriver  10  comprises a housing  11  in which is received a motor (not shown) which drives, via a pinion  74 , a drive gear  72  having its teeth  73  meshing therewith. Further parts of the drive train thus constituted are not shown. Drive gear  72  is mounted on a drive shaft  70  that is aligned with a tool drive shaft  30  on whose outer end is provided a tool receptacle  26 , for example to receive a screwdriver bit. 
     The torque of drive gear  72  can be transferred via an intermediate ring  55  and a cam ring  50  to a throwout ring  36  that is fastened on tool drive shaft  30  in nonrotatable and axially displaceable fashion. 
     Tool drive shaft  30  is displaceable in the direction of its rotation axis  27  with respect to drive shaft  70 . For this purpose, there is provided on the end of tool drive shaft facing toward drive shaft  70  a central bore  41  with which tool drive shaft  30  is guided in axially displaceable fashion on the end of drive shaft  70 . 
     Intermediate ring  55  is mounted in freely rotatable fashion on tool drive shaft  30  and drive shaft  70 . Cam ring  50  is also arranged in freely rotatable fashion on tool drive shaft  30 , between intermediate ring  55  and throwout ring  36 . Throwout ring  36 , on the other hand, is mounted in axially displaceable but nonrotatable fashion on axial guide lands  33  on the outer side of tool drive shaft  30 , which are configured as external lands, in the manner of a wedge profile, that engage into correspondingly shaped grooves on throwout ring  36 . Arranged on drive gear  72 , on the side facing toward intermediate ring  55 , are cam elements  61  having oblique cams of the kind known from U.S. Pat. No. 4,655,103. Correspondingly shaped second cam elements  57 , which are provided on intermediate ring  55 , engage into these first cam elements  61 . These interengaging oblique cam flanks thus form a release clutch that is labeled in its entirety with the number  62 . 
     Drive gear  72  is retained by a retaining ring  71  in the direction toward tool receptacle  26 , and is preloaded on the other side by way of a spring element  46  in the form of a cup spring that hereinafter will be referred to as the second spring element. The cup spring is also retained by a retaining ring  75 , and is supported at the end facing away from drive gear  72  by an axial bearing  76  that is received on housing  11 . Drive shaft  70  is furthermore mounted at this end in housing  11 , in a radial bearing  77  that is configured as a plain bearing. 
     Intermediate ring  55  forms, together with cam ring  50 , an entrainment clutch that is labeled in its entirety with the number  65 . Entrainment clutch  65  has third cam elements  56  in the form of oblique cam surfaces, associated with which are fourth cam elements  52  of corresponding shape on cam ring  50 . Catch elements  100  and  101 , whose shape is evident from FIGS.  2   a  through  2   d,  are provided at the end of these oblique cam surfaces associated with the respective other part. First catch elements  100  are in the form of straight, axially parallel flanks at the outer end of the oblique cam elements  56  on the intermediate ring, and the corresponding catch elements  101  are in the form of straight flanks at the end of the oblique cam elements  52  of cam ring  50 . 
     Cam elements  52 ,  56  and catch elements  100 ,  101  thus form entrainment clutch  65 , with which cam ring  50  is entrained by intermediate ring  55 ; when a certain baseline torque occurs, an axial displacement occurs until catch elements  100 ,  101  engage positively into one another. 
     Also constituted, between cam ring  50  and throwout ring  36 , is a disconnect clutch, labeled in its entirety with the number  54 , which comprises first claw elements  51  with straight, axially parallel flanks on cam ring  50 , and second claw elements  37  with correspondingly shaped straight flanks on throwout ring  36 . 
     Axial guide lands  33  on tool drive shaft  30  have a first, tool-side end  34  and a second end  35  facing toward drive gear  72 . Arranged between second end  35  and cam ring  50  is a first spring element  45  in the form of a helical spring, surrounding tool drive shaft  30 , which preloads tool drive shaft  30  in a direction facing away from cam ring  50 . Second spring element  46  in the form of the cup spring is, as already mentioned, arranged between drive gear  72  and a radial bearing  77 . 
     A third spring element  47 , which is also configured as a helical spring surrounding the tool drive shaft, is clamped between the first, tool-side end  34  of axial guide lands  33  and axial stop  31 , in order to preload throwout ring  36  toward drive gear  72 . 
     Throwout ring  36  can be locked, by way of a locking means that is labeled in its entirety with the number  43 , in a position that is slid forward against the force of third spring element  47  toward tool receptacle  26 , thereby preventing throwout ring  36  from sliding back toward drive gear  72 . This locking means is configured as a ball catch that has a total of three small balls  39  that are guided in the radial direction in transverse bores of tool drive shaft  30 , and has one central large ball  40  that is preloaded, by a fourth spring element  48  that is received in a blind hole  49  on the tool-side end of drive shaft  70 , toward tool receptacle  26  and toward small balls  39  that are guided in transverse bores  38 . Bore  41  is prolonged at the tool-side end, in the direction of tool receptacle  26 , by a blind hole  32 , such that a smaller diameter of blind hole  32  constitutes a seating surface  42  for precisely fitted reception of central ball  40 . 
     Small balls  39  are preloaded via central ball  40  outward in the radial direction by the force of fourth spring element  48 . If throwout ring  36  is then moved toward tool receptacle  26  sufficiently far that small balls  39  are no longer prevented by the inner surface of throwout ring  36  from emerging outward, small balls  39  can then, in response to the spring force of fourth spring element  48 , move outward into radial bores  38  until they are prevented from emerging further by second claw elements  37 , arranged above them, of throwout ring  36 . In this position, throwout ring  36  is prevented from moving back toward drive gear  72 . This locking action remains effective until fourth spring element  48  is unloaded, so that small balls  39  move back, in response to third spring element  47 , into their radial bores  38 , so that throwout ring  36  is disengaged and moves toward drive gear  72  in response to third spring element  47  and against the force of first spring element  45 . 
     The release torque of release clutch  62 , which is constituted by the cam elements of drive gear  72  and of intermediate ring  55 , of course depends on the shape and especially on the flank angle of cam elements  57 ,  61 . The release torque is also influenced by the spring constant and length of second spring element  46 . 
     A variety of measures are conceivable for achieving easy adjustment of the release torque. A particularly simple design results if only the overlap of the flanks of first cam elements  61  and of second cam elements  57  is modified. For this purpose, intermediate ring  55  can be adjusted in the direction of drive gear  72  with the aid of an adjusting sleeve, by way of a radial bearing  60  that is enclosed between retaining rings  58 ,  59  on intermediate ring  55  and adjusting sleeve  13  that is fastened to the housing. Adjusting sleeve  13  is joined via threads  12  to housing  11 , and can thus be adjusted in the axial direction by rotation. 
     In order to make possible manual adjustment from outside, a snap ring  14  is provided that can be pulled toward tool receptacle  26  against the force of a helical spring  18  and is joined nonrotatably, via an axial guide  17 , to adjusting sleeve  13 . Provided on the housing-side end of snap ring  14 , in the circumferential direction, is a plurality of snap lugs  15  that can be snapped in various angular positions in between corresponding recesses on housing  11  in order thereby to immobilize snap ring  14  in nonrotatable fashion in a desired angular position. To rotate adjusting sleeve  13 , all that is therefore necessary is for snap ring  14  to be pulled, against the force of helical spring  18 , toward tool receptacle  26  and then rotated, and finally it is once again held in a new predefined angular position, in a manner secured against further rotation, by snap lugs  15 . Helical spring  18  is enclosed in a suitable hollow cylindrical recess of snap ring  14  and held at the outer end of snap ring  14  by a retaining ring  16  that is fastened on a sleeve  19  that is immovably press-joined in this region to tool drive shaft  30 . Inner retaining ring  16  is immobilized in the axial direction, after the installation of helical spring  18  on sleeve  19 , by way of a further preceding retaining ring  20 . 
     The depth stop labeled in its entirety with the number  21  is a depth stop of known design, for example in accordance with EP 0 401 548 B1, that can simply be slid onto the outer end of sleeve  19  until it rests against retaining ring  16 . A recessed O-ring  24  provides immobilization. Depth stop  21  is configured as a multi-part plastic part in which threads  22  allow axial adjustment of end surface  25  at the outer end of the depth stop. An inner adjusting sleeve  28  of the depth stop can be immobilized in snap-locked fashion in various angular positions with respect to an outer stop sleeve  29  of depth stop  21 , for which purpose two balls  29   a  are provided that engage in various angular positions, under the action of elastic O-rings  23 , into correspondingly shaped grooves on stop sleeve  29 . 
     As already mentioned, depth stop  21  can be pulled off as a unit from sleeve  19 . 
     The manner of operation of the screwdriver, with the depth stop pulled off and with noiseless torque-dependent shutoff, will be explained below with reference to FIGS.  2   a  through  2   d.  The manner of operation of the screwdriver with depth stop  21  in place will then be explained with reference to FIGS.  3   a  through  3   d.    
     A tool  105  in the form of a screwdriver bit is inserted, for example, into the tool receptacle in order to drive a screw  102  into a surface  104 . 
     With the depth stop removed, the screwdriver is first, as shown in FIG.  2   a,  placed with tool  105  onto head  103  of screw  102  and pressed down, so that both release clutch  62  and entrainment clutch  65  and disconnect clutch  54  are closed, so that when the machine is subsequently switched on, torque can be transferred from drive gear  72  to tool drive shaft  30 , and screw  102  can thus be driven in. 
     After switching on, the position shown in FIG.  2   b  is established during the screwdriving operation, since because of the relatively shallow slope of cam elements  52 , intermediate ring  55  and cam ring  50  slide out of one another until ultimately catch elements  100 ,  101  come into engagement, thus ensuring positive entrainment of cam ring  50  by intermediate ring  55 . At the same time, cam ring  50  is displaced, in response to the pressure and torque, sufficiently far toward tool  105  that throwout ring  36  is held in its slid-forward position by locking means  43 . 
     In FIG.  2   a,  first spring element  45  is compressed between cam ring  50  and throwout ring  36 , third spring element  47  is in an extended position, and fourth spring element  48  is compressed. 
     In the position according to FIG.  2   b,  third spring element  47  is somewhat shortened by the slid-forward throwout ring  36 , and first spring element  45  is still compressed, while fourth spring element  48  is somewhat elongated by the slid-forward cam ring  50 . 
     When screw  102  has been practically completely driven into surface  104 , the torque rises sharply toward the end of the screwdriving operation, so that the release torque of release clutch  62  is overcome and drive gear  72  is displaced, against the force of second spring element  46 , until cam elements  57 ,  61  (as shown in FIG.  2   c ) come out of engagement and the torque being transferred thus decreases to a value of zero. As a consequence, cam ring  50  is displaced in response to first spring element  45  toward intermediate ring  55 , so that disconnect clutch  54  releases, thus resulting in the position according to FIG.  2   d,  in which cam ring  50  and intermediate ring  55 , together with drive gear  72 , can continue to rotate but claw elements  51  of cam ring  50  and claw elements  37  of throwout ring  36  cannot come into engagement, this being ensured by the fact that throwout ring  36  is locked in the slid-forward position. 
     When the screwdriving operation is then terminated and axial pressure on the screwdriver is released, fourth spring element  48  thus relaxes, which results in disengagement of locking means  43 . Since the spring force of fourth spring element  48  is now less than the spring force of third spring element  47 , throwout ring  36  is pushed back into its starting position and disconnect clutch  54  is thus “loaded.” 
     A new screwdriving operation can now begin. 
     When working with the depth stop in place, what first results—as shown in FIG.  3   a —when the screwdriver is placed with tool  105  on the head of screw  103  is a position in which, as in FIG.  2   a,  drive gear  72 , intermediate ring  55 , cam ring  50 , and throwout ring  36  are pressed together, so that when the machine is then switched on, a torque is transferred to tool  105 . 
     When the machine is switched on, cam ring  50  once again moves (as shown in FIG.  3   b ) in response to the torque toward throwout ring  36 , the latter simultaneously being locked in a position that is slid forward toward tool  105 . 
     When depth stop  21  then encounters surface  104  with its end surface  25 , shortly before screw  102  is completely driven in, tool drive shaft  30  continues to follow screw  102  that is being driven in. As screw head  103  is countersunk, claw elements  37 ,  51  come out of engagement so that the torque briefly decreases. First spring element  45  now pushes cam ring  50  toward intermediate ring  55 , so that disconnect clutch  54  is completely disconnected and even continued rotation of the drive train does not cause chattering, since the distance between claw elements  37  and  51  has been sufficiently increased by the backward movement of cam ring  50  along oblique cam elements  52 ,  56 . 
     This situation is shown in FIG.  3   d.    
     FIG.  3   c  shows the situation, shortly before the release of disconnect clutch  54 , in which there is still a certain overlap (labeled S 2 ) between claw elements  37 ,  51  while screw head  103  can still be driven in a corresponding amount that is labeled S 1 . As soon as overlap S 2  becomes zero, disconnect clutch  54  releases; this then results in noiseless disconnection as already described. 
     The spring constants and length of spring elements  45 ,  47  and  48  should advantageously be coordinated with one another. Correspondingly, the shape and arrangement of the cam elements and catch elements should be coordinated with one another. In this context, cam elements  52 ,  56  should have less of a slope than cam elements  57 ,  61  in order to allow cam ring  50  to move forward toward throwout ring  36  before release clutch  62  releases. 
     If the screwdriver is used with the depth stop, then preferably release clutch  62  is set to a high release torque so that torque-dependent shutoff does not occur before shutoff by way of the depth stop has been achieved.