Abstract:
A planetary gearbox for a power tool has a planetary carrier and a rotatable sleeve with sun wheel toothing arranged centrally on the planetary carrier. The sleeve has a radial section with outer toothing. Planet wheels are positioned between planetary carrier and radial section and mesh with the sun wheel toothing. A switching ring gear surrounds the planet wheels and has an inner toothing meshing with the planet wheels. The switching ring gear is axiallay moveable on the planet wheels between first and second end positions for switching a transmission ratio. In the second end position the switching ring gear engages the outer toothing of the radial section. A synchronization disk, rotating with the rotary sleeve, is positioned between planet wheels and radial section and acts directly or indirectly by friction on the switching ring gear when the latter is moved from the first into the second end position.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a switchable planetary gearbox, in particular, for a hand-held power tool, comprising a planetary carrier supporting on one end face several planet wheels whose toothing meshes permanently with a sun wheel toothing of a central rotary sleeve. The planetary gearbox further comprises a switching ring gear surrounding the planet wheels and meshing permanently with the toothing of the planet wheels. The switching ring gear is longitudinally slidable and, for switching a transmission stage of the planetary gearbox, can be moved into engagement with an outer circumferential toothing that is provided on the circumference of a radial section of the rotary sleeve covering the end face of the planet wheels facing away from the planetary carrier. 
   As is known in the art, planetary gearboxes are comprised essentially of a central sun wheel on which the planet wheels supported on a planetary carrier are rolling. Usually three planet gear wheels are supported externally on the concentrically arranged ring gear. Such a gearbox is suitable, in particular, for use in hand-head working tools such as power drills because the configuration of the planetary gearbox provides a favorable ratio between size and transmittable power for a relatively high possible transmission ratio. 
   German patent DE 42 13 291 C2 discloses a planetary gearbox for a hand-held hammer drill wherein the gearbox acts by means of a crown gear onto the drive spindle of the drill. In order to be able to shift into the different gears of the hammer drill, the planetary gear is provided with different transmission stages wherein shifting between the stages is realized by means of an axially movable switching ring gear moveable into several displacement positions. One of the transmission stages of the gearbox corresponds to a position of the switching ring gear in which the switching ring gear is blocked by a locking member that is provided on the housing of the gearbox and engages the toothing of the switching ring gear for blocking. By axial movement of the partial switching ring gear by means of a gear shifting grip, the transmission stage can be switched in that the toothing of the switching ring gear is moved into engagement with the outer toothing of a gear member that covers the planet wheels radially. In the known planetary gearbox, the radial section supporting the outer toothing is provided on the central sleeve that supports the sun wheel toothing or is kinematically coupled therewith. 
   On the planetary gearbox of the power tools, usually an increased wear is observed during operation of the power tool and this wear is worsened even more by repeated shifting during operation when idling or operating under load. Particularly the inner toothing of the switching ring gear and the outer toothing of the web that is to switched or blocked are subject to the wear effects. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to further develop the gearbox of the aforementioned kind such that the wear effects are counteracted and the service life of the gearbox is increased. 
   In accordance with the present invention, this is achieved in that between the planet wheels and the radial section of the sleeve supporting the outer toothing a synchronization disk is arranged such on the sleeve that it is entrained by the sleeve and in that, upon movement of the switching ring gear in the direction toward the outer toothing, the synchronization disk acts frictionally directly or indirectly on the switching ring gear. 
   The invention is based on the finding that the increased wear effects occurring upon increased switching processes between the transmission stages are caused by the high speed differences between the switching ring gear and the component supporting the outer toothing. With the configuration according to the invention comprising a synchronization disk entrained by the central sleeve, the switching ring gear when approach the outer toothing is accelerated by the synchronization disk and is synchronized to the speed of the sleeve and thus of the outer toothing. Because the switching ring gear during the switching or shifting process is pushed across the synchronization disk, either the outer circumference of the synchronization disk contacts the inner toothing of the switching ring gear and acts therefore frictionally on the inner toothing of the switching ring gear or the synchronization disk acts frictionally on the planet wheels and through them indirectly onto the switching ring gear. A satisfactory frictional connection between the synchronization disk and the switching ring gear without impairment of the longitudinal (axial) movement of the switching ring gear is achieved expediently by providing the synchronization disk with a diameter that matches approximately the tip circle of the toothing of the switching ring gear. It was found to be especially advantageous when the synchronization disk has a diameter that is minimally oversized relative to the tip circle of the inner toothing of the switching ring gear. 
   In a simple and compact configuration a positive-locking drive of the synchronization disk can be realized through the sun wheel toothing of the sleeve when the synchronization disk is provided at its inner circumference with at least one radial nose switching that in the mounted position of the synchronization disk engages the sun wheel toothing of the sleeve. Expediently, there are several radial noses on the inner circumference of the synchronization disk arranged at a rotary angle spacing in accordance with the pitch of the sun wheel toothing so that a strong positive-locking drive action is realized while a uniform force introduction into the synchronization disk is realized. 
   In order to improve friction engagement of the synchronization disk on the switching ring gear, the synchronization disk can be provided on its circumference with an angled edge so that a damaging effect of the fast-rotating toothing of the switching ring gear onto the edge of the synchronization disk can be counteracted in this way. 
   The synchronization disk is particularly resistant in regard to wear effects caused by the action of the ring gear toothing when its outer circumference is formed by several radially displaceable contact sections. As soon as the switching ring gear has been pushed across the synchronization disk, the contact sections resting against the inner toothing of the switching ring gear are displaced and in this way protected against damaging effects or destruction. It is particularly advantageous when the contact sections are configured as contact jaws that are arranged on deflectable spring arms. Such an advantageous configuration of the synchronization disk according to the invention can be realized by providing appropriate cutouts in the synchronization disk by simple means, for example, by stamping, wherein the contact jaws, the spring arms, and a central ring for slipping the disk onto the sleeve form a monolithic component. 
   In an advantageous configuration of the invention, the synchronization disk is arranged in a gap between the planet wheels and a planetary carrier of another planetary gear stage; this provides a multi-stage planetary gearbox with synchronized shifting action of a very compact configuration. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a longitudinal section of a planetary gearbox. 
       FIG. 2  is a cross-section along the line II-II of  FIG. 1 . 
       FIG. 3  is a longitudinal section of the planetary gearbox in a second transmission position. 
       FIG. 4  is a cross-section of the planetary gearbox according to section line IV-IV of  FIG. 3 . 
       FIG. 5  is first embodiment of a synchronization disk in axial view. 
       FIG. 6  is a side view of the synchronization disk of  FIG. 5  viewed in a direction of arrow VI. 
       FIG. 7  is an alternative configuration of a synchronization disk in axial view. 
       FIG. 8  is a side view of the synchronization disk according to  FIG. 7 . 
       FIG. 9  is a detail view of the detail IX a  FIG. 7 . 
       FIG. 10  is a another embodiment of a synchronization disk. 
       FIG. 11  is a cross-section of the synchronization disk according to  FIG. 10 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following description same parts are identified by same reference numerals. 
     FIG. 1  shows a cross-section of a planetary gearbox  1  for a power tool, not illustrated, such as a power drill or the like, that is arranged between the drive motor of the power tool and its working spindle. The planetary gearbox  1  has in its housing  2  several gear stages that can be combined in different ways by a shifting device to be described in the following and, depending on the shifted position, transmit the speed of the motor at different transmission ratios onto the drive spindle and the tool of the power tool. The three gear stages are each designed as planetary gears and thus provide a favorable ratio between minimal size and transmittable power. The speed and the torque of the drive motor are introduced by a drive sleeve  4  into the gearbox  1  wherein the drive sleeve  4  is a central sun wheel of the first transmission stage. First planet wheels  5  are rolling on the sun wheel toothing of the drive sleeve  4  and are rotatably guided on a planetary carrier. The first planet wheels are supported on the toothing of a first ring gear  3  that is supported in the housing  2  in the illustrated embodiment. 
   The speed of the planetary carrier  6  of the first planet wheels  5  provides the input speed for the axially neighboring second transmission stage. In this connection, the planetary carrier  6  of the first planet wheels  5  is fixedly connected to a second sleeve  8  that is coaxially positioned relative to the drive sleeve  4 ; the sleeve  8  is provided on its circumference with a sun wheel toothing  9  and forms the sun wheel of the second planetary gear stage. In the present embodiment, the first planetary carrier  6  that is embodied essentially radially to the axis of rotation if the gearbox  1  and the sun wheel sleeve  8  of the second gear stage that is configured primarily axially form together a monolithic part. On the sun wheel toothing  9  of the central sleeve  8  of the second gear stage the second planet wheels  10  are rolling and are supported on the second planetary carrier  12 . The second planetary carrier  12  and the sun wheel sleeve  11  of the third planetary gear stage together form a monolithic part. Third planet wheels  15  mesh with the sun wheel sleeve  11 . The third planet wheels  15  are supported on the toothing of a third ring gear  19  and are supported by means of bolts  16  rotatably on the planetary carrier  17 . By rotary movement of the planetary carrier  17  that is created by the rolling action of the third planet wheels  15  on the sun wheel toothing  14  is transmitted as output speed of the gearbox  1  onto the output shaft  18 . 
   The switching ring gear  13  of the second gear stage, whose inner toothing meshes constantly with the three planet wheels  10  of the second gear stage, is arranged to be longitudinally (axially) slidable. By movement of the switching ring gear  13  shifting of the transmission ratio can be realized. The switching ring gear  13  is provided at its circumference with a circumferential groove  32  that is engaged by a gearshift lever, not illustrated. The switching ring gear  13  is thus movable in the axial direction of the main axis of rotation  37  of the gearbox  1  within a space in which in the axial direction the first planetary carrier  6  and the second planetary carrier  12  as well as the planet wheels  10  supported on the second planetary carrier  12  are arranged. In the end position illustrated in  FIG. 1  the switching ring gear  13  is movable into the switching position illustrated in  FIG. 3  in which the inner toothing  20  of the switching ring gear  13  is in engagement with an outer toothing  7  that is provided on the circumference of the radially extending first planetary carrier  6 . The configuration of the gearbox  1  corresponds in other respects to the illustration of  FIG. 1  and the corresponding description. The outer circumferential toothing  7 , as a result of the monolithic configuration of the first planetary carrier  6  with the sun wheel  8  of the second gear stage, is fixedly coupled to the rotation of the sun wheel toothing  9 . When the switching ring gear  13  is moved into the engagement position with the outer toothing  7  as illustrated in  FIG. 3 , the speed of the switching ring gear  13  is increased and the transmission ratio of the second gear stage is changed. When shifting down the transmission ratio of the gearbox  1 , the inner circumferential toothing  20  of the movable switching ring gear  13  is disengaged from the outer toothing  7  of the planetary carrier  6  and, by reducing the speed, is moved into the end position of  FIG. 1 . 
   In the gap between the radial planetary carrier  6  of the first gear stage and the exposed end faces of the second planet wheels  10 , a synchronization disk is arranged that can be entrained by the sun wheel sleeve  8  of the second transmission stage; the synchronization disk extends radially into the area of the outer toothing  7 . The radial synchronization disk is positioned in the section plane II-II of  FIG. 1  and IV-IV of  FIG. 3 . As can be seen in the cross-sectional illustrations of  FIGS. 2 and 4 , the synchronization disk  21  projects radially with its outer circumference into the area of the outer circumferential toothing  7  and is contacted in the corresponding position of the switching ring gear  13  by the inner toothing  20  of the switching ring gear  13 . When the switching ring gear  13  is to be brought by a shifting action into engagement with the outer toothing  7 , the inner toothing  20  of the switching ring gear  13  must contact the outer circumference of the synchronization disk  21  and is thus accelerated by frictional forces. Since the synchronization disk  21  is entrained by the sun wheel toothing  9  of the rotary sleeve  8 , the synchronization disk  21  rotates constantly at the speed of the outer toothing  7  that, as it is a monolithic part of the sleeve  8 , synchronously rotates with the rotary sleeve  8 . The frictional forces between the synchronization disk  21  and the inner toothing  20  brings the switching ring gear  13  up to the speed of the outer toothing  7 . By synchronizing the switching ring gear  13  and the outer toothing  7  before engagement, the wear caused by high loads on the tooth flanks is prevented. The synchronization disk can be very thin, e.g., less than 2 mm, and preferably has a thickness of approximately 0.5 mm; therefore, the disk  21  takes up only little space and is insertable in a simple way when assembling the planetary gearbox. 
   In  FIGS. 5 through 11  configurations of the synchronization disk are illustrated. The synchronization disks  21 ,  26 ,  28  have a wall thickness d of advantageously 0.5 mm and have an inner circumference  36  with which they can be placed onto the rotary sleeve  8  of the second gear stage. In order to ensure a positive-locking engagement of the synchronization disk  21 ,  26 ,  28 , the inner circumference  36  is provided with radial noses  27  which in the mounted position of the synchronization disk engage the sun wheel toothing. Advantageously, several radial noses are provided that are arranged in accordance with the pitch of the sun wheel toothing at the appropriate rotary angle position. The radial noses  27  illustrated in detail in  FIG. 9  have expediently a tooth contour that matches that of the sun wheel toothing  9 . 
   An especially preferred configuration of the synchronization disk  21  according to the invention is illustrated in  FIGS. 5 and 6 . An optimal spring behavior of the outer circumference of the disk loaded by the ring gear toothing is achieved in that the contact sections  34  contacted by the toothing are formed on contact jaws  25  that are displaceably connected to spring arms  24 . By recesses  35  in the synchronization disk  21 , produced, for example, by stamping, two spring arms  24  are provided that converge at their center and support the contact jaws  25 . The contact section  34  is thus protected against wear or even destruction by the toothing of the switching ring gear and, when contacted by the toothing, yields radially while the spring arms  24  exert a corresponding pressure forces onto the tooth tips of the switching ring gear toothing  20 . 
   The base of the spring arms  24  are connected to the circumference of a central annular member  22  of the synchronization disk  21  with which the synchronization disk  21  by means of its radial noses is movable on the sun wheel toothing. The synchronization disk according to the invention is a monolithic part comprising the contact jaws  25 , the spring arms  24  and the central securing ring  22  for a positive-locking entrainment by the rotary sleeve  8 ; it can be produced, for example, by stamping. In the present embodiment the synchronization disk  21  is provided with three radially displaceable contact jaws  25  that are distributed uniformly about the circumference of the synchronization disk  21 . As can be seen in  FIGS. 2 and 4 , the synchronization disk  21  can be mounted advantageously in such a rotational position that the three content jaws  25  are positioned so as to overlap the end faces of the planet wheels  10  and in this way protect the bearing of the gear wheels. 
   The synchronization of the speed of the switching ring gear  13  can be realized directly, as realized, for example, by the synchronization disk  21  according to  FIG. 5 . In order to provide frictional connection between the synchronization disk  21  and the inner toothing  20  of the switching ring gear  13 , the contact jaws  25  have a diameter that is matched such that the circumscribed circle of the rotational movement extends radially into the area of the outer toothing such that at least the tip circle of the toothing  20  of the switching ring gear  13  is reached. The tip circle of the toothing  20  of the switching ring gear  13  is safely reached when the diameter of the synchronization disk  21  has an appropriate oversize. 
   The synchronization disk  26  illustrated in  FIGS. 7 and 8  has a plane circular disk member with a concentric inner circumference  36 . The entire edge of the synchronization disk centers the switching ring gear  13  and accelerates it by friction during the switching process. The outer diameter of this synchronization disk  26  is minimally smaller than the tip circle of the inner circumferential toothing  20  of the switching ring gear  13 . In this way, the synchronization disk acts indirectly, i.e., through the second planet wheels  10 , onto the switching ring gear  13 . 
   The synchronization disk  28  illustrated in  FIGS. 10 and 11  is provided with an angled edge  29  which provides a centering action when pushing on the toothing of the switching ring gear  13 . By friction that results through this centering action, the switching ring gear  13  is accelerated. An optimal behavior is achieved for a bending angle α of the edge  29  relative to the plane of the disk  28  of approximately 160 degrees. 
   While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.