Abstract:
A snap ring for shafts or bores is proposed, which is able to be axially fixed in position by snapping into place in a circumferential groove. The snap ring is provided with a centering ring which, when the case of the snap ring is installed in the circumferential groove, extends with radial clearance to an annular clip of the snap ring, which is disposed approximately concentrically to the circumferential groove.

Description:
FIELD OF THE INVENTION 
   The present invention is directed to a snap ring. 
   BACKGROUND INFORMATION 
   Snap retaining rings are already known which are used for axially securing structural components, such as bearings, gears, or sealing rings to shafts or bores. Snap rings of this kind can be designed to engage with radially inwardly open circumferential grooves, in bores, or with radially outwardly open circumferential grooves, in shafts. These snap rings exist in various removable and non-removable designs. They also constitute the subject matter of various standards (e.g., DIN, ISO). The snap rings are normally grooved with undersized and/or oversized dimensions, so that, once inserted into a corresponding circumferential groove, they are held by self-action in the shaft or bore, under prestressing. For example, International Patent Application WO 79/12170 discloses a snap ring which is provided with a centering member that extends with radial clearance to a circumferentially disposed annular clip of the snap ring which forms two limbs. 
   SUMMARY OF THE INVENTION 
   The advantage of the snap ring according to the present invention is that, in addition to the axial retaining function, it also enables a centering action to be performed between a bore and a shaft or spindle to be inserted therein during assembly. In this manner, one can prevent a shaft sealing ring located between a bore and a shaft from becoming damaged, for example, by sharp edges or offsets during assembly due to the shaft and bore becoming skewed. Thus, one avoids a premature failure of the sealing action of the shaft sealing ring. 
   Due to the fact that the radial cross-sections of the two limbs of the snap ring taper off towards their unattached ends, the snap ring is uniformly deformed in response to its two limbs being compressed upon installation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a plan view of a snap ring according to the present invention, having a centering function in accordance with a first exemplary embodiment. 
       FIG. 2  illustrates a plan view of a snap ring according to the present invention, having a centering function in accordance with a second exemplary embodiment. 
       FIG. 3  is a part-sectional view through a hammer drill, which has a snap ring according to the present invention, having a centering function. 
   

   DETAILED DESCRIPTION 
   In  FIG. 1 ,  10  denotes a snap ring which has a concentrically disposed, or approximately annular, slotted clip  11  of resilient material, in particular of spring steel. At its two free ends, clip  11  has lugs  12 ,  13 , through each of which perforations  14 ,  15  are cut. As is generally known, into perforations  14 ,  15 , one may insert snap ring pliers, which, by changing the distance between lugs  12 ,  13 , make it possible to vary the diameter of clip  11  in order to install snap ring  10 . 
   In  FIG. 1 , snap ring  10  is designed as an internal ring for a radially inwardly open circumferential groove and is, therefore, suited for axially securing a component to a bore. Located inside clip  11  is a centering ring  17 , which is joined to clip  11  by way of a web  16 . Centering ring  17  is provided with a center bore  18 , which is disposed approximately concentrically with respect to snap ring  10  and to a corresponding circumferential groove into which snap ring  10  is insertable. On the side of clip  11  facing opposite web  16 , a notch  19  is provided, which divides clip  11  into two limbs  11   a, b . Limbs  11   a, b  are formed with a radial cross-section that tapers off toward the unattached ends, resulting in a uniform deformation when snap ring  10  is installed. Located at each of the mutually opposing surfaces of lugs  12 ,  13  are flat portions  12   a ,  13   a , which are used as mutual stop faces. In this context, flat portions  12   a ,  13   a  are aligned in parallel to radial traces  36 ,  37 , respectively, which run through a midpoint  35  of snap ring  10 . The stop faces ensure that the material stress that clip  11  is subject to during installation of snap ring  10  is kept within acceptable limits. 
     FIG. 2  illustrates a second exemplary embodiment of a snap ring  210  having a centering function. Equivalent parts and parts performing equivalent functions as those shown in  FIG. 1  are denoted in  FIG. 2  by reference numerals which are formed by adding a prefix “2” to the corresponding reference numerals shown in  FIG. 1 . In comparison to the exemplary embodiment according to  FIG. 1 , the second exemplary embodiment according to  FIG. 2  is distinguished by web  216  being located in the vicinity of a lug  212 . In this context, centering ring  217  is likewise encircled by clip  211 , so that snap ring  210  shown in  FIG. 2  is likewise designed as an internal ring. 
     FIG. 3  depicts an application case for a snap ring  10  according to the present invention. Here,  FIG. 3  shows a partial section through a driving device  21  of a hammer drill. In the left half of the illustration of  FIG. 3 , the driving device is shown in a final assembled position, while in the right half, it is shown during assembly. 
   An electromotor  22  has a motor shaft  23 , which is provided on the inside with an armature pinion  24 . In this context, motor shaft  23  is rotationally mounted via an antifriction roller bearing  25  at a gear housing  26 . Seated next to and in front of antifriction bearing  25  in a through-hole  27  in gear housing  26  is a sealing ring  28 , which, by way of its sealing lip  29 , seals off a gear compartment  30  from a motor compartment  31 . For that purpose, sealing lip  29  engages on the outer surface of motor shaft  23  (left half of the illustration in  FIG. 3 ). Within through-hole  27 , sealing ring  28  is axially secured by snap ring  10 . In this context, snap ring  10  is seated, under prestressing, in a concentrically disposed, internal groove  32  in gear housing  26 . 
   In the right half of  FIG. 3 , driving device  21  is shown in its assembled position. Here, antifriction bearing  25  is pressed onto motor shaft  23  and is installed, together with motor shaft  23  and electromotor  22 , in through-hole  27 . In so doing, armature pinion  24  initially reaches through centering bore  18  in centering ring  17 , and is radially guided by the same. In response to further insertion of driving device  21 , armature pinion then reaches through the sealing opening formed by sealing lips  29 , deeper into bore  27 , until it subsequently engages fully with gears  33 ,  34  in gear compartment  30 , as shown in the left half of the illustration. Centering ring  17 , which, together with snap ring  10 , forms one unit, prevents the sealing lip from being damaged by armature pinion  24 , which may be sharp-edged, during insertion of driving device  21 . To this end, centering bore  18  is designed to be approximately concentric with circumferential groove  32 . 
   The present invention is not limited to the described exemplary embodiments. Thus, when working with a snap ring designed as an external ring for shafts, it is also possible for the centering ring to wrap around the outside of the clip. In place of one web, a plurality of webs may also be provided for joining the centering ring and clip.