Abstract:
A tension roller ( 1 ) for a traction drive is provided, having a running wheel ( 2 ) mounted on an anti-friction bearing and a spacer ( 4   a ). A sealing cap ( 13   a ) is provided between the running wheel ( 2 ) and the spacer ( 4   a ) and allows a captivated arrangement of all components of the tension roller.

Description:
BACKGROUND  
       [0001]     The invention relates to a seal for an antifriction bearing of a tension roller or a deflection roller, which is positioned using a spacer. The seal comprises a sealing cap, which covers an annular gap between an inner bearing ring and an outer bearing ring of the antifriction bearing. The sealing cap rotates with a bearing ring and is spaced axially from the rolling bodies of the antifriction bearing, and is guided while maintaining a sealing gap to the spacer.  
         [0002]     German published application DE 41 33 777 A1 shows the construction of a tension roller for a traction drive. The roller-supported tension roller comprises an inner bearing ring, which is arranged on an adjusting bushing in connection with a spacer washer and mounted on the housing, especially the crankcase of an internal combustion engine via a separate attachment bolt. The known tension roller features no measure for connecting the spacer captively to the tensioning device in the preassembled state of the tensioning device. The known seal is unsuitable for vehicles used for off-road driving, which is associated with traveling through water or with a large amount of dirt entering into the installation space provided for the internal combustion engine.  
         [0003]     Furthermore, for achieving a defined installation position it is known to provide tension rollers with a spacer, on which preferably the inner ring of the antifriction bearing is positioned. Attachment means, especially a threaded connector, are guided through the longitudinal bore hole of the spacer and the bearing inner ring, in order to fix the structural unit, the tension roller, and also the spacer, for example, to an internal combustion engine. Such spacers have a centering shoulder for holding the inner bearing ring and also a flange, which extends radially over the entire end-side contour of the antifriction bearing. On the outside, the flange, with a cylindrical collar, covers a hub region of a running wheel, which is connected free of rotational play to the outer bearing ring of the antifriction bearing. This known construction requires a securing device for the spacer to the tension roller during the assembly, for example in the form of a separate securing device, which is unnecessary after successful assembly of the tension roller.  
       SUMMARY  
       [0004]     The invention is based on the objective of providing a tension roller, which can be assembled easily and economically and whose associated spacer is connected captively to the tension roller.  
         [0005]     This objective is realized according to the features of claim  1 . Accordingly, the tension roller or deflection roller according to the invention comprises a sealing cap, which is mounted detachably indirectly or directly to the outer bearing ring of the tension roller with a positive and/or frictional fit. Furthermore, the sealing cap is designed with play and connected to the spacer providing the formation of a sealing labyrinth. According to the invention, the sealing cap enables a structural unit, for which the components, the tension roller, the spacer, and also the sealing cap are connected captively to each other. Thus, the entire structural unit can be fed preassembled to a mounting device, which, for example, automatically mounts the structural unit according to the invention on the internal combustion engine. The invention reduces the cycle times for assembly and enables assembly that is optimized in terms of cost.  
         [0006]     In the construction of the tension roller or deflection roller according to the invention, the roller comprises a running wheel, which surrounds the antifriction bearing on the outside and on which the traction means of the traction drive are guided. The antifriction bearing is preferably centered with a positive fit on a spacer, wherein the structural unit comprising the components of the tension roller and spacer is mounted detachably to a housing of the internal combustion engine.  
         [0007]     According to the invention, advantageously, in comparison with the known state of the art, a sealing cap is allocated to the previously described component, the tension roller. Furthermore, the sealing lip fixed in position indirectly or directly on the outer bearing ring of the antifriction bearing detachably with a positive and/or frictional fit forms a sealing labyrinth with the spacer. For this purpose, the sealing labyrinth is shaped so that the spacer is connected captively and with play to the sealing cap. Consequently, the invention enables a structural unit, for which all of the components, namely the tension roller, the spacer, and also the sealing cap, are assembled captively.  
         [0008]     Advantageous configurations of the invention are the subject matter of the dependent claims  2  to  18 .  
         [0009]     Advantageously, the tension roller comprises a plastic running wheel, which can also be designated as a plastic pulley, which surrounds the outer bearing ring of the antifriction bearing. This measure guarantees economical production of the running wheel through a plastic injection molding process, wherein this process enables direct injection molding around the outer bearing ring.  
         [0010]     The plastic running wheel, which is advantageously provided with reinforcement ribs, possesses sufficient stiffness and has a weight advantage in comparison to a steel running wheel. Advantageously, the plastic running wheel is provided with an axially extending shoulder formed as a closed cylinder.  
         [0011]     In an installation position, a cylindrical leg of the sealing cap overlaps the shoulder of the running wheel. Tabs of the leg connected integrally to the cylindrical leg and directed advantageously partially radially inwards engage in a snap-on groove shape of the axially extending shoulder of the running wheel, shaped as a circular ring groove.  
         [0012]     The sealing cap according to the invention is provided advantageously with at least one, preferably with several symmetrical bore holes or openings in the cylindrical leg of the sealing cap. The shape or arrangement of the bore holes is set, so that contaminant particles or fluids can be discharged from an annular gap limited by the antifriction bearing and the sealing cap. The discharge of contaminants due to centrifugal force in the operating state, i.e., when the tension roller is rotating, can be optimized by beveling the contours of the axial shoulder of the track roller in order, in this way, to optimize the discharge of contaminants from the intermediate space formed as an annular gap.  
         [0013]     A rotationally fixed attachment of the sealing cap to the running wheel of the tension roller is desirable. For this purpose, it presents itself according to the invention to provide the sealing cap with an axially directed projection, which engages in an installation position with a positive fit in an end recess of the axial shoulder. Furthermore, the invention includes alternative solutions in order to create an effective rotational lock between the track roller and the sealing cap.  
         [0014]     A configuration of the sealing labyrinth according to the invention between the sealing cap and the spacer provides that the radial leg of the sealing cap engages with play in an annular groove of the spacer. The engagement of the leg in the annular groove is designed structurally so that it is optimized in terms of assembly on one hand and the sealing effect on the other hand. For this purpose, in particular a radial overlap of ≧0.5 mm between the inner contours of the sealing cap and the wall height on the spacer in the region of the annular groove is suitable. Here, the radial overlap can be affected by the material selection of the sealing cap and also the structural shape, in that this exhibits a certain elasticity. Therefore, for assembly a certain radial excursion of the radial leg of the sealing cap is set, wherein this automatically returns elastically when reaching the annular groove in the spacer and engages in the annular groove with play. For simplifying the assembly or for preventing damage, especially to the sealing cap, this has reduced wall thickness zones advantageously distributed peripherally in the region of the radial leg. This measure, advantageously combined with a circular bevel, on the end on the relevant outer surface of the spacer and also on the inside on the radial leg of the sealing cap, creates a simplified, nondestructive assembly of the sealing cap.  
         [0015]     For improving the effect of the sealing labyrinth, the annular groove in the spacer is defined by groove walls, whose heights are different from each other. The annular groove facing away from the antifriction bearing exceeds the height of the opposite annular groove, so that overall an extended sealing gap is set in the region of the sealing labyrinth. This construction principle decisively improves the sealing quality and thus reduces the entrance of contaminants or fluids via the sealing gap of the sealing labyrinth into the interior between the antifriction bearing and the sealing cap when the internal combustion engine is running.  
         [0016]     According to the invention, the invention further includes the shape of a spacer, whose radial leg is allocated with play in the installation position on a shoulder, which is formed between the antifriction bearing and the sealing cap. This shape is suitable for an assembly of the sealing cap, according to which the antifriction bearing in connection with the track roller is positioned on a centering pin of the spacer, before the sealing cap can then be fixed to the track roller fed axially over the spacer.  
         [0017]     A defined allocation of the components, antifriction bearing, and spacer is achieved advantageously by the spacer having a centering collar or a centering pin, on which the inner bearing ring of the antifriction bearing is pressed. This construction guarantees a proper angle alignment of the antifriction bearing necessary for the function of the traction drive in connection with the track roller on the spacer.  
         [0018]     As a measure for simplifying the assembly, according to the invention, the cylindrical rim of the sealing cap is also provided with cuts distributed peripherally, which extend in a limited way into the radial leg. During assembly, the rim can thus recede radially in a nondestructive manner.  
         [0019]     In another advantageous configuration of the invention, the sealing cap is provided with crimping in the region of the radial leg. This feature enables, for one, a defined axial distance of the sealing labyrinth to the antifriction bearing. Furthermore, the crimping improves the elasticity of the sealing cap, whereby, in particular, the assembly of the sealing cap in an annular groove of the spacer is simplified.  
         [0020]     As an alternative to an arrangement of the sealing cap with play on the spacer in the region of the sealing labyrinth, according to the invention it is possible to provide a seal, especially a felt ring. This felt ring reduces the sealing gap and optimizes the sealing effect without disadvantageous, long-lasting contact on the spacer. Thus, the seal quality is improved without simultaneously affecting the mechanical loading of the antifriction bearing due to higher component temperatures.  
         [0021]     As an alternative to a felt seal or a felt ring in the region of the sealing labyrinth, according to the invention a grease collar can be provided on the inside on the radial leg of the sealing cap. For this purpose, a high viscosity, semifluid grease is suitable, which adheres permanently to the sealing cap and thus also supports the sealing effect.  
         [0022]     The sealing cap according to the invention can be produced without cutting from a metallic material by a deep-drawing process. Alternatively, a plastic sealing cap is suitable, whereby an injection molding process that is economical for large quantities is possible. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     In the figures, tension rollers are shown in connection with differently formed sealing caps according to the invention. Shown are:  
         [0024]      FIG. 1 a  tension roller in a half section, whose sealing cap forms a sealing labyrinth with a shoulder of the spacer;  
         [0025]      FIG. 2 a  tension roller, in which the associated sealing cap engages in an annular groove of the spacer for forming a sealing labyrinth;  
         [0026]      FIG. 3  the tension roller according to  FIG. 2  in a longitudinal section. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]      FIG. 1  shows a tension roller  1 , whose construction comprises a running wheel  2 , which is produced from plastic and which can rotate relative to a spacer  4   a  through the use of an antifriction bearing  3 . In the installed state, the tension roller  1  is guided through a longitudinal bore hole  6  of the spacer  4   a  and fixed to the antifriction bearing  3  supported threaded connector  5 . The spacer  4   a  is provided with a centering collar  7 , on which an inner ring  8  of the antifriction bearing  3  is positioned preferably by a press fit and is supported on the end on a shoulder  9  of the spacer  4   a.  An outer ring  10  of the antifriction bearing  3  is surrounded on the outside by the running wheel  2  and thus connected with a positive fit. Rolling bodies  12  guided in a cage  11  are arranged between the inner ring  8  and outer ring  19  of the antifriction bearing  3  spaced radially apart from each other.  
         [0028]     Furthermore, the tension roller  1  provides a sealing cap  13   a,  which seals, on one side, an annular gap  14  set between the spacer  4   a  and the running wheel  2  and furthermore guarantees a captive connection of the spacer  4   a  to the tension roller  1 . For this purpose, the sealing cap  13   a  is positioned on a shoulder  16  of the running wheel  2  through a cylindrical rim  15 . Here, the cylindrical rim  15  overlaps the axially extending shoulder  16  and is here connected with a positive fit by partially radially inwardly directed tabs  17  with a positive fit in an annular groove  18 , which has a snap-on roller shape, of the shoulder  16 . With a radially inwardly directed leg  19   a,  the sealing cap  13   a  is guided to an outer surface  21  of the spacer  4   a  while maintaining a sealing gap  20 . The free end of the radial leg  19   a  is furthermore spaced axially from a radial shoulder  22  of the spacer  4 , so that a sealing labyrinth  23   a  is located between the radial leg  19  and the spacer  4   a.    
         [0029]     Furthermore, a rotational lock  24  is provided between the sealing cap  13   a  and the running wheel  2 . For this purpose, an axially aligned projection  25  of the sealing cap  13   a  engages with a positive fit in a correspondingly shaped recess  26  of the axially directed shoulder  16  of the running wheel  2 . The radial leg  19   a  of the sealing cap  13   a  further comprises a crimped section  27 , with which a defined distance between the antifriction bearing  3  and the sealing cap  13   a  can be defined. Furthermore, the crimped section  27  enables a certain elasticity in order to simplify the assembly of the sealing cap  13   a.  As a measure to reduce the sealing gap  21 , it is also possible provide on the inside of the radial leg  29  an annular groove  28  for holding a sealing ring. For this purpose, a felt ring  39  is suitable, which is guided on the outer surface  21  of the sealing cap  13   a,  after a start-up phase forms a tightly defined sealing gap. The sealing cap  13   a  is also provided with at least one bore hole  40  in the region of the cylindrical rim  15 . The bore hole  40  has the task of being able to discharge contaminants let into the annular gap  14  in the operating state, i.e., when the running wheel  2  is rotating, based on centrifugal force.  
         [0030]      FIG. 2  shows the tension roller  1  having a structure that, for the most part, is the same as that shown in  FIG. 1 . Below, the differences are explained relative to the tension roller  1  illustrated in  FIG. 1 . The spacer  4   b  forms an annular groove  29 , in which the free end of the radial leg  19   b  of the sealing cap  13   b  engages with play in a positive fit. For this purpose, the free end of the radial leg  19   b  is axially at a distance in the installation position to the groove walls  30 ,  31  and a groove base  32  of the annular groove  29 . This arrangement forms the sealing labyrinth  23   b.    FIG. 2  shows the sealing cap  13   b  in the installation position, in which a radial overlap “Y” between inner contours of the radial leg  19   b  of the sealing cap  13   b  and the groove wall  31  or the outer surface  35  of the spacer  4   b  attached thereto is set. Through the radial overlap “Y” in connection with the positive-fit attachment of the sealing cap  13   b  to the running wheel  2 , as explained in the description to  FIG. 1 , a captive arrangement of all components of the tension roller  1  is set for forming a structural unit  34 . The spacer  4   b  and also the sealing cap  13   b  are provided with structural measures in order to simplify the assembly of these components. The spacer  4   b  has a circular outer bevel  36  on the end in a transition zone between the shoulder  33  and an outer surface  35 . Adapted for this purpose, the radial leg  19   b  of the spacer  4   a  is provided with an inner bevel  37 , which together simplify the assembly of the components, the sealing cap  13   b  and the spacer  4   b.    
         [0031]     As another measure, which simplifies assembly, the sealing cap  13   b  is provided in the region of the radial leg  19   b  partially with zones  38 , which extend radially starting from the inner contours and which have a small wall thickness, whereby for the assembly of the sealing cap  13   b  onto the spacer  4   b,  the radial leg  19   b  can expand radially more easily and thus produces a nondestructive assembly. The wall thickness reduced zone  38  has a positive effect especially in connection with the crimped section  27  in the region of the radial leg  19   b  in order to achieve a desired elasticity of the sealing cap  13   b,  which is necessary for nondestructive assembly. As an alternative to different wall thicknesses, length-limited radial cuts in the region of the zone  38  are suitable. As further assembly simplification, the sealing cap  13   b  is provided with cuts  41 , which extend over the entire length of the cylindrical rim  15  and reach into the leg  19   b.    
         [0032]      FIG. 3  shows the tension roller  1  in longitudinal section, which forms the structural unit  34  together with the sealing cap  13   b  and also the spacer  4   b.  This illustration also includes a threaded connector  5 , with which the structural unit can be fixed detachably, for example, to a housing of an internal combustion engine not shown in  FIG. 3 . For this purpose, the threaded connector  5  is inserted into the longitudinal bore hole  6  of the spacer  4   b.  The connector head  42  is supported flat on the inner ring  8  of the antifriction bearing  3 . In the installation position, the threaded connector  5  creates a frictional, tensioned support of the inner ring  8  on the shoulder  33  of the spacer  4   b,  which is supported on the internal combustion engine by an end side  43  thereof.  
       Reference Symbols  
       [0000]    
       
           1  Tension roller  
           2  Running wheel  
           3  Antifriction bearing  
           4   a  Spacer  
           4   b  Spacer  
           5  Threaded Connector  
           6  Longitudinal bore hole  
           7  Centering collar  
           8  Inner ring  
           9  Shoulder  
           10  Outer ring  
           11  Cage  
           12  Rolling body  
           13   a  Sealing cap  
           13   b  Sealing cap  
           14  Annular gap  
           15  Rim  
           16  Shoulder  
           17  Tab  
           18  Annular groove  
           19   a  Leg  
           19   b  Leg  
           20  Sealing gap  
           21  Outer surface  
           22  Shoulder  
           23   a  Sealing labyrinth  
           23   b  Sealing labyrinth  
           24  Rotational lock  
           25  Projection  
           26  Recess  
           27  Crimped section  
           28  Annular groove  
           29  Annular groove  
           30  Groove wall  
           31  Groove wall  
           32  Groove base  
           33  Shoulder  
           34  Structural unit  
           35  Outer surface  
           36  Outer bevel  
           37  Inner bevel  
           38  Zone  
           39  Sealing ring  
           40  Bore hole  
           41  Cut  
           42  Screw head  
           43  End