Abstract:
The invention relates to an automatic belt tensioner comprising a basic part that is connected to a tensioning part so as to be rotatable about a common axis of rotation, a helical spring that is joined to the basic part and the tensioning part, and a wrapping bush which is wrapped at least in some areas with a radial enveloping force by means of the helical spring. According to the invention, the material of the wrapping bush contains reinforced plastic in order to ensure that the belt tensioner provides good damping and good cushioning properties if possible during the entire service life thereof while being universally usable and having a simple design.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 10/584,101, filed Apr. 5, 2007, which application claims the benefit of German Application Ser. No. 20319886.7, filed Dec. 22, 2003. The entire disclosures of each of the above applications are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The invention relates to an automatic belt tensioner with the characteristics of the preamble of claim  1 . 
       BACKGROUND 
       [0003]    DE 40 10 928 C2 discloses an automatic belt tensioner of this kind for tensioning a belt in a belt-drive system. This way, a tensioned state of the belt is intended to be maintained during the entire service life. The belt is tensioned with a wheel provided on a tensioning arm. 
         [0004]    Depending on the application conditions of the automatic belt tensioner, the belt is placed in varying states of vibration by the driving and driven assemblies. The vibrations of the belt are transmitted via the tensioning arm to the housing of the automatic belt tensioner. The helical spring is supported at one end with turns on a wrapping bush, which transmits the forces acting upon it to a spring sleeve. The wrapping bush ensures a more even distribution of the frictional force to the spring sleeve. This way higher torque can be achieved, and the damping action is more effective. The wrapping bush additionally offers effective support for the turns of the helical spring and is actively involved in the damping effect during operation. Despite the friction that occurs during operation, the interacting components are intended to maintain these properties if possible without decreased function. 
         [0005]    It is the object of the invention to improve a belt tensioner of this kind such that it provides good damping and good cushioning properties if possible during the entire service life of the belt tensioner, while being universally usable and having a simple design. 
         [0006]    This object is achieved according to the invention with a belt tensioner with the characteristics of claim  1 . 
       SUMMARY 
       [0007]    The enveloping turns of the helical spring can mate very well with the wrapping bush, thus producing a very good force-fit connection. The material of the wrapping bush comprising reinforced plastic is sufficiently tough and wear-resistant compared to the kind of wrapping bush made of non-ferrous metal. This way, any friction occurring at the seams to adjoining components, particularly to the helical spring, can be absorbed during the entire service life of the automatic belt tensioner. The damping properties of the belt tensioner therefore likewise remain substantially the same during the entire service life of the belt tensioner. The wrapping bush is more wear-resistant and remains more dimensionally stable. 
         [0008]    According to a particular option, the plastic can be fiber-reinforced. The plastic may comprise particularly glass fibers for reinforcement. The fibers sufficiently reinforce the otherwise soft plastic material so that the helical spring has a good fit and support on the wrapping bush. The wrapping bush, however, remains sufficiently flexible for elastic movements and is more wear-resistant. 
         [0009]    Particularly advantageous with this device could be a sphere-reinforced plastic, comprising in particular glass spheres for reinforcement. This embodiment of the invention is suited for high belt tension levels and has lasting, good dimensional stability and wear-resistance properties. 
         [0010]    Advantageously, the wrapping bush can accommodate right- and left-handed helical springs. This way, the same wrapping bush can be universally equipped with left- or right-handed helical springs, depending on the tensioning direction at the installation location. 
         [0011]    In a particular variant, a peripheral edge of the wrapping bush may comprise inclines corresponding to the course of a left-handed turn in one area and that of a right-handed turn in another area. The peripheral edge supports potential spring turns of the helical spring sufficiently well, and the generated enveloping force can be transmitted to the wrapping bush with the least possible loss of force and torque. 
         [0012]    In a particularly advantageous embodiment of the automatic belt tensioner, the helical spring can envelope the wrapping bush with less than one full turn, particularly with more than or equal to a half or 0.7 turn. This way, a sufficiently large contact area of the radial enveloping force on the wrapping bush is guaranteed. Contrary to expectations, this small wrapping area suffices in order to maintain the belt tension as continuously as possible on the one hand and in order to produce sufficiently great stability and friction on the adjoining components for vibration damping purposes on the other hand. 
         [0013]    In another variant of the invention, the wrapping bush may comprise a chamfered peripheral edge on the free end. This chamfered configuration ensures smooth action of the spring turn on the wrapping bush. 
         [0014]    In a particularly advantageous variant of the automatic belt tensioner, the wrapping bush envelopes a spring sleeve at least in some areas and the spring sleeve comprises at least one recess on the circumference, which recess engages with a step provided in the spring sleeve in the circumferential direction and/or axial direction. This way, the wrapping bush is fixed in place so as to resist axial displacement in relation to the spring sleeve and/or so as to resist rotational movements. 
         [0015]    A special option may be provided if the step of the spring sleeve comprises an inclined surface in the axial direction, which surface widens the wrapping bush up to the engagement position during assembly. This ensures that the wrapping bush easily slides on the spring sleeve. 
         [0016]    In another variant of the invention, at least one retaining step may be provided on the free end opposite the peripheral edge of the wrapping bush, which step engages in a recess provided in the spring sleeve to resist rotational movements. 
         [0017]    This way, the wrapping bush is fixed non-rotationally in its position in relation to the spring sleeve. 
         [0018]    In a particularly advantageous design, the spring sleeve may comprise at least one depression for receiving a lubricant on the inside. As a result of the depression, sufficient lubricant may be stored and provided during the entire service life of the belt tensioner. The supply of the lubricant on the inside of the spring sleeve favors the friction and damping behaviors to the adjoining component. 
         [0019]    The depression may extend particularly in the axial direction, and it may particularly have a design that is notched in its cross-section. Sufficient lubricant is applied to the inside of the spring sleeve across the entire length. 
         [0020]    Due to the notched depression, a sufficiently large lubricant supply and/or lubricant feed volume for vibration damping are provided. 
         [0021]    Advantageously, a spring sleeve enveloped at least in some areas by the wrapping bush may comprise a supporting base collar, which may be broken down into several areas distributed across the circumference. The base collar may support the spring sleeve in relation to the basic part on the components attached thereto in a very stable manner in terms of shape and position and due to the small amount of material that is required does not result in significantly added weight. 
         [0022]    In another variant of the invention, a spring sleeve surrounded at least in some areas by the wrapping bush may comprise a supporting base collar, wherein at least one area of the base collar comprises a projecting spring end support. 
         [0023]    This way, a free spring end of the helical spring is supported very well up to a detent area of the spring ends in the basic part. 
         [0024]    In another variant of the invention, the wrapping bush surrounds a spring sleeve at-least in some areas, wherein the wrapping bush and the spring sleeve are produced together in a multi-component tool. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0025]    The drawing illustrates an exemplary embodiment of the invention, which is explained in more detail hereinafter, wherein: 
           [0026]      FIG. 1  is a sectional drawing of an automatic belt tensioner according to the invention, 
           [0027]      FIG. 2  is a perspective view of a wrapping bush of a belt tensioner according to the invention, 
           [0028]      FIG. 3  is a lateral view of the wrapping bush from  FIG. 2 , 
           [0029]      FIG. 4  is a perspective illustration of a wrapping bush and a spring sleeve according to the invention in the assembled state, 
           [0030]      FIG. 5  is a perspective illustration of the spring sleeve with the wrapping bush in a view rotated by 90° in relation to  FIG. 4 , and 
           [0031]      FIG. 6  is a perspective illustration of individual turns of a helical spring, which surrounds the wrapping bush placed on the spring sleeve. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 1  shows an assembly of the automatic belt tensioner  1  according to the invention. 
         [0033]    It shows a basic part  2 , which can be rotated relative to a tensioning part  3  about a common axis of rotation  4 . The common axis of rotation  4  extends centrically in the axial direction in a bolt  5 . One end  6  of the bolt  5  is firmly connected to the basic part  2 . On the opposite end  7  of the bold  5 , a pressed-on flange sleeve  8  is held in place with the help of a washer  9 . 
         [0034]    The tensioning part  3  has a pot shape with an inner wall  10 . The inner wall  10  has an inside  56  and an outside  17 . The tensioning part  3  is connected to the flange sleeve  8  on the inside  56  so as to be able to rotate about a common axis of rotation  4 . 
         [0035]    A helical spring  11  is disposed around the outside  17  of the inner wall  10  of the tensioning part  3 . The turn  12  of the helical spring  11  is engaged on one spring end with the tensioning part  3  and supported thereon. 
         [0036]    On the other spring end, the last turn  13  is connected to the basic part  2  on the opposite side of the helical spring  11  and supported thereon. 
         [0037]    The helical spring  11  surrounds a wrapping bush  14  with slightly more than one turn  13 ,  44 . The remaining turns have no contact with the wrapping bush and the spring sleeve  15 . 
         [0038]    The wrapping bush  14  surrounds the spring sleeve  15  and rests against it. The outside diameter  46  of the wrapping bush  14  is about 1 mm larger than the inside diameter  45  of the helical spring  11  in the relaxed state. Due to the larger outside diameter  46  of the wrapping bush  14 , the helical spring  11  is pre-stressed in the illustrated assembled state. 
         [0039]    The inside of the spring sleeve  16  is connected to the outside  17  of the wall  10  of the tensioning part  3  in a frictionally engaged manner. The spring sleeve  15  is supported with a base collar  37  on the bottom surface  50  in relation to the basic part  2 . 
         [0040]    A tension pulley  18  is rotatably connected to a deflecting arm  62  formed on the tensioning part  3  via a radial bearing  20  with the help of a screw  19 . The deflecting arm  62  is disposed in a parallel spaced manner in the axial direction from the common axis of rotation  4 . As a result, a lever arm  64  is geometrically formed, the lever length of which is the distance between an axis of rotation  63  of the tension pulley  18  and the common axis of rotation  4 . 
         [0041]      FIG. 2  shows a perspective view of a wrapping bush  14 , which is made of sphere-reinforced plastic. The glass sphere reinforcement produces increased rigidity and increased stability of the wrapping bush  14 . 
         [0042]    On the periphery, the wrapping bush  14  comprises in the axial direction a continuous slot  21 . The slot  21  is formed by a lateral left edge  33  and a lateral right edge  34 . The wrapping bush  14  on the free end thereof  43  has a chamfered outer peripheral edge  26 . The chamfered peripheral edge  26  is interrupted with several recesses  22 ,  23 ,  24  and one chamfer  25 . 
         [0043]    The recesses  22 ,  23  have the contour of an elongated hole and are disposed diametrically symmetrically opposed in the axial direction in the periphery of the wrapping bush. 
         [0044]    Another recess  24  has a more rectangular contour, which is disposed diametrically symmetrically opposed to the slot  21  in the axial direction on the periphery of the wrapping bush  14 . 
         [0045]    The chamfer  25  extends across the entire circumference of the wrapping bush  14  and is disposed in the radial direction on the outside of the free end  43 . 
         [0046]    On the opposite peripheral edge  27  of the wrapping bush  14 , two steps  28 ,  29  are provided. The steps  28 ,  29  have a rectangular shape that is raised in the axial direction in relation to the peripheral edge  27 . 
         [0047]      FIG. 3  illustrates the side view of the wrapping bush from  FIG. 2 , wherein the peripheral edge  26  has inclines  30 ,  31  corresponding to the course of a right-handed turn in an 
         [0048]    area extending from the lateral right edge  34  of the slot  26  and corresponding to the course of a left-handed turn extending from the lateral left  33 . The inclines extend to the recess  24 , respectively. 
         [0049]      FIG. 4  shows a spatial illustration of a spring sleeve  15  with a wrapping bush  14 . 
         [0050]      FIG. 5  shows a view that is rotated by 90° in relation to  FIG. 4 . 
         [0051]      FIG. 4  and  FIG. 5  on the inside of the spring sleeve  15  show several notch-like depressions  35 . The depressions  35  extend along the axial direction of the spring sleeve  15  across the entire length of the inside  49 . The depressions  35  store lubricant. 
         [0052]    The spring sleeve  15  on the periphery thereof comprises a continuous elongated slot  32  in the axial direction. The spring sleeve  15  comprises a supporting base collar  37  projecting in the radial direction, which collar is broken down into several substantially evenly distributed areas  51 ,  52 ,  53 ,  54 ,  55  across the circumference. 
         [0053]    The areas  51 ,  52  are disposed mirror-symmetrically to each other on the edges of the slot  32 . The area  53  is rotated clockwise by about 90° in relation to the area  52 . The area  55  is disposed diametrically symmetrically opposed to the area  53  in the axial direction. 
         [0054]    The areas  53 ,  55  comprise continuous recesses  38 ,  48  provided along the axial direction. The area  54  is disposed diametrically opposed to the slot  32  and in the radial direction on the free end thereof comprises a peripheral web  42 . In the area  54 , an area of a spring end support  41  projecting in the radial direction in relation to the web  42  is integrally formed. 
         [0055]    On the outside  60  of the spring sleeve  15 , two longitudinal steps  39 ,  57  are disposed diametrically opposed in the axial direction. They extend from the free peripheral edge, which is disposed axially opposite from the base collar. The step  39  comprises an inclined surface  40  in the axial direction. Proceeding from the start  58  of the inclined surface  40 , it is raised with a positive incline to the end  59 . Starting with the end  59 , the step  39  is integrally formed in a planar fashion along the axial direction to its end. The step  57  has the same configuration as the step  39 . 
         [0056]    In  FIG. 4  and  FIG. 5  the wrapping bush  14  is placed on the spring sleeve  15  such that the slot  21  of the wrapping bush  14  is aligned with the slot  32  of the spring sleeve  15 . The retaining steps  28 ,  29  provided on the wrapping bush  14  engage in a non-rotational manner in the recesses  38 ,  48  provided in the spring sleeve. The steps  39 ,  58  fasten the wrapping bush  14  via the recess  22 ,  23  so as not to rotate and slide on the spring sleeve  15 . 
         [0057]    The inclined surface  40  widens the wrapping bush  14  up to the engagement position during assembly with the spring sleeve  15 . The wrapping bush  14  can slide easily across the steps  39 ,  57  until the steps  39 ,  57  completely engage in the recesses  22 ,  23  of the wrapping bush  14 . 
         [0058]    The wrapping bush  14  and the spring sleeve  15  have been produced together in a multi-component tool. This multi-component tool can be used to produce the wrapping bush  14  and the spring sleeve  15  separately by means of molding, the two parts being ejected separately after molding and assembled. 
         [0059]    Optionally, depending on the design of the multi-component tool, the wrapping bush  14  and the spring sleeve  15  can be molded together in the tool so that the wrapping bush and the spring sleeve leave the tool already in the assembled state, as is shown for example in  FIGS. 4 and 5 . Although they are produced in the same tool, they remain separate parts, which can be displaced relative to each other. 
         [0060]    The wrapping bush  14  is made of sphere-reinforced plastic, the plastic being a polyamide (PA 6.6.) that has been reinforced with glass spheres. The spring sleeve is made exclusively of a polyamide (PA 4.6). 
         [0061]      FIG. 6  shows a spatial illustration of individual turns of a helical spring  11 , which surround the wrapping bush  14  and the spring sleeve  15 . One spring end  36  rests on the spring end support  41 . A turn  13  of the helical spring  11  is supported on the web  42  of the supporting base collar  37  of the spring sleeve  15  in the radial direction. To this end, the turn  13  of the helical spring rests on the web  42 , which ensures good force transmission properties. The spring end  36  is supported very well up to the detent area in the basic part  2  by the projecting spring end support  41  of the area  54 . The turns  13 ,  44  envelope the wrapping bush  14 . 
         [0062]    Optionally, the helical spring  11  surrounds the wrapping bush  14  with more or less an entire turn, particularly with more than or equal to a half or 0.7 turn. 
         [0063]    The mode of operation and operating principle of the exemplary embodiment illustrated in the drawing of an automatic belt tensioner according to the invention will be explained hereinafter. 
         [0064]    A belt provided in a belt system of a motor vehicle is pre-stressed to a certain belt tension using an automatic belt tensioner. 
         [0065]    The automatic belt tensioner  1  assumes a pre-stressed state so that the belt tensioner  1  automatically compensates for weather- and/or wear-related belt stretch. 
         [0066]    In addition, the belt vibrates as a result of the revolutions of the belt in a belt system. These belt vibrations are transmitted to the deflecting arm  62  of the tensioning part  3 . 
         [0067]    By rotating the tensioning part  3  in relation to the basic part  2 , the helical spring  11  is deflected and radially pre-stressed. As a result of the deflection of the helical spring  11 , torque is applied to the spring, thus increasing or decreasing the inside diameter  45  of the helical spring  11 . The torque of the helical spring tensions the tensioning part  3  about the common axis of rotation  4 , with the deflecting arm  62  with the tension pulley  18  pre-stressing the belt to a defined belt tension. 
         [0068]    The helical spring  11  produces a radial enveloping force that is distributed substantially evenly across the entire circumference of the wrapping bush  14 . As a result, the outside diameter  46  of the wrapping bush and the outside diameter  65  of the spring sleeve  15  are reduced. The spring sleeve  15  is pushed against the friction surface  17  of the tensioning part  3  with the inside  16 . 
         [0069]    This creates a frictionally engaged connection between the friction surface  17  of the tensioning part  3  and the inside  16  of the spring sleeve  15 . The frictionally engaged connection is so tight that the torque produced by the helical spring  11  can be transmitted to the tensioning part  3 . 
         [0070]    The radial enveloping force is sufficiently great for continuously transmitting the torque to the tensioning part  3  and for producing sufficiently high stability and friction on the adjoining components for vibration damping purposes. 
         [0071]    The material of the wrapping bush  14  comprises reinforced plastic, as a result of which the enveloping turns  13 ,  44  of the helical spring  11  can mate particularly well with the wrapping bush  14 , creating a very good force-fit connection. Additionally, the wrapping bush  14  is sufficiently tough and wear-resistant and can withstand the friction occurring from the spring sleeve  15  during the entire service life of the automatic belt tensioner  1 . The reinforced plastic ensures that the wrapping bush  14  permanently maintains dimensional stability and is wear-resistant. 
         [0072]    The spring turn  44  of the left-handed helical spring  11  comes in contact with an area on the chamfered peripheral edge  26 , which comprises an incline  30  corresponding to the course of a left-handed turn. The enveloping force produced by the helical spring  11  is transmitted to the wrapping bush  14  nearly without loss of force and torque due to this support of the turn  44 . 
         [0073]    The same wrapping bush  14  can also be provided with right-handed helical springs. Depending on the tensioning direction, it is therefore universally usably at the installation location. For this reason, the wrapping bush  14  comprises on the chamfered peripheral edge  26  also an area, which is configured with the incline  31  corresponding to the course of a right-handed turn. 
         [0074]    During the occurring relative motions between the turn  44  and the wrapping bush  14 , the spring turn  44  can act particularly smoothly via the chamfer  25  on the chamfered peripheral edge  26 . 
         [0075]    The damping solid body and fluid friction is influenced by the radial enveloping force, the materials used for the wrapping bush and/or the spring sleeve and the lubricant. In a defined configuration of these parameters, the automatic belt tensioner  1  was statically excited by the belt, for example with a frequency of 2 Hertz, and the vibration was dampened by about 40%. If however the belt tensioner  1  was excited with a higher frequency, e.g. 20 Hertz, the friction damping effect increased to as much as 55%. The damping of the belt vibrations is stable throughout the entire service life. These values can vary when selecting the afore-mentioned parameters differently.