Abstract:
A plate-link chain for a belt-driven conical-pulley transmission having a continuously variable transmission ratio and having a large number of link plates pivotally connected with each other via pairs of rocker members that each includes two rocker members. The rocker members extend transversely to the longitudinal direction of the plate-link chain and are positioned in openings in the link plates. Curved contact surfaces are provided on the rocker members and on the link plate openings, along which curved surfaces of the rocker members and link plates bear against each other to transmit force. Curved rolling surfaces are provided on the rocker members, along which contacting rocker members of a rocker member pair roll against each other and/or slide on each other on pitch lines to transmit force. The link plate openings have at least three inwardly extending, convexly curved regions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plate-link chain, in particular for a belt-driven conical-pulley transmission having a continuously variable transmission ratio, having a large number of link plates pivotally connected with each other via pairs of rocker members that comprise two rocker members each, the rocker members running transverse to the longitudinal direction of the plate-link chain and being situated in openings in the link plates and there being curved contact surfaces situated on the rocker members and the link plates, along which curved surfaces the rocker members and link plates bear against each other to transmit force, and there being curved rolling surfaces situated on the rocker members, along which the rocker members roll on each other and/or slide on each other on pitch lines to transmit force. 
     2. Description of the Related Art 
     Such a plate-link chain can be employed for example as a means of transmitting tractive force in a belt-driven conical-pulley transmission for a motor vehicle or the like, and there transmit the tractive force by means of frictional contact between the rocker members and the conical disk surfaces of the two conical disk pairs. The plate-link chain may also be designed as a toothed chain and transmit tractive force from a driving to a driven chain wheel. 
     A plate-link chain designed as a toothed chain normally has a device for tensioning the toothed chain in the slack strand. This device for tensioning the toothed chain serves for example to prevent pulsating of the toothed chain due to vibration excitation, and also to shape the entry process of the teeth of the toothed chain onto a chain wheel so that tooth skipping is prevented. On the chain wheels the toothed chain is deflected in such a way that the center of curvature of the portion of the toothed chain that is curved in the region of the deflection lies within the closed chain section. 
     In contrast, when a chain tensioner in the form for example of a chain tensioning bar acts on the back of the link plates, the toothed chain undergoes a curvature that differs from the curvature that occurs in the region of the deflection; the particular portion of the toothed chain which is acted on by the chain tensioner is curved in the opposite direction and the center of curvature of this portion of the toothed chain lies outside of the closed chain section of the plate-link chain. A curvature of this sort is referred to as swing-back. 
     To limit the deflection angle of the swing-back process for example from the stretched position, in known versions of plate-link chains for belt-driven conical-pulley transmissions and toothed chains there is provision for limiting the swing-back in the joint of the lower zone of an adjacent link plate. 
     The mode of functioning here is such that a rocker member comes into contact with a region of the lower contact surface of the adjacent link plate. Thus the striking of the rocker member on the contact surface of the adjacent link plate occurs in a zone that is already critically loaded due to the transmission of tensile force from the rocker member to the link plate. Hence in this zone of concentrated tension due to the transmission of tensile force, yet another additional overlay of forces occurs, and thus tensions due to the swing-back protection. In the operation of the toothed chain this can result in increased wear, and ultimately to early fatigue failure. The fatigue strength of the toothed chain is reduced. 
     Plate-link chains that have become known heretofore had symmetrical rocker members, which were situated in openings in the link plates. These known rocker members are symmetrical in construction in reference to a plane of symmetry that divides the rocker members into an upper and a lower half. As a result of this configuration, a distance from the inner peripheral rim of the opening that receives the rocker members to an outer peripheral edge of the link plate in the region of a so-called lower yoke is made smaller, and thus the cross sectional region available for transmitting force is reduced in size. 
     In consequence, a concentration of tension appears in this region between the opening of the link plate and the edge of the link plate, which ultimately results in a reduction of the service life and of the force transmitting capability of the plate-link chain. To counter this problem, a plate-link chain has already become known which has asymmetrical rocker members in the direction of the rocker member height and thereby makes sure that the workpiece stresses which arise in the upper and lower contact surface regions between rocker member and link plate are significantly reduced, so that the service life of the chain increases as a result. 
     With a plate-link chain of this sort it is significant that the asymmetrical rocker members are inserted into the openings in the link plates in the correct orientation, since otherwise the pitch surfaces of the rocker members that are intended for transmitting force cannot roll on each other as intended, with the consequence that jamming of the rocker members in the opening can occur, and thus a malfunction that may result in failure of the plate-link chain. 
     To achieve this correct orientation of the rocker members in the openings of the link plates, a plate-link chain has already become known on the basis of unpublished German patent application DE 10 2005 061 081.1, owned by the assignee of the present application, whose link plates have a region that is bowed (curved) in an inward direction, so that if the rocker members are oriented incorrectly an overlapping of the outer contour of the rocker members with the inside contour of the opening occurs in the link plates, so that the rocker member which is not installed in the correct orientation can no longer be inserted into the opening of the link plate, and in this way erroneous installation of the rocker members in the openings of the link plates is avoided. 
     It has been found that this known plate-link chain already provides an improvement compared to the plate-link chain described above, in regard to additional tension on the tension-critical zone in the region of the lower yoke of the link plate. But even this known plate-link chain has room for improvement in regard to the stress in the described tension-critical zone due to the striking of the rocker member on a contact surface of an adjacent link plate to protect against swing-back. 
     Starting from this point, an object of the present invention is now to refine the known plate-link chain in such a way that the force applied to the plate-link chain due to the striking of the rocker member on the link plate to limit the swing-back angle takes place in a less tension-critical zone along the opening of the link plate. 
     SUMMARY OF THE INVENTION 
     To solve this problem, the invention now has the features indicated in claim  1 . Advantageous refinements thereof are described in the additional claims. 
     The object is accordingly achieved by a plate-link chain, in particular for a belt-driven conical-pulley transmission with variable transmission ratio, having a large number of link plates pivotally connected with each other via pairs of rocker members that comprise two rocker members each, the rocker members running transverse to the longitudinal direction of the plate-link chain and being situated in openings in the link plates and there being curved contact surfaces situated on the rocker members and the link plates, along which curved surfaces the rocker members and link plates bear against each other to transmit force, and there being curved rolling surfaces situated on the rocker members, along which the rocker members roll on each other and/or slide on each other on pitch lines to transmit force, the openings having at least three regions that are curved convexly inward. 
     Preferably, it is provided that two of the inwardly curved regions, namely a first inwardly curved region and a second inwardly curved region, when seen in the cross sectional view in the direction of the rocker member height, lie essentially within a region that is formed by a first contact point line through pitch lines of two adjacent rocker member pairs in a swing-back, and a second contact point line through pitch lines of two adjacent rocker member pairs when the plate-link chain is in the completely bent state. 
     Preferably, it is further provided that a third inwardly curved region lies outside of the region that is formed by a first contact point line through pitch lines of two adjacent rocker member pairs in a swing-back and a second contact point line through pitch lines of two adjacent rocker member pairs when the plate-link chain is in the completely bent state. 
     Preferably, it is further provided that when the plate-link chain is in the bent state the third inwardly curved region lies radially outside of the region that is formed by a contact point line through pitch lines of two adjacent rocker member pairs in a swing-back and a second contact point line through pitch lines of two adjacent rocker member pairs when the plate-link chain is in the completely bent state. 
     Preferably, it is further provided that the rocker members are asymmetrically formed in a cross section running in the longitudinal direction of the plate-link chain in the direction of the rocker member height. 
     The object identified above is also achieved by a link plate for use in a plate-link chain and having openings for receiving rocker members, wherein the openings have at least three inwardly convexly curved regions. 
     The object identified above is also achieved through the use of a plate-link chain in accordance with the invention in a belt-driven transmission, in particular a belt-driven conical-pulley transmission with variable transmission ratio. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic representation of a portion of a known plate-link chain in the form of a toothed chain in a swing-back process; 
         FIG. 2  shows on the right side an enlarged view of an opening in a plate-link chain of the type shown in  FIG. 1  to explain the striking of a rocker member on a link plate during a swing-back process, and in the left side of the drawing an enlarged view of the opening to explain the contact-point line or pitch line. 
         FIG. 3  is a side view of a link plate in accordance with the invention; 
         FIG. 4  shows two adjacent plates of the type shown in  FIG. 3  within a plate-link chain; 
         FIG. 5  shows an enlarged view of an opening in a link plate corresponding with the link plate shown in  FIGS. 3 and 4 ; 
         FIG. 6  shows an enlarged view of openings and rocker members of two adjacent plates corresponding with the link plate shown in  FIG. 4  when the plate-link chain is in an extended condition; 
         FIG. 7  is a side view similar to  FIG. 6  when the plate-link chain is in a swing-back condition; 
         FIG. 8  is a side view similar to  FIG. 7  showing a region enclosed by a set of contact point lines. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a portion of a known plate-link chain with two adjacent link plates  1  and  5  and rocker members  3 ,  4  situated in openings  2 . The longitudinal direction, also referred to as the chain running direction, is designated as L, the upward direction is identified by an arrow  8 . When passing around a conical disk pair of a conical pulley transmission, the plate-link chain is bent contrary to the direction of arrow  8 , so that arrow  8  simultaneously marks the radial outward direction when the chain is passing around a conical disk pair. In this known plate-link chain in the form of a toothed chain, during a swing-back process which is represented by the dashed link plate  5  and its swiveling motion in the upward direction in the plane of the drawing, a contact takes place between the dashed rocker member  4  of the dashed link plate  5  and the link plate  1  depicted with a solid line, in the region of the bottom of the opening  2  of link plate  1  designated as  9 . In this contact region a relatively high tension prevails in link plate  1 . The plate-link chain is designed as a toothed plate-link chain, and includes two teeth  12  per link plate  1 . The plate-link chain can also be designed as a plate-link chain without teeth  12 , however. 
       FIG. 2  shows in the right half of the drawing an enlarged depiction of the region of opening  2 , with rocker member  4  in swiveled position due to the swiveling motion of the dashed link plate  5  in  FIG. 1 . Rocker member  3  belongs to the right-hand link plate  1  in  FIG. 1 , while rocker member  4  belongs to the left-hand link plate  5  in  FIG. 1 , so that when a swiveling motion of link plate  5  occurs during a swing-back of the toothed chain, a force-transmitting contact takes place between a lower contact surface  6  of rocker member  4  and a lower contact surface  7  of opening  2  of link plate  1 . 
       FIG. 2  shows in the left half of the drawing pitch line  10  between the two rocker members  3 ,  4  in the tight chain strand. The two rocker members  3 ,  4  roll on each other along a respective pitch surface  13 , and form the pitch line  10  in the tight strand. If this pitch line  10  is joined with a pitch line  10  of another adjacent rocker member pair, then it is possible to stretch through these two lines which project perpendicular to the plane of the drawing, which are dots  10  in the two-dimensional depiction, a contact point line or pitch line  14 , which connects the contact points of adjacent rocker member pairs with each other. As  FIG. 2  shows in the right-hand illustration, in the event of swing-back of the known plate-link chain the contact zone designated as  9  lies between rocker member  4  and link plate  1  in the height direction of the rocker members, below contact point line  14 . 
       FIG. 3  shows a link plate  16  in accordance with the invention, with openings in accordance with the invention that have been given the reference labels  19  and  19 ′. The rocker members  17  and  18  assigned to link plate  15  are depicted in the openings  19 ,  19 ′.  FIG. 4  shows two adjacent plates  16  in accordance with  FIG. 3  within the arrangement of a plate-link chain  15 . The plates are designated with the reference labels  16  and  16 ′, with link plate  16  being depicted with solid lines and link plate  16 ′ being depicted with dashed lines. As can be seen, one rocker member  17  of the link plate  16  depicted with solid lines and one rocker member  18  of the link plate  16 ′ depicted with dashed lines form a rocker member pair  20 . The rocker member pairs  20  form a rocker joint, in which the rocker members  17 ,  18  roll on each other. The openings  19 ,  19 ′ have curved contact surfaces  34  on the plates, against which the rocker members bear with contact surfaces  35  on the rocker members to transfer force. 
       FIG. 5  shows an opening  19 , here the opening  19  depicted on the left in  FIG. 3 . The opening  19  includes three regions curved convexly toward the inside, i.e. in the direction of an imaginary center point  25  of the opening, namely a first inward-curved convex region A, a second inward-curved convex region B and a third inward-curved convex region C. Opening center point  25  can be understood for example as the center of mass of opening  19 . Opening center point  25  serves here only to describe more exactly what is meant by convex curvature.  FIG. 6  shows with a solid line opening  19  in accordance with  FIG. 5  and opening  19 ′ of a neighboring link plate  16 ′ (not shown) adjacent to the right in the drawing plane of  FIG. 6 , as well as with a solid line the rocker member  17  assigned to opening  19  and with a dashed line the rocker member  18  assigned to opening  19 ′. Here rocker members  17 ,  18  are inserted into openings  19  and  19 ′ of link plates  16  and  16 ′. Rocker members  17 ,  18  are asymmetrically formed in the direction of the rocker member height, which is designated with a double arrow  27  in  FIG. 6 , with a wider region in upper half  29  of the rocker member in the direction of the double arrow  28  than in the lower half  30  of the rocker member. Rocker member  18  is supported in opening  19 ′ of the right-hand link plate  16 ′ in  FIG. 4  (depicted with dashed lines), while rocker member  17  is supported in opening  19  of the left-hand link plate  16 , depicted in the drawing with solid lines. 
     Rocker members  17 ,  18  are in contact along a pitch line  21  that extends in the direction of the drawing plane.  FIG. 6  shows the pitch line  21  with a plate-link chain  15  that is stretched, i.e. straight and not curved, bent or deflected.  FIG. 7  shows the depiction in accordance with  FIG. 6  with a back-oscillating plate-link chain  15 . A swing-back moment M Back  is exerted here on the plates  16 , which causes a relative rotation of the rocker members  17 ,  18  in their respective openings  19  and  19 ′. In the depiction in  FIG. 3  a relative rotation of rocker member  18  in opening  19  in the direction of arrow  22  is caused by the moment M Back  depicted in  FIG. 7 ; correspondingly, a relative rotation of rocker member  17  is caused with respect to opening  19  in the direction of arrow  22 ′ in  FIG. 3 . That causes a shift of pitch line  21  to occur, as depicted in  FIG. 7 . Drawn in  FIG. 7  is pitch line  21  as drawn in  FIG. 6 , as well as a pitch line  21 ′ that is assumed in the swing-back process depicted in  FIG. 7 . The inwardly curved region C, which is identified in  FIG. 7  for the opening  19  depicted with a solid line, prevents the relative rotation of the particular rocker member, here of rocker member  18 , in the respective opening  19 ,  19 ′, depicted on the basis of  FIG. 8  for rocker member  18  in opening  19 . Also depicted in  FIG. 7  is the contact region  9  between opening  19  and rocker member  17 . The convexly curved first region A serves as a limitation of the swing-back angle of rocker member  17  with respect to opening  19  or to the link plate  16  assigned to opening  19 . Further migration of the pitch line  21 ′ in the depiction in  FIG. 7  is prevented in this way. The convexly curved third region C together with the convexly curved second region B holds rocker member  18  in a nominal position with respect to opening  19 . 
       FIG. 8  shows for the opening  19  depicted in  FIG. 5  the region in which the pitch line  21  depicted in  FIG. 7  is placed in the extreme possible positions of the plate-link chain, that is, in the completely bent state and during swing-back. The figure depicts a connecting line between the contact points  21  of two adjacent link plates when the plate-link chain  15  is in the fully deflected state; this is designated as a second contact point line  23 . Also depicted is a connecting line between the contact points  21  of two adjacent rocker member pairs  20  during swing-back of the plate-link chain; this is designated as the first contact point line  24 . The contact point line forms a set of lines for all possible bending angles of the plate-link chain. This overlaps a region bounded by the contact point lines  23 ,  24 . The two contact point lines  23 ,  24  thus enclose a region  26  shown with shading in  FIG. 8 . Now the invention provides for the first convexly curved region A and the second convexly curved region B to be located in the shaded region  26 , i.e. between contact point lines  23  and  24 . The invention also provides for the third convexly curved region C to lie outside of the region  26  enclosed by the contact point lines  23  and  24 , namely on the radially outer side when the plate-link chain is in the deflected state, which is thus radially on the outside for example when the plate-link chain is passing around a conical disk pair for example during operation. In the depiction in  FIG. 1 , the radially outward direction is identified by the arrow  8 . On the side lying radially inside the contact point line  24  there are no convexly inward curved regions. 
     Now if a swing-back motion of the plate-link chain occurs, this results in a swiveling motion of the particular link plate in the direction of the arrows  31  in  FIG. 4 , and thus to a relative rotating motion of the braced rocker member in the opening of the adjacent link plate, i.e. in  FIG. 5  to a relative motion of rocker member  18  relative to opening  19 ′ of the right-hand link plate  16 . As that occurs, a face  33  of rocker member  17  comes in contact with the third convexly inward curved region C of opening  19 , so that a contact region  11  occurs which is depicted in  FIG. 7 . Rocker member  17  now butts against second convexly inward curved region B of opening  19  and third convexly inward curved region C of opening  19 , so that further rotation is prevented. The contact with the two convexly curved regions B, C causes a much lower stress in the lower region of plate-link chain  16 , i.e. the region facing the teeth  12 , than created by the contact between rocker member and link plate in contact region  9  in the existing art. 
     Although particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit of the present invention. It is therefore intended to encompass within the appended claims all such changes and modifications that fall within the scope of the present invention.