Abstract:
The invention provides a device for stretching a transmission chain which is closed in itself and is made up from a number of adjacent links which are, in the longitudinal direction of the chain, mutually intercoupled by pairs of longitudinal rocker elements and in which the ends of at least one rocker element operate torque transmittingly with the pulley sheaves of a 5 pulley sheave transmission, said device comprising at least two supporting surfaces lying at a distance of each other and supporting the chain according to an arc, and provided with means to generate in this chain a tensile force leading to a surpassing of the limit of elasticity of the link material. 
     To improve the stretching and more particularly to prevent an uncontrolled bending of 10 the rocker elements during the treatment of the chain with all drawbacks thereof the invention proposes that at least one of the supporting surfaces is configured to support the radial inner area of at least a part of the chain. Thus bending of the rocker elements is prevented and the treatment of the chain is improved considerable.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a device for stretching a continuous transmission chain having a number of adjacent links which are intercoupled in the longitudinal direction of the chain by pairs of longitudinal rocker elements in which the respective ends of at least one rocker element of each pair cooperate in a torque transmitting way with pulley sheaves of a pulley sheave transmission, said device comprising at least one first and one second supporting surface which lie at a distance from each other and support a chain to be treated at least partially along an arcuate path, and having means to generate in this chain tensile stresses of such magnitude that the limit of elasticity of the material of the links is at least locally surpassed. The invention also relates to a method for stretching such a transmission chain. 
       DISCUSSION OF THE PRIOR ART 
       [0002]    Increasing the strength of the material of the links of an endless transmission chain by stretching while (locally) surpassing the limit of elasticity of this material in order to improve the properties of the chain is a known method described in 1966 in an article by Dr. Ing. Otto Dittrich, published in February 1966 in VDI Zeitschrift 108. A transmission chain which can be treated in this way for instance, is a chain described in U.S. Pat. No. 5,728,021 (van Rooij) and US 2006/030442 A1 (van Rooij). 
         [0003]    Furthermore, U.S. Pat. No. 6,824,484 describes how this method can be implemented using two sets of conical sheaves, between which the rocker elements of a chain to be treated are accommodated and which are each clamped by means of its corresponding control system of a conventional continuous variable transmission. The Dutch Patent Specification 1 018 594, corresponding therewith, also documents this prior art. 
         [0004]    The use of this known set of conical sheaves is the most obvious solution to the problem of how to support a transmission chain of the kind referred to above while stretching it. The known method and the apparatus used for this solution have a number of drawbacks and imperfections. Mounting the chain between the conical sheaves is time consuming, and the shape and dimension of the surfaces of these conical sheaves must be accurately adapted to the shape and the dimension of the protruding ends of the rocker pins of the chain and particularly to the configuration of the end surface of the pins, which is commonly curved in two directions. The most important drawback, however, lies in the fact that the loading of the rocker pins and of the links as well during the stretching of the chain is totally different from the loading which occurs in the chain during the normal operation thereof. There will occur an uncontrolled bending of the rocker pins so that the rocker pins which cooperate with the edges of the openings in the link will load the material around theses edges in a way which is quite different from the loading which occurs during normal operation. It is, in fact, impossible to define the local plastic deformation which occurs during such a pre-loading of the link material exactly so that, when this operation is finished, one does, in fact, know that certain parts of the link have been loaded beyond the limit of elasticity but one does not know accurately which parts these are and how far they are loaded. A check of the treated chains later on is, of course, impossible, so that a manufacturer who delivers chains treated in such a way is, in fact, never sufficiently sure about the quality thereof and cannot guarantee that a certain chain meets the requested specifications, unless the chain is over-designed with a higher safety margin. This, however, leads to higher costs, waste of material and greater dimensions of the chain. 
         [0005]    Furthermore U.S. Pat. No. 4,515,576 discloses a continuously variable transmission having on the one hand a pair of adjustably pulley sheaves and on the other hand a relatively wide toothed gear wheel. A so-called “silent chain” comprising toothed links, is slung over this gearwheel while pressure pads fixed to the outermost links are clamped between the pulley sheaves. The teeth of the links rest in the shallow spaces between the teeth of the gearwheel and the chain is tensioned by means of a pressure roller. 
         [0006]    There is no indication in this disclosure that the chain is ever to be tensioned in such a way that the links are loaded beyond their limit of elasticity and, indeed, if they should be loaded in such a way, the results which are obtained by means of the invention cannot be realized because the links of the chain are supported by the summits of the triangular parts thereof so that the resulting stresses in the links are directed in an incorrect direction and have no beneficial effect. 
         [0007]    U.S. Pat. No. 1,966,831 discloses a kind of similar transmission in which every other link is provided at both its ends with a downwardly directed lug of which the end surface rests against the side of a tooth of the gearwheel. Pressure members protruding through the bodies of the pins cooperate with the surfaces of the pulley sheaves. Here, too, nothing in the disclosure hints at any beneficial loading of the chain and the stresses introduced into the links by the cooperation of the lugs with the gear teeth are not directed in the correct direction to have any beneficial effect on the links. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention aims to obviate these drawbacks of the prior art such as outlined above. To this end the invention proposes that at least one of the supporting surfaces is configured to support the radial inner area of at least a part of the chain, such that essentially only stresses running in the longitudinal direction of the respective links are generated in these links. 
         [0009]    With these measures, any bending of the rocker pins—which are now not supported anymore on their ends—is positively prevented so that all the drawbacks and disadvantages related thereto do not occur anymore. 
         [0010]    Preferably at least one supporting surface is configured to support the radial inner edges of at least a part of the links. 
         [0011]    The supporting surface can then be configured in such a way that a link with a hollow end edge configuration is supported in two points which lie at a distance of each other. 
         [0012]    The supporting surface is preferably at least a part of the outer surface of a cylinder and this outer surface is convexly or concavely curved. 
         [0013]    In another preferred embodiment at least one supporting surface is built up to form a number of partial support surfaces, each configured to support at least a part of the radial inner end edge of at least one rocker element of each pair of rocker elements out of a number of adjacent rocker elements as seen in the longitudinal direction of the chain so that the rocker elements and not the links, are supported between the ends of the rocker elements. 
         [0014]    In that case, each partial support surface can be made up from an end edge of a plate-shaped finger of which the thickness is adapted to the interspace which is present between adjacent links. The finger, in combination with a number of similar fingers, protrudes radially from the outer surface of a common rotatingly supported bearer. The positioning pattern of these fingers is adapted to the configuration of the link packets of the chain. 
         [0015]    In a preferred embodiment the respective blade-shaped fingers each protrude from the outer circumference of a ring-shaped bearer made from plate material which together constitute the support surface. A number of these ring-shaped bearers are, together with interpieces of suitable thickness, stacked into a unit which is carried by a central shaft on which the circumferential distances between adjacent fingers are adapted to the predefined and known distribution of the pitch of a chain to be treated. 
         [0016]    The invention also provides a method for stretching a continuous transmission chain having a number of adjacent links which are intercoupled in the longitudinal direction of the chain by pairs of longitudinal rocker elements in which the respective ends of at least one rocker element can cooperate in a torque transmitting way with pulley sheaves of a pulley sheave transmission, using at least one first and one second supporting surface which lie at a distance from each other to support a chain to be treated at least partially along an arcuate path to generate in this chain tensile stresses of such a magnitude that the limit of elasticity of the material of the links is at least locally surpassed, while supporting the radial inner area of at least a part of the chain. In executing this method the inner end edges of a number of links adjacent each other in the longitudinal direction of the chain can be supported according to an arcuate surface, while then at least part of the respective inner end edges of at least one rocker element of each pair are supported according to an arcuate supporting configuration. 
     
     
       DESCRIPTION OF THE DRAWING 
         [0017]      FIG. 1  is a side view an embodiment of a chain to be preloaded, in which the links are supported on the inner end edges thereof by a support surface. 
           [0018]      FIG. 2  is an enlarged scale view of  FIG. 1 . 
           [0019]      FIGS. 3   a - 3   e  shows five different possible embodiments according to the invention.  FIG. 4  is an enlarged scale view of the embodiment according to  FIG. 3   a.    
           [0020]      FIG. 5  is an enlarged scale view of the embodiment according to  FIG. 3   b.    
           [0021]      FIG. 6  is another embodiment according to the invention. 
           [0022]      FIG. 7  is an embodiment in which the rocker pins of a chain to be pre loaded are directly supported by blade-shaped supporting fingers. 
           [0023]      FIGS. 8   a - 8   c  show cross-section, lower end view and end view, respectively, of the configuration of a chain to be preloaded by means of the embodiment according to  FIG. 7 ; 
           [0024]      FIG. 9  is an upper end view an embodiment having a supporting core with supporting fingers. 
           [0025]      FIG. 10  is a side view of the embodiment of  FIG. 9 . 
           [0026]      FIG. 11   a  is a cross-section of a core with supporting fingers, built up from a stack of individual plates. 
           [0027]      FIG. 11   b  is an upper end view of the core of  FIG. 11   a.    
           [0028]      FIGS. 12   a ,  12   b  and  12   c  show side views of the plates of  FIGS. 11   a  and  11   b.    
           [0029]      FIG. 13  is an end view of three supporting rollers for a chain to be preloaded. 
           [0030]      FIG. 14  shows a complete device, constructed in accordance with the principle shown in  FIG. 13 . 
           [0031]      FIG. 15  shows the way in which an endless transmission chain such a chain treated by a device according to the invention, co-operates with a pair of conical pulley sheaves. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0032]    In  FIG. 1  reference numeral  2  refers to an endless transmission chain built up from individual links such as indicated with reference numerals  4   a ,  4   b ,  4   c  which are mutually coupled by pairs of pin-shaped rocker elements; two of such elements are in the figure indicated with reference numerals  6  and  8  respectively. Such a chain is known from EP a 741 255 BI in the name of applicant, which is hereby incorporated herein. 
         [0033]    To subject this chain to a pre-loading treatment so that the material of the links is stretched beyond the limit of elasticity thereof, the chain is guided around two cylindrical supporting rollers having different respective diameters, namely a first supporting roller  10  with radius R 1  and a second supporting roller  12  with preferably a greater radius R 2 . Both the supporting rollers are pressed away from each other with a force indicated by F so that such stresses are generated in the chain  2  at the link material around the link openings, namely the area where the pins contact the links is subject to compressing stresses and will deform plastically, so that the strength of this material is permanently increased. 
         [0034]    As discussed previously, the use of pre-loading is known from the prior art. However, contrary to the way of supporting the chain as known from U.S. Pat. No. 6,824,484 and the Dutch Patent Specification 1 018 594 respectively, in which the chain is supported by means of the ends of the rocker elements  6 ,  8  which are supported by the Vshaped supporting surfaces of the pulley sheaves of a common continuously variable transmission with all the disadvantages which go therewith as described hereinbefore, the present invention proposes to locate this support at the radial inner areas of the chain. In a first embodiment, shown in  FIG. 1-6 , this is done so that the radially inner edges of the respective links rest, during their travel over cylindrical rollers, such as the rollers  10 - 12  in  FIG. 1 , on the outer surface of these rollers, in the way as shown in  FIG. 2 .  FIG. 2  shows a supporting roller  14  with a radius of curvature Rr and a link  18  which rests upon the outer surface  16  thereof; this figure also shows the rocker pins  20  and  22  respectively. As shown, the configuration of the lower link surface  23  presents a hollow, concave portion with radius of curvature Rs, bounded by two convex edge parts  24  and  26  respectively. The drawing shows the state in which the end edges of these edge parts  24 ,  26  rest on the roller surface  16 . In an optimal situation, the radius of curvature Rr of the supporting roller  14  is equal to the radius of curvature Rs of this hollow part—the lower link circumference then lies fully against the outer surface and the contact stresses are minimal. 
         [0035]    During the preloading, the rollers  10  and  12  respectively rotate along their respective axes in the direction of the arrows  28  and  30  respectively so that the chain will move in the direction of the arrow  32 . 
         [0036]    In the embodiment according to  FIG. 1  the tensile forces in the chain  2  are generated when the rollers  10  and  12  respectively are pressed away from each other with a defined force F. 
         [0037]      FIGS. 3   a - 3   e  show examples of configurations of supporting rollers in which a supporting roller with relatively great diameter is shown on the right hand side and a supporting roller with small diameter on the left hand side. The chain to be treated is in these five drawings is indicated with the same reference numeral, namely reference numeral  40 ; the axis (axis of rotation) of the right hand roller is indicated with  42  and same of the left hand roller with  44 . 
         [0038]      FIG. 3   a  shows an embodiment in which the right hand roller  46  and the left hand roller  48  both have a circle-cylindrical outer surface, indicated with  50  and  52  respectively. 
         [0039]      FIG. 3   b  shows an embodiment in which the right hand roller  54  has a concave outer surface  56  and the left hand roller has a convex outer surface  60 . The radius of curvature of the surface  56  is indicated with R 1  and the radius of curvature of surface  60  with R 2 . 
         [0040]    Of course combinations of the above described configurations are possible, thus a combination in which a roller with a convex or concave outer surface is combined with a cylindrical roller is contemplated. All these combinations depend upon the distribution of the loading which one wants to effect in the links. 
         [0041]      FIG. 3   c  shows a right hand roller  62  with a circle-cylindrical outer surface  64  while the left hand roller  66  has a cylindrical supporting surface  68  bounded by to guiding flanges  70   a ,  70   b.    
         [0042]      FIG. 3   d  shows two supporting rollers, the right hand one,  72 , with a cylindrical supporting surface  74  and the left hand one,  76 , shown in cross-section also with a cylindrical supporting surface  78  which is bounded by guiding flanges  80   a ,  80   b , which enclose the chain locally and support it, namely at the position of the links which lie at the outer edges  81   a ,  81   b  of the chain  40 . 
         [0043]    Finally  FIG. 3   e  shows an embodiment in which both the right hand roller  82  and the left hand roller  84  has a cylindrical supporting surface  86  and  88  respectively (in this respect this embodiment is the same as the one according to  FIG. 3   a ), but in which the left hand roller  84  is combined with two guide rollers  90 ,  92  with flanges to guide the chain  40  enclosed therein between. 
         [0044]      FIG. 4  shows in more detail an embodiment corresponding to the one which is shown in  FIG. 3   a . Here is shown the big supporting roller  100  with cylindrical supporting surface  102 , and rotatingly supported by the shaft  104 , as well as the smaller supporting, roller  106 , also with a cylindrical supporting surface  108  and supported by the shaft  110 . The chain which is to be stretched is indicated with  112  and this figure shows clearly how this chain is built up in the known way, from links packets  114  coupled by rocker assemblies  116  which each comprise a longer pin  118  which, during use of the chain in a CVT cooperates with the pulley surfaces thereof and a shorter rocker pin  120  which cooperates with the pin  118 . 
         [0045]      FIG. 5  shows a similar configuration but here the bigger roller  100   a  has a concave supporting surface having a radius of curvature Rh while the smaller roller  106   a  has a convex supporting surface  108   a  with radius of curvature Rc. 
         [0046]    During the stretching of a chain it is important that the chain remains very well centered on the outer surfaces of the respective rollers. When the outer surface of one of these rollers is convex there will be, as known in itself, a self-centering effect so that one need not fear that the chain will run off the roller. Examples of a cross-guiding of the chain are already given in the  FIGS. 3   c ,  3   d  and  3   e.    
         [0047]      FIG. 6  shows a favorable way of guiding the chain using the centering of the pinshaped rocker elements thereof by means of conical guiding surfaces which cooperate with these pins.  FIG. 6  shows a first supporting roller  130  with relatively great diameter, fixed to the rotating shaft  132  and having a cylindrical outer surface  134 ; this surface  134  is enclosed by two guiding flanges  136  and  138  respectively with conical guiding surfaces  140  and  142  respectively. They enclose with a small play the protruding rocker pins  144  of the chain  146  which is to be preloaded. This play is indicted with d 1  and d 2  respectively. The other supporting roller  147  which is fixed to the shaft  148  also has a plane cylindrical supporting surface  150 , here, too, this supporting surface  150  is enclosed by two flanges  152  and  154  with conical guiding surfaces  156  and  158  respectively which enclose the protruding pins  159  with a small play (indicated with d 3  and d 4  respectively. 
         [0048]    In all embodiments described herein, one can use supporting rollers with a cylindrical, a convex or a concave configuration of the outer surface thereof and of every possible combination thereof so that any desired pattern of permanent stresses can be realized in a chain which has been subjected to the pre-loading treatment. 
         [0049]    The embodiments previously described hereinbefore have in common the fact that within the scope of the general main idea of the application—the supporting of a chain to be preloaded on the inner area thereof—use is made of supporting rollers on which rest the inwardly directed end edges of the links. It is, however, also possible to use a configuration in which a chain to be preloaded is not supported under the end edges of the links but under the longitudinal end edges of the rocker pins which intercouple these links. Such an embodiment is shown in  FIG. 7  to and including  14 . 
         [0050]      FIG. 7  shows a chain  160 , which is also constituted of links  162  intercoupled by rocker assemblies  163 ; the latter consist each of a first pin  164  of which the ends, during use of the chain in a CVT, cooperate in a torque transmitting way with the surfaces of the pulley sheaves thereof, and second, shorter, pins  166 . During the preloading the respective lower (inwardly directed) end edges of these pins (indicated with reference numerals  164   a ,  166   a  for the pins which are drawn in link  162 ) rest on the supporting end edges  168  of blade-shaped fingers  170  which protrude radially from a central core  172 , which can rotate around the axis  174 . The thickness of these blade-shaped fingers  170  is such that—as will be discussed—these fingers fit in the spaces which are always present between the link packets of a chain. So, for instance, after rotation in the direction of the arrow  165 , the finger  170   a  will fit into the space which is present between the end parts of the links  162 ,  162   a  which are directed towards each other to support the pins of the rocker assembly  163   a . This finger has a thickness which is just a little bit smaller than the thickness of the links. During the process of pre-loading, the rocker pins and not the links are supported at several positions simultaneously between the ends of the rocker pins but not at their ends. Thus, bending of the rocker pins is absolutely impossible. 
         [0051]      FIG. 8   a  shows a cross-section over the line IIXa-liXa in  FIG. 8   b  of a chain  180  of which in this drawing a part is shown in an upper plan view while the same chain  180  is shown in  FIG. 8   c  in a side view. The cross-section goes through the pin  182  which constitutes in combination with the cooperating pin  184  a rocker assembly  186 . 
         [0052]    As particularly shown in  FIG. 8   a , the individual links do not lie—as seen in the crossdirection of the chain, all against each other; there is in this case a space  230  between the links  202  and  204  and a space  232  between the links  204  and  206 ; a subsequent space  234  is to be found between the links  210  and  212  and a space  236  between the links  212  and  214 ; furthermore there is a space  238  between the links  218  and  220  and a space  240  between the links  220  and  222  while finally one finds a space  242  between the links  224  and  226  and a space  244  between the links  228  and  231 . In these spaces the blade-shaped fingers  170  shown in  FIG. 7  fit and ultimately these fingers come to lie against the under edges of the rocker elements such as the rocker elements  164   a  and  166   a . The links have an assembly pattern which, as shown in  FIG. 8   b , repeats itself after every three rocker member assemblies, such as known. 
         [0053]      FIG. 9  shows an upper view and  FIG. 10  shows a side view of a circle-cylindrical core  240  with fingers  244  protruding from the outer surface  242  thereof; these are not all of them indicated individually with a reference numeral in this  FIG. 9 . The pattern thereof is such that they fit between the openings which are present between the links, such as shown in  FIG. 8   b . Such a core with protruding blade-shaped supporting fingers can, for instance, be made by spark erosion. 
         [0054]    It is, however, also possible to make such a core with protruding blade-shaped supporting fingers as a stack of individual ring-shaped elements with radially protruding bladeshaped fingers in the way as shown in  FIGS. 11   a - 11   b  and  12   a - 12   c .  FIGS. 12   a ,  12   b  and  12   c  show three, generally similar but in detail mutually different rings  250 ,  252 ,  254  from thin plate material, each with radially protruding supporting fingers which are not specified individually but which are each indicated with reference numeral  256 . Each ring  250 ,  252 ,  254  has a cylindrical inner boundary  258  with a square locating cutout  260 . As  FIG. 11   a  and  11   b  show a number of such rings are combined into the stack  262  which is shown in  FIG. 11   b  in upper view and this according to a pattern which corresponds to the pattern of the interspaces in the chain to be preloaded. This stack is, in combination with the key  264  by means of the clamping nut  266  fixed to the end  268  of the shaft  270  which is by means of the bearings  272 ,  274  supported in a suitable frame  276  and which can be driven in any suitable way at the end  278  of the shaft. 
         [0055]    It will be clear that by a suitable choice of the orientation of the fingers  256  around the surface of the ring  250  (a measure of which can for instance be the angle a between the axis  280  of such a finger and the vertical centerline  282  of the ring), any configuration of the link packets can be taken into account, also situations in which there is, as seen in the longitudinal direction of the chain a varying pitch, thus a varying centerline distance between individual pairs of rocker pins. 
         [0056]    A complete device for stretching a chain in which the above mentioned principles are used is illustrated in  FIGS. 13 and 14 . 
         [0057]      FIG. 13  shows schematically and in end view the configuration used in such an apparatus. There are two upper supporting rollers  320 ,  322  each with a circle-cylindrical surface and one lower supporting roller  262  which has the configuration as shown in  FIG. 6 , thus in which the cylindrical supporting surfaces is bounded by two flanges with conical guide surfaces. The chain to be preloaded is indicated with  325 . 
         [0058]    The apparatus shown in  FIG. 14  and indicated in its entirety with reference numeral  302  comprises as base plate  304  and a very stiff, schematically shown, frame  306  with parallellepipedum-shaped outer dimensions. Near the upper end thereof this frame carries two shafts, not indicated with a reference numeral and supported by bearings  309   a  and  311   a  in the frame, each having at their end which is visible in the drawing a cylindrical supporting surface  321  and  323  respectively. Below these shafts there is a third shaft  324  with a cylindrical supporting surface  326  bounded by guiding flanges  328 ,  330  in the way as shown in  FIG. 6 . This shaft  324  is supported by two suitable bearings (not shown) in a yoke  324  which encloses the frame  306  and has the long sides  336   a ,  336   b  which run along the front and rear side of the frame  306  and the short side  338   a ,  338   b . The yoke is supported by the frame  306  by means of the shaft  340 . The yoke can tilt over a limited angle around the shaft  340  and is actuated by a linear actuator  342  which acts in two directions and which rests via the pressure sensor  344  upon the base plate  304 ; the piston rod  346  thereof is coupled to the short side  338   b  of the yoke  340  as close as possible to the plane of symmetry through the three pairs of supporting surfaces. 
         [0059]    Finally there is a displacement sensor  350  which is coupled by means of arm  352  with the frame and by means of the finger  354  with the arm  338   b  of the yoke  334 . 
         [0060]    The operation of the device will be clear. By retracting the double acting actuator  342  the displaceable shaft with its corresponding supporting surface will move upwardly and a chain which is to be preloaded can then be mounted around the three respective shafts. Thereafter a controlled supply of hydraulic pressure medium results into an upward movement of the piston rod  346  so that the chain is pretensioned with a predetermined force. Then the initial length of the chain is measured by means of the sensors  350 ,  354 . Finally the piston rod and with it the end  338   b  of the yoke is pressed upwardly with a greater force so that the shaft which is supported by the yoke moves downwardly and the chain is preloaded while surpassing the limit of elasticity of the links. During this operation the shaft  308  is driven rotatingly by means which are not shown. After this operation the lasting elongation can be measured by means of the sensors  350 , 354 . 
         [0061]    It will be clear that the mounting of the chain, the pretension, the measuring of the initial length, the rotatingly driving of the chain and the stretching of the chain can not only be effected manually but also in an automated process during which for each chain the particulars as measured are stored. 
         [0062]      FIG. 15  shows schematically the known way in which a transmission chain according to the invention, in this case the chain  370 , cooperates with the conical surfaces of the pulley sheaves  372   a ,  372   b ;  374   a ,  374   b  of a continuously variable transmission. As shown the ends of the pins  364  are clamped between these surfaces. The pulleys  372   a ,  372   b  can, for instance, be the driving pulleys while the chain  370  transmits a torque via the pins  364  and the links  360  to the driven pulleys  374   a , 374   b . The axial position of the conical sheave  3721 ) is controlled by a (not shown) actuator which moves this sheave in the direction of the arrows  376  while the axial position of the conical sheave  374   b  is controlled by a (not shown) actuator which moves the sheave in the direction of the arrows  378 . The respective movements are such that, when one sheave moves to the left (in the drawing) the other moves to the right, and opposite so that the chain  370  remains centered.