Abstract:
A plate link chain of the present invention has rocker link elements configured such that the frictional end surfaces have a profile, which deviates from a planar surface in both circumferential and radial orientations. In a preferred embodiment the end surface profiles are defined by radii of predetermined dimensions in the range of 5 to 50 millimeters with the radius formed in the radial plane being larger than the radius formed in the circumferential plane. The radii originate from midpoints, which are located at predetermined distances from the rocking surfaces, to form substantially spherical end surfaces that are either symmetric or asymmetric for selected applications. The substantially spherical end surfaces are designed to reduce the edge transfer forces and tracking error of the rocker link elements and to improve wear characteristics and the stability of frictional engagement of the transmission in operation.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims foreign priority benefits under 35 U.S.C. § 119(a-d) to German patent application 199 04 950.5, filed Feb. 6, 1999 by Dr. André Linnenbrügger, André Teubert, and Klaus Scheufele for an invention entitled Laschenkette (“Plate Link Chain”). 
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates generally to improvements in power trains of the type wherein the means for transmitting torque from the rotary output element of an internal combustion engine to a rotary driven element (such as the output shaft of a continuously variable transmission) comprises a torque monitoring sensor integrated with such transmission, in which a plate link chain including a plurality of rocker link elements is trained over a pair of adjustable pulleys or sheaves. More particularly, the present invention relates to improvements in the rocker elements, which interconnect the individual links of the plate link chain, to enhance the stability of frictional engagement of such a transmission over its entire operating range. 
     Continuously variable transmissions and torque monitoring sensors of the above outlined character are disclosed, for example, in commonly owned U.S. Pat. No. 5,879,253 entitled: “Torque Monitoring Apparatus”, filed Nov. 26, 1997 and in commonly owned U.S. Pat. No. 5,725,447 entitled: “Power Train with Infinitely Variable Ratio Transmission ”, filed Dec. 14, 1995 and are incorporated herein by this reference. 
     Such continuously variable transmissions typically include parallel pairs of axially movable pulleys or sheaves attached to the driven and output shafts of the transmission, which are actuated by hydraulic piston and cylinder assemblies. The torque sensor is designed to axially shift the adjustable sheaves into frictional engagement with the plate link chain, which is trained over a pair of such parallel sheaves, with a force depending upon the transmitted loads or upon the transmitted torque. 
     Each sheave or pulley is comprised of a pair of coneshaped discs or flanges wherein one flange is fixed to the driven and/or output shaft and the other is axially movable relative thereto. The friction surfaces of the flanges are generally conical, but vary from a true geometric cone profile to being slightly curved and/or quasi-spherical in axial cross-section to reduce wear between the plate link chain and the flanges. Further, it is advantageous in some instances to utilize asymmetrical sheaves comprised of confronting flanges with different quasi-sherical profiles to provide optimum wear and tracking characteristics. 
     The quasi-spherical profile of the flanges is useful in limiting the effects of so-called track misalignment or tracking error, that is, inclined running of the plate link chain that occurs due to the geometry of the flanges being forced into contact with the end surfaces of the rocker link elements in the plate link chain upon making a change in the transmission ratio during operation. The rocker link elements also function to interconnect the individual links of the plate link chain. The end faces of the rocker link elements may be curved and/or partially spherical and are designed to frictionally engage the contact surfaces of the flanges. 
     It has been shown that the quasi-spherical profile of the flanges and the curved end surfaces of the rocker link elements have different force transfer characteristics as the transmission ratio changes and, particularly when either of the two extreme transmission ratios in the operating range of the transmission are selected. At these operating extremes the rocker link elements transfer forces at their edges only. As a result a very high specific pressure will occur at the contact points between the rocker link elements and the flanges. In high performance transmissions locally excessive wear can result. Pitting at the contact surfaces of the rocker link elements may occur and the surfaces of the flanges will wear prematurely with the danger of hydrodynamic slippage. 
     Thus, the present invention has been developed to enhance the stability of frictional engagement of a continuously variable transmission in general and, more particularly, to reduce the edge transfer force and to limit the tracking error in the rocker link elements of the plate link chain, to improve the wear characteristics of the rocker link elements, and to overcome other shortcomings of the prior art. 
     2. Description of Related Prior Art 
     Continuously variable transmissions and torque sensors of the above outlined character and suitable for use with the present invention are disclosed, for example, in U.S. Pat. No. 5,725,447 to Friedman and in U.S. Pat. No. 5,879,253 to Friedman, et al. The torque sensors, which are disclosed in these prior patents, are designed to establish a clamping engagement between component parts of a torque transmitting apparatus depending upon the load or depending upon the transmitted torque. As a rule such torque sensors function to ensure a frictional engagement between the hydraulically adjustable, sheaves and the rocker link elements of the plate link chain, which are urged towards each other by a force depending upon the transmitted loads or the transmitted torque. 
     The application of an excessive force for urging these components together results in excessive wear whereas the application of an insufficient force entails slippage and also excessive wear between the sheaves and the rocker link elements of the plate link chain, which are maintained in frictional engagement with one another. 
     One example of a prior art plate link chain for a continuously variable transmission wherein the friction surfaces of the rocker link elements are essentially part spherical for cooperation with part spherical, cone-shaped surfaces of the such sheaves is disclosed in U.S. Pat. No. 5,792,013 (hereinafter &#39;013 patent). With reference to the (&#39;013) patent drawings, to prevent engagement of the edge regions of the rocker link elements ( 32 ,  33 ) with the respective cone-shaped flanges, contact surface lines ( 54 ,  55 ) located radially outwardly or inwardly, respectively, from a central surface line ( 49 ,  53 ) are inclined by an angle (δ) with respect to the central or base line. The angle of inclination (δ) increases, in positive or negative direction, respectively, starting at such central or base surface line about the intersection with the rocking surfaces ( 41 ,  42 ) in the direction of the cone-shaped surface ( 44 ) of the respective cone disk in engagement with the respective rocker link element. 
     However, this modification of the contour of the end facing friction surface ( 43 ) of the rocker link elements in the (&#39;013) patent is provided only in the horizontal (i.e. circumferential) plane defined by the axis ( 46 ). In contrast, the present invention provides a substantially spherical or quasi-spherical end surface formed on the rocker link elements defined by two substantially perpendicular radii originating in both the horizontal (i.e. circumferential) and radial planes with respect to the axis of the rocker link element. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an improved plate link chain for a continuously variable transmission wherein the frictional contact surfaces of the rocker link elements have a profile which deviates from a planar surface in both the horizontal (i.e. circumferential) and radial planes relative to the longitudinal axes of the rocker link elements. The frictional contact surfaces of the rocker link elements are defined by radii machined to predetermined dimensions, which originate at predetermined distances from reference surfaces on the rocker link elements to form generally spherical and/or quasi-spherical contact surfaces for engagement with the pulleys or sheaves of the transmission. It has been shown that when the rocker link elements are modified in accordance with the present invention, the edge transfer forces generated during frictional engagement are substantially reduced, which in turn limits tracking error of the rocker link elements and improves wear characteristics of the components 
     In view of the above, it is an object of the present invention to improve the stability of frictional engagement of a continuously variable transmission in general and thereby obtain improved power and energy transfer by improving the frictional engagement conditions between the plate link chain and the friction surfaces of the sheaves. 
     Another object of the present invention is to provide an improved plate link chain for a continuously variable transmission in which the frictional surfaces of the rocker link elements are configured such that the edge transfer of forces and tracking error of the rocker link elements are substantially reduced and/or effectively eliminated. 
     Another object of the present invention is to provide an improved plate link chain for a continuously variable transmission wherein the frictional surfaces of the rocker link elements have a profile deviating from a planar surface and being defined by predetermined radii in both horizontal (i.e. circumferential) and radial orientations relative to the longitudinal axis of the rocker link elements. 
     Another object of the present invention is to provide an improved plate link chain for a continuously variable transmission wherein the rocker link elements interconnect the individual chain links by means of an anti-rotation device formed therein which positively locks the rocker link elements to their corresponding chain links. Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features of the present invention are set forth in the appended claims. The invention itself however, as well as other features and advantages thereof will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures, wherein: 
     FIG. 1 is an abbreviated schematic representation of a hydraulically controlled continuously variable transmission of the PRIOR ART wherein the improved plate link chain of the present invention is utilized; 
     FIG. 2 is an enlarged, simplified view of the PRIOR ART transmission of FIG. 1 showing the quasi-spherical friction surfaces of the sheave flanges and the partially spherical engagement surfaces of the rocker link elements; 
     FIG. 3 is a side elevational view of a PRIOR ART plate link chain showing numerous pairs of rocker link elements within a plurality of individual chain links; 
     FIG. 4 is a highly enlarged, partial sectional view showing engagement between the friction surface of a sheave flange with the end surface of a rocker link element and labeled PRIOR ART; 
     FIG. 5 is a schematic view of taken along line  5 — 5  of FIG. 4 illustrating sequential rocker link elements in different positions and labeled PRIOR ART; 
     FIG. 6 taken collectively is comprised of partial, radial sectional views illustrating the rocker link elements of FIG. 5 in respectively different positions wherein: 
     FIG. 6A corresponds to the rocker link element position of rocker link element  33   a  shown in chain-dotted representation in FIG. 5, 
     FIG. 6B corresponds to the rocker link element  33   b  shown in fill-line position in FIG. 5, and 
     FIG. 6C to the rocker line element  33   c  shown in broken-line position in FIG. 5; 
     FIG. 7 is a perspective schematic and enlarged view of an end portion of a rocker link element of the PRIOR ART; 
     FIG. 8 is a perspective schematic and enlarged view of an end portion of a rocker link element in which the end surfaces thereof are modified in accordance with the present invention; and 
     FIG. 9 taken collectively are partial, longitudinal section views of alternative embodiments of a rocker link element modified in accordance with the present invention wherein: 
     FIG. 9A represents a rocker link element having an asymmetric frictional contact surface defined by the radius R 3  in the plane shown, 
     FIG. 9B represents a rocker link element having a symmetric frictional contact surface defined by the radius R 4  in the plane shown, and 
     FIG. 9C represents a rocker link element having a flat frictional contact surface with radii formed at the corner edges thereof 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Prior to describing the present invention in detail, it may be beneficial to briefly review the structure and operation of a conventional continuously variable transmission insofar as necessary for an understanding of the present invention 
     Referring to FIG. 1 there is shown therein a schematic view of a hydraulically controlled continuously variable transmission, indicated generally at  10  and labeled Prior Art. The transmission  10  includes a pair of adjustable pulleys or sheaves being coupled to an output shaft  1  and a driven shaft  2  disposed in parallel relation. The adjustable sheaves are comprised of cone-shaped discs or flanges  3 ,  7  and  4 ,  8  respectively which are coaxially mounted on the output and driven shafts  1  and  2 . The flanges  3 ,  4  together with the piston/cylinder assemblies  5 ,  6  are coupled to the fixed, rotatably supported flanges  7 ,  8 . A plate link chain  9  including a plurality of steel plate links is trained over and extends between the sheaves comprised of the flange pairs  3 ,  7  and  4 ,  8 . 
     The piston/cylinder assemblies  5 ,  6  receive hydraulic fluid under pressure from a pressure source or pump  100  over a four-control spool valve  11  and hydraulic lines  12  and  13 . The driven shaft  2  is mechanically coupled to a torque sensor  14 , which receives hydraulic fluid from line  15  in fluid communication with the valve  11 . The flow of this fluid is throttled in correspondence with the torque being transmitted. Excess hydraulic fluid is delivered through line  16  without pressure and used for lubrication of the chain  9 . 
     The throttled fluid also controls the pressure on the drive piston/cylinder assembly  5 . The piston/cylinder  5  includes a circumferential groove  17  formed therein. A so-called slider  18  slides in the groove  17  and is mechanically coupled to a lever  19  of a transmission control element or handle  20 . The lever  19  is also linked to control the spool  21  of the spool valve  11 . 
     Since the operation and function of such continuously variable transmissions are well known to those skilled in the art, further detailed discussion of the same is not deemed necessary, and reference is made to the disclosure in the aforementioned commonly owned U.S. Pat. Nos. 5,879,253 and 5,725,447. 
     For purposes of explanation of the present invention, such a continuously variable transmission is further illustrated in an enlarged view in FIG. 2 in which four cone-shaped discs or flanges  24 - 27  with quasi-spherical surfaces are shown affixed to shafts  22  and  23  respectively in rotatable engagement therewith. The flanges  24  and  26  are axially secured on their respective shafts whereas the flanges  25 ,  27  integrated with the piston/cylinder assemblies  28 ,  29  are axially shiftable as indicated by directional arrows  30 ,  31  but also rotatable with the shafts  22 ,  23 . The plate link chain  9  is trained over and runs between the flanges  24 - 27 . 
     In the neutral or base setting of the transmission ratio setting of 1:1, the chain  9  is disposed along a base or centerline  34  as seen in FIG.  2 . Rocker link elements  32  and  33  have opposite end surfaces, which engage the adjacent contact surfaces of the flanges  24 - 27  respectively. 
     Still referring to FIG. 2, it can be seen that the contact surfaces of the flanges  24 - 27  are generally conical in axial cross-section, but deviate from a true geometric cone being partly spherical and/or quasi-spherical. Similarly, the opposed end surfaces or faces of the rocker link elements  32 ,  33  have an essentially semicircular or, rather, a partly spherical outer surface. 
     Referring now to FIG. 3 there is shown therein a detailed side view of the plate link chain  9  wherein the end faces of the rocker elements  32  and  33  are shown. It will be appreciated that the scale of FIG. 3 is enlarged with respect to the figures described hereinabove. The rocker link elements are shaped such that they engage at two positions, as at  35 ,  36  and  37 ,  38  in openings formed in the plate links of the respectively associated links  39  and  40 . Further, the rocker link elements  32 ,  33  are secured against rotation with respect to the associated plate links  39  and  40 . 
     The connecting rocker link elements  32  and  33  are supported against each other for rocking movement over the generally convex shaped rocking surfaces  41  and  42 . The rocking surfaces  41  and  42  permit the rocker link elements  32 ,  33  to roll off against each other when the chain links  39 ,  40  shift from their straight line, aligned position as depicted at the center of FIG. 3 into the angulated position shown at the right side of FIG.  3 . The movement of the chain  9  in which the links  39 ,  40  are aligned on the one hand and then angulated with respect to each other occurs as the chain  9  runs through the gap between the confronting flanges  24 ,  25  and  26 ,  27 . The rocker link elements  32 ,  33  within each pair continuously shift position and roll off each other as the spacing between the flanges  24 - 27  changes depending upon the engagement radius of the flanges  24  with the respective rocker link elements  32 ,  33  during operation 
     FIG. 4 is an enlarged fragmentary view of FIG. 2 which illustrates the engagement of one side of a rocker link element  33  with a flange  24 . It will be seen that the rocker link element  33  has a generally curved and/or partly spherical end surface  43  and, similarly, the flange  24  has a curved and/or quasi-spherical friction surface  44  in cross-section FIG. 4 clearly demonstrates that these two components of the transmission (i.e. the rocker link element  33  and the flange  24 ) are frictionally engaged at a contact position  45 . The curvature of the engagement surface  43  of the rocker link element  33  is such that in the radial direction of the flange  24  adjacent parallel level lines are perpendicular to the longitudinal axis  46  of the rocker link element  33  respectively. 
     FIG. 4 also illustrates two additional possible contact positions. The contact position as at  47  is associated with a smaller operating radius of the flange  24 , and it follows that the contact position as at  48  is associated with a larger radius of engagement. 
     FIG. 5 shows the subject matter of FIG. 4 in a composite view, if one considers the cone-shaped disc or flange  24  to be transparent looking from the left side through such a transparent flange  24 . FIG. 5 depicts three pivoting positions of a rocker link element  33 , shown highly enlarged and representing three different positions of the plate link chain  9  corresponding to three different speeds of the transmission. To better illustrate these different positions, a rocker link element  33   b  corresponding to a base or central position wherein the transmission is operating at approximately a 1:1 ratio is depicted in solid outline in FIG.  5 . Accordingly, the position of a rocker link element  33  associated with a larger operating radius of the plate link chain is shown at  33   a  in chain-dotted outline, and the position shown in broken outline as at  33   c  is associated with a smaller operating radius on the flange  24 . 
     These three pivoting positions of the rocker link element  33   a - 33   c  in accordance with FIG. 5 are represented in FIG. 6 collectively and side-by-side to illustrate the engagement between the flange  24  and the respective rocker link elements. The illustrations in FIGS. 6A-6C are approximate radial sectional views and seen perpendicular to the lines  53 ,  54 , and  55  of FIG. 5 wherein the lines  55 ,  53 , and  54  illustrate a larger, a central or average, and a smaller degree of curvature of the flange  24  respectively in a radial direction. More particularly, line  53  represents a level planar section taken through the contact point  45  as shown in FIG.  4 . Similarly, the lines  54  and  55  represent planar sections taken through the respective contact points  47  and  48  as shown in FIG.  4 . 
     Referring now to FIG. 6A, which corresponds to a larger operating radius as described hereinabove, it will be seen that the friction surface  43  of the rocker link element  33   a  is located within the region of the outer edge and opposite to the rocking surface  41  as seen in FIG.  3 . The position of the rocker link element  33   b  shown in solid outline in FIG.  5  and as further represented in FIG. 6B shows that the friction surface  43  of the rocker link element  33  lies close to the rocking surface  41  (see FIG.  3 ). FIG. 6C, which corresponds to the position as at  33   c  for a smaller operating radius of the rocker link element, illustrates that the friction surface  43  lies entirely at the edge common to the rocking surface  41  (see FIG.  3 ). The same situation, of course, obtains with respect to the rocking surface  42 , which is shown in FIGS. 6A-6C. It will be understood that FIGS. 6A-6C are highly exaggerated; for example, a comparison of FIG. 6A to FIG. 6C demonstrates that the friction surface  43  of the rocker link element  33  provides only a comparatively small surface area for frictional transfer force. Of course, this small surface area will be especially highly loaded. 
     It is known in the prior art to modify the end surfaces  43  of the rocker link elements  33  such that the contact positions on the right and left edges of the rocker link elements  33  are shifted to the center thereof. The end surface line associated with the respective contact positions is essentially tangential to the associated running circumference of the cone-shaped flange  24  as seen in FIG. 6B, and is shifted about the angle δ. This modification of the end surfaces  43  is further illustrated in FIG.  7  and labeled Prior Art. For purposes of illustration the cone-shaped flange  24  has been omitted from FIG.  7 . The perspective view of FIG. 7 demonstrates that at the line  49 , which corresponds to a 1:1 transmission ratio, there is no shift or tilt of the contact line with respect to a theoretical line from perpendicular to the longitudinal axis  46  of the respective rocker link element  33 . Starting at this central or base line  49  corresponding to the transmission ratio 1:1, the tilt or shift increases in the direction of the flange radially outwardly. This shift is such that over the shifted region, the radially outwardly directed shift or inclination will be effective at smaller operating radii with respect to those in which the line  49  controls the transmission ratio. Conversely, and starting from line  49 , a negative shift is used for radial inward operation of the element  33 , which is used within the range suitable for large operating radial of the flange  24 . With respect to a known end surface  50  of the prior art shown schematically in FIG. 7 for comparison, the course of the edge of the facing surface is illustrated by line  51 , starting from a common edge  52 . The resulting surface ensures that the contact surfaces will always be in a median or central portion between the outer edges of the rocker link elements  33  considering the direction of operation of the plate link chain. Thus, the contact surfaces will have sufficient support in the material of the rocker link elements  33 . 
     With reference to FIG. 8, an improved rocker link element  33 ′ in accordance with the present invention will now be described in detail. In comparison to the rocker link element  33  of the prior art wherein the radially outwardly directed shift or inclination of the end surfaces  43  is defined by the angle δ as shown in FIG. 7, the profile of the contact surfaces of the rocker link element  33 ′ of the present invention is produced by forming a first semicircular or quasi-spherical surface in the horizontal and/or circumferential plane of the rocker link element  33 ′ such that this contact surface engages the flanges  24  with the plate link chain running in the direction indicated by directional arrows as at K. In addition, the rocker link element  33 ′ is modified by forming a second semicircular or quasi-spherical contour in a radial orientation and substantially perpendicular to the first semicircular surface as hereinafter described. Such quasi-spherical end surfaces of the rocker link elements  33 ′ are formed by conventional grinding machine equipment or other known manufacturing processes. 
     FIG. 8 illustrates that an end surface  100  of the rocker link element  33 ′ has a substantially spherical or quasi-spherical profile defined by a radius R 1  in the radial direction and a radius R 2  on a perpendicular plane A, K. In the embodiment shown in FIG. 8 it will be seen that the radius R 1  is larger than the radius R 2  with both radii being in the range of 5 to 50 millimeters (mm) and preferably in the range of 10 to 50 mm. 
     Further, it will be understood that the mid-points of the radii R 1 , R 2  are not necessarily centric to the rocker link element  33 ′. For example, in the embodiment shown the mid-point M 2  lies closer to one of the side surfaces  101 ,  102  of the rocker link element than to the other side surface. In an alternative embodiment the mid-point M 2  can be positioned equidistant from the side surfaces  101 ,  102 . 
     Similarly, it can be seen that the mid-point M 1  of the radius R 1  is located closer to the top surface  103  of the rocker link element  33 ′ than to the bottom surface  104 . In an alternative embodiment the mid-point M 1  can be located equidistant from the top and bottom surfaces  103 ,  104 . 
     FIG. 9A shows a partial longitudinal section of an alternative embodiment of a rocker link element  121  of the present invention taken through the plane A, K. It can be seen that the semicircular end surface  120  of the element  121  in the plane shown is defined by the radius R 3  having a mid-point M 3 , which is located at a distance d 1  from the side surface  126  and at distance d 2  from the side surface  125 . It will be seen that the distance d 1  is greater than the distance d 2  resulting in the asymmetric form of the contact surface  120  of the rocker link element  33 ′. 
     FIG. 9B shows a partial longitudinal section of an alternative embodiment of a rocker link element  131  of the present invention taken through the plane A, K. It can be seen that the semicircular end surface  130  of the element  131  in the plane shown is defined by the radius R 4  having a mid-point M 4 , which is located at a distance d 3  away from the side surface  136  and at a distance from the side surface  135 . It can be seen that in this embodiment that the distance d 3  is equal to the distance d 4  resulting in the symmetrical form of the contact surface  130 . 
     FIG. 9C shows a partial longitudinal section of yet another alternative embodiment of a rocker link element  141  of the present invention taken through the plane A, K. In this embodiment the element  141  includes a contact surface  140  that is straight and/or flat in the plane shown with radiused corner edges as at  142  and  143 . The corner radii formed at  142 ,  143  vary within a range proportionate to the dimensions of the rocker link element. 
     It will be understood that each of the alternative embodiments described hereinabove and illustrated in FIGS. 9A-9C also include a semicircular contour formed in the radial direction perpendicular to the plane A, K and defined by the radius R 1 , for example, as described with reference to FIG. 8 hereinabove. 
     Thus, the combination of the semicircular end surfaces defined by the radii R 1  and R 2  as shown in FIG. 8 or, alternatively, R 1  and R 3  or R 1  and R 4  as depicted in FIGS. 9A-9C results in the generally spherical and/or quasi-spherical contact surfaces of the rocker link elements  33 ′ and the improved plate link chain of the present invention. 
     Although not specifically illustrated in the drawings, it should be understood that additional equipment and structural components will be provided as necessary and that all of the components above are arranged and supported in an appropriate fashion to form a complete and operative plate link chain incorporating features of the present invention. 
     It is also understood that variations may be made in the present invention without departing from the scope of the invention. Moreover, although illustrative embodiments of the invention have been described, a latitude of modification, change, and substitution is intended in the foregoing disclosure, and in certain instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.