Abstract:
An improved torque monitoring sensor for an infinitely variable transmission including integrated wear reduction elements designed to minimize the hysteresis associated with physical strains, axial thrust forces, and mechanical friction introduced into components of the torque monitoring sensor during operation is disclosed. In one embodiment the present wear reduction elements include the formation of a symmetrical pattern of elongated slots in the cylindrical sheet metal housing of an axially displaceable cam disc component in the torque monitoring sensor to provide a degree of structural flexibility to the housing. So modified, the cam disc housing undergoes flexion in response to micro-movements generated by abrupt changes in the torque transmitted. The cam disc housing resiliently absorbs such detrimental micro-movements to prevent mechanical transference of such movement into premature frictional wear and corrosion of axially displaceable, mating splines and other components of the torque monitoring sensor. In an alternative embodiment such hysteresis is minimized by the installation of spring elements, which are interposed between the axially displaceable cam disc housing and the mating components thereof, to resiliently absorb such axial micro-movements in the torque transmitting apparatus.

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 07 816.5, filed Feb. 24, 1999 by inventor, Oswald Friedmann, for an invention entitled, “Getriebe” (Transmission). 
     BACKGROUND OF THE INVENTION 
     Field of Invention 
     This invention relates to improvements in power trains of the type wherein the means for transmitting torque from the rotary output element of a primary power source (such as an internal combustion engine) to a rotary driven element (such as the output shaft of an infinitely variable speed transmission) comprises a torque monitoring sensor integrated with such transmission, in which an endless flexible element (such as a belt or chain) is trained over a pair of adjustable pulleys or sheaves. Each pair of sheaves is adjustable by the torque sensor in response to abrupt changes in the transmitted torque to vary the transmission ratio. More particularly, the present invention relates to the integration of wear reduction elements into such a torque monitoring sensor, which function to minimize the hysteresis associated with physical strains introduced into the torque transmitting apparatus in response to abrupt changes in the load or in the torque being transmitted. 
     DESCRIPTION OF RELATED PRIOR ART 
     An infinitely variable ratio transmission, which can be utilized in conjunction with the improved torque sensor of the present invention is disclosed in U.S. Pat. No. 5,169,365 to Friedmann and is incorporated herein by reference. The disclosure in U.S. Pat. No. 5,879,253 entitled: “Torque Monitoring Apparatus”, filed Nov. 26, 1997 by inventors, Oswald Friedmann and Armin Veil, is hereby incorporated herein by this reference; and the disclosure in U.S. Pat. No. 5,725,447 entitled: “Power Train with Infinitely Variable Ratio Transmission”, filed Dec. 14, 1995, by inventors, Oswald Friedmann, Urban Panther, and Ivo Agner, is also hereby incorporated herein by this reference. 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 are designed to ensure a frictional engagement between component parts, which are urged against or toward each other by a force depending upon the transmitted loads or upon the transmitted torque, in such a way that the force acting to urge the component parts into frictional engagement with one another at least approximates the force, which is necessary for the transmission of torque. The application of an excessive force for urging the component parts against each other results in excessive wear whereas the application of an insufficient force entails a slip and hence again excessive wear between the parts which are maintained in frictional engagement with one another. 
     A conventional torque monitoring sensor includes a valve whose operation depends upon the magnitude of transmitted torque. Those portions of the torque sensor which are located downstream of a plenum chamber are constructed and assembled to comprise the aforementioned valve and the plenum chamber receives pressurized hydraulic fluid from a suitable pump. The valve acts as a flow restrictor or throttle, which seals the path for the flow of fluid from the plenum chamber so that the pressure of fluid in the plenum chamber increases in response to abrupt increases or peaks of transmitted torque. This results in a corresponding rise of fluid pressure in the plenum chamber as well as in the cylinder chamber or chambers of one or more piston and cylinder units. The piston and cylinder units are provided to adjust the infinitely variable transmission including a pair of adjustable tapered discs or sheaves and an endless flexible element, which is trained over and serves to transmit torque between the adjustable sheaves. The flexible element may constitute either a belt or a chain. 
     An increase in pressure in the cylinder chamber or chambers brings about a corresponding increase of the clamping force between the endless flexible element and the sheave or sheaves of the transmission. In other words, the frictional engagement between the sheave or sheaves on the one hand and the flexible element on the other hand increases in response to an increase of the transmitted torque and/or in response to the development of an abrupt increase of transmitted torque. 
     In order to adjust the above-described valve, the torque monitoring sensor includes so-called cam discs that are provided with confronting cam faces or ramps bearing upon spherical rolling elements, which are retained between them with a force generated by the source of pressurized hydraulic fluid. If the transmitted torque develops abrupt increases or peaks, especially peaks in the torque being transmitted from the primary power source, the cam discs are caused to move axially and away from each other such that an axially movable portion reduces the effective cross-sectional area of the outlet for the flow of hydraulic fluid from the plenum chamber at a rate proportional to the magnitude of the peaks of transmitted torque. 
     In addition, the cam discs serve as a means for mechanically transmitting at least a portion of the driving torque to adjust the effective cross-sectional area of the outlet from the plenum chamber as a function of the magnitude of transmitted torque. Thus, the proper frictional clamping force between the adjustable sheaves and the endless flexible element of the infinitely variable transmission is maintained. 
     This so-called pumping action in the torque sensor introduces severe physical strains and high axial thrust forces and on the rotating and axially displaceable components in the torque sensor, which can cause premature wear of such components and mechanical failure of the torque transmitting apparatus. Thus, the present invention provides wear reduction elements which are integrated into these components of the torque sensor to minimize the hysteresis produced by the pumping action of the torque monitoring sensor in normal operation. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is an improved torque sensor for an infinitely variable ratio transmission, which includes wear reduction elements integrated into components of the torque sensor or, in the alternative, wear reduction elements mechanically adaptable to such components. The present wear reduction elements are designed to elastically compensate for the physical strains, axial thrust forces and mechanical friction, which are introduced to the rotating and axially displaceable components of the torque sensor during the so-called pumping action of the torque sensor in response to abrupt changes in the load or torque being transmitted in normal operation. 
     In one embodiment the present wear reduction elements include the formation of a symmetrical pattern of circumferentially arranged slots in the cylindrical sheet metal housing of an axially displaceable cam disc component to provide a degree of structural flexibility to the housing. So modified, the cam disc housing undergoes slight flexion in response to micro-movements produced by physical strain and/or axial thrust in the supporting bearings to prevent translation of such micro-movements into premature frictional wear of axially displaceable splines and other components in the torque transmitting apparatus. 
     In an alternative embodiment such physical strains and/or axial micro-movements between torque sensor components are compensated for by the installation of spring elements, which are disposed between the axially displaceable cam disc and the mating components thereof to resiliently absorb such movements in the torque monitoring sensor. 
     In view of the above it is an object of the present invention to provide an improved torque monitoring sensor for an infinitely variable transmission incorporating wear reduction elements for minimizing the hysteresis associated with physical strains and/or axial thrust movements introduced into the torque sensor during normal operation. 
     Another object of the present invention is to provide an improved torque monitoring sensor including wear reduction elements for reducing undesirable micro-movements between mating components such as axially displaceable splines in the torque sensor, which are generated by the physical strains, axial thrust forces, and mechanical friction resulting from abrupt changes in the load and/or the torque transmitted during normal operation. 
     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 axial section view of an infinitely variable transmission of the PRIOR ART wherein the improvements of the present invention are to be utilized; 
     FIG. 1A is an enlarged sectional view of the PRIOR ART transmission of FIG. 1 showing details of the torque sensor and the piston and cylinder assemblies positioned on the driven shaft A; 
     FIG. 2 is a composite axial sectional view of an improved torque monitoring sensor illustrating alternative embodiments of the wear reduction elements of the present invention; 
     FIG. 3 is a top plan view taken along the line  3 — 3  of FIG. 2 showing the details of the displaceable cam disk including the wear reduction slots of the present invention; 
     FIG. 4 is an axial section view taken through the displaceable cam disk showing the angular orientation of the wear reduction slots; and 
     FIG. 5 is an axial section view taken through the juncture of the cam disk and the ring-shaped component showing an alternative embodiment of the wear reduction elements of the present invention including the resilient leaf spring elements. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Prior to describing the improvements of the present torque monitoring sensor in detail, it may be beneficial to review the structure and function of an infinitely variable speed transmission with which the present invention is to be utilized. For purposes of this application it will be understood that the terminology “variable speed transmission,” “infinitely variable transmission,” and “infinitely variable speed transmission” are considered to be substantially identical and interchangeable terms. 
     Referring to FIGS. 1 and 1A, there is shown an infinitely variable transmission labeled PRIOR ART including a first adjustable sheave, indicated generally at  1 , a second adjustable sheave, indicated generally at  2  and an endless flexible element  3 , which is trained over and transmits torque between the sheaves  1  and  2 . The sheave  1  is non-rotatably carried by a rotary input member depicted herein as shaft A, which is parallel to a rotary output member comprising a shaft B, which supports and is non-rotatably connected with the sheave  2 . The sheaves  1  and  2  are comprised of axially movable first flanges  1   a  and  2   a  and axially fixed second flanges  1   b,    2   b  respectively. 
     The flange  1   a  is located at a maximum distance from the flange  1   b  (as shown by solid lines in the upper part of the sheave  1 ) and the flange  2   a  is located at a minimum axial distance from the flange  2   b  (as shown by solid lines in the upper half of the sheave  2  when the ratio of the infinitely variable transmission including the sheaves  1 ,  2  and the flexible element  3  assumes a minimum value). The transmission then functions in an underdrive mode wherein the revolutions per minute (RPM) of the shaft A can greatly exceed the RPM of the shaft B. Alternatively, if the axially movable flange  1   a  is caused to move to a position at a minimum axial distance from the axially fixed flange  1   b  (as shown by solid lines in the lower half of the sheave  1 ), the flange  2   a  is located at a maximum axial distance from the flange  2   b  (as shown in the lower half of the sheave  2 ) and the transmission functions in an overdrive mode because the RPM of the sheave  2  and shaft B exceeds the RPM of the sheave  1  and shaft A by a maximum value. 
     The means for adjusting the sheave  1  (i.e. for moving the flange  1   a  axially and relative to the flange  1   b  comprises a hydraulically operated, primary piston and cylinder assembly, indicated generally at  4 . Similarly, the means for adjusting the sheave  2  (by moving the flange  2   a  axially and relative to the flange  2   b ) comprises a hydraulically operated, primary piston and cylinder assembly, indicated generally at  5 . The chamber  6  of the piston and cylinder assembly  5  includes at least one energy storing element depicted herein as a coil spring  7 , which biases the axially movable flange  2   a  in a direction toward the axially fixed flange  2   b.    
     The tension of the coil spring  7  increases in response to movement of the flange  2   a  axially and away from the flange  2   b  (i.e. when the flexible element  3  which is trained over the sheave  2  is caused to assume a position at a minimum distance from the common axis of the shaft B and sheave  2 . Otherwise stated, the tension of the spring  7  increases in response to a rise in the ratio of the transmission (i.e. to an increase in the RPM of the shaft B relative to the RPM of the shaft A). The coil spring  7  reacts against a cupped member  8  which is rigidly secured to the shaft B, and the spring  7  bears directly upon the axially movable flange  2   a  of the sheave  2 . 
     The primary piston and cylinder assembly  4  operates in parallel with a secondary piston and cylinder assembly, indicated generally at  10 , and the primary piston and cylinder assembly  5  operates in parallel with a secondary piston and cylinder assembly, indicated generally at  11 . The purpose of the secondary piston and cylinder assemblies  10 ,  11  is to vary the ratio of the transmission including the sheaves  1 ,  2  and the flexible element  3 . The secondary assembly  10  defines a cylinder chamber  12 , and the secondary assembly  11  defines a cylinder chamber  13 . The ratio of the transmission is changed in response to admission of pressurized hydraulic fluid into and in response to evacuation of such fluid from the chambers  12  and  13 . To this end, the chambers  12 ,  13  can be connected to a source of pressurized hydraulic fluid (such as a pump) or with one or more fluid evacuating channels, conduits and/or other suitable passages. 
     If the ratio of the transmission is to be changed, one of the chambers  12  or  13  receives pressurized fluid to increase its volume whereas the contents of the other of these chambers is evacuated, at least in part, to reduce its volume. The means for regulating the admission of fluid into and the evacuation of fluid from the cylinder chambers  12  and  13  includes one or more suitable valves. Suitable valves for this purpose are well known in the prior art and can be used in the infinitely variable transmission of FIG. 1 to regulate the flow of fluid into and from the cylinder chambers  12  and  13 . 
     The power train which is shown in FIG. 1 further comprises a hydromechanical torque monitoring device or sensor, indicated generally at  14 , serving to generate a pressure depending upon the magnitude of transmitted torque. In the embodiment which is shown in FIG. 1 and 1A, the torque sensor  14  functions to transmit torque from a driver gear or pinion  15  to the first sheave  1  of the infinitely variable transmission. The driver pinion  15  is mounted on an anti-friction bearing  16  which surrounds the input shaft A. The driver pinion  15  transmits torque to a rotary cam disc  18  of the torque sensor  14  by way of a form-locking connection  17  comprised of a set of mating splines. 
     The cam disc  18  is held in an axially fixed position by the driver pinion  15  and cooperates with an axially movable second cam disc  19  of the torque sensor  14  by way of a form-locking connection  17  (e.g. a set of mating splines). The cam disk  18  is held in axially fixed position by the driver pinion  15  and cooperates with an axially movable second cam disk  19  of the torque sensor  14 . The cam disks  18 ,  19  have confronting cam faces in the form of ramps, which abut one or more spherical spreading elements  20  between the discs  18 ,  19 . The cam-disc  19  is free to move axially, but cannot rotate relative to the input shaft A. To this end, the cam disc  19  comprises a radially outer portion  19   a,  which is radially disposed about the shaft A extending axially and away from the spreading elements  20 . This outer portion  19   a  includes a spline  19   b  in mesh with a mating spline  21   a  on a member  21 , which is mounted on and cannot rotate and/or move axially relative to the shaft A. However, the splines  19   b  and  21   a  permit axial movements of the cam disc  19  relative to the member  21  and shaft A. 
     The component parts of the torque sensor  14  define two plenum chambers  22  and  23 . Such component parts can be said to constitute or resemble walls including a cone-shaped member  24  and members  25 ,  26  which are carried by or form part of the cam disc  19 . The members  24 ,  25  and  26  define the plenum chamber  22 . The member  24  is rigidly secured to the shaft A and the illustrated members  25 ,  26  are shown as separately produced parts (see particularly FIG. 1A) which are non-rotatably affixed to the cam disc  19 . The plenum chamber  23  extends radially outwardly beyond and is axially offset relative to the plenum chamber  22 . This second plenum chamber  23  is bounded in part by the cone-shaped member  24 , by the substantially sleeve-like member  21  which is fixedly connected to the member  24 , and by the ring-shaped member  25  which, as already stated above, forms part of or is affixed to the cam disc  19 . The latter is movable axially of the shaft A and performs the function of a piston. 
     The input shaft A is mounted in a housing  30  by way of a needle bearing  27 , which is disposed at the left-hand side of the torque sensor  14  as viewed in FIGS. 1 and 1A and by way of a thrust roller bearing  28  and a radial roller bearing  29  disposed at the other side of the adjustable sheave  1  as viewed in FIG.  1 . The output shaft B is also mounted in the housing  30  by means of a twin anti-friction rolling bearing  31  at the right-hand side of the assemblies  5  and  11  for the axially movable flange  2   a  of the sheave  2  on the shaft B, and by means of an anti-friction roller bearing  32  to the left of the sheave  2  as shown in FIG.  1 . The twin anti-friction bearing  31  is designed to take up radial stresses as well as two-directional axial stresses. The left-hand axial end of the driven shaft B is provided with a bevel gear  33 , which can be moved into mesh with a complementary gear in the differential of a power train of a motor vehicle or with a complementary gear which is operatively connected with the differential (not shown). 
     In order to generate the pressure which is necessary in order to affect appropriate frictional clamping engagement between the flanges of the sheaves  1 ,  2  and the flexible element  3 , the torque sensor  14  is operatively connected with a source of pressurized hydraulic fluid such as pump  34 . The outlet of the pump  34  is connected with the plenum chamber  22  of the torque sensor  14  by a centrally located, axially extending channel  35  and at least one radially extending channel  36  both formed in the driving shaft A. The outlet of the pump  34  is further connected with the cylinder chamber  6  of the hydraulic piston and cylinder assembly  5 , which acts upon the axially movable flange  2   a  of the sheave  2 . This connection includes a hydraulic fluid line  37 , a centrally located axially extending channel  38  in the driven shaft B, and one or more substantially radially extending channels  39  also formed in the shaft B. 
     The plenum chamber  22  of the torque sensor  14  is connected with the cylinder chamber  9  of the piston and cylinder assembly  4  for the axially movable flange  1   a  of the sheave  1  by a channel  40 , which is not located in the plane of FIG. 1 or  1 A and is indicated by broken lines in these figures. Channel  40  is formed in the ring-shaped member  24 , which is affixed to or integrally formed with the driving shaft A. The channel  40  further establishes permanent fluid communication between the plenum chamber  22  of the torque sensor  14  and the cylinder chamber  9  of the piston and cylinder assembly  4  for the flange  1   a  of the sheave  1 . 
     The driving shaft A is further provided with at least one channel  41  constituting an outlet for the flow of hydraulic fluid from the plenum chamber  22  of the torque sensor  14 . The illustrated channel  41  communicates with or can be caused to communicate with the plenum chamber  22  dependent upon the magnitude of transmitted torque. As shown in FIGS. 1 and 1A, the illustrated channel  41  extends substantially radially and communicates with a second centrally located axially extending channel  42  of the driving shaft A. The channel  42  can also be used as a means for conveying hydraulic fluid from the plenum chamber  22  to one or more component parts forming part of the power train including the torque sensor  14  and the transmission including the sheaves  1 ,  2  and the flexible element  3 . For example, the fluid leaving the plenum chamber  22  via channels  41 ,  42  can be used as a lubricant and/or as a coolant for the component parts of the transmission including the sheaves  1 ,  2  and the flexible element  3 . 
     The means for regulating the rate of flow of hydraulic fluid from the plenum chamber  22  by way of the channel or outlet  41  includes an inner portion  26   a  of the cam disc  19 . The components are arranged such that the axial position of the cam disc  19  changes in response to changes in the magnitude of transmitted torque such that a portion  26   a  of the disc  19  moves axially of the shaft A in covering relation to the channel  41  to throttle the flow of fluid from the plenum chamber  22  dependent upon the magnitude of such torque. It can be said that the portion  26   a  of the cam disc  19  and that portion of the driving shaft A, which defines the channel or outlet  41  constitute a valve and more particularly a throttle valve or flow restrictor for hydraulic fluid leaving the plenum chamber  22  on its way toward one or more component parts, which require cooling and/or lubrication. 
     Thus, the cam disc  19  functions like a piston that moves axially of the shaft A dependent upon the torque which is being transmitted between the cam discs  18  and  19  causing an increase or a reduction of the rate of fluid flow from the plenum chamber  22  via outlet  41 . This results in the establishment, at least in the plenum chamber  22 , of a fluid pressure supplied by the pump  34 , which is indicative of the magnitude of transmitted torque. Since the plenum chamber  22  is communicatively connected with the cylinder chamber  9  and with the cylinder chamber  6  by means of passages  35  through  39 , the fluid pressure in the chambers  6  and  9  is also indicative of the magnitude of transmitted torque. 
     Since the primary piston and cylinder assemblies  4  and  5  are connected in parallel with the respective secondary piston and cylinder assemblies  10  and  11 , the fluid pressure which is supplied for displacement of the axially movable flanges  1   a,    2   a  of the sheaves  1 ,  2  generates forces which are added to the forces generated as a result of fluid pressure in the cylinder chambers  12  and  13  for the purposes of selecting a desired transmission radio. 
     The cylinder chamber  12  of the secondary assembly  10  for the axially movable flange  1   a  of the sheave  1  receives pressurized hydraulic fluid from a discrete source  53  such as a gear pump or a vane pump by way of an axially parallel channel  43  which is formed in the driving shaft A. At least one substantially radially extending bore  44 , which is also formed in the shaft A, communicates with the channel  43 . A circumferentially extending, peripheral groove  45  formed in the shaft A also communicates with the radially extending bore  44 . As shown in FIG. 1, at least one channel  46  is provided in the ring-shaped member  24  and communicates with the groove  45 . A substantially radially extending passage  47  formed in the sleeve-like member  21  communicates with the cylinder chamber  12 . 
     The fluid connection between the vane pump  53  and the cylinder chamber  13  of the piston and cylinder assembly  11  for the axially movable flange  2   a  of the sheave  2  comprises a ring-shaped channel  48  as shown in the lower portion of FIG.  1 . Channel  48  formed in the driven shaft B and surrounds the centrally located channel  38 , and at least one substantially radially extending channel  49  also formed in the shaft B connects the channel  48  with the chamber  13 . A conduit  51  connects the outlet of the pump  53  with the channel  43 , and a conduit  52  connects the outlet of the pump  53  with the channel  48 . A valve  50  or a system of valves (not shown) controls the flow of pressurized fluid from the pump  53  via conduits  51 ,  52  and into channels  43 ,  48  of the shafts A and B respectively. 
     The pump  53  comprises an optional component part of the power train. If this pump is omitted, the power train comprises a valve  54  shown in FIG. 1 by broken lines or a system of valves (not shown) serving to regulate the flow of pressurized hydraulic fluid from the pump  34  to the conduits  51  and  52 . The valve  54  serves to regulate the volumetric flow and/or the pressure of fluid flowing from the pump  34  into the conduits  51  and  52 . 
     The second plenum chamber  23  of the torque sensor  14  is connected in parallel with the first plenum chamber  22 , at least when the fluid in the chamber  23  is maintained under pressure. The plenum chamber  23  is sealed off from the pump  34  when the transmission including the sheaves  1 ,  2  and the flexible element  3  operates in such a way that the rotational speed of the sheave  2  achieves its lowermost) value because the axially movable flanges  1   a  and  2   a  then assume the axial positions, which are shown in the upper portions of the respective sheaves in FIG.  1 . This is due to the fact that, at such times, the composite path defined by the channels, bores and/or analogous passages  55  through  60  does not permit hydraulic fluid to flow from the pump  34  to the plenum chamber  23 . 
     In such instance the axial position of the flange  1   a  is positioned in the upper portion of the sheave  1  as shown in FIG. 1, (i.e. the outer end portion of the bore  60  in the driving shaft A is fully exposed) so that the pressure of fluid in the plenum chamber  23  need not exceed atmospheric pressure. The axial force which the torque sensor  14  then transmits for the purposes of torque transmission and which is being applied to the cam disc  19  is taken up only by the cushion of pressurized hydraulic fluid in the plenum chamber  22 . The fluid pressure in the plenum chamber  22  increases if the torque to be transmitted by the torque sensor  14  increases. As described hereinabove such pressure is regulated by the throttle valve including that portion  26   a  of the cam disc  19  and that portion of the driving shaft A which defines the channel or outlet  41 . 
     If the ratio of the transmission is to be increased, the flange  1   a  of the sheave  1  is moved axially along the driving shaft A in a direction toward the axially fixed flange  1   b,  and the flange  2   a  of the sheave  2  is moved axially of the driven shaft B and away from the axially fixed flange  2   b.  This results in movement of the flange  1   a  toward or all the way to the position shown in the lower half of the sheave  1  and in the movement of the flange  2   a  toward or all the way to the position shown in the lower half of the sheave  2  as seen in FIG.  1 . Axial movements of the flanges  1   a  and  2   a  from the positions shown in the upper halves of the sheaves  1 ,  2  toward the positions shown in the lower halves of the respective sheaves and increasing the ratio of the infinitely variable transmission are initiated by the valve  50 , which is actuated to permit pressurized hydraulic fluid to flow from the pump  53  (or from the pump  34  via valve  54  is the pump  53  is omitted) into the cylinder chamber  12  of the piston and cylinder assembly  10 . At the same time fluid is free to flow from the cylinder chamber  13  of the piston and cylinder assembly  11 . Thus, the volume of fluid in the chamber  12  increases and the volume of fluid in the chamber  13  decreases. 
     The component features which enable the flanges  1   a,    2   a  to move axially of shafts A and B, but which prevent these flanges from turning relative to the respective shafts A, B include spline couplings  61  and  62 . 
     The axial position of the flange  1   a  in which the ratio of the infinitely variable transmission assumes a maximum value is shown by solid lines in the lower half and by phantom lines in the upper half of the sheave  1  as shown in FIG.  1 . The corresponding position of the upper portion of the flexible element  3  is shown by phantom lines in the upper half of the sheave  1  as viewed in FIG.  1 . The flange  2   a  assumes the axial position, which is shown by phantom lines in the lower half and by solid lines in the upper half of the sheave  2  (as viewed in FIG. 1) when the ratio of the transmission is set at a minimum value. 
     The axially movable flange  1   a  of the sheave  1  includes axially spaced apart centering portions  63 ,  64 , which cooperate with the adjacent portions of the periphery of the driving shaft A, and the axially movable flange  2   a  of the sheave  2  comprises axially spaced apart centering portions  65 ,  66  which cooperate with the adjacent portions of the periphery of the driven shaft B. In this configuration the flanges  1   a  and  2   a  are movable axially of the respective shafts A and B without any, or without any appreciable radial play. 
     The centering portions  63 ,  64  of the flange  1   a  cooperate with those portions of the shaft A which define the adjacent outer end portions of the channels or bores  59 ,  60  to form therewith a pair of valves. The flange  1   a  constitutes the axially movable valving element of each of these valves. If the flange  1   a  is caused to move from the solid-line position shown in the upper half of the sheave  1  in an axial direction to the right as most clearly shown in FIG. 1A, flange  1   a  will gradually block the outer end portion of the bore  60  to progressively throttle the flow of hydraulic fluid through such bore. When the flange  1   a  reaches an axial position in which its centering portion  64  seals the outer end portion of the bore  60 , the other centering portion  63  seals the outer end portion of the bore or channel  59 . 
     If the flange  1   a  is caused to continue its axial movement toward the axially fixed flange  1   b,  the centering portion  64  continues to seal the outer end of the bore  60 , but the centering portion  63  advances beyond and exposes the outer end of the bore  59 . This position establishes a gradually increasing connection for the flow of hydraulic fluid between the cylinder chamber  9  of the piston and cylinder assembly  4  and the channel  58  of the shaft A which, in turn, establishes a path for the flow of hydraulic fluid to the plenum chamber  23  through the passages  55 ,  56  and  57 . At such time, the outer end of the bore  60  is at least substantially sealed by the centering portion  64  while the plenum chambers  22 ,  23  are free to communicate with the cylinder chamber  9 . Consequently, the pressure of hydraulic fluid in the plenum chambers  22 ,  23  matches the fluid pressure in the cylinder chamber  9  and also in the cylinder chamber  6  which is in fluid communication with the pump  34  by the channel  35 , by the conduit  37  and by channel  38 . The difference, if any, between the fluid pressures in the plenum chambers  22 ,  23  and cylinder chamber  9  and the cylinder chamber  6  is attributable to losses due to friction between the fluid and the surfaces surrounding the respective paths. 
     Owing to the establishment of a transmission-ratio-dependent connection between the plenum chambers  22  and  23 , the axially effective surface of the pressurized fluid cushion which develops in the torque sensor  14  is increased because the axially effective surfaces in the two plenum chambers  22 ,  23  are added to (i.e. superimposed upon each other). Such increase of the overall dimensions of the axially effective supporting surface ensures that, if the magnitude of the torque remains unchanged, the pressure which is being built up by the torque sensor  14  is reduced at least substantially proportionally to the increase of the effective surface. This, in turn, means that the pressure of hydraulic fluid in the cylinder chambers  9  and  6  is reduced accordingly. Thus, the torque sensor  14  can be resorted to for transmission-ratio-dependent modulation of fluid pressure in superimposition upon that pressure modulation which is dependent upon the magnitude of transmitted torque. Otherwise stated, the torque sensor  14  permits or renders possible a two-stage modulation of the pressure or pressure level. 
     In the power train which is shown in FIGS. 1 and 1A, the mutual positions of the bores  59 ,  60  as well as their positions relative to the centering portions  63 ,  64  of the axially movable flange  1   a  are selected in such a way that the switching over from the establishment of fluid pressure only in the plenum chamber  22  to the establishment of fluid pressure in the plenum chambers  22 ,  23  or vice versa takes place when the ratio of the continuously variable transmission including the sheaves  1 ,  2  and the flexible element  3  equals or approximates one-to-one. It is advisable to ensure that the shift from the plenum chamber  22  to the combination of plenum chambers  22 ,  23  or vice versa take place gradually rather than abruptly for structural or constructional reasons. In other words, it is desirable to establish a transition stage during which the bore  60  is already sealed by the axially movable flange  1   a  while the bore  59  is still sealed from the cylinder chamber  9  of the piston and cylinder assembly  4 . 
     In order to ensure satisfactory operation of the torque sensor  14  and the continuously variable transmission during such transitional stage, the cam disc  19  of the torque sensor  14  must be mounted with freedom of movement in the axial direction of the driving shaft A and the torque sensor comprises means for facilitating a change of the effective volume of the plenum chamber  23 . This enables the torque sensor  14  to function like a pump in that its component parts, which can be said to constitute a piston and a cylinder are movable relative to each other. 
     In the power train of FIGS. 1 and 1A, the compensating means for facilitating a change of the effective volume of the plenum chamber  23  is a so-called tongue or lip seal  67  which is installed in a circumferentially extending annular recess or groove of the ring-shaped member  24  and contacts the adjacent internal cylindrical surface of component  25 . In other words, the lip seal  67  functions to seal the plenum chambers  22 ,  23  from each other. 
     The illustrated lip seal  67  is designed and placed in such a way that it functions as a check valve that permits fluid to flow in only one axial direction from the plenum chamber  22  into the plenum chamber  23 , but prevents the fluid from flowing in the opposite direction. In other words the lip seal  67  prevents an equalization of pressure between the two chambers  22  and  23  whereas a flow through the seal  67  is possible in the other axial direction. 
     Thus, when the cam disc  19  is caused to move in a direction to the right, as viewed in FIGS. 1 and 1A, and when the plenum chamber  23  is otherwise sealed, fluid can flow from the plenum chamber  23  into the plenum chamber  22 . If the cam disc  19  is thereupon caused to move axially in a direction to the left, again as viewed in FIGS. 1 and 1A, the pressure in the plenum chamber  23  can decrease and in some cases air bubbles can form in the oil. However, this will not adversely affect the mode of operation of the torque sensor  14  or the infinitely variable transmission. 
     The lip seal  67  can be replaced by, or even be utilized in conjunction with, a check valve or one-way valve of any standard or other suitable design. If a standard check valve is used in the power train of FIGS. 1 and 1A, it can be mounted in or on the ring-shaped member  24 . In such instance, the illustrated lip seal  67  is or can be replaced with a seal which is effective at all times (i.e. which permits hydraulic fluid from flowing between the plenum chambers  22 ,  23  in either direction). 
     Still further, a check valve performing the function of the lip seal  67  can be installed between the channels  35  and  58 . All that is required is that the selected check valve or valves permit pressurized hydraulic fluid to flow from the plenum chamber  23  into the plenum chamber  22  but not in the opposite direction. 
     From the preceding description of the power train it is clear that when the infinitely variable transmission acts as a step-down transmission (i.e. when the transmission can be said to be operating in an underdrive mode), the axial force which is generated by the cams or ramps of the cam discs  18  and  19  is taken up only by the axially effective surface, which develops in the plenum chamber  22 . On the other hand, when the transmission acts as step-up transmission (i.e. when the transmission can be said to be operating in an overdrive mode), the axial force which is furnished by the ramps or cams of the cam discs  18 ,  19  and acts upon the disc  19  is counteracted by axially effective surfaces in both plenum chambers. Thus, and if the input torque does not change, the pressure generated by the torque sensor  14  when the transmission acts as a step-down transmission is higher than the pressure which is generated by the torque sensor  14  when the transmission acts as a step-up transmission. 
     As described hereinabove, the infinitely variable transmission of FIGS. 1 and 1A is designed in such a way that the switchover point, which causes a connection or separation between the plenum chambers  22 ,  23  takes place when the transmission ratio is within a range of approximately one-to-one. However, such switchover point can be readily shifted in either direction (i.e. toward a higher or a lower transmission ratio) by the simple expedient of properly dimensioning and/or positioning the bores  59 ,  60  of the driving shaft A and/or the centering portions  63 ,  64  which are provided on the axially movable flange  1   a  to control the flow of hydraulic fluid through the respective bores. The term switchover point is not intended to define a single accurately defined axial position of the flange  1   a,  but can also embrace a reasonable range of such axial positions. 
     The connection or separation between the plenum chambers  22  and  23  can also be affected by a special valve designed for this purpose. To this end, the torque sensor  14  can be provided with a channel, which establishes a path for the flow of hydraulic fluid between the plenum chambers  22 ,  23  and the special valve can be installed in such conduit. The valve need not be actuated directly by the axially movable flange  1   a  or  2   a,  but can receive signals for actuation from an externally located energy source. For example, the valve can constitute a hydraulically or pneumatically actuated or an electromagnetic valve, which is actuated in dependency upon the transmission ratio or upon a change of the transmission ratio of the infinitely variable transmission. Highly satisfactory results can be obtained with a so-called 3/2-way valve, which is installed to permit or to interrupt the flow of hydraulic fluid between the plenum chambers  22  and  23 . The 3/2-way valve or another suitable valve could be installed in a conduit connecting the channels  35  and  58  of the driving shaft A. This would render it possible to seal or to dispense with the bores  59  and  60  of the shaft A. The valve would have to be installed and designed in such a way that it permits fluid to flow from the plenum chamber  23  when the plenum chambers  22  and  23  are sealed from each other. All that is necessary is to provide a connection for the flow of fluid from the plenum chamber  23  to the oil sump in response to appropriate setting of the valve (i.e. when the latter seals the plenum chambers  22 ,  23  from each other. 
     When using a valve which is controlled externally (e.g. electromagnetically), it is possible to change the setting of such valve in response to changes in one or more additional parameters. For example, the valve can be actuated in response to detection of abrupt changes (peaks) of torque being transmitted by the power train. This eliminates, or at least reduces, the likelihood of slip between the flexible element  3  and the flanges of the sheave  1  and/or  2  within certain ranges of operation (e.g. within certain ranges of the ratio of the continuously variable transmission. 
     FIGS. 1 and 1A show that the torque sensor  14  is installed between the primary power source and the axially movable flange  1   a  of the sheave  1 . However, the torque sensor  14  can be readily adapted or modified for installation at one or more other locations (e.g. on the driven shaft B). For example, a torque sensor (not shown) similar to or practically identical with the torque sensor  14  of FIGS. 1 and 1A can be installed adjacent to and downstream of the axially movable flange  2   a  of the sheave  2  on the driven shaft B. Further, the power train can employ a plurality of torque sensors (not shown), for example, a first torque sensor on the driving shaft A ahead of the axially movable flange  1   a  (as seen in the direction of power flow) and a second torque sensor on the driven shaft B downstream of the axially movable flange  2   a.    
     FIG. 1 shows that the cylinder chamber  6  of the piston and cylinder assembly  5  for the flange  2   a  is connected with the torque sensor  14 . However, it is also possible to connect the torque sensor  14  with the cylinder chamber  13  in the piston and cylinder assembly  11  to ensure that the pressure of hydraulic fluid in the cylinder chamber  13  is determined by the torque sensor. The piston and cylinder assembly  5  including the cylinder chamber  6  then forms part of the means for changing the ratio of the continuously variable transmission. All that is necessary in order to carry out the above-outlined modifications or the transmission is to switch the connections for the conduits  37  and  52 . 
     It is presently preferred to mass-produce several component parts of the torque sensor  14  from a suitable metallic sheet material. This also applies for the cam discs  18  and  19 . Such parts can be produced in a suitable stamping or embossing machine. 
     Novel improvements to such a torque sensor in accordance with the present invention will now be described in detail. Referring to FIG. 2, there is shown therein an axial sectional view of a detail of the improved torque sensor, indicated generally at  100 , and mounted in operative relation to an axially displaceable flange  101  on the drive shaft A′ of a continuously variable transmission. The corresponding axially fixed flange has been omitted from this illustration. It will be noted that FIG. 2 is a composite view which serves to illustrate alternative embodiments of the present wear reduction means in both the upper and lower portions of this figure simultaneously. 
     The improved torque sensor  100  is comprised of a rotary cam disk  108  fixed to the drive shaft A′, a second axially displaceable cam disc  112  mounted on the drive shaft A′, and a plurality of spherical spreading elements  110  disposed intermediate the cam discs  108  and  112 . The cam discs  108  and  112  have confronting cam faces in the form of ramps  108   a  and  112   a,  abutting the spreading elements  110 , which are distributed evenly in a circumferential pattern between the ramps  108   a  and  112   a.    
     The cam disc  108  is held in axially fixed position by the driver pinion  102  and cooperates with the axially moveable second cam disc  112  by way of a form-locking connection  106  (e.g. a set of mating splines). The driver pinion  102  is mounted on an anti-friction bearing  104 , which is fixedly secured to the shaft A′ as shown. 
     The axially displaceable cam disc  112  includes a generally cylindrical, radially outer housing section  112   b,  which extends axially in a direction away from the spreading elements  110  as shown in FIG.  2 . This outer housing section  112   b  of the cam disc  112  includes an internal spline  114  formed on the inner surface thereof, which engages a mating external spline  116  locking the subassembly comprising the ring-shaped component  117  and the disc-shaped component  120  to the drive shaft A′ in nonrotatable connection. It will be noted in FIG. 2 that this subassembly  117 ,  120  comprises a radially outer, ring-shaped component  117  including the external spline  166  formed thereon that is attached by rivets  118  to the disc-shaped component  120 , which is nonrotatably connected as at  122  to the drive shaft A′. However, the mating splines  114  and  116  are manufactured with adequate clearance therebetween to permit axial displacement between the cam disc  112  and the subassembly  117 ,  120 . 
     The hereinabove described components of the torque monitoring sensor  100  define the two plenum chambers  140  and  142  which are well known and described hereinabove with respect to the Prior Art example in FIGS. 1 and 1A. 
     Because the anti-friction bearing  104  is designed accommodate some tilting movement relative to its axis due to manufacturing tolerances, the driver pinion  102  can be slightly inclined by small angular increments in operation producing a relative movement between the drive shaft A′ and the driver pinon  102  with each revolution of the shaft. Such tilting movement is transmitted to the cam disc  108  and to the cam disc  112  through the spreading elements  110  such that in the mating splines  114  and  116 , a small relative movement is generated upon each revolution of the driver pinion  102  during operation. Such micro-movements are measurable being in the range of 20-30 microns (μm) and act to prevent the introduction of lubricating oil into the mating splines  114  and  116  resulting in fretting, corrosion, and premature wear of the mating splines  114  and  116 . 
     In order to compensate for such micro-movements and the resulting frictional wear and corrosion produced thereby, the present torque monitoring sensor  100  includes structures for reducing such detrimental micro-movements. Such structures integrally form, for example, wear reduction means including, but not limited to, those hereinafter described. 
     In one embodiment a set of elongated wear reduction slots  124  of predetermined dimensions are formed in the cylindrical outer housing section  112   b  of the cam disc  112  as seen in the upper portion of FIG.  2 . The slots  124  are arranged circumferentially about the housing section  112   b  in end-to-end relation with equal gaps as at  127  therebetween as more clearly shown in FIG.  3 . In a preferred embodiment a second set of slots  126  of similar configuration is formed in parallel relation to the slots  124  as seen in FIG. 3 being axially rotated and offset to the slots  124  and symmetrically positioned in relation to the gaps as at  127  between the slots  124 . This circumferential arrangement of the slots  124  is further illustrated in axial section in FIG.  4 . 
     The cylindrical housing section  112   b  of the cam disc  112  including the slots  124  and  126  produces a resilient construction, which extends circumferentially about the section  112   b  and is capable of flexion and elastic compensation for the micro-movements transmitted to the mating splines  114  and  116  by the tilting movements of the driver pinion  102  described hereinabove. Of course, the significantly larger movements caused by the so-called pumping action of the torque sensor  100  resulting from abrupt changes in torque, which causes cam discs  108  and  112  to be suddenly spread apart by the spherical spreading elements  110 , are compensated for by the normal axial movement of the mating splines  114  and  116  during operation. 
     Referring now to the lower portion of FIG. 2 there is shown therein an alternative embodiment of the present wear reduction means, which functions to absorb the micro-movements and/or larger abrupt movements described hereinabove. For this purpose a plurality of leaf spring elements  130  are installed at the juncture of the housing section  112   b  of the cam disc  112  and the proximate surface of the ring-shaped component  117 . The spring elements  130  are generally semicircular in configuration being constructed of a suitable resilient material such as spring steel or other such materials. 
     In this embodiment the terminal end of the housing section  112   b  includes an integral perpendicular flange  136  whereon a first end of each spring element  130  is attached by rivets  134  or other fasteners. The respective opposite end of each spring element  130  is similarly attached to the ring-shaped component  117  as at surface  137  by rivets  132  or other fasteners. 
     Advantageously, the leaf spring elements  130  are symmetrically arranged and circumferentially disposed about the flange  136  in the pattern shown in FIG. 5 such that normal axial meshing of the mating splines  114  and  116  is facilitated. The spring tension exerted by the leaf springs  130  can be taken into account and adjusted for a given application. 
     By the application of the leaf springs  130  as described hereinabove, abrupt changes in the transmission of torque and the resulting transfer of micro-movements to coaxial components such as the mating splines  114  and  116  is significantly reduced. Thus, the present torque sensor  100  is nearly free of hysteresis associated with the severe physical strains, axial thrust forces, and added mechanical friction, which can cause premature wear and mechanical failure of the components of the torque monitoring sensor  100 . 
     It will be appreciated by those skilled in the art that alternative embodiments of the spring elements can be devised in lieu of the leaf spring elements  130 . For example, axially activated helical springs (not shown), which can be positioned in corresponding coaxial indentations (not shown) formed in the flange  136  and the proximate surface as at  137  of the component  117 , will function for this purpose. 
     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 transmission 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.