Patent Publication Number: US-7713153-B2

Title: Infinitely variable transmission

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation-in-part of application Ser. No. 10/504,992, which is the 35 USC 371 national stage of international application PCT/ZA2004/000023 filed on 5 Mar. 2004, which designated the United States of America, and claimed priority to South African Provisional Patent applications 2003/7933 and 2003/9224 filed respectively on 13 Oct. 2003 and 27 Nov. 2003. This application also claims foreign priority to South African patent application 2006/07143 filed on 25 Aug. 2006. The entire contents of all of these applications are hereby expressly incorporated by reference herein. 

   FIELD OF THE INVENTION 
   This invention relates to an incrementally operable IVT (infinitely variable transmission) machine which is intended for high power and high angular velocity operation and which is capable of power transmission in a reverse direction through it for engine braking. 
   BACKGROUND TO THE INVENTION 
   A significant body of prior art relating to IVT machines of the above type exists. Typical examples of these are described in the following publications: Relating to bicycles—U.S. Pat. No. 4,878,883, GB2062142A, GB2135743A, U.S. Pat. No. 4,618,331, U.S. Pat. No. 3,956,944, U.S. Pat. No. 4,832,660, U.S. Pat. No. 5,984,814 and U.S. Pat. No. 4,787,879. Relating to CVT/IVT—WO03/042575 and WO03/078869. Relating to grooved/ribbed cone disc engagement—WO01/75333 and U.S. Pat. No. 4,367,067. Relating to variable sprocket teeth ladder chain—WO94/04411 and U.S. Pat. No. 5,406,863. 
   It will be seen from the specifications of U.S. Pat. No. 4,878,883, GB2062142A, GB2135743A, U.S. Pat. No. 4,618,331, U.S. Pat. No. 3,956,944, U.S. Pat. No. 4,832,660, U.S. Pat. No. 5,984,814 and U.S. Pat. No. 4,787,879 that these machine consist largely of radially positionable engagement devices that operate, either by means of sprocket teeth or frictionally, within fixed tracks, which are spaced radially about a variable sprocket hub. Because of the limited number of engagement devices the flexible member track around them does not constitute a circular arc and their outputs are as a result, pulsed. Another problem with these prior art machines is the non-exact synchronisation of their engagement devices with drive chain links where engagement is accomplished via spring-loaded sprocket teeth or rotatable full sprockets operating in the fixed guides which make these devices suitable only for low speed applications, for example on bicycles. In high speed and high torque applications the above prior art machines are unsuitable. 
   In the cases of WO03/042575 and WO03/078869 the synchronisation problems have largely been solved, but they rely on sprag clutches which do not provide for power transmission in both directions (do not allow for engine braking). 
   In the cases of WO01/75333 and U.S. Pat. No. 4,367,067 the positive synchronised engagement of the chain with the disc grooves/ribs again presents a synchronisation problem. 
   In the cases of WO94/04411 and U.S. Pat. No. 5,406,863 positive engagement is accomplished but the storage of the ladder chain as well as its adjustment presents a problem in high speed applications. 
   The devices in most of the above publications sacrifice synchronised positive engagement for the ability to vary the ratio in infinitely small increments. 
   SUMMARY OF THE INVENTION 
   An IVT machine according to the invention comprises an input shaft, a drive wheel which is rotatable by the input shaft, an output shaft, a ratio changing device which is mounted coaxially on and rotatable with the output shaft, an endless belt which passes over the drive wheel and in an open loop over ratio changing formations which support the belt loop, on the ratio changing device, control means for causing the ratio changing formations to vary the ratio of rotation of the input and output shafts by enlarging and reducing the belt loop dimension about the output shaft axis on the ratio changing device, belt guide means over which the belt is movable, to provide a throat through which the belt enters and leaves its loop on the ratio changing device, and a drive arrangement which is; located on the ratio changing device for the transmission of drive power to the output shaft, engaged with the belt in a portion of its loop on the device, engageable with the belt on both sides of the throat in its transition across the throat during rotation of the ratio changing device, and maintains optimal engagement with the belt in all ratio positions of the belt loop on the ratio changing device. 
   The belt guide means preferably comprises two belt guide wheels which are located in close proximity to each other and which between them define the belt throat. 
   The machine may include a frame member which carries the output shaft and ratio changing device, the input shaft and a belt tensioning arrangement, and a frame element which carries the or each belt guide means and is movable by the controller relatively to the frame member towards and away from the ratio changing device in incremental indexed steps to follow the varying belt loop dimension during ratio changing and to supply and remove predetermined lengths of belt through the belt throat to and from the belt loop on the ratio changing device, as required, while the drive arrangement is clear of the chain throat, as the input and output shaft ratio of rotation of the machine is changed by the controller. 
   The ratio changing device may include a pair of frusto conical discs which are movable by the control means towards and away from each other on the output shaft with their tapered faces facing each other and providing between them the ratio changing formations on which the opposite edges of the belt are supported. 
   The belt may be a chain composed of links which are connected by equally spaced link pins which project from the side edges of the chain and have end surfaces which bear on and are complementally tapered to the angle of taper of the tapered faces of the ratio changing discs to cause the tensioned chain loop to be circular between the discs with the width of the chain being determined by the space between the discs in the low ratio position of the chain between them and the angle of taper of their tapered faces, and the belt wheels are chain sprockets. 
   The frame element may include two spaced arms which project from the remainder of the element and which are each slidably engaged with a formation on one of the ratio changing discs with the arms and the disc formations being adapted to move the discs towards and away from each other on the output shaft as the frame element is moved by the controller away from and towards the discs. 
   The drive arrangement may include a partial chain sprocket having an arcuate length which is greater than the width of the gap in the circular chain loop on the ratio changing device at the chain throat. The drive arrangement sprocket teeth may be separate from and movable relatively to each other with their centres remaining centred on the output shaft axis in all ratio positions of the chain loop on the ratio changing device by guide means which is attached to the output shaft. Conveniently, the sprocket teeth may each be carried on a first end of an arm with the teeth on opposite sides of a central tooth of the partial sprocket being inclined on their arms away from the central tooth, the output shaft is transversely split with its split ends each attached coaxially to a tooth guide disc housing in which pins on the second ends of the tooth arms are movable across the output shaft axis in grooves in the guide disc housing for guiding movement of the teeth towards and away from the output shaft axis as well as simultaneously towards and away from each other to vary the sprocket arc to perfectly match the radius of curvature of the chain loop between the discs at any ratio position of the machine. 
   The drive arrangement may include, in a second form of the invention, a series of undercut grooves in the tapered face of each of the ratio changing discs which extend from the periphery of the disc towards the output shaft with their centrelines spaced from each other over their lengths by a dimension equivalent to the distance separating the axes of chain link pins on a single link and the bases of the grooves are parallel to the tapered faces of the discs. 
   The drive arrangement in this form of the invention may include separate fixed length tooth carriers, which are equal in number to the number of grooves on the discs, which carry sprocket teeth with the centrelines of each of the teeth, in all ratio positions of the chain between the disc, lying on radial lines from the output shaft axis, and formations at the ends of the carriers which are complementally angled to the angle of taper of the groove bases and are engaged in opposite grooves of each series in the ratio changing discs. The number of grooves in each disc series is preferably adequate for the chain teeth on the tooth carriers to be engaged in the grooves of the two opposite series of grooves in the discs to bridge the chain throat while at least one tooth at each end of the drive arrangement remains engaged with the chain on both sides of the throat for a period during the transition of the drive arrangement across the throat. 
   A central groove of each disc series of grooves may lie on a radial line from the output shaft axis and portions of the grooves, towards the output shaft, on either side of the central groove may be curved in the direction of the central groove while maintaining the two link pin axis distance between their centrelines to cause the centrelines of the teeth on the tooth carriers in these grooves to rotate away from the central tooth in ratio changing from the low to high ratio positions of the chain loop between the discs and to rotate towards the central tooth in ratio changing to low range positions of the chain to maintain a partial sprocket tooth curve appropriate to the chain circle at any ratio position between the discs while remaining centred on the output shaft axis while the centrelines of the teeth remain centred on the output shaft axis. 
   The undercut portions of the central groove in each series is(are) preferably equal on both sides of the outer portions of the grooves over their lengths while the undercut portions of the grooves on both sides of the central groove, at the peripheries of the disc, may be offset from the outer portions of the grooves in a direction away from the central groove with the offset of each groove undercut being sequentially greater in grooves which are progressively further from the central groove with the offset of these groove undercuts moving over the lengths of the grooves towards the central groove. 
   The groove engaging formation on the ends of the central tooth carrier may be transverse formations which are engageable through the outer portions of the grooves in the groove undercuts and the formations on the ends of each of the remaining tooth carriers may be an outwardly projecting cylindrical first formation which is a close fit in the outer portions of the grooves and below that a second formation which has a cylindrical stem which has a lesser cross-sectional dimension than the width of the outer portion of the groove and which carries on its free end a radially projecting formation which is a close fit in the undercut portion of the groove in which it is located with its face which bears on the base of the groove being co-planar with the face of the cylindrical formation and the base of the groove at an angle which corresponds to the angle of taper of the tapered faces of the discs and which partially rotates the carrier about its axis through the first formations about the first formation as it is moved along the undercut portion of the groove in ratio changing. 
   In a variation of the second form of the machine a central groove of each disc series of grooves lies on a radial line from the output shaft axis and portions of the grooves, towards the output shaft, on either side of the central groove are curved in the direction of the central groove while maintaining a single link pin axis distance between their centrelines with the outer portions of the undercut portions of each of the grooves, in cross-section, conveniently being symmetrical on either side of the groove centreline. 
   In this variation of the machine the drive arrangement may include drive arrangement bars, which are equal in number to the number of grooves in a disc series, the ends of which are tapered at an angle which corresponds to the angle of taper of the bases of the grooves and grooves in opposite sides of the bars which are parallel to their tapered ends for engagement between the outer portions of the grooves to hold the bars in the grooves with their tapered ends resting on the bases of the grooves. 
   The belt used with this machine may be a chain composed of links which are connected by link pins and which at their centres, between the link pins to which they are connected and from a common edge each include an inwardly arched formation with the top of the formation situated above the axes of adjacent link pins with the arched formations being engageable with and over the drive arrangement bars for the transmission of drive power from the chain to the drive arrangement bars. The links may be arcuate in shape in a common direction in the chain with the arched formations extending into the links from their concave edges. 
   The number of grooves in each disc series is preferably adequate for the drive arrangement bars between the discs to bridge the chain throat while a number of bars remain engaged with the chain on opposite sides of the throat for a period during transition of the drive arrangement bars across the throat during rotation of the discs. 
   In a third form of the invention the ratio changing discs may each include a series of spaced ribs which project outwardly from the surface of the disc and extend from the periphery of the disc towards the output shaft to define between them drive arrangement grooves the bases of which are at the tapered face of the disc and into and from which the chain link pins are located and removed as the drive arrangement traverses the throat prior to or after ratio changing of the machine. The grooves between the ribs, in all ratio positions of the chain between the discs, may be spaced from each other over their lengths by a dimension equivalent to the distance separating the axes of adjacent chain link pins. 
   A central groove of each disc series of grooves may lie on a radial line from the output shaft axis and the portions of the grooves towards the output shaft on either side of the central groove could be curved in the direction of the central groove while maintaining the single link pin axis distance between their centrelines. 
   The number of grooves in each disc series is preferably adequate for the chain link pins to be engaged in the grooves of the two opposite series of grooves in the discs to bridge the chain throat while at least one groove at each end of the drive arrangement remains engaged with the chain on both sides of the throat for a period in the transition of the drive arrangement grooves across the throat. 
   The sides of the ribs may be outwardly tapered from their upper surfaces towards the bases of the grooves between them. 
   The transversely projecting ends of the chain link pins for use with this form of the machine may be coned at an angle of taper which corresponds to the angle of taper of the ratio changing discs with each conveniently carrying a tapered head which is dimensioned to be a nice fit in the tapered grooves between the ribs. The link pin heads may be slidably engaged on the end portions of the pins and the chain includes outer link arrangements on adjacent pairs of pins which are adapted, in a linear portion of the chain, to expose the coned end portions of the pins from their heads and as the chain enters a curve to progressively move the heads towards the coned ends of the pins to facilitate their entry into and exit from the disc drive arrangement grooves at the chain throat. 
   The ratio changing discs in the second and third forms of the invention may each include on their faces opposite their tapered faces an outwardly projecting boss which surrounds the output shaft, a ratio changing gear which is fixed to an externally threaded cylindrical ratio changing gear carrier which is engaged with and freely rotatable on the boss and threadedly engaged with an internally threaded body on the machine frame member so that concomitant rotation of the ratio changing gears will cause the discs to be moved towards and away from each other in dependence on the direction of rotation of the gears. The machine conveniently includes two indexing gears which may be fixed to a common shaft which is journaled for rotation in the machine frame member and are each meshed with a ratio changing gear, a trigger arrangement for snap rotating the indexing gear shaft to cause one or more predetermined partial indexing rotations of the indexing gears and the ratio changing gears in a required direction on demand from the machine controller which simultaneously causes the frame element to be index moved towards or away from the original chain loop between the ratio changing discs as required to supply or remove predetermined lengths of chain to or from the chain loop. 
   The trigger arrangement preferably includes a mechanical triggering energy storage device which snap rotates the indexing gear shaft when triggered by the trigger arrangement. The energy storage device could be is a torsion bar. The indexing gear shaft may be a tube and one end of the torsion bar may be located in and fixed to the indexing gear tube with its second end connected to a suitably geared motor for applying the appropriate torque to the bar in whatever direction of rotation of the indexing gears has been selected by the controller. 
   In a variation of the third form of the invention the ratio changing discs may each include a series of spaced ribs which project outwardly from the surface of the disc and extend from the periphery of the disc towards the output shaft to define between them drive arrangement grooves the bases of which are at the tapered face of the disc. 
   The belt used in this variation of the machine may be an endless band of non-stretch flexible material which includes, on opposite sides, transversely projecting formations which are complementally shaped to the disc drive arrangement grooves. 
   The drive wheel of this machine may be a flanged pulley including on the inner surfaces of its flanges inwardly projecting ribbed formations which correspond to the rib and groove formations on the discs and the remaining belt guide wheels in the machine are rollers. 
   In a further form of the machine of the invention the ratio changing device may be a composite disc arrangement including first and second superimposed flat sided discs, at least three linear slots in the first disc which lie on radial lines from the output shaft, an equal number of curved slots in the second disc, belt supporting pins which are located in and pass through the slots in both discs and project perpendicularly from the first disc and over which the belt loop is supported on the composite disc and means which is operable by the machine control means to partially rotate the second disc relatively to the first to cause the curved slots in it to move the belt support pins radially inwardly or outwardly in the first disc slots to vary the dimension of the belt loop on the pins and so the ratio of rotation of the input and output shafts. 
   The belt of this machine may be a chain having a uniform dimension between its link pins. 
   The drive arrangement of this machine may be that of the first form of the invention. 
   In this specification, including its claims, the meaning of the word “belt” is to be taken to be as defined in The American Heritage Dictionary of the English language as “A continuous band or chain for transferring motion or power from one wheel or shaft to another”. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the IVT machine of the invention are now described by way of non-limiting examples only with reference to the accompanying drawings in which: 
       FIG. 1  is a diagrammatic side elevation of a basic IVT machine of the invention, 
       FIG. 2  is a front elevation of two ratio changing discs of the  FIG. 1  machine, 
       FIG. 3  is an isometric view from above of a practical embodiment of the  FIG. 1  machine as shown in its low ratio position of operation, 
       FIG. 4  is the same view as that of  FIG. 3  showing the machine in its high ratio position of operation, 
       FIG. 5  is a sectioned front elevation of the chain of the  FIG. 3  machine, 
       FIG. 6  is an exploded isometric view of the ratio changing disc and a frame element of the machine of  FIG. 3 , 
       FIG. 7  is a sectional front elevation of the ratio changing arrangement of the  FIG. 3  machine, 
       FIG. 8  is an exploded isometric view of the drive arrangement of the  FIG. 3  machine, 
       FIG. 9  is exploded isometric views of the tooth assembly of the drive arrangement of  FIG. 8 , 
       FIG. 10  is a partially diagrammatic front elevation of the assembled drive arrangement of the machine as shown in the low ratio position of the machine, 
       FIGS. 11 and 12  are side elevations of the  FIG. 3  machine shown respectively in the low and high ratio positions of the machine, 
       FIG. 13  is a perspective view from above of a second embodiment of the IVT machine of the invention, 
       FIG. 14  is an exploded view of a ratio changing disc, the ratio changing gear of the disc and the drive arrangement of the  FIG. 13  machine, 
       FIG. 15  is a sectioned front elevation of the ratio changing arrangement of the  FIG. 13  machine, 
       FIG. 16  is an exploded isometric view of three of the five tooth carriers as used in the drive arrangement of the  FIG. 13  machine, 
       FIGS. 17 and 18  are substantially front elevations of the indexing trigger arrangement of the  FIG. 13  machine, 
       FIG. 19  is a fragmentary front elevation of the disc and drive arrangement of the  FIG. 13  machine, 
       FIGS. 20 and 21  are fragmentary isometric view of a variation of a chain for use with the machine of  FIG. 13  and perhaps others, 
       FIG. 22  is an isometric view of the ratio changing arrangement of a third embodiment of the machine of the invention, 
       FIG. 23  is a perspective view of the ratio changing disc of the  FIG. 22  machine, 
       FIG. 24  is a portion of a chain for use with the  FIG. 22  machine, 
       FIGS. 25 and 26  are front elevations of a chain fragment for use with a variation of the  FIG. 22  machine, 
       FIGS. 27 to 29  are isometric views of a short length of chain for use with the groove variation of the  FIG. 22  machine as shown in  FIG. 25 , 
       FIGS. 30 and 31  are isometric views of yet further variations of the ratio changing discs of the machine of  FIG. 22  for use with a drive band in place of a chain, 
       FIGS. 32 and 33  are fragmentary front elevations of the drive arrangement grooves of the  FIG. 22  ratio changing discs used in the explanation of a mathematical model, 
       FIGS. 34 and 35  are diagrams used in the  FIGS. 32 and 33  mathematical model, 
       FIG. 36  is a diagrammatic side elevation of a fourth embodiment of the IVT machine of the invention, 
       FIGS. 37 to 39  are isometric views of the components of the ratio changing arrangement of the  FIG. 36  machine, 
       FIG. 40  is an isometric view from above and one side of the IVT of the invention with its frame outer side plate and the tapered ratio changing discs omitted, 
       FIG. 41  is a side elevation of  FIG. 40  with the IVT in its low range position of operation, 
       FIG. 42  is the same view as that of  FIG. 41  with the IVT in its high range position of operation, 
       FIG. 43  is a partially diagrammatic end elevation of a portion of the belt tensioning arrangement and the dual drive arrangement of the invention, 
       FIG. 44  is a side elevation seen from the right of  FIG. 43  of the dual drive arrangement, and 
       FIG. 45  is a diagrammatic side elevation of the belt tensioning and the dual drive arrangements which are superimposed on each other. 
   

   DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
   The generic incremental IVT machine  10  of this invention is shown diagrammatically in  FIGS. 1 and 2  to include a driven input shaft  12  which carries a fixed drive sprocket  14 , an idler tension sprocket  16  which is adapted for movement in the direction of the arrows in  FIG. 1  by control or against or by biasing means, not shown, and a ratio varying arrangement indicated generally at  18 . 
   The ratio varying arrangement  18  includes a pair of ratio changing discs  20  which are fixed for rotation to and with the machine output shaft  22 . The discs  20 , as shown in  FIG. 2 , have facing frusto conical faces  24  and are movable, as will be explained below, towards and away from each other on the output shaft  22 , as indicated by the arrows in the drawing. The discs  20  are, however, not common to all embodiments of the machine of this invention and, as will be seen from the final embodiment of the machine described in this specification, could be replaced by discs which do not include tapered faces but perform the same function as the discs  20 . 
   The arrangement  18  additionally includes two idler sprockets  26  which are rotatably mounted in a fixed spatial relationship in close proximity to each other in a control frame element  28  in the machine frame which is not shown in the drawing. The idler sprockets  26  between them define a chain throat  30 . 
   The control frame element  28  is movable, by any suitable control means such as a suitable lead screw or hydraulic actuator arrangement, in the direction of the arrows in  FIG. 1  towards and away from the machine output shaft  22  which is journaled for rotation at a fixed position in the machine frame, and simultaneously to cause the ratio changing discs  20  to be moved towards and away from each other, as required, on the shaft  22 . The frame element  28  is moved in both directions in small incremental steps, the purpose of which is explained below. 
   The ratio varying arrangement  18  further includes a partial sprocket drive arrangement  32  the teeth of which are movable individually or in groups relatively to each other. The drive arrangement  32  is mechanically coupled to the machine output shaft  22  or directly to the tapered faces of frusto conical faces  24  of the ratio changing discs  20 , as will be described in more detail below, for the transmission of drive power to the output shaft  22 . 
   The various rotating components of the machine  10  are interconnected to each other by an endless belt, which in this example is a drive chain  34  as shown by the dotted line in  FIG. 1 . The chain is shown on the disc  20  in  FIG. 2  to be between the low and high ratio positions of the machine. 
   An important feature of the invention is that the distance by which the idler sprockets  26  are separated from each other in the throat  30  must always be less, and preferably substantially so, than the diameter of the almost circular chain  34  track between the ratio changing discs  20  with respect to the output shaft  22  axis, in all operational positions between and including the machine low and high ratio positions. 
   Broadly, the operation of the  FIG. 1  IVT machine  10  is as follows: any suitable prime mover, not shown, is coupled to the input shaft  12  and its drive sprocket  14 . The tension sprocket  16  holds the chain  34  in tension against the portion of the chain  34  which is wedged by the tapered ends of its link pins  36 , which are shown exaggerated in  FIG. 2 , against the sloping faces of frusto conical faces  24  of the discs  20  to counteract uncontrolled radially inward movement of the chain towards the high ratio position of the transmission machine. The teeth of the partial sprocket drive arrangement  32  are engaged between adjacent link pins  36  of the chain  34  at any position in the circumference of the chain between the discs  20  which drive the output shaft  22 . 
   With all of the IVT machine components in the positions shown in  FIG. 1  the prime mover is activated to cause the chain  34  to run on the path illustrated in  FIG. 1 . In so doing the machine output shaft  22  is driven by the drive arrangement  32  through its mechanical coupling with either the output shaft  22  or directly with the discs  20 . 
   To ensure uninterrupted rotation of the discs  20  and the output shaft  22  it is important that the drive arrangement  32  traverses the throat  30  as it is rotated by the chain without any interruption of its circular chain driven motion. To enable this to be done it is necessary that the teeth of the drive arrangement  32  are, in its path across the throat, perfectly engaged with the chain  34  on both sides of the throat  30  before releasing the bight of the chain leaving the throat to ensure continuity of drive force from the chain to the machine output shaft  22  during a complete 360° revolution of the drive arrangement. This throat transition of the drive arrangement must occur in all ratio positions of the chain  34  between the discs  20 . 
   To avoid interference of the chain  34  with whatever drive arrangement  32  is employed by the machine it is important that whatever controls the machine will prevent any ratio changing while the drive arrangement is in the throat  30  zone of the chain circle between the discs  20 . 
   To vary the drive ratio between the input and output shafts of the machine from the  FIG. 1  low ratio position of the chain  34 , the control frame element  28  is moved to the left in the drawing relatively to the machine frame by whatever control means is employed to do so. As the frame element  28  is moved so too are the idler sprockets  26  which it carries. The discs  20  are simultaneously caused by whatever controls them, in this example a forwardly projecting portion of the frame element  28 , to move away from each other on the output shaft  22 . The outward movement of the discs  20  enables the chain link pins  36  and so the chain together with the drive arrangement  32  to be moved between them towards the output shaft with the disc movement causing the chain track between the discs to be reduced in diameter to vary the machine input/output ratio. The chain tension sprocket  16  is simultaneously moved upwardly from its  FIG. 1  position by its control means or bias to maintain tension on the chain during any ratio change of the machine. To again reduce the machine ratio the control frame element  28  is moved to the right in  FIG. 1  with the directional changes of motion of its components described above being concomitantly reversed. 
   The practical first embodiment of the machine of  FIG. 1  is now described in detail with reference to  FIGS. 3 to 12 . 
     FIGS. 3 and 4  illustrate the  FIG. 1  machine  10  in its low and high ratio positions respectively. In these two drawings the same reference numbers are used as are those in  FIG. 1  for the same  FIG. 1  machine components. 
   The chain  34  is a triple chain with the links of the chains located on common link pins  36  as shown in  FIG. 5 . The chain links are spaced from each other by rollers  38  on the link pins  36 , as shown in  FIG. 5 . The projecting ends of the link pins  36  are either flattened or coned, with the alternatives shown in  FIG. 5 , at an angle α which corresponds to the angle of taper of the disc  20  frusto conical faces  24 . The tapered pin ends hold the chain wedged against the disc faces at its selected ratio position between the discs against radially inward movement towards the machine output shaft  22 . The chain results in triple drive sprockets  14 , tension sprockets  16  and the throat defining idler sprockets  26 , as shown in  FIGS. 3 and 4 . 
   As is seen from  FIGS. 3 and 4  and more clearly in  FIGS. 11 and 12 , the idler sprockets  26  do not have clearly pointed sprocket teeth as they play no part in the machine power transmission and are merely profiled to lightly engage the chain between its rollers  38  to guide it in and out of the throat  30  and to avoid interference with the teeth of the partial sprocket drive arrangement in the throat  30  area. 
   The IVT machine is located in a frame member  40  which includes two mirror image side plates  42  as shown in  FIGS. 3 and 4 . The frame side plates each carry bearings, not shown, in which the machine input and output shafts  12  and  22  are journaled for rotation, an incline slot  44  in which the chain tension idler sprockets  16  shaft  46  is movable, a second horizontal slot  48  and formation  50  which carries a biasing means, coil spring  52 , for biasing the tension sprocket shaft  46  upwardly in its slot  44 . 
     FIG. 6  shows the ratio varying arrangement  18  to include the ratio changing disc  20  assembly, the machine output shaft  22  and the control frame element  28 . The frame element  28  includes two side arms  53  and a cross member plate  54  which holds the arms in the spaced relationship shown in  FIG. 6 . The plate  54  carries two pairs of forwardly and oppositely directed arcuate plates  55  with each pair of plates supporting, at their free ends, an axle on which the set of three throat  30  defining sprockets  26  are freely rotatable. The arms  53  are oppositely identical and each includes a pair of outwardly projecting support formations  56  which are slidably located in the horizontal slots  48  in the frame side plates  42 , as shown in  FIG. 3 , to guide the controlled movement of the frame element  28  relatively to the machine frame  40 . The forward ends of the arms  53  are shaped as shown in the drawing to provide guide rails  57  on either side of opposite inwardly slanted guide rail slots  58 . 
   As shown in  FIGS. 6 and 7  the ratio changing discs  20  each include an integral outwardly projecting boss  60  which is recessed at  62  adjacent its outer end, a key slot  64  which is open into a substantially triangular radial slot  66  in the rear face of the disc  20  and a counterweight arrangement  68  for balancing the disc  20  arrangement during rotation. 
   The ratio varying disc  20  arrangement additionally includes, as shown in  FIG. 6 , two bushes  59  which are each grooved on opposite sides with the bases of the grooves being parallel to and spaced from each other by a dimension equivalent to the space which separates the guide rails  57  which define the slots  58  in the forward portions of the frame element  28  arms  53 . The angles of the grooves across the outer surfaces of the bushes  59  correspond to the slant angles of the slots  58 . 
   In the assembled ratio varying arrangement  18  the bushes  59  are located in the recesses  62  in the bosses  60  of the ratio changing discs  20 . The bushes are freely rotatable on the bosses  60 . The guide rails  57 , on either side of the slanted frame element  28  slots  58 , are slidably located in the grooves in the bushes  59 . With this arrangement the frame element is movable towards and away from the relatively fixed disc  20  assembly with its arms  53  supported in and guided by the grooves in the bushes  59  to vary the ratio of the machine by moving the discs  20  away from and towards each other while the flat outer surfaces of the bushes remain normal to the axis of the machine output shaft  22 . 
   The counterweight arrangements  68  each include an inverted U-shaped control member  70  which carries an arcuate balancing weight  72 . The control members  70  each comprise a pair of legs  74  which straddle the disc  20  bosses  60 , a bridge member  76  and, on the rear faces of the legs  74  formations, not shown, which are engaged with and slidable in cross-sectionally T-shaped grooves, also not shown, in the outer faces of the discs to enable the counterweights to be moved towards and away from the output shaft  22 . 
   The machine output shaft, as shown in  FIGS. 7 and 8 , is a two-component composite shaft  22  with each shaft portion carrying on its inner end a drive arrangement sprocket tooth guide disc  78  and a triangular counterweight control device  80 . 
   The counterweight control devices  80  are fixed to the rear faces of the discs  78  with their bases resting on the bases of the slots  64  in the bosses  60  of the ratio changing disc  20 , as shown in  FIG. 7 . The portions of the control devices  80  which are located in the slots  64  and  66  of the discs  20  key the discs  20 , against relative rotation with respect to the output shaft  22  components and their tooth guide discs  78 . The bridge members  76  of the counterweight control members  70  rest on the inclined surfaces of the triangular counterweight control devices  80 . During operation of the IVT machine, centrifugal force generated by the balancing weights  72  holds the bridge members up against the sloping faces of the control devices  80  with the movement of the discs  20 , and the control devices  80 , towards and away from each other during ratio variation causing the counterweight arrangement bridge members  76  to move the counterweights against the sloping faces of the devices  80  towards and away from the output shaft  22  axis to balance the pre-calculated mass imbalance of the disc  20  assembly, such as that which will be caused by the eccentric disposition of the drive arrangement  32  and other components, in the disc assembly. 
   The drive arrangement  32  partial sprocket tooth assembly, as shown in  FIGS. 8 and 9 , comprises a single central tooth  82  and a further two pairs of teeth  84  and  86 . The partial sprocket teeth are carried by lever arms  821 ,  841 , and  861 , as shown in  FIG. 9  with the teeth of each pair of teeth  84  and  86  and their lever arms being mirror images of each other on opposite sides of the central tooth arm. The sprocket tooth  82  lever arm  821  carries adjacent the tooth  82 , a transverse pin  88  which has angled ends as shown in  FIGS. 7 and 9  which, like the link pins  36  of the chain  34 , is moved, while remaining engaged with the chain, radially outwardly and inwardly between the frusto conical faces  24  of the discs  20  as the discs are moved towards and away from each other on the output shaft  22 . The lever arm  821  additionally includes vertical ribs  89  which extend, on opposite sides of the arm  821  between the pin  88  and the free end of the arm. The remaining arms of each pair of tooth arms  841  and  861  each carry, at their lower ends, a transverse pin  90  which is anchored in and projects from both sides of the tooth arm lever. 
   The tooth guide discs  78  on the output shaft components  22  each carry a central almost diametrical slot  92  and on either side of the slot a pair of adjacent grooves  94  and a pair of outer grooves  96 . The grooves  94  and  96  are, as is more clearly seen in  FIG. 10 , bowed and fanned outwardly in the faces of the discs from positions adjacent the base of the slot  92 . 
   The tooth guide discs  78  each additionally include a raised partially peripheral spacer rim  98 , as shown in  FIG. 8 , by means of which the two guide discs and the output shaft portions are coupled together by means of countersunk screws, not shown, with the tooth arms  821 ,  841  and  861  located in and projecting from the open topped cavity between the discs. The fairly substantial ribs  89  on the tooth arm  821  are slidably located in the disc  78  slots  92  and serve as the torque transmission means between the chain  34  and the output shaft  22 . The pins  90  on the remaining tooth arms  841  and  861  are slidably located in the grooves  94  and  96 , as shown in  FIGS. 10 ,  11  and  12 . 
   The drive arrangement  32  partial sprocket tooth assembly is more clearly shown in  FIGS. 9 and 10 . Each of the teeth and the arms which carry them are manufactured from suitable metal plates which are laminated together. 
   The tooth arm  821  includes two outwardly projecting ears which each carry an arcuate slot  100  which, as shown in  FIGS. 9 and 10 , has its radius R 1  of curvature centred on the link pin axis of a chain roller  38  which is engaged, in use, with the tooth  82  on the side of the tooth arm which carries the ear in which it is located. The tooth arms  841  each include a single projecting ear which is directed away from the tooth arm  821  and carries an arcuate slot  102  with its radius of curvature R 2  centred on the axis of link pin  36  chain roller  38  which is engaged with the side of the tooth arm  841  from which the slotted ear projects. The tooth arms  861  each carry an outwardly projecting ear  104  which has a curved upper surface, which is centred on R 2  on which the underside of the ears on the tooth arms  84  are supported. 
   The transverse sides of the tooth lever arms  841  and  861  are centrally slotted over their lengths above and below the projecting ears which they carry, as shown in  FIG. 9 . The upper portions of the slots below the teeth  84  and  86  carry fixed curved guide members  106  and  108  respectively. The guide members  108  are, in the assembled tooth assembly, located to be nice sliding fits in the slots  102  of the ears on the tooth arms  841  with the guide members  106  similarly located in the slots  100  in the ears of the tooth arms  821 . 
   To provide an unbroken partial sprocket surface between the teeth  82 ,  84  and  86  for supporting the chain  34  rollers  38 , the lower portions of the teeth are outwardly flared on a radius equivalent to that of the outer surfaces of the chain rollers  38 . 
   To preserve the continuous chain support surface, as the teeth  82 ,  84  and  86  are moved relatively to each other by their lever arms as the chain radius between the disc  20  frusto conical faces  24  is varied in use, the teeth  84  and  86  each carry only on their outwardly facing sides in the assembly keys  110  and  112  and the central tooth  82  a key  114  on each side of the tooth. The upper surfaces of the keys are all curved to be continuations of the flared lower portions of the teeth. The keys  110  on the teeth  84  are slidably located in slots  116  on the inwardly facing sides of the tooth arms  861  and the keys  114  are similarly located in slots  118  on the arms  841 . 
   The partial sprocket drive arrangement  32  is, in  FIGS. 10 and 11  shown in the low ratio position of the transmission machine with the centres of the sprocket teeth situated on dotted radial lines, shown in  FIG. 10 , from the axis of the machine output shaft  22 , to be optimally engaged between and seated on adjacent chain link rollers  38 . As mentioned above, it is necessary that this orientation of the teeth  82 ,  84  and  86 , relatively to the chain rollers and the machine output shaft axis, is maintained as the machine ratio is changed from the  FIGS. 10 and 11  large radius low ratio position of the drive arrangement  32  and the smaller radius high ratio position as shown in  FIG. 12 . 
   The limit positions of movement of the teeth  82 ,  84  and  86  and their arms between the machine output shaft tooth guide discs  78  are illustrated in  FIGS. 11 and 12 . 
   In the  FIGS. 10 and 11  low ratio position of the chain  34  and drive arrangement  32  tooth assembly the tooth arms  841  and  861  are spread apart, as shown in the drawings by their pin  90  locations in the grooves  94  and  96  and away from the diametrical slot  92  which guides radial movement of the tooth arm  821  and so the entire interconnected tooth assembly. 
   In moving from the  FIGS. 10 and 11  low ratio position of the chain  34  between the separating discs  20 , on demand from the machine controller, towards the  FIG. 12  high ratio position the chain link pins  36  and the tooth assembly arm  821  pin  88  are moved, by the chain  34  tension, radially inwardly against the frusto conical faces  24  of the discs to enable the chain radius of rotation to be reduced relatively to the output shaft axis. In so doing the partial sprocket tooth arms are moved downwardly in their pin  90  grooves  94  and  96 , as shown in  FIG. 10 , and towards each other, as shown in  FIG. 12 . In the tooth assembly moving to this high ratio position of the machine the outwardly inclined tooth carrying portions of the tooth arms  841  and  861  have been partially rotated, on the radii R 1  and R 2  respectively, to fan the dotted radial lines, which pass centrally across the teeth, as shown in  FIG. 10 , outwardly to increase the angle between them, as shown in  FIG. 12 , while remaining centred on the output shaft  22  axis in all ratio positions between the low and high ratio positions shown in  FIGS. 1 ,  11  and  12 . The above groove  94  and  96  and slot  100  and  102  controlled movement of the tooth arms ensures that the teeth  82 ,  84  and  86  will always, in all ratio positions of the machine be optimally engaged between and with the adjacent chain rollers irrespectively of the velocity of the chain and so the ratio changing discs  20  and their composite output shaft  22 . 
   As is mentioned above with reference to  FIGS. 1 ,  6  and  7  the frame element  28 , which is engaged with the ratio changing discs  20  assembly bushes  59  and which carries the chain throat  30  defining sprockets  26 , is movable by the machine control means towards and away from the disc  20  assembly and the output shaft which it carries in incremental steps. The purpose of this incremental movement is precisely to control the length of chain  34  which is introduced into and taken from the chain circle between the discs  20  over the sprockets  26  during ratio changing of the machine in operation. 
   In this embodiment of the invention the chosen chain link length is, as shown in  FIG. 10 , the length L of one chain link as measured between the axes of adjacent link pins  36 . The incremental movement of the frame element  28  by the machine controller will result in one link of the chain being added to or removed from the chain circle to ensure that the chain gaps between the chain link rollers  38  will be absolutely synchronised with the various teeth of the drive arrangement  32  tooth assembly on both internal sides of the chain in the throat  30  as the tooth assembly traverses the throat, as shown in both  FIGS. 11 and 12 . As mentioned above this ratio changing chain movement onto or out of the chain circle between the discs  20  must only be performed when the teeth of the drive arrangement  32  partial sprocket tooth assembly are clear of the chain throat  30 . This synchronisation of the chain arrangement teeth with the chain  34  link gaps makes clean and perfect engagement of the teeth with the chain possible at all design output angular velocities of the output shaft  22 , which could be as high as 6000 rpm, without any interruption of either torque transmission or output angular velocity. 
   As mentioned in the preamble to this specification many known apparently competent IVT&#39;s of the above described type rely on the use of one-way or sprag clutches for their operation with the sprag clutches eliminating the possibility of power transmission in both directions through the machines. In the transmission machine of the invention which is described above there is, however, no impediment to transmission of power from the output shaft  22  to the input shaft  12  so making the machine totally suited to engine braking. 
   A second embodiment of the IVT machine of the invention is shown in  FIG. 13  to include a static frame member  120  which carries a ratio changing assembly  122  and an indexing arrangement  124 . The machine additionally includes a frame element  126  which is movably attached to the frame  120  for movement, by means of the lead screw or electronically controlled hydraulic arrangement of the first embodiment, towards and away from the ratio changing assembly  122 . The frame element  126  is substantially the same as the frame element  28  of the first embodiment of the machine but does not include the forward ends of the arms  53  which carry the slanted guide rails  57  as the ratio changing movement of the assembly  122  is operated, in this embodiment of the invention, by the indexing arrangement  124 . The drawing reference numbers of components of the frame element  28  which are used to identify components and formations which are the same as those in this second embodiment, are used in  FIG. 13 . 
   The ratio changing assembly  122  includes two ratio changing discs  128 , as shown in  FIGS. 14 and 19  which each carry on their tapered facing faces  130 , as best seen in  FIG. 19 , a central linear groove  132  which is centred on the axis of a splined output shaft  138 , and two pairs of outer grooves  134  and  136  with one groove of each pair situated on opposite sides of the central groove  132 . The grooves  134  are inwardly bowed from their outer towards their inner ends with their rate of curvature increasing towards their lower ends. The grooves  136  are similarly bowed with their rate of curvature, as seen in  FIG. 19 , being more exaggerated than that of the grooves  134  towards their lower ends. The groove  132  is, as seen in  FIGS. 14 and 19 , is undercut and is uniformly T-shaped in cross-section over its length while undercut portions of the grooves  134  and  136 , shown in dotted lines in  FIG. 19 , are out of symmetry with the open outer portions of the grooves for a purpose which is explained below. 
   The drive arrangement  140 , in this embodiment of the invention, as shown in  FIGS. 14 ,  16  and  19 , comprises, together with the disc grooves  132 ,  134  and  136 , a central tooth carrier  142 , a first pair of tooth carriers  144  which are adjacent the carrier  142  and a second pair of outer tooth carriers  146 . 
   The drive chain used with the machine of this second embodiment remains the chain  34  of the first embodiment and each of the tooth carriers includes three transversely aligned sprocket teeth which are shaped as shown in  FIGS. 14 ,  16  and  19  with the teeth of each pair of tooth carriers  144  and  146  being, on opposite sides of the central carrier  142 , mirror images of each other. As is clearly seen in  FIG. 16 , the base portions of each of the sprocket teeth on the tooth carriers are outwardly flared, as are those of the previous embodiment, to provide seats for supporting chain rollers  38  on either side of a chain link with which the tooth is engaged in all ratio changing positions of the chain between the discs  128 . 
   The teeth on each of the tooth carriers are fixed to a crossbar  148  and are spaced from each other by a dimension which corresponds to the transversely aligned gaps between the rollers  38  of the chain  34 . 
   The ends of the tooth carrier  142  crossbar  148  each carry a transverse rectangular formation  150  which is angled complementally to the angle of taper of the faces  130  of the facing ratio changing discs  128  and so also the undercut portions of the bases of the disc grooves  132  in which they are slidably located. 
   The ends of the tooth carriers  144  and  146  each include, as shown in  FIG. 16 , an upper outwardly projecting cylindrical formation  152  with its end complementally tapered to the base of the disc groove in which it is located, in use, and a second formation  154  which consists of a cylindrical stem which carries on its free end a radially projecting disc  156 . The cylindrical formations  152  each have a diameter which is a close sliding fit in the outer portions of the grooves  134  and  136  in the faces of the discs  128 . The formation  154  stem has a lesser diameter than that of the formations  152  with its axis being downwardly inclined relatively to that of the formation  152  so that the axis is normal to the base of a disc  128  groove  134  or  136  in which it is located, in use, with the outer surface of its disc  156  coplanar with the tapered face of the formation  152 . The formation  154  disc  156  has a thickness and diameter which is a nice sliding fit in the undercut portions of the grooves  134  or  136 . The upper surfaces of the discs  156  trap the tooth carriers in the grooves against upward or downward movement from their selected ratio positions in the grooves as determined by the degree of separation of the discs. 
   In the assembled ratio changing disc assembly  122  and its drive arrangement  140  assembly, the tapered ends of the formations  150 ,  152  and  154  on the tooth carriers  142 ,  144  and  146  respectively, serve the same purpose as the tapered ends of the chain  34  link pins  36 , as described in connection with the IVT machine of the first embodiment, in wedging against the bases of the disc  128  grooves in which they are located to prevent uncontrolled radial movement of the tooth carriers away from the machine output shaft axis when they are out of contact with the chain  34  when traversing the throat  30  between the sprockets  26  and to enable the tooth carriers to be moved inwardly or outwardly between the discs  128  while their teeth remain exactly engaged with the chain  34  to vary the input/output ratio of the machine as the discs  128  are moved away from and towards each other on the output shaft  138 , as is described below. 
   As is the case with the teeth of the tooth assembly of the previous embodiment of the machine, it is necessary that the teeth of the tooth carriers  144  and  146  be slightly rotated outwardly and away from the tooth carrier  142  and moved closer together as the drive arrangement  140  is moved in their discs  128  grooves  134  and  136  by the chain tension, together with the five tooth carriers  142 ,  144  and  146 , towards the machine output shaft, high ratio, small sprocket radius position, as shown in  FIG. 13 . This is achieved, in this embodiment of the invention by the discs  156  of the tooth carrier formations  154  being moved from the upper position in  FIG. 19  to their dotted lower line positions. In this position the offset undercut portions of the grooves  134  and  136  have slightly rotated the formation  154  discs  156  and so the tooth carriers  144  and  146  and their teeth about the axes of their formations  152  to compensate for the reduction in chain track radius between the discs  128  while keeping the tooth carrier teeth perfectly engaged with the chain. This remains critically important as the drive arrangement  140  teeth traverse the chain throat  30  with its outer teeth engaged with the chain on either side of the throat. In returning the machine to its low ratio, increased chain track radius position the tooth carriers and the chains are moved outwardly between the closing discs  128  with the undercut portion of the grooves  134  and  136  now rotating the tooth carriers  144  and  146  and their teeth in the opposite direction to compensate for the increasing chain track radius. 
   The circumferential spacing of the tooth centres between the tooth carriers  142 ,  144  and  146  in this embodiment of the machine is 2×L as opposed to L in the first embodiment. 
   As with the machine of the previous embodiment, it remains important that any ratio changing, chain lengthening or reduction that takes place between the discs  128  is caused to occur only while the partial sprocket teeth of the drive arrangement  140  are clear of the throat  30  zone of the chain track between the discs  128 . 
   As shown in  FIGS. 13 ,  14  and  15  the tapered ratio changing discs  128 , in this embodiment of the invention, each include a ratio changing gear  158 , as shown in  FIG. 15 . The gears  158  are fixed to and spaced from the outer surfaces of the discs  128  by cylindrical carriers  162  which are rotationally engaged and freely rotatable in recesses  161  in the bosses  160  on the discs as shown in  FIG. 15 . The carriers  162  are externally threaded and threadedly engaged with internally threaded rings  164  which are fixed in the side walls of the frame  120  compartment which houses the ratio changing assembly  122 . The threads on the carriers  162  and the rings  164  are such that, during ratio changing of the machine, the discs  128  will concomitantly be moved towards and away from each other while the gears  158  are rotated in a common direction. 
   The gears  158  are, as shown in  FIG. 13 , meshed with and rotated, in use, by indexing gears  166  of the indexing arrangement  124 . The gears  166  are rotated by and are movable in an axial direction on splined ends of a tubular shaft  168  which is rotatable in bearings, not shown, in the side walls of the ratio changing assembly  122  compartment of the frame member  120 . The gears  166  each include annular side plates  170  which project radially outwardly from the gear teeth, as shown in  FIG. 13 , to provide a rotary channel in which the toothed portions of the gears  158  in the mesh zone of the gears, are trapped so that movement of the gears  158  towards and away from the machine frame during ratio changing will cause the gears  166  to follow their movement on the splined ends of the shafts  168  to hold the gears in mesh without the need for much wider and heavier gears  166 . 
   The indexing arrangement  124  additionally includes an indexing trigger arrangement  172  which is situated in a compartment of the frame member  120  on the outside of the upper gear  166  in  FIG. 13 , a torsion bar  174  which is rotatably located in the bore of the shaft  168  and has one end fixed in any suitable manner to the shaft at or towards its end which carries the trigger arrangement  172  and a geared motor  176  which is connected to the second end of the torsion bar  174  which projects from the shaft  168  on the outside of the frame  120 . 
   The trigger arrangement  172  is shown in  FIGS. 17 and 18  to be composed of two identical pawl and ratchet arrangements which are located in a back to back configuration on the splined end of the shaft  168 . Each of the rotary ratchets  178  carries six ratchet teeth  180  which are uniformly spaced from each other, in this embodiment of the invention, at 60° intervals about the ratchet periphery. The trigger pawls  182  are shaped as shown in the drawings and are each partially rotatable about a common pin  184  the ends of which are anchored in the side walls of the frame compartment in which the trigger arrangement is located, as shown in  FIG. 13 . 
   The control arrangement for the  FIG. 13  machine includes the lead screw or an electrically operable hydraulic indexing arrangement for moving the frame element  126  towards and away from the frame member  120 , and a trigger controller not shown for triggering predetermined incremental indexed movement of the ratio changing discs towards and away from each other. The trigger controller is the prime controller and additionally controls indexed movement of the frame element  126  arrangement. 
   In operation of the  FIG. 13  machine, incremental ratio changing movement of the discs  128  and so the chain track  34  between them is, as with the machine of the previous embodiment, prevented by the machine control arrangement while the partial sprocket arrangement  140  is in the chain throat  30  zone between the discs  128 . 
   With the machine operating and on a command from the primary trigger controller to shift the machine ratio upwardly or downwardly the controller electronics will activate the motor  176  to apply the appropriate torque to and energise the torsion bar  174  in whatever direction has been selected. The shaft  168  is in the meantime held locked against rotation by the trigger pawls  182  which lock the ratchet discs  178  against rotation in either direction, as shown in  FIG. 17 . 
   Whichever trigger pawl  182  is required to be operated against the bias of the torsion bar  176  acting on the ratchets  178  via the shaft  168  is now triggered in the direction of one of the arrows in  FIG. 17  to release the tooth of the ratchet engaged with it to the stored energy of the torsion bar  174 . On release, the ratchets  178  are immediately snap rotated in the required direction to cause the shaft  168 , the gears  166  and the gears  158  to be incrementally rotated to move the discs  128  towards or away from each other as required. The ratchet trigger pawls  182  are gravity biased towards the ratchets  178  and assuming the ratchet in  FIG. 18  is rotated in an anti-clockwise direction, the ratchet tooth  180  which has been released will move the nose of the pawl downwardly onto the ratchet to engage the following tooth as shown in  FIG. 18 . To more positively reset the pawls  182  a spring could be located between and connected to the upwardly projecting trigger arms of the pawls to bias the arms towards each other. To rotate the gears  158  in the opposite direction the motor  176  is rotated by the controller to torque load the ratchets  178  in the opposite direction. 
   The above method of using a mechanical device (torsion bar  174 ) as a triggering energy storage device eliminates the need for far more costly and complicated high power electrical or hydraulic energy storage devices for achieving the same purpose. 
   Obviously, as with the machine of the first embodiment, it will be necessary, in synchronisation with the operation of the indexing arrangement  124 , to incrementally move the frame element  126  towards or away from the ratio changing assembly  122  to feed chain into or from the chain track between the discs  128 . This is achieved, in this embodiment of the invention, in precisely the same manner as the frame element  28  is moved in the machine of the first embodiment. The lead screw or electronically controlled hydraulic control arrangement for moving the frame element  126  is activated by the prime controller which controls and activates the indexing arrangement  124 . 
   The necessary variables which are required for the calculation of the centre lines of the disc  128  grooves  134  and  136  are illustrated in  FIG. 19  and are now described by way of a brief mathematical model. 
   Points P, G, K, M, N, and O lie on a common drive sprocket radius SR (line AG) and are all separated from each other by angle θ with reference to point A at the centre of the machine output shaft which corresponds to chain link lengths L on this drive radius SR. With the X axis being the horizontal through point A and the Y axis being the vertical through point A the X, Y co-ordinates of points H and Q can be calculated, given the drive radius SR and chain link length L, as follows: 
   L2=2·SR2−2·SR·SR·cos(θ) and by solving for θ results in: 
   
     
       
         
           
             
               
                 θ 
                 = 
                 
                   a 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     cos 
                     ⁡ 
                     
                       [ 
                       
                         1 
                         - 
                         
                           
                             L 
                             2 
                           
                           
                             2 
                             · 
                             
                               SR 
                               2 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
             
             
               
                 ( 
                 A 
                 ) 
               
             
           
         
       
     
   
   The equivalent drive radius RE at the midpoint of chain link length L at point Q to point A is therefore perpendicular to line KM and is calculated as: 
   
     
       
         
           
             
               
                 RE 
                 = 
                 
                   
                     [ 
                     
                       
                         SR 
                         2 
                       
                       - 
                       
                         
                           ( 
                           
                             L 
                             2 
                           
                           ) 
                         
                         2 
                       
                     
                     ] 
                   
                   0.5 
                 
               
             
             
               
                 ( 
                 B 
                 ) 
               
             
           
         
       
     
   
   The X, Y co-ordinates of point Q are therefore as follows:
 
 X:QE=RE ·sin( k ·θ)  (C)
 
 Y:AE=RE ·cos( k ·θ)  (D)
 
   Where k is the whole number multiple indicating the chain link length number away from the Y axis, in this case k=2. 
   The X, Y co-ordinates of point H are therefore as follows:
 
 X:HF=RE ·sin( k ·θ)  (E)
 
 Y:AF=RE ·cos( k ·θ)  (F)
 
   Where k is the whole number multiple indicating the chain link length number away from the Y axis, in this case k=4. 
   Combining equations A to F a generalised set of equations for X, Y co-ordinates throughout the entire ratio range of the machine can be derived as follows: 
   
     
       
         
           
             
               
                 X 
                 = 
                 
                   
                     
                       [ 
                       
                         
                           SR 
                           2 
                         
                         - 
                         
                           
                             ( 
                             
                               L 
                               2 
                             
                             ) 
                           
                           2 
                         
                       
                       ] 
                     
                     0.5 
                   
                   · 
                   
                     sin 
                     ⁡ 
                     
                       ( 
                       
                         
                           k 
                           · 
                           a 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           cos 
                           ⁡ 
                           
                             [ 
                             
                               1 
                               - 
                               
                                 
                                   L 
                                   2 
                                 
                                 
                                   2 
                                   · 
                                   
                                     SR 
                                     2 
                                   
                                 
                               
                             
                             ] 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 ( 
                 G 
                 ) 
               
             
           
           
             
               
                 Y 
                 = 
                 
                   
                     
                       [ 
                       
                         
                           SR 
                           2 
                         
                         - 
                         
                           
                             ( 
                             
                               L 
                               2 
                             
                             ) 
                           
                           2 
                         
                       
                       ] 
                     
                     0.5 
                   
                   · 
                   
                     cos 
                     ⁡ 
                     
                       ( 
                       
                         
                           k 
                           · 
                           a 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           cos 
                           ⁡ 
                           
                             [ 
                             
                               1 
                               - 
                               
                                 
                                   L 
                                   2 
                                 
                                 
                                   2 
                                   · 
                                   
                                     SR 
                                     2 
                                   
                                 
                               
                             
                             ] 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 ( 
                 H 
                 ) 
               
             
           
         
       
     
   
   Where k indicates the whole number multiple indicating the chain link length number away from the Y axis. 
   The X, Y co-ordinates of points I and J (centrelines for the outer and inner portions of grooves respectively as SR is varied) can easily be determined by incorporating their fixed relation with respect to point H and line HA which may vary from one sprocket tooth to the other. 
   The above may result in two non-identical centrelines for the outer and inner portions of the grooves  134  and  136  as indicated by the dotted inner undercut portions of the grooves in  FIG. 19 . 
   In a variation of the  FIG. 13  second embodiment of the machine of the invention the chain  34  and the toothed drive arrangement  140  is replaced by the curved chain link chain  184  and the grooved chain engaging drive arrangement bars  186  of  FIGS. 20 and 21 . As shown in the two drawings, the chain  184  is made up of curved link plates  188  which are pivotally coupled together by link pins  190  which carry spacer rollers  192  which are rotatable between the link plates  188 . 
   The undersides of the link plates  188  are rounded into a central arch-shaped bar engaging seat formation  194 , which is most clearly seen on the central facing link  188  in  FIG. 20 . 
   The ends  195  of the drive arrangement bars  186  are tapered to be complemental to and ride on the tapering bases of the grooves  132 ,  134  and  136  of the ratio changing disc  128  with the grooves  196  adjacent their ends located in the outer narrower outer portions of the grooves  132  to  136 . Only four of the five bars  186  of the machine drive arrangement are shown in  FIGS. 20 and 21 . 
   The outer and inner undercut portions of the grooves  132 ,  134  and  136 , when used with chain  184 , are modified to be symmetrical on either side of the centreline of the grooves with this modification of the grooves requiring adaptation of the above groove centreline mathematical model to compensate for the slightly elevated positions of the bar  186  axes, when engaged in the link formations  194 , relatively to the axes of the adjacent link pins  190  in a similar manner to the calculation of points I and J in  FIG. 19 . In this case the centrelines of the grooves may be separated from each other by the distance between the axes of link pins in a single link. 
   The  FIG. 13  machine, other than the above variations, remains unchanged. The use, however, of the chain  184  and the drive bars  186  as the machine drive arrangement provides a simplified chain engagement design in which the torque which is imposed on the tooth carriers  142 ,  144  and  146  is eliminated. 
   The following example is provided to demonstrate the incremental chain movement during ratio changing of the machine of the invention: 
   Assume a chain link length L=12.7 mm and that the circular chain track between the discs  20  needs to vary its length from the high ratio links HRL=20 to its low ratio links LRL=40 chain link lengths then θ HRL =360°/20=18° (the angle of one chain link with reference to the input shaft axis with a circumference of HRL=20) and θ LRL =360°/40=9° (the angle of one chain link with reference to the input shaft axis with a circumference of HRL=40). 
   Using equation A 
                 θ   =     a   ⁢           ⁢     cos   ⁡     [     1   -       L   2       2   ·     SR   2           ]                 (   A   )               
SR can be calculated as
 
   
     
       
         
           
             
               
                 SR 
                 = 
                 
                   
                     [ 
                     
                       
                         L 
                         2 
                       
                       
                         ( 
                         
                           2 
                           - 
                           
                             2 
                             · 
                             
                               COS 
                               ⁡ 
                               
                                 ( 
                                 θ 
                                 ) 
                               
                             
                           
                         
                         ) 
                       
                     
                     ] 
                   
                   0.5 
                 
               
             
             
               
                 ( 
                 I 
                 ) 
               
             
           
         
       
     
   
   The table below provides values of chain link lengths RL on the circumference of the discs  20  from HRL=20 to LRL=40 with the corresponding θ and ratio change percentage calculated as: 
   
     
       
         
           
             
               
                 
                   Ratio 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   change 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   % 
                 
                 = 
                 
                   100 
                   RL 
                 
               
             
             
               
                 ( 
                 J 
                 ) 
               
             
           
         
       
     
   
   The corresponding disc  20  displacement DD of each disc is related to the chain link pin  36  cone angle α ( FIGS. 5 and 15 ) and is calculated as follows:
 
 DD=SRC ·tan(α)  (K)
 
where SRC is the change in SR for consecutive chain link lengths.
 
   If a lead of LS=4.4 mm/revolution is assumed for the ratio changing gear  158  then the rotation ASR required by the adjusting nut will be a constant of: 
                 ASR   =         360   *   DD     LS     =     60   ⁢   °               (   L   )               
as indicated in the following table:
 
   
     
       
         
             
             
             
             
             
             
             
           
             
                 
             
             
                 
               Ratio 
                 
                 
                 
                 
                 
             
             
               RL 
               Change 
               Theta 
               SR 
               SRC 
               DD 
               ASR 
             
             
               chain links 
               % 
               deg 
               mm 
               mm 
               mm 
               deg 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
             
             
             
          
             
               20 
               5.0 
               18.0 
               40.6 
               2.0 
               0.7 
               60 
             
             
               21 
               4.8 
               17.1 
               42.6 
               2.0 
               0.7 
               60 
             
             
               22 
               4.5 
               16.4 
               44.6 
               2.0 
               0.7 
               60 
             
             
               23 
               4.3 
               15.7 
               46.6 
               2.0 
               0.7 
               60 
             
             
               24 
               4.2 
               15.0 
               48.6 
               2.0 
               0.7 
               60 
             
             
               25 
               4.0 
               14.4 
               50.7 
               2.0 
               0.7 
               60 
             
             
               26 
               3.8 
               13.8 
               52.7 
               2.0 
               0.7 
               60 
             
             
               27 
               3.7 
               13.3 
               54.7 
               2.0 
               0.7 
               60 
             
             
               28 
               3.6 
               12.9 
               56.7 
               2.0 
               0.7 
               60 
             
             
               29 
               3.4 
               12.4 
               58.7 
               2.0 
               0.7 
               60 
             
             
               30 
               3.3 
               12.0 
               60.7 
               2.0 
               0.7 
               60 
             
             
               31 
               3.2 
               11.6 
               62.8 
               2.0 
               0.7 
               60 
             
             
               32 
               3.1 
               11.3 
               64.8 
               2.0 
               0.7 
               60 
             
             
               33 
               3.0 
               10.9 
               66.8 
               2.0 
               0.7 
               60 
             
             
               34 
               2.9 
               10.6 
               68.8 
               2.0 
               0.7 
               60 
             
             
               35 
               2.9 
               10.3 
               70.8 
               2.0 
               0.7 
               60 
             
             
               36 
               2.8 
               10.0 
               72.9 
               2.0 
               0.7 
               60 
             
             
               37 
               2.7 
               9.7 
               74.9 
               2.0 
               0.7 
               60 
             
             
               38 
               2.6 
               9.5 
               76.9 
               2.0 
               0.7 
               60 
             
             
               39 
               2.6 
               9.2 
               78.9 
               2.0 
               0.7 
               60 
             
             
               40 
               2.5 
               9.0 
               80.9 
               2.0 
               0.7 
               60 
             
             
                 
             
          
         
       
     
   
   Note that the constant ASR is an approximation since if L is large in comparison to SR the approximation will not be valid. 
   To put the control of the shifting in perspective assume a disc  128  and output shaft  138  speed of 3000 rpm or 50 revolutions per second or 20 ms per revolution. Assume that the transition area over the throat  30 , where no shifting can take place constitutes 60°. Then the available time for shifting ST is calculated as 
           ST   =             360   -   60     360     ·   20     ⁢           ⁢   ms     =     16   ⁢           ⁢   ms             
in which time the discs need to be moved 0.7 mm or the ratio changing gears  158  need to be rotated through 60° depending on the control system and mechanism in use. The average disc speed may be calculated as:
 
   
     
       
         
           
             
               0.7 
               ⁢ 
               
                   
               
               ⁢ 
               mm 
             
             
               16 
               ⁢ 
               
                   
               
               ⁢ 
               ms 
             
           
           = 
           
             43.75 
             ⁢ 
             
                 
             
             ⁢ 
             mm 
             ⁢ 
             
               / 
             
             ⁢ 
             
               s 
               . 
             
           
         
       
     
   
   The control of the control frame element  126 , which movement corresponds to SRC, is to be synchronised with the ratio changing gears  158  in the case of the second embodiment but may be delayed or advanced as is discussed below. 
   Whenever the machine of the invention is shifting up to a higher ratio (SR is decreasing) the movement of the control frame element  28  may be delayed and extended since the transmission would still be able to function if the throat  30  idler sprockets  26  are 2 mm further away from the chain path on the discs  120  and can thus be adjusted after shifting has occurred which would simplify the control dramatically since the time duration is not critical as in the case of the discs  120  movement. 
   Whenever the machine of the invention is shifting down to a lower ratio (SR is increasing) the movement of the control frame  126  needs to occur before the movement of the discs  120  in order to prevent a collision between the idler sprockets  26  and the partial sprocket drive arrangement  32 , but again as mentioned above the time duration is not critical and the control would be simplified. 
   In the event that the IVT machine of the invention is to be used in a motor vehicle the control can further be simplified by making use of the positive engagement high torque nature of the IVT by connecting the output shaft directly via a differential to the wheels of the motor vehicle in which case the maximum speed of the output shaft would thus be in the order of 1300 rpm (maximum wheel rpm) thus further increasing the shifting time. 
   In a third embodiment of the IVT machine of the invention the frusto conical ratio changing discs  128  and the chain  34  of the machine of the second embodiment are replaced by the discs  198  and the modified chain  34  of  FIGS. 23 and 24 . 
   The discs  198  each have a tapered face  200  and a series of ribs  202  which project outwardly from its face  200  to define between them grooves  204 . As is seen in  FIGS. 22 and 23 , the side walls of the grooves  204  taper from their bases outwardly onto the outer surfaces of the ribs  202 . 
   The free ends of the link pins  36  of the chain  34  of the previous machine embodiments carry, as shown in  FIG. 24 , heads  206  which are inwardly tapered towards the slightly coned outer faces  208  of the pins. The angle of taper of the sides of the pin heads  206  corresponds to the angle of taper of the side walls of the disc grooves  204  and their lengths to the depth of the grooves. 
   The ribs  202  and the grooves  204 , in this embodiment of the invention, serve the purpose of the drive arrangements  32  and  140  of the previous embodiments. On rotation of the discs  198  the pin heads  206  of a portion of the circular chain  34  track between the discs are seated in and guided in ratio changing movement in the grooves  204 , and in traversing the chain track throat  30 , merely sequentially slip easily from the grooves  204  at the chain outlet from the throat with fresh pin heads again becoming seated in the leading groove of the series at the chain inlet to the throat  30  without colliding with the ribs  202 . 
   The modified chain  34 , however, results in large pin head  206  angles to enable the pin heads to smoothly engage the ribs  202  which may result in an unbalanced side force on the discs  198  in the ribbed section. 
   In high speed and high torque applications of this embodiment of the machine of the invention the grooves  204  in the discs  198  have the stepped cross-sectional shape shown in  FIG. 25 . The grooves  204  are divided into an outwardly tapered upper portion where the angle of taper of the side walls, when measured from a central plane through the groove, is significantly less than that of the grooves  204  in the  FIG. 23  disc  184 . The lower portions of the groove side walls are parallel sided and normal onto the groove base which is situated at the tapered surface level of the disc. The height of the ribs  202  and so the parallel side wall portions of the grooves  204  decrease very slightly from the large chain track radius at the periphery of the disc, as shown in  FIG. 26 , to that at the high ratio track position adjacent the machine output shaft aperture  210  as shown in  FIG. 23 . 
   The chain  212 , shown in  FIGS. 27 to 29 , for use with the disc grooves  204  of  FIG. 25  is substantially the same as the chain  34  of the previous embodiment except for its modified composite outer chain link arrangement  214 . 
   The chain link arrangements  214  each consist of a portion of an inner link  216  which is fixed to the link pin  36  which carries it and an outer link  218 . The outer link  218  is composed of two link portions  2181  and  21811  which, on the link pins  36 , are held against relative rotation about the pin axes by the tongue and groove formations shown in the drawings. The link portions, are however, movable in the direction of the pin  36  axes relatively to one another. 
   The facing faces of the links  216  and  218  each carry a pair of fixed oppositely directed circular spiral ramps  220  which abut and ride on each other in use. The link portions  2181  and  21811  each include a fixed tapered head  222  having a base in which an end of a link pin  36  is rotatable and slidably movable. The link portions are lightly held on link pins by any suitable means such as an O-ring which is located in an external groove in the pins  36  and frictionally engage with the bores in the pin heads. 
   In use, with the chain  212  following a linear path the high end faces  224  of the pairs of ramps  220  are close together, as shown in  FIG. 28 . As the chain enters a curve, as in  FIG. 29 , the leading link pin will be moved from the  FIG. 28  position to the  FIG. 29  position to cause relative rotation between it and the pin trailing it. The same relative rotation occurs between the pairs of ramps  220  on the pins and the ramps on the links  218  will ride upwardly on those on the links  220  to cause coned ends  208  of the pins  36  to be less exposed from the pin heads  222 . The pin length exposure between the small chain radius high ratio position of the chain track and its large radius low ratio positions between the discs  184  is illustrated in  FIGS. 25 and 26  respectively. The degree of pin  36  exposure from the pin heads  222  is shown highly exaggerated in the drawings with the actual maximum degree of pin exposure in practice being varied by about 0.1 mm. 
   The modified chain enables the side walls of the grooves to have a lesser angle of taper than those of  FIG. 23 , as described above, to improve traction between the chain pin heads  222  and the tapered portion of the grooves  204  of  FIG. 25  while also decreasing the actual force component of the interaction between the pin heads  222  and the side walls of the grooves to facilitate the entry and exit of the pin heads into and from the disc grooves  204 . 
   In yet a further variation of the ratio changing discs, drive arrangement and chain of the  FIG. 13  machine of the invention the discs  128  and chain  34  are replaced by the discs  226  and endless band  228  of  FIGS. 30 and 31 . 
   As is shown in  FIG. 30  the discs  226  have a rib  229  and groove  230  drive arrangement on their tapered faces  231  which is similar to those of the discs  198  of  FIGS. 22 and 23 . The disc  226  grooves do not, however, include tapered side walls and are rounded onto the upper surfaces of the ribs. 
   The band  228  in this variation of the invention could be made from any suitable non-stretch flexible material but is preferably composed of a flat link metal or similar rigid material chain which is embedded in a suitably hard flexible material. The chain links may be suitably shaped to provide reinforcing for transversely directed teeth  231  which are complementally shaped to the disc grooves  230 . Although not shown in  FIG. 31  the belt  228  would obviously also need to be provided with sprocket holes to enable it to be engaged and guided by the throat  30  idler  26 , drive  14  and tension sprocket or sprockets. Alternatively, the drive sprocket  14  of a machine including the discs  226  could be a flat faced pulley having side flanges which include ribbed radially directed teeth so that the pulley when engaged with the band  228  will have an appearance much like the disc arrangement of  FIG. 31 . The tension and idler sprockets  16  and  26  could merely be flanged flat face pulleys all of which make apertures in the band  228  unnecessary. 
   In this specification only the first embodiment of the IVT machine of the invention is described as having a disc balancing arrangement  68 . The remaining embodiments will, however, also to a greater or lesser extent, require balancing which may be provided in any one of a number of ways known in the art of balancing rotating bodies. 
     FIGS. 32 to 34  illustrate the variables pertaining to the calculation, by means of the following mathematical model, the taper angles of the sides of the grooves  204  and ribs  202  of the ratio changing discs  198 . The centrelines of the grooves  204  may be calculated using equations G and H above. 
   Points B, D, E, F and G all lie on the same drive radius SR (line AG) and are spread by angle θ with reference to point A (the centre of conical disc  198 ) which corresponds to chain link lengths L on drive radius SR, as shown in  FIG. 32 . With the X axis being the horizontal through point A and the Y axis being the vertical through point A the X, Y co-ordinates of points B, the groove centre point Xg, Yg, as an example can be calculated, given the drive radius SR and chain link length L, as follows: 
   L2=2·SR2−2·SR·SR·cos(θ) and by solving for θ results in: 
   
     
       
         
           
             
               
                 θ 
                 ⁢ 
                 
                     
                 
                 = 
                 
                   a 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     cos 
                     ⁢ 
                     
                         
                     
                     [ 
                     
                       1 
                       - 
                       
                         
                           L 
                           2 
                         
                         
                           2 
                           · 
                           
                             SR 
                             2 
                           
                         
                       
                     
                     ] 
                   
                 
               
             
             
               
                 ( 
                 I 
                 ) 
               
             
           
         
       
     
   
   The X-Y co-ordinates of point B is thus as follows:
 
 Xg: BC=SR ·sin( k ·θ)  (J)
 
 Yg: AC=SR ·cos( k ·θ)  (K)
 
   Where k indicates the whole number multiple indicating the chain link length number away from the Y axis, thus for example k=3 at point B. Combining equations I to K a generalised set of equations for X-Y co-ordinates can be derived as follows: 
   
     
       
         
           
             
               
                 Xg 
                 = 
                 
                   SR 
                   · 
                   
                     sin 
                     ⁡ 
                     
                       ( 
                       
                         
                           k 
                           · 
                           a 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           cos 
                           ⁡ 
                           
                             [ 
                             
                               1 
                               - 
                               
                                 
                                   L 
                                   2 
                                 
                                 
                                   2 
                                   · 
                                   
                                     SR 
                                     2 
                                   
                                 
                               
                             
                             ] 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 ( 
                 L 
                 ) 
               
             
           
           
             
               
                 Yg 
                 = 
                 
                   SR 
                   · 
                   
                     cos 
                     ⁡ 
                     
                       ( 
                       
                         
                           k 
                           · 
                           a 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           cos 
                           ⁡ 
                           
                             [ 
                             
                               1 
                               - 
                               
                                 
                                   L 
                                   2 
                                 
                                 
                                   2 
                                   · 
                                   
                                     SR 
                                     2 
                                   
                                 
                               
                             
                             ] 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 ( 
                 M 
                 ) 
               
             
           
         
       
     
   
   Where k indicates the whole number multiple indicating the chain link length number away from the Y axis, L the chain link length and SR the current drive radius. For the centre groove AG, obviously k=0. 
   The following provides a mathematical model for calculating the entry and exit angle φ of the pin into the grooves  204  of the conical disc  198  as the chain pin head  206  is engaging and disengaging the conical disc. The chain  34  circumference around the conical discs is calculated as the summation of all the chain link lengths L at drive radius SR around the conical discs, thus, the following relation between the straight length of chain LinDis leaving the conical disc and the corresponding rotation angle, β of the discs  198  can be written as follows: 
   
     
       
         
           
             
               
                 LinDis 
                 = 
                 
                   
                     
                       β 
                       · 
                       L 
                       · 
                       360 
                     
                     
                       360 
                       · 
                       θ 
                     
                   
                   = 
                   
                     
                       β 
                       · 
                       L 
                     
                     θ 
                   
                 
               
             
             
               
                 ( 
                 N 
                 ) 
               
             
           
         
       
     
   
   The above relates to the centre groove AM and can be extended to successive grooves  204  by only adding k·L where k is defined as above and as indicated on  FIG. 33 . Equation N thus results in the following: 
   
     
       
         
           
             
               
                 LinDis 
                 = 
                 
                   
                     
                       β 
                       · 
                       L 
                     
                     θ 
                   
                   + 
                   
                     k 
                     · 
                     L 
                   
                 
               
             
             
               
                 ( 
                 O 
                 ) 
               
             
           
         
       
     
   
   The new X,Y co-ordinates, Xn, Yn, of the groove  204  centre points, after rotation of discs  198  through angle β, as shown in  FIG. 33 , are calculated by performing a rotation around the Z axis on equations L and M as follows:
 
 Xn=Xg ·cos(β)+ Yg ·sin(β)  (P)
 
 Yn=−Xg ·cos(β)+ Yg ·cos(β)  (Q)
 
and by using equation L and M results in:
 
   
     
       
         
           
             
               
                 Xn 
                 = 
                 
                   
                     SR 
                     · 
                     
                       sin 
                       ⁡ 
                       
                         ( 
                         
                           
                             k 
                             · 
                             a 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             cos 
                             ⁡ 
                             
                               [ 
                               
                                 1 
                                 - 
                                 
                                   
                                     L 
                                     2 
                                   
                                   
                                     2 
                                     · 
                                     
                                       SR 
                                       2 
                                     
                                   
                                 
                               
                               ] 
                             
                           
                         
                         ) 
                       
                     
                     · 
                     
                       cos 
                       ⁡ 
                       
                         ( 
                         β 
                         ) 
                       
                     
                   
                   + 
                   
                     SR 
                     · 
                     
                       cos 
                       ⁡ 
                       
                         ( 
                         
                           
                             k 
                             · 
                             a 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             cos 
                             ⁡ 
                             
                               [ 
                               
                                 1 
                                 - 
                                 
                                   
                                     L 
                                     2 
                                   
                                   
                                     2 
                                     · 
                                     
                                       SR 
                                       2 
                                     
                                   
                                 
                               
                               ] 
                             
                           
                         
                         ) 
                       
                     
                     · 
                     
                       sin 
                       ⁡ 
                       
                         ( 
                         β 
                         ) 
                       
                     
                   
                 
               
             
             
               
                 ( 
                 R 
                 ) 
               
             
           
           
             
               
                 Yn 
                 = 
                 
                   
                     
                       - 
                       SR 
                     
                     · 
                     
                       sin 
                       ⁡ 
                       
                         ( 
                         
                           
                             k 
                             · 
                             a 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             cos 
                             ⁡ 
                             
                               [ 
                               
                                 1 
                                 - 
                                 
                                   
                                     L 
                                     2 
                                   
                                   
                                     2 
                                     · 
                                     
                                       SR 
                                       2 
                                     
                                   
                                 
                               
                               ] 
                             
                           
                         
                         ) 
                       
                     
                     · 
                     
                       sin 
                       ⁡ 
                       
                         ( 
                         β 
                         ) 
                       
                     
                   
                   + 
                   
                     SR 
                     · 
                     
                       cos 
                       ⁡ 
                       
                         ( 
                         
                           
                             k 
                             · 
                             a 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             cos 
                             ⁡ 
                             
                               [ 
                               
                                 1 
                                 - 
                                 
                                   
                                     L 
                                     2 
                                   
                                   
                                     2 
                                     · 
                                     
                                       SR 
                                       2 
                                     
                                   
                                 
                               
                               ] 
                             
                           
                         
                         ) 
                       
                     
                     · 
                     
                       cos 
                       ⁡ 
                       
                         ( 
                         β 
                         ) 
                       
                     
                   
                 
               
             
             
               
                 ( 
                 S 
                 ) 
               
             
           
         
       
     
   
   The X,Y co-ordinates of the chain pin, Xp, Yp, when disengaging the discs  198 , after rotation of conical disc through an angle β, are calculated as follows: The X co-ordinate, Xp, is given by the length of chain that is not in contact with the conical disc  198  and is thus presented by LinDis in equation O. The Y co-ordinate is obviously equal to SR, thus: 
   
     
       
         
           
             
               
                 Xp 
                 = 
                 
                   
                     
                       β 
                       · 
                       L 
                     
                     θ 
                   
                   + 
                   
                     k 
                     · 
                     L 
                   
                 
               
             
             
               
                 ( 
                 T 
                 ) 
               
             
           
           
             
               
                 Yp 
                 = 
                 SR 
               
             
             
               
                 ( 
                 U 
                 ) 
               
             
           
         
       
     
   
   In order to find the Xn, Yn co-ordinates, along grooves  204  centre lines, that are the closest distance Dmin, to the pin co-ordinates (Xp,Yp), SR in equations R and S need to be varied, hereafter referred to as SRg, while SR in equations T and U is kept constant until the following equation reaches a minimum:
 
 D min=[( Xn−Xp ) 2 +( Yn−Yp ) 2 ] 0.5   (U)
 
   As an example  FIGS. 33 and 34  indicate point H with co-ordinates (Xn, Yn) where k=2 and the corresponding chain pin head  206  position at N with co-ordinates (Xp, Yp) where N lies on the horizontal line MP a distance SR from the X axis with MN=LinDis+2*L. 
   Substitution into equation U results in: 
   
     
       
         
           
             
               
                 
                   
                     
                       
                         D 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           min 
                           2 
                         
                       
                       = 
                         
                       ⁢ 
                       
                         [ 
                         
                           
                             SRg 
                             · 
                             
                               sin 
                               ( 
                               
                                 
                                   k 
                                   · 
                                   a 
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   cos 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       
                                         L 
                                         2 
                                       
                                       
                                         2 
                                         · 
                                         
                                           SR 
                                           2 
                                         
                                       
                                     
                                   
                                   ) 
                                 
                               
                               ) 
                             
                             · 
                             
                               cos 
                               ⁡ 
                               
                                 ( 
                                 β 
                                 ) 
                               
                             
                           
                           + 
                         
                       
                     
                   
                 
                 
                   
                     
                                                 
                       ⁢ 
                       
                         
                           SRg 
                           · 
                           
                             cos 
                             ( 
                             
                               
                                 k 
                                 · 
                                 a 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 cos 
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     
                                       
                                           
                                       
                                       ⁢ 
                                       
                                         L 
                                         
                                           
                                               
                                           
                                           ⁢ 
                                           2 
                                         
                                       
                                     
                                     
                                       
                                           
                                       
                                       ⁢ 
                                       
                                         2 
                                         · 
                                         
                                             
                                         
                                         ⁢ 
                                         
                                           SR 
                                           
                                             
                                                 
                                             
                                             ⁢ 
                                             2 
                                           
                                         
                                       
                                     
                                   
                                 
                                 ) 
                               
                             
                             ) 
                           
                           · 
                           
                             sin 
                             ⁡ 
                             
                               ( 
                               β 
                               ) 
                             
                           
                         
                         - 
                       
                     
                   
                 
                 
                   
                     
                       
                         
                                                   
                           ⁢ 
                           
                             ( 
                             
                               
                                 β 
                                 · 
                                 
                                   L 
                                   
                                     a 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       cos 
                                       ⁡ 
                                       
                                         ( 
                                         
                                           1 
                                           - 
                                           
                                             
                                               L 
                                               2 
                                             
                                             
                                               2 
                                               · 
                                               
                                                 SR 
                                                 2 
                                               
                                             
                                           
                                         
                                         ) 
                                       
                                     
                                   
                                 
                               
                               + 
                               
                                 k 
                                 · 
                                 L 
                               
                             
                             ) 
                           
                           ] 
                         
                         2 
                       
                       + 
                     
                   
                 
                 
                   
                     
                                                  
                       ⁢ 
                       
                         [ 
                         
                           
                             
                               - 
                               
                                 ( 
                                 
                                   SRg 
                                   · 
                                   
                                     sin 
                                     ( 
                                     
                                       
                                         k 
                                         · 
                                         a 
                                       
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       
                                         cos 
                                         ( 
                                         
                                           1 
                                           - 
                                           
                                             
                                               L 
                                               2 
                                             
                                             
                                               2 
                                               · 
                                               
                                                 SR 
                                                 2 
                                               
                                             
                                           
                                         
                                         ) 
                                       
                                     
                                     ) 
                                   
                                 
                                 ) 
                               
                             
                             · 
                             
                               sin 
                               ⁡ 
                               
                                 ( 
                                 β 
                                 ) 
                               
                             
                           
                           + 
                         
                       
                     
                   
                 
                 
                   
                     
                       
                                                          
                         ⁢ 
                         
                           
                             SRg 
                             · 
                             
                               cos 
                               ( 
                               
                                 
                                   k 
                                   · 
                                   a 
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   cos 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       
                                         L 
                                         2 
                                       
                                       
                                         2 
                                         · 
                                         
                                           SR 
                                           2 
                                         
                                       
                                     
                                   
                                   ) 
                                 
                               
                               ) 
                             
                             · 
                             
                               cos 
                               ⁡ 
                               
                                 ( 
                                 β 
                                 ) 
                               
                             
                           
                           - 
                           SR 
                         
                         ] 
                       
                       2 
                     
                   
                 
               
             
             
               
                 ( 
                 V 
                 ) 
               
             
           
         
       
     
   
   Equation V can be differentiated with respect to SRg, set equal to zero and solved for SRg or Dmin can be iteratively calculated for different values of SRg until a minimum is found. 
     FIG. 34  presents the above variables as they are related to the disc face  200  at point J which is a point perpendicular to the X-Y plane below point H. 
   In order to calculate the entry angle φ, (the chamfer angle on the groove sides and taper angle on the chain pin heads  206 ) it is noted that for the minimum distance Dmin calculated with the above method, SRg will always be larger than SR since the chain is moving away from the conical disc (see  FIGS. 33 and 35 ). Since the chain pins are in contact with the disc at radius from the spirit or scope of the invention as defined by the appended claims.
 
DiskDis=( SRg−SR )·tan(α)  (W)
 
where α is the taper angle of the conical disc face.
 
   Thus the entry of chamfer angle φ can be calculated as follows using equation W: 
   
     
       
         
           
             
               
                 
                   
                     tan 
                     ⁡ 
                     
                       ( 
                       ϕ 
                       ) 
                     
                   
                   = 
                   
                     DiskDis 
                     
                       D 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       min 
                     
                   
                 
                 ⁢ 
                 
                   
 
                 
                 ⁢ 
                 
                   ϕ 
                   = 
                   
                     a 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       tan 
                       ⁡ 
                       
                         [ 
                         
                           
                             
                               ( 
                               
                                 SRg 
                                 - 
                                 SR 
                               
                               ) 
                             
                             · 
                             
                               tan 
                               ⁡ 
                               
                                 ( 
                                 α 
                                 ) 
                               
                             
                           
                           
                             D 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             min 
                           
                         
                         ] 
                       
                     
                   
                 
               
             
             
               
                 ( 
                 X 
                 ) 
               
             
           
         
       
     
   
   The above calculations obviously need to be applied for values of DiskDis smaller than the depth of the disc grooves. It also needs to be repeated for all values of SR (all ratios of the incremental CVT) as well as for all values of k (all the grooves). The largest value of φ obtained in the above calculations needs to be applied to all the grooves and the mating chain pin heads  206 . 
   Note that in order to account for the grooves on the negative X-axis the following can be done: Making X co-ordinate in equation L negative as well as changing equation T to 
           Xp   =         β   ·   L     ϕ     -     k   ·     L   .               
Also note that this equation will only be true for positive values of Xp, thus when the chain pin leave contact with the conical disc at Xp=0 or at the Y axis.
 
     FIGS. 36 to 39  illustrate a variation of the first embodiment of the IVT machine of the invention as described with reference to  FIGS. 1 to 12 . In this variation of the invention the tapered ratio changing discs  20  of the ratio varying arrangement  18  are replaced by a single composite disc arrangement  232 . Other than this the remaining components of the machine remain the same and carry the same reference numbers as in  FIGS. 1 to 12 . The operation of the two machines is substantially identical. 
   The composite disc arrangement  232  is shown in  FIGS. 36 to 39  to include two superimposed discs  234  and  236 . The disc  234 , in this embodiment, carries six radially directed slots  238 , and the composite output shaft  22 , its tooth guide discs  78  and the drive arrangement  32  partial sprocket assembly of the first embodiment of the machine. The disc  234  is fixed to the coupled tooth guide discs  78 . The disc  236  carries six arcuate slots  240  which are positioned on the disc relatively to the slots  238  in the disc  234  as shown in the drawings. The disc  236  is partially rotatable relatively to and against the disc  234 . 
   The discs  234  and  236  are held together by heads  242  of double headed chain  34  support pins  244 , shown in  FIG. 39 , which each pass through the slots  238  and  240  of the discs  234  and  236 . The upper pin  244 , in  FIGS. 37 and 38  passes through and is fixed to the central tooth of the drive arrangement  32  partial sprocket to serve the same purpose as the pin  88  of the machine of the first embodiment. 
   In use, this variation of the machine operates in the same manner as that of  FIGS. 3 to 12  with the only exception being that, instead of the machine controller causing the discs  20  to be moved towards and away from each other in ratio changing by means of the slotted arms on the frame element  28 , the disc  236  is rotated relatively to the disc  234  by the controller activating any suitable mechanism for doing so. 
   The chain supporting pins  244  are shown in the low ratio position of the machine in  FIGS. 36 to 38 . To move the pins to the high ratio position of the machine the disc  236 , as shown in  FIG. 36  is rotated, relatively to the disc  234 , in a clockwise direction to cause its arcuate grooves  240  to drive the pins radially inwardly in the disc  234  slots and to hold them in any selected ratio position on the composite disc  232 . To move the pins back towards their low ratio positions on the disc  232  the disc  236  is merely rotated relatively to the disc  234  in an anticlockwise direction. 
     FIGS. 40 to 45  relate to improvements in the IVT belt tensioning and belt drive arrangements of the various embodiments of the IVT machine which are illustrated and described in U.S. patent application Ser. No. 10/504,992 (the US specification). 
   Reference numbers in  FIGS. 40 to 45  of this specification include reference numbers which are used on common components in  FIGS. 1 to 39  in the drawings of the various IVT embodiments disclosed in the US specification which are substantially the same components as those of  FIGS. 1 ,  3  and  4  with different reference numbers used on other embodiments, and to avoid confusion, only the  FIGS. 1 ,  3  and  4  of the US specification components are used in this specification. Reference numbers which relate to the components of the improvements to the belt tensioning and belt drive arrangements of this invention commence with the number  245  in  FIG. 42 . In  FIGS. 40 to 43  the outer static frame member  40  of the IVT and, with the exception of  FIG. 45 , the IVT ratio changing discs  20  have been omitted for clarity of illustration. 
   The tensioning arrangement of  FIGS. 40 to 43  is shown to include the static frame member  40  of the IVT, the control frame element  28 , which is slidably movable relatively to the static frame member  40  and carries the throat defining sprockets  26 , and the drive belt  34  which, in this case, is the triple chain illustrated in  FIGS. 3 ,  4  and  13  of the US specification. 
   The improved tensioning arrangement of the invention is shown in  FIGS. 40 and 41  to include dual drive shafts  12  and  12 ′ to which are fixed drive sprockets  14  and  14 ′. The chain tensioner idler sprocket  16  is freely rotatable on its shaft  46  the ends of which are slidably located in the opposite horizontal slots  245  in the side plates of the control frame element  28 . The tensioner arrangement additionally includes the tensioning spring  52  which is attached at one end to a post  246  which is fixed to the upper edge of the illustrated IVT static side plate  42 , as best seen in  FIG. 40 , with its remaining end attached to a lever arm  248  which is fixed to a rotatable shaft  250  which is journaled for rotation in the opposite side plates  42  of the IVT. The shaft  250  additionally carries lever arms  252  which are fixed to it on the opposite outer sides of the control frame element  28 , to be oppositely directed to the spring  52  arm  248 . The free ends of the lever arms  252  carry small freely rotatable sprockets or rollers  254 . 
   It will be noticed by looking at  FIGS. 3 ,  4  and  13  of the US specification that a long and powerful spring  52  is employed to maintain adequate tension on the chain  34  and that the tensioning idler sprocket  16  is subjected, at all times, to the high chain  34  load tension during power transmission through the IVT when the portion of chain  34  around idler sprocket is load carrying, while the spring  52  of the improved tensioning arrangement is significantly lighter and shorter and, as will be described below, requires a relatively smaller stretch distance to adequately tension the chain  34 . Thus this system makes use of the relative movement between plate  42  and control frame  28  to keep the spring  52  movement minimized. 
   Belts  256 , on opposite outer sides of the control frame  28 , are attached at a first of their ends  258  to the side plates of the control frame element  28  and are passed over the two small idler sprockets  254  with their second ends being attached to the ends of the idler sprocket  16  shaft  46  as shown in  FIGS. 40 to 42 . The IVT drive chain  34  passes over and is engaged with the drive sprockets  14  and  14 ′, is looped between the ratio changing discs bears on and is engaged with the tensioner idler sprocket  16  as shown in  FIGS. 40 to 42 , between the sprockets  14  and  14 ′. 
   The frame element  28  is moved, as mentioned with reference to  FIG. 1  of the US specification, by any suitable control means, such as a suitable lead screw, between its positions of operation relatively to the IVT side plates  42 , as indicated by the double arrow A in  FIG. 42 . In  FIG. 41  the frame element  28  is shown in the low ratio position of operation of the IVT and in  FIG. 42  in its high ratio range position of operation. 
   In ratio shifting of the IVT from its  FIG. 41  low ratio range position to its  FIG. 42  high ratio range position the control element  28  is moved by its control means to the left from its  FIG. 41  position to hold the chain throat sprockets  26  immediately adjacent the reducing chain loop while chain is being extracted from between its sprockets  26  from the diminishing chain  34  loop between the ratio changing discs  20 . In the control element  28  being moved between the  FIG. 41  low and the  FIG. 42  high ratio range positions the chain tensioning sprocket  16  is held under tension on the chain by an adequate tension force F, shown only in  FIG. 45 , which is provided by the spring  52  through the levers  248  and  252  and the mechanical advantage belt  256  while moving a distance equivalent to the length of the sprocket  16  slot  245  together with the travel distance A, shown in  FIG. 42 , of the control frame element  28 . During the above movement the only movement of lever  248  is very small as indicated in  FIG. 42  and thus a much shorter spring  52  may required while the spring force F may be kept near constant due to the limited stretch of the spring  52   
   The improved IVT chain  34  drive arrangement  260  is shown in  FIGS. 40 ,  43  and  44 . The drive arrangement  260  is a dual drive arrangement which is located on the outside of the IVT side plate  42 , as shown in  FIGS. 40 and 43 . 
   As shown in  FIG. 43 , the chain  34  drive shafts  12  and  12 ′ extend outwardly from the IVT side plates  42  with the shaft  12  carrying a one-way sprag clutch  262  and the shaft  12 ′ a sprag clutch  264 . The inner races of the sprag clutches are fixed to the drive shafts  12  and  12 ′ on which they are located. 
   The one-way sprag clutches are importantly reversed one to the other in that their races lock and unlock in opposite directions of rotation. It is also important to the invention that they lock and unlock at different speeds of rotation, as will be described below. 
   The drive shaft  12  additionally carries a drive tube  266  which is driven by a prime mover, not shown, and is free of the drive shaft  12  but is fixed to the outer race of the sprag clutch  262 . The outer surface of the drive tube  266  carries a ring sprocket  268  which is fixed to its outer surface. The outer race of the drive shaft  121  sprag clutch  264  carries a sprocket  270  which is fixed to it. Sprocket  270  and ring sprocket  268  are coupled for operation in the same direction via chain  272  as is shown in  FIGS. 44 and 45 . 
   As mentioned above the inner races of the sprag clutches  262  and  264  are fixed to the drive shafts  12  and  12 ′ with their outer races being freely rotatable about the drive shafts in opposite directions to each other. In  FIG. 45  the sprag clutches  262  and  264  are shown to lock in opposite directions of rotation in the direction of the arrows C and D respectively and unlock to freewheel in their directions B and E. 
   During operation of the IVT, referring to  FIG. 45 , and assuming that the chain  34  is traveling, in the direction of the arrows shown on the chain, and that power is transmitted in the forward power transmission direction of the IVT, by input power which is applied to the drive tube  266 , by the prime mover through the locked sprag clutch  262  to drive the shaft  12 . Power will therefore be transmitted from the drive tube  266  to the inner race of the clutch  262  through the locked sprag  262 , and so to the chain  34  loop between the IVT output discs  20 , via drive shaft  12  and sprocket  14  fixed to it. 
   The input sprocket  270  and the inner race of the sprag clutch  264  freewheel due to the opposite direction locking arrangement of the sprag clutches  264  and  262 . 
   A chain  34  load tension L therefore only exists in the upper part  271 , in  FIG. 45 , of the chain  34  for this forward mode of power transmission from the drive tube  266  to the input chain  34  ratio changing disc  20 . The total tension on the top part  271  of the chain  34  is therefore L+0.5 F and only 0.5 F in the bottom part  274 , as indicated in  FIG. 45 , for the forward mode of power transmission. 
   During ratio shifting to a higher ratio the chain  34  moves, in  FIG. 42 , towards a smaller radius between the ratio changing discs  20  while the chain tension sprocket  16  moves in the direction of the arrow F in  FIG. 45  to take up the chain slack. Since the sprag clutch  262  is locked and driving this movement of the idler sprocket  16  results in a relative movement of the inner race of the sprag clutch  264  relatively to the sprocket  270  in the direction of the arrow E which is counter to the locking direction of the sprag clutch  264 , thus the slack will be taken up and the IVT will function competently. 
   When shifting the IVT to a lower ratio the chain  34  moves towards a larger radius ( FIG. 41 ) while the chain tensioning idler sprocket  16  moves in the opposite direction to the tensioning force arrow F in  FIG. 45  to compensate for the additional length of chain being fed from the chain throat sprockets onto the ratio changing discs  20 . 
   Since the sprag clutch  262  is locked and driving this movement of the sprocket  16  will result in a relative movement of the inner race of the sprocket  264 , with respect to the sprocket  270 , in the direction of arrow D which is in the locking direction of the sprag clutch  264 . The sprag clutch  264  will under normal conditions lock and will inhibit the slack created by the movement of the sprocket  16  from being taken up and the IVT will not function competently. 
   The above problem was solved by implementing the non-unitary ratio (one of the sprockets has less teeth than the other) between the input power tube  266  sprocket  268  and the input sprocket  270 , which are coupled by the chain  272 , in such a manner that the sprocket  270  rotates faster than the sprocket  268 . With this arrangement the relative movement of the inner race of the sprocket  264 , with respect to the sprocket  270 , in the direction of arrow D is not required since when no relative movement occurs sprocket  14 ′ will rotate faster than sprocket  14  and thus the length of chain  34  between sprocket  14 ′ and  14  over idler sprocket  16  will decrease and movement of sprocket idler  16  in the direction opposite to F will be possible and the IVT machine will operate competently. Important to note is that the maximum rate of this adjustment is equal to above mentioned the nonunity ratio between the sprockets  268  and  270 . 
   For practical purposes the non-unitary ratio between the sprag clutches must be adequate for allowing sufficient speed of the chain  34  slack take-up to be equal to or greater than the rate at which the slack is produced while reducing the spacing between the IVT output discs  20  to allow for the outward movement of the chain  34  loop to a lower ratio. 
   Tests have shown that in shifting the IVT from its highest ratio ( FIG. 42 ) to its lowest ratio ( FIG. 41 ) with a ratio difference of 5% requires a non-unitary ratio difference of the sprockets  268  and  270  of the dual drive arrangement  260  of 5% with the sprocket  270  rotating faster than the sprocket  268 . 
   In motor vehicle engine braking assume the rotation of the CVT in the chain  34  direction of the arrows on it, which is in the same direction as in the above forward powered transmission application, and that the input power is applied to the ratio changing discs  20  by the vehicle wheels. Power is thus transmitted from the discs  20  to the sprocket  270  through the locked sprag clutch  264 , to the input chain  272  and to drive tube  266 . The sprag clutch  262  now freewheels due to the opposite direction locking arrangement of the sprag clutch  264  compared to the sprag clutch  262 . Also note that the drive tube  266  and its sprocket  268  rotate at a slower rate, typically 5%, of rotation than that of the sprag clutch  264  as a result of their non-unitary ratio. 
   The load tension L, due to power transmission during engine braking, thus only exists in the bottom part  274  of the chain  34  in the engine braking mode of power transmission from the ratio changing disc  20  to the chain  34 . The total tension in the bottom part  274  of the chain  34  is L+0.5 F and only 0.5 F in the top part  272 , as indicated in  FIG. 45 , during engine braking where the chain power transmission is in the opposite direction to the forward power transmission from the prime mover while the chain travels in the same direction in both modes of operation. 
   In ratio shifting to higher ratio during engine braking the chain  34  moves to a smaller radius between the ratio changing discs  20  while the chain tensioning idler  16  moves in the direction of the arrow F, in  FIG. 45 , to take up the chain slack. Since the sprag clutch  264  is locked and driving, relative movement of the inner race of the sprag clutch  262  with respect to its outer race and sprocket  266  in the direction of arrow B which is counter to the locking direction of the sprag clutch  262  and thus the IVT machine will function competently. 
   In shifting to a lower ratio in engine braking the chain  34  moves to a larger radius between the ratio changing discs  20  and the tensioning idler sprocket  16  moves in the opposite direction to the arrow F to compensate for the additional length of chain  34  needed between the ratio changing discs  20 . Since the sprag clutch  264  is locked and driving this movement of the sprocket  16  will result in a relative movement of the inner race of the sprag clutch  262  with respect to its outer race and sprocket  266  in the direction of arrow C which is in the locking direction of the sprag clutch  262  if a unity ratio between sprockets  266  and  270  is assumed. Thus sprag clutch  264  will lock and will not allow the slack created by the movement of the tensioning idler  16  to be taken up. 
   However, since sprocket  268  is rotating at a slower rate than the inner race of the sprag clutch  262 , due to the non-unitary ratio, it is able to slow down relatively to the sprag clutch  262  and the chain slack can be taken up. Note that the sprag clutch  262  can only slow down to the point where its speed equals that of the sprocket  268  after which the sprag clutch  262  will lock. 
   The rate of slack take-up requirement is the same as with the forward powered transmission scenario mentioned above. 
   Note that in all of the above cases the chain  34  tension around the chain tensioner idler sprocket  16  remains about 0.5 F. This tension is thus isolated from the power transmission load L and so permits the stretch length and load capacity of the improved spring  54  to be significantly smaller than that required from the spring  52  of the US specification. 
   The foregoing embodiments are intended to be illustrative of the preferred embodiments of the invention. Those of ordinary skill may envisage certain additions, deletions or modifications to the foregoing embodiments which, although not specifically suggested herein, will not depart from the spirit or scope of the invention as defined by the appended claims.