Abstract:
A transmission of the toroidal race rolling traction type, including ratio varying components (“variators”) for such transmissions. A set of rollers transmitting traction between an input disc and an output disc is connected to a hydraulic mechanism by which it is positioned, the roller position determining the transmitted ratio.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to transmissions of the toroidal race rolling traction type. It relates in particular to ratio varying components (“variators”) for such transmissions, in which each of a set of rollers transmitting traction between an input disc and an output disc is connected to a hydraulic mechanism by which it is positioned, the roller position being a key factor in determining the transmitted ratio. 
     2. Background Art 
     Variators of this type are well known in the art, for example from GB-C-1395391, GB-A-2107009, EP-A-0078125 and EP-A-0133330. In common with most prior art variators, these specifications show a set of three rollers transmitting traction between a rotatable input disc and a coaxial and contra rotating output disc, each roller being spaced from the others by 120° of arc around the common axis of the discs. The ratio transmitted from the input to the output disc by each roller is caused to vary by changing the position of that roller in a direction substantially tangential relative to the centre circle of the common torus presented by the input and output disc races. The mechanism for imparting that tangential movement to at least some of the rollers comprises pistons formed at opposite ends of the roller carriage, that is to say the structure carrying the bearings on which the roller rotates, and movable within hydraulic cylinders. 
     In the prior art arrangements, the piston and cylinder assemblies for controlling the rollers necessarily project from the casings of the variator. Whilst this does not cause a problem from an operational point of view, it can be detrimental if the available space for installing the variator is limited. 
     EP-A-0538357 addresses this problem by positioning the cylinders to lie to the same side of a common plane including the axis of the discs. This improves the situation considerably but still results in lateral projections for the piston/cylinder arrangements. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, there is provided a variator of the toroidal-race rolling-traction type comprising: 
     a rotatably mounted input disc; 
     an output disc rotatably mounted coaxially with the input disc; 
     a plurality of rollers transmitting rotation between the input disc and the output disc; 
     a plurality of actuators, each acting upon a respective one of the rollers; and 
     a plurality of levers, each connected to a respective one of the rollers and its associated actuator. 
     By connecting each of the rollers to its associated actuator by means of a lever, there is much more freedom of choice for positioning the actuators, which allows a more compact design of variator to be achieved. 
     Preferably, each roller and its associated actuator is connected to a respective lever. The variator preferably comprises a plurality of levers pivotally mounted about a first axis. The variator may also comprise a lever pivotally mounted about a second axis. The second axis may be inclined to the first axis. 
     Preferably, each of the actuators is mounted to the same side of a plane aligned with and passing through the rotational axis of the variator discs. More preferably, each of the actuators is mounted below a horizontal plane aligned with and passing through the rotational axis of the variator discs. 
     In a preferred embodiment, each of the actuators is located radially outwardly of a common plane extending parallel to the rotational axis of the input and output discs and tangential to the periphery of the larger of the input disc and output disc. 
     In this way, the actuators can all be arranged adjacent to each other “on one side” of the variator which again allows a more compact design of variator. 
     Preferably, the common plane extends substantially horizontally. In this way, all of the actuators can be located beneath the variator discs. 
     Preferably, the common plane is tangential to the lowermost point of the larger of the input and output disc. 
     Preferably, the directions of displacement of the actuators are substantially parallel and preferably the directions of displacement of the actuators are perpendicular to the common plane. 
     In a preferred embodiment, each actuator comprises a piston reciprocably disposed within a cylinder. 
     Preferably, the longitudinal axes of the cylinders are substantially parallel. 
     Preferably, the pistons are displaceable by means of hydraulic pressure and advantageously the cylinders are disposed in a common cylinder block. 
     Preferably the actuators are double-acting, i.e. operable to displace the roller in each of two opposite directions. 
     In accordance with a second aspect of the present invention there is a provided a variator of the toroidal-race rolling-traction type comprising: 
     a rotatably mounted input disc; 
     an output disc rotatably mounted coaxially with the input disc; 
     a plurality of rollers transmitting rotation between the input disc and the output disc; and 
     a plurality of actuators, each acting upon a respective one of the rollers; 
     wherein each of the actuators is located radially outwardly of a common plane extending parallel to the rotational axis of the input and output discs and tangential to the periphery of the larger of the input disc and output disc. 
     By locating all of the actuators as described above, it is possible to achieve a much more compact arrangement and to utilise the available space more efficiently. 
     Preferably, the common plane extends substantially horizontally. More preferably, the common plane is tangential to the lowermost point of the larger of the input disc and output disc. 
     In this way, all of the actuators can be located beneath the variator discs. 
     Preferably, the directions of displacement of the actuators are parallel. For example, the directions of displacement of the actuators may be perpendicular to the common plane. 
     Each actuator may comprise a piston reciprocably disposed within a cylinder. The pistons are preferably displaceable by hydraulic pressure. 
     The longitudinal axes of the cylinders are preferably substantially parallel. The cylinders may be disposed in a common cylinder block. 
     Preferably, the actuators are double-acting. 
     The variator may further comprise a plurality of levers, each connected to a respective one of the rollers and its associated actuator. 
     Preferably, each roller and its associated actuator is connected to a respective lever. 
     The variator preferably comprises a plurality of levers pivotally mounted about a first axis. The variator may also comprise a lever pivotally mounted about a second axis. The second axis may be inclined to the first axis. 
     By way of example only, a specific embodiment of the present invention will now be described, with reference to the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of infinitely variable transmission (IVT) in accordance with the present invention; 
         FIG. 2  is an exploded perspective view of the IVT of  FIG. 1 , with the outer casing removed; 
         FIG. 3  is a front view of the IVT of  FIG. 1 , with the upper casing and front disk removed; 
         FIG. 4  is a rear view of the IVT of  FIG. 1 , with the casing and rear disc removed; and 
         FIGS. 5 to 9  are perspective views of lever/roller assemblies of the IVT of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The attached figures illustrate an infinitely variable transmission (IVT) assembly  10  having an outer upper casing  12  which is mounted on a lower cylinder block  14 . The casing  12  houses an IVT of the toroidal race rolling traction type having a pair of front and rear input discs  18 ,  20  and a common output disc  22 , all mounted on a common rotational axis. 
     The input discs are rotated by an input shaft (not shown) connected to the output of an engine. Drive from the output shaft is transmitted to the two input discs  18 ,  20  by means of splined connections  24 . The input shaft also passes through a bearing (not shown) mounted at the centre of the output disc  22 . 
     The opposing faces of the input discs and output discs are provided with toroidal surfaces which define front and rear toroidal cavities  26 ,  28 . Drive is transmitted from the input discs to the output discs by means of two sets of three roller assemblies  30   a ,  30   b ,  30   c ,  32   a ,  32   b ,  32   c , one set  30 ,  32  of roller assemblies positioned in each of the two toroidal cavities  26 ,  28  and the roller assemblies of each set being spaced apart by approximately 120°. Each roller assembly comprises a disc-like roller  33  rotatably mounted in a roller carriage  34  by means of a stub axle  35 . 
     A high end load is applied hydraulically to one of the input discs (usually the rear disc) which is internally reacted to by tension in the input shaft, thereby clamping the rollers  33  between the discs  18 ,  22  and  20 ,  22 . At the contact between the discs and rollers power is transmitted by a shearing action through a traction fluid. When the contact points are subjected to very high pressures by the end load, the traction fluid greatly increases in viscosity at the contact points and the elasto-hydrodynamic characteristics of the fluid allow driving traction force to be transmitted effectively. 
     In order for power to be transmitted between the discs and rollers a reaction force needs to be provided. Reaction forces are applied hydraulically to the individual rollers, as will be explained, to ensure that reaction torque is shared equally between the rollers and to provide a very direct means of controlling transmitted torque. 
     Output from the variator is taken from the output disc  22 . In the specific embodiment described, the variator  10  is a coaxial variator, i.e. the output from the output disc is taken from a hollow shaft (not shown) connected to the output disc and arranged coaxially with the input shaft and is passed to a gear set together with a drive from the input shaft. In an alternative construction, the output from the variator may be taken from the periphery of the output disc  22  by means of a chain or belt passing around the output disc. 
     The features described above are generally conventional for an IVT of the toroidal race rolling traction type. 
     Reaction torque is applied to the roller  33  of each roller assembly by a respective one of six double-acting reaction pistons  36   a ,  36   b ,  36   c ,  38   a ,  38   b ,  38   c , each of which is slidably disposed in a respective one of six cylinders  40   a ,  40   b ,  40   c ,  42   a ,  44   b ,  44   c  provided in the cylinder block  14 . The longitudinal axes of the cylinders  40 ,  42 , and therefore the axis of movement of the pistons  36 ,  38  are parallel to each other and, in the embodiment described, are all arranged vertically. However, each piston  36 ,  38  does not act directly on its associated roller assembly but instead acts on a lever  44 ,  46  to which the roller assembly is attached. 
     As shown in the figures, the levers in each cavity are not identical. This allows more efficient use of the available space and therefore provides a more compact assembly. Referring firstly to the front toroidal cavity  26  between the front input disc  18  and the output disc  22  and looking from the front of the assembly, a first roller assembly  30   a  is attached via a universal joint (e.g. a “Rose” bearing)  47  to one end of a second order lever  44   a , the fulcrum of the lever being provided by a first fulcrum bar  48  to which the lever is pivotally mounted by means of a bearing  50   a  and the rod  52   a  extending from reaction piston  36   a  being pivotally connected to the lever  44   a  between the two ends of the lever. The fulcrum bar itself is mounted between front and rear bearing lugs  54  on a fulcrum plate  56  positioned on top of the upper surface of the cylinder block  14   a.    
     A second roller assembly  30   b  is attached, also via a universal joint (e.g. a “Rose” bearing)  47 , to one end of a first order lever  44   b , the fulcrum being provided by the fulcrum bar  48  described previously on which the lever  44   b  is mounted by means of a bearing  50   b . The rod  52   b  extending from the reaction piston  36   b  is pivotally mounted to the opposite end of the lever  44   b.    
     The third roller assembly  30   c  of the front toroidal cavity  26  is attached via a universal joint (e.g. a “Rose” bearing)  47  and a connecting arm  45  to a third order lever  44   c , the connecting arm extending from a point between the fulcrum of the lever and the pivotal connection of the lever with a rod  52   c  projecting from the reaction piston  36   c . The fulcrum is provided by a second fulcrum bar  60  extending between two mounting lugs  62  on the upper surface of the fulcrum plate  56  to which the lever is pivotally mounted by means of a bearing  50   c . The longitudinal axis of the second fulcrum bar  60  extends in a plane parallel to that of the first fulcrum bar  48  but displaced downwardly therefrom and inclined towards it. 
     In each case, the universal joint  47  is connected to the roller carriage  34  of the roller assembly. 
     The rear chamber  28  is also provided with first, second and third roller assemblies  32   a ,  32   b ,  32   c  attached to levers  46   a ,  46   b ,  46   c . Roller assemblies  32   a  and  32   b  and levers  46   a  and  46   b  are virtually identical to the roller assemblies  30   a  and  30   b  and levers  44   a  and  44   b  of the front cavity  26  with only detail differences. Roller assembly  32   c  and lever  46   c  are identical to roller assembly  30   c  and lever  46   c  of the front cavity. Levers  44   a  and  44   b  are pivotally mounted on the first fulcrum bar  48  via bearings  50 . The lever  46   c  is pivotally mounted via a bearing  50   c  on a third fulcrum bar  68  which corresponds to the second fulcrum bar  60  of the front chamber  26 . In fact, the positions and orientations of the rollers and levers in the front and rear chambers  26 ,  28  are virtually a mirror image of each other about a plane passing through the centre of the output disc  22  perpendicularly to the rotational axis of the input and output discs  18 ,  20 ,  22  with only detailed differences in the shapes of the levers in the two cavities. 
     As can be seen from the Figures, particularly  FIGS. 3 and 4 , the actuating pistons are all located entirely radially outwardly of the input and output discs  18 ,  20 ,  22  of the variator. It will be seen that all of the actuating pistons are located to the same side of a plane X 1  passing horizontally through the rotational axis of the variator discs. Indeed, the actuating pistons are all located outwardly (with respect to the variator axis) of a single common plane X 2  extending parallel to the rotational axis of the variator discs and tangential to the periphery of the largest of the discs (in this embodiment the diameters of the two input discs  18 ,  20  and of the output disc  22  are equal) and, in this embodiment, extending horizontally. 
     By connecting each actuating piston to its associated roller assembly via a lever and by positioning all of the actuators beyond plane X 2 , it is possible to chose the position of the actuating pistons with much more freedom. As a result, a much more compact arrangement can be achieved. 
     In effect, the actuating pistons are all located “on the same side” of the variator which allows a much more compact arrangement to be made. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.