Abstract:
A fluid display arrangement is disclosed for a rolling-traction continuously-variable ratio transmission unit in which drive is transmitted from one race to another by at least one rotating roller whose outer circumference engages the races, the fluid supply arrangement comprising a shroud mounted in proximity to the roller and a fluid supply conduit, and being characterised in that the shroud has an inner surface providing a circumferential portion adjacent the roller&#39;s outer circumference and two radially extending portions adjacent respective flanks of the roller, a fluid receiving chamber being thereby defined between the roller and the shroud, and the fluid supply conduit being arranged to deliver fluid into the fluid receiving chamber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS: 
   This Application is a National Phase of International Application No. PCT/GB03/00281, filed on Jan. 24, 2003, which claims priority from Great Britain patent application No. 0201631.9, filed on Jan. 24, 2002. 
   BACKGROUND OF THE INVENTION 
   The present invention relates generally to continuously variable transmission units (“variators”) of rolling-traction type and more specifically to an arrangement for supply of fluid to a roller of such a variator. 
   Major components of a known toroidal-race rolling-traction variator  10  are illustrated in  FIG. 1 . Here, two input discs  12 ,  14  are mounted upon a drive shaft  16  for rotation therewith and have respective part toroidal surfaces  18 ,  20  facing toward corresponding part toroidal surfaces  22 ,  24  formed upon a central output disc  26 . The output disc is journalled such as to be rotatable independently of the shaft  16 . Drive from an engine or other prime mover, input via the shaft  16  and input discs  12 ,  14 , is transferred to the output disc  26  via a set of rollers disposed in the toroidal cavities. A single representative roller  28  is illustrated but typically three such rollers are provided in both cavities. An end load applied across the input discs  12 ,  14  by a hydraulic end loading device  15  provides contact forces between rollers and discs to enable the transfer of drive. Drive is taken from the output disc to further parts of the transmission, typically an epicyclic mixer, as is well known in the art and described e.g. in European patent application 85308344.2 (published as EP 0185463). Each roller is mounted in a respective carriage  30  which is itself coupled to a hydraulic actuator  32  whereby a controlled translational force can be applied to the roller/carriage combination along a direction generally tangential to the main axis defined by the shaft  16 . The actuator  32  comprises a hydraulic piston  34  capable of rotation within its cylinder  36 . Such rotation of the piston is associated with a corresponding rotation (or “precession”) of the roller axis about the so-called castor axis, which in the illustrated arrangement is the axis of the piston  34 . As the skilled person is well aware, this precession of the roller axis changes the relative diameters of the paths traced out by the roller  28  on the variator discs  12 ,  14 , thereby changing the variator transmission ratio. Because the rollers always seek an orientation in which their axes intersect the axis of the drive shaft  16  they automatically move and precess to positions in which the so-called reaction torque is determined by the biasing force from the actuators  32 . The  FIG. 1  variator is therefore referred to as being of “torque control” type. 
   The present invention is however potentially applicable to rolling-traction variators of other types including those known in the field as “part” or “half” toroidal. 
   In known rolling-traction variators the variator discs do not make direct contact with the rollers. Instead a film of fluid, referred to as “traction fluid”, is maintained between the surfaces of these components and drive is transmitted between them by virtue of shear of this fluid film. Maintenance of the film is of primary importance since direct roller/disc contact would cause excessive wear. 
   The fluid also has an important function in cooling the variator components, particularly the rollers. In prototype variators the roller operating temperature has been an important factor in determining the power capacity of the variator. The shearing forces in the regions of engagement between variator discs and rollers generate heat, causing the temperature of the rollers (and to a lesser extent of the discs) to rise. Excessive temperatures can (1) damage the rollers themselves (the steel from which they are formed undergoing changes under sustained high temperatures); and (2) impair the performance of the traction fluid, high temperatures and consequent low fluid viscosity leading to a thinner fluid layer between disc and roller, and to higher slip between these components. Sustained high temperatures can also cause the fluid properties to change over time in an undesirable manner. 
   In practice it is found that the variator&#39;s power capacity is limited by the rate of dissipation of heat from the rollers, making improvements in this respect highly important. 
   An arrangement for supplying traction fluid to the variator rollers is disclosed in our European patent 890044 and its US counterpart U.S. Pat. No. 5,971,885. Here a flow of traction fluid is passed through the actuator/carriage assembly to reach a series of nozzles disposed adjacent to the outer periphery of the roller. A spray of fluid is thus supplied onto the roller periphery. 
   There are important incentives to increase the efficiency of utilization of the traction fluid. Provision of the required fluid flow requires energy and so reduces overall transmission efficiency; improvements in fluid utilization allow reduction in the flow volume and hence in the corresponding energy requirement. Additionally, studies have shown that the residence time of fluid on the roller surface is typically shorter than is desirable with a view to maximizing conduction of heat from the rollers. An increase in this residence time again offers potential for a reduction in flow volume but also, or alternatively, increases the roller cooling effect and so potentially allows an increase in the power handling capability of the variator and/or a reduction in roller temperature which may increase roller life. 
   The provision of a shroud in proximity to the roller was proposed in 1938 by W. T. Murdei (U.S. Pat. No. 2,132,751) but to the best of the applicant&#39;s knowledge the idea was not taken up in this field and it is believed that because of the form of the shroud—it comprises only a part-circular rim adjacent the roller&#39;s outer edge—it would have had limited effectiveness. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention there is a fluid supply arrangement for a rolling-traction continuously-variable ratio transmission unit in which drive is transmitted from one race to another by at least one rotating roller whose outer circumference engages the races, the fluid supply arrangement comprising a shroud mounted in proximity to the roller and a fluid supply conduit, and being characterised in that the shroud has an inner surface providing a circumferential portion adjacent the roller&#39;s outer circumference and two radially extending portions adjacent respective flanks of the roller, a fluid receiving chamber being thereby defined between the roller and the shroud, and the fluid supply conduit being arranged to deliver fluid into the fluid receiving chamber. 
   A preferred embodiment of the present invention is for use in a transmission unit of toroidal race type wherein the roller is mounted in a manner allowing its inclination to alter relative to the toroidal races to thereby alter the transmission ratio, the shroud being coupled to the roller&#39;s mounting such as to maintain a constant position relative to the roller. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:— 
       FIG. 1  is a schematic illustration of major components of a variator of known general type; 
       FIG. 2  is a perspective illustration of a roller/carriage/actuator assembly for a variator embodying the present invention, half of the roller and of an associated bearing arrangement and carriage being omitted to expose a section through these components; 
       FIG. 3  is a view along the direction of a main variator axis of major components of a variator assembly embodying the present invention, one of the variator discs being omitted so that the roller/carriage/actuator assemblies can be seen; 
       FIG. 4  is a perspective illustration of a roller/carriage/actuator assembly for a variator according to a second embodiment of the present invention; 
       FIG. 5  is a perspective illustration of a roller/carriage/actuator assembly for a variator according to a third embodiment of the present invention; 
       FIG. 6  is an exploded illustration of a roller/carriage assembly for a variator according to a fourth embodiment of the present invention; 
       FIG. 7  is a plan view of the  FIG. 6  assembly; 
       FIGS. 8 and 9  are sectional views, in axial planes, along arrows A-A and Y-Y of  FIG. 7 , respectively; and 
       FIG. 10  is a sectional illustration of an actuator suitable for incorporation in a variator embodying the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The variator construction illustrated in  FIGS. 2 and 3  differs somewhat from that of  FIG. 1  and its construction and operation will be briefly explained before the fluid supply arrangement itself is considered. Each of the three rollers  100  in the variator cavity  102  defined between variator disc  104  and its counterpart disc (omitted from  FIG. 3 ) is mounted upon a respective carriage  106  which is acted on by two hydraulic actuators  108 ,  110 . The carriages are not free to rotate to accommodate the required precession of the roller axis. Instead the orientation of the carriages is constrained. To appreciate why this is so, note firstly that due to the variator geometry the center of each roller always lies on a circle  112  which is the center circle of the toroidal cavity defined by the discs, as is well known to those skilled in the art Any rotational movement of the carriage could only be about a carriage axis  114  (see  FIG. 3 ) connecting the centers of the actuators  108 ,  110 , since it is about these centers that pistons (one of which is seen at  116  in  FIG. 2 ) provided at both ends of the carriage  106  can rotate in their cylinders such as  118 . However the carriage axis  114  is radially offset from the cavity center circle  112 , as will be apparent from  FIG. 3 . The carriage axis  114  is closer to the main variator axis (defined by the main shaft  120 ) than the cavity center circle  112 . The effect of the offset is to constrain the carriage orientation, which consequently varies only when the discs such as  104  move slightly along the main axis due to compliance and the considerable end load to which they are subject. 
   To allow the rollers  100  to precess as required to vary the transmission ratio, each is mounted upon its carriage  106  through a bearing arrangement comprising a rotary bearing  122 , which allows the roller to rotate about its own axis to transmit drive, and a ball and socket coupling upon which an inner race  126  of the rotary bearing  122  is mounted. A tongue seen at  124  in  FIG. 3  projects from the ball  126  of this coupling into a corresponding slot in the socket, which is formed as a hub  128 , to define a castor axis  130  about which the roller  100  precesses. 
   Looking now at features of the assembly relating to supply of traction fluid to the roller  100 , a source of fluid flow such as a pump (not illustrated) is connected to a hollow stem  152  which extends along the axis of the cylinder  118  and projects into a corresponding axial bore  154  in the piston  116 , forming a seal therewith. Bore  154  leads along an arm  156  of the carriage to a nozzle opening  158  from which fluid is projected toward the roller  100 . 
   A shroud  160  is juxtaposed with the roller  100 . In the illustrated embodiment the roller  100  is largely surrounded by the shroud  160 . The shroud  160  is mounted upon the hub  128  so that it remains in a fixed position relative to the roller  100  despite precession of the roller about the castor axis  130 . That is, the shroud moves along with the roller. The shroud does not contact the roller  100 . In the illustrated embodiment a clearance of approximately 1 mm is maintained between the roller  100  and the shroud  160 . A fluid receiving volume  161  is thus defined between the facing surfaces of the roller and the shroud  160 . The shroud  160  has a curved circumferential wall  162  extending around the majority of the circumference of the roller  100 . Part of the fluid receiving volume is thus formed at  163  between the outermost circumferential surface  165  of the roller and the circumferential wall  162 . The wall is broken however in the regions  164  where the roller must contact the variator discs. The circumferential wall  162  is connected to the hub  128  by upper and lower walls  166 ,  168  lying in generally radial planes (with respect to the axis of the roller  100 ) at opposite faces of the roller  100 . In the illustrated embodiment these are cut away in regions  170  but such cut-aways may be dispensed with. 
   The shroud  160  has two fluid inlet apertures one of which is seen at  172  in  FIG. 2  while the edge of the other is seen at  174 . These apertures are on opposite sides of the roller. Both of the apertures  172 ,  174  lie on the castor axis  130  so that their displacement is minimized as the roller  100  precesses. 
   Furthermore, both apertures  172 ,  174  face along the castor axis  130  to receive fluid from a corresponding nozzle opening aligned therewith. Aperture  172  receives fluid from the aforementioned nozzle  158 . A similarly formed nozzle feeds aperture  174  but cannot be seen in the drawings. 
   Note that there is no sealed connection between the nozzle  158  and the corresponding fluid inlet aperture  172 . To provide such a connection would complicate construction. In the illustrated embodiment there is a short separation of the nozzle  158  from the shroud  160 . A jet of fluid from the nozzle  158  crosses the space between the nozzle and the shroud and so passes into the fluid receiving volume  161  between the roller  100  and the shroud  160 . Within this space the fluid is then circulated due to the action of the rotating roller. The circumferential surface  165  of the roller is consequently reliably coated with traction fluid, thereby maintaining the necessary film of fluid between the roller  100  and the variator discs. There is a constant flow of fluid into and out of the shroud  160  but the presence of the shroud serves to increase residence time of the fluid in the vicinity of the shroud and this has been found to significantly improve roller cooling. Turbulent flow conditions prevail within the fluid receiving volume  161  and the consequent circulation of the fluid again promotes roller cooling. Some drag is inevitably exerted on the roller by the fluid but this energy loss is found to be small. 
   The fluid must be ejected from the nozzle  158  with sufficient velocity to enter the shroud  160  despite centrifugal effects tending to expel fluid through the inlet aperture  172 . 
   It will be understood that the pressure of the traction fluid within the bore  154  in the piston  116  exerts a biasing force on the piston and hence on the roller carriage  106 . However this force is balanced by an opposing and substantially equal force exerted due to the corresponding fluid supply arrangement in the opposing actuator  110  at the opposite end of the carriage so that no significant net force is exerted on the carriage. 
   Nonetheless, the construction can in some respects be simplified by supplying traction fluid to the roller/shroud assembly through a nozzle which is not mounted upon the roller carriage  106  but is instead anchored to the variator&#39;s casing.  FIGS. 4 and 5  illustrate two such alternative arrangements. Many of the components are common to FIGS.  2 , 3 , 4  and  5  and the same reference numerals are used for these throughout. In particular each of the arrangements has a shroud  160  containing the roller  100 . 
   In  FIG. 4  the nozzle is formed at an end  200  of an elbowed conduit  202  which is mounted as seen at  204  to the variator casing  206 . A bore  208  in the casing  206  provides for fluid feed from a pump schematically indicated at  210 . The conduit  202  is shaped and positioned such that it does not foul the roller  100 , carriage  106  or shroud  160  as these components move. The inlet aperture through which fluid ejected from the nozzle  200  is in this drawing labeled  212  and again lies on, and faces along, the castor axis. The nozzle  200  also faces along this axis and thus remains in alignment with the inlet despite movement of the roller, although of course as the carriage  106  moves back and forth the separation of the nozzle  200  from the inlet  212  varies correspondingly. At the opposite side of the roller from the nozzle  200  is a further conduit  220  with a further nozzle  222 . 
     FIG. 5  illustrates an arrangement in which the direction along which the fluid is ejected into the shroud  160  is generally transverse to the castor axis. Here the inlet aperture  250  in the shroud  160 , is in the form of a slot in the shrouds upper wall  166 . The slot lies as close as possible to the castor axis, although the wall  166  is itself slightly displaced from this axis. The slot extends generally along the direction of travel of the carriage  106 . Conduit  252  in this embodiment terminates in a nozzle  254  directed transversely to the castor axis and faces toward the inlet  250 . Due to the positioning of the inlet  250  the nozzle  254  remains aligned therewith despite movement of the roller/shroud assembly. A possible variant of this arrangement, not illustrated, has one of the nozzles formed as at  200  in  FIG. 4  to eject fluid through an opening as at  212  onto the roller&#39;s circumference while the other nozzle, lying on the opposite side of the roller, is formed as at  254  in  FIG. 5  to eject fluid onto a face of the roller. This is considered beneficial with regard to roller cooling. 
   The above described embodiments all use a nozzle to project fluid through an opening in the shroud wall, without the need for a sealed connection between the fluid supply conduit and the shroud. This is constructionally highly convenient. However trials carried out by the inventors have established that, for a given rate of fluid flow, cooling performance is improved by connecting the fluid supply to the shroud, so that the fluid supply conduit communicates with the interior of the shroud through its nozzle opening. A roller/carriage assembly of this type is illustrated in  FIGS. 6 to 9  and the relationship of its main components can best be appreciated from the exploded view provided by  FIG. 6 . The roller itself is seen at  300  and runs on a shaft  302  rotatably carried in two sealed roller bearings  304 ,  306  which are themselves mounted in bores  308 ,  310  of respective carriage casing-halves  312 ,  314 . The two casing halves are bolted together (the bolts themselves are omitted from the drawings, for simplicity) through proximal and distal intermediate carriage casing-parts  316 ,  318 . 
   The shroud is in this embodiment formed by two shroud-halves  320 ,  322  both having a respective radial wall  324 ,  326  of generally circular shape and an upstanding, circular peripheral wall  328 ,  329 . In the assembled shroud the two peripheral walls abut, thereby defining an interior space within the shroud for containing the roller. 
   The shape of the interior of the shroud is important to its function and is best seen in  FIG. 8 . The shroud&#39;s inner surface provides a circumferential, radially inwardly facing, portion  330  adjacent the roller&#39;s outer circumference, serving to restrain fluid from being centrifugally expelled from the roller. The separation between the roller and the shroud in this vicinity is, in the illustrated embodiment, approximately 1 mm. Increased gaps, up to 4-5 mm, may be used here. The shroud&#39;s inner surface also provides a respective generally radially extending portion  334 ,  336  adjacent both of the flanks  338 ,  340  of the roller. These radial portions lie, in the illustrated embodiment, in radial planes. Somewhat different shapes could however be envisaged for these portions—they could, for example, be frusto-conical in shape if this is found to improve flow characteristics. 
   The radially extending portions  334 ,  336  of the shroud define radial mixing chambers alongside the flanks of the roller. 
   Overall, the effect of the shroud is to form a fluid receiving chamber extending around the roller&#39;s outer circumference and at least part of the roller&#39;s flanks. In this way it is found that residence time of fluid in the vicinity of the roller is greatly increased, creating improved heat transfer from the roller to the fluid and so improving roller cooling. Note that in these respects the shrouds illustrated in earlier drawings are similar. 
   The shroud&#39;s peripheral wall  328 ,  329  can be seen to be cut away at positions  342 ,  344  where the roller engages the variator discs. 
   A conduit for supply of cooling fluid is formed through a radial bore  346  and communicating axial bore  348  in the proximal intermediate casing part  316  (see  FIG. 9 ). The axial bore leads to (1) a first radial nozzle bore  350  in the intermediate casing part  316 , communicating with the fluid-receiving chamber formed between the shroud and the roller, the first nozzle bore  350  being positioned to project the fluid onto the roller&#39;s outer circumference, and (2) a pair of fluid conducting galleries  352 ,  354  (see  FIGS. 6 and 8 ) formed by trenches in inner faces of the respective carriage casing-halves  312 ,  314 . Fluid is conducted through the galleries  352 ,  354  to an axially extending gallery  356  formed in the radially innermost face of the distal intermediate casing part  316 , and so to a second radial nozzle bore  358  formed in the shroud wall. The second nozzle bore communicates with the fluid-receiving chamber and projects fluid onto the roller&#39;s circumference. Hence the arrangement serves to diametrically opposite to the other. 
   The roller/carriage assembly of  FIGS. 6 to 9  is to be coupled to a linear actuator with provision for feeding of cooling fluid through an actuator piston. A suitable actuator is illustrated in  FIG. 10 . The actuator construction has in fact been disclosed in our earlier U.S. Pat. No. 5,971,885, the content of which is hereby incorporated by reference, and further details can be found therein. 
   Within a cylinder  400  are working chambers  402 ,  404  which receive fluid at respective pressures to act on enlarged head  408  of a piston  406 . On either side of the enlarged head  408 , the piston has sleeves  410 ,  412  which pass sealingly through respective cylinder end walls  414 ,  416 . A stem  418  is coupled to the piston through a ball and socket joint  420  at one of its ends. The stem&#39;s other end  422  leads to the carriage parts  316 ,  318 , being coupled thereto, but the carriage itself is omitted from  FIG. 10  for the sake of simplicity. Traction fluid from a pump  424  is supplied through a bore  426  extending right the eay through the length of the piston and so output to the bore  346  seen in  FIG. 9 .