Abstract:
A control unit for an infinitely-variable-ratio transmission. The transmission includes a cylinder and a piston with a proximal and a distal end. A support stem is connected to the piston. The piston is hollow and has a head portion for interaction with an associated actuation fluid. A proximal portion extends away from the head portion. The support stem is connected to the proximal portion by an articulated joint and extends from the joint to the head portion to exit from the distal end of the piston.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a control unit suitable for facilitating movement of an object connected thereto between desired positions and relates particularly, but not exclusively, to a control unit in the form of an hydraulically operated piston operably connectable to a roller mechanism in an infinitely-variable-transmission (IVT) or the like. The invention also relates to an IVT incorporating said control unit. 
   2. Background Art 
   Several patent publications of recent years, of which WO90/05860 is an example, describe infinitely-variable-transmissions in which direct connection of each roller to a piston subjected to controlled hydraulic pressure suffices to maintain the angular orientation of each roller—and thus the ratio transmitted by it from an input disc to an output disc—at the appropriate value at all times. The key to the efficacy of such an apparently simple method of roller control is that the torque transmitted by the variator can be controlled by adjustment of the hydraulic pressure. A control system receives inputs representative of all the essential parameters, and sets up within the cylinder the appropriate hydraulic pressure to match the torque reaction associated with the desired orientation, so causing the roller to seek and hold that orientation. 
   One of the problems encountered in practice by IVTs in which rollers are controlled is that the length of the stroke that the piston must execute in order fully to control the roller is relatively long. Consequently, the housing for the piston/cylinder is of such length that it can be difficult to install within the tight confines of some engine or transmission compartments. 
   A solution to the above-mentioned problem is presented in WO 99/54646 in which there is described a roller control unit for a continuously-variable-ratio transmission of the toroidal—race roller traction type, in which the unit comprises a piston/cylinder arrangement characterised by telescopic shrouds of variable length extending between the piston and the end wall. The shrouds act to define, in combination with the piston and cylinder, a chamber for receiving hydraulic actuation fluid and translate between deployed and retracted positions as and when the piston moves. The provision of telescopic shrouds facilitates a reduction in the axial length of the actuation mechanism which is of significant benefit when installing in the tight confines of some engine or transmission compartments. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an alternative control unit which also lends itself to use in confined spaces and which is more easily assembled than some prior arrangements. It is an additional object of the present invention to provide a control unit in the form of an hydraulically operated piston operably connectable to a roller mechanism. It is a still further object of the present invention to provide an infinitely-variable-transmission or the like with a control unit as described herein. 
   Accordingly, the present invention provides a control unit for an infinitely-variable-ratio transmission comprising a cylinder, a piston, having a proximal end and a distal end, and a support stem connected to said piston, said piston being hollow and having a head portion for interaction with associated actuation fluid and a proximal portion extending away from said head portion, characterised in that said support stem is connected to said proximal portion of said piston by means of an articulated joint and extends from said joint through said head portion to exit from said distal end of said piston. 
   The present invention also provides an infinitely-variable-transmission having such a control unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A specific embodiment 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 representation of an infinitely-variable-transmission of known type; and 
       FIG. 2  is a cross-sectional view of a control unit embodying the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , an infinitely-variable-transmission is shown generally at  10  and comprises a pair of outer discs  12 ,  14  connected to a central shaft  16  for rotation therewith and a pair of inner discs  18 ,  20  supported on but rotatable relative to shaft  16 . Each of the confronting faces  12   a ,  14   a ,  18   a ,  20   a  of the discs  12 ,  14 ,  18 ,  20  is profiled such as to define between respective confronting surfaces a pair of toroidal cavities shown at  22 ,  24 . A plurality of hydraulically actuated rollers  26  are circumferentially spaced around each cavity and positioned such as to contact each associated confronting surface in a manner that facilitates the transmission of motion between associated discs through the rollers. An end load mechanism shown in the form of an hydraulic chamber arrangement  28  and associated hydraulic fluid source shown schematically at  30  are provided to urge the various discs together in a manner well known in the art and therefore not described herein. Also shown in  FIG. 1  is an engine  32  or other prime mover for driving shaft  16  directly (as shown) or discs  18 ,  20  by means of a parallel shafting arrangement and transfer mechanism well known in the art and therefore not shown herein for reasons of clarity. The rollers  26  are each actuated in the manner described above with reference to WO 90/05860 by control units best seen in  FIG. 2 . 
   Referring now to the drawings in general but particularly to  FIG. 2 , a control unit  34  suitable for facilitating management of an object—such as a roller  26  of an IVT—between desired position includes an axially displaceable piston  36  and roller support stem  38 . As shown, the piston itself comprises a head portion  40  and first and second axial portions  42 ,  44  of slimmer profile than head  40  and which extend in opposite directions to each other from said head portion  40 . The free end of portion  42  forms a proximal end of the piston  36  and is shaped to receive a proximal end  38   a  of the roller support stem  38  which is itself suitably shaped for being received by the proximal end of the piston  36 . In this particular arrangement the stem  38  is provided with a spherical ball portion  38   b  shaped for being received by a complimentary internally spherical portion  42   b  on portion  42 . Such spherical joints are well known in the art and may be formed by simply swaging (deforming) the concave portion around the ball portion  38   b  and thereby capturing said ball portion within portion  42 . The spherical jointing allows the stem  38  to move laterally in the direction of, for example, arrows B—B. The roller must also be capable of rotation in the direction of arrows A—A. In the present embodiment this facility is provided by virtue of the piston  36  being free to rotate about its axis. Whilst the operation will be described in more detail later herein, it will be appreciated that simpler jointing arrangements can be employed if just one or other of the two motions is desired. For example, a simple pinned joint would facilitate motion in the direction of arrows B—B only. Other arrangements will present themselves to a person skilled in the art. 
   Further features of the control unit  34  include an internal bore  45  within the piston  36  through which the stem  38  extends towards a roller support head  46 . The sizes of the bore  44  and the stem  38  are selected so as to allow the desired degree of stem/roller motion without interference between the two components. If necessary, the outlet end  45   a  of bore  45  may be internally relieved to allow more clearance. The head portion  40  is provided with sealing lands  48  for sealing against an inner surface  50  of an outer ring  52 . Outer ring, or cylinder liner,  52  comprises radially and axially extending portions  54 ,  56  respectively and is shaped to fit within a complimentary hole in a casing portion  58  which may be the casing of the IVT itself Portion  54  is provided with sealing lands  60  which seal against portion  44  and a sealing ring  62  which seals its radially outer edge within the hole in casing  58 . Also provided in portion  54  is a recess  64  which may be formed by segments of a circle or an entire circle, the function of which will be explained later herein. The radially extending portion is also provided with a number of features, the first of which is a circumferentially extending step portion  66  which engages with a corresponding step portion  68  formed in casing  58 . Between them the two step portions  66 ,  68  act to locate the ring or cylinder liner  52  in the desired axial location relative to the casing  58 . Additionally, the ring  52  is provided with an external groove  70  and associated seal  72  for sealing the outer side of the ring relative to the casing  58 . The reasons for this seal will become apparent later herein. A first end of the ring  52  is provided with a tapered portion  74  having a tip  76  for engagement up against an end-cap  78  which is also sealably secured to the casing by means of a circlip  80  or some such device. The other end of portion  52  is provided with a circumferentially extending recess or channel  82  for receiving hydraulic actuation fluid from an inlet  84  provided in casing  58 . The recess  82  extends axially and is provided at one end with a plurality of radially extending holes  86  which connect said channel with first piston chamber  88  formed within the control unit itself As shown, the holes  86  extend into a region of chamber  88  which is radially outward of the external surface of piston head  40  and fluidly connected to recess  64 . The end-cap  78  is also provided with a circumferentially extending recess  92  but this only extends through part of the circumference such that the tip  76  of portion  52  contacts at least a portion of the surface  94  provided on the end-cap  78 . As shown, the recess  92  bridges tip  76  such that hydraulic actuation fluid supplied via inlet  96  passes around tip  76 , into recess  92  and thence into annular chamber  98  within the actuation control unit itself. The end-cap  78  receives portion  42  into a suitably sized cavity  102  provided therein. This cavity may be provided with a fluid drain to ensure fluid therein may be displaced during piston motion. Again, a suitable ring seal  104  is provided between the end-cap  78  and portion  42 . Further components of the  FIG. 2  embodiment include a roller support carriage  46  mounted on the support stem  38  in which is mounted a roller  26  which is itself freely rotatably therein by means of bearings  108  and shaft  110 . 
   Assembly of the above-mentioned arrangement simply requires the insertion of portions  52 ,  54  into a suitably shaped and positioned hole within the casing  58  such that the two step portions  66 ,  68  engage and define the axial positions of portion  52 . Piston  34  is then assembled within liner portion  52  by passing portion  44  through the hole defined by sealing land  60  such that it protrudes through the other side thereof. The roller head portion  46  may then be securely attached to stem  38  by bolting or any other such suitable means before end cap  78  is introduced over the otherwise free end  42  of piston  40 . As described above, end cap  78  is provided with a surface which engages with the tip  76  of portion  52  such as to define the axial portion of end cap  78 . Once in position, end cap  78  is secured within the hole by means of circlips  80  and the assembly process is complete. Disassembly simply requires the reversal of the above-mentioned assembly process. 
   In operation, hydraulic roller control fluid is applied at different pressures to inlets  84 ,  96  by means of a differential pressure control device shown schematically at  110 . The fluid from inlet  84  passes into annular chamber  82  before entering holes  86  and passing into chamber  88 . Fluid entering inlet  96  deviates past tip  76  and into recess  92  before entering annular chamber  98 . Depending upon the pressures within chambers  88 ,  98  the piston will either remain stationary or move in accordance with the change in pressure so as to alter the position of roller  26 . The seals discussed above act to ensure the hydraulic integrity of chambers  88 ,  98 . 
   It will be appreciated that the inventive feature of the above arrangement may be used in a “single acting” piston, that is to say a piston having but one actuation chamber  88 ,  98 . In such an arrangement (not shown) one would simply delete chamber  89  and portion  44  such that actuation is achieved by input of fluid to chamber  98  only. A spring may be used to offer a return assistance against the action of the hydraulic fluid should that prove desirable. 
   It will also be appreciated that, whilst the above arrangement has been described with specific reference to IVTs the actuation mechanism of the control unit may be employed in a number of different situations such as, for example, the operation of robot arms or manipulator devices. 
   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.