Patent Publication Number: US-H2188-H

Title: Transmission system

Description:
FIELD OF INVENTION 
   This invention relates to transmission systems and has particular application to continuously variable transmissions. It is based on the ideas contained in our earlier International Application PCT/NZ99/00186, published as WO 00/45068 entitled Continuously Variable Transmission, and published in the name of Gyro Holdings Limited. 
   BACKGROUND OF THE INVENTION 
   The abstract of that PCT specification PCT/NZ99/00186 (published as WO 00/45068) described one example of a Continuously Variable Transmission. That abstract was based on various configurations including that shown in  FIG. 10 , and said: A transmission is provided which comprises a fixed housing or support  105 , input means  121 ,  156  moveable relative to said support and a torque shaft  112  rotatable about its longitudinal axis and a driven shaft arranged to be rotated about its longitudinal axis by the torque shaft  112 , a first one-way clutch  102  between the torque shaft  112  and driven shaft  104 , linkage means  117 ,  134 ,  135 ,  132 ,  140 ,  147 ,  158 ,  170  rotatable about the axis of rotation of the driven shaft  104  under the influence of said input means  121  and an inertial body  113 ,  160  mounted on the linkage means to be cyclically angularly deflected in response to the input means, the reaction forces generated by the inertial body  113 ,  160  as it is cyclically deflected being applied to the torque shaft  112  as positive and negative torque and the torque shaft  112  being connected over a second one-way clutch  101  opposite to the first one-way clutch  102  either to said support  105  or to the driven shaft  104  over a rotation reversal system  150 ,  151 ,  152  whereby the drive shaft  155  can be rotated by the torque shaft  112  in one sense of rotation only. The inertial body preferably comprises a rotor  113  so that gyroscopic forces are applied to the torque shaft  112 . 
   Various methods were described in said PCT application to generate and control the output torque. The methods described to spin the rotor varied from using an independent source to drive the rotor, to driving the rotor from the transmission input using gear trains and a one-way clutch. 
   The main method described to control the output torque involved controlling the independent source driving the rotor. Therefore when it is desired to maintain the input speed within narrow limits the only option left would be an independent source to drive the rotor to control the output torque by controlling the rotor speed. 
   The method of driving the rotor by an independent source such as an electric motor, while it is attractive poses challenges such as access to power supply, motor construction to withstand complex dynamic conditions and operating environment and therefore a subject for future development. 
   The method of driving the rotor by the input rotation through gear trains and one-way clutch, while it may be satisfactory for non-differential type configurations poses problems when used for differential type configurations as described in FIG.  10 . This is due to the relatively high loadings on the rotor drive gear train caused by the accelerations and decelerations of the sub-frame that carry the rotor. The differential type configuration is preferred in many applications due to compactness, dynamic balancing etc. 
   OBJECT OF THE INVENTION 
   It is an object of this invention to provide improved transmission systems, or systems which will at least provide the public with a useful choice. 
   SUMMARY OF THE INVENTION 
   The subject matter of PCT/NZ99/00186 is incorporated herein by reference. 
   A transmission will be considered a gyroscopic continuously variable transmission (“GVT”) if it comprises or includes: a fixed housing or support; an input member which is either rotatable about an axis of rotation relative to said fixed housing or support or reciprocable along an axis relative to said fixed housing or support; a torque shaft; and an output member arranged to be rotated about an axis of rotation by the torque shaft; a first one-way clutch between the torque shaft and output member; a linkage arrangement rotatable about the axis of the input member under the influence of said input member; and a gyroscopic rotor mounted on the linkage arrangement and having a spin axis which is cyclically angularly deflected in response to the input member to generate gyroscopic reaction forces, the reaction forces generated by the rotor as its axis is cyclically deflected being applied to the torque shaft as positive and negative torque; the first-one way clutch being configured to apply the positive torque to the output member; and the torque shaft being connected over a second one-way clutch opposite to the first one-way clutch either to said housing or support to apply the negative torque to the housing or support, or alternatively to the output member over a rotation reversal system to apply the negative torque to the output member as positive torque; with the arrangement of the first and second one-way clutches being such that the output member is rotated by the torque shaft in one sense of rotation only. 
   We have discovered a number of different ways of controlling the output torque of a continuously variable transmission. These control methods, and different transmission systems include using gyroscopic continuously variable transmission units (“GVT” units) such as described in PCT/NZ99/00186 in conjunction with differential gear units such as epicyclic units or coupling together two or more of the GVT units. In one example we illustrate split power transmission using at least one GVT unit. In another example we illustrate parallel coupling of two GVT&#39;s, in another example we illustrate a series coupling of two or more GVT&#39;s. We also describe varying the torque shaft inertia. We also illustrate differential type configurations of the GVT&#39;s. 
   In one aspect, the invention provides a transmission system containing at least one gyroscopic continuously variable transmission unit, and means for controlling the transmission output by controlling the input shaft, or the torque shaft, or by coupling together two or more gyroscopic continuously variable transmission units. 
   The transmission unit may preferably include a linear reciprocable input shaft, wherein the stroke length or effective stroke length of input shaft is adjustable to adjust the output characteristics of the transmission system. 
   In another aspect, the invention provides a wind turbine including a turbine rotor operatively connected to a shaft, a cam member having a camming surface and which is operatively connected to the shaft such that rotation of the rotor shaft rotates the cam member, and at least one gyroscopic continuously variable transmission unit having a housing fixed relative to a main wind turbine housing and having a reciprocable input member arranged to be reciprocated by the camming surface of the cam member upon rotation of the wind turbine rotor. 
   In another aspect, the invention provides a wind turbine including a turbine rotor operatively connected to a shaft, a cam member having a camming surface and which is fixed relative to a main wind turbine housing, and at least one gyroscopic variable transmission unit having a housing which is arranged to be rotated about a wind turbine rotor shaft axis as the wind turbine rotor rotates, the or each gyroscopic continuously variable transmission unit having a reciprocable input member arranged to be reciprocated by the camming surface of the cam member as the transmission unit(s) is/are moved by the wind turbine rotor. 
   Also described is a GVT having a rotor assembly mounted on the sub-frame and including a rotor with an axis substantially at right angles to the axis of the sub-frame and a one-way clutch to engage the rotor to a fixed member of the sub-frame whereby the speed of the main-frame is imparted to the rotor by the fixed member and the one-way clutch during one half of the rotation of the sub-frame about its axis and during the other half of the rotation the rotation of said fixed member is such that the rotor is allowed to free wheel by the one-way clutch. 
   Means may be provided whereby the speed of rotation of the rotor can be regulated and thereby control the output torque. 
   Alternatively varying the inertia of the torque shaft can control the output torque. This method is effective when the output speed is greater than zero and hence most useful in split power transmission using at least one GVT unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the present invention are described by way of example only, with reference to the accompanying drawings in which: 
       FIG. 1  illustrates the differential type configuration of the GVT. 
       FIG. 2  shows the rotor driving means for a differential type configuration described by the present invention. 
       FIG. 3  shows a means of controlling the rotor speed. In this arrangement a spring-loaded brake is shown with centrifugal release. 
       FIG. 4  shows an epicyclic differential gear unit with provision for split power transmission. 
       FIG. 5  illustrates a parallel coupling between two of the GVT units. 
       FIG. 6  illustrates a series coupling between two of the GVT units. 
       FIG. 7  illustrates storage and retrieval of mechanical energy using GVT units. 
       FIG. 8  illustrates an alternative method of rotor drive to that described in FIG.  2 . 
       FIG. 9  (prior art) illustrates one configuration of the GVT of our earlier PCT/NZ99/00186 and is taken from  FIG. 13  of that document. 
       FIG. 10  illustrates a bearing arrangement for supporting the rotor on the sub-frame. 
       FIG. 11  illustrates a cross-sectional view along line A—A of FIG.  10 . 
       FIG. 12  is a close up view of a single vane of the bearing arrangement of  FIG. 10 , showing useful features. 
       FIG. 13   a  is a schematic part section side view of an arrangement to minimise radial loads on thrust bearings. 
       FIG. 13   b  is a schematic front view of the arrangement of  FIG. 13   a.    
       FIG. 14  is a three dimensional view of a transmission utilising GVT units in parallel. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Gyroscopic continuously variable transmissions are described in our International Patent Application PCT/NZ99/00186, and units such as that shown in  FIG. 13  thereof (see  FIG. 9  of this application) are examples of gyroscopic continuously variable transmission units (called “GVT” units). 
   EXAMPLE 1 
     FIG. 1  shows a differential type of configuration described therein. The transmission may have co-axial shafts  1  and  12 . Shaft  1  is attached to the mainframe  2  while the other shaft is rotatable relative to said mainframe. A sub-frame  3  is rotatable relative to said mainframe with its axis substantially perpendicular to the axes of the co-axial shafts  1  and  12 . A right-angled gear train  7 ,  42  is used to couple the sub-frame  3  to the shaft  12  so that the differential speed between the shaft  12  and the mainframe  2  is transferred to the sub-frame  3 . 
   Shaft  1  is coupled to the input while the shaft  12  is fitted with a pair of opposed one-way clutches  10  and  11 . Clutch  10  is operable to engage the shaft  12  to the transmission housing while the clutch  11  is operable to engage the shaft  12  to the output gear  13 . 
   EXAMPLE 2 
     FIG. 2  shows an arrangement whereby the rotor  9  in  FIG. 1  will be driven by the input rotation without the aid of a gear train. 
   The shaft  8  is concentric with the rotor  9  and locked to the sub-frame  3  by means such as splines at the ends. The rotor  9  is mounted on the shaft  8  on bearings  24 . One-way clutch  25  engages the rotor to the shaft  8 . 
   As the input shaft  1  rotates the differential rotation between the input shaft  1  and the torque shaft  12  is transferred to the shaft  5  by the gears  7  and  42 . As the sub-frame  3  is attached to the shaft  5  it will also rotate and the orientation of the shaft  8  will change relative to the axis of the mainframe  2 . 
   When the axis of the shaft  8  is parallel to the axis of the mainframe the speed of the shaft  8  about its axis reaches a maximum value equal to the input speed. The speed of the shaft  8  about its axis will thus vary sinusoidally as the sub-frame completes a full rotation about its axis, reaching maximum opposite values when the shaft  8  is parallel to the mainframe axis and zero value when the shaft  8  is at right angles to the axis of the mainframe. 
   The one-way clutch  25  will thus impart the input speed to the rotor  9 . 
   It is possible to control the transmission output torque by varying the torque shaft inertia. This would be useful in split power transmission such as shown in FIG.  5  and described below. In order to control the output torque of the gyroscopic continuously variable transmission by varying the torque shaft inertia, sufficient speed should be available on the output shaft of the transmission. This is not always available unless the gyroscopic continuously variable transmission is used in suitable configurations. Such examples are described below. 
   EXAMPLE 3 
   An epicyclic gear unit is shown in  FIG. 4  where the sun gear  36 , the planet carrier  35  and the annulus  34  are all rotatable as in split power transmission. If one of these members is coupled to the output of the gyroscopic continuously variable transmission then it is possible to have the output of the gyroscopic transmission in rotation while the final output may still be at rest. For instance the sun gear may be connected to the GVT output, and the ring gear and the planet carrier to the input and the load respectively or vice versa and the GVT input may be connected to the input of the transmission if desired. Such an arrangement is an example only, and would be suitable for transport applications. 
   In another instance the sun gear may be connected to the load and the ring gear and the planet carrier to the input and the GVT output respectively or vice versa and the GVT input may be connected to the load if desired. Such arrangement is an example only and is suitable for power generation applications. 
   Declutching 
   By combining the epicyclic gear unit of  FIG. 4  with a GVT system in which the inertia of the torque shaft is adjustable, declutching can occur, which is when there is zero output torque at the overall output of the system even when there is input movement. 
   By having adjustable inertia of the torque shaft, the amount of torque applied to the output shaft can be varied. 
   This type of declutching is useful when declutching cannot be achieved by reducing the rotor speed to zero—for example when minimal response time is available or the rotor is being driven by the input motion. 
   Declutching can be achieved in a linearly reciprocating input GVT by selectively freeing the input movement from the linkage arrangement. This could be achieved for example by providing a hydraulic ram as a member of the linkage arrangement with a by-pass valve. By opening the by-pass valve of the hydraulic cylinder, the piston will be free to move relative to the cylinder so that no input movement occurs at the GVT and hence no torque is transferred to the transmission output. When the valve is closed, power will be transmitted through the system. 
   In general, the GVT units can be modified in different ways, and can be combined to allow for greater control over the output. Some of these combinations will be described below. For example a parallel coupling is shown in  FIG. 5. A  series coupling is shown in FIG.  6 . The GVT can also be used as a variator for split power transmission with particular advantage as described with reference to FIG.  4 . Another useful application of the GVT is for efficient storage and retrieval of mechanical energy. 
   The series coupling provides an example using the torque shaft inertia to control the transmission and is provided by using the gyroscopic continuously variable transmissions in series—this is described and illustrated below in example 7. In this case, the input is coupled to the input of the first gyroscopic continuously variable transmission and the output of the first gyroscopic continuously variable transmission is coupled to the input of a second gyroscopic continuously variable transmission. The output from the second gyroscopic continuously variable transmission is coupled to the final output. The torque shaft inertia variation will be provided to the first gyroscopic continuously variable transmission. This example is particularly advantageous for transport applications. 
   In operation, even when the final output speed is. zero the output speed of first unit can be greater than zero with zero output torque. By varying the torque shaft inertia the output speed of the first unit will be varied and hence the input speed to the second unit. 
   EXAMPLE 4 
     FIG. 3  shows an example of arrangement whereby braking action may control the speed of the rotor and thereby the gyroscopic continuously variable transmission. 
   The brake shoe  31  is pressed against the rotor  9  by springs  29 . A centrifugal weight  26  may be used as an example to release the brake. In the arrangement shown a thrust bearing  27  is provided between the centrifugal weight and the stem of the brake  28  and the centrifugal weight is prevented from rotating about the sub-frame axis by the pins  32  between the centrifugal weight  26  and the mainframe  2 . 
   If the sub-frame inertia is so designed that with the rotor  9  locked by the brake the output torque is zero, then the above-described arrangement provides a means of predetermining the input speed below which the output torque is zero i.e. equivalent to de-clutch or neutral gear in convention gear systems. 
   EXAMPLE 5 
   Parallel Coupling 
   This is shown in  FIG. 5. 72  is the input source such as a motor.  80  are GVT units and  76  is the load.  73 ,  74 ,  13  and  75  are gears for the parallel coupling. Several GVT units can be coupled in parallel with no adverse effects. Conventional CVTs transmit torque and therefore when coupled in parallel require exactly identical speed ratios if they are to share the power transmission. This condition does not apply to GVT as it does not transmit torque but rather generates torque, based on speeds of the various components. 
   The advantages of parallel coupling are:
         (a) Several units can be used to transmit power from one or more inputs to one or more outputs.   (b) Because of (a) there is practically no limitation to the overall transmission capacity.       

   EXAMPLE 6 
   Series Coupling 
   An example of this is shown in FIG.  6 . Other than as mentioned here, the numbering is the same as in  FIG. 5. 78  are the GVT output shafts and  77  are couplings. As described previously, series coupling provides the opportunity to control the transmission by varying the inertia of the torque shaft of the first unit. In general the advantage of the series coupling is to provide a variable input speed to the second unit to which the final output is coupled from the output of the first unit to which the transmission input is coupled while the transmission input speed can remain constant. 
   EXAMPLE 7 
   Split Power Transmission 
   This is described in Example 3, with reference to  FIG. 4 , above. The GVT can either input power into the differential unit such as the epicyclic or draw power out of the differential unit. 
   One key advantage of the split power arrangement will be to provide a versatile variable transmission such as the GVT itself but the GVT capacity required can be much less than the overall transmission. For example in wind power application a constant speed generator, variable speed turbine and GVT output can be coupled to the epicyclic and since the turbine torque should vary as a function of the square of the turbine speed for maximum turbine efficiency, the theoretical power capacity required by the GVT is only 14.8% of the turbine capacity. 
   EXAMPLE 8 
   Storage and Retrieval of Mechanical Energy 
   This is schematically shown in FIG.  7 . Other than as mentioned here, the numbering is the same as in  FIG. 5. 79  is a flywheel. 
   One of the unique features of GVT transmissions is their large range of speed ratios. This can be exploited to store and retrieve energy using a flywheel. In order achieve this, a first unit will be coupled to the variable input source and the flywheel and the input torque will be varied to maintain optimum input conditions. The second unit will be used to draw energy from the flywheel to the output and the input torque of the second unit can be varied to match the output requirement. 
   EXAMPLE 9 
     FIG. 8  illustrates a very useful modification to the rotor drive and control described with reference to  FIGS. 1 and 2  above. This is very useful when the input speed is relatively high and constant. This arrangement will avoid very high one-way clutch loadings if the engine speed remains constant at high value but the rotor speed has to vary from zero to maximum. 
     3  is the sub-frame and shaft  8  is fixed to the sub-frame  3  as before.  9  is the rotor. 
   In this arrangement the member  50  is mounted on the shaft  8  with bearings  53  and  57  and a one-way clutch  55  couples the shaft  8  to the member  50 . 
   The member  51  is provided if necessary to balance the gyroscopic and other dynamic forces on the member  50  by providing a one-way clutch  54  in opposite sense to that of  55 . The member  51  may be mounted on the shaft  8  by the bearings  52  and  56 . The member  50  is provided with means to gradually couple the rotor  9  to itself by such as eddy current braking. 
   In this example the rotor is mounted on the members  50  and  51  by the bearings  58  and  59 . 
   In operation, the input speed is raised and maintained at a fixed speed and the members  50  and  51  gain spin speed relative to the shaft  8  but in opposite directions while the rotor does not gain spin speed. However when the coupling means is energised the rotor gradually becomes coupled to the member  50  causing net output torque. 
   Stroke Length Variation 
   The output characteristics of a GVT can be varied by varying the stroke length of the input member/shaft, or at least the effective stroke length. This could be achieved for example by varying the geometry of the linkage arrangement which operatively connects the input member/shaft to the rotor arrangement. The linkage arrangement geometry can be easily varied during the reaction stroke when forces in the linkage arrangement are small. 
   Rotor Bearing Arrangement 
     FIGS. 10 and 11  show a preferred bearing arrangement for supporting the rotor  9 ′ on the sub-frame  3 ′. The rotor includes a boss part  200  having a tapered blind aperture  202 . The rotor will also be provided with a further boss part (not shown) on the opposite side of the rotor, which also has a blind aperture. For the sake of explanation, the rotor can be considered to be symmetrical about line A—A, although that would not be essential. The stubs  8 ′ (only one of which is shown) extend from the sub-frame  3 ′ and are positioned in the blind apertures of the boss parts. Each stub  8 ′ and aperture  202  forms a conical frustum of annular cavity  212  with convex and concave ends formed between the tapered blind apertures  202  and the tapered surfaces of the stubs  8 ′. 
   The annular cavity  212  is divided into linear chambers around the centre line CL of the boss/stub by vanes  208 . The vanes are either positioned in slots in the stubs  8 ′ as shown, or alternatively in slots in the apertures  202  of the boss parts  200 . The vanes can slide radially in the slots. While four vanes  208  are shown in  FIG. 12 , a greater or lesser number of vanes could be provided as required. A greater number of vanes will reduce the net side thrust from oil pressure on the vanes during operation. 
   The ends of the stubs  8 ′ and vanes  208 , the sub-frame surfaces  207 , and the shoulders  1206  of the bosses  200  and the surfaces at the bases of the apertures  202  are all substantially spherical, with centres coincident with the intersection CP of the sub-frame axis and the main frame axis. These surfaces seal the annular cavity  212 . The chambers of the cavity are filled with lubricating fluid. Each oil chamber between the adjacent vanes is in communication with a low pressure lubrication source such as a pump, via independent non-return valves. 
   The vane need not have the broader base  210  and therefore can also appear as in FIG.  11 . 
   Using this arrangement, viscous shear losses can be minimised by providing a relatively large lubricant space, and at the same time flow losses can be minimised through direct contact between the spherical surfaces of the vanes, stubs, sub-frame, and aperture in the rotor. When a greater number of vanes are used, side thrust on each vane due to pressure differences between either side of the vane is reduced. The arrangement shown allows some radial movement between the sub-frame/stub shaft and the rotor while developing the bearing support pressure when the rotor is loaded with fluctuating gyroscopic reaction torque. This bearing arrangement is feasible only because the gyroscopic loading is changing in direction all the time. 
   FIG.  12  and  FIG. 13  show details of the arrangement of the vanes  208  in cross sections. Each vane is slidably mounted in an aperture  216  in the stub shaft  8 ′, and a biasing device such as a spring pad  218  biases the vane radially outwardly relative to the stub shaft. The spring pad is fixed to the stub or the vane so as to inhibit sideways movement and also to act as a partition between the fluid on the left and the right side of the vane. By providing holes  214 , the fluid pressure at the top and the bottom of the vane is equalised. Seals  222  may be provided between the walls of the aperture  216  and the vane if required. Alternatively, a flow path may be provided around the outside of the vanes, so that fluid can flow between each vane and the wall of the respective aperture  216 , to equalize the pressure at the top and bottom of the vanes. The flow path could be provided by apertures in the stubs  8 ′, rather than in the vanes. 
   In operation, oil pressure is developed in the corresponding chambers of the annular cavity  212  when reaction torque is applied on the rotor  9 ′ as the rotor tries to rotate relative to the stubs  8 ′ about the centre CP under the influence of the torque. In general the pressure developed is not equal on either side of the vane. Further the pressure developed will push the vane into the slot unless the pressure force is balanced from the base of the vane. This is achieved by pressure balancing holes  214  and a seal  218  at the base as shown in FIG.  12 . This seal should also provide some spring action to keep the base of the vane away from the base of the slot and provide some lateral stiffness to itself against the force due to unequal pressure on either side of the vane. Seals  222  on the sides of the vanes are not critical. 
   The rotor will attempt to rotate in all directions about its centre point CP. When, for example, the rotor attempts to turn anticlockwise about CP, due to the incompressibility of the lubricating fluid, pressure will develop in the upper chambers  212  of the left hand bearing and the lower chambers of the right hand bearing to resist torque, and a low pressure region will be formed in the lower chambers of the left hand bearing and the upper chambers of the right hand bearing. At that time, lubricant can be delivered into the low pressure chambers from the pump via non-return valves. Similarly, when the rotor attempts to turn clockwise, lubricant can be delivered into the upper chambers of the left hand bearing and lower chambers of the right hand bearing, which will be at low pressure. 
   If desired, a roller or rod could be provided in a groove or aperture in the end of each vane  208  which contacts the wall  202  of the boss  200 . The grooves or apertures will be capable of retaining the rollers, say by having a cross section greater than 180 degrees. The rollers will not be subjected to loading as the oil pressure will take care of the loadings. 
   Minimising Radial Loads for the use of Hydraulic Thrust Bearings 
     FIGS. 13   a  and  13   b  show a GVT having an alternative linkage arrangement for eliminating or minimising radial loads on thrust bearings. In this embodiment, a reciprocating input member  1 ” includes an input shaft  1   a  having an internal chamber in its base, and a piston  1   b  movably received in the chamber to define a double thrust bearing. Alternatively, the chamber could be formed in component  1   b  with the shaft  1   a  being formed as a piston. The chamber will contain a fluid such as lubricating oil, and will be sealed by a seal around the piston shaft. As the input shaft  1   a  moves downwards, a high pressure region develops above the piston, and when the shaft  1   a  moves upwards a high pressure region develops below the piston. This arrangement enhances the rotational movement of the piston within the chamber, which is required for operation of the GVT. The upper and lower parts of the chamber may be in fluid communication with a pump via non-return valves, so fluid can be transferred to the low pressure side. 
   However, with such a thrust bearing it is important to minimise side loadings. In the embodiment shown, a linkage arrangement is provided to reduce the side loadings. As can be seen, the GVT includes a main frame  2 ″, a rotor  9 ″ carried by a sub-frame  3 ″, and a linkage arrangement indicated generally by reference number  12 ″ which connects the sub-frame and input. The input shaft  1   b  is connected to a cross member  12   a.  At one end, the cross member is pivotally connected to a link  12   b,  which at its opposite end is pivotally connected to a crank  12   c.  The crank  12   c  is rigidly attached to the sub-frame  3 ″ which is rotatably mounted on a bearing on a shaft P 1  which is fixed to the main frame. At the other end, the cross member  12   a  is pivotally connected to a link  12   d,  which at its opposite end is pivotally connected to a double crank  12   e  which has two crank parts  12   e ′,  12   e ″ which have opposite orientations to crank  12   c.  The crank  12   e  is not attached to the sub-frame  3 ″ but is rotatably mounted in a similar manner to the sub-frame  3 ″ on a bearing on a shaft P 2  which is collinear to shaft P 1  which is fixed to the main frame. The crank part  12   e ″ is pivotally connected to a link  12   f,  which is pivotally connected to a link  12   g.  The other end of the link  12   g  is pivotally connected to a crank  12   h  which is rigidly attached to the subframe  3 ″. Crank  12   h  has the same orientation as crank  12   c.    
   In operation the force from the reciprocating member  1   b  is applied to the sub-frame cranks  12   c / 12   h  in the same direction and via the links  12   d / 12   b.  The transverse components of forces in  12   d / 12   b  are cancelled allowing  1 ″ to operate as a ram without transverse forces and at the same time allowing the shaft  1   b  to rotate relative to shaft  1   a.    
   Hollow Bearings 
   In the GVT, it is desirable that radial and thrust bearings should have good resistance against Brinelling or contact wear, as well as a high load rating. U.S. Pat. No. 5,071,265 and U.S. Pat. No. 5,033,877 describe thrust and radial bearings respectively in which the rollers are hollow. Such bearings are marketed by Kaydon Corporation of Muskegon, Mich., USA, under the HOLO-ROL trade mark. Those bearings have the advantage of reducing centrifugal loading from the rollers, and are shock absorbent due to being relatively flexible. They also generally have good radial stiffness. However, the bearings described in those documents have relatively low load rating. It is believed that by reducing the size of the apertures in the rollers relative to the outer diameter of the rollers, that will maintain the roller strength and load capacity and life of the bearings whilst still reducing contact stress (although by a lesser amount). 
   INDUSTRIAL APPLICATION 
   The transmission systems of this specification can be used in a number of different ways. Some of the examples are particularly suited to continuously variable transmissions for automotive use. Some of the systems described are particularly suited to the storage of energy, where the input shaft is subjected to fluctuating loads, for example windmill or wind turbine devices. 
     FIG. 14  shows a transmission using a number of reciprocable input GVT units in parallel. The embodiment shown is particularly useful for use in a wind turbine, but has other applications such as wave power or automotive. The wind turbine has a shaft  300  which will generally be rotatably driven by the wind turbine rotor (not shown). The rotor shaft  300  is operatively connected to a cam arrangement  302 , which transfers motion to the input members of a plurality of reciprocating input GVT units  304 . The outputs of the GVT units drive a gear arrangement  306 , which in turn drives an output member  307 . 
   The cam arrangement  302  has an annular cam member  304  having a camming surface  306 . The camming surface is configured to provide reciprocal motion of the input members  308  of the GVT units  304 . A roller arrangement  310  is provided at the end of each GVT input member  308 , and runs along the camming surface  306  as the cam member  304  is rotated by the wind turbine shaft  300 . The reciprocating motion of the GVT input members  308  causes movement of a linkage member  312 , which in turn moves an inner frame member  314  which carries a gyroscopic rotor  316 . Precession of the rotor results in rotation of an outer frame member  318  about an axis parallel to the input member  308 . Positive and negative torque from the outer frame member  318  are rectified by a pair of one way clutches inside a clutch housing  320 , and the positive torque is transmitted to an output member  324  of each GVT. The output of each GVT is operatively connected to a respective gear  324 , and the gears  324  are meshed with a main output gear  326  which transmits torque to the turbine output member  307 . 
   In operation, as the wind turbine rotor rotates, the shaft  300  rotates, which results in rotation of the cam member  304 . The portions of the camming surface  306  closest to the GVT units drive the GVT inputs  308  inwards, which result in precession of the axes of the GVT rotors. Positive and negative torque are rectified by the GVT arrangements, and positive torque is delivered to the gear members  324  and ultimately to the main output  307 . A further camming surface or spring arrangement may be provided to drive the GVT inputs  308  outwards following their inward movements. 
   The high possible speed ratio of a reciprocating input GVT results in a high wind turbine output member  307  speed for a low wind turbine rotor shaft  300  speed. 
   In the illustrated embodiment, the housing of each GVT unit is fixed relative to a wind turbine housing (not shown), and the cam member rotates relative to the wind turbine housing. In an alternative embodiment, the cam member could be fixed relative to the wind turbine housing, and the rotor shaft  300  could be configured to rotate the GVT units about the rotor shaft  300  axis to reciprocate their inputs. This is again suitable for wind turbines because of the relatively low turbine speeds. In this embodiment, reaction forces in the GVT units will drive their inputs outwardly following the inward movement from the camming surfaces. The rotation of the GVT units can be controlled to control the reaction force applied to the GVT input members, which drive them outwardly following the inward movement. A separate drive could be used to move, or alter the movement of, the GVT&#39;s relative to the camming surface. 
   That feature also has application for other GVT&#39;s, and the GVT housings could be rotated to control the reaction force which drives the GVT input outwardly. If the main GVT frame (such as  2 ″ in  FIG. 13   b ) is not moving, by rotating the GVT housing that will rotate the main frame, to provide the returning force for the GVT input member. 
   In the embodiment shown, regulation of output power could be achieved by sliding the cam and/or GVT units in an axial direction. 
   The turbine shaft can be locked by locking one or more the input linkages for maintenance and other purposes. 
   Other types of cams could be used to provide the reciprocating motion of the GVT inputs, for example axial (as shown), radial or oblique cams could be used. The wind turbine could use a single GVT unit if desired. 
   Many variations of the transmission systems described above are possible, and all such combinations of the GVT units, or other control systems described above, are possible, and are deemed to be covered herein whether or not such combinations are explicitly described, as for example the series of parallel coupling of different units. 
   Finally, various other alterations and modifications may be made to the foregoing without departing from the spirit or scope of this invention.