Abstract:
A fluid machine for a pneumatic or hydraulic drive system, said fluid machine being able to work as a fluid motor or as a fluid pump, comprising: at least two piston assemblies each comprising a piston means ( 110   a - c ), the at least two piston assemblies being operable to cause sequential reciprocating movement of the pistons means ( 110   a - c ); a drive member ( 120 ) rotatable about an axis and providing an annular, wave-like surface ( 122 ) extending at least partially radially to the axis, towards which the piston means ( 110   a - c ) project, wherein, in case of working as a fluid motor, the pistons means ( 110   a - c ) are arranged to drive rotation of the drive member ( 120 ) about the axis at least by a pushing action on said wave-like surface ( 122 ) or, in the case of working as a fluid pump, the piston means ( 110   a - c ) are arranged to cooperate with said wave-like surface ( 122 ) so that rotation of the drive member ( 120 ) drives sequential reciprocating motion of the piston means ( 110   a - c ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a fluid motor for a pneumatic or hydraulic drive system, and a fluid pump for such a system. 
       BACKGROUND 
       [0002]    Drive systems incorporating fluid motors and fluid pumps are known. The object of the present invention is to provide a fluid motor and a fluid pump that each operate more efficiently than known fluid motors and pumps. 
       SUMMARY OF THE INVENTION 
       [0003]    According to the present invention, there is provided a fluid motor for a pneumatic or hydraulic drive system, comprising: at least two piston assemblies each comprising a corresponding piston means, the at least two piston assemblies being operable to cause sequential reciprocating movement of the pistons means; a drive member rotatable about an axis and providing a surface radial to the axis and extending continuously around, onto which the pistons means may project; wherein the pistons means are arranged to drive rotation of the member about the axis at least by cooperating with said wave-like surface. 
         [0004]    According to the present invention, there is further provided a fluid pump for a pneumatic or hydraulic drive system, comprising: a drive member rotatable about an axis and providing an annular, wave-like surface extending at least partially radially to the axis; at least two piston assemblies each comprising a corresponding piston means, wherein the pistons means project towards the wave-like surface, wherein the at least two piston assemblies are arranged to cooperate so that rotation of the drive member about the axis drives sequential reciprocating motion of the piston means at least by a pushing action on said piston means. 
         [0005]    Optional and/or preferred features of the present invention are defined in the dependent claims. 
         [0006]    The fluid motor and the fluid pump improve upon fluid pumps and fluid motors disclosed in WO2014195666, providing more efficient transmission. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0007]    Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures in which: 
           [0008]      FIG. 1  is a view of a hub assembly incorporating a fluid motor in an accordance with an embodiment, the hub assembly being in built form; 
           [0009]      FIG. 2  is a side, exploded view of the hub assembly; 
           [0010]      FIG. 3  is a perspective side, exploded view of the hub assembly; 
           [0011]      FIG. 4  is a cross-sectional view of the hub assembly; 
           [0012]      FIG. 5  is a view of a fluid pump in accordance with an embodiment; 
           [0013]      FIG. 6  is a side, exploded view of the fluid pump; 
           [0014]      FIG. 7  is a perspective side, exploded view of the fluid pump; 
           [0015]      FIG. 8  is a view of the fluid pump in assembled form, with an outer casing and end plate absent; and 
           [0016]      FIG. 9  is a view of cross-sectional view of the fluid pump in assembled form. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0017]    Like parts are denoted by like numerals throughout. 
         [0018]    In the following, a hub assembly for a wheel of a bicycle incorporating a fluid motor in accordance with an embodiment will be described. A fluid pump operable by a pedalling action will also be described, which can be coupled to the fluid motor to drive rotation of the hub. 
         [0019]    Certain terminology will be used in the following description for convenience and reference only, and should not be considered limiting. The term “fluid” encompasses both liquids and gases. In the context of hydraulic systems, this term should be considered to be a substantially incompressible flowable material such as a liquid or gel, for example oil. In the context of pneumatic systems, this term should be considered to be a gas, typically an inert gas such as nitrogen or air. A “forwards direction” is the angular direction of rotation in which a hub assembly or drive shaft of a fluid pump turns when the bicycle incorporating the hub assembly or the drive shaft is moving in a forwards direction. 
         [0020]    The hub assembly to be described is intended for use in a bicycle, to drive a rear wheel of the bicycle. The hub assembly may alternatively be used in the front wheel of a bicycle. The fluid motor that is incorporated in the hub assembly has other applications. Application of a fluid motor in accordance with embodiments and/or a hub assembly in accordance with other embodiments is not limited to use in a bicycle. For example, embodiments may be used in a wheel of other kinds of vehicle such as motorcycles, scooters, cars, heavy goods vehicles and heavy equipment. “Heavy equipment” refers to heavy-duty vehicles, in particular those specifically designed for performing construction tasks, most frequently ones involving earthwork operations. Embodiments may also be used in other hydraulic systems where reduction or amplification of rotational force is desired, or where conversion of pressure to rotary motion is desired. 
         [0021]    Referring to  FIGS. 1 to 4 , the hub assembly is configured for attaching to a frame of a bicycle. This may be done by welding, for example, or by means enabling quick release of a wheel from a bicycle. The hub assembly has some parts that are fixed relative to the frame, a motion conversion mechanism, and other parts that rotate relative to an axis of the hub assembly. 
         [0022]    The fixed parts include a main structural member, indicated generally at  10 , a threaded nut  12 , a first end plate  14  and a threaded end piece  16 . The main structural member  10  comprises a cylindrical rod  18 , a first cylindrical block portion  20   a ,  20   b  of greater diameter than the rod  18 , a second cylindrical block portion  22  of greater diameter than the first cylindrical block  20   a ,  20   b , an annular stepped seat portion  24 , three frame portions  26   a - c  and a second end plate  28 . The main structural member is formed of a single piece, although it could be formed of multiple parts and assembled. 
         [0023]    The cylindrical rod  18  extends from a first side of the hub assembly to the second side. First and second ends of the rod  18  extend for attachment to the frame of the bicycle. Each of the cylindrical parts mentioned above have as their central axis the axis of rotation of the rotatable parts of the hub assembly. The first block portion has a part  20   a  thereof adjacent the second block portion  22 , which is threaded. The second block portion  22  has a threaded outer surface. 
         [0024]    Each of the frame portions  26   a - c  form a cylinder portion, which partially define a respective fluid chamber. The second end plate  28  has three holes (one shown at  29 ) therein each enabling an external fluid-containing line (not shown) to sealingly connect with a corresponding one of the chambers so that the chamber and the line are in fluid communication. Each fluid-containing line is connected to a pressure generation system, which is configured to cause the fluid in each fluid-containing line to reciprocate or pulsate and thus move into and out of the corresponding chamber. 
         [0025]    The motion conversion mechanism includes three pistons  30   a - c  spaced at angular intervals around the central axis of the hub assembly. The cylinder portions provided by the frame portions  26   a - c  and the pistons  30   a - c  are configured to cooperate so that each of the pistons  30   a - c  can reciprocate in a corresponding one of the cylinder portions. Each piston  30   a - c  has an annular groove  32   a - c  extending therearound in which a lip seal  31  is located to prevent egress of fluid from the chambers. 
         [0026]    Each piston  30   a - c  has a body and a head end and is arranged for reciprocating movement parallel to the central axis. The head end has three roller pieces  36   a - c  held to a projection of the body by a pin  37 . A first and second of the roller pieces extend each from a respective side of each piston and these engage with the corresponding frame portion  26   a - c  to support reciprocating movement thereof. The frame portions  26   a - c  provide, for each piston, a corresponding elongate slot  38   a - c  into which the first of these roller pieces extends to support reciprocating movement of the piston parallel to the axis. The frame portions  26   a - c  also provide, for each piston, a corresponding elongate recess  40   a - c  into which the second of these roller pieces extends to support reciprocating movement of the piston parallel to the axis. The frame portions  26   a - c  also having slits  39  therein enabling rotational movement of the drive cam  42 , which is described in greater detail below. 
         [0027]    The motion conversion mechanism also includes a drive cam indicated generally at  42 , and an annular bearing assembly  44 . The annular bearing assembly  44  is mounted on the stepped portion  24 . The stepped portion  24  provides a cylindrical annular surface on which the annular bearing assembly  44  sits, such that an inner surface of the annular bearing assembly  44  and an outer cylindrical surface of the stepped portion are flush. A radial surface of the stepped portion  24  prevents movement of the annular bearing assembly  44  beyond the stepped portion towards the first cylindrical disc  28 . The nut  12  is located on the second cylindrical block  22  by screw engagement, to prevent lateral movement of the annular bearing assembly  44  in the other direction. “Lateral” movement should herein be considered to be movement lengthwise of the central axis. 
         [0028]    The drive cam  42  comprises a cylindrical portion  46 , a circumferential ratcheting portion  48  and a driven portion  50 . The drive cam  42  is located over the annular bearing assembly  44 , so that the drive cam  42  can rotate on the annular bearing assembly. An inner surface of the cylindrical portion fits flush over the outer surface of the annular bearing assembly  44 . 
         [0029]    The driven portion  50  provides a wave-like surface against which the heads  36   a - c  of the pistons  30   a - c  project. The wave-like surface extends continuously around the axis to present an annular surface that faces in a direction parallel to the central axis. By “wave-like”, it should be understood that the surface extends smoothly around the central axis and the radial location of the surface changes along the central axis. The surface may vary sinusoidally, for example. There are two peaks and two troughs in the surface, although in other embodiments the number of peaks and troughs may differ. The pistons  30   a - c  and this surface are arranged to cooperate so that when the pistons are driven so as to extend repeatedly in a consecutive sequence, the pistons  30   a - c  drives rotational motion of the drive member  42  in a forwards direction. 
         [0030]    The wave-like surface is sufficiently smooth as to allow movement of the surface against the pistons  30   a - c . In other embodiments, rollers may not be provided and other means of maintaining low friction between the wave-like surface and the heads of the pistons may. 
         [0031]    The annular bearing assembly  44  and the drive cam  42  are held in place on the threaded second block portion  22  by the nut  12 . Thus, lateral movement of the drive cam  42  is prevented. 
         [0032]    The hub assembly includes an outer sleeve  50 . First and second spaced circumferential flanges  52   a ,  52   b  extend radially from the outer sleeve  50 . Each has a plurality of regularly spaced holes therein to which spokes of a bicycle wheel may be secured. In other embodiments, spokes may not be required and the hub assembly may be otherwise integrated into a bicycle wheel. The outer sleeve comprises first and second cylindrical end portions  50   a ,  50   b  at which the diameter of the outer sleeve  50  is larger than over an intermediate portion thereof. This results in an annular stepped internal surface at each end of the outer sleeve  50 . First and second annular sleeve bearing assemblies  56   a ,  56   b  are each sized to locate in the outer sleeve  50 , so that each sleeve bearing assembly  56   a ,  56   b  is located flush against a respective one of the stepped internal surfaces. The sleeve bearing assemblies  56   a ,  56   b  are located to have the central axis at their axis and function to enable the outer sleeve  50  to rotate freely therearound. 
         [0033]    The outer sleeve  50  is arranged to contain the motion conversion mechanism. The first and second ends  52   a ,  52   b  of the outer sleeve  52  are respectively arranged to locate against the first and second end plates  14 ,  28 . This is achieved by each of the first and second end plates  14 ,  28  having an annular flange  58   a ,  58   b  extending around a circumferential outer surface thereof. Respective inner surfaces of the first and second ends  52   a ,  52   b  of the outer sleeve  50  respectively locate flush on the circumferential outer surface of the first and second end plates  14 ,  28 . The flanges  58   a ,  58   b  prevent lateral movement of the outer sleeve  50 . 
         [0034]    The threaded end piece  16  is secured to the threaded part  22   b  of the first block portion by screw engagement. To this end, both are sized appropriately. The threaded end piece  16  is secured against the first end plate  14 . The threaded end piece  16  is secured to press against the first end plate  14 , which presses against the first sleeve bearing assembly  56   b . The first sleeve bearing assembly  56   a  presses against a radial part of the stepped internal surface of the first end of the outer sleeve  52 . The second sleeve bearing assembly  56   b  is pressed by a radial part of the other stepped internal surface at the second end  52   b  of the outer sleeve. This presses against the flange  58   b  of the second end plate  28 . The result is that lateral movement of the outer sleeve  52  is prevented, but rotational movement of the outer sleeve  52  is permitted, subject to operation of the motion conversion mechanism. 
         [0035]    Although not shown, the outer sleeve  52  has an inwardly directed pawl that engages with the ratcheted portion  48  of the drive cam  42 . This provides a freewheel mechanism for the hub assembly, such that the hub can be rotated from its exterior in a forwards direction without engaging the interior motion conversion mechanism. Alternative freewheel mechanisms are known in the art and may be alternatively employed in other embodiments. Alternatively, in embodiments a freewheel mechanism may be absent and the drive cam  42  may be fixedly coupled or integrally formed with the outer sleeve  52  so that one cannot be moved without the other moving. 
         [0036]    In operation, fluid is provided sequentially to each of the fluid chambers via the fluid-containing lines. This causes each of the pistons  30   a - c  to sequentially extend and retract. Extension of the pistons  30   a - c  against the wave-like surface causes rotational motion of the drive cam  42  in a forwards direction. Rotation of the drive cam  42  in the forwards direction causes the freewheel mechanism to engage the outer sleeve  52 , causing rotation of the outer sleeve, and thus a wheel of which the hub assembly forms part. 
         [0037]    It will be appreciated by the skilled person that various modifications may be made to the hub assembly described above and the fluid motor incorporated in the hub assembly. 
         [0038]    As the skilled person will appreciate, in other embodiments the arrangement of the pistons and the wave-like surface may differ. Preferably but not essentially, the wave-like surface and the pistons may be configured so that the sequence of reciprocating movement of the pistons  30   a - c  causes rotational movement of the drive member  42  in a forwards direction only. 
         [0039]    A pressure generating system may be configured to cause fluid in each fluid containing line to move into the corresponding chamber in turn. Alternatively, depending on the shape of the drive cam, the hub assembly may be configured so that more than one piston pushes the drive cam at one time. It will be clear to the skilled person that there are various ways that a number of pistons may be configured to cooperate with the drive cam to cause it to rotate in a desired direction. 
         [0040]    A fluid pump is now described with reference to  FIGS. 5 to 9 , which may be used with the fluid motor described above. The fluid pump works using similar principles to the fluid motor described above. 
         [0041]    The fluid pump includes some parts that are fixed relative to the frame of a bicycle, a motion conversion mechanism, and rotating parts. Fixed parts comprise a cylindrical casing  100 , first and second annular bearing assemblies  104   a ,  104   b , and first and second annular end plates  106   a ,  106   b . A rotatable drive shaft  102  extends through the first and second annular bearing assemblies  104   a ,  104   b . The first and second annular bearing assemblies  104   a ,  104   b  carry the drive shaft  102  and allow low friction rotation of the drive shaft  102  about its central axis. The first and second annular end plates  106   a ,  106   b  extend inwardly from respective circular end edges of the cylindrical casing  100  to encase the first and second annular bearing assemblies  104   b . The first annular end plate  106   a  and the cylindrical casing  100  are formed of a single piece, although this need not be the case. The second end plate  106   b  and an end of the cylinder casing remote from the first end plate  106   a  have radially extending flanges  107   a ,  107   b ,save for where a window is provided in the cylindrical casing  100  for passage of fluid transmission lines. These flanges are arranged to lie flush one against the other and for attachment to each other. Holes in each flange enable the flanges to be bolted together, although the flanges may be otherwise attached together, for example by riveting. 
         [0042]    The second annular end plate  106   b  has three piston assemblies mounted thereon. Each piston assembly includes a cylinder portion  108   a - c  and a corresponding piston  110   a - c . Each cylinder portion  108   a - c  has a chamber therein defined by the walls of the cylinder portion  108   a - c  and an end of the respective piston  110   a - c . Each cylinder portion  108   a - c  has an aperture therein forming an inlet/outlet to the chamber, to which a fluid-containing line  112   a - c  is sealingly attached. The cylinder portions  108   a - c  are integrally formed with the second end plate  106   b , although they may be formed separately and attached. The fluid-containing lines  112   a - c  extends each from the respective cylinder portion  108   a - c  and are held in a mount  109 . The mount  109  is integrally formed with the second end plate  106   b , although may be formed separately and then attached. When the fluid pump is mounted on a bicycle frame, the fluid-containing lines preferably run along a chain stay to the fluid motor. The fluid-containing lines may run inside the chain stays. The chain stays may indeed be shaped to form part of the fluid-containing lines. Alternatively, the fluid-containing lines may extend though other tubes of a bicycle frame. 
         [0043]    Each piston  110   a - c  is mounted to allow reciprocating movement in the corresponding cylinder portion  108   a - c . Each cylinder portion  108   a - c  has a pair of facing slots  114   a - c  in sides thereof, extending parallel to the axis of the drive shaft  102 . Each piston  110   a - c  has a pin  116   a - c  extending therethrough. Each end of each pin  116   a - c  is moveable in a respective slot of the corresponding cylinder portion  108   a - c , to guide and support movement of the pistons  110   a - c  parallel to the axis of the drive shaft  102 . In variants, the piston  110   a - c  may have square cross-section, for example, to stop rotation of the pistons as they reciprocate in the cylinder portions  108   a - c.    
         [0044]    The drive shaft  102  is configured at each end thereof for mounting of an end of a crank arm (not shown). Where a crank arm is mounted, a pedal (also not shown) is also operatively attached to the other end of the crank arm to enable rotation of the drive shaft  102  with a pedalling action. The ends of the drive shaft  102  are shown as splined, but may be otherwise shaped for engagement of the crank arm. 
         [0045]    The fluid pump is for mounting in a bottom bracket of a bicycle frame. The bottom bracket may be larger than a conventional standard bottom bracket to accommodate the cylindrical casing  100 . Alternatively, the fluid pump may be modified from that shown in the figures so that it fits in a bottom bracket of a standard size. 
         [0046]    A motion conversion means includes a cam member  120  and the pistons  110   a - c . The cam member  120  is mounted on and rotatable about the drive shaft  102 . The cam member  120  is formed of a part-cylindrical piece  121  and a mounting portion  123 . The part-cylindrical piece  121  extends around the drive shaft  102  coaxially therewith. The mounting portion  123  mounts the part-cylindrical piece  121  on the drive shaft  102 . The part-cylindrical piece  121  provides an annular wave-like surface  122 . The wave-like surface is as characterised above in relation to the fluid motor. The annular surface  122  extends continuously around the drive shaft  102  coaxially therewith and faces near ends of the pistons  110   a - c . The wave-like surface has a four peaks and troughs, although in other embodiments a greater or lesser number may be provided. The pistons  110   a - c  and the cam member  120  are respectively disposed so that rotation of the drive member  120  causes the annular surface  122  to sequentially drive the pistons  110   a - c  into their respective cylinder portions  108   a - c.    
         [0047]    The cylinder portions  108   a - c  have slits  111   a - c  therein located to enable the part-cylindrical piece  121  to pass therethrough to the extent appropriate. This aids compactness and rigidity of the fluid pump, while enabling the cylinder portions  108   a - c  to extend to provide support for the pistons  110   a - c.    
         [0048]    The ends of the pistons  110   a - c  near the annular surface  122  also have slits  125   a - c  therein (“piston slits”). An annular edge of the part-cylindrical piece  121  including a portion of the annular surface  122  engages in the piston slits  125   a - c . This results in the portion of the annular surface  122  that pushes the pistons  110   a - c  abutting the pins of the pistons. The pins are rotatable about their axes. This aids smoothness of operation of the fluid pump. In a variant embodiment, the slit may not be present and the annular surface  122  may simply abut against an end of a respective body of the pistons  110   a - c . The ends may be curved, for example to have a semi-circular cross-section, for the sake of smoothness of operation. 
         [0049]    The cam member  120  is fixedly mounted onto the drive shaft  102 . The drive shaft  102  has a number of projections extending circumferentially around it forming a spline  124 . The mounting portion  123  has a plurality of projections for engaging with the spline  124 , so that rotation of the drive shaft  102  causes rotation of the cam member  120 . In variant embodiments, the cam member  120  is integrally formed with the drive shaft  102 . 
         [0050]    The mounting portion  123  is located between the spline  124  and the first annular bearing assembly  104   a . An annulus  126  around the drive shaft  102  is located to abut against the second annular bearing assembly  104   b . These parts are sized so that lateral movement along the drive shaft  102  is substantially prevented. The spline  124  and the annulus  126  are preferably integrally formed with the drive shaft  102 . 
         [0051]    In variant embodiments, the fluid pump may include a ratcheting assembly is configured so that rotation of the drive shaft  102  by a pedalling action in a forwards direction results in the drive shaft  102  turning in the same direction, whereas turning of the drive shaft  102  in the reverse direction does not. 
         [0052]    In operation, the drive shaft  102  is rotated by a user of the bicycle with a pedalling action in a forwards direction. The rotation of the drive shaft  102  causes the cam member  120  to rotate about the axis of the drive shaft  102 . As the annular surface  122  rotates, the annular surface pushes the pistons  110   a - c  into the respective cylinder portions  108   a - c . When a piston  110   a - c  is pushed into the respective cylinder portion  108   a - c , the end of the piston pushes fluid from the corresponding chamber. This results in a pulse in the fluid, which pushes a piston in the fluid motor to which the fluid pump is coupled. 
         [0053]    Typically, the nature of the hydraulic system comprising the fluid pump and the fluid motor will result in each piston  110   a - c  rebounding from the respective cylinder portion  108   a - c . In a variant, a spring or other resilient means may be provided so that each piston  108   a - c  is biased towards an extended position. 
         [0054]    Thus, rotation of the cam member  120  results in repeated sequential movement of the pistons  110   a - c  into and out of the corresponding cylinder portions  108   a - c , which causes reciprocating movement of fluid in the fluid-containing lines. 
         [0055]    The pump may be operated other than by a pedalling action. The drive shaft  102  may be rotated by any suitable means, for example an electric motor, a wheel or rotor of a turbine. 
         [0056]    Various modifications may be made to the above described embodiments, as will be clear to the skilled person. 
         [0057]    As mentioned above, the fluid pump described with reference to  FIGS. 1 to 4  and the fluid pump described with reference to  FIGS. 5 to 9  may be used together, in a bicycle or, possibly in a modified form, in other applications. It should be understood that the hub assembly described above can be used with a different design of pump than the one described—other designs of pump may be configured to cause reciprocating movement of fluid in one or more fluid-containing lines. In other words, the particular pump described is not essential to the motor. Similarly, the fluid pump described above can be used to drive a different design of fluid motor than the one described—other designs of fluid motor may be configured to be driven by reciprocating movement of fluid in one or more fluid-containing lines. 
         [0058]    It is well known for a fluid pump to drive circulation of a fluid. The fluid pump described above may be modified for a circulatory fluid system by having separate inlet and outlet apertures to the chambers with coupled fluid transmission lines. Similarly, the fluid motor may be modified to be driven by circulating fluid by modifying each fluid chamber having separate inlet and outlet apertures coupled to fluid transmission lines. The hub assembly described above may be modified to be driven by circulating fluid. Such circulatory fluid systems may include an accumulator, and supply of fluid to the fluid motor may be regulated using a regulation system including the accumulator. The fluid pump described herein may be implemented with a fluid motor described in WO2014195666, the disclosure of which is herein incorporated by reference. The fluid motor described herein may be implemented with a fluid pump described in this document. This document describes separately hydraulic systems in which fluid reciprocates/pulsates in lines and in which fluid circulates. 
         [0059]    The applicant hereby discloses in isolation each individual feature or step described herein and any combination of two or more such features, to the extent that such features or steps or combinations of features and/or steps are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or steps or combinations of features and/or steps solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or step or combination of features and/or steps. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.