AU2005213707B2

AU2005213707B2 - Rotary hydraulic machine and controls

Info

Publication number: AU2005213707B2
Application number: AU2005213707A
Authority: AU
Inventors: George Kadlicko
Original assignee: Concentric Rockford Inc
Current assignee: Concentric Rockford Inc
Priority date: 2004-02-11
Filing date: 2005-02-11
Publication date: 2011-10-27
Anticipated expiration: 2025-02-11
Also published as: CA2825598A1; CA2554798A1; EP1714034A1; CA2554798C; KR101224599B1; AU2005213707A1; JP2007522387A; BRPI0507630B1; KR20060116244A; JP2011174469A; WO2005078284A1; BRPI0507630A; EP1714034B1

Abstract

A variable capacity hydraulic machine has a rotating group located within a casing and a control housing secured to the casing to extend across and seal an opening in the casing. The control housing accommodates a control circuit and a pair of sensors to sense change in parameters associated with the rotating group. One of the sensors is positioned adjacent the barrel on the rotating group to sense rotational speed and the other senses displacement of the swashplate. The control housing accommodates a control valve and accumulator to supply fluid to the control valve.

Description

WO 2005/078284 PCT/US2005/004723 1 ROTARY HYDRAULIC MACHINE AND CONTROLS 2 3 BACKGROUND OF THE INVENTION 4 5 FIELD OF THE INVENTION 6 [00011 The present invention relates to hydraulic machines. 7 8 DESCRIPTION OF THE PRIOR ART 9 [00021 There are many different types of hydraulic machines that can be used to convert 10 mechanical energy into fluid energy and vice versa. Such machines may be used as a pump in 11 which mechanical energy is converted into a flow of fluid or as a motor in which the energy 12 contained in a flow of fluid is converted into mechanical energy. Some of the more sophisticated 13 hydraulic machines are variable capacity machines, particularly those that utilize an inclined 14 plate to convert rotation into an axial displacement of pistons or vice versa. 15 [0003] Such machines are commonly referred to as swashplate pumps or motors and have 16 the attribute that they can handle fluid under relatively high pressure and over significant range 17 of flows. A particular advantage of such machines is the ability to adjust the capacity of the 18 machine to compensate for different conditions imposed upon it. 19 [0004] The swashplate machines are, however, relatively complex mechanically with 20 rotating and reciprocating components that must be manufactured to withstand large hydraulic 21 and mechanical forces. These constraints lead to a reduction in the efficiency due to mechanical 22 and hydraulic losses, a reduced control resolution due to the mechanical inefficiencies and the 23 required size and mass of the components and a relatively expensive machine due to the 24 manufacturing complexity. 25 [00051 In use as a variable capacity machine the swashplate is modulated to achieve a 26 desired movement of component of a machine, either a position, rate of movement or applied 27 force. 28 [0006] The movement of the swashplate is usually controlled by a valve supplying fluid to an 29 actuator that acts through a compression spring on the swashplate. Control signals for the valve 30 are generated from a set controller and a feedback, typically provided by a sensed parameter. In its simplest form the feedback may be provided by the operator who simply opens and closes the valve to achieve the desired movement or positioning of the component. More sophisticated controls however sense preselected parameters and provide feedback signals to a valve controller. The valve controller may be mechanical, hydraulic but 5 more usually electronic to offer greater versatility in the control functions to be performed. [0007] The control of the swashplate is determined to a large extent by the response of the system to changes of the sensed parameter. In order for effective response to be obtained, the valve must be able to supply the actuators controlling the swashplate with 10 fluid under pressure at all times. At the same time, however, the pressure of fluid delivered by or to the machine may vary and accordingly a source of pressure at optimum conditions may not be available. The common technique to provide pressurized fluid is to use a separate charge pump but this is expensive and inefficient. [00081 The response of the machine is also dependent on the mechanical and hydraulic 15 losses present in the machine during its operation. A mechanically inefficient machine will not respond consistently as loads on the machine vary and the dynamics and static operating characteristics may differ significantly leading to a less predictable response. [0008a] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. 20 [0009] It is an object of a preferred embodiment of the present invention to obviate or mitigate the above disadvantages. [0009a] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. 25 [0009b] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". SUMMARY OF THE INVENTION 30 [0009c] In accordance with an aspect of the present invention, there is provided a rotary hydraulic machine having a housing, a rotating group located within said housing and 2 including a plurality of variable capacity chambers defined between pistons slideable within respective cylinders, said pistons being displaceable relative to said cylinders upon rotation of said barrel to vary the volume of said chambers and thereby induce a flow of fluid through said chambers from an inlet port to an outlet port as said rotating 5 group rotates, an adjustment assembly including an actuator to adjust the stroke of said pistons in said cylinder and thereby adjust the capacity of said machine, a fluid supply for said actuator and a control valve interposed between said fluid supply and said actuator to control flow to said actuator, said fluid supply including a conduit to convey pressurized fluid from one of said ports to a load, a hydraulic accumulator connected to 10 said conduit to store pressurised fluid from said conduit and supply stored fluid to said control valve, and a check valve between said accumulator and said conduit to inhibit flow from said accumulator to said conduit upon reduction of pressure in said conduit below that of said accumulator whilst maintaining the application of stored fluid to said control valve. 15 [0009d] In accordance with another aspect of the present invention, there is provided a rotary hydraulic machine having a housing, a rotating group located within said housing and including a plurality of variable capacity chambers defined between pistons slideable within respective cylinders, said pistons being displaceable relative to said cylinders upon rotation of said barrel to vary the volume of said chambers and thereby 20 induce a flow of fluid through said chambers from an inlet port to an outlet port as said rotating group rotates, an adjustment assembly including a pair of actuators operable upon said rotating group to adjust the stroke of said pistons in said cylinder and thereby adjust the capacity of said machine, a fluid supply for said actuators, and a control valve interposed between said fluid supply and said actuator to control flow to said actuators, 25 said fluid supply including a pressurised fluid source, a hydraulic accumulator to store pressurised fluid from said source and apply stored fluid to said control valve and a check valve to inhibit flow from said accumulator to said source upon reduction of pressure at said source below that of said accumulator whilst maintaining the application of stored fluid to said control valve, each of said actuators being single acting and having 30 a spring to bias respective ones to said actuators to a maximum capacity with one of said springs having a greater bias than the other to move said adjustment assembly to a position of maximum capacity in the absence of pressurised fluid at said control valve. 2a [0009e] In accordance with another aspect of the present invention, there is provided a rotary hydraulic machine having a housing, a rotating group located within said housing and including a plurality of variable capacity chambers defined between pistons slideable within respective cylinders, said pistons being displaceable relative to said 5 cylinders upon rotating of said barrel to vary the volume of said chambers and thereby induce a flow of fluid through said chambers from an inlet port to an outlet port as said rotating group rotates, an adjustment assembly including an actuator operable upon said rotating group to adjust the stroke of pistons in said cylinder and thereby adjust the capacity of said machine, a fluid supply for said actuator and a control valve interposed 10 between said fluid supply and said actuator to control flow to said actuator, said fluid supply including a pressurised fluid source, a hydraulic accumulator to store pressurised fluid from said source and a check valve between said accumulator and said source to inhibit flow from said accumulator to said source upon reduction of pressure at said source below that of said accumulator, said valve and said accumulator each being 15 located in respective bores in said housing and interconnected by an internal gallery. 10009f] In accordance with another aspect of the present invention, there is provided a hydraulic machine comprising a housing, a rotating group rotatably mounted within said housing and including a barrel and a plurality of pistons assemblies axially slideable in cylinders in said barrel, and a swashplate assembly to engage said pistons and induce 20 reciprocation thereof as said barrel rotates in said housing, a port plate interposed between said barrel and said housing and effective to connect respective ones of said cylinders alternatively with an inlet port and an outlet port, each of said piston assemblies having a piston and a slipper assembly acting between said swashplate and said piston to transfer loads therebetween, said slipper assembly including a base having 25 a planar bearing surface engagable with said swashplate and a spherical bearing on an oppositely directed side and engagable with a part spherical recess in said piston said base including a spigot projecting from said oppositely directed side and said spherical bearing having a through bore to receive said spigot, said through bore having a counterbore of greater diameter than said through bore at an end thereof remote from 30 said base to permit enlargement of said spigot to retain said spherical bearing on said spigot. 2b 10009g] In accordance with another aspect of the present invention, there is provided a slipper assembly for a piston assembly of a rotary hydraulic machine, said slipper assembly comprising a base having a planar bearing surface disposed on one side for engagement with a swashplate and a spherical bearing disposed on an oppositely 5 directed side for engagement with a part spherical recess in said piston and said base including a spigot projecting from said oppositely directed side and said spherical bearing having a through bore to receive said spigot, said through bore having a counterbore of greater diameter than said through bore at an end thereof remote from said base to permit enlargement of said spigot to retain said spherical bearing on said 10 spigot. [0009h] In accordance with another aspect of the present invention, there is provided a piston assembly for a rotating hydraulic machine comprising a piston having a spherical recess at one end thereof and a slipper assembly including a base having a planar bearing surface on one side and a spherical bearing on an oppositely directed side thereof, said 15 spherical bearing being located within said spherical recess to provide limited pivotal movement between said piston and slipper assembly and said base including a spigot projecting from said oppositely directed side and said spherical bearing having a through bore to receive said spigot, said through bore having a counterbore of greater diameter than said through bore at an end thereof remote from said base to permit enlargement of 20 said spigot to retain said spherical bearing on said spigot. 10009i1] In accordance with another aspect of the present invention, there is provided a method of forming a piston assembly for a rotary hydraulic machine comprising the steps of forming a part spherical cavity in one end of a piston to an axial depth greater than a diameter of said cavity, inserting therein a complementary spherical bearing of a 25 slipper assembly, and deforming the walls of said cavity to conform to the surface of said spherical bearing said step of deforming said walls including the step of applying a radial load about an equator of said spherical bearing after said walls conform to said surface to provide a clearance between said cavity and said spherical bearing and facilitate relative pivotal movement therebetween. 30 10009j] In accordance with another aspect of the present invention, there is provided a rotary hydraulic machine comprising a housing, a rotating group within said housing including a barrel and a plurality of pistons slidable within cylinders formed in said 2c barrel, a swashplate operable upon said pistons to induce reciprocation thereof in respective ones of said cylinders to transfer fluid between an inlet port and an outlet port as said barrel rotates about a longitudinal axis, and an actuator operable upon said swashplate to rotate it about an axis of rotation and adjust the disposition thereof relative 5 to said housing and thereby vary the stroke of said pistons in said cylinders, said swashplate having a bearing surface engagable with a complementary surface on said housing and a fluid bearing interposed between said surfaces, said bearing being supplied with fluid through a pressure compensated flow control valve to maintain a predetermined flow of fluid as pressure at said ports varies. 10 10009k] In accordance with another aspect of the present invention, there is provided a rotary hydraulic machine having a housing including a casing, a rotary group located within said casing and including barrel rotatable in said housing and having a plurality of pistons axially slideable in cylinders in said barrel, and a swashplate assembly to engage said pistons and induce reciprocation thereof as said barrel rotates to transfer fluid 15 between a pair of ports, an actuator acting upon said swashplate to adjust the disposition thereof relative to said barrel and thereby adjust the stroke of said pistons in said barrel, and a valve to control flow to said actuator in response to control signals obtained from a control circuit having at least one sensed input thereto indicative of a parameter of said rotating group, said control circuit being located in a control housing secured to said 20 casing and having an inwardly directed surface extending across an aperture in said casing to seal said aperture, a sensor assembly located on said surface and operatively associated with said rotating group to sense said parameter. 1000911 In accordance with another aspect of the present invention, there is provided a hydraulic machine comprising: 25 a housing; a rotary group rotatably mounted within said housing, said rotary group including a barrel, a plurality of pistons axially slidable in cylinders in said barrel; a swashplate assembly to engage said pistons and induce reciprocation thereof as said barrel rotates in said housing; and 30 a port plate interposed between said barrel and said housing, and being effective to connect respective ones of said cylinders alternatively with an inlet port and an outlet port, said port plate having a face biased into engagement with a sealing face on one of 2d said barrel and said housing and hydraulically connected to the other of said barrel and said housing through an annular sleeve extending between and in sealing engagement with said port plate and said other of said barrel and said housing; whereby upon rotation of said barrel relative to said housing, said faces are 5 maintained in sealing contact by said bias and fluid is transferred between one of said posts and said cylinders through said annular sleeve, misalignment between said port plate and said other of said barrel and said housing being accommodated by said annular sleeve. [0009m] In accordance with another aspect of the present invention, there is provided a 10 rotary hydraulic machine comprising a housing, a rotating group within said housing including a barrel and a plurality of pistons slideable within cylinders formed in said barrel, a swashplate operable upon said pistons to induce reciprocation thereof in respective ones of said cylinders to transfer fluid between an inlet port and an outlet port as said barrel rotates about its axis of rotation, and an actuator operable upon said 15 swashplate to adjust the disposition thereof relative to said housing and thereby vary the stroke of said pistons in said cylinders, said swashplate having a bearing surface engagable with a complementary surface on said housing and a fluid bearing interposed between said surfaces, said fluid bearing including a pair of recesses formed between said surfaces and each extending in a direction to bridge said ports and a fluid supply to 20 provide fluid to said.recesses. 10009n] In accordance with another aspect of the present invention, there is provided a rotary hydraulic machine having a rotating group including a plurality of variable capacity chambers defined by pistons sliding within respective cylinders, said pistons being displaceable relative to said cylinders upon rotation of said group to vary the 25 volume of said chambers and thereby induce a flow of fluid through said chambers from an inlet port to an outlet port, an adjustment assembly including an actuator operable upon said rotating group to adjust the stroke of said pistons and thereby vary the capacity of said machine, a fluid supply for said actuator and a control valve interposed between said fluid supply and said actuator to control flow to said actuator, said valve 30 having a first position in which flow through said valve is inhibited and being movable from said first position to vary the capacity of said machine, said valve being controlled by a controller having an output to adjust said valve and receiving input signals from at 2e least one transducer, said one transducer sending a signal representative of pressure delivered at said outlet port and said controller operating upon said actuator to maintain pressure at said outlet at a predetermined valve. 100101 In accordance to one aspect to the present invention, there is provided a rotary 5 hydraulic machine having a housing, and a rotating group located within the housing. The rotating group includes a plurality of variable capacity chambers defined between pistons slideable within respective cylinders. The pistons are displaceable relative to the cylinders upon rotation of the barrel to vary the volume of the chambers and thereby induce a flow of fluid through the chambers from an inlet port to an outlet port as the 10 rotating group rotates. An adjustment assembly includes an actuator operable upon the rotating group to adjust the stroke of the pistons in the cylinder and thereby adjust the capacity of the machine. A fluid supply is provided for the actuator and a control valve is interposed between the fluid supply and the actuator to control flow to the actuator. The fluid supply includes a pressurised fluid source and a 15 2f WO 2005/078284 PCT/US2005/004723 1 hydraulic accumulator to store pressurised fluid from the source. A check valve is located 2 between the accumulator and the source to inhibit flow from the accumulator to the source upon 3 reduction of pressure at said source below that of said accumulator. 4 [0011] Preferably the control valve is a closed centre valve and is moveable from a centred 5 position in which flow to and from the actuator is inhibited to a first position in which flow to the 6 actuator from the accumulator is permitted and to a second position in which flow from the 7 actuator to a drain is permitted. 8 9 BRIEF DESCRIPTION OF THE DRAWINGS 10 [0012] Embodiments of the invention will now be described by way of example only with 11 reference to the accompanying drawings in which: 12 [0013] Figure 1 is a side elevation of a hydraulic machine. 13 [0014] Figure 2 is a top view of the hydraulic machine of Figure 1. 14 [00151 Figure 3 is a view on the line III-In of Figure 2. 15 [0016] Figure 4 is a view on the line IV-IV of Figure 1. 16 [0017] Figure 5 is a perspective view of the rotating components of the machine shown in 17 Figures 3 and 4. 18 [0018] Figure 6 is an exploded perspective view of the component shown in Figure 5. 19 [0019] Figure 7 is a front perspective view, partly in section of the assembly shown in 20 Figure 3. 21 [0020] Figure 8 is a perspective view of a portion of the machine in the direction of arrow 22 VIII-VIII of Figure 3. 23 [0021] Figure 9 is an enlarged view of the portion of the machine shown in Figure 4 within 24 the circle A. 25 [0022] Figure 10 is a schematic representation of the assembly of a set of components used 26 in the machine of Figures 4 and 5. 27 [00231 Figure 11 is a view on the line XI-XI of Figure 1. 28 [0024] Figure 12 is a top view on the line XII-XII of Figure 1. 29 [0025] Figure 13 is a view similar to Figure 12 showing alternate positions of the 30 components of the machine shown in Figures 4 and 5. 3 WO 2005/078284 PCT/US2005/004723 1 [0026] Figure 14 is a view on the line XIV-XIV of Figure 1. 2 [00271 Figure 15 is a section on line XV-XV of Figure 3. 3 [0028] Figure 16 is a view on the line XVI-XVI of Figure 15. 4 [00291 Figure 17 is a schematic hydraulic circuit showing the operation of the components 5 shown in figure 1 to 16. 6 [0030] Figure 18 is a section through a tool used to assemble the components shown 7 schematically in Figure 10. 8 [0031] Figure 19 is a detailed view of a portion of the tool shown in Figure 18. 9 [0032] Figure 20 is a plan view of a further tool used to assemble the components shown in 10 Figure 10. 11 [0033] Figure 21 is a view similar to Figure 4 of an alternative embodiment of machine. 12 [0034] Figure 22 is a front view of a port plate used in the embodiment of Figure 4. 13 [0035] Figure 23 is a side view of the port plate of Figure 22. 14 [0036] Figure 24 is a rear view of the port plate of Figure 23. 15 [0037] Figure 25 is a section on the line XXV - XXV of Figure 22. 16 [0038] Figure 26 illustrates the sequential movement of a cylinder across a port plate of 17 Figure 22 18 [0039] Figure 27 is an exploded perspective view of a further embodiment of port plate; 19 [0040] Figure 28 is a rear perspective view of the port plate of Figure 27; 20 [0041] Figure 29 is a front view of the port plate of Figure 27; 21 [0042] Figure 30 is a section on the line XXX-XXX of Figure 29; 22 [0043] Figure 31 is a section on the line XXXI-XXXI of Figure 29; 23 [0044] Figure 32 is a section on the line XXXII-XXXII of Figure 29; 24 [0045] Figure 33 is an end view of an alternative embodiment of swashplate 25 26 DESCRIPTION OF THE PREFERRED EMBODIMENTS 27 [00461 Referring therefore to Figures 1 through 4, a hydraulic machine 10 includes a housing 28 12 formed from a casing 14, an end plate 16 and a control housing 18. The casing 14 has an 29 opening 15 on its upper side with a planar sealing surface 17 around the opening 15. The control 30 housing 18 has a lower surface 19 that extends across the opening 15 and is secured to the casing 4 WO 2005/078284 PCT/US2005/004723 1 14. The control housing 18, end plates 16 and casing 14 define an internal cavity 20 in which the 2 rotating group 22 of the machine 10 is located. 3 [0047] As can be seen in Figures 3, 4, 5 and 6, the rotating group 22 includes a drive shaft 24 4 that is rotatably supported in the casing 14 on a roller bearing assembly 26 and sealed with a seal 5 assembly 28. One end of the drive shaft 24 projects from the casing and includes a drive 6 coupling in the form of a key 30 for connection to a drive or driven component (not shown) e.g. 7 an engine, electric motor or wheel assembly. The opposite end 32 of the drive shaft 24 is 8 supported in a roller bearing 34 located in a bore 36 of the end plate 16. The shaft 24 is thus free 9 to rotate along a longitudinal axis A-A of the housing 12. 10 [0048] A barrel 40 is secured to the shaft 24 by a key 42 located in a key way 44 formed in 11 the shaft 24. The barrel 40 similarly has a key way 46 that allows the barrel 40 to slide axially 12 onto the shaft 24 and abut against a shoulder 48 formed on a drive shaft 24. The barrel 40 is 13 provided with a set of axial bores 50 uniformly spaced about the axis of the shaft 24 and 14 extending between oppositely directed end faces 52,54. As can be seen in greater detail in 15 Figure 9, each of the bores 50 is lined with a bronze sleeve 56 to provide a sliding bearing for a 16 piston assembly 58, described in greater detail below. 17 [0049] A toothed ring 60 is secured on the outer surface of the barrel 40 adjacent the end 18 face 52. The toothed ring 60 has a set of uniformly spaced teeth 62 each with a square section 19 and is a shrink fit on the barrel 40. The barrel 40 is formed from aluminium and the toothed ring 20 60 from a magnetic material. The barrel 40 has reduced diameter adjacent to the ring 60 so that 21 the teeth 62 project radially from the surrounding surface of the barrel 40. 22 [0050] A port plate 64 is located adjacent to the end face 54 and has a series of ports 66 at 23 locations corresponding to the bores 50 in the barrel 40. The port plate 64 is located between the 24 barrel 40 and the end plate 16 and is biased into engagement with the end plate 16 by coil springs 25 68 and a conical washer 70. The coil springs 68 are positioned at the radially outer portion of the 26 barrel 40 and between adjacent bores 50 to bias the radially outer portion of the plate 64 into 27 engagement with the end plate 16. As seen more clearly in Figure 9, the conical washer 70 is 28 located at the radially inner portion of the barrel 40 and its radially outer edge received in a 29 recess 72 formed in the port plate 64 to urge the inner portion against the end plate 16. The port 30 plate 64 is thus free to float axially relative to the barrel 40. 5 WO 2005/078284 PCT/US2005/004723 1 [0051] To provide fluid transfer between the bores 50 and the ports 66, an annular sleeve 74 2 is located within each of the bores 50 and sealed by an O-ring 76. The opposite end of the sleeve 3 74 is received in the circular recess 67 of the port 66, as best seen in Figure 9, and is located 4 axially by a shoulder 68 provided on the sleeve 74. A fluid tight seal is thus provided between 5 the barrel 40 and the port plate 64. The ports 66 smoothly transform from a circular cross 6 section facing the bore 50 to an arcuate slot for co-operation with conduits 78, 79 formed in the 7 end plate 16. 8 [0052] As most readily seen in Figure 8, the end plate 16 has a pair of kidney ports 80,82 9 disposed about the bore 36. The kidney ports 80, 82 connect pressure and suction conduits 78, 10 79 respectively to fluid entering and leaving the bores 50. The end plate 16 has a circular 11 bearing face 84 that is upstanding from the end plate 16 and has a set of radial grooves 86 12 formed in a concentric band about the axis of the shaft 24. The grooves 86 provide a hydro 13 dynamic bearing between the port plate 64 and the bearing face 84 in order to maintain a seal 14 whilst facilitating relative rotation between the port plate 64 and face 84. 15 [00531 Referring again to Figure 4 and 9, each of the piston assemblies 58 is axially slideable 16 within a respective sleeve 56 and comprises a tubular piston 90 and a slipper 92 interconnected 17 by a ball joint 94. The piston 90 is formed from a tube that is heat treated and ground to 18 diameter to be a smooth sliding fit within the sleeves 56. As can be seen in greater detail in 19 Figure 10, the outer surface of one end 96 of the piston 90 is reduced as indicated at 98 and a part 20 spherical cavity 100 formed on the inner walls of the end 96. The cavity 100 is dimensioned to 21 receive a ball 102 with a through bore 104. The cavity 100 has an axial depth greater than the 22 radius of the ball 102 so that the inner walls extend beyond the equator of the ball 102. The bore 23 104 in ball 102 is stepped as indicated at 106 to provide an increased diameter at its inner end. 24 [00541 During the first step of forming of the piston assembly 58, indicated at 109, the ball 25 102 is inserted in the cavity 100 with the bore 104 aligned generally with the axis of the piston 26 90. To retain the ball 102 in the cavity 100, the reduced section 98 of the piston 90 at the end 96 27 is swaged about the ball 100 indicated in Figure 10 (b). 28 [0055] Slipper 92 that has a stem 110 and a base 112 is inserted into the bore 104 (step (c)). 29 A passageway 114 is formed through the stem 110 to communicate between the interior of the 6 WO 2005/078284 PCT/US2005/004723 1 piston 90 and a recess 116 formed in the base 112. The slipper 92 is secured to the ball 102 by 2 swaging, the end of the stem 110 so it is secured by the step 106, as shown in step (d). 3 [0056] After securing the slipper to the ball, a radial force is applied to the equator of the ball 4 as indicated by the arrows F in Figure 10e that has the effect of displacing the material on the 5 equator to provide a small clearance between the ball 102 and cavity 100. This clearance enables 6 the ball joint 94 to rotate smoothly within the cavity 100 whilst maintaining an effective seal 7 from the interior of the piston. 8 [00571 The process shown in Figure 10 may conveniently be performed using the tool set 9 shown in Figures 18, 19 and 20. A tool set 120 has a fixed die 122 and a moveable die 124. The 10 fixed die 122 is secured to a base plate 126 and has a central pin 128 on which the piston 90 is 11 located. A supporting sleeve 130 supports the upper end of the piston 90 adjacent to the 12 reduction 98. The pin 128 also aligns the ball 102 by extending into the bore 104 of the ball 102. 13 [0058] The moveable die 124 is formed with a part spherical recess 132 dimensioned to 14 engage the end 96 and form it about the ball 102. The moveable die may be advanced into 15 engagement with the ball 102 through the action of a press in which the tool set 120 is mounted. 16 [00591 After forming, the piston assembly 58 is inserted into a 3 disk die 134 shown in 17 Figure 20. The 3 disk die has a pair of driven rollers 135 and an idler roller 136 that are disposed 18 around the circumference of the end 96 of the piston assembly 58 to form point contact with the 19 outer surface 98. The idler roller 136 is moveable along a radial path by means of a hydraulic 20 cylinder 137 that applies a constant force to the roller 136. The advance of the roller is 21 controlled by a flow control valve 138 until the material surrounding the equator of the ball 102 22 is sufficiently displaced to provide free movement of the ball within the cavity. 23 [0060] Referring again to Figures 4, 5 and 6 of the base 112 of the slipper 92 engages a 24 swashplate assembly 140 supported within the housing 14. The swashplate assembly 140 25 includes a semi cylindrical swashplate 142 having a generally planar front face 144 and an 26 arcuate rear face 146. The planar front face 144 has a recess 148 to receive a lapped plate 150 27 against which the slippers 92 bear. The slippers 92 are held against the plate 150 by a retainer 28 152 that has holes 154 through which the piston assemblies 58 project. The holes 154 are 29 dimensioned to engage the outer periphery of the base 112 of the slipper 92 and inhibit axial 30 movement relative to the plate 150. The retainer 152 is located axially by a pair of C-shaped 7 WO 2005/078284 PCT/US2005/004723 1 clamps 156 that are secured to the front face 144 of the swashplate 142. The base 112 thus bears 2 against the lapped face of the plate 150 as the barrel is rotated by the drive shaft 24. 3 [0061] The rear face 146 of the swashplate 142 is supported on a complimentary curved 4 surface 158 of the casing 14 opposite the end plate 16. The rear face 146 is coated with a 5 polymer to reduce friction between the face 146 and surface 158. A suitable polymer coating is a 6 nylon coating formulated from type 11 polyamide resins, such as that available from Rohm & 7 Haas under the trade name CORVEL. A 70 000 series has been found suitable although other 8 grades may be utilized depending on operating circumstances. After deposition on the face 146, 9 the coating is ground to a uniform thickness of approximately 0.040 inches. Alternatively, it has 10 been found satisfactory to harden the face 146 and apply a TEFLON TM coating. 11 [00621 As seen in Figure 7, a pair of grooves 160, 162 respectively are formed in the rear 12 face 146 and terminate prior to the linear edges of the face 146 to provide a pair of closed 13 cavities. The grooves 160, 162 are generally aligned with the kidney ports 80, 82 formed in the 14 end plate 16 and it will be noted that the width of the groove 160 which is aligned with the 15 pressure conduit is greater than the width of the groove 162 aligned with the suction conduit. 16 Fluid is supplied to the grooves 160, 162 through internal passageways 164, 166 respectively 17 formed in the casing 14. Flow through the passageways is controlled by a pair of pressure 18 compensated flow control valves 168 that supply a constant flow of fluid to the grooves 160, 19 162. The grooves 160, 162 thus provide a fluid bearing for the rear face 146 against the surface 20 158 to facilitate rotational movement of the swashplate 142. 21 [0063] Adjustment of the swashplate 142 about its axis of rotation is controlled by a pair of 22 actuators 170, 172 respectively located in the casing 14. As shown most clearly in Figures 5 and 23 11, each of the actuators 170, 172 includes a cylinder 174 in which a piston 176 slides. Each of 24 the cylinders 174 is received within a bore 178 formed in the casing 14 and extending from the 25 end plate 16 into the cavity 20. The cylinders 174 have an external thread 180 which engages 26 with an internal thread on the bore 178 to secure the cylinder in the casing 14. The end plate 16 27 (Figure 8) has a pair of recesses 192 that fit over the end of the pistons 176. The self contained 28 actuator, 170, 172 located in the casing 14 ensures that axial load generated by the actuators 170 29 are imposed on the casing 14 rather than across the joint between the end plate 16 and casing 14 30 to maintain integrity of the housing 12. To avoid distortion of the cylinders 174 during 8 WO 2005/078284 PCT/US2005/004723 1 assembly, it has been found preferable to form the cylinder 174 as two components, namely a 2 body 174a which is located in the bore 178 by a shoulder and an end cap 174b carrying the 3 threads 180. The cap 174b bears against the end of the body 174a to hold it in the bore 178. 4 [0064] The cylinder 174 is provided with cross drillings 182 to permit fluid supplied through 5 internal passageways 183 (Fig. 12) in the housing 14 to flow to and from the interior of the 6 cylinder 174. A spring 184 acts between the cylinder 174 and piston 176 to bias it outwardly 7 into engagement with the swashplate assembly 140. Preferably one of the springs 184 has a 8 greater axial force than the other so that the swashplate is biased to a maximum strike position in 9 the absence of fluid in the actuators 170, 172. 10 [0065] The actuators 170, 172 bear against a horseshoe extension 186 of the swashplate 142 11 that projects outwardly above the barrel 40. The extension 186 has a pair of, part cylindrical 12 cavities 188 at opposite ends into which a cylindrical pin 190 is located. The cavities 188 are 13 positioned such that the outer surface of the pin 190 is tangential to a line passing through the 14 axis of rotation of the swashplate. The end face of piston 176 engages the outer surface of the pin 15 190 to control the position of the swashplate. 16 [0066] As illustrated in Figure 13, extension of the piston 176 of one of the actuators 170, 17 172 will induce rotation of the swashplate assembly 140 in the casing 14 and cause a 18 corresponding retraction of the other of the actuators 170, 172. The assembly 140 slides over the 19 curved surface 158 and as the assembly 140 rotates, the pins 190 maintain contact with the end 20 face of the pistons 170. The position of the pins 190 on a common diameter of the swashplate 21 assembly ensures that a rolling motion, rather than sliding, is provided across the end face of the 22 pistons 176 to reduce friction during the adjustment. As can be seen in Figure 13, the actuators 23 170, 172 are disposed to provide a full range of rotation on both sides of a neutral or no stroke 24 position with rolling contact being made over this range of motion. 25 [0067] Flow to the actuators 170, 172 is controlled by a control valve 200, Figure 14, located 26 in the control housing 18. The control valve 200 is a solenoid operated, spool valve having a 27 centred position in which no flow is permitted through the valve. The spool may be moved to 28 either side of the centred position to apply pressure to one of the actuators and connect the other 29 actuator to drain. The control housing 18 is shown in greater detail in Figures 3, 15 and 16 has a 30 peripheral skirt 191 extending from a base 192. A pair of bores 193, 194 extend through the base 9 WO 2005/078284 PCT/US2005/004723 1 192 to receive control valve 200 and an accumulator 220 respectively. Fluid is supplied to the 2 bores 193, 194 by an internal supply gallery 195 and a drain gallery 196 is connected between 3 the bore 193 and the cavity 20 of the casing 12. Internal galleries 197, 198 also communicate 4 between the bore 193 and the internal passageways 183 connected to actuators 170, 172. The 5 valve 200 controls the flow from the internal supply gallery 196 to the actuators and drain as will 6 be described below. 7 [00681 The fluid flow controlled by the control valve 200 is obtained from the pressure 8 conduit 78 and supplied through an accumulator 220 located in the bore 194 of control housing 9 18 adjacent to the control valve 200. The accumulator, shown in Figure 14, includes a piston 10 222 slideable within a cylinder 224 and biased by a spring 226 to a minimum volume. The 11 piston 222 has a seal 223 and carries a stop 228 that limits displacement of the piston 222 within 12 the cylinder 224. The piston 222 may be formed in two pieces to facilitate insertion of the seal 13 223. The stop 228 in combination with the spring 226 effectively establishes a maximum stored 14 pressure for the accumulator 220. The supply gallery 195 extends through a branch conduit 227 15 to the interior of cylinder 224 and is connected with the pressure conduit 78 through a check 16 valve 230 located in an internal bore 232 in the housing 14. The check valve 230 ensures that 17 the pressure fluid in the accumulator 220 is maintained as the pressure supplied to conduit 78 18 fluctuates and that control fluid is available to the valve 200. The supply gallery 195 is also 19 connected to the pressure compensated flow control valves 168 to ensure a constant flow of fluid 20 to the bearings 160, 162. 21 [00691 To provide control signals to the valve 200, a block 202 is secured to the swashplate 22 142 within the horseshoe extension 186 and presents a planar surface 204. A position sensor 206 23 engages the planar surface 204 eccentrically to the axis of rotation of the swashplate assembly 24 140 to provide a signal indicative of the disposition of the swashplate assembly 140. The 25 position sensor 206 includes a pin 208 slideable within a sensing block 210 that extends 26 downwardly from the control housing 18. The pin 208 is formed from a stainless steel so as to 27 be non-magnetic and has a magnet 212 inserted at its inner end. The sensing block 210 28 accommodates a Hall effect sensor 214 in a vertical bore 215 where it is sealed to prevent 29 migration of oil from the cavity 20 to the control housing 18. The sensor 214 provides a varying 10 WO 2005/078284 PCT/US2005/004723 1 signal as the pin 208 moves axially within the block 210. The Hall effect sensor thus provides a 2 position signal that varies as the swashplate is rotated by the actuators 170, 172. 3 [00701 The sensing block 210 also carries a further Hall effect sensor 216 located in a bore 4 217 extending through the block 210 to a nose 219 positioned adjacent to the toothed ring 60. 5 The sensor 216 is sealed in the bore 217 and provides a fluctuating signal as the teeth 62 pass it 6 so that the frequency of the signal is an indication of rotational speed of the barrel 22. The 7 control signals obtained from the Hall effect sensors 214 and 216 are supplied to a control circuit 8 board 218 located within the control housing 18. Further input signals, such as a set signal from 9 a manual control, a temperature signal indicating the temperature of fluid in the machine, and a 10 pressure signal indicating the pressure of fluid in the pressure conduit 78, are obtained from 11 transducers located in or adjacent to the conduits 78, 80. The input signals are, also fed to the 12 control circuit board 218 which implements a control algorithm using one or more of the set, 13 pressure, temperature and flow signals fed to it. The output from the control circuit board 216 is 14 provided to the control valve 200 which is operable to control the flow to or from the actuators 15 171, 172 in response to the control signal received. 16 [0071] The operation of the machine 10 will now be described. For the purpose of the 17 description it will be assumed that the machine is functioning as a pump with the shaft 24 driven 18 by a prime mover such as an electric motor or internal combustion engine. Initially, the bias of 19 the springs has moved the swashplate 140 to a position of maximum stroke and fluid in the 20 accumulator 220 has discharged through the flow control valves 168. Rotation of the shaft 24 21 and barrel 40 causes full stroke reciprocation of the pistons 58 as the slippers 92 move across the 22 lapped plate 150 to discharge fluid into the pressure port 78. The fluid is delivered through the 23 check valve 230 to the supply gallery 195 to provide fluid to the control valve 200 and charge the 24 accumulator 220. 25 [0072] In its initial condition, the control is set to move, the swashplate assembly 140 to a 26 neutral or no-flow position. Accordingly, as fluid is supplied to the control valve 200, it is 27 directed to the actuator 170 to move the swashplate 140 to the neutral position. As the 28 swashplate moves toward the neutral position, the pin 208 of position sensor 206 follows the 29 movement and adjusts the position signal provided to the board 218. Upon attainment of the 30 neutral position, the flow to the actuator 170 is terminated by the valve 200. In this position, the 11 WO 2005/078284 PCT/US2005/004723 1 barrel 22 is rotating but the piston assembly 58 is not reciprocating within the barrel. The 2 accumulator 220 is charged to maintain supply to the flow control valves 168 through the gallery 3 195, and to the control valve 200. 4 [0073] After initialization, the circuit board 218 receives a signal indicating a movement of 5 the swashplate assembly 140 to a position in which fluid is supplied to the pressure port 78. The 6 signal may be generated from the set signal, such as a manual operator, or from a pressure 7 sensing signal and results in a control signal supplied to the valve 200. The valve 200 is moved 8 to a position in which it supplies fluid to the actuator 170 and allows fluid from the actuator 172 9 to flow to a sump. The supply fluid to the actuator 170 causes the piston 176 to extend and bear 10 against the pin 190. The internal pressure applied to the piston 176 causes rotation of the 11 swashplate assembly 140 with the surface 146 sliding across the surface 158. Until such time as 12 pressure is delivered to the pressure port 78, the, pressurized fluid is supplied from the 13 accumulator 220 through the control valve and into the interior of the actuator 170 to induce the 14 rotation. As the swashplate assembly is rotated about its axis, the slippers 92 are retained against 15 the lapped plate 150 and the stroke of the pistons 90 is increased. Fluid is thus drawn through 16 the suction port 69 past the kidney port 82 and into the pistons as they move outwardly from the 17 barrel. Continued rotation moves the pistons into alignment with the pressure port 78 and expels 18 fluid from the cylinders as the pistons 90 move into barrel. The pressure supplied to the port 78 19 is also delivered to the internal supply galleries 195 to replenish the accumulator 220. 20 [0074] As the swashplate rotates, the pin 208 follows the movement of the planar surface 21 204 and provides a feedback signal indicative of the capacity of the barrel assembly 22. The 22 signal from the toothed ring 60 also provides a feedback signal indicative of rotation so that the 23 combination of the signal from the pin 208 and the signal from the ring 60 may be used to 24 compute the flow rate from the pump. If the set signal is a flow control signal then the 25 combination of the speed and position are used to offset the set signal and return the valve 200 to 26 a neutral position once the required flow is attained. Similarly, if the set signal indicates a 27 pressure signal, then the pressure in the port 78 is monitored and the valve returned to neutral 28 upon the set pressure being obtained. 29 [0075] As the swashplate 142 is adjusted, the flow of fluid into the grooves 160, 162 on the 30 rear face 146 of the swashplate is controlled by the flow of the control valves 168 so that a 12 WO 2005/078284 PCT/US2005/004723 1 constant support for the swashplate is maintained. Similarly, the port plate 64 is maintained 2 against the end face by the action of the spring 68, 70 to maintain a fluid tight seal for the 3 passage of fluid into and out of the barrel assembly 40. 4 [0076] Movement of the swashplate to a position in which pressurized fluid is delivered to 5 the port 78 recharges the accumulator 220 as well as supplying flow to the actuators 170 and 172 6 and the grooves 160, 162. If the swashplate assembly 140 is returned to a neutral position, the 7 pressurized fluid in the accumulator 220 is sufficient to provide the control function and maintain 8 the balance of the swashplate 142. 9 [00771 During adjustment of the swashplate 142, the rolling action of the pins 190 across the 10 end faces of the pistons 176 further minimizes the frictional forces applied to the swashplate 140 11 and thereby reduces the control forces that must be applied. 12 10078] It will also be appreciated that by providing the ball joint 94 as part of the slipper, the 13 forces imposed on the slipper are minimized and the angle of adjustment available increased to 14 enhance the range of follow rates that are available. 15 [0079] All movement of the swashplate 140 is followed by the pin 208 and variations in the 16 rotational speed are sensed by the pickup 216 to permit the control board 218 to provide 17 adjustment of the control parameters. It will also be noted that the control function is located in 18 the housing 18 separate from the rotating component so that the control board 218 and associated 19 electric circuit is not subject to the hydraulic fluid that might adversely affect their operation. 20 [0080] The provision of the key 42 on the shaft 24 inhibits relative rotation between the shaft 21 and barrel and thus reduces the oscillation and fretting that otherwise occurs with a typical 22 splined connection. Any misalignment between the barrel and port plate 64 is accommodated by 23 the spring biasing applied to the port plate 64 by the springs 68, 70 so that the keyed connection 24 to the shaft is possible. 25 [0081] The accumulator provides a supply of pressure fluid to the control valve 200 to 26 enhance the response to variations in the control signal when the pressure in the discharge 27 system falls below the accumulator setting. 28 [00821 If the machine 10 is to be utilized as a motor, it will be appreciated that the pin 208 is 29 operable to follow movement of the swashplate to either side of a neutral condition and therefore 30 provide reversibility of the output shaft 24 that is used to drive a load. During such operation, 13 WO 2005/078284 PCT/US2005/004723 1 the line 78 will be at a low pressure but the accumulator 220 supplies fluid to the control valve 2 200 to maintain control of the swashplate. 3 [0083] In the above embodiment, the port plate is biased against the end plate and floats 4 relative to the barrel 40. An alternative embodiment is shown in Figures 21 to 26 in which like 5 components are denoted with like reference numerals with a suffix 'a' added for clarity. 6 [00841 In the arrangement shown in Figures 21 to 26, the port plate 64a is arranged to float 7 relative to the end plate 16a and for relative rotation to occur between the barrel 40a and the port 8 plate 64a. The port plate 64a is biased into sealing engagement with the barrel 40a by springs 9 68a received in a counterbore 68a. In this way, minor misalignment between the barrel and, end 10 plate is accommodated. The counterbore 68a is sealed to the end plate 16a by sleeves 74a that 11 accommodate axial movement and maintain a seal with O-rings 76a. 12 [0085] As can be seen from Figure 22, the port plate 64a has a pair of kidney shaped ports 13 300, 302. The port 300 extends through the plate 64a with a central web 304 recessed from the 14 front face 306 of the plate 64a. The rear face 308 as shown in Figure 24, is undercut as indicated 15 at 310 to provide a clearance between the plate 64a and the end wall 16a. 16 [0086] The port 302 extends partially through the plate 64a and is intersected by three 17 pressure ports 312 that extend from the rear face 308. Each of the ports 312 is configured to 18 receive a sleeve 74a which engages in complimentary recesses in the end face 16a to provide a 19 sealed communication between the plate 64a and the end face 16a. 20 [0087] A restricted orifice 314 is formed at the inner end of the counterbore 68a so as to 21 extend through to the front face 306. The orifice provides a restricted access to the chamber 22 formed by the sleeve 74a within the counterbore 68a and is positioned between the kidney ports 23 300, 302. A V-shaped notch 316 is formed in the front face 306 and progressively increases in 24 breadth and depth toward the leading edge of the kidney port 302. 25 [0088] In operation, the front face 306 of plate 64a is forced against the end face of the barrel 26 40a. The bores 50a are located at the same radius as the kidney ports 300, 302 and therefore pass 27 successively over the port plate as the barrel 40 rotates. As the bores 50a traverse the port 300 28 fluid is induced into the cylinders. Similarly, as the bores 50a traverse the port 302, fluid is 29 expelled from the cylinders and directed through the sleeves 74a to the pressure conduit 78a. 14 WO 2005/078284 PCT/US2005/004723 1 During this rotation, the face 306 is maintained by the springs 68a against the barrel 40a to 2 maintain an effective seal. 3 [0089] It will be noted that the adjacent ends of the ports 300, 302 are spaced apart by a 4 distance greater than the diameter of the bores 50a. This is shown is Figure 26A where the 5 disposition of the bores at a particular position of the barrel 40a is shown. The bore 50a shown 6 in chain dot line is associated with a piston that has just passed bottom-dead center, ie. the 7 maximum volume of the cylinder and is starting to move axially to expel fluid. However, the 8 rate of movement of the piston is relatively small by virtue of the sinusoidal nature of the 9 induced movement. In the position shown in Figure 26A, the cylinder has just passed the 10 terminal portion of the inlet port 300 but the small land created between the end of the bore and 11 the terminal edge of the port 302 is such that there is a small leakage from the piston into the low 12 pressure port 300. It will also be observed from Figure 26A that the orifice 314 is positioned 13 within the cylinder. 14 100901 As the barrel continues to rotate as shown in Figure 26B, the bore is centered over the 15 orifice 314 and the limited movement of the piston is accommodated by compression of the fluid 16 and components within the chamber 68a. Again, because of the sinusoidal nature of the motion, 17 the axial displacement is minimized during this portion of the rotation. Further rotation of the 18 barrel 40a brings the bore 50a to a position shown in Figure 26C in which it overlaps the notch 19 316 and therefore fluid in the cylinder may be expelled into the high pressure kidney port 302. 20 The tapered dimensions of the notch 316 allows the oil to progressively enter the port 302 to 21 avoid an abrupt transition and thereby reduce potential noise. At this time the cylinder is still in 22 communication with the bore 68a and high pressure fluid within that bore can be expelled 23 through the orifice 314 and into the pressure port 302. 24 [0091] Continued rotation, as shown in Figure 26D moves the bore 50a so it begins to 25 overlap the kidney part 302 and has unrestricted access to the pressure conduit 78a. 26 [00921 Similarly, as the bore 50a moves from the inlet port 300 to the pressure port 302, a 27 circumferentially spaced bore indicated at 50a' on Figure 26A moves from the high pressure 28 kidney port 302 to the suction port. As can be seen from Figure 26A, as the piston approaches 29 top-dead center, the communication with the high pressure port is progressively reduced until, as 30 it moves to the position shown in Figure 26C, it is in communication with the orifice 314. 15 WO 2005/078284 PCT/US2005/004723 1 Again, the piston is at its minimum rate of axial movement as it passes the top-dead center and 2 the continued displacement of fluid can be accommodated within the chamber 68a. At the 3 position shown in Figure 26D, the piston has gone past top-dead center and is being moved 4 towards bottom-dead center. In this position however, it is not in communication with the low 5 pressure kidney port 300 and the residual pressure within the chamber 68a replenishes the fluid 6 within the cylinder to avoid cavitation. As the barrel continues to rotate, the cylinder is put into 7 communication with the low pressure port and the fluid is drawn into the cylinder. 8 [0093] It will be seen therefore that as the barrel 40a rotates, the pistons are alternatively 9 connected to pressure and section ports 302, 300 and that the spacing of the ports is such as to 10 inhibit leakage between the high pressure and low pressure chambers. The provision of the 11 restricted orifice 314 together with the balancing chamber 68a accommodates the small change 12 in volume as the pistons go over bottom-dead center or top-dead center as well as providing a 13 balancing force to maintain the port plate against the end of the barrel 40a. The undercut 310 14 provides a relatively unrestricted ingress of fluid into the cylinders to enhance the efficiency of 15 the machine and inhibit cavitation. 16 [00941 A further embodiment of port plate similar to that shown in Figures 21 to 26 is 17 illustrated in Figures 27 through 32 in which like reference numerals will be utilised to identify 18 like components with a suffix b added for clarity. 19 [00951 In the arrangement of Figures 27 through 32, the port plate 64b is arranged to float 20 relative to the end plate 16b and for relative rotation to occur between the barrel 40b and the port 21 plate 64b as described above with respect to Figures 21 to 26. The port plate 64b has a pair of 22 kidney shaped ports 300b, 302b. The port 300b extends through the plate 64b with a central web 23 304b recessed from the front face 306b of the plate 64b. A hydro dynamic bearing 320 is formed 24 on the periphery of the front face 306b to mate with the end face of the barrel 40b. The port 25 302b extends partially through the plate 64b from the front face 306b and is intersected by 26 pressure ports 312b that extend from a rear face 308b best seen in Figure 28. 27 [0096] The rear face 308b has a pair of upstanding walls 322, 324 that extend around the 28 periphery of the ports 300b, 302b respectively. A groove 326, 328 is provided in each of the 29 walls 322, 324 to receive respective sealing rings 330, 332. A radial shoulder 334 is formed at 30 the rear face 308b and is a snug fit within a bore 336 provided in the front face of the end plate 16 WO 2005/078284 PCT/US2005/004723 1 16b. A circlip 338 co-operates with a grove formed in the bore 336 to retain the port plate 64a 2 within the bore 336. 3 [00971 Kidney shape inlet and outlet ducts 340, 342 respectively are provided at the base of 4 the bore 336 and are of complimentary shape to the walls 322, 324 respectively to permit the 5 walls 340, 342 to rest within the ducts. The ducts 340, 342 communicate with the inlet conduit 6 and outlet conduit (not shown) to supply fluid to the rotating group and convey fluid away from 7 the rotating group as is conventional. The sealing rings 330, 332 ensure a fluid tight fit between 8 the walls 322, 324 and their respective ducts 340, 342 whilst accommodating limited axial 9 movement. 10 [0098] The port plate 64b is biased away from the end plate 16b by springs 68b. The springs 11 68b are accommodated within the ducts 340, 342 and act against the end face 308 to provide the 12 necessary bias against the force generated by the pressure of fluid in the barrel. A balancing 13 chamber is formed at diametrically opposed locations on the plate 64b by sleeve 74b. As best 14 seen in Figure 31, the sleeves 74b are accommodated within counter bores 344 in the plate 64b. 15 A restricted orifice 314b connects the counter bore 344 with the front face 306b. The sleeve 74b 16 are axially moveable within the counter bores 344 and are sealed by o-rings on the periphery of 17 the sleeve 74b. The balancing chamber are located at the cross over between the pressure and 18 suction ports to accommodate the transition. 19 [0099] The operation is similar to that described above with respect to Figures 21 through 20 26. To maintain an effective seal between the port plate 64b and barrel, the area of the recesses 21 342 is selected to have a slightly greater effective area than the port 302b, typically in the range 22 of 2 to 5% greater, with 3% preferred. A positive bias from the pressurized fluid is thus provided 23 to supplement the action of the spring 68b and maintain a seal between the port plate and the 24 barrel. It is found that if the machine is maintained under pressure but with no rotation, there is a 25 tendency for the pressure fluid to creep between the port plate and barrel and separate the sealing 26 surfaces. The provision of the enlarged area for the port provides a positive bias even without 27 rotation of the barrel relative to the port plate to maintain the ceiling effect. If a perfect seal in 28 assumed between the face of the barrel and the port plate, a differential in area of 25% is found 29 to be suitable. In practice, such an area differential when combined with the inevitable pressure 17 WO 2005/078284 PCT/US2005/004723 1 gradient at the edge of the port produces an effective differential in the order of 3% to maintain 2 effective sealing. 3 [00100] An alternative embodiment of swasplate is shown in Figure 33 in which like 4 components will be denoted with like reference numerals and a suffix 'a' added for clarity. In 5 the embodiment described in Figure 7 above, the grooves 160, 162 are aligned with the kidney 6 ports 80, 82 so as to provide increased load carrying capacity for the high pressure loading of the 7 pistons. 8 [001011 In the embodiment of Figure 33, the grooves 160a, 162a extend in a direction to 9 bridge the kidney ports 80, 82 and have a varying area to accommodate the loads imposed.. As 10 can be seen in Figure 27, each of the grooves 160a, 162a is generally an inverted L-shape with an 11 enlarged head 350 and an elongate tail 352. Flow to the grooves 160a, 162a is controlled by 12 respective flow control valves 168a. A land 352 is provided in the head 350 to adjust the bearing 13 area. 14 [00102] The head 350 is generally aligned with the line of action of the actuators 170, 172 to 15 provide an enlarged bearing area whilst the tails 352 provide a bearing area for balance of the 16 forces. In this manner, the grooves 160a, 162a are located to provide a fluid bearing in which the 17 higher forces are distributed between the two grooves and the shape of the groove used to 18 compensate for difference loading. It will be noted that the tail 352 is of varying width to 19 provide an increased area in opposition to the high pressure loads with a reduced area to oppose 20 the low pressure loads. It will be appreciated that the grooves 160a, 162a may be contoured to 21 suit the loading characteristics of the particular machine and provide uniform support for the 22 swashplate. 23 18

Claims

1. A rotary hydraulic machine having: a housing; a rotating group located within said housing and including a plurality of variable 5 capacity chambers defined between pistons slideable within respective cylinders, said pistons being displaceable relative to said cylinders upon rotation of said barrel to vary the volume of said chambers and thereby induce a flow of fluid through said chambers from an inlet port to an outlet port as said rotating group rotates; an adjustment assembly including an actuator to adjust the stroke of said pistons in 10 said cylinder and thereby adjust the capacity of said machine; a fluid supply for said actuator and a control valve interposed between said fluid supply and said actuator to control flow to said actuator, said fluid supply including a conduit to convey pressurized fluid from one of said ports to a load; a hydraulic accumulator connected to said conduit to store pressurised fluid from said 15 conduit and supply stored fluid to said control valve; and a check valve between said accumulator and said conduit to inhibit flow from said accumulator to said conduit upon reduction of pressure in said conduit below that of said accumulator whilst maintaining the application of stored fluid to said control valve.

2. A rotary hydraulic machine according to claim 1 wherein said control valve is a 20 closed centre valve and is moveable from a centred position in which flow to and from said actuator is inhibited to a first position in which flow to said actuator from said accumulator is permitted and to a second position in which flow from said actuator to a drain is permitted.

3. A rotary hydraulic machine according to claim 2 wherein a pair of actuators are 25 utilised in said adjustment assembly and when said valve is in said first position, to one of said actuators is connected through said valve to said accumulator and the other of said actuators is connected to drain, and, when said valve is in said second position, said one of said actuators is connected to drain and said other of said actuators is connected through said valve to said accumulator. 19

4. A rotary hydraulic machine according to claim 3 in which each of said actuators is single acting.

5. A rotary hydraulic machine according to claim 4 wherein each of said actuators is a linear actuator having a piston displaceable within a cylinder. 5

6. A rotary hydraulic actuator according to claim 5 wherein each of said actuators includes a spring to bias said actuator to a maximum capacity.

7. A rotary hydraulic actuator according to claim 6 wherein said one of said springs has a greater bias than the other to move said adjustment assembly to a position of maximum capacity in the absence of pressurised fluid in said accumulator. 10

8. A rotary hydraulic machine according to claim 1 wherein said accumulator includes a piston displaceable within a cylinder by application of fluid pressure against a spring bias.

9. A rotary hydraulic machine according to claim 8 wherein a stop is provided to limit displacement of said piston and thereby limit the force applied by said spring. 15

10. A rotary hydraulic machine according to claim 9 wherein said spring is a mechanical spring located within said cylinder.

11. A rotary hydraulic machine according to claim 10 wherein said spring is a coil spring and said stop is located within said cylinder and extends through said coil spring.

12. A rotary hydraulic machine according to claim 1 wherein said valve and said 20 accumulator are each located in respective bores in said housing and are interconnected by an internal gallery.

13. A rotary hydraulic machine according to claim 12 wherein said one of said ports is connected by an internal bore to said accumulator and said check valve is located in said internal bore. 25

14. A rotary hydraulic machine according to claim 13 wherein said internal bore is connected to said internal gallery to provide fluid to both said accumulator and said valve. 20

15. A rotary hydraulic machine according to claim 14 wherein said valve is a closed centre valve to inhibit flow of fluid through said valve in the absence of a control signal to adjust said stroke of said pistons.

16. A rotary hydraulic machine according to claim 15 wherein said adjustment 5 assembly includes a pair of actuators and said valve operates to supply fluid to one of said actuators from said source and connect the other of said actuators to a drain.

17. A rotary hydraulic machine having: a housing; a rotating group located within said housing and including a plurality of variable 10 capacity chambers defined between pistons slideable within respective cylinders, said pistons being displaceable relative to said cylinders upon rotation of said barrel to vary the volume of said chambers and thereby induce a flow of fluid through said chambers from an inlet port to an outlet port as said rotating group rotates; an adjustment assembly including a pair of actuators operable upon said rotating 15 group to adjust the stroke of said pistons in said cylinder and thereby adjust the capacity of said machine; a fluid supply for said actuators; and a control valve interposed between said fluid supply and said actuator to control flow to said actuators; 20 said fluid supply including: a pressurised fluid source; a hydraulic accumulator to store pressurised fluid from said source and apply stored fluid to said control valve; and a check valve to inhibit flow from said accumulator to said source upon 25 reduction of pressure at said source below that of said accumulator whilst maintaining the application of stored fluid to said control valve, each of said actuators being single acting and having a spring to bias respective ones to said actuators to a maximum capacity with one of said springs having a greater bias than the other to move said 21 adjustment assembly to a position of maximum capacity in the absence of pressurised fluid at said control valve.

18. A rotary hydraulic machine according to claim 17 wherein said pressurised fluid source is derived from one of said ports. 5

19. A rotary hydraulic machine having: a housing; a rotating group located within said housing and including a plurality of variable capacity chambers defined between pistons slideable within respective cylinders, said pistons being displaceable relative to said cylinders upon rotating of said barrel to vary 10 the volume of said chambers and thereby induce a flow of fluid through said chambers from an inlet port to an outlet port as said rotating group rotates; an adjustment assembly including an actuator operable upon said rotating group to adjust the stroke of pistons in said cylinder and thereby adjust the capacity of said machine; 15 a fluid supply for said actuator and a control valve interposed between said fluid supply and said actuator to control flow to said actuator; said fluid supply including: a pressurised fluid source; a hydraulic accumulator to store pressurised fluid from said source; and 20 a check valve between said accumulator and said source to inhibit flow from said accumulator to said source upon reduction of pressure at said source below that of said accumulator, said valve and said accumulator each being located in respective bores in said housing and interconnected by an internal gallery.

20. A rotary hydraulic machine according to claim 19 wherein said control valve is a 25 closed centre valve and is moveable from a centred position in which flow to and from said actuator is inhibited to a first position in which flow to said actuator from said accumulator is permitted and to a second position in which flow from said actuator to a drain within said housing is permitted. 22

21. A rotary hydraulic machine according to claim 20 wherein a pair of actuators are utilised in said adjustment assembly and when said valve is in said first position, to one of said actuators is connected through said valve to said accumulator and the other of said actuators is connected to drain, and, when said valve is in said second position, said 5 one of said actuators is connected to drain and said other of said actuators is connected through said valve to said accumulator.

22. A rotary hydraulic machine according to claim 21 wherein said pressurised fluid supply is derived from said ports.

23. A rotary hydraulic machine according to claim 22 wherein said one of said ports 10 is connected by an internal bore to said accumulator and said check valve is located in said internal bore.

24. A rotary hydraulic machine according to claim 23 wherein said internal bore is connected to said internal gallery to provide fluid to both said accumulator and said valve. 15

25. A rotary hydraulic machine according to claim 24 wherein said valve is a closed centre valve to inhibit flow of fluid through said valve in the absence of a control signal to adjust said stroke of said pistons.

26. A rotary hydraulic machine according to claim 25 wherein said adjustment assembly includes a pair of actuators and said valve operates to supply fluid to one of 20 said actuators from said source and connect the other of said actuators to a drain.

27. A rotary hydraulic machine according to claim 26 wherein said actuators are located in respective bores in said housing and internal galleries connect said actuators and said valve.

28. A rotary hydraulic machine substantially as herein described with reference to any 25 one of the embodiments of the invention illustrated in the accompanying drawings and/or examples. 23