Title:
Floating cup pump having swashplate mounted cup elements
Kind Code:
A1


Abstract:
A floating cup pump assembly incorporating a tilted swashplate structure with cup elements projecting away from either side of the swashplate structure. The swashplate structure is positioned between a first group of matedly engaged piston elements and a second group of matedly engaged piston elements. The piston elements rotate around a first axis and the cup elements rotate around a different axis causing the cups to reciprocate relative to the piston elements.



Inventors:
Nelson, Bryan E. (Lacon, IL, US)
Mehta, Viral S. (Peoria, IL, US)
Shah, Kirat (Dunlap, IL, US)
Application Number:
12/112475
Publication Date:
11/05/2009
Filing Date:
04/30/2008
Assignee:
CATERPILLAR INC. (Peoria, IL, US)
Primary Class:
Other Classes:
91/506, 417/271
International Classes:
F04B27/22
View Patent Images:
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20060251533Fluid metering with a disposable membrane type pump unitNovember, 2006Nighy et al.
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Primary Examiner:
LOPEZ, FRANK D
Attorney, Agent or Firm:
Caterpillar c/o LEYDIG, VOIT & MAYER, LTD (TWO PRUDENTIAL PLAZA SUITE 4900 180 N. STETSON AVE, CHICAGO, IL, 60601, US)
Claims:
What is claimed is:

1. A pump assembly comprising: a tilted swashplate structure; a first plurality of cup elements projecting away from a first side of said swashplate structure and a second plurality of cup elements projecting away from a second side of said swashplate structure facing away from said first side, said swashplate structure being disposed between a first plurality of piston elements and a second plurality of piston elements; said first plurality of piston elements projecting away from a first rotatable piston support towards said first side of said swashplate structure, at least one member of said first plurality of piston elements matedly engaging at least one member of said first plurality of cup elements; said second plurality of piston elements projecting away from a second rotatable piston support towards said second side of said swashplate structure, at least one member of said second plurality of piston elements matedly engaging at least one member of said second plurality of cup elements; at least one of said first rotatable piston support and said second rotatable piston support being adapted to rotate about a first axis, and at least one of said first plurality of cup elements and said second plurality of cup elements being adapted to rotate about a second axis in angled relation to said first axis.

2. The pump assembly as recited in claim 1, wherein at least one of said first rotatable piston support and said second rotatable piston support is disposed about a rotatable shaft assembly extending along said first axis.

3. The pump assembly as recited in claim 2, wherein each of said first rotatable piston support and said second rotatable piston support is disposed about said rotatable shaft assembly extending along said first axis.

4. The pump assembly as recited in claim 1, wherein said swashplate structure is supported in pivoting relation relative to a rotatable shaft assembly extending along said first axis.

5. The pump assembly as recited in claim 4, wherein at least one of said first plurality of cup elements and said second plurality of cup elements is supported at a carrier plate disposed adjacent said swashplate structure, said carrier plate including an opening disposed circumferentially about said rotatable shaft assembly, said opening being positioned axially along said rotatable shaft assembly in overlapping relation to at least a portion of a convex surface of a curved surface support element, said opening having a diameter greater than a leading edge of said curved surface support element and including a beveled or curved engagement surface adapted to slidingly engage said convex surface of said curved surface support element.

6. The pump assembly as recited in claim 5, wherein said curved surface support element is non-integral with said rotatable shaft assembly.

7. The pump assembly as recited in claim 6, wherein said curved surface support element is held in non-rotatable relation relative to said rotatable shaft assembly, such that rotation of said rotatable shaft assembly is translated to said curved surface support element.

8. The pump assembly as recited in claim 7, wherein said curved surface support element includes an interior portion adapted to engage a cooperating splined surface of said rotatable shaft assembly.

9. The pump assembly as recited in claim 8, wherein said interior portion of said curved surface support element includes a pattern of grooves, and said cooperating splined surface of said rotatable shaft assembly includes a pattern of ridges adapted to engage said grooves.

10. The pump assembly as recited in claim 8, wherein said interior portion of said curved surface support element includes a pattern of ridges, and said cooperating splined surface of said rotatable shaft assembly includes a pattern of grooves adapted to engage said ridges.

11. The pump assembly as recited in claim 7, wherein said leading edge of said curved surface support element projects towards said swashplate structure and wherein said curved surface support element is continuously biased towards said swashplate structure.

12. A pump assembly comprising: a tilted swashplate structure; a first plurality of cup elements projecting away from a first side of said swashplate structure and a second plurality of cup elements projecting away from a second side of said swashplate structure facing away from said first side, said swashplate structure being disposed between a first plurality of piston elements and a second plurality of piston elements, said first plurality of cup elements being mounted at a first carrier plate disposed adjacent the first side of said swashplate structure, said second plurality of cup elements being mounted at a second carrier plate disposed adjacent the second side of said swashplate structure; said first plurality of piston elements projecting away from a first rotatable piston support towards said first side of said swashplate structure, at least one member of said first plurality of piston elements matedly engaging at least one member of said first plurality of cup elements; said second plurality of piston elements projecting away from a second rotatable piston support towards said second side of said swashplate structure, at least one member of said second plurality of piston elements matedly engaging at least one member of said second plurality of cup elements; said first rotatable piston support and said second rotatable piston support each being disposed about a rotatable shaft assembly extending along a first axis and each of said first rotatable piston support and said second rotatable piston support being rotatable around said first axis, said swashplate structure being supported in pivoting relation relative to said rotatable shaft assembly, and each of said first carrier plate and said second carrier plate being rotatable about a second axis in angled relation to said first axis.

13. The pump assembly as recited in claim 12, said first carrier plate being supported at a convex surface of a first curved surface support element, said first curved surface support element being disposed circumferentially about said rotatable shaft assembly, said second carrier plate being supported at a convex surface of a second curved surface support element, said second curved surface support element being disposed circumferentially about said rotatable shaft assembly, said first carrier plate including a first carrier plate opening disposed circumferentially about said rotatable shaft assembly, said first carrier plate opening being positioned axially along said rotatable shaft assembly in overlapping relation to at least a portion of said first curved surface support element, said first carrier plate opening having a diameter greater than a leading edge of said first curved surface support element and including a beveled or curved engagement surface adapted to slidingly engage said convex surface of said first curved surface support element said second carrier plate including a second carrier plate opening disposed circumferentially about said rotatable shaft assembly, said second carrier plate opening being positioned axially along said rotatable shaft assembly in overlapping relation to at least a portion of said second curved surface support element, said second carrier plate opening having a diameter greater than a leading edge of said second curved surface support element and including a beveled or curved engagement surface adapted to slidingly engage said convex surface of said second curved surface support element.

14. The pump assembly as recited in claim 13, wherein each of said first curved surface support element and said second curved surface support element is non-integral with said rotatable shaft assembly.

15. The pump assembly as recited in claim 14, wherein each of said first curved surface support element and said second curved surface support element is held in non-rotatable relation relative to said rotatable shaft assembly, such that rotation of said rotatable shaft assembly is translated to each of said first curved surface support element and said second curved surface support element.

16. The pump assembly as recited in claim 15, wherein each of said first curved surface support element and said second curved surface support element includes an interior portion adapted to engage a cooperating splined surface of said rotatable shaft assembly.

17. The pump assembly as recited in claim 15, wherein said leading edge of said first curved surface support element projects towards said first side of said swashplate structure and said first curved surface support element is continuously biased towards said first side of said swashplate structure and wherein said leading edge of said second curved surface support element projects towards said second side of said swashplate structure and said second curved surface support element is continuously biased towards said second side of said swashplate structure.

18. A method for pumping a fluid, the method comprising the steps of: providing said fluid to a pump having a tilted swashplate structure defining a backing support for a first plurality of cup elements projecting away from a first side of said swashplate structure and a second plurality of cup elements projecting away from a second side of said swashplate structure facing away from said first side, said first plurality of cup elements matedly engaging a first plurality of piston elements, said second plurality of cup elements matedly engaging a second plurality of piston elements; introducing at least a portion of said fluid into said first plurality of cup elements and said second plurality of cup elements; reciprocating said first plurality of cup elements and said second plurality of cup elements relative to the matedly engaged piston elements; and expelling said fluid in a pressurized state.

Description:

TECHNICAL FIELD

This patent disclosure relates generally to pump assemblies and, more particularly, to floating cup pump assemblies utilizing a plurality of piston elements disposed around a first rotating surface and a plurality of complimentary cup elements disposed around a second rotating surface in angled relation to the piston elements. The cup elements reciprocate relative to the piston elements during rotation.

BACKGROUND

Pumping devices utilizing a plurality of piston elements mounted around a first rotor and a plurality of complimentary cup elements projecting away from a swash plate in angled relation to the piston rotor are generally known. United States Patent Application No. 2006/0222516 in the name of Achten, having a publication date of Oct. 5, 2006, discloses one such device. Embodiments of pumps described in this reference include a centrally disposed rotor having a plurality of pistons projecting away from both sides of the rotor. A pair of cooperating drum plates disposed outboard from the rotor support an arrangement of cup elements or drum sleeves adapted to house distal portions of the pistons. The rotor supporting the pistons rotates around a first axis of rotation. The drum plates rotate in angled relation to the first axis. The rotor supporting the pistons is rotated in tandem with the drum plates during operation. Due to the angle between the rotor and the drum plates, the cups are caused to stroke along the length of the corresponding piston elements such that the volume occupied by the piston elements is alternately increased and decreased during the rotational cycle. Thus, fluid introduced into a cup element when the complimentary piston is in a substantially withdrawn position may be pressurized and expelled as the cup is pushed inwardly during the rotational cycle.

In the noted reference, each of the drum plates housing the cup elements rotates around a convex centering surface or ball guide. In order to balance forces generated within the pump, the drum plates on either side of the central rotor are mounted and operated with substantial symmetry. A lack of symmetry leads to the pump operating in an unbalanced condition. Such unbalanced operation may degrade performance and introduce stresses which can cause damage. The need to maintain a substantially matched arrangement of drum plates in the prior device gives rise to a relatively complex initial construction process to ensure the desired matched angle and spacing on each side of the central rotor. Carrying out this initial construction may require a relatively high level of skill. Accordingly, an alternative construction which promotes balanced operation while reducing complexity is desirable.

BRIEF SUMMARY

The disclosure describes, in one aspect, a floating cup pump structure having a swashplate structure including a first side and an opposing second side facing away from the first side. A first plurality of cup elements projects away from the first side of the swashplate structure and a second plurality of cup elements projects away from the second side of the swashplate structure. The swashplate structure is positioned between a first group of piston elements mounted on a first rotatable piston support and a second group of piston elements mounted on a second rotatable piston support. At least one member of the first group of piston elements is adapted to engage a complimentary cup element projecting away from the first side of the swashplate structure. At least one member of the second group of piston elements is adapted to engage a complimentary cup element projecting away from the opposing side of the swashplate structure. The swashplate structure is angled relative to at least one of the rotatable piston supports.

In another aspect, this disclosure describes a method for pumping a fluid. The method includes providing a fluid to a pump having a tilted swashplate structure. A first plurality of cup elements projects away from a first side of the swashplate structure and a second plurality of cup elements projects away from a second side of the swashplate structure facing away from the first side. The first plurality of cup elements engages a first plurality of piston elements and the second plurality of cup elements engages a second plurality of piston elements. At least a portion of the fluid is introduced into the first plurality of cup elements and the second plurality of cup elements. The first plurality of cup elements and the second plurality of cup elements are reciprocated relative to the engaged piston elements, and the fluid is expelled in a pressurized state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away schematic view illustrating components of an exemplary floating cup pump assembly consistent with this disclosure;

FIG. 2 is an exploded schematic assembly view illustrating a curved surface support element relative to a rotatable shaft assembly as may be used in the exemplary floating cup pump assembly of FIG. 1; and

FIG. 3 is a cut-away schematic view illustrating a distal portion of a piston element at the interior of a cooperating cup element.

DETAILED DESCRIPTION

This disclosure relates to a floating cup pump assembly incorporating a swashplate structure with cup elements projecting away from a first side and an opposed second side of the swashplate structure. The swashplate structure is positioned between a first group of engaged piston elements and a second group of engaged piston elements. The swashplate structure is tilted to define angled backing support surfaces for carriers supporting the cup elements. The piston elements rotate around a first axis and the carriers supporting the cup elements follow the rotational movement of the piston elements. Due to the angled backing support provided by the swashplate structure, the cups are pushed around a second axis in angled relation to the first axis thereby causing the cups to reciprocate relative to the piston elements.

Reference will now be made to the drawings, wherein like reference numerals designate like elements in the various views. FIG. 1 illustrates a pump assembly 10 adapted to be mounted within a housing 11. In this exemplary construction, a rotatable shaft assembly 12 extends along a first axis 13. The rotatable shaft assembly 12 is adapted for rotation around the first axis 13 by use of an engine or other external power source. As illustrated in FIGS. 1 and 2, the exemplary pump assembly 10 includes a swashplate structure 14 in the form of a disk or plate structure. As shown, the swashplate structure 14 is mounted in tilted orientation relative to the rotatable shaft assembly 12. In this regard, the swashplate structure 14 is mounted around the rotatable shaft assembly 12 by a bearing connection 16 or the like such that swashplate structure 14 may tilt or wobble in a direction corresponding generally to the first axis 13 during operation as represented by the double arrows and as will be described more fully hereinafter.

In the exemplary construction illustrated in FIG. 1, the swashplate structure 14 defines a backing support for an arrangement of first cup elements 18 having openings projecting away from a first face of the swashplate structure 14 and an arrangement of second cup elements 19 projecting away from a second face of the swashplate structure 14. In the illustrated construction, the arrangement of first cup elements 18 is mounted on a first carrier plate 44 disposed adjacent to the first face of the swashplate structure 14. The arrangement of second cup elements 19 is mounted on a second carrier plate 45 disposed adjacent to the second face of the swashplate structure 14. The first carrier plate 44 and the second carrier plate 45 are substantially free-floating such that the arrangement of first cup elements 18 and the arrangement of second cup elements 19 may move circumferentially during operation as will be described further hereinafter.

As shown, the first cup elements 18 matedly engage distal portions of a plurality of complementary first piston elements 20. The second cup elements 19 matedly engage distal portions of a plurality of complementary second piston elements 21. The first piston elements 20 extend away from a first rotatable piston support 22. The second piston elements 21 extend away from a second rotatable piston support 23. As illustrated, the first rotatable piston support 22 and the second rotatable piston support 23 are disposed radially about rotatable the shaft assembly 12 in generally opposing relation to one another on either side of the swashplate structure 14. According to the illustrated construction, the first piston elements 20 have a generally hollow, frusto-conical configuration with an increased diameter distal portion and a fluid passageway 26 running along the length from the distal portion to a proximal portion held at the first rotatable piston support 22. Likewise, the second piston elements 21 have a generally hollow, frusto-conical configuration with an increased diameter distal portion and a fluid passageway 27 running along the length from the distal portion to a proximal portion held at the second rotatable piston support 23. However, other suitable constructions may likewise be utilized as desired. It is to be understood that while the cross-sectional view of FIG. 1 illustrates one pair of first cup elements 18 and one pair of second cup elements 19, numerous first cup elements 18 are arranged in a circumferential pattern to project away from a first side of the swashplate structure 14. Likewise, numerous second cup elements 19 are arranged in a circumferential pattern to project away from an opposing second side of swashplate structure 14. Numerous first piston elements 20 are arranged circumferentially around first rotatable piston support 22 so as to matedly engage complementary first cup elements 18 during operation. Numerous second piston elements 21 are arranged circumferentially around second rotatable piston support 23 so as to matedly engage complementary second cup elements 19 during operation. Although the first piston elements 20 and the second piston elements 21 are illustrated as being in substantially aligned, opposing relation, it is also contemplated that the first piston elements 20 and the second piston elements 21 may be offset relative to one another if desired.

In the illustrated construction of FIG. 1, the first rotatable piston support 22 and the second rotatable piston support 23 are operatively connected in substantially coaxial relation to rotatable shaft assembly 12 such that rotation of rotatable shaft assembly 12 causes the first rotatable piston support 22 and the second rotatable piston support 23 to rotate about the first axis 13. However, the first carrier plate 44 and the second carrier plate 45 are oriented at an angle relative to the rotatable shaft assembly 12 and the first axis 13 due to the angled orientation of the swashplate structure 14 which defines a backing support. Accordingly, the first cup elements 18 and the second cup elements 19 supported thereon are rotatable around a second axis 15 disposed in angled relation to the rotatable shaft assembly 12.

According to the exemplary construction, the first carrier plate 44 is supported radially in this angled orientation by a first curved surface support element 40 alternatively referred to as a “ball guide” which is arranged about the rotatable shaft assembly 12. Likewise, the second carrier plate 45 is supported radially in this angled orientation by a second curved surface support element 41. As best illustrated through joint reference to FIGS. 1 and 2, each of the first curved surface support element 40 and the second curved surface support element 41 may include a convex exterior support surface 42 adapted to engage a carrier plate 44 operatively connected across one side of the swashplate structure 14. In the illustrated construction, the convex exterior support surface 42 tapers inwardly from a base portion 46 of enhanced diameter towards a leading edge 48 of reduced diameter such that the leading edge 48 projects generally towards the swashplate structure 14.

By way of example only, and not limitation, it is contemplated that each of the first curved surface support element 40 and the second curved surface support element 41 may have a substantially unitary construction formed by techniques such as casting, powder metallurgy, or other suitable formation techniques using metal alloys or other materials adapted to withstand substantial cyclical stresses. However, it is likewise contemplated that portions may be formed separately and thereafter joined together if desired. According to one contemplated practice, the first curved surface support element 40 and/or the second curved surface support element 41 may be formed separately from components of the rotatable shaft assembly 12 such that the first curved surface support element 40 and/or the second curved surface support element 41 is non-integral with the rotatable shaft assembly 12. Accordingly, the first curved surface support element 40 and/or the second curved surface support element 41 may be held in separable relationship relative to the rotatable shaft assembly 12. That is, the first curved surface support element 40 and/or the second curved surface support element 41 may be subject to nondestructive removal from the rotatable shaft assembly 12 upon disassembly of the pump assembly 10. Of course, the first curved surface support element 40 and/or the second curved surface support element 41 may also be formed in integral relation with the rotatable shaft assembly 12 by techniques such as casting, machining or the like.

By way of example only, and not limitation, FIG. 2 illustrates one arrangement for operative connection between the rotatable shaft assembly 12 and an independently formed curved surface support element. In the illustrated arrangement, the rotatable shaft assembly 12 includes a splined collar 50 having a pattern of ridges 52 extending longitudinally along a portion of the splined collar 50. The ridges 52 are adapted to cooperatively engage a pattern of grooves 54 arranged around an interior portion of the curved surface support element. Accordingly, the curved surface support element may slide over rotatable shaft assembly 12 until engaging the splined collar 50. At the splined collar 50, the ridges 52 engage the grooves 54 thereby preventing relative rotational movement between the curved surface support element and the rotatable shaft assembly 12. However, the curved support element may nonetheless retain the ability to engage in some degree of sliding movement relative to the rotatable shaft assembly 12. Of course, it is to be understood that the illustrated construction is exemplary only and that any number of other constructions may likewise be utilized. By way of example only, and not limitation, in one such alternative arrangement the interlocking ridges and grooves may be reversed if desired such that the ridges are disposed at the interior of the curved surface support element with corresponding grooves being located along the splined collar 50.

As shown in FIG. 1, the rotatable shaft assembly 12 extends through a first carrier plate opening 60 in the first carrier plate 44 and through a corresponding second carrier plate opening 61 in the second carrier plate 45. Each of the first carrier plate opening 60 and the second carrier plate opening 61 has a diameter sized to permit acceptance of the leading edge of the corresponding first curved surface support element 40 or second curved surface support element 41 without passing the base portion. In the exemplary construction, the first curved surface support element 40 is continuously biased inwardly towards the first carrier plate opening 60 and the swashplate structure 14 by use of a first compression spring 64 or other biasing elements disposed at positions around the rotatable shaft assembly 12. Likewise, the second curved surface support element 41 is continuously biased inwardly towards the second carrier plate opening 61 and the swashplate structure 14 by use of a second compression spring 65 or other biasing elements disposed at positions around the rotatable shaft assembly 12. In operation, the first compression spring 64 and the second compression spring 65 apply compression forces which operate along a line of force substantially parallel to the rotatable shaft assembly 12 and the first axis 13. As shown, the first compression spring 64 or other biasing elements may operate directly against the first curved surface support element 40 and the first rotatable piston support 22 without the need for intermediate structures, although such intermediate structures such as anti-friction rings and the like may be used if desired. Likewise, the second compression spring 65 or other biasing elements may operate directly against the second curved surface support element 41 and the second rotatable piston support 23 without the need for intermediate structures, although such intermediate structures such as anti-friction rings and the like may be used if desired. It is also contemplated that spacer sleeve or other spacing element may be used in place of the first compression spring 64 and the second compression spring 65 if desired.

In the illustrated construction, the first carrier plate opening 60 is surrounded by a first beveled or curved engagement surface 62 adapted to engage the convex exterior support surface of the first curved surface support element 40 in substantially complimentary relation. Likewise, the second carrier plate opening 61 is surrounded by a second beveled or curved engagement surface 63 adapted to engage the convex exterior support surface of the second curved surface support element 41 in substantially complimentary relation. As the rotatable shaft assembly 12 rotates during operation, the first carrier plate 44 and the second carrier plate 45 are likewise caused to rotate due to circumferential pushing action by the first piston elements 20 and the second piston elements 21. During this rotation, the swashplate structure 14 does not rotate but may carry out a dynamic wobbling motion in the axial direction as forces are applied and relieved during different stages of the rotational cycle. During this wobbling motion portions of the first beveled engagement surface 62 move axially along the first curved surface support element 40 and portions of the second beveled engagement surface 63 move axially along the second curved surface support element 41. Thus, the first curved surface support element 40 and the second curved surface support element 41 provide radial support while nonetheless permitting the first carrier plate 44 and the second carrier plate 45 to wobble in concert with the swashplate structure 14 to accommodate forces applied to opposing faces of the swashplate structure 14 during operation.

Referring jointly to FIGS. 1 and 3, during operation of the pump assembly 10, a fluid such as oil, hydraulic fluid, cooling fluid or the like may be introduced through a first inlet opening 70 and a second inlet opening 71. As shown, the first inlet opening 70 is positioned for alignment with a first fluid passageway 26 in a first piston element 20 when the first piston element 20 is at a position of maximum withdrawal relative to a corresponding first cup element 18. Likewise, the second inlet opening 71 is positioned for alignment with a second fluid passageway 27 in a second piston element 21 when the second piston element 21 is at a position of maximum withdrawal relative to a corresponding second cup element 19. As best illustrated in FIG. 3, the first cup elements 18 have a cross-sectional shape and size substantially corresponding to distal portions of the first piston elements 20. The second cup elements 19 likewise have a cross-sectional shape and size substantially corresponding to distal portions of the second piston elements 21. In the illustrated construction, piston rings 74 are used to provide a substantially fluid tight sealing relation. However, it is also contemplated that piston rings 74 may be eliminated if a sufficient direct sealing relation can be achieved.

Regardless of whether or not piston rings 74 are utilized, the first cup elements 18 circumferentially surround distal portions of corresponding first piston elements 20 such that the first piston elements 20 cooperate with interior boundary walls of the first cup elements 18 to define a plurality of variable volume first compression chambers 80. Likewise, the second cup elements 19 circumferentially surround distal portions of corresponding second piston elements 21 such that the second piston elements 21 cooperate with interior boundary walls of the second cup elements 19 to define a plurality of variable volume second compression chambers 81. As rotatable shaft assembly 12 rotates around the first axis 13, a corresponding circumferential rotation is imparted to the first rotatable piston support 22 and to the second rotatable piston support 23. As the first rotatable piston support 22 and the second rotatable piston support 23 rotate around the first axis 13, the first piston elements 20 and the second first piston elements 21 impart a circumferential pushing force to the engaged first cup elements 18 and second cup elements 19 thereby causing the first carrier plate 44 and the second carrier plate 45 to rotate circumferentially. Due to the orientation of the swashplate structure 14, the first carrier plate 44 and the second carrier plate 45 rotate around the second axis 15 in angled relation to the first axis 13. Due to the different axis of rotation, during the rotational cycle, the first cup elements 18 reciprocate relative to the first piston elements 20 and the second cup elements 19 reciprocate relative to the second piston elements 21. This reciprocating action gives rise to changes in the volumetric capacity of the first compression chambers 80 and the second compression chambers 81. In this regard, the volumetric capacity cycles progressively between a high capacity filling stage with the first piston elements 20 and the second piston elements 21 substantially withdrawn as shown in the upper left and lower right portions of FIG. 1 and a low capacity expulsion stage with the first piston elements 20 and the second piston elements 21 substantially fully inserted as shown in the upper right and lower left portions of FIG. 1. At the low capacity expulsion stage the first fluid passageways 26 and the second fluid passageways 27 become aligned with first outlet ports 84 and second outlet ports 85 thereby allowing the fluid to be expelled in a pressurized state. The flows from the first outlet ports 84 and the second outlet ports 85 may thereafter be combined to form a single fluid stream if desired. The floating engagement between the curved surface support elements and the beveled or curved engagement surfaces allows for naturally occurring minor tilting adjustments during the rotational cycle.

INDUSTRIAL APPLICABILITY

The industrial applicability of the pump assembly described herein will be readily appreciated from the foregoing discussion. Pump assemblies consistent with the present disclosure may be used to convey fluids through various systems in an efficient manner while maintaining proper operative relation of the various components. By way of example only, and not limitation, exemplary fluids conveyed by the pump assembly may include lubricants, hydraulic fluids, cooling fluids and the like.

In practice, a pump assembly consistent with this disclosure may be utilized in environments such as industrial equipment, transportation vehicles and the like where substantial durability is required. In such environments, a self-balancing swashplate structure supporting an arrangement of cup elements engaging piston elements on either side of the swashplate structure may tend to balance forces and promote stability of operation.

It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to examples herein are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure or claims more generally. Accordingly, this disclosure contemplates the inclusion of all modifications and equivalents of the subject matter recited in the appended claims as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context.