RADIAL PISTON PUMPS AND MOTORS

Abstract

A radial piston pump 101 comprising a rotor 103 is disclosed. The rotor 103 includes a drive shaft 105 arranged to transmit rotary motion to or from the pump 101 and a piston housing 102 including at least one piston chamber 104, the at least one piston chamber 104 being arranged to receive a piston 108. The drive shaft 105 and the piston housing 102 are integrally formed.

Claims

1. A radial piston pump comprising a rotor, the rotor including a drive shaft arranged to transmit rotary motion to or from the pump and a piston housing including at least one piston chamber, the at least one piston chamber being arranged to receive a piston and wherein the drive shaft and the piston housing are integrally formed.

2. A radial piston pump according to claim 1, wherein the pump further comprises a main housing, the rotor being mounted for rotation relative to the main housing, the main housing comprising a first cam surface arranged to control the radial movement of a piston located in the at least one piston chamber when the pump is in use and wherein the main housing and the first cam surface are integrally formed.

3. A radial piston pump according to claim 2, wherein the rotor further comprises a sequencing assembly arranged to control the flow of fluid into and out of the at least one piston chamber as the rotor rotates relative to the main housing and wherein at least part of the sequencing assembly is integrally formed with the rotor and/or the main housing.

4. A radial piston pump according to claim 3, wherein the sequencing assembly comprises a first set of ports integrally formed with the rotor.

5. A radial piston pump according to claim 3, wherein the sequencing assembly comprises a second set of ports integrally formed with the main housing.

6. A radial piston pump according to claim 5, wherein the main housing further comprises at least one integrally formed pump inlet or pump outlet and at least one integrally formed flow gallery connecting the at least one pump inlet or pump outlet with a port of the second set.

7. A radial piston pump according to claim 2, wherein the main housing further comprises a second cam surface spaced apart from the first cam surface.

8. A radial piston pump according to claim 1, wherein the rotor includes a first series of piston chambers spaced apart around the circumference of the piston housing at a first location and a second series of piston chambers spaced apart around the circumference of the piston housing at a second location, spaced apart from the first location along the longitudinal axis of the rotor.

9. (canceled)

10. A radial piston pump according to claim 1, wherein the pump is an inside impinged pump.

11. (canceled)

12. (canceled)

13. A method of manufacturing a radial piston pump, the pump comprising a drive shaft arranged to transmit rotary motion to or from the pump and a piston housing including at least one piston chamber, the piston chamber being arranged to receive a piston, the method comprising the step of forming a rotor including the drive shaft and the piston housing as a single piece using an additive manufacturing process.

14. A method according to claim 13, wherein the pump further comprises a main housing, the main housing comprising a first cam surface arranged to control the radial movement of a piston located in that at least one piston chamber, and wherein the method further comprises the step of forming the main housing and the first cam surface as a single piece using an additive manufacturing process.

15. (canceled)

16. (canceled)

17. A radial piston pump comprising at least one piston mounted for reciprocal movement in a piston housing and a cam including a cam surface arranged to control the motion of the at least one piston when the piston housing rotates relative to the cam about a first axis, wherein the cam is mounted for axial movement relative to the piston housing along the first axis and the profile of the cam surface varies across the width of the cam such that moving the cam relative to the piston housing along the first axis changes the motion of the piston.

18. A radial piston pump according to claim 17, wherein the profile of the cam surface varies across the width of the cam such that moving the cam relative to the piston assembly along the first axis changes the amplitude of the piston motion.

19. A radial piston pump according to claim 17, wherein the profile of the cam surface varies across the width of the cam such that moving the cam relative to the piston assembly along the first axis changes the frequency of the piston motion.

20. (canceled)

21. (canceled)

22. A radial piston pump according to claim 17, wherein the piston is mounted for reciprocal movement in a piston chamber formed in the piston housing and the pump further comprises a sequencing element arranged to permit the flow of fluid into and out of the piston chamber as the piston housing rotates relative to the sequencing assembly about the first axis, and wherein the cam is mounted for rotation about the first axis relative to the sequencing element such that the phase difference between the movement of the piston and the flow of fluid to and from the piston chamber can be varied.

23. A radial piston pump according to claim 17, wherein a hydraulic actuator is arranged to move the cam relative to the piston assembly along the first axis.

24. A radial piston pump according to claim 17, wherein the cam surface is located radially outside the piston housing.

25. A radial piston pump according to claim 17, wherein the pump is an internally impinged radial piston pump.

26. A radial piston pump according to claim 17, wherein the pump comprises a plurality of piston assemblies, each piston assembly including at least one of the plurality of pistons, a roller arranged to follow the cam surface when the piston housing rotates relative to the cam surface, and a thrust bearing, the axis of the thrust bearing being parallel to the first axis.

27. A radial piston pump according to claim 17, wherein the profile of the cam surface is arranged to provide 2 or more piston cycles per revolution.

28. A method of varying the flow of fluid through a radial piston pump, the piston pump comprising a piston housing including a plurality of pistons mounted therein and a cam surface, each piston being connected to a cam follower arranged to follow the cam surface when the piston housing rotates relative to the cam surface about a first axis, and wherein the profile of the cam surface varies with distance along the first axis, the method comprising the steps of: rotating the piston housing relative to the cam surface at a first location such that a first piston motion is produced, rotating the piston housing relative to the cam surface at a second location, spaced apart from the first location along the first axis, such that a second, different, piston motion is produced.

29. (canceled)

30. A method according to claim 28, wherein the piston pump further comprises a sequencing element and the method further comprises the step of rotating the cam about the first axis from a first angular position relative to the sequencing element to a second angular position relative to the sequencing element such that the flow of fluid through the pump is reversed.

31. (canceled)

32. (canceled)

33. A radial piston pump comprising a primary cam surface, at least one secondary cam surface and at least one piston assembly comprising a first piston, the first piston being mounted for reciprocal movement in a piston housing, said piston housing being arranged to rotate relative to the primary cam surface, the piston assembly further comprising a primary roller connected to the first piston and arranged to follow the primary cam surface when the piston housing rotates relative to the primary cam surface, and a secondary roller connected to the first piston and arranged to follow a secondary cam surface as the primary roller follows the primary cam surface.

34. A radial piston pump according to claim 33, wherein the piston housing is arranged to rotate relative to the at least one secondary cam surface.

35. (canceled)

36. (canceled)

37. (canceled)

38. A radial piston pump according to claim 33, wherein the at least one secondary cam surface defines a recess arranged to receive the secondary roller while the primary roller follows the primary cam surface.

39. (canceled)

40. (canceled)

41. A radial piston pump according to claim 33, wherein the piston assembly comprises a second piston, the first and second pistons being arranged on either side of the primary roller.

42. (canceled)

43. (canceled)

44. (canceled)

45. (canceled)

46. A radial piston pump according to claim 33, wherein the primary or secondary roller comprises a member connected to the piston assembly by a roller bearing and the pump is arranged such that, in use, the surface of the roller adjacent to the cam surface is the outer surface of the member.

47. A radial piston pump according to claim 33, wherein the piston assembly comprises a thrust bearing.

48. (canceled)

49. (canceled)

50. (canceled)

51. (canceled)

52. (canceled)

Description

DESCRIPTION OF THE DRAWINGS

[0104] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0105] FIG. 2 shows a schematic cross-sectional view of a pump according to a first embodiment of the invention;

[0106] FIG. 3 shows a schematic plan view of the pump of the first embodiment.

[0107] FIG. 4 shows a cross-sectional view of a pump according to a second embodiment of the invention;

[0108] FIG. 5 shows a perspective view of the rotor of the pump of the second embodiment;

[0109] FIG. 6 shows a perspective view of (a) the front and (b) the rear of the main housing of the pump of the second embodiment;

[0110] FIG. 7 shows a perspective view of the piston assembly of the pump of the second embodiment;

[0111] FIG. 8 shows a cross-sectional schematic view of a pump according to a third embodiment of the invention;

[0112] FIG. 9 shows a cross-sectional view of a pump according to a fourth embodiment of the invention.

[0113] FIG. 10 shows a perspective cross-sectional view of the piston housing of the pump of the fourth embodiment;

[0114] FIG. 11 shows a perspective view of the cam of the pump of the fourth embodiment;

[0115] FIG. 12 shows a perspective view of the piston assembly of the pump of the fourth embodiment.

[0116] FIG. 13 shows a perspective view of a piston assembly of a pump in accordance with a fifth embodiment.

DETAILED DESCRIPTION

[0117] FIG. 2 shows a cross-sectional schematic view of a pump 101 in accordance with a first example embodiment of the invention. The pump 101 comprises a rotor 103 including an integrally formed drive shaft 105 and piston housing 102. The piston housing 102 comprises a plurality of radially extending tube-like walls 102a that appear rectangular when viewed in cross-section in FIG. 2 and which project from the outer surface of the rotor 103. Each cylindrical wall 102a is spaced apart from the other cylindrical walls 102a and defines a piston chamber 104 in which a piston 108 is received. The piston chamber walls 102a (and the corresponding pistons 108) are arranged in two rows, each row extending around the circumference of the rotor 103. The two rows are spaced apart along the longitudinal axis of the rotor 103, labelled A in FIG. 2. In the cross-sectional view of FIG. 2, four pistons 108 can be seen; one pair of pistons 108 on either side (upper and lower) of the rotor 103. The two pistons 108 of each pair are joined by a pin 114 that extends through the distal end of each piston 108. The pin 114 is mounted for rotation relative to the two pistons 108. Located between each pair of pistons 108, along the axis of the pin 114 is a roller 110 mounted for rotation relative to the pistons 108 and the pin 114. The two pistons 108, pin 114, and roller 110 may together be referred to as a piston assembly 106. A flow gallery 118 in the single piece rotor 103 links each piston chamber 104 to a port 120 formed in an inside surface of the rotor 103. When assembled, as shown in FIG. 2, the roller 110 contacts an inward facing primary cam surface 112. The outer surface of the pin 114 simultaneously contacts an outward facing secondary cam surface 116 at either end. The two secondary cam surfaces 116 are spaced apart along the longitudinal axis A of the rotor 103 and are located radially inside and concentric with the primary cam surface 112. The primary cam surface 112 and left-hand side secondary cam surface 116 are integrally formed as part of a main housing 122. Also integrally formed with the main housing 122 is a central cylindrical projection 124, which appears rectangular when viewed in cross-section in FIG. 2. The projection 124 is concentrically located with respect to the cam surfaces 112, 116 and extends from the rear wall of the housing 122, shown on the left hand side of FIG. 2 into a cavity the radial extent of which is defined by the primary cam surface 112. The rotor 103 is mounted for rotation on the cylindrical projection 124 such that the ports 120 formed in the inside surface of the rotor 103 (the rotor-side ports 120) are aligned axially with a series of ports 121 (the main-housing side ports 121) extending around the circumference of the projection 124. A lid 130 closes off the cavity defined by the cam surface 112. The right-hand side secondary cam surface 116 is integrally formed with the lid 130. The drive shaft 105 projects through an aperture in the lid 130. A plurality of flow galleries (not shown) extend along the interior of the projection 124 and link each port 121 with either a pump inlet (not shown), in which case the port 121 is an inlet port 121.sub.in or a pump outlet (not shown), in which case the port 121 is an outlet port 121.sub.out.

[0118] FIG. 3 shows a cross-sectional plan view of the pump of FIG. 2. When viewed in cross-section in FIG. 3 it can be seen that the profile of the primary cam surface 112 includes two regions of reduced radius 112a located at approximately 90 degrees and 270 degrees around its circumference. The cam surface 112 also includes two regions of increased radius 112b located at approximately 0 degrees and 180 degrees. Accordingly, the profile of the primary cam surface 112 varies periodically with a frequency of two. The profile of the secondary cam surface 116 varies in a similar manner such that the radial distance between the primary cam surface 112 and secondary cam surface 116 remains substantially constant around the closed-loop cam surfaces.

[0119] In use, rotation of the drive shaft 105 causes the piston housing 102 which is formed as a single piece with the drive shaft 105 to rotate. Roller bearing 110 and pin 114 each follow the corresponding cam surface 110, 116 as the piston housing 102 moves relative to the main housing 122. As a piston moves towards a region of reduced radius 112a the radius of the inward-facing cam surface 112 decreases and the piston is pushed into the piston chamber 104 expelling the liquid located therein through flow gallery 118 to port 120. Similarly, as a piston moves towards a region of increased radius 112b the radius of the primary cam surface 112 increases and so does the radius of the secondary cam surface 116. As a result of the increase in radius of the secondary, outward facing, cam surface 116, the contact between the pin 114 and the cam surface 116 pulls the piston 108 out of its piston chamber 104 drawing liquid into the piston chamber 104 through flow gallery 118 and port 120.

[0120] As the rotor rotates relative to the main housing each rotor-side port 120 moves into and out of alignment with the ports 121 formed in the main housing. Outlet ports 121.sub.out formed in the main housing 122 are located opposite regions where the radius of the cam surface 112 reduces with rotation. Accordingly, as fluid is expelled from the piston chamber 104 the rotor-side port 120 comes into alignment with a main housing-side outlet port 121.sub.out connected to the pump outlet and the fluid in the piston chamber 104 is expelled to the pump outlet via the ports 120,121.sub.out. Similarly, inlet ports 121.sub.in formed in the main housing 122 are located opposite regions of increasing radius of the cam surface 112. As a piston 108 moves out of its piston chamber 104 the rotor-side port 120 comes into alignment with a main housing-side inlet port 121.sub.in connected to the pump inlet and fluid is drawn into the piston chamber 104 from the pump inlet via the ports 120,121.sub.in. As the profile of the cam surfaces 112, 116 has a frequency of two, this cycle is repeated twice for each complete rotation of the piston housing 102 relative to the main housing 122 and the pump may be referred to as a two-stroke pump.

[0121] The passage above describes the apparatus 101 being used as a pump. It will be appreciated that the apparatus 101 can also be used as a motor by driving a flow of fluid through the apparatus 101 and thereby turning the drive shaft 105.

[0122] The rotor 103 including piston housing 102 and drive shaft 105 is made as a single part in steel using an additive manufacturing process. The main housing 122 including piston housing 102, cylindrical projection 124, primary cam surface 112 and a secondary cam surface 116 is also made as a single part using an additive manufacturing process. The piston 108 is made using an additive manufacturing process. Once the rotor 103 and main housing 122 have been formed using additive manufacturing, subtractive manufacturing techniques are used to finish the components.

[0123] Providing primary and secondary rollers 110, 114 and multiple cam surfaces 112,116 in accordance with the present embodiment may remove the need for a spring arranged to urge each piston outwards (as discussed with reference to FIG. 1) and accordingly further reduce the number of components and potentially the size of the pump.

[0124] Pumps in accordance with the present embodiment may be smaller and/or more efficient than prior art pumps for a given flow rate for a number of reasons. Integrating multiple functions (for example the drive shaft, piston housing and elements of the sequencing functions in one component allows for the number of components to be reduced, in particular because additional bearings and seals that would have been needed between separate components are no longer required. Using additive manufacturing to produce the rotor, main housing, lid and elements of the piston assembly increases design freedom allowing each component to be more efficiently packaged. Using additive manufacturing to produce various components allows the commercial production of features such as the radially projecting piston chamber walls which can reduce the weight of a component compared to prior art pumps.

[0125] FIG. 4 shows a cross sectional view of a pump 201 in accordance with a second example embodiment of the invention. FIGS. 5 to 7 show the rotor, main housing, and piston assembly respectively of the pump of the second embodiment in more detail.

[0126] Only those aspects of the second embodiment which differ significantly from the first embodiment will be discussed here.

[0127] The rotor 203 of the pump of the second embodiment (see FIG. 5 for more detail) comprises a drive shaft 205 having an output spline 205a at a first end which is integrally formed with the piston housing 202 at the other end. The piston chamber walls 202a of the piston housing 202 are arranged in two parallel rings extending around the circumference of the housing 202 with cross-bracing 102b extending between each wall 202a.

[0128] The main housing 222 (see FIG. 6 for more detail) comprises a cam surface 212 having a profile with four lobes. That is to say the cam surface 212 has a frequency of four and the pump 201 is a four stroke pump. The housing 222 includes two external ports 232; a pump inlet and a pump outlet. A series of flow channels 218 extends between the external ports 132 and the internal ports 220. The exterior of the flow channels can be seen in FIG. 6(b). The flow galleries 118 are also seen in cross section in FIG. 4, with several branching, curvilinear flow galleries 218 extending along the interior of the projection 224 and connecting the main housing-side ports 120 with the pump inlet/outlet.

[0129] Each piston 208 of a piston assembly 206 (see FIG. 7) has a cavity 208a extending along the length of the piston. An outlet aperture 208b is formed in the wall of the cavity 208a adjacent the distal end of the piston 208. As in the previous embodiment, the pistons 208 are arranged symmetrically either side of a primary roller 110. An interlocking shaft 244 extends thorough the upper end of both pistons 208 and the roller 210, and protrudes beyond the pistons 208. A needle bearing 214 sits on each protruding end of the interlocking shaft 244. In use, the outer surface of the outer race of each needle bearing 214 rolls along a secondary cam surface 216 formed in a slot 224. The roller bearing 210 of each piston assembly 206 sits radially outside the piston housing 202 and contacts the inward facing cam surface 212.

[0130] In use, the cavity 208a of each piston 208 is filled with a liquid having a similar density to the liquid being moved by the pump. Liquid may flow from the cavity 208a to the cam surface 212 via the outlet 208b thereby providing a hydraulic bearing between the roller 210 and the cam surface 212.

[0131] Pumps in accordance with the present embodiment may experience reduced radial thrust loads as the hollow piston has a reduced inertia compared with prior art pistons which may allow them to run at higher frequencies. Interlocking the two pistons 108 such that their position relative to one another is fixed has been found to better balance the loads experienced by the piston assembly.

[0132] FIG. 8 shows a cross-sectional view of a variable displacement radial piston pump 301 in accordance with a third embodiment of the invention. Only those aspects of the third embodiment which differ significantly from the first and second embodiments will be discussed in detail. In contrast to the first and second embodiments, the primary cam surface 312 of the third embodiment forms part of a component, cam 311, which is separate from the main housing 322. The cam surface 312 of the cam 311 is flared such that the inner diameter of the cam surface 312 increases with distance along the longitudinal axis of the pump. Each piston assembly 306 of the third embodiment is associated with a different pair of secondary cam surfaces 316. The secondary cam surfaces 316 of the third embodiment are integrally formed in the piston housing 302. Each secondary cam surface 316 of the third embodiment defines a slot 317 (shown in cross-section in FIG. 8). When assembled, as shown in FIG. 8, the roller 310 contacts the cam surface 312 of the cam 311. Each end of the pin 314 is located in a corresponding slot 317 and in contact with the secondary cam surface 316 that defines the slot.

[0133] In use, the cam 311 is mounted for movement along the longitudinal axis of the pump (labelled A in FIG. 8). As a result of the flaring of the cam surface 312 when the cam 311 is moved parallel to the drive shaft 305 the profile of the portion of the cam surface 312 with which the roller bearing 310 is in contact will change and accordingly the movement of the piston will be altered. In the third embodiment, the degree of excursion of the piston increases as the cam is moved to the right of FIG. 8 and decreases as the cam is moved to the left. Thus, by varying the axial position of the cam 311 relative to the piston assemblies 306 of the piston housing 304 the displacement of the pistons, and accordingly the volumetric flow rate of the pump can be varied. Pumps in accordance with the second embodiment may therefore allow for increased efficiency over a wider range of speeds that prior art pumps. Mounting the cam 311 for movement along an axis parallel to that of the drive shaft may also allow pumps in accordance with the second embodiment to have a more compact design than prior art variable displacement pumps.

[0134] In use, slot 317 in piston housing 306 rotates with the piston assembly relative to the cam and each end of the pin 314 moves up and down in the slot 317 as the roller 310 follows the cam surface 312. Each end of the pin 314 rolls on the secondary cam surface 316 of the slot 317.

[0135] Using a secondary roller 314 in combination with a primary roller 310 may allow both the torque loads generated by the interaction of the cam surface 312 and roller 310 to be rolled. In pumps in accordance with the present embodiment this may reduce the amount of work required to rotate the piston housing 302 relative to the cam surface 310, thereby increasing the efficiency of the pump. It may also remove the need for a separate bearing between the rotor 303 and the protrusion of the main housing 324 (or in pumps having a separate drive shaft and piston housing reducing the load may remove the need for a bearing between those two components). Removing the need for separate bearings may reduce the complexity and/or cost of the pump, reduce maintenance costs and/or extend the life of the pump, increase the efficiency of the pump and/or allow the size of the pump to be reduced.

[0136] FIG. 9 shows a cross-sectional view of a variable displacement radial piston pump 401 in accordance with a fourth embodiment of the invention. FIG. 10 shows the piston housing 402 of the fourth embodiment in more detail.

[0137] FIG. 11 shows the cam 411 of the fourth embodiment in more detail. At a first end, the cam surface 412 is substantially circular, while at the other end, the cam surface 412 curves in a periodic manner creating a profile with six lobes 412a and a larger minimum diameter than the circle of the first end. The profile of the cam varies gradually across the width of the cam surface between the circular profile of the first end and the lobed profile of the second end.

[0138] FIG. 12 shows a close-up view of a piston assembly 406 for use in the pump 401 of the fourth embodiment. As in the previous embodiments, two pistons 408 are located on either side of a roller bearing 410 that, in use, follows cam surface 412. A shaft 414 extends through the centre of the roller 410 and out the far side of both pistons 408. The shaft 414 is connected to each piston 408 via a needle bearing 446 which allows the shaft 414 to roll relative to the rest of the piston assembly 406. In addition to the primary roller 410 and the secondary roller 414 the piston assembly 406 of the third embodiment includes a pair of thrust bearings 450, one on either side of the roller 410.

[0139] In use, axial thrust bearings 450 react the load generated by the sliding movement of the cam 411 relative to the piston assembly 406. Accordingly, pumps in accordance with the fourth embodiment may experience lower frictional loses than comparable pumps without axial bearings.

[0140] FIG. 13 shows a piston assembly 506 for use in a fifth example embodiment of the invention. In contrast to the embodiments described above the piston assembly 506 of the fifth embodiment comprises only a single piston 508. At the distal end of the piston 508 the piston assembly 506 comprises a roller bearing 510 that, in use, follows a corresponding primary cam surface (not shown). A shaft 514 extends perpendicular to the longitudinal axis of the piston 508 and is connected to the piston 508 via a pair of needle bearings 546 which allow the shaft 514 to roll relative to the rest of the piston assembly 506. The roller bearing 510, shaft 514, and needle bearings 546 are arranged such that the piston assembly is symmetrical about the centre line of the piston 508. In contrast to the previous embodiments, the axis of rotation of the secondary roller 514 is radially offset from the axis of rotation of the primary roller 510. The piston 508 of the fifth embodiment is hollow, with the internal cavity 508a being sealed such that the piston is filled with air.

[0141] Having a single piston per primary roller may reduce the contact stress on the primary roller in comparison to pumps having two pistons in each piston assembly. This may be particularly advantageous for variable displacement pumps due to the reduced contact area between the roller and the cam surface as a result of the cam surface being non-parallel with the longitudinal axis of the roller.

[0142] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0143] For example, while the embodiments are described above as pumps, it will be appreciated that they can also be used as hydraulic motors. While the examples given above have an integrally formed rotor and main housing, it will be appreciated that there may be situations where it is advantageous to have the elements of the rotor and/or main housing formed separately.

[0144] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.