Patent Application
20100143173
This invention relates to mechanical means for forcing a fluid to move; to pumps for fluids, and in particular to rotating pumps based on the swash-plate or nutating plate principle.
Most pumps are positive displacement types based on reciprocating pistons moving within cylinders, including seals and controlled by valves. Centrifugal pumps or axial-flow types having impellers are not positive displacement types. The present kind of pump, a swashplate pump, could be regarded as a combination between a peristaltic pump (as used in medical applications) and a lobe pump. It is a positive displacement type of pump, since there is an ideally perfect, rotating line of seal that separates the fluid being pushed out of the pump from fluid being admitted to the pump. It is also capable of use in reverse when converting a pressure differential in a fluid into rotational motion—if an application requires that.
This invention does not concern that form of pump in which there is an eccentric disk that couples a motor drive to one or more piston pumps—such as is used in hydraulic motors. In this invention the plate or disk itself, operating within a defined space, contacts the flowable material to be pumped
One problem noted with swash plate pumps is that when driven faster, the mass of the disk that is caused to oscillate in a nutating fashion has, of course, a reaction and the entire pump including the disk exhibits pronounced vibration which in turn causes noise, attacks fastenings, and causes wear. To some extent, this effect may be minimised by the judicious use of counterweights or removed material and transfer of any strains to within the rotating shaft only, but the effect cannot be completely removed. The disk has to carry seals, resist wear, and be a rigid separator between parts of differing internal pressures.
The art of design of swashplate pumps consists in part of making compromises between particular parameters, such as the maximum angle the disk can assume, the disk diameter, the speed of shaft rotation, and so on. As long as vibration caused by imbalance remains an issue, this class of pump is somewhat compromised for pumping gas (air) due to the higher speeds required than when pumping liquids.
Alfred Parker in U.S. Pat. No. 3,942,384 and in U.S. Pat. No. 5,735,172 has previously described the concept of a swash-plate machine, such as a pump and the present invention is derived from that type. Bec ker in U.S. Pat. No. 2,997,000 (see
To overcome the vibration inherent in even a well-balanced swash plate pump having a single nutating swash plate, and to facilitate assembly of same. Also, to minimise any pulsatile component of flow since pulsatility can be a problem such as for flow measurement.
The object of this invention may be stated as to provide an improved pump based on the swash plate principle, or at least to provide the public with a useful choice.
A swashplate pump of the type having a rotatable shaft that causes a nutating disk to oscillate in a nutatory manner within a corresponding, closely fitting chamber inside a body of the pump, the oscillation thereby causing, when in use, a transient sealed cavity (delimited at an inner periphery by an inner (spherical) perimeter of the disk, at an outer periphery by the outer perimeter of the disk, from behind at a rotationally moving line where a functional seal exists between the disk and an adjacent conical plate, and from in front by a divider plate passing through a notch, sealed by means of a trunnion, in the nutating disk and held at a fixed position where it interrupts both the chambers) to rotate from a first position at which the transient sealed cavity may receive a flowable material from a contiguous input port to a second position adjacent a contiguous output port so that the flowable material is expressed therefrom by an internally developed pressure wherein the swashplate pump has a first and a second separate pumping chamber containing a corresponding first and second nutating disk respectively, both chamber s surrounding and sharing a common, shaped shaft; each disk being attached to the shaft so that when in use each disk is caused to oscillate in a direction opposite to that of the other disk, so that a tendency for motion of the pump body arising from a reaction to the forced oscillation of the first nutating disk is substantially cancelled by complementary movement of the second nutating disk.
Preferably the shaft includes a first and a second bearing portion each fabricated at a selected angle to the axis of the entire shaft, bent, rotatable shaft, the angle of the first portion being substantially the same as the supplement of the angle of the second portion, so that the bearing portions of the shaft as a whole are symmetrical.
In a related aspect, any couple about the axis of the pump that caused by imposed motion of one swash plate is cancelled out by an opposite couple caused by imposed motion of the other swash plate, so that vibration of the pump as a whole is substantially reduced over the amount of vibration developed by a single swash-plate pump.
Preferably the divider plate and the associated port of the first pumping chamber is located at a selected position that is at a controlled angle or phase diffrence around the rotatable shaft in relation to the position of the divider plate along with the associated port of the second pumping chamber.
Preferably that angle is 90 degrees; since a 90 degrees angle gives good balance between two counter-nutating disk using a trunnion and divider plate to stop rotation. Further, having the dividers at 90 degrees ensures that the torsional imbalance component set up in both plates also cancels out along with the backwards and forwards nutating plate mass imbalance.
Preferably both sides of each swash plate are employed so that each swash plate has two separate pumping compartments and so that the pump has 4 pumping compartments altogether. Preferably each swash plate within a cavity (here termed A and B) is transected by one divider plate for each swash plate, the divider plate also serving to specify the location of an inlet and an outlet port for each pumping compartment (here termed A1 and A2 on each side of the A swash plate; B1 and B2 on each side of the B swash plate).
Preferably the position of a first divider plate dividing swash plate (A) is rotationally separated by an angle of 90 degrees from the position of a second divider plate dividing swash plate (B) so that the pumping compartments A1, A2 are rotationally separated by an angle of 90 degrees from the pumping compartments B1, B2 and as a result (a) the load on a motor driving the pump is more steady through an entire revolution, and (b) the pump delivers four evenly spaced pulses of fluid per revolution through the outlet valves.
In a related aspect, the angle between the first output port associated with a divider plate within the first pumping cavity, and the second output port associated with a divider plate within the second pumping cavity is a right angle, so that when in use one complete revolution of the shaft of the pump causes four evenly spaced pump output events to occur, thereby reducing fluctuations in the load imposed by the pump on a source of motive power.
In a second broad aspect, the invention provides a dual swash-plate pump wherein both output ports of either the first or the second pumping cavity are joined together so that the issuing flowable material flows from the joined-together output port more evenly.
In a related aspect, both output ports of both the first and the second pumping cavity are joined together so that the issuing flowable material flows more evenly.
Optionally, a one-way valve is provided for at least one port; more preferably on the exhaust or outlet ports.
In a yet further related aspect, in addition to use of complementary movements of the pair of nutating disks in order to minimise external movement, mass has been removed from the nutating parts of the pump as far as possible, while not sacrificing rigidity and ability to absorb wear, so that less work is required to cause the disks to complete their cycle and so that fewer and smaller internals strains are caused.
In a third broad aspect the pump is provided with ports that are mounted across corners of the housing (as referred to a cross-sectional view) and along edges of the housing (as referred to a perspective view), so that better mechanical access to the port outlets is provided.
The description of the invention to be provided herein is given purely by way of example and is not to be taken in any way as limiting the scope or extent of the invention.
Throughout this specification unless the text requires otherwise, the word “comprise” and variations such as “comprising” or “comprises” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.
The structural core of a swash plate pump which is a mechanism for causing movement of fluids by means of a nutating disk rather than by an impeller or a piston includes (a) a circular swash plate and means for causing the plate to move in a nutating fashion (rather like the wobbling of a coin, if dropped obliquely on to a surface) (b) an opposing frustro-conical cone, (c) a fixed part-spherical cap over the perimeter of the swash plate and (d) usually one cut but sometimes more, made across the swash plate which allows a fixed divider plate to interrupt the cavity made between the cone and the swash plate. In practice, both sides of each swash plate are normally used in any swash plate pump. One component of nutatory motion is a to-and-fro rocking motion about an axis of rotation, while the other is rotation of the peak displacement about an axis, both at the frequency of rotation, so that all parts involved should be finished as part-spherical surfaces centered on the axis of rotation. In pumps according the invention the swash plate does not actually rotate, because it is prevented from rotating by the divider plate even though the drive shaft inside the oblique supporting bearings is rotating. The motion and resulting forces exerted on the drive shaft as a result of forced motion of the swash plate are not equivalent to the forces developed by an obliquely mounted though balanced flywheel, which are just like those of a normally mounted flywheel in a plane perpendicular to the axis of rotation. The forces are derived from the forced to-and-fro motion because the swash plate is “thrown” to and fro.
Preferably the swash plate oscillates (as referred to a cross-sectional view as in
More preferably the swash plate oscillates (as referred to a cross-sectional view) through an angle of about 20 degrees.
Fluid is admitted at an inlet port (which optionally has a one-way valve) into a space bounded on a first side by a fixed frustro-conical cone and on a second side by a movable disk, the swash plate, which is forced to move in a nutating motion. The initial “behind” boundary of the space when the space is at the port is the fixed divider plate at its trailing surface, and the “before” boundary is the present position of the sealing contact between the swash plate and the cone. As a result of the nutating motion the swash plate presses sequentially so as to make a sealing contact at a continuous sequence of radial lines around the circumference of the cone, “chasing” a bolus of fluid from the inlet port towards an outlet port. The “behind” boundary becomes another sealing contact between the swash plate and the cone, and the “before” boundary becomes the leading surface of the fixed divider plate. The fluid is forced, under increasing pressure from the advancing “behind” boundary of the compartment owing to motion of the swash plate, to leave the pump through the outlet port, which is usually provided with a non-return valve.
Preferred materials for the body of the pump include cast iron (preferably a high-nickel alloy for low corrosion), stainless steel, aluminium, and injection-moulded plastics. This type of pump also relies on sliding close contacts or seals to ensure that the bolus of fluid being pumped is fully contained while it is moved through the pump. Slideable seals that close the pumping space (see below), including around the cut made across the swash plate are provided, to reduce the need for precise dimensional control during manufacture of co-operating parts and to allow for wear and inevitable thermal expansion of co-operating parts because heat will be developed during use by inevitable friction and at localised areas by compression of a fluid (particularly if it is a gas) being pumped.
Please note that the drawings reproduced herein show a design which may be varied before production takes place. For that reason, shapes and proportions may alter although the shapes shown serve to illustrate the principles of the invention.
Refer to
Note that the A set of ports and the B set of ports are shown at a preferred 90 degrees offset to each other. The A1 set of ports; inlet (106) and outlet (105) ports, assuming shaft rotation is clockwise) and the A2 set of ports: inlet (108) and outlet (107) ports, relate to both sides of a first swash plate, while the B1 set of ports (inlet 109, outlet 110) and the B2 set of ports (inlet 111, outlet 112) relate to both sides of a second swash plate. Either the A or the B assembly on its own provides two deliveries or output pulses per revolution, output at 180 degree intervals relative to each other, because both sides of each swash plate (B plate: 301) are active. Further, adding the 90 degrees offset by means of placement of the respective divider plates (not by alteration of the shaped shaft 102—see
The DSWP is shown with mounting brackets 103 for mounting on to a supporting surface. There may be a small amount of remaining vibration from the machine at the rate of rotation (in the range of 20-30 Hz possibly including harmonics thereof). This may arise for instance if the swash plates were used in an asymmetrical manner. The worst-case situation might be if sides A1 and B1 were used to pump water while sides A2 and B2 were unused or pumped a gas. Nevertheless, the couples resulting from a single moving swash plate are compensated by the other moving swash plate. A preferred supporting surface is an elastomeric anti-vibration mount supporting both the DSWP and a drive motor (not shown) coupled to the drive shaft. The drive motor (not shown) is typically an induction motor, and for one example size of pump it has about 11 kW power rating, optionally driven by variable-speed drive electronics.
The circular coneplate housings (such as 104—
The upper left part of the section is cut though the “A” divider plate 305, while in the “B” half to the right, the divider plate is not shown, being far from the plane of section. Part of the B1 pumping compartment is the upper empty space to the left of the “B” swash plate 301. (Note that practical swash plates will be hollowed out in order to reduce mass, such as by means of a series of radially, inwardly directed drilled holes or by casting techniques analogous to “lost wax” methods. Part of the B2 pumping compartment is the lower right empty space to the right of the “B” swash plate. In this embodiment, the physical positions of the swash plates at any time are mirror images of each other so that the couples generated by imposed movement of either swash plate are substantially cancelled out by opposite imposed movement of the other swash plate. Further, having the dividers at 90 degrees ensures that the torsional imbalance component set up in both plates also tends to be cancelled out, along with the backwards and forwards nutating plate mass imbalance discussed previously.
The fixed divider plate is “swept” by side-to-side movement of the trunnion seal shown in part here and for example in
SEALS.
Seal(s) 1: between the fixed housing and the part-spherical swash plate base, using circumferential, annular seals shown in
Seal(s) 2: as previously described in patent specifications by the Applicants, comprises a ring seal 616, 617 within the periphery of each swash plate (except where the swash plate is transected by the divider plate and related sealing means). This seal has a similar construction to that of seal 1, employing a separate resilient means, although re-design of the seal may allow incorporation of the property of resilience within the seal itself. This seal presses against the outer housing shown for example at 603. The outer housing has a part-circular inner aspect centered on the axis of nutatory motion of the swash plate.
Seal(s) 3: also previously described by the Applicants is illustrated in the present application in
Seal 4: also previously described by the Applicants is not illustrated in the present specification although it is likely to be used in practical versions of the invention. It comprises additional sealing means between each cone plate and the facing side of the swash plate. Each sealing means is a radial strip of a bearing grade plastics, pressed outward by an underlying resilient strip, but prevented from coming out of the groove within the cone plate (usually) by a widened or “T”-shaped base.
Another change made from earlier versions of swash-plate pump for use in this embodiment is reduction of the oblique angle from 30 to 20 degrees inclusive. The consequent reduction in the seal sliding velocity per revolution at the divider plate and at the inner and outer edges of the or each swash plate in particular allows a faster revolution rate. The optimum angle may be a function of the particular material being pumped.
This Example comprises use of different port placements, such as on the edge rather than on the face of the housing. The pump is provided with ports that are mounted across corners of the housing (as referred to a cross-sectional view) and along edges of the housing (as referred to a perspective view), so that better mechanical access to the port outlets is provided.
It is possible that the housing between the two swash pump units will need to be more substantial than is shown, since the individual couples still exist between one swash plate unit and the other and flexion of the drive shaft will result in strains on the housing. The cone plate may be separate from the housing.
A motor may be constructed about the centre 402 of the driving shaft.
The invention specifies two plates. An odd number of in-line swash plates such as 3 or 5 does not appear to be an easily balanced configuration, and even numbers of in-line swash plates greater than 2 seems to be a more complicated solution than the simple manufacture and supply of more dual-plate pumps, along with economy of scale and easier maintenance.
A variation in which one, pumping swash pump is combined with a “dummy swash plate” of similar mass, made to move in a complementary manner, but not actually contained within a proper pumping chamber is technically possible though likely to be not cost-effective.
For a three-swash cavity design, it may be possible to balance swash plate vibrations by placing the swash plates on separately driven though locked, in relation to each other, shafts that are held in a frame and positioned at the corners of an equilateral triangle or at the corners of a square, for example, although this solution seems relatively inelegant as compared to an in-line solution.
The invention provides a pump useful in food technology and in biotechnology, because the fluid being pumped is not exposed to strong shearing forces, and there is substantially no contamination by lubricants of the fluid being pumped.
The pump output is relatively constant at least for liquids, in part because of the inherent mode of operation of a swashplate pump as compared to that of a piston-type pump, and in part because two (three) or four separate outputs may be combined. This characteristic facilitates use of accurate flow measuring devices such as in the petroleum industry or in the chemical industry.
This dual swashplate pump exhibits a substantially reduced amount of vibration during use, as compared to a single plate swash pump. Previous patent specifications for a single swash plate within one mechanism attempted to cope with vibration arising from the nutatory motion of the swash plate by including weights and drilled-out parts about the shaft on which the swash plate was made to undergo its specific motion. Other options for the reduction of significant vibration have been considered in previous patent specifications, (such as reduction of mass and use of external counterbalances).
Of course, the principles described herein may be applied to any particular scale or size of pump.
Finally, it will be understood that the scope of this invention as described by way of example and/or illustrated herein is not limited to the specified embodiments. Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents, then such equivalents are included as if individually set forth. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions are possible without departing from the scope and spirit of the invention as set forth in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 553347 | Feb 2007 | NZ | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NZ08/00024 | 2/20/2008 | WO | 00 | 2/17/2010 |
