EP2438302B1

Movatterモバイル変換

Info

Publication number: EP2438302B1
Application number: EP09785228.9A
Authority: EP
Inventors: Justin Rorke Buckland; Stuart Andrew Hatfield; James Edward Mccrone; Richard Janse Van Rensburg
Original assignee: Technology Partnership PLC
Current assignee: Technology Partnership PLC
Priority date: 2009-06-03
Filing date: 2009-06-03
Publication date: 2015-09-23
Anticipated expiration: 2029-06-03
Also published as: BRPI0924510B1; BRPI0924510A2; SG176225A1; RU2511832C2; CA2764334A1; AU2009347422B2; EP2438302A1; JP5623515B2; AU2016200869A1; JP2012528981A; CN102459899B; WO2010139918A1; CA2764334C; AU2016200869B2; AU2009347422A1; MX2011012974A; RU2011153727A; CN102459899A; BRPI0924510B8

Description

BACKGROUND OF THEINVENTION

1. Field of the Invention

The illustrative embodiments of the invention relate generally to a pump for fluid and, more specifically, to a pump having a substantially disc-shaped cavity with substantially circular end walls and a side wall and a valve for controlling the flow of fluid through the pump.

2. Description of Related Art

The generation of high amplitude pressure oscillations in closed cavities has received significant attention in the fields of thermo-acoustics and pump type compressors. Recent developments in non-linear acoustics have allowed the generation of pressure waves with higher amplitudes than previously thought possible.
It is known to use acoustic resonance to achieve fluid pumping from defined inlets and outlets. This can be achieved using a cylindrical cavity with an acoustic driver at one end, which drives an acoustic standing wave. In such a cylindrical cavity, the acoustic pressure wave has limited amplitude. Varying cross-section cavities, such as cone, horn-cone, bulb have been used to achieve high amplitude pressure oscillations thereby significantly increasing the pumping effect. In such high amplitude waves the non-linear mechanisms with energy dissipation have been suppressed. However, high amplitude acoustic resonance has not been employed within disc-shaped cavities in which radial pressure oscillations are excited until recently. International Patent Application No. PCT/GB2006/001487, published asWO 2006/111775 (the '487 Application), discloses a pump having a substantially disc-shaped cavity with a high aspect ratio, i.e., the ratio of the radius of the cavity to the height of the cavity.
Such a pump has a substantially cylindrical cavity comprising a side wall closed at each end by end walls. The pump also comprises an actuator that drives either one of the end walls to oscillate in a direction substantially perpendicular to the surface of the driven wall. The spatial profile of the motion of the driven end wall is described as being matched to the spatial profile of the fluid pressure oscillations within the cavity, a state described herein as mode-matching. When the pump is mode-matched, work done by the actuator on the fluid in the cavity adds constructively across the driven end wall surface, thereby enhancing the amplitude of the pressure oscillation in the cavity and delivering high pump efficiency. In a pump which is not mode-matched there may be areas of the end wall wherein the work done by the end wall on the fluid reduces rather than enhances the amplitude of the fluid pressure oscillation in the fluid within the cavity. Thus, the useful work done by the actuator on the fluid is reduced and the pump becomes less efficient. The efficiency of a mode-matched pump is dependent upon the interface between the driven end wall and the side wall. It is desirable to maintain the efficiency of such pump by structuring the interface so that it does not decrease or dampen the motion of the driven end wall thereby mitigating any reduction in the amplitude of the fluid pressure oscillations within the cavity.
Such pumps also require a valve for controlling the flow of fluid through the pump and, more specifically, a valve being capable of operating at high frequencies. Conventional valves typically operate at lower frequencies below 500 Hz for a variety of applications. For example, many conventional compressors typically operate at 50 or 60 Hz. Linear resonance compressors known in the art operate between 150 and 350 Hz. However, many portable electronic devices including medical devices require pumps for delivering a positive pressure or providing a vacuum that are relatively small in size and it is advantageous for such pumps to be inaudible in operation so as to provide discrete operation. To achieve these objectives, such pumps must operate at very high frequencies requiring valves capable of operating at about 20 kHz and higher which are not commonly available. To operate at these high frequencies, the valve must be responsive to a high frequency oscillating pressure that can be rectified to create a net flow of fluid through the pump.
WO2006/111775 discloses a fluid pump having one or more actuators and a substantially cylindrical cavity, wherein axial oscillations of the end walls of the cavity cause radial oscillations of fluid pressure in the cavity.
WO94/19609 discloses a displacement pump whose cavity volume changes during a cycle of the pump.

SUMMARY

According to an the present invention, a pump comprising: a pump body having a substantially cylindrical shape defining a cavity for containing a fluid, the cavity being formed by a side wall closed at both ends by end walls, at least one of the end walls being a driven end wall having a central portion and a peripheral portion extending radially outwardly from the central portion of the driven end wall; an actuator operatively associated with the central portion of the driven end wall to cause an oscillatory motion of the driven end wall, thereby generating displacement oscillations of the driven end wall in a direction substantially perpendicular thereto with an annular node between the centre of the driven end wall and the side wall when in use; a first aperture disposed at any location in the cavity other than at the location of the annular node and extending through the pump body; a second aperture disposed at any location in the pump body other than the location of said first aperture and extending through the pump body; and, a flap valve disposed in at least one of said first aperture and second aperture; whereby the displacement oscillations generate corresponding radial pressure oscillations of the fluid within the cavity of said pump body causing fluid flow through said first and second apertures when in use; characterized by an isolator operatively associated with the peripheral portion of the driven end wall to reduce dampening of the displacement oscillations; and in that said flap valve comprises: a first plate having apertures extending generally perpendicular through said first plate; a second plate having first apertures extending generally perpendicular through said second plate, the first apertures being substantially offset from the apertures of said first plate; a spacer disposed between said first plate and said second plate to form a cavity therebetween in fluid communication with the apertures of said first plate and the first apertures of said second plate; and, a flap disposed and moveable between said first plate and said second plate, said flap having apertures substantially offset from the apertures of said first plate and substantially aligned with the first apertures of said second plate; whereby said flap is motivated between said first and second plates in response to a change in direction of the differential pressure of the fluid across said flap valve.
Other objects, features, and advantages of the illustrative embodiments are described herein and will become apparent with reference to the drawings and detailed description that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1A to 1C show a schematic cross-section view of a first pump according to an illustrative embodiment of the inventions that provide a positive pressure, a graph of the displacement oscillations of the driven end wall of the pump, and a graph of the pressure oscillations of fluid within the cavity of pump.

Figure 2 shows a schematic top view of the first pump ofFigure 1A.
Figure 3 shows a schematic cross-section view of a second pump according to an illustrative embodiment of the inventions that provides a negative pressure.
Figure 4 shows a schematic cross-section view of a third pump according to an illustrative embodiment of the inventions having a frusto-conical base.
Figure 5 shows a schematic cross-section view of a fourth pump according to another illustrative embodiment of the invention including two actuators.
Figure 6A shows a schematic cross-section view of the pump ofFigure 3 andFigure 6B shows a graph of pressure oscillations of fluid within the pump as shown inFigure 1C.
Figure 6C shows a schematic cross-sectional view of an illustrative embodiment of a valve utilized in the pump ofFigure 3.
Figure 7A shows a schematic cross-section view of an illustrative embodiment of a valve in a closed position, andFigure 7B shows an exploded, sectional view of the valve ofFigure 7A taken alongline 7B-7B inFigure 7D.
Figure 7C shows a schematic perspective view of the valve ofFigure 7B.
Figure 7D shows a schematic top view of the valve ofFigure 7B.
Figure 8A shows a schematic cross-section view of the valve inFigure 7B in an open position when fluid flows through the valve.
Figure 8B shows a schematic cross-section view of the valve inFigure 7B in transition between the open and closed positions.
Figure 9A shows a graph of an oscillating differential pressure applied across the valve ofFigure 7B according to an illustrative embodiment.
Figure 9B shows a graph of an operating cycle of the valve ofFigure 7B between an open and closed position.
Figure 10 shows a schematic cross-section view of a portion of the valve ofFigure 7B in the closed position according to an illustrative embodiment.
Figure 11A shows a schematic cross-section view of a modified version of the valve ofFigure 7B having release apertures.
Figure 11B shows a schematic cross-section view of a portion of the valve inFigure 11A.
Figure 12A shows a schematic cross-section view of two valves ofFigure 7B, one of which is reversed to allow fluid flow in the opposite direction from the other according to an illustrative embodiment.
Figure 12B shows a schematic top view of the valves shown inFigure 12A.
Figure 12C shows a graph of the operating cycles of the valves ofFigure 12A between an open and closed position.
Figure 13 shows a schematic cross-section view of the a bi-directional valve having two valve portions that allow fluid flow in opposite directions with both valve portions having a normally-closed position according to an illustrative embodiment.
Figure 14 shows a schematic top view of the bi-directional valves ofFigure 13.
Figure 15 shows a schematic cross-section view of a bi-directional valve having two valve portions that allow fluid flow in opposite directions with one valve portion having a normally closed position and the other having a normally open position according to an illustrative embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description of several illustrative embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific preferred embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is understood that other embodiments may be utilized and that logical structural, mechanical, electrical, and chemical changes may be made without departing from the spirit or scope of the invention. To avoid detail not necessary to enable those skilled in the art to practice the embodiments described herein, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the illustrative embodiments are defined only by the appended claims.
Figure 1A is a schematic cross-section view of apump 10 according to an illustrative embodiment of the invention. Referring also toFigure 1B, pump 10 comprises a pump body having a substantially cylindrical shape including acylindrical wall 19 closed at one end by abase 18 and closed at the other end by aend plate 17 and a ring-shapedisolator 30 disposed between theend plate 17 and the other end of thecylindrical wall 19 of the pump body. Thecylindrical wall 19 andbase 18 may be a single component comprising the pump body and may be mounted to other components or systems. The internal surfaces of thecylindrical wall 19, thebase 18, theend plate 17, and theisolator 30 form acavity 11 within thepump 10 wherein thecavity 11 comprises aside wall 14 closed at both ends byend walls 12 and 13. Theend wall 13 is the internal surface of thebase 18 and theside wall 14 is the inside surface of thecylindrical wall 19. Theend wall 12 comprises a central portion corresponding to the inside surface of theend plate 17 and a peripheral portion corresponding to the inside surface of theisolator 30. Although thecavity 11 is substantially circular in shape, thecavity 11 may also be elliptical or other shape. Thebase 18 andcylindrical wall 19 of the pump body may be formed from any suitable rigid material including, without limitation, metal, ceramic, glass, or plastic including, without limitation, inject-molded plastic.
Thepump 10 also comprises apiezoelectric disc 20 operatively connected to theend plate 17 to form anactuator 40 that is operatively associated with the central portion of theend wall 12 via theend plate 17. Thepiezoelectric disc 20 is not required to be formed of a piezoelectric material, but may be formed of any electrically active material that vibrates such as, for example, an electrostrictive or magnetostrictive material. Theend plate 17 preferably possesses a bending stiffness similar to thepiezoelectric disc 20 and may be formed of an electrically inactive material such as a metal or ceramic. When thepiezoelectric disc 20 is excited by an electrical current, theactuator 40 expands and contracts in a radial direction relative to the longitudinal axis of thecavity 11 causing theend plate 17 to bend, thereby inducing an axial deflection of theend wall 12 in a direction substantially perpendicular to theend wall 12. Theend plate 17 alternatively may also be formed from an electrically active material such as, for example, a piezoelectric, magnetostrictive, or electrostrictive material. In another embodiment, thepiezoelectric disc 20 may be replaced by a device in a force-transmitting relation with theend wall 12 such as, for example, a mechanical, magnetic or electrostatic device, wherein theend wall 12 may be formed as an electrically inactive or passive layer of material driven into oscillation by such device (not shown) in the same manner as described above.
Thepump 10 further comprises at least two apertures extending from thecavity 11 to the outside of thepump 10, wherein at least a first one of the apertures may contain a valve to control the flow of fluid through the aperture. Although the aperture containing a valve may be located at any position in thecavity 11 where theactuator 40 generates a pressure differential as described below in more detail, one preferred embodiment of thepump 10 comprises an aperture with a valve located at approximately the centre of either of theend walls 12,13. Thepump 10 shown inFigures 1A and 1B comprises aprimary aperture 16 extending from thecavity 11 through thebase 18 of the pump body at about the centre of theend wall 13 and containing avalve 46. Thevalve 46 is mounted within theprimary aperture 16 and permits the flow of fluid in one direction as indicated by the arrow so that it functions as an outlet for thepump 10. Thesecond aperture 15 may be located at any position within thecavity 11 other than the location of theaperture 16 with avalve 46. In one preferred embodiment of thepump 10, the second aperture is disposed between the centre of either one of theend walls 12,13 and theside wall 14. The embodiment of thepump 10 shown inFigures 1A and 1B comprises twosecondary apertures 15 extending from thecavity 11 through theactuator 40 that are disposed between the centre of theend wall 12 and theside wall 14. Although thesecondary apertures 15 are not valved in this embodiment of thepump 10, they may also be valved to improve performance if necessary. In this embodiment of thepump 10, theprimary aperture 16 is valved so that the fluid is drawn into thecavity 11 of thepump 10 through thesecondary apertures 15 and pumped out of thecavity 11 through theprimary aperture 16 as indicated by the arrows to provide a positive pressure at theprimary aperture 16.
Referring toFigure 3, thepump 10 ofFigure 1 is shown with an alternative configuration of theprimary aperture 16. More specifically, the valve 46' in the primary aperture 16' is reversed so that the fluid is drawn into thecavity 11 through the primary aperture 16' and expelled out of thecavity 11 through thesecondary apertures 15 as indicated by the arrows, thereby providing suction or a source of reduced pressure at the primary aperture 16'. The term "reduced pressure" as used herein generally refers to a pressure less than the ambient pressure where thepump 10 is located. Although the term "vacuum" and "negative pressure" may be used to describe the reduced pressure, the actual pressure reduction may be significantly less than the pressure reduction normally associated with a complete vacuum. The pressure is "negative" in the sense that it is a gauge pressure, i.e., the pressure is reduced below ambient atmospheric pressure. Unless otherwise indicated, values of pressure stated herein are gauge pressures. References to increases in reduced pressure typically refer to a decrease in absolute pressure, while decreases in reduced pressure typically refer to an increase in absolute pressure.
Referring now toFigure 4, apump 70 according to another illustrative embodiment of the invention is shown. Thepump 70 is substantially similar to thepump 10 ofFigure 1 except that the pump body has a base 18' having an upper surface forming the end wall 13' which is frusto-conical in shape. Consequently, the height of thecavity 11 varies from the height at theside wall 14 to a smaller height between theend walls 12,13' at the centre of theend walls 12,13'. The frusto-conical shape of the end wall 13' intensifies the pressure at the centre of thecavity 11 where the height of thecavity 11 is smaller relative to the pressure at theside wall 14 of thecavity 11 where the height of thecavity 11 is larger. Therefore, comparing cylindrical and frusto-conical cavities 11 having equal central pressure amplitudes, it is apparent that the frusto-conical cavity 11 will generally have a smaller pressure amplitude at positions away from the centre of the cavity 11: the increasing height of thecavity 11 acts to reduce the amplitude of the pressure wave. As the viscous and thermal energy losses experienced during the oscillations of the fluid in thecavity 11 both increase with the amplitude of such oscillations, it is advantageous to the efficiency of thepump 70 to reduce the amplitude of the pressure oscillations away from the centre of thecavity 11 by employing a frusto-conical cavity 11 design. In one illustrative embodiment of thepump 70 where the diameter of thecavity 11 is approximately 20 mm, the height of thecavity 11 at theside wall 14 is approximately 1.0 mm tapering to a height at the centre of the end wall 13' of approximately 0.3 mm. Either one of theend walls 12,13 or both of theend walls 12,13 may have a frusto-conical shape.
Referring now toFigure 5, apump 60 according to another illustrative embodiment of the invention is shown. Thepump 60 is substantially similar to thepump 10 ofFigure 1 except that it includes asecond actuator 62 that replaces thebase 18 of the pump body. Theactuator 62 comprises asecond disc 64 and a ring-shapedisolator 66 disposed between thedisc 64 and theside wall 14. Thepump 60 also comprises a secondpiezoelectric disc 68 operatively connected to thedisc 64 to form theactuator 62. Theactuator 62 is operatively associated with theend wall 13 which comprises the inside surfaces of thedisc 64 and theisolator 66. Thesecond actuator 62 also generates an oscillatory motion of theend wall 13 in a direction substantially perpendicular to theend wall 13 in a manner similar to theactuator 40 with respect to theend wall 12 as described above. When theactuators 40, 62 are activated, control circuitry (not shown) is provided to coordinate the axial displacement oscillations of the actuators. It is preferable that the actuators are driven at the same frequency and approximately out-of-phase, i.e. such that the centres of theend walls 12, 13 move first towards each other and then apart.
The dimensions of the pumps described herein should preferably satisfy certain inequalities with respect to the relationship between the height (h) of thecavity 11 and the radius (r) of the cavity which is the distance from the longitudinal axis of thecavity 11 to theside wall 14. These equations are as follows: $r / h > 1.2;$
and $h^{2} / r > 4 x 10^{- 10} meters .$
In one embodiment of the invention, the ratio of the cavity radius to the cavity height (r/h) is between about 10 and about 50 when the fluid within thecavity 11 is a gas. In this example, the volume of thecavity 11 may be less than about 10 ml. Additionally, the ratio of h²/r is preferably within a range between about 10^-3 and about 10^-6 meters where the working fluid is a gas as opposed to a liquid.
In one embodiment of the invention thesecondary apertures 15 are located where the amplitude of the pressure oscillations within thecavity 11 is close to zero, i.e., the "nodal" points of the pressure oscillations. Where thecavity 11 is cylindrical, the radial dependence of the pressure oscillation may be approximated by a Bessel function of the first kind and the radial node of the lowest-order pressure oscillation within thecavity 11 occurs at a distance of approximately 0.63r ± 0.2r from the centre of theend wall 12 or the longitudinal axis of thecavity 11. Thus, thesecondary apertures 15 are preferably located at a radial distance (a) from the centre of theend walls 12,13, where (a) ≈ 0.63r ± 0.2r, i.e., close to the nodal points of the pressure oscillations.
Additionally, the pumps disclosed herein should preferably satisfy the following inequality relating the cavity radius (r) and operating frequency (f) which is the frequency at which theactuator 40 vibrates to generate the axial displacement of theend wall 12. The inequality equation is as follows: $\frac{k_{0} (c_{s})}{2 π f} \leq r \leq \frac{k_{0} (c_{f})}{2 π f}$
wherein the speed of sound in the working fluid within the cavity 11 (c) may range between a slow speed (c_s) of about 115 m/s and a fast speed (c_f) equal to about 1,970 m/s as expressed in the equation above, and k₀ is a constant (k₀ = 3.83). The frequency of the oscillatory motion of theactuator 40 is preferably about equal to the lowest resonant frequency of radial pressure oscillations in thecavity 11, but may be within 20% therefrom. The lowest resonant frequency of radial pressure oscillations in thecavity 11 is preferably greater than 500Hz.
Referring now to thepump 10 in operation, thepiezoelectric disc 20 is excited to expand and contract in a radial direction against theend plate 17 which causes theactuator 40 to bend, thereby inducing an axial displacement of the drivenend wall 12 in a direction substantially perpendicular to the drivenend wall 12. Theactuator 40 is operatively associated with the central portion of theend wall 12 as described above so that the axial displacement oscillations of theactuator 40 cause axial displacement oscillations along the surface of theend wall 12 with maximum amplitudes of oscillations, i.e., anti-node displacement oscillations, at about the centre of theend wall 12. Referring back toFigure 1A, the displacement oscillations and the resulting pressure oscillations of thepump 10 as generally described above are shown more specifically inFigures 1B and 1C, respectively. The phase relationship between the displacement oscillations and pressure oscillations may vary, and a particular phase relationship should not be implied from any figure.
Figure 1B shows one possible displacement profile illustrating the axial oscillation of the drivenend wall 12 of thecavity 11. The solid curved line and arrows represent the displacement of the drivenend wall 12 at one point in time, and the dashed curved line represents the displacement of the drivenend wall 12 one half-cycle later. The displacement as shown in this figure and the other figures is exaggerated. Because theactuator 40 is not rigidly mounted at its perimeter, but rather suspended by theisolator 30, theactuator 40 is free to oscillate about its centre of mass in its fundamental mode. In this fundamental mode, the amplitude of the displacement oscillations of theactuator 40 is substantially zero at anannular displacement node 22 located between the centre of theend wall 12 and theside wall 14. The amplitudes of the displacement oscillations at other points on theend wall 12 have an amplitudes greater than zero as represented by the vertical arrows. Acentral displacement anti-node 21 exists near the centre of theactuator 40 and a peripheral displacement anti-node 21' exists near the perimeter of theactuator 40.
Figure 1C shows one possible pressure oscillation profile illustrating the pressure oscillation within thecavity 11 resulting from the axial displacement oscillations shown inFigure 1B. The solid curved line and arrows represent the pressure at one point in time, and the dashed curved line represents the pressure one half-cycle later. In this mode and higher-order modes, the amplitude of the pressure oscillations has acentral pressure anti-node 23 near the centre of thecavity 11 and aperipheral pressure anti-node 24 near theside wall 14 of thecavity 11. The amplitude of the pressure oscillations is substantially zero at theannular pressure node 25 between thecentral pressure anti-node 23 and theperipheral pressure anti-node 24. For a cylindrical cavity, the radial dependence of the amplitude of the pressure oscillations in thecavity 11 may be approximated by a Bessel function of the first kind. The pressure oscillations described above result from the radial movement of the fluid in thecavity 11, and so will be referred to as the "radial pressure oscillations" of the fluid within thecavity 11 as distinguished from the axial displacement oscillations of theactuator 40.
With further reference toFigures 1B and 1C, it can be seen that the radial dependence of the amplitude of the axial displacement oscillations of the actuator 40 (the "mode-shape" of the actuator 40) should approximate a Bessel function of the first kind so as to match more closely the radial dependence of the amplitude of the desired pressure oscillations in the cavity 11 (the "mode-shape" of the pressure oscillation). By not rigidly mounting theactuator 40 at its perimeter and allowing it to vibrate more freely about its centre of mass, the mode-shape of the displacement oscillations substantially matches the mode-shape of the pressure oscillations in thecavity 11, thus achieving mode-shape matching or, more simply, mode-matching. Although the mode-matching may not always be perfect in this respect, the axial displacement oscillations of theactuator 40 and the corresponding pressure oscillations in thecavity 11 have substantially the same relative phase across the full surface of theactuator 40 wherein the radial position of theannular pressure node 25 of the pressure oscillations in thecavity 11 and the radial position of theannular displacement node 22 of the axial displacement oscillations ofactuator 40 are substantially coincident.
As theactuator 40 vibrates about its centre of mass, the radial position of theannular displacement node 22 will necessarily lie inside the radius of theactuator 40 when theactuator 40 vibrates in its fundamental mode as illustrated inFigure 1B. Thus, to ensure that theannular displacement node 22 is coincident with theannular pressure node 25, the radius of the actuator (r_act) should preferably be greater than the radius of theannular pressure node 25 to optimize mode-matching. Assuming again that the pressure oscillation in thecavity 11 approximates a Bessel function of the first kind, the radius of theannular pressure node 25 would be approximately 0.63 of the radius from the centre of theend wall 13 to theside wall 14, i.e., the radius of the cavity 11 (r) as shown inFigure 1A. Therefore, the radius of the actuator 40 (r_act) should preferably satisfy the following inequality:r_act ≥ 0.63r.
Theisolator 30 may be a flexible membrane which enables the edge of theactuator 40 to move more freely as described above by bending and stretching in response to the vibration of theactuator 40 as shown by the displacement of the peripheral displacement oscillations 21' inFigure 1B. The flexible membrane overcomes the potential dampening effects of theside wall 14 on theactuator 40 by providing a low mechanical impedance support between the actuator 40 and thecylindrical wall 19 of thepump 10 thereby reducing the dampening of the axial oscillations of the peripheral displacement oscillations 21' of theactuator 40. Essentially, flexible membrane 31 minimizes the energy being transferred from theactuator 40 to theside wall 14, which remains substantially stationary. Consequently, theannular displacement node 22 will remain substantially aligned with theannular pressure node 25 so as to maintain the mode-matching condition of thepump 10. Thus, the axial displacement oscillations of the drivenend wall 12 continue to efficiently generate oscillations of the pressure within thecavity 11 from thecentral pressure anti-node 23 to theperipheral pressure anti-node 24 at theside wall 14 as shown inFigure 1C.
Figure 6A shows a schematic cross-section view of the pump ofFigure 3 andFigure 6B a graph of the pressure oscillations of fluid within the pump as shown inFigure 1C. The valve 46' (as well as the valve 46) allows fluid to flow in only one direction as described above. The valve 46' may be a check valve or any other valve that allows fluid to flow in only one direction. Some valve types may regulate fluid flow by switching between an open and closed position. For such valves to operate at the high frequencies generated by theactuator 40, thevalves 46 and 46' must have an extremely fast response time such that they are able to open and close on a timescale significantly shorter than the timescale of the pressure variation. One embodiment of thevalves 46 and 46' achieve this by employing an extremely light flap valve which has low inertia and consequently is able to move rapidly in response to changes in relative pressure across the valve structure.
Referring toFigures 7A-D such a flap valve,valve 110 is shown according to an illustrative embodiment. Thevalve 110 comprises a substantiallycylindrical wall 112 that is ring-shaped and closed at one end by aretention plate 114 and at the other end by a sealingplate 116. The inside surface of thewall 112, theretention plate 114, and the sealingplate 116 form acavity 115 within thevalve 110. Thevalve 110 further comprises a substantiallycircular flap 117 disposed between theretention plate 114 and the sealingplate 116, but adjacent the sealingplate 116. Theflap 117 may be disposed adjacent theretention plate 114 in an alternative embodiment as will be described in more detail below, and in this sense theflap 117 is considered to be "biased" against either one of the sealingplate 116 or theretention plate 114. The peripheral portion of theflap 117 is sandwiched between the sealingplate 116 and the ring-shapedwall 112 so that the motion of theflap 117 is restrained in the plane substantially perpendicular the surface of theflap 117. The motion of theflap 117 in such plane may also be restrained by the peripheral portion of theflap 117 being attached directly to either the sealingplate 116 or thewall 112, or by theflap 117 being a close fit within the ring-shapedwall 112, in an alternative embodiments. The remainder of theflap 117 is sufficiently flexible and movable in a direction substantially perpendicular the surface of theflap 117, so that a force applied to either surface of theflap 117 will motivate theflap 117 between the sealingplate 116 and theretention plate 114.
Theretention plate 114 and the sealingplate 116 both haveholes 118 and 120, respectively, which extend through each plate. Theflap 117 also hasholes 122 that are generally aligned with theholes 118 of theretention plate 114 to provide a passage through which fluid may flow as indicated by the dashedarrows 124 inFigures 6C and8A. Theholes 122 in theflap 117 may also be partially aligned, i.e., having only a partial overlap, with theholes 118 in theretention plate 114. Although theholes 118, 120, 122 are shown to be of substantially uniform size and shape, they may be of different diameters or even different shapes without limiting the scope of the invention. In one embodiment of the invention, theholes 118 and 120 form an alternating pattern across the surface of the plates as shown by the solid and dashed circles, respectively, inFigure 7D. In other embodiments, theholes 118, 120, 122 may be arranged in different patterns without effecting the operation of thevalve 110 with respect to the functioning of the individual pairings ofholes 118, 120, 122 as illustrated by individual sets of the dashedarrows 124. The pattern ofholes 118, 120, 122 may be designed to increase or decrease the number of holes to control the total flow of fluid through thevalve 110 as required. For example, the number ofholes 118, 120, 122 may be increased to reduce the flow resistance of thevalve 110 to increase the total flow rate of thevalve 110.
When no force is applied to either surface of theflap 117 to overcome the bias of theflap 117, thevalve 110 is in a "normally closed" position because theflap 117 is disposed adjacent the sealingplate 116 where theholes 122 of the flap are offset or not aligned with theholes 118 of the sealingplate 116. In this "normally closed" position, the flow of fluid through the sealingplate 116 is substantially blocked or covered by the non-perforated portions of theflap 117 as shown inFigures 7A and 7B. When pressure is applied against either side of theflap 117 that overcomes the bias of theflap 117 and motivates theflap 117 away from the sealingplate 116 towards theretention plate 114 as shown inFigures 6C and8A, thevalve 110 moves from the normally closed position to an "open" position over a time period, an opening time delay (T_o), allowing fluid to flow in the direction indicated by the dashedarrows 124. When the pressure changes direction as shown inFigure 8B, theflap 117 will be motivated back towards the sealingplate 116 to the normally closed position. When this happens, fluid will flow for a short time period, a closing time delay (T_c), in the opposite direction as indicated by the dashedarrows 132 until theflap 117 seals theholes 120 of the sealingplate 116 to substantially block fluid flow through the sealingplate 116 as shown inFigure 7B. In other embodiments of the invention, theflap 117 may be biased against theretention plate 114 with theholes 118, 122 aligned in a "normally open" position. In this embodiment, applying positive pressure against theflap 117 will be necessary to motivate theflap 117 into a "closed" position.. Note that the terms "sealed" and "blocked" as used herein in relation to valve operation are intended to include cases in which substantial (but incomplete) sealing or blockage occurs, such that the flow resistance of the valve is greater in the "closed" position than in the "open" position.
The operation of thevalve 110 is a function of the change in direction of the differential pressure (ΔP) of the fluid across thevalve 110. InFigure 7B, the differential pressure has been assigned a negative value (-ΔP) as indicated by the downward pointing arrow. When the differential pressure has a negative value (-ΔP), the fluid pressure at the outside surface of theretention plate 114 is greater than the fluid pressure at the outside surface of the sealingplate 116. This negative differential pressure (-ΔP) drives theflap 117 into the fully closed position as described above wherein theflap 117 is pressed against the sealingplate 116 to block theholes 120 in the sealingplate 116, thereby substantially preventing the flow of fluid through thevalve 110. When the differential pressure across thevalve 110 reverses to become a positive differential pressure (+ΔP) as indicated by the upward pointing arrow inFigure 8A, theflap 117 is motivated away from the sealingplate 116 and towards theretention plate 114 into the open position. When the differential pressure has a positive value (+ΔP), the fluid pressure at the outside surface of the sealingplate 116 is greater than the fluid pressure at the outside surface of theretention plate 114. In the open position, the movement of theflap 117 unblocks theholes 120 of the sealingplate 116 so that fluid is able to flow through them and the alignedholes 122 and 118 of theflap 117 and theretention plate 114, respectively, as indicated by the dashedarrows 124.
When the differential pressure across thevalve 110 changes back to a negative differential pressure (-ΔP) as indicated by the downward pointing arrow inFigure 8B, fluid begins flowing in the opposite direction through thevalve 110 as indicated by the dashedarrows 132, which forces theflap 117 back toward the closed position shown inFigure 7B. InFigure 8B, the fluid pressure between theflap 117 and the sealingplate 116 is lower than the fluid pressure between theflap 117 and theretention plate 114. Thus, theflap 117 experiences a net force, represented byarrows 138, which accelerates theflap 117 toward the sealingplate 116 to close thevalve 110. In this manner, the changing differential pressure cycles thevalve 110 between closed and open positions based on the direction (i.e., positive or negative) of the differential pressure across thevalve 110. It should be understood that theflap 117 could be biased against theretention plate 114 in an open position when no differential pressure is applied across thevalve 110, i.e., thevalve 110 would then be in a "normally open" position.
Referring again toFigure 6A, thevalve 110 is disposed within the primary aperture 46' of thepump 10 so that fluid is drawn into thecavity 11 through the primary aperture 46' and expelled from thecavity 11 through thesecondary apertures 15 as indicated by the solid arrows, thereby providing a source of reduced pressure at the primary aperture 46' of thepump 10. The fluid flow through the primary aperture 46' as indicated by the solid arrow pointing upwards corresponds to the fluid flow through theholes 118, 120 of thevalve 110 as indicated by the dashedarrows 124 that also point upwards. As indicated above, the operation of thevalve 110 is a function of the change in direction of the differential pressure (ΔP) of the fluid across the entire surface of theretention plate 114 of thevalve 110 for this embodiment of a negative pressure pump. The differential pressure (Δ*P) is assumed to be substantially uniform across the entire surface of theretention plate 114 because the diameter of theretention plate 114 is small relative to the wavelength of the pressure oscillations in thecavity 115 and furthermore because thevalve 110 is located in the primary aperture 46' near the centre of thecavity 115 where the amplitude of the central pressure anti-node 71 is relatively constant. When the differential pressure across thevalve 110 reverses to become a positive differential pressure (+ΔP) as shown inFigures 6C and8A, thebiased flap 117 is motivated away from the sealingplate 116 against theretention plate 114 into the open position. In this position, the movement of theflap 117 unblocks theholes 120 of the sealingplate 116 so that fluid is permitted to flow through them and the alignedholes 118 of theretention plate 114 and theholes 122 of theflap 117 as indicated by the dashedarrows 124. When the differential pressure changes back to the negative differential pressure (-ΔP), fluid begins to flow in the opposite direction through the valve 110 (seeFigure 8B), which forces theflap 117 back toward the closed position (seeFigure 7B). Thus, as the pressure oscillations in thecavity 11 cycle thevalve 110 between the normally closed and open positions, the pump 160 provides a reduced pressure every half cycle when thevalve 110 is in the open position.
The differential pressure (ΔP*) is assumed to be substantially uniform across the entire surface of theretention plate 114 because it corresponds to the central pressure anti-node 71 as described above, it therefore being a good approximation that there is no spatial variation in the pressure across thevalve 110. While in practice the time-dependence of the pressure across the valve may be approximately sinusoidal, in the analysis that follows it shall be assumed that the differential pressure (ΔP) between the positive differential pressure (+ΔP) and negative differential pressure (-ΔP) values can be represented by a square wave over the positive pressure time period (t_P+) and the negative pressure time period (t_P-) of the square wave, respectively, as shown inFigure 9A. As differential pressure (ΔP) cycles thevalve 110 between the normally closed and open positions, thepump 10 provides a reduced pressure every half cycle when thevalve 110 is in the open position subject to the opening time delay (T_o) and the closing time delay (T_c) as also described above and as shown inFigure 9B. When the differential pressure across thevalve 110 is initially negative with thevalve 110 closed (seeFigure 7A) and reverses to become a positive differential pressure (+ΔP), thebiased flap 117 is motivated away from the sealingplate 116 towards theretention plate 114 into the open position (seeFigure 7B) after the opening time delay (T_o). In this position, the movement of theflap 117 unblocks theholes 120 of the sealingplate 116 so that fluid is permitted to flow through them and the alignedholes 118 of theretention plate 114 and theholes 122 of theflap 117 as indicated by the dashedarrows 124, thereby providing a source of reduced pressure outside the primary aperture 46' of thepump 10 over an open time period (t_o). When the differential pressure across thevalve 110 changes back to the negative differential pressure (-ΔP), fluid begins to flow in the opposite direction through the valve 110 (seeFigure 7C) which forces theflap 117 back toward the closed position after the closing time delay (T_c). Thevalve 110 remains closed for the remainder of the half cycle or the closed time period (t_c).
Theretention plate 114 and the sealingplate 116 should be strong enough to withstand the fluid pressure oscillations to which they are subjected without significant mechanical deformation. Theretention plate 114 and the sealingplate 116 may be formed from any suitable rigid material such as glass, silicon, ceramic, or metal. Theholes 118, 120 in theretention plate 114 and the sealingplate 116 may be formed by any suitable process including chemical etching, laser machining, mechanical drilling, powder blasting, and stamping. In one embodiment, theretention plate 114 and the sealingplate 116 are formed from sheet steel between 100 and 200 microns thick, and theholes 118, 120 therein are formed by chemical etching. Theflap 117 may be formed from any lightweight material, such as a metal or polymer film. In one embodiment, when fluid pressure oscillations of 20 kHz or greater are present on either the retention plate side 134 or the sealing plate side 136 of the valve, theflap 117 may be formed from a thin polymer sheet between 1 micron and 20 microns in thickness. For example, theflap 117 may be formed from polyethylene terephthalate (PET) or a liquid crystal polymer film approximately 3 microns in thickness.
In order to obtain an order of magnitude estimate for the maximum mass per unit area of theflap 117 according to one embodiment of the invention, it is again assumed that the pressure oscillation across thevalve 110 is a square wave as shown inFigure 9A and that the full pressure differential is dropped across theflap 117. Further assuming that theflap 117 moves as a rigid body, the acceleration of theflap 117 away from the closed position when the differential pressure reverses from the negative to the positive value may be expressed as follows: $\ddot{x} = \frac{P}{m}$
wherex is the position of theflap 117,ẍ represents the acceleration of theflap 117,P is the amplitude of the oscillating pressure wave, and m is the mass per unit area of theflap 117. Integrating this expression to find the distance, d, traveled by theflap 117 in a time t, yields the following: $d = \frac{P}{2 m} t^{2}$
This expression may be used to estimate the opening time delay (T_o) and the closing time delay (T_c), in each case from the point of pressure reversal.
In one embodiment of the invention, theflap 117 should travel the distance between theretention plate 114 and the sealingplate 116, the valve gap (v_gap) being the perpendicular distance between the two plates, within a time period less than about one quarter (25%) of the time period of the differential pressure oscillation driving the motion of theflap 117, i.e., the time period of the approximating square wave (t_pres). Based on this approximation and the equations above, the mass per unit area of the flap 117 (m) is subject to the following inequality: $m < \frac{P}{2 d_{gap}} \frac{{t_{pres}}^{2}}{16}, or alternatively m < \frac{P}{2 d_{gap}} \frac{1}{16 f^{2}}$
whered_gap is the flap gap, i.e., the valve gap (v_gap) minus the thickness of theflap 117, and f is the frequency of the applied differential pressure oscillation (as illustrated inFigure 10). In one embodiment,P may be 15kPa, f may be 20kHz, andd_gap may be 25 microns, indicating that the mass per unit area of the flap 117 (m) should be less than about 60 grams per square meter. Converting from mass per unit area of the flap 117 (m), the thickness of theflap 117 is subject to the following inequality: $δ_{flap} < \frac{P}{2 d_{gap}} \frac{1}{16 f^{2}} \frac{1}{ρ_{flap}}$
where ρ_flap is the density of theflap 117 material. Applying a typical material density for a polymer (e.g., approximately 1400 kg/m³), the thickness of theflap 117 according to this embodiment is less than about 45 microns for the operation of avalve 110 under the above conditions. Because the square wave shown inFigure 9A in general overestimates the approximately sinusoidal oscillating pressure waveform across thevalve 110, and further because only a proportion of the pressure difference applied across thevalve 110 will act as an accelerating pressure difference on theflap 117 , the initial acceleration of theflap 117 will be lower than estimated above and the opening time delay (T_o) will in practice be higher. Therefore, the limit on flap thickness derived above is very much an upper limit, and in practice, to compensate for the decreased acceleration of theflap 17, the thickness of theflap 17 may be reduced to satisfy the inequality of Equation 5. Theflap 117 is thinner so that it accelerates more quickly to ensure that the opening time delay (T_o) is less than about one quarter (25%) of the time period of the differential pressure oscillation (t_pres).
Minimizing the pressure drop incurred as air flows through thevalve 110 is important to maximizing valve performance as it affects both the maximum flow rate and the stall pressure that are achievable. Reducing the size of the valve gap (v_gap) between the plates or the diameter of theholes 118, 120 in the plates both increase the flow resistance and increase the pressure drop through thevalve 110. According to another embodiment of the invention, the following analysis employing steady-state flow equations to approximate flow resistance through thevalve 110 may be used to improve the operation of thevalve 110. The pressure drop for flow through ahole 118 or 120 in either plate can be estimated using the Hagan-Pouisille equation: $Δ p_{hole} = \frac{128 {μqt}_{plate}}{{πd}_{hole}^{3}}$
where µ is the fluid dynamic viscosity, q is the flow rate through the hole, t_plate is the plate thickness, and d_hole is the hole diameter.
When thevalve 110 is in the open position as shown inFigure 7B, the flow of fluid through the gap between theflap 117 and the sealing plate 116 (the same value as the flap gapd_gap) will propagate generally radially through the gap to a first approximation after exiting thehole 120 in the sealingplate 116 before contracting radially into thehole 118 in theretention plate 114. If the pattern of theholes 118, 120 in both plates is a square array with a sealing length, s, between theholes 118 of theretention plate 114 and theholes 120 of the sealingplate 116 as shown inFigures 7B and7D, the pressure drop through thecavity 115 of thevalve 110 may be approximated by the following equation: $Δ p_{gap} = \frac{6 μq}{{πd}_{gap}^{3}} \ln (2 {(\frac{s}{d_{hole}} + 1)}^{2})$
Thus, the total pressure drop (approximately Δp_gap + 2* Δp_hole) can be very sensitive to changes in the diameter of theholes 118, 120 and the flap gapd_gap between theflap 117 and the sealingplate 116. It should be noted that a smaller flap gapd_gap, which can be desirable in order to minimize the opening time delay (T_o) and the closing time delay (T_c) of thevalve 110, may increase the pressure drop significantly. According to the equation above, reducing the flap gapd_gap from 25 microns to 20 microns doubles the pressure loss. In many practical embodiments of the valve, it is this trade-off between response time and pressure drop that determines the optimal flap gapd_gap between theflap 117 and the sealingplate 116. In one embodiment, the optimal flap gapd_gap falls within an approximate range between about 5 microns and about 150 microns.
In setting the diameter of theholes 120 of the sealingplate 116, consideration should be given both to maintaining the stress experienced by theflap 117 within acceptable limits during operation of the valve 110 (such stresses being reduced by the use of a smaller diameter for theholes 120 of the sealing plate 116) and to ensuring that the pressure drop through theholes 120 does not dominate the total pressure drop through thevalve 110. Regarding the latter consideration, a comparison between equations 6 & 7 above for the hole and gap pressure drops yields a minimum diameter for theholes 120 at which the hole pressure drop is about equal to the valve gap pressure drop. This calculation sets a lower limit on the desirable diameter of theholes 120 above which diameter the hole pressure drop quickly becomes negligibly small..
Regarding the former consideration relating to the stress experienced by theflap 117 in operation,Figure 10 illustrates a portion of thevalve 110 ofFigure 7B in the normally closed position. In this position, theflap 117 is subjected to stress as theflap 117 seals and blocks thehole 120 in the sealingplate 116 causing theflap 117 to deform in the shape of a dimple extending into the opening of theholes 120 as illustrated. The level of stress on theflap 117 in this configuration increases with the diameter of theholes 120 in the sealingplate 116 for a givenflap 117 thickness. Theflap 117 material will tend to fracture more easily if the diameter of theholes 120 is too large, thus leading to failure of thevalve 110. In order to reduce the likelihood that theflap 117 material fractures, thehole 120 diameter may be reduced to limit the stress experienced by theflap 117 in operation to a level which is below the fatigue stress of theflap 117 material.
The maximum stress experienced by theflap 117 material in operation may be estimated using the following two equations: $\frac{Δ p_{\max} r_{hole}^{4}}{{Et}^{4}} = K_{1} \frac{y}{t} + K_{2} {(\frac{y}{t})}^{3}$
$\frac{σ_{\max} r_{hole}^{4}}{{Et}^{4}} = K_{3} \frac{y}{t} + K_{4} {(\frac{y}{t})}^{2}$
where r_hole is the radius of thehole 120 of the sealingplate 116, t is theflap 117 thickness, y is theflap 117 deflection at the centre of thehole 120, Δp_max is the maximum pressure difference experienced by theflap 117 when sealed, E is the Young's Modulus of theflap 117 material, and K₁ to K₄ are constants dependant on the details of the boundary conditions and the Poisson ratio of theflap 117. For a givenflap 117 material and geometry of theholes 120,equation 8 can be solved for the deformation, y, and the result then used in equation 9 to calculate stress. For values of y « t, the cubic and squared y/t terms inequations 8 and 9 respectively become small and these equations simplify to match small plate deflection theory. Simplifying these equations results in the maximum stress being proportional to the radius of theholes 120 squared and inversely proportional to theflap 117 thickness squared. For values of y»t or for flaps that have no flexural stiffness, the cubic and squared y/t terms in the two equations become more significant so that the maximum stress becomes proportional to thehole 120 radius to the power 2/3 and inversely proportional to theflap 117 thickness to the power 2/3.
In one embodiment of the invention, theflap 117 is formed from a thin polymer sheet, such as Mylar having a Poisson ratio of 0.38, and is clamped to the sealingplate 116 at the edge of theholes 120. The constants K₁ to K₄ can be estimated as 6.23, 3.04, 4.68 and 1.73, respectively. Using these values inEquations 8 and 9 and assuming that the thickness of theflap 117 is about 3 microns with a Young's Modulus of 4.3GPa under 500mbar pressure difference, the deflection (y) of theflap 117 will be approximately 1µm for a hole radius of 0.06mm, about 4µm for a hole radius of 0.1mm, and about 8µm for a hole radius of 0.15mm. The maximum stresses under these conditions will be 16, 34 and 43MPa, respectively. Considering the high number of stress cycles applied to theflap 117 during the operation of thevalve 110, the maximum stress per cycle tolerated by theflap 117 should be significantly lower than the yield stress of theflap 117 material in order to reduce the possibility that theflap 117 suffers a fatigue fracture, especially at the dimple portion of theflap 117 extending into theholes 120. Based on fatigue data compiled for a high number of cycles, it has been determined that the actual yield stress of theflap 117 material should be at least about four times greater than the stress applied to theflap 117 material (e.g., 16, 34 and 43MPa as calculated above). Thus, theflap 117 material should have a yield stress as high as 150MPa to minimize the likelihood of such fractures for a maximum hole diameter in this case of approximately 200 microns.
Reducing the diameter of theholes 120 beyond this point may be desirable as it further reducesflap 117 stress and has no significant effect on valve flow resistance until the diameter of theholes 120 approach the same size as the flap gapd_gap. Further, reduction in the diameter of theholes 120 permits the inclusions of an increased number ofholes 120 per unit area of thevalve 110 surface for a given sealing length (s). However, the size of the diameter of theholes 120 may be limited, at least in part, by the manner in which the plates of thevalve 110 were fabricated. For example, chemical etching limits the diameter of theholes 120 to be greater than approximately the thickness of the plates in order to achieve repeatable and controllable etching results. In one embodiment, theholes 120 in the sealingplate 116 being between about 20 microns and about 500 microns in diameter. In another embodiment, theretention plate 114 and the sealingplate 116 are formed from sheet steel about 100 microns thick, and theholes 118, 120 are about 150 microns in diameter. In this embodiment thevalve flap 117 is formed from polyethylene terephthalate (PET) and is about 3 microns thick. The valve gap (v_gap) between the sealingplate 116 and theretention plate 114 is around 25 microns.
Figures 11A and 11B illustrate yet another embodiment of thevalve 110,valve 310, comprising release holes 318 extending through theretention plate 114 between theholes 118 in theretention plate 114. The release holes 322 facilitate acceleration of theflap 117 away from theretention plate 114 when the differential pressure across thevalve 310 changes direction, thereby further reducing the response time of thevalve 310, i.e., reducing the closing time delay (T_c). As the differential pressure changes sign and reverse flow begins (as illustrated by dashed arrows 332), the fluid pressure between theflap 117 and the sealingplate 112 decreases and so theflap 117 moves away from theretention plate 114 towards the sealingplate 116. The release holes 318 expose theoutside surface 317 of theflap 117 in contact with theretention plate 114 to the pressure differential acting to close thevalve 310. Also, the release holes 318 reduce thedistance 360 that fluid must penetrate between theretention plate 114 and theflap 117 in order to release theflap 117 from theretention plate 114 as illustrated inFigure 11B. The release holes 318 may have a different diameter than theother holes 118, 120 in the valve plates. InFigures 11A and 11B, theretention plate 114 acts to limit the motion of theflap 117 and to support theflap 117 in the open position while having a reduced surface contact area with thesurface 317 of theflap 117.
Figures 12A and 12B show twovalves 110 as shown inFigure 7A wherein onevalve 410 is oriented in the same position as thevalve 110 ofFigure 7A and theother valve 420 is inverted or reversed with theretention plate 114 on the lower side and the sealingplate 116 on the upper side. Thevalves 410, 420 operate as described above with respect tovalve 110 ofFigures 7A-7C and8A-8B, but with the air flows in opposite directions as indicated by dashedarrow 412 for thevalve 410 and dashedarrow 422 for thevalve 420 wherein one valve acts as an inlet valve and the other acts as an outlet valve.Figure 12C shows a graph of the operating cycle of thevalves 410, 420 between an open and closed position that are modulated by the square-wave cycling of the pressure differential (ΔP) as illustrated by the dashed lines (seeFigures 9A and 9B). The graph shows a half cycle for each of thevalves 410, 420 as each one opens from the closed position. When the differential pressure across thevalve 410 is initially negative and reverses to become a positive differential pressure (+ΔP), thevalve 410 opens as described above and shown bygraph 414 with fluid flowing in the direction indicated by thearrow 412. However, when the differential pressure across thevalve 420 is initially positive and reverses to become a negative differential pressure (-ΔP), thevalve 420 opens as described above and shown bygraph 424 with fluid flowing in the opposite direction as indicated by thearrow 422. Consequently, the combination of thevalves 410, 420 function as a bi-directional valve permitting fluid flow in both directions in response to the cycling of the differential pressure (ΔP). Thevalves 410, 420 may be mounted conveniently side by side within the primary aperture 46' of thepump 10 to provide fluid flow in the direction indicated by the solid arrow in the primary aperture 46' as shown inFigure 6A for one half cycle, and then in the opposite direction (not shown) for the opposite half cycle.
Figures 13 and14 show yet another embodiment of thevalves 410, 420 ofFigure 12A in which twovalves 510, 520 corresponding tovalves 410, 420, respectively, are formed within asingle structure 505. Essentially, the twovalves 510, 520 share a common wall or dividingbarrier 540 which in this case is formed as part of thewall 112, although other constructions may be possible. When the differential pressure across thevalve 510 is initially negative and reverses to become a positive differential pressure (+ΔP), thevalve 510 opens from its normally closed position with fluid flowing in the direction indicated by thearrow 512. However, when the differential pressure across thevalve 520 is initially positive and reverses to become a negative differential pressure (-ΔP), thevalve 520 opens from its normally closed position with fluid flowing in the opposite direction as indicated by thearrow 522. Consequently, the combination of thevalves 510, 520 function as a bi-directional valve permitting fluid flow in both directions in response to cycling of the differential pressure (ΔP).
Figure 15 shows yet another embodiment of a bi-directional valve 555 having a similar structure as thebi-directional valve 505 ofFigure 14. Bi-directional valve 551 is also formed within a single structure having twovalves 510, 530 that share a common wall or dividing barrier 560 which is also formed as part of thewall 112. Thevalve 510 operates in the same fashion as described above with theflap 117 shown in the normally closed position blocking theholes 20 as also described above. However, thebi-directional valve 550 has asingle flap 117 having afirst flap portion 117a within thevalve 510 and asecond flap portion 117b within thevalve 530. Thesecond flap portion 117b is biased against theplate 516 and comprisesholes 522 that are aligned with theholes 120 of theplate 516 rather than theholes 118 of theplate 514 unlike the valves described above. Essentially, the valve 130 is biased by theflap portion 117b in a normally open position as distinguished from the normally closed position of the other valves described above. Thus, the combination of thevalves 510, 530 function as a bi-directional valve permitting fluid flow in both directions in response to the cycling of the differential pressure (ΔP) with the two valves opening and closing on alternating cycles.

Claims

A pump (10) comprising:
a pump body having a substantially cylindrical shape defining a cavity (11) for containing a fluid, the cavity being formed by a side wall (14) closed at both ends by end walls (12,13), at least one of the end walls being a driven end wall (12) having a central portion and a peripheral portion extending radially outwardly from the central portion of the driven end wall;
an actuator (40) operatively associated with the central portion of the driven end wall to cause an oscillatory motion of the driven end wall, thereby generating displacement oscillations of the driven end wall in a direction substantially perpendicular thereto with an annular node between the centre of the driven end wall and the side wall when in use;
a first aperture (16) disposed at any location in the cavity other than at the location of the annular node and extending through the pump body;
a second aperture (14) disposed at any location in the pump body other than the location of said first aperture and extending through the pump body; and,
a flap valve (46) disposed in at least one of said first aperture and second aperture;
whereby the displacement oscillations generate corresponding radial pressure oscillations of the fluid within the cavity of said pump body causing fluid flow through said first and second apertures when in use;characterized by an isolator (30) operatively associated with the peripheral portion of the driven end wall to reduce dampening of the displacement oscillations; and in that
said flap valve comprises:
a first plate (116) having apertures (120) extending generally perpendicular through said first plate;
a second plate having first apertures extending generally perpendicular through said second plate (114), the first apertures (118) being substantially offset from the apertures of said first plate;
a spacer (112) disposed between said first plate and said second plate to form a cavity (115) therebetween in fluid communication with the apertures of said first plate and the first apertures of said second plate; and,
a flap (117) disposed and moveable between said first plate and said second plate, said flap having apertures (122) substantially offset from the apertures of said first plate (116) and substantially aligned with the first apertures of said second plate (114);
whereby said flap (117) is motivated between said first and second plates in response to a change in direction of the differential pressure of the fluid across said flap valve.
The pump (10) of claim 1, wherein said second plate (114) comprises second apertures (318) extending generally perpendicular through said second plate (114) and being spaced between the first apertures of said second plate, whereby the second apertures are offset from the apertures of said flap (117).
The pump (10) of claim 1, wherein said flap (117) is disposed adjacent either one of said first (116) and second (114) plates in a first position when the differential pressure is substantially zero and movable to the other one of said first and second plates in a second position when a differential pressure is applied, whereby said flap is motivated from the first position to the second position in response to a change in direction of the differential pressure of the fluid across said flap valve and back to the first position in response to a reversal in the direction of the differential pressure of the fluid.
The pump (10) of claim 3, wherein said flap (117) is disposed adjacent said second plate (114) in a normally open position, whereby the fluid flows through said flap valve when said flap is in the first position and the flow of the fluid is blocked by said flap valve when said flap is in the second position.
The pump (10) of claim 3, wherein said flap (117) is disposed adjacent said first plate (116) in a normally closed position, whereby the flow of the fluid is blocked by said flap valve when said flap is in the first position and the fluid flows through said flap valve when said flap is in the second position.
The pump (10) of claim 4 and claim 5, wherein said second plate (114) further comprises second apertures (318) extending generally perpendicular through said second plate and spaced between the first apertures of said second plate, whereby the second apertures are offset from the apertures of said flap when in the second position.
A pump (10) according to claim 1, wherein said first (116) and second (114) plates are formed from a substantially rigid material selected from the group consisting of metal, plastic, silicon, and glass.
A pump (10) according to claim 7, wherein the metal is steel having a thickness between about 100 and about 200 microns.
A pump (10) according to claim 1, wherein said flap (117) and either one of said first (116) and second (114) plates are separated by a distance between about 5 microns and about 150 microns when said flap is disposed adjacent to the other said plate.
A pump (10) according to claim 9, wherein said flap (117) is formed from a polymer having a thickness of about 3 microns and the distance between said flap and either one of said first and second plates is between about 15 microns and about 50 microns when said flap is disposed adjacent to the other said plate.
A pump (10) according to claim 10, wherein said flap (117) is formed from a light-weight material selected from the group consisting of a polymer and metal.
A pump (10) according to claim 11, wherein the light-weight material is a polymer having a thickness of less than about 20 microns.
A pump (10) according to claim 12, wherein the polymer is polyethylene terephthalate or a liquid crystal film having a thickness of about 3 microns.
A pump (10) according to claim 1, wherein the apertures (120) in said first plate are less than about 500 microns in diameter.
A pump (10) according to claim 1, wherein said flap (117) is formed from a polymer having a thickness of about 3 microns and the apertures in said first plate are less than about 150 microns in diameter.
A pump (10) according to claim 1, wherein said first (116) and second (114) plates are formed from steel having a thickness of about 100 microns, and wherein the apertures (120) of said first plate, the first apertures (118) of said second plates, and the apertures (122) of said flap (117) are about 150 microns in diameter, and wherein said flap is formed from a polymer film having a thickness of about 3 microns.
A pump (10) according to claim 1, wherein said first (116) and second (114) plates, said spacer (112), and said flap (117) comprise a first valve portion (410), and said flap valve further comprises a second valve portion (420) comprising:
a first plate (116) having apertures (120) extending generally perpendicular through said first plate;
a second plate (114) having first apertures (118) extending generally perpendicular through said second plate, the first apertures being substantially offset from the apertures of said first plate;
a spacer (112) disposed between said first plate and said second plates to form a cavity therebetween in fluid communication with the apertures of said first plate and the first apertures of said second plate; and
a flap (117) disposed and moveable between said first plate and said second plate, said flap having apertures (122) substantially offset from the apertures of said first plate and substantially aligned with the first apertures of said second plate;
whereby said flap is motivated between said first and second plates in response to a change in direction of the differential pressure of the fluid across said flap valve; and
wherein said first (410) and second (420) valve portions are oriented with respect to the differential pressure to permit fluid to flow through said two portions of said valve in opposite directions in response to cycling of the differential pressure of the fluid across said valve.
The pump (10) of claim 17, wherein said flap (117) of each valve portion is disposed adjacent either one of said first and second plates in a first position when the differential pressure is substantially zero and moveable to the other one of said first and second plates in a second position when a differential pressure is applied, whereby each of said flaps is motivated from the first position to the second position in response to a change in direction of the differential pressure of the fluid across said flap valve and back to the first position in response to a reversal in direction of the differential pressure of the fluid.
The pump (10) of claim 17, wherein said first (410) and second (420) valve portions are oriented in opposite directions respecting the differential pressure, and said flap of each valve portion is disposed adjacent said second plate in a normally open position, whereby the fluid flows through each of said valve portions when said flaps are in the first position and the flow of the fluid is blocked by said valve portions when said flaps are in the second position.
The pump (10) of claim 17, wherein said first (410) and second (420) valve portions are oriented in opposite directions respecting the differential pressure, and said flap of each valve portion is disposed adjacent said first plate in a normally closed position, whereby the flow of the fluid is blocked by said valve portions when said flaps are in the first position and the fluid flows through said valve portions when said flaps are in the second position.
The pump (10) of claim 17, wherein said first (410) and second (420) valve portions are oriented in opposite directions respecting the differential pressure, said flap of said first valve portion being disposed adjacent said first plate in a normally closed position whereby the flow of the fluid is blocked by said first valve portion when said flap is in the first position and the fluid flows through said first valve portion when said flap is in the second position, and said flap of said second valve portion being disposed adjacent said second plate in a normally open position whereby the fluid flows through said second valve portion when said flap is in the first position and the flow of the fluid is blocked by said second valve portion when said flap is in the second position.
The pump (10) of claim 1 wherein the oscillatory motion generates radial pressure oscillations of the fluid within the cavity causing fluid flow through said first aperture and second aperture.
The pump (10) of claim 22 wherein the lowest resonant frequency of the radial pressure oscillations is greater than about 500 Hz.
The pump (10) of claim 22 wherein the frequency of the oscillatory motion is about equal to the lowest resonant frequency of the radial pressure oscillations.
The pump (10) of claim 22 wherein the frequency of the oscillatory motion is within 20% of the lowest resonant frequency of the radial pressure oscillations.
The pump (10) of claim 22 wherein the oscillatory motion is mode-shape matched to the radial pressure oscillations.
The pump (10) of claim 1 wherein said flap valve is a bi-directional valve for controlling the flow of fluid in two directions, said bi-directional valve comprising at least two valve portions (410,420) for controlling the flow of fluid, each of said valve portions comprising:
a first plate (116) having apertures (120) extending generally perpendicular through said first plate;
a second plate (114) having apertures (118) extending generally perpendicular through said second plate, the first apertures being substantially offset from the apertures of said first plates;
a spacer (112) disposed between said first plate and said second plates to form a cavity therebetween in fluid communication with the apertures of said first plate and the apertures of said second plate; and
a flap (117) disposed and moveable between said first and second plates, said flap having apertures (122) substantially offset from the apertures of said first plate and substantially aligned with the apertures of said second plate;
whereby said flap is motivated between said first and second plates in response to a change in direction of the differential pressure of the fluid across said valve; and,
wherein said first and second valve portions are oriented with respect to the differential pressure to permit fluid to flow through said two portions of said valve in opposite directions in response to cycling of the differential pressure of the fluid across said valve.
The pump (10) of claim 27, wherein said flap (117) of each valve portion (410,420) is disposed adjacent either one of said first and second plates in a first position when the differential pressure is substantially zero and moveable to the other one of said first and second plates in a second position when a differential pressure is applied, whereby each of said flaps are motivated from the first position to the second position in response to a change in direction of the differential pressure of the fluid across said valve and back to the first position in response to a reversal in the direction of the differential pressure of the fluid.