Patent Application
20090060728
This disclosure pertains to, inter alia, gear pumps and other pumps configured to operate in a substantially primed condition to urge flow of a liquid. The subject pumps and pump-heads include various types having one or more rotary members, such as meshed gears, or at least one pumping member that operates continuously in a cyclic manner. More specifically, the disclosure pertains to pumps and pump-heads capable of accommodating a volume expansion of the liquid in the pump-head such as by a freezing event, a pressure fluctuation, or the like.
Several types of pumps are especially useful for pumping liquids and other fluids with minimal back-flow and that are amenable to miniaturization. An example is a gear pump. Another example is a piston pump. A third example is a variation of a gear pump in which the rotary pumping members have lobes that interdigitate with each other. Gear pumps and related pumps have experienced substantial acceptance in the art due to their comparatively small size, quiet operation, reliability, and cleanliness of operation with respect to the fluid being pumped. Gear pumps and related pumps also are advantageous for pumping fluids while keeping the fluids isolated from the external environment. This latter benefit has been further enhanced with the advent of magnetically coupled pump-drive mechanisms that have eliminated leak-prone hydraulic seals that otherwise would be required around pump-drive shafts.
Gear pumps have been adapted for use in many applications, including applications requiring extremely accurate delivery of a fluid to a point of use. Consequently, these pumps are widely used in medical devices and scientific instrumentation. Developments in many other areas of technology have generated new venues for accurate pumps and related fluid-delivery systems. Such applications include, for example, delivery of liquids in any of various automotive applications.
Automotive applications are demanding from technical, reliability, and environmental viewpoints. Technical demands include spatial constraints, ease of assembly and repair, and efficacy. Reliability demands include requirements for high durability, vibration-resistance, leak-resistance, maintenance of hydraulic prime, and long service life. Environmental demands include internal and external corrosion resistance, and ability to operate over a wide temperature range.
A typical automotive temperature range includes temperatures substantially below the freezing temperature of water and other dilute aqueous liquids. These temperatures can be experienced, for example, whenever an automobile is left out in freezing winter climate. In contrast to many other substances, water and most aqueous solutions tend to expand as they undergo the phase change from liquid to ice. As is well known in household plumbing systems exposed to sub-freezing temperatures, the static pressures produced by freeze-expansion are sufficiently high to fracture pipe. Thus, these pressures can cause substantial damage to a pump that is coupled in a primed condition to a hydraulic circuit exposed to a sub-freezing temperature.
In view of the above, the simplest solution that might be proposed is simply to add anti-freeze to the liquid or to constitute the liquid with sufficient solute to depress its freezing point. Unfortunately, changing the liquid in these ways changes the composition and possibly other important properties of the liquid, which may render the liquid ineffective for its intended purpose. Hence, there is a need for pumps that can effectively withstand the internal pressure generated by a freezing condition without exhibiting damage that otherwise would be caused by freeze-expansion.
There is also a need for pumps that exhibit reduced pressure pulsatility of the output stream of liquid being pumped. Although many types of gear pumps, for example, deliver substantially continuous output streams, the output streams nevertheless tend to exhibit at least some pressure pulsatility that is synchronous with the rate at which increments of liquid between successive gear teeth are delivered downstream by the pump-head. Output-pressure pulsatility, a dynamic rather than static phenomenon, is exhibited by many types of pumps, including conventional gear pumps, piston pumps, and the like. Certain types of pumps, such as piston pumps, tend to exhibit a higher-amplitude output-pressure pulsatility than other types, such as gear pumps. Nevertheless, certain highly precise applications would be better served using pumps, otherwise highly effective for their assigned uses, that produce substantially less output pulsation than their conventional counterparts.
The needs articulated above are met by, inter alia, pumps, pump-heads, and methods as disclosed herein. The subject pumps and pump-heads operate in a substantially primed condition. Since liquids are substantially non-compressible, conventional pumps operating in a primed condition are vulnerable to pressure damage if liquid in the pumps is allowed to freeze and thus undergo freeze-expansion (and if the liquid is one, such as water, that expands as it freezes). I.e., in a conventional primed pump, it may be very difficult or impossible for the liquid to find additional hydraulic space for expansion as the liquid freezes. Conventional primed pumps also tend to exhibit pressure fluctuations generated by the particular pumping action of the “pumping member” of the pump, such as contra-rotating gears, reciprocating piston, or the like. Pumps as disclosed herein automatically provide additional hydraulic space, as needed, to absorb these pressure increases, whether of relatively low amplitude accompanying the pumping action or of relatively high magnitude as generated during freezing. This provision of additional hydraulic space can occur repeatedly for an indefinite length of time, which is effective in reducing pressure fluctuations accompanying pumping action, and can be maintained indefinitely in a static manner, which is effective for reducing a pressure increase in the pump accompanying freezing of the liquid in the pump.
An embodiment of a pump comprises a pump housing defining a pump cavity, at least one inlet, and at least one outlet. The pump housing includes at least one interior non-wearing location that contacts liquid in the pump housing when the pump housing is primed with the liquid. The pump includes a movable pumping member situated in the pump cavity. The pumping member, when driven to move, urges flow of the liquid from the inlet through the pump cavity to the outlet. At least one pressure-absorbing member is located inside the pump housing at the non-wearing location and contacts the liquid. “In the pump housing” can be any location in the pump cavity, the inlet(s), and the outlet(s), including any additional internal cavity of the pump housing contacting the liquid and in fluid communication with the pump cavity, such as, but not limited to, a magnet-cup cavity. The pressure-absorbing member has a compliant property so as to exhibit a volumetric compression when subjected to a pressure increase in the liquid contacting the pressure-absorbing member. This volumetric compression is sufficient to alleviate at least a portion of the pressure increase. Alleviating the pressure increase can be sufficient to prevent freeze-expansion damage to the pump, and/or can be sufficient to reduce pressure fluctuations in the pumped liquid, such as at the outlet of the pump. Alleviation of pressure fluctuations is further facilitated by the pressure-absorbing member also exhibiting a volumetric expansion when subjected to a pressure decrease in the liquid contacting the pressure-absorbing member.
In certain embodiments of the pump, the movable pumping member comprises a rotatable pumping member, such as at least one gear. These gear-including embodiments typically have at least one “driving” gear and at least one “driven” gear that contra-rotate about their respective axes in the usual manner of gear pumps. In other embodiments the movable pumping member comprises at least one piston that typically undergoes a reciprocating motion.
The pressure-absorbing member(s) desirably are respective units of a closed-cell foam material. Example materials of this type include, but are not limited to, silicone closed-cell foams, fluorosilicone closed-cell foams, polyurethane closed-cell foams, any of various rubber-based closed-cell foams, and the like. Certain applications are favorably served by a pressure-absorbing member being a high-stiffness closed-cell foam material such as, but not limited to, aluminum closed-cell foam. The material for the pressure-absorbing member can be selected based on chemical inertness, flexibility, contractile stiffness, ease of manufacturability in the sizes and shapes needed, etc.
A pump as summarized above, aside from the “mover” used to actuate the pump, is usually termed a “pump-head.” Pump-heads can be manufactured and distributed as units that can be coupled to various movers. Example movers are any of various types of motors that can be coupled directly or indirectly to the movable pumping member in the pump-head. Actuation of the mover causes corresponding motion of the movable pumping member in the pump cavity. An example mover includes a magnet coupled to the movable pumping member, and a magnet driver magnetically coupled to the magnet to move the magnet (e.g., rotate it about its axis) and thus move the pumping member in the pump cavity. Pumps including magnetic movers are generally termed “magnetically actuated” pumps. Such pumps are advantageous because they allow elimination of leak-prone dynamic seals such as shaft seals. Alternatively, the mover can include a mechanical, rather than magnetic, coupling to the movable pumping member such as, for example, a direct coupling to the armature of an electrical motor.
Any of various embodiments of the pump can further include at least one sensor in fluid communication with the liquid in the pump housing. Example sensors include, but are not limited to, pressure sensors, temperature sensors, flow sensors, chemical sensors, and the like. Desirably, at least one pressure-absorbing member is situated, in the pump housing, adjacent the sensor to protect the sensor from pressure extremes and/or to smooth pressure fluctuations in the vicinity of the sensor. More than one sensor can be used.
According to another aspect, gear pump-heads are provided. An embodiment of such a pump-head comprises a pump housing that defines a gear cavity, at least one inlet hydraulically coupled to the gear cavity, at least one outlet hydraulically coupled to the gear cavity, and at least one interior non-wearing location that contacts liquid in the pump housing. At least one driving gear and one driven gear are enmeshed with each other in the gear cavity. At least one pressure-absorbing member is located inside the pump housing at the non-wearing location and contacts the liquid. The pressure-absorbing member has a compliant property so as to exhibit a volumetric compression when subjected to a pressure increase in the liquid contacting the pressure-absorbing member. The volumetric compression is sufficient to alleviate at least a portion of the pressure increase.
The pump housing of the gear pump-head can further include a cup-housing. The cup-housing defines a cup cavity in hydraulic communication with the gear cavity. The cup cavity contains the liquid and a rotatable driven magnet that is coupled to the driving gear such that rotation of the magnet about its axis causes corresponding rotation of the driving gear and thus of the driven gear. A convenient location for a pressure-absorbing member is in the cup cavity. These embodiments can impart rotation to the magnet by magnetically coupling the magnet to a second magnet, called a “driving” magnet mounted on the armature of a motor. Alternatively, rotation of the magnet in the cup can be caused by placing a stator in coaxial surrounding relationship to, but outside of, the cup-housing. The stator is magnetically coupled to the magnet so as to cause, whenever the stator is electrically energized, rotation of the magnet. This latter embodiment eliminates the driving magnet.
As noted above, the gear pump-head can further comprise at least one sensor in fluid communication with the liquid in the pump housing. At least one pressure-absorbing member desirably is situated, in the pump housing, adjacent the sensor to protect the sensor from pressure extremes and/or to reduce pressure fluctuations in the vicinity of the sensor.
According to another aspect, hydraulic circuits are provided. An exemplary circuit comprises a pump, such as any of the embodiments summarized above, a liquid source hydraulically connected upstream of the pump to the pump inlet, and a liquid-discharge port hydraulically connected downstream of the pump to the pump outlet. The pump can be, by way of example, a gear pump or a piston pump. But it will be understood that these specific pumps are not intended to be limiting. Various other specific types of pumps can readily accommodate at least one pressure-absorbing member as discussed herein.
Also provided are methods, in the context of a method for pumping a liquid using a substantially primed pump, for preventing a fluid cavity of the pump from experiencing at least a threshold magnitude of pressure increase in the liquid in the fluid cavity. An embodiment of such a method comprises placing a pressure-absorbing member at a non-wearing location within the fluid cavity of the pump. The pressure-absorbing member is configured to undergo a volumetric contraction in the fluid cavity whenever the liquid in the fluid cavity experiences the pressure increase, wherein the volumetric contraction of the pressure-absorbing member is sufficient to reduce the pressure increase. The threshold magnitude can be, for example, a pressure that would be generated in the fluid cavity if the liquid in the fluid cavity became at least partially frozen. In such a case, the pressure-absorbing member desirably is configured to undergo a volumetric contraction sufficient to prevent damage to the pump that otherwise would occur from the at least partial freezing of the liquid in the fluid cavity. Alternatively or in addition, the threshold magnitude is a pressure generated in the fluid cavity as a result of a pressure fluctuation of the liquid in the fluid cavity accompanying operation of the pump.
Also provided are methods, in the context of a method for pumping a liquid using a substantially primed pump, for reducing a pressure fluctuation in liquid being urged to flow by the pump. An embodiment of such a method comprises placing a pressure-absorbing member at a non-wearing location within a fluid cavity of the pump. The pressure-absorbing member desirably is configured to undergo volumetric changes in the fluid cavity as the liquid in the fluid cavity is being pumped by the pump, wherein the volumetric changes are sufficient to reduce the pressure fluctuation.
The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
This disclosure is set forth in the context of representative embodiments that are not intended to be limiting in any way.
As used herein, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the term “coupled” encompasses mechanical as well as other practical ways of coupling or linking items together, and does not exclude the presence of intermediate elements between the coupled items.
The described things and methods described herein should not be construed as being limiting in any way. Instead, this disclosure is directed toward all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The disclosed things and methods are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed things and methods require that any one or more specific advantages be present or problems be solved.
Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed things and methods can be used in conjunction with other things and method. Additionally, the description sometimes uses terms like “produce” and “provide” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.
In the following description, certain terms may be used such as “up,” “down,”, “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” and the like. These terms are used, where applicable, to provide some clarity of description when dealing with relative relationships. But, these terms are not intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” surface can become a “lower” surface simply by turning the object over. Nevertheless, it is still the same object.
A first embodiment of a pump 10 is depicted in
It will be understood that “gear” as used herein encompasses rotary members configured as conventional pump gears as well as any of various other rotary members having lobes, teeth or the like that interdigitate with the same of a second such member to produce, when contra-rotated relative to each other, fluid flow.
The stator 40 comprises wire windings 42 associated with an iron core 44 that surrounds the cup-housing 28 in a coaxial manner. The windings 42 are selectively energized by electronics 46 also contained within the outer casing 16. Power is supplied to the electronics 46 via the connectors 22. Thus, energization of the stator 40 causes axial rotation of the magnet 30, which rotates the driving gear 34, which rotates the driven gear 36. This contra-rotation of the gears 34, 36 urges flow of liquid through the cavity 38. For improved operation with certain liquids, the cavity 38 optionally may include a suction shoe (not detailed).
The fitting block 24 defines passageways leading to and from the cavity 38 and connecting the cavity to the inlet and outlet ports 26. If desired or required, the fitting block 24 also includes a pressure transducer 48 (that can be hydraulically connected to the outlet 26, for example). The pressure transducer 48 includes an electrical connector 50 permitting electrical connection of the pressure transducer 48 in a manner that establishes feedback control of energization of the stator 40. The fitting block 24 is coupled to the end plate 18 and is sealed against the rim of the cup-housing 28 to establish, within the cup-housing 28, a cup cavity 52. The cup cavity 52 is sealed using a static seal 54 (e.g. an O-ring). The cup cavity 52 is in hydraulic communication with the gear cavity 38, and hence both are wetted by the pumped liquid, as noted above. Also, during normal operation, at least the cup cavity 52 and gear cavity 38 are substantially primed with the liquid being pumped.
Also contained within the pump cavity, more specifically within the cup cavity 52 of this embodiment, is a pressure-absorbing member 56. In this embodiment the pressure-absorbing member 56 is located adjacent the distal end of the magnet and secured by a retaining ring 58. In other embodiments the retaining ring 58 can be eliminated, or another securing means can be used, as appropriate. The retaining ring 58 keeps the member 56 in position to prevent the member from interfering with rotation of the magnet 30.
The pressure-absorbing member 56 can be made of any of various materials allowing the pressure-absorbing member 56 to compress or contract in response to an increase in pressure of the liquid inside the cup cavity 52 and/or inside the pump cavity 38. The pressure increase can be static, such as accompanying freezing of the liquid inside the pump cavity, or dynamic, such as a corresponding portion of a pressure fluctuation in the liquid as it is being pumped. For absorbing freeze-expansion pressure, the pressure-absorbing member 56 desirably has sufficient compressible volume such that, if the liquid inside the primed cavity freezes and expands, the resulting increase in pressure inside the cavity causes the pressure-absorbing member 56 to contract sufficiently to “absorb” the expansion and thus prevent a buildup of pressure inside the pump that would otherwise damage the pump. By way of example, water and dilute aqueous solutions exhibit a maximum expansion of approximately 11% by volume upon undergoing the phase transition from liquid to solid. By contracting in response to this volume increase, the pressure-absorbing member 56 prevents freeze damage to the pump such as fracture of the cup-housing 28, damage to the magnet 30, damage of the pressure transducer 48, and/or damage to other parts of the pump 10. If the pressure-absorbing member is intended only to attenuate pressure fluctuations, it can be smaller than a corresponding member intended to protect against freeze-expansion, depending upon the amplitude of the target pressure fluctuations.
The gear pump can be made of any of various materials that are inert to the particular liquid to be pumped. For example, and not intending to be limiting, PEEK can be used for the gears 34, 36, the cup-housing 28, and the retaining ring 58.
In addition to its pressure-absorption capability, the member 56 also desirably is chemically inert to the fluid being pumped and desirably maintains its pressure compliance and integrity over the full operating temperature range of the pump 10. Not intending to be limiting, an exemplary material for fabricating the member 56 is fluorinated silicone closed-cell foam, which is highly inert and maintains flexibility over a wide temperature range. As made of such material, the member 56 can be cut, punched, or molded, for example, into a size and shape suitable for placement in the pump. Other candidate materials are ordinary silicone closed-cell foam, polyurethane closed-cell foam, and any of various rubber closed-cell foams. The “closed cell” property is important because an open-cell configuration would absorb the liquid over time, which would compromise the pressure-absorption function.
It is not always necessary that the pressure-absorbing member 56 be rubbery in consistency. Stiffer configurations may be suitable for certain conditions or fluids. An exemplary stiffer material than the elastomeric closed-cell foams discussed above is aluminum closed-cell foam. Closed-cell materials essentially are assemblages of multiple gas bladders, and there are no particular limits on size and/or number of bladders. The bladders can be large or small, few or many, all substantially the same size or of variable size. Parameters such as size, thickness, stiffness, and composition of the pressure-absorbing member can be selected depending upon the size and type of pump-head, the composition of the liquid to be pumped by the pump-head, the forces expected to be experienced by the pressure-absorbing member, the volumetric expansion expected if the liquid in the pump-head freezes, the magnitude of pressure fluctuations to be damped, the particular environment of the pressure-absorbing member inside the pump-head, etc. Another advantage of the pressure-absorbing member is that it can respond very rapidly to pressure increases.
In addition to or aside from its role in absorbing the pressure associated with freeze-expansion, the member 56 also effectively absorbs pressure fluctuations imparted to the pumped liquid by rotation of the gears 34, 36. These pressure fluctuations are an inherent consequence of many types of pumps relying upon rotating or other moving pumping members to urge flow of liquid. The fluctuations are typically of a regular, periodic nature, having a period that is proportional to the periodicity of the motion of the gears or other movable pump members. Although the fluctuations are normally of relatively low magnitude, at least in gear pumps, the fluctuations can be significant in certain applications and/or with certain other types of pumps such as piston pumps. In gear pumps, the pressure fluctuations arise by the fact that the contra-rotating gears have teeth between which are spaces with defined volumes occupied by liquid being urged by the gears to flow. The member 56 absorbs the pressure fluctuations by momentarily contracting a small amount in response to the respective momentary “pulse” of pumped liquid exiting the space between gear teeth. These volumetric responses by the member 56 can be very rapid, sufficiently rapid to coincide with and to be substantially in phase with the corresponding pressure fluctuations. By automatically experiencing periodic contractions and expansions in response to (and in synchrony with) the pressure fluctuations, the pressure-absorbing member 56 effectively damps these pressure fluctuations. Thus, the pressure-absorbing member 56 can be employed advantageously in the pump housing even if the pump housing is not expected to be subjected to a freezing condition.
In an experiment investigating the degree to which a pressure-absorbing member can damp pressure fluctuations at the outlet of a gear pump, reductions in magnitude of at least 10% were observed with a pump including the member versus a pump lacking the member. It will be appreciated that, as the pumping volume changes relative to the contractile volume of the pressure-absorbing member, the contractile volume can be tailored for specific applications. The size of pressure-absorbing member 56 useful for damping pressure fluctuations may be smaller than a pressure-absorbing member 56 that must contract sufficiently to absorb a pressure associated with freezing liquid in the pump housing.
Magnified detail of the region shown in
The second embodiment is otherwise similar to the first embodiment, except that the pressure-absorbing member 56 has a different location inside the cup-housing than shown in
In alternative configurations, the pressure-absorbing member is located at any of various other locations in the cup-housing. Example alternative locations include, but are not limited to, mounting on the magnet itself and mounting coaxially with the cup in a manner in which the inside walls of the cup-housing are lined with the pressure-absorbing member.
The first and second embodiments are magnetically driven pumps. But, principles disclosed herein are not limited to magnetically driven pumps. Magnetic drive is advantageous in general because it usually eliminates the need for a dynamic seal (e.g. a seal around a drive shaft coupled to the rotary member(s)). Pumps having dynamic seals (such as a shaft seal) typically do not have magnets or magnet cups, but they nevertheless are useful for many applications. Shaft seals are susceptible to damage caused by excess pressure inside the pump-head, such as pressure that would be generated by freeze-expansion of liquid inside the pump-head. Including at least one pressure-absorbing member inside such a pump-head would help protect the dynamic seal, and thus the pump itself, from freeze-expansion damage. Including at least one pressure-absorbing member in contact with the fluid path inside the pump-head also would provide damping of pressure fluctuations as described above. The manner in which the pump is actually driven does not significantly alter these needs or the remedies provided by including at least one pressure-absorbing member in the pump housing.
Hence, possible alternative locations of the pressure-absorbing member 56 are not limited to the magnet cup, regardless of whether the pump is magnetically driven. In general, possible locations in substantially any pump-head are any internal non-wearing surfaces inside the pump housing contacted by the pumped liquid. In some pump-heads, a suitable non-wearing surface may exist on the rotary member(s) of the pump. Also, alternatively to a single location, the pressure-absorbing member 56 can be located in multiple locations in the pump-head. In this embodiment, the pressure-absorbing member is located near the outlet 26. Reference is made to
An alternative configuration is shown in
Yet another alternative configuration is a combination of the configurations of
In yet another alternative configuration, the transducer 142 is a flow-meter rather than a pressure transducer, for example. A flow-meter usually is connected in series with the outlet 26, allowing a pressure-absorbing member to be situated in a manner similar to that shown in
In yet other alternative configurations, respective pressure-absorbing members are inserted in any of various bores inside the pump-head, such as other fitting bores or connecting bores. These other bores, similar to the outlet 26, are non-wearing locations in the pump-head and hence are suitable locations for pressure-absorbing members. The particular location selected will depend, at least in part, on the size and layout of the pump-head, the accessibility of the location from a mechanical, machining, or molding point of view, and the particular pressure-absorbing specifications being addressed.
The range of candidate pump-heads is not limited to gear pumps. An exemplary alternative type of pump-head, without intending to be limiting, is a valveless piston pump. A valveless piston pump is disclosed in, for example, U.S. Patent Publication No. 2007-0237658, incorporated herein by reference. See particularly
Reference is now made to
This embodiment is directed to a hydraulic circuit comprising a pump such as that described above. The circuit 100 is shown in
The circuit 100 in
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.
This application claims priority to, and the benefit of, U.S. Provisional Patent Application No. 60/967,125, filed on Aug. 30, 2007, incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60967125 | Aug 2007 | US |
