US20070071616A1

US20070071616A1 - Segmented driven-magnet assemblies for pumps, and pumps comprising same

Info

Publication number: US20070071616A1
Application number: US11/376,599
Authority: US
Inventors: Steven Owen; Terence Loughrey
Original assignee: Micropump Inc
Current assignee: Micropump Inc
Priority date: 2005-09-27
Filing date: 2006-03-14
Publication date: 2007-03-29

Abstract

Driven-magnet assemblies are disclosed for use in magnetically actuated pumps such as gear pumps. An exemplary assembly includes a magnet-flux-ring assembly and a molded body. The magnet-flux-ring assembly includes a flux ring having inner and outer surfaces that are concentric around an axis, and multiple magnet segments at respective radial positions around the axis. Each magnet segment has a respective inner surface, outer surface, first end, second end, and lateral sides. The inner surfaces are attached side by side to the outer surface of the flux ring around the flux ring. The outer surfaces form an outer surface of the assembly. The molded body has at interior portion, a first end, and a second end. The interior portion is situated radially inwardly of, and attached to, the inner surface of the flux ring. The first end is integral with the interior portion and captures the first ends of the magnet segments relative to the flux ring. The second end is integral with the interior portion and configured to capture the second ends of the magnet segments relative to the flux ring. The outer surface of the assembly is substantially bare.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application corresponds to, and claims the benefit under 35 U.S.C. §119(e) of, U.S. Provisional application No. 60/721,420, filed on Sep. 27, 2005, and incorporated by reference in its entirety herein.

FIELD

This disclosure pertains, inter alia, to pumps, such as gear pumps, as used for pumping liquids and other fluids in a hydraulic system. More specifically, the disclosure pertains to pumps that are magnetically driven. Even more specifically, the disclosure pertains to driven magnets used with such pumps.

BACKGROUND

For urging flow of and/or for pressurizing fluids, pumps are available in a large variety of configurations, most of which are specific for their respective applications. One type of pump that has found widespread acceptance for use in a variety of applications involving pumping of liquids and other fluids is the gear pump.
A “gear pump” encompasses any of various pumps utilizing at least two impellers or rotors (i.e., “gears”) that are contrarotated relative to each other in a casing or housing, wherein at least one of the gears is a driving gear and the remaining gear(s) in the pump is a driven gear. One popular type of gear pump is a “cavity pump,” which comprises at least two meshed contrarotatable gears situated in a gear cavity defined by a housing enclosing the meshed gears. During operation, fluid entering the cavity pump moves around the gear cavity in the spaces between the gear teeth or lobes to a discharge, or outlet, port of the gear cavity. A cavity pump is also termed an “external gear pump” in the art.
Reasons for which gear pumps have experienced substantial acceptance in the art include their comparatively small size, quiet and pulseless operation, reliability, and cleanliness of operation with respect to the fluid being pumped. Gear pumps also are advantageous because they keep the pumped fluid 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. Such applications include, for example, delivery of liquids in medical and chemical instrumentation.
Certain emerging applications of hydraulic systems in which gear pumps and certain other types of pumps are advantageous require that the systems be miniaturized. In many of these applications, the pumps still must exhibit high reliability and/or long operating life. These applications also typically require stringent attention to the avoidance of leaks, accommodation of the pump and other hydraulic components within tight spatial constraints, and/or operation within a very limited energy budget. Achieving these aims has revealed a need for smaller, more reliable, and more efficient gear pumps and other types of pumps.
One focus of efforts to meet the need for smaller pumps is directed to the drive mechanisms for the pumps. Many types of gear pumps (and certain other types of pumps) made nowadays are magnetically driven. A magnetic drive generally provides effective minimization of contamination, from the drive mechanism, of the fluid being pumped because magnetic coupling allows components in the pump head to be physically separated and sealed from the drive mechanism. Basically, a magnetic drive comprises a driven magnet that, when rotated about an axis or otherwise actuated (“driven”), delivers a corresponding motion to one or more active components in the pump head. For example, in earlier types of magnetically driven gear pumps, the driven magnet (sealed inside a “magnet cup” and rotationally coupled to at least one of the pump gears) is magnetically coupled to an external driving magnet that is rotated about an axis by a motor armature. As the driving magnet rotates, so does the driven magnet.
In many recent pump configurations, the driving magnet and motor armature have been eliminated, thereby reducing mass and volume of the pump, by magnetically coupling the driven magnet to a motor stator. In these “integrated pump/motor” devices sequential actuation of the electrical windings in the stator causes rotation of the driven magnet in the same manner as if the driven magnet were an armature associated with the stator of a stepper motor or analogous type of motor. In this regard, reference is made, for example, to U.S. Pat. Nos. 5,096,390 and 5,197,865, both incorporated herein by reference.
A driven magnet in a conventional integrated pump/motor device typically comprises one or more cylindrical or toroidal magnets arranged on an axis and providing two or more magnet poles (at least one “N” pole and at least one “S” pole). The magnet(s) are usually either “ceramic-ferrite” type or bonded neodymium (Nd) type, the latter being made by suspending NdFeB granules in a resin and compression-forming and curing the suspension into a cylinder or toroid. The magnet(s) may or may not be associated with a flux ring. The magnet(s), and flux ring if included, are encapsulated in plastic (see, e.g., U.S. Pat. Nos. 4,414,523 and 6,007,312, both incorporated herein by reference) and magnetized to induce the desired number, direction, and strength of poles. The driven magnet is inserted into a magnet cup that hermetically seals the driven magnet from the outside environment while providing sufficient clearance space for rotation of the driven magnet inside the magnet cup. The driven magnet is mechanically coupled to at least one gear (or other active pump component), such that rotation of the driven magnet causes corresponding running of the pump. Inside the magnet cup, a small amount of the fluid being pumped is usually circulated in the clearance space so as to bathe the driven magnet.
Whereas the plastic encapsulant is effective for preventing corrosion of the driven magnet, the encapsulant inherently takes up space and increases the distance between the magnet(s) in the driven magnet and the driving magnet or stator located outside the magnet cup. This additional distance weakens the strength of the magnetic coupling through the magnet cup to the driven magnet. Since miniaturization results in a smaller driven magnet, which generally produces a weaker magnetic field than a larger magnet of the same type, and since the magnetic field produced by the driven magnet must be sufficiently strong to achieve reliable magnetic coupling through the magnet cup, conventional encapsulation substantially limits how small a driven magnet can be. In other words, a conventional driven magnet that has been miniaturized too much produces a magnetic field that is simply too weak to provide effective magnetic coupling across the encapsulant, the bathing fluid, and the wall of the magnet cup for effective and reliable operation of the pump. With such a weak driven magnet, the pump receives insufficient torque for operation at the normal rotational velocity (e.g., 500-6000 rpm) of the driven magnet. Simply omitting the encapsulant to avoid this problem structurally weakens the driven magnet too much and renders it susceptible to corrosion. These adverse effects can be a critical disadvantage in miniaturized pump systems that must operate, for example, without failure for extremely long periods of time.
Therefore, there is a need for improved driven magnets for use in magnetically driven pumps, especially miniaturized pumps used in applications where the pumps' small sizes and ranges of pressure and flow can be advantageously used.

SUMMARY

The needs summarized above, as well as other needs, are met by driven magnets, magnetically driven pump heads, pump assemblies, and hydraulic circuits as disclosed herein.
According to a first aspect, driven-magnet assemblies are provided for magnetically driven pumps. One embodiment of such an assembly comprises multiple magnet segments and a “cage.” Each magnet segment has a first end, a second end, and lateral edges. The magnet segments are situated at respective positions around a rotational axis in an arrangement that has an inner surface and an outer surface, wherein the inner and outer surfaces are coaxial about the rotational axis. The cage holds the magnet segments relative to each other in the arrangement, and comprises an interior portion, a first end, a second end, and at least one longitudinal outer portion. The interior portion is situated, coaxially with the arrangement, between the rotational axis and the inner surface of the arrangement, such that the inner surface of the arrangement is coupled to the interior portion of the cage and the magnet segments radially surround the interior portion. The first end of the cage is coupled to the interior portion and to the first ends of the magnet segments so as to hold the first ends of the magnet segments relative to each other in the arrangement. The second end of the cage is coupled to the interior portion and to the second ends of the magnet segments so as to hold the second ends of the magnet segments relative to each other in the arrangement. The first and second ends of the cage are coupled together on the outer surface of the arrangement by at least one longitudinal outer portion extending between the first and second ends substantially flush with the outer surface.
The “cage” is termed thus because it is configured to hold the magnet segments relative to each other in the assembly without having to encapsulate the magnet segments fully. In particular, the cage leaves the outer surface substantially “bare” (i.e., most to all the outer surface is not encapsulated), which allows substantial reduction of the radial distance over which the driven-magnet assembly is magnetically coupled to a source of a rotating magnetic field (e.g., a motor stator). “Substantially bare” encompasses situations in which at least one longitudinal outer portion extends over the outer surface between the first and second ends of the cage.
In the assembly summarized above, the arrangement can comprise, by way of example, four magnet segments, wherein the magnetic polarity alternates from radially inwardly directed to radially outwardly directed from one magnet segment to the next. In this embodiment each magnet segment can be configured as a respective quarter cylinder, wherein the magnet segments in the arrangement are situated side-by-side (but not necessarily touching each other) to form a cylindrical arrangement of magnet segments around and coaxial with the interior portion of the cage. The driven-magnet assembly further can comprise a flux ring having an inner surface and an outer surface, wherein the inner surface of the arrangement is coupled to the outer surface of the flux ring, and the inner surface of the flux ring is coupled to the interior portion of the cage.
The first end of the cage can be configured for rotational coupling to a coaxially rotatable pump component so as to cause corresponding rotation of the pump component about the axis whenever the driven magnet is rotated about the axis. For example, the pump component can be a gear of a gear pump. More specifically in this example, the pump component can be a driving gear of the gear pump.
According to another aspect, pumps are provided that comprise a pump housing and a driven-magnet assembly such as the driven-magnet assembly summarized above. The pump housing encloses an active pump-component that, when rotated about an axis, generates a liquid-pumping force urging liquid to flow through the pump housing. The driven-magnet assembly is coupled to the active pump-component in a manner that causes the active pump-component to rotate about its axis whenever the driven-magnet assembly is rotated about its axis. For example, the pump can be a gear pump in which the active pump-component comprises at least one gear. More specifically in this example, a driving gear can be coupled to the driven-magnet assembly. A driven gear is interdigitated (meshed) with the driving gear so as to rotate about its axis whenever the driving gear is caused to rotate about its axis by the driven-magnet assembly. The pump further can comprise a “rotating-magnetic-field device” that is configured to be magnetically coupled to the driven-magnet assembly in a manner causing rotation of the driven-magnet assembly about its axis. For example, the rotating-magnetic-field device can comprise a stator that, when energized, produces a rotating magnetic field that is coupled to the driven-magnet assembly. Alternatively, the rotating-magnetic-field device can be a rotatable magnetic hub (e.g., attached to and rotated by an armature of a motor) as used in many types of conventional magnetic-drive gear pumps. The pump housing further can comprise a magnet cup that houses the driven-magnet assembly within the pump housing. In this configuration the rotating-magnetic-field device can be situated in surrounding relationship coaxially with the driven-magnet assembly in the magnet cup, such that rotation of the rotating-magnetic-field device causes corresponding rotation of the driven-magnet assembly inside the magnet cup.
A driven-magnet assembly according to another embodiment comprises multiple magnet segments each having a first end, a second end, and lateral sides. The magnet segments are situated at respective positions around a rotational axis in an arrangement in which the magnet segments collectively define an inner surface and an outer surface of the arrangement. The inner and outer surfaces are coaxial about the rotational axis. The assembly also includes a molded body that holds the magnet segments relative to each other in the arrangement. The molded body comprises an interior portion, a first end, and a second end. The interior portion is situated between the rotational axis and the inner surface of the arrangement. The interior portion is coaxial with the arrangement such that the inner surface of the arrangement is coupled to the interior portion and the magnet segments radially surround the interior portion. The first end is coupled to the interior portion and to the first ends of the magnet segments so as to hold the first ends of the magnet segments relative to each other in the arrangement, and the second end is coupled to the interior portion and to the second ends of the magnet segments so as to hold the second ends of the magnet segments relative to each other in the arrangement. The outer surface of the arrangement is substantially bare.
The molded body further can comprise at least one longitudinal outer portion that is coupled to the first and second ends of the molded body and that extends between the first and second ends substantially flush with the outer surface. In one embodiment the magnet segments are situated side-by-side (not necessarily touching each other) in the arrangement and the molded body comprises multiple longitudinal outer portions, wherein each longitudinal outer portion extends along respective lateral sides of adjacent magnet segments.
This driven-magnet assembly further can comprise a flux ring having an inner surface and an outer surface, wherein the inner surface of the arrangement is coupled to the outer surface of the flux ring, and the inner surface of the flux ring is coupled to the interior portion of the cage.
According to yet another embodiment, a driven-magnet assembly comprises a magnet-flux-ring assembly and a molded body. The magnet-flux-ring assembly comprises a flux ring having an inner surface and an outer surface configured concentrically around a rotational axis, and multiple magnet segments arranged at respective radial positions around the rotational axis. The magnet segments each have a respective inner surface, outer surface, first end, second end, and lateral sides. The inner surfaces are attached to the outer surface of the flux ring such that the magnet segments are arranged side-by-side (but not necessarily touching each other) around the flux ring, and the outer surfaces collectively form an outer surface of the magnet-flux-ring assembly. The molded body has an interior portion, a first end, and a second end. The interior portion is situated radially inwardly of, and attached to, the inner surface of the flux ring. The first end is integral with the interior portion and is configured so as to capture the first ends of the magnet segments relative to the flux ring. The second end is integral with the interior portion and is configured so as to capture the second ends of the magnet segments relative to the flux ring. The outer surface of the magnet-flux-ring assembly is substantially bare.
The molded body further can comprise at least one longitudinal outer portion that is integral with the first and second ends and that extends between the first and second ends along respective lateral sides of adjacent magnet segments substantially flush with the outer surface of the magnet-flux-ring assembly. In a particular embodiment the molded body comprises multiple longitudinal outer portions, and the lateral edges of the magnet segments include chamfers or analogous features that define, in the magnet-flux-ring assembly, channels between adjacent magnet segments attached to the outer surface of the flux ring. In this configuration the longitudinal outer portions are situated in the channels, substantially flush with the outer surface of the magnet-flux-ring assembly. Alternatively, the longitudinal outer portion(s) can be situated in other respective channels defined in the outer surfaces of the magnet segments.
The lateral edges of adjacent magnet segments attached to the outer surface of the flux ring can be configured to define respective voids extending radially from the outer surface of the magnet-flux-ring assembly to the outer surface of the flux ring. In this configuration the molded body further can comprise radial portions extending through the voids and coupling the longitudinal outer portions with the flux ring.
Another embodiment of a pump comprises a pump housing enclosing an active pump-component that, when rotated about an axis, generates a liquid-pumping force urging flow of liquid through the pump housing. The pump also includes a driven-magnet assembly such as that summarized above.
Another aspect is directed to magnetically actuated gear pumps. An embodiment of such a gear pump comprises a pump housing that includes a pump cavity and a magnet cup. Enclosed within the pump cavity are a driving gear and a driven gear. The driving gear is rotatable about a first axis, and the driven gear is interdigitated (meshed) with the driving gear and is rotatable about a second axis. A driven-magnet assembly, such as any of the configurations summarized above, is rotationally coupled to the driving gear. The gear pump further can comprise a stator (or other suitable rotating-magnetic-field device) situated coaxially surrounding the magnet cup such that energization of the stator causes the stator to produce a magnetic field rotating about the first axis. The rotating magnetic field produced by the stator is magnetically coupled through the magnet cup to the driven-magnet assembly so as to cause corresponding rotation of the driven-magnet assembly about the first axis.
Yet another embodiment of a driven-magnet assembly comprises a flux ring, multiple (e.g., at least four) magnet segments, and a non-magnetic cage. The flux ring is configured as a hollow cylinder having a rotational axis, an outer surface, and an inner surface. Each magnet segment has a first end, a second end, lateral edges, an outer-radius surface, and an inner-radius surface. Each segment produces a respective magnetic field that is either directed radially inwardly or radially outwardly. The inner-radius surfaces of the magnet segments are mounted to the outer surface of the flux ring such that the magnet segments collectively form a radial arrangement of magnet segments around the axis of rotation, the outer-radius surfaces of the magnet segments collectively form an outer surface of the radial arrangement, and the respective magnetic fields alternate in direction from one magnet segment to the next around the flux ring. The cage holds the magnet segments relative to each other in the arrangement. The cage comprises an interior portion attached coaxially to the inner surface of the flux ring, a first end integral with the interior portion and attached to the first ends of the magnet segments in the arrangement, a second end integral with the interior portion and attached to the second ends of the magnet segments in the arrangement, and at least one longitudinal outer portion. At least one longitudinal outer portion is integral with and extends, parallel to the rotational axis, from the first to the second ends of the cage on the outer surface of the arrangement, substantially flush with the outer surface.
The cage desirably is molded in situ (e.g., of a plastic material) to the flux ring and magnet segments.
Desirably, the inner-radius surfaces of the magnet segments are bonded to the outer surface of the flux ring, and lateral edges of adjacent magnet segments are bonded together (but not necessarily touching each other) in the arrangement.
The lateral edges of the magnet segments can be provided with respective chamfers or analogous features that define channels (e.g., U-shaped, V-shaped, square-shaped, or other appropriate transverse profile) between adjacent magnet segments in the arrangement. In this configuration the cage desirably comprises multiple longitudinal outer portions that are situated in the channels, flush with the outer surface of the arrangement. Alternatively, the longitudinal outer portions can be situated in any of various other respective channels defined in the outer surfaces of the magnet segments, or in any analogous manner by which the longitudinal outer portions do not project beyond the outer surfaces of the magnet segments.
The first end of the cage can be configured to “capture” the first ends of the magnet segments together circumferentially, and the second end of the cage can be configured to “capture” the second ends of the magnet segments together circumferentially.
Another embodiment of a gear pump comprises a pump housing that defines a pump cavity and a magnet cup having an axis. A driving gear is meshed with a driven gear in the pump cavity, and a driven-magnet assembly (such as that summarized above) is situated coaxially inside the magnet cup and coupled to the driving gear such that rotation of the driven-magnet assembly about the axis causes corresponding rotation of the driving gear about the axis.
Another aspect is directed to hydraulic circuits that comprise a pump such as any of the pumps summarized above. For example, the pump can be a gear pump. An embodiment of such a circuit includes a first conduit leading from the gear pump to a location and a second conduit leading from the location to the gear pump. The gear pump urges flow of a liquid from the gear pump through the first conduit to the location and from the location through the second conduit to the gear pump.
The foregoing and additional features and advantages of the disclosed technology will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A)-1(C) are respective orthogonal views of a driven-magnet assembly according to a first representative embodiment.
FIG. 1(D) is a section along the lines A-A in FIG. 1(A).
FIGS. 2(A)-2(B) are respective orthogonal views of the magnet-flux-ring assembly of the driven-magnet assembly of the first representative embodiment.
FIG. 2(C) is a section along the lines A-A in FIG. 2(A).
FIGS. 3(A)-3(B) are respective end views of magnet segments, having opposite polarity, used in the first representative embodiment.
FIG. 3(C) is an orthogonal view to FIGS. 3(A) and 3(B).
FIG. 4 is a perspective exploded view of an exemplary embodiment of a gear-pump head that includes a driven-magnet assembly according to the first representative embodiment.
FIGS. 5(A)-5(C) are respective orthogonal views of a driven-magnet assembly according to a second representative embodiment.
FIG. 5(D) is a section along the lines A-A in FIG. 5(A).
FIGS. 6(A)-6(B) are respective orthogonal views of the magnet-flux-ring assembly of the driven-magnet assembly of the second representative embodiment.
FIG. 6(C) is a section along the lines A-A in FIG. 6(A).
FIGS. 7(A)-7(B) are respective end views of magnet segments, having opposite polarity, used in the second representative embodiment.
FIG. 7(C) is an orthogonal view to FIGS. 7(A) and 7(B).
FIG. 8 is a perspective exploded view of an exemplary embodiment of a gear-pump head that includes a driven-magnet assembly according to the second representative embodiment.
FIG. 9 is a schematic diagram of an exemplary fluid-circulation loop that includes a gear pump according to any of various configurations disclosed herein.

DETAILED DESCRIPTION

This disclosure is set forth in the context of representative embodiments that are not intended to be limiting in any way. The representative embodiments include, for example, driven-magnet assemblies and pump heads comprising same. The present disclosure is directed toward all novel and non-obvious features and aspects of these and other embodiments, alone and in various combinations and sub-combinations with one another. The disclosed technology is not limited to any specific aspect or feature, or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present or problems be solved.
A first representative embodiment of a driven-magnet assembly 10 is shown in FIGS. 1(A)-1(D), 2(A)-2(C) and 3(A)-3(C). FIGS. 1(A)-1(D) are respective orthogonal views of the complete driven-magnet assembly 10, FIGS. 2(A)-2(C) are respective orthogonal views of the magnet segments mounted to the flux ring, and FIGS. 3(A)-3(C) are respective orthogonal views of one of the magnet segments.
Turning first to FIGS. 1(A)-1(D), the driven-magnet assembly 10 comprises four magnet segments 12 a, 12 b, 12 c, 12 d, an optional flux ring 14, and an optional shaft 16. As shown in FIG. 2(A), the magnet segments 12 a-12 d are mounted, in an arrangement having radial symmetry and in which the magnet segments have alternating opposing polarity (open arrows 13 a, 13 b), to the outside diameter of the flux ring 14 to form a magnet-flux-ring assembly 18. Returning to FIGS. 1(A)-1(D), a plastic “cage” 20 is formed, by molding, to the ends, to the inside, and to certain locations on the outside of the magnet-flux-ring assembly 18. The shaft 16 is inserted coaxially into a bore 22 defined in the cage 20 on a first end 24 of the cage, and a “double-D” bore 26 (or analogous rotational coupling) is defined in the cage on a second end 28 of the cage, as discussed later below. Alternatively to being a separate part as shown, the shaft 16 can be a respective portion of the first end 24 of the cage 20.
Turning now to FIGS. 3(A)-3(C), since this embodiment has four magnet segments 12 a-12 d, each magnet segment 12 has a general shape of a quarter-cylinder having an inner radius r and an outer radius R. The inner radius r defines an inside surface 30, and the outer radius R defines an outside surface 32. In the arrangement of magnet segments 12 a-12 d, the outside surfaces 32 collectively form an “outer surface” 33 of the arrangement, and the inside surfaces 30 collectively form an “inside surface” 35 of the arrangement (FIG. 2(C)). Each magnet segment 12 also has lateral edges 34 a, 34 b and ends 36 a, 36 b. The outside diameter of the flux ring 14 is substantially equal to 2r, and the diameter of the outer surface 33 is substantially equal to 2R. The lateral edges 34 a, 34 b in this embodiment are configured with respective chamfers 38 a, 38 b or analogous features that define, when the magnet segments 12 a-12 d are assembled side-by-side (but not necessarily touching each other) onto the flux ring 14, a longitudinal channel 40 in the outer surface 33 at the intersection of each pair of adjacent magnet segments (FIG. 2(A)). The chamfers 38 a, 38 b terminate at respective steps 42 a, 42 b (FIG. 3(C)) that define, when the magnet segments 12 a-12 d are assembled onto the flux ring 14, a radial channel 44 at the intersection of each pair of adjacent magnet segments (FIG. 2(A)). Note that the radial channels 44 are formed on each end of the magnet-flux-ring assembly 18. Each magnet segment 12 desirably also defines, along each lateral edge 34 a, 34 b, at least one semicircular void 46 (FIG. 3(C)) extending through the thickness of the magnet segment. The semicircular voids 46 define, when the magnet segments 12 a-12 d are assembled side-by-side onto the flux ring 14, corresponding holes 48 (FIG. 2(B)) extending radially from the respective longitudinal channel 40 to the surface of the flux ring 14.
The particular depicted configurations of the chamfers 38 a, 38 b that form longitudinal channels 40 having V-shaped transverse profiles (see FIG. 2(A)) are exemplary only. Alternatively, by way of example, the lateral edges 34 a, 34 b can be configured to form, when the magnet segments are assembled, longitudinal channels having U-shaped or square-shaped transverse profiles.
The magnet segments 12 a-12 b can be made of any suitable magnetic and/or magnetizable substance. Exemplary materials are bonded or sintered SmCo₅(samarium cobalt), ceramic (“ferrite”, strontium carbonate+iron oxide), AlNiCo (aluminum-nickel-cobalt, or “alnico”), and bonded or sintered NdFeB (neodymium-iron-boron). NdFeB is especially desirable due to its very high magnetic strength per unit mass and its excellent moldability and sinterability. Both “bonding” and “sintering” involve forming a rigid magnets from very small particles of magnet material, but bonding is usually performed using a resin, whereas sintering is not. Sintering is more desirable than bonding because sintering produces substantially stronger magnets, of the same material, than bonding.
It is possible to form (especially by molding) at least some of the magnet segments joined together by a sprue or the like, wherein the conjoined magnet segments are assembled onto a flux ring (if used). I e., it is not necessary that the magnet segments be formed separately from one another. Conjoined magnet segments may facilitate there assembly into a driven-magnet assembly.
Since these magnetic materials are readily corroded by exposure to air and to many liquids, the magnet segments 12 desirably are plated with at least one layer of a corrosion-resistant material such as Ni. For example, in this particular embodiment, the magnet segments 12 a-12 d are made of NdFeB and are plated three times: first with Ni (e.g., 100-300 μin thick), then with Cu (e.g., 100-300 μin thick), then again with Ni (e.g., 100-300 μin thick). An exemplary Ni-plating standard is ASTM 733B, Type V, Class 5, SC3. An exemplary Cu-plating standard is AMS 2418, class 1. Alternatively to plating with successive layers of Ni, Cu, and Ni, a single (e.g., thicker, such as 1000 μin) layer of Ni can be plated onto the magnet segments. As an alternative to plating the magnet segments and flux ring, if used, before assembling them together, it is possible to plate the entire assembly of magnets and flux ring. Plating before assembling generally is preferred for superior corrosion resistance.
The magnet segments 12 can be magnetized before or after assembling the segments onto the flux ring 14. Magnetizing the segments before assembling typically yields segments that produce stronger magnetic fields, and hence magnetizing before assembly usually is desirable. Also, in the instance of magnet segments made of sintered NdFeB, it is difficult to magnetize an assembly of the segments in a polar array. In this particular embodiment, of the four magnet segments 12 a-12 d in the magnet-flux-ring assembly 18, two are magnetized to produce a field extending radially outwardly (open arrows 13 b in FIG. 3(B)), and the other two are magnetized to produce a field extending radially inwardly (open arrows 13 a in FIG. 3(A)). Although the count of four magnet segments 12 in the arrangement of this embodiment is not intended to be limiting, generally an even number of magnet segments is used in the arrangement as a result of the magnet segments having alternating polarity one to the next. The number of magnet segments actually used in the arrangement depends upon considerations of overall size of the driven-magnet assembly 10 and the particular application. For example, the driven-magnet assembly 10 alternatively can have six, eight, or ten (or more) magnet segments. Generally, a larger number of magnet segments, when magnetically coupled to a correspondingly larger number of driving coils of a stator, tend to reduce a “cogging” phenomenon that can be caused by back-emf generated in the driven-magnet assembly 10. But, the smaller the driven-magnet assembly, the more difficult it is to configure it with more than four magnet segments.
The flux ring 14 in this embodiment, as noted above, has an outside radius substantially equal to the inside radius of the magnet segments 12. The flux ring 14 is made of any suitable magnetic material such as carbon steel or mild steel. Since many candidate materials, including carbon steel, are readily corroded, the flux ring 14 desirably is plated with at least one layer of a corrosion-resistant material such as Ni. For example, in this particular embodiment, the flux ring 14 is made of carbon steel and is plated, e.g., first with Ni (e.g., 100-300 μin thick), then with Cu (e.g., 100-300 μin thick), then again with Ni (e.g., 100-300 μin thick), or plated with a single thick layer (e.g., 1000 μin) of Ni. Exemplary plating standards for these materials are as noted above. The flux ring 14 is not required and can be omitted, but is desirable because it effectively shapes and concentrates the magnetic flux produced by the magnet segments 12.
The magnet segments 12 a-12 d are mounted onto the flux ring 14 so that each pair of diametrically opposing segments has respective fields directed radially inward or directed radially outward, and so that adjacent magnet segments 12 on the flux ring 14 have opposing field directions. Thus, around the circumference of the magnet-flux-ring assembly 18, the field direction alternates from one segment to the next (see FIG. 2(A)). The magnet segments 12 are mounted to the flux ring 14 using a suitable adhesive that is inert to the fluid to be pumped. For example, in this particular embodiment, an acrylic adhesive is used. The adhesive desirably is applied not only to the inside-radius surface 30 of each magnet segment 12 but also to the lateral edges 34 a, 34 b of the magnet segments so as to bond the lateral edges to each other. The lateral edges can be touching each other or can be separated to allow more adhesive (and/or more “cage” material, see below) to be applied between them.
FIGS. 2(A)-2(C) depict the magnet-flux-ring assembly 18 comprising the flux ring 14 with magnet segments 12 a-12 d mounted to it. Note that the outer surface 33 of the arrangement of magnet segments 12 is the outer surface of the magnet-flux-ring assembly 18. FIG. 2(A) depicts the alternating radial field directions (large open arrows 13 a, 13 b) around the flux ring 14. Also evident (FIG. 2(B)) are the longitudinal channels 40 extending lengthwise, on the outside of the magnet-flux-ring assembly 18, parallel to the rotational axis A. Also evident are the radial channels 44 on both ends of the assembly. FIG. 2(B) also depicts one of the holes 48 extending radially inwardly toward the flux ring 14.
After completing assembly of the magnet segments 12 to the flux ring 14, the resulting magnet-flux-ring assembly 18 is subjected to at least one step that forms the “cage” 20 (FIGS. 1(A)-1(D)) around the magnet-flux-ring assembly. Turning to FIG. 1(D), the cage 20 in this embodiment is an integral cage comprising an interior portion 50, the first end 24 (including a first set of radial portions 54; see FIG. 1(C)), the second end 28, and longitudinal outer portions 58 that extend parallel to the axis A. All these portions are formed in situ by at least one molding step performed with respect to the magnet-flux-ring assembly 18. The interior portion 50 fills the cavity in the flux ring 14 bounded by the inside radius 60 of the flux ring, except for a central, axial bore 62 that extends fully along the axis A from the first end 24 to the second end 28. Thus, in this embodiment, the magnet segments 12 a-12 d are coupled via the flux ring 14 to the interior portion 50. In this embodiment the first end 24 (FIG. 1(C)) includes a central portion 64, an inner rim 66, an outer rim 68, and radial portions 54 extending in a spoke-like manner between the inner rim 66 and the outer rim 68. The radial portions 54 extend along and at least fill the radial channels 44 between adjacent magnet segments 12. The central portion 64 defines an axial bore 22 (having a slightly greater diameter than the axial bore 62) that is configured to receive the shaft 16. (Alternatively, the shaft 16 can be formed as an integral part of the central portion 64.) In this embodiment the second end 28 includes an extension 74 that defines the orifice 26 or the like having a female configuration (e.g., the “double-D” configuration shown) suitable for rotationally coupling to a corresponding male shaft of a driven gear, discussed later below. The longitudinal outer portions 58 extend along the outer surface 33 of the arrangement of magnet segments, parallel to the axis A. The outer portions 58 fill the longitudinal channels 40 and thus connect together the first and second ends 24, 28. A second set of radial portions 78 extends through and fills the holes 48 and thus connects, at mid-length, each of the longitudinal outer portions 58 with the flux ring 14 (and thus with the interior portion 50).
The longitudinal outer portions 58 are substantially flush with the outer surface of the driven-magnet assembly 10 (which is the outer surface 33 of the arrangement of magnet segments), which means that the longitudinal outer portions 58 do not project radially beyond the outer surface. The longitudinal outer portions 58 hold the magnet segments 12 a-12 d relative to each other and against the flux ring 14 without the need for a full layer of plastic (as found in conventional driven-magnet assemblies) over the outer surface of the driven-magnet assembly 10. By eliminating the outer layer of plastic and by forming the longitudinal outer portions 58 substantially flush with the outer surface, the gap traversed by the magnetic flux between the magnet segments 12 and a motor stator (or other “rotating-magnetic-field device”) situated to drive the driven-magnet assembly 10, is made correspondingly narrower, thereby providing a stronger magnetic coupling between these components. This stronger magnetic coupling is especially advantageous in miniaturized pumps.
The cage 20 desirably is an integral unit that, without encapsulating the entire magnet-flux-ring assembly 18, securely holds the magnet segments 12 to the flux ring 14 and maintains the relative positions of the magnet segments with each other, even with rotation of the driven-magnet assembly 10 at normal rotational velocity (e.g., 500-6000 rpm) during normal use for extended periods of time. Specifically, the interior portion 50 is integrally coupled to the first and second ends 24, 28; the central portion 64 of the first end 24 is integrally coupled, via the radial portions 54, to the outer rim 66; and the outer rim 66 is integrally coupled to the second end 28 via the longitudinal outer portions 58 (which are integrally coupled at mid-length via the radial portions 78 to the flux ring 14). The radial portions 54 and the longitudinal outer portions 58 act cooperatively to retain the magnet segments on the flux ring 14. Also, the second end 28 and the outer rim 66 of the first end 24 captures and holds the magnet segments 12 together and to the flux ring 14 as well as to the interior portion 50. After prolonged rotation of the driven-magnet assembly 10, if the adhesive holding a magnet segment 12 to the flux ring 14 should fail, the cage 20 nevertheless holds the magnet securely to the flux ring and relative to the other magnet segments, thereby ensuring substantially prolonged operational life of the driven-magnet assembly.
The cage 20 desirably is made of molded plastic. The plastic can be any suitable polymeric material having sufficient mechanical strength and inertness to the pumped fluid to provide the intended function of the cage, as well as have good molding characteristics. Particularly suitable polymeric materials are in the general category of “engineering plastics,” and can be reinforced, e.g., with glass fibers or other suitable material. Exemplary engineering plastics include, but are not limited to, PEEK (polyetheretherketone), PPS (poly(ρ-phenylene sulfide), polysulfone, and polyetherimide. PPS has perhaps better flow in the mold used for forming the cage 20 and has a lower molding temperature than PEEK. It is desirable that the selected plastic have a low coefficient of thermal expansion, and advantageous that the coefficient of thermal expansion of the selected plastic be as close as possible to the coefficient of thermal expansion of the magnet segments.
Molding the cage 20 can be performed using one molding step or multiple molding (e.g., “overmolding”) steps. Molding in one step usually requires a more sophisticated mold in which the magnet-flux-ring assembly 18 can be positioned in exactly the right location for forming the cage 20. In either molding approach, it is desirable to pre-heat the magnet-flux-ring assembly 18 in the mold before introducing the molding resin into the mold. Overmolding can be performed as generally described, for example, in U.S. Pat. No. 4,414,523 or 6,007,312, both incorporated herein by reference.
By way of example, and not intending to be limiting in any way, representative dimensions for this embodiment are as follows: The length of the driven-magnet assembly 10 is 0.824 inch (not including the shaft 16), and the outside diameter is 0.620 inch. Each magnet segment 12 has a diameter D=2R=0.620 inch, an inside radius d=2r=0.444 inch, and an axial length of 0.470 inch. The flux ring 14 has an outer diameter of 0.444 inch, an inside diameter of 0.205 inch, and a length of 0.470 inch.
FIG. 4 depicts the driven-magnet assembly 10 assembled into a gear-pump head 80 comprising a magnet cup 82, a driving gear 84, a driven gear 86, a set of bearings 88 a, 88 b for the driving gear 84, a set of bearings 90 a, 90 b for the driven gear 86, and a pump housing 85 comprising a face plate 92, a cavity plate 94, and a cover plate 96. Specifically, the driving gear 84 has shafts 100 a, 100 b (desirably formed integrally with the rest of the gear) that are journaled in the bearings 88 a, 88 b, respectively. The driven gear 86 has shafts 102 a, 102 b (desirably formed integrally with the rest of the gear) that are journaled in the bearings 90 a, 90 b, respectively. The bearings 88 a, 90 a (each configured as a bushing) are inserted in respective bores 104 a, 106 a in the cover plate 96, and the bearings 88 b, 90 b are inserted in respective bores 104 b, 106 b in the face plate 92. The gears 84, 86 interdigitate (mesh) together and are nested in a cavity 98 defined in the cavity plate 94.
The face plate 92, cavity plate 94, cover plate 96, and magnet cup 82 can be made of any suitable material such as, but not limited to, a rigid metal (desirably a metal that does not corrode in the presence of the liquid being pumped), a ceramic material, or a rigid polymeric (“plastic”) material. All these components need not be made of the same material. For example, the plates 92, 94, 96 can be made of the same material (e.g., a metal) and the magnet cup 82 can be made of a rigid polymer. Specific examples of candidate materials include, but are not limited to, stainless steel, aluminum alloy, polyetheretherketone (PEEK), poly(ρ-phenylene sulfide (PPS), and polyimide. The plastics can be molded and/or machined, and can be reinforced with any of various suitable fibers or particles. Particularly desirable materials are PEEK (molded and/or machined) for the magnet cup 82 and “316” stainless steel for the plates 92, 94, 96 and shaft 16.
The gears 84, 86 can be made of a suitable polymer (e.g., PEEK), a ceramic, or a suitable metal such as stainless steel. The gears 84, 86 need not be made of the same material or by the same fabrication method.
The bearings 88 a, 88 b, 90 a, 90 b desirably are made of sapphire. Example alternative bearing materials are silicon carbide, ceramic, and Vespel (brand of polyimide, made by DuPont).
Metal parts can be machined or cast (e.g., by investment casting, the latter being followed by finish machining, as required). Ceramics can be cast and/or machined. With respect to any of these components made from a plastic material, the plastic can be partially or completely molded to the respective configurations. For example, the components can be molded, followed by finish machining, or made entirely by molding without any need for secondary machining. Alternatively, they can be made entirely by machining, which is usually a more expensive fabrication method than molding, but does allow the holding of extremely tight dimensional tolerances.
The magnet cup 82 includes a mounting flange 112 shaped and configured to be attached to the cover plate 96 such that the axis A of the magnet cup is aligned with the rotational axis of the driving gear 84. To create a seal between the mounting flange 112 and the cover plate 96, a respective O-ring (not shown) or analogous static-seal means is used. The O-ring desirably is nested in a respective gland (not shown) defined in the cover plate 96 or in the mounting flange 112. A gasket-type seal usually would not require a gland.
The plates 92, 94, 96 are assembled together using screws 108 or analogous fasteners that extend through respective holes 110 in the flange 112 of the magnet cup 82 and through respective holes 114, 116, 118 in the plates 92, 94, 96, respectively. Pins 119 can be used, if desired or necessary, to align the plates 92, 94, 96 accurately with each other. As an alternative to using the screws 108, the pump head 80 can be held together using clamps, adhesive, or the like. Pins 121 can be used, if necessary or desired, to align the pump housing 85 with a manifold or the like (not shown).
When the plates 92, 94, 96 are assembled together by a means other than use of a sealing adhesive, they can be sealed by respective O-rings (or analogous static-seal means, not shown) situated in respective glands (only one gland 120 shown) defined in the face plate 92 and cover plate 96. Exemplary O-ring materials are Viton (a fluoroelastomer made by DuPont), EPDM (ethylene-propylene rubber), Buna-N (nitrile rubber), silicone rubber, or other elastomeric material that is suitable for the pumping conditions and fluid.
Desirably, the bearings 88 a, 88 b, 90 a, 90 b are “lube-less,” relying upon the pumped liquid itself to provide lubrication between each bearing and its respective gear shaft 100 a, 100 b, 102 a, 102 b. The plates 92, 94, 96 desirably are configured (with appropriate flow channels or the like, not shown) and the gears 84, 86 desirably are configured (with axial bores 122, 124, respectively) so as to conduct a stream of lubricating fluid through and around the bearings as the pump is running.
The driven-magnet assembly 10 is rotationally coupled to the driving gear 84 via the shaft 100 a that extends through the bore 104 a in the cover plate 96 to the driven-magnet assembly 10. The shaft 100 a has a terminal configuration (such as a convex “double-D” configuration) that mates into the complementary axial bore 26 (e.g., concave “double-D” configuration) defined in the extension 74 on the second end 28 of the driven-magnet assembly 10. Thus, rotation of the driven-magnet assembly 10 about the axis A causes corresponding rotation of the driving gear 84 about the same axis. Alternatively to the “double-D” configuration of this rotational coupling, other couplings can be used such as any of various splined or keyed couplings.
The driven-magnet assembly 10 is inserted coaxially into the magnet cup 82. To keep the driven-magnet assembly 10 rotationally centered inside the magnet cup 82, the shaft 16 fits into a respective bearing 126 (e.g., sapphire bushing) in a corresponding bore 128 in the magnet cup 82. During operation of the pump, pumped fluid circulates into the magnet cup 82, into the bearing 126 (note axial bore in the shaft 16) and around the rotating driven-magnet assembly 10.
The assembly comprising the gears 84, 86; bearings 88 a, 88 b, 90 a, 90 b, 126; plates 92, 94, 96; driven-magnet assembly 10, and magnet cup 82 constitutes an exemplary “gear-pump head” 80. Generally, a “pump head” is a device that converts mechanical energy (supplied by a motor or other prime mover coupled to the pump head) into fluid energy used to move a fluid into, through, or out of a hydraulic system. A “gear-pump head” is a pump head in which conversion of mechanical energy into fluid energy is performed by gears that can be coupled to a motor or other prime mover that causes the gears to rotate, thereby causing the pump head to function as a gear pump.
In the depicted assembly, each gear 84, 86 has multiple teeth or lobes, oriented radially with respect to the axis of rotation of the gear, that mesh with corresponding teeth or lobes, respectively, in the mating gear. As the gears 84, 86 are contrarotated, fluid entering the space between the teeth or lobes of each gear is transported by the gears from an entrance (“inlet”) port 132 to a discharge (“outlet”) port 134 defined in the face plate 92. In addition, contrarotation of the gears 84, 86 creates pressure differentials inside the pump head 80 that urge circulation of pump fluid through the bearings and around the rotating driven-magnet assembly 10.
The inlet port 132 allows liquid, to be pumped, to enter the pump head 80, and the outlet port 134 discharges liquid pumped by the pump head 80. During operation of the pump head 80, the outlet port 134 typically is at a higher pressure than the inlet port 132. This pressure differential is exploited for bathing, using a small but continuous stream of the fluid being pumped, as noted above, the bearings 88 a, 88 b, 90 a, 90 b, the shafts 100 a, 100 b, 102 a, 102 b, and the gears 84, 86. In addition, a small portion of the pumped liquid circulates into the magnet cup 82, in which the outside of the driven-magnet assembly 10 is continuously bathed with the liquid. This circulation is facilitated by the axial bore 62 of the driven-magnet assembly 10, which directs a small flow of the liquid to the shaft 16 and bearing 126. Circulation of fluid in this manner is facilitated by the bores 122, 124, 62, as well as by additional channels and passages (not shown) defined, for example, in one or more of the plates 92, 94, 96. In this regard, reference is made to U.S. patent application Ser. No. 11/025,760, incorporated herein by reference. This circulation of liquid through various parts of the pump head detaches any debris that may have deposited in the bearings and other locations in the pump head, entrains the debris in the liquid, and thereby flushes the debris from the pump head. The liquid also provides a lubricant cushion between each of the journaled shafts and its respective bearing.
Driving the pump head 80 of this embodiment is achieved using a stator 136 that, as an exemplary “rotating-magnetic-field device,” fits coaxially around the exterior of the magnet cup 82. (Alternatively, the pump head 80 can be driven using a rotating magnetic hub, or “driving magnet,” coupled to the armature of a motor, in the manner of many types of conventional magnetic-drive pumps.) The stator 136 comprises multiple electrical windings that are energized in sequence by a “driver” circuit 138 in a manner analogous to the energization of a stepper motor. I e., the windings are energized in a progressive manner around the stator 136, which causes corresponding rotation of the driven-magnet assembly 10 inside the magnet cup 82. The driver circuit 138 need not be separate from the stator 136 as shown, but rather can be integrated into the stator 136 itself.
Rotation of the driven-magnet assembly 10 responsively to energization of the stator 136 is made possible by the magnetic coupling of the driven-magnet assembly 10 to the stator 136. The integrated configuration of the stator 136 with the pump head 80, as described above, is highly desirable because the stator 136 occupies substantially less space than a motor including an armature to which a driving magnet is affixed. Also, the bore of the stator can be fit very snugly to the outside diameter of the magnet cup 82, which minimizes the gap traversed by the magnetic fields between by the stator 136 and the driven-magnet assembly 10. Minimizing this gap provides stronger coupling, which allows for the application of more torque to the driven-magnet assembly 10 by the stator 136. Key to minimizing the gap is the elimination, from the driven-magnet assembly 10, of the outer layer of plastic found on conventional driven-magnet assemblies. Thus, the magnet segments 12 of the driven-magnet assembly 10 are situated in very close proximity to the stator 136.
The system shown in FIG. 4 can include any of various controls and encoders that provide feed-back signals concerning, for example, any of temperature, pressure, and flow rate, as well as rotational velocity of the driven-magnet assembly 10.
A second representative embodiment of a driven-magnet assembly 210 is shown in FIGS. 5(A)-5(D), 6(A)-6(C) and 7(A)-7(C). FIGS. 5(A)-5(D) are respective orthogonal views of the complete driven-magnet assembly 210, FIGS. 6(A)-6(C) are respective orthogonal views of the magnet segments mounted to the flux ring, and FIGS. 7(A)-7(C) are respective orthogonal views of one of the magnet segments.
Turning first to FIGS. 5(A)-5(D), the driven-magnet assembly 210 comprises four magnet segments 212 a, 212 b, 212 c, 212 d, a flux ring 214, and a shaft 216. As shown in FIG. 6(A), the magnet segments 212 a-212 d are mounted, with radial symmetry and with alternating opposing polarity (open arrows 213 a, 213 b), to the outside diameter of the flux ring 214 to form a magnet-flux-ring assembly 218. Returning to FIGS. 5(A)-5(D), a plastic “cage” 220 is formed, by molding, to the ends, to the inside, and to certain locations on the outside of the magnet-flux-ring assembly 218. The shaft 216 is inserted coaxially into a bore 222 defined in the cage 220 on a first end 224 of the cage, and a “double-D” bore 226 is defined in the cage on a second end 228 of the cage, as discussed later below. Alternatively to being a separate part as shown, the shaft 216 can be a respective portion of first end 224 of the cage 220.
Turning now to FIGS. 7(A)-7(C), each magnet segment 212 of this embodiment has a general shape of a quarter-cylinder having an inner radius r and an outer radius R. The inner radius r defines an inside surface 230, and the outer radius R defines an outside surface 232. The magnet segment 212 also has opposing lateral edges 234 a, 234 b and opposing ends 236 a, 236 b. The outside diameter of the flux ring 214 is substantially equal to 2r, and the outside diameter of the outer surface 232 is substantially equal to 2R. The lateral edges 234 a, 234 b are configured with respective chamfers 238 a, 238 b or analogous features that define, when the magnet segments 212 a-212 d are assembled side-by-side (but not necessarily touching each other) onto the flux ring 214, a longitudinal channel 240 at the intersection of each pair of adjacent magnet segments (FIG. 6(A)). The channel 240 can have, e.g., a V-shaped, U-shaped, square-shaped, or other suitable transverse profile. The chamfers 238 a, 238 b desirably do not extend to the ends 236 a, 236 b, but rather end at respective steps 242 a, 242 b (FIG. 7(C)). When the magnet segments 212 a-212 d are assembled onto the flux ring 214, a respective radial channel 244 is defined by respective steps 242 a, 242 b at the intersection of each pair of adjacent magnet segments (FIG. 6(A)). The radial channels 244 desirably are formed on each end of the magnet-flux-ring assembly 218. Each magnet segment 212 desirably also defines, along each lateral edge 234 a, 234 b, at least one semicircular void 246 (FIG. 7(C)) extending through the thickness of the magnet segment. The semicircular voids 246 define, when the magnet segments 212 a-212 d are assembled onto the flux ring 214, corresponding holes 248 (FIG. 6(B)) extending radially from the respective longitudinal channel 240 to the surface of the flux ring 214.
The magnet segments 212 a-212 b can be made of any suitable magnetic and/or magnetizable substance, as discussed above with respect to the magnet segments of the first representative embodiment. Since the magnetic materials are readily corroded by exposure to air and to many liquids, the magnet segments 212 made from them desirably are plated with at least one layer of a corrosion-resistant material, as discussed above in connection with the first representative embodiment.
In this particular embodiment, of the four magnet segments 212 a-212 d in the magnet-flux-ring assembly 218, two are magnetized to produce a field extending radially outwardly (open arrows 213 b in FIG. 7(B)), and the other two are magnetized to produce a field extending radially inwardly (open arrows 213 a in FIG. 7(A)). Although the count of four magnet segments 212 in this embodiment is not intended to be limiting, generally an even number of magnet segments is used, as discussed above with respect to the first representative embodiment.
The flux ring 214 is not required and can be omitted; but, when present, it more effectively shapes and concentrates the magnetic flux produced by the magnet segments 212.
The magnet segments 212 a-212 d are mounted onto the flux ring 214 so that each pair of diametrically opposing segments has respective fields directed radially inward or directed radially outward, and so that adjacent magnet segments 212 on the flux ring 214 have opposing field directions. Thus, around the circumference of the magnet-flux-ring assembly 218, the field direction alternates from one segment to the next (see FIG. 6(A)). The magnet segments 212 are mounted to the flux ring 214 using a suitable adhesive that is inert to the fluid to be pumped. The adhesive desirably is applied not only to the inside-radius surface 230 of each magnet segment 212 but also to the lateral edges 234 a, 234 b of the magnet segments so as to bond the lateral edges to each other. The lateral edges can be touching each other or can be separated to allow more adhesive (and/or more “cage” material, see below) to be applied between them.
FIGS. 6(A)-6(C) depict the magnet-flux-ring assembly 218 comprising the flux ring 214 with magnet segments 212 a-212 d mounted to it. FIG. 6(A) depicts the alternating radial field directions (large open arrows 213 a, 213 b) around the flux ring 214. Also evident (FIGS. 6(B) and 6(C)) are the longitudinal channels 240 extending lengthwise, on the outside of the magnet-flux-ring assembly 218, parallel to the rotational axis A, and the radial channels 244 on both ends of the assembly. FIG. 6(B) also depicts one of the holes 248 extending radially inwardly at midlength of each junction of adjacent magnet segments 212.
After completing assembly of the magnet segments 212 to the flux ring 214, the resulting magnet-flux-ring assembly is subjected to at least one molding step that forms the plastic “cage” 220 (FIGS. 5(A)-5(D)) around the magnet-flux-ring assembly 218. Turning to FIG. 5(D), the cage 220 in this embodiment comprises an interior portion 250, the first end 224 (including a first set of radial portions 254; see FIG. 5(C)), the second end 228, longitudinal outer portions 258, and a second set of radial portions (discussed later below). All these portions are formed in situ as an integral cage 220 by the at least one molding step performed with respect to the magnet-flux-ring assembly 218. The interior portion 250 fills the cavity in the flux ring 214 bounded by the inside radius 260 of the flux ring, except for a central, axial bore 262 that extends fully along the axis A from the first end portion 224 to the second end 228. In this embodiment the first end 224 (FIG. 5(C)) includes an outer rim 268 and radial portions 254 extending inwardly in a spoke-like manner from the outer rim 268. The radial portions 254 extend along and at least fill the radial channels 244 between adjacent magnet segments 212. The axial bore 262 of the interior portion 250 is configured to receive the shaft 216. (Alternatively, the shaft can be formed as an integral part of the first end portion 224.) In this embodiment the second end 228 defines the orifice 226 or the like having a configuration (e.g., the “double-D” configuration shown) suitable for rotationally coupling to a driven gear. The longitudinal outer portions 258 extend along and fill the longitudinal channels 240 and connect together the first and second ends 224, 228.
The longitudinal outer portions 258 are substantially flush with the outer surface of the magnet assembly 210 and hold the magnet segments 212 a-212 d relative to each other and against the flux ring 214 without the need for a full layer of plastic (as found in conventional driven-magnet assemblies) over the entire outside surface of the driven-magnet assembly 210. By eliminating the outer layer of plastic and by forming the longitudinal outer portions 258 substantially flush with the outer surface, the gap traversed by the magnetic flux between the magnet segments 212 and a motor stator (or other “rotating-magnetic-field device”) is made correspondingly narrower, thereby providing stronger magnetic coupling between these components. The second set of radial portions 278 extends through and fills the holes 248 and thus connects together, at mid-length, each of the longitudinal outer portions 258 with the interior portion 250. Thus, the cage 220 is an integral unit that, without encapsulating the entire magnet-flux-ring assembly 218, securely holds the magnet segments 212 to the flux ring 214 and maintains the relative positions of the magnet segments with each other, even with rotation of the driven-magnet assembly 210 at normal rotational velocity (e.g., 500-6000 rpm) during normal use for extended periods of time.
The plastic material used for forming the cage 220 is any suitable plastic (polymeric) material, as discussed above in connection with the first representative embodiment. Molding the cage 220 can be performed using one molding step or two molding (overmolding) steps, as in the first representative embodiment.
By way of example, and not intending to be limiting in any way, representative dimensions for this embodiment are as follows: The length of the driven-magnet assembly 210 is 1.025 inch (not including the shaft 216), and the outside diameter is 0.290 inch. Each magnet segment 212 has an outside diameter D=2R=0.290 inch, an inside diameter d=2r=0.129 inch, and an axial length of 0.920 inch. The flux ring 214 has an outer diameter of 0.129 inch, an inside diameter of 0.0750 inch, and a length of 0.920 inch.
FIG. 8 depicts the driven-magnet assembly 210 assembled into a gear-pump head 280 comprising a magnet cup 282, a driving gear 284, a driven gear 286, a set of bearings 288 a, 288 b for the driving gear 284, a set of bearings 290 a, 290 b for the driven gear 286, and a pump housing 285 comprising a face plate 292, a cavity plate 294, and a cover plate 296. Respective materials for these components are as described in connection with the first representative embodiment. The gears 284, 286 interdigitate (mesh) together and are nested in a cavity 298 defined in the cavity plate 294. The driving gear 284 has integral shafts 300 a, 300 b that are journaled in the bearings 288 a, 288 b, respectively. The driven gear 286 has integral shafts 302 a, 302 b that are journaled in the bearings 290 a, 290 b, respectively. The bearings 288 a, 290 a (each configured as a bushing) are inserted in respective bores 304 a, 306 a in the cover plate 296, and the bearings 288 b, 290 b are inserted in respective bores 304 b, 306 b (not shown, but see FIG. 4) in the face plate 292.
The magnet cup 282 includes a mounting flange 312 shaped and configured to mate coaxially with the cover plate 296. To create a seal between the mounting flange 312 and the cover plate 296, a respective O-ring (not shown) or analogous static-seal means is used. The O-ring desirably is nested in a respective gland (not shown) defined in the cover plate 296 or in the mounting flange 312.
The plates 292, 294, 296 defining the pump housing 285 are assembled together using screws 308 or analogous fasteners that extend through respective holes 310 in a flange 312 of the magnet cup 282 and through respective holes 314, 316, 318 of the plates 292, 294, 296, respectively. Pins 319 can be used, if desired or required, to align the plates 292, 294, 296 accurately with each other. As an alternative to using the screws 308, the pump head 280 can be held together using clamps, adhesive, or the like.
When the plates 292, 294, 296 are assembled together by a means other than use of a sealing adhesive, they can be sealed by respective O-rings (or analogous seals, not shown) situated in respective glands (only one gland 320 shown) defined in the face plate 292 and cover plate 296. Exemplary O-ring materials are as discussed above in connection with the first representative embodiment.
Desirably, the bearings 288 a, 288 b, 290 a, 290 b are “lube-less,” relying upon the pumped liquid itself to provide lubrication between each bearing and its respective gear shaft 300 a, 300 b, 302 a, 302 b. The plates 292, 294, 296 desirably are configured (with appropriate flow channels or the like, not shown) and the gears 284, 286 desirably are configured (with axial bores 322, 324, respectively) so as to conduct a stream of lubricating fluid through and around the bearings as the pump is running.
The driven-magnet assembly 210 is rotationally coupled to the driving gear 284 via the shaft 300 a that extends through the bore 304 a in the cover plate 296 to the driven-magnet assembly 210. The shaft 300 a has a terminal configuration (such as a convex “double-D” configuration that mates into the complementary axial bore 226 (e.g., concave “double-D” configuration) defined in the second end 228 of the driven-magnet assembly 210. Thus, rotation of the driven-magnet assembly 210 about the axis A causes corresponding rotation of the driving gear 284 about the same axis. Alternatively to the “double-D” configuration of this rotational coupling, other couplings can be used such as any of various splined or keyed couplings.
The driven-magnet assembly 210 is inserted coaxially into the magnet cup 282. To keep the driven-magnet assembly 210 rotationally centered inside the magnet cup 282, the shaft 216 fits into a respective bearing 326 (e.g., sapphire bushing) in a corresponding bore 328 in the magnet cup 282. During operation of the pump, pumped fluid circulates into the magnet cup 282, into the bearing 326 (note axial bore in the shaft 216) and around the rotating driven-magnet assembly 210.
The assembly comprising the gears 284, 286; bearings 288 a, 288 b, 290 a, 290 b, 326; plates 292, 294, 296; driven-magnet assembly 210, and magnet cup 282 constitutes an exemplary “pump head” 280, defined generally as described earlier above. In the embodiment of FIG. 8, an inlet port 332 and outlet port 334 are provided in the face plate 292. As discussed generally with respect to the first representative embodiment, contrarotation of the gears 284, 286 creates pressure differentials inside the pump head 280 that urge circulation of pump fluid through the bearings and around the rotating driven-magnet assembly 210.
Driving the pump head 280 of this embodiment is achieved using a stator 336, as an exemplary “rotating-magnetic-field device,” that fits coaxially around the exterior of the magnet cup 282. (Alternatively, the pump head can be driven using a rotating magnetic hub, or “driving magnet,” coupled to the armature of a motor, in the manner of many types of conventional magnetically driven pumps.) The stator 336 comprises multiple electrical windings that are energized in sequence by a “driver” circuit (not shown, but see FIG. 4) in a manner as described in connection with the first representative embodiment.
FIG. 9 depicts an exemplary hydraulic circuit. Shown are a pump 400 as described above, a first location 402, and a second location 404. The outlet port 406 of the pump 400 is connected hydraulically to the first location 402. Downstream of the first location is the second location 404. The pump 400, first location 402, and second location 404 are hydraulically connected together in the circuit by hydraulic lines 410, 412, 414. Liquid, urged by the pump 400 to exit the outlet port 406, passes through the hydraulic line 410 to the first location 402. Fluid flows (as urged by the pump 400) through the hydraulic line 412 from the first location 402 to the second location 404. Fluid also flows from the second location 404 through the hydraulic line 414 to the inlet port 420 of the pump 400. The pump 400 recirculates the liquid back to the locations 402, 404.
Although pump heads (including driven-magnet assemblies) as described above were developed in response to a need for miniaturized pumps that can be used in a highly confined space, pumps as described herein are not to be regarded as limited to any specific application. The configurations disclosed herein readily allow any of various expansions or contractions in scale, and can be used advantageously in any of a wide variety of applications, including applications not characterized by confined space.
Whereas the disclosure was presented in the context of a driven-magnet assembly being coupled specifically to a gear pump, it will be understood that the subject driven-magnet assembly alternatively can be coupled to any of various other pump configurations including an internal component that is driven in a manner originating in the rotational motion of the driven-magnet assembly.
Although the cages 20, 220 were described above as being molded of a polymeric material, it is possible for a cage to be molded or otherwise formed of a metal. The metal desirably would not be magnetic or magnetizable. If the metal were molded, it desirably would have a melting temperature that is less than a temperature that would damage the magnet segments or any plating on the magnet segments. It alternatively is possible for the metal to be formed around the magnet segments by pressure-forming using a suitable die. In other alternative configurations, the cage is molded or otherwise formed of a ceramic material.
Any of various other alternative configurations are possible. For example, the molded cage need not have any longitudinal outer portions extending lengthwise across the outer surface of the driven-magnet assembly, especially if the end portions of the cage have a configuration sufficient for holding the magnet segments together. (For example, the end portions can be configured for attachment, in a “snap-together” manner or thread-together manner, to an interior portion of the cage, wherein each end portion has a cavity or other void or depression configured to receive the respective ends of the magnet segments.) In other embodiments the cage includes as few as one longitudinal outer portion coupling the end portions together. Furthermore, the longitudinal outer portion(s) need not extend along the lateral junctions of adjacent magnet segments. In alternative configurations, the longitudinal outer portion(s) extend anywhere along the outside surface of the magnet segments, wherein respective channel(s) can be formed in the outside surface for this purpose. The longitudinal outer portion(s) are substantially flush with the outside surface of the magnet segments, especially from the standpoint of reducing the gap between the driving and driven magnetic fields. The substantially flush configuration also helps reduce hydraulic drag imparted to the rotating driven-magnet assembly by the fluid in the magnet cup. In an embodiment in which the longitudinal outer portion(s) were formed to a slightly greater outside diameter than the magnetic segments, it is possible for the longitudinal outer portions to act as a bearing for the driven-magnet assembly, running against the inside-diameter wall of the magnet cup.
Also, as noted earlier above, the driven-magnet assembly need not have a flux ring. Omitting the flux ring may change one or more performance characteristics of the driven-magnet assembly as coupled magnetically to the rotating-magnetic-field device, but the driven-magnet assembly will still exhibit its intended function.
In other alternative embodiments of the driven-magnet assembly, the cage can be formed of multiple parts that are attached together for use. For example, as noted above, the first and second ends of the cage can be formed as respective “caps” that are attached to (e.g., “snapped” onto) respective ends of the interior portion. These caps can be configured with voids or pockets for receiving respective ends of magnet segments as the caps are assembled to the interior portion. Alternatively to being attached to the interior portion of the cage, the caps can be assembled to respective axial ends of the flux ring. Further alternatively, the interior portion, one end, and the longitudinal outer portion(s) of the cage can be molded in situ to the magnet-flux-ring assembly, and the remaining end of the cage can be made separately and assembled (e.g., in a snap-on manner) to the driven-magnet assembly after the molding step.
In other alternative embodiments of the driven-magnet assembly, instead of having the shaft extend from the assembly as described herein, the interior portion of the cage can be provided with a bushing for receiving a shaft that is connected coaxially to the magnet cup. Further alternatively, the interior portion of the cage can be provided with an axial through-bore that acts as a bearing surface, wherein the shaft can be mounted in a manner such that the shaft supports and aligns the driven-magnet assembly.
In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are only currently preferred examples of the disclosed technology and should not be taken as limiting the scope of the disclosed technology. Rather, the scope of the disclosed technology is defined by the following claims and their equivalents. We therefore claim all that comes within the scope and spirit of these claims.

Claims

1. A driven-magnet assembly for a magnetically driven pump, the assembly comprising:

multiple magnet segments each having a first end, a second end, and lateral edges, the magnet segments being situated at respective positions around a rotational axis in an arrangement having an inner surface and an outer surface, the inner and outer surfaces being coaxial about the rotational axis; and

a cage holding the magnet segments relative to each other in the arrangement, the cage comprising an interior portion, a first end, a second end, and at least one longitudinal outer portion, the interior portion being situated between the rotational axis and the inner surface of the arrangement and coaxially with the arrangement such that the inner surface of the arrangement is coupled to the interior portion of the cage and the magnet segments radially surround the interior portion, the first end of the cage being coupled to the interior portion and to the first ends of the magnet segments so as to hold the first ends of the magnet segments relative to each other in the arrangement, and the second end of the cage being coupled to the interior portion and to the second ends of the magnet segments so as to hold the second ends of the magnet segments relative to each other in the arrangement, the first and second ends of the cage being coupled together on the outer surface of the arrangement by the at least one longitudinal outer portion extending between the first and second ends substantially flush with the outer surface.

2. The assembly of claim 1, wherein the at least one longitudinal outer portion is parallel to the rotational axis.

3. The assembly of claim 1, wherein:

the first end of the cage is integral with the interior portion;

the second end of the cage is integral with the interior portion; and

the at least one longitudinal outer portion is integral with the first and second ends of the cage.

4. The assembly of claim 1, further comprising a flux ring having an inner surface and an outer surface, wherein the inner surface of the arrangement is coupled to the outer surface of the flux ring, and the inner surface of the flux ring is coupled to the interior portion of the cage.

5. The assembly of claim 1, wherein:

the lateral edges of the magnet segments have respective chamfers that define channels between adjacent magnet segments in the arrangement;

the cage comprises multiple longitudinal outer portions; and

the longitudinal outer portions are situated in the respective channels, substantially flush with the outer surface of the arrangement.

6. The assembly of claim 1, wherein:

the lateral edges of adjacent magnet segments of the arrangement define at least one respective void extending radially from the outer surface of the arrangement to the inner surface of the arrangement; and

the cage includes respective radial portions extending through the voids and coupling the longitudinal outer portions of the cage with the interior portion of the cage.

7. The assembly of claim 6, wherein the radial portions are coupled to respective longitudinal outer portions at substantially mid-length of the longitudinal outer portions.

8. The assembly of claim 1, wherein:

the first end of the cage is configured to capture the first ends of the magnet segments together circumferentially; and

the second end of the cage is configured to capture the second ends of the magnet segments together circumferentially.

9. The assembly of claim 1, wherein:

the ends of the magnet segments have respective stepped profiles that define radial channels between adjacent magnet segments in the arrangement; and

at least one of the first and second ends of the cage comprises radial portions that fill respective radial channels.

10. The assembly of claim 9, wherein:

the at least one end of the cage comprises an inner portion and an outer portion; and

the radial portions extend between the inner portion and the outer portion.

11. The assembly of claim 1, wherein the first end of the cage is configured for rotational coupling to a coaxially rotatable pump component so as to cause corresponding rotation of the pump component about the axis whenever the driven magnet is rotated about the axis.

12. The assembly of claim 11, wherein:

the pump is a gear pump; and

the coaxially rotatable pump component is a driving gear of the gear pump.

13. The assembly of claim 1, wherein the cage is made of a polymeric material.

14. The assembly of claim 1, wherein the magnet segments in the arrangement have alternating magnetic polarity from one magnet segment to the next.

15. The assembly of claim 14, wherein:

the arrangement comprises four magnet segments; and

the magnetic polarity alternates from radially inwardly directed to radially outwardly directed from one magnet segment to the next.

16. The assembly of claim 15, wherein:

each magnet segment is configured as a respective quarter cylinder;

the magnet segments in the arrangement are situated side-by-side to form a cylinder of magnets around and coaxial with the interior portion of the cage.

17. The assembly of claim 16, further comprising a flux ring having an inner surface and an outer surface, wherein the inner surface of the arrangement is coupled to the outer surface of the flux ring, and the inner surface of the flux ring is coupled to the interior portion of the cage.

18. A pump, comprising:

a pump housing enclosing an active pump-component that, when rotated about an axis, generates a liquid-pumping force urging liquid to flow through the pump housing; and

a driven-magnet assembly that is rotatable about an axis and that is coupled to the active pump-component in a manner that causes the active pump-component to rotate about its axis whenever the driven-magnet assembly is rotated about its axis, the driven-magnet assembly comprising (i) multiple magnet segments each having a first end, a second end, and lateral edges, the magnet segments being situated at respective positions around a rotational axis in an arrangement having an inner surface and an outer surface, the inner and outer surfaces being coaxial about the rotational axis; and (ii) a cage holding the magnet segments relative to each other in the arrangement, the cage comprising an interior portion, a first end, a second end, and at least one longitudinal outer portion, the interior portion being situated between the rotational axis and the inner surface of the arrangement and coaxially with the arrangement such that the inner surface of the arrangement is coupled to the interior portion of the cage and the magnet segments radially surround the interior portion, the first end of the cage being coupled to the interior portion and to the first ends of the magnet segments so as to hold the first ends of the magnet segments relative to each other in the arrangement, and the second end of the cage being coupled to the interior portion and to the second ends of the magnet segments so as to hold the second ends of the magnet segments relative to each other in the arrangement, the first and second ends of the cage being coupled together on the outer surface of the arrangement by the at least one longitudinal outer portion extending between the first and second ends substantially flush with the outer surface.

19. The pump of claim 18, wherein:

the pump is a gear pump; and

the active pump-component comprises at least one gear.

20. The pump of claim 18, wherein the active pump-component comprises a driving gear coupled to the driven-magnet assembly, and a driven gear interdigitated with the driving gear so as to rotate about its axis whenever the driving gear is caused to rotate about its axis by the driven-magnet assembly.

21. The pump of claim 18, further comprising a rotating-magnetic-field device configured to be magnetically coupled to the driven-magnet assembly in a manner causing rotation of the driven-magnet assembly about its axis.

22. The pump of claim 21, wherein the rotating-magnetic-field device comprises a stator that, when energized, produces a rotating magnetic field that is coupled to the driven-magnet assembly.

23. The pump of claim 22, wherein:

the pump housing further comprises a magnet cup housing the driven-magnet assembly within the pump housing; and

the stator is situated in surrounding relationship coaxially with the driven-magnet assembly in the magnet cup, such that energization of the stator causes corresponding coaxial rotation of the driven-magnet assembly in the magnet cup.

24. A driven-magnet assembly for a magnetically driven pump, the assembly comprising:

multiple magnet segments each having a first end, a second end, and lateral sides, the magnet segments being situated at respective positions around a rotational axis in an arrangement in which the magnet segments collectively define an inner surface and an outer surface of the arrangement, the inner and outer surfaces being coaxial about the rotational axis; and

a molded body holding the magnet segments relative to each other in the arrangement, the molded body comprising an interior portion, a first end, and a second end, the interior portion being situated between the rotational axis and the inner surface of the arrangement and coaxially with the arrangement such that the inner surface of the arrangement is coupled to the interior portion and the magnet segments radially surround the interior portion, the first end being coupled to the interior portion and to the first ends of the magnet segments so as to hold the first ends of the magnet segments relative to each other in the arrangement, and the second end being coupled to the interior portion and to the second ends of the magnet segments so as to hold the second ends of the magnet segments relative to each other in the arrangement, thereby leaving the outer surface of the arrangement substantially bare.

25. The assembly of claim 24, wherein the molded body further comprises at least one longitudinal outer portion that is coupled to the first and second ends of the molded body and extends between the first and second ends substantially flush with the outer surface.

26. The assembly of claim 25, wherein:

the magnet segments are situated side-by-side in the arrangement;

the molded body comprises multiple longitudinal outer portions;

each longitudinal outer portion extends along respective lateral sides of adjacent magnet segments.

27. The assembly of claim 24, further comprising a flux ring having an inner surface and an outer surface, wherein the inner surface of the arrangement is coupled to the outer surface of the flux ring, and the inner surface of the flux ring is coupled to the interior portion of the cage.

28. A driven-magnet assembly for a magnetically driven pump, the assembly comprising:

a magnet-flux-ring assembly comprising (i) a flux ring having an inner surface and an outer surface configured concentrically around a rotational axis and (ii) multiple magnet segments arranged at respective radial positions around the rotational axis, the magnet segments each having a respective inner surface, outer surface, first end, second end, and lateral sides, the inner surfaces being attached to the outer surface of the flux ring such that the magnet segments are arranged side-by-side around the flux ring, and the outer surfaces collectively form an outer surface of the magnet-flux-ring assembly; and

a molded body having an interior portion, a first end, and a second end, the interior portion being situated radially inwardly of, and attached to, the inner surface of the flux ring, the first end being integral with the interior portion and configured so as to capture the first ends of the magnet segments relative to the flux ring, the second end being integral with the interior portion and configured so as to capture the second ends of the magnet segments relative to the flux ring, the outer surface of the magnet-flux-ring assembly being substantially bare.

29. The assembly of claim 28, wherein the molded body further comprises at least one longitudinal outer portion that is integral with the first and second ends and that extends between the first and second ends along respective lateral sides of adjacent magnet segments substantially flush with the outer surface of the magnet-flux-ring assembly.

30. The assembly of claim 29, wherein:

the molded body comprises multiple longitudinal outer portions;

the lateral edges of the magnet segments include chamfers that define, in the magnet-flux-ring assembly, channels between adjacent magnet segments attached to the outer surface of the flux ring; and

the longitudinal outer portions are situated in the channels, substantially flush with the outer surface of the magnet-flux-ring assembly.

31. The assembly of claim 30, wherein:

the lateral edges of adjacent magnet segments attached to the outer surface of the flux ring define respective voids extending radially from the outer surface of the magnet-flux-ring assembly to the outer surface of the flux ring; and

the molded body further comprises radial portions extending through the voids and coupling the longitudinal outer portions with the flux ring.

32. The assembly of claim 28, wherein the interior portion of the molded body defines a bore extending along the rotational axis.

33. The assembly of claim 32, further comprising a shaft seated in the bore, the shaft being configured to facilitate rotation of the driven-magnet assembly about the rotational axis.

34. A pump, comprising:

a driven-magnet assembly for a magnetically driven pump, the assembly comprising (i) a magnet-flux-ring assembly comprising (a) a flux ring having an inner surface and an outer surface configured concentrically around a rotational axis and (b) multiple magnet segments arranged at respective radial positions around the rotational axis, the magnet segments each having a respective inner surface, outer surface, first end, second end, and lateral sides, the inner surfaces being attached to the outer surface of the flux ring such that the magnet segments are arranged side-by-side around the flux ring, and the outer surfaces collectively form an outer surface of the magnet-flux-ring assembly; and (ii) a molded body having an interior portion, a first end, and a second end, the interior portion being situated radially inwardly of, and attached to, the inner surface of the flux ring, the first end being integral with the interior portion and configured so as to capture the first ends of the magnet segments relative to the flux ring, the second end being integral with the interior portion and configured so as to capture the second ends of the magnet segments relative to the flux ring, the outer surface of the magnet-flux-ring assembly being substantially bare.

35. A magnetically actuated gear pump, comprising:

a pump housing, comprising a pump cavity and a magnet cup;

a driving gear and a driven gear enclosed within the pump cavity, the driving gear being rotatable about a first axis, and the driven gear being interdigitated with the driving gear and being rotatable about a second axis; and

a driven-magnet assembly rotationally coupled to the driving gear, the driven-magnet assembly comprising (i) multiple magnet segments each having a first end, a second end, and lateral edges, the magnet segments being situated at respective positions around the first axis in an arrangement having an inner surface and an outer surface, the inner and outer surfaces being coaxial about the first axis; and (ii) a cage holding the magnet segments relative to each other in the arrangement, the cage comprising an interior portion, a first end, a second end, and at least one longitudinal outer portion, the interior portion being situated between the first axis and the inner surface of the arrangement and coaxially with the arrangement such that the inner surface of the arrangement is coupled to the interior portion of the cage and the magnet segments radially surround the interior portion, the first end of the cage being coupled to the interior portion and to the first ends of the magnet segments so as to hold the first ends of the magnet segments relative to each other in the arrangement, and the second end of the cage being coupled to the interior portion and to the second ends of the magnet segments so as to hold the second ends of the magnet segments relative to each other in the arrangement, the first and second ends of the cage being coupled together on the outer surface of the arrangement by the at least one longitudinal outer portion extending between the first and second ends substantially flush with the outer surface.

36. The gear pump of claim 35, further comprising a stator situated coaxially surrounding the magnet cup such that energization of the stator causes the stator to produce a magnetic field rotating about the first axis, the rotating magnetic field produced by the stator being magnetically coupled through the magnet cup to the driven-magnet assembly so as to cause corresponding rotation of the driven-magnet assembly about the first axis.

37. A magnetically actuated gear pump, comprising:

a pump housing, comprising a pump cavity and a magnet cup;

a driven-magnet assembly rotationally coupled to the driving gear, the driven-magnet assembly comprising (i) multiple magnet segments each having a first end, a second end, and lateral sides, the magnet segments being situated at respective positions around the first axis in an arrangement in which the magnet segments collectively define an inner surface and an outer surface of the arrangement, the inner and outer surfaces being coaxial about the first axis; and (ii) a molded body holding the magnet segments relative to each other in the arrangement, the molded body comprising an interior portion, a first end, and a second end, the interior portion being situated between the first axis and the inner surface of the arrangement and coaxially with the arrangement such that the inner surface of the arrangement is coupled to the interior portion and the magnet segments radially surround the interior portion, the first end being coupled to the interior portion and to the first ends of the magnet segments so as to hold the first ends of the magnet segments relative to each other in the arrangement, and the second end being coupled to the interior portion and to the second ends of the magnet segments so as to hold the second ends of the magnet segments relative to each other in the arrangement, thereby leaving the outer surface of the arrangement substantially bare.

38. The gear pump of claim 37, further comprising a stator situated coaxially surrounding the magnet cup such that energization of the stator causes the stator to produce a magnetic field rotating about the first axis, the rotating magnetic field produced by the stator being magnetically coupled through the magnet cup to the driven-magnet assembly so as to cause corresponding rotation of the driven-magnet assembly about the first axis.

39. A magnetically actuated gear pump, comprising:

a pump housing, comprising a pump cavity and a magnet cup;

a driven-magnet assembly rotationally coupled to the driving gear, the driven-magnet assembly comprising (i) a magnet-flux-ring assembly comprising (a) a flux ring having an inner surface and an outer surface configured concentrically around a rotational axis and (b) multiple magnet segments arranged at respective radial positions around the rotational axis, the magnet segments each having a respective inner surface, outer surface, first end, second end, and lateral sides, the inner surfaces being attached to the outer surface of the flux ring such that the magnet segments are arranged side-by-side around the flux ring, and the outer surfaces collectively form an outer surface of the magnet-flux-ring assembly; and (ii) a molded body having an interior portion, a first end, and a second end, the interior portion being situated radially inwardly of, and attached to, the inner surface of the flux ring, the first end being integral with the interior portion and configured so as to capture the first ends of the magnet segments relative to the flux ring, the second end being integral with the interior portion and configured so as to capture the second ends of the magnet segments relative to the flux ring, the outer surface of the magnet-flux-ring assembly being substantially bare.

40. The gear pump of claim 39, further comprising a stator situated coaxially surrounding the magnet cup such that energization of the stator causes the stator to produce a magnetic field rotating about the first axis, the rotating magnetic field produced by the stator being magnetically coupled through the magnet cup to the driven-magnet assembly so as to cause corresponding rotation of the driven-magnet assembly about the first axis.

41. In a magnetically driven gear pump, a driven-magnet assembly, comprising:

a flux ring configured as a hollow cylinder having a rotational axis, an outer surface, and an inner surface;

at least four magnet segments each having a first end, a second end, lateral edges, an outer-radius surface, and an inner-radius surface and each producing a respective magnetic field that is either directed radially inwardly or radially outwardly, the inner-radius surfaces of the magnet segments being mounted to the outer surface of the flux ring such that the magnet segments collectively form a radial arrangement of magnet segments around the axis of rotation, the outer-radius surfaces of the magnet segments collectively form an outer surface of the radial arrangement, and the respective magnetic fields alternate in direction from one magnet segment to the next around the flux ring; and

a non-magnetic cage holding the magnet segments relative to each other in the arrangement, the cage comprising an interior portion attached coaxially to the inner surface of the flux ring, a first end integral with the interior portion and attached to the first ends of the magnet segments in the arrangement, a second end integral with the interior portion and attached to the second ends of the magnet segments in the arrangement, and at least one longitudinal outer portion integral with and extending, parallel to the rotational axis, from the first to the second ends of the cage on the outer surface of the arrangement, substantially flush with the outer surface.

42. The assembly of claim 41, wherein the cage is molded in situ to the flux ring and magnet segments.

43. The assembly of claim 41, wherein the cage is molded of plastic.

44. The assembly of claim 41, wherein:

the inner-radius surfaces of the magnet segments are bonded to the outer surface of the flux ring; and

lateral edges of adjacent magnet segments are bonded together in the arrangement.

45. The assembly of claim 41, wherein:

the cage comprises multiple longitudinal outer portions; and

the longitudinal outer portions are situated in the channels, substantially flush with the outer surface of the arrangement.

46. The assembly of claim 41, wherein:

the lateral edges of adjacent magnet segments of the arrangement define respective voids extending radially from the outer surface of the arrangement to the outer surface of the flux ring; and

the cage includes radial portions extending through the voids and coupling the longitudinal outer portions of the cage with the flux ring.

47. The assembly of claim 46, wherein the radial portions are coupled to the longitudinal outer portions at substantially mid-length of the longitudinal outer portions.

48. The assembly of claim 41, wherein:

49. The assembly of claim 41, wherein:

50. The assembly of claim 41, further comprising a rotational coupling of the driven-magnet assembly to a driving gear, the coupling being configured such that rotation of the driven-magnet assembly about the rotational axis causes corresponding rotation of the driving gear about the rotational axis.

51. The assembly of claim 50, wherein the rotational coupling comprises a bore defined in the second end of the cage that is configured to receive a complementarily shaped shaft of the driving gear.

52. A gear pump, comprising:

a pump housing defining a pump cavity and a magnet cup having an axis;

a driving gear meshed with a driven gear in the pump cavity;

a driven-magnet assembly, configured as recited in claim 42, situated coaxially inside the magnet cup and coupled to the driving gear such that rotation of the driven-magnet assembly about the axis causes corresponding rotation of the driving gear about the axis.

53. The gear pump of claim 52, further comprising a stator situated outside but coaxially with the magnet cup so as to cause rotation of the driven-magnet assembly about the axis in the magnet cup whenever the stator is energized.

54. A driven-magnet assembly for a magnetically driven pump, the assembly comprising:

magnet means for providing a sequentially alternating magnetic polarity around a rotational axis, the magnet means comprising multiple magnet segments having an inside surface, an outside surface, a first end, a second end, and lateral edges, the magnet segments being situated side-by-side and with sequentially alternating magnetic polarity around the rotational axis and the outside surfaces of the magnet segments collectively forming an outer surface of the magnet means; and

cage means, situated relative to the magnet means, for holding the inside surfaces of the magnet segments relative to each other and for capturing the first and second ends of the magnet segments relative to each other, during rotation of the driven-magnet assembly about the rotational axis, while leaving the outer surfaces of the magnet segments substantially bare.

55. The driven-magnet assembly of claim 54, wherein the magnet means further comprises flux-ring means for shaping and concentrating respective magnetic fields produced by the magnet segments around the rotational axis.

56. A hydraulic circuit, comprising:

a gear pump as recited in claim 35;

a first conduit leading from the gear pump to a location; and

a second conduit leading from the location to the gear pump, wherein the gear pump urges flow of a liquid from the gear pump through the first conduit to the location and from the location through the second conduit to the gear pump.

57. A hydraulic circuit, comprising:

a gear pump as recited in claim 37;

a first conduit leading from the gear pump to a location; and

58. A hydraulic circuit, comprising:

a gear pump as recited in claim 39;

a first conduit leading from the gear pump to a location; and