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Segmented driven-magnet assemblies for pumps, and pumps comprising sameRelated Patent Categories: Pumps, Motor Driven, Electric Or Magnetic Motor, Rotary Expansible Chamber Pump, Interengaging Rotary Pumping MembersSegmented driven-magnet assemblies for pumps, and pumps comprising same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070071616, Segmented driven-magnet assemblies for pumps, and pumps comprising same. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] This application corresponds to, and claims the benefit under 35 U.S.C. .sctn.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 [0002] 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 [0003] 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. [0004] 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. [0005] 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. [0006] 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. [0007] 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. [0008] 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. [0009] 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. [0010] 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. [0011] 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. [0012] 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 [0013] 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. [0014] 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. [0015] 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. [0016] 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. [0017] 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. [0018] 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. [0019] 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. [0020] 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. Continue reading about Segmented driven-magnet assemblies for pumps, and pumps comprising same... 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