Electric water pump with continual axial magnetic attraction

Abstract

An electric pump includes a casing, an impeller, and an electric motor. The casing defines an inlet, an outlet, and a pumping chamber. The impeller rotates in the pumping chamber along an axis, the inlet ingressing fluid axially, and the outlet egressing fluid transversely. The motor includes a rotor and a stator operable to interact with one another via a magnetic air gap. The stator is provisioned by a printed circuit board (PCB) and a magnetically permeable stator core. The PCB is disposed transverse to the axis and has a first face proximal to the air gap and a second face distal to the air gap, the stator core disposed adjacent to the PCB second face. The rotor includes a permanent magnet structure connected to the impeller and rotatable so that a continual magnetic attractive force is directed along the axis between the magnet structure and the stator core.

Description

ELECTRIC WATER PUMP WITH CONTINUAL AXIAL MAGNETIC ATTRACTIONCross Reference to Related Applications

[0001] This application claims the benefit of US Provisional Patent Application No. 63 / 634,099 filed April 15, 2024, the contents of which are incorporated herein by reference in their entirety, where permitted.Field of Art

[0002] This disclosure relates generally to the field of electric water pumps.Background

[0003] Axial flux electric water pumps are known in the art. An example of such a pump that utilizes a printed circuit board (PCB) stator is disclosed in W02023 / 082002 published May 19, 2023. In this pump the motor rotor is disposed in the fluid to be pumped and thus can be affected by various loads imposed by the impeller as the result of its pumping activity. These loads may require the use of robust bearings which add a source of complication in manufacture and durability.

[0004] It would be beneficial to improve upon the forces experienced by such pumps to, for example, reduce cost or improve durability.Summary

[0005] In one aspect, an electric pump is provided which includes a casing, an impeller, and an electric motor. The casing defines a fluid inlet, a fluid outlet, and a pumping chamber fluidly connected to the inlet and the outlet. The impeller is mounted for rotation in the pumping chamber about a rotational axis, the inlet being configured to ingress fluid in a direction along the rotational axis and the outlet being configured to egress fluid in a direction transverse to the rotational axis. The electric motor includes a rotor and a stator operable to electromagnetically interact with one another via a magnetic air gap. The stator is provisioned by a printed circuit board (PCB) and a magnetically permeable stator core. The PCB is disposed transverse to the rotational axis and has a first face proximal to the magnetic air gap and a second, opposing, face distal to the magnetic air gap, the stator corebeing disposed adjacent to the second face of the PCB. The rotor includes a permanent magnet structure connected to the impeller and rotatable about the rotational axis. In this manner a continual magnetic attractive force is directed along the rotational axis between the permanent magnet structure and the stator core.

[0006] The continual magnetic force can be used to counteract opposing forces generated by the impeller in operation. The magnitude of the continual magnetic force can also be configured to seat the impeller against a single transversely orientated bearing surface in the pump.

[0007] Accordingly, the impeller can be floatingly journalled so as have some freedom of motion or play along the rotational axis, and the magnitude of the continual magnetic attractive force can be greater than an opposing force generated by the impeller at a maximal operating rotational velocity of the impeller and at a maximal operating pressure generated by the impeller such that the impeller is impeded from floating along the rotational axis.

[0008] The opposing force can include a force arising from an ingress of fluid into the pumping chamber from the inlet and can include a force arising from a pressure differential between a periphery of the pumping chamber and a center of the pumping chamber.

[0009] In one embodiment the impeller can be fixed to a spindle, and the magnitude of the continual magnetic attractive force can be such to ensure that the spindle bears against a bearing surface orientated transverse to the rotational axis at the maximal operating rotational velocity of the impeller and at the maximal operating pressure generated by the impeller.

[0010] In such embodiments, a bushing can be disposed between the spindle and the bearing surface.

[0011] In another embodiment a shaft can be mounted in the casing along the rotational axis, and the impeller can include a hub portion rotatable about the shaft. The magnitude of the continual magnetic attractive force can be such to ensure that the hub portion bears against a bearing surface orientated transverse to the rotational axis at the maximal operating rotational velocity of the impeller and at the maximal operating pressure generated by the impeller.

[0012] In such embodiments, a bushing can be disposed between the impeller hub portion and the bearing surface. More particularly, the casing can include a pedestal portion and the shaft can be anchored into the pedestal and features a pad that provides the transverse bearing surface. The bushing can include a longitudinal portion configured to fit over at least a portion of the shaft and a transverse portion configured to sit over the pad.

[0013] The permanent magnet structure can include a permanent magnet having a plurality of alternating magnetic pole faces configured as a ring, and the stator core can be configured as a ring which overlaps and is coextensive with the ring of alternating magnetic pole faces. In this manner, the continual magnetic attractive force can present a centering force for the impeller.

[0014] The PCB can be mounted within the casing such that the PCB first face and the PCB second face are exposed to fluid being pumped. More particularly, the casing can include a peripheral wall with standoffs for supporting the PCB, and the peripheral wall can includes a toroidal rebate which nestles the stator core ring. This peripheral wall can be provisioned in the form of a casing cover.

[0015] In another aspect, an electric pump includes is provided which includes a casing, a shaft mounted in the casing, an impeller mounted about the shaft, and an electric motor connected to the impeller. The casing defines a fluid inlet, a fluid outlet, and a pumping chamber fluidly connected to the inlet and the outlet. The inlet is configured to ingress fluid in a direction along a pump rotational axis and the outlet is configured to egress fluid in a direction transverse to the rotational axis. The shaft is mounted to the casing and defines the rotational axis. The shaft includes a pad that provides a bearing surface orientated transverse to the rotational axis. The impeller includes a rotational hub floatingly journalled about the shaft so as to have freedom of motion along the rotational axis. The electric motor is disposed within the casing and includes a rotor and a stator operable to electromagnetical ly interact with one another via a magnetic air gap. The rotor includes a permanent magnet ring fixedly connected to the impeller and rotatable about the shaft, the permanent magnet ring having a plurality of alternating magnetic pole faces pointing in the direction of the rotational axis. The stator is provisioned by a printed circuit board (PCB) and a magnetically permeable stator core ring. The PCB is disposed transverse to the rotational axis and has a first face proximal to the magnetic air gap and a second, opposing,face distal to the magnetic air gap. The stator core ring is mounted adjacent to the second face of the PCB and configured to be coextensive with the permanent magnet ring. In this manner a continual magnetic attractive force is directed along the rotational axis between the permanent magnet ring and the stator core ring, the magnitude of the continual magnetic attractive force being such that the impeller remains seated and bears against the pad bearing surface at the maximal operating rotational velocity of the impeller and at the maximal operating pressure generated by the impeller.

[0016] According to this aspect, the pad bearing surface can be the sole transversely orientated surface against which the impeller bears and the shaft can be the sole axially orientated surface against which the impeller bears. A bushing can be provisioned with a longitudinal portion configured to sit between the shaft and the impeller and a transverse portion configured to sit between the pad bearing surface and the impeller.Brief Description of Drawings

[0017] The foregoing and other aspects of this disclosure may be better appreciated having regard to the attached drawings, in which:

[0018] Figure 1 is a cross-sectional view of an electric water pump according to a first embodiment;

[0019] Figure 2 is a cross-sectional perspective view of an electric motor utilized in the first embodiment;

[0020] Figure 3 is a cross-sectional view of the electric motor shown in Figure 2 schematically illustrating flux lines;

[0021] Figure 4 is a cross-sectional view of a portion of the electric water pump shown in Figure 1 , schematically illustrating applied forces;

[0022] Figure 5 is a cross-sectional view of an electric water pump according to a second embodiment;

[0023] Figure 6 is an isolated perspective view of a casing cover utilized in the electric water pump shown in Figure 5; and

[0024] Figure 7 is a cross-sectional view of the electric water pump shown in Figure 5, schematically illustrating current leakage paths.Detailed Description of Example Embodiments

[0025] For simplicity and clarity of illustration, where considered appropriate, reference numerals may be repeated among the Figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiment or embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiments described herein. It should be understood at the outset that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below.

[0026] The terms ‘comprising’ and ‘including’ and their various conjugations (e.g. ‘comprises’) will be understood to be inclusive and open-ended, and not exclusive. This means that if an element A includes or comprises an element B, it will be understood that element A could include or comprise other elements in addition to including or comprising element B. The term ‘having’ and its various conjugations are also to be understood as being open-ended in the same way as ‘comprising’ and ‘including’. These terms are not to be interpreted to exclude the presence of other features, steps or components.

[0027] As used herein, the terms “about” and “approximately” are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions.

[0028] Various terms used throughout the present description may be read and understood as follows, unless the context indicates otherwise: "or" as used throughout is inclusive, as though written "and / or"; singular articles and pronouns as used throughout include their plural forms, and vice versa; similarly, gendered pronouns include their counterpart pronouns such that pronouns should not be understood as limiting anything described herein to use, implementation, performance, etc. by a single gender; "exemplary"should be understood as "illustrative" or "exemplifying" and not necessarily as "preferred" over other embodiments. Further definitions for terms may be set out herein; these may apply to prior and subsequent instances of those terms, as will be understood from a reading of the present description. It will also be noted that the use of the term "a" or "an" will be understood to denote "at least one" in all instances unless explicitly stated otherwise or unless it would be understood to be obvious that it must mean "one".

[0029] Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

[0030] As used in this document, "attached" in describing the relationship between two connected parts includes the case in which the two connected parts are "directly attached" with the two connected parts being in contact with each other, and the case in which the connected parts are "indirectly attached" and not in contact with each other, but connected by one or more intervening other part(s) between.

[0031] As used in this document, terms describing relative positions of elements such as ‘top’, ‘upper’, ‘bottom’, ‘lower’, or other analogous terms will be understood to refer to the placement of the described element during use of the apparatus of which it is a part unless the context would make it clear that it is otherwise. It will be understood that the aforementioned placement of an element, for example, can still be considered its placement even when the object that it is a part of is lying in some position other than the position in which it will be used. As an example, if reference is made to a device having an upper member, it will be understood that the upper member is being described as having an upper position when the device that it is a part of is in use or is in position for use, unless the context would make it clear that it is otherwise. Further to this example, it will be understood that the aforementioned upper member of the object can still be considered its uppermember even when the object is lying on its side, for storage, or for transport, or for some other reason.

[0032] The embodiments of the disclosures described herein are exemplary (e.g., in terms of materials, shapes, dimensions, and constructional details) and do not limit by the claims appended hereto and any amendments made thereto. Persons skilled in the art will appreciate that there are yet more alternative implementations and modifications possible, and that the following examples are only illustrations of one or more implementations. The scope of the disclosure, therefore, is only to be limited by the claims appended hereto and any amendments made thereto.

[0033] Figure 1 shows a cross-sectional view of an electric water pump 100. The pump 100 includes an outer housing or casing 102 which defines an inlet 106 for the ingress of fluid, an outlet 108 for the egress of fluid, and a pumping chamber 150 fluidly connecting the inlet 106 and outlet 108.

[0034] A shaft or spindle 114 can be mounted for rotation within the casing 102 and pumping chamber 150 and defines a rotational axis A-A of the pump 100. As illustrated, the inlet 106 is configured to ingress fluid in a direction along the rotational axis (i.e., the axial direction) and the outlet 108 is configured to egress fluid circumferentially, in a direction transverse to the axial direction. A pumping element such as a centrifugal-type impeller 118 can be fixed to the spindle 114 and disposed in the pumping chamber 150 to convey fluid flow to the outlet 108 from the inlet 106. The pumping chamber 150 can be configured with a volute 152 to increase fluid pressure between the inlet 106 and outlet 108 as is generally known in the art per se. The volute 152 can be provisioned through appropriate forming of an inner circumferential wall 102W of the casing 102 in the vicinity of the pumping chamber 150 and / or by offset of the spindle 114 within the pumping chamber 150 relative to its center.

[0035] The casing 102 can include an integrally formed hub 113 within the inlet 106, with the hub 113 being supported in the inlet 106 by integrally formed struts 107. The casing 102 can also include a wall 112 with an integrally formed hub 115. A first thrust bearing or bushing 116A and a second thrust bearing or bushing 116B can be installed within the hubs 113, 115, respectively, for journaling the spindle 114 and functioning as bearing surfaces. This dual hub structure can be beneficial in limiting or forestalling any appreciable axial freedom of motion or play of the spindle 114.

[0036] Referring additionally to Figure 2, an electric motor 120 comprising a rotor 120A and a stator 120B can be disposed within the casing 102. The rotor 120A interacts electromagnetical ly with the stator 120B through a magnetic air gap 130. The rotor 120A and stator 120B of the illustrated embodiment are disposed in the pumping chamber 150 and surrounded by fluid.

[0037] The rotor 120A can include a permanent magnet structure 124 that is fixed relative to the impeller 118. For example, as shown in Figure 1 , the permanent magnet structure 124 can be press-fit onto the spindle 114 thus maintaining a fixed relationship between the permanent magnet structure 124 and the impeller 118. Alternatively, the permanent magnet structure 124 can be mechanically fastened to a rear flange portion 122 of the impeller 118. The aforementioned are merely examples of how the permanent magnet structure 124 can be mounted in a fixed relationship with respect to the impeller 118. Alternatively, the permanent magnet structure 124 can be mounted in a fixed relationship with respect to the impeller 118 in any other suitable way.

[0038] The permanent magnet structure 124 can comprise a back-iron disc 126 with a permanent magnet ring 128 adhered thereto. The permanent magnet ring 128 can be segmented circumferentially into magnets of alternating pole faces, as shown in the figures.

[0039] The stator 120B can include a printed circuit board (PCB) 110 and a stator core 132.

[0040] The PCB 110 can carry electrical windings for a plurality of electrical phases. Various electrical stator winding configurations can be employed as known in the art per se, one of which is disclosed in W02023 / 082002 published May 19, 2023.

[0041] The stator core 132 can be formed, for example, from ferrite with a relatively high permeability yet relatively high electrical resistivity. The stator core 132 can be configured in the form of a toothless ring 134 mounted on a face 110B of the PCB 110 distal to the magnetic air gap 130. In the illustrated embodiment the toothless stator core ring 134 is configured and disposed so as to overlap and be co-extensive with the permanent magnet ring 128. The casing 102 can include an internal toroidal rebate 102R along casing wall 112 to support the stator core 132.

[0042] Referring additionally to Figure 3 which shows, schematically, a magnetic flux path (stippled lines 136) for a portion of the illustrated electric motor 120 in cross-sectionalview, it will be seen that the magnetic flux path extends through the stator core 132. The stator core 132 can provision a low reluctance path to complete flux loops between adjacent magnet poles of opposite polarity. This low reluctance path can concentrate flux density and, compared to a coreless stator, can improve flux alignment resulting in higher flux linkage between the stator and rotor, improving efficiency. The toothless nature of the illustrated stator core can reduce cogging torque in comparison to a toothed core.

[0043] In operation, a leakage current can flow about the impeller 118 through the magnetic air gap 130. In addition, if the permanent magnet structure 124 is fixed to the spindle 114 as shown in Figure 1 , a small clearance gap 122G can be provisioned between the rear flange portion 122 of the impeller 118 and the permanent magnet structure 124 and a leakage current can also flow about the impeller through the clearance gap 122G. Such leakage currents can arise due to an operational radial pressure differential, with fluid pressure being relatively low near the rotational axis A-A and increasing in pressure with increasing radial direction. The pressure differential can cause the leakage current(s) to flow through the magnetic air gap 130 and clearance gap 122G (if provided) and through tolerances that exist between the spindle 114 and the permanent magnet structure 124, which provide a fluid path to the inlet 106. Alternatively, dedicated passageways (not shown) may be provided as shown, for example, in W02023 / 082002 published May 19, 2023, in the permanent magnet structure 124 and the impeller 118 which provide a fluid path to the inlet 106.

[0044] Some of the forces acting within the pump 100 will now be discussed in greater detail. Referring additionally to the partial cross-sectional view of the pump 100 in Figure 4, when the electric motor 120 is operated to rotate the impeller 118, a force is generated axially on the fluid in the inlet 106 to cause the fluid to flow toward the pumping chamber 150 along a first axial direction (which may be referred to herein as the “inward” axial direction). Under Newton’s third law, the impeller 118 exerts a force, schematically represented by reference arrow AF1 , in an opposite axial direction (which may be referred to herein as the “outward” axial direction) in reaction to the momentum of the incoming fluid. In addition, the relatively high fluid pressure differential on the circumferentially outer portions of the magnetic air gap 130 and clearance gap 122G (if provisioned) also generates an outward axial force, schematically represented by reference arrow AF2. The relativelyhigh fluid pressure differential on the circumferentially outer portions of the magnetic air gap 130 and clearance gap 122G (if provisioned) may also not be very uniform in the circumferential direction, leading to tilting forces relative to the axial direction. These outward axial and tilt forces may increase with increasing pump output.

[0045] To ameliorate these forces, the electric motor 120 utilizes a single sided rotor in an axial flux topology in order to develop a continual magnetic attractive force (schematically represented by reference arrow MF) between the rotor 120A and stator 120B in the inward axial direction which counteracts at least in part the outward axial forces AF1 + AF2 presented by the impeller 118 in operation. This magnetic attractive force MF, which may be continual, is generated between the permanent magnet structure 124 and the stator core 132 and may always be present, not varying appreciably with the rotational speed of the impeller or the pump output. The magnitude of the continual magnetic attractive force MF depends on the geometry of the permanent magnet structure 124 and the stator core 132, the specific materials used for these components, and the spacing of the magnetic air gap 130. Furthermore, as the illustrated toothless ring 134 of the stator core 132 is configured and arranged in a manner co-extensive with the permanent magnet ring 128 the continual magnetic attractive force MF is deployed circumferentially and thus generates a radially inward centering force (schematically represented by reference arrows CF) that counteracts at least in part the aforementioned tilting forces that arise in operation. These counteracting forces presented by electric motor 120 result in an overall pressure x velocity profile on the bearing surfaces 117 (see Figure 1 ) that is relatively stable over the pump operating range, enabling improved bearing performance in comparison to a pump that does not provision such counteracting force.

[0046] Figure 5 shows a cross-sectional view of an electric pump 200, which is a variant of electric pump 100.

[0047] Electric pump 200 utilizes a fixed axle 214 about which an impeller 218 rotates. This eliminates the need for the rotating spindle 114, the hubs 113 and 115, and bushings 116A and 116B utilized in the electric pump 100. Instead, the fixed axle 214 of electric pump 200 can feature a shaft 220 about which the impeller 218 can rotate and can feature an anchoring shank 224 that can be embedded, such as by press fit, into a pedestal 228 that can be formed in a peripheral wall 212 of casing 202. The anchoring shank 224 can featurea toroidal pad 226 that can be seated atop the pedestal 228 and can be disposed transverse to or perpendicular to the shaft 220 so as to function as a transverse bearing surface. A cone-like or top-hat-like bushing 230 can be fitted over the shaft 220. The bushing 230 can include a longitudinal portion 230L and a transverse portion 230T. The longitudinal portion 230L can be configured to fit over the shaft 220 and into a rotational hub portion 218H of the impeller 218. The transverse portion 230T can be ensconced between the toroidal pad 226 and a transversely oriented end portion 218E of the impeller hub 218H.

[0048] In the electric pump 200, the permanent magnet structure 124 can be fixed to a rear flange 222 of the impeller 218.

[0049] Referring additionally to Figure 6, the peripheral wall 212 of casing 202 can be provisioned by a cover 212C that can be fixed to the remainder of the casing 202 such as by welding, ultrasonic welding, adhesives, bolts, screws or any other attachment method known in the art per se. The cover 212C can feature a series of raised pads 240 which can present a clearance space 210 between the PCB 110 and the cover 212C. Referring additionally to Figure 7, this clearance space 210 along with the magnetic air gap 130 can enable leakage currents (represented by stippled lines 250) to flow via fluid paths extending from the outer circumferential periphery of the volute 152, across a first face 110A of the PCB 110 proximal to the permanent magnetic structure 124 and across a second, opposing, face 110B of the PCB 110 distal to the permanent magnetic structure 124, and through tolerances that exist about the bushing 230, to the inlet 106.

[0050] Electric pump 200 takes advantage of the axially inward continual magnetic attractive force MF which in this embodiment is configured with a magnitude that is large enough to keep the impeller 218 seated against or otherwise connected to the transverse axle pad 226 at the maximal output pressures and / or fluid outlet velocity capabilities of the electric pump 200. In this manner, the impeller 218 is precluded from floating axially during operation. As discussed previously, in this embodiment the overall pressure x velocity profile on the bearing surfaces of the bushing 230 is also relatively stable over the pump operating range, enabling improved bearing performance.

[0051] In pump 100 the axially inward continual magnetic attractive force MF can also be configured with a magnitude that is large enough to keep the impeller 118 seated againstor otherwise connected to the transverse bearing surfaces presented by hub 115 at the maximal output pressures and / or fluid outlet velocity capabilities of the electric pump 100.

[0052] Those skilled in the art will appreciate that a wide variety of additional modifications may be made to the embodiments disclosed herein whilst being in conformance with the appended claims.

Claims

ClaimsWhat is claimed is:1 . An electric pump, comprising: a casing, the casing defining a fluid inlet, a fluid outlet, and a pumping chamber fluidly connected to the inlet and the outlet; an impeller mounted for rotation in the pumping chamber about a rotational axis, wherein the inlet is configured to ingress fluid in a direction along the rotational axis and the outlet is configured to egress fluid in a direction transverse to the rotational axis; and an electric motor disposed within the casing, the electric motor comprising a rotor and a stator operable to electromagnetically interact with one another via a magnetic air gap, wherein the stator is provisioned by a printed circuit board and a magnetically permeable stator core, the PCB being disposed transverse to the rotational axis and having a first face proximal to the magnetic air gap and a second, opposing, face distal to the magnetic air gap, the stator core being disposed adjacent to the second face of the PCB, and wherein the rotor includes a permanent magnet structure fixedly connected to the impeller and rotatable about the rotational axis, whereby a continual magnetic attractive force directed along the rotational axis is present between the permanent magnet structure and the stator core.

2. An electric pump according to claim 1 , wherein the impeller is floating ly journalled so as have some play along the rotational axis, and wherein the magnitude of the continual magnetic attractive force is greater than an opposing force generated by the impeller at a maximal operating rotational velocity of the impeller and at a maximal operating pressure generated by the impeller such that the impeller is impeded from floating along the rotational axis.

3. An electric pump according to claim 2, wherein the opposing force includes a force arising from an ingress of fluid into the pumping chamber from the inlet.

4. An electric pump according to claim 3, wherein the opposing force includes a force arising from a pressure differential between a periphery of the pumping chamber and a center of the pumping chamber.

5. An electric pump according to claim 2, wherein the impeller is fixed to a spindle, and the magnitude of the continual magnetic attractive force is such that the spindle bears against a bearing surface orientated transverse to the rotational axis at the maximal operating rotational velocity of the impeller and at the maximal operating pressure generated by the impeller.

6. An electric pump according to claim 3, including a bushing disposed between the spindle and the bearing surface.

7. An electric pump according to claim 2, including a shaft mounted in the casing along the rotational axis, and wherein the impeller includes a hub portion rotatable about the shaft, and the magnitude of the continual magnetic attractive force is such that the hub portion bears against a bearing surface orientated transverse to the rotational axis at the maximal operating rotational velocity of the impeller and at the maximal operating pressure generated by the impeller, said transverse bearing surface being the sole transversely orientated bearing surface against which the impeller bears.

8. An electric pump according to claim 7, including a bushing disposed between the impeller hub portion and the bearing surface.

9. An electric pump according to claim 8, wherein the casing includes a pedestal portion the shaft is anchored into the pedestal, and the shaft features a pad that provides the transverse bearing surface.

10. An electric pump according to claim 9, wherein the bushing includes a longitudinal portion configured to sit over at least a portion of the shaft and a transverse portion configured to sit over the pad.11 . An electric pump according to claim 1 , wherein: the permanent magnet structure includes a permanent magnet having a plurality of alternating magnetic pole faces configured as a ring; and the stator core is configured as a ring which overlaps and is coextensive with the ring of alternating magnetic pole faces.

12. An electric pump according to claim 11 , wherein the impeller is floating ly journalled so as have some play along the rotational axis, and wherein the magnitude of the continual magnetic attractive force is greater than an opposing force generated by the impeller at a maximal operating rotational velocity of the impeller and at a maximal operating pressure generated by the impeller such that the impeller is impeded from floating along the rotational axis.

13. An electric pump according to claim 12, wherein the PCB is mounted within the casing such that the PCB first face and the PCB second face are exposed to fluid being pumped.

14. An electric pump according to claim 13, wherein the casing includes a peripheral wall with standoffs for supporting the PCB, and wherein the peripheral wall includes a toroidal rebate which nestles the stator core ring.

15. An electric pump, comprising: a casing, the casing defining a fluid inlet, a fluid outlet, and a pumping chamber fluidly connected to the inlet and the outlet, wherein the inlet is configured to ingress fluid in a direction along a pump rotational axis and the outlet is configured to egress fluid in a direction transverse to the rotational axis;a shaft mounted to the casing so as to define said rotational axis, the shaft including a pad that provides a bearing surface orientated transverse to the rotational axis; an impeller mounted for rotation about the shaft in the pumping chamber, the impeller having a rotational hub being floating ly journalled about the shaft so as to have freedom of motion along the rotational axis; an electric motor disposed within the casing, the electric motor comprising a rotor and a stator operable to electromagnetically interact with one another via a magnetic air gap, wherein the rotor includes a permanent magnet ring fixedly connected to the impeller and rotatable about the shaft, the permanent magnet ring having a plurality of alternating magnetic pole faces pointing in the direction of the rotational axis; wherein the stator is provisioned by a printed circuit board and a magnetically permeable stator core ring, the PCB being disposed transverse to the rotational axis and having a first face proximal to the magnetic air gap and a second, opposing, face distal to the magnetic air gap, the stator core ring being mounted immediately adjacent to the second PCB face and configured to be coextensive with the permanent magnet ring; whereby a continual magnetic attractive force is directed along the rotational axis between the permanent magnet ring and the stator core ring, the magnitude of the continual magnetic attractive force being such that the impeller remains seated and bears against the pad bearing surface at the maximal operating rotational velocity of the impeller and at the maximal operating pressure generated by the impeller.

16. An electric pump according to claim 15 wherein the pad bearing surface is the sole transversely orientated surface against which the impeller hub bears and the shaft is the sole axially orientated portion against which the impeller hub bears.

17. An electric pump according to claim 16, including a bushing having a longitudinal portion configured to sit between the shaft and the impeller hub and a transverse portion configured to sit between the pad bearing surface and a transverse portion of the impeller hub.

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