PUMP

Abstract

 A pump 1 comprises a motor 2; an impeller 3 configured to be rotated by the motor 2 to flow fluid; and a pump case 4 for forming a pump room 11 in which the impeller 3 being accommodated. The impeller 3 is a closed-type impeller having a front shroud 33, a rear shroud 32 and a plurality of blades 31 therebetween. The impeller 3 is arranged so that the front shroud 33 faces to the pump case 4 with an interspace 6 therebetween in the axial direction Ax of the impeller 3. The pump 1 is characterized by further comprising a flow suppressing means 7 configured to suppress the flow of the fluid in the radial direction Rad of the impeller 3in the interspace 6.

Description

TECHNICAL FIELD

[0001] The invention relates generally to a pump, and more particularly, to a pump configured to suppress the generation of the reflux in a pump-room.

BACKGROUND ART

[0002] In the past, it has been known a centrifugal pump including an impeller for flowing fluid, a pump room for accommodating the impeller, and a motor for rotating the impeller. The centrifugal pump is configured to flow the fluid by the centrifugal force due to rotation of the impeller. For the impeller of such a centrifugal pump, there has been known a flow passage-parting type impeller (closed-type impeller) and a flow passage-opened type impeller (open-type impeller). The closed-type impeller includes a front shroud, a rear shroud, and impeller blades therebetween. Thereby, the closed-type impeller is configured to part the flow passage from the pump room. On the other hand, the open-type impeller is not provided with the front shroud, and therefore the flow passage is not parted in the pump room.

[0003] The closed-type impeller is provided at its rotation center with an inlet part (inlet opening) for sucking the fluid into the flow passage. When the impeller is rotated, the fluid is flown in the flow passage through the inlet part, flown toward the outer circumference side of the impeller due to the centrifugal force, and discharged to the space of the pump room outer than the impeller. Therefore, in the pump room, space near the inlet part is to have lower pressure than the space outer than the impeller. As a result, a part of the fluid will flow from the outer space than the impeller toward the space near the inlet part through the interspace between the front shroud and a pump case (herein, the pump case forming the pump room). Such the phenomenon is called as reflux.

[0004] JP2008-240656A (thereafter, referred to as patent document 1) discloses a pump provided with a pressing-back means composed of such as blade-shaped ribs or grooves extending from the center to the outer circumference side of the front shroud. The pressing-back means is provided at the surface of the front shroud facing to the pump case. In this pump, the pressing-back means puts the pressure directing toward the outer circumference side of the impeller on the fluid during rotation of the impeller. The fluid flown into the above mentioned interspace is pressed-back to the outer circumference side, thereby the pump prevents the reverse flow by the reflux.

[0005] In the prior pump of patent document 1, the impeller with the pressing-back means not only acts as a pump-impeller for making the fluid in the flow passage flow by the impeller blades, but also performs the work of pressing back the fluid in the interspace toward outer circumference side of the impeller by the pressing-back means. Therefore, the load of the impeller of the prior pump is increased because of the additional work of pressing-back the fluid. Besides, in the prior pump, a stream along with the radial direction of the impeller (toward inner circumference side or outer circumference side) is generated in the above mentioned interspace. As a result, pumping performance and pumping efficiency of the prior pump has been lowered.

DISCLOSURE OF THE INVENTION

[0006] The present invention is developed in view of the above problem, it is an object of the present invention to provide a pump which can suppress the generation of radial directional stream (such as reflux) in the interspace between a pump case and a front shroud so as to reduce the loss of pumping performance and pumping efficiency.

[0007] In order to resolve the above problem, a pump of the present invention comprises: a motor; an impeller configured to be rotated by said motor to flow fluid; and a pump case for forming a pump room in which said impeller being accommodated, wherein said impeller is a closed-type impeller having a front shroud, a rear shroud and a plurality of blades therebetween, and wherein said impeller is arranged so that said front shroud faces to said pump case with an interspace therebetween in the axial direction of said impeller, characterized in that said pump further comprises a flow suppressing means configured to suppress the flow of the fluid in the radial direction of said impeller in said interspace.

[0008] In this pump, it is preferable that said flow suppressing means is dynamic pressure grooves for generating dynamic pressure in said interspace between said impeller and said pump case, said dynamic pressure grooves being provided either at a surface of said front shroud facing to said pump case or at a surface of said pump case facing to said front shroud.

[0009] In this pump, it is preferable that said flow suppressing means is dimples for generating turbulent flow in said interspace between said impeller and said pump case, said dimples being provided at at least one of a surface of said front shroud facing to said pump case and a surface of said pump case facing to said front shroud.

[0010] In this pump, it is preferable that said flow suppressing means is a coating film for repelling said fluid, said coating film being provided at at least one of a surface of said front shroud facing to said pump case and a surface of said pump case facing to said front shroud.

[0011] In this pump, it is preferable that said flow suppressing means is grooves provided at a surface of said pump case facing to said front shroud, said grooves being arranged side by side in the circumferential direction around the rotation axis of said impeller.

[0012] In this pump, it is preferable that said dynamic pressure grooves are arranged to form a Herringbone shape.

[0013] By virtue of the above configuration, it can suppress the generation of radial directional stream in the interspace, such as reflux, between the pump case and the front shroud. Besides, it can reduce the loss of pumping performance and pumping efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Preferred embodiments of the invention will now be described in further details. Other features and advantages of the present invention will become better understood with regard to the following detailed description and accompanying drawings where:

FIG. 1 is an axis directional-section view of a pump of an embodiment;

FIG. 2, composed of FIG. 2A and 2B, is an external view of the pump of the embodiment, FIG. 2A is a planar view thereof, and FIG. 2B is a side view thereof;

FIG. 3, composed of FIG. 3A and 3B, is an explanation view of a flow suppressing means of the embodiment, FIG. 3A is a planar view of a pump case seeing from a fluid space of a pump room, and FIG. 3B is an enlarged view of A1 region in FIG. 1;

FIG. 4, composed of FIG. 4A and 4B, is an explanation view of a flow suppressing means of another embodiment, FIG. 4A is a planar view of a pump case seeing from a fluid space of a pump room, and FIG. 4B is an enlarged view of a region corresponding to A1 region in FIG. 1;

FIG. 5, composed of FIG. 5A and 5B, is an explanation view of a flow suppressing means of further another embodiment, FIG. 5A is an axis directional-section view of a pump, and FIG. 5B is an enlarged view of A2 region in FIG. 5A; and

FIG. 6 is a schematic planar view of an impeller of the embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] Embodiments of the present invention is described below with reference to drawings.

[0016] As shown in FIG. 1, a pump 1 of an embodiment includes a motor 2 as a driving source, an impeller 3 driven by the motor 2, and a housing 8. The housing 8 is composed of a pump case 4 and a body case 14. The pump 1 further includes a connection part 13 (refer to FIG. 2B) for electrically connecting the motor 2 with an outside power supply. The pump 1 is partitioned into a pump room 11 for flowing liquid and a motor section 12 isolated from the liquid in the pump room 11. The pump room 11 is formed by a separating plate 5 for dividing the pump room 11 from the motor section 12 and the pump case 4. The pump case 4 composes an outer envelope of the pump 1 at the pump room 11 side. That is, fluid space for flowing the fluid is formed thereinside by joining the pump case 4 to the separating plate 5. The impeller 3 is disposed inside the fluid space. As shown in FIGS. 1 and 2, the pump case 4 is provided with an inlet part (intake) 41 for sacking outer fluid into the pump room 11, and a discharging part (discharging opening) 42 for discharging the fluid in the pump room 11 toward outside. Note that, in the following explanation, the fluid is assumed to be water, but the fluid is not limited to water. Besides, in the present embodiment, the word of "facing (or face)" means the confronting condition in which specified surfaces of two objects are arranged face-to-face with each other, unless particularly defined.

[0017] As shown in FIG. 1, the motor 2 includes an annular stator 21 having a coil 221, a control part 22 configured to control the motor-drive, a cylindrical-shaped rotor 23 having a plurality of magnets 24, and a substantially column-shaped supporting shaft 26 for rotatably supporting the rotor 23. The stator 21 and the control part 22 are arranged in the motor section 12. The rotor 23 and the supporting shaft 26 are arranged in the pump room 11.

[0018] The control part 22 controls the motor-drive by controlling the current flowing through the coil 211 of the stator 21. Magnetic field is generated by electrifying the coil 211 of the stator 21 by the control part 22, and the rotor 23 rotates around the supporting shaft 26. The control part 22 and the stator 21 are fixed to the separating plate 5 by molding material filling in the motor section 12. That is, the body case 14 is formed of the molding material. The body case 14 protects the constituent elements in the motor section 12, such as the stator 21 and the control part 22, from exterior moisture or dust. The body case 14 composes an outer envelope of the pump 1 at the motor section 12 side, as shown in FIG. 2. Additionally, the motor section 12 is provided with the connection part 13 exposing to its appearance. The connection part 13 is configured to electrically connect the control part 22 with a converter (not shown) connected with the external power supply. The electric power is supplied from the external power supply to the control part 22 via the converter.

[0019] As shown in FIG. 1, the rotor 23 and the supporting shaft 26 are arranged substantially concentric with the stator 21 at inner side of the stator 21. The supporting shaft 26 is arranged at inner side of the rotor 23. In the present embodiment, the supporting shaft 26 is rotational center of the rotor 23. For simplicity, axial direction of the supporting shaft 26 is described as "axial direction Ax", the radial direction of the supporting shaft 26 is described as "radial direction Rad", the circumferential direction around the above mentioned rotation center is described as "circumferential direction Ci", and they are used as the criteria of directions in the following description. Also, in the present description, "planar view" means seeing in the axial direction Ax.

[0020] The cylindrical-shaped rotor 23 has a plurality of the magnets 24 arranged along the circumferential direction Ci. The outer peripheral surface of the rotor 23 is covered by a cylindrical-shaped cover 25. The cover 25 has higher stiffness than the magnet 24. The cover 25 is formed of non-magnetic rigid member such as stainless steel. The cover 25 protects the rotor 23 from attrition caused by friction between the rotor 23 and foreign substance (such as iron powder) being flowed in the pump room 11 together with the fluid during the rotation of the rotor 23. The rotor 23 is provided integrally with the impeller 3 at one end thereof in the axial direction Ax. The impeller 3 is formed substantially concentric with the rotor 23. The rotor 23 rotates together with the impeller 3.

[0021] The impeller 3 includes a rear shroud (rear plate) 32, a front shroud (front plate) 33, and a plurality of blades 31 (refer to FIGS. 1, 6).

[0022] The rear shroud 32 is formed in annular-shape in the planar view. The rear shroud 32 spreads outwardly in the radial direction Rad from the abovementioned one end of the rotor 23. The rear shroud 32 is formed substantially concentric with the rotor 23.

[0023] The front shroud 33 is formed in circular-shape having an opening at its center (annular-shape) in the planar view. The front shroud 33 is positioned to face to the rear shroud 32. The front shroud 33 is positioned apart from the rear shroud 32 by a predetermined distance in the axial direction Ax. The front shroud 33 is composed of a substantially annular-shaped flat plate part 34a, a substantially annular-shaped incline part 34b, and a step part 34c. The flat plate part 34a spreads in a substantially perpendicular direction to the axial direction Ax. The incline part 34b spreads inwardly from the inner circumference end of the flat plate part 34a. The step part 34c is extendedly provided from the inner circumference of the incline part 34b. The surface (lower side in FIG. 1) of the flat plate part 34a facing to the rear shroud 32 is slightly inclined so as to come closer towards outer circumference. The other surface (upper side in FIG. 1) of the flat plate part 34a is substantially perpendicular to the axial direction Ax. The incline part 34b is inclined so as to be away from the rear shroud 32 towards the inner circumference, and has planar surface. The step part 34c is formed so that the planar surface thereof (lower side in FIG. 1) facing to the rear shroud 32 is inclined in substantially same tilt with that of the incline part 34b. The other surface (upper side in FIG. 1) of the step part 34c is substantially perpendicular to the axial direction Ax. There is formed a step between the step part 34c and the incline part 34b. As shown in FIG. 1, the distance between the front shroud 33 and the rear shroud 32 is gradually narrow towards radially outward of the impeller 3. Also, the distance between the inner circumference of the front shroud 33 and the pump case 4 is narrower than that between the outer circumference of the front shroud 33 and the pump case 4. Herein, the step part 34c is provided with an inlet opening part 35 at the inner circumference end thereof. The inlet opening part 35 is formed in a cylindrical shape. The inlet opening part 35 is projects from the step part 34c in the direction away from the rear shroud 32 along the axial direction Ax.

[0024] The blades 31 are provided in a facing space between the front shroud 33 and the rear shroud 32 (thereafter, referred to as "space between the shrouds"). The blade 31 is formed in a wall-shape radially extending in the radial direction Rad. A plurality of the blades 31 are arranged in substantially equal interval in the circumferential direction Ci. The blades 31 separate the space between the shrouds into a plurality of spaces (as a fan-shape) in the circumferential direction Ci. Each of the blades 31 is preferably inclined in the circumferential direction Ci. As shown in FIG. 6, each of the blades 31 may be formed in a curved radial fashion extending from the center to the outer circumference of the impeller 3.

[0025] In the present embodiment, the impeller 3 includes the space between the shrouds as the flow passage which is divided in plural spaces by the blades 31. The inlet opening part 35 side, which is inner circumference side of the front shroud 33, is the upstream side of this flow passage. Also, the outer circumference side of the space between the shrouds is the downstream side of this flow passage. The impeller 3 of the present embodiment is so-called closed-type (flow passage-parting type) impeller in which the flow passage is parted from the pump room 11 by the front shroud 33. When the impeller 3 rotates together with the rotor 23, the fluid is flown from the inner circumference side to the outer circumference side of the impeller 3 through the flow passage due to centrifugal force. Also, the fluid is flown in the circumferential direction Ci by the turning force. That is, the fluid is pushed out toward the outer circumference side of the impeller 3 by the blades 31 during the rotation of the impeller 3.

[0026] The separating plate 5 includes a cylindrical part 51, a bottom part 52 closing one end of the cylindrical part 51, a flange part 54 spreading outwardly from the other end (an end which is not closed by the bottom part 52) of the cylindrical part 51, and a covering member 55 for protecting the inner surface of the cylindrical part 51.

[0027] Seeing in the radial direction Rad, the cylindrical part 51 is positioned between the rotor 23 and the stator 21. The bottom part 52 is positioned between the rotor 23 and the control part 22. As a result, the inside space of the cylindrical part 51 of the separating plate 5 forms a rotor-accommodating space of the pump room 11 for accommodating the rotor 23. The outside space of the separating plate 5 forms the motor section 12. The bottom part 52 is provided with a first supporting part 53 at the rotor-accommodating space side surface facing with the cylindrical part 51. A first end 26a of the supporting shaft 26 is fixed to the first supporting part 53.

[0028] A first surface 54a of the flange part 54 faces to an end (upper end in FIG. 1) of the stator 21 in the axial direction Ax. The first surface 54a composes the motor section 12 side surface. A second surface 54b of the flange part 54, which being the other side, faces to the rear shroud 32 of the impeller 3. The second surface 54b composes the pump room 11 side surface. Also, the outer circumference of the second surface 54b of the flange part 54 is contacted with the pump case 4 at outward than the pump room 11 in a manner a sealing member (such as O-ring) 56 being disposed therebetween. Therefore, the contacted portion between the flange part 54 and the pump case 4 is in a water-tight condition by the compressed sealing member 56. The contacted portion prevents the fluid in the pump room 11 from being leaked outward.

[0029] The covering member 55 covers the second surface 54b exposed in the pump room 11, outer circumferential part of the bottom part 52, and the whole of the inner surface of the cylindrical part 51. The covering member 55 is formed of non-magnetic rigid member such as stainless steel. The covering member 55 protects the separating plate 5 from attrition caused by foreign substance (such as iron powder) being flowed in the pump room 11 together with the fluid.

[0030] The pump case 4 is mainly composed of a roof part 44 and a sidewall part 45. The roof part 44 is formed in substantially circular shape in the planar view and facing to the second surface 54b. The sidewall part 45 is provided extendedly in the axial direction Ax from the outer circumference end of the roof part 44. The extended end (lower end in FIG. 1) of the sidewall part 45 contacts with the second surface 54b. One surface (upper side in FIG. 1) of the roof part 44 composes a pump room 11 side outer envelope of the pump 1. The other surface 44a (lower side in FIG. 1) of the roof part 44 composes the inner surface of the pump room 11. The surface 44a of the roof part 44 composing the abovementioned inner surface spreads in the substantially perpendicular direction to the axial direction Ax, and forms a planar surface. This surface 44a just faces to a surface 33a of the front shroud 33 (upper surface in FIG.1 of the flat plate part 34a, incline part 34b, and the step part 34c). In the following, the surface 44a of the roof part 44 is referred to as facing surface (first facing surface) 44a, and the surface 33a of the front shroud 33 is referred to as facing surface (second facing surface) 33a. That is, the pump case 4 has the first facing surface 44a facing to the front shroud 33 of the impeller 3. The front shroud 33 of the impeller 3 has the second facing surface 33a facing to the pump case 4.

[0031] The outer circumference part of the roof part 44 is provided with a drainage hole 43 for draining off the residual fluid in the pump room 11. The residual fluid can be drawn off through the drainage hole 43 when the pump 1 is not driven. The circular-shaped roof part 44 is provided with the tubular-shaped inlet part 41 and a second supporting part 46 at the center thereof. The second supporting part 46 is supported by a plurality of supporting ribs 47. The second supporting part 46 is fixed to a second end 26b of the supporting shaft 26. The supporting shaft 26 is positioned and supported in the pump room 11 by the first supporting part 53 and the second supporting part 46.

[0032] As shown in FIGS 1 and 2, the inlet part 41 is substantially composed of a cylindrical-shaped inlet cylinder 41a. The upper end (upstream end) of the inlet cylinder 41a protrudes outward from the roof part 44. The lower end (downstream end) of the inlet cylinder 41a extends from the roof part 44 into the pump room 11. The inlet opening part 35 is arranged concentrically around the lower end of the inlet cylinder 41 a so that the inlet opening part 35 can freely rotate. The inner space of the inlet cylinder 41 a is communicated with the flow passage of the impeller 3 via the inlet opening part 35. The upper end of the inlet cylinder 41a will be connected to be communicated with an external first pipe (not shown). The fluid flown into the inlet cylinder 41a from outside drifts into the abovementioned space between the shrouds flowing through the intervals between the supporting ribs 47.

[0033] As shown in FIGS 1 and 2, the sidewall part 45 is provided with the discharging part 42. The discharging part 42 is substantially composed of a cylindrical-shaped discharging tube 42a. The discharging tube 42a protrudes from the sidewall part 45 in the inclined direction between the radial direction Rad and the circumferential direction Ci. The upstream end of the discharging tube 42a opens in the pump room 11. The downstream end of the discharging tube 42a protrudes outward the sidewall part 45. The downstream end of the discharging tube 42a will be connected to be communicated with an external second pipe (not shown).

[0034] When the impeller 3 is rotated, the present pump 1 sucks the fluid from the first pipe into the flow passage of the impeller 3 through the inlet cylinder 41a, flows the fluid in the flow passage into the pump room 11, and discharges the fluid in the pump room 11 to the second pipe through the discharging tube 42a.

[0035] Herein, in the pump 1 having the closed-type impeller 3, the interspace 6 in the pump room 11 composed between the front shroud 33 and the roof part 44 might act as a passage for reflux during the rotation of the impeller 3. In this case, the reflux (reverse flow) is generated in the interspace 6. In order to overcome this problem, the present pump 1 is further provided with a flow suppressing means 7, as shown in FIG. 1. The flow suppressing means 7 is configured to suppress the flow in the radial direction Rad (radial directional flow; such as reflux) in the interspace 6.

[0036] As shown in FIG.3, the flow suppressing means 7 of present embodiment is composed of dynamic pressure grooves (dynamic pressure generating grooves) 71. The dynamic pressure grooves 71 are provided at the facing surface 44a of the roof part 44 (which is the surface of the pump case 4 facing to the front shroud 33). Note that, the drainage hole 43 is not shown in FIG. 3A.

[0037] The dynamic pressure groove 71 is formed in a v-shape in the planar view. The tip (intersection of two-sides) of the v-shape of the groove 71 is convex in the circumferential direction Ci. In detail, the tip of the v-shape of the groove 71 is convex into the rotation direction Tr of the impeller 3 (refer to FIG. 3A). A plurality of the dynamic pressure grooves 71 are provided at substantially whole circumference of the facing surface 44a of the roof part 44. The dynamic pressure grooves 71 are arranged in a substantially equal interval along the circumferential direction Ci. The facing surface 44a is provided with two lines of the plurality of the dynamic pressure grooves 71 along the circumferential direction Ci. In the facing surface 44a, one line of the dynamic pressure grooves 71 is provided at the facing position to the flat plate part 34a of the front shroud 33. In the facing surface 44a, the other line of the dynamic pressure grooves 71 is provided at the position outer than the outer circumference of the front shroud 33. In other words, the flow suppressing means 7 is composed of a dynamic pressure groove structure having a plurality of the dynamic pressure grooves 71 arranged along the circumferential direction Ci. Particularly in the present embodiment, the flow suppressing means 7 is composed of a plurality of the dynamic pressure groove structures (first dynamic pressure groove structure 71A and second dynamic pressure groove structure 71 B) arranged side by side in the radial direction of the impeller 3. Each of the dynamic pressure groove structures (71A, 71B) has a plurality of the dynamic pressure grooves 71 arranged along the circumferential direction Ci. The radius of the first dynamic pressure groove structure 71A is smaller than that of the outer circumferential end of the front shroud 33. The radius of the second dynamic pressure groove structure 71B is larger than that of the outer circumferential end of the front shroud 33.

[0038] By virtue of providing the dynamic pressure grooves 71 (71A, 71B), dynamic pressure is generated by the dynamic pressure grooves 71 in the interspace 6 along the circumferential direction Ci during the rotation of the impeller 3. As a result, it seems that a wall (virtual wall) preventing the flow in the radial direction Rad is generated along the whole circumference of the interspace 6. Because the virtual wall is generated in the interspace 6, the fluid is hard to flow in the radial direction Rad. Therefore, the loss of the pumping performance and pumping efficiency caused by the flow in the radial direction Rad (such as reflux) can be reduced. As shown in FIG. 3B, in the facing surface 44a, one line of the dynamic pressure grooves 71 (first dynamic pressure groove structure 71A) is provided at the facing position to the flat plate part 34a, and the other line of the dynamic pressure grooves 71 (second dynamic pressure groove structure 71B) is provided at outward than the circumference of the front shroud 33. As a result, the (wall of) dynamic pressure along the circumferential direction Ci can be generated near the circumferential end of the front shroud 33 in the interspace 6. That is, the wall can be generated at the circumferential end (upstream end of the reflux passage) or near the circumferential end (the position in the reflux passage near to the circumferential end in downstream side). In other words, the wall can be generated at the space between the neighbor of the outer circumference end of the front shroud 33 and the pump case 4. Therefore, the flow of the fluid in the radial direction Rad is suppressed in the interspace 6. Besides, because the reflux is suppressed at the outer circumference end side of the interspace 6, it can prevents foreign substances (such as iron powders) from being flowed in the space between the outer surface of the inlet opening part 35 and the roof part 44 (this position being narrowest in the interspace 6). As a result, it can protect the inlet opening part 35 and so on from abrasion caused by friction by the foreign substance.

[0039] In the present embodiment, the dynamic pressure grooves 71 are provided so as to form a Herringbone shape. The shape of the dynamic pressure groove 71 is not limited in the v-shape, and it may be u-shape and so on. The dynamic pressure grooves 71 may be provided at the facing surface 33a of the front shroud 33 as substitute for providing at the roof part 44. In this configuration, the dynamic pressure grooves 71 may be provided at whole of the facing surface 33a (that is, at the flat plate part 34a, the incline part 34b and the step part 34c). The dynamic pressure grooves 71 may be provided only at the flat plate part 34a. The dynamic pressure grooves 71 may be provided only at the flat plate part 34a and the incline part 34b. The number of the line of the dynamic pressure grooves 71, where the dynamic pressure grooves 71 being arranged along the circumferential direction Ci, is not limited two, and may be three or more. The dynamic pressure grooves 71 may be provided only in one line at the facing surface 44a of the pump case 4 in a facing position to the flat plate part 34a. The dynamic pressure grooves 71 may be further provided either at the outer surface of the inlet opening part 35 or a surface region of the roof part 44 facing to the outer surface of the inlet opening part 35, in addition to at the facing surface 44a or 33a.

[0040] As shown in FIG. 4, the flow suppressing means 7 of the pump of another embodiment is dimples (dimple grooves) 72 provided at the facing surface 44a of the roof part 44. In this embodiment, the flow of the fluid in the radial direction Rad in the interspace 6 is also prevented. In the following, duplicate explanation with the above mentioned embodiment provided with the dynamic pressure groove 71 is omitted. Note that, the drainage hole 43 is not shown in FIG. 4A.

[0041] The dimple (dimple groove) 72 is formed in a hemispherical concave groove (recess). A plurality of the dimples 72 are provided at whole circumference of the facing surface 44a of the roof part 44 along the circumferential direction Ci. The dimples 72 are provided on the facing surface 44a at substantially whole area facing to the flat plate part 34a and area outward thereof. The dimple 72 is formed so as to be adjacent to another dimple 72 in the circumferential direction Ci and the radial direction Rad. As shown in FIG. 4A, the plurality of the dimples 72 are arranged at the lattice points of two-dimensional hexagonal lattice. Besides, the plurality of the dimples 72 are arranged at the facing surface 44a of the pump case 4 in an annual manner.

[0042] In the present embodiment, any line along the radial direction Rad connecting the center and the outer circumference of the facing surface 44a intersects with at least one dimples 72 (at the circumferential end of the interspace 6 or downstream neighbor thereof). Because dimples 72 are provided whole circumference of the interspace 6, it generates turbulent flow at substantially whole of the circumference of the interspace 6 and downstream neighbor thereof during the rotation of the impeller 3. The generated turbulent flow acts as a wall (virtual wall) to prevent the fluid from flowing in the radial direction Rad. As a result, the fluid is hard to flow in the radial direction Rad in the interspace 6. Therefore, the loss of the pumping performance and pumping efficiency caused by the flow in the radial direction Rad (such as reflux) can be reduced. Besides, because the reflux is suppressed at the outer circumference end side of the interspace 6, it can prevents foreign substances (such as iron powders) from being flowed in the space between the outer surface of the inlet opening part 35 and the roof part 44 (this position being narrowest in the interspace 6). As a result, it can protect the inlet opening part 35 and so on from abrasion caused by friction by the foreign substance.

[0043] The dimples 72 may be provided at the facing surface 33a of the front shroud 33 as substitute for providing at the roof part 44. The dimples 72 may be provided both at the facing surface 44a of the roof part 44 and the facing surface 33a of the front shroud 33. In case of providing the dimples 72 at both the facing surfaces 44a and 33a, it is preferred that dimples 72 at the facing surface 33a are arranged so as to face to the dimple 72 of the facing surface 44a in the axial direction Ax. The dimples 72 may be provided at whole of the facing surface 44a and/or whole of the facing surface 33a. The dimples 72 may be provided only at the flat plate part 34a and/or the facing region of the roof part 44 to the flat plate part 34a. The dimples 72 may be provided only at both the flat plate part 34a and the incline part 34b, and/or the facing region of the roof part 44 to the flat plate part 34a and incline part 34b. The dimples 72 may be further provided at the outer surface of the inlet opening part 35 and/or a surface region of the roof part 44 facing to this outer surface.

[0044] As shown in FIG. 5, the flow suppressing means 7 of the pump of further another embodiment is coating film 73 provided both at the facing surface 44a and 33a. In this embodiment, the flow of the fluid in the radial direction Rad in the interspace 6 is also prevented. In the following, duplicate explanation with the above mentioned embodiment provided with the dynamic pressure groove 71 is omitted.

[0045] The coating film 73 is formed on substantially whole of the facing surface 33a of the front shroud 33, outer surface and the top end in the axial direction Ax of the inlet opening part 35, substantially whole of the inner surface of the roof part 44 (the facing surface 44a and the surface region facing to the inlet opening part 35), and outer surface of the downstream end of the inlet cylinder 41a. In case that the fluid is water, the coating film 73 is formed of water repellent material having higher hydrophobic character than the material of the pump case 4 and the front shroud 33. The coating film 73 is formed by coating the above mentioned surfaces by the water repellent material. The water repellent material is preferred to be Fluorine-based water repellent material or silicone-based water repellent material.

[0046] In the present embodiment, because the facing surfaces 44a and 33a are provided with the coating, capillary action becomes not likely to occur (in other words, the fluid is not likely to wet to the facing surface 44a, 33a) in the interspace 6. Therefore, the fluid is hard to flow in the interspace 6 because of the surface tension. That is, if the wettability of the fluid to the coating film 73 is sufficiently low, the fluid may form a sphere-shape by the surface tension. The sphere-shaped fluid 8 seems to act as a "wall" and prevent the flow of the fluid in the radial direction Rad. As a result, the fluid is hard to flow in the radial direction Rad in the interspace 6. Therefore, the loss of the pumping performance and pumping efficiency caused by the flow in the radial direction Rad (such as reflux) can be reduced. Besides, because the reflux is suppressed at the outer circumference end side of the interspace 6, it can prevents foreign substances (such as iron powders) from being flowed in the space between the outer surface of the inlet opening part 35 and the roof part 44 (this position being narrowest in the interspace 6). As a result, it can protect the inlet opening part 35 and so on from abrasion caused by friction by the foreign substance.

[0047] The coating film 73 may be provided only at the facing surfaces 44a and 33a. The coating film 73 may be provided only at either roof part 44 or the front shroud 33. The coating film 73 may be provided only at either the facing surface 44a or the facing surface 33a. In the facing surfaces 44a, 33a, the coating film 73 may be provided only at the outer circumferential end of the interspace 6 or neighbor thereof (that is, upstream end of the reflux passage), such as at the flat plate part 34a or facing region thereto. For the case of oil pump, the coating film 73 is formed by coating oil repellent material having higher lipophobic character than the material of the pump case 4 and front shroud 33.

[0048] The flow suppressing means 7 may be the dynamic pressure grooves 71 or the dimples 72, and the coaling film 73 (water repellent coating or oil repellent coating). In this configuration, the dynamic pressure grooves 71 or the dimples 72 may be provided at the circumference of the interspace 6 or neighbor thereof, and coating film 73 may be provided at inner side than the dynamic pressure grooves 71 or the dimples 72.

[0049] As described in the embodiment and the another embodiment, the flow suppressing means 7 is preferably a plurality of grooves (71, 72) provided at the surface 44a of the pump case 4 facing to the front shroud 33 or at the surface 33a of the front shroud 33 facing to the pump case 4. Preferably, these grooves are arranged side by side along the circumferential direction Ci around the rotation axis (that is, around the supporting shaft 26 of the motor 2) of the impeller 3. These grooves provided at the facing surface 44a of the pump case 4 is preferably face to the front shroud 33 (in other words, they are preferably provided inner than the outer circumference end of the front shroud 33). As a result, the fluid is hard to flow in the inner side of the flow suppressing means 7 in the interspace 6.

[0050] Although the present invention has been described with reference to certain preferred embodiments, numerous modifications and variations can be made by those skilled in the art without departing from the true spirit and scope of this invention, namely claims.

Claims

1. A pump comprising:

a motor (2);

an impeller (3) configured to be rotated by said motor (2) to flow fluid; and

a pump case (4) for forming a pump room (11) in which said impeller (3) being accommodated,

wherein said impeller (3) is a closed-type impeller having a front shroud (33), a rear shroud (32) and a plurality of blades (31) therebetween, and

wherein said impeller (3) is arranged so that said front shroud (33) faces to said pump case (4) with an interspace (6) therebetween in the axial direction (Ax) of said impeller (3),

characterized in that

said pump (1) further comprises a flow suppressing means (7) configured to suppress the flow of the fluid in the radial direction (Rad) of said impeller (3) in said interspace (6).

2. The pump as set forth in claim 1,
wherein said flow suppressing means (7) is dynamic pressure grooves (71) for generating dynamic pressure in said interspace (6), said dynamic pressure grooves (71) being provided either at a surface (33a) of said front shroud (33) facing to said pump case (4) or at a surface (44a) of said pump case (4) facing to said front shroud (33).

3. The pump as set forth in claim 1,
wherein said flow suppressing means (7) is dimples (72) for generating turbulent flow in said interspace (6), said dimples (72) being provided at at least one of a surface (33a) of said front shroud (33) facing to said pump case (4) and a surface (44a) of said pump case (4) facing to said front shroud (33).

4. The pump as set forth in claim 1,
wherein said flow suppressing means (7) is coating film (73) for repelling said fluid, said coating film (73) being provided at at least one of a surface (33a) of said front shroud (33) facing to said pump case (4) and a surface (44a) of said pump case (4) facing to said front shroud (33).

5. The pump as set forth in any one claims of 1 to 3,
wherein said flow suppressing means (7) is grooves (71 or 72) provided at a surface (44a) of said pump case (4) facing to said front shroud (33), said grooves (71, 72) being arranged side by side in the circumferential direction (Ci) around the rotation axis of said impeller (3).

6. The pump as set forth in claim 2,
wherein said dynamic pressure grooves (71) are arranged to form a Herringbone shape.

Drawing