Impeller and magnetic levitation pump

Abstract

To provide a technique for producing an impeller in which a positional resilience force in an axial direction is applied at a low cost.SOLUTION: An impeller of the present disclosure includes: a cylindrical impeller body in which a plurality of balance holes are formed to penetrate in an axial direction; a plurality of blades which are provided at an interval therebetween in a circumferential direction on an end face on one side of the impeller body in an axial direction; and a cover plate which are provided on one side of the plurality of blades in an axial direction and in which an inlet of a delivery fluid is formed on a radial inner side than the plurality of blades. A rotation about an axial line allows the delivery fluid flown from the inlet to flow out to a radial outer side from a gap between blades adjacent in a circumferential direction. The end face of the impeller body has: a plurality of flow path faces positioned between the blades adjacent in the circumferential direction; and a contact face positioned on a radial inner side than the plurality of blades so as to be respectively connected to the plurality of flow path faces, the contact face guiding the delivery fluid flown from the inlet in a contacting manner to each of the flow path faces. An opening on one side of each of the balance holes in an axial direction is positioned at least on one of inside and outside of a range of the inlet when the impeller is viewed from one side in an axial direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an impeller and a magnetic levitation pump. [Background technology]

[0002] A magnetically levitated pump rotates an impeller by magnetically levitating it relative to a housing and supporting it without contact. If the impeller moves in the axial direction while rotating, it may come into contact with the housing and be damaged. For this reason, a magnetically levitated pump impeller needs a mechanism that applies a position restoring force to push the impeller back to the other axial direction when it moves to one side in the axial direction (see, for example, Figure 2 of Patent Document 1).

[0003] The impeller of the magnetic levitation pump described in Patent Document 1 includes an impeller body having a plurality of relief bores, a disk-shaped partition element, and a plurality of vanes fixed to the outer periphery of the partition element. Each vane has a first vane above the partition element and a second vane below the partition element.

[0004] The first blade generates a main flow of fluid above the partition plate, flowing from the inlet to the outlet of the housing due to centrifugal force caused by the rotation of the impeller. This main flow acts on the impeller, pulling it axially upward. The second blade generates a circulating flow below the partition plate, in which the transferred fluid flows from top to bottom on the radially outer side of the impeller body, then flows from bottom to top on the radially inner side of the impeller body (balance hole). This circulating flow acts on the impeller, pulling it axially downward.

[0005] During operation of a magnetic levitation pump, the load on the upper axial direction and the reverse load on the lower axial direction are balanced, thereby maintaining the impeller in a predetermined axial position. If the impeller moves axially downward from this state due to an external force, the flow rate of the circulating flow decreases, and the reverse load on the lower axial direction becomes smaller. As a result, the load on the upper axial direction acts predominantly as a position restoring force on the impeller. Conversely, if the impeller moves axially upward due to an external force, the flow rate of the circulating flow increases, and the reverse load on the lower axial direction becomes larger. As a result, the reverse load acts predominantly as a position restoring force on the impeller. These position restoring forces limit movement of the impeller in both axial directions from the predetermined position. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 9,115,725 Summary of the Invention [Problem to be solved by the invention]

[0007] The impeller of the magnetic levitation pump described above is equipped with a partition plate that separates the main flow from the circulating flow and applies an axial restoring force to the impeller in addition to the impeller body and blades, which increases the number of parts and increases the manufacturing cost of the impeller.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to provide a technique that enables an impeller on which an axial position restoring force acts to be manufactured at low cost. [Means for solving the problem]

[0009] (1) The present disclosure provides an impeller comprising: a cylindrical impeller body formed with a plurality of balance holes passing therethrough in the axial direction; a plurality of blades spaced apart circumferentially on an end face on one axial side of the impeller body; and a cover plate provided on the one axial side of the plurality of blades, with a transfer fluid inlet formed in the center, the impeller rotating around an axis to cause the transfer fluid flowing in from the inlet to flow radially outward from between the circumferentially adjacent blades, the end face of the impeller body having a plurality of flow path surfaces located between the circumferentially adjacent blades, and abutment surfaces located radially inward of the plurality of blades so as to be connected to each of the plurality of flow path surfaces, the abutment surfaces for contacting the transfer fluid flowing in from the inlet and guiding it to each of the flow path surfaces, and the opening on the one axial side of each of the balance holes being located at least either within or outside the range of the inlet when the impeller is viewed from the one axial side.

[0010] As a result of extensive research, the inventors of the present application discovered that an axial position restoring force acts on the impeller even if the impeller does not have a partition plate, and based on this finding, they completed the impeller described above in (1).

[0011] That is, according to the impeller disclosed herein, when the impeller body is rotated, the transfer fluid flowing in through the inlet of the cover plate strikes the abutment surface on one axial side of the impeller body, generating a main flow that flows out radially outward along multiple flow path surfaces connected to the abutment surface. This main flow applies a load that pulls the impeller toward one axial side. Furthermore, a portion of the transfer fluid that flows out radially outward of the impeller flows around to the other axial side of the impeller body, passes through each balance hole, and generates a circulating flow that flows toward the one axial side of the impeller body. This circulating flow applies a reverse load that pulls the impeller toward the other axial side. Therefore, even in an impeller that does not use a conventional partition plate, one of the load and the reverse load acts on the impeller as the axial position restoring force, making it possible to manufacture an impeller that is subject to an axial position restoring force at low cost.

[0012] (2) In the impeller of (1), the inlet is a circular hole formed around the axis, and when R is the radius of the inlet and L is the distance from the center of gravity of the opening in at least one of the plurality of balance holes to the axis, it is preferable that the relationship L / R > 0.763 is satisfied.

[0013] As a result of further extensive research, the inventors of the present application discovered that the impeller can be held in the proper axial position by the position restoring force when the radius R of the inlet of the cover plate and the distance L from the center of gravity of the opening of the balance hole to the axis of the impeller body satisfy the relationship L / R > 0.763, and based on this finding, they completed the impeller described in (2) above. With this impeller, the impeller can be held in the proper axial position by the position restoring force, thereby reducing pressure loss of the transported fluid and effectively preventing the impeller from colliding with other components and being damaged.

[0014] (3) In the impeller of (1) or (2) above, when the balance hole is viewed from one side in the axial direction, the opening is preferably formed in an arc shape centered on the axis. In this case, the balance hole openings are formed in an arc shape, which makes them longer in the circumferential direction than if they were formed in a circular shape with the same opening area as the arc shape. This increases the circumferential width of the circumferential flow that flows out of the balance hole openings and toward the radially outer flow path surface, allowing the mainstream and circumferential flow to merge uniformly in the circumferential direction. As a result, the transfer fluid is less likely to stagnate in the region where the mainstream and circulating flow merge, allowing the transfer fluid to flow radially outward more efficiently.

[0015] (4) The magnetic levitation pump of the present disclosure comprises a housing having an inlet and an outlet for a transport fluid, an impeller of any one of (1) to (3) above arranged within the housing, a motor for driving the impeller to rotate, and a magnetic bearing for supporting the impeller in a non-contact manner while rotating. The magnetic levitation pump achieves the same effects as the impeller, and since there is no pressure loss in the transported fluid caused by the conventional partition plate, the transport performance of the magnetic levitation pump can be improved. [Effects of the Invention]

[0016] According to the present disclosure, an impeller on which an axial position restoring force acts can be manufactured at low cost. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view illustrating a magnetic levitation pump according to an embodiment of the present disclosure. FIG. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the impeller of the magnetic levitation pump. [Figure 3] This is a cross section taken along the arrow II in FIG. [Figure 4] FIG. 4 is an enlarged view of a main part of FIG. 3 showing a balance hole of the impeller body. [Figure 5] FIG. 1 is an explanatory diagram of verification test 1. [Figure 6] 1 is a graph showing the results of verification test 1. [Figure 7] 10 is a table showing the results of verification test 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] Next, preferred embodiments will be described with reference to the accompanying drawings. [Overall configuration] Fig. 1 is a schematic cross-sectional view showing a magnetically levitated pump 1 according to an embodiment of the present disclosure. In Fig. 1, the magnetically levitated pump 1 of this embodiment (hereinafter simply referred to as "pump 1") is a centrifugal pump. The pump 1 includes a housing 2, an impeller 3, a motor 4, and a magnetic bearing 5.

[0019] Hereinafter, in this disclosure, the direction along the axis X of the pump 1 is the axial direction of the pump 1 and will be simply referred to as the "axial direction." The direction perpendicular to the axis X is the radial direction of the pump 1 and will be simply referred to as the "radial direction." The direction rotating around the axis X is the circumferential direction of the pump 1 and will be simply referred to as the "circumferential direction."

[0020] The housing 2 includes a housing main body 21, a top wall 22, and a bottom wall 23. The housing main body 21 includes a first cylindrical portion 21a and a second cylindrical portion 21b formed cylindrically about the axis X, and an annular portion 21c connecting the first cylindrical portion 21a and the second cylindrical portion 21b. The first cylindrical portion 21a is formed on the axially upper side (one axial side, the same applies hereinafter) of the housing main body 21. The second cylindrical portion 21b has a smaller diameter than the first cylindrical portion 21a and is formed on the axially lower side (the other axial side, the same applies hereinafter) of the housing main body 21. The outer peripheral edge of the annular portion 21c is connected to the axially lower end of the first cylindrical portion 21a. The inner peripheral edge of the annular portion 21c is connected to the axially upper end of the second cylindrical portion 21b.

[0021] The top wall 22 is formed in a substantially conical plate shape and closes the axially upper opening of the first cylindrical portion 21a. The bottom wall 23 is formed in a disk shape and closes the axially lower opening of the second cylindrical portion 21b. The housing 2 further has an inlet 24 through which the transferred fluid is sucked and an outlet 25 through which the transferred fluid is discharged. The inlet 24 is formed in the center of the top wall 22. The outlet 25 is formed at a predetermined position in the circumferential direction of the first cylindrical portion 21a.

[0022] The impeller 3 is disposed within the housing 2 so as to be rotatable about the axis X. When the impeller 3 rotates, the transported fluid is sucked into the housing 2 through the suction port 24 and is discharged to the outside of the housing 2 through the discharge port 25 by centrifugal force. Details of the impeller 3 will be described later.

[0023] The motor 4 drives the impeller 3 to rotate. The motor 4 has a stator 11 disposed outside the housing 2 and a rotor 12 attached to the impeller 3. The stator 11 has a fixed magnetic portion 11a made of a magnetic material such as iron, and a winding 11b wound around the fixed magnetic portion 11a. The rotor 12 is disposed inside the impeller 3. The rotor 12 is made of at least one of a permanent magnet, a magnetic material such as iron, and a conductor such as copper. When the pump 1 is operated, a current is applied to the winding 11b of the stator 11. This generates a rotating magnetic field, causing the rotor 12 to rotate together with the impeller 3 around the axis X.

[0024] The magnetic bearing 5 supports the rotating impeller 3 in a non-contact manner. The magnetic bearing 5 has a magnetic support portion 5a arranged outside the housing 2 and a supported portion 5b provided on the impeller 3. In this embodiment, the motor 4 also serves as the magnetic bearing 5. Specifically, the stator 11 of the motor 4 also serves as the magnetic support portion 5a, and the rotor 12 of the motor 4 also serves as the supported portion 5b. The impeller 3 rotates while being supported in a non-contact manner due to the magnetism generated from the magnetic support portion 5a to the supported portion 5b. The magnetic bearing 5 may also be provided separately from the motor 4.

[0025] [Impeller] Fig. 2 is an enlarged cross-sectional view showing the impeller 3. In Fig. 2, the rotor 12 of the motor 4 is not shown. Fig. 3 is a cross-sectional view taken along the line II in Fig. 1. In Figs. 2 and 3, the impeller 3 has an impeller body 31, a plurality of blades 33 (four in Fig. 3), and a cover plate 34.

[0026] The impeller body 31 is formed in a cylindrical shape centered on the axis X. The rotor 12 is provided within the impeller body 31 (see FIG. 1). With the impeller 3 supported in a non-contact manner by the magnetic bearings 5, a first annular space S1 is formed between the outer peripheral surface 31a of the impeller body 31 and the inner peripheral surface of the second cylindrical portion 21b of the housing body 21. With the impeller 3 supported in a non-contact manner, a second space S2 is formed between the axially lower end face 31b of the impeller body 31 and the bottom wall 23.

[0027] The plurality of blades 33 are provided at equal intervals in the circumferential direction on the axially upper end face 31c of the impeller body 31. Each blade 33 is formed in a substantially triangular shape when viewed from above in the axial direction. Each blade 33 has a first side surface 33a, a second side surface 33b, and an outer surface 33c.

[0028] The first side surface 33a and the second side surface 33b of each blade 33 are surfaces perpendicular to the end surface 31c of the impeller body 31, and extend while curving from the radially inner side toward the radially outer end of the impeller body 31. The outer surface 33c of each blade 33 is an arcuate surface having the same radius of curvature as the outer peripheral surface 31a of the impeller body 31. Note that the shape of each blade 33 is not limited to the shape of this embodiment.

[0029] The cover plate 34 is provided axially above the plurality of blades 33 so as to cover these blades 33. The cover plate 34 in this embodiment is fixed to the axially upper end surface of each blade 33. The cover plate 34 is formed, for example, in a circular shape centered on the axis X. The outer diameter of the cover plate 34 is the same as the outer diameter of the impeller body 31. An inlet 35 through which the transfer fluid flows into the impeller 3 is formed in the center of the cover plate 34. The inlet 35 is formed radially inward of the plurality of blades 33. The inlet 35 in this embodiment is a circular hole centered on the axis X. Note that the inlet 35 may have a shape other than a circular hole. Furthermore, the inlet 35 may be formed in a size that allows the radially inner ends of the plurality of blades 33 to be seen when viewing the impeller 3 from above in the axial direction.

[0030] The axially upper end face 31c of the impeller body 31 has a plurality of (four in FIG. 3) flow path surfaces 31c1 located between circumferentially adjacent blades 33, and abutment surfaces 31c2 located radially inward of the plurality of blades 33. The abutment surfaces 31c2 are formed in a circular shape around the axis X at the center of the end face 31c. The radially outer ends of the abutment surfaces 31c2 are connected to the plurality of flow path surfaces 31c1, respectively.

[0031] Each flow path surface 31c1 extends radially while curving when viewed from above in the axial direction. The transfer fluid that flows into the impeller 3 from the inlet 35 directly contacts the contact surface 31c2. The transfer fluid that contacts the contact surface 31c2 is divided radially along the contact surface 31c2 and is guided to each flow path surface 31c1.

[0032] Between each flow path surface 31c1 of the impeller body 31 and the cover plate 34, between circumferentially adjacent blades 33, a flow path 36 is formed through which the transfer fluid in the impeller 3 flows from the radially inner side to the radially outer side along each flow path surface 31c1. The radially outer opening of each flow path 36 serves as an outlet 37 through which the transfer fluid flows out of the impeller 3. Therefore, a plurality of outlets 37 through which the transfer fluid flows out of the impeller 3 are formed on the outer periphery of the impeller 3.

[0033] [Balance Hall] A plurality of balance holes 32 are formed in the impeller body 31 radially inward of the rotor 12 (see FIG. 1) and penetrate the body in the axial direction. In the impeller body 31 of this embodiment, four balance holes 32 are formed at equal intervals in the circumferential direction around the axis X. Axial upper openings 32a of the plurality of balance holes 32 are located radially inward of each flow path surface 31c1 and radially outward of the abutment surface 31c2. A portion of the transport fluid passes through each balance hole 32 from the axial lower side to the axial upper side.

[0034] FIG. 4 is an enlarged view of a main portion of FIG. 3 showing the balance holes 32. In FIGS. 3 and 4, the opening 32a of each balance hole 32 is formed, for example, in an arc shape when viewed in the axial direction. Each balance hole 32 has an inner arc surface 32b and an outer arc surface 32c formed about the axis X, and a pair of side surfaces 32d extending radially. The radius of curvature R1 of the inner arc surface 32b of each balance hole 32 is smaller than the radius R of the inlet 35. The radius of curvature R2 of the outer arc surface 32c of each balance hole 32 is larger than the radius R of the inlet 35. Therefore, in this embodiment, when the impeller 3 is viewed from above in the axial direction, the opening 32a of each balance hole 32 is located both within the range of the inlet 35 (within the circle of radius R) and outside the range (outside the circle of radius R). Each balance hole 32 is formed in an arc shape identical to the opening 32a throughout its entire axial direction.

[0035] The opening 32a of each balance hole 32 may be located radially inward of the flow path surface 31c1, or may be located across the radially inner side of the flow path surface 31c1 and the radially outer side of the abutment surface 31c2. When the impeller 3 is viewed from above in the axial direction, the opening 32a of each balance hole 32 may be located only within the range of the inlet 35, or only outside the range of the inlet 35. The shape of the balance hole 32 is not limited to this embodiment, and may be formed, for example, in a circular shape when viewed in the axial direction. The number of balance holes 32 is not limited to this embodiment.

[0036] [Transport fluid flow] 2 and 3, when the pump 1 is operated and the impeller 3 rotates around the axis X, the transfer fluid is sucked in through the suction port 24 of the housing 2 and flows into the impeller 3 through the inlet 35 of the impeller 3. The transfer fluid that has flowed into the impeller 3 abuts against the abutment surface 31c2 of the impeller body 31, where it is divided radially, and flows radially outward along the abutment surface 31c2 due to the centrifugal force generated by the rotation of the impeller 3.

[0037] As a result, the transfer fluid flows into the flow paths 36 between adjacent blades 33, flows further radially outward along the flow path surface 31c1 of the impeller body 31, and flows out radially outward of the impeller 3 from each outlet 37. Most of the transfer fluid that flows out of the impeller 3 is discharged out of the housing 2 from the discharge port 25 of the housing 2. Therefore, within the rotating impeller 3, a flow of the transfer fluid is generated from the suction port 24 of the housing 2 to the discharge port 25. Hereinafter, this flow will be referred to as the "main flow."

[0038] A remaining portion of the transfer fluid that has flowed out of the impeller 3 passes through the first space S1 and the second space S2 in the housing 2 in this order, and flows from the axially lower side of the impeller body 31 into each balance hole 32. The transfer fluid that has flowed into each balance hole 32 flows from the opening 32a of each balance hole 32 to the axially upper side of the impeller body 31. The transfer fluid that has flowed into the axially upper side of the impeller body 31 flows radially outward due to the centrifugal force and then flows out of the impeller 3 again. Therefore, within the housing 2, a flow is generated in which the transfer fluid circulates between the radially inner side (balance hole 32) and the radially outer side (first space S1) of the impeller body 31. Hereinafter, this flow will be referred to as a "circulation flow."

[0039] [Positional restoring force] The impeller 3 is subjected to a load F1 by the main flow, which pulls it axially upward. Specifically, in the middle of the main flow, the transferred fluid flows from the radially inner side to the radially outer side along the axially upper end face 31c (contact surface 31c2) of the impeller body 31, generating negative pressure in the center of the end face 31c of the impeller body 31. This negative pressure causes a load F1 to act on the impeller 3 in the axially upward direction. Hereinafter, this load F1 will also be referred to as the "upward load F1."

[0040] The circulating flow acts on the impeller 3, pulling it downward in the axial direction, as a load F2. Specifically, during the circulating flow, the transfer fluid flows from the axially lower side (second space S2) of the impeller body 31 into each balance hole 32, generating negative pressure in the center of the axially lower end face 31b of the impeller body 31. This negative pressure causes a load F2 to act downward in the axial direction on the impeller 3. Hereinafter, this load F2 will also be referred to as a "downward load F2."

[0041] During operation of the pump 1, the upward load F1 and the downward load F2 are balanced, thereby maintaining the impeller 3 at a predetermined axial position. This predetermined axial position is preferably an appropriate position (hereinafter referred to as the appropriate position). As shown in Figure 2, the appropriate position is a position where the axially upper end face 31c of the impeller body 31 is flush with the axially upper inner surface 21c1 of the annular portion 21c of the housing body 21, thereby minimizing pressure loss of the transported fluid.

[0042] When the impeller 3 moves axially downward due to an external force from a state in which both loads F1 and F2 are balanced, the second space S2 narrows, reducing the flow rate of the circulating flow. As a result, the downward load F2 becomes smaller, and the upward load F1 acts more dominantly on the impeller 3 than the downward load F2. Therefore, the upward load F1 acts as a position restoring force, pushing the impeller 3, which has moved axially downward, back upward in the axial direction toward the predetermined position.

[0043] On the other hand, when the impeller 3 moves axially upward due to an external force from a state in which both loads F1 and F2 are balanced, the second space S2 widens, increasing the flow rate of the circulating flow. As a result, the downward load F2 increases, and the downward load F2 acts more dominantly on the impeller 3 than the upward load F1. Therefore, the downward load F2 acts as a position restoring force on the impeller 3, pushing the impeller 3, which has moved axially upward, downward toward its predetermined position. As a result, either the upward load F1 or the downward load F2 acts on the impeller 3 as an axial position restoring force.

[0044] 3 and 4, in order to maintain the impeller 3 at an appropriate axial position by a position restoring force, it is preferable that the balance holes 32 and the inlet 35 satisfy the relationship of the following formula (1). L / R>0.763 (1) L is the distance from the center of gravity G of the opening 32a of each balance hole 32 to the axis X. The "center of gravity of the opening 32a" refers to the center of gravity of the shape of the opening 32a when the balance hole 32 is viewed from above in the axial direction (one axial side). R is the radius of the inlet 35. It is sufficient that at least one of the multiple balance holes 32 satisfies the relationship of the above formula (1).

[0045] [Verification test 1] Verification test 1 was conducted to determine whether an axial position restoring force acts appropriately on the impeller 3 when each balance hole 32 of the impeller body 31 is located at P1, P2, and P3 as shown below when viewed from above in the axial direction. P1: Each balance hole 32 is located only outside the range of the entrance 35. P2: Each balance hole 32 is located both within the range of the entrance 35 and outside the range of the entrance 35 (this embodiment). P3: Each balance hole 32 is located only within the range of the entrance 35.

[0046] FIG. 5 is an explanatory diagram of Verification Test 1. In Verification Test 1, for each of the cases P1 to P3, the impeller 3 was displaced in the range of -5 mm to +1 mm relative to the origin in the Y direction (axial direction), and the load in the Y direction (positional restoring force) acting on the rotating impeller 3 was calculated using fluid analysis software. The origin in the Y direction was set to a position on the axially upper end face 31c of the impeller body 31 in the appropriate position, as shown in FIG. 5. The range in which the impeller 3 was displaced in the Y direction during this test (-5 mm to +1 mm) was a range in which the impeller 3 did not collide with the top wall 22 and bottom wall 23 of the housing 2. Note that the flow rate of the transported fluid was the same for all of the cases P1 to P3.

[0047] Fig. 6 is a graph showing the results of Verification Test 1. As shown in Fig. 6, in all of the cases of P1 to P3, within the range of displacement of impeller 3 in the Y direction, a state occurs in which the load in the Y direction acting on impeller 3 becomes zero, that is, a state in which the upward load F1 on the positive side of the Y direction and the downward load F2 on the negative side of the Y direction are balanced. Therefore, in all of the cases of P1 to P3, it was confirmed that a position restoring force acts appropriately on impeller 3 so that impeller 3 does not collide with housing 2.

[0048] [Verification test 2] Next, verification test 2 was conducted to determine whether the balance hole 32 and the inlet 35 of this embodiment satisfying the relationship of formula (1) above allows the impeller 3 to be held in the appropriate axial position by the position restoring force. In verification test 2, the impeller 3 was fixed in the appropriate position (Y = 0 mm) in Fig. 5, and the load in the Y direction (position restoring force) acting on the impeller 3 was calculated using fluid analysis software when the value of L / R was changed. In this test, the flow rate of the transported fluid when the value of L / R was changed was also under the same conditions.

[0049] In the pump 1 of this embodiment, due to the structure of the centrifugal pump, the upward load F1 is greater than the downward load F2, so the impeller 3 moves axially upward from the appropriate position. Therefore, the downward load F2 acts as a position restoring force on the impeller 3 moving axially upward. In other words, if the load in the Y direction is a negative value, the downward load F2 acts as a position restoring force, balancing the upward load F1 and the downward load F2, and it can be considered that the impeller 3 can be maintained in the appropriate position.

[0050] FIG. 7 is a table showing the results of Verification Test 2. As shown in FIG. 7, when L / R is 0.7629, that is, when L / R<0,763, the load in the Y direction is a positive value. In contrast, when L / R is 0.7836, that is, when L / R>0,763, the load in the Y direction is a negative value. Therefore, it was confirmed that by satisfying the relationship of the above formula (1), the downward load F2 (a negative Y direction load) acts as a positional restoring force, and the impeller 3 can be maintained in the appropriate position.

[0051] [Action and effect] In the magnetic levitation pump 1 and impeller 3 of this embodiment, when the impeller body 31 is rotated, the transfer fluid that flows in from the inlet 35 of the cover plate 34 hits the abutment surface 31c2 on the axially upper side of the impeller body 31, generating a main flow that flows out radially outward along the multiple flow path surfaces 31c1 connected to the abutment surface 31c2. This main flow acts on the impeller 3, pulling it axially upward. In addition, a circulating flow is generated in which a portion of the transfer fluid that flows out radially outward of the impeller 3 flows around to the axially lower side of the impeller body 31, passes through each balance hole 32, and flows axially upward of the impeller body 31. This circulating flow acts on the impeller 3, pulling it axially downward.

[0052] Therefore, even with an impeller 3 that does not use a conventional partition plate, an axial position restoring force acts on the impeller 3, so it is possible to manufacture an impeller 3 that acts on an axial position restoring force at low cost. Also, since there is no pressure loss in the transported fluid that would otherwise occur with a conventional partition plate, the transport performance of the transported fluid by the pump 1 can be improved.

[0053] The radius R of the inlet 35 of the cover plate 34 and the distance L from the center of gravity G of the balance hole 32 to the axis X of the impeller body 31 satisfy the relationship L / R>0.763, so the impeller 3 can be held in the appropriate axial position by the position restoring force. This reduces pressure loss of the transported fluid and effectively prevents the impeller 3 from colliding with the top wall 22 or bottom wall 23 of the housing 2 and being damaged.

[0054] Because the openings 32a of each balance hole 32 are formed in an arc shape, they are longer in the circumferential direction than if they were formed in a circular shape with the same opening area as the arc shape. This increases the circumferential width of the circumferential flow that flows out of the openings 32a of each balance hole 32 and toward each radially outer flow path surface 31c1, allowing the mainstream and circulating flow to merge uniformly in the circumferential direction. As a result, the transfer fluid is less likely to stagnate in the region where the mainstream and circulating flow merge, allowing the transfer fluid to flow radially outward more efficiently.

[0055] The openings 32a of each balance hole 32 are located both within and outside the range of the inlet 35. As a result, a portion of the openings 32a of each balance hole 32 is located outside the range of the inlet 35, which reduces the area where the main flow flowing in axially downward from the inlet 35 and the circulating flow flowing out axially upward from the openings 32a directly meet. As a result, the main flow can flow radially outward more efficiently. In addition, it is possible to prevent the circulating flow from being obstructed by the main flow.

[0056] Furthermore, because each balance hole 32 is formed in the same shape as the opening 32a over its entire axial direction, a portion of each balance hole 32 is located within the range of the inlet 35 over its entire axial direction. This makes it possible to increase the volume of the supported portion 5b (rotor 12) provided radially outward of the balance hole 32 within the impeller body 31, compared to when the entire balance hole 32 is located outside the range of the inlet 35 over its entire axial direction. As a result, the magnetism generated from the magnetic support portion 5a to the supported portion 5b is stronger, allowing the magnetic bearing 5 to support the impeller 3 more stably in a non-contact state.

[0057] [others] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above meaning, and is intended to include any modifications within the scope of the claims and meaning equivalent to the claims. [Explanation of symbols]

[0058] 1. Magnetic levitation pump 2. Housing 3 impeller 4 motors 5. Magnetic bearings 24 Intake port 25 Outlet 31 Impeller body 31c end face 31c1 Channel surface 31c2 Contact surface 32 Balance Hole 32a aperture 33 Feather 35 Entrance G center of gravity X axis

Claims

1. a cylindrical impeller body having a plurality of balance holes formed therethrough in the axial direction; a plurality of blades provided at intervals in a circumferential direction on an end surface on one axial side of the impeller body; a cover plate provided on one side of the plurality of blades in the axial direction, the cover plate having an inlet for a transfer fluid formed in a central portion thereof, An impeller that rotates about an axis to cause a transfer fluid that has flowed in from the inlet to flow outward in a radial direction from between the blades that are adjacent in the circumferential direction, The end surface of the impeller body is a plurality of flow path surfaces located between the blades adjacent to each other in the circumferential direction; a contact surface that is located radially inward of the plurality of blades so as to be connected to each of the plurality of flow path surfaces, and that contacts the transport fluid that has flowed in from the inlet and guides it to each of the flow path surfaces, An impeller, wherein an opening on the one axial side of each balance hole is located at least either within or outside the range of the inlet when the impeller is viewed from the one axial side.

2. the inlet is a circular hole formed around the axis, 2. The impeller according to claim 1, wherein a relationship of L / R>0.763 is satisfied, where R is a radius of the inlet and L is a distance from the center of gravity of the opening of at least one of the plurality of balance holes to the axis.

3. The impeller according to claim 1 , wherein the opening is formed in an arc shape centered on the axis when the balance hole is viewed from one side in the axial direction.

4. a housing having an inlet and an outlet for a transport fluid; An impeller according to any one of claims 1 to 3, disposed within the housing; a motor that rotates and drives the impeller; and a magnetic bearing that supports the impeller in a non-contact manner while rotating.

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