Motor pump

Abstract

To provide a motor pump that can ensure the torsional strength of the mounting section of the main shaft to which the impeller is attached, while suppressing the generation of fluid vortices and backflow downstream of the main shaft. [Solution] The motor pump comprises a first impeller, a main shaft to which the first impeller is fixed, a motor for rotating the first impeller, and a casing that houses the first impeller and the main shaft and has a fluid passage through which fluid flows. The downstream end of the main shaft is positioned in the fluid passage, and the main shaft has a mounting portion to which the first impeller is attached, and a smaller diameter portion positioned downstream of the mounting portion and having a smaller diameter than the mounting portion.

Description

Technical Field

[0001] The present invention relates to a motor pump.

Background Art

[0002] Conventionally, a motor pump including an impeller, a motor that rotates the impeller, and a casing that houses the impeller has been known. Patent Document 1 discloses a motor pump having a first impeller, a second impeller disposed downstream of the first impeller, and a main shaft to which the first impeller and the second impeller are fixed. When the first impeller is rotated by a motor, the rotational force of the first impeller is transmitted to the second impeller via the main shaft, and the first impeller and the second impeller rotate integrally.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conventional motor pump, the diameter of the main shaft is constant, and the flow passage area downstream of the main shaft is relatively small. Therefore, on the downstream side of the main shaft, the flow passage area suddenly expands, resulting in the separation of the fluid flow, and the generation of fluid vortices and backflows. Although it is conceivable to reduce the diameter of the main shaft in order to suppress the sudden expansion of the flow passage area, if the overall diameter of the main shaft is reduced, there is a possibility that the torsional strength of the mounting portion of the main shaft to which the impeller is attached cannot be sufficiently ensured. In this case, it is difficult to apply a large rotational force to the impeller to rotate it at high speed.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a motor pump capable of suppressing the generation of fluid vortices and backflows on the downstream side of the main shaft while ensuring the torsional strength of the mounting portion of the main shaft to which the impeller is attached. [Means for solving the problem]

[0006] (1) A motor pump according to one aspect of the present invention comprises a first impeller, a main shaft to which the first impeller is fixed, a motor for rotating the first impeller, and a casing that houses the first impeller and the main shaft and has a flow path through which fluid flows, wherein the downstream end of the main shaft is located in the flow path, and the main shaft has a mounting portion to which the first impeller is attached, and a small-diameter portion located downstream of the mounting portion and having a smaller diameter than the mounting portion.

[0007] (2) The motor pump according to (1) further comprises a second impeller located downstream of the first impeller and fixed to the main shaft, wherein the second impeller may be attached to the small diameter portion.

[0008] (3): In the motor pump according to (2), the impeller diameter of the first impeller and the impeller diameter of the second impeller may be equal.

[0009] (4) In the motor pump according to (2) or (3), the outer diameter of the inlet of the first impeller and the outer diameter of the inlet of the second impeller may be equal.

[0010] (5) In a motor pump relating to any one of (2) to (4), the inner diameter of the inlet of the second impeller may be smaller than the inner diameter of the inlet of the first impeller.

[0011] (6): In the motor pump according to (2), the impeller diameter of the second impeller may be smaller than the impeller diameter of the first impeller.

[0012] (7): In a motor pump relating to any one of (1) to (6), the motor may include a rotor fixed to the first impeller and a stator positioned radially outward from the rotor.

[0013] (8) In a motor pump relating to any one of (2) to (6), the casing may include a suction casing arranged upstream of the first impeller and having a suction port for drawing in the fluid, a discharge casing arranged downstream of the second impeller and having a discharge port for discharging the fluid, and an intermediate casing arranged between the suction casing and the discharge casing and housing the second impeller. [Effects of the Invention]

[0014] According to one aspect of the present invention described above, it is possible to provide a motor pump that can suppress the generation of fluid vortices and backflow downstream of the main shaft while ensuring the torsional strength of the mounting portion of the main shaft to which the impeller is attached. [Brief explanation of the drawing]

[0015] [Figure 1] This is a diagram showing a motor pump according to the first embodiment. [Figure 2] This is a perspective view of the main shaft according to the first embodiment. [Figure 3] (a) is a diagram illustrating the fluid flow in a conventional motor pump, and (b) is a diagram illustrating the fluid flow in a motor pump according to the first embodiment. [Figure 4] This figure shows a motor pump according to the second embodiment. [Figure 5] This is a perspective view of the main axis of a modified example of the first embodiment. [Figure 6] This is a cross-sectional view of the main shaft according to another modification of the first embodiment. [Figure 7] This is a cross-sectional view of the main shaft according to another modification of the first embodiment. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0017] <First Embodiment> FIG. 1 is a diagram showing a motor pump 1 according to the first embodiment. The motor pump 1 includes a first impeller 10, a second impeller 20, a main shaft 30, a motor 40, a casing 50, a first bearing 60, and a second bearing 70. Inside the casing 50, a flow path FP through which a fluid (handling liquid) flows is formed. The casing 50 is formed with a suction port 50a for sucking in the fluid and a discharge port 50b for discharging the fluid.

[0018] <Direction Definition> In this specification, the direction along the center line CL of the motor pump 1 is referred to as the axial direction. When viewed from the axial direction, the direction intersecting the center line CL of the motor pump 1 is referred to as the radial direction, and the direction of orbiting around the center line CL of the motor pump 1 is referred to as the circumferential direction. Also, in the flow path FP of the casing 50, the fluid flows from the suction port 50a toward the discharge port 50b. The upstream side in the flow direction of the fluid is simply referred to as the upstream side or the suction side. The downstream side in the flow direction of the fluid is simply referred to as the downstream side or the discharge side.

[0019] The first impeller 10 is disposed in the flow path FP of the casing 50. The first impeller 10 is fixed to the main shaft 30. When the first impeller 10 rotates, the fluid sucked into the first impeller 10 is pressurized and discharged to the outside of the first impeller 10. In the illustrated example, the first impeller 10 is a centrifugal impeller, and the fluid pressurized by the first impeller 10 is discharged in a direction perpendicular (radial direction) to the center line CL. Note that the first impeller 10 may be a mixed-flow impeller.

[0020] The first impeller 10 has a first main plate 11, a first side plate 12, a plurality of first blades 13, and a first boss portion 14. In the present embodiment, the first side plate 12 and the rotor 41 of the motor 40 described later are integrated. Also, the first main plate 11, the first side plate 12, the plurality of first blades 13, and the first boss portion 14 may be integrally formed. The first main plate 11, the first side plate 12, the plurality of first blades 13, and the first boss portion 14 may be separately formed and joined after forming.

[0021] The first main plate 11 is disc-shaped. The first side plate 12 is positioned opposite the first main plate 11. The first wing 13 is positioned between the first main plate 11 and the first side plate 12. Multiple first wings 13 are arranged in a circumferential direction. The first boss portion 14 is cylindrical and is located in the center of the first main plate 11. The first boss portion 14 is the part that connects to the main shaft 30.

[0022] The second impeller 20 is positioned in the flow path FP of the casing 50. The second impeller 20 is positioned downstream of the first impeller 10. The second impeller 20 is fixed to the main shaft 30. The rotational force of the first impeller 10 is transmitted to the second impeller 20 via the main shaft 30. As the second impeller 20 rotates, the fluid drawn into the second impeller 20 is pressurized and discharged to the outside of the second impeller 20. In the illustrated example, the second impeller 20 is a centrifugal impeller, and the fluid pressurized by the second impeller 20 is discharged in a direction perpendicular to the centerline CL (radial direction). The second impeller 20 may also be a diagonal flow impeller.

[0023] The second impeller 20 has a second main plate 21, a second side plate 22, a plurality of second wings 23, and a second boss portion 24. The second main plate 21, the second side plate 22, the plurality of second wings 23, and the second boss portion 24 may be integrally molded. Alternatively, the second main plate 21, the second side plate 22, the plurality of second wings 23, and the second boss portion 24 may be molded separately and then joined together after molding.

[0024] The second main plate 21 is disc-shaped. The second side plate 22 is positioned opposite the second main plate 21. The second wing 23 is positioned between the second main plate 21 and the second side plate 22. Multiple second wings 23 are arranged in a circumferential direction. The second boss portion 24 is cylindrical and is located in the center of the second main plate 21. The second boss portion 24 is the part that connects to the main shaft 30.

[0025] In this embodiment, the impeller diameter D11 of the first impeller 10 is equal to the impeller diameter D21 of the second impeller 20. Note that the impeller diameter is the diameter of the main plate of the impeller. Also, the inlet outer diameter D12 of the first impeller is equal to the inlet outer diameter D22 of the second impeller 20. Note that the inlet outer diameter is the outer diameter of the upstream inlet of the impeller. Furthermore, the inlet inner diameter D23 of the second impeller 20 is smaller than the inlet inner diameter D13 of the first impeller 10. Note that the inlet inner diameter is the inner diameter of the upstream inlet of the impeller and is equivalent to the outer diameter of the boss portion of the impeller. That is, the outer diameter of the second boss portion 24 of the second impeller 20 is smaller than the outer diameter of the first boss portion 14 of the first impeller 10.

[0026] The main shaft 30 is positioned on the centerline CL of the motor pump 1. The main shaft 30 extends in the axial direction. The first impeller 10 and the second impeller 20 are fixed to the main shaft 30.

[0027] Figure 2 is a perspective view of the main spindle 30. As shown in Figures 1 and 2, the main spindle 30 has a mounting portion 32 and a small-diameter portion 33 located downstream of the mounting portion 32. The diameter of the small-diameter portion 33 is smaller than the diameter of the mounting portion 32. A step is formed between the mounting portion 32 and the small-diameter portion 33. The downstream end 30a of the main spindle 30 is located in the flow path FP of the casing 50.

[0028] The mounting portion 32 has a substantially cylindrical shape. The first impeller 10 is attached to the mounting portion 32. The mounting portion 32 has a circular cross-section with a chamfered edge. Specifically, two first flat portions 32a are formed on the outer circumference of the mounting portion 32. That is, the mounting portion 32 has a double-chamfered structure. The first boss portion 14 of the first impeller 10 has an insertion hole that corresponds to the shape of the mounting portion 32. The first boss portion 14 is inserted into the mounting portion 32. As a result, the rotational force of the first impeller 10 is transmitted to the main shaft 30. Furthermore, because the mounting portion 32 has a double-chamfered structure, the torque that can be transmitted from the first impeller 10 to the main shaft 30 is increased compared to the case of a single-chamfered structure.

[0029] As shown in Figure 1, a restricting member 36 is provided on the downstream side of the mounting portion 32. The restricting member 36 is cylindrical and is inserted into the small diameter portion 33. The outer diameter of the restricting member 36 is larger than the diameter of the mounting portion 32. The restricting member 36 abuts against the step between the mounting portion 32 and the small diameter portion 33 and the first boss portion 14 from the downstream side. The movement of the first impeller 10 downstream is restricted by the restricting member 36 abutting against the first boss portion 14 from the downstream side.

[0030] The small-diameter portion 33 has a roughly cylindrical shape. The second impeller 20 is attached to the small-diameter portion 33. The small-diameter portion 33 has a circular cross-section with a chamfered edge. Specifically, two second flat portions 33a are formed on the outer circumference of the small-diameter portion 33. That is, the small-diameter portion 33 has a double-chamfered structure. The second boss portion 24 of the second impeller 20 has an insertion hole that corresponds to the shape of the small-diameter portion 33. The second boss portion 24 is inserted into the small-diameter portion 33. As a result, the rotational force of the main shaft 30 is transmitted to the second impeller 20. Furthermore, because the small-diameter portion 33 has a double-chamfered structure, the torque that can be transmitted from the main shaft 30 to the second impeller 20 is increased compared to the case of a single-chamfered structure.

[0031] The first planar portion 32a and the second planar portion 33a are formed parallel to each other. In this embodiment, the first planar portion 32a and the second planar portion 33a are formed on the same plane. In this case, machining of the spindle 30 becomes easier.

[0032] A sleeve 37 is provided between the regulating member 36 and the second boss portion 24. The sleeve 37 is cylindrical and is inserted through the small diameter portion 33. The sleeve 37 forms a predetermined distance between the first impeller 10 and the second impeller 20. By providing the regulating member 36 and the sleeve 37, the distance between the first impeller 10 and the second impeller 20 can be easily controlled. The regulating member 36 and the sleeve 37 may be formed integrally.

[0033] Furthermore, a second rotating bearing body 71 of the second bearing 70, which will be described later, is positioned downstream of the second boss portion 24. The second rotating bearing body 71 is cylindrical and is inserted through the small diameter portion 33.

[0034] The first impeller 10 and the second impeller 20 are fixed to the main shaft 30 by fastening fasteners (not shown) to both ends of the main shaft 30, for example, with the first boss portion 14 inserted through the mounting portion 32 and the second boss portion 24 inserted through the small diameter portion 33. As shown in Figure 2, threaded portions 34 and 35 to which the fasteners are fastened may be provided at the upstream end of the mounting portion 32 and the downstream end of the small diameter portion 33, respectively. However, even in this case, the downstream end 30a of the main shaft 30 is located in the flow path FP of the casing 50.

[0035] A regulating member 36 and a sleeve 37 are positioned between the first impeller 10 and the second impeller 20, and a second rotating side bearing body 71 is positioned downstream of the second impeller 20. The first impeller 10 is sandwiched between a fastener and the regulating member 36, and the second impeller 20 is sandwiched between the sleeve 37, the second rotating side bearing body 71 and the fastener. As a result, the first impeller 10 and the second impeller 20 are firmly fixed to the main shaft 30. The main shaft 30 may be in the shape of a bolt with a head. For example, a bolt head may be formed at the upstream end of the main shaft 30 instead of a threaded portion 34, and the first impeller 10 and the second impeller 20 may be fixed to the main shaft 30 by the bolt head and fastener. A bolt head may be formed at the downstream end of the main shaft 30 instead of a threaded portion 35.

[0036] The motor 40 rotates the first impeller 10. The motor 40 comprises an annular rotor 41 fixed to the first impeller 10 and a stator 42 positioned radially outward from the rotor 41. The stator 42 is fixed to the casing 50. The motor 40 is, for example, a permanent magnet motor. In this case, the rotor 41 has a rotor core and permanent magnets attached to the rotor core. The motor 40 may also be an induction motor, a reluctance motor, or the like.

[0037] The rotor 41 rotates relative to the stator 42. Since the rotor 41 is fixed to the first impeller 10, the rotational force of the rotor 41 acts on the first impeller 10. The rotational force acting on the first impeller 10 is transmitted to the second impeller 20 via the main shaft 30. Therefore, when the rotor 41 rotates relative to the stator 42, the first impeller 10, the main shaft 30, and the second impeller 20 rotate together as a unit around the centerline CL of the motor pump 1.

[0038] The rotor 41 is housed in the rotor holder 43. The rotor holder 43 is integrally formed with the first impeller 10 (first side plate 12). The rotor holder 43 rotates together with the rotor 41 around the centerline CL of the motor pump 1.

[0039] The casing 50 houses the first impeller 10, the second impeller 20, the main shaft 30, and the motor 40. The casing 50 includes a suction casing 51, a discharge casing 52, an intermediate casing 53, and a stator casing 54.

[0040] The suction casing 51 is located upstream (suction side) of the first impeller 10. The suction casing 51 has a suction port 50a. The discharge casing 52 is located downstream (discharge side) of the second impeller 20. The discharge casing 52 has a discharge port 50b. The suction port 50a and the discharge port 50b are located on the centerline CL of the motor pump 1.

[0041] The intermediate casing 53 is an annular partition separating the downstream side (discharge side) of the first impeller 10 from the upstream side (suction side) of the second impeller 20. The intermediate casing 53 houses the second impeller 20. In this embodiment, the intermediate casing 53 is held by an intermediate casing holder 55. The intermediate casing 53 is fixed to the discharge casing 52 via the intermediate casing holder 55.

[0042] The stator casing 54 houses the stator 42. The stator casing 54 is located radially outward from the first impeller 10. The stator casing 54 is located between the suction casing 51 and the discharge casing 52. The stator casing 54 is fixed to the suction casing 51 and the discharge casing 52.

[0043] The first bearing 60 rotatably supports the first impeller 10. The first bearing 60 has a first rotating-side bearing body 61 fixed to the rotor holder 43 and a first stationary-side bearing body 62 fixed to the suction casing 51. The first stationary-side bearing body 62 is positioned radially inward from the first rotating-side bearing body 61. The first rotating-side bearing body 61 is a rotating member that rotates with the rotation of the first impeller 10 (rotor 41), while the first stationary-side bearing body 62 is a stationary member that does not rotate even when the first impeller 10 rotates.

[0044] The second bearing 70 rotatably supports the main shaft 30. The second bearing 70 includes a second rotating-side bearing body 71 fixed to the small-diameter portion 33 of the main shaft 30, and a second stationary-side bearing body 72 fixed to the intermediate casing 53 via a second partition plate 84, which will be described later. The second stationary-side bearing body 72 is positioned radially outward from the second rotating-side bearing body 71. The second rotating-side bearing body 71 is a rotating member that rotates with the rotation of the first impeller 10 (main shaft 30), while the second stationary-side bearing body 72 is a stationary member that does not rotate even when the first impeller 10 rotates.

[0045] The motor pump 1 includes a plurality of first return vanes 81 and a first partition plate 82 that guide the fluid discharged from the first impeller 10 toward the second impeller 20. The first return vanes 81 are positioned on the rear side of the first impeller 10. The first return vanes 81 face the first main plate 11 of the first impeller 10. The first return vanes 81 are fixed to the intermediate casing 53. The plurality of first return vanes 81 are arranged, for example, to extend in a spiral shape. The first partition plate 82 separates the first main plate 11 from the first return vanes 81. The first partition plate 82 is fixed to the first return vanes 81. The first return vanes 81 and the first partition plate 82 may be integrally molded.

[0046] The motor pump 1 includes a plurality of second return vanes 83 and a second partition plate 84 that guide the fluid discharged from the second impeller 20 toward the discharge port 50b. The second return vanes 83 are located on the rear side of the second impeller 20. The second return vanes 83 face the second main plate 21 of the second impeller 20. The second return vanes 83 are fixed to the intermediate casing 53. The plurality of second return vanes 83 are arranged, for example, to extend in a spiral shape. The second partition plate 84 separates the second main plate 21 from the second return vanes 83. The second partition plate 84 is fixed to the second return vanes 83. The second return vanes 83 and the second partition plate 84 may be integrally molded.

[0047] Referring to Figure 1, the fluid (handled liquid) flow in the flow path FP of the casing 50 will be explained. In Figure 1, the fluid flow is indicated by arrows. When the motor pump 1 is operated, the fluid is drawn in from the suction port 50a. The fluid is pressurized by the rotation of the first impeller 10 and discharged to the outside of the first impeller 10. The fluid discharged to the outside of the first impeller 10 collides with the stator cannon 44 of the stator 42, and its flow direction is changed. After that, the fluid flows through the first return vane 81 and flows towards the second impeller 20. The fluid is pressurized by the rotation of the second impeller 20 and discharged to the outside of the second impeller 20. The fluid discharged to the outside of the second impeller 20 collides with the inner circumferential surface of the intermediate casing 53, and its flow direction is changed. After that, the fluid flows through the second return vane 83 and is discharged from the discharge port 50b.

[0048] As shown in Figure 3(a), in conventional motor pumps, the diameter of the main shaft 130 is constant, and the flow area FA1 (more specifically, the flow area of ​​the fluid after passing through the second return vane 83) downstream of the main shaft 130 is relatively small. As a result, the flow area (outlet area OA) rapidly expands downstream of the main shaft 130, causing fluid flow separation, fluid vortices, and backflow. Reducing the diameter of the main shaft 130 can be considered to suppress the rapid expansion of the flow area, but if the overall diameter of the main shaft 130 is reduced, it may not be possible to ensure sufficient torsional strength at the mounting portion of the main shaft 130 to which the first impeller 10 is attached. Since the first impeller 10 receives all of the rotational force of the rotor 41, it is desirable that the part of the main shaft 130 to which the first impeller 10 is attached has higher torsional strength than the part to which the other impellers (second impeller 20) are attached. If the torsional strength of the mounting portion of the main shaft 130 to which the first impeller 10 is attached cannot be sufficiently secured, it will be difficult to apply a large rotational force to the first impeller 10 and rotate it at high speed.

[0049] As shown in Figure 3(b), the motor pump 1 of this embodiment is provided with a small-diameter section 33 on the main shaft 30. This allows for a larger flow path area FA2 in the small-diameter section 33 compared to the case where the small-diameter section 33 is not provided. Furthermore, if the outlet area OA is the same for the motor pump 1 of this embodiment and a conventional motor pump, the ratio of the flow path area FA2 to the outlet area OA in the motor pump 1 (FA2 / OA) is larger than the ratio of the flow path area FA1 to the outlet area OA in the conventional motor pump (FA1 / OA). Therefore, a rapid expansion of the flow path area (outlet area OA) downstream of the main shaft 30 can be suppressed, and the generation of fluid vortices and backflow can be suppressed. In addition, since the first impeller 10 is attached to a mounting section 32 that has a larger diameter than the small-diameter section 33, the torsional strength of the mounting section 32 of the main shaft 30 to which the first impeller 10 is attached can be ensured even when the small-diameter section 33 is provided. Therefore, a large rotational force can be applied to the first impeller 10, allowing it to rotate at high speed. Furthermore, by providing the small-diameter section 33, the degree of freedom in designing the flow paths of the first impeller 10 and the second impeller 20 can be improved. In addition, by providing the small-diameter section 33, the radial blade length of the first return blade 81 and the second return blade 83 can be increased. Therefore, the fluid flow can be stabilized.

[0050] As described above, the motor pump 1 according to this embodiment comprises a first impeller 10, a main shaft 30 to which the first impeller 10 is fixed, a motor 40 for rotating the first impeller 10, and a casing 50 that houses the first impeller 10 and the main shaft 30 and has a fluid passage FP formed inside. The downstream end 30a of the main shaft 30 is located in the fluid passage FP. The main shaft 30 has a mounting portion 32 to which the first impeller 10 is attached, and a small-diameter portion 33 located downstream of the mounting portion 32 and having a smaller diameter than the mounting portion 32.

[0051] With this motor pump 1, since the main shaft 30 is provided with a small-diameter section 33, it is possible to suppress the rapid expansion of the flow area downstream of the main shaft 30, thereby suppressing the generation of fluid vortices and backflow. Furthermore, since the first impeller 10 is attached to a mounting section 32 that has a larger diameter than the small-diameter section 33, the torsional strength of the mounting section 32 of the main shaft 30 to which the first impeller 10 is attached can be ensured even when the small-diameter section 33 is provided. In other words, with the motor pump 1 of this embodiment, it is possible to suppress the generation of fluid vortices and backflow downstream of the main shaft 30 while ensuring the torsional strength of the mounting section 32 of the main shaft 30 to which the first impeller 10 is attached.

[0052] Furthermore, the motor pump 1 also includes a second impeller 20, which is positioned downstream of the first impeller 10 and fixed to the main shaft 30. The second impeller 20 is attached to the small-diameter section 33. With this configuration, the torsional strength of the mounting section 32 of the main shaft 30 to which the first impeller 10, which is subjected to rotational force from the motor 40, is attached can be ensured while providing the second impeller 20.

[0053] Furthermore, the impeller diameter D11 of the first impeller 10 is equal to the impeller diameter D21 of the second impeller 20. The inlet outer diameter D12 of the first impeller 10 is equal to the inlet outer diameter D22 of the second impeller 20. The inlet inner diameter D23 of the second impeller 20 is smaller than the inlet inner diameter D13 of the first impeller 10. With this configuration, even when a small diameter section 33 is provided, the head capacity and flow rate capacity of the motor pump 1 can be maintained.

[0054] Furthermore, the casing 50 includes a suction casing 51 positioned upstream of the first impeller 10 and having a suction port 50a for drawing in fluid, a discharge casing 52 positioned downstream of the second impeller 20 and having a discharge port 50b for discharging fluid, and an intermediate casing 53 positioned between the suction casing 51 and the discharge casing 52 and housing the second impeller 20. With this configuration, the casing 50 can be easily assembled.

[0055] <Second Embodiment> Next, the motor pump 1A according to the second embodiment will be described. Since the basic configuration of the motor pump 1A according to this embodiment is the same as that of the first embodiment, the differences will be described in detail.

[0056] Figure 4 shows a motor pump 1A according to this embodiment. As shown in Figure 4, in this embodiment, the impeller diameter D21 of the second impeller 20 is smaller than the impeller diameter D11 of the first impeller 10. Also, the inlet outer diameter D22 of the second impeller 20 is equal to the inlet outer diameter D12 of the first impeller. The inlet inner diameter D23 of the second impeller 20 is smaller than the inlet inner diameter D13 of the first impeller 10. Note that the inlet outer diameter D22 of the second impeller 20 may be smaller than the inlet outer diameter D12 of the first impeller.

[0057] Here, if the distance between the second impeller 20 and the intermediate casing 53 is small, the fluid discharged from the second impeller 20 will immediately collide with the intermediate casing 53, resulting in a large pressure loss. In this embodiment, the distance between the second impeller 20 and the intermediate casing 53 is increased by making the impeller diameter D21 of the second impeller 20 smaller than the impeller diameter D11 of the first impeller 10. This suppresses the immediate collision of the fluid discharged from the second impeller 20 with the intermediate casing 53, thereby reducing the pressure loss.

[0058] As described above, in the motor pump 1A according to this embodiment, the impeller diameter D21 of the second impeller 20 is smaller than the impeller diameter D11 of the first impeller 10. This configuration prevents the fluid discharged from the second impeller 20 from immediately colliding with the casing 50 (intermediate casing 53), thereby reducing pressure loss.

[0059] The technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0060] For example, as shown in Figure 5, in the main shaft 30, the first planar portion 32a of the mounting portion 32 may be positioned radially outward from the second planar portion 33a of the small diameter portion 33. In this case, the diameter of the mounting portion 32 can be made larger, and the torsional strength of the mounting portion 32 of the main shaft 30 to which the first impeller 10 is attached can be more reliably ensured.

[0061] Furthermore, in the above embodiment, the mounting portion 32 and the small diameter portion 33 have a double-chamfered structure. However, the present invention is not limited thereto. The mounting portion 32 only needs to have a structure that allows the rotational force of the first impeller 10 to be transmitted to the main shaft 30, and the small diameter portion 33 only needs to have a structure that allows the rotational force of the main shaft 30 to be transmitted to the second impeller 20. For example, as shown in Figure 6(a), the mounting portion 32 has a cross-section in which a projection 32b projecting radially outward is formed on the outer circumferential surface of the circular cross-section, and as shown in Figure 6(b), the small-diameter portion 33 may have a cross-section in which a projection 33b projecting radially outward is formed on the outer circumferential surface of the circular cross-section. In this case, a recess is formed in the insertion hole of the first boss portion 14 into which the projection 32b is fitted, and a recess is formed in the insertion hole of the second boss portion 24 into which the projection 33b is fitted. Alternatively, as shown in Figure 7(a), the mounting portion 32 may have a cross-section in which a groove 32c recessed radially inward is formed on the outer surface of the circular cross-section, and as shown in Figure 7(b), the small diameter portion 33 may have a cross-section in which a groove 33c recessed radially inward is formed on the outer surface of the circular cross-section. In this case, the insertion hole of the first boss portion 14 has a projection that fits into the groove 32c, and the insertion hole of the second boss portion 24 has a projection that fits into the groove 33c.

[0062] Furthermore, without departing from the spirit of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described embodiments and modifications may be combined as appropriate. [Explanation of Symbols]

[0063] 1. 1A motor pump 10. First Impeller 20. Second Impeller 30 main axis 30a downstream end 32 Mounting part 33 Small diameter section 40 motors 41 Rotor 42 Stator 50 casing 50a suction port 50b outlet 51 Suction casing 52 Discharge casing 53 Intermediate casing D11 First impeller diameter D12 Outer diameter of the inlet of the first impeller D13 Inlet inner diameter of the first impeller D21 Impeller diameter of the second impeller D22 Inlet outer diameter of the second impeller D23 Inlet inner diameter of the second impeller

Claims

1. The first impeller and The main shaft to which the first impeller is fixed, A motor that rotates the first impeller, A casing that houses the first impeller and the main shaft, and has a fluid passage formed inside through which fluid flows, Equipped with, The downstream end of the main shaft is positioned in the flow path. The main shaft has a mounting portion to which the first impeller is attached, and a smaller diameter portion located downstream of the mounting portion and having a smaller diameter than the mounting portion. Motor pump.

2. The system further comprises a second impeller, which is positioned downstream of the first impeller and fixed to the main shaft, The second impeller is attached to the small diameter section. The motor pump according to claim 1.

3. The impeller diameter of the first impeller and the impeller diameter of the second impeller are equal. The motor pump according to claim 2.

4. The outer diameter of the inlet of the first impeller is equal to the outer diameter of the inlet of the second impeller. The motor pump according to claim 2 or 3.

5. The inner diameter of the inlet of the second impeller is smaller than the inner diameter of the inlet of the first impeller. The motor pump according to claim 2 or 3.

6. The impeller diameter of the second impeller is smaller than the impeller diameter of the first impeller. The motor pump according to claim 2.

7. The motor comprises a rotor fixed to the first impeller and a stator positioned radially outward from the rotor. The motor pump according to claim 1.

8. The aforementioned casing is A suction casing is positioned upstream of the first impeller and has a suction port for drawing in the fluid, A discharge casing is positioned downstream of the second impeller and has a discharge port formed from which the fluid is discharged, An intermediate casing is positioned between the suction casing and the discharge casing and houses the second impeller, Having, The motor pump according to claim 2.

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