JP2005171825A - Fluid conveyance machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid conveyance machine of a small and compact structure for enabling high speed operation. <P>SOLUTION: A double suction type impeller 21 is disposed to a rotational shaft, and the impeller and a pump casing 31 disposed to surround the impeller constitute a double suction type pump 16. The rotational shaft 11 is supported in a non-contact state by magnetically levitated motors 12, 13 having a radial magnetic bearing function and a motor function, and is rotary driven. The double suction type pump 16 has a pressure balance mechanism positioning the rotational shaft in an axial direction. Preferably, the double suction type pump 16 is disposed at an approximately center of the rotational shaft 11. and two magnetically levitated motors 12, 13 are disposed on both sides of the pump 16 of the rotational shaft 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fluid conveyance machine, and more particularly to a fluid machine such as a pump suitable for high-speed operation.

  In an ordinary electric motor, the air gap magnetic flux distribution between the stator and the rotor is rotationally symmetric, and in principle, no magnetic levitation force in the radial direction is generated. On the other hand, the magnetic levitation motor can generate a radial force by unevenly distributing a magnetic flux distribution in which two rotating magnetic fields between the rotor and the stator are superimposed. That is, two rotating magnetic fields different in number of poles by ± 2 are formed on the stator, and by applying two rotating magnetic fields different in pole number, a static magnetic force in the radial direction is applied to the rotor, and a rotational driving force is applied to the rotor. A magnetic levitation motor to be applied is known (see Patent Document 1, Non-Patent Documents 1 and 2).

  In other words, this magnetic levitation motor combines the functions of a radial magnetic bearing and a motor, and has the function of supporting the rotor in a radial direction by the magnetic levitation force while generating a rotational driving force for the rotor. Have. The function of supporting the rotating shaft in the radial direction in a non-contact manner makes it possible to support the shaft of the rotating shaft in a non-contact manner even in an environment where a normal bearing cannot be used, for example, in an atmosphere in an ultra-low temperature vacuum. Further, since the rotating shaft is supported in a non-contact manner, friction and wear do not occur at all, and it is also suitable for a fluid transporting machine that extremely dislikes impurities such as ultrapure water.

JP-A-8-144987 "Prototypes and applications inside and outside bearingless drives" Annual Conference of Industrial Applications Division of the Institute of Electrical Engineers of Japan [1] p23-28. August 2002, Kagoshima University Christian Redmann, Paeul Meuter, Angelo Ramella, Thomas Gempp: `` 30kW Bearingless Cannedmotor Pump on The Test Bed '' Seventh International Symp. On Magnetic Bearings, ETH Zurich (2000)

  Further, during operation, a normal centrifugal pump generates a fluid force in the suction direction (axial direction), increasing the load on the axial bearing. Therefore, when the output of the pump is increased by an operation such as increasing the rotational speed, the axial force applied to the rotating shaft increases. In order to support the increased axial force, the axial magnetic bearing must be enlarged to cope with it, so that the shaft dimension becomes longer.

  In addition, when an impeller or an axial magnetic bearing is attached to the end of the rotating shaft, the rotational frequency limit determined by the bending frequency is reduced because the bending frequency of the rotating shaft is lower compared to the case where these are in the center of the rotating shaft. There is a problem that it ends up. Furthermore, since the amount of eccentricity due to bending of the rotating shaft increases, the weight imbalance of the rotating shaft increases, and a large vibration may occur at high speed rotation.

  Further, since the output of the centrifugal pump increases as the rotational speed increases, the impeller can be reduced in size by high-speed rotation operation if the output is the same. This downsizing can reduce the weight of the rotating body, increase the resonance frequency of the shaft, and facilitate magnetic levitation control. However, high-speed operation of the pump induces cavitation and leads to breakage of the impeller, so there is a limit to increasing the rotational speed.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fluid conveyance machine having a compact and compact structure capable of high-speed operation.

  The fluid conveyance machine of the present invention includes a double suction type impeller on a rotary shaft, and constitutes a double suction type pump together with a pump casing arranged so as to surround the impeller, and the rotary shaft is a radial magnetic bearing. A non-contact supported and rotationally driven by a magnetic levitation motor having both a function and a motor function, wherein the both suction pumps are provided with a pressure balance mechanism for positioning the rotating shaft in the axial direction. It is.

  According to the present invention, the rotary shaft is supported in the radial direction in a non-contact manner by the magnetic levitation motor, and positioned in the thrust direction by the pressure balance mechanism of both suction pumps. Can be omitted. For this reason, the axial length of a rotating shaft can be shortened. In addition, since the rotating shaft is supported in a non-contact manner by a magnetic levitation motor, bearing friction and wear do not occur, and the rotational speed limit determined by the bending frequency increases due to the shortening of the rotating shaft, making the structure suitable for high-speed operation. can get. By arranging a pump equipped with both suction type impellers, the rotational speed at which cavitation begins to occur can be increased, which makes it difficult for cavitation to occur even at high speed operation, and a stable pump. High speed operation is possible. Further, by increasing the rotational speed, it is possible to achieve high output and small size of the pump.

  Here, it is preferable that the both suction type pumps are arranged at substantially the center of the rotary shaft, and the two magnetic levitation motors are arranged on both sides of the pump of the rotary shaft. As a result, the frequency of the axis eigenvalue is increased, and the levitation stability region is expanded to a higher frequency, which can contribute to the improvement of levitation stability.

  The pump casing preferably includes a double volute. Thereby, the radial component of the fluid force acting on the rotating body can be reduced, and energy loss can be reduced. The pump casing may include a diffuser. Also by this, the radial component of the fluid force acting on the rotating body can be reduced, and energy loss can be reduced.

  Further, the pressure balance mechanism for positioning the rotating shaft in the axial direction includes a pair of variable gaps between the both sides of the both suction type impellers and the casing, and the size of the pair of variable gaps, It is preferable to balance the pressure on both sides of the both suction type impellers. Thereby, the rotary shaft provided with the pump impeller can be easily and reliably positioned in the axial direction without using an axial disk and an axial bearing.

  In general, according to the present invention, it is possible to provide a fluid conveyance machine such as a pump that shortens the shaft length, minimizes the influence of cavitation and enables high-speed operation, thereby reducing the size and size and increasing the output. it can.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, in each figure, the same code | symbol is attached | subjected to the member or element which has the same function, and the duplicate description is abbreviate | omitted.

  FIG. 1 shows a double suction pump (fluid transfer machine) according to an embodiment of the present invention. The fluid conveyance machine includes a double suction pump 16 at the center, and its rotary shaft 11 is rotationally driven by magnetic levitation motors 12 and 13 disposed on both sides of the pump 16 and is supported in a non-contact manner as a radial magnetic bearing. ing. Displacement sensors 19 are arranged on both sides of the magnetic levitation motors 12 and 13, and the magnetic levitation motor is controlled by a controller (not shown) based on the measured displacement of the rotary shaft 11, and the rotary shaft 11 is levitated and supported at a predetermined position. Touch-down bearings 20 are disposed on both sides of the displacement sensor 19.

  Both suction type pumps 16 are centrifugal pumps that are provided with symmetrical impellers 21 and pressurize the fluid sucked in the axial direction from both the left and right sides in the centrifugal direction (radial direction and tangential direction of the outer periphery). That is, the fluid sucked from the suction port 17 flows through the flow paths 17a and 17b on both sides of the pump casing 31, flows axially into the pump chamber 16b from the opening 16a of the casing, and is added in the centrifugal direction by the impeller 21. And discharged from the discharge port 18 through the double volute 22 shown in FIG.

  FIG. 2 shows a cross-sectional configuration of the main part of the pump 16. A double suction impeller 21 is fixed to the rotary shaft 11, and the fluid pressurized in the centrifugal direction by the rotation of the impeller 21 is guided to the discharge port 18 through the volute 22. The volute 22 is provided with a partition wall 23, whereby two volutes 22a and 22b can be formed, and the whole is a double volute. The volutes 22a and 22b are provided with respective inlets A and B, and the inlets A and B are arranged at rotationally symmetric positions rotated by 180 ° with respect to the rotation axis. Thus, by using the double volute type having two volute inlets A and B inside the casing, the radial component of the fluid force pressurized by the impeller can be greatly reduced. As a result, the efficiency of the pump can be increased, and a quiet operation becomes possible.

  FIG. 3 shows an enlarged cross-sectional configuration inside the pump casing. As described above, the impeller 21 fixed to the rotating shaft 11 has a both-suction type left-right symmetrical structure, and the blade that rotates the fluid sucked from the openings 16a of the casings 31 on the left and right sides in the axial direction. Pressure is applied in the centrifugal direction by the blades (blades) of the wheel 21 and the air is discharged from the discharge port 18 through the double volute 22 (22a, 22b) as described above.

  That is, in the double suction type pump 16, fluid is sucked in from the left and right sides along the axial direction of the rotating shaft 11, and the inside of the shrouds 32, 32 is radial (and the tangential direction of the outer periphery) by the rotating impeller 21. The fluid is pressurized. Therefore, axial thrust (thrust force) in the axial direction is evenly generated on the left and right, so that basically no axial bearing is required. The pump 16 is provided with a pressure balance mechanism for positioning the rotary shaft 11 in the axial direction by the double suction pump 16.

The impeller 21 includes left and right symmetric shrouds 32 and 32, and the convex portions 32 a and 32 b face the inner surface of the casing 31 to form gaps. That is, a pair of gaps _CAL and _CAR are formed between the convex portion 32a of the shroud 32 and the inner side surface of the casing 31, and constitute a gap resistance in which the pressurized fluid returns to the suction side of the impeller. . Similarly, a pair of clearance C _R also between the inner circumferential surface of the convex portion 32b and the casing 31 of the shroud _32, C _R is formed, the gap resistance of the return flow path to the suction side of the similarly pressurized fluid It is composed.

The operation of this pressure balance mechanism is as follows. If the rotating shaft 11 moves to the left side in the figure, the left gap _CAL becomes smaller and the right gap _CAR becomes larger. Accordingly, the pressure _{P L} of the chamber 35L is increased, whereas the pressure _{P R} of the chamber 35R is reduced. Therefore, the pressure _P L, the magnitude difference between the _{P R,} the rotation shaft 11 fixed thereto and the shroud 32, 32 chambers 35L, is returned to the substantially central portion of the 35R, are positioned here. Incidentally, the convex portion 32b of the shroud 32 has sufficient axial length to lie along the inner peripheral surface 31b of the casing 31, that the rotation shaft 11 is kept constant the clearance C _R be moved in the axial direction it can. Thereby, the clearance resistance in the return flow path to the fluid chambers 35L and 35R of the fluid pressurized by the pump can be kept constant.

で求められる。 Next, consider cavitation. In a normal so-called single suction pump, the suction specific speed S, which serves as an index of the cavitation generation limit, is determined by its required effective suction head: H _NPSH [m], flow rate: Q [m ³ / min], and rotational speed n _S [min− ¹ ]

Is required.

により求めることができる。同じ揚程かつ同じ流量の片吸込ポンプと両吸込ポンプでは、それぞれのキャビテーション発生限界の回転速度は上の２つの式より

で関係づけられる。これにより両吸込ポンプにおいては、理論上、キャビテーションが発生し始める回転速度は片吸込ポンプに比べ√２倍になり、その分だけ高速回転が実用上可能になることを意味している。 Double-suction pumps are symmetrical in axial direction, it is characterized in that both with respect to the axis is suction port is the rotational speed and n _d, the suction specific speed

It can ask for. For single suction pumps and double suction pumps with the same head and flow rate, the rotational speed of each cavitation generation limit is

Are related. As a result, in both the suction pumps, the rotational speed at which cavitation starts theoretically becomes √2 times that in the single suction pump, which means that high speed rotation is practically possible.

  Next, support and driving of the rotating shaft by the magnetic levitation motors 12 and 13 will be described. The magnetic levitation motors 12 and 13 form two rotating magnetic fields having a number of poles different by ± 2 by windings (not shown) provided on the stator 14, and rotationally drive the rotor 15 fixed to the rotating shaft 11 and support the magnetic levitation. Is. That is, by forming, for example, a two-pole and four-pole rotating magnetic field on the stator 14, the rotor 15 is driven to rotate as a motor by the two-pole rotating magnetic field, and the two-pole rotating magnetic field and the four-pole rotating magnetic field are superimposed. Thus, a static magnetic flux distribution in the radial direction is formed, and by controlling the magnitude, the rotary shaft 11 can be levitated and supported at an arbitrary position as a radial magnetic bearing.

  The floating position of the rotating shaft 11 is controlled by a quadrupole rotating magnetic field supplied to the stator 14 by a control device (not shown) so that the position of the rotating shaft is detected by the displacement sensor 19 and the rotating shaft 11 is supported at a predetermined position. This can be done by adjusting the magnitude and phase of the (control magnetic field).

By adopting a magnetic levitation motor instead of an independent motor and magnetic bearing, not only the number of components can be reduced, but also the rotational axis length can be shortened. As a result, high-speed rotation and cost improvements are achieved. Note that the non-contact support of the rotating shaft 11 by the magnetic levitation motors 12 and 13 is only in the radial direction. However, when the rotating body is supported in a completely non-contact manner, an axial magnetic bearing is further required in the prior art.
The structure of a general axial magnetic bearing is composed of a disk fixed to a shaft and electromagnets arranged to face each other so as to sandwich the disk from the axial direction. In the configuration of a rotary machine having an axial magnetic bearing, the entire length of the rotary shaft becomes long. For this reason, the dangerous frequency of the shaft is lowered, and high-speed rotation becomes difficult as described above. Further, since the axial bearing is added, the surface area of the rotating body increases, and as the surface area increases, the friction loss of the fluid surrounding the rotating body increases, and as a result, the energy loss of the device also increases.

  However, by combining the suction pumps 16 having the pressure balance mechanism described above with the magnetic levitation motors 12 and 13, the axial magnetic bearing is completely unnecessary. As a result, the rotating shaft can be shortened, so that the resonance frequency can be increased, and the fluid loss that has occurred in the axial magnetic bearing portion can be eliminated. Further, by arranging both the suction pumps 16 at the center of the shaft and the magnetic levitation motors 12 and 13 at both ends thereof, a light and compact device can be obtained, and the weight imbalance of the rotating shaft can be eliminated. As a result, the frequency of the shaft eigenvalue increases, which can contribute to the floating stability of the rotating body.

  If the dimensions of the motors located on both sides of the pump are made equal in this arrangement, the rotary shaft 11 can be made to be completely symmetrical in the axial direction including the pump portion. Can take a value. In addition, since the two magnetic levitation motors have the same dimensions, the shaft support rigidity of the two magnetic levitation motors is completely matched, so that no bearing imbalance occurs and high-speed rotation is facilitated. Further, by making the two motor structures the same, a mass production effect is produced.

  Furthermore, by making the pump casing into the double volute type described above, the radial component of the fluid force acting on the rotating body can be greatly reduced. As a result, the radial displacement of the rotating body supported by magnetic levitation becomes minute and vibrations It is possible to provide a fluid transfer machine with a small amount. The effect of reducing the vibration in the radial direction is that the radial component of the fluid force acting on the rotating body is not affected by the shape of the double volute casing as described above, but also by the properly arranged diffuser 26 as shown in FIG. It can be greatly reduced and a similar effect can be obtained.

  As is clear from the above description, the combination of both suction pumps and a magnetic levitation motor eliminates the need for an axial magnetic bearing, shortens the shaft length, and is a lightweight and compact fluid transfer machine. Can be provided. In addition, the reduction in shaft length and the difficulty of generating cavitation in both suction pumps make it possible to rotate at a higher speed than before, which is useful for reducing the size of the pump and increasing the output.

  In addition, the said embodiment described one aspect | mode of the Example of this invention, Of course, a various deformation | transformation Example is possible, without deviating from the meaning of this invention.

It is front sectional drawing of the fluid conveyance machine of one Embodiment of this invention. It is sectional drawing which shows the structural example of the volute part of the fluid conveyance machine shown in FIG. It is front sectional drawing which shows the structural example inside the pump of the fluid conveyance machine shown in FIG. It is sectional drawing which shows the other structural example of the volute part of the fluid conveyance machine shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Rotating shafts 12 and 13 Magnetic levitation motor 14 Stator 15 Rotor 16 Both suction type pump 16a Opening part 16b Pump chamber 17 Suction port 17a, 17b Flow path 18 Discharge port 19 Displacement sensor 21 Impeller 22, 22a, 22b Volute 23 Partition 26 the diffuser 31 casing 31b the inner peripheral surface 32 the shroud 32a of the casing, 32b convex portion 35L, 35R chamber _{C AL, C AR, C R} clearance _P L, _{P R} pressure

Claims (6)

A rotary suction shaft is provided with a double suction impeller, and a double suction pump is configured with a pump casing arranged so as to surround the impeller,
The rotating shaft is non-contact supported and rotated by a magnetic levitation motor having a radial magnetic bearing function and a motor function,
The both-suction type pump includes a pressure balance mechanism for positioning the rotating shaft in an axial direction.   2. The fluid according to claim 1, wherein the both suction type pumps are arranged at substantially the center of the rotary shaft, and the two magnetic levitation motors are arranged on both sides of the pump of the rotary shaft. Conveying machine.   The fluid conveying machine according to claim 1, wherein the pump casing includes a double volute.   The fluid transport machine according to claim 1, wherein the pump casing includes a diffuser.   The pressure balance mechanism that positions the rotating shaft in the axial direction includes a pair of variable gaps between both sides of the both suction type impellers and the casing. The fluid conveying machine according to claim 1 or 2, wherein the pressures on both sides of the suction type impeller are balanced. 3. The fluid conveyance machine according to claim 1, wherein the magnetic levitation motor forms two rotating magnetic fields having a number of poles different by ± 2 in the stator, and rotationally drives the rotor and supports the magnetic levitation. 4. .

Images