JP5630488B2 - Centrifugal compressor - Google Patents

Description

  The present invention relates to a centrifugal compressor including a vaned diffuser around an impeller.

  Centrifugal compressors are operated from a low flow rate when the rotational speed is low to a high flow rate when the rotational speed is high. When the flow rate is high, as shown in FIG. 5, since the velocity component V1 in the radial direction of the impeller is large, the gas easily flows to the diffuser, and there are relatively few problems. However, when the flow rate is low, as shown in FIG. 6, the velocity component V2 in the circumferential direction of the impeller increases, the gas flowing to the diffuser decreases, and the flow velocity also decreases. For this reason, a stall is likely to occur in the diffuser, and there is a problem that a low flow rate range in which operation is possible is limited. Many countermeasures have been proposed in the past in order to eliminate the problem at the time of low flow rate in such a centrifugal compressor and expand the operable low flow rate region.

  For example, by providing a vane that can be rotated by driving means on the diffuser wall and changing the inlet angle of the vane according to the flow rate, gas in the low flow rate region can easily flow into the diffuser, and compression efficiency is achieved by the gas rectifying effect. A means to increase Further, for example, Patent Document 1 discloses a configuration in which a vane set at a constant inlet angle is fixed to one diffuser wall, and the vane is inserted into a groove formed in the other diffuser wall across the diffuser. ing. One diffuser wall to which the vane is fixed is displaced to the other diffuser wall side by interposing one of a number of spacers provided between the vane and the casing, and the flow passage width of the diffuser is appropriately reduced. For this reason, the gas has an increased velocity component in the radial direction even at a low flow rate, and easily flows into the diffuser.

  Patent Document 2 is configured such that one of the diffuser walls having no vanes can be displaced to the other diffuser wall side by driving means, and the flow path of the diffuser is narrowed by moving one of the diffuser walls during low flow operation. Is disclosed. In Patent Document 2, by narrowing the diffuser passage width during low-flow operation, the velocity component in the radial direction of the low-flow gas supplied from the impeller is increased, and the gas easily flows into the diffuser.

JP 50-54909 A JP 2008-95678 A

  In the prior art in which the inlet angle of the vane provided on the diffuser wall is variably configured, the configuration of the driving means and the connecting means for changing the inlet angle of the vane is complicated. In addition, the vane is appropriately rotated according to the flow rate during operation based on the inlet angle adapted to a predetermined flow rate, and changes the inlet angle. It is difficult to change the angle appropriately. As a result, the conventional technique has a problem that as the distance from the reference flow rate increases, the difference between the angle of the gas flow direction and the inlet angle of the vane increases, and the compression efficiency decreases.

  Since the prior art disclosed in Patent Document 1 must be replaced as appropriate, it is difficult to put it to practical use in a centrifugal compressor that is operated while the flow rate continuously fluctuates from a low flow rate to a high flow rate. Furthermore, since the conventional technique and Patent Document 1 have a configuration in which the vane always regulates the entire width of the flow path of the diffuser, the vane itself becomes a resistance of the gas flowing into the diffuser especially when the high flow operation is performed. It has a common problem of disturbing the flow and reducing the compression efficiency.

  In Patent Document 2, it is possible to increase the flow velocity at a low flow rate by moving the diffuser wall and narrowing the flow passage width of the diffuser and increase the velocity component in the radial direction. It is unstable and has a problem that the compression efficiency cannot be sufficiently increased.

  An object of the present invention is to increase compression efficiency in a centrifugal compressor having a vaned diffuser wall regardless of changes in flow rate conditions from low flow rate to high flow rate.

In the present invention of claim 1, the rotating shaft is supported by a back plate forming a part of the casing, and a plurality of blades are provided on the curved peripheral surface of the impeller fixed to the rotating shaft, and a pair of blades are provided around the impeller. A centrifugal compressor that arranges a diffuser partitioned by a diffuser wall and a volute that communicates with the diffuser, sucks gas by rotation of the impeller during operation from low flow rate to high flow rate, and supplies the compressed gas to the diffuser A plurality of vanes having a constant inlet angle are provided on one of the diffuser walls so as to face the other diffuser wall, and the length of the vane in the radial direction is the diameter of the one diffuser wall. is set to be shorter than the length of the direction, the outer peripheral portion and inner peripheral portion of the one of the diffuser walls each flexible member Then, a driving means that is attached to the back plate and is connected to the one diffuser wall in a part of the casing, and the flexible members at the outer peripheral portion and the inner peripheral portion of the one diffuser wall are A part of the diffuser is formed together with one diffuser wall, and the one diffuser wall is separated from the position where the plurality of vanes approach the other diffuser wall and at least the extended portion of the curved peripheral surface of the impeller. The flow path width of the diffuser is determined by the pair of diffuser walls, and the vane is positioned between the pair of diffuser walls in the entire flow rate region from a low flow rate to a high flow rate. characterized by.

According to the first aspect of the present invention, the angle of the flow direction of the gas supplied from the impeller to the diffuser with respect to the inlet angle of the vane can be stabilized regardless of the change in the flow rate condition from the low flow rate to the high flow rate. The compression efficiency of the centrifugal compressor can be increased at any flow rate. In addition, when one diffuser wall is farthest away from the other diffuser wall, the vane opens the diffuser, so that the gas flow during high flow operation is not affected by the vane, and the compression efficiency can be sufficiently increased. it can.
In addition, the entire diffuser wall defining the diffuser can be moved with a simple configuration. Further, during operation on the high flow rate side, the gas flow from the impeller to the diffuser is guided by the flexible member, and no step is formed in the flow path, so that the gas can flow smoothly.

  According to a second aspect of the present invention, an annular space is formed on the outer peripheral side of the impeller of the back plate, the one diffuser wall is interposed in the annular space, and an outer peripheral portion and an inner portion of the one diffuser wall are interposed. Each of the peripheral flexible members is formed in an annular shape.

The present invention according to claim 3 is characterized in that short blades are arranged between a plurality of blades provided in the impeller, so that the space between the blades is widened and the suction efficiency of gas is increased. Gas can be narrowed down by a long blade and a short blade, and the compression efficiency of gas can be improved.
According to a fourth aspect of the present invention, in the above centrifugal compressor, a distance between a surface of the vane facing the other diffuser wall and the other diffuser wall can be changed.

  The present invention can increase the compression efficiency regardless of changes in the flow rate condition in the operation of the centrifugal compressor provided with the vanered diffuser wall.

It is a longitudinal cross-sectional view which shows the time of high flow operation of the centrifugal compressor in this embodiment. It is the sectional view on the AA line of FIG. It is a fragmentary longitudinal cross-section which shows the time of low flow operation of a centrifugal compressor. It is explanatory drawing which shows the flow of a vane and gas. It is explanatory drawing which shows the vane and the flow of gas in the conventional high flow volume driving | operation. It is explanatory drawing which shows the vane and the flow of gas in the conventional low flow volume driving | operation.

  Hereinafter, the present embodiment will be described with reference to FIGS. In the specification of the present application, the left side of FIG.

  The casing of the centrifugal compressor embodying the present invention is configured by joining the first casing 1 and the second casing 2 by appropriate means (not shown). A rotating shaft 5 to which an impeller 4 is fixed is rotatably supported by a back plate 3 that forms a part of the first casing 1 and extends in the radial direction via a bearing 6 with a sealing function. Although the rotating shaft 5 is not shown in the figure, for example, a turbine rotated by exhaust gas from an automobile engine is used as a driving source. The rotating shaft of the turbine is configured coaxially with the rotating shaft 5, and the impeller 4 of the rotating shaft 5 is rotated by the rotation of the turbine.

  The impeller 4 has six long blades (hereinafter simply referred to as blades) 7 attached at equal intervals on a curved peripheral surface 4a whose diameter increases from the front to the rear, and a central portion between the blades 7. It has six short blades 8 attached. The length of the short blade 8 is about one half of the length of the blade 7. The second casing 2 includes a parallel flow path 10 and a suction port 11 that expands in a funnel shape in front of a funnel-shaped space 9 that houses the impeller 4. A cochlear-shaped volute 14 that communicates with the diffuser 12 through the diffuser 12 and the communication space 13 is formed around the impeller 4. Therefore, the gas sucked from the suction port 11 by the rotation of the impeller 4 is supplied to the diffuser 12 while being compressed by the centrifugal force of the impeller 4 and further compressed. The gas compressed by the diffuser 12 is sent to the discharge port 15 through the communication space 13 and the volute 14 and supplied to a predetermined operating mechanism (not shown).

  An annular space 16 is formed on the back plate 3 on the outer peripheral side of the impeller 4 and is divided into an inner back plate 3a and an outer back plate 3b. The diffuser 12 is defined by a pair of diffuser walls 17 and a diffuser wall 18 disposed at a position facing the diffuser wall 17. The diffuser wall 17 is configured by a wall surface in which a part of the second casing 2 is erected in an annular shape, and the diffuser 12 is defined by the rear surface of the diffuser wall 17 and the volute 14 is defined by the front surface.

  The diffuser wall 18 is formed in an annular shape and is mounted in the annular space 16. Annular flexible members 20 and 21 fixed by a sandwiching plate 19 are provided on the inner peripheral portion and the outer peripheral portion of the diffuser wall 18. The inner peripheral part of the flexible member 20 is fixed to the inner back plate 3 a by the sandwiching plate 22, and the outer peripheral part of the flexible member 21 is fixed to the outer back plate 3 b by the sandwiching plate 23. Accordingly, the diffuser wall 18 is supported by the back plate 3 so as to be movable in the direction of the rotational axis of the impeller 4 by the bending of the flexible members 20 and 21. The flexible members 20, 21 form a part of the diffuser 12 together with the one diffuser wall 18.

  The diffuser wall 18 is connected to a driving means 25 attached to a part of the first casing 1 through a link mechanism 24. As the driving means 25, various means such as a hydraulic cylinder, a solenoid, a rotary solenoid, a servo motor, or a stepping motor can be used. Although not shown, the drive means 25 is driven by a drive command from a control device based on a detection signal from a rotational speed detection device of the rotary shaft 5 or a flow rate detection device of gas sucked by the impeller 4. For this reason, when the driving means 25 rotates by the driving amount commanded from the control device, the diffuser wall 18 can move to the diffuser wall 17 side by a predetermined amount or move in a direction opposite to the diffuser wall 17 by a predetermined amount.

  On the other hand, a plurality (17 in this embodiment) of vanes 26 are integrally provided on the diffuser wall 18 so as to face the diffuser 12. The vanes 26 are evenly arranged around the impeller 4 as shown in FIG. The vane 26 is formed in a spindle shape whose back side is slightly curved with respect to the rotation direction of the impeller 4, and is arranged so as to be inclined in the rotation direction of the impeller 4.

  The vane 26 has a radial reference line X1 whose longitudinal reference line X1 is perpendicular to the central axis of the rotary shaft 5, that is, the rotational axis of the impeller 4 (matches the radial velocity component V1 of the gas shown in FIG. 4). The inlet angle β is set to be inclined by a certain angle in the rotation direction of the impeller 4. The inlet angle β is set to an angle most suitable for the flow direction F3 (see FIG. 4) of the gas supplied from the impeller 4 to the diffuser 12 during operation at an arbitrary flow rate between a low flow rate and a high flow rate. Note that the arbitrary flow rate for setting the inlet angle β is preferably based on the flow rate on the high flow rate side rather than the low flow rate side from the configuration of the present invention.

  The operation of this embodiment configured as described above will be described based on FIGS. 1, 3 and 4 in comparison with the conventional fixed vane shown in FIGS. In addition, the code | symbol F1, F2, and F3 described in each figure show the flow direction of the gas supplied to the diffuser 12. FIG. V1 indicates a velocity component in the radial direction of the gas supplied to the diffuser 12, and V2 indicates a velocity component in the circumferential direction of the gas supplied to the diffuser 12. X1 indicates a reference line in the length direction of the vane 26, and X2 indicates a radial line orthogonal to the rotation axis of the impeller 4 (center axis of the rotation shaft 5). α1, α2, and α3 indicate angles of the gas flow directions F1, F2, and F3 with respect to the velocity component V1 in the radial direction (which coincides with the radial line X2). β represents the inlet angle of the vane 26 inclined in the rotational direction of the impeller 4 with respect to the velocity component V1 in the radial direction (which coincides with the radial line X2). As described above, the inlet angle β in each figure is a constant angle most suitable for the gas flow direction F3 at an arbitrary flow rate between a low flow rate and a high flow rate.

  FIG. 5 shows the gas flow when the centrifugal compressor is operated at a high flow rate. Since the gas has a high velocity component V1 in the radial direction, the gas flow direction F1 is directed in the radial direction. However, the gas flow angle α1 decreases, and the angle difference with respect to the inlet angle β of the vane 26 increases in the direction opposite to the rotation of the impeller 4. For this reason, even if the centrifugal compressor increases the amount of gas flowing into the diffuser 12, the rectification function by the vane 26 is lowered, and the compression efficiency is lowered. Further, the increase in the angle difference at the time of a high flow rate causes the vane 26 to become an obstacle to the gas flow, which further reduces the compression efficiency. The angle difference between the gas flow angle α1 and the inlet angle β of the vane 26 increases as the flow rate increases, and the reduction in the compression efficiency of the centrifugal compressor increases.

  FIG. 6 shows the gas flow when the centrifugal compressor is operated at a low flow rate. At a low flow rate, the gas flow velocity is low, and the circumferential velocity component V2 increases. For this reason, the gas flow direction F2 is greatly inclined in the rotation direction of the impeller 4, and the gas flow angle α2 is increased. Therefore, the angle difference between the gas flow angle α2 and the inlet angle β of the vane 26 increases in the rotation direction of the impeller 4, so that the gas does not easily flow into the diffuser 12 and the rectifying function by the vane 26 is also reduced, so that the compression efficiency is improved. descend. The angle difference between the gas flow angle α2 and the inlet angle β of the vane 26 increases as the flow rate decreases, and the reduction in the compression efficiency of the centrifugal compressor increases.

  As shown in FIGS. 5 and 6, even if the fixed vane 26 is installed as in the prior art, the gas flow angles α1, α2 and the inlet angle of the vane 26 on both the high flow rate side and the low flow rate side. The angle difference with β was increased, and the compression efficiency could not be sufficiently increased. The occurrence of such a problematic angle difference could not be resolved even if the vane 26 is made movable as in the prior art and the inlet angle β is changed.

  In this embodiment, as shown in FIG. 4, the inlet angle β of the vane 26 fixed to the diffuser wall 18 is initially set to an angle most suitable for the gas flow direction F3 at a predetermined arbitrary flow rate. The flow rate of the vane 26 functions as a rectifier, and the compression efficiency can be sufficiently increased. The inlet angle β is preferably set by selecting an arbitrary flow rate in a low flow rate state at a low rotation, such as when starting the centrifugal compressor. However, the arbitrary flow rate for setting the inlet angle β can be selected at the middle flow rate higher than the low flow rate or on the higher flow rate side than the middle flow rate.

  When the flow rate changes from the arbitrary flow rate to the low flow rate side, the driving means 25 is actuated by a command from a control device (not shown), and the diffuser wall 18 moves to the diffuser wall 17 side as shown in FIG. The vane 26 is disposed at a position that regulates the entire width of the flow path of the diffuser 12. The movement of the diffuser wall 18 narrows the flow passage width of the diffuser 12 and the flow passage area of the diffuser 12 is reduced. For this reason, the velocity component V1 in the radial direction of the gas supplied from the impeller 4 is increased, and the angle difference between the gas flow angle α3 and the inlet angle β is substantially the same level as that at the time of the initial setting at the predetermined arbitrary flow rate. Maintained. Therefore, the gas rectifying effect by the vane 26 is sufficiently generated, and the centrifugal compressor can obtain high compression efficiency as in the case of an arbitrary flow rate set in advance.

  When the flow rate changes from the preset arbitrary flow rate to the high flow rate side, the driving means 25 is operated by a command from a control device (not shown), and the diffuser wall 18 is separated from the diffuser wall 17 as shown in FIG. Move to. The flow path width of the diffuser 12 is wider than that at an arbitrary flow rate set in advance by the movement of the diffuser wall 18, and the flow path area is increased. For this reason, the velocity component V1 in the radial direction of the gas is reduced, and the gas flow direction F3 is inclined toward the vane 26 side. Therefore, the angle difference between the gas flow angle α3 and the inlet angle β is maintained at substantially the same level as at the initial setting at the preset arbitrary flow rate, and the centrifugal compressor is as high as at the preset arbitrary flow rate. Compression efficiency can be obtained. Further, the diffuser wall 18 retreats with a high flow rate to sequentially open the flow path of the diffuser 12. In the last retracted position, the surface of the vane 26 that faces the diffuser wall 17 is separated to the position of the extension of the curved peripheral surface 4a of the impeller 4, so that the diffuser 12 is completely opened. For this reason, the space | interval of the vane 26 and the diffuser wall 17 becomes substantially the same as the space | interval of the exit part of the gas in the impeller 4, and the flow of the gas which flows in into the diffuser 12 is not inhibited by the vane 26. Therefore, the optimum flow angle can be maintained even at high flow rates, and high compression efficiency can be obtained. The diffuser wall 18 may be set so that the vane 26 moves backward to a position further away from the position of the extended portion of the curved peripheral surface 4a.

  As described above, the present embodiment is configured such that the diffuser wall 18 provided with the vanes 26 moves in a direction approaching or separating from the diffuser wall 17 in accordance with a flow rate supplied from the impeller 4 to the diffuser 12. . With this configuration, the angle difference between the gas flow angle α3 and the inlet angle β of the vane 26 can be maintained at a constant level in any operation at a low flow rate to a high flow rate. Further, since the entire width of the flow path of the diffuser 12 is opened during high flow rate operation, the vane 26 does not hinder the flow of gas flowing into the diffuser 12. Therefore, the compression efficiency can be increased in all operations from the low flow rate to the high flow rate of the centrifugal compressor.

The above-described embodiment has the following operational effects.
(1) The compression efficiency can be increased in the operation from the low flow rate to the high flow rate of the centrifugal compressor.
(2) Since the vane 26 is fixed to the diffuser wall 18, the configuration is simple.
(3) Since the angle difference between the gas flow angle α3 and the inlet angle β of the vane 26 is kept almost constant at any flow rate, the operating range on the low flow rate side can be expanded.
(4) Due to the presence of the flexible members 20 and 21, gas leakage from the diffuser 12 can be prevented without requiring other means.

  The present invention is not limited to the configuration of the above-described embodiment, and various modifications are possible within the scope of the spirit of the present invention, and can be implemented as follows.

(1) The impeller 4 can be composed of only the blades made of long blades without the short blades 8.
(2) A vane 26 is provided on the diffuser wall 17 on the volute 14 side so as to be movable, and the diffuser wall 18 can be configured as a fixed wall.
(3) Both of the diffuser walls 17 and 18 can be configured to be movable toward and away from each other.

(4) The flexible members 20 and 21 can be formed of elastically deformable members made of rubber, resin, fiber reinforced resin, thin metal plate, or the like.

DESCRIPTION OF SYMBOLS 1 1st casing 2 2nd casing 3 Back plate 4 Impeller 4a Curved surrounding surface 5 Rotating shaft 7 Blade 8 Short blade 12 Diffuser 14 Volute 16 Annular space 17, 18 Diffuser walls 19, 22, 23 Clamping plates 20, 21 Flexible Member 25 driving means 26 vane

Claims (4)

A diffuser that supports a rotating shaft by a back plate that forms a part of the casing, includes a plurality of blades on the curved peripheral surface of the impeller fixed to the rotating shaft, and is partitioned by a pair of diffuser walls around the impeller, and In the centrifugal compressor that arranges a volute that communicates with the diffuser, sucks gas by rotation of the impeller during operation from low flow rate to high flow rate, and supplies the compressed gas to the diffuser.
A plurality of vanes having a constant inlet angle are provided on one of the diffuser walls so as to face the other diffuser wall,
The radial length of the vane is set shorter than the radial length of the one diffuser wall,
The outer peripheral portion and the inner peripheral portion of the one diffuser wall are each attached to the back plate by a flexible member, and driving means for connecting to the one diffuser wall is disposed in a part of the casing,
The flexible member of the outer peripheral part and the inner peripheral part of the one diffuser wall forms a part of the diffuser together with the one diffuser wall,
The one diffuser wall is movably disposed between a position where the plurality of vanes approach the other diffuser wall and a position spaced at least to an extension of the curved peripheral surface of the impeller ;
The flow path width of the diffuser is determined by the pair of diffuser walls,
The centrifugal compressor is characterized in that the vane is located between the pair of diffuser walls in the entire flow rate region from a low flow rate to a high flow rate .   An annular space is formed on the outer peripheral side of the impeller of the back plate, the one diffuser wall is interposed in the annular space, and the flexible members on the outer peripheral portion and the inner peripheral portion of the one diffuser wall are respectively annular. 2. The centrifugal compressor according to claim 1, wherein the centrifugal compressor is formed.   The centrifugal compressor according to claim 1 or 2, wherein a short blade is disposed between a plurality of blades provided in the impeller.   The centrifugal compressor according to any one of claims 1 to 3, wherein a distance between a surface of the vane facing the other diffuser wall and the other diffuser wall is changeable.

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