Impeller cover and balance adjusting device for impeller

Abstract

The present invention provides an impeller cover attached to an impeller provided with a hub and blades. The impeller cover covers at least a part of the hub, and is provided with a cover surface provided with a suction port and a ventilation port for gas. The impeller cover is provided with a tool insertion part into which a tool is inserted so that the blade of the tool is exposed from the cover surface. The impeller cover includes: a suction passage that communicates with the suction port and through which the gas passes; and a gas passage that communicates with the ventilation port and through which the gas passes.

Description

Impeller cover and impeller balance adjustment device

[0001] The present disclosure relates to an impeller cover and an impeller balancing device.

[0002] Patent Document 1 discloses a turbine rotor having a rotational balance correction portion provided on the back surface of the turbine wheel. The rotational balance of the turbine rotor is adjusted by cutting the rotational balance correction portion with a cutting tool. Patent Document 2 discloses a machining method in which a workpiece is machined while removing chips using a chip suction head.

[0003] International Publication No. 2014 / 128930 Patent Publication No. 2005-125472

[0004] When adjusting the rotational balance of the impeller, it is desirable to cut the hub at a position where scattering of chips is not a problem. Specifically, to prevent chips from getting into the bearing that supports the impeller's rotating shaft, it is desirable to cut the axial tip of the hub, which is opposite the back side of the impeller. On the other hand, the amount of balance adjustment increases the farther away from the rotating shaft, but because the outer diameter of the tip of the hub is smaller than that of the base end on the back side, there is a possibility that balance adjustment will be insufficient.

[0005] The present disclosure describes an impeller cover and an impeller balance adjusting device that can adjust the rotational balance of an impeller while suppressing scattering of chips.

[0006] One example of the present disclosure is an impeller cover attached to an impeller having a hub and blades. The impeller cover includes: a cover surface that covers at least a portion of the hub and has a gas suction port and a vent port; a tool insertion portion into which a tool is inserted so that the tool blade is exposed from the cover surface; a suction passage that communicates with the suction port and through which gas passes; and a gas passage that communicates with the vent port and through which gas passes.

[0007] The impeller cover is attached to the impeller, and the tool is inserted into the tool insertion section so that the tip of the tool is exposed from the cover surface and in contact with the hub. When the tool is driven in this state, it cuts the hub and adjusts the rotational balance of the impeller. Chips generated by cutting the hub are sucked out through the suction port along with gas, preventing them from scattering to unexpected locations. In addition, the tool has a separate air vent from the suction port, which allows for the creation of a stable airflow when sucking in the chips. As a result, the rotational balance of the impeller can be adjusted while preventing chips from scattering.

[0008] In some examples, the cover surface may include a distal cover portion facing the distal end, which is one of the axial ends of the hub, and a proximal cover portion facing the proximal end, which is the other end and has a larger outer diameter than the distal end. The tool insertion portion may include a tool opening provided in the cover surface so that a tool blade is exposed, and the tool opening may be located closer to the proximal cover portion than the distal cover portion. The hub has a larger outer diameter at the proximal end than at the distal end. By locating the tool opening closer to the proximal cover portion than the distal cover portion, cutting can be performed closer to the proximal end, resulting in a larger amount of balance adjustment compared to cutting closer to the distal end. In addition, chips generated near the proximal end are sucked in through the suction opening, preventing them from scattering to undesired locations, such as getting around the rotating shaft.

[0009] In some examples, the tool insert includes a tool port provided on the cover surface so that a tool blade is exposed, and the tool port may be located closer to the vent port than the suction port. Chips generated when the tool cuts the hub are carried by the gas flowing in from the vent port toward the suction port and are sucked in through the suction port.

[0010] In some examples, the cover surface may include a tip cover portion facing the tip end, which is one of both axial end portions of the hub, and a base cover portion facing the base end, which is the other axial end and has a larger outer diameter than the tip end, and the suction port may be located closer to the tip cover portion than the vent port.

[0011] In some examples, the area of ​​the suction port may be larger than the area of ​​the vent port, which can increase the suction flow rate when sucking up chips.

[0012] In some examples, the cover surface may have a circumferential direction corresponding to the circumferential direction of the hub, and multiple vent holes may be provided on the cover surface in the circumferential direction. This allows gas to be taken in from multiple locations in the circumferential direction, making it possible to suction chips and prevent chips from leaking.

[0013] In some examples, the cover surface may include a tip cover portion facing the tip end, which is one of both axial end portions of the hub, and a base cover portion facing the base end, which is the other end and has a larger outer diameter than the tip end, the suction port may be disposed in the tip cover portion, and the suction passage may extend in the axial direction of the impeller. Chips can be sucked from the tip end of the hub, which is on the front side of the impeller.

[0014] In some examples, the cover surface may be provided along the shroud surface, including the outer edge of the blade. When adjusting the cutting position using the tool, the position adjustment is performed by slightly rotating the impeller without changing the position of the tool. In this case, if the cover surface is provided along the shroud surface, the impeller cover does not interfere with the rotation of the impeller. Therefore, the impeller can be rotated with the impeller cover attached, improving workability.

[0015] An impeller balancing device according to one example of the present disclosure includes an impeller cover attached to an impeller having a hub and blades, a suction device connected to the impeller cover for sucking in gas, a tool for cutting the hub, and a tool driving device for driving the tool. The impeller cover includes a cover surface that covers at least a portion of the hub and has a gas suction port and a vent port, a tool insertion portion into which the tool is inserted so that the tool blade is exposed from the cover surface, a suction passage communicating with the suction port, and a gas passage communicating with the vent port.

[0016] With the impeller balance adjustment device, chips generated when the tool cuts the hub are sucked out through the suction port together with gas, preventing the chips from scattering to unexpected locations. Furthermore, gas flows in through the vent port in conjunction with the suction of the chips, enabling stable chip suction. As a result, the rotational balance of the impeller can be adjusted while preventing chips from scattering.

[0017] In some examples, the apparatus may further include a gas supply device that supplies compressed gas to the gas passage. Supplying compressed gas makes it easier to send chips toward the suction port.

[0018] In some examples, the suction flow rate of the suction device may be greater than the supply flow rate of the gas supplied by the gas supply device. By making the suction flow rate greater than the supply flow rate of the compressed gas, more chips can be sucked in.

[0019] According to some examples of the present disclosure, the rotational balance of the impeller can be adjusted while suppressing scattering of chips.

[0020] Fig. 1 is a schematic side view showing an example of an impeller balance adjustment device and a rotary machine. Fig. 2 is a front view of an impeller with an impeller cover attached. Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. Fig. 4 is a plan view showing the front portion of the impeller cover. Fig. 5 is a perspective view showing the back portion of the impeller cover. Fig. 6 is a side view showing an example of an impeller cover attached to an impeller. Fig. 7 is a cross-sectional perspective view showing an example of an impeller cover attached to an impeller. Fig. 8 is a schematic view showing an example of an impeller balance adjustment device.

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals.

[0022] 1 shows an electric supercharger as an example of a rotating machine. These rotating machines 100 are becoming faster and more sophisticated every year, and as a result, there is a strong demand for stability in the rotating machines 100. Therefore, it is important to check and adjust the rotor stability at normal rotation speeds or higher, i.e., the rotational balance of the impellers 50, 60. Rotational balance refers to the amplitude of vibration relative to the rotational speed of the rotating shaft, and if the amplitude of vibration exceeds a predetermined value, it can be determined that the rotational balance has been impaired.

[0023] For example, the rotary machine 100 includes a compressor 110, a motor 120, and a turbine 130. The rotary machine 100 drives the compressor 110 with the motor 120, which is powered by electricity. The compressor 110 receives power from the motor 120 via a rotating shaft 140 and compresses air. The compressed air is discharged to, for example, an internal combustion engine. The turbine 130, for example, recovers exhaust gas discharged from the internal combustion engine and assists in the rotation of the rotating shaft 140.

[0024] The motor 120 is accommodated in a housing 121. The bearing 122 is disposed within the housing 121. The rotating shaft 140 is supported by the bearing 122. Impellers 50 and 60 are fixed to both ends of the rotating shaft 140. The impeller 50 on the compressor 110 side is, for example, a compressor impeller. The impeller 60 on the turbine side is, for example, a turbine impeller.

[0025] For example, the impeller balancing device 1 can be used to adjust the rotational balance of the impeller 60. The impeller balancing device 1 corrects the weight imbalance of the impeller 60 by cutting a predetermined portion of the impeller 60, thereby adjusting the rotational balance of the impeller 60.

[0026] As shown in Figures 2 and 3, the impeller 60 comprises a hub 61 that is attached to and fixed on the rotating shaft 140, and a plurality of blades 62 that are arranged at equal intervals along the circumferential direction (e.g., the rotational direction) of the hub 61.

[0027] The hub 61 has two ends in the axial direction of the rotating shaft 140, one end being a tip end 61b and the other end being a base end 61a. The base end 61a is the end on the back side of the impeller 60, and the tip end 61b is the end opposite the base end 61a in the axial direction. For example, the outer diameter of the hub 61 gradually increases from the tip end 61b to the base end 61a. For example, the outer diameter of the hub 61 is smallest at the tip end 61b and largest at the base end 61a. The tip end 61b of the hub 61 is fixed to the rotating shaft 140 by a fastener 70 (for example, a nut).

[0028] The blades 62 are erected from the hub surface 61c and extend from the tip end 61b to the base end 61a of the hub 61, forming a complex shape. The blades 62 each include a trailing edge 62a near the base end 61a of the hub 61, a leading edge 62b near the tip end 61b, and a shroud 62c that curves to connect the leading edge 62b and the trailing edge 62a. The outer edge of the blade 62 is formed by, for example, the leading edge 62b, the trailing edge 62a, and the shroud 62c. In each drawing, the shroud 62c of the blade 62 is shown as a straight line for simplification.

[0029] The blades 62 are arranged at equal intervals in the circumferential direction of the impeller 60. The outer edges of the blades 62 move along substantially the same trajectories when the impeller 60 is rotating. The shroud surface 62d indicates the trajectories of the outer edges of the blades 62, and for example, indicates the trajectory of the shroud 62c.

[0030] When adjusting the rotational balance of the impeller 60, the hub surface 61c is machined. For example, exposed hub surfaces 61d exist between adjacent blades 62 in the circumferential direction on the hub surface 61c. The hub surfaces 61d are the target of machining. The amount of rotational balance adjustment increases as the machining location radially moves away from the rotary shaft 140, resulting in a higher adjustment effect relative to the amount of machining. The outer diameter of the hub 61 increases as the machining location moves axially away from the tip end 61b. In other words, the outer diameter of the hub 61 increases axially as it approaches the base end 61a. Therefore, machining a portion closer to the base end 61a than the tip end 61b increases the amount of rotational balance adjustment. Furthermore, because the base end 61a is thicker than the tip end 61b, machining the vicinity of the base end 61a can prevent damage to the hub 61.

[0031] The impeller balancing device 1 (see FIG. 1) includes an impeller cover 2 attached to an impeller 60, a suction device 3 connected to the impeller cover 2 and configured to suck in a gas G (e.g., air), a tool 4 for cutting the hub 61, and a tool driving device 5 for driving the tool 4. Chips C generated by cutting the hub 61 are sucked in by the suction device 3 and discharged to the outside of the impeller cover 2. The impeller balancing device 1 may also include a gas supply device 6 for supplying compressed gas G (e.g., compressed air) into the impeller cover 2.

[0032] 2 and 3, the impeller cover 2 is attached to the impeller 60. The impeller cover 2 has a first direction D1 that is a direction along the axial direction of the impeller 60 or the hub 61 based on the state in which the impeller cover 2 is attached to the impeller 60, and a second direction D2 that is a direction along the circumferential direction of the impeller 60 or the hub 61 based on the state in which the impeller cover 2 is attached to the impeller 60. The impeller cover 2 also has a third direction D3 that is a direction along the radial direction of the impeller 60 or the hub 61 based on the rotation axis 140. Hereinafter, without any additional explanation, when the term "axial direction" is used, it means the first direction D1, when the term "circumferential direction" is used, it means the second direction D2, and when the term "radial direction" is used, it means the third direction D3.

[0033] The impeller cover 2 includes a cover body 21 that houses at least a portion of the impeller 60, and a fixing portion 22 (e.g., a flange) that is provided to protrude from the cover body 21. The cover body 21 is fixed to a housing 121 (e.g., a motor housing) of the rotary machine 100 via the fixing portion 22.

[0034] 3, 4, and 5, the cover body 21 has a back portion 21a that faces the impeller 60 in the axial direction D1, and a front portion 21b that is on the opposite side of the back portion 21a in the axial direction D1. The back portion 21a has a recess that accommodates at least a portion of the impeller 60. This recess is the cover surface 7. The cover surface 7 is arranged so as to cover at least a portion of the hub 61 of the impeller 60. The cover surface 7 is arranged so as to follow, for example, the shroud surface 62d (see FIG. 3) when installed on the impeller 60. "Likely following the shroud surface 62d" means that the cover surface 7 is spaced apart from the shroud surface 62d while maintaining substantially the same shape facing the shroud surface 62d.

[0035] The cover surface 7 includes a hub surface cover portion 71 (see FIG. 5 ) that faces the hub 61 in the radial direction D3, and a shaft end cover portion 72 that faces the tip end portion 61 b ​​of the hub 61 in the axial direction D1. The shaft end cover portion 72 faces the fastening portion 70 that fixes the impeller 60 to the rotary shaft 140.

[0036] The hub face cover portion 71 includes a base end cover portion 73 that faces the base end 61a of the hub 61, and a tip end cover portion 74 that faces the tip end 61b of the hub 61. The hub face cover portion 71 can be understood as being divided into two regions, for example, in the axial direction D1 of the blade 62. Of the two regions, the region that is closer to the base end cover portion 73 than the tip end cover portion 74 in the axial direction D1 is the base end cover region 71B, and the region that is closer to the tip end cover portion 74 in the axial direction D1 than the base end cover region 71B is the tip end cover region 71A. Note that the tip end cover region 71A also includes the region that extends beyond the tip end cover portion 74 to the axial end cover portion 72.

[0037] The cover surface 7 has a first opening, a second opening, and a third opening. The first opening is a tool opening 8 through which the blade of the tool 4 that cuts the hub 61 is exposed. The second opening is a discharge opening 9 (an example of a vent port) through which the gas G passes. The third opening is a suction opening 10 through which the gas G is sucked. The tool opening 8, the discharge opening 9, and the suction opening 10 can each have various shapes. For example, they may be a shape defined by curves such as a circle or an ellipse, a shape defined by straight lines such as a polygon, or a shape defined by a combination of straight lines and curves.

[0038] A hub surface 61d is disposed between adjacent blades 62 (see FIG. 3). The hub surface 61d is exposed, avoiding the blades 62. The hub surface 61d is the portion to be cut, and the space to which the hub surface 61d is exposed is a cutting space Ac. A plurality of cutting spaces Ac are formed on the impeller 60 in the circumferential direction D2. The plurality of cutting spaces Ac are formed so as to be partitioned by the plurality of blades 62.

[0039] The tool opening 8 is disposed in a position facing the space Ac to be cut when the impeller cover 2 is attached to the impeller 60. The tool opening 8 is provided so that the blade of the tool 4 can pass through and is guided to a position that avoids the blade 62. For example, the tool opening 8 has a shape and dimensions that face one of the spaces Ac to be cut. The tool opening 8 is provided so as to avoid the movement trajectory of the tool 4 when cutting the hub surface 61d. The tool opening 8 has, for example, an elongated hole shape that is long in the axial direction D1 of the rotation shaft 140. The tool 4 inserted into the tool opening 8 moves along the tool opening 8 to cut the hub 61.

[0040] The discharge port 9 is disposed adjacent to the tool port 8. The discharge port 9 is provided at a position closer to the base end cover portion 73 than the tool port 8. For example, the discharge port 9 is disposed next to the tool port 8 in the axial direction D1. A part or all of the discharge port 9 is disposed in the base end cover portion 73. The discharge port 9 is formed with a size and shape that can fit between adjacent blades 62.

[0041] The discharge port 9 has, for example, an elongated opening shape (e.g., rectangular) that is long in the circumferential direction D2 (see FIG. 5). Both end portions 9a of the discharge port 9 in the circumferential direction D2 are arranged to follow the shape of the blade 62 and are close to the blade 62. By arranging the discharge port 9 to follow the shape of the blade 62, it is possible to prevent the connection portion (root portion) between the hub surface 61c and the blade 62 from becoming a dead space and causing chips C to remain.

[0042] The suction port 10 is provided at a position that allows it to communicate with the cutting target space Ac. "Communicable" means that it is fluidly connected. The suction port 10 is provided so as to overlap a portion of the cutting target space Ac. The suction port 10 is disposed at a position closer to the tip cover part 74 than the base end cover part 73. For example, part or all of the suction port 10 is provided in the tip cover part 74.

[0043] The cover body 21 includes a tool insertion portion 80 into which the tool 4 is inserted, a suction passage 11 communicating with the suction port 10 , and a gas passage 91 communicating with the discharge port 9 .

[0044] The tool insertion portion 80 includes the tool opening 8, a guide hole (e.g., a tool guide hole 81) communicating with the tool opening 8 and penetrating the cover body 21, and a tool introduction opening 82. The tool introduction opening 82 is provided on the opposite side of the tool opening 8, and the tool guide hole 81 is disposed between the tool introduction opening 82 and the tool opening 8. The tool 4 is inserted into the tool guide hole 81 through the tool introduction opening 82 and is held in the tool opening 8 with the blade 41 exposed. The tool opening 8 and the tool introduction opening 82 are elongated holes that are long in the axial direction D1 to allow movement of the tool 4 during cutting. The tool guide hole 81 penetrates the cover body 21 to linearly connect the tool opening 8 and the tool introduction opening 82. The tool guide hole 81 is a hole that continues in the same shape in a direction (e.g., a linear direction) from the tool opening 8 to the tool introduction opening 82, and has, for example, a constant inner diameter. The tool 4 moves within the tool guide hole 81 along the longitudinal direction of the tool opening 8 and the tool introduction opening 82 .

[0045] The suction passage 11 is provided to communicate with the suction port 10 and to pass through the cover body 21. The suction passage 11 has a pipe connection part 12 arranged at the end opposite to the suction port 10. The pipe connection part 12 is, for example, a thread groove, and is connected to the pipe part 3a of the suction device 3 (see FIG. 1).

[0046] The gas passage 91 is in communication with the discharge port 9 and is provided to penetrate the cover body 21. The gas passage 91 is a bent passage so as to avoid the tool insertion portion 80. The gas passage 91 has a gas inlet portion 92 arranged at the end opposite the discharge port 9. The gas inlet portion 92 is, for example, a piping connection portion, and is a threaded groove to which the piping portion 6a (see FIG. 1) of the gas supply device 6 or the like is connected. When the gas supply device 6 is not in use, the gas inlet portion 92 can also function as an opening open to the atmosphere.

[0047] 1, the suction device 3 is, for example, a commercial vacuum cleaner, and includes a pipe section 3a connected to a pipe connection section 12 (see FIG. 4) of the suction passage 11, and a suction section 3b connected to the pipe section 3a. The pipe section 3a is, for example, a tube connectable to the pipe connection section 12. The suction section 3b generates negative pressure by, for example, rotating a fan, and sucks gas G containing chips C from inside the impeller cover 2 through the pipe section 3a. The suction section 3b can adjust the suction flow rate as needed.

[0048] The gas supply device 6 includes a piping section 6a connected to a gas inlet section 92 (see FIG. 4) of the gas passage 91, and a compressor section 6b connected to the piping section 6a. The piping section 6a is a tube or the like that can be connected to the gas inlet section 92. The compressor section 6b generates compressed gas G (e.g., compressed air) and supplies the gas G into the impeller cover 2 via the piping section 6a. The compressor section 6b can appropriately adjust the supply flow rate of the gas G.

[0049] The relationship between the suction device 3 and the gas supply device 6 is set, for example, so that the suction flow rate is greater than the supply flow rate of the compressed gas G. To satisfy this condition, for example, the area of ​​the suction port 10 may be set to be greater than the area of ​​the discharge port 9. Furthermore, to satisfy this condition, the opening degrees of the valves provided in the suction device 3 and the gas supply device 6 may be adjusted. By satisfying the above condition, the gas G supplied into the cover surface 7 is less likely to leak from gaps other than the suction port 10. As a result, it is possible to prevent chips C from scattering outside the impeller cover 2.

[0050] The tool 4 is a cutting tool with a blade 41 at its tip (see FIGS. 2 and 3 ). The tool 4 is driven so that the blade 41 moves (for example, translationally or rotationally) to cut the hub surface 61 d. The tool driving device 5 includes a tool holder that holds the tool 4, a motor and gear mechanism that move the tool 4 for cutting, a control unit that controls the motor, etc. The tool 4 held in the tool holder is inserted into the tool insertion portion 80 and is placed so that the blade 41 is exposed from the tool opening 8 and abuts against the hub surface 61 d. The tool driving device 5 translates the tool 4, for example, along the slope of the hub surface 61 c, causing the blade 41 to bite into the hub surface 61 d and cut the hub surface 61 d.

[0051] A method for adjusting impeller balance using the impeller balancing device 1 will be described. For example, the rotational balance of the impeller 60 of the rotary machine 100 is measured and evaluated in advance. In measuring the rotational balance, the rotating shaft 140 is rotated, and the amplitude of the impeller 60 is measured, particularly when the rotating shaft 140 is rotated at high speed. Based on the acquired measurement values, an evaluation is made as to whether the amplitude of the vibration exceeds a predetermined threshold. If the threshold is exceeded, it is evaluated that there is an imbalance in the impeller balance. This evaluation is made, for example, by a PC equipped with a CPU and memory acquiring the measurement values ​​and comparing the acquired measurement values ​​with the threshold values ​​stored in the memory. Alternatively, this evaluation may be made by the operator who acquired the measurement values.

[0052] If there is an imbalance in the impeller balance, the rotational balance of the impeller 60 is adjusted. For example, a method for adjusting impeller balance may include an installation step of covering the impeller 60 with the impeller cover 2, a cutting step of cutting the hub surface 61d covered by the impeller cover 2, and a suction step of sucking and discharging chips C generated by cutting the hub surface 61d. The method for adjusting impeller balance may also include an air supply step of supplying compressed gas G (e.g., compressed air) into the impeller cover 2 from the discharge port 9 of the cover surface 7. The method for adjusting impeller balance may also include a target change step of changing the hub surface 61d to be cut, and after the target change step, a suction step, an air supply step as needed, and a cutting step may again be performed.

[0053] (Mounting process) The rotating machine 100 is installed in a position where the hub surface 61c can be cut using the impeller balancing device 1. In this state, the rotational position of the impeller 60 is aligned. The impeller cover 2 is mounted on the aligned impeller 60 so that the cover surface 7 covers part of the hub 61. The tool port 8, at least a part of the discharge port 9, and at least a part of the suction port 10 of the impeller cover 2 are arranged so as to face the same space Ac to be cut.

[0054] The suction passage 11 of the impeller cover 2 is connected to the piping 3a of the suction device 3, and the gas passage 91 is connected to the piping 6a of the gas supply device 6. The tool 4 held by the tool driving device 5 is inserted into the tool insertion portion 80. The blade 41 of the tool 4 is exposed from the cover surface 7 and contacts the hub surface 61d.

[0055] (Suction Process and Air Supply Process) When the suction process is started, the suction device 3 is driven before cutting is performed by the tool driving device 5, and the suction flow rate is measured in advance. The air supply process is carried out in conjunction with the suction process. For example, the gas supply device 6 is driven while the suction device 3 is driven, and it is confirmed whether or not the suction device 3 is performing appropriate suction. As a direct confirmation method, for example, it is possible to check whether or not gas G is leaking from the gap between the impeller 60 and the impeller cover 2. As an indirect confirmation method, it is confirmed whether or not the suction flow rate is higher than the compressed air supply flow rate, and if it is higher, it is evaluated that appropriate suction is being performed.

[0056] (Cutting Process) If it is determined that appropriate suction is being performed, the suction process and air supply process are maintained, and the cutting process is performed in this state. The tool driving device 5 drives the tool 4 to thinly cut the hub surface 61d. The amount of rotational balance adjustment increases the farther away from the rotation axis 140 the cutting is performed. The tool opening 8, from which the blade 41 is exposed, is positioned closer to the base end cover portion 73 than to the tip cover portion 74. Therefore, the blade 41 of the tool 4 can cut an area where the rotational balance adjustment efficiency is high.

[0057] Chips C generated by cutting with the tool 4 are blown away by gas G (e.g., compressed air) introduced from the discharge port 9. The blown away chips C are sucked by the suction device 3 and, together with the gas G, pass through the suction port 10 and are discharged to the outside of the impeller cover 2. Therefore, even if the surface of the portion near the base end 61a of the hub 61 is cut, the chips C can be prevented from scattering to the outside of the impeller cover 2. As a result, problems such as the chips C scattering to the outside entering the bearing 122 inside the housing 121 do not occur.

[0058] When cutting is completed, the supply of gas G by the gas supply device 6 is stopped, and then the suction of chips C by the suction device 3 is stopped. By stopping the supply of gas G and then stopping the suction, scattering of chips C remaining inside is prevented.

[0059] (Target Changing Process) After the supply and suction of the gas G are stopped, the blade 41 of the tool 4 retracts so as to fit within the tool insertion portion 80. In this state, the impeller 60 is rotated slightly, and the rotational position of the impeller 60 is adjusted so that the cutting target space Ac is changed. The cover surface 7 is provided so as to fit along the shroud surface 62d. Therefore, the impeller 60 can be rotated for predetermined adjustment without removing the impeller cover 2. For example, the impeller 60 is rotated so that the tool opening 8, which faced one cutting target space Ac, faces the adjacent cutting target space Ac. In this state, the rotation of the impeller 60 is restricted and the impeller 60 is positioned, and the suction process, air supply process, and cutting process are performed again.

[0060] The suction process, the air supply process, and the cutting process constitute one cycle, and several cycles of processes are repeated with a target changing process in between, to adjust the overall rotational balance in the circumferential direction D2 of the impeller 60. After the rotational balance adjustment is performed, for example, the rotational balance is measured.

[0061] The operation and effects of the impeller cover 2 and the impeller balancing device 1 will now be described. When adjusting the rotational balance of the impeller 60, the impeller cover 2 is attached to the impeller 60 so that the cover surface 7 covers a portion of the hub 61. The tool 4 is inserted into the tool insertion portion 80 and positioned so that the tip blade 41 is exposed from the tool opening 8 and in contact with the hub surface 61d. The tool driving device 5 moves the tool 4 to cut the hub surface 61d. Chips C generated during cutting are entrained in the airflow and sucked through the suction port 10 along with the gas G. Because the chips C are sucked out through the suction port 10, they are prevented from scattering to unexpected locations. In addition, the provision of a discharge port 9 (an example of an air vent) separate from the suction port 10 enables the formation of a stable airflow when sucking in the chips C. As a result, the impeller cover 2 and the impeller balancing device 1 enable the rotational balance of the impeller 60 to be adjusted while preventing chips C from scattering.

[0062] The impeller cover 2 and impeller balance adjustment device 1 forcibly suck out chips C through the suction port 10 to prevent them from scattering. Therefore, there is no need to decide the cutting location while taking into consideration the scattering of chips C, and when adjusting the rotation balance, cutting can be performed by selecting a cutting location with high adjustment efficiency. As a result, balancing defects caused by insufficient adjustment of the rotation balance are eliminated, and the overall product yield is improved.

[0063] Furthermore, the impeller cover 2 and the impeller balance adjustment device 1 can prevent chips C from scattering, so that regardless of which position on the hub 61 is cut, the scattered chips C are less likely to enter the bearing 122 in the housing 121, preventing the chips from affecting the bearing function.

[0064] Furthermore, in the impeller cover 2 and the impeller balancing device 1, for example, compressed gas G can be supplied from the discharge port 9. The supply of compressed gas G enables stable suction of chips C. Furthermore, instead of supplying compressed gas G, the discharge port 9 can be opened to the atmosphere. When the discharge port 9 is opened to the atmosphere, gas G flows in from the discharge port 9 in conjunction with the suction of gas G from the suction port 10, ensuring an airflow for sucking out chips C.

[0065] The discharge port 9 is arranged to face one of the spaces Ac to be cut. The discharge port 9 has a shape and dimensions corresponding to the arrangement of the blades 62. For example, a plurality of blades 62 are arranged side by side in the circumferential direction D2. A space Ac to be cut is formed between adjacent blades 62. Both ends of the discharge port 9 in the circumferential direction D2 are located close to each of the adjacent blades 62 and are arranged to follow the shape of the blades 62 (the shape of the shroud 62c). By matching the shape of the discharge port 9 to the shape of the blades 62, stagnation of the airflow is eliminated, and the collection efficiency of the chips C is improved.

[0066] Furthermore, the width of the discharge port 9 in the circumferential direction D2 can be set to be the same as or larger than the width of the space Ac to be cut in the circumferential direction D2 between adjacent blades 62. By setting the width of the discharge port 9 in the circumferential direction D2 to be equal to or larger than the width of the space Ac to be cut, an airflow can be generated in the entire gap between adjacent blades 62, and chips C can be prevented from remaining in the corners (dead spaces) at the bases of the blades 62.

[0067] Here, the suction rate of the gas G passing through the suction port 10 is set in accordance with, for example, the width or area of ​​the discharge port 9 in the circumferential direction D2, or the supply rate of the gas G supplied from the discharge port 9. Therefore, as the width of the discharge port 9 in the circumferential direction D2 increases, the suction flow rate must be increased accordingly. Therefore, by making the width of the discharge port 9 in the circumferential direction D2 the same as the width of the space to be cut Ac, it is possible to prevent chips C from remaining in the dead space, improve operating efficiency, and prevent energy loss. Note that "similar to the width of the space to be cut Ac" means that the width of the discharge port 9 in the circumferential direction D2 and the width of the space to be cut Ac are substantially the same. For example, when both ends of the discharge port 9 in the circumferential direction D2 are positioned close to the adjacent blades 62, the width of the discharge port 9 is the same as the width of the space to be cut Ac.

[0068] For example, the tool port 8 is positioned closer to the base end cover portion 73 than to the tip cover portion 74. By positioning the tool port 8 closer to the base end cover portion 73 than to the tip cover portion 74, cutting can be performed at a position closer to the base end 61 a of the hub 61, and the amount of adjustment of the rotational balance is greater than when cutting is performed at a position closer to the tip end 61 b. Furthermore, because chips C generated at a position close to the base end 61 a are sucked in through the suction port 10, scattering to undesirable positions, such as scattering around the back side of the impeller 60 and entering the housing 121, can be prevented.

[0069] For example, the tool port 8 is located closer to the discharge port 9 than the suction port 10. Chips C generated when the hub 61 is cut with the tool 4 are carried by the gas G flowing in from the discharge port 9 toward the suction port 10 and are sucked in from the suction port 10.

[0070] For example, the suction port 10 is positioned closer to the tip cover portion 74 than the discharge port 9. The flow of gas G between the cover surface 7 and the impeller 60 flows from the discharge port 9 toward the suction port 10. The suction port 10 is positioned closer to the tip cover portion 74 than the discharge port 9. Therefore, the airflow that has entrained the chips C flows toward the tip portion 61b of the hub 61, not toward the base end portion 61a. As a result, the chips C are less likely to get around to the back side of the impeller 60.

[0071] For example, the area of ​​the suction port 10 is larger than the area of ​​the discharge port 9. When the area of ​​the suction port 10 is larger than the area of ​​the discharge port 9, the suction flow rate when sucking the chips C can be increased.

[0072] For example, the cover surface 7 is provided along the shroud surface 62d that includes the outer edge of the blade 62. When adjusting the cutting position by the tool 4, the position of the impeller 60 to be cut is adjusted by slightly rotating the impeller 60 without changing the position of the tool 4. In this case, if the cover surface 7 is provided along the shroud surface 62d, the impeller cover 2 does not interfere with the rotation of the impeller 60. Therefore, the impeller 60 can be rotated with the impeller cover 2 attached, improving workability.

[0073] For example, the impeller balancing device 1 includes a gas supply device 6 that supplies compressed gas G to the gas passage 91. By supplying compressed gas G by the gas supply device 6, it becomes easier to send the chips C toward the suction port 10. Note that if the chips C can be collected using only the suction flow rate, the discharge port 9 can be opened to the atmosphere, and the gas supply device 6 can be omitted.

[0074] For example, the suction flow rate by the suction device 3 is greater than the supply flow rate of the compressed gas G by the gas supply device 6. By making the suction flow rate greater than the supply flow rate of the compressed gas G, more chips C can be sucked.

[0075] An example of an impeller balancing device 1A will be described with reference to Figures 6 and 7. The impeller balancing device 1A has structures, devices, etc. in common with the impeller balancing device 1 described with reference to Figures 2 and 3, etc. Therefore, in the impeller balancing device 1A, structures, devices, etc. in common with the impeller balancing device 1 are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0076] The impeller balancing device 1A includes an impeller cover 2A attached to the impeller 60, a suction device 3 connected to the impeller cover 2A and configured to suck in gas G, a tool 4 configured to cut the hub surface 61d, and a tool driving device 5 configured to drive the tool 4. The impeller balancing device 1A may also include a gas supply device 6 configured to supply compressed gas G into the impeller cover 2A.

[0077] The impeller cover 2A includes a cover body 21A and a fixing portion 22A (e.g., a flange) fixed to the housing 121. The cover body 21A is attached so as to surround the entire circumference of the impeller 60 in the circumferential direction D2. The cover body 21A includes a cover surface 7A that covers the entire hub surface 61c. The cover surface 7A has a generally tapered inner circumferential surface formed along the shroud surface 62d (see FIG. 3). The cover surface 7A includes a base end cover portion 73A and a tip end cover portion 74A. The cover surface 7A includes a plurality of discharge ports 9A (an example of a vent port) arranged along the circumferential direction D2, and a plurality of gas passages 91A and gas introduction ports 92A that communicate with the discharge ports 9A. The discharge ports 9A are located closer to the base end cover portion 73A than the tip end cover portion 74A. For example, the plurality of discharge ports 9A are arranged at equal intervals in the base end cover portion 73A.

[0078] The impeller 60 includes a plurality of blades 62 arranged side by side in the circumferential direction D2. The plurality of blades 62 are arranged at equal intervals, and a cutting space Ac is formed between adjacent blades 62, with the hub surface 61d exposed. The plurality of discharge ports 9A are arranged corresponding to the plurality of cutting spaces Ac. For example, when the impeller cover 2A is attached to the impeller 60, the discharge ports 9A are arranged so as to face different cutting spaces Ac.

[0079] The cover body 21A includes a suction passage 11A extending in the axial direction D1. The cover surface 7A does not include a shaft end cover portion 72 (see FIG. 5 ), but instead includes a suction port 10A communicating with the suction passage 11A. The suction port 10A is located closer to the tip cover portion 74A than the base end cover portion 73A. For example, the suction port 10A is located in the tip cover portion 74A so as to surround the tip end portion 61b of the impeller 60 in the circumferential direction D2.

[0080] The cover body 21A has a tool insertion portion 80A into which the tool 4 is inserted. The tool insertion portion 80A has a tool opening 8A provided in the cover surface 7A. The tool opening 8A is an elongated hole extending in the axial direction. The tool 4 moves in the longitudinal direction of the tool opening 8A while following the inclination of the hub surface 61c to cut the hub 61.

[0081] The impeller balance adjustment device 1A adjusts the rotational balance by cutting the hub 61 of the impeller 60. Chips C generated by cutting the hub 61 are sucked out from the suction port 10A together with gas G, preventing the chips C from scattering to unexpected locations. Furthermore, gas G flows in from the discharge port 9A in conjunction with the suction of the chips C, creating a stable airflow that guides the chips C to the suction port 10A. As a result, the rotational balance of the impeller 60 can be adjusted while preventing the chips C from scattering.

[0082] The impeller cover 2A also has a plurality of discharge ports 9A arranged in the circumferential direction D2 on the cover surface 7A. This allows gas G to be taken in from a plurality of locations in the circumferential direction D2, making it possible to suck in chips C, and therefore chips C are less likely to remain. The suction port 10A is disposed in the tip cover portion 74A, and the suction passage 11A extends in the axial direction D1 of the impeller 60. This allows chips C to be sucked in from the tip portion 61b of the hub 61, which is on the front side of the impeller 60.

[0083] An example of an impeller balancing apparatus 1B will be described with reference to Fig. 8. The impeller balancing apparatus 1B includes, for example, structures and devices common to the above-described impeller balancing apparatuses 1 and 1A. Therefore, in the impeller balancing apparatus 1B, structures and devices common to the impeller balancing apparatuses 1 and 1A are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0084] The impeller balancing device 1B includes an impeller cover 2B attached to the impeller 60, a suction device 3 connected to the impeller cover 2B and configured to suck in gas G, a tool 4 for cutting the hub surface 61d, and a tool driving device 5 for driving the tool 4. The impeller balancing device 1B also includes a gas supply device 6B for supplying compressed gas G into the impeller cover 2B.

[0085] The impeller cover 2B has a cover surface 7B that covers at least a portion of the hub 61. For example, the cover surface 7B does not follow the shroud surface 62d (see FIG. 3 ) but has a shape that is substantially different from the shroud surface 62d and is provided so as to be spaced apart from the shroud surface 62d. The impeller cover 2B has a tool insertion section 80B into which the tool 4 is inserted, a gas passage 91B through which compressed gas G and the like pass, and a suction passage 11B through which gas G containing chips C passes. The tool insertion section 80B has a tool opening 8B.

[0086] The impeller 60 has a plurality of spaces Ac to be cut in the circumferential direction D2. The cover surface 7B has a tool port 8B facing one of the spaces Ac to be cut and a discharge port 9B adjacent to the tool port 8B. The discharge port 9B communicates with a gas passage 91B. The gas passage 91B branches into a plurality of passages from the discharge port 9B. A plurality of gas introduction portions 92B are provided at the end of the gas passage 91B opposite the discharge port 9B. The plurality of gas introduction portions 92B are each connected to a piping portion 6c of the gas supply device 6B.

[0087] The gas supply device 6B includes a compressor unit 6d and a piping unit 6c connected to the compressor unit 6d. The piping unit 6c branches into a plurality of communication pipes 6f, and each of the communication pipes 6f is connected to a gas introduction unit 92B.

[0088] The cover surface 7B has a suction port 10B. The area of ​​the suction port 10B is larger than the total area of ​​the multiple discharge ports 9B. The cover body 21B has a suction passage 11B that communicates with the suction port 10B. The suction passage 11B is provided so as to penetrate the cover body 21B. One end of the suction passage 11B is the suction port 10B, and the other end is a pipe connection portion 12B. The pipe connection portion 12B is connected to the pipe portion 3a of the suction device 3. The suction flow rate of the suction device 3 is set to be larger than the supply flow rate of the compressed gas G by the gas supply device 6.

[0089] The impeller balance adjustment device 1B adjusts the rotational balance by cutting the hub 61 of the impeller 60. Chips C generated by cutting the hub 61 are sucked out from the suction port 10B together with gas G, preventing the chips C from scattering to unexpected locations. Furthermore, gas G flows in from the discharge port 9B in conjunction with the suction of the chips C, creating a stable airflow that guides the chips C to the suction port 10B. As a result, the rotational balance of the impeller 60 can be adjusted while preventing the chips C from scattering.

[0090] The impeller balancing method using the above-described impeller balancing devices 1A, 1B includes an installation step of covering the impeller 60 with the impeller cover 2A, 2B, a cutting step of cutting the hub surface 61d covered by the impeller cover 2A, 2B, and a suction step of sucking and discharging chips C generated by cutting the hub surface 61d. The impeller balancing method may also include an air supply step of supplying compressed gas G (e.g., compressed air) into the impeller cover 2A, 2B from the outlets 9A, 9B of the cover surfaces 7A, 7B. The impeller balancing method may also include a target changing step of changing the hub surface 61d to be cut, and after the target changing step, a suction step, an air supply step if necessary, and a cutting step may again be performed.

[0091] Next, the combinations of the impeller covers 2, 2A, and 2B and the impeller balancing devices 1, 1A, and 1B according to the present disclosure will be described with reference to the reference numerals in the drawings.

[0092] [First aspect] The impeller cover (2, 2A, 2B) is attached to an impeller (60) having a hub (61) and blades (62), and includes: a cover surface (7, 7A, 7B) that covers at least a part of the hub (61) and has a suction port (10, 10A, 10B) and a discharge port (9, 9A, 9B) for a gas (G); a tool insertion portion (80, 80A, 80B) into which a tool (4) is inserted so that a blade (41) of the tool (4) is exposed from the cover surface (7, 7A, 7B); a suction passage (11, 11A, 11B) that communicates with the suction port (10, 10A, 10B) and through which the gas (G) passes; and a gas passage (91, 91A, 91B) that communicates with the discharge port (9, 9A, 9B) and through which the gas (G) passes.

[0093] [Second Aspect] This is the impeller cover (2, 2A, 2B) according to the [First Aspect], wherein the cover surface (7, 7A, 7B) includes a tip cover portion (74, 74A) facing the tip portion (61 b), which is one of both ends in the axial direction (D1) of the hub (61), and a base cover portion (73, 73A) facing the base portion (61 a), which is the other end and has a larger outer diameter than the tip portion (61 b), and the tool insertion portion (80, 80A, 80B) includes a tool opening (8) provided in the cover surface (7, 7A, 7B) so that the blade (41) of the tool (4) is exposed, and the tool opening (8) is located closer to the base cover portion (73, 73A) than the tip cover portion (74, 74A).

[0094] [Third Aspect] The impeller cover (2, 2A, 2B) according to the [First Aspect] or [Second Aspect], wherein the tool insertion portion (80, 80A, 80B) has a tool opening (8) provided in the cover surface (7, 7A, 7B) so that the blade (41) of the tool (4) is exposed, and the tool opening (8) is located closer to the vent opening (9, 9A, 9B) than the suction opening (10, 10A, 10B).

[0095] [Fourth Aspect] The cover surface (7, 7A, 7B) includes a tip cover portion (74, 74A) facing the tip portion (61 b), which is one of both ends in the axial direction (D1) of the hub (61), and a base cover portion (73, 73A) facing the base portion (61 a), which is the other end and has a larger outer diameter than the tip portion (61 b), and the suction port (10, 10A, 10B) is located closer to the tip cover portion (74, 74A) than the vent port (9, 9A, 9B) in the impeller cover (2, 2A, 2B) according to any one of [First Aspect] to [Third Aspect].

[0096] [Fifth Aspect] In the impeller cover (2, 2A, 2B) according to any one of [First Aspect] to [Fourth Aspect], the area of ​​the suction port (10, 10A, 10B) is larger than the area of ​​the vent port (9, 9A, 9B).

[0097] [Sixth Aspect] The impeller cover (2A) is according to any one of [First Aspect] to [Fourth Aspect], wherein the cover surface (7A) has a circumferential direction (D2) corresponding to the circumferential direction (D2) of the hub (61), and the vent holes (9A) are provided in plurality in the circumferential direction (D2) of the cover surface (7A).

[0098] [Seventh Aspect] The cover surface (7A) includes a tip cover portion (74A) facing the tip portion (61b), which is one of both ends in the axial direction (D1) of the hub (61), and a base cover portion (73A) facing the base portion (61a), which is the other end and has a larger outer diameter than the tip portion (61b), and the suction port (10A) is disposed in the tip cover portion (74A), and the suction passage (11A) extends in the axial direction (D1) of the impeller (60), in this impeller cover (2A) according to any one of [First Aspect] to [Sixth Aspect].

[0099] [Eighth Aspect] The impeller cover (2, 2A) according to any one of [First Aspect] to [Seventh Aspect], wherein the cover surface (7, 7A) is provided along the shroud surface (62d) including the outer edge of the blade (62).

[0100] [Ninth Aspect] The impeller cover (2, 2A, 2B) according to any one of [First Aspect] to [Eighth Aspect] further includes a cover body (21, 21A, 21B) having a cover surface (7, 7A), and the tool insertion portion (80, 80A, 80B) includes: a tool opening (8) provided in the cover surface (7, 7A) so that a blade (41) of a tool (4) is exposed; a guide hole (81) communicating with the tool opening (8) and provided so as to pass through the cover body (21, 21A, 21B); and a tool introduction opening (82) communicating with the guide hole (81) and provided on the opposite side to the tool opening (8).

[0101] [Tenth Aspect] The impeller cover (2, 2A, 2B) according to the ninth aspect, wherein the guide hole (81) penetrates the cover body (21, 21A, 21B) so as to linearly connect the tool opening (8) and the tool introduction opening (82).

[0102] [Eleventh Aspect] In the impeller cover (2, 2A, 2B) according to the ninth or tenth aspect, the tool opening (8) and the tool introduction opening (82) are elongated holes extending in the axial direction of the hub (61).

[0103] [Twelfth Aspect] The impeller cover (2, 2A, 2B) according to any one of [First Aspect] to [Eleventh Aspect] further includes a cover body (21, 21A, 21B) having a cover surface (7, 7A), the suction passage (11, 11A, 11B) is provided so as to penetrate the cover body (21, 21A, 21B), and the gas passage (91, 91A, 91B) is provided so as to penetrate the cover body (21, 21A, 21B).

[0104] [Thirteenth Aspect] A thirteenth aspect of the present invention includes an impeller cover (2, 2A, 2B) according to any one of the above aspects, a suction device (3) connected to the impeller cover (2, 2A, 2B) for sucking gas (G), a tool (4) for cutting the hub (61), and a tool driving device (5) for driving the tool (4). The impeller cover (2, 2A, 2B) covers at least a part of the hub (61), and has suction ports (10, 10A, 10B) for the gas (G) and vents (9, 9A). the impeller balance adjustment device (1, 1A, 1B) comprising a cover surface (7, 7A, 7B) having a blade (41) of the tool (4), a tool insertion portion (80, 80A, 80B) into which the tool (4) is inserted so that the blade (41) of the tool (4) is exposed from the cover surface (7, 7A, 7B), a suction passage (11A) communicating with the suction port (10A), and a gas passage (91, 91A, 91B) communicating with the vent port (9, 9A, 9B).

[0105] [14th Aspect] The impeller balance adjustment device (1, 1A, 1B) according to [13th Aspect] further includes a gas supply device (6) that supplies compressed gas (G) to the gas passages (91, 91A, 91B).

[0106] [15th Aspect] In the impeller balancing device (1, 1A, 1B) according to [14th Aspect], the suction flow rate by the suction device (3) is greater than the supply flow rate of the compressed gas (G) by the gas supply device (6).

[0107] The impeller cover and impeller balancing device according to the present disclosure are not limited to the above-described examples and may be modified in various ways. For example, the above-described examples may be used in combination with one another depending on the required purpose and effect. Furthermore, the impeller to which the impeller cover is attached or the impeller whose rotational balance is adjusted by the impeller balancing device is not limited to a turbine impeller but may also be a compressor impeller. The cover surface of the impeller cover may be spaced outward from the shroud surface and may have a different shape relative to the shroud surface. The cover surface may also be provided with multiple air intakes. The vent may be located closer to the tip cover than the air intakes. For example, the rotating machine whose rotational balance is adjusted by the impeller cover and impeller balancing device is not limited to an electric supercharger but may include various rotating machines equipped with an impeller. The rotating machine may be not only a rotating machine that supplies compressed air to an internal combustion engine, but also a rotating machine that supplies compressed air to a fuel cell.

[0108] REFERENCE SIGNS LIST 1, 1A, 1B Impeller balance adjustment device 2, 2A, 2B Impeller cover 21, 21A, 21B Cover body 3 Suction device 4 Tool 41 Blade 5 Tool driving device 6 Gas supply device 7, 7A, 7B Cover surface 8, 8A, 8B Tool port 9, 9A, 9B Discharge port 10, 10A, 10B Suction port 11, 11A, 11B Suction passage 60 Impeller 61 Hub 62 Blade 61a Base end portion 61b Tip portion 62d Shroud surface 73 Base end cover portion 74 Tip cover portion 80, 80A, 80B Tool insertion portion 91, 91A, 91B Gas passage G Gas D1 Axial direction D2 Circumferential direction

Claims

1. An impeller cover to be attached to an impeller having a hub and blades, comprising: a cover surface covering at least a portion of the hub, and having a gas suction port and a vent port; a tool insertion portion into which the tool is inserted so that the blade of the tool is exposed from the cover surface; a suction passage communicating with the suction port and through which the gas passes; and a gas passage communicating with the vent port and through which the gas passes.

2. An impeller cover as described in claim 1, wherein the cover surface comprises a tip cover portion facing one of the axial ends of the hub, which is the tip end, and a base cover portion facing the other end, which is the base end having a larger outer diameter than the tip end, and the tool insertion portion comprises a tool opening provided in the cover surface so that a blade of the tool is exposed, and the tool opening is positioned closer to the base cover portion than the tip cover portion.

3. An impeller cover as described in claim 1, wherein the tool insertion portion has a tool opening provided in the cover surface so that a blade of the tool is exposed, and the tool opening is positioned closer to the vent hole than the suction opening.

4. An impeller cover as described in claim 3, wherein the cover surface comprises a tip cover portion facing the tip end, which is one of both axial ends of the hub, and a base cover portion facing the base end, which is the other end and has a larger outer diameter than the tip end, and the suction port is positioned closer to the tip cover portion than the ventilation port.

5. The impeller cover according to claim 1, wherein an area of ​​said suction opening is larger than an area of ​​said vent opening.

6. The impeller cover according to claim 1, wherein said cover surface has a circumferential direction corresponding to the circumferential direction of said hub, and said vent holes are provided in a plurality in said circumferential direction of said cover surface.

7. An impeller cover as described in claim 6, wherein the cover surface comprises a tip cover portion facing one of the axial ends of the hub, which is the tip end, and a base cover portion facing the other end, which is the base end having an outer diameter larger than that of the tip end, the suction port being disposed in the tip cover portion, and the suction passage extending in the axial direction of the impeller.

8. An impeller cover according to claim 1, wherein said cover surface is provided along a shroud surface including an outer edge of said blade.

9. An impeller cover as described in claim 1, further comprising a cover body having the cover surface, wherein the tool insertion portion comprises: a tool opening provided in the cover surface so that a blade of the tool is exposed; a guide hole communicating with the tool opening and provided so as to pass through the cover body; and a tool introduction opening communicating with the guide hole and provided on the opposite side to the tool opening.

10. The impeller cover according to claim 9, wherein said guide hole penetrates said cover body so as to linearly connect said tool opening and said tool introduction opening.

11. The impeller cover according to claim 10, wherein the tool opening and the tool introduction opening are elongated holes extending in the axial direction of the hub.

12. The impeller cover according to claim 11, wherein the suction passage is provided so as to penetrate through the cover body, and the gas passage is provided so as to penetrate through the cover body.

13. An impeller balance adjustment device comprising: an impeller cover attached to an impeller having a hub and blades; a suction device connected to the impeller cover and sucking in gas; a tool for cutting the hub; and a tool driving device for driving the tool, wherein the impeller cover comprises: a cover surface covering at least a portion of the hub and having a gas suction port and an air vent; a tool insertion portion into which the tool is inserted so that the blade of the tool is exposed from the cover surface; a suction passage communicating with the suction port; and a gas passage communicating with the air vent.

14. The impeller balancing apparatus of claim 13, further comprising a gas supply device for supplying compressed gas to said gas passage.

15. The impeller balancing device according to claim 14, wherein a suction flow rate by said suction device is greater than a supply flow rate of said gas supplied by said gas supply device.

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