Fan actuator and fan motor having same

Abstract

Disclosed are a fan actuator and a fan motor having same. The fan motor comprises: an impeller which receives power from a motor and rotates around a rotation shaft; and an excitation device which reduces noise generated by the impeller. The excitation device comprises: a coil to which power is applied; a yoke rotatably mounted on the impeller; and a magnet coupled to the yoke so as to rotate together with the impeller about the rotation shaft with respect to the coil, wherein an axial-direction excitation force can be applied to the impeller by electromagnetic interaction between the magnet and the coil. Accordingly, fan noise can be reduced.

Description

Fan actuator and fan motor having the same

[0001] The present invention relates to a fan actuator capable of reducing fan noise and a fan motor having the same.

[0002] An air purifier is a device that draws in indoor air, filters it, and then expels the filtered, clean air back into the room. Therefore, air purifiers may be equipped with a fan motor to force airflow.

[0003] The rotation of a fan motor inevitably generates noise, which can be uncomfortable for users indoors. In particular, the Blade Pass Frequency (BPF) noise generated by the fan (also known as the "impeller") of the fan motor is a low-frequency noise that can cause significant discomfort to users.

[0004] To ensure user comfort, measures are needed to reduce the noise generated by air purifiers. A common noise reduction method is passive, which involves attaching sound-absorbing or sound-insulating materials to the noise source.

[0005] However, air purifiers have perforations to inhale and expel indoor air, and sound-absorbing or sound-insulating materials cannot be attached to these perforations. Therefore, this passive noise reduction method is difficult to apply to air purifiers.

[0006] Due to the above-mentioned disadvantages, noise can be reduced by lowering the rotation speed of the fan or applying a humpback whale or owl wing-shaped shape to the fan blades.

[0007] However, the above method of lowering the rotation speed has the disadvantage of making it difficult to maintain the fan's flow rate. In addition, the shape of the hump or owl wing has limitations in reducing noise.

[0008] The purpose of the present invention is to provide a fan motor having a structure capable of solving the above-described problems.

[0009] The first purpose is to provide a fan actuator having a structure capable of directly operating a fan to reduce low-frequency noise generated from fan blades, and a fan motor having the same.

[0010] The second purpose is to provide a fan motor having a structure capable of efficiently reducing fan noise without attaching sound-insulating or sound-absorbing materials to the fan blades, without reducing the rotation speed of the fan, or without applying a humpback whale hump or owl wing-shaped structure to the fan blades.

[0011] The third purpose is to provide a fan actuator having a structure capable of effectively reducing fan noise at all locations rather than at a specific location, and a fan motor having the same.

[0012] The fourth purpose is to provide a fan actuator having a structure applicable to various types of fans and a fan motor having the same.

[0013] The fifth purpose is to provide a fan actuator having a structure capable of increasing the efficiency of magnetic force for applying a driving force, and a fan motor having the same.

[0014] The sixth purpose is to provide a fan actuator having a structure capable of generating high output with low current to generate a driving force, and a fan motor having the same.

[0015] As a result of intensive research, the inventors of the present invention have found that the first to sixth objectives of the present invention can be achieved by the following embodiments of the present invention.

[0016] In order to achieve the above-described object, a fan actuator according to the present invention includes an impeller that receives power from a motor and rotates around a rotational axis; an excitation device that reduces noise generated from the impeller, the excitation device including: a coil to which power is applied; a yoke rotatably mounted on the impeller; and a magnet coupled to the yoke so as to rotate together with the impeller around the rotational axis with respect to the coil, and an axial excitation force can be applied to the impeller by electromagnetic interaction between the magnet and the coil.

[0017] In one example, the yoke and the magnet may be mounted at the center of the impeller. The coil may be fixedly coupled to one axial side of the motor.

[0018] According to one example, the magnet may surround the rotational axis, and one side of the yoke may be coupled to contact one axial side of the magnet. The other side of the yoke may be arranged to be radially spaced from the outer surface of the magnet. The coil may be arranged to be spaced apart from the other side of the yoke and the outer surface of the magnet with an air gap between them.

[0019] In one example, the impeller may include a hub; and a plurality of blades extending radially outward from an outer surface of the hub. The yoke and the magnet may be mounted on one axial side of the hub.

[0020] According to another example, the impeller may include a hub; a plurality of blades spaced apart from each other along a circumference of the hub radially outside the hub; an inner blade guide extending radially outwardly from an outer surface of the hub and connecting inner ends of the plurality of blades; and an outer blade guide having a suction portion and spaced apart from the inner blades radially outside the hub and connecting outer ends of the plurality of blades. The yoke and the magnet may be mounted on one axial side of the hub.

[0021] According to another example, the impeller may include a hub; a plurality of blades spaced apart in a circumferential direction along a periphery of the hub; the impeller may include an inner bushing coupled to the rotational shaft; an outer bushing disposed on an outer side of the inner bushing and coupled to the hub; and an anti-vibration member disposed between the inner bushing and the outer bushing and connected to the inner bushing and the outer bushing. The yoke and the magnet may be mounted on one axial side of the outer bushing.

[0022] According to one example, the yoke, the coil, and the magnet may be arranged between the downstream side of the hub and the upstream side of the motor based on the airflow direction.

[0023] In one example, the yoke, the coil and the magnet may be arranged on the inside of the hub when viewed axially.

[0024] In one example, the yoke, the coil, and the magnet may each be formed in a cylindrical ring shape. The diameter of the yoke may be larger than the diameter of the coil. The diameter of the coil may be larger than the diameter of the magnet.

[0025] According to one example, the yoke may include a top yoke that contacts one axial side of the magnet and extends in the radial direction of the magnet; an axially extending yoke that is radially spaced from the outer surface of the magnet and extends in the axial direction; and a radially extending yoke that contacts the other axial side of the magnet and extends in the radial direction of the magnet from the axially extending yoke.

[0026] In one example, the coil may be provided as a bobbinless coil.

[0027] According to one example, the motor may include a motor housing; a stator provided inside the motor housing; and a rotor coupled to the rotational shaft and rotating about the stator. The coil may be supported by a coil support member extending from one axial side of the motor housing toward the impeller.

[0028] In one example, the coil may be arranged to radially overlap the N pole of the magnet and not overlap the S pole of the magnet.

[0029] A fan motor according to the present invention may include a housing; a motor installed inside the housing; an impeller that receives power from the motor and rotates around a rotational axis; and a fan actuator that applies an axial excitation force to the impeller. The fan actuator may include a coil support portion extending from one axial side of the motor toward the impeller; a coil supported by the coil support portion; a magnet that surrounds the rotational axis and applies the excitation force through electromagnetic interaction with the coil; and a yoke that is rotatably mounted to the impeller and contacts at least one surface of the magnet to transmit magnetic flux of the magnet to the coil.

[0030] According to one example, the fan motor may further include a noise detection unit that detects a noise signal generated from the impeller; and a control unit that receives the detection signal of the noise detection unit and controls the excitation force of the fan actuator. The control unit may generate an acoustic signal having the same frequency as the noise generated from the fan by the excitation force but with an opposite phase, thereby canceling out the noise of the fan.

[0031] According to an embodiment of the present invention, the following effects can be achieved.

[0032] First, a fan actuator that reduces fan noise can be configured with a coil, a magnet, and a yoke. The coil is positioned between the magnet and the yoke, so that the magnetic flux generated by the magnet is transmitted to the coil. The electromagnetic interaction between the coil and the magnet can generate an axial excitation force.

[0033] A fan actuator generates an acoustic signal by directly applying a force generated by the electromagnetic interaction between a coil and a magnet to the impeller. The acoustic signal has the same frequency as, but opposite in phase to, the low-frequency noise generated by the impeller as it rotates, known as fan noise (BPF). This allows it to cancel out the fan noise.

[0034] Through this, the fan actuator can receive an ANC control signal from the control unit to reduce fan noise.

[0035] Second, the fan actuator can be installed at the center of the impeller. This allows it to be applied to various impeller configurations. For example, it can be applied to a mixed-flow fan, a structure in which the tips of multiple blades are connected to each other by blade guides.

[0036] Third, the coil, magnet, and yoke can each be formed into a ring shape. The magnet and yoke can rotate together with the impeller, with the coil between them. This allows the coil, magnet, and yoke to effectively reduce fan noise in all radial directions, rather than just at a specific location.

[0037] Fourth, the yoke is composed of a metal material that allows magnetic flux to flow. The yoke may include a first yoke and a second yoke. One side of the first yoke (an axially extending yoke) and the magnet may be separated by a preset air gap. The other side of the first yoke (a radially extending yoke) is in contact with one side of the magnet. The second yoke is in contact with the other side of the magnet.

[0038] A coil is placed between the axial extension yoke of the first yoke and the magnet.

[0039] Through this, the yoke can efficiently transmit the magnetic force of the magnet to the coil by concentrating the magnetic flux generated from the magnet toward the coil and increasing the magnetic flux density.

[0040] Fifth, the coil is a bobbinless coil, minimizing the air gap and shortening the magnetic flux travel distance. This allows the magnetic flux generated from the magnet's north pole to circulate back to the magnet's south pole through the second yoke, the coil, and the first yoke, even when the current applied to the coil is low. This allows the fan actuator to generate high output with low power consumption.

[0041] FIG. 1 is a conceptual diagram showing the appearance of a fan motor according to one embodiment of the present invention.

[0042] Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1, showing the internal configuration of the fan motor.

[0043] Figure 3 is a bottom view of the fan actuator in Figure 2, viewed from the bottom, with the fan actuator installed inside the housing.

[0044] Figure 4 is a conceptual diagram showing the fan actuator in Figure 3 in an exploded form.

[0045] Fig. 5 is a cross-sectional view showing the fan actuator combined in Fig. 4.

[0046] Figure 6 is an exploded view of the fan actuator in Figure 4, and is a conceptual diagram showing the coil support unit coupled to the motor housing.

[0047] Figure 7 is an enlarged view of VII in Figure 1, and is a conceptual diagram showing the magnetic flux movement path of the magnet.

[0048] Figure 8 is a conceptual diagram showing how an axial force is directly applied to the impeller by the electromagnetic interaction between the magnet and the coil in Figure 6.

[0049] Figure 9 is a conceptual diagram for explaining Self-ANC (Active Noise Control) according to the present invention.

[0050] Figure 10 is a graph showing the fan noise reduction effect of a fan motor equipped with an actuator according to the present invention.

[0051] Fig. 11 is a graph showing the results of an experiment on a noise reduction device according to one embodiment of the present invention, and measuring noise at a location 1 m away from the front of an air purifier.

[0052] Hereinafter, a fan actuator and a fan motor equipped with the same according to an embodiment of the present invention will be described in detail with reference to the attached drawings.

[0053] In the following description, descriptions of some components may be omitted to clarify the features of the present invention.

[0054] 1. Definition of Terms

[0055] Terms that include ordinal numbers, such as first, second, etc., may be used to describe various components, but the components are not limited by these terms. These terms are used solely to distinguish one component from another.

[0056] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0057] As used herein, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0058] The term “fan motor” used in the following description can be understood as a concept meaning a device that sucks in or blows air by rotating a fan using power such as an electric motor.

[0059] As used herein, “radial” or “radial” means a shape that extends out in all directions from a central point like spokes of a wheel.

[0060] “Axial” as used in the following description means the longitudinal direction of the axis of rotation.

[0061] As used in the following description, “radial direction” means the longitudinal direction of a line segment from the center of a circle or cylinder to a point on the circumference (circumference).

[0062] As used in the following description, “circumferential” means the direction of the circumference of a circle.

[0063] 2. Description of the configuration of a fan motor (100) according to one embodiment of the present invention

[0064] Figure 1 is a conceptual diagram showing the appearance of a fan motor (100) according to one embodiment of the present invention.

[0065] Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1, showing the internal configuration of a fan motor (100).

[0066] Figure 3 is a bottom view of the fan actuator (140) provided inside the housing (110) in Figure 2.

[0067] Figure 4 is a conceptual diagram showing the fan actuator (140) in Figure 3 in an exploded form.

[0068] Fig. 5 is a cross-sectional view showing the fan actuator (140) combined in Fig. 4.

[0069] Figure 6 is an exploded view of the fan actuator (140) in Figure 4, and is a conceptual diagram showing the coil support (146) coupled to the motor housing (135).

[0070] The fan motor (100) of the present invention can be applied to home appliances such as air purifiers.

[0071] In one embodiment of the present invention, the fan motor (100) may be placed on the inner lower part of an air purifier, such as an aero tower, which is arranged to be vertically elongated with respect to the ground.

[0072] The fan motor (100) can be configured to suck in air through an opening formed at the bottom of the air purifier and discharge it upward.

[0073] A fan motor (100) according to the present invention includes a housing (110), an impeller (120), and a motor (130). The housing (110) can form the exterior of the fan motor (100). The housing (110) is configured to accommodate the impeller (120) and the motor (130).

[0074] The housing (110) may be formed in a cylindrical shape. The housing (110) may extend in a circumferential direction. The housing (110) may extend in a vertical direction. A receiving portion is formed inside the housing (110) to receive the impeller (120) and the motor (130). The receiving portion of the housing (110) is formed to penetrate in a vertical direction.

[0075] A first opening (111) is formed at the lower end of the housing (110). The first opening (111) is formed to communicate with the suction portion (1231) of the impeller (120) to be described later. The first opening (111) is formed to surround the suction portion (1231) in the circumferential direction.

[0076] The inner surface of the lower part of the housing (110) can be spaced radially outward from the outer surface of the suction part (1231).

[0077] A second opening (112) is formed at the upper end of the housing (110). The second opening (112) is configured to discharge air. An impeller (120) and a vane (139) may be provided between the first opening (111) and the second opening (112).

[0078] Air flows in one direction (e.g., up and down) by the impeller (120). The air can pass through the vane (139) described later in the first opening (111) and then be discharged upward through the second opening (112).

[0079] A first through-hole (113) and a second through-hole (114) may be formed to penetrate radially through the upper side of the housing (110). The first through-hole (113) and the second through-hole (114) may be arranged to face each other radially along the outer circumferential surface of the housing (110).

[0080] The first through-hole (113) and the second through-hole (114) may be combined with components installed inside the air purifier. Alternatively, the first through-hole (113) or the second through-hole (114) may serve as a passage for inserting wires, etc. for supplying power to the motor (130) described later, from the outside to the inside of the housing (110).

[0081] The housing (110) may have a plurality of fastening members (115). For example, the fastening members (115) may serve to fasten and support the housing (110) to the interior of the air purifier. Fastening members such as screws may be fastened to the fastening members (115).

[0082] The impeller (120) may be implemented in the form of a diagonal fan. However, the shape of the impeller (120) is not limited thereto, and the shape of the impeller (120) may be implemented in various forms, such as an axial fan and a centrifugal fan.

[0083] The impeller (120) includes a hub (121), an inner blade guide (122), an outer blade guide (123), and a plurality of blades (124).

[0084] The hub (121) can be formed in a cylindrical shape. A hollow portion is formed on the inside of the hub (121) so that the rotation shaft (131) of the motor (130) described later passes through it.

[0085] The rotation shaft (131) is formed to protrude and extend in the axial direction from one side of the motor (130) toward the hub (121) of the impeller (120). The rotation shaft (131) extends in the axial direction through the center of the housing (110).

[0086] A center bushing (125) is provided between the rotation shaft (131) and the hub (121). The center bushing (125) may be configured to include an inner bushing (1251), an outer bushing (1252), and a vibration-proof member (1253). The inner bushing (1251) is formed in a cylindrical shape.

[0087] A through hole is formed in the center of the inner bushing (1251) so that the rotation shaft (131) passes through it. The inner bushing (1251) is formed to surround the outer circumference of the rotation shaft (131). The rotation shaft (131) can be press-fitted to the inner bushing (1251) through the through hole.

[0088] The outer bushing (1252) is formed in a cylindrical shape. The outer bushing (1252) is arranged radially outwardly from the outer surface of the inner bushing (1251). The outer bushing (1252) is formed to surround the outer surface of the inner bushing (1251).

[0089] The outer bushing (1252) is press-fitted onto the inner surface of the hub (121). Accordingly, the rotation shaft (131) and the impeller (120) can rotate together.

[0090] An anti-vibration member (1253) is provided between the outer bushing (1252) and the inner bushing (1251). The anti-vibration member (1253) is formed in a cylindrical shape. The anti-vibration member (1253) may be formed of, for example, a rubber material. The anti-vibration member (1253) extends radially between the outer bushing (1252) and the inner bushing (1251). The anti-vibration member (1253) also extends circumferentially.

[0091] The outer surface of the anti-vibration member (1253) may be connected to the inner surface of the outer bushing (1252) and formed integrally. The inner surface of the anti-vibration member (1253) may be connected to the outer surface of the inner bushing (1251) and formed integrally.

[0092] Through this, the vibration-proof member (1253) can prevent vibration generated from the motor (130) from being transmitted to the impeller (120) through the rotating shaft (131).

[0093] An inner blade guide (122) is provided on the outer surface of the hub (121). The inner blade guide (122) may be composed of a radial extension portion (1221) and a first inclined portion (1222). The radial extension portion (1221) extends radially outward from the outer surface of the hub (121). The radial extension portion (1221) may extend circumferentially along the periphery of the hub (121).

[0094] The first inclined portion (1222) extends at a predetermined angle with respect to the axial direction from the outer end of the radial extension portion (1221). The first inclined portion (1222) may extend circumferentially along the perimeter of the radial extension portion (1221).

[0095] The radial extension portion (1221) and the first inclined portion (1222) can be formed as one body.

[0096] The connection between the radial extension (1221) and the first inclined portion (1222) is formed in a rounded curved shape. This can reduce air flow resistance.

[0097] On the inner side of the connection between the radial extension portion (1221) and the first inclined portion (1222), a plurality of inner ribs (1223) can be formed to protrude in the radial and axial directions.

[0098] A plurality of inner ribs (1223) are arranged at equal intervals along the circumference of the radial extension portion (1221). Through this, the inner ribs (1223) can increase the rigidity of the connection portion between the radial extension portion (1221) and the first inclined portion (1222).

[0099] The first slope (1222) extends in the circumferential direction and can connect the inner ends of a plurality of blades (124) to be described later.

[0100] The inner blade guide (122) can form a path for air intake together with the outer blade guide (123) described later.

[0101] The outer blade guide (123) may be configured to include a suction portion (1231) and a second inclined portion (1232). The suction portion (1231) is formed in a circular ring shape. The diameter of the suction portion (1231) is formed to be larger than the maximum diameter of the hub (121) or the radial extension (1221). The diameter of the suction portion (1231) may be formed to be larger than the maximum diameter of the first inclined portion (1222).

[0102] The suction portion (1231) can be extended in the axial direction. Through this, the suction portion (1231) can induce the air suction direction of the impeller (120) in the axial direction.

[0103] The diameter of the suction part (1231) is formed smaller than the inner diameter of the housing (110). An annular space may be formed between the outer surface of the suction part (1231) and the inner surface of the housing (110).

[0104] The second inclined portion (1232) may be formed to be inclined at a preset angle from one axial end of the suction portion (1231) toward the inner surface of the housing (110). The second inclined portion (1232) may extend circumferentially along the periphery of the suction portion (1231).

[0105] The inclination angle of the second slope portion (1232) is inclined with respect to the axial direction. The inclination angle of the second slope portion (1232) may be equal to or greater than the inclination angle of the first slope portion (1222). An annular space may be formed between the first slope portion (1222) and the second slope portion (1232).

[0106] An annular space can be formed between the first slope (1222) and the second slope (1232). Through this, air can pass through the impeller (120).

[0107] The second slope (1232) is configured so that its diameter gradually expands from the upstream side connected to the suction side (1231) toward the downstream side based on the direction of air movement.

[0108] The second inclined portion (1232) is configured to connect the outer ends of a plurality of blades (124) to be described later. The diameter of the second inclined portion (1232) may be larger than the diameter of the first inclined portion (1222).

[0109] The suction portion (1231), the first slope portion (1222) and the second slope portion (1232) can guide the air flow direction.

[0110] A plurality of blades (124) are provided between the first slope (1222) and the second slope (1232). The inner end of the blade (124) is connected to the outer circumference of the inner blade guide (122). The outer end of the blade (124) is connected to the inner circumference of the outer blade guide (123).

[0111] A plurality of blades (124) are arranged spaced apart from each other in the circumferential direction along the periphery of the first inclined portion (1222) and the second inclined portion (1232).

[0112] The blade (124) may be formed to be inclined at a preset angle with respect to the radial direction on the outer surface of the first inclined portion (1222). Alternatively, the blade (124) may be formed to be inclined at a preset angle with respect to the radial direction on the inner surface of the second inclined portion (1232).

[0113] The inclination angle of the blade (124) may vary from the first inclination portion (1222) to the second inclination portion (1232). The blade (124) has a gentle slope compared to the inclination angles of the first inclination portion (1222) and the second inclination portion (1232). The blade (124) may be formed into a curved shape with a preset curvature.

[0114] Through this, the blade (124) can rotate the air in a circumferential direction.

[0115] Air can be axially sucked in through the suction portion (1231), which is the inlet of the impeller (120). The air can be rotated by the blade (124) and sucked into the annular space between the first inclined portion (1222) and the second inclined portion (1232). The air can be discharged through the downstream ends of the first inclined portion (1222) and the second inclined portion (1232).

[0116] The impeller (120) can be fastened to the end of the rotation shaft (131) to prevent it from being axially separated from the rotation shaft (131).

[0117] The inner bushing (1251) may be formed to protrude further in the axial direction than the vibration-proof member (1253) and the outer bushing (1252).

[0118] A screw portion may be formed at one end of the rotation shaft (131). A lock nut (126) may be fastened to the screw portion.

[0119] Through this, the inner bushing (1251) can be restricted from moving axially by the lock nut (126). The lock nut (126) can prevent the impeller (120) from being axially disengaged from the rotation axis (131).

[0120] The motor (130) may be placed downstream of the impeller (120) with respect to the direction of air movement. The motor (130) may be configured to include a rotation shaft (131), a rotor (133), and a stator (134). The motor (130) may further include a motor housing (135) capable of accommodating the rotation shaft (131), the rotor (133), and the stator (134).

[0121] The motor housing (135) can form the exterior of the motor (130). The motor housing (135) can form the outer periphery of the motor (130).

[0122] One side of the rotation shaft (131) can be configured to penetrate the center of the motor housing (135).

[0123] The rotation shaft (131) can be rotatably supported by a plurality of bearings (132a, 132b).

[0124] A plurality of bearings (132a, 132b) can be press-fitted to one side and the other side of the rotation shaft (131) with the rotor (133) interposed therebetween. The bearings (132a, 132b) can be implemented as ball bearings.

[0125] Ball bearings can be configured to include multiple balls, an inner ring, and an outer ring.

[0126] The inner and outer rings are in cloud contact with the inner and outer surfaces of the ball, respectively, so that the ball can be supported rotatably. The outer ring can be fixedly installed in the motor housing (135) or the housing (110). The inner ring can surround the rotation shaft (131) and be press-fitted to the outer surface of the rotation shaft (131).

[0127] The rotation shaft (131) can be rotatably supported with respect to the motor housing (135) or housing (110) by bearings (132a, 132b).

[0128] The rotor (133) may include a permanent magnet. The rotor (133) may optionally further include a rotor core. The rotor core may be coupled to a rotational shaft (131). The rotor core may be equipped with a permanent magnet. The permanent magnet may be mounted on the rotational shaft (131) or the rotor core.

[0129] The stator (134) may be configured to include a stator core and a stator coil.

[0130] The stator coil can be wound around the stator core through a plurality of slots formed on the inside of the stator core. The stator coil can form a three-phase coil (145) depending on the number of slots.

[0131] A three-phase AC power supply can be applied to the stator coil.

[0132] When power is applied to the stator coil, a magnetic field is formed around the stator coil. Through this, the permanent magnet can interact with the magnetic field of the stator coil to rotate the rotor (133).

[0133] A rotor receiving hole may be formed to penetrate axially on the inside of the stator core. The stator (134) may be formed to surround the rotor (133).

[0134] The rotor (133) can be mounted on a rotation shaft (131) so as to be rotatable relative to the stator (134).

[0135] According to this, the motor (130) can transmit power to the impeller (120) through the rotation shaft (131) to rotate the impeller (120).

[0136] A motor receiving portion (116) is provided inside the housing (110). The motor receiving portion (116) is configured to receive a motor (130). The motor receiving portion (116) is positioned downstream of the impeller (120) with respect to the direction of air movement.

[0137] The motor receiving portion (116) may be formed in a combination of a cylindrical shape and a conical shape. A motor receiving space is formed inside the motor receiving portion (116). The motor receiving portion (116) is formed to have a diameter larger than the outer diameter of the motor (130) and smaller than the inner diameter of the housing (110).

[0138] A plurality of support parts (117) are provided on the inner surface of a portion of a cylindrical motor receiving part (116). The support parts (117) can support the outer surface of the motor (130). The support parts (117) are configured to restrict the motor (130) from moving in the radial direction.

[0139] A plurality of support members (117) are arranged at equal intervals in the circumferential direction along the outer surface of the motor (130). The support members (117) may extend radially from the inner surface of the motor receiving member (116). The support members (117) may extend axially from the inner surface of the motor receiving member (116).

[0140] The inner end of the support member (117) can be in contact with the outer surface of the motor (130) and support the outer surface of the motor (130).

[0141] A plurality of coupling portions (137) are provided on the inner surface of a portion of a cylindrical motor receiving portion (116). The coupling portions (137) may protrude radially inward from the inner surface of the motor receiving portion (116). The coupling portions (137) may extend axially from the inner surface of the motor receiving portion (116).

[0142] A plurality of connecting parts (137) can be arranged to be spaced apart alternately from a plurality of supporting parts (117) in the circumferential direction along the inner surface of the motor receiving part (116).

[0143] The plurality of connecting parts (137) may have connecting holes formed on the inside so that a connecting member such as a screw or the like can be connected thereto. Through this, the connecting parts (137) may be used to secure and support the motor receiving part (116) inside the case of an air purifier or the like.

[0144] An axial movement restriction portion (138) may be provided on another part of the motor receiving portion (116) formed in a cone shape (the lower part of the motor receiving portion (116) based on the drawing).

[0145] The axial movement restriction member (138) can be arranged toward one axial side of the motor (130) that faces the hub (121) of the impeller (120) in the axial direction.

[0146] The axial movement limiting portion (138) may extend radially from another portion of the motor receiving portion (116) to surround one axial side of the motor (130).

[0147] The axial movement restriction member (138) may extend circumferentially from another part of the motor receiving member (116) to surround one axial side of the motor (130).

[0148] Through this, the axial movement restriction member (138) can wrap around one axial side of the motor (130), thereby restricting the motor (130) from axially moving toward the inside of the motor receiving member (116).

[0149] A plurality of vanes (139) may be provided inside the housing (110). The vanes (139) may extend radially from the outer surface of the motor receiving portion (116) toward the inner surface of the housing (110). The inner end of the vane (139) is connected to the outer surface of the motor receiving portion (116), and the outer end of the vane (139) is connected to the inner surface of the housing (110).

[0150] A plurality of vanes (139) may extend axially. The vanes (139) may extend axially, but may be formed in a curved shape that is bent in the direction of rotation of the impeller (120) or in the direction opposite to the direction of rotation with respect to the axial direction.

[0151] For example, the upstream end of the vane (139) with respect to the airflow direction may be formed to be bent with a predetermined curvature in the rotational direction of the impeller (120). The downstream end of the vane (139) may be formed to be bent with a curvature smaller than the curvature of the upstream end of the vane (139) with respect to the rotational direction of the impeller (120). That is, the downstream end of the vane (139) may be formed to be gently convergent in the axial direction from the upstream end of the vane (139) to the downstream end.

[0152] According to this, the vane (139) can easily convert the rotational flow of air formed by the impeller (120) into the axial direction.

[0153] The rotation shaft (131) extends axially from one side of the motor housing (135) and can penetrate the hub (121) of the impeller (120).

[0154] The fan motor (100) may include an excitation device capable of reducing fan noise by having an impeller (120) (also referred to as a 'fan'). The excitation device may be implemented as a fan actuator (140).

[0155] The fan actuator (140) can apply axial vibration to the impeller (120) using magnetic force.

[0156] Below, the configuration and operation of the fan actuator (140) will be described.

[0157] 3. Description of the configuration of a fan actuator (140) according to one embodiment of the present invention

[0158] A fan actuator (140) can be mounted on the impeller (120). The fan actuator (140) can be located at the center of the impeller (120).

[0159] In particular, the fan actuator (140) can be mounted on the outer bushing (1252) of the impeller (120). The outer bushing (1252) is press-fitted onto the inner surface of the hub (121) of the impeller (120). Through this, the driving force generated from the fan actuator (140) can be well transmitted to the hub (121) of the impeller (120).

[0160] In addition, the fan actuator (140) includes a magnet (141) extending circumferentially along the periphery of the hub (121) at the center of the impeller (120), thereby effectively reducing fan noise at all locations along the circumference, rather than at a specific location of the impeller (120).

[0161] A fan actuator (140) according to the present invention may be configured to include a magnet (141), a yoke (142), and a coil (145).

[0162] The magnet (141) provides magnetic force, such as attractive force and repulsive force, as a power source of the excitation force.

[0163] The magnet (141) is formed in a circular ring shape. An axial through hole is formed in the center of the magnet (141). The magnet (141) has an outer circumferential surface and an inner circumferential surface extending along the circumferential direction. In addition, a thickness of the magnet (141) is formed between the outer circumferential surface and the inner circumferential surface of the magnet (141).

[0164] The thickness of the magnet (141) can be extended along the circumferential direction.

[0165] The magnet (141) can be mounted on the outer bushing (1252) among the center bushings (125).

[0166] The inner diameter of the magnet (141) may be formed to be larger than the diameter of the rotation shaft (131). The inner diameter of the magnet (141) may be formed to be larger than or equal to the inner diameter of the outer bushing (1252).

[0167] One axial side and the other axial side of the magnet (141) may be formed as a plane. One axial side of the magnet (141) may be arranged to face axially toward one axial side of the first yoke (143) to be described later.

[0168] The axial side of the magnet (141) can be arranged to face the axial side of the second yoke (144) described later.

[0169] The yoke (142) may be configured to include a first yoke (143) and a second yoke (144). The yoke (142) may be made of a metal material such as iron. The yoke (142) provides a path along which the magnetic flux of the magnet (141) can move.

[0170] The first yoke (143) may be formed in a circular ring shape. The first yoke (143) may be configured with a radially extending yoke (1431) and an axially extending yoke (1432).

[0171] The radial extension yoke (1431) is formed to extend radially. The radial extension yoke (1431) can extend circumferentially along the inner circumference of the magnet (141).

[0172] The inner end of the radially extending yoke (1431) may be axially aligned with the inner surface of the magnet (141), and the outer end of the radially extending yoke (1431) may extend further radially outward from the outer surface of the magnet (141). The radial length of the radially extending yoke (1431) may be extended to be greater than the thickness of the magnet (141).

[0173] The radial extension yoke (1431) is arranged to face one axial side of the magnet (141). The radial extension yoke (1431) is formed to contact one axial side of the magnet (141).

[0174] The axial extension yoke (1432) may extend axially from the outer end of the radial extension yoke (1431) toward one axial side of the motor (130). The axial extension yoke (1432) may extend circumferentially along the outer circumference of the magnet (141).

[0175] The axial extension yoke (1432) is formed to surround the outer surface of the magnet (141). The axial extension yoke (1432) is arranged radially spaced apart from the outer surface of the magnet (141) at a preset interval.

[0176] The axial length of the axial extension yoke (1432) can be extended to be equal to or longer than the axial length of the magnet (141).

[0177] The magnet (141) has a N pole and a S pole. The N pole may be formed on one axial side of the magnet (141). The N pole may be positioned toward the motor (130). It may be formed on the upper part of the magnet (141) based on the drawing.

[0178] The S pole may be formed on the axial side of the magnet (141). The S pole may be positioned toward the impeller (120). It may be formed at the bottom of the magnet (141) based on the drawing.

[0179] The N pole and S pole can each be formed to extend along the circumference of the magnet (141).

[0180] However, the N pole and S pole of the magnet (141) are not limited to the arrangement and formation position of the magnet (141) described above, and may be changed depending on the installation position and direction of the magnet (141).

[0181] At least a portion of the axial extension yoke (1432) is arranged to face the N pole of the magnet (141) in the radial direction.

[0182] The second yoke (144) may be formed in a circular shape. The second yoke (144) is mounted on one axial side of the magnet (141) facing the motor (130). The second yoke (144) may be formed to correspond to the shape of one axial side of the magnet (141).

[0183] Here, corresponding means that the shape of the second yoke (144) and the shape of one axial side of the magnet (141) are the same or similar to each other. For example, one axial side of the second yoke (144) and the magnet (141) are circular.

[0184] The second yoke (144) is formed to cover one axial side of the magnet (141). The second yoke (144) can be in contact with one axial side of the magnet (141). The second yoke (144) can be in contact with the N pole of the magnet (141). In this specification, the second yoke (144) may be referred to as a top yoke (142).

[0185] The radial extension yoke (1431) of the first yoke (143) can come into contact with the S pole of the magnet (141).

[0186] The coil (145) can be placed between the first yoke (143) and the magnet (141). The coil (145) can be implemented as a bobbinless coil.

[0187] A bobbin is a circular or polygonal frame for winding wire to create a coil (145). A bobbinless coil is one that is made in the form of a coil (145) by winding wire without a bobbin.

[0188] The coil (145) according to the present embodiment may be placed between the axially extending yoke (1432) of the first yoke (143) and the magnet (141). The coil (145) may be formed by winding a single strand of wire in a circumferential direction and continuously stacking them along the axial direction. The coil (145) may be formed in a cylindrical shape. The coil (145) may extend in the circumferential direction. The coil (145) may extend in the axial direction.

[0189] The outer surface of the coil (145) may be coated with an insulating material.

[0190] The diameter of one strand of coil (145) can form the thickness of the cylindrical coil (145).

[0191] The inner surface of the coil (145) may be spaced apart from the outer surface of the magnet (141) by an air gap, and the outer surface of the coil (145) may be spaced apart from the inner surface of the axial extension yoke (1432) of the first yoke (143) by an air gap.

[0192] The above air gap can be formed within the range of 0.1 mm to 0.5 mm. If the size of the air gap is less than 0.1 mm, the magnetic flux travel distance between the magnet (141) and the yoke (142) becomes shorter, so that the magnetic flux of the magnet (141) can be better transmitted to the coil (145) through the air gap. However, it is difficult to precisely process the diameter of the magnet (141) and the yoke (142) so as to have the air gap.

[0193] In addition, if the size of the air gap exceeds 0.5 mm, the magnetic flux travel distance between the magnet (141) and the yoke (142) becomes short, so the magnetic flux of the magnet (141) is not well transmitted to the coil (145) through the air gap, and there is a problem in that the excitation force generated by the mutual electromagnetic action between the magnet (141) and the coil (145) becomes weak.

[0194] The inner circumferential diameter of the coil (145) is larger than the outer diameter of the magnet (141), and the outer circumferential diameter of the coil (145) is smaller than the inner diameter of the axially extending yoke (1432) of the first yoke (143). Through this, the coil (145) can be placed between the axially extending yoke (1432) of the first yoke (143) and the magnet (141).

[0195] The coil (145) is implemented as a bobbinless coil, so that the gap between the magnet (141) and the axial extension yoke (1432) of the first yoke (143), i.e., the air gap, can be minimized. In addition, the bobbinless coil (145) can efficiently transmit the magnetic force of the magnet (141) by shortening the travel distance of the magnetic flux transmitted from the magnet (141) to the coil (145) by minimizing the air gap.

[0196] The axial length of the coil (145) is formed to be shorter than the axial length of the magnet (141).

[0197] The coil (145) may be arranged axially spaced from the radially extending yoke (1431) of the first yoke (143). One end of the coil (145), for example, the lower end of the coil (145) based on the drawing, may be radially aligned with the axial center of the magnet (141).

[0198] The lower part of the coil (145) can be arranged to radially coincide with the boundary line of the N pole and S pole of the magnet (141).

[0199] The coil (145) may be arranged to face the N pole of the magnet (141) in the radial direction. The coil (145) may be arranged to overlap the N pole of the magnet (141) in the radial direction. The coil (145) may be arranged to overlap a portion of the magnet (141) and a portion of the axial extension yoke (1432) of the first yoke (143) in the radial direction.

[0200] Through this, the magnetic force lines from the N pole of the magnet (141) can reach the coil (145) at the shortest distance.

[0201] The magnet (141) and the yoke (142) are mounted on one axial side of the outer bushing (1252) so as to be rotatable with respect to the coil (145). The magnet (141) and the yoke (142) can be rotated together with the impeller (120) as the rotation shaft (131) rotates.

[0202] The coil (145) can be fixed to the motor housing (135) or housing (110) by the coil support (146).

[0203] The coil support (146) may be formed in a cylindrical ring shape. The coil support (146) is made of an insulating material such as plastic. The coil support (146) is connected to one axial end of the coil (145).

[0204] The coil support (146) is not arranged between the magnet (141) and the yoke (142). More specifically, the coil support (146) supports the axial end of the coil (145), but is not arranged between the magnet (141) and the axially extending yoke (1432) of the first yoke (143). Accordingly, the coil support (146) does not block the magnetic flux of the magnet (141) from flowing to the yoke (142).

[0205] Through this, the coil support (146) can prevent the current applied to the coil (145) from leaking to the motor housing (135) or the housing (110). The coil support (146) can block the magnetic field generated in the coil (145) from being transmitted to the motor housing (135) or the housing (110).

[0206] Figure 7 is an enlarged view of VII in Figure 1, and is a conceptual diagram showing the magnetic flux movement path of the magnet (141).

[0207] Figure 8 is a conceptual diagram showing the application of axial force directly to the impeller (120) by the electromagnetic interaction between the magnet (141) and the coil (145) in Figure 6.

[0208] Figure 8 is a conceptual diagram showing the application of axial force directly to the impeller (120) by the electromagnetic interaction between the magnet (141) and the coil (145) in Figure 6.

[0209] Below, the operation of the fan actuator (140) of the present invention will be described.

[0210] When an AC voltage is applied to the coil (145), a magnetic field is generated around the coil (145). An electromagnetic interaction occurs between the magnet (141) and the coil (145). For example, attractive and repulsive forces are generated between the magnet (141) and the coil (145).

[0211] The magnetic force such as attraction and repulsion is weaker the farther the distance between the magnet (141) and the coil (145), and is stronger the closer the distance between the magnet (141) and the coil (145).

[0212] In this embodiment, the coil (145) is positioned radially facing the magnet (141) with an air gap. In addition, since the coil (145) is a bobbinless coil without a bobbin, the air gap can be further reduced by the thickness of the bobbin.

[0213] As the air gap between the magnet (141) and the coil (145) decreases, the magnetic flux travel distance of the magnet (141) is shortened.

[0214] Due to this, even if the size of the current applied to the coil (145) is small, the magnetic flux of the magnet (141) can be transmitted smoothly.

[0215] The yoke (142) is composed of a first yoke (143) and a second yoke (144). The first yoke (143) includes an axially extending yoke (1432) and a radially extending yoke (1431). The axially extending yoke (1432) is located at the shortest distance in the radial direction from the N pole of the magnet (141).

[0216] The magnet (141) circulates along the following magnetic flux path.

[0217] The magnetic flux (bundle of magnetic force lines) generated from the N pole of the magnet (141) passes through the coil (145) through the air gap and is transmitted to the axial extension yoke (1432).

[0218] Continuing, the magnetic flux moves from the axial extension yoke (1432) of the first yoke (143) to the radial extension yoke (1431) of the first yoke (143).

[0219] The above magnetic flux is again transmitted to the S pole of the magnet (141) in contact with the radial extension yoke (1431).

[0220] The second yoke (144) is mounted so as to contact one axial side of the magnet (141). The second yoke (144) has a flat surface extending in the radial direction (or a flat plate with a flat upper surface and a flat lower surface based on the drawing). The second yoke (144) is made of a metal material that allows magnetic force to pass through.

[0221] Through this, the second yoke (144) can induce the magnetic flux movement path of the magnet (141) to be transmitted in the radial direction. That is, the second yoke (144) can easily transmit the magnetic flux of the magnet (141) to the coil (145) and the axial extension yoke (1432) of the first yoke (143).

[0222] The second yoke (144) increases the magnetic flux density of the air gap and concentrates the movement of the magnetic flux, thereby enabling more efficient transmission of the magnetic flux to the coil (145).

[0223] According to this configuration, the fan actuator (140) can reduce low-frequency noise, i.e., fan noise (BPF), by directly applying an axial force to the impeller (120) through the electromagnetic interaction between the magnet (141) and the coil (145).

[0224] 4. Description of an ANC control method for reducing fan noise according to an embodiment of the present invention.

[0225] Figure 9 is a conceptual diagram for explaining Self-ANC (Active Noise Control) according to the present invention.

[0226] Axial fans generate BPF noise, a low-frequency noise, depending on the number of fan blades structurally.

[0227] In this embodiment, in order to minimize BPF (Blades pass frequency), an axial fan may be provided with an impeller (120) in the axial direction to perform active noise control (ANC).

[0228] The frequency of the fan BPF generated at the suction portion (1231) and discharge portion of the impeller (120) is the same, but their phases are opposite to each other.

[0229] The noise characteristics of the suction part (1231) and the discharge part of the impeller (120), which have the same frequency and opposite phases, can be applied to the fan motor (100) of the present invention to reduce fan noise.

[0230] As described above, low-frequency noise (BPF) is generated in the impeller (120). This low-frequency noise has a frequency and phase of a certain size.

[0231] In order to reduce the above low-frequency noise, an ANC signal is generated to actively excite the impeller (120) through the fan actuator (140). The fan actuator (140) generates an acoustic signal having the same frequency but opposite phase to the low-frequency noise in the impeller (120), thereby canceling out the low-frequency noise of the impeller (120).

[0232] The control unit (150) is electrically connected to the noise detection unit (151). The control unit (150) can receive a detection signal from the noise detection unit (151) and control the fan actuator (140).

[0233] For example, the control unit (150) can adjust the current applied to the coil (145) of the fan actuator (140) according to the measurement value received from the noise detection unit (151).

[0234] Through this, the control unit (150) controls the fan actuator (140) to directly operate the impeller (120), thereby generating an acoustic signal having the same frequency and magnitude as the fan noise signal generated from the impeller (120) but with an opposite phase, thereby canceling out the fan noise.

[0235] Referring to Fig. 9, the sound signal and the noise signal have the same diameter (frequency) of a semicircle, but are located on opposite sides of the radial center line passing radially through the center of the impeller (120) (the phases are opposite to each other).

[0236] Figure 10 is a graph showing the fan noise reduction effect of a fan motor (100) equipped with an actuator according to the present invention.

[0237] Fig. 11 is a graph showing the results of an experiment on a noise reduction device according to one embodiment of the present invention, and measuring noise at a location 1 m away from the front of an air purifier.

[0238] In this embodiment, the fan motor (100) may be configured to include a noise detection unit (151), a control unit (150), and a fan actuator (140).

[0239] The noise detection unit (151) is configured to measure the sound pressure level of fan noise generated from the impeller (120) installed inside the air purifier. The noise detection unit (151) may be implemented as a microphone.

[0240] The unit of noise is dB. The louder the noise, the greater the sound pressure. The difference in loudness can be very large depending on the type of noise. For example, the noise of human conversation is approximately 100,000 times louder than the noise of a jet engine.

[0241] Because sound pressure ranges are wide, noise can be expressed in terms of sound pressure level (SPL). The unit of SPL is the same as the unit of noise, dB. To narrow down the wide range of sound pressure, SPL can be logarithmically transformed.

[0242] For reference, the sound level that humans can hear in air is 20 μPa, which is 0 dB when converted to SPL.

[0243] In Figure 11, dBA is displayed on the Y-axis, which is the A-weighting assigned to each frequency component of the measured value. The reason for assigning A-weighting is to reflect the human ear in the measured value.

[0244] The human ear has different sensitivity to different frequencies. Therefore, the sound pressure level assigned an A-weighting factor that reflects the ear's sensitivity is called the A-weighted sound level. Its unit is dBA.

[0245] A fan motor (100) equipped with a fan actuator (140) according to the present embodiment was installed inside an air purifier, and noise was measured at a location 1 m away from the front of the air purifier before and after controlling the fan actuator (140), and the results of comparison are as follows.

[0246] Referring to Fig. 10, it can be seen that after controlling the fan actuator (140), the noise was reduced by 6.2 dB (approximately 2 times) at 252 Hz and by 5.2 dB at 503 Hz compared to before controlling the fan actuator (140).

[0247] Referring to Fig. 11, it can be seen that after controlling the fan actuator (140), the noise was reduced by 6 dBA at 251 Hz and 3 dBA at 501 Hz compared to before controlling the fan actuator (140).

Claims

1. An impeller that receives power from a motor and rotates around a rotation axis; Including a noise reducing device generated from the above impeller, The above device, A coil to which power is applied; a yoke rotatably mounted on the impeller; and A fan actuator comprising a magnet coupled to the yoke so as to rotate together with the impeller about the rotational axis with respect to the coil, and applying an axial force to the impeller by electromagnetic interaction between the magnet and the coil.

2. In paragraph 1, The above yoke and the above magnet are mounted at the center of the impeller, A fan actuator in which the above coil is fixedly connected to one axial side of the above motor.

3. In paragraph 1, The above magnet surrounds the above rotation axis, One side of the yoke is coupled to be in contact with one axial side of the magnet, and the other side of the yoke is arranged to be spaced apart from the outer surface of the magnet in the radial direction. A fan actuator in which the coil is spaced apart from the other side of the yoke and the outer surface of the magnet with an air gap between them.

4. In paragraph 1, The above impeller, herbs; and It comprises a plurality of blades extending radially outward from the outer surface of the above hub, A fan actuator in which the above yoke and the above magnet are mounted on one axial side of the above hub.

5. In paragraph 1, The above impeller, Herb; A plurality of blades spaced apart along the circumference of the hub on the radially outer side of the hub; An inner blade guide extending radially outwardly from the outer surface of the hub and connecting the inner ends of the plurality of blades; It comprises an outer blade guide having a suction portion and spaced radially outward from the inner blade and connecting the outer ends of the plurality of blades, A fan actuator in which the above yoke and the above magnet are mounted on one axial side of the above hub.

6. In paragraph 1, The above impeller, Herb; A plurality of blades spaced apart in a circumferential direction along the periphery of the above hub; An inner bushing coupled to the above rotating shaft; An outer bushing arranged on the outside of the inner bushing and coupled to the hub; and A vibration-proof member is disposed between the inner bushing and the outer bushing and is connected to the inner bushing and the outer bushing, A fan actuator in which the above yoke and the above magnet are mounted on one axial side of the above outer bushing.

7. In any one of paragraphs 4 to 6, A fan actuator in which the yoke, the coil, and the magnet are arranged between the downstream side of the hub and the upstream side of the motor based on the airflow direction.

8. In any one of paragraphs 4 to 6, A fan actuator wherein the yoke, the coil and the magnet are arranged on the inside of the hub when viewed in the axial direction.

9. In paragraph 1, The above yoke, the coil, and the magnet are each formed in a cylindrical ring shape, A fan actuator wherein the diameter of the yoke is larger than the diameter of the coil, and the diameter of the coil is larger than the diameter of the magnet.

10. In paragraph 1, The above yoke is, A top yoke that contacts one axial side of the magnet and extends in the radial direction of the magnet; An axially extending yoke that is spaced radially from the outer surface of the magnet and extends axially; and A fan actuator comprising a radially extending yoke that is in contact with the axially extending side surface of the magnet and extends in the radial direction of the magnet from the axially extending yoke.

11. In paragraph 1, The above coil is a fan actuator provided with a bobbinless coil.

12. In paragraph 1, The above motor, motor housing; A stator provided inside the above motor housing; and A rotor coupled to the above rotational axis and rotating with respect to the stator, A fan actuator wherein the coil is supported by a coil support member extending from one axial side of the motor housing toward the impeller.

13. In paragraph 1, A fan actuator in which the coil is arranged to overlap radially with the N pole of the magnet and not overlap with the S pole of the magnet.

14. Housing; A motor installed inside the above housing; An impeller that receives power from the above motor and rotates around a rotation axis; A fan actuator is included that applies axial force to the impeller, The above fan actuator, A coil support extending from one axial side of the motor toward the impeller; A coil supported on the above coil support member; A magnet that surrounds the above-mentioned rotation axis and applies the above-mentioned force through electromagnetic interaction with the coil; and A fan motor comprising a yoke rotatably mounted on the impeller and in contact with at least one surface of the magnet to transmit the magnetic flux of the magnet to the coil.

15. In paragraph 14, A noise detection unit that detects noise signals generated from the above impeller; It further includes a control unit that receives a detection signal from the noise detection unit and controls the driving force of the fan actuator, The above control unit is a fan motor that generates an acoustic signal having the same size and frequency as the noise generated from the impeller but with an opposite phase by the above excitation force to cancel out the noise of the impeller.

Images