Centrifugal fan

Abstract

A centrifugal fan comprises an upper cover, a base and an impeller. The upper cover is provided with an air inlet, the base and the upper cover are combined to form a fan frame, and an air outlet is formed between the upper cover and the radial outer end of the base. The impeller is rotatably arranged in the fan frame and comprises a plurality of fan blades, an upper ring and a bottom plate, and the fan blades are connected between the upper ring and the bottom plate. An air flow channel is formed between any two adjacent ones of the upper ring, the bottom plate and the fan blades, and the two ends of the air flow channel face the air inlet and the air outlet respectively. The air flow channel is provided with a first position, a second position, a third position and a fourth position which are sequentially arranged from the air inlet to the air outlet. The first position has a first axial height, the second position has a second axial height, the third position has a third axial height, and the fourth position has a fourth axial height. The first axial height is larger than the second axial height, the second axial height is smaller than the third axial height, and the third axial height is larger than the fourth axial height.

Description

Technical Field

[0001] The present disclosure relates to a centrifugal fan. Background Art

[0002] Fans are commonly used heat dissipation components. When running, fans will make some noise, especially when running at high speed, which is easy to produce significant noise. Therefore, how to reduce noise is an important issue in fan design. Utility Model Content

[0003] In view of this, an object of the present disclosure is to provide a low-noise centrifugal fan.

[0004] To achieve the above-mentioned purpose, according to some embodiments of the present disclosure, a centrifugal fan includes an upper cover, a base and an impeller. The upper cover has an air inlet, the base and the upper cover are combined to form a fan frame, and the upper cover and the radial outer end of the base form an air outlet. The impeller is rotatably arranged in the fan frame, and includes a plurality of blades, an upper ring and a bottom plate, and the blades are connected between the upper ring and the bottom plate. An air flow channel is formed between any two adjacent ones of the upper ring, the bottom plate and the blades, and the two ends of the air flow channel face the air inlet and the air outlet respectively. The air flow channel has a first position, a second position, a third position and a fourth position arranged in sequence from the air inlet to the air outlet. The first position has a first axial height, the second position has a second axial height, the third position has a third axial height, and the fourth position has a fourth axial height. The first axial height is greater than the second axial height, the second axial height is less than the third axial height, and the third axial height is greater than the fourth axial height.

[0005] In one or more embodiments of the present disclosure, in the radially outward direction, the gap between the upper cover and the upper ring has multiple vertical heights, and the vertical heights are not all the same. The sizes of the vertical heights are large-small-large or small-large-small in sequence.

[0006] In one or more embodiments of the present disclosure, at least one of the plurality of fan blades has an outer edge, the outer edge faces the air outlet and includes a rectangular serrated structure.

[0007] In one or more embodiments of the present disclosure, the upper ring extends radially outward from the outer edge of the fan blade to form an upper ring outer edge bottom surface, and the bottom plate extends radially outward from the outer edge of the fan blade to form a bottom plate outer edge top surface, wherein the upper ring outer edge bottom surface is parallel to the bottom plate outer edge top surface.

[0008] In one or more embodiments of the present disclosure, the third axial height is smaller than the first axial height, and the fourth axial height is smaller than the second axial height.

[0009] In one or more embodiments of the present disclosure, the upper ring has a first wavy surface facing the base plate, and the base plate has a second wavy surface facing the upper ring, wherein the axial height variation of the air flow channel at the first position, the second position, the third position and the fourth position is generated by the first wavy surface and the second wavy surface.

[0010] In one or more embodiments of the present disclosure, the inner edge of at least one fan blade is exposed at the central opening of the upper ring and the air inlet. The upper edge surface of the inner edge close to the air inlet is a flat surface, a curved surface, an inclined surface or a concave surface. The number of the fan blades is 18 or 36.

[0011] In one or more embodiments of the present disclosure, the upper cover has an upper cover air outlet bottom surface adjacent to the air outlet, the base has a base air outlet top surface adjacent to the air outlet, and the upper cover air outlet bottom surface faces the base air outlet top surface, wherein in a direction radially away from the fan blade from the outer edge of the fan blade, the vertical distance between the upper cover air outlet bottom surface and the base air outlet top surface is large-small-large or small-large-small in sequence.

[0012] In one or more embodiments of the present disclosure, the upper cover and the base are connected by a plurality of connecting columns, and the upper cover, the base and the connecting columns together form an air outlet. The cross section of the connecting column is circular, polygonal, teardrop-shaped or other shapes with convex curved surfaces.

[0013] In one or more embodiments of the present disclosure, the upper ring has an upper surface having a first platform area and a second platform area, wherein the air inlet, the first platform area and the second platform area are arranged in sequence in the axial horizontal height.

[0014] In one or more embodiments of the present disclosure, the upper surface of the upper ring further has an inclined surface or a vertical surface located between the first platform area and the second platform area.

[0015] In summary, the centrifugal fan disclosed herein achieves noise reduction and improved operating efficiency through at least one of the following structural features: (1) the fan frame has two annular grooves, and the impeller has two annular protrusion structures corresponding to the two annular grooves, wherein the annular protrusion structure on the outer side is bent in a direction away from the air inlet of the fan; (2) the impeller includes an upper ring, a bottom plate, and a plurality of fan blades connected between the upper ring and the bottom plate, and the fan blades divide the space between the upper ring and the bottom plate into a plurality of air flow channels. From the air inlet to the air outlet, the air flow channels First it shrinks and then expands, and then it shrinks again after expanding (the air flow channel has at least three width changes); (3) The outer edge of the fan blade contains a rectangular serrated structure; (4) The inner edge of the fan blade is exposed at the air inlet; (5) The upper edge surface of the inner edge of the fan blade close to the air inlet is a flat surface, a curved surface, an inclined surface or a concave surface; (6) The number of fan blades is 18 or 36; (7) The size of the fan frame at the air outlet is large-small-large or small-large-small; (8) The cross-section of the connecting column connecting the upper cover and the base is circular, polygonal, teardrop-shaped or other shapes with convex curved surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to make the above and other objects, features, advantages and implementation methods of the present disclosure more obvious and understandable, the attached drawings are described as follows:

[0017] Figure 1 A diagram showing a centrifugal fan according to an embodiment of the present disclosure;

[0018] Figure 2 To illustrate Figure 1 An exploded view of a centrifugal fan is shown;

[0019] Figure 3 To illustrate Figure 2 A top view of an impeller of a centrifugal fan is shown;

[0020] Figure 4 To illustrate Figure 1 The centrifugal fan is shown in cross-section at the line segment 4-4';

[0021] Figure 5 To illustrate Figure 4 An enlarged view of the centrifugal fan shown at the position indicated by the frame line 5;

[0022] Figure 6 A partially enlarged cross-sectional view of a centrifugal fan according to another embodiment of the present disclosure is shown;

[0023] Figure 7 A partially enlarged cross-sectional view of a centrifugal fan according to another embodiment of the present disclosure is shown.

[0024]

Explanation of symbols

[0025] 12: Centrifugal fan

[0026] 13: Fan frame

[0027] 14: Air inlet

[0028] 15: Air outlet

[0029] 16: Base

[0030] 17: Axle tube

[0031] 20: Upper cover

[0032] 21: First annular groove

[0033] 22: Second annular groove

[0034] 23: Top

[0035] 30: Stator assembly

[0036] 31: Driver circuit board

[0037] 32: Coil assembly

[0038] 35: Bearing

[0039] 50,50A,50B: Impeller

[0040] 51: first annular protrusion structure

[0041] 52, 52B: Second annular protrusion structure

[0042] 53,53A,53B: Sheung Wan

[0043] 54: Central opening

[0044] 55,55A: Upper surface

[0045] 56: Bottom plate

[0046] 57: Fan blade

[0047] 58: Inner Edge

[0048] 59: Outer edge

[0049] 60: shaft

[0050] 61: First wavy surface

[0051] 62: Second wavy surface

[0052] 63: First End

[0053] 64: Second End

[0054] 65: Rectangular serrated structure

[0055] 66: Axial extension

[0056] 67: radial extension

[0057] 68,69: Incline

[0058] 68A: Vertical surface

[0059] 71: First platform area

[0060] 72: Second platform area

[0061] 80: Connection port

[0062] 81: Bottom of the outer edge of the upper ring

[0063] 82: Top surface of outer edge of bottom plate

[0064] 83: Connecting column

[0065] 84: Bottom of the upper cover air outlet

[0066] 85: Top surface of the air outlet of the base

[0067] A1: First position

[0068] A2: Second position

[0069] A3: Third position

[0070] A4: Fourth position

[0071] D1,D2: Direction

[0072] G: Gap

[0073] P: Air flow channel

[0074] R: Axis

[0075] W1: First axial height

[0076] W2: Second axial height

[0077] W3: third axial height

[0078] W4: Fourth axial height DETAILED DESCRIPTION

[0079] In order to make the description of the present disclosure more detailed and complete, reference may be made to the attached drawings and various embodiments described below. The elements in the drawings are not drawn to scale and are provided only for the purpose of illustrating the present disclosure. Many practical details are described below to provide a comprehensive understanding of the present disclosure, however, a person of ordinary skill in the relevant art should understand that the present disclosure can be implemented without one or more of the practical details, and therefore, these details should not be used to limit the present disclosure.

[0080] Please refer to Figure 1 . Figure 1 The figure is a diagram showing a centrifugal fan 12 according to an embodiment of the present disclosure. As shown in the figure, the centrifugal fan 12 includes a fan frame 13 and an impeller 50. The fan frame 13 has an air inlet 14 and at least one air outlet 15. The air inlet 14 is arranged at the center of the fan frame 13, and the air outlet 15 is arranged on the side of the fan frame 13. The impeller 50 is rotatably arranged in the fan frame 13. The impeller 50 is configured to rotate around an axis R. When the impeller 50 rotates, air can be introduced into the fan frame 13 through the air inlet 14, and then the air can be blown out through the air outlet 15.

[0081] like Figure 1 As shown, in some embodiments, the fan frame 13 includes a base 16 and an upper cover 20, and the base 16 and the upper cover 20 are combined to form the fan frame 13. The upper cover 20 has a central opening as an air inlet 14 of the fan frame 13. At least one gap is maintained between the upper cover 20 and the base 16 as an air outlet 15. Specifically, the air outlet 15 is formed between the upper cover 20 and the radial outer end of the base 16. The impeller 50 can be arranged in the space between the base 16 and the upper cover 20. The base 16 and the upper cover 20 can be combined by screw locking or other suitable methods. In some embodiments, the fan frame 13 also includes a connection port 80, and the connection port 80 is, for example, an electrical connector for connecting to a system using the centrifugal fan 12 to allow the system to transmit signals to the centrifugal fan 12.

[0082] Please refer to Figure 2 . Figure 2 To illustrate Figure 1 Exploded view of the centrifugal fan 12 shown. As shown in the figure, the impeller 50 includes an upper ring 53, a bottom plate 56 and a plurality of blades 57. The upper ring 53 and the bottom plate 56 are arranged opposite to each other, the upper ring 53 is located on the side of the impeller 50 facing the upper cover 20, and the bottom plate 56 is located on the side of the impeller 50 facing the base 16 (in other words, the bottom plate 56 is located on the side of the impeller 50 away from the upper cover 20). The upper ring 53 has a central opening 54, and the central opening 54 faces the air inlet 14. The blades 57 are connected between the upper ring 53 and the bottom plate 56, and divide the space between the upper ring 53 and the bottom plate 56 into a plurality of air flow channels P. The upper cover 20 and the base 16 are connected by a plurality of connecting columns 83, and the upper cover 20, the base 16 and the connecting columns 83 together constitute the air outlet 15. The cross section of the connecting column 83 is, for example, circular, polygonal, teardrop-shaped or other shapes with convex curved surfaces. When the cross section of the connecting column 83 is a teardrop shape or other shapes with a convex curved surface, the centrifugal fan 12 can achieve higher operating efficiency and lower operating volume.

[0083] like Figure 2As shown, each air flow channel P is defined by the upper ring 53, the bottom plate 56 and any two adjacent blades 57, and the two ends of the air flow channel P respectively face the air inlet 14 and the air outlet 15 of the fan frame 13. When the impeller 50 rotates, air can be introduced into the fan frame 13 through the air inlet 14 and enter the air flow channel P of the impeller 50, and finally the air is blown out through the air outlet 15.

[0084] like Figure 2 As shown, in some embodiments, the centrifugal fan 12 further includes a stator assembly 30, which is disposed in the fan frame 13 and configured to drive the rotor assembly including the impeller 50 to rotate. In some embodiments, the stator assembly 30 includes a driving circuit board 31 and a coil assembly 32, and the coil assembly 32 is disposed on the driving circuit board 31 and electrically connected to the driving circuit board 31. When the coil assembly 32 is energized, a magnetic field is generated to drive the rotor assembly with a magnet to rotate (the magnet is not shown in the figure; for example, the magnet can be disposed in the impeller 50). In some embodiments, the coil assembly 32 can include a winding frame and a plurality of coils wound on the winding frame.

[0085] like Figure 2 As shown, in some embodiments, the rotor assembly further includes a shaft member 60, the top end of which is fixed to the impeller 50. A bearing 35 is disposed on the base 16, and the bearing 35 is coupled to the shaft member 60 to support the rotational movement of the rotor assembly. In some embodiments, the base 16 includes a shaft tube 17, which protrudes toward the upper cover 20, and the bearing 35 is disposed in the shaft tube 17, and the shaft member 60 extends to the center hole of the shaft tube 17 and penetrates the bearing 35. In some embodiments, the drive circuit board 31 and the coil assembly 32 of the stator assembly 30 are disposed on the base 16 and are disposed around the shaft tube 17.

[0086] Please refer to Figure 3 . Figure 3 To illustrate Figure 2 1 is a top view of the impeller 50 of the centrifugal fan 12. As shown in the figure, each blade 57 has an inner edge 58 and an outer edge 59 opposite to each other, the inner edge 58 is adjacent to the center of the upper ring 53 and the bottom plate 56, and the outer edge 59 is adjacent to the outer periphery of the upper ring 53 and the bottom plate 56 and faces the air outlet 15 of the fan frame 13. The inner edge 58 of the blade 57 can be exposed to the central opening 54 of the upper ring 53 and to the air inlet 14 of the fan frame 13 (see FIG. Figure 1 ). Through the above-mentioned technology, the centrifugal fan 12 can obtain higher operating efficiency and lower operating volume. In addition, the upper edge surface of the inner edge 58 close to the air inlet 14 is a flat surface, a curved surface, an inclined surface or a concave surface. When the upper edge surface is a curved surface, an inclined surface or a concave surface, the operating efficiency of the centrifugal fan 12 can be further improved and the operating volume of the centrifugal fan 12 can be reduced.

[0087] In some embodiments, the fan blades 57 have a curved shape. The number of the fan blades 57 is preferably 18 or 36. When the fan blades 57 are at this number, the operating efficiency of the centrifugal fan 12 can be further improved and the operating volume of the centrifugal fan 12 can be reduced.

[0088] Please refer to Figure 4 . Figure 4 To illustrate Figure 1 The centrifugal fan 12 is shown in cross-section at line segment 4-4'. As shown in the figure, in some embodiments, the outer edge 59 of each fan blade 57 includes a rectangular sawtooth structure 65 (also refer to Figure 2 ), the rectangular sawtooth structure 65 includes one or more protruding rectangular teeth, and a recess may be provided between two adjacent rectangular teeth. When the impeller 50 rotates, the rectangular sawtooth structure 65 has the effect of breaking up the vortex near the air outlet 15, which helps to reduce the noise generated by the centrifugal fan 12. In some embodiments, the rectangular sawtooth structure 65 includes at least two rectangular teeth to effectively reduce noise.

[0089] In addition, the upper ring 53 has an upper ring outer edge bottom surface 81 extending radially outward from the outer edge 59, and the bottom plate 56 has a bottom plate outer edge top surface 82 extending radially outward from the outer edge 59. When the upper ring outer edge bottom surface 81 is parallel to the bottom plate outer edge top surface 82, the centrifugal fan 12 can achieve higher operating efficiency and lower operating volume.

[0090] The upper cover 20 has an upper cover air outlet bottom surface 84 adjacent to the air outlet 15, and the base 16 has a base air outlet top surface 85 adjacent to the air outlet 15, and the upper cover air outlet bottom surface 84 faces the base air outlet top surface 85. When the vertical distance between the upper cover air outlet bottom surface 84 and the base air outlet top surface 85 changes in size from the outer edge 59 in a direction radially away from the fan blades 57 in sequence of large-small-large or small-large-small, the centrifugal fan 12 can obtain higher operating efficiency and lower operating volume.

[0091] Please refer to Figure 5 . Figure 5 To illustrate Figure 4 The centrifugal fan 12 is shown in an enlarged view at the position indicated by the frame line 5. Figure 4 and Figure 5As shown, in some embodiments, the air flow channel P has a variable cross-sectional area. In some embodiments, the air flow channel P has a first axial height W1 at the first position A1, a second axial height W2 at the second position A2, a third axial height W3 at the third position A3, and a fourth axial height W4 at the fourth position A4, and the first position A1, the second position A2, the third position A3, and the fourth position A4 are arranged in sequence from the air inlet 14 to the air outlet 15, wherein the first axial height W1 is greater than the second axial height W2, the second axial height W2 is less than the third axial height W3, and the third axial height W3 is greater than the fourth axial height W4. In other words, between the first position A1 and the second position A2, the air flow channel P is reduced, between the second position A2 and the third position A3, the air flow channel P is expanded, and between the third position A3 and the fourth position A4, the air flow channel P is reduced again. In other words, from the air inlet 14 to the air outlet 15, the air flow path P first narrows and then widens, and then narrows again (that is, the air flow path P has three width changes). The air flow path P with a variable cross-sectional area can make the air flow more stable after passing through, which helps to reduce the noise generated by the centrifugal fan 12.

[0092] It should be noted that the term "axial" used in this article refers to the direction in which the axis R of rotation of the impeller 50 extends (i.e., direction D1 marked in the figure), and the term "radial" refers to the direction pointing laterally outward from the axis R (i.e., direction D2 marked in the figure).

[0093] like Figure 4 and Figure 5 As shown, in some embodiments, the upper ring 53 has a first wavy surface 61 facing the bottom plate 56 and connected to the fan blade 57, the bottom plate 56 has a second wavy surface 62 facing the upper ring 53 and connected to the fan blade 57, and the axial height variation of the air flow channel P at the first position A1, the second position A2, the third position A3 and the fourth position A4 is generated by the first wavy surface 61 and the second wavy surface 62. The wave crest positions of the first wavy surface 61 and the second wavy surface 62 can be aligned with each other in the axial direction, and the wave trough positions of the first wavy surface 61 and the second wavy surface 62 can be aligned with each other in the axial direction.

[0094] like Figure 4 and Figure 5 As shown, in some embodiments, the third axial height W3 of the air flow channel P is less than the first axial height W1, and the fourth axial height W4 is less than the second axial height W2. In other words, between the second position A2 and the third position A3, the air flow channel P expands under the limitation of the first axial height W1 being no wider than the first position A1.

[0095] like Figure 4 and Figure 5As shown, in some embodiments, the air flow channel P may have more than three width variations. For example, the air flow channel P may have a fifth axial height at the fifth position, the fifth position is between the fourth position A4 and the air outlet 15, and the fifth axial height is greater than the fourth axial height W4 (that is, between the fourth position A4 and the fifth position, the air flow channel P expands). For example, the air flow channel P may have a sixth axial height at the sixth position, the sixth position is between the fifth position and the air outlet 15, and the sixth axial height is less than the fifth axial height (that is, between the fifth position and the sixth position, the air flow channel P shrinks). And so on. In some embodiments, the fifth axial height of the air flow channel P is less than the third axial height W3. In some embodiments, the sixth axial height of the air flow channel P is less than the fourth axial height W4.

[0096] like Figure 4 and Figure 5 As shown, the upper ring 53 of the impeller 50 extends from the air inlet 14 to the air outlet 15. In order to allow the impeller 50 to rotate freely, the upper ring 53 does not contact the upper cover 20 of the fan frame 13, and there is a gap G between the upper ring 53 and the upper cover 20. When the centrifugal fan 12 is running, due to the existence of the gap G, part of the air will enter the gap G from the end of the gap G adjacent to the air outlet 15 to generate a countercurrent airflow. In some embodiments, in the radially outward direction, the gap G has multiple vertical heights, and the aforementioned vertical heights are not all the same. In the radially outward direction, the size of the aforementioned vertical height is large-small-large or small-large-small in sequence, at which time the running volume of the centrifugal fan 12 can be further reduced and the running efficiency of the centrifugal fan 12 can be improved.

[0097] like Figure 4 and Figure 5 As shown, in some embodiments, a first annular groove 21 and a second annular groove 22 are provided on the inner side surface (i.e., the side facing the gap G) of the upper cover 20 of the fan frame 13. The first annular groove 21 and the second annular groove 22 are arranged in sequence around the air inlet 14, and the first annular groove 21 is located between the air inlet 14 and the second annular groove 22.

[0098] like Figure 4 and Figure 5 As shown, in some embodiments, the upper ring 53 includes a first annular protrusion structure 51 and a second annular protrusion structure 52 (also refer to Figure 2). The first annular protrusion structure 51 and the second annular protrusion structure 52 are arranged on the upper surface 55 of the upper ring 53 facing the upper cover 20, and correspond to the first annular groove 21 and the second annular groove 22 respectively. The first annular protrusion structure 51 and the second annular protrusion structure 52 are arranged around the central opening 54 of the upper ring 53, and the first annular protrusion structure 51 is located between the central opening 54 and the second annular protrusion structure 52. The first annular protrusion structure 51 protrudes axially toward the first annular groove 21, and the second annular protrusion structure 52 protrudes toward the second annular groove 22, and is bent in a direction away from the air inlet 14 (or bent in a direction away from the central opening 54 of the upper ring 53), so that a groove facing away from the air inlet 14 and the central opening 54 is formed between the second annular protrusion structure 52 and the upper surface 55 of the upper cover 20.

[0099] like Figure 4 and Figure 5 As shown, the arrangement of the first annular groove 21, the second annular groove 22, the first annular protrusion structure 51 and the second annular protrusion structure 52 causes the flow path of the countercurrent airflow to change in the radial and axial directions, which helps to reduce the countercurrent airflow, reduce the noise generated by the centrifugal fan 12, and improve the efficiency of the centrifugal fan 12.

[0100] like Figure 4 and Figure 5 As shown, in some embodiments, the second annular protrusion structure 52 has an opposite first end 63 and a second end 64, the first end 63 is connected to the upper surface 55 of the upper ring 53, and the second end 64 is away from the upper surface 55 of the upper ring 53 and away from the rotation axis R of the impeller 50 (or, away from the central opening 54 of the upper ring 53) relative to the first end 63. Therefore, the second annular protrusion structure 52 extending from the first end 63 to the second end 64 has an axial component and a radial component.

[0101] like Figure 4 and Figure 5 As shown, in some embodiments, the second annular protrusion structure 52 includes an axial extension portion 66 and a radial extension portion 67, and the axial extension portion 66 is connected between the upper surface 55 of the upper ring 53 and the radial extension portion 67. The radial extension portion 67 is substantially perpendicular to the axial extension portion 66 and forms an L-shaped structure together with the axial extension portion 66.

[0102] like Figure 4 and Figure 5As shown, in some embodiments, the first annular protrusion structure 51 and the second annular protrusion structure 52 are disposed at one end of the upper ring 53 adjacent to the air inlet 14, and correspondingly, the first annular groove 21 and the second annular groove 22 are disposed adjacent to the air inlet 14. In other embodiments, the first annular protrusion structure 51 and the second annular protrusion structure 52 may also be disposed at one end of the upper ring 53 adjacent to the air outlet 15, and correspondingly, the first annular groove 21 and the second annular groove 22 are disposed adjacent to the air outlet 15.

[0103] like Figure 4 and Figure 5 As shown, in some embodiments, the first annular protrusion structure 51 is higher than the second annular protrusion structure 52, that is, in the axial direction, the distance between the first annular protrusion structure 51 and the top surface 23 of the upper cover 20 (that is, the surface of the upper cover 20 away from the impeller 50 and the base 16) is smaller than the distance between the second annular protrusion structure 52 and the top surface 23 of the upper cover 20. Correspondingly, the bottom surface of the first annular groove 21 may be higher than the bottom surface of the second annular groove 22, that is, in the axial direction, the distance between the bottom surface of the first annular groove 21 and the top surface 23 of the upper cover 20 is smaller than the distance between the bottom surface of the second annular groove 22 and the top surface 23 of the upper cover 20.

[0104] like Figure 4 and Figure 5 As shown, in some embodiments, the upper surface 55 of the upper ring 53 has a first platform area 71 and a second platform area 72, the first platform area 71 is located between the first annular protrusion structure 51 and the second annular protrusion structure 52, and the second platform area 72 is located on the side of the second annular protrusion structure 52 away from the first annular protrusion structure 51. The second platform area 72 is lower than the first platform area 71, that is, in the axial direction, the distance between the second platform area 72 and the top surface 23 of the upper cover 20 is greater than the distance between the first platform area 71 and the top surface 23 of the upper cover 20. Specifically, in the horizontal height of the axial direction, the air inlet 14, the first platform area 71 and the second platform area 72 are arranged in sequence. The design of the height difference between the first platform area 71 and the second platform area 72 helps to further reduce the backflow airflow and achieve a better effect of reducing the fan noise. The first platform area 71 and the second platform area 72 can be arranged roughly along the radial direction D2 as shown in the figure, or can be arranged inclined to the direction D2.

[0105] like Figure 4 and Figure 5As shown, in some embodiments, the upper surface 55 of the upper ring 53 further has an inclined surface 68 located between the first platform area 71 and the second platform area 72. In this embodiment, the inclined surface 68 is located outside the second annular protrusion structure 52, and together with the second annular protrusion structure 52, forms a groove facing away from the air inlet 14 and the central opening 54. In some embodiments, the upper surface 55 of the upper ring 53 further has an inclined surface 69 located between the second platform area 72 and the outer periphery of the upper ring 53.

[0106] Please refer to Figure 6 . Figure 6 The present embodiment is a partially enlarged cross-sectional view of a centrifugal fan according to another embodiment of the present disclosure. The difference between the present embodiment and the aforementioned embodiment is that the upper surface 55A of the upper ring 53A of the impeller 50A has a vertical surface 68A instead of the aforementioned inclined surface 68, and the vertical surface 68A connects the first platform area 71 and the second platform area 72 with a height difference.

[0107] Please refer to Figure 7 . Figure 7 A partial enlarged cross-sectional view of a centrifugal fan according to another embodiment of the present disclosure is shown. Different from the aforementioned embodiment, the second annular protrusion structure 52B of the upper ring 53B of the impeller 50B of the present embodiment is an arc-shaped structure. The second annular protrusion structure 52B has a first end 63 and a second end 64 opposite to each other, the first end 63 is connected to the upper surface 55 of the upper ring 53B, and the second end 64 is away from the upper surface 55 of the upper ring 53B and away from the rotation axis of the impeller 50B (or, away from the central opening 54 of the upper ring 53) relative to the first end 63. Therefore, the second annular protrusion structure 52B extending from the first end 63 to the second end 64 has an axial component and a radial component, which can also achieve the effect of reducing the backflow airflow.

[0108] In summary, the centrifugal fan disclosed herein achieves noise reduction and improved operating efficiency through at least one of the following structural features: (1) the fan frame has two annular grooves, and the impeller has two annular protrusion structures corresponding to the two annular grooves, wherein the annular protrusion structure on the outer side is bent in a direction away from the air inlet of the fan; (2) the impeller includes an upper ring, a bottom plate, and a plurality of fan blades connected between the upper ring and the bottom plate, and the fan blades divide the space between the upper ring and the bottom plate into a plurality of air flow channels. From the air inlet to the air outlet, the air flow channels First shrink and then expand, and then shrink again after expansion (the air flow channel has at least three width changes); (3) The outer edge of the fan blade contains a rectangular serrated structure; (4) The inner edge of the fan blade is exposed at the air inlet; (5) The upper edge surface of the inner edge of the fan blade close to the air inlet is a flat surface, a curved surface, an inclined surface or a concave surface; (6) The number of fan blades is 18 or 36; (7) The size of the fan frame at the air outlet is large-small-large or small-large-small; (8) The cross-section of the connecting column connecting the upper cover and the base is circular, polygonal, teardrop-shaped or other shapes with convex curved surfaces.

[0109] Although the present disclosure has been disclosed in the above embodiments, it is not intended to limit the present disclosure. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be based on the scope defined by the attached claims.

Claims

1. A centrifugal fan, characterized in that: Include: An upper cover having an air inlet; A base, combined with the upper cover to form a fan frame, and an air outlet is formed between the upper cover and the radial outer end of the base; and an impeller rotatably disposed in the fan frame and comprising a plurality of blades, an upper ring and a bottom plate, wherein the plurality of blades are connected between the upper ring and the bottom plate, and an air flow channel is formed between the upper ring, the bottom plate and any two adjacent ones of the plurality of blades, wherein two ends of the air flow channel face the air inlet and the air outlet respectively; The air flow channel has a first position, a second position, a third position and a fourth position, and the first position, the second position, the third position and the fourth position are arranged in sequence from the air inlet to the air outlet, wherein the first position has a first axial height, the second position has a second axial height, the third position has a third axial height and the fourth position has a fourth axial height, wherein the first axial height is greater than the second axial height, the second axial height is less than the third axial height, and the third axial height is greater than the fourth axial height.

2. The centrifugal fan according to claim 1, wherein: In the radially outward direction, the gap between the upper cover and the upper ring has a plurality of vertical heights, and the plurality of vertical heights are not all the same.

3. The centrifugal fan according to claim 2, wherein: In the radially outward direction, the sizes of the plurality of vertical heights are in the order of large-small-large or small-large-small.

4. The centrifugal fan according to claim 1, wherein: At least one of the plurality of fan blades has an outer edge, which faces the air outlet and includes a rectangular sawtooth structure.

5. The centrifugal fan according to claim 4, characterized in that: in The upper ring extends radially outward from the outer edge to form an upper ring outer edge bottom surface; and The bottom plate extends radially outward from the outer edge to form a bottom plate outer edge top surface, wherein the upper ring outer edge bottom surface is parallel to the bottom plate outer edge top surface.

6. The centrifugal fan according to claim 1, wherein: The third axial height is smaller than the first axial height, and the fourth axial height is smaller than the second axial height.

7. The centrifugal fan according to claim 1, wherein: The upper ring has a first wavy surface facing the base plate, and the base plate has a second wavy surface facing the upper ring, wherein the axial height variation of the air flow channel at the first position, the second position, the third position and the fourth position is generated by the first wavy surface and the second wavy surface.

8. The centrifugal fan according to claim 1, wherein: The inner edge of at least one of the fan blades is exposed at a central opening of the upper ring and the air inlet.

9. The centrifugal fan according to claim 8, characterized in that: The upper edge surface of the inner edge close to the air inlet is a flat surface, a curved surface, an inclined surface or a concave surface.

10. The centrifugal fan according to claim 1, wherein: The number of the plurality of blades is 18 or 36.

11. The centrifugal fan according to claim 1, wherein: in The upper cover has an upper cover air outlet bottom surface adjacent to the air outlet; and The base has a base air outlet top surface adjacent to the air outlet, and the bottom surface of the upper cover air outlet faces the top surface of the base air outlet, wherein in a direction radially away from the multiple fan blades from the outer edges of the multiple fan blades, the vertical distance between the bottom surface of the upper cover air outlet and the top surface of the base air outlet is large-small-large or small-large-small in sequence.

12. The centrifugal fan according to claim 1, wherein: The upper cover and the base are connected via a plurality of connecting columns, and the upper cover, the base and the plurality of connecting columns together form the air outlet.

13. The centrifugal fan according to claim 12, wherein: The cross sections of the multiple connection pillars are circular, polygonal, teardrop-shaped or other shapes with convex curved surfaces.

14. The centrifugal fan according to claim 1, wherein: The upper ring has an upper surface, and the upper surface has a first platform area and a second platform area, wherein the air inlet, the first platform area and the second platform area are arranged in sequence at the horizontal height of the axial direction.

15. The centrifugal fan according to claim 14, wherein: The upper surface of the upper ring further has an inclined surface or a vertical surface located between the first platform area and the second platform area.

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