Silencing type centrifugal fan

Abstract

The utility model discloses a noise reduction type centrifugal fan which comprises a fan frame, the fan frame is provided with a bottom plate, side walls extending upwards from the periphery of the bottom plate and a cover plate arranged above the side walls in a covering mode and opposite to the bottom plate, and a hollow cavity is defined by the bottom plate, the side walls and the cover plate jointly; the at least one air inlet is formed in the cover plate in a penetrating manner; the at least one air outlet is defined by the bottom plate, the side wall and the cover plate; the fan wheel assembly is rotatably assembled in the fan frame and located under the air inlet; the airflow channel is formed between the outer periphery of the fan wheel assembly and the inner wall surface of the side wall; the tongue opening part is formed on the side wall close to the air outlet and is positioned at one end of the airflow channel; the resonant cavity is formed in the tongue opening part and is in an upward opening shape, and the cover plate covers an opening in the upper portion of the resonant cavity so as to seal the resonant cavity; and the silencing opening is communicated with the resonant cavity and the airflow channel, so that noise can be controlled.

Description

Technical Field

[0001] The present application relates to a silencer type centrifugal fan. Background Art

[0002] With the rapid development of computer technology in recent years, the operating speed of computers has been continuously improved.

[0003] Generally speaking, in order to prevent the electronic components inside the computer host from overheating and causing temporary or permanent failure of the electronic components, fans are usually installed on the power supply, central processing unit (CPU) and graphics processing unit (GPU) of the computer host, which are easy to heat up, to quickly dissipate the heat energy generated by the electronic components when they are running at high speed, so as to reduce the temperature of the electronic components themselves, so that the operation of the computer host can be smoother. However, the rotation of the fan will generate vibration noise, and when the above vibration noise falls into the user's receiving range, it will affect the user's auditory perception, that is, it will affect the user's operating comfort. Therefore, how to reduce the volume of noise is a problem that technicians in this field have always faced. Utility Model Content

[0004] The purpose of this application is to provide a new silent centrifugal fan to solve the above technical problems.

[0005] To achieve the above objectives, this application adopts the following technical solutions:

[0006] A silent centrifugal fan, comprising:

[0007] The fan frame comprises a bottom plate, side walls extending upward from the bottom plate, and a cover plate arranged above the side walls and opposite to the bottom plate, wherein the bottom plate, the side walls and the cover plate are jointly arranged to form a hollow cavity;

[0008] At least one air inlet is formed through the cover plate;

[0009] At least one air outlet is defined by the bottom plate, the side wall and the cover plate;

[0010] The fan wheel assembly is rotatably assembled in the fan frame and is located directly below the air inlet;

[0011] An air flow channel is formed between the outer periphery of the impeller assembly and the inner wall surface of the side wall;

[0012] A tongue portion is formed on the side wall adjacent to the air outlet and located at one end of the air flow channel;

[0013] The airflow channel starts at the end where the tongue mouth is located, and its width along the radial direction of the impeller assembly gradually increases, and a pressurized area is formed at the end where the tongue mouth is located;

[0014] A resonance cavity is formed at the tongue mouth and is open upward, and the cover plate is arranged on the opening above the resonance cavity to close the resonance cavity;

[0015] The side of the tongue portion close to the air flow channel includes an inner wall defining the resonance cavity;

[0016] The silencer port connects the resonance cavity and the air flow channel.

[0017] Furthermore, the muffler port is a first muffler groove formed by a groove-shaped groove formed by partially concavely upwards on the lower surface of the cover plate corresponding to the resonance cavity position;

[0018] The first muffler groove goes over the upper edge of the inner wall to connect the air flow channel with the resonance cavity.

[0019] Furthermore, the muffler port further includes a second muffler groove formed by the upper edge of the inner wall being recessed downward, the second muffler groove runs through the thickness direction of the inner wall and is open upward;

[0020] The first silencer groove corresponds to the second silencer groove in the up-down direction, and the first silencer groove and the second silencer groove together form a channel connecting the airflow channel and the resonance cavity.

[0021] Furthermore, the muffler port is a second muffler groove formed by the upper edge of the inner wall being recessed downward, and the second muffler groove runs through the thickness direction of the inner wall and is open upward;

[0022] The lower surface of the cover plate covers the second silencer groove to form a channel connecting the air flow channel and the resonance cavity.

[0023] Furthermore, the height of the muffler port in the vertical direction is not less than 20% and not more than 75% of the depth of the resonance cavity;

[0024] The depth of the resonance cavity is the maximum distance between the inner bottom surface of the resonance cavity and the lower surface of the cover plate covering the resonance cavity.

[0025] Furthermore, the height of the silencer port in the up-down direction is not less than 40% and not more than 60% of the depth of the resonance cavity.

[0026] Furthermore, the ratio of the width of the silencer port to the outer diameter of the impeller assembly is greater than 0 and not greater than 12.5%.

[0027] Furthermore, the ratio of the width of the silencer port to the outer diameter of the impeller assembly is not less than 5.5% and not more than 12.5%.

[0028] Furthermore, the ratio of the width of the silencer port to the outer diameter of the impeller assembly is 9%.

[0029] Furthermore, the cover plate is integrally extended and bent upward at a position around the air inlet to form a step portion, so that the upper surface of the step portion is higher than the upper surface of the cover plate, and the lower surface of the step portion is higher than the lower surface of the cover plate;

[0030] The first muffler groove is formed at a position of the cover plate adjacent to the step portion;

[0031] The outer surface of the cover plate portion forming the first muffler groove is flush with the upper surface of the step portion;

[0032] The inner surface of the cover plate portion forming the first silencing groove is flush with the lower surface of the step portion.

[0033] Furthermore, the transition position between the step portion and the cover plate is aligned with the outer periphery of the impeller assembly in the up-down direction.

[0034] Furthermore, the inner wall protrudes into the cavity at a middle position along the front-to-back direction to form an inflection point, so as to define the inner wall into a front wall and a rear wall integrally connected at the inflection point;

[0035] The front wall constitutes an inner wall of one side of the air outlet, so that the width of the air outlet along the left and right directions gradually expands from the inside to the outside;

[0036] The inflection point serves as the starting point of the airflow channel;

[0037] The rear end wall constitutes a portion of the inner wall of the air flow channel in the pressurized area;

[0038] The silencer port is formed at a middle position of the front wall along the front-to-back direction and / or the silencer port is formed at a middle position of the rear end wall along the front-to-back direction.

[0039] The beneficial effect of the present application is that, compared with the prior art, the noise can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present application will be further described below in conjunction with drawings and embodiments.

[0041] Figure 1 It is a three-dimensional schematic diagram of the first embodiment of the silent centrifugal fan of the present application.

[0042] Figure 2 yes Figure 1 A top view of a silent centrifugal fan is shown.

[0043] Figure 3 yes Figure 1 A top view of a silent centrifugal fan is shown, wherein the dotted line portion is for illustrating the internal structure covered by the cover plate.

[0044] Figure 4 yes Figure 1The partial three-dimensional exploded view of the silent centrifugal fan shown in the figure specifically shows the three-dimensional schematic diagram after the cover plate is separated.

[0045] Figure 5 yes Figure 1 The silent centrifugal fan shown is a top view with the cover removed.

[0046] Figure 6 It is Figure 3 Section view along line AA.

[0047] Figure 7 It is a three-dimensional schematic diagram of the second embodiment of the silent centrifugal fan of the present application, specifically showing the three-dimensional schematic diagram after the cover plate is separated.

[0048] Figure 8 It is a three-dimensional schematic diagram of the third embodiment of the silent centrifugal fan of the present application, specifically showing the three-dimensional schematic diagram after the cover plate is removed.

[0049] Fig. 9 It is a three-dimensional schematic diagram of the fourth embodiment of the silent centrifugal fan of the present application, specifically showing the three-dimensional schematic diagram after the cover plate is separated.

[0050] Fig.10 It is a trend diagram of the width of the silencer port 3 of the silencer centrifugal fan of the present application and the speed output variation of the fan. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0052] In order to illustrate the technical solution described in this application, the following is a description through specific embodiments. For the accuracy of the full description of this application, all directions involved should be referred to as Figure 1 For reference, the direction of the X-axis is defined as the left-right direction; the direction of the Y-axis is defined as the up-down direction; and the direction of the Z-axis is defined as the front-back direction.

[0053] Please refer to Figures 1 to 6As shown, a silent centrifugal fan disclosed in the present application can be mainly used in electronic products such as laptop computers and tablet computers. The silent centrifugal fan includes: a fan frame, a stator assembly (not shown), and a fan wheel assembly 2. The fan frame has a bottom plate 11, a side wall 12 extending upward from the bottom plate 11, and a cover plate 13 arranged above the side wall 12 and opposite to the bottom plate 11. The bottom plate 11, the side wall 12 and the cover plate 13 are jointly arranged to form a hollow cavity 10. The fan frame is also formed with an air inlet 111 formed by penetrating the cover plate 13 and an air outlet 112 formed on the side plate 12 and defined by the bottom plate 11, the side wall 12 and the cover plate 13. The stator assembly is fixedly assembled in the cavity 10, and the fan wheel assembly 2 is rotatably assembled in the fan frame and is located directly below the air inlet 111. Electromagnetic coupling is formed between the stator assembly and the impeller assembly 2. The stator assembly drives the impeller assembly 2 to rotate, sucking air from the air inlet 111 and blowing it out through the air outlet 112 to achieve the effect of wind dissipation and heat dissipation.

[0054] Please refer to Figures 3 to 5 As shown, the impeller assembly 2 includes a housing portion (not labeled), a plurality of blade portions (not labeled) uniformly extending outward from the periphery of the housing portion, a structural ring (not labeled, also called a silent ring) integrally connecting the outer edges of the plurality of blade portions, and a magnet member (not labeled) fixedly disposed in or below the housing portion. An airflow channel 113 is formed between the outer periphery of the impeller assembly 2 and the inner wall surface of the side wall 12.

[0055] Furthermore, the side wall 12 is adjacent to the air outlet 112 and is formed with a tongue portion (not numbered) at one end of the airflow channel 113. The airflow channel 113 starts at the end where the tongue portion is located, and the width along the radial direction of the impeller assembly 2 gradually increases, and a pressurized area is formed at the end where the tongue portion is located. A resonance cavity 123 that is concave downward and open upward is formed at the tongue portion, and a portion of the cover plate 13 is covered at the opening above the resonance cavity 123 to close the resonance cavity 123.

[0056] Among them, the side of the tongue portion close to the airflow channel 113 includes an inner wall 120 that defines a resonance cavity 123. The inner wall 120 protrudes into the cavity 10 at the middle position along the front-to-back direction to form an inflection point 124, so as to define the inner wall 120 as a front section wall 121 and a rear end wall 122 that are integrally connected at the position of the inflection point 124. The front section wall 121 constitutes an inner wall of one side of the air outlet 112, so that the width of the air outlet 112 along the left-right direction gradually expands from the inside to the outside. The inflection point 124 serves as the starting point of the airflow channel 113. The rear end wall 122 constitutes a part of the inner wall of the flow channel of the pressurized area of ​​the airflow channel 113. In this embodiment, preferably: the inner surface of the front section wall 121 is a flat surface, and the inner surface of the rear end wall 122 is an arc surface.

[0057] Please refer to Figures 1 to 6 As shown, the lower surface of the cover plate 13 corresponding to the resonance cavity 123 is partially recessed upward to form a groove-shaped first muffler groove 31. The first muffler groove 31 passes over the upper edge of the inner wall 120 to connect the airflow channel 113 with the resonance cavity 123. The first muffler groove 31 forms a muffler port 3.

[0058] Through the design of the silencer port 3, when the silencer centrifugal fan of the present application is working, the sound (noise) can enter the resonance cavity 123 through the silencer port 3, and the sound wave energy compresses the air in the resonance cavity 123, rubbing against the inner wall, thereby consuming the energy of the noise, achieving the purpose of reducing the noise. It has been verified by experiments that the noise can be effectively reduced by 1dB to 2dB. Optionally, the interface of the silencer port 3 can be circular, elliptical, oblong or polygonal, etc. In the present application, a polygon (quadrilateral) is preferred. The width of the silencer port 3 described in the full text of the present application refers to the maximum width of the silencer port 3, and the height of the silencer port 3 refers to the maximum height of the silencer port 3.

[0059] Please refer to Figure 7 As shown, it is a second embodiment of the silent centrifugal fan of the present application. In the second embodiment, the upper edge of the inner wall 120 is recessed downward to form a second silencer groove 32, and the second silencer groove 32 forms a silencer port 3. The second silencer groove 32 runs through the thickness direction of the inner wall 120 and is open upward. The lower surface of the cover plate 13 covers the second silencer groove 32 to form a channel connecting the airflow channel 113 and the resonance cavity 123. In the second embodiment, the silencer port 3 is formed at the middle position of the rear end wall 122 along the front-to-back direction.

[0060] Please refer to Figure 8As shown, it is the third embodiment of the silent centrifugal fan of the present application. In the third embodiment, the upper edge of the inner wall 120 is recessed downward to form a second silencer groove 32, and the second silencer groove 32 forms a silencer port 3. The second silencer groove 32 runs through the thickness direction of the inner wall 120 and is open upward. The lower surface of the cover plate 13 covers the second silencer groove 32 to form a channel connecting the airflow channel 113 and the resonance cavity 123. In the third embodiment, the silencer port 3 is formed in the middle position of the front wall 121 along the front-to-back direction.

[0061] Please refer to Fig. 9 As shown, it is the fourth embodiment of the muffler centrifugal fan of the present application. In the fourth embodiment, the lower surface of the cover plate 13 corresponding to the position of the resonance cavity 123 is partially recessed upward to form a groove-shaped first muffler groove 31. The upper edge of the inner wall 120 is recessed downward corresponding to the position of the first muffler groove 31 to form a second muffler groove 32, and the second muffler groove 32 runs through the thickness direction of the inner wall 120 and is open upward. The first muffler groove 31 passes over the upper edge of the inner wall 120. The first muffler groove 31 and the second muffler groove 32 together form a channel connecting the airflow channel 113 and the resonance cavity 123.

[0062] Of course, the silent centrifugal fan of the present application may also have a fifth embodiment (not shown). In the fifth embodiment, a silencer port 3 is provided at the middle position of the front wall 121 along the front-to-back direction and at the middle position of the rear wall 122 along the front-to-back direction.

[0063] Please refer to Figures 1 to 9 As shown, in the above four embodiments of the present application, the cover plate 13 is integrally extended and bent upward at a position around the air inlet 111 to form a step portion 131, so that the upper surface of the step portion 131 is higher than the upper surface of the cover plate 13, and the lower surface of the step portion 131 is higher than the lower surface of the cover plate 13. Figures 1 to 6 The first embodiment shown and Fig. 9 In the third embodiment shown, the first silencer groove 31 is formed at a position of the cover plate 13 adjacent to the step portion 131. The outer surface 311 of the portion of the cover plate 13 forming the first silencer groove 31 is flush with the upper surface of the step portion 131. The inner surface 312 of the portion of the cover plate 13 forming the first silencer groove 31 is flush with the lower surface of the step portion 131. Further, in a preferred embodiment, the transition position (crease position) between the step portion 131 and the cover plate 13 is aligned with the outer periphery of the impeller assembly 2 in the up-down direction (alignment here means basic alignment, and the transition position (crease position) between the step portion 131 and the cover plate 13 falls within the range of 3 mm inward in the radial direction and 3 mm outward in the radial direction of the outer periphery of the impeller assembly 2 in the up-down direction, and both fall within the alignment range defined here).

[0064] In the present application, the step portion 131 can effectively enhance the mechanical strength of the cover plate 13 on the one hand; on the other hand, it can make the edge of the air inlet 111 flat and smooth, so that the cross section of the air inlet channel formed through the air inlet 111 to the flow channel gap between the fan blades is uniform, which is conducive to reducing the generation of noise. In addition, the silencer 3 is designed at the junction of the upper edge of the side wall 12 and the lower surface of the cover plate 13 to facilitate processing.

[0065] Furthermore, in all embodiments of the present application, in order to effectively reduce noise, the height of the muffler port 3 along the vertical direction is designed to be not less than 20% of the depth of the resonance cavity 123 and not more than 75% of the depth of the resonance cavity 123; more preferably, the height of the muffler port 3 along the vertical direction is not less than 40% of the depth of the resonance cavity 123 and not more than 60% of the depth of the resonance cavity 123. The depth of the resonance cavity 123 refers to the maximum distance between the inner bottom surface of the resonance cavity 123 and the lower surface of the cover plate 13 covering the resonance cavity 123.

[0066] Furthermore, in all embodiments of the present application, in order to effectively reduce noise, the ratio of the width of the silencer port 3 to the outer diameter of the impeller assembly 2 is designed to be greater than 0 and not greater than 12.5%; a more preferred implementation is that the ratio of the width of the silencer port 3 to the outer diameter of the impeller assembly 2 is not greater than 12.5% ​​and not less than 5.5%; when the ratio of the width of the silencer port 3 to the outer diameter of the impeller assembly 2 is 9%, the effect is best.

[0067] In this application, for example, Figure 7 (Second embodiment) and Figure 8 (Third embodiment) The actual noise and performance test comparison was carried out for the conventional design scheme without the silencer port 3. The centrifugal fan with a 80mm*80mm structure (the width of the fan in the X-axis direction is 80mm, and the width in the Z-axis direction is also 80mm) was selected for this test; the outer diameter of the impeller assembly 2 is 56mm; the width of the silencer port 3 is selected from five specifications, namely: 1mm, 3mm, 5mm, 7mm, and 9mm; the height of the silencer port 3 along the up and down directions is uniformly specified as 50% (the height of the silencer port 3 along the up and down directions is 50% of the depth of the resonance cavity 123); when the noise is set at 38dB-A, the fan speed output change trend diagram is as follows Fig.10 As shown, the L1 line represents the form without the muffler port 3 (traditional form); the L2 line represents the form of the second embodiment; and the L3 line represents the form of the third embodiment. It can be clearly seen that the change in the width of the muffler port 3 affects the change in the speed. Since the noise is positively correlated with the fan speed, the muffler port 3 described in the present application has the effect of improving the noise.

[0068] It should be noted that in the present application, the width of the silencer port 3 should be related to the overall dimensions of the centrifugal fan. For example, in some centrifugal fans with very small dimensions, it is obviously unreasonable to set a silencer port 3 with a larger width, and it is also impossible to achieve the technical effect of the present application. Considering that in the existing design, there is a specific proportional relationship between the overall dimensions of different centrifugal fans and the outer diameter of the impeller assembly 2, in the present application, a specific relationship is designed between the design width of the silencer port 3 and the outer diameter of the impeller assembly 2 to avoid the above-mentioned problems (such unreasonable situations of setting a silencer port 3 with a larger width in some fans with smaller dimensions), so that the design range of the silencer port 3 with a suitable width can be quickly selected in the design of centrifugal fans of different specifications. Combined with the above-mentioned experimental sample data, it is finally concluded that the size optimization design range of the silencer port 3 as described above can effectively reduce noise.

[0069] In the above experiments, the height of the silencer port 3 was standardized, and the width of the silencer port 3 was selected in multiple forms for experimental testing. In addition to the above experimental tests, in the design of this application, the width of the silencer port 3 was also standardized, and the height of the silencer port 3 was selected in multiple forms for experimental testing. Finally, it was concluded that the preferred design range described above can effectively reduce noise. Of course, in this application, the test of the sample is not only for Figure 7 (Second embodiment) and Figure 8 (The third embodiment) is limited to this, and multiple embodiments disclosed in the specification of this application have been tested and verified, and all can meet the preferred design range of the size of the silencer port 3 described above.

[0070] In other embodiments, the number of the silencer ports 3 can be multiple. When multiple silencer ports 3 are provided, the width of the silencer ports 3 refers to the sum of the widths of the multiple silencer ports 3 . Similarly, the height of the silencer ports 3 refers to the sum of the heights of the multiple silencer ports 3 .

[0071] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and that the present application can be implemented in other specific forms without departing from the spirit or essential features of the present application. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present application is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present application.

[0072] In addition, it should be understood that although the present specification is described according to embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other design methods that can be understood by those skilled in the art.

Claims

1. A silent centrifugal fan, characterized in that: include: A sash frame, comprising a bottom plate (11), side walls (12) extending upward from the bottom plate (11), and a cover plate (13) disposed above the side walls (12) and opposite to the bottom plate (11), wherein the bottom plate (11), the side walls (12), and the cover plate (13) are jointly arranged to form a hollow cavity (10); At least one air inlet (111) is formed through the cover plate (13); At least one air outlet (112) is defined by the bottom plate (11), the side wall (12) and the cover plate (13); A fan wheel assembly (2) is rotatably assembled in the fan frame and is located directly below the air inlet (111); An air flow channel (113) is formed between the outer periphery of the impeller assembly (2) and the inner wall surface of the side wall (12); A tongue portion, formed on the side wall (12) adjacent to the air outlet (112) and located at one end of the air flow channel (113); The airflow channel (113) has the end where the tongue mouth is located as a starting point, and its width along the radial direction of the impeller assembly (2) gradually increases, and a pressurized area is formed at the end where the tongue mouth is located; A resonance cavity (123) is formed at the tongue mouth and is open upwards, and the cover plate (13) is arranged to cover the opening above the resonance cavity (123) to close the resonance cavity (123); A side of the tongue portion close to the airflow channel (113) includes an inner wall (120) defining a resonance cavity (123); The silencer port (3) is connected to the resonance cavity (123) and the air flow channel (113).

2. The silent centrifugal fan according to claim 1, characterized in that: The muffler port (3) is a first muffler groove (31) in the form of a groove formed by partially concavely upwards the lower surface of the cover plate (13) at a position corresponding to the resonance cavity (123); The first silencer groove (31) passes over the upper edge of the inner wall (120) to connect the airflow channel (113) with the resonance cavity (123).

3. The silent centrifugal fan according to claim 2, characterized in that: The muffler port (3) further comprises a second muffler groove (32) formed by a downward depression of the upper edge of the inner wall (120); the second muffler groove (32) penetrates the thickness direction of the inner wall (120) and is open upward; The first silencer groove (31) and the second silencer groove (32) correspond to each other in the up-down direction, and the first silencer groove (31) and the second silencer groove (32) together form a channel connecting the airflow channel (113) and the resonance cavity (123).

4. The silent centrifugal fan according to claim 1, characterized in that: The silencer opening (3) is a second silencer groove (32) formed by a downward depression of the upper edge of the inner wall (120); the second silencer groove (32) penetrates the thickness direction of the inner wall (120) and is open upward; The lower surface of the cover plate (13) covers the second silencer groove (32) to form a channel connecting the airflow channel (113) and the resonance cavity (123).

5. The silent centrifugal fan according to any one of claims 1 to 4, characterized in that: The height of the silencer port (3) in the vertical direction is not less than 20% of the depth of the resonance cavity (123) and not more than 75% of the depth of the resonance cavity (123); The depth of the resonance cavity (123) is the maximum distance between the inner bottom surface of the resonance cavity (123) and the lower surface of the cover plate (13) covering the resonance cavity (123).

6. The silent centrifugal fan according to claim 5, characterized in that: The height of the silencer port (3) in the up-down direction is not less than 40% of the depth of the resonance cavity (123) and not more than 60% of the depth of the resonance cavity (123).

7. The silent centrifugal fan according to any one of claims 1 to 4, characterized in that: The ratio of the width of the silencer port (3) to the outer diameter of the impeller assembly (2) is greater than 0 and not greater than 12.5%.

8. The silent centrifugal fan according to any one of claims 1 to 4, characterized in that: The ratio of the width of the silencer port (3) to the outer diameter of the impeller assembly (2) is not less than 5.5% and not more than 12.5%.

9. The silent centrifugal fan according to any one of claims 1 to 4, characterized in that: The ratio of the width of the silencer port (3) to the outer diameter of the impeller assembly (2) is 9%.

10. The silent centrifugal fan according to claim 2 or 3, characterized in that: The cover plate (13) is integrally extended and bent upward at a position around the air inlet (111) to form a step portion (131), such that the upper surface of the step portion (131) is higher than the upper surface of the cover plate (13), and the lower surface of the step portion (131) is higher than the lower surface of the cover plate (13); The first muffler groove (31) is formed at a position of the cover plate (13) adjacent to the step portion (131); The outer surface (311) of the portion of the cover plate (13) forming the first muffler groove (31) is flush with the upper surface of the step portion (131); The inner surface (312) of the portion of the cover plate (13) that forms the first muffler groove (31) is flush with the lower surface of the step portion (131).

11. The silent centrifugal fan according to claim 10, characterized in that: The transition position between the step portion (131) and the cover plate (13) is aligned with the outer periphery of the impeller assembly (2) in the up-down direction.

12. The silent centrifugal fan according to any one of claims 1 to 4, characterized in that: The inner wall (120) protrudes into the cavity (10) at a middle position along the front-to-back direction to form an inflection point (124), so as to define the inner wall (120) into a front wall (121) and a rear wall (122) integrally connected at the inflection point (124); The front wall (121) constitutes an inner wall of one side of the air outlet (112), so that the width of the air outlet (112) in the left-right direction gradually expands from the inside to the outside; The inflection point (124) serves as the starting point of the airflow channel (113); The rear end wall (122) constitutes a portion of the inner wall of the air flow channel (113) in the pressurized area; The silencer port (3) is formed at a middle position of the front wall (121) along the front-rear direction and / or the silencer port (3) is formed at a middle position of the rear end wall (122) along the front-rear direction.

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