An acoustic mode modulation noise reduction heat dissipation fan outer frame

Abstract

This invention discloses an outer frame for a cooling fan used for acoustic modal modulation noise reduction, comprising an outer frame body (1) and an air intake shroud (2); the outer frame body (1) includes a casing (4), an outer frame support (5), and a motor support (6); the casing (4), the outer frame support (5), and the motor support (6) are mounted on the outer frame body (1); the air intake shroud (2) is a parameterized shaped pipe section controlled by a sine or cosine function, fixedly connected to and adapted to the outer frame body (1); the axial length L, the average radius R of the lip profile, and the lobe amplitude A of the air intake shroud (2) are determined by the size of the cooling fan rotor blades and the location of the sound source; the combination of the number of lobes k of the lip profile of the air intake shroud (2) is determined by the number of main acoustic modes of the cooling fan; and the initial phase φ of the lip profile of the air intake shroud (2) is determined by the number of main acoustic modes of the cooling fan. i Determined by the phase of the primary acoustic modes. This invention can modulate different circumferential acoustic modes generated by the dynamic and static interference of any cooling fan and significantly suppress noise.

Description

A frame for acoustic modal modulation noise reduction and heat dissipation fan Technical Field

[0001] This invention relates to the field of noise reduction technology for cooling fans, and more particularly to a cooling fan frame for acoustic modal modulation noise reduction. Background Technology

[0002] Axial flow cooling fans are widely used for heat dissipation in various industrial equipment. With the continuous improvement of computing power, charging power, and equipment integration, greater heat flux densities are generated inside these devices. To increase airflow and remove heat within a limited space, the only solution is usually to increase fan speed. However, this continuous increase in fan speed generates significant aerodynamic noise. Sometimes, to meet equipment noise standards, it is necessary to reduce equipment performance to decrease heat generation. Therefore, aerodynamic noise has become a bottleneck in improving equipment performance. How to reduce fan aerodynamic noise within the compact space inside equipment has become a key focus in this field.

[0003] Due to the interference between the rotor and stator blades, the unsteady aerodynamic forces on the surface of the cooling fan blades generate specific acoustic modes that propagate through space. These modes collectively constitute the single-tone noise of the blade passing frequency and its harmonics. The higher the fan speed and flow rate, the more significant the interference and the more pronounced the single-tone noise. The smaller the distance between the rotor and stator blades of the cooling fan further intensifies the interference. Additionally, the shroud, cut by a rectangular frame, introduces non-uniform airflow interference with the rotor blades. This interference is similar to the static-dynamic interference and may become dominant. To reduce the single-tone noise generated by fan interference, common practices include increasing the distance between the rotor and stator blades, improving the design of the rotor and stator blade shapes, and designing the shape of the outer frame shroud to avoid airflow interference. However, adjusting the rotor and stator blade distance negatively impacts the overall size of the machine; selecting the blade shape involves a complex balance between aerodynamic performance and noise; and while a complete shroud provides clear noise reduction, further improvements are difficult.

[0004] Another approach is to reduce noise by artificially introducing a secondary sound source that cancels out the original fan noise source. This can be achieved by introducing additional components or designing the fan frame shape. Existing publicly available designs sometimes introduce secondary interference sources by adding support pillars at the inlet, and then adjusting the distance between the pillars and the fan to control the intensity of the secondary interference source. However, this is generally only applicable to duct fans. Others reduce single-tone noise by adding an additional obstacle on the fan intake side that extends from the hub into the flow channel. However, this significantly affects the flow area and thus the flow rate. Furthermore, installing a stationary obstacle at the rotating hub requires an external fixing frame, which is difficult to implement in cooling fan product design.

[0005] Therefore, those skilled in the art are dedicated to developing a compact and easy-to-implement housing for acoustic modal modulation noise reduction and heat dissipation fans to solve the above problems. Summary of the Invention

[0006] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is how to reduce the single-tone noise generated by the interference between the moving blades and stationary blades of the axial cooling fan.

[0007] To achieve the above objectives, the present invention provides an outer frame for an acoustic modal modulation noise reduction cooling fan, characterized in that it includes an outer frame body (1) and an air intake shroud (2); the outer frame body (1) includes a casing (4), an outer frame support (5), and a motor support (6); the casing (4), the outer frame support (5), and the motor support (6) are all disposed on the outer frame body (1); the air intake shroud (2) is a parameterized shaped pipe section controlled by a sine or cosine function, fixedly connected to and adapted to the outer frame body (1); the axial length L, the average radius R of the lip profile, and the lobe amplitude A of the air intake shroud (2) are determined by the size of the cooling fan rotor blades and the location of the sound source; the combination of the number of lobes k of the lip profile of the air intake shroud (2) is determined by the number of main acoustic modes of the cooling fan; and the initial phase φ of the lip profile of the air intake shroud (2) is determined by the number of lobes k of the lip profile of the air intake shroud (2). i Determined by the phase of the primary acoustic modes.

[0008] Furthermore, the initial phase φ of the lip profile of the air intake shroud (2) i Experiments have shown that a relatively good initial phase φ can be obtained by uniformly traversing angles within a range of at most 2π / k. i Values.

[0009] Furthermore, the air intake shroud (2) is disposed on the outer frame body (1) and is closely connected to the outer frame body (1).

[0010] Furthermore, the air intake shroud (2) is provided with a shroud support (7), and the shroud support (7) is fixedly connected to the outer frame body (1).

[0011] Furthermore, the circumferential profile of the lip of the fairing (2) is designed such that the radius r is a sine function of the circumferential angle φ, r = R + Asink(φ + φ i The cross-sectional profile of the flow guide (2) is continuously transitioned to a circle along the axial direction.

[0012] Furthermore, the circumferential profile of the lip of the fairing (2) is designed such that the radius r is a cosine function of the circumferential angle φ, r = R + Acosk(φ + φ i -π / 2), the cross-sectional profile of the flow guide (2) is continuously transitioned to a circle along the axial direction.

[0013] Furthermore, the circumferential profile of the lip of the fairing (2) is designed as a combination of the radius r and the sine function of the circumferential angle φ, r = R + A1sink1(φ + φ i1 )+A2sink2(φ+φ i2 The cross-sectional profile of the flow guide (2) is continuously transitioned to a circle along the axial direction.

[0014] Furthermore, the circumferential profile of the lip of the fairing (2) is designed as a combination of the radius r and the cosine function of the circumferential angle φ, r = R + A1cosk1(φ + φ i1 -π / 2)+A2cosk2(φ+φ i2 -π / 2), the cross-sectional profile of the flow guide (2) is continuously transitioned to a circle along the axial direction.

[0015] Furthermore, the circumferential profile of the lip of the fairing (2) is designed as a combination of the radius r and the sine function of the circumferential angle φ, r = R + A1sink1(φ + φ i1 )+A2sink2(φ+φ i2 )+…+A n sink n (φ+φ in ), where n≥3, and the cross-sectional profile of the guide shield (2) is continuously transitioned to a circle along the axial direction.

[0016] Furthermore, the circumferential profile of the lip of the fairing (2) is designed as a combination of the radius r and the cosine function of the circumferential angle φ, r = R + A1cosk1(φ + φ i1 -π / 2)+A2cosk2(φ+φ i2 -π / 2)+…+A n cosk n (φ+φ in -π / 2), where n≥3, the cross-sectional profile of the guide shield (2) is continuously transitioned to a circle along the axial direction.

[0017] Compared with traditional methods and apparatus, the present invention has the following advantages:

[0018] This invention improves the unsteady aerodynamic forces on rotor blades by artificially introducing secondary interference noise sources. It can modulate different circumferential acoustic modes generated by the dynamic-static interference of any cooling fan and significantly suppress single-tone noise superimposed by modes. Since it does not change the blade shape, it greatly simplifies the fan design process and expands the noise optimization space.

[0019] Introducing a secondary interference noise source by shaping the outer side of the casing has minimal impact on the fan's aerodynamic performance. The secondary interference noise source naturally acts on the blade tip region, coinciding with the original interference noise source region, which helps to better cancel out the original interference noise source. Since shaping the outer side of the casing requires no other fixing devices, the structure is compact and easy to implement in cooling fan products.

[0020] By rationally designing a sine / cosine shaped air intake shroud, lower noise levels can be achieved compared to fans with uniform air intake. Furthermore, for existing fan products, no changes to the existing configuration are required; a split-type sine / cosine shaped air intake shroud can effectively eliminate single-tone noise, making the design and use convenient.

[0021] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0022] Figure 1 is a schematic diagram of the overall structure of the integral k=8 sine / cosine shaped air intake fairing according to a preferred embodiment of the present invention;

[0023] Figure 2 is a three-dimensional structural schematic diagram of an integral k=8 sine / cosine shaped air intake fairing according to a preferred embodiment of the present invention;

[0024] Figure 3 is a schematic diagram of the overall structure of the integral k=4 sine / cosine shaped air intake fairing according to a preferred embodiment of the present invention;

[0025] Figure 4 is a schematic diagram of the overall structure of the integrated k=4 and k=8 combined sine / cosine shaped air intake fairing according to a preferred embodiment of the present invention;

[0026] Figure 5 is a schematic diagram of the overall structure of a split k=8 sine / cosine shaped air intake fairing according to a preferred embodiment of the present invention;

[0027] Figure 6 is a schematic diagram of the overall structure of a split k=4 sine / cosine shaped air intake fairing according to a preferred embodiment of the present invention;

[0028] Figure 7 shows the sound pressure level of the main circumferential acoustic modes under the action of the ideally designed sine / cosine shaped air intake shroud according to a preferred embodiment of the present invention, as a function of the initial phase φ. i The theoretical optimal variation diagram;

[0029] Figure 8 shows the sound pressure level of the main circumferential acoustic modes as a function of the initial phase φ under the action of a non-ideal sine / cosine shaped air intake shroud according to a preferred embodiment of the present invention. i The theoretical changes are shown in the diagram.

[0030] Among them, 1-outer frame body, 2-sine / cosine shaped air intake fairing, 3-rotor blade, 4-casing, 5-outer frame support, 6-motor support, 7-fairing support. Detailed Implementation

[0031] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0032] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components is appropriately exaggerated in the drawings. In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. The terms "installed," "connected," and "linked" should be interpreted broadly, for example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components. For those skilled in the art, the specific meaning of the above terms in the present invention can be understood according to the specific circumstances.

[0033] Example 1:

[0034] As shown in Figures 1, 2, and 3, this embodiment discloses a cooling fan frame structure for acoustic modal modulation noise reduction, including a main frame 1 and a sine / cosine shaped air intake shroud 2. The main frame consists of the cooling fan casing 4 (excluding the rotor blades 3 and the motor), a frame support 5, and a motor support 6. The sine / cosine shaped air intake shroud 2 is a parameterized shaped pipe section controlled by a sine / cosine function and is adapted to the main frame 1. The sine / cosine shaped air intake shroud 2 is disposed on the main frame 1 and is tightly connected to it. The axial length L, the average radius R of the lip profile, and the lobe amplitude A of the sine / cosine shaped air intake shroud are determined by the size of the cooling fan rotor blades and the location of the sound source. The combination of the number of lobes k of the lip profile of the sine / cosine shaped air intake shroud is determined by the number of main acoustic modes of the cooling fan. The initial phase φ of the lip profile of the sine / cosine shaped air intake shroud is... iDetermined by the phase of the primary acoustic modes.

[0035] As shown in Figure 3, the outer frame 1 includes a motor support 6. When the rotor blades 3 rotate, they interfere with the motor support 6, inducing unsteady forces on the blades and generating single-tone noise of the blade passing frequency and its harmonics. According to the dynamic-static interference mode calculation formula, the number of rotor blades 3 (B) and the number of motor supports 6 (V) determine the number of main dynamic-static interference circumferential acoustic modes, while the amplitude of the main circumferential acoustic modes determines the magnitude of the single-tone noise. The amplitudes of these main circumferential acoustic modes can be obtained by spatial Fourier transform using test data from a circumferentially distributed microphone array. The circumferential profile of the lip of the sine / cosine shaped air intake fairing 2 is designed as a sine function of the radius r and the circumferential angle φ: r = R + Asink(φ + φ). i Or the cosine function r = R + Acosk(φ + φ) i -π / 2), the cross-sectional profile of the fairing continuously transitions to a circle along the axial direction. The circumferential shape with varying radius introduces circumferential non-uniform air intake, interfering with rotor blade 3 and generating a secondary interference noise source, namely the secondary blade interference force. A well-designed secondary interference noise source superimposed on the original interference noise source can reduce the amplitude of the interference force on rotor blade 3 and change its frequency, thereby modulating the generated circumferential acoustic modes and reducing single-tone noise. The number of modulated modes is related to the number of rotor blades B and the number of lobes k of the sine / cosine shaped air intake fairing. The effect of the secondary interference source is related to the blade height and the average circular radius R of the lip profile. The non-uniformity or interference intensity of the secondary interference noise source is related to the lobe amplitude A. The cancellation effect of the secondary interference noise source and the original noise source is related to the initial phase φ of the lip profile. i The value of is related to .

[0036] As shown in Figures 1 and 2, the diameter of the rotor blade 3 of the cooling fan in this embodiment is approximately 110mm. After leaving the blade tip clearance, the flow diameter is set to 116mm, i.e., the inner diameter of the casing 4 is 116mm, and the outer frame support 5 is set as a 120mm square. The number of rotor blades 3 is 7, and the number of supports 6 of the motor support is set to 11. As shown in Figure 3, due to the influence of the square outer frame, the supports of the motor support 6 are divided into 4 groups. According to the acoustic modal test, the interference between the rotor blades 3 and the motor support 6 produces the main circumferential mode number m = -1. According to the dynamic and static interference mode calculation formula m = B - λ, it can be known that when the number of rotor blades is 7, λ = 8, indicating that the rotor blades mainly interfere with the structure with a circumferential period of 8 or a harmonic number of 8. In order to generate secondary interference forces of the same frequency and opposite phase, the circumferential period of the sine / cosine shaped air intake shroud should be 8 or the harmonic number should be 8. Therefore, k can be selected as 2, 4, or 8. To reduce the amplitude of the modulated mode m=-1 or to shift it to another dominant mode, the number of lobes k of the sine / cosine shaped inlet shroud is set to 8, thereby generating a secondary interference force with the same frequency as the original interference force. Based on numerical calculations or sound source localization experiments, it can be determined that the original noise source on the rotor blade is mainly distributed near the blade tip region, i.e., around 80% of the blade height. The secondary non-uniform intake should act within this blade height range and superimpose with the original noise source. Therefore, the axial distance of the shroud is selected as L=6mm, and the average circular radius R of the inner lip profile is selected as R=61mm, which is 3mm larger than half the flow diameter. At this point, L / R≈0.098. To keep the flow diameter constant, the lobe amplitude A=3mm is selected, making the minimum lip radius equal to half the flow diameter.

[0037] Initial phase φ of the lip shape line i The selection can be obtained through experiments. Figures 7 and 8 show the sound pressure levels of the main circumferential acoustic modes after superposition as a function of the initial phase φ. i The theoretical trend of change. When the sine / cosine shaped air intake fairing is ideally designed, the secondary noise sources it introduces have the same amplitude as the primary noise sources, and can completely cancel out the primary noise sources at certain initial phases, as shown in Figure 7. However, for non-ideally designed sine / cosine shaped air intake fairings, the secondary noise sources introduced differ in amplitude from the primary noise sources, and their cancellation effect is weakened, as shown in Figure 8. A better initial phase φ can be obtained by uniformly traversing angles within a range of at most 2π / k. i The optimal method is to determine the phase information of the original primary acoustic modes through sound field testing and numerical calculations to guide the initial phase φ. i The value of .

[0038] In practical use, firstly, a fan outer frame body 1 is fabricated according to the dimensions of the fan rotor blades 3. The fan flow diameter is determined based on the rotor impeller diameter 3 and the required tip clearance. The casing 4 and support structure 5 are determined based on the outer frame assembly conditions. The number of motor supports 6 is designed based on the motor support requirements and the number of moving blades. Then, the original sound source distribution positions on the rotor blades after the fan outer frame body 1 and rotor impeller 3 are determined through numerical calculations or experimental tests. Based on this, the axial length L, the average radius R of the lip profile, and the lobe amplitude A of the sine / cosine shaped air intake shroud 2 are designed. The number of original main circumferential sound modes is determined based on the dynamic and static interference modal calculation theory formula, numerical calculations, or experimental tests. Based on this, the number of lobe k or a combination of k of the lip profile of the sine / cosine shaped air intake shroud 2 is designed. Finally, the approximate phase of the original main sound modes is determined through numerical calculations or experimental tests. Based on this, the initial phase φ of the lip profile of the sine / cosine shaped air intake shroud 2 is designed. i The range of values ​​is determined by uniformly selecting values ​​within this range and manufacturing corresponding fan frame structures for assembly. Noise performance is tested to determine the optimal fan frame structure design parameters.

[0039] Example 2:

[0040] As shown in Figure 4, when multiple modes of the original circumferential acoustic spectrum of the fan have large amplitude values, a single-lobe sine / cosine shaped air intake shroud 2 may not be able to cancel them out simultaneously. In this case, multiple sine / cosine functions with different lobe numbers need to be combined to control the lip profile of the shroud 2. The circumferential lip profile of the sine / cosine shaped air intake shroud 2 is designed as a combination of sine functions with radius r equal to the circumferential angle φ: r = R + A1sink1(φ + φ). i1 )+A2sink2(φ+φ i2 )+…+Ansink n (φ+φ in ), where n≥2, or a combination of cosine functions r=R+A1cosk1(φ+φ i1 -π / 2)+A2cosk2(φ+φ i2 -π / 2)+…+A n cosk n (φ+φ in -π / 2), where n≥2, and the cross-sectional profile of the fairing continuously transitions to a circle along the axial direction.

[0041] Based on Example 1, combinations of lobe numbers k=4 and k=8 are selected, while the designs of L, R, and A remain consistent with Example 1. To ensure a constant flow area, the average circular radius R of the lip profile of the sine / cosine shaped air intake shroud 2, minus the superposition of lobe amplitudes (A1+A2), is set to equal half the flow diameter of the cooling fan; therefore, A1=A2=1.5mm can be selected. Initial phase φi1 and φ i2 The value of can be determined in two steps. First, the preferred initial phase is determined by ergonomic noise test under k=4 or k=8 respectively, and then it remains unchanged in the superposition model.

[0042] Example 3:

[0043] This invention can also be applied to the noise improvement design of existing fans. As shown in Figures 5 and 6, when the structure of the original fan outer frame 1 is determined, a split sine / cosine shaped air intake shroud 2 can be designed and tightly connected to the outer frame 1 through the shroud support 7. The determination of the original noise source of the fan and the determination of the parameters of the sine / cosine shaped air intake shroud 2 are consistent with the process of Embodiment 1 and Embodiment 2, only the issue of adapting the shroud support 7 to the fan outer frame 1 needs to be considered.

[0044] In this embodiment, the rotor blades 3 and motor support 6 of the existing fan are consistent with those in Embodiments 1 and 2. Complex mutual interference occurs between the inlet slit of the outer frame body 1, the rotor blades 3, and the motor support 6. According to modal testing, the main circumferential acoustic mode is still -1. Numerical calculation confirms that the main source of interference force is the interference between the non-uniform air intake introduced by the inlet slit and the rotor blades 3. Therefore, a shroud with a beam number k = 4 is selected to introduce secondary non-uniform air intake to cancel out the original non-uniform air intake. The axial length of the sine / cosine shaped air intake shroud 2 is selected as L = 10 mm, and the average circle radius is selected as R = 66 mm to adapt to the existing fan outer frame body 1. At this time, the beam amplitude is still set as A = 3 mm. The initial phase φ within the range of 2π / k is tested. i By taking the values, we obtained the design parameters with the lowest noise. The average sound pressure level at a distance of 1m in the far field was reduced by 6.0dBA compared to the existing prototype fan, demonstrating a strong noise reduction capability.

[0045] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A frame for a heat dissipation fan used for acoustic modal modulation noise reduction, characterized in that, The system includes an outer frame body (1) and an air intake shroud (2); the outer frame body (1) includes a casing (4), an outer frame support (5), and a motor support (6); the casing (4), the outer frame support (5), and the motor support (6) are all mounted on the outer frame body (1); the air intake shroud (2) is a parametrically shaped pipe section controlled by a sine or cosine function, which is fixedly connected to and adapted to the outer frame body (1); the axial length L, the average radius R of the lip profile, and the lobe amplitude A of the air intake shroud (2) are determined by the size of the cooling fan rotor blades and the location of the sound source; the number of lobes k or a combination of k of the lip profile of the air intake shroud (2) is determined by the number of the main circumferential acoustic modes of the cooling fan; and the initial phase Φ of the lip profile of the air intake shroud (2) is determined by the number of the main circumferential acoustic modes of the cooling fan. i Determined by the phase of the main circumferential acoustic modes; the circumferential profile of the lip of the air intake shroud (2) is designed such that the radius r is a sine function of the circumferential angle Φ, r = R + Asink(Φ + Φ i The cross-sectional profile of the air intake shield (2) is continuously transitioned to a circle along the axial direction; or, the circumferential profile of the lip of the air intake shield (2) is designed such that the radius r is a cosine function of the circumferential angle Φ, r = R + Acosk(Φ + Φ). i -π / 2), the cross-sectional profile of the air intake shroud (2) is continuously transitioned to a circle along the axial direction; or, the circumferential profile of the lip of the air intake shroud (2) is designed as a combination of a radius r and a sine function of the circumferential angle Φ, r = R + A1sink1(Φ + Φ i1 )+ A2sink2(Φ+Φ i2 The cross-sectional profile of the air intake shield (2) is continuously transitioned to a circle along the axial direction; or, the circumferential profile of the lip of the air intake shield (2) is designed as a combination of radius r and cosine function of circumferential angle Φ, r = R + A1cosk1(Φ + Φ i1 -π / 2)+ A2cosk2(Φ+Φ i2 -π / 2), the cross-sectional profile of the air intake shroud (2) is continuously transitioned to a circle along the axial direction; or, the circumferential profile of the lip of the air intake shroud (2) is designed as a combination of a radius r and a sine function of the circumferential angle Φ, r = R + A1sink1(Φ + Φ i1 )+ A2sink2(Φ+Φ i2 )+…+ A n sink n (Φ+Φ in ), where n≥3, the cross-sectional profile of the air intake shroud (2) is continuously transitioned to a circle along the axial direction; or, the circumferential profile of the lip of the air intake shroud (2) is designed as a combination of the radius r being the cosine function of the circumferential angle Φ, r= R + A1cosk1(Φ+Φ i1 -π / 2)+ A2cosk2(Φ+Φ i2 -π / 2)+…+ A n cosk n (Φ+Φ in -π / 2), where n≥3, the cross-sectional profile of the air intake shroud (2) is continuously transitioned to a circle along the axial direction.

2. The outer frame for acoustic modal modulation noise reduction and heat dissipation fan as described in claim 1, characterized in that, The air intake shroud (2) is disposed on the outer frame body (1) and is closely connected to the outer frame body (1).

3. The outer frame for acoustic modal modulation noise reduction and heat dissipation fan as described in claim 1, characterized in that, The air intake shroud (2) is provided with a shroud support (7), and the shroud support (7) is fixedly connected to the outer frame body (1).

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