Axial flow fan and automobile

Abstract

The invention discloses an axial flow fan and an automobile, and relates to the technical field of axial flow fans, and the axial flow fan comprises a center hub used for being connected with a motor shaft; the plurality of first blades are respectively connected with the central hub; the second blades are attached to the first blades, and sawtooth parts are arranged on the second blades; in a normal state, the sawtooth part does not exceed the outer edge of the first blade; the noise reduction driving assembly is arranged on the central hub, and the power output end of the noise reduction driving assembly is connected with the blade root of each second blade; when the axial flow fan meets preset conditions, the second blades are driven to extend out of the outer edges of the first blades, and noise generated by the fan is restrained through the sawtooth parts on the second blades.

Description

Technical Field

[0001] The present application belongs to the technical field of axial flow fans, and in particular relates to an axial flow fan and a car. Background Art

[0002] Axial flow fans are a core equipment widely used in industrial production and life. A series of key technical problems need to be overcome in the design and manufacturing process to ensure their excellent performance, high energy efficiency and long-term reliability. This includes optimizing the fan blade shape to improve air flow efficiency, balancing the speed and power output to achieve the best energy efficiency ratio; at the same time, controlling the noise level to reduce interference with the environment and operators. Axial flow fans that produce effects on heat exchangers in the thermal management system of new energy heavy trucks. For heavy trucks, the vehicle thermal management system has a large demand for heat dissipation, and has high requirements for the aerodynamic performance of axial flow fans. In the thermal management system, in order to meet the corresponding functional requirements, the weight and volume of the axial flow fan will increase. In particular, the fan will generate greater noise when running at high speed, which directly affects people's physiological and mental health. The main source of these noises is the aerodynamic noise generated when the axial flow fan is working, which is the noise generated by the interaction between gas and gas and gas and object. Excessive fan noise will interfere with normal communication in the car, forcing the driver and passengers to raise the volume to hear each other clearly, thus affecting the driving experience and comfort. Continuous fan noise will increase the driver's mental stress and make them more prone to fatigue, thus affecting driving safety and comfort. If the driver is in this environment for a long time, he may become irritable and fatigued, increasing the risk of traffic accidents. Summary of the invention

[0003] The present application provides an axial flow fan and a car, aiming to solve the technical problem of high noise of axial flow fans in the prior art at least to a certain extent.

[0004] In order to solve the above technical problems, this application adopts the following technical solutions:

[0005] A first aspect of an embodiment of the present application provides an axial flow fan, comprising: a central hub for connecting a motor shaft; a plurality of first blades, respectively connected to the central hub; a plurality of second blades, fitted with the first blades, the second blades being provided with a serration; under normal conditions, the serration does not extend beyond the outer edge of the first blade; a noise reduction drive assembly, arranged on the central hub, the power output end of the noise reduction drive assembly being connected to the blade root of each of the second blades; so that when the axial flow fan meets preset conditions, each of the second blades is driven to extend from the outer edge of the first blade, and the noise generated by the fan is suppressed by the serration on the second blade.

[0006] In some embodiments, a plurality of sliding openings are provided at intervals along the circumferential direction on the central hub, and the sliding openings match the shape of the root of the second blade, so that when the noise reduction drive assembly drives the second blade to move relative to the sliding openings, the second blade is always in contact with the first blade.

[0007] In some embodiments, the noise reduction drive assembly includes: a drive ring, which is rotatably arranged on the inner side of the center hub, and the second blade is connected to the drive ring through the sliding opening; a circle of driven gear grooves is arranged on the inner side of the drive ring; a driving member, which is fixed to the center hub, and the power output of the driving member is equipped with a driving gear, and the driving gear is meshed with the driven gear groove. The driving ring is driven by the driving member to rotate relative to the hub to drive the second blade to slide in the sliding opening, and the serrations on the second blade extend relative to the outer edge of the first blade.

[0008] In some embodiments, the driving member is a driving motor, the driving motor is fixed to the central hub via a fixing frame, and the power output end of the driving motor is drivingly connected to the driving gear.

[0009] In some embodiments, the inner wall of the central hub is provided with a circle of sliding grooves, the sliding grooves are connected to the sliding opening, and the driving ring is rotatably disposed in the sliding track.

[0010] In some embodiments, the serration portion is disposed at a trailing edge of the second blade and is located at a leading edge of the second blade in a rotation direction.

[0011] In some embodiments, the second blade includes a blade body and a serrated portion; the blade body is connected to the noise reduction drive assembly, and the angles between the serrations on the serrated portion and the air outlet surface of the second blade are different.

[0012] In some embodiments, along the center to the circumference of the axial flow fan, the angle between each of the saw teeth and the air outlet surface tends to increase.

[0013] In some embodiments, the included angle between the sawtooth on the sawtooth portion closest to the central hub and the second blade reference plane is 60°; the included angle between two adjacent sawtooths is 5°.

[0014] A second aspect of an embodiment of the present application provides a car, in which the axial flow fan is provided.

[0015] It can be seen from the above technical solution that the present application has at least the following advantages and positive effects:

[0016] An axial flow fan in the present application is provided with a second blade that can extend from the outer edge of the first blade, and a serration portion is provided on the second blade. When running at medium and low speeds, the second blade does not extend, thereby ensuring that the fan has a high air volume performance. When running at high speed, the noise reduction drive component drives each of the second blades to extend from the outer edge of the first blade, and the serration portion on the second blade forms a row of counter-rotating vortex pairs at the trailing edge of the fan, thereby changing the tail vortex structure, weakening the spanwise correlation of the downstream wake zone, and reducing the flow turbulence pulsation intensity near the trailing edge, thereby reducing the far-field radiation of the noise, optimizing the aerodynamic characteristics of the fan, and thus reducing the generation of noise.

[0017] A car in the present application uses an axial flow fan, and a second blade that can extend from the outer edge of the first blade is provided, and a serration portion is provided on the second blade. When running at medium and low speeds, the second blade does not extend, thereby ensuring that the fan has a high air volume performance. When running at high speeds, the noise reduction drive component drives each of the second blades to extend from the outer edge of the first blade, and the serration portion on the second blade forms a row of counter-rotating vortex pairs at the trailing edge of the fan, thereby changing the tail vortex structure, weakening the spanwise correlation of the downstream wake zone, and reducing the flow turbulence pulsation intensity near the trailing edge, thereby reducing the far-field radiation of noise, optimizing the aerodynamic characteristics of the fan, and thus reducing the generation of noise; optimizing the vehicle driving environment, reducing the noise inside the vehicle, reducing traffic accidents caused by noise, and improving the user's vehicle comfort and riding experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 is a structural schematic diagram of an axial flow fan in an embodiment of the present application;

[0020] Figure 2 is a structural schematic diagram of an axial flow fan in an embodiment of the present application;

[0021] Figure 3 is a front view of an axial flow fan in an embodiment of the present application;

[0022] Figure 4 is a simplified structural diagram of a noise reduction drive assembly of an axial flow fan in an embodiment of the present application;

[0023] Figure 5 It is a transmission schematic diagram of a noise reduction drive assembly of an axial flow fan in an embodiment of the present application;

[0024] Figure 6 It is a schematic diagram of the partial structure of the second blade of an axial flow fan in an embodiment of the present application.

[0025] The following are the descriptions of the reference numerals:

[0026] 100, central hub; 200, first blade; 300, second blade; 310, serration; 410, drive ring; 411, driven gear groove; 420, drive gear; 430, drive motor; 440, fixing frame; 500, guide ring. DETAILED DESCRIPTION

[0027] In order to make the technical personnel in the technical field to which the present application belongs to understand the present application more clearly, the technical scheme in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0028] Figure 1 is a structural schematic diagram of an axial flow fan in an embodiment of the present application, Figure 3 is a front view of an axial flow fan in an embodiment of the present application; Figure 1 and Figure 2As shown, the fan includes: a central hub 100 for connecting to a motor shaft; a plurality of first blades 200, which are distributed in an annular manner around the central hub 100, and the roots of the plurality of first blades 200 are respectively connected to the central hub 100; a guide ring 500, which is sleeved on the tail ends of the plurality of first blades 200; a plurality of second blades 300, which are fitted with the first blades 200, and the second blades 300 are provided with a serration 310; under normal conditions, the serration 310 does not exceed the outer edge of the first blade 200; a noise reduction drive assembly, which is arranged on the central hub 100, and the power output end of the noise reduction drive assembly is connected to the root of each second blade 300; so that when the axial flow fan meets the preset conditions, each second blade 300 is driven to extend from the outer edge of the first blade 200, and the noise generated by the fan is suppressed by the serration 310 on the second blade 300. By providing a second blade 300 that can extend from the outer edge of the first blade 200, and providing a serration 310 on the second blade 300, when running at medium and low speeds, the second blade 300 does not extend, thereby ensuring that the fan has a high air volume performance. When running at high speeds, the noise reduction drive component drives each of the second blades 300 to extend from the outer edge of the first blade 200, and the serration 310 on the second blade 300 forms a row of counter-rotating vortex pairs at the trailing edge of the fan, thereby changing the tail vortex structure, weakening the spanwise correlation of the downstream wake zone, and reducing the flow turbulence pulsation intensity near the trailing edge, thereby reducing the far-field radiation of the noise, optimizing the aerodynamic characteristics of the fan, and reducing the generation of noise.

[0029] In some embodiments, a plurality of threaded holes are provided on the center hub 100, and the center hub 100 is connected to the motor shaft via a flange. When the motor is energized, the first blade 200 and the second blade 300 are driven to rotate. Flanges of different sizes are installed on the threaded holes of the center hub 100 to accommodate motors of different specifications, thereby improving the adaptability of the fan.

[0030] In some embodiments, by setting the guide ring 500, the airflow gradually becomes uniform after a certain distance from the fan, preventing the occurrence of obvious high-speed and low-speed areas and the backflow phenomenon that reduces efficiency. By setting the guide ring 500, the wind resistance can also be reduced, so that the air intake of the fan is increased. When the wind flow is divided, the resistance it encounters will be reduced, and the flow will be smoother, thereby increasing the air volume. At the same time, the reduction of wind flow resistance also means that the friction between the wind flow and the surface of the fan blade is reduced, and the noise will naturally be reduced.

[0031] In some embodiments, the central hub 100 is provided with a plurality of sliding openings arranged at intervals along the circumferential direction, and the sliding openings match the shape of the root of the second blade 300, so that when the noise reduction drive assembly drives the second blade 300 to move relative to the sliding openings, the second blade 300 always fits with the first blade 200. The second blade 300 passes through the sliding openings and is connected to the drive ring 410. The sliding openings can limit the sliding stroke of the second blade 300, thereby preventing the second blade 300 from being separated from the first blade 200 under the drive of the noise reduction drive assembly.

[0032] See also Figure 2 and Figure 4 , Figure 4 is a simplified structural diagram of a noise reduction drive assembly of an axial flow fan in an embodiment of the present application;

[0033] In some embodiments, the noise reduction drive assembly includes: a drive ring 410, which is relatively rotatably arranged on the inner side of the central hub 100, and the second blade 300 passes through the sliding opening and is connected to the drive ring 410; a circle of driven gear grooves 411 is arranged on the inner side of the drive ring 410; a drive member, which is fixed to the central hub 100, and the power output of the drive member is equipped with a drive gear 420, and the drive gear 420 is meshed with the driven gear groove 411, and the drive ring 410 is driven by the drive member to rotate relative to the hub to drive the second blade 300 to slide in the sliding opening, and the sawtooth portion 310 on the second blade 300 extends relative to the outer edge of the first blade 200. When running at medium and low speeds, the drive member does not work, and the second blade 300 does not extend, so as to ensure that the air volume performance of the fan is high. When the fan rotates to a specified speed, a signal is sent to the drive member through the control system of the car, and the drive member drives each second blade 300 to extend from the outer edge of the first blade 200 after receiving the signal. This feature allows the fan to flexibly adjust the sawtooth state according to the actual air volume demand: in the scenario of low air volume demand, the sawtooth shrinks to reduce unnecessary airflow resistance and ensure that the air volume accurately matches the demand; when the air volume demand is high, the sawtooth automatically extends to increase the interaction between the sawtooth and the airflow, effectively reducing the operating noise and achieving a dynamic balance between air volume and noise control.

[0034] See also Figure 2 and Figure 5 , Figure 5 It is a transmission schematic diagram of a noise reduction drive assembly of an axial flow fan in an embodiment of the present application;

[0035] In some embodiments, the driving member is a driving motor 430, and the driving motor 430 is fixed to the central hub 100 through a fixing frame 440, and the power output end of the driving motor 430 is connected to the driving gear 420. Specifically, the power output end of the driving motor 430 is directly connected to the driving gear 420, and the driving motor 430 drives the transmission gear to rotate, so as to drive the driving ring 410 to rotate. In other embodiments, the driving motor 430 can also be connected to the driving gear 420 through a worm gear, and the use of a worm gear can change the installation position of the driving motor 430 and reduce the space occupied by the driving motor 430.

[0036] In some embodiments, the inner wall of the central hub 100 is provided with a circle of sliding grooves, the sliding grooves are connected to the sliding opening, and the driving ring 410 is rotatably arranged in the sliding track. The sliding grooves can reduce the friction between the driving ring 410 and the inner wall of the central hub 100, and increase the practical efficiency of the driving ring 410; at the same time, the sliding grooves can also limit the driving ring 410, and can prevent the driving ring 410 from moving in other directions, so that the transmission of the driving motor 430 is more stable.

[0037] See also Figure 3 and Figure 6 , Figure 6 It is a schematic diagram of the partial structure of a second blade 300 of an axial flow fan in an embodiment of the present application.

[0038] In some embodiments, the serration 310 is disposed at the trailing edge of the second blade 300 and is located at the front edge of the second blade 300 in the rotation direction. Since the wind flow is larger at the trailing edge of the fan blade, the serration 310 is disposed on the trailing edge blade to reasonably organize the wake flow to improve the stability of the compressor, and the stability of the fan / compressor is enhanced by utilizing the serration flow to the vortex tube to entrain the main flow and the interaction between the flow to the vortex tube and the wake shear layer.

[0039] In some embodiments, the second blade 300 includes a blade body and a sawtooth portion 310; the blade body is connected to the noise reduction drive assembly, and the sawtooth on the sawtooth portion 310 has different angles with the air outlet surface of the second blade 300. Specifically, along the center to the circumference of the axial flow fan, the angle between each sawtooth and the air outlet surface tends to increase. The sawtooth on the sawtooth portion 310 closest to the central hub 100 has an angle of 60° with the reference plane of the second blade 300; the angle between two adjacent sawtooths is 5°. Neatly arranged serrations can significantly reduce the intensity of turbulent flow pulsation near the trailing edge, but the cross-flow effect between the serrations will intensify the disturbance of the three-dimensional mixing layer, accelerate the fluid rolling from the pressure surface to the suction surface, change the pressure distribution on both sides, and generate additional medium and high-frequency noise; and setting serrations with different angles to the wind outlet surface weakens the cross-flow effect between the tooth gaps, reduces the influence of the three-dimensional mixing layer on the trailing edge turbulence, stabilizes the pressure distribution of the serration gaps, and can effectively suppress medium and high-frequency noise to a certain extent; at the same time, the different angles to the wind outlet surface can reduce wind resistance, thereby reducing vibration and noise during fan operation, and can make the wind direction more evenly dispersed, reduce the noise caused by excessive local wind speed, optimize the aerodynamic characteristics of the fan, and reduce the noise generated by turbulence and eddy currents.

[0040] In some embodiments, see the table below, the axial flow fan in the present application is subjected to performance tests with a first fan having blades without serrations and a second fan having blades with serrations at the same angle to the air outlet surface. The results are shown in Tables 1 and 2 below, wherein Table 1 is a performance comparison of the three fans at a diameter of 750 mm and a rotation speed of 1600 rpm, and Table 2 is a performance comparison of the three fans at a diameter of 750 and a rotation speed of 2500 rpm. Table 1 Flow rate (m3 / s) Static pressure(pa) Shaft power (kW) Noise level (dB) First Fan 5.57 450 6.67 79.62 Second fan 5.59 450 6.62 77.84 Axial-flow fans 5.62 450 6.54 75.78 Improvement effect / / / 3.84 Table 2 Flow rate (m3 / s) Static pressure(pa) Shaft power (kW) Noise level (dB) First Fan 8.58 450 10.49 94.21 Second fan 8.12 450 10.84 91.76 Axial-flow fans 8.56 450 10.52 90.12 Improvement effect / / / 4.09

[0041] It can be seen from the above table that compared with conventional fans, under the same back pressure, the air volume of the present invention is increased by 6-10%, and the noise is reduced by 3dB-5dB compared with the same conventional fan blades and Putuo serrated fans; it can meet the noise reduction requirements of the fan.

[0042] In some embodiments, multiple spoilers can be fixed on the first blade and the second blade. When the airflow passes through the spoiler blocks, high-intensity induced vortices can be generated to mix the high-energy fluid outside the boundary layer with the fluid inside the boundary layer, delay the separation of the suction surface boundary layer flow, control the local backflow and boundary layer thickening on the blade surface, enhance the airfoil lift, and suppress the generation of fan noise.

[0043] In some embodiments, the distribution angle between each first blade 200 can also be adjusted. When the fan blades rotate, they will form periodic pressure waves in the air. These pressure waves propagate at a certain frequency, forming a specific noise spectrum. This frequency is directly related to the rate at which the blade passes through the air, so it is called the blade passing frequency (BPF). In addition, the uniformity of the incoming flow, the design of the blades, and the structure of the fan will affect the generation and intensity of the BPF noise; and setting the first blades 200 with different distribution angles can optimize the flow field and structure of the fan, which can effectively reduce the BPF noise.

[0044] The second aspect of the embodiment of the present application provides a car, in which the axial flow fan is provided. By providing a second blade that can extend from the outer edge of the first blade, and providing a serrated portion on the second blade, when running at medium and low speeds, the second blade does not extend, thereby ensuring that the fan has a high air volume performance. When running at high speeds, the noise reduction drive assembly drives each of the second blades to extend from the outer edge of the first blade, and the serrated portion on the second blade forms a row of counter-rotating vortex pairs at the trailing edge of the fan, thereby changing the tail vortex structure, weakening the spanwise correlation of the downstream wake zone, and reducing the flow turbulence pulsation intensity near the trailing edge, thereby reducing the far-field radiation of the noise, optimizing the aerodynamic characteristics of the fan, and thus reducing the generation of noise; optimizing the driving environment of the vehicle, reducing the noise inside the vehicle, reducing traffic accidents caused by noise, and improving the comfort and riding experience of users.

[0045] It can be seen from the above technical solution that the present application has at least the following advantages and positive effects:

[0046] An axial flow fan in the present application is provided with a second blade that can extend from the outer edge of the first blade, and a serration portion is provided on the second blade. When running at medium and low speeds, the second blade does not extend, thereby ensuring that the fan has a high air volume performance. When running at high speed, the noise reduction drive component drives each of the second blades to extend from the outer edge of the first blade, and the serration portion on the second blade forms a row of counter-rotating vortex pairs at the trailing edge of the fan, thereby changing the tail vortex structure, weakening the spanwise correlation of the downstream wake zone, and reducing the flow turbulence pulsation intensity near the trailing edge, thereby reducing the far-field radiation of the noise, optimizing the aerodynamic characteristics of the fan, and thus reducing the generation of noise.

[0047] A car in the present application uses an axial flow fan, and a second blade that can extend from the outer edge of the first blade is provided, and a serration portion is provided on the second blade. When running at medium and low speeds, the second blade does not extend, thereby ensuring that the fan has a high air volume performance. When running at high speeds, the noise reduction drive component drives each of the second blades to extend from the outer edge of the first blade, and the serration portion on the second blade forms a row of counter-rotating vortex pairs at the trailing edge of the fan, thereby changing the tail vortex structure, weakening the spanwise correlation of the downstream wake zone, and reducing the flow turbulence pulsation intensity near the trailing edge, thereby reducing the far-field radiation of noise, optimizing the aerodynamic characteristics of the fan, and thus reducing the generation of noise; optimizing the vehicle driving environment, reducing the noise inside the vehicle, reducing traffic accidents caused by noise, and improving the user's vehicle comfort and riding experience.

[0048] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0049] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise" and "counterclockwise" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0050] In this application, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0051] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0052] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. An axial flow fan, characterized in that: include: a center hub for connecting to the motor shaft; A plurality of first blades are respectively connected to the central hub; A plurality of second blades, which are fitted with the first blades, and the second blades are provided with sawtooth portions; In a normal state, the serrations do not extend beyond the outer edge of the first blade; A noise reduction drive assembly is arranged on the central hub, and a power output end of the noise reduction drive assembly is connected to the blade root of each second blade; when the axial flow fan meets preset conditions, each second blade is driven to extend from the outer edge of the first blade, and the noise generated by the fan is suppressed by the serrated portion on the second blade.

2. The axial flow fan according to claim 1, characterized in that: The central hub is provided with a plurality of sliding openings spaced apart along the circumferential direction, and the sliding openings match the shape of the root of the second blade, so that the second blade is always in contact with the first blade during the process in which the noise reduction drive assembly drives the second blade to move relative to the sliding opening.

3. The axial flow fan according to claim 2, characterized in that: The noise reduction driving component comprises: A driving ring is relatively rotatably arranged on the inner side of the central hub, and the second blade passes through the sliding opening and is connected to the driving ring; a circle of driven gear grooves is arranged on the inner side of the driving ring; A driving member is fixed to the central hub, and a driving gear is installed on the power output of the driving member. The driving gear is engaged with the driven gear groove. The driving member drives the driving ring to rotate relative to the hub to drive the second blade to slide in the sliding opening, and the serration on the second blade extends relative to the outer edge of the first blade.

4. The axial flow fan according to claim 3, characterized in that: The driving member is a driving motor, which is fixed to the central hub via a fixing frame, and a power output end of the driving motor is drivingly connected to the driving gear.

5. The axial flow fan according to claim 2, characterized in that: The inner wall of the central hub is provided with a circle of sliding grooves, the sliding grooves are communicated with the sliding opening, and the driving ring is rotatably arranged in the sliding track.

6. The axial flow fan according to any one of claims 1 to 5, characterized in that: The sawtooth portion is arranged at the trailing edge of the second blade and is located at the front edge of the second blade in the rotation direction.

7. The axial flow fan according to any one of claims 1 to 5, characterized in that: The second blade includes a blade body and a serrated portion; the blade body is connected to the noise reduction drive assembly, and the angles between the serrations on the serrated portion and the air outlet surface of the second blade are different.

8. The axial flow fan according to claim 7, characterized in that: Along the center to the circumference of the axial flow fan, the angle between each sawtooth and the air outlet surface tends to increase.

9. The axial flow fan according to claim 8, characterized in that: The included angle between the sawtooth on the sawtooth portion closest to the central hub and the second blade reference plane is 60°; the included angle between two adjacent sawtooths is 5°.

10. An automobile, characterized in that: The automobile is provided with an axial flow fan as claimed in any one of claims 1 to 9.

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