Compound air prefilter

Abstract

The application discloses a composite air rough filter, which comprises an upper rough filter disc, a lower rough filter disc and a plurality of cyclone tubes connected between the upper and lower rough filter discs; an air inlet cylinder is connected between the upper and lower rough filter discs, each cyclone tube is located in the air inlet cylinder, and a plurality of air inlet holes are uniformly distributed on the cylinder wall of the air inlet cylinder; the outlet of each cyclone tube is communicated with an air outlet pipe, the lower rough filter disc outside the air inlet cylinder is connected with a vertically arranged inner connecting cylinder, the inner connecting cylinder is connected with an outer connecting cylinder through cyclone blades towards the radial outer part, and the bottom end of the annular cavity serves as an air inlet; the outer connecting cylinder is connected with a circumferential shell upwards, the circumferential shell is connected with an upper connecting ring at the top end, and the upper connecting ring is integrated with the upper rough filter disc; the upper connecting ring is connected with an upper shell upwards; and a plurality of primary ash outlet openings which are communicated with the environment are arranged on the circumferential shell. The application integrates the cyclone blades and the cyclone tubes, improves the pre-filtering effect and the product life through multi-stage separation. The air inlet cavity is matched with the negative pressure state to improve the primary filtering effect.

Description

Technical Field

[0001] This invention relates to air filtration technology for motor vehicles. Background Technology

[0002] Commercial vehicles, agricultural vehicles, and engineering vehicles operate in environments with high levels of dust, which places high demands on air filtration. They generally employ a two-stage filtration structure consisting of an air pre-filter (also known as a coarse filter) and an air filter.

[0003] Air pre-filters used in the market include swirl vane type and airflow inlet swirl tube type. The working principle of the swirl vane type is: the airflow enters the housing in a swirling direction through the impeller of the housing, and then enters the intake pipe after passing through the swirl vanes inside the housing; this method has the simplest structure, poor reliability, low filtration efficiency, and high requirements for the matching engine;

[0004] The airflow directly enters the cyclone tube type pre-filter, which uses multiple cyclone tubes. The separation efficiency is better than that of the cyclone blade type, but it is difficult to maintain, has poor dust discharge, and the working pressure is concentrated in the cyclone tube. The airflow enters the cyclone tube from the side, and the overall rainproof performance of the product is poor. Summary of the Invention

[0005] The purpose of this invention is to provide a composite air coarse filter that simultaneously employs swirl blades and multiple swirl tubes, improving rainproof performance through bottom air intake and enhancing air pre-filtration efficiency through two-stage swirl filtration.

[0006] To achieve the above objectives, the composite air coarse filter of the present invention includes an upper coarse filter plate, a lower coarse filter plate, and a plurality of swirling tubes connected between the upper and lower coarse filter plates, with each swirling tube spaced apart; an air inlet cylinder is connected between the upper and lower coarse filter plates, and each swirling tube is located inside the air inlet cylinder, with a plurality of air inlet holes evenly distributed on the cylinder wall of the air inlet cylinder.

[0007] The outlet of each cyclone tube is connected to the exhaust pipe, which is connected to the upper and lower coarse filter plates; the exhaust pipe extends downwards out of the lower coarse filter plate.

[0008] The lower coarse filter plate outside the air intake is connected to a vertically arranged inner connecting cylinder. The inner connecting cylinder is connected to an outer connecting cylinder radially outward through swirl blades. Multiple swirl blades are evenly arranged circumferentially in the annular cavity formed between the inner and outer connecting cylinders and are used to generate circumferential rotation of the upward airflow. The bottom end of the annular cavity serves as the air intake.

[0009] The outer connecting cylinder is connected upward to the circumferential shell, and the top of the circumferential shell is connected to the upper connecting ring. The upper connecting ring is integrated with the upper coarse filter disc radially inward. The upper connecting ring is connected upward to the upper shell. The circumferential shell is provided with several primary ash outlets that communicate with the environment.

[0010] The lower coarse filter plate is connected to a dust collection chamber, and the side wall of the dust collection chamber is provided with a ash discharge port. The ash discharge port is threaded or snapped with a ash discharge cover.

[0011] The upper housing and the upper coarse filter plate form a pre-filtered air chamber. The upper end of the air outlet pipe is connected to the pre-filtered air chamber, and the lower end of the air outlet pipe passes through the dust collection chamber and is used to connect to the inlet pipe of the air filter of the motor vehicle.

[0012] Each cyclone tube has the same structure, including an upper tube fixedly connected to the upper coarse filter plate and a lower tube fixedly connected to the lower coarse filter plate. The bottom of the lower tube is a hollow frustum-shaped cone that is larger at the top and smaller at the bottom. The bottom end of the lower tube passes through the lower coarse filter plate and extends into the dust collection chamber, serving as the dust discharge port of the cyclone tube. The dust discharge port of the cyclone tube serves as the secondary ash discharge port.

[0013] The upper end of the upper tube passes through the upper coarse filter plate, extends into the pre-filtered clean air chamber, and serves as the outlet of the cyclone tube;

[0014] The upper and lower pipes are arranged on the same axis, and both ends of the upper and lower pipes are open; the middle and lower part of the upper pipe extends downward into the lower pipe and is radially connected to a swirl vane, which is evenly distributed circumferentially, and the fit clearance between the radial outer end of each swirl vane and the inner wall of the lower pipe is less than or equal to 0.2 mm; the swirl vane is used to make the downward airflow form a rotating airflow.

[0015] The annular opening formed by the upper end of the lower tube and the outer wall of the upper tube serves as the inlet of the cyclone tube.

[0016] With the radial exterior as the outward direction, the diameter of the upper end of the circumferential shell is smaller than the diameter of its lower end, making its generatrix a sloping line that is higher on the inside and lower on the outside;

[0017] The inner connecting cylinder is connected to the guide cylinder at the top, and the guide cylinder is coaxial with the circumferential shell; the upper diameter of the guide cylinder is larger than its lower diameter, so that its generatrix is ​​an oblique line with the outside higher than the inside.

[0018] The air intake chamber is formed by the air guide tube and the circumferential shell, which is narrow at the top and wide at the bottom.

[0019] The narrow-at-the-top and wide-at-the-bottom width of the intake chamber is matched with the predetermined negative pressure state of the engine, so that the swirling speed of the airflow at the first-stage ash outlet matches the negative pressure state at that location, forming a small amount of outward leakage airflow at the first-stage ash outlet.

[0020] The bottom wall of the dust collection chamber has a vertical cross-section in the shape of a herringbone, with a high middle and low sides; two ash discharge ports are provided at the lowest points of the bottom walls on both sides of the dust collection chamber.

[0021] The present invention has the following advantages:

[0022] The design objectives of this invention are:

[0023] 1. The two-stage pre-filtration composite structure of swirl blades and swirl tubes, with bottom air intake, improves rainproof performance.

[0024] 2. The intake space is contracted, and the inertia of dust particles is increased by increasing the flow rate, so that larger dust particles can be discharged from the first-stage ash outlet against the negative pressure direction, thereby improving the first-stage pre-filtration effect.

[0025] 3. The structure of the cyclone tube with air intake in the middle, air outlet at the top, and secondary ash discharge at the bottom combined with the dust collection chamber improves the secondary pre-filtration effect and facilitates secondary ash discharge.

[0026] 4. The dust collection chamber has a structure that facilitates cleaning, with side openings and an inclined bottom surface that is higher inside and lower outside.

[0027] This invention integrates swirl blades and a swirl tube into one unit, performing multi-stage separation of dust and other contaminants, reducing pressure on the swirl tube, and extending product lifespan. This invention separates dust multiple times, improving pre-filtration efficiency and providing cleaner intake air for the air filter, resulting in purer airflow entering the engine after air filtration.

[0028] This invention features a bottom-intake structure. During use, the negative pressure at the engine of the vehicle is conducted to the air intake through the exhaust pipe, creating an upward airflow at the intake. Compared to previous side-intake systems, this improves rain protection. Furthermore, this invention employs swirl blades and swirl tubes for secondary swirl filtration of the airflow, enhancing air pre-filtration efficiency.

[0029] The air intake also serves as a dust barrier, improving the air pre-filtration effect on the one hand, and allowing the airflow to enter the space inside the air intake more evenly in the circumferential direction to supply each vortex tube for secondary pre-filtration on the other.

[0030] Dust may clump together in the dust collection chamber, sometimes requiring manual cleaning by staff. The ash discharge port is located on the side wall of the dust collection chamber, which makes it easier for staff to open the ash discharge cover for cleaning compared to a lower ash discharge port. Specifically, when dust clumps together, it is more convenient to open the ash discharge cover and clean the accumulated dust from the side.

[0031] The cyclone tube is divided into an upper tube and a lower tube. Air enters in the middle, the lower end is connected to the dust collection chamber for dust discharge, and the upper end is connected to the pre-filtered clean air chamber for clean air to flow out. This structure enhances the effect of secondary filtration through cyclone (the primary filtration effect is generated by the cyclone blades) and facilitates air discharge and dust discharge, improving the convenience of dust discharge compared to the past.

[0032] As the airflow moves upward through the intake chamber, the cross-section of the flow channel decreases, and the airflow velocity increases. This makes it easier for dust particles in the airflow to be discharged into the environment through the primary ash outlet under the influence of inertia, thus improving the effectiveness of the primary pre-filtration. Due to the negative pressure effect transmitted from the vehicle engine, the airflow at the primary ash outlet does not flow outward in large quantities against the direction of negative pressure; only dust particles with high inertia easily flow out of the primary ash outlet.

[0033] Structurally, the narrow-at-the-top and wide-at-the-bottom width of the intake chamber is matched to the predetermined engine negative pressure state. This achieves the effect of virtually no airflow entering or leaving the primary ash outlet, with only a small amount of outward leakage and dust with high inertia flowing out. Maintaining a small amount of outward leakage is to prevent a large amount of unfiltered external gas from entering the invention, which would reduce the pre-filtration effect.

[0034] In principle, the greater the upward contraction of the intake chamber (the narrower the top relative to the bottom), the faster the airflow velocity at the primary ash outlet, and the easier it is for the air to leak out. The lower the predetermined engine negative pressure value (the greater the negative pressure), the easier it is for the airflow at the primary ash outlet to flow inward and the less likely it is to leak out. Through experiments, a suitable matching state can be obtained.

[0035] The bottom wall of the dust collection chamber is higher in the middle and lower on both sides. The ash discharge port is connected to the lowest point of the bottom wall of the dust collection chamber. This structure prevents dust from accumulating in the middle of the dust collection chamber and allows it to easily slide naturally to the ash discharge port, which facilitates ash discharge. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the present invention;

[0037] Figure 2 yes Figure 1 AA section view;

[0038] Figure 3 yes Figure 2 BB cross-sectional view;

[0039] Figure 4 yes Figure 1 The right view;

[0040] Figure 5 This is a three-dimensional structural schematic diagram of the present invention;

[0041] Figure 6 It is a schematic diagram of the assembly structure of the upper and lower coarse filter discs, the dust collection chamber, and each cyclone tube;

[0042] Figure 7 This is a schematic diagram of the upper tube of the cyclone tube;

[0043] Figure 8 This is a schematic diagram of the structure of the dust collection chamber and the air outlet pipe.

[0044] Figure 9 yes Figure 2 Enlarged view of point A in the middle. Detailed Implementation

[0045] like Figures 1 to 9 As shown, the composite air coarse filter of the present invention includes an upper coarse filter disk 1, a lower coarse filter disk 2, and a plurality of swirling tubes connected between the upper and lower coarse filter disks 1 and 2, with each swirling tube arranged at intervals.

[0046] An air inlet cylinder 3 is connected between the upper coarse filter plate 1 and the lower coarse filter plate 2. Each cyclone tube is located inside the air inlet cylinder 3. Multiple air inlet holes 4 are evenly distributed on the cylinder wall of the air inlet cylinder 3.

[0047] The outlet of each cyclone tube is connected to the exhaust pipe 5, which is connected to the upper coarse filter plate 1 and the lower coarse filter plate 2; the exhaust pipe 5 extends downwards out of the lower coarse filter plate 2.

[0048] The lower coarse filter plate 2 outside the air inlet cylinder 3 is connected to a vertically arranged inner connecting cylinder 6. The inner connecting cylinder 6 is connected to an outer connecting cylinder 8 radially outward through a swirl vane 7. Multiple swirl vanes 7 are evenly arranged circumferentially in the annular cavity formed between the inner connecting cylinder 6 and the outer connecting cylinder 8 and are used to generate circumferential rotation of the upward airflow. The bottom end of the annular cavity serves as the air inlet 9.

[0049] The outer connecting cylinder 8 is connected upward to the circumferential shell 10, and the top of the circumferential shell 10 is connected to the upper connecting ring 14. The upper connecting ring 14 is connected to the upper coarse filter plate 1 in the radial and inward direction. The upper connecting ring 14 is connected upward to the upper shell 15. The circumferential shell 10 is provided with several primary ash outlets 11 that communicate with the environment.

[0050] This invention features a bottom-intake structure. During use, the negative pressure at the engine of the vehicle is transmitted to the air intake 9 through the exhaust pipe 5. Air intake 9 then draws in air from bottom to top, improving rain protection compared to conventional side-intake systems. This invention also employs swirl vanes 7 and swirl tubes for secondary swirl filtration of the airflow, enhancing air pre-filtration efficiency.

[0051] The air intake spool 3 also serves as a dust barrier, improving the air pre-filtration effect on the one hand, and allowing the airflow to enter the space inside the air intake spool 3 more evenly in the circumferential direction to supply each swirl tube for secondary pre-filtration on the other.

[0052] The lower coarse filter plate 2 is connected downward to the dust collection chamber 12. The dust collection chamber 12 has a dust discharge port 13 on its side wall. The dust discharge port 13 is threaded or snapped with a dust discharge cover. The dust discharge port 13 is equipped with a dust discharge cover, which is a conventional technology. The dust discharge cover is not shown in the figure.

[0053] The upper housing 15 and the upper coarse filter plate 1 form a pre-filtered air chamber 16. The upper end of the air outlet pipe 5 communicates with the pre-filtered air chamber 16, and the lower end of the air outlet pipe 5 passes through the dust collection chamber 12 and is used to connect to the inlet pipe of the air filter of the motor vehicle.

[0054] Each cyclone tube has the same structure, including an upper tube 17 fixedly connected to the upper coarse filter plate 1 and a lower tube 18 fixedly connected to the lower coarse filter plate 2. The bottom of the lower tube 18 is a hollow frustum-shaped cone with a larger top and a smaller bottom. The bottom end of the lower tube 18 passes through the lower coarse filter plate 2 and extends into the dust collection chamber 12, serving as the dust collection port of the cyclone tube. The dust collection port of the cyclone tube serves as the secondary ash outlet 19.

[0055] The upper end of the upper tube 17 passes through the upper coarse filter plate 1 and extends into the pre-filtered clean air chamber 16, serving as the outlet 20 of the cyclone tube;

[0056] The upper tube 17 and the lower tube 18 are arranged coaxially, with both ends of the upper and lower tubes 17 and 18 being open. The lower middle part of the upper tube 17 extends downward into the lower tube 18 and is radially connected to a swirl vane 21. The swirl vanes 21 are evenly distributed circumferentially, and the fit clearance between the radial outer end of each swirl vane 21 and the inner wall of the lower tube 18 is less than or equal to 0.2 mm. The fit clearance of less than or equal to 0.2 mm serves two purposes: firstly, it facilitates assembly, and secondly, it prevents the downward airflow inside the swirl tube from being effectively guided by the swirl vane 21 due to excessive clearance. The swirl vane 21 is used to form a rotating airflow from the downward airflow. The annular opening formed by the upper end of the lower tube 18 and the outer wall of the upper tube 17 serves as the inlet 22 of the swirl tube.

[0057] Dust may clump together in the dust collection chamber 12, sometimes requiring manual cleaning by staff. The ash discharge port 13 is located on the side wall of the dust collection chamber 12. Compared to a lower ash discharge port, a lower one makes it easier for staff to open the ash discharge cover for cleaning. Specifically, when dust clumps together, it is more convenient to open the ash discharge cover and clean the accumulated dust from the side.

[0058] The cyclone tube is divided into an upper tube 17 and a lower tube 18. Air enters in the middle, and the lower end is connected to the dust collection chamber 12 for dust discharge. The upper end is connected to the pre-filter clean air chamber 16 for clean air to flow out. This structure enhances the effect of secondary filtration through cyclone (the primary filtration effect is generated by the cyclone blades 7) and facilitates air discharge and dust discharge, improving the convenience of dust discharge compared to the past.

[0059] With the radial exterior as the outward direction, the upper diameter of the circumferential shell 10 is smaller than its lower diameter, making its generatrix a sloping line with the inner side higher than the outer side; the inner connecting cylinder 6 is connected upward to the guide cylinder 23, which is coaxial with the circumferential shell 10; the upper diameter of the guide cylinder 23 is larger than its lower diameter, making its generatrix a sloping line with the outer side higher than the inner side; the guide cylinder 23 and the circumferential shell 10 form an annular air intake cavity 24 that is narrow at the top and wide at the bottom.

[0060] As the airflow passes through the intake chamber 24 from bottom to top, the cross-section of the flow channel becomes smaller, and the airflow velocity increases. This makes it easier for dust particles in the airflow to be discharged into the environment through the primary ash outlet 11 under the influence of inertia, thus improving the effect of the primary pre-filtration. Due to the negative pressure effect transmitted from the vehicle engine, the airflow at the primary ash outlet 11 will not flow outward in large quantities against the direction of negative pressure; only dust particles with high inertia can easily flow out of the primary ash outlet 11.

[0061] The narrow-at-the-top and wide-at-the-bottom width of the intake chamber 24 is matched with the predetermined negative pressure state of the engine, so that the airflow swirl speed at the first-stage ash outlet 11 matches the negative pressure state at that location, forming a small amount of outward leakage airflow at the first-stage ash outlet 11.

[0062] Structurally, the intake chamber 24 is narrower at the top and wider at the bottom to match the predetermined engine negative pressure state. This achieves the effect that the airflow at the primary ash outlet 11 is essentially non-intake and non-exhaustible, with only a small amount of outflowing air and dust with high inertia flowing out. Maintaining a small amount of outflowing air is to prevent a large amount of unfiltered external gas from entering the invention, which would reduce the pre-filtration effect.

[0063] In principle, the greater the upward contraction of the intake chamber 24 (the narrower the top relative to the bottom), the faster the airflow velocity at the primary ash outlet 11, and the easier it is for the air to leak out. The lower the predetermined engine negative pressure value (the greater the negative pressure), the easier it is for the airflow at the primary ash outlet 11 to flow inward and the less likely it is to leak out. By changing the degree of upward contraction of the intake chamber 24 in a limited number of actual tests or simulation experiments, a suitable matching state can be obtained for the predetermined negative pressure state generated by the engine.

[0064] The bottom wall of the dust collection chamber 12 has a vertical cross-section in the shape of a herringbone, with a high middle and low sides; two ash discharge ports 13 are provided at the lowest points of the bottom walls on both sides of the dust collection chamber 12.

[0065] The bottom wall of the dust collection chamber 12 is higher in the middle and lower on both sides. The ash discharge port 13 is connected to the lowest point of the bottom wall of the dust collection chamber 12. This structure prevents dust from accumulating in the middle of the dust collection chamber 12 and allows it to easily slide down to the ash discharge port 13, which facilitates ash discharge.

[0066] When in use, this invention is installed on a motor vehicle (especially a commercial vehicle, agricultural vehicle or engineering vehicle with a large filtration load). The exhaust pipe 5 is connected to the inlet pipe of the motor vehicle's air filter, and the air inlet 9 is downward and open to the atmosphere.

[0067] When the engine is running, it generates negative pressure, which is transmitted along the intake piping system to the exhaust pipe 5 in this invention. Within this invention, negative pressure causes ambient gas outside the intake port 9 to enter from bottom to top. The swirl vanes 7 at the intake port 9 transform the rising airflow into a rotating rising airflow. As it passes through the narrow-at-the-top, wide-at-the-bottom intake chamber 24, the flow velocity increases, and the inertia of dust particles in the airflow increases. Larger dust particles, possessing greater inertia, are discharged through the primary ash outlet 11 after resisting the negative pressure. The airflow and another portion of dust, under the influence of negative pressure, enter the internal space of the intake cylinder 3 through multiple intake holes 4 on the side wall of the intake cylinder 3, and enter the lower pipe 18 through the inlet 22 of the swirl tube. Guided by the swirl vanes 21, a downward rotating airflow is formed. The dust in the rotating airflow (especially large dust particles), possessing greater downward inertia, enters the ash discharge chamber through the lower end of the lower pipe 18 (secondary ash outlet 19). Because the dust discharge cover is not open during normal operation, the dust collection chamber 12 has a higher air pressure than the upper pipe 17 of the vortex tube due to the inability of airflow to flow out. The relatively high air pressure in the dust collection chamber 12, and the hollow frustum shape of the bottom of the lower pipe 18 (larger at the top and smaller at the bottom) increases the downward resistance of airflow. Therefore, dust with greater inertia will enter the dust collection chamber 12, while the airflow, due to the high downward flow resistance and the absence of an air outlet in the dust collection chamber 12, will flow upward through the upper pipe 17 into the pre-filtered air chamber 16, and then downward through the air outlet pipe 5 to be sent to the air filter of the motor vehicle. After being filtered by the air filter, it is used for engine combustion.

[0068] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A composite air coarse filter, comprising an upper coarse filter disc, a lower coarse filter disc, and a plurality of cyclone tubes connected between the upper and lower coarse filter discs, wherein the cyclone tubes are spaced apart; characterized in that: An air inlet cylinder is connected between the upper and lower coarse filter discs. All cyclone tubes are located inside the air inlet cylinder, and multiple air inlet holes are evenly distributed on the cylinder wall. The outlet of each cyclone tube is connected to the exhaust pipe, which is connected to the upper and lower coarse filter plates; the exhaust pipe extends downwards out of the lower coarse filter plate. The lower coarse filter plate outside the air intake is connected to a vertically arranged inner connecting cylinder. The inner connecting cylinder is connected to an outer connecting cylinder radially outward through swirl blades. Multiple swirl blades are evenly arranged circumferentially in the annular cavity formed between the inner and outer connecting cylinders and are used to generate circumferential rotation of the upward airflow. The bottom end of the annular cavity serves as the air intake. The outer connecting cylinder is connected upward to the circumferential shell, and the top of the circumferential shell is connected to the upper connecting ring. The upper connecting ring is integrated with the upper coarse filter plate in the radial direction and inward. The upper connecting ring is connected upward to the upper shell. The circumferential shell is provided with several primary ash outlets that communicate with the environment. The swirl blades and swirl tubes work together in function. The swirl blades are used to perform primary centrifugal separation of the airflow entering the air inlet and reduce the load on the swirl tubes. The swirl tubes are used to perform secondary filtration of the airflow after primary separation. The two-stage structure together improves the pre-filtration efficiency.

2. The composite air coarse filter according to claim 1, characterized in that: The lower coarse filter plate is connected to a dust collection chamber, and the side wall of the dust collection chamber is provided with a ash discharge port. The ash discharge port is threaded or snapped with a ash discharge cover. The upper housing and the upper coarse filter plate form a pre-filtered air chamber. The upper end of the air outlet pipe is connected to the pre-filtered air chamber, and the lower end of the air outlet pipe passes through the dust collection chamber and is used to connect to the inlet pipe of the air filter of the motor vehicle. Each cyclone tube has the same structure, including an upper tube fixedly connected to the upper coarse filter plate and a lower tube fixedly connected to the lower coarse filter plate. The bottom of the lower tube is a hollow frustum-shaped cone that is larger at the top and smaller at the bottom. The bottom end of the lower tube passes through the lower coarse filter plate and extends into the dust collection chamber, serving as the dust discharge port of the cyclone tube. The dust discharge port of the cyclone tube serves as the secondary ash discharge port. The upper end of the upper tube passes through the upper coarse filter plate, extends into the pre-filtered clean air chamber, and serves as the outlet of the cyclone tube; The upper and lower pipes are arranged on the same axis, and both ends of the upper and lower pipes are open; the middle and lower part of the upper pipe extends downward into the lower pipe and is radially connected to a swirl vane, which is evenly distributed circumferentially, and the fit clearance between the radial outer end of each swirl vane and the inner wall of the lower pipe is less than or equal to 0.2 mm; the swirl vane is used to make the downward airflow form a rotating airflow. The annular opening formed by the upper end of the lower tube and the outer wall of the upper tube serves as the inlet of the cyclone tube.

3. The composite air pre-filter according to claim 1, characterized in that: With the radial exterior as the outward direction, the diameter of the upper end of the circumferential shell is smaller than the diameter of its lower end, making its generatrix a sloping line that is higher on the inside and lower on the outside; The inner connecting cylinder is connected to the guide cylinder at the top, and the guide cylinder is coaxial with the circumferential shell; the upper diameter of the guide cylinder is larger than its lower diameter, so that its generatrix is ​​an oblique line with the outside higher than the inside. The air intake chamber is formed by the air guide tube and the circumferential shell, which is narrow at the top and wide at the bottom.

4. The composite air pre-filter according to claim 3, characterized in that: The narrow-at-the-top and wide-at-the-bottom width of the intake chamber is matched with the predetermined negative pressure state of the engine, so that the swirling speed of the airflow at the first-stage ash outlet matches the negative pressure state at that location, forming a small amount of outward leakage airflow at the first-stage ash outlet.

5. The composite air coarse filter according to any one of claims 2 to 4, characterized in that: The bottom wall of the dust collection chamber has a vertical cross-section in the shape of a herringbone, with a high middle and low sides; two ash discharge ports are provided at the lowest points of the bottom walls on both sides of the dust collection chamber.

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