Variable diameter and pitch screw rotor and vacuum pump

Abstract

The utility model discloses a variable diameter variable pitch screw rotor, including intermeshing left rotors and right rotors, the end face profile of left rotors with right rotors is same, all by 7 curves first and last connected closed, wherein 7 curves include involute section AB, circular arc section BC, dedendum circular arc section CD, circular arc section DE, cycloid equidistant curve section EF, dedendum circular arc section FG and circular arc conjugate curve section GA, the circular arc BC of left rotors is intermeshed with the circular arc conjugate curve A'G' of right rotors, and the rest line sections are sequentially intermeshed according to the rotating direction of left rotors and right rotors respectively, the screw pitch of left rotors and right rotors is segmented along the axial direction, the left rotors are conical along the air inlet end to the air outlet end, and the right rotors are conical along the air inlet end to the air outlet end. The utility model further provides a vacuum pump. The device provided by the utility model can effectively improve the internal compression ratio and efficiency of the vacuum pump.

Description

Technical Field

[0001] This utility model belongs to the field of vacuum pump design technology, and particularly relates to a variable diameter and variable pitch screw rotor and a vacuum pump. Background Technology

[0002] Dry screw vacuum pumps are widely used in semiconductor, biological, pharmaceutical, chemical, and aerospace industries due to their oil-free operation, low maintenance costs, high vacuum performance, and environmental friendliness. As the core component of a dry twin-screw vacuum pump, the performance of the screw rotor directly determines the pump's efficiency. Factors such as the end face profile, internal compression ratio, sealing performance, and volumetric gradient of the screw rotor directly affect the pumping speed, power consumption, and ultimate vacuum. Therefore, optimizing the screw rotor design is crucial for improving pump performance.

[0003] Patent document CN119308848A discloses a symmetrical tooth profile variable pitch twin-screw rotor and vacuum pump, which includes a male rotor and a female rotor that mesh with each other. The end face profiles of the male rotor and the female rotor are exactly the same, each formed by connecting 12 segments of curves. Six of the curves include, in sequence, the tooth tip arc ab, the first segment of the epicycloid bc, the second segment of the epicycloid cd, the tooth root arc de, the third segment of the epicycloid ef, and the fourth segment of the epicycloid fg. The other six curves are arranged in a centrally symmetrical manner with the above six curves. The pitch of the male rotor and the female rotor decreases circumferentially from the intake end to the exhaust end.

[0004] Patent document CN115143107 discloses a conical rotor and a dry double screw with a conical rotor. Its end face profile is composed of several curves, including a circular arc cycloid segment, a tooth root circular arc segment, and an Archimedean spiral segment. There are sharp points with uneven connections, which can easily lead to stress concentration. Furthermore, it is prone to deformation and wear after being eroded by fluid, thereby reducing the life and sealing performance of the screw rotor, increasing gas leakage, and affecting the ultimate vacuum and pumping speed of the pump.

[0005] Despite the important role of twin-screw vacuum pumps in industry, existing technologies still face several challenges. The variable-pitch screw rotor structure commonly used in industry is relatively simple, especially with limited research on variable cross-section and variable-pitch conical screw rotors. This results in bulky and heavy equipment, increasing material consumption and the difficulty of transportation and installation. Furthermore, existing pumps suffer from low power transmission accuracy and efficiency, are prone to vibration and noise, affecting operational stability and efficiency. Poor sealing performance also leads to serious gas leakage problems, further reducing pumping efficiency and ultimate vacuum levels. Utility Model Content

[0006] The purpose of this invention is to provide a variable pitch screw rotor and a vacuum pump, which can effectively improve the internal compression ratio and efficiency of the vacuum pump.

[0007] To achieve the first objective of this utility model, the following technical solution is provided: a variable diameter and variable pitch screw rotor, comprising a left-hand rotor and a right-hand rotor that mesh with each other, wherein the end face profiles of the left-hand rotor and the right-hand rotor are the same, each consisting of 7 curve segments connected end to end, wherein the 7 curve segments include an involute segment AB, a circular arc segment BC, a tooth tip circular arc segment CD, a circular arc segment DE, a cycloidal equidistant curve segment EF, a tooth root circular arc segment FG, and a circular arc conjugate curve segment GA;

[0008] The arc BC of the left-hand rotor meshes with the conjugate curve A'G' of the arc of the right-hand rotor, and the remaining line segments mesh sequentially according to the respective rotation directions of the left-hand rotor and the right-hand rotor;

[0009] The pitch of the left-hand rotor and the right-hand rotor varies in segments along the axial direction;

[0010] The left-hand rotary rotor is cone-shaped from the air inlet end to the air outlet end;

[0011] The right-hand rotary rotor is cone-shaped from the air inlet to the air outlet.

[0012] This invention achieves a variable diameter and variable pitch screw rotor configuration by continuously and gradually changing the tooth tip circle radius R1(z) and tooth root circle radius R2(z) along the axial coordinate Z at different axial positions of the screw rotor from the intake end to the exhaust end, while keeping the sum of the radii constant. The screw pitch P(z) changes along the axial direction according to a preset function. Through dual-parameter coordinated control, a screw rotor configuration with variable diameter and variable pitch is realized.

[0013] Specifically, the profile of the involute segment AB is constrained by the base circle radius, the tooth tip radius of the rotor, and the tooth root radius of the rotor, and its expression is as follows:

[0014]

[0015] Wherein, the initial angle R b R1 represents the base circle radius, R2 represents the rotor tooth tip radius, and R3 represents the rotor tooth root radius.

[0016] Specifically, the profile of the arc segment BC is constructed by constraining the base circle radius, the rotor's tooth tip circle radius, and the fillet radius of the arc segment BC, as expressed below:

[0017]

[0018] Among them, the deflection angle R b R1 represents the base circle radius, R4 represents the tooth tip radius of the rotor, and R5 represents the fillet radius of the arc segment BC.

[0019] Specifically, the tooth tip arc segment CD is constructed by constraining the radius of the rotor's tooth tip arc, and its expression is as follows:

[0020]

[0021] Where R1 represents the radius of the rotor tooth tip arc.

[0022] Specifically, the arc DE is constructed by constraining the fillet radius of DE, and its expression is as follows:

[0023]

[0024] Where R3 represents the radius of the tooth root arc DE.

[0025] Specifically, the equidistant curve EF is constructed by constraining the pitch circle radius, the rotor tooth tip arc radius, the rotor tooth root arc radius, and the tooth root arc DE radius, and its corresponding fitting curve segment is the arc segment E′D′.

[0026] Specifically, the tooth root arc segment FG is constructed by constraining the radius of the rotor's tooth root arc, and its expression is as follows:

[0027]

[0028] Where R3 represents the radius of the rotor tooth root arc.

[0029] Specifically, the conjugate curve segment GA is constructed by constraining the pitch circle radius and the fillet radius of the arc segment BC, and its corresponding fitted curve segment is the arc segment C′B′.

[0030] Specifically, the cones of both the left and right rotary rotors are tapered from the air inlet to the air outlet, and the angle between the edge of the cone and the screw is 0 to 5°.

[0031] To achieve the second objective of this utility model, the following technical solution is provided: a vacuum pump, comprising the aforementioned variable diameter and variable pitch screw rotor.

[0032] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0033] By rationally designing the variation law of rotor tooth tip circle radius, tooth root circle radius and pitch, the variable diameter and variable pitch screw rotor structure can be flexibly adjusted, thereby realizing the gradient change of the working volume inside the pump;

[0034] The variable cross-section and variable pitch structures generate internal compression respectively, while the variable diameter and variable pitch screw rotor has both of these compression effects at the same time, which significantly improves its internal compression ratio and enables it to achieve a higher internal compression ratio, thereby improving its working efficiency and performance. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the variable diameter and variable pitch screw rotor provided in this embodiment;

[0036] Figure 2 This is a schematic diagram of the right-hand rotor provided in this embodiment;

[0037] Figure 3 This is a schematic diagram of the left-handed rotor provided in this embodiment;

[0038] Figure 4 This is a schematic diagram of the rotor end face profile provided in this embodiment;

[0039] Figure 5 This is a schematic diagram of the profile meshing of the variable diameter and variable pitch screw rotor in different axial sections provided in this embodiment;

[0040] Figure 6 A schematic diagram of the conical helix of the variable diameter and variable pitch screw rotor provided in this embodiment; Detailed Implementation

[0041] To better understand the content of this embodiment, the following explanations will be given regarding letter variables:

[0042] Z1 is the axial distance of the intake section, Z2 is the axial distance of the intermediate compression section, Z3 is the axial distance of the exhaust section, and α is the axial distance of the exhaust section. cone R is the cone angle. b R1 is the radius of the base circle; R2 is the radius of the pitch circle; R3 is the radius of the root circle; R4 is the radius of the fillet of BC; R5 is the radius of the fillet of DE; t is the angular parameter; α is the initial angle of the involute AB; β is the deflection angle of segment EF; θ is the central angle of arc BC; m is the x-coordinate of the center O1; n is the y-coordinate of the center O1.

[0043] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. The components of the embodiments of this utility model described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this utility model provided in the accompanying drawings is not intended to limit the scope of the claimed utility model, but merely to illustrate selected embodiments of the utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.

[0044] like Figure 1As shown, the variable diameter and variable pitch screw rotor provided in this embodiment has two screw rotors.

[0045] like Figure 2 and Figure 3 As shown, there are left-hand and right-hand rotors that mesh precisely with each other. The profile structure and pitch variation of the left-hand and right-hand rotors are exactly the same, with only the direction of rotation being different.

[0046] The variable diameter and variable pitch screw rotor adopts the same set of profile equations, which includes key parameters, such as... Figure 4 As shown, the tooth tip radius R1 and tooth root radius R3, and the pitch circle radius R2 of the two screw rotors satisfy the following formula:

[0047] 2*R2=R1+R3;

[0048] As the airflow changes from the intake to the exhaust, the tip radius R1 gradually decreases, while the root radius R3 gradually increases, and their sum remains constant. This design ensures that the pitch circle radius R2 of the two screw rotors remains constant throughout the entire operation, allowing the rotation axes of the two screw rotors to be placed in parallel.

[0049] More specifically, the variable diameter and variable pitch screw rotor is conical in shape, and its cone angle α is... cone The cone angle α remains consistent throughout the entire length of the screw rotor and does not change. cone The cone angle is consistent with that of the dry twin-screw vacuum pump body; cone angle α cone The following formula is used to calculate:

[0050]

[0051] Among them, R 1max R is the maximum radius (mm) of the tooth tip arc CD; 1min The minimum radius (mm) of the tooth tip arc CD.

[0052] Where L is the axial length (mm) of the screw rotor, which in this embodiment is the length in the Z direction, that is, the sum of Z1, Z2 and Z3.

[0053] In this embodiment, the cone angle α cone A value between 0 and 5° is usually suitable, at which point the rotor's overall performance is relatively good.

[0054] like Figure 4As shown, the end face profile of the screw rotor consists of seven curves connected end to end, forming a sealed end face profile. These seven curves are: involute segment AB, circular arc segment BC, tooth tip circular arc segment CD, circular arc segment DE, cycloidal equidistant curve segment EF, tooth root circular arc segment FG, and circular arc conjugate curve segment GA. All curves in the profile are smoothly connected without any sharp points, which can effectively reduce backflow leakage at sharp points. Therefore, it can effectively improve the mechanical properties of the rotor and the overall sealing performance, making the vacuum pump's overall performance superior.

[0055] The profile of the involute segment AB is generated by the geometric constraint relationship between the base circle radius Rb and the rotor tooth tip circle radius R1 and tooth root circle radius R3, and its parametric equation is as follows:

[0056]

[0057] Wherein, the initial angle

[0058] exist Figure 4 In the equation, the parametric equation of the circular arc BC is as follows:

[0059]

[0060] in,

[0061] exist Figure 4 In the middle, the parametric equation of the tooth tip circle CD is as follows:

[0062]

[0063] exist Figure 4 In the equation, the parametric equation of the circular arc DE is as follows:

[0064]

[0065] exist Figure 4 In the equation, the parametric equation of the equidistant curve EF of the cycloid is generated by the geometric constraint relationship of the pitch circle radius R2, the addendum circle radius R1, the dedendum circle radius R3 and the meshing arc R5, and the corresponding fitting curve segment is the arc segment E′D′.

[0066] exist Figure 4 In the middle, the parametric equation of the tooth root arc FG is as follows:

[0067]

[0068] exist Figure 4 In the above, the parametric equation of the conjugate curve GA is generated by the geometric constraint relationship between the pitch circle radius R2 and the meshing arc R4, and its corresponding fitted curve segment is the arc segment C′B′:

[0069] in,

[0070] m=(R1-R4)cos(β), n=(R1-R4)sin(β);

[0071] Where R1 is the radius of the addendum arc BC; R2 is the radius of the base circle; R3 is the radius of the root arc DE; R4 is the radius of the fillet of BC; R5 is the radius of the fillet of DE; t is the angular parameter; α is the initial angle of the involute AB; β is the deflection angle of segment EF; θ is the central angle of arc BC; m is the x-coordinate value of the center O1; and n is the y-coordinate value of the center O1.

[0072] The profile production method provided in the above embodiments is as follows:

[0073] 1) Definition of parametric equations (as mentioned above): Based on the meshing characteristics of the screw rotor, a profile parametric equation consisting of 7 curve segments was established, covering the addendum circle, root circle and transition curve;

[0074] 2) Assigning key parameters: Input the core parameter values ​​such as the addendum circle radius R1 and the dedendum circle radius R3, and generate the curves for each segment through equations;

[0075] 3) Trimming and Closure: Trim the generated curves to remove redundant parts and retain the profile that forms a closed space, ensuring that each curve segment is connected end to end to form a complete end face profile.

[0076] Both left-hand and right-hand screw rotors employ... Figure 4 The same set of profiles shown consists of 7 curve segments that mesh precisely with each other and rotate periodically. During the rotation process:

[0077] The involute AB of the left-handed rotor meshes with the involute BA of the right-handed rotor;

[0078] The circular arc BC of the left-handed rotor meshes with the conjugate curve AG of the circular arc of the right-handed rotor;

[0079] The tooth tip arc CD of the left-hand rotary engine meshes with the tooth root arc GF of the right-hand rotary engine;

[0080] The circular arc DE of the left-hand rotor meshes with the equidistant curve FE of the cycloid of the right-hand rotor;

[0081] The equidistant curve EF of the cycloid of the left-hand rotor meshes with the circular arc ED of the right-hand rotor;

[0082] The root arc FG of the left-hand rotary engine meshes with the tip arc DC of the right-hand rotary engine;

[0083] The conjugate arc GA of the left-handed rotor meshes with the arc CB of the right-handed rotor.

[0084] like Figure 5 The diagram shown is a schematic of the axial cross-section profile gradient design provided in this embodiment. Figure 5 (a) is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the axial section of axis I; Figure 5 (b) is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the axial section of axis II; Figure 5 (c) in the diagram is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the axial section of section III; Figure 5 (d) in the diagram is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the axial section of the N axis; Figure 5 (e) in the diagram is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the V axial cross-section profile; Figure 5 (f) in the diagram is a schematic diagram of the meshing of the cross-sectional profile of the variable diameter and variable pitch screw rotor in the VI axis. Figure 5 (g) in the diagram is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the VII axial cross-section profile; Figure 5 (h) in the diagram is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the VIII axial cross-section profile; Figure 5 (i) in the diagram is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the IX axial section profile; Figure 5 (g) in the figure is a schematic diagram of the meshing of the variable diameter and variable pitch screw rotor in the X-axis cross-sectional profile.

[0085] The design process is as follows:

[0086] 1) Axial segmentation modeling: Divide the screw rotor from the intake end to the exhaust end into 10 equal parts and define 11 axial sections (numbered I to XI);

[0087] Variable diameter parameter control: On the axial coordinate Z, a continuous gradual change law is set for the tooth addendum circle radius R1(z) and tooth root circle radius R3(z), satisfying the following constraints:

[0088] R1(z) + R3(z) = constant value

[0089] By adjusting the axial variation functions of R1(z) and R3(z) (such as linear, nonlinear, or piecewise functions), different variable cross-section structures can be generated. Figure 5 (Example is a preferred solution);

[0090] 3) Section profile generation: at any axial position Z n Substitute the current R1(Z) n ) and R3(Z n ) value, using the same profile equation ( Figure 4 Automatically generate corresponding cross-sectional profiles;

[0091] 4) Model accuracy optimization: Increasing the number of axial sections (e.g., from 11 to more) can improve the accuracy of the three-dimensional model of the variable diameter and variable pitch screw rotor.

[0092] Technological advantages and scalability

[0093] 1) Unified equation-driven: All cross-sectional profiles are based on the same parametric equation, and only the key radius parameters need to be adjusted to adapt to different working conditions;

[0094] 2) Flexible design boundaries: By customizing the axial variation law of R1(z) and R3(z) (such as gradual rate and curve shape), rotors that are adapted to specific compression ratio, flow rate or strength requirements can be quickly generated.

[0095] 3) Engineering applicability: This method is applicable to scenarios such as screw vacuum pumps and expander compressors, and the development cycle is significantly shortened through parametric design.

[0096] Due to the use of a continuously gradually changing cross-section design, the internal compression ratio of the screw rotor gradually decreases from the intake end to the exhaust end, thereby achieving internal compression and effectively improving the internal compression ratio and energy efficiency of the screw rotor.

[0097] More specifically, the screw rotor includes an intake section (Z1), a compression section (Z2), and an exhaust section (Z3).

[0098] like Figure 6 The diagram shown is a schematic of the conical helix of a variable diameter, variable pitch screw rotor, and its parametric equation is:

[0099]

[0100] The variation law of axial taper in the conical helix is ​​consistent with the axial variation law of the custom tooth tip circle R1(z) (such as the gradual change rate and curve shape), that is, r(t) in the above formula is consistent with the radius value R1(z) of the tooth tip circle.

[0101] Therefore, by determining the axial variation law of the tooth tip circle R1(z), x(t) and y(t) can be obtained, which means the variation law of the axial taper in the conical helix can be obtained.

[0102] In the above formula, z(t) determines the pitch variation law P(t) of the conical helix.

[0103] In this embodiment, the pitch is the largest at the intake end and the smallest at the exhaust end. The pitch of the compression section gradually decreases from the largest pitch at the intake end to the smallest pitch at the exhaust end.

[0104] like Figure 6 As shown, the positions and profile structures of the intake section profile (a), exhaust section profile (k), and intermediate section profile (f) in the conical spiral are marked.

[0105] The pitch variation law of the intake section (Z1) is P1. In the preferred embodiment of this utility model, a constant pitch variable cross section design is adopted, with a constant value Pa from ω0 to ω1, and the pitch value Pa is the maximum.

[0106] The pitch variation law of the compression section (Z2) is P2. In the preferred embodiment of this utility model, a variable pitch and variable cross section design is adopted, and the pitch gradually decreases from Pa to Pb from ω1 to ω2.

[0107] The pitch variation law of the exhaust section (Z3) is P3. In the preferred embodiment of this utility model, a constant pitch variable cross section design is adopted, and the pitch value Pb is a constant from ω2 to ω3, and the pitch value Pb is the minimum.

[0108] By giving z(t) = P(t), that is, by adjusting P1, P2, and P3 to change along the axial direction according to a preset function, a rotor that adapts to specific compression ratio, flow rate, or strength requirements can be flexibly and quickly generated to meet actual working conditions.

[0109] This also clearly demonstrates the specific design method for variable diameter and variable pitch screw rotors:

[0110] 1) Construct a family of variable cross-section lines using the variable diameter method;

[0111] 2) Determine the pitch variation pattern and draw the variable pitch conical helix;

[0112] 3) Insert the corresponding cross-sectional profile at the preset pitch position and scan along the preset helix;

[0113] 4) Ensure that the starting points of each cross-sectional profile are aligned to guarantee the accuracy of the model;

[0114] 5) Finally, generate the required three-dimensional model of the variable diameter and variable pitch screw rotor.

[0115] This embodiment also provides a vacuum pump, which includes the aforementioned variable diameter, variable pitch screw rotor. Using the aforementioned screw rotor can significantly improve the pumping speed, internal compression ratio, and ultimate vacuum of a twin-screw vacuum pump, while ensuring high efficiency and energy saving.

[0116] In summary, the beneficial effects of this utility model are as follows:

[0117] By flexibly adjusting the design requirements, the variable diameter and variable pitch screw rotor structure can be flexibly adjusted through the rational design of the rotor tooth tip circle radius, tooth root circle radius, and pitch variation law, thereby achieving a gradient change in the working volume within the pump. This design can meet different specific design requirements such as pumping speed and power consumption.

[0118] The variable cross-section and variable pitch structure generate internal compression, while the variable diameter and variable pitch screw rotor simultaneously possesses both compression effects. Therefore, its internal compression ratio is significantly improved, enabling a higher internal compression ratio and thus enhancing its working efficiency and performance.

[0119] With its compact structure and high energy efficiency, this variable diameter and variable pitch screw rotor has a compact structure that can provide higher working efficiency with a smaller volume and weight, significantly improving energy efficiency and meeting the requirements of harsh working conditions.

[0120] With its excellent ultimate vacuum performance, the rotor design makes it easier for the pump to achieve higher ultimate vacuum levels and adapt to more demanding working environments, especially with significant advantages in high vacuum applications.

[0121] By improving the structural stability of the exhaust end, the variable diameter and variable pitch screw rotor effectively avoids the problem of thin-plate formation that occurs in conventional variable pitch rotors, thus improving its structural stability. This design reduces backflow leakage and extends service life, thereby ensuring long-term efficient operation.

[0122] Wide adaptability: Due to the above-mentioned optimized design, the screw rotor of this invention can adapt to more demanding working conditions, especially in special applications such as high pressure, high temperature, or high vacuum.

[0123] Furthermore, the terms "upper," "lower," "inner," "outer," "front," and "rear" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Unless otherwise specifically stated, the relative steps, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of this invention.

[0124] Of course, the above description is only a specific embodiment of the present utility model and is not intended to limit the scope of the present utility model. All equivalent changes or modifications made to the structure, features and principles described in the claims of the present utility model should be included in the scope of the claims of the present utility model.

[0125] Finally, it should be noted that the above-described embodiments are merely specific implementations of this utility model, used to illustrate the technical solution of this utility model, and not to limit it. The protection scope of this utility model is not limited thereto. Although this utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the technical scope disclosed in this utility model. These modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model, and should all be covered within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the scope of the claims.

Claims

1. A variable-diameter, variable-pitch screw rotor, comprising a left-handed rotor and a right-handed rotor meshing with each other, characterized in that, The end face profiles of the left-hand rotary and the right-hand rotary are the same, both consisting of 7 closed curve segments connected end to end. The 7 curve segments include involute segment AB, circular arc segment BC, tooth tip circular arc segment CD, circular arc segment DE, cycloidal equidistant curve segment EF, tooth root circular arc segment FG, and circular arc conjugate curve segment GA. The arc BC of the left-hand rotor meshes with the conjugate curve A'G' of the arc of the right-hand rotor, and the remaining line segments mesh sequentially according to the respective rotation directions of the left-hand rotor and the right-hand rotor; The pitch of the left-hand rotor and the right-hand rotor varies in segments along the axial direction; The left-hand rotary rotor is cone-shaped from the air inlet end to the air outlet end; The right-hand rotary rotor is cone-shaped from the air inlet to the air outlet.

2. The variable diameter and variable pitch screw rotor according to claim 1, characterized in that, The profile of the involute segment AB is constrained by the base circle radius, the tip radius of the rotor's teeth, and the root radius of the rotor's teeth, and its expression is as follows: Wherein, the initial angle R b R1 represents the base circle radius, R2 represents the rotor tooth tip radius, and R3 represents the rotor tooth root radius.

3. The variable diameter and variable pitch screw rotor according to claim 1, characterized in that, The profile of the arc segment BC is constructed by constraining the base circle radius, the rotor's tooth tip circle radius, and the fillet radius of the arc segment BC, and its expression is as follows: Among them, the deflection angle R b R1 represents the base circle radius, R4 represents the tooth tip radius of the rotor, and R5 represents the fillet radius of the arc segment BC.

4. The variable diameter and variable pitch screw rotor according to claim 1, characterized in that, The tooth tip arc segment CD is constructed by constraining the radius of the rotor's tooth tip arc, and its expression is as follows: Where R1 represents the radius of the rotor tooth tip arc.

5. The variable diameter and variable pitch screw rotor according to claim 1, characterized in that, The arc DE is constructed by constraining the fillet radius of DE, and its expression is as follows: Where R3 represents the radius of the tooth root arc DE.

6. The variable diameter and variable pitch screw rotor according to claim 1, characterized in that, The equidistant curve EF is constructed by constraining the pitch circle radius, the rotor tooth tip arc radius, the rotor tooth root arc radius, and the radius of the tooth root arc DE.

7. The variable diameter and variable pitch screw rotor according to claim 1, characterized in that, The tooth root arc segment FG is constructed by constraining the radius of the rotor's tooth root arc, and its expression is as follows: Where R3 represents the radius of the rotor tooth root arc.

8. The variable diameter and variable pitch screw rotor according to claim 1, characterized in that, The conjugate curve segment GA is constructed by constraining the pitch circle radius and the fillet radius of the arc segment BC.

9. The variable diameter and variable pitch screw rotor according to claim 1, characterized in that, Both the left and right rotary rotors are cones that gradually narrow from the air inlet to the air outlet, and the angle between the edge of the cone and the screw is 0 to 5°.

10. A vacuum pump, characterized in that, Including the variable diameter and variable pitch screw rotor as described in any one of claims 1 to 9.

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