Variable-diameter variable-pitch screw rotor and vacuum pump

Abstract

The variable-diameter variable-pitch screw rotor comprises a left rotor and a right rotor which are meshed with each other, the end face molded lines of the left rotor and the right rotor are the same, and each of the left rotor and the right rotor is formed by connecting seven sections of curves end to end in a closed mode. Wherein the seven sections of curves comprise an involute section AB, a circular arc section BC, a tooth crest circular arc section CD, a circular arc section DE, a cycloid equidistant curve section EF, a tooth root circular arc section FG and a circular arc conjugate curve section GA; the circular arc BC of the left rotator is meshed with the circular arc conjugate curve A 'G' of the right-handed rotor, and other line segments are sequentially and correspondingly meshed according to the respective rotation directions of the left rotator and the right-handed rotor; the screw pitch of the left rotor and the screw pitch of the right rotor are changed in a segmented mode in the axial direction; the whole left rotator is conical from the air inlet end to the air outlet end; the right-handed rotation rotor is integrally in a conical shape from the air inlet end to the air outlet end. The invention further provides the vacuum pump. The device provided by the invention can effectively improve the internal compression ratio and efficiency of the vacuum pump.

Description

Technical Field

[0001] The present invention belongs to the technical field of vacuum pump design, and particularly relates to a variable-diameter and variable-pitch screw rotor and a vacuum pump. Background Art

[0002] Dry screw vacuum pumps are widely used in fields such as semiconductors, biology, pharmaceuticals, chemicals, aerospace, etc. due to their oil-free operation, low maintenance cost, high vacuum performance, and environmental protection characteristics. As the core component of a dry twin-screw vacuum pump, the performance of the screw rotor directly determines the working efficiency of the pump. Factors such as the end face profile, internal compression ratio, sealing performance, and volume gradient of the screw rotor directly affect the pumping speed, power consumption, and ultimate vacuum degree of the pump. Therefore, optimizing the design of the screw rotor is crucial for improving the pump performance.

[0003] Patent document CN119308848A discloses a symmetric tooth profile variable-pitch twin-screw rotor and a 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, and are both formed by connecting 12 segments of curves end to end. Among them, six segments of curves successively include the top tooth arc ab, the first epicycloid bc, the second epicycloid cd, the bottom tooth arc de, the third epicycloid ef, and the fourth epicycloid fg. The other six segments of curves are centrosymmetrically arranged with the above six segments of curves; the pitch of the male rotor and the female rotor decreases circumferentially from the suction end to the exhaust end.

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

[0005] Although twin-screw vacuum pumps play an important role in industry, there are still multiple challenges in the existing technology. The variable-pitch screw rotor structure commonly used in industry is relatively simple, especially the research on conical screw rotors with variable cross-sections and variable pitches is less, resulting in a relatively large and heavy equipment structure, increasing material consumption and the difficulty of transportation and installation. At the same time, the existing pumps have low power transmission accuracy and efficiency, are prone to vibration and noise, affecting the operation stability and working efficiency of the pump, and due to poor sealing performance, the gas leakage problem is serious, further reducing the pumping efficiency and ultimate vacuum degree. Summary of the Invention

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

[0007] To achieve the first object of the present invention, the following technical solutions are provided: A variable-diameter and variable-pitch screw rotor, comprising a left rotor and a right rotor that mesh with each other. The end face profiles of the left rotor and the right rotor are the same, and both are closed by connecting 7 segments of curves end to end. Among them, the 7 segments of curves include an involute segment AB, an arc segment BC, a tip arc segment CD, an arc segment DE, a cycloidal equidistant curve segment EF, a root arc segment FG, and an arc conjugate curve segment GA;

[0008] The arc BC of the left rotor meshes with the arc conjugate curve A'G' of the right rotor, and the remaining line segments are sequentially meshed in accordance with the respective rotation directions of the left rotor and the right rotor;

[0009] The pitches of the left rotor and the right rotor vary in segments along the axial direction;

[0010] The left rotor is tapered as a whole from the intake end to the exhaust end;

[0011] The right rotor is tapered as a whole from the intake end to the exhaust end.

[0012] In the present invention, at different axial positions from the suction end to the exhaust end of the screw rotor, the tip circle radius R1(z) and the root circle radius R2(z) vary continuously along the axial coordinate Z, and the sum of the radii is constant. A variable cross-section structure is formed by adopting a variable-diameter method; the pitch P(z) varies along the axial direction according to a preset function law; through the coordinated regulation of two parameters, a variable-diameter and variable-pitch screw rotor configuration is achieved.

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

[0014]

[0015] Among them, the initial angle R b represents the base circle radius, R1 represents the tip arc radius of the rotor, and R3 represents the root arc radius of the rotor.

[0016] Specifically, the profile of the arc segment BC is constructed by being constrained by the base circle radius, the tip circle radius of the rotor, and the fillet radius of the arc segment BC, and its expression is as follows:

[0017]

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

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

[0020]

[0021] Among them, R1 represents the tooth tip arc radius of the rotor.

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

[0023]

[0024] Among them, R3 represents the radius of the tooth root arc DE.

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

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

[0027]

[0028] Among them, R3 represents the tooth root arc radius of the rotor.

[0029] Specifically, the arc conjugate curve segment GA is constructed by being constrained by 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 tapers of the left rotor and the right rotor are both tapers that gradually decrease from the air inlet end to the air outlet end, and the angle between the side of the taper and the screw is 0 to 5°.

[0031] In order to achieve the second object of the present invention, the following technical solution is provided: a vacuum pump, including the variable diameter and variable pitch screw rotor described above.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] By reasonably designing the variation rules of the rotor tooth tip circle radius, tooth root circle radius, and pitch, the structure of the variable diameter and variable pitch screw rotor can be flexibly adjusted, so as to realize the gradient change of the working volume in the pump;

[0034] The variable cross-section and variable pitch structures respectively generate internal compression, and the variable diameter and variable pitch screw rotor simultaneously has these two compression effects, and its internal compression ratio is significantly improved, and a high internal compression ratio can be achieved, thereby improving its working efficiency and performance. Brief Description of the Drawings

[0035] Figure 1 Schematic diagram of the variable diameter and variable pitch screw rotor provided in this embodiment;

[0036] Figure 2 Schematic diagram of the right rotor provided in this embodiment;

[0037] Figure 3 Schematic diagram of the left rotor provided in this embodiment;

[0038] Figure 4 Schematic diagram of the rotor end face profile provided in this embodiment;

[0039] Figure 5 Schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor at different axial sections provided in this embodiment;

[0040] Figure 6 Schematic diagram of the conical helix of the variable diameter and variable pitch screw rotor provided in this embodiment; Detailed implementation manners

[0041] For better understanding of the content of this embodiment, the following is an explanation of the alphabetic variables in advance:

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

[0043] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

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

[0045] As shown in Figure 2 and Figure 3 shown, there are a left rotor and a right rotor, which are precisely meshed with each other. Moreover, the profile line structures and pitch variation laws of the left rotor and the right rotor are exactly the same, except for the difference in the rotation direction.

[0046] The variable-diameter and variable-pitch screw rotors adopt the same set of profile equations, which contain key parameters such as Figure 4 shown, the tip arc radius R1 and the root arc radius R3. And the pitch circle radii R2 of the two screw rotors satisfy the following formula:

[0047] 2*R2 = R1 + R3;

[0048] As the change from the suction end to the discharge end occurs, the tip arc radius R1 gradually decreases, while the root arc radius R3 gradually increases, and their sum always remains unchanged. Through this design, it is ensured that the pitch circle radius R2 of the two screw rotors remains unchanged during the entire working process, enabling the rotation axes of the two screw rotors to be placed parallel.

[0049] More specifically, the variable-diameter and variable-pitch screw rotor is overall conical, and its cone angle α cone remains consistent throughout the length of the screw rotor without any change; this cone angle α cone is consistent with the cone angle of the dry twin-screw vacuum pump body; the cone angle α cone is calculated according to the following formula:

[0050]

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

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

[0053] In this embodiment, the value of the cone angle α cone is usually more appropriate between 0 and 5°, and at this time, the comprehensive performance of the rotor is relatively excellent.

[0054] As shown in Figure 4As shown, the profile curve of the screw rotor end face is composed of seven curve segments, namely involute segment AB, circular arc segment BC, tip circular arc segment CD, circular arc segment DE, cycloidal equidistant curve segment EF, root circular arc segment FG, and circular arc conjugate curve segment GA, which are connected end to end in sequence to form a sealed end face profile curve. All the curves in the profile curve are smoothly connected without cusps, which can effectively reduce the leakage of clearance backflow at the cusps. Therefore, it can effectively improve the mechanical performance of the rotor and the overall sealing performance, making the comprehensive performance of the vacuum pump better.

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

[0056]

[0057] where the initial angle

[0058] In Figure 4 , the parametric equations of the circular arc BC are as follows:

[0059]

[0060] where,

[0061] In Figure 4 , the parametric equations of the tip circular arc CD are as follows:

[0062]

[0063] In Figure 4 , the parametric equations of the circular arc DE are as follows:

[0064]

[0065] In Figure 4 , the parametric equations of the cycloidal equidistant curve EF are generated by the geometric constraint relationship between the pitch circle radius R2, the tip circle radius R1, the root circle radius R3, and the meshing circular arc R5. Its corresponding fitted curve segment is the circular arc segment E′D′;

[0066] In Figure 4 , the parametric equations of the root circular arc FG are as follows:

[0067]

[0068] In Figure 4 , the parametric equations of the circular arc conjugate curve GA are generated by the geometric constraint relationship between the pitch circle radius R2 and the meshing circular arc R4. Its corresponding fitted curve segment is the circular arc segment C′B′:

[0069] where,

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

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

[0072] And the profile production method provided by the above embodiment is as follows:

[0073] 1) Definition of parametric equations (as described above): Based on the meshing characteristics of the screw rotor, a profile parametric equation composed of 7 segments of curves is established, covering the addendum circle, the dedendum circle and the transition curve;

[0074] 2) Assignment of key parameters: Input the core parameter values such as the addendum circle radius R1 and the dedendum circle radius R3, and generate each segment of curve through the equation;

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

[0076] Both the left-handed screw rotor and the right-handed screw rotor adopt Figure 4 the same set of profiles shown, which are all composed of 7 segments of curves. They mesh precisely with each other and rotate periodically. During the rotation process:

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

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

[0079] The addendum arc CD of the left rotor meshes with the dedendum arc GF of the right rotor;

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

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

[0082] The dedendum arc FG of the left rotor meshes with the addendum arc DC of the right rotor;

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

[0084] Such asFigure 5 As shown, it is a schematic diagram of the axial cross-section profile gradient design provided in this embodiment, where Figure 5 (a) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅰ axial cross-section; Figure 5 (b) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅱ axial cross-section; Figure 5 (c) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅲ axial cross-section; Figure 5 (d) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅳ axial cross-section; Figure 5 (e) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅴ axial cross-section; Figure 5 (f) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅵ axial cross-section; Figure 5 (g) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅶ axial cross-section; Figure 5 (h) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅷ axial cross-section; Figure 5 (i) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅸ axial cross-section; Figure 5 (g) in it is the schematic diagram of the profile engagement of the variable diameter and variable pitch screw rotor in the Ⅹ axial cross-section.

[0085] The design process is as follows:

[0086] 1) Axial segmentation modeling: The screw rotor is evenly divided into 10 equal parts from the suction end to the discharge end, and 11 axial cross-sections (numbered Ⅰ to Ⅺ) are defined;

[0087] Variable diameter parameter control: On the axial coordinate Z, set the continuous gradient law of the tip circle radius R1(z) and the 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, non-linear or piecewise functions), different variable cross-section structures ( Figure 5 The example is the preferred scheme);

[0090] 3) Section profile generation: At any axial position Z n , substitute the current R1(Z n ) and R3(Z n ) values, and use the same profile equation ( Figure 4 ) to automatically generate the corresponding section profile;

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

[0092] Technical advantages and scalability

[0093] 1) Unified equation drive: All cross-sectional profiles are based on the same parametric equation. Only by adjusting the key radius parameter can it meet the requirements of different working conditions;

[0094] 2) Flexible design of boundaries: By customizing the axial variation laws of R1(z) and R3(z) (such as gradual change rate, curve shape), rotors suitable for specific compression ratios, flow rates or strength requirements can be quickly generated;

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

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

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

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

[0099]

[0100] The variation law of the axial taper in the conical spiral is consistent with the axial variation law of the custom tooth tip circle R1(z) (such as gradual change rate, 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, that is, the variation law of the axial taper in the conical spiral can be obtained.

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

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

[0104] As Figure 6 shown, the positions and profile structures of the suction end cross-sectional profile (a), the exhaust end cross-sectional profile (k) and the intermediate cross-sectional profile (f) in the conical spiral are marked.

[0105] The pitch variation law of the suction section (Z1) is P1. In the preferred embodiment of the present invention, an equal pitch variable cross-section design is adopted. From ω0 to ω1, it is a fixed value Pa, and the pitch value Pa is the largest;

[0106] The pitch variation law of the compression section (Z2) is P2. In the preferred embodiment of the present invention, a variable pitch variable cross-section design is adopted. From ω1 to ω2, it is a gradual change mode, and the pitch gradually decreases from Pa to Pb;

[0107] The pitch variation law of the exhaust section (Z3) is P3. In the preferred embodiment of the present invention, an equal pitch variable cross-section design is adopted. From ω2 to ω3, it is a fixed value Pb, and the pitch value Pb is the smallest;

[0108] By giving z(t)=P(t), that is, adjusting the variation of P1, P2, and P3 along the axis according to a preset function law, a rotor adapted to specific compression ratio, flow rate, or intensity requirements can be flexibly and quickly generated to meet the actual working condition requirements.

[0109] Thus, the specific design method of the variable diameter and variable pitch screw rotor can also be clearly shown:

[0110] 1) Construct a series of variable cross-section profile families through the variable diameter method;

[0111] 2) Determine the pitch variation law and draw a variable pitch conical spiral;

[0112] 3) Insert the corresponding cross-section profiles at the preset pitch positions and perform a scan along the preset spiral;

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

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

[0115] This embodiment also provides a vacuum pump, which includes the above-mentioned variable diameter and variable pitch screw rotor. The vacuum pump adopting the above screw rotor can significantly improve the pumping speed, internal compression ratio, and ultimate vacuum degree of the twin-screw vacuum pump, and ensure the high efficiency and energy saving of the vacuum pump.

[0116] To sum up, the beneficial effects of the present invention:

[0117] Flexibly adjust the design requirements. By reasonably designing the variation laws of the rotor tip circle radius, root circle radius, and pitch, the structure of the variable diameter and variable pitch screw rotor can be flexibly adjusted, thereby realizing the gradient change of the working volume inside the pump. This design can meet different specific design requirements such as pumping speed and power consumption;

[0118] Double compression effect. The variable cross-section and variable pitch structures respectively produce internal compression, while the variable diameter and variable pitch screw rotor has both of these compression effects at the same time. Therefore, its internal compression ratio is significantly increased, enabling a relatively high internal compression ratio to be achieved, thereby enhancing its working efficiency and performance;

[0119] Compact structure and high energy efficiency. This variable diameter and variable pitch screw rotor has a compact structure and can provide higher working efficiency while occupying a smaller volume and weight, significantly improving energy efficiency and meeting the requirements of harsh working conditions;

[0120] Excellent ultimate vacuum performance. This rotor design enables the pump to more easily reach a higher ultimate vacuum, adapting to a more stringent working environment, especially having obvious advantages in high-vacuum applications;

[0121] Improve the structural stability at the exhaust end. The variable diameter and variable pitch screw rotor effectively avoids the problem of lamination of the conventional variable pitch rotor at the exhaust end, improving the structural stability. This design reduces the clearance reflux leakage, increases the service life, and thus ensures long-term efficient operation;

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

[0123] In addition, the terms "upper", "lower", "inner", "outer", "front", and "rear" are only used for descriptive purposes 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 the present invention.

[0124] Of course, the above are only specific embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Any equivalent changes or modifications made according to the structure, features, and principles described in the scope of the patent application of the present invention should be included within the scope of the patent application of the present invention.

[0125] Finally, it should be noted that: the above embodiments are only specific implementation manners of the present invention, used to illustrate the technical solutions of the present invention, rather than limiting them. The protection scope of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: any person skilled in the art within the technical scope disclosed by the present invention can still modify the technical solutions described in the foregoing embodiments, or can easily think of changes, or make equivalent replacements for some of the technical features; and these modifications, changes, or replacements 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 the present invention, and should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A variable-diameter and variable-pitch screw rotor, comprising a left rotor and a right rotor that mesh with each other, characterized in that, The end face profiles of the left rotor and the right rotor are the same, both of which are closed by connecting 7 curves end to end. The 7 curves include an involute segment AB, an arc segment BC, a tip arc segment CD, an arc segment DE, a cycloidal equidistant curve segment EF, a root arc segment FG, and an arc conjugate curve segment GA; The arc BC of the left rotor meshes with the arc conjugate curve A'G' of the right rotor, and the remaining line segments are meshed in sequence according to the respective rotation directions of the left rotor and the right rotor; The pitches of the left rotor and the right rotor vary in segments along the axial direction; The left rotor is tapered from the intake end to the outlet end as a whole; The right rotor is tapered from the intake end to the outlet end as a whole.

2. The variable-diameter and variable-pitch screw rotor according to claim 1, wherein The profile of the involute segment AB is constructed by constraining with the base circle radius, the tip arc radius of the rotor, and the root arc radius of the rotor. The expression is as follows: radius, R1 represents the tip arc radius of the rotor, and R3 represents the root arc radius of the rotor.

3. The variable diameter and variable pitch screw rotor according to claim 1, wherein The profile of the arc segment BC is constructed by constraining with the base circle radius, the tip circle radius of the rotor, and the fillet radius of the arc segment BC. The expression is as follows: Among them, the deflection angle R b represents the base circle radius, R1 represents the addendum arc radius of the rotor, and R4 represents the fillet radius of the arc segment BC.

4. The variable-diameter and variable-pitch screw rotor according to claim 1, wherein The tip arc segment CD is constructed by constraining with the tip arc radius of the rotor. The expression is as follows: Among them, R1 represents the tip arc radius of the rotor.

5. The variable-diameter and variable-pitch screw rotor according to claim 1, wherein, The arc DE is constructed by constraining with the fillet radius of DE. The expression is as follows: Among them, R3 represents the radius of the root arc DE.

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

7. The variable-diameter and variable-pitch screw rotor according to claim 1, characterized in that, The root arc segment FG is constructed by constraining with the root arc radius of the rotor. The expression is as follows: Among them, R3 represents the root arc radius of the rotor.

8. The variable-diameter and variable-pitch screw rotor according to claim 1, wherein The arc conjugate curve segment GA is constructed by constraining with 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 The tapers of the left rotor and the right rotor are both tapers that gradually narrow from the intake end to the outlet end, and the angle between the side of the taper and the screw is 0 to 5°.

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

Images