A variable pitch screw vacuum pump

Abstract

This invention provides a variable pitch screw vacuum pump, belonging to the field of pump body technology. It solves the problem that existing variable pitch screw vacuum pumps require increased screw length to achieve higher pumping efficiency. This variable pitch screw vacuum pump includes a pump body containing two rotors. Each rotor has K helical turns, and the total length of the rotor is L. The screw pitch from the inlet to the outlet is P1 to Pi, respectively. One rotor is left-handed, and the other is right-handed, and the two rotors mesh with each other. The end face profile of one rotor rotates around the center of rotation by a central angle θ. The rotor has a helical coordinate equation, including X, Y, and Z axes. The outer circumference of the rotor is formed by rotating the curves along the helical curve on the end face profile. The rotor of this variable pitch screw vacuum pump can be adjusted to the optimal pitch for different needs, thereby reducing the rotor length while achieving high pumping efficiency.

Description

Technical Field

[0001] This invention belongs to the field of pump technology and relates to a variable pitch screw vacuum pump. Background Technology

[0002] A screw vacuum pump is a pumping device that uses a pair of screws to rotate synchronously at high speed in opposite directions within the pump casing to generate suction and exhaust.

[0003] Most screw rotors in current screw vacuum pumps are of two types:

[0004] One type is the equal pitch screw. Equal pitch screws are easy to manufacture and are more similar to the rotors of screw gas compressors and screw liquid transfer pumps. On the other hand, the equal pitch screw vacuum pump's non-internal compression exhaust method utilizes the removal of impure gases containing solid particulate impurities or condensable vapors, making it more suitable for dry vacuum pumps.

[0005] Another type is the variable pitch screw, usually a sudden change variable pitch screw. The simplest variable pitch method in terms of geometry is to directly connect two equal pitch screws with the same end face profile but different leads in series, so that the pump's intake and exhaust compression ratio is equal to the lead ratio of the two screws. During the pumping process, the gas to be pumped is drawn in from the longer lead end, and after being transported without compression for a certain distance, it is rapidly compressed at the interface of the two screws within one rotation of the screw. Its volume reduction ratio is equal to the pump's compression ratio. Then, after being transported without compression for a certain distance again, it connects to the exhaust port, the pressure rises to the exhaust pressure, and finally, it is discharged from the pump body together with the backflow gas.

[0006] The two types of screws mentioned above are composed of one or more equal-pitch screws. In actual production, the gas is compressed, and compression can only be performed in one section. During the production process, the working vacuum at the inlet end of the pump body is high. When it approaches the outlet, the pressure difference increases, which leads to a decrease in pumping speed. If the above structure is to achieve a high pumping efficiency, the length of the screw needs to be designed to be relatively long, resulting in a large overall axial length and volume of the pump body. Summary of the Invention

[0007] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a variable pitch screw vacuum pump. The technical problem to be solved by this invention is: how to solve the problem that existing variable pitch screw vacuum pumps require increasing the length of the screw to achieve higher pumping efficiency.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] A variable pitch screw vacuum pump includes a pump body containing two rotors. The rotors have K helical turns, a total length of L, and helical pitches P1 to Pi from the inlet to the outlet. One rotor is left-handed, and the other is right-handed, and the two rotors mesh with each other. The profile of one rotor end face rotates about its rotation center by a central angle θ.

[0010] The equation for calculating the central angle θ is:

[0011] θ = 2Ωkt;

[0012] In the formula, t∈[0~1];

[0013] The coordinate equation of the rotor's helix is:

[0014] X(θ) = R sin θ;

[0015] Y(θ) = R cos θ;

[0016] Z(θ)=P(θ)=LA(1-t)-B(sin(90(1-t))) n ;

[0017] In the formula, R is the distance from any point on the end face profile to the center of rotation, L = A + B, A = KPi, where Pi is the minimum pitch at the exhaust end of the rotor, and A ranges from 0.5L to 0.7L, taking a smaller value when the rotor compression ratio needs to be increased and a larger value when the rotor compression ratio needs to be decreased; n ranges from 10 to 40, taking a larger value when the rotor compression ratio needs to be increased and a smaller value when the rotor compression ratio needs to be decreased. The outer circumferential surface of the rotor is formed by rotating each segment of the curve on the end face profile along the helix.

[0018] The central angle is formed by rotating the rotor around its own axis (Z-axis) at a point on the rotor end face profile. Before rotor forming, the rotor end face profile and the rotor helix need to be determined. Then, the outer circumference of the rotor is formed by rotating the curves of each segment of the rotor end face profile along the helix. In order to minimize the screw length while ensuring high pumping efficiency, a variable pitch rotor is used. Each screw pitch of this variable pitch rotor is different and needs to be designed according to the air pressure at the pump inlet. The central angle θ in the above helix coordinate equation is obtained by the value of the ratio variable t and the change of the number of helical turns k on the rotor, and is determined by the helix from the X-axis, Y-axis, and Z-axis. The overall shape and direction of the spiral, especially the direction of the Z-axis, needs to be determined based on the different pitches of the rotor. Therefore, the helix algorithm on the Z-axis requires the selection of multiple fixed values ​​A, B, and n. These fixed values ​​are determined by the magnitude of the air pressure at the pump inlet. The specific change of the Z-axis spiral is achieved by changing the parameters A and n, which can flexibly obtain different gradual compression ratios, from large to small. This ensures that the formula can adjust the rotor's spiral, i.e., the various pitches of the rotor, according to the specific air pressure at the pump inlet. The rotor can be adjusted to the optimal pitch for different needs, thereby achieving high pumping efficiency while reducing the rotor length.

[0019] In the aforementioned variable pitch screw vacuum pump, when the central angle θ rotates in the opposite direction, the rotors are obtained with opposite helices, and the rotors formed by the rotation of the two helices mesh with each other.

[0020] By rotating in the opposite direction at angle θ, opposite helices can be obtained, thus allowing the rotors derived from the two opposing helices within the variable pitch screw vacuum pump to mesh with each other.

[0021] In the variable pitch screw vacuum pump mentioned above, the value of n is larger when the gas pressure at the pump body inlet is low, and the value of n is smaller when the gas pressure at the pump body inlet is high.

[0022] The value of n is adjusted according to the air pressure at the pump inlet. For example, if the air pressure at the inlet is 3 kPa, n is set to 50, which results in a high compression ratio of the screw rotor and lower shaft power. If the air pressure at the inlet is 30 kPa, n is set to 30, which results in a lower compression ratio of the screw rotor and lower shaft power. Therefore, by adjusting the value of n, the screw pitch can be adjusted for different inlet air pressures to achieve the goal of lower shaft power, reduce the driving power required by the pump body, and further improve the performance and pumping efficiency of the variable pitch screw vacuum pump.

[0023] In the aforementioned variable pitch screw vacuum pump, the formula for calculating the compression power of the variable pitch screw vacuum pump is: P w =S1ΔP1+……+S i ΔPi ,

[0024] In the formula, i = K-1,

[0025] S1……S i Let ΔP1 be the geometric pumping speed of each stage of the rotor, ..., ΔP2. i This represents the pressure difference between each stage of the rotor.

[0026] By selecting appropriate values ​​of A and n based on different inlet pressures, a smaller compression power can be obtained for the variable pitch screw vacuum pump.

[0027] By calculating the compression power of the vacuum pump, the pumping speed can be reduced to 2.46 times when the pressure difference is small. When the pressure difference near the outlet increases, the pumping speed is reduced, thus enabling the variable pitch screw vacuum pump to achieve high energy efficiency.

[0028] In the aforementioned variable pitch screw vacuum pump, the volume of each sealed cavity formed by the rotor and the pump body when the vacuum pump rotates is:

[0029]

[0030] In the formula, S(θ) is the area of ​​the extraction space formed by the meshing of the two rotors at different central angles, and dθ is a variable, θ∈[a~a+4π].

[0031] The above equation is formed by integrating the volume of each sealed cavity segment after taking the area of ​​the air extraction space created by the meshing of the two existing rotors at different central angles, the derivative of the helical coordinate function and the variable dθ. The volume of the sealed cavity formed by the rotor and pump body can be quickly measured when the central angle is constantly changing.

[0032] In the aforementioned variable pitch screw vacuum pump, the end face profiles and outer peripheral surfaces of the two rotors are identical, and the rotating helixes are either left-handed or right-handed.

[0033] This design makes the machining of variable pitch screw vacuum pumps easier and reduces manufacturing costs.

[0034] Compared with existing technologies, this variable pitch screw vacuum pump has the following advantages:

[0035] 1. This formula can flexibly obtain different gradual compression ratios, starting large and decreasing, by changing the parameters A and n. This ensures that the formula can adjust the rotor's helix, i.e., the various pitches of the rotor, according to the specific inlet air pressure of the pump body. The rotor can be adjusted to the optimal pitch for different needs, thereby achieving high pumping efficiency while reducing the rotor length, effectively utilizing space, and saving the overall volume of the variable pitch screw vacuum pump.

[0036] 2. When selecting fixed parameters, the pitch of the screw rotor can be adjusted by the air pressure at the pump body inlet, thereby improving the pumping efficiency of the variable pitch screw vacuum pump. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the rotor in this invention, showing a spiral line.

[0038] Figure 2 This is a front view of the rotor in this invention.

[0039] Figure 3 This is a schematic diagram of the rotor pitch varying with the central angle and taking multiple n values ​​in this invention.

[0040] Figure 4 This is a schematic diagram of the rotor pitch varying with the central angle in this invention, where A is 0.6L and n is 25.

[0041] Figure 5 This is a schematic diagram of the different meshing states of the two rotors rotating from 0° to 330° in this invention.

[0042] Figure 6 This is a schematic diagram of the different meshing states of the two rotors rotating from 360° to 720° in this invention.

[0043] In the diagram, 1 represents the rotor; 2 represents the end face profile; and 3 represents the helix. Detailed Implementation

[0044] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0045] like Figure 1 As shown, this variable pitch screw vacuum pump includes a pump body, within which two rotors 1 are housed. The pump body structure and how to connect it to the pump body can be described using existing technology, therefore, this will not be elaborated upon further, and the accompanying drawings do not provide a schematic representation.

[0046] Specifically, such as Figure 1-6 As shown, rotor 1 has K helical turns, and its total length is L. The pitch of rotor 1 from the intake end to the exhaust end is P1 to Pi. The two rotors 1 are one left-handed and one right-handed, and the two rotors mesh with each other. The angle of rotation of the end face profile of one of the rotors 1 around the center of rotation is the central angle θ.

[0047] The equation for calculating the central angle θ is:

[0048] θ = 2Ωkt;

[0049] In the formula, t∈[0~1];

[0050] The coordinate equation of the helix 3 of rotor 1 is:

[0051] X(θ) = R sin θ;

[0052] Y(θ) = R cosθ;

[0053] Z(θ)=P(θ)=LA(1-t)-B(sin(90(1-t))) n ;

[0054] In the formula, R is the distance from any point on the end face profile 2 to the center of rotation, L = A + B, A = KPi, where Pi is the minimum pitch at the exhaust end of the rotor 1, and A ranges from 0.5L to 0.7L, taking a smaller value when the compression ratio of rotor 1 needs to be increased and a larger value when the compression ratio of rotor 1 needs to be decreased; n ranges from 10 to 40, taking a larger value when the compression ratio of rotor 1 needs to be increased and a smaller value when the compression ratio of rotor 1 needs to be decreased. The outer circumference of rotor 1 is formed by rotating the curves on the end face profile 2 along the spiral line 3. When the central angle θ rotates in the opposite direction, the spiral line 3 of rotor 1 is obtained in the opposite direction. The rotor 1 formed by the rotation of the two spiral lines 3 meshes with each other. The value of n is larger when the air pressure at the pump body inlet end is low and smaller when the air pressure at the pump body inlet end is high.

[0055] The central angle is formed by rotating the rotor 1 around its own axis Z after one point on the end face profile 2 of the rotor 1 rotates. Before the rotor 1 is formed, the end face profile 2 and the helix 3 of the rotor 1 need to be determined. Then, the outer circumference of the rotor 1 is formed by rotating the curves on the end face profile 2 of the rotor 1 along the helix 3. In order to minimize the length of the screw while ensuring high pumping efficiency, a variable pitch rotor 1 is used. Each pitch of the variable pitch rotor 1 is different and needs to be designed according to the air pressure at the pump inlet. The coordinate equation of the helix 3 and the central angle θ are obtained by the value of the ratio variable t and the change of the number of helical turns k on the rotor 1, and by measuring the X-axis, Y-axis and Z-axis. The overall shape and direction of the spiral 3 are determined. The direction of the Z-axis needs to be determined for different pitches of rotor 1. Therefore, in the algorithm of the spiral 3 on the Z-axis, multiple fixed values ​​A, B, and n need to be selected. These fixed values ​​are determined by the magnitude of the air pressure at the pump inlet. The specific change of the spiral 3 on the Z-axis is achieved by changing the parameters A and n. Different gradual compression ratios, starting large and then decreasing, can be flexibly obtained. This ensures that the formula can adjust the spiral 3 of rotor 1, i.e., the various pitches of rotor 1, according to the specific air pressure at the pump inlet. Rotor 1 can be adjusted to the optimal pitch for different needs, thereby reducing the length of rotor 1 while achieving high pumping efficiency.

[0056] The formula for calculating the compression power of a variable pitch screw vacuum pump is: Pw =S1ΔP1+……+S i ΔP i ,

[0057] In the formula, i = K-1,

[0058] S1……S i Let ΔP1 be the geometric pumping speed of each stage of rotor 1, ..., ΔP i Given the pressure difference of each stage of rotor 1, appropriate values ​​of A and n are selected based on different inlet pressures to obtain a smaller compression power of the variable pitch screw vacuum pump.

[0059] The rotor 1 of the variable pitch screw vacuum pump rotates, and each section of the seal formed by the rotor and the pump body

[0060] The cavity volume is:

[0061]

[0062] In the formula, S(θ) is the area of ​​the air extraction space formed by the meshing of the two rotors 1 at different central angles, and dθ is a variable, θ∈[0~4π].

[0063] The end face profiles 2 and outer peripheral surfaces of the two rotors 1 are identical, and the rotating helix 3 is divided into left-handed and right-handed.

[0064] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A variable pitch screw vacuum pump, comprising a pump body, wherein the pump body is provided with two rotors (1), characterized in that, The rotor (1) has K spiral turns, the total length of the rotor (1) is L, the pitch of the rotor (1) from the intake end to the exhaust end is P1 to Pi, the two rotors (1) are one left-handed and one right-handed respectively, and the two rotors (1) mesh with each other, the end face profile (2) of one of the rotors (1) rotates around the rotation center by a central angle θ. The equation for calculating the central angle θ is: θ = 2Ωkt; In the formula, t∈[0~1]; The coordinate equation of the helix (3) of the rotor (1) is: X(θ) = R sinθ; Y(θ) = R cosθ; Z(θ)=P(θ)=LA(1-t)-B(sin(90(1-t))) n ; In the formula, R is the distance from any point on the end face profile (2) to the center of rotation, L = A + B, A = KPi, where Pi is the minimum pitch of the exhaust end of the rotor (1), and the range of A is 0.5L to 0.7L. When the compression ratio of the rotor (1) needs to be increased, a smaller value is taken, and when the compression ratio of the rotor (1) needs to be decreased, a larger value is taken; the range of n is 10 to 40. When the compression ratio of the rotor (1) is increased, a larger value is taken, and when the compression ratio of the rotor (1) needs to be decreased, a smaller value is taken. The outer circumferential surface of the rotor (1) is formed by rotating along the spiral line (3) through the curves of each segment on the end face profile (2).

2. The variable pitch screw vacuum pump according to claim 1, characterized in that, When the central angle θ rotates in the opposite direction, a helix (3) opposite to that of the rotor (1) is obtained, and the rotor (1) formed by the rotation of the two helixes (3) meshes with each other.

3. The variable pitch screw vacuum pump according to claim 1 or 2, characterized in that, The value of n is larger when the air pressure at the pump inlet is low, and the value of n is smaller when the air pressure at the pump inlet is high.

4. The variable pitch screw vacuum pump according to claim 1 or 2, characterized in that, The formula for calculating the compression power of the variable pitch screw vacuum pump is: P w =S1ΔP1+……+S i ΔP i , In the formula, i = K-1, and K is the number of spiral turns mentioned above; S1……S i Let ΔP1……ΔP be the geometric pumping speed of each stage of rotor (1). i The pressure difference is the pressure difference of each stage of the rotor (1).

5. The variable pitch screw vacuum pump according to claim 1 or 2, characterized in that, When the rotor (1) of the variable pitch screw vacuum pump rotates, the volume of each sealed cavity formed by the rotor (1) and the pump body is: In the formula, S(θ) is the area of ​​the air extraction space formed by the meshing of the two rotors (1) at different central angles, and dθ is a variable, θ∈[0~4π].

6. The variable pitch screw vacuum pump according to claim 1 or 2, characterized in that, The end face profiles (2) and outer circumferences of the two rotors (1) are the same, and the rotating helixes (3) are divided into left-handed and right-handed.

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