CN103062057B - A kind of screw-type vacuum pump - Google Patents

Abstract

The invention discloses a screw type vacuum pump. A screw vacuum pump, the screw vacuum pump includes two rotors with the same shape and opposite rotation directions, the rotors are center-symmetric; the rotors are composed of two center-symmetric blades, and the end surface profile of each blade includes sequential Connected first profile, second profile, third profile, fourth profile and fifth profile, said fifth profile being connected to the first profile of another blade. The invention reduces the workload of many aspects of design and processing, reduces the processing cycle of the rotor, and is beneficial to the popularization and application of screw vacuum pumps and the improvement of work performance. In addition, the rotor of the present invention has only two symmetrical blades, each blade has only five molding lines, and the rotor structure is relatively simple, which further reduces the workload of design and processing.

Description

A screw vacuum pump

technical field

The invention relates to the field of pump body manufacture, and more specifically relates to a screw vacuum pump.

Background technique

The screw vacuum pump is an ideal dry pump that appeared in the 1990s. It has great application prospects and development potential, and occupies a very important position in the vacuum pump market. The dry screw vacuum pump uses a pair of screws to perform synchronous high-speed reverse rotation in the pump casing to generate suction and exhaust. Its main advantages are compact structure, long life, good dynamic balance, no need for lubrication and high pumping speed. It is mainly used in high-purity vacuum process. The vacuum degree is extremely high, and it can adapt to harsh working conditions. It has the ability to extract condensate and particle-containing gases, and is especially suitable for the fields of electronics, chemical industry, and medicine.

The claw-type dry vacuum pump is a non-contact dry vacuum pump with a large compression ratio, which can directly discharge the atmosphere and handle solid particles. The pump is a positive displacement vacuum pump, and its working cycle can be divided into three processes: suction, compression and exhaust. Its core element is a pair of intermeshing rotors used for air extraction, and the design of the rotor profile is the key technology. Different tooth profiles directly determine the technical performance of the vacuum pump's ultimate vacuum, pumping speed, volumetric efficiency, vibration and other parameters.

An existing claw-type dry vacuum pump is shown in Fig. 1, and the profile line of the rotor end surface is the intersection line between the rotor tooth surface and the vertical plane of the rotor axis. If the profiled wire on the end surface rotates at a constant speed around the Z axis and moves at a constant speed along the Z axis, the curved surface formed by the profiled wire on the end surface in space is the tooth surface of the screw rotor.

The shape of the pair of rotors of the special claw vacuum pump is different, in which the first rotor is composed of arcs, straight lines and cycloids, and the contour line of the second rotor is the conjugate line of the first rotor. The composition of the first rotor profile is: segment AB is a cycloid, which is conjugate to the sharp point on the right side of the second rotor; segment BC is a circular arc with a radius of R1, and the center of the circle is at point O1; segment CD is a straight line, parallel On the X-axis and the distance from the X-axis is R1, tangent to the BC arc; the DE segment is an arc, the radius is R2, and the center of the circle is O2; the EF segment is a straight line, which is parallel to the y-axis and tangent to the arc DE ; The FG section is also a cycloid, which is conjugate to the point F on the rotor 2 and symmetrical to the center of the AB section.

This special claw-shaped line has a high volume utilization coefficient and pumping speed, and has good overall performance, but the design of the rotor is complicated and the processing process is troublesome, which increases the processing cycle of the rotor and affects its popularization and application and working performance. improve.

Contents of the invention

The technical problem to be solved by the invention is to provide a screw type vacuum pump which can simplify the design and facilitate the processing.

The purpose of the present invention is achieved through the following technical solutions:

A screw vacuum pump, the screw vacuum pump includes two rotors with the same shape and opposite directions of rotation, the rotors are center-symmetric; the rotors are composed of two center-symmetric blades, and the end surface profile of each blade consists Connected first profile, second profile, third profile, fourth profile and fifth profile, said fifth profile being connected to the first profile of another blade.

Further, it is assumed that the boundary line of the two blades of the rotor is the X axis, and the symmetrical center of the rotor is the first intersection point; the intersection of the fifth shape line and the X axis forms a second intersection point; the first intersection point is on the X axis; the The first profile is an arc of the dedendum, and the included angle formed around the first intersection point is α ₁ ; the second profile is the envelope generated by the third profile of another rotor, which is formed around the first intersection point The included angle is α ₂ ; the third type line is an equal-angle helix or arc, and the included angle formed around the first intersection point is α ₃ ; the fourth type line is the addendum arc, which forms around the first intersection point The included angle is α ₄ ; the fifth-type line is a cycloid, one end of which is connected to the endpoint of the fourth-type line, and the other end is connected to the second intersection point; the α ₁ +α ₂ +α ₃ +α ₄ = 180°. The profile line of the rotor in this technical solution is composed of cycloids, contour lines and the continuous and smooth connection of the inner and outer circles of the rotor. This profile will not interfere with the meshing line. This profile can achieve complete sealing and the sealing line is short. . Although this type of line also has leakage triangles, the leakage between stages is small and the area utilization factor is high, so the pumping efficiency is high.

The most difficult part of the entire rotor tooth surface is the concave tooth surface, which requires high shape accuracy and position accuracy, so as to ensure the pumping performance of the pump. However, the tooth profile structure of the rotor in this technical solution is relatively simple, except that the profile line corresponding to the fifth profile line is a concave tooth surface (the profile line of the end surface is concave, and the tooth surface formed by scanning), the other tooth surfaces are straight tooth surfaces, which is convenient Manufacturing.

Further, the equation of the first type of line is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\ζ}\right)=R_r\cos \mathrm{\ζ}\\ {\mathrm{the\; y}}_1\left(\mathrm{\ζ}\right)=R_r\sin \mathrm{\ζ}\end{array}\right.$ π-α ₁ ≤ζ≤π

Where ζ is the angle between any point on the first profile line and the first intersection point and the X-axis; R _r is the radius of the dedendum arc with the first intersection point as the center.

Further, the second profile is an envelope generated by the third profile of another rotor, its radius of curvature ρ>0, and its parameter equation is:

Wherein ζ is the angle between any point of the second profile line and the first intersection point and the X-axis; is the rotor angle, a is the rotor center distance; O ₁ is the first intersection point, O ₁₁ is the second intersection point; |O ₁ O ₁₁ | is the distance between the first intersection point and the second intersection point; Rt is the radius of the addendum circle, and r ₁ is the radius of the meshing circle.

Further, the third type line is a circular arc centered at the second intersection point, and its parameter equation is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\ζ}\right)=l+R^{\′}\cos \mathrm{\ζ}\\ {\mathrm{the\; y}}_1\left(\mathrm{\ζ}\right)=R^{\′}\sin \mathrm{\ζ}\end{array}\right.$ α ₄ ≤ζ≤π/2

Among them, ζ is the angle between any point of the third model line and the second intersection point and the X axis; R' is the arc radius of the third model line.

Further, the fourth type line is an arc on the addendum circle centered at the first intersection point, and its parameter equation is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\ζ}\right)=R_t\cos \mathrm{\ζ}\\ {\mathrm{the\; y}}_1\left(\mathrm{\ζ}\right)=R_t\sin \mathrm{\ζ}\end{array}\right.$ 0≤ζ≤α ₄

Where ζ is the angle between any point of the fourth profile and the first intersection point and the X-axis; Rt is the radius of the addendum circle.

Further, the fifth type line is a cycloid generated by the meshing circle as the base circle and the meshing circle of another rotor, and its parameter equation is:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.$

Where ζ is the angle between any point on the fifth profile and the first intersection point and the X-axis; Rt is the radius of the addendum circle.

Further, the equation of the first type of line is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\&zeta;}\right)=R_r\cos \mathrm{\&zeta;}\\ {\mathrm{the\; y}}_1\left(\mathrm{\&zeta;}\right)=R_r\sin \mathrm{\&zeta;}\end{array}\right.$ π-α ₁ ≤ζ≤π

The second profile is an envelope generated by the third profile of another rotor, its radius of curvature ρ>0, and its parameter equation is:

The third type line is a circular arc with the second intersection point as the center, and its parameter equation is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\&zeta;}\right)=l+R^{\&prime;}\cos \mathrm{\&zeta;}\\ {\mathrm{the\; y}}_1\left(\mathrm{\&zeta;}\right)=R^{\&prime;}\sin \mathrm{\&zeta;}\end{array}\right.$ α ₄ ≤ζ≤π/2

The fourth profile is an arc on the addendum circle with the first intersection as the center, and its parameter equation is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\&zeta;}\right)=R_t\cos \mathrm{\&zeta;}\\ {\mathrm{the\; y}}_1\left(\mathrm{\&zeta;}\right)=R_t\sin \mathrm{\&zeta;}\end{array}\right.$ 0≤ζ≤α ₄

The fifth type line is a cycloid generated by the meshing circle as the base circle and the meshing circle of another rotor, and its parameter equation is:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.$

Among them, the parameter ζ of the third profile is the angle between any point of the third profile and the second intersection point and the X-axis, and the parameter ζ of the other profile lines is the connection line between any point of the corresponding profile line and the first intersection point and X The included angle of the shaft; R _r is the radius of the dedendum arc centered at the first intersection point; is the rotor angle, a is the rotor center distance; O ₁ is the first intersection point, O ₁₁ is the second intersection point; |O ₁ O ₁₁ | is the distance between the first intersection point and the second intersection point; Rt is the radius of the addendum circle, r ₁ is the radius of the meshing circle; R' The arc radius of the tertiary line.

Further, the screw rod Rt=60mm, Rr=20mm, r1=40mm, a=Rt+Rr=2r1=80mm, Po=60mm, pumping speed n=3000r/min, and the Po is the thread pitch.

The inventors have found that the existing rotor profiles are diverse, and the calculation and solution of the conjugate curve is more complicated, which brings a lot of inconvenience to the design work. At the same time, the profile lines of the two conjugate rotors are not the same, which causes troubles in the processing of the rotors. The processing cycle of the rotor is increased, which affects its popularization and application and the improvement of work performance. Since the present invention uses two rotors with exactly the same shape, and the center of the rotors is symmetrical, as long as the profile line of a symmetrical part of one rotor is designed, the profile line of the other part can be obtained, thereby obtaining the profile line of the entire rotor. Greatly reduce the workload of design, processing, etc., and reduce the processing cycle of the rotor, which is beneficial to the popularization and application of screw vacuum pumps and the improvement of work performance; in addition, the rotor of the present invention has only two symmetrical blades, and each blade has only Five molding lines, the rotor structure is relatively simple, which further reduces the workload of design and processing.

Description of drawings

Fig. 1 is the rotor schematic diagram of existing a kind of screw vacuum pump;

Fig. 2 is a profile schematic diagram of the rotor of the embodiment of the present invention;

Fig. 4 is a schematic diagram of a rotor tooth surface of a rotor according to an embodiment of the present invention;

Fig. 3 is a schematic diagram of area utilization of the rotor according to the embodiment of the present invention.

Detailed ways

A screw vacuum pump comprises two rotors with the same shape and opposite directions of rotation, and the rotors are center symmetrical.

The inventors have found that the existing rotor profiles are diverse, and the calculation and solution of the conjugate curves is more complicated, which brings a lot of inconvenience to the design work. At the same time, the profile lines of the two conjugate rotors are different, causing troubles in the processing of the rotors, and adding The processing cycle of the rotor is increased, which affects its popularization and application and the improvement of work performance. Since the present invention uses two rotors with exactly the same shape, and the center of the rotors is symmetrical, as long as the profile line of a symmetrical part of one rotor is designed, the profile line of the other part can be obtained, thereby obtaining the profile line of the entire rotor. It greatly reduces the workload of many aspects of design and processing, reduces the processing cycle of the rotor, and is beneficial to the popularization and application of screw vacuum pumps and the improvement of work performance.

The present invention will be further described below in conjunction with the accompanying drawings and preferred embodiments.

Rotor end profile line: the intersection line between the rotor tooth surface and the vertical plane of the rotor axis.

Rotor tooth surface: If the end surface profile is rotated at a constant speed around the Z axis, and at the same time moves along the Z axis at a constant speed, the curved surface formed by the end surface profile in space is the screw rotor tooth surface.

Conjugate curve: The conjugate curve ensures that the two curves are continuously tangent and envelope each other during the meshing process.

Envelope: In geometry, the envelope of a family of curves is a curve that is tangent to every line of the family of curves at least at one point. (The curve family is an infinite set of some curves, and they have some specific relationships. In soil mechanics, the stress-strain relationship of soil determined by multiple limit Mohr stress circles is a straight line.)

Area utilization coefficient: The so-called area utilization coefficient or area utilization refers to the ratio of the cross-sectional area contained between the surface curve of the rotor and the surface of the pump inner chamber to the cross-sectional area of the pump chamber when viewed from the cross-section of the pump chamber.

As shown in Figure 2, the screw vacuum pump includes two rotors with the same shape and opposite rotation, and the rotors are center-symmetric. The rotor is composed of two centrally symmetrical blades, and the end surface profile of each blade includes the first profile, the second profile, the third profile, the fourth profile and the fifth profile, the fifth profile connected with the first type line of another blade;

Let the intersection line of the two blades of the rotor be the X-axis, and the symmetrical center of the rotor be the first intersection point; the second intersection point is formed by the intersection of the fifth shape line and the X-axis; the first intersection point is on the X-axis; the first shape line is a section of tooth The root arc, the angle formed around the first intersection point is α ₁ ; the second profile is the envelope generated by the third profile line of another rotor, and the angle formed around the first intersection point is α ₂ ; The third type line is an equal-angle helix or arc, and the included angle formed around the first intersection point is α ₃ ; the fourth type line is the addendum arc, and the included angle formed around the first intersection point is α ₄ ; The fifth-type line is a cycloid, one end of which is connected to the end point of the fourth-type line, and the other end is connected to the second intersection point; α ₁ +α ₂ +α ₃ +α ₄ =180°.

The equation of section a1-b1 of the first molded line is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\&zeta;}\right)=R_r\cos \mathrm{\&zeta;}\\ {\mathrm{the\; y}}_1\left(\mathrm{\&zeta;}\right)=R_r\sin \mathrm{\&zeta;}\end{array}\right.$ π-α ₁ ≤ζ≤π(1)

The second profile b1-c1 section is an envelope generated by the third curve of another rotor, and this section of profile line is obtained according to the principle of meshing with the c2d2 section of the rotor 2. In order to ensure that the envelope curve of section b1c1 is smooth, the curve conjugated to section c2d2 on rotor 2 should be convex, that is, its radius of curvature ρ>0. The parameter equation of section c2d2 of profile line of rotor 2 is

$\left\{\begin{array}{c}{x}_2\left(\mathrm{\&zeta;}\right)=l+R^{\&prime;}\cos \mathrm{\&zeta;}\\ {\mathrm{the\; y}}_2\left(\mathrm{\&zeta;}\right)=R^{\&prime;}\sin \mathrm{\&zeta;}\end{array}\right.$ α ₄ ≤ζ≤π/2(2)

In the formula, R'＝|O ₁₁ c ₁ | is the arc radius of c2d2 section,

Transform the coordinates of formula (2) to get

formula, is the rotor angle, a is the rotor center distance. Equation (3) is the curve family equation, and the envelope supplementary condition

Arranged by formula (3) (4)

Combining formulas (3) and (5) is the equation of the type line segment b1c1.

The c1-d1 segment of the third molded line is a circular arc with the second intersection point as the center, and its parameter equation is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\&zeta;}\right)=l+R^{\&prime;}\cos \mathrm{\&zeta;}\\ {\mathrm{the\; y}}_1\left(\mathrm{\&zeta;}\right)=R^{\&prime;}\sin \mathrm{\&zeta;}\end{array}\right.$ α ₄ ≤ζ≤π/2(6)

The fourth profile line d1-e1 is an arc on the addendum circle centered at the first intersection point, and its parameter equation is:

$\left\{\begin{array}{c}{x}_1\left(\mathrm{\&zeta;}\right)=R_t\cos \mathrm{\&zeta;}\\ {\mathrm{the\; y}}_1\left(\mathrm{\&zeta;}\right)=R_t\sin \mathrm{\&zeta;}\end{array}\right.$ 0≤ζ≤α ₄ (7)

The segment e1-f1 of the fifth type line is a cycloid generated by the meshing circle as the base circle and the meshing circle of another rotor, and its parameter equation is:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Wherein the parameter ζ of the third profile is the angle between any point of the third profile and the second intersection point and the X-axis, and the parameter ζ of the other profile lines is the connection line between any point of the corresponding profile line and the first intersection point and X The included angle of the axis; R _r is the radius of the dedendum arc centered at the first intersection point; is the rotor angle, a is the rotor center distance; O ₁ is the first intersection point, O ₁₁ is the second intersection point; |O ₁ O ₁₁ | is the distance between the first intersection point and the second intersection point; Rt is the radius of the addendum circle, r ₁ is the radius of the meshing circle; R' The arc radius of the tertiary line.

The profile line of the end surface of the rotor in this embodiment is composed of cycloids, contour lines, and the continuous and smooth connection of the inner and outer circles of the rotor. This profile will not interfere with the meshing line. This profile can achieve complete sealing, and the sealing line is short. . Although this type of line also has leakage triangles, the leakage between stages is small and the area utilization factor is high, so the pumping efficiency is high.

As shown in Figure 3, the most difficult part of the entire rotor tooth surface is the concave tooth surface, which requires high shape accuracy and position accuracy, so as to ensure the pumping performance of the pump. However, the tooth structure of the rotor in this technical solution is relatively simple, except that the profile line corresponding to the fifth profile line is a concave tooth surface (the profile line of the end surface is concave, and the tooth surface formed by scanning), the other tooth surfaces are straight tooth surfaces, which is convenient Manufacturing.

The performance of the screw vacuum pump of the present invention will be illustrated through analysis and demonstration below.

1. Area utilization factor and pumping speed

As shown in Figure 4, the shaded part represents the cross-sectional area of the inner cavity of the screw vacuum pump, and the rest of the non-shaded part is the cross-sectional area included between the surface curve of the rotor and the surface of the pump inner cavity. The area ratio of the unshaded part and the shaded part is The area utilization coefficient, represented by the letter K, reflects the utilization degree of the total area within the diameter range of the rotor, that is, the greater the area utilization ratio, the higher the effective utilization degree of the pump cavity.

Referring to Figure 4, we can see that:

$\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

A2, A3, and A5 are all fan-shaped, and the areas are

${\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}$

A ₃ =γ ₃ R′ ² /2

${\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}$

Among them, γ ₂ , γ ₃ and γ ₅ are the radians corresponding to the sector respectively.

The corresponding area can be obtained by integrating the equation of the e1f1 section of the end surface profile

${\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; \&Integral;</span>\mathrm{<span\; class="notranslate">\; wx</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; +</span>{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}$

$<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}$

in $\mathrm{\&phi;}=\arccos \frac{r_1}{R_t}$

Integrate equation (3) to get its corresponding area

in,

Theoretical pumping speed S: It is the volume of gas discharged by the pump per unit time, that is, the gas of a volume between the teeth discharged by the screw rotor rotating one revolution. Because there are two screws meshing and rotating, it needs to be multiplied by a factor of 2, so the theoretical pumping speed is

S＝2nπPKR _t ² (10)

In the formula, n is the screw rotor speed, and P is the screw lead.

1. Quantitative example of rotor end profile parameters

Now give an example to quantitatively illustrate the superiority of the rotor end profile of the present invention: screw rod Rt=60mm, Rr=20mm, r1=40mm, a=Rt+Rr=2r1=80mm, Po=60mm, pumping speed n=3000r/min, According to the above formula, the screw lead P=360mm, A1=345.4mm, A2=936mm, A3=1204.9mm, A4=381.5mm, A5=104mm can be obtained, and the area utilization factor can be obtained according to the formula (9)

$\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 936</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1204.9</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 381.5</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 104</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 345.4</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; 60</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.6</span>}$

Since the ratio of the diameter of the rotor root circle to the diameter of the addendum circle, that is, the ratio of the inner and outer diameters of the rotor ρ, is an important factor affecting the theoretical pumping speed, its range should be between 0.30 and 0.65. The smaller the ρ, the larger the theoretical pumping speed S and the higher the efficiency. In this example, ρ=0.33. The area utilization factor of this type of line has been greatly improved, reaching 60%, and its theoretical pumping speed has been simultaneously improved.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (3)

1. A screw vacuum pump, characterized in that, the screw vacuum pump comprises two rotors identical in shape and opposite in direction of rotation, and the rotors are centrally symmetrical; the rotors are composed of two centrally symmetrical blades, each blade The profiled lines of the end face include the first profiled line, the second profiled line, the third profiled line, the fourth profiled line and the fifth profiled line connected in sequence, and the fifth profiled line is connected with the first profiled line of another blade; Let the intersection line of the two blades of the rotor be the X axis, and the symmetrical center of the rotor be the first intersection point; the intersection of the fifth type line and the X axis forms the second intersection point; the first intersection point is on the X axis; the first type The line is a segment of dedendum arc, and the angle it forms around the first intersection point is α ₁ ; the second profile is the envelope generated by the third profile line of another rotor, and the angle it forms around the first intersection point is is α ₂ ; the third type line is an equal-angle helix or arc, and the included angle formed around the first intersection point is α ₃ ; the fourth type line is the addendum arc, and the included angle formed around the first intersection point is α ₄ ; the fifth-type line is a cycloid, one end of which is connected to the endpoint of the fourth-type line, and the other end is connected to the second intersection point; the α ₁ +α ₂ +α ₃ +α ₄ =180° ; The equation of the first type of line is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}$ Wherein ζ is the angle between any point of the first profile line and the first intersection point and the X-axis; R _r is the radius of the dedendum arc with the first intersection point as the center; The second profile is an envelope generated by the third profile of another rotor, its radius of curvature ρ>0, and its parameter equation is: Wherein ζ is the angle between any point of the second profile line and the first intersection point and the X-axis; is the rotor angle, a is the rotor center distance; O ₁ is the first intersection point, O ₁₁ is the second intersection point; |O ₁ O ₁₁ | is the distance between the first intersection point and the second intersection point; Rt is the radius of the addendum circle, r ₁ is the radius of the meshing circle; The third type line is a circular arc with the second intersection point as the center, and its parameter equation is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}$ Wherein ζ is the angle between any point of the third profile line and the connection line of the second intersection point and the X axis; the arc radius of the R' third profile line; The fourth profile is an arc on the addendum circle with the first intersection as the center, and its parameter equation is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}$ Where ζ is the angle between any point of the fourth profile line and the first intersection point and the X-axis; Rt is the radius of the addendum circle; The fifth type line is a cycloid generated by the meshing circle as the base circle and the meshing circle of another rotor, and its parameter equation is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.$ Where ζ is the angle between any point on the fifth profile and the first intersection point and the X-axis; Rt is the radius of the addendum circle. 2. A kind of screw vacuum pump as claimed in claim 1, is characterized in that, the equation of described first molding line is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}$ The second profile is an envelope generated by the third profile of another rotor, its radius of curvature ρ>0, and its parameter equation is: The third type line is a circular arc with the second intersection point as the center, and its parameter equation is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}$ The fourth profile is an arc on the addendum circle with the first intersection as the center, and its parameter equation is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}$ The fifth type line is a cycloid generated by the meshing circle as the base circle and the meshing circle of another rotor, and its parameter equation is: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&zeta;</span>}\end{array}\right.$ Among them, the parameter ζ of the third profile is the angle between any point of the third profile and the second intersection point and the X-axis, and the parameter ζ of the other profile lines is the connection line between any point of the corresponding profile line and the first intersection point and X The included angle of the shaft; R _r is the radius of the dedendum arc centered at the first intersection point; is the rotor angle, a is the rotor center distance; O ₁ is the first intersection point, O ₁₁ is the second intersection point; |O ₁ O ₁₁ | is the distance between the first intersection point and the second intersection point; Rt is the radius of the addendum circle, r ₁ is the radius of the meshing circle; R' The arc radius of the tertiary line. 3. A screw vacuum pump as claimed in claim 2, characterized in that, said screw Rt=60mm, Rr=20mm, r1=40mm, a=Rt+Rr=2r1=80mm, Po=60mm, pumping speed n=3000r/min, the Po is the thread pitch.