A screw vacuum pump

Abstract

The present invention provides a screw vacuum pump, belonging to the technical field of vacuum equipment. It solves the problem of low pumping efficiency of the existing screw vacuum pump. This screw vacuum pump includes a pump body, and two rotors are arranged in the pump body. The end face profiles of the two rotors are each formed by sequentially connecting six profiles: tooth top arc A1A2, straight line A2A3, curve A3A4, curve A4A5, tooth root arc A5A6, and epicycloid A6A1 end to end. The end point A3 of the straight line A2A3 is located on the pitch circle. The curve A3A4 is the conjugate curve of the straight line A2A3. When the two rotors rotate, the starting point A2 of the straight line A2A3 on one rotor can move along the curve A4A5 on the other rotor, that is, the curve A4A5 on one rotor is the locus line of point A2 on the other rotor. The present invention has the advantages of high pumping efficiency and convenient manufacturing.

Description

Technical Field

[0001] The present invention belongs to the technical field of vacuum equipment and relates to a screw vacuum pump. Background Art

[0002] A screw vacuum pump is a positive displacement vacuum pump. The core component of the screw vacuum pump is a pair of non-contact screw rotors that mesh with each other. The two rotors are finely dynamically balanced and supported by bearings and installed in the pump housing. There is a certain gap between the rotors. Therefore, the design of the rotors needs to achieve non-interference of the tooth surfaces during synchronous meshing motion. The end face profile design of the rotors will directly affect the performance of the screw vacuum pump, such as sealing performance, pumping efficiency, area utilization coefficient, etc., and will also affect the processing cost of the rotors.

[0003] At present, the rotor profiles widely used in the market for screw vacuum pumps mainly include rotor profiles with involute and trochoid, etc. In order to ensure that the rotor profiles can be completely conjugate and the meshing performance of the rotors, the rotor profiles of conventional screw vacuum pumps are formed by connecting multiple curves end to end. For example, a smooth rotor profile of a twin-screw vacuum pump and its design method disclosed in a patent document (Application No.: 201910051620.0), the smooth end face profile of the twin-screw vacuum pump rotor is composed of a circular arc conjugate line a1b1, a circular arc b1c1, a tooth top circular arc c1d1, a parabolic-like curve d1e1, a parabolic-like conjugate line e1f1, and a tooth root circular arc f1a1 that are connected end to end in sequence. The design of this rotor profile has the following deficiencies: The rotor profile of the screw vacuum pump is formed by connecting multiple smooth curves. Although the two rotors can be completely conjugate and have good meshing performance, the rotor with this rotor profile has a larger size, so it will occupy a larger space inside the pump, resulting in a small area utilization coefficient of the vacuum pump and a small flow space for the medium, and thus affecting the pumping efficiency of the vacuum pump; in addition, this rotor profile is formed by connecting six mutually different curves end to end. When processing the curves, there are high processing requirements for the curvature of each curve and the shape of the transition surface at the curve endpoints, etc. Therefore, this rotor also has the disadvantage of high processing difficulty and it is difficult to improve the processing efficiency. Summary of the Invention

[0004] The object of the present invention is to provide a screw vacuum pump in view of the above problems existing in the prior art. The technical problem to be solved by the present invention is: how to improve the pumping efficiency of the screw vacuum pump.

[0005] The object of the present invention can be achieved through the following technical solutions: A screw vacuum pump, comprising a pump body, wherein two rotors are arranged in the pump body, characterized in that the end surface profiles of the two rotors are formed by connecting six segments of profiles, namely, a tooth top arc A1A2, a straight line A2A3, a curve A3A4, a curve A4A5, a tooth root arc A5A6, and an epicycloid A6A1, in sequence, the end point A3 of the straight line A2A3 is located on the pitch circle, and the curve A3A4 is a conjugate curve of the straight line A2A3. When the two rotors rotate, the starting point A2 of the straight line A2A3 on one of the rotors can move close to the curve A4A5 on the other rotor, that is, the curve A4A5 on one of the rotors is the trajectory line of the point A2 on the other rotor.

[0006] The coordinate equation of the straight line A2A3 is:

[0007] x=a+dcost, y=b+dsint;

[0008] The coordinate equation of the curve A3A4 is:

[0009] x=(a+dcost)cos(θ 1 +θ 2 )+(b+dsint)sin(θ 1 +θ 2 )-(R 1 +R 2 )sinθ 2 ,

[0010] y=(a+dcost)sin(θ 1 +θ 2 )-(b+dsint)cos(θ 1 +θ 2 )+(R 1 +R 2 )cosθ 2 ,

[0011] Where a is the x-coordinate value of the starting point A2 of the straight line A2A3, b is the y-coordinate value of the starting point A2 of the straight line A2A3, d is the length of the straight line A2A3, the two rotors are rotor one and rotor two, R 1 is the pitch radius of rotor 1, R 2 is the pitch radius of rotor 2, θ 1 and θ 2 Indicates the angle of rotation of rotor 1 and rotor 2 when they are meshing and rotating, θ 1 / θ 2 =R 2 / R 1 , t is the angle between the straight line A2A3 and the x-axis, which is given by We can get t and θ 1 The functional relationship of .

[0012] In this rotor profile, according to the parameters of the straight line A2A3 such as the x - coordinate value, y - coordinate value, and length, as well as parameters such as the pitch circle radius, substituting them into the coordinate equation of the curve A3A4, the curve A3A4 is obtained. The curve A3A4 and the straight line A2A3 are a pair of conjugate curves, and the point A3 is located on the pitch circle. In this way, when the two rotors rotate, the straight line A2A3 on one rotor can make good contact with the curve A3A4 on the other rotor, avoiding the formation of a leakage area and affecting the pumping efficiency. At the same time, this rotor profile also includes the curve A4A5. When the two rotors rotate, the starting point A2 of the straight line A2A3 on one rotor can move along the curve A4A5 on the other rotor, which can also avoid the formation of a leakage area. Therefore, the design of this rotor profile ensures that after A2A3 adopts a straight line, it can still meet the meshing performance requirements between rotor one and rotor two, can avoid the formation of a leakage triangular area and affect the pumping efficiency, and there will be no problem of tooth surface interference of the rotor. And because the straight line A2A3 in this rotor profile adopts a straight - line design, the straight - line part where A2A3 is located is similar to forming a "missing angle", which makes the size of the rotor significantly reduced on the basis of ensuring the meshing performance, reduces the space occupied by the rotor in the pump, and increases the space for gas flow in the pump body, so that the amount of gas flowing through the pump body per unit time increases, and further improves the pumping efficiency of the vacuum pump.

[0013] In addition, after A2A3 adopts a straight line, there is no requirement for the machining of the curvature size. During machining, a milling cutter can be used to mill back and forth to form it, which can further reduce the machining difficulty. At the same time, the straight - line part of A2A3 can also be used as the reference of the tooling fixture, making the assembly and manufacturing of the screw vacuum pump more convenient. At the same time, the straight line A2A3 and the curve A4A5 are transitioned by a curve A3A4 with a small radian, so that the straight line A2A3 and the curve A3A4 are smoothly transitioned to form a smooth surface with a common machining possibility, which can significantly improve the machining efficiency of the rotor.

[0014] In the above - mentioned screw vacuum pump, the included angle t value between the straight line A2A3 and the x - axis is + 12 degrees to - 12 degrees. Preferably, the t value is + 10 degrees. In the straight line A2A3, the coordinate equation of its starting point A2 is: x = B 1 cosθ, y = B 1 sinθ, where θ is the included angle between the connection line from the starting point A2 of the straight line to the rotation center O of the rotor and the x - axis. After selecting a point on the tooth tip arc, both the x - coordinate value a and y - coordinate value b of A2 are determined. After selecting an appropriate t value, the length of the straight line A2A3 and the position of the end point A3 are also determined.

[0015] In the above - mentioned screw vacuum pump, the coordinate equation of the curve A4A5 is:

[0016] x = B 2 cosθcos(θ 1 + θ 2 ) + B 2 sinθsin(θ 1 + θ 2 ) - (R 1 + R 2 )sinθ 2 ,

[0017] y = B 2 cosθsin(θ 1 + θ 2 ) - B 2 sinθcos(θ 1 + θ 2 ) + (R 1 + R 2 )cosθ 2 ,

[0018] wherein, B 2 is the addendum arc radius dimension of the second rotor.

[0019] This design enables a smooth connection between the root arc A5A6 and the curve A3A4 by the curve A4A5. This not only ensures that the rotor forms a fully sealed profile without leakage triangles but also constitutes a smooth surface with the possibility of common machining, thus improving the machining efficiency.

[0020] In the above screw vacuum pump, the equation of the epicycloid A6A1 is:

[0021] x = Csinθ 1 - Dsin(θ 1 + θ 2 ), y = Ccosθ 1 - Dcos(θ 1 + θ 2 ),

[0022] wherein, C = R 1 + R 2 , C is the center distance between the first rotor and the second rotor, and D is the distance from the center of the moving circle to the cycloid.

[0023] In the above screw vacuum pump, the end profiles of the first rotor and the second rotor are the same. Such a design makes the machining of the screw vacuum pump more convenient and can reduce the manufacturing cost.

[0024] Compared with the prior art, the present screw vacuum pump has the following advantages:

[0025] 1. In this screw vacuum pump, the rotor profile can not only ensure a smooth transition of the profile, but also form a fully sealed profile, resulting in good meshing performance between Rotor 1 and Rotor 2 and no leakage triangle. Therefore, a very low ultimate vacuum can be achieved, and the pumping efficiency is also improved. Compared with the cycloidal profile on the market, the pumping efficiency is increased by at least two percentage points.

[0026] 2. The design of this screw vacuum pump can reduce the size of the rotor, providing a larger flow space for the medium inside the pump, thereby improving the pumping efficiency of the screw vacuum pump. Description of the Drawings

[0027] Figure 1 is a schematic view of the end face profile of Rotor 1 in this screw vacuum pump Figure 1 。

[0028] Figure 2 is the meshing state of Rotor 1 and Rotor 2 in this screw vacuum pump Figure 1 。

[0029] Figure 3 is a schematic view of the end face profile of Rotor 1 in this screw vacuum pump Figure 2 。

[0030] Figure 4 is the meshing state of Rotor 1 and Rotor 2 in this screw vacuum pump Figure 2 。

[0031] Figure 5 is the meshing state of Rotor 1 and Rotor 2 in this screw vacuum pump Figure 3 。

[0032] Figure 6 is the meshing state of Rotor 1 and Rotor 2 in this screw vacuum pump Figure 4 。

[0033] Figure 7 is the meshing state of Rotor 1 and Rotor 2 in this screw vacuum pump Figure 5 。

[0034] In the figure, 1. Rotor 1; 2. Rotor 2. Detailed Implementation Modes

[0035] The following are specific embodiments of the present invention in combination with the drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0036] Embodiment 1

[0037] This screw vacuum pump includes a pump body with two rotors disposed therein, namely Rotor 1 and Rotor 2. The structure of the pump body and how Rotor 1 and Rotor 2 are connected to the pump body can adopt existing technologies, so no redundant description will be given herein, and no schematic illustration is provided in the drawings either.

[0038] As Figures 1 to 3 shown, the end face profiles of rotor 1 and rotor 2 of this screw vacuum pump are each formed by sequentially connecting six profiles: tooth tip arc A1A2, straight line A2A3, curve A3A4, curve A4A5, tooth root arc A5A6, and epicycloid A6A1. The tooth tip arc A1A2 is an arc curve with R = B 1 , where B 1 is the tooth tip arc radius dimension of rotor 1. The starting point A2 of the straight line A2A3 is located on the tooth tip arc and the ending point A3 is located on the pitch circle. The curve A3A4 is the conjugate curve of the straight line A2A3. The tooth root arc A5A6 is an arc curve with R = C - B 2 , where B 2 is the tooth tip arc radius dimension of rotor 2.

[0039] When the two rotors of this screw vacuum pump rotate, as Figure 2 , Figure 4 and Figure 5 shown, the straight line A2A3 on one rotor can contact the curve A3A4 on the other rotor. And, as Figure 6 shown, the starting point A2 of the straight line A2A3 on one rotor can move along the curve A4A5 on the other rotor. Therefore, the design of this rotor profile ensures that after A2A3 adopts a straight line, it can still meet the meshing performance requirements between rotor 1 and rotor 2, can avoid forming a leakage triangular area that affects the pumping efficiency, and there will be no tooth surface interference problem of the rotor.

[0040] Specifically, the coordinate equation of the straight line A2A3 is:

[0041] x = a + dcost, y = b + dsint, where a is the x - coordinate value of the starting point A2 of the straight line A2A3, b is the y - coordinate value of the starting point A2 of the straight line A2A3, d is the length of the straight line A2A3, and t is the angle between the straight line A2A3 and the x - axis. Preferably, the value of the angle t between the straight line A2A3 and the x - axis is +10 degrees.

[0042] The coordinate equation of the curve A3A4 is:

[0043] x = (a + dcost)cos(θ 1 + θ 2 )+(b + dsint)sin(θ 1 + θ 2 )-(R 1 + R 2 )sinθ 2

[0044] y = (a + dcost)sin(θ 1 + θ2 ) - (b + dsin t)cos(θ 1 + θ 2 ) + (R 1 + R 2 )cosθ 2

[0045] In the formula, R 1 is the pitch circle radius of rotor 1, R 2 is the pitch circle radius of rotor 2, θ 1 and θ 2 represent the respective rotation angles of rotor 1 and rotor 2 during meshing rotation, θ 1 / θ 2 = R 2 / R 1 , from formula the functional relationships of t and θ 1 can be obtained.

[0046] In the straight line A2A3, the coordinate equation of its starting point A2 is: x = B 1 cosθ, y = B 1 sinθ, where θ is the angle between the line connecting the starting point A2 of the straight line to the rotation center O of the rotor and the x-axis. After selecting a point on the tooth tip arc, the x coordinate value a and y coordinate value b of A2 are both determined. After selecting an appropriate t value, the length of the straight line A2A3 and the position of the end point A3 are also determined, where B 1 / d = 1.3 - 1.6, preferably 1.49, B 1 is the tooth tip arc radius dimension of rotor 1.

[0047] The coordinate equation of the curve A4A5 is:

[0048] x = B 2 cosθcos(θ 1 + θ 2 ) + B 2 sinθsin(θ 1 + θ 2 ) - (R 1 + R 2 )sinθ 2 ,

[0049] y = B 2 cosθsin(θ 1 + θ 2 ) - B 2 sinθcos(θ 1 + θ 2 ) + (R 1 + R 2 )cosθ 2 , where B2 is the radius dimension of the tip arc of the second rotor 2.

[0050] Combined with Figure 2 、 Figure 3 and Figure 7 as shown, the equation of the epicycloid A6A1 is:

[0051] x = Csinθ 1 - Dsin(θ 1 + θ 2 ),y = Ccosθ 1 - Dcos(θ 1 + θ 2 );

[0052] where C = R 1 + R 2 , C is the center distance between the first rotor 1 and the second rotor 2. Regarding the epicycloid, that is, when a moving circle rolls without slipping outside a fixed circle, the locus of a fixed point on the circumference of the moving circle is the cycloid A6A1, and D is the distance from the center of the moving circle to a point on the cycloid A6A1. Here, D can be understood as the radius of the moving circle.

[0053] In this screw vacuum pump, the end face profiles of the first rotor 1 and the second rotor 2 can be different. After determining the parameter values of one rotor profile, such as the pitch circle radius, outer diameter dimension, that is, the radius of the tip arc, the rotor profile of the other rotor can be obtained according to the coordinate equation. Of course, the end face profiles of the first rotor 1 and the second rotor 2 can also be exactly the same.

[0054] In this rotor profile, the straight line A2A3 in the rotor profile adopts a straight-line design. The straight-line part where the straight line A2A3 is located is similar to forming a "missing corner". In this way, while ensuring the meshing performance of the two rotors, the size of the rotors is significantly reduced, the space occupied by the rotors in the pump is reduced, and the space for gas flow in the pump body becomes larger, so that the amount of gas flowing through the pump body per unit time increases, and further improves the pumping efficiency of the vacuum pump. In addition, after the straight line A2A3 adopts a straight line, there is no requirement for the machining of the curvature size. During machining, a milling cutter can be used to mill back and forth to form it, which can further reduce the machining difficulty. At the same time, the straight line A2A3 part can also be used as the reference of the tooling tool, making the assembly and manufacturing of the screw vacuum pump more convenient.

[0055] Embodiment 2

[0056] The structure and principle of this embodiment are basically the same as those of Embodiment 1. The difference is that: the included angle t value between the straight line A2A3 and the x-axis is +12 degrees.

[0057] Embodiment 3

[0058] The structure and principle of this embodiment are basically the same as those of the first embodiment. The difference lies in that the included angle t between the straight line A2A3 and the x-axis is -12 degrees.

[0059] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains may make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

[0060] Although terms such as 1. Rotor 1; 2. Rotor 2 are used more frequently herein, the possibility of using other terms is not excluded. The use of these terms is only for more conveniently describing and explaining the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A screw vacuum pump, comprising a pump body, and two rotors are arranged in the pump body. Characterized in that, The end face profiles of the two rotors are each formed by sequentially connecting six profiles of a tooth top arc A1A2, a straight line A2A3, a curve A3A4, a curve A4A5, a tooth root arc A5A6, and an epicycloid A6A1 end to end. The end point A3 of the straight line A2A3 is located on the pitch circle. The curve A3A4 is the conjugate curve of the straight line A2A3. When the two rotors rotate, the starting point A2 of the straight line A2A3 on one rotor can move along the curve A4A5 on the other rotor. The coordinate equation of the straight line A2A3 is: x = a + dcost, y = b + dsint; The coordinate equation of the curve A3A4 is: x = (a + d cos t) cos(θ 1 + θ 2 ) + (b + d sin t) sin(θ 1 + θ 2 ) - (R 1 + R 2 ) sin θ 2 , y = (a + d cos t) sin(θ 1 + θ 2 ) - (b + d sin t) cos(θ 1 + θ 2 ) + (R 1 + R 2 ) cos θ 2 , Wherein, a is the x - coordinate value of the starting point A2 of the straight line A2A3, b is the y - coordinate value of the starting point A2 of the straight line A2A3, d is the length of the straight line A2A3, the two rotors are rotor one and rotor two, R 1 is the pitch - circle radius of rotor one, R 2 is the pitch - circle radius of rotor two, θ 1 and θ 2 represent the respective rotation angles of rotor one and rotor two during meshing rotation, θ 1 / θ 2 = R 2 / R 1 , t is the angle between the straight line A2A3 and the x - axis, and the functional relationship between t and θ can be obtained from the formula; 1 ​ The coordinate equation of the curve A4A5 is: x = B 2 cosθcos(θ 1 + θ 2 ) + B 2 sinθsin(θ 1 + θ 2 ) - (R 1 + R 2 )sinθ 2 , y = B 2 cosθsin(θ 1 + θ 2 ) - B 2 sinθcos(θ 1 + θ 2 ) + (R 1 + R 2 )cosθ 2 , where B 2 is the radius dimension of the tip arc of the second rotor (2).

2. The screw vacuum pump according to claim 1, Characterized in that, The equation of the epicycloid A6A1 is: x = Csinθ 1 -Dsin(θ 1 +θ 2 ),y = Ccosθ 1 -Dcos(θ 1 +θ 2 ), Wherein, C = R 1 + R 2 , C is the center distance between the first rotor (1) and the second rotor (2), and D is the distance from the center of the moving circle to the cycloid.

3. The screw vacuum pump according to claim 1 or 2, Characterized in that, The end face profiles of the rotor one (1) and the rotor two (2) are the same.

4. The screw vacuum pump according to claim 1 or 2, Characterized in that, The included angle t value between the straight line A2A3 and the x-axis is +12 degrees to -12 degrees.

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