KR101883894B1 - Screw vacuum pump - Google Patents

Abstract

If one of the curves forming the axial cross-sectional shape of the spiral teeth is created with the epitrochoid curve by a screw vacuum pump having a pair of screw rotors, the clearance between the spiral teeth of both screw rotors is wide at the rotation center side, And becomes narrower toward the outer peripheral side.
In the first curve, in the case where the clearance between the tooth surfaces of the helical teeth 22a and 22b is set to zero, in the radial direction of the epitrochoid curve created at the point on the second circular arc of the other screw rotor the coordinates (X _t, Y _t), the coordinates and the linear expression (equation 1) compensation in accordance with each of (α), and each coordinate (X = X _t after correction cosα-Y _t sinα, which is calculated from Y = X _t sin alpha + Y _t cos alpha).

Description

Screw vacuum pump

The present invention provides a pair of screw rotors each having a helical teeth of an isosceles tooth in a reverse direction of torsion, the pair of screw rotors are housed in the casing in a state of being in non-contact with each other, to a screw vacuum pump which sucks air from one end of a casing by synchronous rotation of a screw rotor and discharges the air from the other end.

This type of screw vacuum pump is known, for example, from Patent Document 1. In this prior art example, the axial cross-sectional shape of the spiral tooth is formed by a first circular arc centered on the rotational center of the screw rotor constituting the tooth bottom, and a second circular arc centering around the rotational center of the screw rotor, A second arc, and a first curve and a second curve connecting the first arc and the second arc, respectively. The first curve is created by an epitrochoid curve created as a point on the second circular arc of the other screw rotor in a pair and the second curve is created by a hypothetical rack constituted by a predetermined curve It is created.

A screw vacuum pump of this type compresses a gas sucked from an intake port of a casing between a screw rotor and a casing and compresses the gas while discharging the compressed gas from a discharge port of the casing. At this time, if the clearance between the tooth surfaces of the helical teeth is made large so that the helical teeth are not interfered with each other, the backward flow amount of the gas flowing back through the gap increases, resulting in a decrease in the pump capacity. For this reason, it is preferable that a clearance between the tooth surfaces of the both helical teeth when the pair of screw rotors are brought into contact with each other without contacting the pair of screw rotors is made equal over the entire length in the radial direction It is necessary to design it to be as small as possible (for example, 0.05 mm).

If the first curve connecting the first circular arc and the second circular arc is created by the epitrochoid curve as in the conventional example, the clearance between the spiral teeth of the both screw rotors is wide at the rotation center side and is directed toward the outer peripheral side It became clear that it became narrower. It can be considered that this is due to the fact that the pitch angle [theta] p of the spiral teeth at an arbitrary distance R in the diameter direction from the rotation center of the screw rotor is different. Therefore, the inventors of the present invention have conducted intensive research to calculate a correction angle? In accordance with the pitch angle? P at the distance R from the rotation center of the screw rotor, and calculate the correction angle? It has been found that a clearance between the tooth surfaces of both helical teeth can be made equal over the entire length in the radial direction by correcting the coordinates.

Patent Document 1: JP-A-8-189485

SUMMARY OF THE INVENTION The present invention has been made in view of the above disadvantages, and it is an object of the present invention to provide a screw vacuum pump in which the clearance between the tooth surfaces of the helical teeth when the pair of screw rotors are brought into contact with each other without contact is equal.

In order to solve the above problem, a pair of screw rotors each having a spiral value of an isosceles tooth in a torsion direction in the opposite direction is provided, and these pair of screw rotors are stored in the casing in a state of being in non-contact with each other, The screw vacuum pump of the present invention, in which the screw is driven from one end of the casing by rotation and is discharged from the other end, is characterized in that the axial angle of the spiral teeth has a circular arc shape in which a first arc, A second arc formed around the center of rotation of the screw rotor constituting the tooth line portion and a first curve and a second curve connecting the first arc and the second arc, Axis direction and the Y-axis direction, and the first curve is a pair of the case where the clearance between the tooth surfaces of the both helical teeth is zero Coordinates _{(X t = 2Acosθ-r d} cos (2θ), Y t = 2Asinθ-r d sin (2θ) in the radial direction of the second epi-trochoid curve Changsung a point on the circumference of the screw rotor and the other forms, a is half the amount of the screw between the rotation of the rotor center of gravity, r _d is the correction according to the radius, θ is a rotation angle) and the correction angle calculated by the coordinates and the linear expression (mathematical expression 1) (α) of the second arc, (X = X _t cos alpha - Y _t sin alpha, Y = X _t sin alpha + Y _t cos alpha) after the correction.

(Where P is the pitch of the helical teeth, R is the radial distance from the center of the rotary shaft of the screw rotor, and DG is the distance between the teeth of the helical teeth)

According to the present invention, in order to calculate the correction angle? In accordance with the pitch angle? P at the distance R from the rotation center of the screw rotor and to correct the coordinates of the epitrochoid curve, It is possible to reduce the clearance between the tooth surfaces of the helical teeth at the same time in the radial direction as much as possible.

In the present invention, it is preferable that the second curve is formed by combining an epicycloidal curve and an involute curve.

1 is a cross-sectional view for explaining the configuration of a screw vacuum pump which is an embodiment of the present invention.
Fig. 2 (a) is a view showing the axial cross-sectional shape of the spiral teeth, Fig. 2 (b) is a view showing the axial cross-sectional shape of the spiral teeth, FIG.
Fig. 3 (a) is a view showing a state in which one screw rotor is cut at an inner diameter which becomes a spiral value of the screw rotor, Fig. 3 (b) Fig.
4 is a graph for explaining the reason why the clearance between the spiral teeth of a pair of screw rotors changes.
5 is a graph for explaining the correction of the coordinates of the first curve.

Referring to Fig. 1, SP is a screw vacuum pump which is an embodiment of the present invention. The screw vacuum pump SP is provided with a cylindrical casing 1 and a connecting pipe (not shown in the drawing) from a facility (vacuum chamber or the like) (Not shown). On the other side (lower side in Fig. 1) of the casing 1, there is provided a discharge port 12 for discharging the gas in the casing 1 to the outside. The pair of screw rotors 2 ₁ and 2 ₂ contact the helical teeth 22a and 22b formed integrally with the rotating shafts 21a and 21b in the operating space 1a in the casing ₁ , And is stored in an engaged state. In the following, be based on the illustrated position in Figure 1, the screw rotors of the pair _{(21, 22)} the direction of the rotational axis (21a, 21b) are extending in the vertical direction, and a direction perpendicular thereto in the horizontal direction , And directions are used.

The upper surface opening and the lower surface opening of the casing 1 are closed by the intake side cover 13a and the discharge side cover 13b which hermetically seal the working space 1a therein. Bearings 3a and 3b are respectively assembled to the intake side cover 13a and the discharge side cover 13b and the upper and lower ends of the rotating shafts 21a and 21b of the pair of left and right screw rotors 2 ₁ and 2 ₂ Respectively. The lower end portions of the rotating shafts 21a and 21b extend to the lower portion of the discharge side cover 13b and the gears 4a and 4b of the same type engaged with each other are respectively extruded. In addition, the right screw the lower rotary shaft (21a) of the rotor _(21), the coupling, and (5a) is installed, it is connected to a coupling (5b) provided on the drive shaft 61 of the drive motor (6) driving the motor (6 Is introduced into the rotary shaft 21a. The two screw rotors 2 ₁ and 2 ₂ are rotated in the opposite directions synchronously with each other and the gas sucked from the intake port 11 of the casing 1 passes through the screw rotors 2 ₁ and 2 ₂ and the casing 1, And is compressed at the end portion of the helical teeth 22a and 22b and discharged from the discharge port 12. [

The spiral teeth 22a and 22b of the screw rotors 2 ₁ and 2 ₂ are spaced apart from each other by a distance (height in the vertical direction), that is, a pitch P (or lead) between the spiral teeth 22a and 22b, And the twist directions thereof are opposite to each other. As shown in Fig. 2 (a) to Fig. 2 (c), the teeth of the spiral teeth 22a and 22b, The first circular arc t1 and the second circular arc t2 constituting the rotation center tc of the rotary shafts 21a and 21b and the tooth line portion (between Tc and Td in Fig. 2 (b) A second circular arc t2 having the center of rotation tc of the screw rotor 2 ₁ and 2 ₂ and a first curve t3 connecting the first circular arc t1 and the second circular arc t2, (Between Tb and Tc in Fig. 2 (b)) and a second curve t4 (between Td and Ta in Fig. 2 (b)). The second curve t4 is formed by combining, for example, an epitrochoid curve and an involute curve.

Here, the epitaxial that the first curve (t3) that make up each helical value (22a) of the screw rotor ₍₂₁₎ of one side, Changsung to a second point on the arc (t2) of the other side of the screw rotor ₍₂₂₎ The gap between the helical teeth 22a and 22b is wider on the rotation center tc side of the rotation shafts 21a and 21b as shown in Figs. 3 (a) and 3 (b) As shown in Fig. This is because the pitch angle? P of the spiral teeth 22a, 22b at the arbitrary distance R in the radial direction from the rotation center tc is different, that is, as shown in Fig. 4, For example, A, B, and C, and the angles? P1,? P2, and? P3 formed when the pitches are equal to each other are different from each other. Therefore, it is necessary to correct the gap between the helical teeth 22a and 22b for each angle to be constant.

In this embodiment, the first point on the second arc (t2) of the curve (t3) the, amount helical value (22a, 22b) the other side of the screw rotor ₍₂₂₎ when the clearance between the zero hit of coordinates _{(X t = 2Acosθ-r d} cos (2θ), Y t = 2Asinθ-r d sin (2θ), a is a positive screw rotors _{(21, 22)} in the radial direction of the epi-trochoid curve Changsung in of the rotation center (tc) half of the distance, r _d, the second radius of the circular arc (t2), θ is a rotation angle), the coordinates and the linear expression (mathematical expression 1) correction according to the correction angle (α) is calculated as (X = X _t cos 留 -Y _t sin 留, Y = X _t sin 留 + Y _t cos 留) after the correction.

[Equation 1]

That is, referring to FIG. 5, when the first curve t3 is the epitrochoid curve, the curves shown by dashed lines in FIG. 5 are drawn (X _t = 2 A cos θ - r _d cos (2θ), Y _t = 2 Asin θ -r _d sin (2θ). in addition, the pitch angle (θp) of this time, the screw rotor, considering the distance (R) from the rotation center (tc) of the (2 _1, 2 _2), quadratic expression (mathematical expression 2 ).

Next, ij can be expressed by the following equation (3), where ij is the distance to be moved from the position where the clearance between the tooth surfaces of the helical teeth 22a, 22b is zero, As shown in FIG. In this case, P is the pitch of the helical teeth 22a and 22b, R is the radial distance from the center of the rotary shafts 21a and 21b, and DG is the distance between the teeth of the helical teeth 22a and 22b.

From the above equations (2) to (4), the correction angle (?) Can be expressed by the above formula (1) do. 5 shows the coordinate system when the rotation centers of the screw rotors 2 ₁ and 2 ₂ are set to (X, Y) = 0, 0, and the coordinate system shown in FIG. 2 (b) State.

As described above, the correction angle? Is determined, and the coordinates (X _t , Y _t ) of the epitrochoid curve when the clearance between the tooth surfaces of the helical teeth 22a, 22b is set to zero are determined according to the correction angle? The first curve t3 is obtained by connecting coordinates (X = X _t cos 留 -Y _t sin 留, Y = X _t sin 留 + Y _t cos 留) shown by the solid line in Figure 5. According to the above embodiment, the correction angle? Is calculated in accordance with the pitch angle? P at the distance R from the rotation center tc of the screw rotors 2 ₁ and 2 ₂ , The clearance between the tooth surfaces of the helical teeth 22a and 22b when the pair of screw rotors 2 ₁ and 2 ₂ are brought into noncontact engagement with each other is equally and simultaneously Can be made small.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto. In the above embodiment, the second curve t4 is formed by combining the Epicycloid curve and the involute curve. However, the second curve t4 is not limited thereto. For example, a sine curve, a cycloid curve, Okay. The number of screw rotors 2 ₁ and 2 ₂ may be not more than one and two or more sets.

One… Casing, 2 ₁ , 2 ₂ ... Screw rotors, 21a, 21b ... The rotating shafts 22a, 22b ... Spiral teeth, t1 ... The first arc, t2 ... Second arc, t3 ... The first curve, t4 ... The second curve.

Claims (2)

And a pair of screw rotors each having a spiral value of an isosceles value in a torsion direction opposite to each other. The pair of screw rotors are housed in the casing in a state where they are not in contact with each other in a noncontact manner, A screw vacuum pump for sucking and discharging from another end,
The cross section of the helical teeth in the axial direction has a first circular arc centered on the rotational center of the screw rotor constituting the tooth bottom, a second circular arc centering on the rotational center of the screw rotor constituting the tooth tooth line, Wherein the first curve and the second curve are created by connecting a first arc and a second arc,
Axis direction and the Y-axis direction are orthogonal to each other in the axial cross section of the screw rotor,
The first curve is a coordinate in the radial direction of the epitrochoid curve created at the point on the second circular arc of the other screw rotor constituting the pair when the clearance between the tooth surfaces of the two helical teeth is zero (X _t = _{-r d cos (2θ), Y} t = 2Asinθ-r d sin (2θ), a is a positive half of the screw between the rotation of the rotor center distance, rd is the radius of the second arc, θ is a rotation angle), and the coordinates (X = X _t cos 留 -Y _t sin 慣, Y = X _t sin 慣 + Y _t cos 留) after the correction in accordance with the correction angle (留) calculated in the equation (1) Screw vacuum pump.
[Equation 1]

(Where P is the pitch of the helical teeth, R is the radial distance from the center of the rotary shaft of the screw rotor, and DG is the distance between the teeth of the helical teeth)
The screw vacuum pump according to claim 1, wherein the second curve is formed by combining an epitrochoid curve and an involute curve.

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