JP2924997B2 - Screw machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a screw machine used as, for example, a vacuum pump, a compressor, or an expander.

[0002]

2. Description of the Related Art In a screw machine, gas is surrounded by an inner wall of a rotor casing and a screw groove of a screw rotor, and is further trapped by engaging a screw portion of a screw rotor with a screw portion of a counterpart screw rotor. It has become.
Then, with the rotation of the screw rotor, the meshing portion of the screw portion moves from the suction side to the discharge side, and along with this, the gas in the screw groove also moves and is discharged from the discharge end. Since the tooth profile is kept out of contact with the mating tooth profile and the rotor casing with a slight gap, it is not in contact with it.Therefore, in order to minimize leakage from these gaps, there is little notch due to interference between the tooth profiles,
Further, it is necessary that the degree of freedom in designing the width of the outer peripheral portion facing the rotor casing is high.

Conventionally, the following tooth profile is known.

The tooth profile of the screw-type vacuum pump disclosed in Japanese Utility Model Laid-Open Publication No. 63-14884 is rectangular, so that interference occurs when the tooth shapes mesh with each other, and a notch is provided to prevent the interference. In addition, in this tooth profile, the outer peripheral width is necessarily １ ／ of the pitch.

[0005] Japanese Patent Publication No. 64-8193 is known as a screw tooth profile in which interference does not occur and a complete seal line is formed. This known example is used for a pump that handles liquid, and since the outer peripheral portion is sealed with the liquid and leakage is small, a high lift can be obtained at one pitch only by forming a complete seal line at the meshing portion. As for the tooth profile, a single point continuous contact tooth profile is used on the rotation transmitting side and a trochoid tooth profile is used on the driven side in a section perpendicular to the axis. However, when an arc or a cycloid tooth is used as the one-point continuous contact tooth, the outer peripheral width is determined by the radius of the tip arc and the radius of the root arc. In other words, none of the known techniques has a degree of freedom in designing the outer peripheral width.

A screw compressor disclosed in Japanese Patent Application Laid-Open No. Sho 62-291486 is known as a screw tooth profile whose outer peripheral width can be freely set. In this known example, the addendum arc and the root arc are connected by an Archimedes curve, and connection cannot be made smoothly at this connection point. Therefore, when this portion is machined, there is a problem that tool damage is increased.

In a conventional screw compressor, the discharge end face of the screw rotor is sealed with a casing to form a compression chamber. In this case, there is a risk that the casing and the screw rotor are thermally deformed due to the heat of compression, and the discharge end face of the screw rotor comes into contact with the casing.

The vacuum pump disclosed in Japanese Patent Application Laid-Open No. 3-111690 is known to reduce the volume of the groove on the discharge side from the volume of the groove on the suction side to prevent a drop in efficiency due to a sudden change in pressure or backflow during discharge. Have been. In this known example, the transfer capacity is reduced by using a plurality of rotors having different screw groove volumes, numbers, and pitches.

As described above, as the tooth profile of the screw machine, a completely continuous seal line can be formed without interference with the mating tooth profile, and the outer peripheral portion is optimally determined by the discharge rate, the compression ratio, and the outer peripheral clearance. A degree of freedom in design is required so that the outer peripheral width is as large as possible. In addition, if the connection of the curves is not smooth, there is a problem that the tool for machining the portion is greatly damaged and productivity is deteriorated.

Further, when a compression chamber is formed by sealing a discharge end face of a screw rotor with a casing as in a conventional screw compressor and compression is performed, the casing and the screw rotor are thermally deformed by the compressor.
There is a danger that the casing will come into contact with the discharge end face of the screw rotor. However, if the screw groove in the transfer process is opened to the discharge port without performing compression, the gas will flow back rapidly from the discharge port into the screw groove due to the large pressure difference between the screw groove and the discharge port, causing vibration and noise. Occurs. Further, power for pushing out the gas flowing backward is required, and the efficiency is reduced.

[0011]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a screw machine in which the outer peripheral width can be freely designed and interference does not occur.

[0012]

According to the present invention, a pair of screw rotors having the same tooth profile and opposite torsion directions mesh with each other in a non-contact state, and rotate synchronously to suck and discharge gas. In the screw machine, the outer peripheral portion and the tooth bottom portion having the same axial cross-sectional shape of the tooth profile of the screw rotor and being equidistant with the pitch line therebetween and equal in length to each other, and connecting the outer peripheral portion and the tooth bottom portion to each other 2 One of those curves is point-symmetric with respect to a pitch point which is an intersection with the pitch line and smoothly connected to the outer peripheral portion and the tooth bottom portion, and the other curve is a mating screw. This is a curve that is created at a point on the outer circumference of the rotor and becomes a trochoid curve on a cross section perpendicular to the axis.

According to the present invention, one of the two curves is a sine curve passing through a pitch point.

According to the present invention, one of the two curves is a straight line passing through the pitch point and an arc continuing from the straight line.

Further, according to the present invention, the pair of screw rotors has a plurality of screw grooves that do not communicate between the suction end and the discharge end, and a discharge space is formed between the discharge end face of the screw rotor and the discharge port. The entire surface of the discharge end face of the screw rotor is opened to the discharge space.

Further, according to the present invention, the pair of screw rotors has a plurality of screw grooves which do not communicate between the suction end and the discharge end, and the leads of the screw grooves are made smaller from the suction end to the discharge end. I have.

Further, according to the present invention, the pair of screw rotors has a plurality of screw grooves which do not communicate between the suction end and the discharge end, and a discharge space is formed between the discharge end face of the screw rotor and the discharge port. The entire surface of the discharge end face of the screw rotor is opened to the discharge space, and the lead of the screw groove is reduced from the suction end to the discharge end.

[0018]

In the screw machine constructed as described above, the tooth profile of the screw rotor is such that one line connecting the outer peripheral portion and the root portion is a point-symmetric curve with respect to the pitch point.
Since the other curve is a trochoid curve created on the outer circumference of the mating screw rotor, a curve symmetrical with respect to the pitch point, such as a sine curve or a straight line, can arbitrarily select an inclination angle at the pitch point with respect to the pitch line. . Therefore, the outer peripheral width determined by the inclination angle is set without any limitation, and is constituted by a continuous curve from the tooth root to the tooth tip, and the productivity is good without significantly damaging the working tool. By changing the outer peripheral width in this manner, a screw machine with less leakage can be provided.

The discharge end face of the screw rotor is open to the discharge space, so that there is no risk of contact due to thermal deformation.

The pitch of the screw groove is changed from the suction side to the discharge side so as to be small, so that the pressure fluctuation at the discharge end is reduced.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, a pump casing A forming the entire exterior is provided with a rotor casing 1,
A bottom cover 4 which is composed of a central casing 2 and a lower casing 3 and is also a lubricant reservoir is attached to the bottom. A pump chamber B is formed inside the rotor casing 1 and has a figure-eight cross section, and the screw rotors 5A, 5A,
B is stored. Further, the screws 5A, 5B are fixed to the upper ends of the rotating shafts 6A, 6B supported by the upper bearings 8A, 8B and the lower bearings 9A, 9B, and the screw teeth thereof are in a non-contact state in which the twist directions are opposite to each other. It is engaged with. A motor rotor chamber C is formed on one rotating shaft 6A side in the lower casing 3, a motor 10 is mounted on the rotating shaft 6A in a motor stator casing 12, and the other rotating shaft 6B is a lower timing. The gears 7A and 7B are rotated in opposite directions so that the screw rotors 5A and 5B are synchronized with each other so as to mesh with each other.

A suction port F is provided in the upper part of the rotor casing 1, and a discharge space 21 is provided between discharge end faces of the screw rotors 5A and 5B and a discharge port G provided on a side surface of the central casing 2. Are formed, and the entire discharge end surfaces of the screw rotors 5A and 5B are open.

The screw rotors 5A and 5B have tooth-shaped shaft cross-sectional shapes as shown in FIG. That is, the outer peripheral portion ab and the tooth bottom portion cd are both straight lines that are equidistant with respect to the pitch line P1 and whose lengths are equal to each other,
The curved part bc is smoothly connected to the tooth bottom part cd by a continuous curve L point-symmetric with respect to the pitch point Pc, and the outer peripheral part a
The curve which can freely set the length of b and the tooth bottom cd, and the curve part de is a curve which is formed at a point corresponding to the point a on the outer periphery of the mating screw rotor and becomes a trochoid curve on a section perpendicular to the axis. It is comprised by each.

FIGS. 3 and 4 show, as an example of the tooth shape, an axial section and a section perpendicular to the axis in which the above-mentioned curved portion bc is constituted by a sine curve L1. The same applies to the curved portion de. The curved portion de is a trochoid curve in a section perpendicular to the axis, but is a curve obtained from the trochoid curve in an axial section.

The curved portion bc in the above embodiment is a sine curve. In FIGS. 5 and 6, as another example, the curved portion bc is a curve L obtained by combining the arcs bb ₁ and cc ₁ with the straight line b1c1.
2 shows an axial cross section and a cross section perpendicular to the axis of the tooth profile shape constituted by 2.

Next, the mode of operation of the present invention will be described.

The rotating shaft 6A is directly driven by the motor 10 and the rotating shaft 6B is driven via timing gears 7A and 7B.
The screw rotors 5A and 5B mesh with each other and rotate in opposite directions.

The tooth profile of the screw rotor 5A is such that one of the lines connecting the outer peripheral portion ab and the tooth bottom portion cd has a pitch point P
Since the curve bc which is point-symmetric with respect to c and the trochoid curve created at the point a corresponding to the outer peripheral portion of the counterpart screw rotor 5B are employed as the other curve de, there is no interference of the tooth profile and the notch is required. In addition, a complete seal line is formed and leakage is small. Further, the outer peripheral width is not limited by the pitch and the diameter of the addendum arc and the root arc, the seal width is appropriately set, and the groove width is not reduced.

Next, the change in the effective number of screw grooves will be described.

In FIGS. 7 and 8, five screw grooves are formed by the engagement of the screw rotor 5A and the screw rotor 5B. However, the suction side and the discharge side at both hatched ends are open. It is shown that the number of effective grooves in which gas in the grooves is sealed changes by rotation, and becomes three to four.

In FIGS. 9 and 10, the screw rotors have suction sides 15A, 15B and discharge sides 15C, 15C.
It is shown that the number of effective grooves changes from 2 to 4 because of separation into D.

As described above, the screw rotor 5
Even if the entire discharge end surfaces of the discharge ends A and 5B are open to the discharge space 21, if there are a plurality of non-communicating screw grooves, that is, effective grooves, gas does not blow out from the suction end to the discharge end, and the gas is effectively transferred. A process is performed. Therefore, the central casing 2 and the screw rotors 5A and 5B do not come into contact with each other due to thermal deformation due to the heat of compression.

In FIG. 11, the screw rotor 25
Since the screw grooves A and 25B communicate from the suction end to the discharge end, the pitch of the discharge side Y portion is smaller than the pitch of the suction side X portion.

As described above, when the pitch of the screw groove in the Y portion is changed to be small, the volume of the screw groove is reduced and the pressure is increased. Therefore, the pressure change at the discharge end,
Backflow is reduced, vibration and noise are suppressed, and required power is also reduced. The change of the pitch may be stepwise or continuous.

12 to 19 are views for explaining that the tooth profile of the screw machine according to the present invention does not interfere. In FIG. 12, reference numerals are shown in accordance with FIG. 4, but in FIGS. 13 to 19, the screw rotors 5A and 5B are shown in these figures in order to sequentially rotate.
Lines 2A and 2B connecting the center and the point b are shown, and the others are omitted. As can be seen from these figures, there is no problem in meshing.

FIG. 20 shows the outer peripheral width (between arcs a and b and arcs c and d) with the same inter-shaft outer diameter and tooth root diameter as compared to FIG.
This is an example in which the interval is changed. As described above, the angle between the line L in FIG. 2 and the pitch line P1 is increased.

FIG. 21 is a diagram showing a cross section perpendicular to the axis in the case where the curves L1 and L1 ', that is, the curves bc and b'c' are sine curves in the case of a double thread screw. The reference numerals are all the same as those in the above-described embodiment, and the other screws are shown with dashes. In this example, the same operation and effect as described above can be obtained.

As described above, according to the present invention, the outer peripheral width can be freely designed and interference does not occur.

[0040]

As described above, according to the present invention, the following effects can be obtained, and a screw machine with low vibration, low noise and small required power can be obtained.

The tooth profile of the screw rotor is such that one line connecting the outer peripheral portion and the tooth bottom portion is a point-symmetric curve with respect to the pitch point, and the other is a trochoid curve created by the outside of the mating screw rotor. There is no interference, there is no need to provide a notch, and a complete seal line is formed with little leakage.

The outer peripheral width can be determined without being restricted by the pitch and the diameter of the addendum arc and the root arc, the seal width on the outer peripheral surface can be set appropriately, and the volume of the groove of the screw rotor can be reduced. It never gets smaller.

When a discharge space is provided between the discharge end face of the screw rotor and the discharge port, and the entire discharge end face of the screw rotor is opened to the discharge space, a small gap is formed between the discharge end face of the screw rotor and a conventional screw vacuum pump. The casing surface that was arranged with securing is no longer necessary,
There is no danger that the screw rotor discharge end face and the casing come into contact due to thermal expansion, and at the same time, the assemblability is improved.

When the volume of the groove opening at the discharge end is reduced by gradually or continuously reducing the lead of the screw groove of the screw rotor from the suction side to the discharge side, the amount of gas flowing backward from the discharge end is reduced. As a result, the vibration and noise are reduced, and the required power is also reduced.
Further, the groove volume can be reduced without reducing the number of effective grooves between the suction end and the discharge end.

[Brief description of the drawings]

FIG. 1 is a side sectional view schematically showing an embodiment of the present invention.

FIG. 2 is an axial sectional view showing one embodiment of the present invention.

FIG. 3 is an axial sectional view showing another embodiment of the present invention.

FIG. 4 is a cross-sectional view perpendicular to the axis of FIG. 3;

FIG. 5 is an axial sectional view showing another embodiment of the present invention.

FIG. 6 is a sectional view taken along a line perpendicular to the axis of FIG. 5;

FIG. 7 is an explanatory diagram showing the effective number of grooves of a screw rotor.

FIG. 8 is an explanatory diagram showing a change in the number of effective grooves of the screw rotor.

FIG. 9 is an explanatory view showing the number of effective grooves when the screw rotor is of a separated type.

FIG. 10 is an explanatory diagram showing a change in the number of effective grooves when the screw rotor is of a separated type.

FIG. 11 is an explanatory view showing an embodiment in which the lead of the screw rotor of the present invention is changed.

FIG. 12 shows the engagement of a screw machine according to the invention.

FIG. 13 shows the engagement of a screw machine according to the invention.

FIG. 14 shows the engagement of a screw machine according to the invention.

FIG. 15 shows the engagement of a screw machine according to the invention.

FIG. 16 shows the engagement of a screw machine according to the invention.

FIG. 17 shows the engagement of a screw machine according to the invention.

FIG. 18 shows the engagement of a screw machine according to the invention.

FIG. 19 shows the engagement of a screw machine according to the invention.

FIG. 20 is a diagram showing an outer peripheral width changed according to the present invention.
FIG.

FIG. 21 is a sectional view taken at right angles to an axis, showing still another embodiment of the present invention.

[Explanation of symbols]

 A: Pump casing B: Pump chamber C: Motor rotor chamber 1: Rotor casing 2: Central casing 3: Lower casing 4: Bottom cover 5A, 5B: Screw rotor 6A, 6B: Rotating shaft 7A, 7B: Timing gear 8A, 8B: Upper bearing 9A, 9B: Lower bearing 10: Motor 12: Motor stator casing 15A to 15D: Screw rotor 21: Discharge space 25A, 25B: Screw rotor

Claims (4)

(57) [Claims] 1. A screw machine which meshes in a non-contact state with a pair of screw rotors having the same tooth profile and opposite torsion directions and rotating in synchronization with each other to suck and discharge gas. The outer peripheral portion and the tooth bottom portion having the same axial cross-sectional shape and both being straight and equidistant with respect to the pitch line and having the same length, and two curves connecting the outer peripheral portion and the tooth bottom portion are formed. One is point-symmetric with respect to a pitch point which is an intersection with the pitch line and is smoothly connected to the outer peripheral portion and the tooth bottom, and the other curve is created at a point on the outer periphery of the mating screw rotor, A screw machine characterized by a trochoidal curve on a section perpendicular to the axis. 2. A pair of screw rotors has a plurality of screw grooves that do not communicate between a suction end and a discharge end, and a discharge space is provided between a discharge end face of the screw rotor and a discharge port. 2. The screw machine according to claim 1, wherein the entire discharge end face is opened to a discharge space. 3. A pair of screw rotors having a plurality of screw grooves which do not communicate between the suction end and the discharge end, and wherein the leads of the screw grooves are reduced from the suction end to the discharge end. Item 6. The screw machine according to Item 1. 4. A pair of screw rotors has a plurality of screw grooves that do not communicate between a suction end and a discharge end, and a discharge space is provided between a discharge end surface of the screw rotor and a discharge port. 2. The screw machine according to claim 1, wherein the entire discharge end face is opened to the discharge space, and the lead of the screw groove is reduced from the suction end to the discharge end.