JPH08338386A - Screw compressor - Google Patents

Abstract

PURPOSE: To obtain a screw compressor which can reduce a noise depending on a discharge pulsation securely. CONSTITUTION: In a screw compressor 1 in which a pair of screw form rotors 3 and 4 are rotated in a casing 2, and a fluid sucked from its one end is compressed in the axial direction, and discharged from a discharge port 6 formed at the other end, intermediate ports 8a and 8b to pick up the pulsation flow on the way of compression whose phase is slipped to the final pulsation flow descharged from the discharge port 6 are provided in the casing 2. And the intermediate ports 8a and 8b, and the discharge port 6, are connected through a bypass passage 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw compressor used for a supercharger of an internal combustion engine, and more particularly to a screw compressor which reduces noise due to discharge pulsation.

[0002]

2. Description of the Related Art In a screw compressor, as shown in FIG. 4, a screw type male rotor a and a female rotor b meshing with the screw type rotor are reversely rotated in a casing c, and a fluid sucked from one end of the rotor c. Is introduced into a compression space defined by the rotors a and b and the casing c, is axially fed under pressure, and is discharged from a discharge port formed at the other end.

By the way, in such a screw compressor, discharge pulsation having a frequency determined by the number of rotor revolutions × the number of rotor teeth cannot be avoided due to its structure. That is, the pulsating flow having the above frequency is intermittently discharged from the discharge port of the screw compressor as the rotors a and b rotate, and noise having a frequency based on the discharge pulsation is generated.

As a countermeasure against this, as shown in FIG. 5, the inner wall e of the casing c near the discharge port d is machined into a taper shape along the axial direction to form a rotor tooth groove f forming a compression space.
And a discharge port d are gradually communicated with each other to weaken the degree of pulsation, and a noise reduction technique has been proposed (Japanese Patent Laid-Open No. 2-191890).

[0005]

However, according to the test and research conducted by the present inventor, it was found that such a proposal does not significantly reduce noise, although the effect of weakening the pulsation of the discharge pressure is recognized. This is because the above proposal is actually nothing more than a modification of the shape of the discharge port d so that the discharge timing is slightly advanced, and does not essentially prevent pulsation.

An object of the present invention, which was devised in view of the above circumstances, is to provide a screw compressor capable of reliably reducing noise due to discharge pulsation.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention rotates a pair of screw-shaped rotors in a casing, axially pumps a fluid sucked from one end thereof, and forms the fluid at the other end. In the screw compressor that discharges from the discharge port that has been discharged, the casing is provided with an intermediate port that takes out a pulsating flow during compression that is out of phase with respect to the final pulsating flow that is discharged from the discharge port. And the discharge port are connected via a bypass passage.

The intermediate port is provided 100% of one pitch in the portion one pitch before the rotor from the discharge port of the casing.
In this case, it may be located 25 to 75% on the suction side from the discharge port.

The intermediate port may be an elongated hole formed substantially parallel to the ridgeline of the thread of the screw-shaped rotor.

[0010]

According to the structure of the above function, the pulsating flow in the middle of compression taken out from the intermediate port of the casing is guided to the discharge port through the bypass passage. Here, since the pulsating flow extracted from the intermediate port is out of phase with the pulsating flow discharged from the discharge port, the pulsating flows interfere with each other so as to cancel each other, and the discharge pulsation weakens. Therefore, the noise due to the discharge pulsation is surely reduced.

According to the construction of (1), since the intermediate port is located on the suction end side of 25% to 75% of the rotor 1 pitch from the discharge port, the phase of the pulsating flow during compression taken out from the intermediate port is from the discharge port. It is guaranteed that the final pulsating flow to be ejected is approximately half-phase out of phase. Therefore, the discharge pulsation is reliably canceled.

Further, since the intermediate port is positioned one pitch before the rotor from the discharge port (that is, immediately before discharge), the pressure of the pulsating flow in the course of compression taken out from the intermediate port is finally discharged from the discharge port. It approaches the pressure of pulsating flow. Therefore, the discharge pulsation is effectively canceled by these interferences.

According to the construction of (1), the fluid is pumped by the movement of the ridgeline of the screw thread with the rotation of the screw rotor. Therefore, by forming the intermediate port in parallel with the screw thread, the intermediate port is formed. The pulsating flow with the same phase is taken out. Therefore, by using the pulsating flow having the same phase as described above, the discharge pulsation is accurately canceled.

[0014]

An embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a plan view of a main part of a screw compressor according to this embodiment, and FIG. 2 is a side sectional view thereof.

As shown in the figure, a screw type male rotor 3 and a female rotor 4 meshing with the male type rotor 3 are rotatably housed in a casing 2 of a screw compressor 1. These rotors 3 and 4 are meshed with gears (not shown) provided at their shaft ends, so that they can rotate in reverse synchronously with a very small gap (several tens of μ). ing.

The casing 2 has a suction port 5 formed at one end in the axial direction and a discharge port 6 formed at the other end. According to this configuration, the rotors 3 and 4 rotate in opposite directions, so that the fluid (air) sucked from the suction port 5 enters the compression space 7 defined by the rotors 3 and 4 and the casing 2. It is guided, transferred while being compressed in the axial direction as the rotor rotates, and finally discharged from the discharge port 6 with the aforementioned pulsation.

The screw compressor 1 is used as a general-purpose compressor or a supercharger for automobile engines.
That is, a pulley (not shown) is provided on the rotary shaft of either one of the rotors 3 or 4, and this pulley is driven via a belt by a pulley provided on the crank shaft of the electric motor or engine. ing.

The feature of this embodiment is that the casing 2 is provided with an intermediate port 8a for taking out a pulsating flow in the middle of compression which is out of phase with respect to the final pulsating flow discharged from the discharge port 6. , 8b, and the intermediate port 8
And the discharge port 6 are connected via a bypass passage 9 formed in the casing 2.

Specifically, the intermediate port 8 is an elongated hole formed in parallel with the ridgeline 10 of the screw threads of the screw-shaped rotors 3 and 4, and extends from the opening of the discharge port 6 of the casing 2 to the rotors 3 and 4. 1 pitch P before 1 pitch P of
When it is set to 100%, it is provided on the 25 to 75% suction side X (50% suction side X in this embodiment) from the discharge port. However, the position of the intermediate port 8 is not limited to this range, and may be any position where a pulsating flow having a phase shifted from the final pulsating flow discharged from the discharge port 6 is taken out.

The intermediate ports 8a and 8b are provided for each of the rotors 3 and 4, and the space between them is divided by the central portion 11 of the casing 1. Because, if the portion 11 between the intermediate ports 8a and 8b is assumed to be continuous, all the fluid to be compressed (air) that is axially pumped in the compression space 7 as the rotors 3 and 4 rotate. The reason is that the compressed fluid of the compressed fluid cannot be maintained up to the discharge port 6 by leaking to the bypass passage 9 side through the continuous intermediate ports 8a and 8b.

The bypass passage 9 is formed in the casing by electric discharge machining or the like. However, when the casing is cast, the bypass passage 9 may be formed by a core or the like, or the bypass passage 9 may be attached to the casing after the passage is processed as a separate component.
The bypass passage 9 has a passage cross section formed in an elongated hole shape similar to that of the intermediate port 8. The passage inner surface 1 of the discharge port 6 is
It is connected to 2. The opening 13 of the inner surface 12 of the passage is also formed in the shape of an elongated hole.

The opening edges 6a and 6b of the discharge port 6 are formed parallel to the ridgelines 10 and 10 of the screw threads of the screw rotors 3 and 4, respectively. Because the ridgelines 10, 10 of the screw thread move with the rotation of the screw-shaped rotors 3, 4, the fluid to be compressed is pumped, so that the ridgeline 10,
This is because forming the discharge port 6 in parallel with 10 eliminates compression leakage and improves compression efficiency.

The operation of this embodiment having the above configuration will be described.

The pulsating flow during compression taken out from the intermediate ports 8a and 8b of the casing 2 is bypass passages 9 and 9.
Through the discharge port 6. Here, since the pulsating flows taken out from the intermediate ports 8a and 8b are out of phase with the pulsating flows discharged from the discharge port 6 as shown in FIG. 3, they interfere with each other so as to cancel each other out. However, the discharge pulsation weakens. Therefore, the noise due to the discharge pulsation is surely reduced.

More specifically, since the intermediate ports 8a and 8b are located on the suction side of the discharge port 6 by 50% of the rotor 1 pitch P, the phase of the pulsating flow during compression taken out from the intermediate ports 8a and 8b is the discharge. As shown in FIG. 3, the final pulsating flow discharged from the port 6 is out of phase by approximately half. Therefore, the discharge pulsation in the discharge port 6 is reliably canceled.

Further, since the intermediate ports 8a and 8b are located in front of the discharge port 6 by the pitch P of the rotor 1 (that is, immediately before the discharge), the intermediate ports 8a and 8b shown by the one-dot chain line in FIG.
The pressure of the pulsating flow in the course of compression taken out from the valve approaches the pressure of the final pulsating flow discharged from the discharge port 6 indicated by the broken line. Therefore, due to these interferences, the discharge pulsation is effectively canceled as shown by the solid line.

In addition, the screw compressor 1 has the ridge lines 10 and 10 of the screw threads as the screw rotors 3 and 4 rotate.
Since the fluid is pumped by the movement of the, the intermediate ports 8a, 8b are formed in the shape of an elongated hole in parallel with the ridgelines 10, 10 of the screw threads, so that the pulsation with the same phase from the intermediate ports 8a, 8b. A large amount of flow is taken out. Therefore, by using a large amount of pulsating flow with the same phase,
The discharge pulsation in the discharge port 6 is exactly canceled.

Since the phase shift of the pulsating flow between the intermediate ports 8a and 8b and the discharge port 6 is kept constant regardless of the speed of rotation of the rotors 3 and 4, the pulsation of the discharge pressure is wide in a wide operating range. Can be significantly reduced (7 dB or more). Therefore, the screw compressor 1 can keep the noise level low in a wide operating range, and is suitable for use as a general-purpose compressor severe against noise, a supercharger for automobiles, and the like.

Further, since it is not necessary to use a special additional mechanism for reducing noise, the screw compressor 1 with extremely low cost and low noise can be realized.

[0031]

As described above, according to the screw compressor of the present invention, noise due to discharge pulsation can be surely reduced.

[Brief description of drawings]

FIG. 1 is a partial plan view of a screw compressor according to an embodiment of the present invention.

FIG. 2 is a side sectional view of the screw compressor.

FIG. 3 is a diagram showing a pressure immediately before a discharge port of the screw compressor, a pressure at an intermediate port, and a pressure inside the discharge port where these are combined.

FIG. 4 is a perspective view showing a rotor of a screw compressor.

FIG. 5 is a side sectional view of a conventional screw compressor.

[Explanation of symbols]

 1 Screw Compressor 2 Casing 3 Rotor 4 Rotor 6 Discharge Port 8a Intermediate Port 8b Intermediate Port 9 Bypass Passage 10 Thread Ridge Line P 1 Pitch X Suction Side

Claims (3)

[Claims] 1. A screw compressor in which a pair of screw-shaped rotors are rotated in a casing, and a fluid sucked from one end of the rotor is axially pumped and discharged from a discharge port formed at the other end of the rotor. An intermediate port for extracting a pulsating flow in the middle of compression that is out of phase with respect to the final pulsating flow discharged from the discharge port is provided, and the intermediate port and the discharge port are connected via a bypass passage. Characteristic screw compressor. 2. The intermediate port has a pitch of 100 at a position one pitch before the rotor from the discharge port of the casing.
The screw compressor according to claim 1, wherein the screw compressor is located on the suction side from the discharge port by 25 to 75% when expressed as%. 3. The screw compressor according to claim 1, wherein the intermediate port is an elongated hole formed substantially parallel to a ridgeline of a screw thread of the screw-shaped rotor.