JPH06100188B2 - Oil-free screw vacuum pump - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oil-free screw vacuum pump composed of a pair of spiral male and female rotors.

[Conventional technology]

As a conventional example closest to the present invention, a case where a conventional oil-free screw compressor is operated as a vacuum pump will be described.

FIGS. 1 and 2 show the structure of this oil-free screw compressor. 1 is a plan sectional view, 2
The figure is a sectional view taken along the line AA of FIG. The male rotor 4 and the female rotor 5 are housed in the main casing 1 so as to be meshed with each other with a small clearance, and by the roller bearings 8 and 9 in the stuffing boxes 6 and 7 attached to the suction casing 2 and the main casing 1. It is rotatably supported.
The thrust load that acts on these rotors is
Backed by 10. Shaft seals 11 and 12 are provided between the working chamber and the bearings to prevent oil from entering the working chamber and prevent compressed gas from leaking from the working chamber. A pinion 13 is attached to the shaft end of the male rotor 4 on the driving side, and is driven by a speed increasing gear (not shown).
The timing gears 14 and 15 transmit power to the female rotor 5 and adjust the clearance between the male and female rotors so that they do not come into contact with each other.

The gas sucked from the suction port 16 enters the working chamber formed by the male rotor 4, the female rotor 5, and the main casing 1, is compressed by the rotation of both rotors, and is discharged from the discharge port 17.

As a known example of this type, Hiroshi Ishii, "Vacuum Technology Course 2, Vacuum Pump" (Nikkan Kogyo Shimbun (Showa 40-2-25)
There is one described in P.84-85).

[Problems to be Solved by the Invention]

When such an oil-free screw compressor is started in a state where the suction pressure is atmospheric pressure, the sucked gas is compressed according to the design pressure ratio until the discharge port opens.
Therefore, the pressure in the working chamber rises from the suction side toward the discharge side. When using this oil-free screw compressor as a vacuum pump, the discharge pressure is atmospheric pressure,
The compressor has compressed more than necessary.

When a conventional oil-free screw compressor is used as a vacuum pump, there is a drawback that the torque increases when the suction pressure is near atmospheric pressure because of the excessive compression.

It should be noted that an auxiliary discharge port is provided at the position where the throttle volume before the discharge port opening on the casing discharge side end face of the screw compressor is slightly enlarged to prevent the pressure inside the closed volume of the compressor from becoming abnormally large. This is described in Japanese Utility Model Publication No. 53-116810.

However, if the invention described in Japanese Utility Model Laid-Open No. 53-116810 is applied to an oil-free screw vacuum pump, the following problems occur.

(1) In the case of an oil-free screw vacuum pump, a shaft seal device (shaft seal 11) is provided between the bearing that supports the rotor and the compression chamber (working chamber) to prevent leakage of lubricating oil to the compression chamber. However, in order to provide the auxiliary discharge port on the casing discharge end face, the shaft sealing device must be provided away from the discharge end face to the bearing side, and therefore the rotor must be lengthened and supported by the bearing. , The critical speed of the rotor decreases. In particular, in an oil-free screw vacuum pump, the rotor must be rotated at high speed in order to obtain a high degree of vacuum, but if the device described in Japanese Utility Model Laid-Open No. 53-116810 is adopted, the rotor will rotate at high speed due to a reduction in critical speed. Can not do it.

(2) Since the auxiliary discharge port is provided on the end face on the discharge side of the casing, the auxiliary discharge port is provided only at a position where the throttle volume before the discharge port opening is slightly enlarged, and therefore the pressure in the working chamber is close to the discharge pressure. Since the air cannot be extracted until the oil-free screw vacuum pump is started, if it is operated with the suction pressure near atmospheric pressure such as when starting the oil-free screw vacuum pump, it will be compressed to a pressure significantly higher than atmospheric pressure depending on the compression ratio of the vacuum pump. Even if the auxiliary discharge port is provided, the effect of reducing the axial torque can hardly be expected.

(3) When the auxiliary discharge port is provided on the end face on the discharge side of the casing, the discharge port is blocked while the lobe portion of the rotor passes, so that the time for discharging the gas from the working chamber becomes extremely short. With a vacuum pump whose pressure level is lower than that of a compressor,
Since the pressure difference between the inside and outside of the auxiliary discharge port is small, it is necessary to lengthen the opening time to the working chamber space in order to exhaust sufficiently.
If the auxiliary discharge port is provided on the end face on the discharge side of the casing, a sufficient effect cannot be obtained.

An object of the present invention is to prevent an increase in axial torque due to excessive internal compression and to minimize the axial torque, so that driving with a low-capacity drive source is possible and the critical speed of the rotor is reduced. The purpose is to obtain an oil-free screw vacuum pump that can rotate at high speed.

[Means for Solving the Problems]

To achieve the above object, the present invention includes a pair of male and female rotors having spiral land portions and groove portions, which rotate while meshing with each other around two parallel axes, and a casing for housing both rotors. In an oil-free screw vacuum pump that forms a working chamber and squeezes out suction gas trapped in the working chamber from the discharge port as the rotor rotates, when the working chamber pressure rises to a pressure higher than atmospheric pressure. It is characterized in that a plurality of pressure adjusting devices for extracting gas into the working chamber are provided in a plurality of locations on a side wall of a rotor housing portion of the casing in a rotor axial direction.

[Action]

Since the present invention is provided with a plurality of pressure adjusting devices in the axial direction of the rotor, the pressure in the working chamber becomes higher than the atmospheric pressure during the operation with the suction pressure at or near the atmospheric pressure. When the pressure in the chamber becomes higher than the atmospheric pressure, the pressure adjusting device provided in that portion releases the gas in the working chamber to the outside, so that the pressure in the working chamber can be reduced to the atmospheric pressure level. As the suction pressure is closer to the atmospheric pressure, the gas in the working chamber is compressed to the atmospheric pressure or higher at a position closer to the suction side, so that the pressure adjusting device provided in the device closer to the suction side operates. As the suction pressure becomes lower, the gas in the working chamber becomes atmospheric pressure or higher at a position closer to the discharge side, so that the pressure adjusting device closer to the discharge side operates sequentially. If the suction pressure drops sufficiently and the working chamber pressure does not reach atmospheric pressure before reaching the discharge port, none of the pressure regulators will operate and all gas drawn from the suction port will be discharged from the discharge port. To be done.

Particularly, in the present invention, on the side wall of the rotor housing portion of the casing,
Pressure regulator (auxiliary discharge port) for extracting gas from the working chamber
Since the area of the tip portion of the screw rotor is very small, the time during which the pressure adjusting device is opened to the working chamber space can be lengthened. Therefore, even if the pressure difference between the inside and the outside of the pressure adjusting device is small, the gas in the working chamber compressed to atmospheric pressure or more can be reliably exhausted from the pressure adjusting device,
The pressure in the working chamber can always be kept below the atmospheric pressure level.

Since the present invention operates as described above, even when the suction pressure is close to the atmospheric pressure, the pressure in the working chamber can always be kept below the atmospheric pressure level, and unnecessary internal compression can be prevented. Therefore, according to the present invention, since the axial torque can be minimized, a drive source having a small capacity can be used.

Further, according to the present invention, since the pressure adjusting device for extracting the gas in the working chamber is provided on the side wall of the rotor housing portion of the casing, it is not necessary to lengthen the rotor for the pressure adjusting device equipment. Therefore, since the critical speed of the rotor is not reduced, the rotor can be rotated at a high speed, and a high-performance oil-free screw vacuum pump can be obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 3, 4, and 5.

FIG. 3 is a front sectional view of the oil-free screw vacuum pump, but the basic structure is the same as that of the oil-free screw compressor, and the parts denoted by the same reference numerals as in FIGS. 1 and 2 are the same parts. Therefore, the description is omitted.

In the lower part of the side wall 1a of the rotor housing portion of the casing 1, several bleed holes 18a, 18b, 18c for bleeding the gas in the working chamber are opened in the axial direction, and pressure adjusting devices 19a, 19 are provided respectively.
b and 19c are attached.

4 and 5 are enlarged sectional views of the pressure adjusting device 19a. The other pressure adjusting devices 19b and 19c are also the same. FIG. 4 shows a state when the pressure of the working chamber 25 communicating with the extraction hole 18a is below atmospheric pressure, and FIG. 5 shows a state when the pressure exceeds the atmospheric pressure.

When the working chamber 25 is under atmospheric pressure, the valve rod 21 in the valve box 20 is supported by its own weight by the spring 22, and the working chamber 25
When the pressure is lower than the atmospheric pressure, the bleed hole 18a is closed by being in contact with the main body casing side wall 1a by the upward force generated by the pressure difference between the bleed hole 18a and the atmosphere. On the other hand, when the pressure in the working chamber 25 becomes higher than the atmospheric pressure and the pressure is sufficient to overcome the spring 22, the valve rod 21 is pushed downward, and the gas in the working chamber 25 is discharged from the valve box 20 through the bleed hole 18a.
It passes through the inner clearance 26 and is released to the outside through the atmosphere opening port 24. The arrow in FIG. 5 shows the gas flow at this time. An O-ring 23 is attached to the valve rod 21.

As described above, the pressure adjusting devices 19a, 19b, and 19c are installed in the working chamber 2
When the pressure of 5 becomes slightly higher than the atmospheric pressure by the amount considering the strength of the spring 22, the gas in the working chamber 25 is released to the outside, and the pressure in the working chamber 25 is lowered to the atmospheric pressure level. To have.

When the oil-free vacuum pump equipped with the pressure adjusting devices 18a, 18b, 18c is operated at a suction pressure and a discharge pressure of atmospheric pressure, for example, at the time of starting, the gas sucked from the suction port 16 enters the working chamber. The volume of the working chamber decreases with the rotation of both male and female rotors, but pressure regulators 19a, 19b, 19c
Sequentially operate according to the pressure in the working chamber, and reach the discharge port 17 without being compressed to a pressure significantly higher than atmospheric pressure. When the suction pressure is sufficiently reduced and the working chamber pressure does not reach the atmospheric pressure before the working chamber reaches the discharge port, the bleed holes 18a, 18b, 18c are all closed and the vacuum pump is the same as before. Drive.

As described above, if the pressure in the working chamber is kept below approximately atmospheric pressure, even when operating in a state where the suction pressure is near atmospheric pressure,
It is possible to prevent an increase in shaft torque due to unnecessary compression, and it is possible to reduce the output of the drive motor to, for example, about half. Further, if the pressure adjusting device according to the present embodiment is used, it is not necessary to throttle the intake valve at the time of starting or to start at a low rotation speed, and the torque at the time of starting is automatically controlled without external control. It is possible to prevent the increase.

Further, according to the present embodiment, the pressure adjusting device is not provided on the casing discharge side end face as in the conventional case, but is provided on the side wall 1a of the rotor housing portion of the casing, so the rotor is lengthened by the pressure adjusting device. It is not necessary and does not reduce the critical speed of the rotor, so that high speed rotation is possible and a good performance oil-free screw vacuum pump is obtained.

It should be noted that the pressure adjusting device does not have to be provided at a plurality of points in a straight line in the axial direction of the rotor, but at a plurality of points in the axial direction of the rotor so that they can be sequentially operated according to the pressure in the working chamber. Good.

〔The invention's effect〕

According to the present invention, even when the oil-free screw vacuum pump is operated in a state where the suction pressure is about atmospheric pressure, it is possible to prevent the pressure in the working chamber from significantly higher than atmospheric pressure, and By reducing the work required for internal compression, it is possible to reduce the axial torque in the same operating state, so that there is an effect that the oil-free screw vacuum pump can be driven by a drive source with a small output.

Further, according to the present invention, since it is not necessary to lengthen the rotor for installing the pressure adjusting device, it is possible to obtain a high-performance oil-free screw vacuum pump capable of rotating at high speed without lowering the critical speed of the rotor. There is.

[Brief description of drawings]

FIG. 1 is a plan sectional view of an oil-free screw compressor,
2 is a sectional view taken along the line AA of FIG. 1, FIG. 3 is a front sectional view showing an embodiment of the oil-free screw vacuum pump of the present invention, and FIGS. 4 and 5 are pressures shown in FIG. It is an expanded sectional view of an adjustment device part. DESCRIPTION OF SYMBOLS 1 ... Main casing, 1a ... Casing side wall, 4 ... Male rotor, 5 ... Female rotor, 16 ... Suction port, 17 ... Discharge port, 18a, 18b, 18c ... Bleed hole, 19a, 19b, 19c ... Pressure adjusting device.

Front page continuation (72) Inventor Riichi Uchida 502 Jinritsucho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hiritsu Manufacturing Co., Ltd. Lecture 2 Vacuum Pump "Nikkan Kogyo Shimbun (Sho 40-2-25) P. 84-85

Claims (1)

[Claims] 1. A working chamber is formed by a pair of male and female rotors having spiral land portions and groove portions and rotating around two parallel axes while meshing with each other, and a casing accommodating both rotors. In an oil-free screw vacuum pump that presses out the suction gas trapped in the working chamber from the discharge port with the rotation of the rotor, the gas inside the working chamber is changed when the working chamber pressure rises to a pressure higher than atmospheric pressure. An oil-free screw vacuum pump, wherein a pressure adjusting device for extracting air is provided at a plurality of positions on a side wall of a rotor housing portion of the casing in a rotor axial direction.