JPS61106993A - Screw vacuum pump - Google Patents

Abstract

PURPOSE:To reduce the driving torque of a screw vacuum pump by reversing the rotation of its rotor in accordance with an inlet pressure. CONSTITUTION:A screw vacuum pump is connected with a vacuum tank 29 by inlet and exhaust pipes 40-46 through solenoid valves 31-34. The rotation of a high-frequency motor 26 is reversed by switching electromagnetic switches 35 and 36 in the power circuit of the motor 26 by means of a pressure switch 30 provided in the vacuum tank 29. On starting the vacuum pump, the solenoid valves 31, 32 and 33, 34 are held closed and opened, respectively; the electromagnetic switches 35 and 36 are held ON and OFF, respectively. When the vacuum tank pressure decreases below a set pressure, the pressure switch 30 is actuated to open and close the electromagnetic switches 35 and 36, respectively, changing over the motor 26 to a normal direction of rotation. This reduces the starting torque of the vacuum pump.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a screw type vacuum pump, and particularly to a method for reducing the starting torque of a vacuum pump.

[Background of the invention]

A screw type fluid machine has a structure in which compressed gas is discharged from a fixed discharge boat without a valve mechanism. Therefore, the compression ratio of the gas is constant, and when the suction pressure changes, the internal pressure within the working chamber also changes, and the final pressure may become higher than the discharge pressure.

Screw vacuum pumps usually have a suction pressure of 10 Torr.
Since the discharge pressure is operated at 760 Torr (atmospheric pressure), the pressure ratio is higher and the discharge boat is smaller than in the case of a compressor. When starting a vacuum pump like this, the suction pressure is atmospheric pressure, so an abnormally large internal compression occurs in the working chamber, and in such cases, a much larger drive torque is required than the vacuum pump's normal operating torque. shall be.

When a screw fluid machine internally compresses more than the design pressure ratio, a method for bypassing this overcompressed gas from an auxiliary discharge valve to reduce the internal compression and drive torque is disclosed in Japanese Patent Application Laid-Open No. 51-2013 and Utility Model Application No. 51-2013. 51-34006. It is known as Utility Model Publication No. 53-116810. However, all of these systems require a complicated auxiliary discharge valve mechanism and have the disadvantage of being expensive.

Furthermore, as shown in Japanese Utility Model Application No. 59-41691, there is a method in which the rotation speed of the vacuum pump is controlled using an inverter to prevent the drive motor from becoming overloaded, but the inverter is very expensive. In addition, although the driving power of the vacuum pump is reduced by the lower rotational speed, the driving torque does not change much, so there is a drawback that the motor cannot be made smaller.

[Purpose of the invention]

An object of the present invention is to reduce the driving torque of a screw vacuum pump with a simple mechanism, particularly to reduce the starting torque at startup, to make the motor smaller, and to provide an inexpensive screw vacuum pump.

+4 (Summary of the invention) Figure 1 shows a model of a screw fluid machine, and the present invention will be explained in detail using this figure.A male rotor 1 and a female rotor 2 are connected to each other in a casing 3. The two rotors and the casing rotate while meshing, and a working chamber is formed by the two rotors and the casing.Among these working chambers, the volume of the working chamber 4 changes as the rotor rotates, compressing or expanding the gas in the working chamber, but the The chamber 5 has a constant volume and only transports the gas within the working chamber.

Here, the direction of rotation 8 in which the volume of the working chamber 4 decreases with the rotation of the rotor, as in a compressor, is defined as normal rotation, and the direction of rotation 9, in which the volume of the working chamber 4 increases as the rotor rotates, as in an expander, is defined as reverse rotation.

The casing is provided with a boat 6 with a large opening area and a small boat 7. In the case of forward rotation, the boat 6 becomes the gas suction boat and the boat 7 becomes the discharge hoe 1-, and in the case of reverse rotation, the boat 7 becomes the gas suction boat. is the suction port, and boat 6 is the discharge boat.

When the rotor rotates in the forward direction, the working chamber 10 captures the low-pressure gas molecules flying around in the suction boat 6, increases the pressure to atmospheric pressure, and discharges it from the discharge port 7, resulting in a large exhaust speed as shown by the solid line in FIG. and lower suction pressure can be achieved. When the rotor is rotated in the opposite direction, there is no compression of gas in the working chamber, but the gas molecules that entered the working chamber 11 from the boat 7 are forced to be carried to the boat 6, so they move from the boat 7 to the boat 6. Exhaust action occurs. In this case, the boat 7 and the gas flow path (not shown) communicating with it are smaller than the boat 6, and the conductance is also lower, so the exhaust characteristics as a vacuum pump are inferior to those in the case of forward rotation, but the suction pressure is In a viscous region ranging from atmospheric pressure to several tens of Torr, even reverse rotation provides a sufficient exhaust effect, and its characteristics are as shown by the broken line in FIG.

FIG. 3 shows the relationship between suction pressure and drive torque of a screw vacuum pump, where the solid line shows the characteristic when the rotor is rotating in the forward direction, and the broken line shows the characteristic when the rotor is rotating in the reverse direction. When the rotor rotates forward, the driving torque at startup is very large, but as the suction pressure decreases, the driving torque also decreases, and when the suction pressure falls below 100 to 200 Torr, the driving torque remains constant regardless of the suction pressure. Show value. This is because in the case of forward rotation, the volume of the working chamber 10 that sucks in gas is large, and when the suction pressure is high, internal compression causes overcompression just before the working chamber communicates with the discharge port 7. .

On the other hand, when the rotor is rotated in the opposite direction, the volume of the working chamber 11 that sucks gas is small and the gas inside the working chamber acts to expand, so overcompression does not occur and the rotor is driven as shown by the broken line in Fig. 3. Torque is small.

Therefore, when starting the vacuum pump, the rotor is rotated in the opposite direction.
By switching the rotor to forward rotation when the suction pressure becomes low, it becomes possible to operate the screw vacuum pump with a small motor with low drive torque.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 4, 5, 6, and 7. Here, FIG. 4 shows a cross section taken along line BB in FIG. 5, and FIG. 5 shows a cross section taken along line AA in FIG.

The male rotor 1 and the female rotor 2 are rotatably supported by rolling bearings 12 and 13 degrees 14.15 in the main casing 3a and the discharge casing 3b. Timing gears 20 and 21 are attached to the shaft ends of the rotors, and the gap between the male and female rotors is adjusted so that they do not come into contact with each other. If lubricating oil from the bearing enters the working chamber, these oil molecules may flow back into the exhaust system and contaminate the system, so shaft sealing devices 16, 17, 18 are installed between the bearing and the working chamber. , 19 are incorporated.

The male rotor 1 and the high-frequency drive motor 26 are coupled via a spline joint 22.

The bearings 12 and 13 are lubricated by surining the oil in the oil reservoir 24.
This is done by spraying lubrication at bearing 14,
15. The bearings of the timing gears 20, 21 and the high-frequency motor 26 are supplied with lubricating oil from the oil supply pump (not shown) through the oil supply port 25, which is opened at the axes of the high-frequency motor rotor and the male rotor 1 ( (both not shown). Cooling water is also passed through the water cooling jackets 27 and 28 to cool the vacuum pump body and the high frequency motor.

When the high-frequency motor rotates forward, gas is sucked in from port 6, compressed and pressurized within the working chamber, and then discharged from port 7. When the high frequency motor is rotated in reverse, the gas sucked into the working chamber from port 7 is discharged from port 6.

In FIG. 6, the screw vacuum pump connects suction/exhaust pipes 40, 41 via a vacuum chamber 29 and solenoid valves 31, 32, 33, 34.
, 42, 43, 44, 45, 46. In addition, a pressure switch in the vacuum chamber 29 switches the electromagnetic switches 35 and 36 of the power supply circuit of the high frequency motor 26 to rotate the motor in forward and reverse directions.

When the vacuum pump is started, the solenoid valves 31 and 32 are opened; 33.
34 is closed, electromagnetic switch 35 is closed, and 36 is closed.
is open. Since the motor is wired to rotate in reverse when the electromagnetic switch 35 is closed, the gas in the vacuum chamber 29 is sucked into the vacuum pump through the port 7 through the pipe 40°41.42, and is discharged from the port 7. It is then discharged through pipes 43 and 44.

When the pressure inside the vacuum chamber drops below the set pressure, the pressure
'1 switch 30 operates, opens electromagnetic switch 35,
6 is closed and the motor 26 is switched to forward rotation.

At the same time, solenoid valves 31 and 32 are closed and valves 33 and 34 are opened, so the gas in the vacuum chamber is sucked into port 6 via piping 45, discharged from port 7, and exhausted via piping 42 and 46. . In FIG. 6, 37 is a start switch, 38 is a stop switch, and 39 is an auxiliary relay.

[Effects of the Invention] As described above, according to the present invention, the starting torque of the screw vacuum pump can be reduced, and the pump driving motor can be made smaller.

Further, it is possible to construct an inexpensive vacuum pump and exhaust system without requiring a complicated mechanism such as an auxiliary discharge valve.

Furthermore, by preventing overcompression within the vacuum pump, the compressive load acting on the screw rotor is reduced, and the deflection of the rotor is reduced, thereby improving the reliability of the vacuum pump. Furthermore, it is possible to downsize the bearing and reduce mechanical loss, which also makes it possible to downsize the motor and save energy.

[Brief explanation of the drawing]

Figure 1 is a model diagram of the mechanism of a screw fluid machine, Figure 2 is a diagram showing the exhaust characteristics of a screw vacuum pump, and Figure 3 is a diagram showing the relationship between suction pressure and driving torque of a screw vacuum pump. Figure 4. FIG. 5 is a cross-sectional view of the screw vacuum pump, FIG. 6 is a piping system diagram of an embodiment of the present invention, and FIG. 7 is a circuit diagram showing a part of the operating circuit. DESCRIPTION OF SYMBOLS 1...Male rotor, 2...Female rotor, 3...Casing, 6...Port, 7...Port, 26...High frequency motor, 29...Vacuum chamber, 30... Pressure switch, 31, 32° 1st 1000 /DO, /Q
/Entrance pressure gradient (Ding OYr)

Claims (1)

[Scope of Claims] 1. A working chamber is formed by a pair of male and female rotors that have spiral land portions and grooves and rotate around two parallel axes while meshing with each other, and a casing that houses both rotors. In a screw-type vacuum pump that forms a rotor, changes the volume of the working chamber as the rotor rotates, and sucks in and discharges gas into the working chamber, the direction of rotation of the rotor is reversed according to suction pressure. A screw type vacuum pump featuring: 2. The screw vacuum pump according to claim 1, wherein the rotor is rotated in a direction that reduces the volume of the working chamber when the suction pressure is higher than the set pressure.