JP2001207992A - Turbo dry pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a turbo dry pump which requires neither to upsize a dynamic pressure gas bearing nor to provide a cooling system for the bearing. SOLUTION: A communicating passage 7 is provided outside a pump housing 1 for communication between an inlet 1K and an outlet 1H of the turbo pump mechanism and is provided with an open/close valve 8 for opening and closing the passage. Fore and aft differential pressure of the turbo pump mechanism can be adjusted so as not to become equal to or higher than a specified pressure through the operation of this open/close valve 8. This open/close valve also serves as a regulating valve 8V, and a drive mechanism 16 is provided for driving the regulating valve 8V based on a signal output from an inverter circuit 11 controlling the rotation of a rotor 2, a main component of the turbo pump mechanism. Accordingly, the communicating passage is automatically opened and closed according to the rotational speed of the rotor 2, and an axial load on the rotor 2 can be adjusted to within an acceptable load of a foil bearing 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turbo-type dry pump which operates without bringing oil into a housing and is used for applications requiring an oil-free environment.

[0002]

2. Description of the Related Art In a dry pump of this type, a rotor is axially mounted in a cylindrical housing via a dynamic pressure gas bearing, and gas compression is performed between the rotor and a stator formed on the inner periphery of the housing. A turbo-type pump mechanism for performing a pumping operation is provided to compress gas from an intake port at one axial end of the housing and discharge the gas to an exhaust port at the other axial end of the housing. This circumferential pump is a non-contact type and belongs to a turbo type pump. In addition, this turbo type dry pump can evacuate from the state of atmospheric pressure and can create a vacuum region. Mechanical ball bearings, magnetic bearings, or hydrostatic bearings have been used as bearings in such dry pumps, but these days they are convenient for maintenance, have a long life, and reduce initial costs and running costs. Dynamic pressure gas bearings that can be developed have been proposed.

The dynamic pressure gas bearing includes a foil bearing using a thin piece, ie, a foil, a tilting pad bearing using a tilting pad, and a spiral bearing employing a spiral system. For example, in the case of a foil bearing, the foil is installed in a cantilever shape while the supporting surface to be supported and the surface of the rotating body to be supported are closely opposed to each other, and the foil forms a wedge-shaped gap that gradually narrows in the rotation direction. . And gas (gas)
And generate a dynamic pressure to support the rotating body against the substrate surface. Therefore, a completely oil-free environment (dry) is realized instead of using oil like a ball bearing.

[0004]

Since the dynamic pressure gas bearing generates an air flow by the rotation of the rotating body to generate a dynamic pressure, the allowable load is proportional to the rotation speed (rotation speed) of the rotating body. It is in. That is, the maximum allowable load capacity increases as the rotation speed of the rotating body increases, and the relationship between this rotation speed and the maximum allowable load capacity is represented by a curve L shown in FIG.
It is as follows. For example, the load capacity is 120 at 10,000 rpm, and 300 at 30,000 rpm. However, exhausting along the curve L means that the bearing operates in a limit state, and the exhaust operation is normally performed in a safe operation indicated by a dashed curve A.

Incidentally, the load applied to the thrust bearing that supports the axial (thrust) direction of the rotating body largely depends on the pressure difference before and after gas compression. This is because each circumferential pump is provided on the rotating body, and a load acts in the axial direction due to a pressure difference between before and after the pump, and the rotating body is urged. That is, when the pressure on the intake side decreases (becomes vacuum), the load applied to the thrust bearing increases. Therefore, when the capacity of the chamber evacuated (evacuated) by the dry pump is small, the chamber is sufficiently evacuated before the rotation of the rotor is accelerated to the rated rotation speed. Therefore, even when the safe driving of the curve A is performed, the exhaust characteristic becomes as shown by the broken line curve B shown in FIG. 4, and the load exceeds the allowable load of the thrust bearing and reaches the point K. In such a state, a load exceeding the permissible load is applied to the bearing, resulting in damage to the bearing, and the pump function cannot be maintained. Therefore, it is necessary to increase the allowable load by increasing the size of the hydrodynamic gas bearing of the thrust bearing.

[0006] However, when the size of the bearing is increased, the loss in the bearing increases, and the problem of increased heat generation occurs. In order to prevent this heat generation, it is necessary to provide a system for supplying a cooling gas. Therefore, the size of the bearing portion increases, but the increase in the size of the bearing inevitably leads to an increase in the size of the pump. An object of the present invention is to provide a turbo type dry pump which solves such a problem.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a turbo-type dry pump provided by the present invention connects an intake port side and an exhaust port side of a turbo-type pump mechanism outside a pump housing. A communication passage is provided, and an on-off valve for opening and closing the passage is provided in the communication passage. Therefore, by operating this on-off valve, the differential pressure before and after the turbo pump mechanism is adjusted so as not to exceed a predetermined value, and the dynamic pressure gas bearing is maintained within its allowable load capacity. Further, the turbo-type dry pump according to the present invention is configured such that the on-off valve is configured as a control valve whose communication path can be adjusted, and a signal generation mechanism for generating a signal related to the rotation speed of a rotor that is a main body of the turbo-type pump mechanism; A drive mechanism for driving the control valve based on an output signal from a signal generation mechanism is provided. Therefore, the opening and closing of the communication passage is automatically adjusted according to the rotation speed of the rotating body, the axial load on the rotating body is adjusted within the allowable load, and the safe driving can be continued.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A turbo type dry pump according to the present invention will be described below with reference to an embodiment shown in the drawings. FIG. 1 is a turbo-type dry pump DP firstly provided by the present invention.
FIG. 1 is a view showing a basic configuration of the present invention, and shows a longitudinal section of the entire pump.

The main part of the dry pump DP is composed of a cylindrical housing 1 and a rotating body (hereinafter referred to as a rotor) 2 rotatably mounted on the inside of the housing 1 by a gas dynamic pressure bearing described later. ing. Specifically, the housing 1 has a bottomed shape as shown in the drawing, and an upper opening at one end in the axial direction is an intake port 1K, and an exhaust port 1H is provided in the middle stage as the other end in the axial direction. A circumferential pump is constituted by a combination of a circumferential portion of the rotor 2 and a stator formed on the inner circumference of the housing 1. The circumferential flow pump is provided in a plurality of stages, that is, in a plurality of stages in the axial direction of the rotor 2.

In the following, this structure will be described in detail. First, a thread groove 1M is formed in the upper part of the inner periphery of the housing 1, and the upper cylindrical part 2P of the rotor 2 is opposed to the thread groove 1M so as to approach the thread groove 1M. I have. A combination of the screw groove 1M and the cylindrical portion 2P of the rotor 2 constitutes a so-called screw groove pump mechanism NP. The rotation of the rotor 2 compresses the molecules in the viscous flow region of the gas and sends it downward.

Further, a plurality of stator units 1T, specifically, seven stages, are stacked in the middle of the inner periphery of the housing 1 in the axial direction. On the other hand, the rotor circumferential portion 2B, which is inserted between the stators 1T, is provided facing the rotor 2 from the middle to the lower side. The two are, of course, non-contact, but the combination forms a circumferential pump. By the operation of the multi-stage circumferential flow pump (hereinafter referred to as a turbo pump mechanism) TP, the gas pressure-fed by the screw groove pump mechanism NP is further compressed and pressure-fed downward, and is discharged through the exhaust path 1R to the exhaust port 1H. Will be exhausted. That is, each stage of the circumferential flow pump compresses the gas on its circumference, sends out the gas to the next stage of the circumferential flow pump through the flow path 1N at the end, and sequentially performs exhaust at each stage. It is.

The basic principle of the turbo-type dry pump and its operation have been described above. The rotor 2 has an H-shaped cross section as shown in the drawing, and its center is connected to the rotary drive mechanism and the shaft is Is being worn. That is, reference numeral 3 denotes a rotary drive shaft which is arranged on the axis of the housing 1. The rotary drive shaft 3 is provided with a flange portion 3F for a bearing at a middle stage, and an electric motor (motor) 4 is integrally installed below the flange portion 3F. The electric motor 4 includes an armature winding 4M provided on the inner periphery of the housing 1 corresponding to the armature and a rotor winding 3M provided on the rotary drive shaft 3 corresponding to the rotor.
The rotation driving shaft 3 is rotated at a high speed by the supply of electric energy 9 from the outside. In the drawing, reference numeral 3S denotes a screw portion at the upper end of the rotary drive shaft 3 which cooperates with the nut 3N to fix the rotor 2 to the rotary drive shaft 3.

The rotating body, that is, the rotor 2 is mounted on the housing 1 by a bearing mechanism composed of a dynamic pressure gas bearing. That is, the dynamic pressure gas bearing in the illustrated example is a foil type bearing, and more specifically, a plurality of thrust foil bearings 5 as thrust bearings are uniformly arranged around the upper and lower gaps between the flange portion 3F and the housing 1. . By being installed above and below the flange portion 3F, it is possible to cope with a strong thrust force. On the other hand, the rotary drive shaft 3
Above and below, radial foil bearings 6 are installed in two upper and lower stages in a gap with the cylindrical portion 1E of the housing 1.
The rotor 2 is smoothly and non-contacted by these two foil bearings 5 and 6.

In FIG. 1, reference numeral 1F denotes a cooling gas supply port, and the cooling gas supplied from the cooling port cools the two foil bearings 5, 6.

The above configuration is a configuration of a conventional turbo-type dry pump, and the present invention has a configuration in which a new mechanism is added in order to maintain the function of the dynamic pressure gas bearing. is there. That is, in order to prevent the load on the dynamic pressure gas bearing from increasing due to a large differential pressure between the intake port 1K side and the discharge port 1H side, the present invention provides the turbo type pump mechanism with the intake side and the exhaust side outside the housing 1. A communication path (bypass path) communicated with the communication path is provided. In the figure, reference numeral 7 denotes a communication pipe which is a main body of the communication path. In the illustrated example, the communication pipe 7 is formed as a member that also serves as an exhaust port 1H, but an opening / closing valve 8 that opens and closes the communication path is provided in the middle stage.

The upper end of the communication passage 7 is connected to the upper end of the turbo-type pump mechanism TP, that is, the outlet side opening of the communication hole 1S formed at the intake port side, while the lower end is the same turbo-type pump mechanism TP. It is directly connected to the lower end of the pump mechanism TP, that is, the opening of the exhaust path 1R that functions as a communication hole on the exhaust port side, that is, the exhaust port 1H. Accordingly, the opening and closing operation of the on-off valve 8 allows the intake port side and the exhaust port side of the turbo pump mechanism TP to communicate with each other outside the housing 1 or to shut off.

Since the turbo type dry pump provided by the present invention has the above-described configuration, it operates as follows.
That is, when an external rotation command is issued to the motor 4, the electric energy 9 is supplied to start driving and the rotor 2 is driven.
Is gradually driven from low-speed rotation to high-speed rotation, for example, high-speed rotation of tens of thousands of rpm. Then, the thread groove pump mechanism N
At P, the gas from the intake port 1K is pumped, and is further compressed by the turbo-type pump mechanism TP and exhausted to the exhaust port 1H side.

In this case, even if the intake port 1 is rotated at a high speed, the safe operation of the curve shown in FIG.
The K side has a low pressure (vacuum), while the exhaust port 1H has a high pressure (atmospheric pressure), so that a large pressure difference is generated between the two, and the rotor 2 is loaded with an axial (thrust) force directed upward from below. However, they will be received by the foil thrust bearing 5.

In the turbo-type dry pump, when the operation is started, that is, at the time of low-speed rotation at the time of start-up and stop, the on-off valve 8 on the communication pipe 7 is opened so that the communication hole 1S and the exhaust passage 1R are connected. The exhaust operation is performed in a state where the pressures on the intake side and the exhaust side are the same. Therefore, at the time of startup, the pressure difference does not occur because the intake port 1K side and the exhaust port 1H side are communicated outside the housing 1, that is, gas compression is not performed, so that no thrust force is generated. As the rotation speed of the rotor 2 increases and the exhaust speed increases,
The exhaust proceeds by closing the on-off valve 8 and performing the work of compression.

In this case, when the capacity of the chamber to be exhausted is small, the differential pressure between the intake port 1K and the exhaust port 1H increases rapidly as the exhaust gas progresses, and the safe operation curve A tends to change from the safe operation curve A to the curve B. However, by opening the on-off valve 8, the rotor 2
Generation of the thrust force can be suppressed within the allowable load amount. If necessary, the degree of opening of the on-off valve 8 can be adjusted irrespective of the progress of the exhaust, and the value of the load due to the differential pressure can be adjusted to a predetermined value or less.

Further, the present invention provides a turbo-type dry pump for automatically adjusting the opening and closing of the communication passage. That is,
The thrust force generated in the rotor 2 due to the pressure difference between the intake port 1K side and the exhaust port 1H side is automatically adjusted within the allowable load amount. Specifically, the on-off valve is configured as an on-off control valve capable of automatically controlling the opening thereof, and the safe operation is automatically performed by driving the on-off control valve in accordance with the rotation speed of the rotor 2. Is to be maintained. This is because the ultimate pressure (the maximum amount of the bearing load at each rotation speed) is determined according to the rotation speed of the rotor 2 when the open / close control valve is closed. This becomes possible by determining the opening of the control valve for each number. As a result, safe driving is ensured even when the pressure difference suddenly occurs.

FIGS. 2 and 3 show the structure of the automatic control type turbo dry pump. That is, FIG. 2 is a diagram showing a configuration of an inverter system in which the electric energy 9 to the motor is controlled by an inverter circuit to perform high-speed operation, and FIG. 3 detects the rotation speed of the rotor 2 and It is a figure showing composition of a rotation speed detection system which controls automatically the opening of the passage of communication pipe 7 according to rotation speed. First, the communication pipe 7 is provided with a control valve 8V capable of adjusting the degree of opening of the communication path, and a drive actuator 12 for operating the adjustment by an electric signal. The drive actuator 12 is configured to receive an electric signal from the inverter circuit 11.

First, in the inverter system, the motor 4
An inverter circuit 11 is provided in a control unit 10 for supplying electric energy 9 to the control unit 10. The inverter circuit 11 controls the amount of electric energy supplied to the motor 4 in accordance with the rotation speed control pattern of the motor 4. At the same time, the inverter circuit 11 drives a signal corresponding to the number of rotations of the motor, that is, a signal of the output frequency. Actuator 1
Feed to 2. As a result, the opening and closing of the communication passage is automatically controlled. This method has a very simple structure. FIG. 3 shows an embodiment of the rotation speed detection system, and is an enlarged view of a main part showing only a mechanism for detecting the rotation of the rotation drive shaft 3 integrated with the rotor 2. In the figure, reference numeral 13 denotes a rotary drive shaft 3
And one detecting body is provided at a peripheral position eccentric from the center of rotation. Reference numeral 14 denotes a high-frequency magnetic field generator for detecting the proximity of the detector 13. The oscillating circuit provided therein is affected by an eddy current loss generated inside the detector 13 when the detector 13 approaches within a predetermined distance. Is output. That is, the detector 13 and the high-frequency magnetic field generator 14 constitute a so-called proximity switch. The proximity switch functions as a rotation detector when the detector 13 is circulated by the rotation of the rotary drive shaft 3. The output signal S as the rotation detector is input to the control unit 10 of the motor 4 shown in FIG.

Accordingly, a signal to that effect is input from the control unit 10 to the drive actuator 12 in accordance with the rotation speed (rotation speed) of the rotor 2, and the control valve 8V operates to adjust the opening of the communication passage. That is, as the allowable load capacity of the bearing increases as the speed increases, the control valve 8 operates to gradually close the communication passage. By such an operation, the thrust force on the rotor 2 is suppressed within the allowable load amount. In this way, the intake port 1K of the turbo-type pump mechanism
The generation of the thrust force on the rotor 2 due to the pressure difference between the pressure side and the exhaust port 1H side is set within the allowable load amount of the dynamic pressure gas bearing.

The turbo type dry pump provided by the present invention has been described in detail above, but is not limited to the above and illustrated examples, but includes various modifications. First, the communication path, which is a basic configuration in the present invention, is required to be installed outside the housing. However, the outside of the housing means other than the pump chamber, and therefore, the outside of the housing. The present invention is not limited to being provided at a physically distant position. This is because the generation of the differential pressure is a problem in the pump chamber, and it is only necessary to connect the parts other than the pump chamber to solve the problem. Therefore, the object is achieved even if the communication passage is not provided outside the housing 1 as in the illustrated example, but is provided in a thickness that does not communicate with the pump chamber of the housing 1. A communication pipe may be inserted into the thick portion of the housing 1, or a pipe-shaped passage may be formed within the thickness of the housing 1. Then, an on-off valve is provided in the communication path in the thick portion of the housing 1.

Regarding the position where the communication passage is installed,
It is premised that it is within the area of the turbo pump mechanism, but it is not limited to being installed at both ends of this area as in the illustrated example. For example, the intake side of the communication passage may be provided at an intermediate stage region position of the turbo pump mechanism TP. In this case, the turbo-type pump mechanism TP above the intermediate stage position which is not bypassed performs compression work, but the load on the bearing is reduced due to the decrease in the compression ratio. Various types of valves, such as a globe valve, a gate valve, and a needle valve, can be used for the on-off valve.

Further, various modifications can be given to the turbo-type dry pump secondly provided by the present invention, that is, a configuration in which the opening and closing of the communication passage is automatically controlled in accordance with the rotation speed of the rotor 2. For example, when a method of detecting the rotation of the rotor 2 is employed, it is needless to say that the invention is not limited to the method using the proximity switch as shown in the illustrated example, but may employ many widely known rotation detecting mechanisms. Further, in the illustrated example, the screw groove pump is installed in the preceding stage of the turbo type pump mechanism, but it is not always necessary to provide this screw groove pump. The present invention covers all these modified embodiments.

[0028]

The turbo-type dry pump provided by the present invention is as described in detail above. Therefore, when the pump is started or stopped, the pressure difference between the intake side and the exhaust side of the turbo-type pump mechanism is reduced. The increase in size is eliminated, and the load can be kept within the allowable load amount of the dynamic pressure gas bearing. Therefore, it is not necessary to increase the size of these bearings, that is, the bearings can be reduced in size, and bearing loss at high speed rotation can be reduced. As a result, the power consumption of the motor is reduced, and the bearings are small and generate little heat.This eliminates the need for conventional means for cooling the bearings, thus reducing the size, simplification and cost of the entire pump. And provide an economical dry pump.

[Brief description of the drawings]

FIG. 1 is a view showing a configuration of a turbo type dry pump according to the present invention.

FIG. 2 is a diagram showing a configuration of a turbo type dry pump provided secondly to the present invention.

FIG. 3 is a diagram showing a main part of a turbo type dry pump provided secondly to the present invention.

FIG. 4 is a graph showing characteristics of a turbo type dry pump.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Housing 1K ... Inlet 1H ... Exhaust port 2 ... Rotor 3 ... Rotary drive shaft 4 ... Motor 5 ... Foil thrust bearing 6 ... Radial foil bearing 7 ... Communication pipe 8 ... Open / close Valve 8V ... Control valve 9 ... Electrical energy 10 ... Control unit 11 ... Inverter circuit 12 ... Drive actuator 13 ... Detector 14 ... High frequency magnetic field generator TP ... Turbo pump mechanism

Claims (2)

[Claims] 1. A pump for gas compression, wherein a rotating body is axially mounted in a cylindrical housing via a dynamic pressure gas bearing and between a circumferential portion of the rotating body and a stator formed on an inner circumference of the housing. Circumferential flow pumps are provided in multiple stages in the axial direction of the rotating body to compress the gas from the intake port at one axial end of the housing and discharge the gas to the exhaust port at the other axial end of the housing. In turbo type dry pumps,
A communication passage for communicating the intake port side and the exhaust port side of the multi-stage circumferential pump outside the housing is provided, and an on-off valve for opening and closing the passage is provided in the communication passage. Turbo type dry pump. 2. An on-off valve comprising a control valve capable of adjusting an opening degree of a communication passage, a signal generating mechanism for generating a signal relating to a rotation speed of a rotor, and the control valve based on a signal from the signal generating mechanism. A turbo-type dry pump characterized in that a drive mechanism for driving the opening / closing operation of the motor is provided, and the opening degree of the communication passage is adjusted according to the rotation speed of the rotating body.