JP2837895B2 - Reciprocating gas compressor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to compressors or pumps, and more particularly to various gas compressors or liquid pumps for the nuclear industry, air for the food industry and various precision industries, etc. The present invention relates to gas compressors and pumps for various liquids, compressors or pumps for various combustible gases or liquids, and exhaust devices or vacuum pumps in all these fields.

(Prior Art) In the above-mentioned industrial field, a gas to be compressed (or a working fluid)
It is often necessary to avoid the inclusion of lubricating oil.

For this purpose, a structure (so-called oilless piston) that avoids the use of lubricating oil in the sliding portion between the piston and the cylinder is provided, or a complicated facility for removing lubricating oil in the gas to be compressed ( Various types of separators and activated carbon filters).

FIG. 4 shows an example of an oilless piston currently used in a gas compressor or the like. A Teflon ring containing a filler such as graphite, which corresponds to a piston ring, is brought into close contact with a metal ring, and is further surrounded by a labyrinth. Is generally provided. In a normal piston ring, fluid pressure acts on its inner surface to expand the ring, so the contact pressure between the piston ring and the cylinder is increased, increasing the airtightness and promoting wear. In the case of a non-lubricated piston, the Teflon ring and the ring are closely attached to the piston body without providing a notch, in order to prevent acceleration of wear.
As described above, in the case of a non-lubricated piston, the inner surface of the cylinder is made highly smooth, and at the same time, a high self-lubricating polymer compound (polyimide resin, fluorine resin, etc.) is used as the material of the piston or piston ring to improve wear resistance. A material in which a filler to be dispersed was used was used. Further, in order to reduce the amount of wear, measures such as lowering the average piston speed as much as possible have been used. A decrease in the average piston speed caused an increase in the size of the compressor, and an increase in vibration was inevitable due to an increase in the mass of the reciprocating portion.

Another prior art method is to mechanically support the piston with a piston rod below and a support rod extending above the piston rod to avoid contact between the piston rod and the cylinder. According to this method, contact between the piston and the cylinder can be avoided, but it is unavoidable to use lubricating oil for a mechanical support such as a support rod. In addition, while the radial support accuracy of the mechanical support portion is about several tens to several hundreds of microns, the gap between the piston and the cylinder needs to be larger than that, so that gas leakage in the gap portion may occur. Relatively large, increasing efficiency is not easy.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of the prior art, and is intended to provide a gas compressor that is small and lightweight, has low internal leakage, and is capable of significantly increasing the rotation speed. Aim.

(Means for Solving the Problems) In the present invention, a piston reciprocating in a cylinder is held at the center of the cylinder by an active magnetic bearing, and a very small gap (10 μm or less) is held therebetween. This achieves the above object.

(Operation) In the present invention, an active magnetic bearing (position sensor, electromagnet and electronic circuit for controlling the same) in which a piston reciprocating inside the cylinder is installed on one or both of the upper (or side) and lower portions of the cylinder. ), The radial position of the piston is supported and controlled by magnetic force (attraction force), and the radial position of the piston is controlled so as not to contact the cylinder. Specifically, the position of the piston or piston rod in the radial direction is detected by an electromagnetic sensor, an electrostatic sensor, or an optical sensor at a position (x, y directions) 90 ° apart from each other in a plane perpendicular to the piston axis. Then, a deviation from a set position (usually the cylinder center line) is electrically amplified and calculated, and the currents of the electromagnets facing each other in the x and y directions are controlled to increase or decrease, thereby holding the piston on the cylinder center line. The accuracy of the piston position can be adjusted in a wide range by the amplification (gain) of the operational amplifier.

(Embodiment) Embodiment 1 FIG. 1 is a diagram showing a sectional view of a cylinder portion and a crankshaft portion of a compressor of the present invention.

A piston (2) is provided inside the cylinder (1), and a piston rod (7) is fixed to a lower portion of the piston (2) as in a normal compressor, and a crosshead (9) and a connecting rod are provided. (10) and the crankshaft (11) are connected. A support rod (5) is fixed to the upper part of the piston (2). In the cylinder (1) are two active magnetic bearings (3),
(4) is provided above and below the piston (2), and the support rod (5) and the piston rod (7) are inserted into the magnetic bearings (3) and (4), respectively, so that the piston (2) is moved in the radial direction. Supported. In the cylinder (1), partition plates (6) and (8) are further provided adjacent to the inside of the magnetic bearings (3) and (4). The support rod (5) and the piston rod (7) are made of a magnetic material to exert the magnetic force of the magnetic bearing and are made to have a small gap with respect to the magnetic bearings (3) and (4). Have been. As a result, the piston can be positioned with high accuracy with respect to the center line of the cylinder,
Friction between the piston and the cylinder can be completely eliminated. With such a structure, the piston (2) reciprocates while receiving a rotational force of the crankshaft (11) while maintaining a fine gap with the cylinder (1). In this drawing, the load acting on the bearing (3) when placed on the upper part is relatively small, but the load acting on the lower magnetic bearing (4) is transmitted from the connecting rod (10) to the crosshead (9). Since a horizontal component force (load) acting through the contact is added, a larger supporting force is required as compared with the upper part.

Both or one of the spaces formed between the piston (2) and the partition plates (6) and (8) is connected via a suction valve and a discharge valve (not shown) provided at the ends thereof. Pumps the working fluid.

Embodiment 2 FIG. 2 shows a cross section of a cylinder portion in another embodiment of the present invention. In this embodiment, the magnetic bearing above the piston (2) in FIG. 1 is omitted, and the magnetic bearing (3) is disposed on the outer or inner side of the cylinder. Thus, the piston is directly supported by the active magnetic bearing. Therefore, it is necessary to use a magnetic material (ferromagnetic material) such as steel for all or a part of the material constituting the piston. For the same reason, the partition wall between the cylinder or the magnetic bearing and the piston is made of a non-magnetic material, and its thickness needs to be as thin as possible. When the thickness of the cylinder is small, it is difficult to maintain the strength. To solve this problem, the partition between the magnetic bearing (3) and the piston passage is made of a non-magnetic material, and the thickness is reduced as much as possible to reduce the strength of the partition. A method in which the magnetic bearing itself bears a load, a method in which a strength member is arranged on the outer periphery of the magnetic bearing to bear the strength, and the like can be considered. The load acting on the lower magnetic bearing (4) is the same as in the case of FIG.

FIG. 3 shows a cross section of a cylinder portion in still another embodiment of the present invention. This embodiment is different from the embodiment shown in FIG. 1 in that the active magnetic bearing below the piston is omitted and a relatively large load in the horizontal direction is borne by using a conventional mechanical crosshead support mechanism. It is. Therefore, a crosshead guide (12) is provided on the outer periphery of the crosshead (9). This embodiment is a single-acting type in which the pumping operation is performed only in the space below the piston, and a double partition plate is provided below the piston in order to prevent leakage of the working gas. In addition, although not shown, a liquid seal structure is adopted at the piston rod penetration portion of the lower partition plate to completely prevent the working gas from leaking to the outside. A charcoal filter for removing oil vapor is provided. Although the present embodiment is mainly aimed at improving the economy, it has disadvantages associated with the limitation of the number of revolutions due to the increase in the mass of the crosshead and the use of lubricating oil between the crosshead and the crosshead guide. Other points are the same as those in FIG.

The above embodiment is an example of a vertical arrangement, but it is also possible to arrange a single cylinder horizontally, a left-right symmetric horizontal arrangement, or a V-shaped / star-shaped cylinder arrangement.

In each embodiment, a labyrinth or a stuffing box (filling box) is used as a measure to reduce the gas or liquid passing through the gap between the piston rod or the support rod penetration portion at the center of the partition plate provided above and below the cylinder.
The method is appropriate. In particular, the former is preferable from the viewpoint of preventing abrasion because it is non-contact.

In these embodiments, since the connecting rod, the crankshaft, and the like are practically oil-lubricated, there is a possibility that a small amount of lubricating oil may enter the cylinder. Therefore, when it is necessary to particularly limit the lubricating oil content, it is possible to take measures such as providing the lower partition plate twice and returning the gas and the like between the two to the suction side through the filter.

It is also effective to employ a so-called labyrinth piston in which multi-level irregularities are provided around the piston in order to reduce the amount of leakage in the gap between the piston and the cylinder.

Performance Evaluation Using a helium compressor based on the embodiment shown in FIG. 3, the effects of the present invention were confirmed as follows. In the present embodiment, a labyrinth piston having a multi-level unevenness around the periphery is employed to prevent a reduction in volumetric efficiency due to the flow of the working gas.

FIG. 5 is a graph showing the relationship between the rotational speed and the radial amplitude measured at the position of the magnetic bearing above the piston. The X-axis and the Y-axis in the drawing are respectively 45 ° apart from the crankshaft direction in the horizontal section of the magnetic bearing. In the figure, the peak observed near the rotational speed of about 300 rpm is a resonance point generated by the rigidity of the magnetic bearing and the mass of the supporting object including the piston and the like. Further, the reason why the amplitude increases as the rotation speed increases is that the rigidity of the magnetic bearing is changed by an electronic circuit according to the rotation speed and that the exciting force increases with the rotation speed.

6a and 6b show the state of vibration of the piston at a rotational speed of 1,200 rpm using helium at a pressure of FMPa as a working fluid. FIG. 6a is a Lissajous figure showing the two-dimensional vibration trajectory of the piston in the horizontal plane measured at the position of the magnetic bearing, and the X axis and the Y axis are mutually different from the crankshaft direction.
The direction is 45 degrees apart, the downward right direction is the direction of the crank rotation surface, and the upward direction is the crankshaft direction. No. 6b
The figure shows the time change of the vibration displacement. From these, the amplitude of the piston in the horizontal plane is large in the direction of the crank rotation surface,
It can be seen that the maximum amplitude is about ± 20 μm.

FIG. 7 is a measurement result showing the relationship between the actual flow rate (air volume) at 1,000 rpm and the volumetric efficiency and the boosted value.

As is apparent from FIGS. 5 to 7, the rotational speed of the conventional oilless piston type compressor was about 300 rpm, whereas the compressor of this embodiment can operate at a maximum of 1200 rpm. Met. Higher speed operation is possible by reducing the weight of the reciprocating part. Further, the radial amplitude (with respect to the cylinder center line) of the piston was 40 μm pp or less at the maximum (see FIGS. 5 and 6). Furthermore, the volumetric efficiency of the compressor (the ratio of the volume to the piston displacement) is the rated design point (suction pressure: 40 kg / cm ² , even if the gap machining accuracy between the piston and cylinder is relatively low (about 150 μm). Discharge pressure: 45kg / cm
² ) is about 70%, and can be further improved by increasing the processing accuracy.

(Effect of the Invention) As described above, in the present invention, the piston is precisely positioned on the cylinder center line by the active magnetic bearing using the radial position sensor, the operational amplifier and the electromagnet in the x and y directions of the piston, Since a very small gap is maintained between the piston and the cylinder, wear of the piston and the cylinder is completely eliminated, and energy loss can be minimized. For this reason, compared with the conventional oilless piston type compressor, the rotation speed can be significantly increased,
Not only the size and weight of the device can be reduced, but also the maintenance work can be significantly reduced. Further, since the gap between the piston and the cylinder can be made extremely small, a decrease in volumetric efficiency due to internal leakage of the fluid can be avoided. Further, since almost no maintenance is required, there is an effect that radiation exposure generated when using a gas containing a radioactive substance can be greatly reduced. In addition, the compressor (pump) can be hermetically sealed, and external leakage of radiation gas and the like can be prevented. In addition,
The invention requiring little maintenance can be expected to bring great benefits even in harsh natural environments or narrow shipboard environments, such as in applications such as natural gas transport, LPG compression and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 to FIG. 3 are sectional views of a cylinder portion of a compressor of the present invention, FIG. 4 is a partial sectional view of a conventional oilless piston, FIG. FIG. 6 is a graph showing the relationship between the radial amplitude and the rotation speed of the piston in the embodiment shown in FIG. 3. FIGS. 6a and 6b show the rotation speed of the piston in the embodiment shown in FIG. 7 is a graph showing the relationship between the volumetric efficiency and the actual air flow and the boosted value in the embodiment shown in FIG. (Description of reference numerals of main parts) 1 ... Cylinder 2, 2 ... Piston 3,4 ... Magnetic bearing 5 ... Support rod 6,8 ... Partition plate 7 ... Piston rod 9 ... Cross head 10 ... Connecting Rod 11 …… Crankshaft

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-244178 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F04B 39/00

Claims (2)

(57) [Claims] 1. A reciprocating compressor in which a cylinder is provided with electromagnetic support means to support a piston in a radial direction, wherein a piston is provided inside the cylinder, a piston rod is provided below the piston, and a vertical Two magnetic bearings are provided in the part, the piston rod is inserted into and supported by the lower magnetic bearing, and the piston is supported by an upper magnetic bearing provided on the outer or inner side of the upper part of the cylinder. Reciprocating compressor. 2. A reciprocating compressor in which a cylinder is provided with electromagnetic support means to support a piston in a radial direction, wherein a piston is provided inside the cylinder, a piston support rod is provided above the piston, and a piston support rod is provided below the piston. A piston rod is provided, a piston support rod is inserted and supported in an upper magnetic bearing, and a piston rod is inserted and supported in a bearing of a lower partition plate, and the piston rod has a mechanical crosshead and a crosshead guide surrounding it A reciprocating compressor.