EP4647603A1

EP4647603A1 - Railway air compressor unit

Info

Publication number: EP4647603A1
Application number: EP25159092.3A
Authority: EP
Inventors: Akira Takahashi; Tsuyoshi Nachi
Original assignee: Nabtesco Corp
Current assignee: Nabtesco Corp
Priority date: 2024-05-10
Filing date: 2025-02-20
Publication date: 2025-11-12
Also published as: CN120926091A; JP2025171808A

Abstract

A railway air compressor unit (1, 201, 401) relating to one aspect of the present invention includes: an oil-free air compressor (2) configured to compress air drawn thereto and discharge the compressed air; a first filter (5) provided in an air drawing path (3) through which the air is drawn into the air compressor (2), the first filter (5) having fibers to collect dust particles drawn into the air drawing path (3); and a second filter (6, 206, 406) provided in the air drawing path (3), the second filter (6) being configured to electrically or magnetically collect the dust particles.

Description

TECHNICAL FIELD

The present invention relates to a railway air compressor unit.

BACKGROUND

Patent Literature 1 discloses a vehicle air compressor unit for compressing air suctioned through an air inlet of an air compressor. The air inlet of the air compressor is provided with an air filter. The air filter is designed to control the flow of dust particles into the air compressor.

RELEVANT REFERENCE

LIST OF RELEVANT PATENT LITERATURE

Patent Literature 1: Japanese Patent Application Publication No. 2005-076481

SUMMARY

There are oil-free and oil air compressors. Demand for oil-free air compressors is growing since they do not require the cumbersome process of oil injection. Oil-free air compressors have less lubrication and are more likely to deteriorate due to dust particles than oil air compressors. Therefore, air compressors equipped with conventional air filters may only have limited durability.
The present invention is intended to overcome the above drawback, and one object thereof is to provide a railway air compressor unit with a more durable air compressor.
To overcome the above problem, aspects of the present invention are configured as follows.

(1) An aspect of the present invention provides a railway air compressor unit including: an oil-free air compressor configured to compress air drawn thereto and discharge the compressed air; a first filter provided in an air drawing path through which the air is drawn into the air compressor, the first filter having fibers to collect dust particles drawn into the air drawing path; a second filter provided in the air drawing path, the second filter being configured to electrically or magnetically collect the dust particles.
According to the implementation, having the second filter configured to electrically or magnetically collect dust particles, the railway air compressor unit can effectively collect fine dust particles that can be hardly collected by the fibers alone. As a result, the air compressor can be more durable.
(2) In the railway air compressor unit of (1), the second filter may be configured to electrostatically collect the dust particles and positioned downstream from the first filter in a direction in which the air is drawn.
(3) The railway air compressor unit of (1) or (2) may further include a casing housing therein the air compressor, the casing being configured to open toward a given direction. The first and second filters may be positioned in front of the air compressor when seen from the given direction.
(4) The railway air compressor unit of any one of (1) to (3) may further include a support plate supporting the air compressor from below in a vertical direction and extending in a horizontal direction. The second filter may be positioned lower than the support plate in the vertical direction.
(5) The railway air compressor unit of any one of (1) to (4) may further include a control box provided in the air drawing path, the control box housing therein a control unit for controlling the air compressor.
(6) In the railway air compressor unit of (5), the air compressor may be positioned downstream from the control box in the direction in which the air is drawn, and the second filter may be located between the control box and the air compressor.
(7) In the railway air compressor unit of any one of (1) to (6), the air compressor may be a scroll air compressor.

ADVANTAGEOUS EFFECTS

As a result, the air compressor can be more durable.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically shows the configuration of a railway air compressor unit relating to a first embodiment.
Fig. 2 is a view from the direction of the arrow II of Fig. 1.
Fig. 3 illustrates a first filter used in the first embodiment.
Fig. 4 illustrates a second filter used in the first embodiment.
Fig. 5 schematically shows the configuration of a railway air compressor unit relating to a second embodiment.
Fig. 6 is a perspective view showing a filter structure relating to a third embodiment.
Fig. 7 schematically shows the configuration of a railway air compressor unit relating to a fourth embodiment.
Fig. 8 schematically illustrates a second filter relating to the fourth embodiment.
Fig. 9 shows how an activation signal for an air compressor is related to the ON/OFF state of an electromagnet in the fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes railway air compressor units relating to embodiments of the present invention with reference to the attached drawings. Railway air compressor units are used in, for example, brakes and air springs in railway vehicles as a source of compressed air. In the following description, terms such as "parallel," "orthogonal," "center" and "coaxial" describe relative or absolute positions. These terms are not only strictly used but also allow some tolerances and relative differences in angle and distance as long as the same effects can be still produced. In the drawings used for the following description, the respective members are shown to different scales into recognizable sizes.

Fig. 1 schematically shows the configuration of a railway air compressor unit 1 relating to a first embodiment. Fig. 2 is a view from the direction of the arrow II of Fig. 1. Fig. 3 illustrates a first filter 5 used in the first embodiment. Fig. 4 illustrates a second filter 6 used in the first embodiment. Referring to Figs. 1 to 4, the railway air compressor unit 1 includes: an oil-free air compressor 2 for drawing and compressing air and outputting the compressed air, a first filter 5 located on a drawing path 3 through which the air is drawn into the air compressor 2, the first filter 5 having fibers to collect dust particles drawn into the drawing path 3, and a second filter 6 located on the drawing path 3, the second filter 6 being configured to electrically collect dust particles.
The air compressor 2 relating to the present embodiment is a scroll air compressor. The scroll air compressor (not shown) includes a fixed scroll and an orbiting scroll. The fixed and orbiting scrolls are each constituted by a circular base plate and a spiral wrap provided on one of the surfaces of the end plate. The fixed and orbiting scrolls face each other with their wraps being interleaved. In operation, with the fixed and orbiting scrolls facing each other, the orbiting scroll may orbit around the fixed scroll, so that a gas is sucked into the air compressor through the outermost periphery of the wraps. Once drawn, the gas fills the compression chamber between the respective scrolls. The volume of the compression chamber decreases as the orbiting scroll moves in an orbiting manner. This can compress the gas. The compressed gas is discharged through a port located at the center of the base plate.
A tip seal is provided at the end of the wraps of the fixed and orbiting scrolls. The tip seal is accommodated in a seal groove, into which a compressed gas is introduced. The compressed gas creates back pressure, which can press the tip seal against the base plate. In this manner, the tip seal seals between the wraps and the base plate.
The railway air compressor unit 1 includes an electric motor 7 for applying a rotational force to the orbiting scroll. The electric motor 7 includes a stator and a rotor. The electric motor 7 can output a rotational force upon application of electricity to the stator and resulting rotation of the rotor. In the present embodiment, the power produced by the electric motor 7 (the rotational force produced by the rotor) is transmitted to the air compressor 2 via a belt 10. This is called a belt scheme.
The output shaft of the rotor is coupled with a drive pulley 11. The rotational shaft of the air compressor 2 (for example, the shaft on which the eccentric pin of the orbiting scroll is provided) is coupled with a driven pulley 12. Between the drive pulley 11 and the driven pulley 12, a tensioner 13 is provided to regulate the tension of the belt 10. The belt 10 is wound around the drive pulley 11, the driven pulley 12 and the tensioner 13. The rotational force of the rotor is transmitted to the rotational shaft of the air compressor 2 via the belt 10. Using the rotational force of the rotor, the air compressor 2 suctions air into the space (compression chamber) between the fixed scroll and the orbiting scroll and discharges the air compressed in the compression chamber.
The scheme of transmitting power from the electric motor 7 to the air compressor 2 may not be limited to the belt scheme, but can be a built-in or coupling scheme. In the built-in scheme, the air compressor and electric motor are coaxially integrated (the rotational shaft of the air compressor is directly coupled with the output shaft of the electric motor). According to the coupling scheme, the air compressor and electric motor are integrated with each other by means of a coupling (the rotational shaft of the air compressor is coupled with the output shaft of the electric motor by means of a coupling). The power transmission scheme from the electric motor 7 to the air compressor 2 can be modified as required by design specifications.
The railway air compressor unit 1 includes a casing 20, where the air compressor 2 and electric motor 7 are housed. The casing 20 includes a support plate 21 supporting the air compressor 2 from below in the vertical direction and extending in the horizontal direction. The electric motor 7 is positioned vertically below the support plate 21. For example, the electric motor 7 may be fixed onto the support plate 21 in a suspended manner.
In the following description, an XYZ orthogonal coordinate system is used as required. The X direction represents the width direction of the casing 20. The Y direction represents the depth direction of the casing 20. The Z direction represents the height direction that is orthogonal to the width and depth directions of the casing 20 (the X and Y directions). The following description is made referring to the arrows shown in the drawings and indicating the X, Y and Z directions. The head side and the tail side of each arrow indicate the positive (+) side and the negative (-) side, respectively. The upper side and the lower side in the vertical direction are respectively denoted as the +Z side and the -Z side.
The railway air compressor unit 1 has a duct hose 30 forming a drawing path 3 through which the air is drawn into the air compressor 2. The duct hose 30 extends around the air compressor 2 and electric motor 7 and is curved in various directions. The duct hose 30 may include a plurality of tubes and joints. The duct hose 30 can be configured in any other manners (for example, can extend in any other directions) as required by the design specifications.
For example, the first filter 5 is a glass fiber filter, a synthetic fiber filter, an unwoven fabric filter or the like. The first filter 5 can be configured in various other manners as required by design specifications as long as it is made from fibers that can collect dust particles drawn into the drawing path 3.
The first filter 5 is positioned upstream from the air compressor 2 in the air drawing direction. In Fig. 1, the air drawing direction is indicated by the outline arrow. The first filter 5 is positioned near the start of the duct hose 30 (near the inlet). The first filter 5 may be provided in a first box 31 that is in communication with the inlet of the duct hose 30. The dust particles drawn into the drawing path 3 are partly collected by the fibers of the first filter 5 (see Fig. 3).
In the present embodiment, the second filter 6 is configured to electrostatically collect dust particles. For example, the second filter 6 is made from an electrostatic filter charged with static electricity, an electrically charged filtration material having electrically charged chemical fibers, or the like. The second filter 6 can be configured in various other manners as required by design specifications as long as it can electrically collect dust particles.
The second filter 6 is positioned downstream from the first filter 5 in the air drawing direction. The second filter 6 is provided in a portion of the duct hose 30 that extends downstream from the first filter 5 (the +X-Z portion of the first box 31) toward the -X-Z direction. The second filter 6 may be provided in a second box 32 that is connected to a portion (the -X-Z portion) of the duct hose 30. After passing through the first filter 5, the dust particles may be electrostatically collected by the second filter 6 (see Fig. 4).
A cover 33 may be provided on the -X portion of the casing 20 so as to cover the first and second boxes 31 and 32. A dust-proof screen 34 may be provided on the -X-side portion of the cover 33. The first filter 5 may be positioned downstream from the dust-proof screen 34 in the air drawing direction.
In the present embodiment, the casing 20 is configured to open toward one side (the -X side). Fig. 2 shows the railway air compressor unit 1 without the cover 33 and other components from the -X side. The first and second filters 5 and 6 are in front of the air compressor 2 when seen from the -X side. The first and second filters 5 and 6 are positioned on the -X side of the air compressor 2. When seen from the -X side, at least part of the air compressor 2 does not overlap either one of the first and second filters 5 and 6. When seen from the -X side, part of the air compressor 2 (the -Y portion) overlaps the first filter 5. When seen from the -X side, no part of the air compressor 2 overlaps the second filter 6.
The air drawing path 3 has a portion that is upstream from the first filter 5 and that is positioned above the support plate 21 in the vertical direction. The first box 31 is positioned vertically higher than the support plate 21. The second filter 6 is positioned vertically lower than the support plate 21. The second box 32 is positioned vertically lower than the support plate 21.
The railway air compressor unit 1 further includes a control box 40 housing therein a control unit (not shown) for controlling the air compressor 2. The control box 40 is provided in the middle of the air drawing path 3. The control box 40 has an inlet 41 and an outlet 42 through which air passes. The inlet 41 and outlet 42 are in communication with the air drawing path 3.
The control unit includes, for example, a memory and a processor such as a CPU (Central Processing Unit) that are connected to each other via a bus. The processor reads a pressure control program stored in a storage unit (not shown) and stores the read pressure control program in the memory. The processor executes the pressure control program stored in the memory.
The control box 40 is shaped like a rectangular parallelepiped box. The control box 40 is adjacent to the +X portion of the casing 20. The air inlet 41, which is in communication with the air drawing path 3, is provided in the -X-Z portion of the control box 40 and extends in the X direction. The air outlet 42 in communication with air drawing path 3 is provided in the -X+Z portion of the control box 40 and extends in the X direction. The control box 40 is provided in a portion of the duct hose 30 that extends downstream from the second filter 6 (the +X portion of the second box 32) toward the +X direction (the air inlet 41).
The air compressor 2 is positioned downstream from the control box 40 in the air drawing direction. The air compressor 2 (the air inlet, which is not shown) is provided in the portion of the duct hose 30 that extends from the -X+Z portion of the control box 40 (the opening of the outlet 42) toward the -X side. A device box 50 housing therein devices such as a pressure switch and a safety valve may be provided on the +Z portion of the control box 40.

As described above, the railway air compressor unit 1 relating to the present embodiment includes: the oil-free air compressor 2 configured to compress air drawn thereto and discharge the compressed air; the first filter 5 provided in the air drawing path 3 through which the air is drawn into the air compressor 2, the first filter 5 having fibers to collect dust particles drawn into the air drawing path 3; and the second filter 6 provided in the air drawing path 3, the second filter 6 being configured to electrically collect the dust particles.
Having the second filter 6 configured to electrically collect the dust particles, the railway air compressor unit 1 can effectively collect fine dust particles (metal powder such as iron powder that determines the lifetime of the oil-free air compressor 2), which can be hardly collected by the fibers. As a result, the air compressor can be more durable. Iron powder is abundantly present in the environment where railways operate and can be effectively collected.
In the railway air compressor unit 1 relating to the present embodiment, the second filter 6 is configured to electrostatically collect dust particles and positioned downstream from the first filter 5 in the air drawing direction. In this way, since the upstream first filter 5 collects coarse dust particles, the second filter 6 can have an extended lifetime. The second filter 6 is less likely to be clogged with dust particles when compared with the case where the second filter 6 is positioned upstream from the first filter 5. This can reduce an excessive change in pressure from being caused by the second filter 6 in the air drawing direction.
The railway air compressor unit 1 relating to the present embodiment further includes the casing 20 housing therein the air compressor 2. The casing 20 is configured to open toward a given direction. The first and second filters 5 and 6 are in front of the air compressor 2 when seen from the given direction. As a result, the air compressor 2 does not hinder any attempts of inspecting and maintaining the first and second filters 5 and 6 from the front side in the given direction. The first and second filters 5 and 6 can be thus easily inspected and maintained.
The railway air compressor unit 1 relating to the present embodiment further includes the support plate 21 supporting the air compressor 2 from below in the vertical direction and extending in the horizontal direction. The second filter 6 is positioned vertically lower than the support plate 21. In this manner, the second filter 6 does not interfere with attaching and detaching the air compressor 2 in the horizontal direction along the support plate 21. The air compressor 2 can be thus easily inspected and maintained.
The railway air compressor unit 1 relating to the present embodiment further includes the control box 40 that is provided in the middle of the air drawing path 3. The control box 40 houses therein the control unit for controlling the air compressor 2. In this manner, the air flowing into the control box 40 through the air drawing path 3 can be used to cool the control unit.
The air compressor 2 used in the railway air compressor unit 1 relating to the present embodiment is a scroll type. In the above-described manner, the scroll air compressor 2 can achieve an extended lifetime.

The following describes a railway air compressor unit 201 relating to a second embodiment. In the following description, the parts having the same functions as in the first embodiment will have the same names and reference numerals, and their functions will not be specifically described.
Fig. 5 schematically shows the configuration of the railway air compressor unit 201 relating to the second embodiment. Referring to Fig. 5, the air compressor 2 is positioned downstream from the control box 40 in the air drawing direction in the railway air compressor unit 201 relating to the second embodiment. The second filter 206 is located between the control box 40 and the air compressor 2.
The second filter 206 is provided in the portion of the duct hose 30 that extends downstream from the control box 40 (from the opening of the outlet 42) toward the -X direction. The second filter 206 may be provided in the box connected with a portion of the duct hose 30 (the -X portion of the outlet 42). The second filter 206 may be provided in addition to the second filter 6 relating to the first embodiment. The present embodiment is not limited to the above, and the second filter 206 can be installed in any other manners as required by the design specifications.
In the railway air compressor unit 201 relating to the second embodiment, the air compressor 2 is positioned downstream from the control box 40 in the air drawing direction. The second filter 206 is located between the control box 40 and the air compressor 2. Dust particles may flow into the control box 40 through the air drawing path. In the second embodiment, the dust particles flowing out of the control box 40 (through the outlet 42) can be collected by the second filter 206. The dust particles can be thus prevented from flowing into the air compressor 2.

The following describes a filter structure 304 relating to a third embodiment. In the following description, the parts having the same functions as in the first and second embodiments will have the same names and reference numerals, and their functions will not be specifically described.
Fig. 6 is a perspective view showing the filter structure 304 relating to the third embodiment. Referring to Fig. 6, the filter structure 304 includes a first tubular member 305 that is shaped like a tube, and a second tubular member 306 that is shaped like a tube around the outer periphery of the first tubular member 305. The first and second tubular members 305 and 306 are provided in the air drawing path 3 through which the air is drawn into the air compressor 2. The first and second tubular members 305 and 306 are coaxially arranged. The present embodiment is not limited to the above, and the filter structure 304 may additionally include a third tubular member, or other tubular members. The filter structure 304 can be configured in any other manners as required by the design specifications.
In the first tubular member 305, a filter selected from among the first and second filters 5 and 6 is provided. In the second tubular member 306, the other one of the first or second filter 5 or 6 is provided. The first and second filters 5 and 6 are only required to be provided in the air drawing path 3 through which the air is drawn into the air compressor 2.

The following describes a railway air compressor unit 401 relating to a fourth embodiment. In the following description, the parts having the same functions as in the first to third embodiments will have the same names and reference numerals, and their functions will not be specifically described.
Fig. 7 schematically shows the configuration of the railway air compressor unit 401 relating to the fourth embodiment. Fig. 8 schematically illustrates a second filter 406 relating to the fourth embodiment. Fig. 9 shows how an activation signal for the air compressor 2 is related to the ON/OFF state of an electromagnet in the fourth embodiment. Referring to Figs. 7 to 9, the second filter 406 configured to magnetically collect dust particles is provided in the fourth embodiment. The second filter 406 is positioned upstream from the first filter 5 in the air drawing direction.
The first filter 5 is positioned upstream from the air compressor 2 in the air drawing direction. A dehumidifier 8 may be provided downstream from the air compressor 2, in order to dehumidify the compressed air discharged from the air compressor 2. A tank 9 may be provided downstream from the dehumidifier 8. The dehumidifier 8 and/or tank 9 can be installed in any other manners as required by design specifications.
In the present embodiment, the second filter 406 is configured to electromagnetically collect dust particles. For example, the second filter 406 includes an electromagnet or the like. Referring to the example shown in Fig. 8, the second filter 406 is an annular member (an example of a support member) having four (one or more) iron cores (an example of a core made of a magnetic material) radially extending from the outer periphery of the annular member and electric wires wound around the iron cores. The present embodiment is not limited to the above, and the second filter 406 can be configured in various other manners as required by design specifications as long as it can magnetically collect dust particles.
In the fourth embodiment, the control unit (not shown) may switch the electromagnetic force of the second filter 406 (for example, switch on or off the electromagnet) in synchronization with an operation signal (for example, an activation signal) for the air compressor 2. For example, the electromagnet is turned on if the activation signal for the air compressor 2 indicates the ON state. The electromagnet can thus attract iron powder in the drawn air.
On the other hand, the electromagnet is turned off if the activation signal for the air compressor 2 indicates the OFF state. The iron powder adhering to the electromagnet can be accordingly released to the outside as the internal pressure of the air compressor 2 is released and this resultantly causes a backflow of air. In the fourth embodiment, upon suspension of the air compressor 2, the iron powder adhering to the electromagnet is released as the electromagnetic force is no longer applied. Therefore, the railway air compressor unit 401 no longer requires maintenance work for removing dust particles.
The railway air compressor unit 401 relating to the present embodiment includes: the oil-free air compressor 2 configured to compress air drawn thereto and discharge the compressed air; the first filter 5 provided in the air drawing path 3 through which the air is drawn into the air compressor 2, the first filter 5 having fibers to collect dust particles drawn into the air drawing path 3; and the second filter 406 provided in the air drawing path 3, the second filter 6 being configured to magnetically collect the dust particles.
Having the second filter 406 configured to magnetically collect dust particles, the railway air compressor unit 401 can effectively collect fine dust particles (metal powder such as iron powder that may determine the lifetime of the oil-free air compressor 2) that can be hardly collected by the fibers alone. As a result, the air compressor can be more durable. The iron powder is abundantly present in the environment where railways operate and can be effectively collected.
In the railway air compressor unit 401 relating to the present embodiment, the second filter 406 is configured to electromagnetically collect dust particles and positioned upstream from the first filter 5 in the air drawing direction. The upstream second filter 406 can collect fine dust particles, so that the first filter 5 can achieve an extended lifetime. The first filter 5 is less likely to be clogged with dust particles when compared with the case where the first filter 5 is positioned upstream from the second filter 406. This can reduce an excessive change in pressure from being caused by the first filter 5 in the air drawing direction.

The technical scope of the present invention is not limited to the embodiments described above but is susceptible of various modifications within the purport of the present invention.
According to the foregoing embodiments, the casing that houses therein the air compressor and that is configured to open toward a given direction is further provided, and the first and second filters are in front of the air compressor from the given direction. The present invention, however, is not limited to such. For example, the first and second filters may be positioned behind the air compressor from the given direction. How the first and second filters are arranged relative to the air compressor from the given direction may be modified as required by the design specifications.
According to the foregoing embodiments, the support plate supporting the air compressor from below in the vertical direction and extending in the horizontal direction is further provided, and the second filter is arranged lower than the support plate in the vertical direction. The present invention, however, is not limited to such. For example, the second filter may be positioned higher than the support plate in the vertical direction. How the second filter is arranged relative to the support plate may be modified as required by the design specification.
The railway air compressor units relating to the foregoing embodiments further include the control box that is provided in the middle of the air drawing path and that houses therein the control unit for controlling the air compressor. The present invention, however, is not limited to such. For example, the control box may be provided at a different site than in the air drawing path. How the control box is installed can be modified as required by the design specifications.
In the railway air compressor units relating to the embodiments, a scroll air compressor is employed. The present invention, however, is not limited to such. For example, the air compressor may be a reciprocating air compressor including a piston that can reciprocate to change the volume to compress air, a screw air compressor having a pair of screw rotors that can rotate to change the volume between the threads to compress air, or a turbo air compressor having an impeller that can rotate at high speed to impart velocity energy to air to compress the air. The type of air compressor can be selected as required by the design specifications.
The functions of the control unit according to the embodiments described above may be implemented in a program stored on a computer-readable storage medium, and the program stored on the storage medium may be loaded onto a computer system that then executes the program for processing. The "computer system" mentioned above may include an operating system (OS) or hardware such as peripheral devices. The "computer-readable storage medium" mentioned above refers to a storage device such as a portable medium like a flexible disc, a magneto-optical disc, a ROM (Read Only Memory), a flash memory or other writable non-volatile memory, and a DVD (Digital Versatile Disc), and a hard disk built-in to the computer system.
Further, the "computer-readable storage medium" includes storage media that retain the program for some period of time, like a volatile memory (for example, DRAM (Dynamic Random Access Memory)) in an information processing device receiving the program through a network such as the Internet or a communication line such as a telephone line, or in a computer system that operates as a client. The program mentioned above may be transmitted from a computer system that includes a storage device or the like storing the program to another computer system through a transmission medium or by a transmission wave in a transmission medium. The "transmission medium" for transmitting the program refers to a medium that operates to transmit information, like a network (communication network) such as the Internet or a communication line (communication wire) such as the telephone line. Only a part of the functions described above may be implemented in the above program. Further, the functions described above may be implemented by a combination of the above program and other programs previously stored on the computer system. That is, the above program may be what is called a difference file (a difference program).
The elements of the embodiments described above may be replaced with known elements within the purport of the present invention. Further, the modification examples described above may be combined. The foregoing embodiments disclosed herein describe a plurality of physically separate constituent parts. They may be combined into a single part, and any one of them may be divided into a plurality of physically separate constituent parts. Irrespective of whether or not the constituent parts are integrated, they are acceptable as long as they are configured to attain the object of the invention. According to the foregoing embodiments disclosed herein, a plurality of functions may be distributively provided. Some or all of these functions may be integrally provided. Conversely, a different plurality of functions may be integrally provided. Some or all of these functions can be distributively provided. Irrespective of whether the functions are integrally or distributively provided, they are acceptable as long as they are configured to attain the object of the invention.

<EXAMPLES>

The railway air compressor units relating to the embodiments of the present invention will now be described with reference to specific examples. The following examples are provided solely as the specific examples of the application of the present invention and thus not interpreted as limitative.

Table 1 shows the results of evaluating the degree of wear of a tip seal constituting a scroll air compressor. The belt scheme was employed as the scheme of transmitting power to the scroll air compressor. Evaluations were made based on "running behavior tests," which were performed with or without an electrostatic filter (W/ Electrostatic filter, W/O Electrostatic filter). In Table 1, the item "Particle Counter" represents the number of passed dust particles that had a particle size of 0.3 µm or more from among the dust particles that passed within 20 seconds while the air compressor was in operation (the measurement was performed on the ambient air upstream from the particle counter), "Collected Dust Particles" the relative amount (ratio) of the respective components of the passed dust particles that were collected and analyzed by SEM-EDX, where the respective values were derived based on the amount of the iron component found in tests without an electrostatic filter, and "Degree of Wear of Tip Seal" represents the relative amount (ratio) of wear of the tip seal that was derived based on the amount of wear of the tip seal observed in tests without an electrostatic filter.

[Table 1]

	Particle Counter (Number of Passed Dust Particles During 20 Seconds In Operation) > 0.3 µm		Collected Dust Particles (Analyzed by SEM-EDX)			Degree of Wear of Tip Seal
			Al	Si	Fe	Degree of Wear of Tip Seal
Running: Behavior Test	w/o Electrostatic Filter	127,136	0.01	0.16	1	1
Running: Behavior Test	w/ Electrostatic Filter	156,282	0.04	0.26	0.65	0.46

According to Table 1, the running behavior tests confirmed that the iron component accounted for a large ratio in the dust particles. The iron component ratio was lower in tests with an electrostatic filter than in tests without an electrostatic filter. The degree of wear of the tip seal was lower in tests with an electrostatic filter than in tests without an electrostatic filter. These results indicated that more iron-based particles were collected when an electrostatic filter was used than when no electrostatic filter was used. The test results showed that the iron powder can be effectively collected even in an environment where iron power is abundantly present. Therefore, the air compressor can achieve improved durability. The railway environment tends to have a lot of iron due to the wheels and rails. With the use of magnetic force, the iron powder can be efficiently collected.

LIST OF REFERENCE NUMBERS

1: railway air compressor unit
2: air compressor
3: air drawing path
5: first filter
6: second filter
20: casing
21: support plate
40: control box
201: railway air compressor unit
206: second filter
401: railway air compressor unit
406: second filter

Claims

A railway air compressor unit (1, 201, 401) comprising:
an oil-free air compressor (2) configured to compress air drawn thereto and discharge the compressed air;

a first filter (5) provided in an air drawing path (3) through which the air is drawn into the air compressor (2), the first filter (5) having fibers to collect dust particles drawn into the air drawing path (3);

a second filter (6, 206, 406) provided in the air drawing path (3), the second filter (6, 206, 406) being configured to electrically or magnetically collect the dust particles.
The railway air compressor unit (1) of claim 1, wherein the second filter (6) is configured to electrostatically collect the dust particles and positioned downstream from the first filter (5) in a direction in which the air is drawn.
The railway air compressor unit (1) of claim 1 or 2, further comprising
a casing housing therein the air compressor (2), the casing being configured to open toward a given direction,

wherein the first and second filters (5 and 6) are positioned in front of the air compressor (2) when seen from the given direction.
The railway air compressor unit (1) of claim 1 or 2, further comprising
a support plate supporting the air compressor (2) from below in a vertical direction and extending in a horizontal direction,

wherein the second filter (6) is positioned lower than the support plate in the vertical direction.
The railway air compressor unit (1, 201, 401) of claim 1 or 2, further comprising
a control box provided in the air drawing path (3), the control box housing therein a control unit for controlling the air compressor (2).
The railway air compressor unit (201) of claim 5,
wherein the air compressor (2) is positioned downstream from the control box in a direction in which the air is drawn, and

wherein the second filter (206) is located between the control box and the air compressor (2).
The railway air compressor unit (1, 201, 401) of claim 1 or 2, wherein the air compressor (2) is a scroll air compressor.