Gas compressor

Abstract

To provide a gas compressor which reduces wear, damage, etc. of piston rings caused by friction between the piston rings and a cylinder inner surface to maintain excellent performance and improve durability.SOLUTION: A gas compressor for compressing a gas includes: a cylinder; a piston which is inserted into the cylinder and compresses a gas in the cylinder; and a piston ring group 14 comprising a plurality of annular piston rings disposed between the piston and the cylinder. The piston rings are respectively provided with abutment parts 23a, 23b, 23c, 23d, 23e. When a direction in which the gas in the cylinder is compressed is set to the front side and a direction opposite to the front side is set to the rear side, an abutment gap Wa of the first piston ring 13a located at the foremost side is larger than an abutment gap of an arbitrary second piston ring 13b located at the rear side relative to the first piston ring 13a.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a gas compressor for compressing gases such as hydrogen gas.

Background Art

[0002] In recent years, considering the impact on global warming and air pollution, the use of fuel cell vehicles (FCVs) has been expanding. Along with this, the demand for hydrogen stations that supply hydrogen, which is the fuel for fuel cell vehicles, has also been increasing. At a hydrogen station, hydrogen compressed by a gas compressor can be supplied to a fuel cell vehicle via a dispenser.

[0003] In a gas compressor, the volume inside the cylinder is reduced by reciprocating a piston inserted into the cylinder, thereby compressing the gas. A piston ring for preventing leakage of the compressed gas is attached to the outer peripheral surface of the piston.

[0004] For example, Patent Document 1 proposes a gas compressor provided with a resinous ring-shaped first sliding member (piston ring) that slides relative to a sliding member. In the gas compressor, amorphous carbon films are formed on both sliding surfaces of the first sliding member and the sliding member, and on the sliding surface, the carbon content in the surface portion of the amorphous carbon film is configured to be higher than the carbon content in the portion inside the surface portion. In this way, by forming a specific film on the sliding surfaces of the sliding member and the sliding member, the replacement life due to wear of the sliding member can be extended.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, as the pressure of the gas compressed by the compressor increases, the friction between the piston ring and the inner wall surface of the cylinder increases. Therefore, simply forming a film on the sliding surface, as in the gas compressor described in Patent Document 1, may not satisfy the required durability.

[0007] The present invention has been made in view of such problems, and an object thereof is to provide a gas compressor that can reduce wear and breakage of the piston ring due to friction between the piston ring and the inner surface of the cylinder, maintain excellent performance, and improve durability.

Means for Solving the Problems

[0008] The present invention has the following configuration (1). (1) A gas compressor for compressing gas, a cylinder, a piston inserted into the cylinder for compressing the gas in the cylinder, a piston ring group composed of a plurality of annular piston rings disposed between the piston and the cylinder, a driving device for moving the piston in the axial direction of the cylinder and the piston, and having, each of the plurality of piston rings has a part opened to form a closing portion, when the direction in which the gas compressed in the cylinder is located is defined as the front side and the direction opposite to the front side is defined as the rear side, a gas compressor characterized in that the closing gap of the first piston ring located on the most front side is larger than the closing gap of any second piston ring located on the rear side of the first piston ring.

[0009] Further, a preferred embodiment according to the present invention has the following configurations (2) to (6). (2) The gas compressor according to (1), wherein the gap at the joint of the first piston ring is larger than the gaps at the joints of all the other piston rings. (3) The gas compressor according to (1) or (2), wherein the gap at the joint of the piston ring located on the rearmost side among the plurality of piston rings is smaller than the gaps at the joints of all the other piston rings. (4) When any one piston ring except the piston ring located on the rearmost side among the plurality of piston rings is defined as the nth piston ring, and any piston ring located on the rear side of the nth piston ring is defined as the (n + 1)th piston ring, the gap at the joint of the nth piston ring is the same as or larger than the gap at the joint of the (n + 1)th piston ring. The gas compressor according to any one of (1) to (3). (5) When any one piston ring except the piston ring located on the rearmost side among the plurality of piston rings is defined as the nth piston ring, and any piston ring located on the rear side of the nth piston ring is defined as the (n + 1)th piston ring, the gap at the joint of the nth piston ring is larger than the gap at the joint of the (n + 1)th piston ring. The gas compressor according to any one of (1) to (3). (6) The piston ring group is composed of (n + 1) piston rings, and the gaps at the joints of all the piston rings from the first piston ring to the nth piston ring are each larger than the gaps at the joints of all the piston rings located on the rear side of it. The gas compressor according to any one of (1) to (5).

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a gas compressor that can reduce wear, breakage, etc. of the piston rings, maintain excellent performance, and improve durability.

Brief Description of the Drawings

[0011]

Figure 1A

Figure 1B

Figure 1C

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0012] The inventor has intensively studied a method for reducing the pressure applied to the piston ring during compression by a gas compressor and improving its durability. As a result, it has been found that by controlling the relationship of the joint gaps between the piston ring that is most pressured during gas compression among a plurality of piston rings and the other piston rings, the pressure on the piston rings can be dispersed.

[0013] Hereinafter, the gas compressor according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[0014] FIGS. 1A to 1C are diagrams sequentially showing the operations of the gas compressor according to an embodiment of the present invention. Further, FIG. 2 is a schematic diagram showing a piston ring group of the gas compressor according to an embodiment of the present invention. First, the configuration of the gas compressor 10 according to the present embodiment will be described with reference to FIGS. 1A and 2. The gas compressor 10 includes a cylinder 11 configured in a bottomed cylindrical shape, a piston 12 inserted into the cylinder 11, and a drive device (not shown) that reciprocates the piston 12 in the axial direction of the cylinder 11. Specifically, a connecting rod 21 is connected to the piston 12, and the piston 12 and the drive device (not shown) are connected via the connecting rod 21 and a crankshaft (not shown).

[0015] Near the bottom 11a of the cylinder 11, an air supply port 15 and an exhaust port 16 are provided, and an intake valve 17 and an exhaust valve 18 configured to be openable and closable are attached to the air supply port 15 and the exhaust port 16, respectively.

[0016] Further, a plurality of piston rings (first to fifth piston rings 13a, 13b, 13c, 13d, 13e) are attached between the piston 12 and the inner peripheral surface of the cylinder 11, and these plurality of piston rings constitute a piston ring group 14. The piston ring group 14 is in sliding contact with the inner peripheral surface of the cylinder 11. Then, as the piston 12 reciprocates, each piston ring slides on the inner peripheral surface of the cylinder 11.

[0017] The piston rings will be specifically described below. FIG. 2 is a schematic diagram showing a piston ring group of a gas compressor according to an embodiment of the present invention. Although FIG. 2 shows only the piston ring group 14, the following description will be made by simulating the state of being attached to the piston rings in a gas compressor (not shown). As shown in FIG. 2, the piston ring group 14 is composed of five piston rings. In the present embodiment, the direction in which the gas 19 compressed in the cylinder 11, i.e., the top dead center side of the piston 12, is located is defined as the "front side", and the piston ring located on the most front side is the first piston ring 13a. Also, the direction opposite to the front side, i.e., the bottom dead center side of the piston, is defined as the "rear side", and in order from the front side to the rear side, they are the first piston ring 13a, the second piston ring 13b, the third piston ring 13c, the fourth piston ring 13d, and the fifth piston ring 13e.

[0018] The first to fifth piston rings 13a, 13b, 13c, 13d, 13e are annular and have the function of suppressing gas leakage. Also, if the piston rings were completely annular, deformation or breakage would occur when they thermally expand, so each piston ring has a part that is open, forming the joint portions 23a, 23b, 23c, 23d, 23e. In the present embodiment, the joint gap of the first piston ring 13a is designated as Wa, the joint gap of the second piston ring 13b is designated as Wb, the joint gap of the third piston ring 13c is designated as Wc, the joint gap of the fourth piston ring 13d is designated as Wd, and the joint gap of the fifth piston ring 13e is designated as We. And they are configured to gradually decrease in order from the joint gap Wa to the joint gap We. Note that in this specification, the "joint gap" refers to the gap that occurs at the joint portion of the piston ring when it is incorporated into the cylinder.

[0019] The operation of the gas compressor 10 configured as described above will be described below with reference to FIGS. 1A to 1C. As shown in FIG. 1A, the piston 12 is moved to the rear side (bottom dead center side) by the drive device. At this time, since the intake valve 17 is opened and the exhaust valve 18 is closed, gas 19 is supplied into the cylinder through the air supply port 15.

[0020] Next, as shown in FIG. 1B, the piston 12 is moved to the front side by the drive device. At this time, both the intake valve 17 and the exhaust valve 18 are closed, and the pressure of the gas 19 in the cylinder rises.

[0021] Thereafter, as shown in FIG. 1C, with the piston 12 reaching the top dead center, the exhaust valve 18 is opened, so that the compressed gas 19 is discharged through the exhaust port 16, and the gas is supplied to, for example, a dispenser (not shown).

[0022] Here, taking the first piston ring 13a as an example, the pressure applied to the first piston ring 13a during and after gas compression will be specifically described with reference to the drawings. As shown in FIG. 3A, the first piston ring 13a is attached to a groove 22 formed circumferentially on the outer peripheral surface of the piston 12. In the state shown in FIG. 3A, the first piston ring 13a is in contact with the rear side wall surface of the groove 22, and a front side gap portion 31a is formed between the first piston ring 13a and the front side wall surface 22b of the groove 22. Also, a groove bottom side gap portion 25 is formed between the first piston ring 13a and the groove bottom surface 22a (diameter center direction side wall surface) of the groove 22.

[0023] When the piston 12 moves forward, a land pressure PLa is generated above the first piston ring 13a, pushing the first piston ring 13a downward from the front side to the rear side in the axial direction of the cylinder 11. Also, the radially outer end surface of the first piston ring 13a has, for example, a barrel shape, and a land pressure PLa is applied to the first piston ring 13a in the direction from the radially outer end surface side toward the radially center side. Further, a groove bottom pressure PGa having a magnitude approximately equal to the land pressure PLa is applied to the radially center side end surface of the first piston ring 13a in the direction toward the outside in the radial direction.

[0024] Note that since the first piston ring 13a has a joint portion 23a with a joint gap Wa, a part of the gas moves to the land portion 24b between the first piston ring 13a and the second piston ring 13b through the joint gap Wa during gas compression. Therefore, the first piston ring 13a is pushed upward from the rear side to the front side in the axial direction of the cylinder 11 by the land pressure PLb in the land portion 24b. Also, a land pressure PLb is applied to the first piston ring 13a in the direction from the radially outer end surface side toward the radially center side.

[0025] Thereafter, as shown in FIG. 3B, when the piston 12 moves rearward past the top dead center, the gas in the cylinder is discharged, so the land pressure PLa decreases. Also, since inertial force and frictional force are applied to the first piston ring 13a, the first piston ring 13a contacts the front side wall surface in the groove 22. As a result, a rear side gap portion 31b is formed between the first piston ring 13a and the rear side wall surface of the groove 22. In such a state, the land pressure PLa is applied to the first piston ring 13a from the radially outer end face side toward the radially center side and from the axially front side toward the axially rear side. On the other hand, due to the land pressure PLb in the land portion 24b, the first piston ring 13a is pushed upward from the axially rear side to the axially front side of the cylinder 11. Also, the land pressure PLa is applied to the first piston ring 13a from the radially outer end face side toward the radially center side, and the groove bottom pressure PGa is applied from the radially center side end face toward the radially outer end side.

[0026] If, as shown in FIG. 4, the gap portions 23a, 23b, 23c, 23d, 23e of the first piston ring 13a, the second piston ring 13b, the third piston ring 13c, the fourth piston ring 13d, and the fifth piston ring 13e all have the same gap W, the land pressure on the front side of the first piston ring 13a becomes significantly greater than the land pressure on the rear side of the first piston ring 13a. As a result, the force pushing up the first piston ring 13a and the force applied from the radially outer end face side to the radially center side of the first piston ring 13a become weaker, and the contact pressure between the radially outer end face of the first piston ring 13a and the cylinder 11 increases.

[0027] In contrast, in the present embodiment, as shown in FIG. 2, the gap Wa at the joint of the first piston ring 13a is formed to be larger than the gap Wb at the joint of the second piston ring 13b. Further, the gap Wb at the joint of the second piston ring 13b is formed to be larger than the gap Wc at the joint of the third piston ring 13c. The same relationship applies to the following fourth piston ring 13d and fifth piston ring 13e. That is, the land pressure PLa of the land portion 24a above the first piston ring 13a gradually decreases until it reaches the land pressure of a land portion (not shown) below the fifth piston ring 13e.

[0028] Therefore, when calculating the ratio of the land pressure on the front side to the land pressure on the rear side for adjacent land portions, the configuration of the present embodiment results in a smaller ratio. For this reason, the force pushing up the first piston ring 13a by the land pressure PLb and the force acting from the radially outer end face side to the radially center side on the first piston ring 13a are strengthened. As a result, the contact pressure between the radially outer end face of the first piston ring 13a and the cylinder 11 can be reduced, and wear, breakage, etc. of the piston ring due to friction between the two can be reduced, thereby improving durability.

[0029] In the present embodiment, the gaps Wa, Wb, Wc, Wd, and We at the joints of the five piston rings are formed to gradually decrease from the front side to the rear side. More generally, among the plurality of piston rings, the piston ring at an arbitrary position except for the piston ring located on the rearmost side is defined as the nth piston ring, and the piston ring at an arbitrary position located on the rear side of the nth piston ring is defined as the (n + 1)th piston ring. In this case, in the present embodiment, the gaps at the joints of all the piston rings from the first piston ring 13a to the nth piston ring (the fourth piston ring 13d) are each configured to be larger than the gaps at the joints of the piston rings from the second piston ring 13b to the (n + 1)th piston ring (the fifth piston ring 13e). However, the present invention is not limited to such a configuration.

[0030] For example, if the gap Wa of the first piston ring 13a located on the most front side is larger than the gap of any piston ring located on the rear side of this first piston ring 13a, the above effect can be obtained. Further, among the plurality of piston rings, not only the first piston ring 13a located on the most front side but also the other piston rings are preferably formed to be the same as or larger than the gap of the piston ring located on the rear side thereof.

[0031] The number of piston rings constituting the piston ring group 14 is not limited. However, the gap Wa of the first piston ring 13a is preferably larger than the gaps of all the other piston rings. Further, among the plurality of piston rings, the gap of the piston ring located on the most rear side (the fifth piston ring 13e in the present embodiment) is also preferably smaller than the gaps of all the other piston rings.

[0032] Further, if the conditions of the present invention are satisfied, when comparing the relationship between the nth piston ring and any (n + 1)th piston ring located on the rear side of the nth piston ring, the gap of the nth piston ring may be the same as the gap of the (n + 1)th piston ring. However, it is more preferable that the gap of the nth piston ring is larger than the gap of the (n + 1)th piston ring.

[0033] Furthermore, there may be a piston ring having an arbitrary gap between the nth piston ring and the (n + 1)th piston ring. However, the piston ring group 14 is composed of (n + 1) piston rings, and it is particularly preferable that the gaps of all the piston rings from the first piston ring to the nth piston ring are each larger than the gaps of all the piston rings located on the rear side thereof.

[0034] Using FIG. 2, a specific example of the present invention will be described. For example, the gap Wb at the joint of the second piston ring 13b and the gap Wc at the joint of the third piston ring 13c may be the same. Also, a piston ring having a joint gap larger than that of the second piston ring 13b may be disposed between the second piston ring 13b and the third piston ring 13c. Further, the joint gap of the fifth piston ring 13e may be larger than the joint gap of the fourth piston ring 13d.

[0035] Generally, as shown in FIGS. 3A and 3B, one piston ring is disposed for one groove. As a special form, an example in which a plurality of piston rings are disposed for one groove is also conceivable. In the present invention, a general configuration in which one piston ring is disposed for one groove is applied.

[0036] In the present embodiment, from the viewpoints of durability and reliability, an iron-based material can be used as the material of the piston ring, and the applied iron-based material may be steel including special steel or cast iron. Among iron-based materials, it is preferable to use stainless steel as the material of the piston ring, and it is more preferable to use martensitic stainless steel equivalent to SUS440B or SUS410J1 defined in the JIS standard.

[0037] The gas compressor according to the present invention is particularly suitable when used under the condition that the internal cylinder pressure is 16 (MPa) or more and 120 (MPa) or less. Further, the gas compressor is not limited to a gas compressor for a hydrogen station, and can be used for engines, factory equipment using compressed air, various gas pressure feeding systems, and the like. The gas to be compressed is not particularly limited, and air, fuel gas, etc. can be applied in addition to hydrogen.

Example

[0038] Hereinafter, the present invention will be described more specifically by giving invention examples and comparative examples, but the present invention is not limited to these examples.

[0039] <Inventive Example> As an inventive example, as shown in Fig. 2, a gas compressor (4-cycle engine) equipped with five piston rings having different joint clearances was assumed, and the behavior of each piston ring and the force applied to the outer side in the radial direction of each piston ring were obtained by simulation. The conditions used in the simulation are shown below.

[0040] Piston behavior analysis software: Excite Piston & Rings (manufactured by AVL) Rotation speed: 3000 rpm Cylinder diameter: 76 mm Stroke: 75.6 mm Connecting rod length: 144 mm

[0041] Joint clearance Wa of the first piston ring 13a: 8.375 mm Joint clearance Wb of the second piston ring 13b: 5 mm Joint clearance Wc of the third piston ring 13c: 2.75 mm Joint clearance Wd of the fourth piston ring 13d: 1.25 mm Joint clearance We of the fifth piston ring 13e: 0.25 mm Linear expansion coefficient of the material constituting the first to fifth piston rings: 11×10 -6 / K In-cylinder pressure: 90 (MPa)

[0042] <Comparative Example> As a comparative example, as shown in Fig. 4, a gas compressor (4-cycle engine) equipped with five piston rings having the same joint clearances was assumed, and in the same manner as in the above inventive example, the behavior of each piston ring and the force applied to the outer side in the radial direction of each piston ring were obtained by simulation. Among the conditions used in the simulation, the conditions other than the joint clearances of the piston rings in the comparative example were the same as those in the inventive example. The joint clearances of the piston rings and the in-cylinder pressure in the comparative example are shown below.

[0043] Joint clearance W of the first to fifth piston rings: 0.25 mm In-cylinder pressure: 90 (MPa)

[0044] FIG. 5 is a graph showing the behavior of the piston ring in the gas compressor of the invention example. Further, FIG. 6 is a graph showing the behavior of the piston ring in the gas compressor of the comparative example.

[0045] In FIGS. 5 and 6, the vertical axis represents the position of each piston ring in the cylinder axis direction. As shown in FIG. 3A, taking the first piston ring 13a as an example, a front-side gap portion 31a is formed between the first piston ring 13a and the front-side wall surface 22b of the groove 22. For example, when the crank angle is 0°, the first piston ring 13a is in contact with the rear-side wall surface of the groove 22, the axial distance of the front-side gap portion 31a is H (mm), and the distance between the first piston ring 13a and the rear-side wall surface of the groove 22 is 0 (mm). This state is set as 0%.

[0046] On the other hand, as shown in FIG. 3B, when the first piston ring 13a comes into contact with the front-side wall surface in the groove 22, a rear-side gap portion 31b is formed between the first piston ring 13a and the rear-side wall surface of the groove 22. At this time, the axial distance between the first piston ring 13a and the rear-side wall surface of the groove 22 becomes H (mm), and this state is set as 100%. Similarly, for the second piston ring 13b to the fifth piston ring 13e, these positions are represented by a graph.

[0047] In the invention example, from the first piston ring 13a to the fifth piston ring 13e, it is designed such that the mating gap gradually becomes smaller step by step. As a result, as shown in FIG. 5, for the first piston ring 13a to the fourth piston ring 13d, they are in a state of gradually and evenly rising according to the crank angle.

[0048] In contrast, in the comparative example, the first piston ring 13a is in a lifted state from before the crank angle reaches 90° until it approaches 630°, but the second piston ring 13b and the third piston ring 13c lift later compared to the first piston ring 13a. Also, the period of lifting is shorter than that of the first piston ring 13a and is not uniform.

[0049] FIG. 7 is a graph showing the force applied to the outer radial direction of each piston ring in the gas compressor of the inventive example. Further, FIG. 8 is a graph showing the force applied to the outer radial direction of each piston ring in the gas compressor of the comparative example. In FIGS. 7 and 8, the maximum value of the force applied to the first piston ring in the gas compressor of the comparative example is set to 1, and the other forces are represented as ratios to the above maximum value.

[0050] As shown in FIGS. 7 and 8, the maximum force applied to the first piston ring of the inventive example is about 0.8 times that of the maximum force applied to the first piston ring of the comparative example. Further, in the comparative example, the force applied to the second piston ring and subsequent rings is 0.1 times or less compared to the first piston ring. On the other hand, the forces applied to the outer radial directions of the second to fifth piston rings of the inventive example are about 0.7 times, about 0.4 times, about 0.2 times, and about 0.1 times, respectively, compared to the first piston ring of the comparative example. It can be seen that the forces applied to each piston ring are more dispersed in the inventive example.

[0051] From these facts, it was shown that when using the gas compressor of the inventive example, the friction between the first piston ring and the inner surface of the cylinder can be further reduced. Therefore, according to the present invention, wear, breakage, etc. of the piston ring can be reduced, and excellent performance of the gas compressor can be maintained.

Explanation of reference numerals

[0052] 10 Gas compressor 11 Cylinder 12 Piston 13a First piston ring 13b Second piston ring 13c Third piston ring 13d Fourth piston ring 13e Fifth piston ring 14 Piston ring group 22 Groove 23a, 23b, 23c, 23d, 23e Joint 24a and 24b land portions 25 bottom groove side clearance portion W, Wa, Wb, Wc, Wd, We closing gaps

Claims

1. A gas compressor for compressing gas, comprising: a cylinder; a piston inserted into the cylinder for compressing the gas in the cylinder; a piston ring group composed of a plurality of annular piston rings disposed between the piston and the cylinder; a driving device for moving the piston in the axial direction of the cylinder and the piston; and having a part of each of the plurality of piston rings is open to form a mating portion; when the direction in which the gas compressed in the cylinder is located is defined as the front side and the direction opposite to the front side is defined as the rear side, a mating gap of a first piston ring located on the foremost side is larger than a mating gap of any second piston ring located on the rear side of the first piston ring. A gas compressor characterized by this.

2. The gas compressor according to claim 1, characterized in that the mating gap of the first piston ring is larger than the mating gaps of all other piston rings.

3. The gas compressor according to claim 1 or 2, characterized in that a mating gap of a piston ring located on the rearmost side among the plurality of piston rings is smaller than the mating gaps of all other piston rings.

4. When any one piston ring except the piston ring located on the rearmost side among the plurality of piston rings is defined as the nth piston ring and any piston ring located on the rear side of the nth piston ring is defined as the (n + 1)th piston ring, the mating gap of the nth piston ring is the same as or larger than the mating gap of the (n + 1)th piston ring. The gas compressor according to claim 1, characterized by this.

5. When any one piston ring except the piston ring located on the rearmost side among the plurality of piston rings is defined as the nth piston ring and any piston ring located on the rear side of the nth piston ring is defined as the (n + 1)th piston ring, the mating gap of the nth piston ring is larger than the mating gap of the (n + 1)th piston ring. The gas compressor according to claim 1, characterized by this.

6. The piston ring group consists of (n + 1) piston rings, and the joint gaps of all the piston rings from the first piston ring to the nth piston ring are each larger than the joint gaps of all the piston rings located on the rear side thereof. The gas compressor according to claim 4 or 5 is characterized by this.

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