Double-cylinder symmetrical rack-driven piston compressor structure and gas compression method

Abstract

The invention discloses a double-cylinder symmetrical rack-driven piston compressor structure and a gas compression method.The compressor structure comprises a rack cylinder arranged in a compressor cylinder body, the two ends of the rack cylinder are each provided with a piston, and the two ends of the compressor cylinder body are each connected with a compression air cylinder in a sealed mode; the piston is correspondingly arranged in the compression air cylinder; a cavity is formed in the rack cylinder, a gear rotor is arranged in the cavity, and a rack meshed with the gear rotor is machined on the inner wall of the cavity; an air inlet valve and an exhaust valve are arranged on the compression air cylinder, the rack cylinder is driven to do reciprocating motion through rotating motion of the gear rotor, then the piston is driven to do reciprocating motion in the compression air cylinder, the volume of a volume cavity of the compression air cylinder is changed, and the air suction, compression and exhaust processes are achieved. The double-side rack and gear rotor meshing driving structure is adopted, direct driving of the crankshaft and the piston is achieved, moving parts of the piston compressor are reduced, and meanwhile the overall size of the piston compressor is reduced.

Description

Technical Field

[0001] This invention belongs to the field of reciprocating piston machinery, specifically relating to a dual-cylinder symmetrical rack and pinion driven piston compressor structure and a gas compression method. Background Technology

[0002] A reciprocating compressor is a type of compressor that uses the reciprocating motion of a piston to pressurize and transport gas. It is widely used in industrial manufacturing, commercial refrigeration and cooling, and petrochemical industries. Traditional reciprocating compressors employ a crank-connecting rod drive structure, converting the rotational motion of the crankshaft into the reciprocating motion of the piston. After decades of development, the manufacturing and assembly processes for reciprocating compressors have matured. However, in the field of small commercial refrigeration compressors, the traditional crank-connecting rod mechanism results in a larger overall size for the reciprocating compressor, and the planar motion connection between the crankshaft and connecting rod requires sufficient oil lubrication to reduce bearing wear. Furthermore, the overturning force exerted on the moving piston by the crank-connecting rod mechanism affects the lifespan of the seals and the smoothness of compressor operation. In today's increasingly competitive global manufacturing environment, lean manufacturing and cost reduction are crucial paths for technological transformation and upgrading. Therefore, improving the energy efficiency and reducing the cost of reciprocating compressors remain important research topics. Summary of the Invention

[0003] The purpose of this invention is to address the problems in the prior art by providing a dual-cylinder symmetrical rack and pinion driven piston compressor structure and a gas compression method. It adopts a double-sided rack and pinion rotor meshing drive structure to achieve direct drive of the crankshaft and piston. The rack and pinion drive structure replaces the traditional crank connecting rod structure, reducing the moving parts of the piston compressor and also reducing the overall size of the piston compressor.

[0004] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, a dual-cylinder symmetrical rack-driven piston compressor structure is provided, including a rack cylinder disposed inside the compressor cylinder body, with a piston disposed at each end of the rack cylinder, and a compression cylinder sealed to each end of the compressor cylinder body, the pistons being correspondingly placed inside the compression cylinders; the rack cylinder has a cavity inside, a gear rotor is disposed in the cavity, and a rack that meshes with the gear rotor is machined on the inner wall of the cavity; the compression cylinder is provided with an intake valve and an exhaust valve, the rotational motion of the gear rotor drives the rack cylinder to reciprocate, thereby driving the piston to reciprocate within the compression cylinder, causing the volume of the compression cylinder cavity to change, realizing the intake, compression and exhaust processes.

[0005] As a preferred embodiment, a motor is installed outside the compressor cylinder, and the gear rotor is connected to the motor shaft of the motor via a key, so that the motor drives the gear rotor to rotate.

[0006] As a preferred embodiment, the cavity is opened along the axial direction of the rack cylinder, and the rack is machined on the inner walls of the upper and lower sides of the cavity. Through meshing, the rotational motion of the gear rotor is converted into the linear reciprocating motion of the rack cylinder. The side of the cavity facing the motor is flat-cut and fitted with a rack cylinder cover. The rack cylinder and the rack cylinder cover are pressed and fixed by screws. The groove-shaped boss of the rack cylinder cover is matched and constrained with the groove of the compressor cylinder body. The rack cylinder and the rack cylinder cover are assembled to form a cylindrical structure.

[0007] As a preferred embodiment, the piston is machined with three piston rings, wherein the first piston ring is made of polytetrafluoroethylene.

[0008] As a preferred option, the piston is hollowed out to reduce its weight, and the piston and rack cylinder are machined into an integral structure by laser welding.

[0009] As a preferred embodiment, the compressor cylinder body is connected to the compression cylinders at both ends by flange bolts, circumferentially positioned by the bosses of the compression cylinders, and sealed with sealing rings.

[0010] As a preferred embodiment, the pistons at both ends of the rack cylinder are symmetrically distributed with the compression cylinder, forming a first compression chamber and a second compression chamber.

[0011] As a preferred embodiment, the rack cylinder has an oil inlet at its upper part and an oil outlet at its lower part; the compressor cylinder body is provided with an oil inlet and an oil outlet; oil is sprayed to lubricate the pistons at both ends of the rack cylinder and the gear rotor inside the rack cylinder through the oil inlet on the compressor cylinder body; the lubricating oil inside the rack cylinder flows into the compressor cylinder body through the lower oil outlet and is discharged through the oil outlet of the compressor cylinder body together with the lubricating oil passing through the piston.

[0012] As a preferred embodiment, the piston stroke is calculated according to the following expression:

[0013] In the formula, S For compressor stroke, m For gear module, z This refers to the number of teeth on the gear. The angle through which the gear rotates.

[0014] Secondly, a gas compression method based on a dual-cylinder symmetrical rack-and-pinion driven piston compressor structure is provided, including: The gear rotor rotates, the piston at one end of the rack cylinder is at the top dead center, and the piston at the other end of the rack cylinder is at the bottom dead center. The piston at the top dead center moves to the bottom dead center, and the piston at the bottom dead center moves to the top dead center. The gear rotor meshes with the rack of the rack cylinder, which is converted into the rack cylinder moving linearly to one side. The compression cylinder at one end of the rack cylinder draws in air, and the compression cylinder at the other end of the rack cylinder compresses and exhausts air. The piston at one end of the rack cylinder, which has moved to the bottom dead center, moves to the top dead center. The piston at the other end of the rack cylinder, which has moved to the top dead center, moves to the bottom dead center. The gear rotor, through meshing with the rack of the rack cylinder, converts the rack cylinder into linear motion to the other side. The compression cylinder at one end of the rack cylinder, which has completed the intake, compresses and exhausts air, while the compression cylinder at the other end of the rack cylinder, which has completed the compression and exhaust, begins to intake air.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: This invention relates to a dual-cylinder symmetrical rack and pinion driven piston compressor structure. Through the precise meshing of racks on both sides with a gear rotor, the rotational motion of the gear rotor is efficiently converted into the linear reciprocating motion of the piston structure, successfully achieving a direct-drive mode for the crankshaft and piston. Under this driving method, the overturning moment acting on the piston is greatly reduced. Compared to traditional drive structures, the piston experiences more balanced and stable forces during movement, effectively reducing piston wobble and wobbling caused by overturning moment. This significantly reduces the vibration amplitude during piston compressor operation, improves the smoothness and reliability of equipment operation, reduces noise caused by vibration and wear on equipment components, and extends the compressor's service life. The rack and pinion drive structure of this invention cleverly replaces the traditional crank-connecting rod structure. The traditional crank-connecting rod structure contains multiple complex moving parts, such as the crankshaft and connecting rod. These parts cooperate with each other during movement, increasing the complexity of the mechanical structure and making the compressor's performance and reliability susceptible to problems such as wear and clearance between components. The gear and rack drive structure of this invention simplifies the transmission path, reduces the number of moving parts, lowers the probability of mechanical failure, and improves transmission efficiency and precision, making the compressor's operation more stable and reliable. By reducing the number of moving parts, this invention optimizes the overall structure of the piston compressor, allowing for a smaller overall size while meeting the same compression function and performance requirements. This not only reduces the space occupied by the compressor during installation and use, improving space utilization, but also reduces the amount of raw materials used and simplifies processing steps and assembly complexity during manufacturing. From raw material procurement to production, and then to subsequent transportation, installation, and maintenance, costs at each stage are effectively controlled, thereby significantly reducing the overall cost of the piston compressor and enhancing the product's market competitiveness. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the technical solutions of this application. The illustrative embodiments and descriptions of this application are only for explaining this application and do not constitute an improper limitation on the scope of protection of this application. The drawings described below are some embodiments of the technical solutions of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is an exploded view of the structure of a dual-cylinder symmetrical rack and pinion driven piston compressor according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the three-dimensional model structure of the gear rotor according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the piston and rack cylinder structure according to an embodiment of the present invention; Figure 4 This is a schematic diagram showing the fit between the grooved boss of the rack cylinder head and the groove of the compressor cylinder body in an embodiment of the present invention; Figure 5 This is a schematic diagram of the oil circuit of a dual-cylinder symmetrical rack and pinion driven piston compressor according to an embodiment of the present invention; Figure 6 This is a schematic diagram illustrating the working process of a dual-cylinder symmetrical rack and pinion driven piston compressor according to an embodiment of the present invention. In the attached diagram: 1-Motor; 2-Motor shaft; 3-Flat key; 4-Gear rotor; 5-Rack cylinder; 51-Piston; 6-Rack cylinder cover; 7-Piston ring; 8-Compressor cylinder body; 9-Compressor cylinder; 10-Intake valve; 11-Exhaust valve; 12-Sealing ring. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] It should be noted that, in the description of the embodiments of the present invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0020] Furthermore, in the description of this invention, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] Please see Figure 1 This invention proposes a dual-cylinder symmetrical rack and pinion driven piston compressor structure. The structure includes a rack cylinder 5 housed inside a compressor cylinder body 8. A piston 51 is located at each end of the rack cylinder 5. A compression cylinder 9 is sealed to each end of the compressor cylinder body 8, with the pistons 51 correspondingly positioned inside the compression cylinder 9. The rack cylinder 5 has an internal cavity containing a gear rotor 4. The structure of the gear rotor 4 is as follows... Figure 2 As shown, a rack is machined on the inner wall of the cavity to mesh with the gear rotor 4. The compression cylinder 9 is equipped with an intake valve 10 and an exhaust valve 11. The rotational motion of the gear rotor 4 drives the rack cylinder 5 to reciprocate, which in turn drives the piston 51 to reciprocate within the compression cylinder 9, causing a volume change in the compression cylinder 9's chamber, thus realizing the intake, compression, and exhaust processes. In this embodiment of the invention, the piston 51 and the rack cylinder 5 are an integral structure, and the rack cylinder cover 6 is connected to the rack cylinder 5 by screws, as shown... Figure 3 As shown, in one possible implementation, the piston 51 is hollowed out to reduce its weight, and the piston 51 and the rack cylinder 5 are processed into an integral structure by laser welding.

[0022] Furthermore, in this embodiment of the invention, a motor 1 is provided on the outside of the compressor cylinder 8, and the gear rotor 4 is connected to the motor shaft 2 of the motor 1 via a key 3, so that the motor 1 drives the gear rotor 4 to rotate.

[0023] The internal cavity of the rack cylinder 5 is opened along the axial direction of the rack cylinder 5. The rack is machined on the upper and lower inner walls of the cavity. Through meshing, the rotational motion of the gear rotor 4 is converted into the linear reciprocating motion of the rack cylinder 5. Please refer to [link / reference]. Figure 4 The cavity facing the motor 1 is cut flat and fitted with a rack cylinder cover 6. The rack cylinder 5 and the rack cylinder cover 6 are pressed and fixed by screws. The groove-shaped boss of the rack cylinder cover 6 is matched and constrained with the groove of the compressor cylinder 8. The rack cylinder 5 and the rack cylinder cover 6 are assembled to form a cylindrical structure.

[0024] In one possible implementation, the piston 51 is machined with three piston rings 7, of which the first piston ring 7 is made of polytetrafluoroethylene (PTFE). The first piston ring has the highest sealing priority because it directly contacts the high-pressure gas in the cylinder, bearing the greatest pressure difference and impact force. Its sealing performance directly affects equipment efficiency (such as compressor discharge capacity) and safety (such as preventing leakage of flammable and explosive gases). PTFE has an extremely low coefficient of friction and excellent self-lubricating properties, allowing it to quickly form a stable oil film (even without oil lubrication), reducing the risk of leakage under high pressure. Simultaneously, its elastic deformation capability allows it to tightly conform to the cylinder wall, compensating for minor manufacturing errors or wear, ensuring an initial sealing effect. Subsequent piston rings mainly perform oil scraping, pressure equalization, and auxiliary sealing functions. For example, the second ring may be used to scrape excess lubricating oil from the cylinder wall, while the third ring further equalizes pressure and reduces residual leakage. Subsequent rings need to withstand the friction and wear generated by the piston's reciprocating motion; therefore, they are often made of metal materials (such as cast iron or steel) or composite materials (such as metal with a PTFE coating) to balance wear resistance and cost. PTFE is expensive (several times more expensive than ordinary metal materials) and difficult to process (requiring special molds and processes). Using PTFE only in critical sealing areas can significantly reduce overall costs. Furthermore, pure PTFE has low tensile strength and impact resistance, making it difficult to withstand the oil scraping or pressure equalization loads required by subsequent rings alone. Therefore, subsequent rings typically use a metal matrix combined with a PTFE coating or filled with modified PTFE (such as glass fiber or graphite) to enhance mechanical properties. Multi-ring piston systems achieve efficient sealing through "step-by-step pressure reduction." The first ring undertakes the primary sealing task, while subsequent rings further reduce residual leakage. Using PTFE only in the first ring maximizes its sealing advantages while avoiding seal failures in subsequent rings due to material mismatch. For example, if subsequent rings also use PTFE, insufficient wear resistance may lead to incomplete oil scraping, increasing the risk of oil contamination. Since the first ring is in direct contact with the high-pressure medium, its wear rate is usually faster than subsequent rings. Designing it as a replaceable PTFE ring reduces maintenance costs (eliminating the need to replace the entire piston ring assembly). The standardized design of PTFE rings (such as open-type and stepped-type) makes them easy to install and adjust, while subsequent rings may require customized design due to functional differences, further highlighting the modular advantages of PTFE rings.

[0025] In one possible implementation, the compressor cylinder body 8 is connected to the compression cylinders 9 at both ends by flange bolts, the compression cylinder 9 is circumferentially positioned by the bosses of the compression cylinder 9, and is sealed by sealing rings 12.

[0026] The dual-cylinder symmetrical rack-driven piston compressor structure described in this embodiment of the invention has pistons 51 at both ends of the rack cylinder 5 symmetrically distributed with the compression cylinder 9, forming a first compression chamber (compression chamber I) and a second compression chamber (compression chamber II).

[0027] Please see Figure 5 The rack cylinder 5 has an oil inlet at its upper part and an oil outlet at its lower part. The compressor cylinder body 8 is equipped with an oil inlet and an oil outlet. Oil is sprayed through the oil inlet on the compressor cylinder body 8 to lubricate the pistons 51 at both ends of the rack cylinder 5 and the gear rotor 4 inside the rack cylinder 5. The lubricating oil inside the rack cylinder 5 flows into the compressor cylinder body 8 through the lower oil outlet and is discharged through the oil outlet of the compressor cylinder body 8 together with the lubricating oil passing through the pistons 51.

[0028] The stroke of piston 51 in this embodiment of the invention is calculated according to the following expression:

[0029] In the formula, S For compressor stroke, m For gear module, z This refers to the number of teeth on the gear. The angle through which the gear rotates.

[0030] Please see Figure 6 Another embodiment of the present invention also proposes a gas compression method based on the aforementioned dual-cylinder symmetrical rack-and-pinion driven piston compressor structure, comprising: The gear rotor 4 rotates (assuming the gear rotor 4 rotates counterclockwise). The piston 51 at one end of the rack cylinder 5 is at the top dead center (piston 1 in compression chamber I), and the piston 51 at the other end of the rack cylinder 5 is at the bottom dead center (piston 2 in compression chamber II). The piston 51 at the top dead center moves to the bottom dead center, and the piston 51 at the bottom dead center moves to the top dead center. The gear rotor 4 meshes with the rack of the rack cylinder 5, which is converted into linear motion of the rack cylinder 5 to one side. The compression cylinder 9 at one end of the rack cylinder 5 draws in air (air intake in compression chamber I), and the compression cylinder 9 at the other end of the rack cylinder 5 compresses and exhausts air (compression exhaust in compression chamber II). Piston 51, which has moved to the bottom dead center at one end of rack cylinder 5, moves to the top dead center (piston 1 in compression chamber I). Piston 51, which has moved to the top dead center at the other end of rack cylinder 5, moves to the bottom dead center (piston 2 in compression chamber II). Gear rotor 4, through meshing with the rack of rack cylinder 5, converts rack cylinder 5 into linear motion to the other side. Compressor cylinder 9, which has completed air intake at one end of rack cylinder 5, compresses and exhausts air (compression chamber I compresses and exhausts air). Compressor cylinder 9, which has completed air compression and exhaust at the other end of rack cylinder 5, begins to intake air (compression chamber II intakes air).

[0031] The dual-cylinder symmetrical rack and pinion driven piston compressor structure of this invention helps to reduce the overall size of the piston compressor, reduce the number of vulnerable parts, and improve the overall reliability of the piston compressor, providing an effective reference solution for the development of new piston compressor models.

[0032] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0033] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

[0034] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-cylinder symmetrical rack and pinion driven piston compressor structure, characterized in that, The compressor includes a rack cylinder (5) located inside the compressor cylinder body (8). A piston (51) is provided at each end of the rack cylinder (5). A compression cylinder (9) is sealed to each end of the compressor cylinder body (8). The piston (51) is placed inside the compression cylinder (9). The rack cylinder (5) has a cavity inside, in which a gear rotor (4) is provided. A rack that meshes with the gear rotor (4) is machined on the inner wall of the cavity. An intake valve (10) and an exhaust valve (11) are provided on the compression cylinder (9). The rack cylinder (5) is driven to reciprocate by the rotation of the gear rotor (4), which in turn drives the piston (51) to reciprocate in the compression cylinder (9), causing the volume of the compression cylinder (9) to change, thereby realizing the intake, compression and exhaust processes.

2. The dual-cylinder symmetrical rack and pinion driven piston compressor structure according to claim 1, characterized in that, The compressor cylinder (8) is equipped with a motor (1) on its outside. The gear rotor (4) is connected to the motor shaft (2) of the motor (1) via a key (3). The motor (1) drives the gear rotor (4) to rotate.

3. The dual-cylinder symmetrical rack and pinion driven piston compressor structure according to claim 2, characterized in that, The cavity is opened along the axial direction of the rack cylinder (5). The rack is machined on the inner walls of the upper and lower sides of the cavity. The rotational motion of the gear rotor (4) is converted into the linear reciprocating motion of the rack cylinder (5) through meshing. The side of the cavity facing the motor (1) is flat-cut and fitted with the rack cylinder cover (6). The rack cylinder (5) and the rack cylinder cover (6) are fixed by screws. The groove-shaped boss of the rack cylinder cover (6) is matched and constrained with the groove of the compressor cylinder body (8). The rack cylinder (5) and the rack cylinder cover (6) are assembled to form a cylindrical structure.

4. The dual-cylinder symmetrical rack and pinion driven piston compressor structure according to claim 1, characterized in that, The piston (51) is machined with three piston rings (7), wherein the first piston ring (7) is made of polytetrafluoroethylene.

5. The dual-cylinder symmetrical rack and pinion driven piston compressor structure according to claim 1, characterized in that, The piston (51) is hollowed out to reduce its weight, and the piston (51) and rack cylinder (5) are processed into an integral structure by laser welding.

6. The dual-cylinder symmetrical rack and pinion driven piston compressor structure according to claim 1, characterized in that, The compressor cylinder body (8) is connected to the compression cylinders (9) at both ends by flange bolts. The compression cylinder (9) is circumferentially positioned by the boss and is sealed with a sealing ring (12).

7. The dual-cylinder symmetrical rack and pinion driven piston compressor structure according to claim 1, characterized in that, The pistons (51) at both ends of the rack cylinder (5) are symmetrically distributed with the compression cylinder (9) to form a first compression chamber and a second compression chamber.

8. The dual-cylinder symmetrical rack and pinion driven piston compressor structure according to claim 1, characterized in that, The rack cylinder (5) has an oil inlet at the top and an oil outlet at the bottom. The compressor cylinder body (8) is provided with an oil inlet and an oil outlet. The pistons (51) at both ends of the rack cylinder (5) and the gear rotor (4) inside the rack cylinder (5) are lubricated by spraying oil through the oil inlet on the compressor cylinder body (8). The lubricating oil inside the rack cylinder (5) flows into the compressor cylinder body (8) through the oil outlet at the bottom and is discharged through the oil outlet of the compressor cylinder body (8) together with the lubricating oil passing through the piston (51).

9. The dual-cylinder symmetrical rack and pinion driven piston compressor structure according to claim 1, characterized in that, The stroke of the piston (51) is calculated according to the following expression: In the formula, S For compressor stroke, m For gear module, z This refers to the number of teeth on the gear. The angle through which the gear rotates.

10. A gas compression method based on the dual-cylinder symmetrical rack and pinion driven piston compressor structure according to any one of claims 1 to 9, characterized in that, include: The gear rotor (4) rotates, the piston (51) at one end of the rack cylinder (5) is at the top dead center, and the piston (51) at the other end of the rack cylinder (5) is at the bottom dead center. The piston (51) at the top dead center moves to the bottom dead center, and the piston (51) at the bottom dead center moves to the top dead center. The gear rotor (4) is converted into the rack cylinder (5) moving to one side by meshing with the rack of the rack cylinder (5). The compression cylinder (9) at one end of the rack cylinder (5) draws in air, and the compression cylinder (9) at the other end of the rack cylinder (5) compresses and exhausts air. The piston (51) at one end of the rack cylinder (5) has moved to the bottom dead center and moves to the top dead center. The piston (51) at the other end of the rack cylinder (5) has moved to the top dead center and moves to the bottom dead center. The gear rotor (4) is converted into the rack cylinder (5) moving to the other side by meshing with the rack of the rack cylinder (5). The compression cylinder (9) at one end of the rack cylinder (5) performs compression and exhaust, and the compression cylinder (9) at the other end of the rack cylinder (5) performs compression and exhaust.

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