reciprocating compressor

Abstract

To provide a reciprocation compressor which can reduce a dead volume by reducing a side force at a compression stroke.SOLUTION: A reciprocation compressor comprises: a crankshaft 2 having a rotation axial line Rs which is offset to a center axial line Cc of a cylinder 4; a piston 5 forming a compression chamber 14 together with the cylinder, and reciprocating in the cylinder; and a connecting rod 6 connected to the crankshaft 2 at one side so as to be turnable, fixed to the piston 5 at the other side, and oscillating by a turning motion of the crankshaft. The piston 5 has an apex face 51 constituting a wall face of the compression chamber, a slide face 52 sliding with an internal peripheral face 4a of the cylinder 4 within a range which is defined according to a range of an oscillation angle of the connecting rod 6, and a first non-slide face 53 having a shape for connecting the apex face 51 and the slide face 52, and avoiding contact with the internal peripheral face 4a of the cylinder 4. At least a part of the first non-slide face 53 is located near the internal peripheral face of the cylinder 4 rather than a first virtual extension curved face 52V1 which is formed by virtually extending the slide face 52 to the apex face 51 side.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a reciprocating compressor in which a piston reciprocates within a cylinder.

Background Art

[0002] In a reciprocating compressor, a piston is connected to a crankshaft via a connecting rod, and a rotational force of a rotational drive source such as an electric motor is converted into a reciprocating motion of the piston by the crankshaft to compress a gas or the like. Among reciprocating compressors, there are those in which a piston is connected to the tip (small end) of a connecting rod via a bearing, and the piston reciprocates without tilting with respect to the cylinder while rocking with respect to the connecting rod. On the other hand, there are those in which a piston is fixed to the tip of a connecting rod, and the piston reciprocates while rocking with respect to the cylinder. That is, there is a reciprocating compressor provided with a rocking type piston that rocks integrally with the connecting rod. The latter enables improvement in durability by reduction of movable parts, weight reduction, low noise, and cost reduction by reduction of the number of parts, as compared with the former.

[0003] As an example of a reciprocating compressor provided with a rocking type piston, there is one described in Patent Document 1. In the reciprocating compressor described in Patent Document 1, a spherical piston that reciprocates while sliding within a cylinder rocks in an intake stroke to form a depression on the piston spherical surface at a portion that slidably contacts the inner peripheral surface of the cylinder, and an intake port for sucking fluid into the compression chamber from the piston rod (connecting rod) side is formed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the reciprocating compressor described in Patent Document 1, the rotation axis of the crankshaft intersects with the central axis of the cylinder. In this structure, when the swing angle of the piston (piston rod) is large, the force acting between the piston and the cylinder during the compression stroke (hereinafter referred to as the side force) increases accordingly. As a result, the friction between the cylinder and the piston increases, leading to energy loss. Therefore, there is a desire to suppress the side force during the compression stroke. Thus, by adopting an offset structure in which the rotation axis of the crankshaft is arranged at a position shifted without intersecting the central axis of the cylinder, it is possible to reduce the side force during the compression stroke.

[0006] Also, in the reciprocating compressor described in Patent Document 1, by making the piston that swings integrally with the piston rod spherical, even when the swing angle of the piston with respect to the cylinder is large, it can slide smoothly with respect to the inner peripheral surface of the cylinder, so it is possible to reduce the risk of damage to the piston. However, compared with a cylindrical piston that is swingably connected to the connecting rod via a bearing, a spherical piston will increase the dead volume of the compression chamber. Since the size of the dead volume is a factor in the reduction of the discharge performance of the compressor (reduction of the discharge flow rate and reduction of the volumetric efficiency), there is a desire to reduce the dead volume.

[0007] Also, in the reciprocating compressor described in Patent Document 1, since the piston is spherical, it is necessary to maintain the airtightness of the compression chamber by line contact between the piston and the cylinder. This configuration may result in lower airtightness of the compression chamber than in the case of sealing by surface contact between the aforementioned cylindrical piston and the cylinder. Therefore, a method of attaching a piston ring to the piston can be considered. However, since the piston ring swings with respect to the cylinder along with the swinging motion of the piston, when the swing angle of the piston is large, the sealing performance of the piston ring may not be fully exhibited. However, in a reciprocating compressor adopting an offset structure for reducing the side force during the compression stroke, since the swing of the piston ring during the compression stroke can be suppressed, the sealing performance of the piston ring during the compression stroke can be maintained.

[0008] However, in the case of an offset structure, since the rocking motion of the piston becomes asymmetric, in order to exhibit the sealing performance of the piston ring, it is necessary to mount the piston ring so as to be inclined with respect to the top surface of the piston. When the piston ring is mounted on the piston in this way, the area of the outer peripheral surface of the piston existing on the top surface side rather than the piston ring increases, resulting in an increase in the dead volume of the compression chamber.

[0009] The present invention has been made to solve the above problems, and an object thereof is to provide a reciprocating compressor capable of reducing the side force acting between the piston and the cylinder during the compression stroke and reducing the dead volume.

Means for Solving the Problems

[0010] This application includes a plurality of means for solving the above problems. For example, a cylinder having a central axis, a crankshaft having a rotational axis offset with respect to the central axis of the cylinder, a compression chamber formed together with the cylinder, a piston reciprocating in the cylinder, one side being rotatably connected to the crankshaft and the other side being fixed to the piston, and a connecting rod that swings with respect to the cylinder by the rotational motion of the crankshaft. The piston includes a top surface that forms a part of the wall surface of the compression chamber, and is determined according to the range of the swing angle of the connecting rod with respect to the central axis of the cylinder. predetermined range formed over a a sliding surface that slides on the inner peripheral surface of the cylinder spherical shape and a sliding surface, formed outside the and has a first non-sliding surface that connects the top surface and the sliding surface and avoids contact with the inner peripheral surface of the cylinder. At least a part of the first non-sliding surface is located closer to the inner peripheral surface of the cylinder than a first virtual extension curved surface obtained by virtually extending the sliding surface toward the top surface side.

Effects of the Invention

[0011] According to the present invention, by offsetting the crankshaft with respect to the cylinder, it is possible to reduce the rocking angle of the piston during the compression stroke, and by forming at least a part of the first non-sliding surface of the piston on the outer peripheral side (radial outside) of the first virtual extended curved surface, the gap between the first non-sliding surface of the piston and the inner peripheral surface of the cylinder is reduced. Therefore, it is possible to reduce the side force acting between the piston and the cylinder during the compression stroke and reduce the dead volume. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the reciprocating compressor of the present invention will be described with reference to the drawings. [First Embodiment] The configuration of the first embodiment of the reciprocating compressor of the present invention will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view showing the first embodiment of the reciprocating compressor of the present invention.

[0014] In FIG. 1, the reciprocating compressor 1 compresses a gas such as air using a crank mechanism and discharges the compressed gas to a tank (not shown) or the like. Specifically, the reciprocating compressor 1 includes a crankshaft 2 that is driven by a rotational drive source (not shown) such as an electric motor to perform a rotational motion, a crankcase 3 that rotatably houses the crankshaft 2, a cylinder 4 attached to the crankcase 3, a piston 5 that reciprocates inside the cylinder 4, and a connecting rod 6 that connects the piston 5 and the crankshaft 2.

[0015] The crankshaft 2 rotates about the axis of rotation Rs. The crankshaft 2 is rotatably supported by a bearing (not shown) disposed in the crankcase 3 and rotates about the axis of rotation Rs. The crankshaft 2 includes a crank journal 21 rotatably supported by the bearing, a crank pin 22 located at an eccentric position with respect to the axis of rotation Rs, a crank arm 23 connecting the crank journal 21 and the crank pin 22, and a balance weight 24 for adjusting the balance during rotation. The crank pin 22 is rotatably connected to one end (the large end portion 62 described later) of the connecting rod 6 via a bearing 7. As the bearing 7, for example, a rolling bearing or a sliding bearing can be used. Note that the bearing 7 can also be configured integrally with either the connecting rod 6 or the crankshaft 2. The crankcase 3 is provided with a breathing hole 3a that communicates the inside and outside of the case 3.

[0016] The cylinder 4 has a central axis Cc and is attached such that the opening on one side (the lower side in FIG. 1) communicates with the inside of the crankcase 3. Further, a cylinder head 8 is attached to the other end (the upper side in FIG. 1) of the cylinder 4 via a valve plate 9. The cylinder head 8 has an intake chamber 8a for taking in gas from the outside and an exhaust chamber 8b for discharging the compressed gas to the outside. The valve plate 9 closes the opening on the other side of the cylinder 4 and has an intake hole 9a that communicates the inside of the cylinder 4 (the compression chamber 14 described later) with the intake chamber 8a of the cylinder head 8 and a discharge hole 9b that communicates the inside of the cylinder 4 with the exhaust chamber 8b of the cylinder head 8.

[0017] A reed valve type intake valve 10 and a discharge valve 11 are attached to the valve plate 9. The intake valve 10 allows the gas in the intake chamber 8a of the cylinder head 8 to flow into the cylinder 4 through the intake hole 9a while preventing the gas in the cylinder 4 from flowing into the intake chamber 8a through the intake hole 9a. The discharge valve 11 allows the gas in the cylinder 4 to flow into the exhaust chamber 8b of the cylinder head 8 through the discharge hole 9b while preventing the gas in the exhaust chamber 8b from flowing into the cylinder 4 through the discharge hole 9b.

[0018] The piston 5 is fixed to the other end portion (the small end portion 63 described later) of the connecting rod 6 without using a bearing and is integrated with the connecting rod 6. That is, when the crankshaft 2 rotates, the piston 5 is a rocking type piston (rocking piston) that reciprocates while rocking in the cylinder 4 integrally with the connecting rod 6. The fixing method of the piston 5 and the connecting rod 6 can be fastening with bolts, welding, press-fitting, etc. The piston 5 is formed of a material different from that of the connecting rod 6, for example, in order to achieve both the sliding characteristics of the piston 5 in an environment where lubricating oil is not used and the mechanical strength of the connecting rod 6. The piston 5, together with the cylinder 4 and the valve plate 9, forms a compression chamber 14 for compressing gas. As the piston 5 reciprocates in the cylinder 4, the compression chamber 14 repeatedly expands and contracts. The intake valve 10 and the discharge valve 11 are opened and closed in accordance with the expansion and contraction of the compression chamber 14. By adopting a configuration in which lubricating oil is not supplied to the piston 5, there is an advantage that lubricating oil does not mix into the gas in the compression chamber 14. If a large amount of lubricating oil flows into the compression chamber 14, there is a concern about a decrease in reliability such as a decrease in the efficiency of the compressor due to a decrease in the intake air volume and damage to valve bodies and the like due to liquid compression. Details of the structure of the piston 5 will be described later.

[0019] A piston ring 12 for improving the airtightness of the compression chamber 14 is attached to the piston 5. The piston ring 12 is formed so that the airtightness of the compression chamber 14 is maintained during the compression stroke while sliding smoothly in the cylinder 4 in a state of being attached to the piston 5. Specifically, the piston ring 12 is a member having an outer peripheral surface that is a substantially cylindrical surface and a substantially C-shaped cross-section, and has a joint (not shown). The outer diameter of the piston ring 12 is set to be slightly larger than the inner diameter of the cylinder 4 in a natural state. For this reason, in a state where the piston ring 12 attached to the piston 5 is inserted into the cylinder 4, the outer peripheral surface of the piston ring 12 is substantially in close contact with the inner peripheral surface 4a of the cylinder 4 due to the reaction force caused by the deformation of the piston ring 12, thereby maintaining the airtightness of the compression chamber 14.

[0020] The connecting rod 6 has a straight rod portion 61, a cylindrical large end portion 62 provided at one end of the straight rod portion 61, and a hemispherical small end portion 63 provided at the other end of the straight rod portion 61. The straight rod portion 61 has a tapered shape from the large end portion 62 side toward the small end portion 63 side. The large end portion 62 is a portion connected to the crank pin 22 of the crankshaft 2 via a bearing 7, and is rotatable about the central axis Cb of the bearing 7 as a rotation axis. The small end portion 63 has a spherical side connected to the straight rod portion 61 and a circular flat portion connected to the piston 5. A straight line connecting the rotation axis (central axis Cb of the bearing 7) of the cylindrical large end portion 62 and the center of the hemispherical small end portion 63 is the center line Cr of the connecting rod 6, and the straight rod portion 61 extends along the center line Cr of the connecting rod 6.

[0021] The reciprocating compressor 1 according to the present embodiment has an offset structure in which the rotation axis Cs of the crankshaft 2 (crank journal 21) is offset (in a separated position) without intersecting the central axis Cc of the cylinder 4. In this offset structure, in order to reduce the force acting between the piston 5 and the cylinder 4 during the compression stroke (hereinafter referred to as side force), the rotation axis Rs of the crankshaft 2 is configured to be offset in the pressing direction of the piston 5 against the inner peripheral surface 4a of the cylinder 4 during the compression stroke with respect to the central axis Cc of the cylinder 4. For example, as shown in FIG. 1, when the cylinder 4 is located above the crankshaft 2 and the crankshaft 2 rotates counterclockwise, the rotation axis Rs of the crankshaft 2 is arranged at a position separated by an offset amount δ to the left with respect to the central axis Cc of the cylinder 4. Conversely, when the crankshaft 2 rotates clockwise, the rotation axis Rs of the crankshaft 2 is arranged at a position separated by an offset amount δ to the right with respect to the central axis Cc of the cylinder 4.

[0022] Next, the characteristics of the offset structure of the reciprocating compressor according to the present embodiment will be described with reference to FIGS. 1 to 3. FIG. 2 is a characteristic diagram showing the relationship between the rocking angle of the piston and the connecting rod with respect to the crank angle. FIG. 3 is a diagram showing the relationship between the inclination angle of the piston ring with respect to the cylinder and the gas leakage amount. In FIG. 2, the horizontal axis θ represents the crank angle, and the vertical axis β represents the rocking angle of the piston and the connecting rod. In FIG. 3, the horizontal axis represents the inclination angle of the piston ring with respect to the cylinder, and the vertical axis represents the gas leakage amount (mass flow rate) of the gas leaking from the gap between the piston ring and the cylinder.

[0023] In FIG. 1, the crank angle θ, which is the rotation angle of the crankshaft 2, is set to 0° when the crank pin 22 is located at the lowest point, and the counterclockwise direction is defined as the positive direction. The acute angle formed by the center line Cr of the connecting rod 6 (which also coincides with the center axis 5b of the piston 5 described later) with respect to the central axis Cc of the cylinder 4 is defined as the rocking angle β. The rocking angle β is a positive value when the central axis Cb of the bearing 7 is located on the left side of the central axis Cc of the cylinder 4, and a negative value when the central axis Cb of the bearing 7 is located on the right side of the central axis Cc of the cylinder 4.

[0024] As a comparative example for the offset structure of the present embodiment, a configuration different from the offset structure is considered. That is, when the rotation axis Rs of the crankshaft 2 intersects the central axis Cc of the cylinder 4 (that is, when the offset amount δ is 0), the rocking motion of the piston 5 and the connecting rod 6 is symmetric with respect to the central axis Cc of the cylinder 4. In this case, the maximum value of the rocking angle β during the compression stroke (while the piston 5 moves from the bottom dead center to the top dead center) is equal to the maximum value of the rocking angle β during the suction stroke (while the piston 5 moves from the top dead center to the bottom dead center).

[0025] On the other hand, in the case of the offset structure of the present embodiment, the rocking motions of the piston 5 and the connecting rod 6 become asymmetric with respect to the central axis Cc of the cylinder 4. That is, as shown in FIG. 2, the change of the rocking angle β with respect to the crank angle θ is vertically asymmetric with respect to the horizontal axis. Specifically, the absolute value β1 of the maximum rocking angle in the compression stroke becomes smaller than the absolute value β2 of the maximum rocking angle in the intake stroke. Further, the absolute value β1 of the maximum rocking angle in the compression stroke becomes smaller than the absolute value of the maximum rocking angle in the compression stroke in the comparative example where the offset amount δ is 0. Thus, in the offset structure, compared with the comparative example where the offset amount δ is 0, the absolute value of the maximum rocking angle in the compression stroke can be suppressed to be small, and accordingly, the force (side force) acting between the piston 5 and the cylinder 4 in the compression stroke can be reduced.

[0026] Further, by suppressing the maximum value of the swing angle β during the compression stroke to a small value, the airtightness of the compression chamber 14 during the compression stroke by the piston ring 12 can be surely maintained. This is due to the following reason. The sealing characteristics of the compression chamber 14 by the piston ring 12 are, for example, as shown in FIG. 3. That is, within a range where the inclination angle of the outer peripheral surface (substantially cylindrical surface) of the piston ring 12 with respect to the inner peripheral surface 4a (substantially cylindrical surface) of the cylinder 4 is from 0° to a certain small range, the amount of gas leakage from the compression chamber 14 to the outside (inside the crankcase 3) can be extremely reduced. This is because when the inclination angle is small, the piston ring 12 is in a substantially surface contact state with the cylinder 4, and the gap with the cylinder 4 is appropriately sealed by the piston ring 12. On the other hand, when the inclination angle of the piston ring 12 becomes large, the piston ring 12 is in a state of single-side contact with the inner peripheral surface 4a of the cylinder 4, and the contact state between the piston ring 12 and the cylinder 4 changes from a surface contact state to a line contact or point contact state. As a result, as the inclination angle of the piston ring 12 increases, the sealing characteristics of the piston ring 12 deteriorate, and the amount of gas leakage from the compression chamber 14 increases. In the present embodiment, since the piston ring 12 is attached to the swing-type piston 5 (rocking piston), the inclination angle of the piston ring 12 changes according to the change in the swing angle β of the piston 5 and the connecting rod 6. In the offset structure of the present embodiment, since the swing angle β during the compression stroke becomes small, the inclination angle of the piston ring 12 also becomes small. Therefore, the amount of gas leakage from the compression chamber 14 during the compression stroke is less than that in the comparative example where the offset amount δ is 0.

[0027] Next, the structure of the piston constituting a part of the first embodiment of the reciprocating compressor of the present invention will be described with reference to FIGS. 1, 2, 4, and 5. FIG. 4 is a view showing a piston with a piston ring attached and its peripheral structure in the first embodiment of the reciprocating compressor of the present invention. FIG. 5 is a perspective view showing the piston alone in the first embodiment of the reciprocating compressor of the present invention.

[0028] In FIGS. 4 and 5, the piston 5 is formed in a substantially disk shape and has an outer peripheral surface that can smoothly reciprocate while oscillating within the cylinder 4 (see FIG. 1). The piston 5 has a top surface 51 that forms a part of the wall surface of the compression chamber 14 (see FIG. 1), and a sliding surface 52 and non-sliding surfaces 53 and 54 as the outer peripheral surfaces. The sliding surface 52 is a curved surface that slides against the inner peripheral surface 4a of the cylinder 4 during oscillation and reciprocation. The non-sliding surfaces 53 and 54 are curved surfaces that are continuous with the sliding surface 52 and are formed in a shape that avoids contact with the inner peripheral surface 4a of the cylinder 4.

[0029] The shape of the piston 5 has geometric constraints from the perspective of the mechanism movement. Since the reciprocating compressor 1 of the present embodiment has an offset structure in which the crankshaft 2 is offset with respect to the cylinder 4, the oscillating movements of the piston 5 and the connecting rod 6 are asymmetric with respect to the central axis Cc of the cylinder 4. Therefore, the piston 5 is formed asymmetrically (left-right asymmetric with respect to the central axis 5b in FIG. 4) with respect to the plane including the central axis 5b of the piston 5 and the rotation axis of the large end portion 62 of the connecting rod 6 (that is, the central axis Cb of the bearing 7) in accordance with its asymmetric oscillating movement. Here, the central axis 5b of the piston 5 is a straight line passing through the center point 5a of the sliding surface 52 described later and the rotation axis of the large end portion 62 of the connecting rod 6 (the central axis Cb of the bearing 7), and also coincides with the center line Cr of the connecting rod 6.

[0030] The top surface 51 is formed, for example, in a planar shape. However, as shown in FIG. 4, the top surface 51 is formed as an inclined surface that is not parallel but inclined with respect to the orthogonal plane 5c of the piston 5 in accordance with the asymmetric rocking motion of the piston 5 with respect to the central axis Cc of the cylinder 4. Here, the orthogonal plane 5c of the piston 5 is a plane that is orthogonal to the central axis 5b of the piston 5 and includes a later-described center point 5a of the sliding surface 52. The top surface 51 is formed so as to be substantially parallel to the valve plate 9 when the piston 5 is located at the top dead center (see FIG. 6 described later). Specifically, the top surface 51 is formed as an inclined surface that approaches the orthogonal plane 5c of the piston 5 as it goes in the same direction as the offset direction of the crankshaft 2 with respect to the cylinder 4 (left direction in FIG. 4). Note that the top surface 51 may be configured to be provided with a convex portion that can be inserted into the discharge hole 9b at a position facing the groove portion for avoiding contact with the intake valve 10 (see FIG. 1) and the discharge hole 9b (see FIG. 1).

[0031] The sliding surface 52 is formed in a spherical shape having a diameter smaller than the cylinder diameter of the cylinder 4 in order to enable the piston 5 to smoothly rock and reciprocate within the cylinder 4. The center point 5a of the spherical sliding surface 52 is located on the extension line of the center line Cr of the connecting rod 6. The sliding surface 52 is a curved surface formed over a range of a sliding angle φ determined according to the range of the rocking angle β in the rocking motion of the connecting rod 6. For example, as shown in FIG. 2, when the maximum rocking angle (absolute value) of the stroke toward the top dead center (compression stroke) is β1 and the maximum rocking angle (absolute value) of the stroke toward the bottom dead center (intake stroke) is β2, among the sliding surfaces 52 shown in FIG. 4, the sliding surface 52 on the same side as the offset direction (left direction in FIG. 4) with respect to the central axis 5b of the piston 5 (left side in FIG. 4) has a range of the sliding angle φ on the top surface 51 side of β1 and a range of the sliding angle φ on the connecting rod 6 side of β2 with respect to the orthogonal plane 5c of the piston 5. Conversely, the sliding surface 52 on the side opposite to the offset direction with respect to the central axis 5b of the piston 5 (right side in FIG. 4) has a range of the sliding angle φ on the top surface 51 side of β2 and a range of the sliding angle φ on the connecting rod 6 side of β1 with respect to the orthogonal plane 5c of the piston 5.

[0032] The non-sliding surface is a curved surface formed outside the range of the sliding angle φ determined according to the range of the rocking angle β in the rocking motion of the connecting rod 6, and has a first non-sliding surface 53 connecting the top surface 51 and the sliding surface 52, and a second non-sliding surface 54 extending from the sliding surface 52 toward the connecting rod 6 side. The first non-sliding surface 53 is formed as a curved surface located on the outer peripheral side (radial outside) of a spherical first virtual extended curved surface 52V1 obtained by virtually extending the sliding surface 52 toward the top surface 51 side. That is, the first non-sliding surface 53 is formed to be located closer to the inner peripheral surface 4a of the cylinder 4 than the first virtual extended curved surface 52V1 of the sliding surface 52 when the piston 5 is disposed in the cylinder 4.

[0033] However, the first non-sliding surface 53 needs to be non-contact with respect to the inner peripheral surface 4a of the cylinder 4 even when the rocking motion of the connecting rod 6 (piston 5) reaches the maximum rocking angle. That is, when the piston 5 is at the maximum rocking angle, it is required that the first non-sliding surface 53 is a curved surface located radially inside the curved surface that coincides with the inner peripheral surface 4a of the cylinder 4.

[0034] For example, as shown in FIG. 2, in the swinging motion of the connecting rod 6 (piston 5), assume that the maximum swing angle during the compression stroke is β1 and the maximum swing angle during the intake stroke is β2. For convenience of explanation, among the first non-sliding surfaces 53, the portion on the same side as the offset direction of the crankshaft 2 (the left side in FIG. 4) is referred to as the offset-side non-sliding surface 531, and the portion on the side opposite to the offset direction (the right side in FIG. 4) is referred to as the anti-offset-side non-sliding surface 532. In order for the offset-side non-sliding surface 531 to be a curved surface that coincides with the inner peripheral surface 4a of the cylinder 4, it is the case where it becomes the first cylindrical surface 531c that is orthogonal to the first plane 5e that forms the same angle β1 as the maximum swing angle during the compression stroke with respect to the orthogonal surface 5c of the piston 5. On the other hand, in order for the anti-offset-side non-sliding surface 532 to be a curved surface that coincides with the inner peripheral surface 4a of the cylinder 4, it is the case where it becomes the second cylindrical surface 532c that is orthogonal to the second plane 5f that forms the same angle β2 as the maximum swing angle during the intake stroke with respect to the orthogonal surface 5c of the piston 5. In this case, since the shape of the offset-side non-sliding surface 531 is different from the shape of the anti-offset-side non-sliding surface 532, usually, a ridge line 533 is formed at the connection portion between the offset-side non-sliding surface 531 and the anti-offset-side non-sliding surface 532. However, the ridge line 533 is rounded, and the offset-side non-sliding surface 531 and the anti-offset-side non-sliding surface 532 are smoothly connected. That is, the ridge line 533 disappears due to rounding. Therefore, in FIG. 4, for convenience of explanation, the ridge line 533 is shown by a two-dot chain line, but in other figures, the ridge line 533 is not shown. Note that in FIG. 4, the ridge line 533 is located approximately at the center in the left-right direction, but it can be set at an arbitrary position. That is, it is possible to change as needed the position in the circumferential direction at which the offset-side non-sliding surface 531 and the anti-offset-side non-sliding surface 532 are connected.

[0035] Thus, the first non-sliding surface 53 is located on the inner circumferential side (radial inner side) of a first cylindrical surface 531c that is orthogonal to a first plane 5e forming the same angle as the maximum rocking angle β1 in the compression stroke with respect to the orthogonal surface 5c of the piston 5, and a second cylindrical surface 532c that is orthogonal to a second plane 5f forming the same angle as the maximum rocking angle β2 in the intake stroke with respect to the orthogonal surface 5c of the piston 5, thereby making it possible to avoid contact with the inner circumferential surface 4a of the cylinder 4 during the rocking motion of the piston 5. In addition, the first non-sliding surface 53 of the present embodiment is formed so as to be located on the outer circumferential side (radial outer side) of the first virtual extended curved surface 52V1 of the sliding surface 52.

[0036] On the other hand, the second non-sliding surface 54 is formed, for example, on a curved surface that coincides with a spherical second virtual extended curved surface 52V2 obtained by virtually extending the sliding surface 52 toward the connecting rod 6 side. That is, the second non-sliding surface 54 is a spherical curved surface obtained by extending the sliding surface 52 toward the connecting rod 6 side, and is configured as an outer circumferential surface that does not contact the inner circumferential surface of the cylinder 4.

[0037] As shown in FIG. 5, an annular groove 55 for mounting a piston ring 12 is provided on the outer circumferential surface of the piston 5. The annular groove 55 is provided, for example, within the region of the sliding surface 52 (the range of the sliding angle φ shown in FIG. 4). Further, the annular groove 55 (piston ring 12) is inclined with respect to the top surface 51 so as to approach the top surface 51 of the piston 5 as it goes in the same direction as the offset direction of the crankshaft 2 (left direction in FIG. 4). That is, the annular groove 55 is formed such that the portion on the same side as the offset direction is located closer to the top surface 51 than the portion on the opposite side of the offset direction. Note that part or all of the annular groove 55 (piston ring 12) can also be provided outside the range of the sliding angle φ.

[0038] Next, the operation and effects of the reciprocating compressor according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 6. FIG. 6 is an explanatory view showing a state when the piston is at the top dead center in the first embodiment of the reciprocating compressor of the present invention.

[0039] The reciprocating compressor 1 shown in Fig. 1 has a crankshaft 2 rotated by a rotary drive source (not shown) such as an electric motor (in Fig. 1, a counterclockwise rotational movement). When the crankshaft 2 rotates, the piston 5 reciprocates while oscillating within the cylinder 4 with its radial movement constrained by the oscillating movement of the connecting rod 6. In the intake stroke where the piston 5 moves from the top dead center to the bottom dead center, the compression chamber 14 expands, the intake valve 10 opens, and gas is sucked into the compression chamber 14 from the intake chamber 8a in the cylinder head 8. At the same time, gas is sucked into the compression chamber 14 through the gap between the piston 5 (piston ring 12) and the cylinder 4 from within the crankcase 3. On the other hand, in the compression stroke where the piston 5 moves from the bottom dead center to the top dead center, the compression chamber 14 contracts, the gas within the compression chamber 14 is compressed, and the discharge valve 11 opens to discharge the gas to the outside through the exhaust chamber 8b in the cylinder head 8.

[0040] In the reciprocating compressor 1 according to the embodiment, by adopting an offset structure in which the rotation axis Rs of the crankshaft 2 is offset with respect to the central axis Cc of the cylinder 4, as shown in Fig. 2, the maximum value of the oscillation angle β of the piston 5 and the connecting rod 6 during the compression stroke is reduced. As a result, the force (side force) acting between the piston 5 and the cylinder 4 during the compression stroke can be reduced.

[0041] In addition, in the reciprocating compressor 1 according to the embodiment, a piston ring 12 is attached to the piston 5. By reducing the oscillation angle β of the piston 5 during the compression stroke by the offset structure, the inclination angle of the piston ring 12 with respect to the cylinder 4 is reduced. Therefore, as shown in Fig. 3, high airtightness of the compression chamber 14 can be ensured by the sealing performance of the piston ring 12.

[0042] Incidentally, when the piston 5 is positioned at the top dead center, as shown in FIG. 6, a gap (hereinafter referred to as the top clearance ε) for avoiding the collision between the piston 5 and the valve plate 9 is provided between the top surface 51 of the piston 5 and the valve plate 9. From the viewpoint of compressor performance, it is ideal that the volume of the compression chamber 14 becomes zero when the piston 5 is at the top dead center. However, in reality, there is a volume due to the top clearance ε and other gaps. The volume of the compression chamber 14 when the piston 5 is at the top dead center is called the dead volume. The size of the dead volume is one of the factors causing the reduction of the discharge performance of the compressor (reduction of the discharge flow rate and reduction of the volumetric efficiency). In order to realize a highly efficient compressor, it is desirable to reduce the dead volume.

[0043] As one of the causes of the generation of the dead volume, in addition to the top clearance ε, there is a gap between the outer peripheral surface of the piston 5 and the inner peripheral surface 4a of the cylinder 4. In the present embodiment, since the seal of the gap between the piston 5 and the cylinder 4 is made by the piston ring 12, the gap G between the outer peripheral surface of the piston 5 located on the top surface 51 side of the piston ring 12 and the inner peripheral surface 4a of the cylinder 4 becomes one of the factors of the dead volume. Therefore, in order to reduce the dead volume, it is necessary to reduce the gap G (see FIG. 6) between the outer peripheral surface (a part of the sliding surface 52 (the right side part in FIG. 5) and the first non-sliding surface 53) of the piston 5 located on the top surface 51 side of the annular groove 55 where the piston ring 12 is mounted and the inner peripheral surface 4a of the cylinder 4.

[0044] As one of the measures to reduce the dead volume, it is conceivable to reduce the area (region) of the outer peripheral surface (a part of the sliding surface 52 and the first non-sliding surface 53) of the piston 5 located on the top surface 51 side of the annular groove 55. This can be realized by configuring the position of the annular groove 55 to be closer to the top surface 51 side. When the annular groove is brought closer to the top surface 51, the thickness (wall thickness) of the disk-shaped portion sandwiched between the annular groove and the top surface 51 becomes thinner accordingly. From the viewpoint of ensuring the strength required to hold the piston ring 12 in the annular groove, the wall thickness of the disk-shaped portion cannot be made less than a predetermined value.

[0045] In the present embodiment, since the top surface 51 is inclined so as to approach in the same direction as the offset direction of the crankshaft 2 with respect to the annular groove 55 (the left direction in FIGS. 4 and 5), the thickness of the disk-shaped portion is such that the portion on the same side as the offset direction (the left side in FIGS. 4 and 5) is the thinnest portion. The thickness of the thinnest portion is determined as the minimum value achievable from the viewpoint of material strength. On the other hand, among the disk-shaped portion, the thickness of the portion on the side opposite to the offset direction (the right side in FIGS. 4 and 5) is thicker than the portion on the same side as the offset direction. From the viewpoint of dead volume, due to the inclination of the top surface 51 with respect to the annular groove 55, the portion of the disk-shaped portion on the side opposite to the offset direction is in an unfavorable situation. In other words, in the configuration where the opposing surface of the top surface 51 and the valve plate 9 is parallel at the top dead center of the piston 5, the wall thickness of a part of the disk-shaped portion sandwiched between the annular groove and the top surface 51 becomes thick due to the offset structure.

[0046] In the present embodiment, as shown in FIG. 6, since the first non-sliding surface 53 located on the top surface 51 side with respect to the annular groove 55 (piston ring 12) is formed to be located on the outer peripheral side (radial direction outside) of the first virtual extended curved surface 52V1 of the spherical sliding surface 52, the gap G between the first non-sliding surface 53 of the piston 5 and the inner peripheral surface 4a of the cylinder 4 can be reduced. That is, the dead volume can be reduced without bringing the annular groove 55 (piston ring 12) closer to the top surface 51.

[0047] Also, the gap between the first non-sliding surface 53 of the piston 5 and the inner peripheral surface 4a of the cylinder 4 is one of the leakage paths of the compressed gas from the inside of the compression chamber 14 to the outside (the inside of the crankcase 3). Therefore, by forming the first non-sliding surface 53 to be located on the outer peripheral side of the first virtual extended curved surface 52V1 of the spherical shape, the gap G between the first non-sliding surface 53 and the inner peripheral surface 4a of the cylinder 4 becomes smaller, so that the leakage amount of the compressed air during the compression stroke can also be reduced.

[0048] Also, in the present embodiment, as shown in FIG. 4, an offset-side non-sliding surface 531 of the first non-sliding surface 53 is formed as a curved surface that substantially coincides with a first cylindrical surface 531c orthogonal to a first plane 5e at an angle with respect to the orthogonal surface 5c of the piston 5 that is the maximum swing angle β1 in the compression stroke (however, it does not contact the inner peripheral surface 4a of the cylinder 4). At the same time, the anti-offset-side non-sliding surface 532 is formed as a curved surface that substantially coincides with a second cylindrical surface 532c orthogonal to a second plane 5f at an angle with respect to the orthogonal surface 5c of the piston 5 that is the maximum swing angle β2 in the intake stroke (however, it does not contact the inner peripheral surface 4a of the cylinder 4). According to this configuration, the first non-sliding surface 53 of the piston 5 can be brought closest to the inner peripheral surface 4a of the cylinder 4 without contacting the inner peripheral surface 4a of the cylinder 4. That is, by forming the offset-side non-sliding surface 531 as a curved surface that substantially coincides with the first cylindrical surface 531c and forming the anti-offset-side non-sliding surface 532 as a curved surface that substantially coincides with the second cylindrical surface 532c, the dead volume can be minimized.

[0049] As described above, the reciprocating compressor 1 according to the first embodiment includes a cylinder 4 having a central axis Cc, a crankshaft 2 having a rotation axis Rs offset with respect to the central axis Cc of the cylinder 4, a piston 5 that forms a compression chamber 14 together with the cylinder 4 and reciprocates within the cylinder 4, and a connecting rod 6 that is rotatably connected to one side with respect to the crankshaft 2 and fixed to the piston 5 on the other side, and swings with respect to the cylinder 4 by the rotational movement of the crankshaft 2. The piston 5 includes a top surface 51 that forms a part of the wall surface of the compression chamber 14, a sliding surface 52 that slides on the inner peripheral surface 4a of the cylinder 4 within a range determined according to the range of the swing angle β of the connecting rod 6 with respect to the central axis Cc of the cylinder 4, and a first non-sliding surface 53 that connects the top surface 51 and the sliding surface 52 and has a shape that avoids contact with the inner peripheral surface 4a of the cylinder 4. At least a part of the first non-sliding surface 53 is located closer to the inner peripheral surface 4a of the cylinder 4 than a first virtual extension curved surface 52V1 obtained by virtually extending the sliding surface 52 toward the top surface 51 side.

[0050] According to this configuration, by offsetting the crankshaft 2 with respect to the cylinder 4, it is possible to reduce the rocking angle β in the compression stroke of the piston 5, and by forming at least a part of the first non-sliding surface 53 of the piston 5 on the outer peripheral side (radial outside) of the first virtual extended curved surface 52V1, the gap G between the first non-sliding surface 53 of the piston 5 and the inner peripheral surface 4a of the cylinder 4 becomes smaller. Therefore, while reducing the side force acting between the piston 5 and the cylinder 4 during the compression stroke, the dead volume of the compression chamber 14 can be reduced. In addition, since the gap G between the first non-sliding surface 53 of the piston 5 and the inner peripheral surface 4a of the cylinder 4 becomes smaller, leakage of the compressed gas from the compression chamber 14 through the gap G can be suppressed.

[0051] Also, in the reciprocating compressor 1 according to the present embodiment, the entire first non-sliding surface 53 is located closer to the inner peripheral surface 4a of the cylinder 4 than the first virtual extended curved surface 52V1. According to this configuration, since the gap G between the first non-sliding surface 53 of the piston 5 and the inner peripheral surface 4a of the cylinder 4 becomes smaller over the entire circumference, the dead volume of the compression chamber 14 can be further reduced, and leakage of the compressed gas from the compression chamber 14 can be further suppressed.

[0052] Also, in the reciprocating compressor 1 according to the present embodiment, the piston 5 is asymmetric with respect to a plane including the rotation axis (central axis Cb of the bearing 7) on the large end portion 62 side (one side) of the connecting rod 6 and the central axis 5b of the piston (center line Cr connecting the large end portion 62 side (one side) and the small end portion 63 side (the other side) of the connecting rod 6). According to this configuration, it is possible to configure a piston having a shape corresponding to the asymmetric rocking motion of the piston 5 and the connecting rod 6 with respect to the cylinder 4 caused by the offset structure.

[0053] Further, in the reciprocating compressor 1 according to the present embodiment, a piston ring 12 is mounted on the outer peripheral surface of the piston 5, and the piston ring 12 is inclined with respect to the top surface 51 so as to approach the top surface 51 as it goes in the same direction as the offset direction of the rotation axis Rs of the crankshaft 2 with respect to the central axis Cc of the cylinder 4. According to this configuration, the airtightness of the compression chamber 14 by the piston ring 12 can be ensured in the offset structure.

[0054] [Second Embodiment] Next, a second embodiment of the reciprocating compressor of the present invention will be described with reference to FIG. 7. FIG. 7 is a view showing a piston with a piston ring mounted thereon and its peripheral structure in the second embodiment of the reciprocating compressor of the present invention. In FIG. 7, those having the same reference numerals as those shown in FIGS. 1 to 6 are the same parts, and thus detailed description thereof will be omitted.

[0055] The difference between the second embodiment of the reciprocating compressor of the present invention shown in FIG. 7 and the first embodiment is that the shape of the second non-sliding surface 54A on the outer peripheral surface of the piston 5A is different. Specifically, the second non-sliding surface 54 of the piston 5 according to the first embodiment is formed in a curved surface that coincides with a second virtual extension curved surface 52V2 obtained by virtually extending the spherical sliding surface 52 toward the link 6 side (see FIG. 4). On the other hand, the second non-sliding surface 54A of the piston 5A according to the present embodiment is formed in a curved surface located on the outer peripheral side (radial outside) of the second virtual extension curved surface 52V2. That is, the entire second non-sliding surface 54A is formed so as to be closer to the inner peripheral surface 4a of the cylinder 4 than the second virtual extension curved surface 52V2 of the spherical sliding surface 52 when the piston 5A is disposed in the cylinder 4. As a result, the region where the gap between the second non-sliding surface 54A of the piston 5A and the inner peripheral surface 4a of the cylinder 4 becomes smaller increases compared to the case of the first embodiment.

[0056] In the reciprocating compressor according to the second embodiment described above, similarly to the first embodiment, by offsetting the crankshaft 2 with respect to the cylinder 4, it is possible to reduce the swing angle β in the compression stroke of the piston 5A, and at least a part of the first non-sliding surface 53 of the piston 5A is formed on the outer peripheral side (radial outside) of the first virtual extended curved surface 52V1, so that the gap G between the first non-sliding surface 53 of the piston 5A and the inner peripheral surface 4a of the cylinder 4 becomes smaller. Therefore, while reducing the side force acting between the piston 5A and the cylinder 4 during the compression stroke, the dead volume of the compression chamber 14 can be reduced, and the leakage of the compressed gas from the compression chamber 14 through the gap G can be suppressed.

[0057] Also, the piston 5A in the reciprocating compressor according to the present embodiment further has a second non-sliding surface 54A that extends from the sliding surface 52 to the opposite side of the top surface 51 and avoids contact with the inner peripheral surface 4a of the cylinder 4. At least a part of the second non-sliding surface 54A is located closer to the inner peripheral surface 4a of the cylinder 4 than the second virtual extended curved surface 52V2 obtained by virtually extending the sliding surface 52 to the opposite side of the top surface 51.

[0058] According to this configuration, since at least a part of the second non-sliding surface 54A is formed on the outer peripheral side (radial outside) of the second virtual extended curved surface 52V2, the gap between the second non-sliding surface 54A of the piston 5A and the inner peripheral surface 4a of the cylinder 4 becomes smaller, so that the gas leakage from the compression chamber 14 during the compression stroke can be further suppressed.

[0059] Also, in the reciprocating compressor according to the present embodiment, the entire second non-sliding surface 54A of the piston 5A is located closer to the inner peripheral surface 4a of the cylinder 4 than the second virtual extended curved surface 52V2. According to this configuration, since the gap between the second non-sliding surface 54A of the piston 5A and the inner peripheral surface 4a of the cylinder 4 becomes smaller over the entire circumference, the leakage of the compressed gas from the compression chamber 14 can be further suppressed.

[0060] [Third Embodiment] Next, a third embodiment of the reciprocating compressor of the present invention will be described with reference to FIG. 8. FIG. 8 is a view showing a piston with a piston ring mounted thereon and its peripheral structure in the third embodiment of the reciprocating compressor of the present invention. In FIG. 8, components having the same reference numerals as those shown in FIGS. 1 to 7 are the same parts, and thus detailed descriptions thereof are omitted.

[0061] The difference between the third embodiment of the reciprocating compressor of the present invention shown in FIG. 8 and the first embodiment is that the shape of the first non-sliding surface 53B on the outer peripheral surface of the piston 5B is different. The first non-sliding surface 53 of the piston 5 according to the first embodiment is formed such that the entire circumference (the entire periphery) thereof is located on the outer peripheral side (radial outer side) of the first virtual extended curved surface 52V1 of the spherical sliding surface 52 (see FIG. 4). On the other hand, the first non-sliding surface 53B of the piston 5B according to the second embodiment is formed such that only a part thereof is located on the outer peripheral side of the first virtual extended curved surface 52V1.

[0062] Specifically, among the first non-sliding surfaces 53B of the piston 5B, only the anti-offset side non-sliding surface 532 located on the side opposite to the offset direction of the crankshaft 2 (the left direction in FIG. 8) (the right side in FIG. 7) is formed to be located on the outer peripheral side of the first virtual extended curved surface 52V1 of the sliding surface 52. On the other hand, the offset side non-sliding surface 531B of the first non-sliding surface 53B, which is located on the same side as the offset direction (the left side in FIG. 7), is formed as a curved surface that coincides with the first virtual extended curved surface 52V1 of the sliding surface 52. The volume of the gap G between the anti-offset side non-sliding surface 532 and the inner peripheral surface 4a of the cylinder 4 among the first non-sliding surfaces 53B is larger than the volume of the gap G between the offset side non-sliding surface 531B and the inner peripheral surface 4a of the cylinder 4 due to the inclination of the top surface 51 with respect to the piston ring 12. That is, the anti-offset side non-sliding surface 532 side contributes more to the increase in the dead volume than the offset side non-sliding surface 531B. Therefore, in the present embodiment, the configuration is such that the gap G between the anti-offset side non-sliding surface 532 and the inner peripheral surface 4a of the cylinder 4 is reduced.

[0063] In the reciprocating compressor according to the third embodiment described above, similar to the first embodiment, by offsetting the crankshaft 2 with respect to the cylinder 4, it is possible to reduce the swing angle β in the compression stroke of the piston 5B, and at least a part of the first non-sliding surface 53B of the piston 5B is formed on the outer peripheral side (radial outside) of the first virtual extended curved surface 52V1, so that the gap G between the first non-sliding surface 53B of the piston 5B and the inner peripheral surface 4a of the cylinder 4 becomes smaller. Therefore, while reducing the side force acting between the piston 5B and the cylinder 4 during the compression stroke, the dead volume of the compression chamber 14 can be reduced, and the leakage of the compressed gas from the compression chamber 14 through the gap G can be suppressed.

[0064] Also, in the reciprocating compressor according to the present embodiment, among the first non-sliding surfaces 53B of the piston 5B, only the anti-offset side non-sliding surface 532 (portion) located on the side opposite to the offset direction of the rotation axis Rs of the crankshaft 2 with respect to the central axis Cc of the cylinder 4 is located closer to the inner peripheral surface 4a of the cylinder 4 than the first virtual extended curved surface 52V1. According to this configuration, while reducing the dead volume of the compression chamber 14 and suppressing the gas leakage from the compression chamber 14, the amount of material used for manufacturing the piston 5B can be reduced.

[0065] [Fourth Embodiment] Next, a fourth embodiment of the reciprocating compressor of the present invention will be described with reference to FIGS. 9 to 12. FIG. 9 is a schematic cross-sectional view showing the fourth embodiment of the reciprocating compressor of the present invention. FIG. 10 is a view showing the piston ring of mounting none a piston and its peripheral structure. FIG. 11 is a perspective view showing the piston alone in the fourth embodiment of the reciprocating compressor of the present invention. FIG. 12 is an explanatory view showing the dead volume in the fourth embodiment of the reciprocating compressor of the present invention. In FIGS. 9 to 12, those having the same reference numerals as those shown in FIGS. 1 to 8 are the same parts, and thus their detailed description will be omitted.

[0066] The difference between the fourth embodiment of the reciprocating compressor of the present invention shown in Fig. 9 and the first embodiment is that the piston 5C is not equipped with piston rings. Specifically, as shown in Figs. 10 and 11, the piston 5C of the present embodiment is different from the piston 5 of the first embodiment in that an annular groove 55 (see Fig. 5) is not formed on the outer peripheral surface. As shown in Fig. 11, a valley line 56 (broken line in Fig. 11), which is the boundary between the sliding surface 52 and the first non-sliding surface 53, appears over the entire circumference on the outer peripheral surface of the piston 5C. On the other hand, in the piston 5 of the first embodiment, due to the formation of the annular groove 55, only a part of the valley line 56 (broken line in Fig. 5), which is the boundary between the sliding surface 52 and the first non-sliding surface 53, appears. The other configurations and structures of the piston 5C of the present embodiment are the same as those of the first embodiment.

[0067] As described above, as one of the causes of the generation of the dead volume, there is the gap between the outer peripheral surface of the piston 5C shown in Fig. 12 and the inner peripheral surface 4a of the cylinder 4. In the present embodiment, the seal of the gap between the piston 5C and the cylinder 4 is achieved by the line contact between the sliding surface 52 of the piston 5C and the inner peripheral surface 4a of the cylinder 4. Therefore, when the piston 5C is located at the top dead center, the gap G between the outer peripheral surface (a part of the sliding surface 52 and the first non-sliding surface 53) of the piston 5C located on the top surface 51 side and the inner peripheral surface 4a of the cylinder 4, which is more than the contact part (annular part) between the spherical sliding surface 52 of the piston 5C and the cylindrical inner peripheral surface 4a of the cylinder 4, becomes one of the factors of the dead volume. In addition, the gap between the outer peripheral surface of the piston 5C and the inner peripheral surface 4a of the cylinder 4 is one of the leakage paths of the compressed gas from the inside of the compression chamber 14 to the outside (inside the crankcase 3).

[0068] In the reciprocating compressor according to the fourth embodiment described above, similarly to the first embodiment, by offsetting the crankshaft 2 with respect to the cylinder 4, it is possible to reduce the swing angle β in the compression stroke of the piston 5C, and at least a part of the first non-sliding surface 53 of the piston 5C is formed on the outer peripheral side (radial outside) of the first virtual extended curved surface 52V1, so that the gap G between the first non-sliding surface 53 of the piston 5C and the inner peripheral surface 4a of the cylinder 4 becomes smaller. Therefore, while reducing the side force acting between the piston 5C and the cylinder 4 during the compression stroke, the dead volume of the compression chamber 14 can be reduced, and the leakage of the compressed gas from the compression chamber 14 through the gap G can be suppressed.

[0069] Further, the reciprocating compressor according to the present embodiment is configured not to mount the piston ring 12 on the outer peripheral surface of the piston 5C. According to this configuration, while reducing the dead volume of the compression chamber 14 and suppressing the gas leakage from the compression chamber 14, the configuration of the reciprocating compressor can be simplified.

[0070] [Others] Note that the present invention is not limited to the first to fourth embodiments described above, and includes various modification examples. The above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Also, it is possible to add, delete, or replace other configurations for a part of the configuration of each embodiment.

[0071] For example, in the first to fourth embodiments described above, an example in which the sliding surfaces 52 of the pistons 5, 5A, 5B, and 5C are spherical surfaces is shown. However, if the sliding surface of the piston can smoothly swing and reciprocate in the cylinder 4, a geometrically definable curved surface other than the spherical surface, for example, a curved surface approximated to a spherical surface can also be adopted.

[0072] In addition, in the first to fourth embodiments, an example of a configuration in which the pistons 5, 5A, 5B, and 5C have the second non-sliding surfaces 54 and 54A was shown. However, a configuration in which there is no outer peripheral surface (second non-sliding surface) on the side of the connecting rod 6 rather than the sliding surface 52 is also possible for the piston. That is, it is also possible to configure the outer peripheral surface of the piston only with the sliding surface 52 and the first non-sliding surfaces 53 and 53B.

[0073] In addition, in the second embodiment, an example of a configuration in which the entire second non-sliding surface 54A of the piston 5A is formed on the outer peripheral side (radial outside) of the second virtual extended curved surface 52V2 was shown. However, a configuration in which only a part of the second non-sliding surface is formed on the outer peripheral side of the second virtual extended curved surface 52V2 is also possible.

[0074] In addition, in the third embodiment, among the first non-sliding surfaces 53B of the piston 5B, only the non-offset side non-sliding surface 532 (the right side portion in FIG. 8) is formed on the outer peripheral side of the first virtual extended curved surface 52V1, while the offset side non-sliding surface 531B (the left side portion in FIG. 8) is formed on a curved surface that coincides with the first virtual extended curved surface 52V1. An example of the configuration was shown. However, a configuration in which only the offset side non-sliding surface among the first non-sliding surfaces of the piston is formed on the outer peripheral side of the first virtual extended curved surface 52V1, while the non-offset side non-sliding surface is formed on a curved surface that coincides with the first virtual extended curved surface 52V1 is also possible. In this case as well, the position of the ridge line, which is the connecting portion between the offset side non-sliding surface and the non-offset side non-sliding surface, can be arbitrarily set.

Explanation of Reference Numerals

[0075] 1... Reciprocating compressor, 2... Crankshaft, 4... Cylinder, 4a... Inner peripheral surface, 5, 5A, 5B, 5C... Pistons, 6... Connecting rod, 12... Piston ring, 14... Compression chamber, 51... Top surface, 52... Sliding surface, 52V1... First virtual extended curved surface, 52V2... Second virtual extended curved surface, 53, 53B... First non-sliding surface (non-sliding surface), 532... Non-offset side non-sliding surface (portion located on the side opposite to the displacement direction), 54, 54A... Second non-sliding surface, Cc... Central axis line, Rs... Rotation axis line, β... Swing angle

Claims

1. a cylinder having a central axis; a crankshaft having a rotational axis offset with respect to the central axis of the cylinder; a piston that forms a compression chamber together with the cylinder and reciprocates within the cylinder; a connecting rod having one side rotatably connected to the crankshaft and the other side fixed to the piston, and performing a rocking motion with respect to the cylinder by the rotational motion of the crankshaft; and the piston includes a top surface that forms part of the wall surface of the compression chamber; a spherical sliding surface formed over a predetermined range determined according to the range of the rocking angle of the connecting rod with respect to the central axis of the cylinder, and sliding on the inner peripheral surface of the cylinder; a first non-sliding surface formed outside the predetermined range, connecting the top surface and the sliding surface, and having a shape that avoids contact with the inner peripheral surface of the cylinder; at least a part of the first non-sliding surface is located closer to the inner peripheral surface of the cylinder than a first virtual extended curved surface obtained by virtually extending the sliding surface toward the top surface side; a reciprocating compressor.

2. In the reciprocating compressor according to Claim 1, the entire first non-sliding surface is located closer to the inner peripheral surface of the cylinder than the first virtual extended curved surface; a reciprocating compressor.

3. A cylinder having a central axis, a crankshaft having a rotational axis offset with respect to the central axis of the cylinder, a piston that forms a compression chamber together with the cylinder and reciprocates within the cylinder, a connecting rod having one side rotatably connected to the crankshaft and the other side fixed to the piston, and performing a rocking motion with respect to the cylinder by the rotational motion of the crankshaft, and the piston includes a top surface that forms part of the wall surface of the compression chamber, a sliding surface that slides on the inner peripheral surface of the cylinder within a predetermined range determined according to the range of the rocking angle of the connecting rod with respect to the central axis of the cylinder, a first non-sliding surface that connects the top surface and the sliding surface and has a shape that avoids contact with the inner peripheral surface of the cylinder, and at least a part of the first non-sliding surface is located closer to the inner peripheral surface of the cylinder than a first virtual extended curved surface obtained by virtually extending the sliding surface toward the top surface side. Among the first non-sliding surfaces, only the portion located on the side opposite to the offset direction of the rotation axis of the crankshaft with respect to the central axis of the cylinder is located closer to the inner peripheral surface of the cylinder than the first virtual extended curved surface. Reciprocating compressor.

4. In the reciprocating compressor according to claim 1 or 3, The piston further has a second non-sliding surface formed outside the predetermined range, extending from the sliding surface to the side opposite to the top surface, and having a shape that avoids contact with the inner peripheral surface of the cylinder. At least a part of the second non-sliding surface is located closer to the inner peripheral surface of the cylinder than a second virtual extended curved surface obtained by virtually extending the sliding surface to the side opposite to the top surface. Reciprocating compressor.

5. In the reciprocating compressor according to claim 4, The entire second non-sliding surface is located closer to the inner peripheral surface of the cylinder than the second virtual extended curved surface. Reciprocating compressor.

6. In the reciprocating compressor according to claim 1 or 3, The piston is asymmetric with respect to a plane including the rotation axis on one side of the connecting rod and the center line connecting the one side and the other side of the connecting rod. Reciprocating compressor.

7. In the reciprocating compressor according to claim 1 or 3, A piston ring is mounted on the outer peripheral surface of the piston. The piston ring is inclined with respect to the top surface so as to approach the top surface of the piston as it goes in the same direction as the offset direction of the rotation axis of the crankshaft with respect to the central axis of the cylinder. Reciprocating compressor.

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