JP7709286B2 - Reciprocating Compressor - Google Patents

Description

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

In a reciprocating compressor, the piston is connected to a crankshaft via a connecting rod, and the crankshaft converts the torque of a rotary drive source such as an electric motor into reciprocating motion of the piston, thereby compressing gases and the like. In some reciprocating compressors, the piston is connected to the end (small end) of the connecting rod via a bearing, and the piston reciprocates relative to the connecting rod while not tilting relative to the cylinder. In contrast, there are reciprocating compressors in which the piston is fixed to the end of the connecting rod, and the piston reciprocates while rocking relative to the cylinder. In other words, there are reciprocating compressors equipped with a rocking piston that rocks integrally with the connecting rod. Compared to the former, the latter allows for improved durability by reducing moving parts, reduced weight and noise, and reduced costs by reducing the number of parts.

One example of a reciprocating compressor with a rocking piston is described in Patent Document 1. In the reciprocating compressor described in Patent Document 1, a spherical piston that slides back and forth within a cylinder rocks during the suction stroke, and the piston spherical surface at the portion where it makes sliding contact with the inner circumferential surface of the cylinder is recessed to form a suction port for sucking fluid into the compression chamber from the piston rod (connecting rod) side.

Japanese Patent Application Laid-open No. 62-253971

In the reciprocating compressor described in Patent Document 1, the rotation axis of the crankshaft and the central axis of the cylinder are intersected. In this structure, if the oscillation 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 side force) increases accordingly. This increases friction between the cylinder and the piston, leading to energy loss. For this reason, there is a demand to suppress the side force during the compression stroke. Therefore, by adopting an offset structure in which the rotation axis of the crankshaft is positioned at a position offset from the central axis of the cylinder without intersecting it, it is possible to reduce the side force during the compression stroke.

In addition, in the reciprocating compressor described in Patent Document 1, the piston that oscillates integrally with the piston rod is made spherical, so that even if the angle at which the piston oscillates relative to the cylinder is large, it slides smoothly against the inner circumferential surface of the cylinder, reducing the risk of damage to the piston. However, compared to a cylindrical piston that is oscillatably connected to a connecting rod via a bearing, a spherical piston has a larger dead volume in the compression chamber. A large dead volume is a factor in reducing the discharge performance of the compressor (reduced discharge flow rate and reduced volumetric efficiency), so there is a demand for reducing the dead volume.

In addition, 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 a lower airtightness of the compression chamber than in the case of sealing by surface contact between the cylindrical piston and the cylinder described above. Therefore, a method of attaching a piston ring to the piston can be considered. However, since the piston ring oscillates relative to the cylinder in conjunction with the oscillating motion of the piston, if the oscillating angle of the piston is large, the sealing performance of the piston ring may not be fully demonstrated. However, in a reciprocating compressor that employs an offset structure that reduces side forces during the compression stroke, it is possible to suppress the oscillation of the piston ring during the compression stroke, so the sealing performance of the piston ring during the compression stroke can be maintained.

However, in the case of an offset structure, the piston's rocking motion becomes asymmetric, so in order for the piston ring to exert its sealing performance, it is necessary to install the piston ring at an angle to the top surface of the piston. When the piston ring is installed on the piston in this way, the area of the outer circumferential surface of the piston that is on the top surface side of the piston ring increases, resulting in an increase in the dead volume of the compression chamber.

The present invention was made to solve the above problems, and its purpose is to provide a reciprocating compressor that can reduce the dead volume while reducing the side force acting between the piston and cylinder during the compression stroke.

The present application includes a plurality of means for solving the above problems. One example of such an engine is an engine having an internal combustion engine, the internal combustion engine comprising: a cylinder having a central axis; a crankshaft having a rotation axis offset with respect to the central axis of the cylinder; a piston which defines a compression chamber together with the cylinder and reciprocates within the cylinder; and a connecting rod which is rotatably connected to the crankshaft at one end and fixed to the piston at the other end and which oscillates relative to the cylinder in response to the rotational motion of the crankshaft. The cylinder has a top surface that constitutes a part of the wall surface, a spherical sliding surface that is formed over a predetermined range determined according to the range of the swing angle of the connecting rod relative to the central axis of the cylinder and slides against the inner surface of the cylinder, and a first non-sliding surface that is formed outside the predetermined range, connects the top surface and the sliding surface, and has a shape that avoids contact with the inner surface of the cylinder, and at least a portion of the first non-sliding surface is located closer to the inner surface of the cylinder than a first imaginary extended curved surface that virtually extends the sliding surface toward the top surface.

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 circumferential side (radially outward) of the first imaginary extended curved surface, the gap between the first non-sliding surface of the piston and the inner circumferential surface of the cylinder is reduced, so that the dead volume can be reduced while reducing the side force acting between the piston and the cylinder during the compression stroke.
Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments.

1 is a schematic cross-sectional view showing a first embodiment of a reciprocating compressor of the present invention. FIG. FIG. 4 is a characteristic diagram showing characteristics of an offset structure in the reciprocating compressor according to the first embodiment of the present invention. FIG. 4 is a characteristic diagram showing sealing characteristics of a piston ring in the reciprocating compressor according to the first embodiment of the present invention. FIG. 2 is a diagram showing a piston equipped with a piston ring and its surrounding structure in the first embodiment of the reciprocating compressor of the present invention. FIG. 2 is a perspective view showing a piston alone in the reciprocating compressor according to the first embodiment of the present invention. FIG. 2 is an explanatory diagram showing a dead volume in the first embodiment of the reciprocating compressor of the present invention. FIG. 11 is a diagram showing a piston equipped with a piston ring and its surrounding structure in a reciprocating compressor according to a second embodiment of the present invention. FIG. 13 is a diagram showing a piston equipped with a piston ring and its surrounding structure in a reciprocating compressor according to a third embodiment of the present invention. FIG. 11 is a schematic cross-sectional view showing a fourth embodiment of a reciprocating compressor according to the present invention. FIG. 13 is a diagram showing a piston with no piston ring attached and its surrounding structure in a reciprocating compressor according to a fourth embodiment of the present invention. FIG. 13 is a perspective view showing a piston alone in a reciprocating compressor according to a fourth embodiment of the present invention. FIG. 13 is an explanatory diagram showing a dead volume in a fourth embodiment of a reciprocating compressor of the present invention.

Hereinafter, an embodiment of a reciprocating compressor of the present invention will be described with reference to the drawings.
[First embodiment]
The configuration of a first embodiment of a 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 a reciprocating compressor of the present invention.

In FIG. 1, the reciprocating compressor 1 uses a crank mechanism to compress a gas such as air and discharges the compressed gas into a tank (not shown) or the like. Specifically, the reciprocating compressor 1 includes a crankshaft 2 that is driven to rotate by a rotary drive source (not shown) such as an electric motor, a crankcase 3 that rotatably houses the crankshaft 2, a cylinder 4 attached to the crankcase 3, a piston 5 that reciprocates within the cylinder 4, and a connecting rod 6 that connects the piston 5 to the crankshaft 2.

The crankshaft 2 rotates about the rotation axis Rs. The crankshaft 2 has a crank journal 21 that is rotatably supported by a bearing (not shown) arranged in the crankcase 3 and rotates about the rotation axis Rs, a crank pin 22 that is eccentric to the rotation axis Rs, a crank arm 23 that connects 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 of the connecting rod 6 (the large end 62 described below) via a bearing 7. For example, a rolling bearing or a sliding bearing can be used as the bearing 7. The bearing 7 can be integral with either the connecting rod 6 or the crankshaft 2. The crankcase 3 has a ventilation hole 3a that communicates between the inside and outside of the case 3.

The cylinder 4 has a central axis Cc, and is attached so that the opening on one side (lower side in FIG. 1) communicates with the crankcase 3. A cylinder head 8 is attached to the end of the other side (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 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 connects the inside of the cylinder 4 (compression chamber 14 described below) with the intake chamber 8a of the cylinder head 8, and an exhaust hole 9b that connects the inside of the cylinder 4 with the exhaust chamber 8b of the cylinder head 8.

Reed valve-type suction valves 10 and discharge valves 11 are attached to the valve plate 9. The suction valve 10 allows gas in the intake chamber 8a of the cylinder head 8 to flow into the cylinder 4 through the suction hole 9a, while preventing gas in the cylinder 4 from flowing into the intake chamber 8a through the suction hole 9a. The discharge valve 11 allows gas in the cylinder 4 to flow into the exhaust chamber 8b of the cylinder head 8 through the discharge hole 9b, while preventing gas in the exhaust chamber 8b from flowing into the cylinder 4 through the discharge hole 9b.

The piston 5 is fixed to the other end (small end 63 described later) of the connecting rod 6 without a bearing and is integrated with the connecting rod 6. In other words, the piston 5 is a rocking piston (locking piston) that reciprocates while rocking in the cylinder 4 together with the connecting rod 6 when the crankshaft 2 rotates. The piston 5 and the connecting rod 6 can be fixed by 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 without lubricating oil 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. The advantage of not supplying lubricating oil to the piston 5 is that the lubricating oil does not get mixed 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 that reliability will decrease, such as a decrease in compressor efficiency due to a decrease in the intake volume and damage to valve bodies and other parts due to liquid compression. The structure of the piston 5 will be described in detail later.

The piston 5 is fitted with a piston ring 12 for improving the airtightness of the compression chamber 14. The piston ring 12 is formed so that, when fitted to the piston 5, it slides smoothly inside the cylinder 4 while maintaining the airtightness of the compression chamber 14 during the compression stroke. Specifically, the piston ring 12 is a member with an approximately cylindrical outer circumferential surface and an approximately C-shaped portion, 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 its natural state. Therefore, when the piston ring 12 fitted to the piston 5 is inserted into the cylinder 4, the outer circumferential surface of the piston ring 12 is approximately in close contact with the inner circumferential 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.

The connecting rod 6 has a straight rod portion 61, a cylindrical big end 62 provided at one end of the straight rod portion 61, and a hemispherical small end 63 provided at the other end of the straight rod portion 61. The straight rod portion 61 is tapered from the big end 62 side to the small end 63 side. The big end 62 is a part that is connected to the crank pin 22 of the crankshaft 2 via the bearing 7, and is rotatable around the central axis Cb of the bearing 7 as the rotation axis. The spherical side of the small end 63 is connected to the straight rod portion 61, and the circular flat portion is connected to the piston 5. The straight line connecting the rotation axis of the cylindrical big end 62 (the central axis Cb of the bearing 7) and the center of the hemispherical small end 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.

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 (separately positioned) from the central axis Cc of the cylinder 4 without intersecting with it. 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 offset from the central axis Cc of the cylinder 4 in the direction in which the piston 5 presses against the inner circumferential surface 4a of the cylinder 4 during the compression stroke. 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 positioned at a position offset by an offset amount δ to the left of the central axis Cc of the cylinder 4. Conversely, when the crankshaft 2 rotates clockwise, the rotation axis Rs of the crankshaft 2 is positioned at a position offset by an offset amount δ to the right of the central axis Cc of the cylinder 4.

Next, the characteristics of the offset structure of the reciprocating compressor according to this embodiment will be described with reference to Figures 1 to 3. Figure 2 is a characteristic diagram showing the relationship between the crank angle and the swing angle of the piston and connecting rod. Figure 3 is a diagram showing the relationship between the tilt angle of the piston ring relative to the cylinder and the amount of gas leakage. In Figure 2, the horizontal axis θ represents the crank angle, and the vertical axis β represents the swing angle of the piston and connecting rod. In Figure 3, the horizontal axis represents the tilt angle of the piston ring relative to the cylinder, and the vertical axis represents the amount of gas leakage (mass flow rate) leaking from the gap between the piston ring and the cylinder.

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 at its lowest point, and the counterclockwise direction is the positive direction. The angle on the acute side of the center line Cr of the connecting rod 6 (which also coincides with the center line 5b of the piston 5 described below) relative to the center axis Cc of the cylinder 4 is defined as the oscillation angle β. The oscillation angle β is a positive value when the center axis Cb of the bearing 7 is located to the left of the center axis Cc of the cylinder 4, and a negative value when the center axis Cb of the bearing 7 is located to the right of the center axis Cc of the cylinder 4.

As a comparative example of the offset structure of this embodiment, a configuration different from the offset structure is considered. That is, when the rotation axis Rs of the crankshaft 2 intersects with the central axis Cc of the cylinder 4 (i.e., when the offset amount δ is 0), the rocking motion of the piston 5 and the connecting rod 6 is symmetrical 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 (when 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 intake stroke (when the piston 5 moves from the top dead center to the bottom dead center).

In contrast, in the case of the offset structure of this embodiment, the rocking motion of the piston 5 and the connecting rod 6 is asymmetric with respect to the central axis Cc of the cylinder 4. That is, as shown in FIG. 2, the change in the rocking angle β with respect to the crank angle θ is asymmetric up and down with respect to the horizontal axis. Specifically, the absolute value β1 of the maximum rocking angle in the compression stroke is smaller than the absolute value β2 of the maximum rocking angle in the intake stroke. Also, the absolute value β1 of the maximum rocking angle in the compression stroke is smaller than the absolute value of the maximum rocking angle in the compression stroke in the comparative example in which the offset amount δ is 0. In this way, in the offset structure, the absolute value of the maximum rocking angle in the compression stroke can be kept small compared to the comparative example in which the offset amount δ is 0, and the force (side force) acting between the piston 5 and the cylinder 4 in the compression stroke can be reduced accordingly.

In addition, by suppressing the maximum value of the rocking angle β during the compression stroke, the airtightness of the compression chamber 14 during the compression stroke by the piston ring 12 can be reliably maintained. This is for 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 (approximately cylindrical surface) of the piston ring 12 with respect to the inner peripheral surface 4a (approximately cylindrical surface) of the cylinder 4 is from 0° to a certain extent small, the amount of gas leaking 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 state of approximately surface contact 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 partial contact 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, the larger the inclination angle of the piston ring 12, the worse the sealing characteristics of the piston ring 12 become, and the amount of gas leaking from the compression chamber 14 increases. In this embodiment, the piston ring 12 is attached to a rocking piston 5 (locking piston), so the inclination angle of the piston ring 12 changes according to the change in the rocking angle β of the piston 5 and the connecting rod 6. In the offset structure of this embodiment, the rocking angle β during the compression stroke becomes smaller, so the inclination angle of the piston ring 12 also becomes smaller. Therefore, the amount of gas leaking from the compression chamber 14 during the compression stroke becomes smaller than in the comparative example in which the offset amount δ is 0.

Next, the structure of the piston constituting part of the first embodiment of the reciprocating compressor of the present invention will be described with reference to Figures 1, 2, 4, and 5. Figure 4 is a diagram showing a piston with a piston ring attached and its surrounding structure in the first embodiment of the reciprocating compressor of the present invention. Figure 5 is a perspective view showing the piston alone in the first embodiment of the reciprocating compressor of the present invention.

In Figures 4 and 5, the piston 5 is formed in a generally circular disk shape and has an outer peripheral surface that allows it to smoothly reciprocate while oscillating within the cylinder 4 (see Figure 1). The piston 5 has a top surface 51 that forms part of the wall surface of the compression chamber 14 (see Figure 1), and a sliding surface 52 and non-sliding surfaces 53, 54 as its outer peripheral surface. The sliding surface 52 is a curved surface that slides against the inner peripheral surface 4a of the cylinder 4 during the oscillating and reciprocating motion. The non-sliding surfaces 53, 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.

The shape of the piston 5 is subject to geometric constraints from the viewpoint of mechanical motion. Since the reciprocating compressor 1 of this embodiment has an offset structure in which the crankshaft 2 is offset relative to the cylinder 4, the rocking motion of the piston 5 and the connecting rod 6 is asymmetric with respect to the central axis Cc of the cylinder 4. Therefore, the piston 5 is formed asymmetric with respect to a plane including the central axis 5b of the piston 5 and the rotation axis of the big end 62 of the connecting rod 6 (i.e., the central axis Cb of the bearing 7) in accordance with the asymmetric rocking motion (asymmetric with respect to the central axis 5b in FIG. 4). 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 below and the rotation axis of the big end 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.

The top surface 51 is formed, for example, in a flat shape. However, as shown in FIG. 4, the top surface 51 is formed as an inclined surface that is not parallel to the orthogonal surface 5c of the piston 5 in accordance with the asymmetric rocking motion of the piston 5 relative to the central axis Cc of the cylinder 4. Here, the orthogonal surface 5c of the piston 5 is a surface that is orthogonal to the central axis 5b of the piston 5 and includes the center point 5a of the sliding surface 52 described later. The top surface 51 is formed so as to be approximately 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 surface 5c of the piston 5 as it moves in the same direction as the offset direction of the crankshaft 2 relative to the cylinder 4 (left direction in FIG. 4). Note that the top surface 51 can also be configured to have a groove portion for avoiding contact with the intake valve 10 (see FIG. 1) or a convex portion that can be inserted into the discharge hole 9b at a position opposite the discharge hole 9b (see FIG. 1).

The sliding surface 52 is formed in a spherical shape with a diameter smaller than the cylindrical diameter of the cylinder 4 so that the piston 5 can smoothly oscillate and reciprocate within the cylinder 4. The center point 5a of the spherical sliding surface 52 is located on an extension of the center line Cr of the connecting rod 6. The sliding surface 52 is a curved surface formed over a range of sliding angles φ determined according to the range of oscillation angles β in the oscillation motion of the connecting rod 6. For example, as shown in FIG. 2, when the maximum swing angle (absolute value) of the stroke (compression stroke) toward the top dead center is β1 and the maximum swing angle (absolute value) of the stroke (suction stroke) toward the bottom dead center is β2, the sliding surface 52 shown in FIG. 4 on the same side (left side in FIG. 4) as the offset direction (left direction in FIG. 4) with respect to the central axis 5b of the piston 5 has a sliding angle φ range of β1 on the top surface 51 side with respect to the perpendicular surface 5c of the piston 5 and a sliding angle φ range of β2 on the connecting rod 6 side. Conversely, the sliding surface 52 on the opposite side of the offset direction with respect to the central axis 5b of the piston 5 (right side in FIG. 4) has a sliding angle φ range of β2 on the top surface 51 side with respect to the perpendicular surface 5c of the piston 5 and a sliding angle φ range of β1 on the connecting rod 6 side.

The non-sliding surface is a curved surface formed outside the range of the sliding angle φ determined according to the range of the swing angle β in the swinging 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. The first non-sliding surface 53 is formed as a curved surface located on the outer periphery side (radially outward) of the first virtual extension curved surface 52V1 of the spherical shape that virtually extends the sliding surface 52 toward the top surface 51. In other words, when the piston 5 is disposed in the cylinder 4, the first non-sliding surface 53 is formed so as to be located closer to the inner circumferential surface 4a of the cylinder 4 than the first virtual extension curved surface 52V1 of the sliding surface 52.

However, the first non-sliding surface 53 must not come into contact with the inner circumferential surface 4a of the cylinder 4 even when the swinging motion of the connecting rod 6 (piston 5) is at the maximum swing angle. In other words, when the piston 5 is at the maximum swing angle, the first non-sliding surface 53 must be a curved surface located radially inward of the curved surface that coincides with the inner circumferential surface 4a of the cylinder 4.

For example, as shown in FIG. 2, assume that in the rocking motion of the connecting rod 6 (piston 5), the maximum rocking angle of the compression stroke is β1 and the maximum rocking angle of the intake stroke is β2. For convenience of explanation, the portion of the first non-sliding surface 53 on the same side as the offset direction of the crankshaft 2 (left side in FIG. 4) is referred to as the offset side non-sliding surface 531, and the portion on the opposite side to the offset direction (right side in FIG. 4) is referred to as the anti-offset side non-sliding surface 532. For the offset side non-sliding surface 531 to be a curved surface that matches the inner circumferential surface 4a of the cylinder 4, it is the first cylindrical surface 531c that is perpendicular to the first plane 5e that forms the same angle β1 as the maximum rocking angle of the compression stroke with respect to the perpendicular plane 5c of the piston 5. On the other hand, in order for the counter-offset side non-sliding surface 532 to be a curved surface that matches the inner peripheral surface 4a of the cylinder 4, it is necessary for the counter-offset side non-sliding surface 532c to be a second cylindrical surface 532c that is perpendicular to the second plane 5f that forms the same angle β2 as the maximum swing angle of the suction stroke with respect to the perpendicular plane 5c of the piston 5. In this case, since the shape of the offset side non-sliding surface 531 and the shape of the counter-offset side non-sliding surface 532 are different, a ridge line 533 is usually formed at the connection portion between the offset side non-sliding surface 531 and the counter-offset side non-sliding surface 532. However, this ridge line 533 is rounded, and the offset side non-sliding surface 531 and the counter-offset side non-sliding surface 532 are smoothly connected. In other words, the ridge line 533 disappears due to the rounding. Therefore, in FIG. 4, for the 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. In FIG. 4, the ridge line 533 is located approximately in the center in the left-right direction, but it can be set to any position. In other words, the circumferential position at which the offset side non-sliding surface 531 and the anti-offset side non-sliding surface 532 are connected can be changed as necessary.

In this way, the first non-sliding surface 53 is located on the inner circumferential side (radially inward) of the first cylindrical surface 531c perpendicular to the first plane 5e that forms the same angle as the maximum swing angle β1 of the compression stroke with respect to the perpendicular plane 5c of the piston 5, and the second cylindrical surface 532c perpendicular to the second plane 5f that forms the same angle as the maximum swing angle β2 of the intake stroke with respect to the perpendicular plane 5c of the piston 5, thereby making it possible to avoid contact with the inner circumferential surface 4a of the cylinder 4 during the swinging motion of the piston 5. In addition, the first non-sliding surface 53 of this embodiment is formed to be located on the outer circumferential side (radially outward) of the first imaginary extended curved surface 52V1 of the sliding surface 52.

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

As shown in FIG. 5, the outer peripheral surface of the piston 5 is provided with an annular groove 55 for mounting the piston ring 12. 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). The annular groove 55 (piston ring 12) is inclined with respect to the top surface 51 of the piston 5 so as to approach the top surface 51 of the piston 5 as it moves in the same direction as the offset direction of the crankshaft 2 (leftward in FIG. 4). In other words, the annular groove 55 is formed so 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 to the offset direction. Note that the annular groove 55 (piston ring 12) can be provided partially or entirely outside the range of the sliding angle φ.

Next, the operation and effects of the reciprocating compressor according to the first embodiment of the present invention will be described with reference to Figures 1 to 6. Figure 6 is an explanatory diagram showing the state when the piston is at top dead center in the first embodiment of the reciprocating compressor according to the present invention.

In the reciprocating compressor 1 shown in FIG. 1, when the crankshaft 2 is rotated by a rotary drive source (not shown) such as an electric motor (counterclockwise rotation in FIG. 1), the connecting rod 6 swings and reciprocates the piston 5 in the cylinder 4 while the radial movement is restricted. During the intake stroke in which 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, and gas is sucked into the compression chamber 14 from the crankcase 3 through the gap between the piston 5 (piston ring 12) and the cylinder 4. On the other hand, during the compression stroke in which the piston 5 moves from the bottom dead center to the top dead center, the compression chamber 14 contracts, and the gas in the compression chamber 14 is compressed, and the discharge valve 11 opens and the gas is discharged to the outside through the exhaust chamber 8b in the cylinder head 8.

In the reciprocating compressor 1 according to the embodiment, the rotation axis Rs of the crankshaft 2 is offset from the central axis Cc of the cylinder 4 to reduce the maximum value of the oscillation angle β of the piston 5 and the connecting rod 6 during the compression stroke, as shown in FIG. 2. This reduces the force (side force) acting between the piston 5 and the cylinder 4 during the compression stroke.

In addition, in the reciprocating compressor 1 according to the embodiment, a piston ring 12 is attached to the piston 5. By reducing the rocking angle β of the piston 5 during the compression stroke by using an offset structure, the inclination angle of the piston ring 12 relative to the cylinder 4 is reduced. Therefore, as shown in FIG. 3, the sealing performance of the piston ring 12 ensures high airtightness of the compression chamber 14.

When the piston 5 is at the top dead center, as shown in FIG. 6, a gap (hereinafter referred to as top clearance ε) is provided between the top surface 51 of the piston 5 and the valve plate 9 to avoid collision between 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 is 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 that cause a decrease in the discharge performance of the compressor (a decrease in the discharge flow rate and a decrease in volumetric efficiency). To realize a highly efficient compressor, it is desirable to reduce the dead volume.

In addition to the top clearance ε, one of the causes of the dead volume is the gap between the outer peripheral surface of the piston 5 and the inner peripheral surface 4a of the cylinder 4. In this embodiment, the gap between the piston 5 and the cylinder 4 is sealed by the piston ring 12, so 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 is one of the causes 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 of the piston 5 shown in FIG. 5 that is located on the top surface 51 side of the annular groove 55 in which the piston ring 12 is attached (part of the sliding surface 52 (the right side part in FIG. 5) and the first non-sliding surface 53) and the inner peripheral surface 4a of the cylinder 4.

One way to reduce the dead volume is to reduce the region (area) of the outer circumferential surface (part of the sliding surface 52 and the first non-sliding surface 53) located closer to the top surface 51 than the annular groove 55 of the piston 5. This can be achieved by positioning the annular groove 55 closer to the top surface 51. 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. The wall thickness of the disk-shaped portion cannot be made less than a predetermined value from the viewpoint of ensuring the strength required to hold the piston ring 12 in the annular groove.

In this embodiment, the top surface 51 is inclined toward the annular groove 55 as it approaches the offset direction of the crankshaft 2 (leftward in Figs. 4 and 5), so the thickness of the disk-shaped portion is thinnest on the same side as the offset direction (left side in Figs. 4 and 5). The thickness of the thinnest portion is determined from the viewpoint of material strength. On the other hand, the thickness of the disk-shaped portion on the opposite side to the offset direction (right side in Figs. 4 and 5) is thicker than that of the portion on the same side as the offset direction. From the viewpoint of dead volume, the inclination of the top surface 51 with respect to the annular groove 55 makes the portion of the disk-shaped portion opposite the offset direction unfavorable. In other words, in a configuration in which the opposing surfaces of the top surface 51 and the valve plate 9 are parallel at the top dead center of the piston 5, the thickness of a portion of the disk-shaped portion sandwiched between the annular groove and the top surface 51 becomes thicker due to the offset structure.

In this embodiment, as shown in FIG. 6, the first non-sliding surface 53, which is located closer to the top surface 51 than the annular groove 55 (piston ring 12), is formed to be located on the outer periphery (radially outward) than the first imaginary extended curved surface 52V1 of the spherical sliding surface 52, so that the gap G between the first non-sliding surface 53 of the piston 5 and the inner circumferential surface 4a of the cylinder 4 can be reduced. In other words, the dead volume can be reduced without bringing the annular groove 55 (piston ring 12) close to the top surface 51.

The gap between the first non-sliding surface 53 of the piston 5 and the inner circumferential surface 4a of the cylinder 4 is one of the leakage paths for compressed gas from inside the compression chamber 14 to the outside (inside the crankcase 3). Therefore, by forming the first non-sliding surface 53 so that it is positioned on the outer circumferential side of the spherical first imaginary extended curved surface 52V1, the gap G between the first non-sliding surface 53 and the inner circumferential surface 4a of the cylinder 4 is reduced, and the amount of compressed air leaking during the compression stroke can also be reduced.

In this embodiment, as shown in FIG. 4, the offset side non-sliding surface 531 of the first non-sliding surface 53 is formed as a curved surface (however, not in contact with the inner circumferential surface 4a of the cylinder 4) that approximately matches the first cylindrical surface 531c perpendicular to the first plane 5e whose angle with respect to the orthogonal plane 5c of the piston 5 is the maximum swing angle β1 of the compression stroke, and the anti-offset side non-sliding surface 532 is formed as a curved surface (however, not in contact with the inner circumferential surface 4a of the cylinder 4) that approximately matches the second cylindrical surface 532c perpendicular to the second plane 5f whose angle with respect to the orthogonal plane 5c of the piston 5 is the maximum swing angle β2 of the intake stroke. According to this configuration, the first non-sliding surface 53 of the piston 5 can be brought closest to the inner circumferential surface 4a of the cylinder 4 without contacting the inner circumferential surface 4a of the cylinder 4. That is, the offset side non-sliding surface 531 is formed as a curved surface that approximately matches the first cylindrical surface 531c, and the non-offset side non-sliding surface 532 is formed as a curved surface that approximately matches the second cylindrical surface 532c, thereby minimizing the dead volume.

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 from the central axis Cc of the cylinder 4, a piston 5 that reciprocates within the cylinder 4 to form a compression chamber 14 together with the cylinder 4, and a connecting rod 6 that is rotatably connected to the crankshaft 2 at one end and fixed to the piston 5 at the other end and oscillates relative to the cylinder 4 due to the rotational motion of the crankshaft 2. The piston 5 has a top surface 51 that constitutes a part of the wall surface of the compression chamber 14, a sliding surface 52 that slides against the inner circumferential surface 4a of the cylinder 4 within a range determined according to the range of the oscillation angle β of the connecting rod 6 relative 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 circumferential surface 4a of the cylinder 4. At least a portion of the first non-sliding surface 53 is located closer to the inner surface 4a of the cylinder 4 than the first imaginary extended curved surface 52V1, which is an imaginary extension of the sliding surface 52 toward the top surface 51.

According to this configuration, by offsetting the crankshaft 2 with respect to the cylinder 4, it is possible to reduce the rocking angle β of the piston 5 during the compression stroke, and by forming at least a part of the first non-sliding surface 53 of the piston 5 on the outer periphery side (radially outward) of the first virtual extension curved surface 52V1, the gap G between the first non-sliding surface 53 of the piston 5 and the inner circumferential surface 4a of the cylinder 4 is reduced. Therefore, it is possible to reduce the dead volume of the compression chamber 14 while reducing the side force acting between the piston 5 and the cylinder 4 during the compression stroke. In addition, by reducing the gap G between the first non-sliding surface 53 of the piston 5 and the inner circumferential surface 4a of the cylinder 4, it is possible to suppress leakage of compressed gas from the compression chamber 14 through the gap G.

In addition, in the reciprocating compressor 1 according to this embodiment, the entire first non-sliding surface 53 is located closer to the inner circumferential surface 4a of the cylinder 4 than the first imaginary extension curved surface 52V1. With this configuration, the gap G between the first non-sliding surface 53 of the piston 5 and the inner circumferential surface 4a of the cylinder 4 is smaller over the entire circumference, so that the dead volume of the compression chamber 14 can be further reduced and leakage of compressed gas from the compression chamber 14 can be further suppressed.

In addition, in the reciprocating compressor 1 according to this embodiment, the piston 5 is asymmetric with respect to a plane including the rotation axis of the big end 62 side (one side) of the connecting rod 6 (the central axis Cb of the bearing 7) and the central axis 5b of the piston (the central line Cr connecting the big end 62 side (one side) and the small end 63 side (the other side) of the connecting rod 6). With this configuration, it is possible to configure a piston with a shape that corresponds to the asymmetric rocking motion of the piston 5 and the connecting rod 6 relative to the cylinder 4 caused by the offset structure.

In addition, in the reciprocating compressor 1 according to this embodiment, a piston ring 12 is attached to the outer peripheral surface of the piston 5, and the piston ring 12 is inclined relative to the top surface 51 of the piston 5 so as to approach the top surface 51 as it moves in the same direction as the offset direction of the rotation axis Rs of the crankshaft 2 relative to the central axis Cc of the cylinder 4. With this configuration, the piston ring 12 can ensure airtightness of the compression chamber 14 in an offset structure.

[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 diagram showing a piston equipped with a piston ring and its surrounding structure in the second embodiment of the reciprocating compressor of the present invention. In Fig. 7, the same reference numerals as those in Figs. 1 to 6 denote similar parts, and therefore detailed description thereof will be omitted.

The second embodiment of the reciprocating compressor of the present invention shown in FIG. 7 differs from the first embodiment in that the shape of the second non-sliding surface 54A of the outer circumferential 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 as a curved surface that coincides with the second imaginary extension curved surface 52V2 obtained by virtually extending the spherical sliding surface 52 toward the connecting rod 6 (see FIG. 4). In contrast, the second non-sliding surface 54A of the piston 5A according to this embodiment is formed as a curved surface located on the outer circumferential side (radially outward) of the second imaginary extension curved surface 52V2. That is, when the piston 5A is disposed in the cylinder 4, the entire second non-sliding surface 54A is formed so as to be located closer to the inner circumferential surface 4a of the cylinder 4 than the second imaginary extension curved surface 52V2 of the spherical sliding surface 52. As a result, the area where the gap between the second non-sliding surface 54A of the piston 5A and the inner circumferential surface 4a of the cylinder 4 is smaller is increased compared to the first embodiment.

In the reciprocating compressor according to the second embodiment described above, as in the first embodiment, the crankshaft 2 is offset relative to the cylinder 4 to reduce the swing angle β of the piston 5A during the compression stroke, and the gap G between the first non-sliding surface 53 of the piston 5A and the inner peripheral surface 4a of the cylinder 4 is reduced by forming at least a part of the first non-sliding surface 53 of the piston 5A on the outer periphery side (radially outward) of the first imaginary extension curved surface 52V1. Therefore, the dead volume of the compression chamber 14 can be reduced while reducing the side force acting between the piston 5A and the cylinder 4 during the compression stroke, and the leakage of compressed gas from the compression chamber 14 through the gap G can be suppressed.

The piston 5A in the reciprocating compressor according to this 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 is shaped to avoid contact with the inner circumferential surface 4a of the cylinder 4. At least a portion of the second non-sliding surface 54A is located closer to the inner circumferential surface 4a of the cylinder 4 than a second imaginary extension curved surface 52V2 that is an imaginary extension of the sliding surface 52 to the opposite side of the top surface 51.

With this configuration, at least a portion of the second non-sliding surface 54A is formed on the outer periphery (radially outward) side of the second imaginary extended curved surface 52V2, so that the gap between the second non-sliding surface 54A of the piston 5A and the inner circumferential surface 4a of the cylinder 4 is reduced, thereby further suppressing gas leakage from the compression chamber 14 during the compression stroke.

In addition, in the reciprocating compressor according to this embodiment, the entire second non-sliding surface 54A of the piston 5A is located closer to the inner circumferential surface 4a of the cylinder 4 than the second imaginary extension curved surface 52V2. With this configuration, the gap between the second non-sliding surface 54A of the piston 5A and the inner circumferential surface 4a of the cylinder 4 is small over the entire circumference, so that leakage of compressed gas from the compression chamber 14 can be further suppressed.

[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 diagram showing a piston equipped with a piston ring and its surrounding structure in the third embodiment of the reciprocating compressor of the present invention. In Fig. 8, the same reference numerals as those in Figs. 1 to 7 denote similar parts, and therefore detailed description thereof will be omitted.

The third embodiment of the reciprocating compressor of the present invention shown in FIG. 8 differs from the first embodiment in that the shape of the first non-sliding surface 53B of the outer circumferential surface of the piston 5B is different. The first non-sliding surface 53 of the piston 5 according to the first embodiment is formed so that its entirety (whole circumference) is located on the outer circumferential side (radially outward) of the first imaginary extension curved surface 52V1 of the spherical sliding surface 52 (see FIG. 4). In contrast, the first non-sliding surface 53B of the piston 5B according to the second embodiment is formed so that only a portion of it is located on the outer circumferential side of the first imaginary extension curved surface 52V1.

Specifically, of the first non-sliding surface 53B of the piston 5B, only the anti-offset side non-sliding surface 532 located on the opposite side (right side in FIG. 7) to the offset direction of the crankshaft 2 (left direction in FIG. 8) is formed so as to be located more outer than the first imaginary extension curved surface 52V1 of the sliding surface 52. On the other hand, of the first non-sliding surface 53B, the offset side non-sliding surface 531B located on the same side as the offset direction (left side in FIG. 7) is formed into a curved surface that coincides with the first imaginary extension curved surface 52V1 of the sliding surface 52. Of the first non-sliding surface 53B, 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 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. In other words, the non-offset side non-sliding surface 532 is a greater cause of the increase in dead volume than the offset side non-sliding surface 531B. Therefore, in this embodiment, the gap G between the non-offset side non-sliding surface 532 and the inner circumferential surface 4a of the cylinder 4 is made smaller.

In the reciprocating compressor according to the third embodiment described above, as in the first embodiment, the crankshaft 2 is offset relative to the cylinder 4 to reduce the swing angle β of the piston 5B during the compression stroke, and at least a portion of the first non-sliding surface 53B of the piston 5B is formed on the outer periphery side (radially outward) of the first imaginary extension curved surface 52V1, thereby reducing the gap G between the first non-sliding surface 53B of the piston 5B and the inner circumferential surface 4a of the cylinder 4. Therefore, the dead volume of the compression chamber 14 can be reduced while reducing the side force acting between the piston 5B and the cylinder 4 during the compression stroke, and the leakage of compressed gas from the compression chamber 14 through the gap G can be suppressed.

In addition, in the reciprocating compressor according to this embodiment, of the first non-sliding surface 53B of the piston 5B, only the non-offset side non-sliding surface 532 (portion) located on the opposite side of the offset direction of the rotation axis Rs of the crankshaft 2 relative to the central axis Cc of the cylinder 4 is located closer to the inner circumferential surface 4a of the cylinder 4 than the first imaginary extension curved surface 52V1. With this configuration, it is possible to reduce the amount of material used to manufacture the piston 5B while reducing the dead volume of the compression chamber 14 and suppressing gas leakage from the compression chamber 14.

[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 a piston without a piston ring and its surrounding structure in the fourth embodiment of the reciprocating compressor of the present invention. Fig. 11 is a perspective view showing a 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, the same reference numerals as those in Figs. 1 to 8 indicate similar parts, and detailed description thereof will be omitted.

The fourth embodiment of the reciprocating compressor of the present invention shown in FIG. 9 differs from the first embodiment in that the piston 5C does not have a piston ring. Specifically, as shown in FIGS. 10 and 11, the piston 5C of this embodiment is configured such that the annular groove 55 (see FIG. 5) is not formed on the outer peripheral surface, unlike the piston 5 of the first embodiment. As shown in FIG. 11, the outer peripheral surface of the piston 5C has a valley line 56 (dashed line in FIG. 11) as the boundary between the sliding surface 52 and the first non-sliding surface 53 all around. On the other hand, in the piston 5 of the first embodiment, due to the formation of the annular groove 55, the valley line 56 (dashed line in FIG. 5) as the boundary between the sliding surface 52 and the first non-sliding surface 53 only appears partially. The other configurations and structures of the piston 5C of this embodiment are similar to those of the first embodiment.

As mentioned above, one of the causes of the dead volume is the gap between the outer peripheral surface of the piston 5C and the inner peripheral surface 4a of the cylinder 4 shown in FIG. 12. In this embodiment, the gap between the piston 5C and the cylinder 4 is sealed 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 of the piston 5C (part of the sliding surface 52 and the first non-sliding surface 53) located on the top surface 51 side of the part (annular part) where the spherical sliding surface 52 of the piston 5C and the cylindrical inner peripheral surface 4a of the cylinder 4 contact each other is one of the causes 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 compressed gas from inside the compression chamber 14 to the outside (inside the crankcase 3).

In the reciprocating compressor according to the fourth embodiment described above, as in the first embodiment, the crankshaft 2 is offset relative to the cylinder 4 to reduce the swing angle β of the piston 5C during the compression stroke, and at least a portion of the first non-sliding surface 53 of the piston 5C is formed on the outer periphery side (radially outward) of the first imaginary extension curved surface 52V1, thereby reducing the gap G between the first non-sliding surface 53 of the piston 5C and the inner circumferential surface 4a of the cylinder 4. Therefore, the dead volume of the compression chamber 14 can be reduced while reducing the side force acting between the piston 5C and the cylinder 4 during the compression stroke, and the leakage of compressed gas from the compression chamber 14 through the gap G can be suppressed.

In addition, the reciprocating compressor according to this embodiment is configured so that the piston ring 12 is not attached to the outer peripheral surface of the piston 5C. This configuration simplifies the configuration of the reciprocating compressor while reducing the dead volume of the compression chamber 14 and suppressing gas leakage from the compression chamber 14.

[others]
The present invention is not limited to the above-mentioned first to fourth embodiments, and includes various modified examples. The above-mentioned embodiments have been described in detail to easily explain the present invention, and are not necessarily limited to those having all of the configurations described. For example, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

For example, in the first to fourth embodiments described above, the sliding surfaces 52 of the pistons 5, 5A, 5B, and 5C are shown to have a spherical shape. However, as long as the sliding surfaces of the pistons can smoothly oscillate and reciprocate within the cylinder 4, it is also possible to adopt a geometrically definable curved surface other than a spherical shape, for example, a curved surface that approximates a sphere.

In the first to fourth embodiments, examples have been shown in which the pistons 5, 5A, 5B, and 5C have the second non-sliding surfaces 54 and 54A. However, the pistons may also be configured so that the outer circumferential surface (second non-sliding surface) does not exist on the connecting rod 6 side of the sliding surface 52. In other words, the outer circumferential surface of the piston may be configured only with the sliding surface 52 and the first non-sliding surfaces 53 and 53B.

In the second embodiment, an example is shown in which the entire second non-sliding surface 54A of the piston 5A is formed on the outer periphery (radially outward) of the second imaginary extended curved surface 52V2. However, it is also possible to form only a part of the second non-sliding surface on the outer periphery of the second imaginary extended curved surface 52V2.

In the third embodiment, only the anti-offset side non-sliding surface 532 (the right side in FIG. 8) of the first non-sliding surface 53B of the piston 5B is formed on the outer periphery side of the first imaginary extension curved surface 52V1, while the offset side non-sliding surface 531B (the left side in FIG. 8) is formed on a curved surface that coincides with the first imaginary extension curved surface 52V1. However, it is also possible to form only the offset side non-sliding surface of the first non-sliding surface of the piston on the outer periphery side of the first imaginary extension curved surface 52V1, while forming the anti-offset side non-sliding surface on a curved surface that coincides with the first imaginary extension curved surface 52V1. Note that even in this case, the position of the ridge that is the connection between the offset side non-sliding surface and the anti-offset side non-sliding surface can be set arbitrarily.

1...Reciprocating compressor, 2...Crankshaft, 4...Cylinder, 4a...Inner circumferential surface, 5, 5A, 5B, 5C...Piston, 6...Connecting rod, 12...Piston ring, 14...Compression chamber, 51...Top surface, 52...Sliding surface, 52V1...First imaginary extended curved surface, 52V2...Second imaginary extended curved surface, 53, 53B...First non-sliding surface (non-sliding surface), 532...Non-offset side non-sliding surface (part located on the opposite side to the shift direction), 54, 54A...Second non-sliding surface, Cc...Center axis, Rs...Rotation axis, β...Oscillation angle

Claims (7)

a cylinder having a central axis;
a crankshaft having an axis of rotation offset relative 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, the connecting rod swinging relative to the cylinder in response to the rotational movement of the crankshaft,
The piston is
A top surface that constitutes a 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 swing angle of the connecting rod relative to the central axis of the cylinder and sliding on the inner circumferential 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 circumferential surface of the cylinder;
the first non-sliding surface is at least partially located closer to the inner circumferential surface of the cylinder than a first imaginary extended curved surface that is an imaginary extension of the sliding surface toward the top surface side. 2. The reciprocating compressor according to claim 1,
the first non-sliding surface is located entirely closer to the inner circumferential surface of the cylinder than the first imaginary extended curved surface. a cylinder having a central axis;
a crankshaft having an axis of rotation offset relative 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, the connecting rod swinging relative to the cylinder in response to the rotational movement of the crankshaft,
The piston is
A top surface that constitutes a part of the wall surface of the compression chamber;
a sliding surface that slides on an inner circumferential surface of the cylinder within a predetermined range determined according to a range of a swing angle of the connecting rod relative 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 an inner circumferential surface of the cylinder;
At least a portion of the first non-sliding surface is located closer to the inner circumferential surface of the cylinder than a first imaginary extended curved surface that is an imaginary extension of the sliding surface toward the top surface,
wherein only a portion of the first non-sliding surface, which is located on an opposite side to an offset direction of the rotation axis of the crankshaft with respect to the central axis of the cylinder, is located closer to an inner circumferential surface of the cylinder than the first imaginary extension curved surface. 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 an opposite side of the top surface, and having a shape that avoids contact with an inner circumferential surface of the cylinder,
the second non-sliding surface is at least partially located closer to the inner circumferential surface of the cylinder than a second imaginary extended curved surface that is an imaginary extension of the sliding surface to an opposite side of the top surface. The reciprocating compressor according to claim 4,
the second non-sliding surface is located entirely closer to the inner circumferential surface of the cylinder than the second imaginary extended curved surface. The reciprocating compressor according to claim 1 or 3 ,
The piston is asymmetric with respect to a plane including a rotation axis of the one side of the connecting rod and a center line connecting the one side and the other side of the connecting rod. The reciprocating compressor according to claim 1 or 3 ,
A piston ring is attached to the outer circumferential surface of the piston,
the piston ring is inclined with respect to the top surface of the piston so as to approach the top surface of the piston toward the same direction as an offset direction of the rotation axis of the crankshaft from the central axis of the cylinder.