Piston, manufacturing method of the same, and compressor including the same

Abstract

To provide a piston of a compressor which enables improvement of strength compared to conventional arts.SOLUTION: A piston of the invention includes: a resin formation part 36 (a resin piston body) which reciprocates in a cylinder in the axial direction of the cylinder; and a metallic insert component which is embedded in the resin formation part 36 and connected to a connecting rod. The resin formation part 36 has a peripheral groove 33b, in which a piston ring is fitted, on a spherical-shaped circumferential wall surface. The peripheral groove 33b has an inclination different from that of the upper surface of the resin formation part 36 when the resin formation part 36 is viewed from a side surface and has a first groove wall 33b1 and a second groove wall 33b2 facing in a groove width direction in a written order from the piston head 33c side of the resin formation part 36. A gate resin cutting part 33d in the resin formation part 36 is located closer to the connecting rod side than the first groove wall 33b1 of the peripheral groove 33b.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a piston, a manufacturing method thereof, and a compressor equipped with the piston. [Background technology]

[0002] Conventionally, a resin oscillating piston having a metal insert part is known as a piston for a compressor (see, for example, Patent Document 1). A method for manufacturing this piston includes a molding step for obtaining a resin preform with an insert part embedded in a predetermined mold, and a cutting step for obtaining a target piston by cutting off an excess resin-formed portion from the resin preform. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-111556 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the resin preform obtained in the molding process has a skin layer formed by contact with a metal mold and a core layer formed by gradual solidification of the resin inside the skin layer. The core layer is generally thicker than the skin layer and is prone to voids. When the skin layer of the resin preform is removed in the above-mentioned cutting step, the core layer is exposed on the surface of the target piston. If voids appear in the exposed portion of the core layer, stress may be concentrated, which may cause a decrease in the strength of the piston.

[0005] An object of the present invention is to provide a piston that can have improved strength compared to conventional pistons, a method for manufacturing the piston, and a compressor equipped with the piston. [Means for solving the problem]

[0006] The piston of the present invention comprises a resin piston body that reciprocates within a cylinder in the axial direction of the cylinder, and a metal insert part that is embedded inside the piston body and connected to a connecting rod, the piston body having a circumferential groove into which a piston ring is fitted in a spherical circumferential wall surface, the circumferential groove having an inclination different from that of an upper surface of the piston body when the piston body is viewed from the side, and having a first groove wall and a second groove wall that face each other in the groove width direction in that order from the piston head side of the piston body, and a gate resin cutting portion of the piston body is located on the connecting rod side of the first groove wall of the circumferential groove.

[0007] The method for manufacturing a piston of the present invention includes the steps of placing the insert part at a predetermined position in a mold having a cavity that corresponds to the outer shape of the piston body, and molding the piston body by injecting resin into the mold through a gate formed in the mold, wherein the position of the gate is set so as to be away from a position in the cavity corresponding to the circumferential groove in the opposite direction to a position on the piston body corresponding to the piston head.

[0008] The compressor of the present invention includes the above-mentioned piston. Effect of the Invention

[0009] According to the present invention, it is possible to provide a piston that can have improved strength compared to conventional pistons, a manufacturing method thereof, and a compressor including the piston. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a side view of a compressor according to the embodiment of the present invention. [Diagram 2] FIG. 2 is a configuration explanatory diagram of a compressor main body in the compressor shown in FIG. [Diagram 3] FIG. 2 is a side view of the piston and connecting rod assembly. [Figure 4] 4 is a side view of a resin forming portion that constitutes the piston. FIG. [Diagram 5] FIG. 2 is an overall perspective view of a piston ring. [Figure 6A] FIG. 4 is a cross-sectional view taken along the line VIA-VIA of FIG. [Figure 6B] FIG. 6B is a cross-sectional view of FIG. 6A along line VIB-VIB. [Figure 7] FIG. 2 is a configuration explanatory diagram of a manufacturing apparatus used in a method for manufacturing a piston. [Figure 8] FIG. 4 is an explanatory diagram of the position of a gate for supplying molten resin to a die for molding a piston. [Figure 9] 9 is a cross-sectional view taken along line IX-IX of FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a piston, a manufacturing method thereof, and a compressor including the piston according to the present invention will be described in detail with reference to the accompanying drawings. First, the overall configuration of the compressor of this embodiment will be described, and then the piston of this embodiment and the manufacturing method thereof will be described.

[0012] <Compressor> Fig. 1 is a side view of a compressor 10 according to the present embodiment. Fig. 2 is a diagram illustrating the configuration of a compressor body 1 in the compressor 10. Note that the up-down direction in the following description is based on the up-down direction indicated by the arrow in Fig. 1. As shown in FIG. 1, a compressor 10 includes a compressor body 1, an electric motor 2 that drives the compressor body 1, and a tank 3 that stores the fluid compressed and discharged by the compressor body 1. As shown in FIG. 2, the compressor body 1 has a crankcase 21, a cylinder 22 protruding vertically from the crankcase 21, a valve plate 26 closing the upper part of the cylinder 22, a cylinder head 23, and a crankshaft 24 rotatably supported in the center of the crankcase 21.

[0013] As shown in FIG. 1, the compressor body 1 is fixed onto a tank 3 in a state in which a crankshaft 24 (see FIG. 2) is arranged parallel to a rotation axis (not shown) of the electric motor 2. A pulley 4 (see FIG. 1) is fixed to the crankshaft 24 (see FIG. 2). A pulley 5 (see FIG. 1) is fixed to a rotating shaft (not shown) of the electric motor 2 (see FIG. 1). The pulley 4 (see FIG. 1) has blades (not shown). The compressor body 1 dissipates heat by cooling air generated by the rotation of the blades.

[0014] As shown in Fig. 1, a transmission belt 6 is wound around the pulley 4 and the pulley 5. When the electric motor 2 rotates, the crankshaft 24 (see Fig. 2) rotates via the pulley 5, the transmission belt 6, and the pulley 4. The end of a connecting rod 32 (see Fig. 2) attached to the crankshaft 24 via a clamp pin (not shown) performs a circular motion with the rotating crankshaft 24 as the central axis. As a result, a piston 33 (see Fig. 2) attached to the tip of the connecting rod 32 reciprocates while oscillating within the cylinder 22 (see Fig. 2). The compressor 10 (see Fig. 1) stores the fluid compressed in the cylinder 22 (see Fig. 2) in the tank 3 (see Fig. 1).

[0015] In this embodiment, the compressor body 1 is connected to the electric motor 2 via a transmission belt 6 as shown in FIG. 1, but the crankshaft 24 (see FIG. 2) and the rotating shaft (not shown) of the electric motor 2 can also be directly joined by a coupling or the like. Further, the compressor 10 of the present embodiment has been described taking a one-cylinder, one-stage compressor as an example, but is not limited thereto and can also be applied to a multi-cylinder compressor having a plurality of pistons (not shown) and cylinders (not shown) arranged in series or radially with respect to the crankshaft 24. Furthermore, the driving source does not have to be an electric motor, and the present invention can also be applied to, for example, a piston for an engine-driven compressor.

[0016] <Piston> Next, the piston 33 of this embodiment will be described. 2, the piston 33 is a swinging piston integrated with the connecting rod 32. When the piston 33 reciprocates within the cylinder 22, it swings within the cylinder 22 in accordance with the change in angle of the connecting rod 32 relative to the axis of the cylinder 22.

[0017] FIG. 3 is a side view of an assembly As of the piston 33 and the connecting rod 32. As shown in FIG. As shown in FIG. 3, in the assembly As, the tip end of a connecting rod 32 is fixed to a piston 33 by a bolt 35. Piston 33 is mainly composed of a resin formed portion 36, which is the piston main body that forms the approximate outer shape of piston 33, a resin piston ring 34 attached to the peripheral surface of resin formed portion 36 (piston main body), and an insert part 41 (see Figure 6A) described below that is embedded inside resin formed portion 36 (piston main body).

[0018] FIG. 4 is a side view of the resin forming portion 36 which is the piston main body. 4, the resin formed portion 36 is an injection molded product, and has a generally low barrel shape. That is, the resin formed portion 36 has a shape in which the center in the height direction of the body bulges outward in the radial direction. Resin forming portion 36 has at least outer peripheral surface 33a in contact with inner peripheral wall 22a (see FIG. 2) of cylinder 22 (see FIG. 2), and piston head 33c facing inside compression chamber 22b (see FIG. 2) of cylinder 22. Outer peripheral surface 33a of resin forming portion 36 is a spherical surface with a diameter slightly smaller than the inner diameter of cylinder 22.

[0019] As shown in Fig. 4, a circumferential groove 33b into which a piston ring 34 (see Fig. 3) is fitted is formed in the spherical outer circumferential surface 33a (circumferential wall surface) of the resin forming portion 36. The circumferential groove 33b has an inclination different from that of the upper surface of the resin forming portion 36 when viewed from the side. The circumferential groove 33b has a first groove wall 33b1 and a second groove wall 33b2, which are arranged in this order from the piston head 33c side of the resin forming portion 36 that is the piston main body, so as to face each other in the groove width direction.

[0020] Further, in this embodiment, gate resin cutting portion 33d of resin forming portion 36 is set on outer peripheral surface 33a of resin forming portion 36. In Fig. 4, gate resin cutting portion 33d is represented by being shaded for convenience of drawing. It is difficult to determine with the naked eye the trace of gate resin cutting portion 33d in resin forming portion 36 after surface processing.

[0021] In this embodiment, the gate resin cutting portion 33d is formed so as to be spaced apart from the first groove wall 33b1 in the direction opposite to the piston head 33c, as shown in Fig. 4. In other words, the gate resin cutting portion 33d is formed so as to be spaced apart from the first groove wall 33b1 toward the connecting rod 32 (see Fig. 3). In addition, it is preferable that the gate resin cutting portion 33d is formed away from the circumferential groove 33b in the direction opposite to the piston head 33c. In other words, it is preferable that the gate resin cutting portion 33d is formed away from the second circumferential wall 33b2 toward the connecting rod 32 (see FIG. 3).

[0022] Moreover, as will be described in detail later, it is preferable that the gate resin cutting portion 33d of the resin forming portion 36 is set on the anti-load side Us of the piston (see FIG. 8). In this embodiment, the anti-load side Us (see FIG. 8) refers to the opposite side that is not pressed, assuming that the side where the resin forming portion 36 presses the inner circumferential wall 22a (see FIG. 2) of the cylinder 22 by the connecting rod 32 during the compression stroke in which the piston 33 (see FIG. 2) moves toward the top dead center inside the cylinder 22 is defined as the load side Ls (see FIG. 8). The anti-load side Us (see FIG. 8) and the load side Ls (see FIG. 8) of the resin forming portion 36 are determined in advance with a phase difference of 180 degrees when the resin forming portion 36 is designed.

[0023] As the material of the resin forming portion 36, for example, polytetrafluoroethylene (PTFE) having excellent abrasion resistance, or polyphenylene sulfide (PPS) having an excellent thermal expansion coefficient are preferable.

[0024] Next, the piston ring 34 (see FIG. 3) will be described. The piston ring 34 in this embodiment is assumed to be a leak cut piston ring. FIG. 5 is an overall perspective view of the piston ring 34. 5, the piston ring 34 has a step portion (step portion) where the abutment portion 34a overlaps in the axial and radial directions of the piston ring 34. Such a piston ring 34 is capable of expanding and contracting while maintaining sealing performance, and can more reliably reduce blow-by. However, the piston ring 34 in this embodiment is not limited to a leak cut piston ring, and may be another type of step cut piston ring or a C-shaped piston ring.

[0025] As shown in FIG. 5, the piston ring 34 has an anti-rotation recess 34b. The anti-rotation recess 34b is formed in the upper surface of the piston ring 34 at a position shifted in the circumferential direction from the joint portion 34a. Specifically, the anti-rotation recess 34b is formed by partially cutting out the solid portion of the piston ring 34 so as to straddle the upper surface and the inner peripheral surface of the piston ring 34 and to open in a rectangular shape. As will be described in detail later, this anti-rotation recess 34b is adapted to fit into an anti-rotation protrusion 33e (see FIG. 9) that is formed at a position shifted by a predetermined phase from the gate position where the gate resin cutting portion 33d (see FIG. 4) is defined.

[0026] In this embodiment, the material of the piston ring 34 is assumed to be polytetrafluoroethylene (PTFE) or polyphenylene sulfide (PPS), which has an excellent thermal expansion coefficient, but is not limited to this.

[0027] Next, the insert part will be described. Fig. 6A is a cross-sectional view taken along the line VIA-VIA of Fig. 3. Fig. 6B is a cross-sectional view taken along the line VIB-VIB of Fig. 6A. As shown in FIG. 6A, the insert part 41 is embedded inside the resin forming portion 36 that constitutes the piston 33. The insert part 41 is made of a metal such as an aluminum alloy, and has a generally hat-like shape. Specifically, the insert part 41 has a cylindrical portion 41a, a cover portion 41b, and a flange portion 41c. The flange portion 41c is an annular portion that extends radially outward from the lower outer circumferential wall of the cylindrical portion 41a.

[0028] The outer peripheral wall of the cylindrical portion 41a, the upper surface of the lid portion 41b, the upper surface and side surface of the flange portion 41c, and the radial outer side of the lower surface of the flange portion 41c are covered with the resin of the resin forming portion 36. The inner peripheral wall of the cylindrical portion 41a, the lower surface of the lid portion 41b, and the radial inner side of the lower surface of the flange portion 41c are not covered by the resin forming portion 36 and are exposed. That is, a space S is formed between the insert part 41 and the connecting rod 32. In addition, this space S communicates with the outside via the ventilation port Vt. This improves the vibration suppression performance and compression heat dissipation performance of the piston 33 by reducing the mass. 6A, reference numeral 41d denotes a through hole formed in the lid portion 41b. The through hole 41d is filled with the resin of the resin forming portion 36. The through hole 41d increases the bonding strength between the resin forming portion 36 and the insert part 41.

[0029] 6B, a screw hole 41h that opens downward is provided in the lower part of the insert part 41. A bolt 35 that is inserted into the end part of the connecting rod 32 engages with this screw hole 41h. This fixes the piston 33 and the connecting rod 32 together as described above. In addition, reference numeral 34 in Figs. 6A and 6B denotes a piston ring.

[0030] Next, a manufacturing method of the piston 33 (see FIG. 3) of this embodiment will be described. First, a manufacturing device for the piston 33 used in this manufacturing method will be described. FIG. 7 is a schematic diagram illustrating the configuration of the manufacturing apparatus 50. As shown in FIG. As shown in FIG. 7, the manufacturing device 50 is equipped with a mold 51 having a cavity Ca shaped like the resin forming portion 36 (see FIG. 4), which is the piston main body.

[0031] The mold 51 mainly comprises a fixed mold 51a, a movable mold 51b, and a sliding mold 51c. The fixed die 51a forms a lower half of the resin forming portion 36 (see FIG. 4) below the circumferential groove 33b (see FIG. 4). The fixed die 51a is formed with a mounting table 53 for placing the insert part 41 (see FIG. 6A) at a predetermined position in the die 51. Further, a gate 52b provided at the tip of a runner 52a for injecting and supplying molten resin into the mold 51 is connected to the fixed mold 51a, as will be described in detail later.

[0032] The movable die 51b and the sliding die 51c are integrated with each other via a sliding pin 51d to form the upper half of the resin forming portion 36 (see FIG. 4) including the circumferential groove 33b (see FIG. 4). The slide mold 51c forms the circumferential groove 33b (see FIG. 4) in the resin forming portion 36 (see FIG. 4) within the metal mold 51. Specifically, the slide mold 51c consists of a pair of molds each forming half of the circumferential groove 33b (see FIG. 4) extending in the circumferential direction of the resin forming portion 36 (see FIG. 4). Each of the pair of slide dies 51c slides relative to the movable die 51b so as to move away from the molded product (resin forming portion 36) when the die is opened. Although not shown, the sliding pin 51d slides in its axial direction when the mold 51 is opened, thereby releasing the lock of the sliding mold 51c from the movable mold 51b.

[0033] After obtaining a molded product (resin forming portion 36) in mold 51, first slide mold 51c slides and moves to open mold 51. Next, movable mold 51b moves away from fixed mold 51a. Then, runner resin 52a1 (see FIG. 9) and gate resin 52b1 (see FIG. 9) described later are removed from fixed mold 51a in a state where they are connected to molded product (resin forming portion 36).

[0034] Next, a method for manufacturing the piston 33 of this embodiment will be described. This manufacturing method includes the steps of placing an insert part 41 (see FIG. 6A) at a predetermined position in a mold 51 (see FIG. 7) having a cavity Ca (see FIG. 7) that resembles the outer shape of the resin forming portion 36 (see FIG. 4), which is the piston main body, and injecting molten resin into the mold 51 through a gate 52b (see FIG. 7) formed in the mold 51 to form the resin forming portion 36 (see FIG. 4).

[0035] In addition, in this manufacturing method, the position of gate 52b (see FIG. 7) is set to be farther away from a position corresponding to piston head 33c (see FIG. 4) of resin forming portion 36 (see FIG. 4), which is the piston main body, than a position corresponding to first groove wall 33b1 (see FIG. 4) of circumferential groove 33b (see FIG. 4) in cavity Ca (see FIG. 7), in the opposite direction to a position corresponding to piston head 33c (see FIG. 4). Preferably, the position of gate 52b (see FIG. 7) is set to be farther away from a position corresponding to piston head 33c (see FIG. 4) than a position corresponding to circumferential groove 33b (see FIG. 4) in cavity Ca (see FIG. 7), in the opposite direction.

[0036] In addition, in the manufacturing method of the piston 33 of this embodiment, the position of the gate 52b (see FIG. 7) is set on the anti-load side of the resin forming portion 36 (see FIG. 4). Fig. 8 is an explanatory diagram of the position of gate 52b (see Fig. 7). Specifically, Fig. 8 shows the position of gate resin 52b1 connected to the molded product (resin forming portion 36) removed from mold 51 (see Fig. 7). In the following, the position of gate 52b (see Fig. 7) will be explained based on the position of gate resin 52b1 shown in Fig. 8.

[0037] The anti-load side Us and the load side Ls of the resin forming portion 36 of this embodiment shown in Fig. 8 are determined in advance taking into consideration the state in which the resin forming portion 36 is assembled into the cylinder 22 (see Fig. 2). As described above, the load side Ls of the resin forming portion 36 is the side on which the resin forming portion 36 presses the inner circumferential wall 22a (see Fig. 2) of the cylinder 22 in the compression process. The anti-load side Us is set with a phase shift of 180 degrees in the circumferential direction of the resin forming portion 36 relative to the load side Ls.

[0038] If the position of gate 52b relative to cavity Ca of mold 51 shown in Figure 7 is replaced with the position of gate resin 52b1 shown in Figure 8, gate 52b (see Figure 7) is set on the anti-load side Us of the molded product (resin forming portion 36) shown in Figure 8.

[0039] The position of such a gate 52b (see FIG. 7) automatically determines the parting line between the pair of slide dies 51c (see FIG. 7). That is, the parting line of the slide mold 51c (see FIG. 7) is set so as to correspond to the line segment PL connecting the position of the gate resin 52b1 shown in FIG.

[0040] As described above, the resin forming portion 36 in this embodiment is assumed to have an anti-rotation protrusion that fits into the anti-rotation recess 34b of the piston ring 34 (see FIG. 5). The anti-rotation protrusion 33e corresponds to the "anti-rotation portion" in the claims. 9, the anti-rotation protrusion 33e in this embodiment is formed in the circumferential groove 33b of the resin forming portion 36. Specifically, it is assumed that the anti-rotation protrusion 33e protrudes downward from the first groove wall 33b1 of the circumferential groove 33b shown in FIG.

[0041] 8, anti-rotation projection 33e is located on a line segment PL connecting gate 52b shown in FIG. 7, in other words, the position of gate resin 52b1 shown in FIG. 8, and the central axis of resin forming portion 36. That is, anti-rotation projection 33e is formed on a diagonal of gate resin 52b1 across the central axis of resin forming portion 36, which is the piston main body. In other words, in this manufacturing method, anti-rotation projection 33e is formed at a diagonal position of gate 52b (see FIG. 7).

[0042] In the manufacturing method of this embodiment, the runner resin a1 and the gate resin 52b1 are separated from the resin forming portion 36 shown in Fig. 9. As a result, the gate resin cut portion 33d (see Fig. 4) is formed in the resin forming portion 36 at a predetermined position on the outer circumferential surface 33a (see Fig. 4). As shown in Fig. 9, the resin forming portion 36 has a skin layer SL formed by direct contact of the molten resin with the mold 51 (see Fig. 7), and a core layer CL formed inside the skin layer SL by the molten resin hardening more slowly than the skin layer SL. In general, the core layer CL tends to have more voids than the skin layer SL. The core layer CL is exposed at the gate resin cutting portion 33d (see Fig. 4).

[0043] In the manufacturing method of this embodiment, the piston ring 34 shown in FIG. 5 is fitted into the circumferential groove 33b of the resin forming portion 36 shown in FIG. 4 to complete the intended piston 33 (see FIG. 3). At this time, as shown in FIG. 8, the butt portion 34a of the piston ring 34 in this embodiment is disposed at the circumferential center of the load side Ls on which the load is the greatest. Moreover, the anti-rotation protrusion 33e is disposed at a position that is a predetermined distance away in the circumferential direction from the position of the abutment 34a so as to avoid the abutment 34a. Specifically, the positions of the anti-rotation protrusion 33e and the anti-rotation recess 34b are set at a position that is less than 90 degrees from the circumferential center of the abutment 34a, and preferably at a position that is about 45 degrees.

[0044] In addition, in the piston 33 in which the positions of the anti-rotation protrusion 33e and the anti-rotation recess 34b are arranged at a position circumferentially away from the joint portion 34a, it is preferable that the gate resin cutting portion 33d (see Figure 4) is shifted circumferentially so as to maintain a diagonal position with the anti-rotation protrusion 33e and the anti-rotation recess 34b. However, the anti-rotation projection 33e and the anti-rotation recess 34b may be disposed in the same phase as the gate resin cutting portion 33d (see FIG. 4), provided that the gate resin cutting portion 33d is positioned on the anti-load side Us.

[0045] <Action and effect> Next, the piston 33 according to this embodiment, a manufacturing method thereof, and the effects of the compressor 10 including the piston 33 will be described. The piston 33 of this embodiment includes a resin forming portion 36 (a resin piston main body) that reciprocates within the cylinder 22 in the axial direction of the cylinder 22, and a metal insert part 41 that is embedded inside the resin forming portion 36 and is connected to the connecting rod 32. The resin forming portion 36 has a circumferential groove 33b into which a piston ring 34 is fitted, the circumferential groove 33b has a spherical circumferential wall surface, the circumferential groove 33b has an inclination different from that of the upper surface of the resin forming portion 36 when the resin forming portion 36 is viewed from the side, and has a first groove wall 33b1 and a second groove wall 33b2 that face each other in the groove width direction in that order from the piston head 33c side of the resin forming portion 36. A gate resin cutting portion 33d in the resin forming portion 36 is located on the connecting rod 32 side of the first groove wall 33b1 of the circumferential groove 33b. Moreover, the compressor 10 of the present embodiment is provided with such a piston 33.

[0046] In the piston 33 of this embodiment, the gate resin cut portion 33d where the core layer CL that may contain voids is exposed is formed farther from the piston head 33c than the first groove wall 33b1 of the circumferential groove 33b into which the piston ring 34 is fitted. With such a piston 33, the gate resin cut portion 33d, where stress is likely to concentrate due to exposed voids, can be reliably located away from the compression chamber 22b, which becomes high in temperature and pressure. According to the piston 33 of this embodiment, the strength of the piston reciprocating within the cylinder 22 can be further increased.

[0047] In such a piston 33, it is preferable that the gate resin cutting portion 33d is set so as to be farther away from the circumferential groove 33b in the direction opposite to the piston head 33c. According to such a piston 33, the gate resin cut portion 33d can be more reliably located away from the compression chamber 22b, and the strength of the piston can be further increased. Furthermore, according to such a piston 33, the gate resin cut portion 33d is separated from the circumferential groove 33b, so that the structure around the gate 52b in the mold 51 for manufacturing the piston 33 can be simplified.

[0048] In such a piston 33, the gate resin cutting portion 33d is set on the anti-load side Us of the resin forming portion 36 (piston main body). Such a piston 33 improves the durability of the piston 33.

[0049] In such a piston 33, in the piston body, anti-rotation protrusions 33e (anti-rotation portions) of the piston ring 34 are formed diagonally across the central axis of the resin forming portion 36 (piston body) from the gate resin cutting portion 33d. According to such a piston 33, the parting line of the slide die 51c can be laid out so that the anti-rotation protrusion 33e (anti-rotation portion) does not form an undercut.

[0050] In such a piston 33, the anti-rotation protrusion 33e (anti-rotation portion) is shifted a predetermined distance in the circumferential direction of the piston 33 relative to the position of the joint portion 34a of the piston ring 34, and the gate resin cutting portion 33d is shifted in the circumferential direction of the piston 33 so as to maintain a diagonal position with respect to the anti-rotation protrusion 33e (anti-rotation portion).

[0051] With such a piston 33, the parting line of the slide mold 51c can be laid out so that the anti-rotation protrusion 33e (anti-rotation portion) does not form an undercut, and the gate resin cutting portion 33d can be more reliably set on the anti-load side Us.

[0052] In addition, the manufacturing method of the piston 33 in this embodiment includes the steps of placing the insert part 41 at a predetermined position in a mold 51 having a cavity Ca that resembles the outer shape of the resin forming portion 36 (piston main body), and injecting resin into the mold 51 through a gate 52b formed in the mold 51 to mold the resin forming portion 36 (piston main body), and the position of the gate 52b is set so as to be away from the position corresponding to the first groove wall 33b1 in the cavity Ca in the opposite direction to the position corresponding to the piston head 33c of the resin forming portion 36 (piston main body).

[0053] According to this manufacturing method, it is possible to obtain the piston 33 having the above-mentioned effects. Moreover, according to this manufacturing method, unlike conventional pistons (for example, see Patent Document 1), it is possible to form the piston 33 in one shot. As a result, unlike conventional pistons, the exposed portion of the core layer on the surface is further reduced. [Explanation of symbols]

[0054] 22 cylinders 32 Connecting rod 33b Circumferential groove 33b1 1st groove wall 33b2 2nd groove wall 33c piston head 33d Gate resin cutting part 33e Anti-rotation protrusion (anti-rotation part) 34 Piston ring 34a Abutment 36 Resin forming part (piston body) 41 Insert parts 51 Mold Gate 52b Ca Cavity Us anti-load side

Claims

1. A resin piston body that reciprocates within the cylinder in the axial direction; a metal insert part embedded inside the piston body and connected to a connecting rod; Equipped with The piston body has a circumferential groove in which a piston ring is fitted on a spherical circumferential wall surface, the circumferential groove has an inclination different from that of an upper surface of the piston body when the piston body is viewed from a side, and includes a first groove wall and a second groove wall which face each other in a groove width direction in this order from a piston head side of the piston body, The piston has a gate resin cut portion in the piston body that is located closer to the connecting rod than a first groove wall of the circumferential groove.

2. The piston according to claim 1 , wherein the gate resin cut portion is spaced apart from the second groove wall in a direction opposite to the piston head.

3. The piston according to claim 1 , wherein the gate resin cutting portion is located on a non-load side of the piston body.

4. 4. The piston according to claim 3, wherein the piston body has anti-rotation portions for the piston ring at diagonal corners of the gate resin cut portion across a central axis of the piston body.

5. 5. The piston according to claim 4, wherein the anti-rotation portion is spaced a predetermined distance in a circumferential direction of the piston from a position of the abutment portion of the piston ring, and the gate resin cut portion is shifted in the circumferential direction of the piston so as to maintain a diagonal position with respect to the anti-rotation portion.

6. A method for manufacturing a piston according to any one of claims 1 to 5, comprising the steps of: placing the insert part at a predetermined position in a mold having a cavity corresponding to the outer shape of the piston body; a step of injecting a resin into the mold through a gate formed in the mold to mold the piston body; having A method for manufacturing a piston, wherein the position of the gate is set to be away from the position of the piston body corresponding to the piston head in the opposite direction from the position of the piston body corresponding to the circumferential groove in the cavity.

7. A compressor comprising a piston according to any one of claims 1 to 5.

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