Fluid machines with a piston

Abstract: Pistons (17), which are reciprocated by a swash plate of a compressor, have two separate parts joined together. Each piston (17) has a body (21) and a coupler (22). The coupler (22) is connected to the swash plate (16). The body (21) is made of thermosetting resin. The body (21) is molded to the coupler. Accordingly, the piston body (21) to be firmly connected to the coupler (22).

Description: BACKGROUND OF THE INVENTION The present invention relates to a piston in accordance with the preamble of claims 1 and 12 and a method for producing a piston in accordance with claim 1. Japanese Unexamined Patent Publication No. 5-99146 describes a compressor piston 112. As shown in Fig. 6, the resin piston body 130 is compression-molded to and joined to a metal coupler 120, to which a piston rod 113 is coupled. Since most of the piston 112 is made of resin, the piston 112 is relatively light. The light piston reduces inertia when the piston 112 reciprocates. As a result, power losses of the compressor are reduced. However, in the publication, the piston body 130 is made of fluororesin such as polytetrafluoroethylene, which is a thermoplastic resin. Since such thermoplastic resin has poor adhesion to metal, the coupler cannot be joined to the piston with desirable strength. In a typical compressor, rotation of a swash plate is converted into piston reciprocation through shoes. Each piston includes a body and a coupler, which are joined. Each piston is coupled to the swash plate through the shoes, which are retained in the coupler to slide freely. In the typical compressor, force is applied to each piston through the shoes and the coupler by the swash plate. This causes frictional resistance between each piston and the wall of the corresponding cylinder bore. Accordingly, a torsional force is applied to the interface between each piston body and coupler. As a result, the metal couplers may be detached from the piston bodies, which are made of thermoplastic resin. This hinders smooth reciprocation of the pistons and damages the seal between the pistons and the cylinder bores. Document US-A-4 462 302 discloses a piston for cooperating with a driving body of a machine. The piston is made of a first part which may be made of steel, and a second part made of a thermosetting resin which may be enforced by glass fibres. Thus, the document discloses a piston comprising a first part made of steel and a second part made of a thermosetting resin. No further hint at the outlined two-part construction or the method for manufacturing the piston is given. SUMMARY OF THE INVENTION The object of the present invention is to provide a piston for cooperating with a driving body in a machine, especially a piston for cooperating with a swash plate in a compressor, and a method for manufacturing such a piston to allow that the piston is firmly connected to a coupler in a very stable manner, to enable a stable connection over a longer period of use even under changing temperature conditions. This object is achieved by the features of claims 1 and 12 or claim 13, respectively. In accordance with the invention, the piston is provided with a metal coupler having a first thermal expansion coefficient and a body made of a thermosetting resin and having a second thermal expansion coefficient wherein the body is molded to the coupler and the first thermal expansion coefficient is substantially matching the second thermal expansion coefficient. Thus, even under changing temperature conditions, stress induced due to different thermal expansion coefficients is avoided ensuring a long-lasting and stable construction. Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: Fig. 1 is a cross-sectional view of a compressor according to a first embodiment of the present invention; Fig. 2 is a perspective view of a piston in the compressor of Fig. 1; Fig. 3(a) is a side view of one half of an injection mold containing a coupler; Fig. 3(b) is an exploded view of the injection mold of Fig. 3(a); Fig. 4 is a graph showing the proportion of glass fiber (by weight) contained in a piston body in relation to the thermal expansion coefficient; Fig. 5(a) is a side view of an insert in a second embodiment; Fig. 5(b) is a side view of an insert in a third embodiment; Fig. 5(c) is a side view of an insert in a fourth embodiment; and Fig. 6 is a cross-sectional view showing a prior art piston. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A piston for compressors for air-conditioning vehicles according to a first embodiment of the present invention will now be described with reference to Figs. 1-4. As shown in Fig. 1, a front housing member 11 and a rear housing member 13 are coupled to a cylinder block 12. A crank chamber 14 is defined between the front housing member and the cylinder block 12. The front housing member 11, the cylinder block 12, and the rear housing member 13 form the compressor housing. A drive shaft 15 passes through the crank chamber 14 and is rotatably supported between the front housing member and the cylinder member. The drive shaft 15 is coupled to an engine (not shown) through a clutch mechanism such as an electromagnetic clutch. The engine serves as an external drive source. Accordingly, the drive shaft 15 rotates when the clutch is connected during the operation of the engine. A swash plate 16 is coupled to the drive shaft 15 to rotate integrally with the drive shaft 15 in the crank chamber 14. Cylinder bores 12a are formed in the cylinder block 12. The cylinder bores 12a are parallel to the axis L of the drive shaft 15 and are equally spaced about the axis L. Single head pistons 17 are respectively accommodated in the corresponding cylinder bores 12a. Each piston 17 is coupled to the swash plate 16 through a pair of shoes 18. Rotation of the drive shaft 15 is converted into reciprocation of each piston 17 through the swash plate 16 and the shoes 18. Reciprocation of each piston 17 compresses refrigerant gas in the corresponding cylinder bore 12a. In the present embodiment, the drive shaft 15, the swash plate 16, and the shoes 18 form a driving mechanism. All of the pistons 17 are identical, thus the following description will refer to only one of the pistons 17 for simplicity. As shown in Figs. 1 and 2, the piston 17 includes a resin body 21 and a metal coupler 22. The body 21 is joined to the coupler 22. The coupler 22 is made of metal (Al-Si alloy), which is an aluminum containing 7-13 percent of silicon by weight. The coupler 22 is produced by forging or casting. Using aluminum for the coupler 22 reduces the weight of the piston 17. Adding silicon reduces friction between the piston 17 and the inner surface of the corresponding cylinder bore 12a and between the piston 17 and the shoes 18. A recess 23 is formed in the proximal end of the coupler 22. A pair of sockets 23a are formed on the opposed inner surfaces of the recess 23. A pair of shoes 18 are supported in the sockets 23a to hold the periphery of the swash plate 16. Accordingly, the shoes 18 transmit the alternating inclination of the swash plate 16 to the piston 17, which reciprocates the piston 17 axially (along axis S). An anchor 24 is integrally formed on the coupler 22. As shown in Fig. 1, the anchor 24 includes a support shaft 24a and a flange, or a disc 24b. The support shaft 24a extends from center of the end surface of the coupler 22 toward the body 21. The disc 24b is supported by the support shaft 24a. The diameter of the disk 24b is greater than that of the support shaft 24a. The body 21 is joined to the coupler 22 and receives the anchor 24. The coupler 22 of each piston 17 has a partially cylindrical rotation restrictor 23b. The curvature of the restrictor's cylindrical portion is greater than that of each cylinder bore 12a. The center of curvature of each rotation restrictor 23b is displaced from the center of curvature of the corresponding cylinder bore 12a. As each piston 17 reciprocates, the associated rotation restrictor 23b slides along the inner surface of the front housing 11 while preventing the piston 17 from rotating about the axis S. The body 21 includes a columnar head 21a and a pair of struts 21b. The head 21a slides along the surface of the corresponding cylinder bore 12a. The struts 21b extend diagonally from the head 21a to the coupler 22. A trapezoidal hole is formed between the struts 21b to make the piston 17 light. Figs. 3(a) and 3(b) shows an injection mold 31. A cavity 32 is formed in the mold 31. The coupler 22 is placed in the rear portion of the cavity 32. Part of an end surface of the coupler 22 and the anchor 24 are exposed to a front portion of the cavity 32, which defines the body 21. A molding material including a heated phenol resin, which is a thermosetting resin, and glass fibers, which serve as reinforcing material, is injected into the cavity 32 for forming the body 21. Accordingly, the front portion of the cavity 32 is filled with the molding material. The molding material, when solidified, fixes the end surface of the coupler 22 and the anchor 24 to the body 21. As shown in the graph of Fig. 4, the thermal expansion coefficient of a phenol resin containing a relatively small amount of glass fibers is greater than that (18*10 -6 to 24*10 -6 ) of an aluminum alloy containing 7-13 weight percent of silicon, which forms the coupler 22. The thermal expansion coefficient of a phenol resin becomes smaller as the proportion of glass fibers contained in the phenol resin increases. Accordingly, adjusting the proportion of glass fibers contained in the phenol resin makes the thermal expansion coefficient of the body 21 substantially equal to that of the metal coupler 22. That is, the proportion of glass fibers contained in the phenol resin is adjusted within a range of 15-65 weight percent to correspond to aluminum alloy containing 7-13 weight percent of silicon. The illustrated embodiment has the following advantages. A driving force is applied to each body 21 through the shoes 18 and the coupler 22. This causes frictional resistance between the body 21 and the surface of the cylinder bore 12a. Accordingly, a shearing stress which is based on the rotation of the swash plate 16 and reciprocation of the piston 17 is applied to the juncture between the body 21 and the coupler 22. However, in the present embodiment, thermosetting resin is used to form the body 21. Thermosetting resin has better adhesion to metal than thermoplastic material does. Accordingly, the coupler 22 is more firmly joined to the body 21 than in the prior art. Adhesion between the body 21 and the coupler 22 can withstand the torsional force. Thermosetting resin is more heat-resistant than thermoplastic resin is. Accordingly, the body 21 is not softened by heat generated by friction between the piston 17 and the surface of the cylinder bore 12a. Therefore, firm adhesion between the body 21 and the coupler 22 is maintained. As a result, the piston 17 smoothly slides in the cylinder bore 12a, and good seal between the piston 17 and the cylinder bore 12a is maintained. Adding reinforcing material hardens the thermosetting resin and increases the durability of the body 21. Adjusting the proportion of reinforcing material contained in the body 21 alters the thermal expansion coefficient of the body 21 to substantially match that of the coupler 22. Accordingly, the thermal expansion due to friction heat in the body 21 is substantially equal to that of the coupler 22. This prevents internal stresses based on a difference in thermal expansion from being generated at the juncture between the body 21 and the coupler 22. Therefore, the adhesion between the body 21 and the coupler 22 is stable. The resin of the body 21 fills the space between the disc 24b and an end surface of the coupler 22. The disc 24b is perpendicular to the axis S of the piston 17, which prevents axial movement of the body 21 relative to the coupler 22. Accordingly, if the adhesion between the body 21 and the coupler 22 is weakened, separation of the body 21 from the coupler 22 is prevented, which maintains the operation of the compressor. Further embodiments of the present invention will now be described focusing on differences from the first embodiment shown in Figs. 1-4. Fig. 5(a) shows the anchor 24 according to a second embodiment. Grooves 24c are formed in the peripheral surface of the disc 24b of the anchor 24 by a knurling tool. The grooves 24c may include first grooves that extend axially and second grooves that extend circumferentially. Fig. 5(b) shows the anchor 24 according to a third embodiment. A spiral groove 24d centered about the axis S is formed in the peripheral surface of the disc 24b. Fig. 5(c) shows the anchor 24 according to a fourth embodiment. Projections 24e are formed in the peripheral surface of the disc 24b. Recesses may be formed instead of the projections 24e. The disks 24b shown in Figs. 5(a)-5(c) limit rotation of the body 21 relative to the coupler 22. Accordingly, adhesion between the body 21 and the coupler is more stable. The material for making the body 21 may contain molybdenum disulfide, which serves as a solid lubricant. This reduces friction by friction between the body 21 and the surface of the cylinder bore 12a. Examples of thermosetting resins that may be used in the molding are an epoxy resin, an unsaturated polyester resin, a polyamidoimido resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, an urethane resin, and a furan resin. Examples of reinforcing materials other than glass fibers that may be added to the resin are metal fibers, an alumina, carbon fibers, wood powders, an α-cellulose, shell powders, bone powders, and eggshell powders. Combinations of these materials may also be added to the resin material for the body 21. Molding of the body 21 is not limited to injection molding. The body 21 may be molded by softening a granular or powder resin material in a mold. In this case, the coupler is inserted in the resin material and connected to the body 21. In other words, the body 21 may be molded by compression molding. The present invention may be applied to a double-headed piston for double-headed piston compressors. In this case, thermosetting resin piston bodies are respectively connected to both end surfaces of a metal coupler. The present invention may further be applied to a piston for wave cam compressors. In this case, a wave cam that serves as a drive plate forms a piston driving portion. The present invention may further be embodied in other fluid machines such as oil pumps and air pumps.

Claims: A machine comprising a piston cooperating with a driving body, the piston being characterized by : a metal coupler (22) connected to the driving body and having a first thermal expansion coefficient; and a body (21) made of thermosetting resin and having a second thermal expansion coefficient, wherein the body (21) is molded to the coupler (22), the first thermal expansion coefficient substantially matching the second thermal expansion coefficient. The piston according to claim 1, characterized in that a reinforcing material is added to the thermosetting resin to form a molding material. The piston according to claim 2, characterized in that the reinforcing material is glass fiber. The piston according to claim 3, characterized in that the molding material includes from 15 to 65 weight percent glass fiber. The piston according to any one of claims 1 to 4, characterized in that the thermosetting resin is a phenol resin. The piston according to any one of claims 1 to 5, characterized in that the coupler (22) is made of an aluminium alloy containing from 7 to 13 weight percent of silicon. The piston according to any one of claims 1 to 6, characterized in that the coupler (22) has an anchor (24) for engaging the body (21), wherein the anchor (24) prevents relative movement between the coupler (22) and the body (21) in the axial direction of the piston. The piston according to claim 7, characterized in that the molding material of the body (21) surrounds the anchor (24). The piston according to claims 7 or 8, characterized in that the anchor (24) includes a support shaft (24a) extending from the coupler (22) and a flange (24b) located on the support shaft (24a). The piston according to claim 9, characterized in that one of a recess (24c, 24d) and a projection (24e) is formed on the flange (24b) to prevent relative rotation between the coupler (22) and the body (21) about the axis of the piston (17). The piston according to claim 1, characterized in that the coupler (22) has a rotation restrictor (23b) to prevent the piston from rotating about the axis of the piston. A compressor comprising a piston, a swash plate (16) and a drive shaft (13), whereby the rotation of the drive shaft (15) is converted into reciprocation of the piston through the swash plate (16) and a pair of shoes (18), the piston being characterized by : a metal coupler (22) connected to the swash plate (16) and having a first thermal expansion coefficient; and a body (21) made of thermosetting resin and having a second thermal expansion coefficient, wherein the body (21) is molded to the coupler (22), the first thermal expansion coefficient substantially matching the second thermal expansion coefficient. A method of making a piston according to claim 1 or claim 12 comprising: molding a thermosetting resin forming a thermosetting resin body (21) to a metal coupler (22), the thermal expansion coefficient of the thermosetting resin body substantially matching the second thermal expansion coefficient. The method according to claim 13 including: forming a molding material to be used in the molding by adding reinforcing material to the thermosetting resin; and adjusting the proportion of reinforced material in the molding material to alter the thermal expansion coefficient of the thermosetting resin. The method according to claim 14 including: using a glass fiber as the reinforcing material. The method according to claims 14 or 15 including: adding from 15 to 65 weight percent of glass fiber to the thermosetting resin to form the molding material. The method according to any one of claims 14 to 16 including: using a phenol resin as thermosetting resin. The method according to any one of claims 14 to 17 including: forming the coupler (22) with an aluminium alloy containing from 7 to 13 weight percent of silicon.

Inventors: KATO TAKAYUKI, SUGIOKA TAKAHIRO, TAKAMATSU MASATO, KATO, TAKAYUKI, SUGIOKA, TAKAHIRO, TAKAMATSU, MASATO
Applicants: TOYOTA JIDOSHOKKI KK, KABUSHIKI KAISHA TOYOTA JIDOSHOKKI
Application year: 2000
Main classification: F04B27
IPC codes: F04B53, F04B27, F04B39