Seal ring

Abstract

To provide a seal ring capable of improving resistance during assembly into an annular groove even when it is a small-diameter PPS seal ring.SOLUTION: A seal ring 1 has one abutment 5, and is a molded body of a polyphenylene sulfide resin composition, where the bending modulus is 10000 MPa or less, the bending strain exceeds 2.0%, and an inner peripheral surface 3 of the ring on both sides of an abutment facing part 5F has a thin part 6 that reduces a radial thickness of the ring. The radial thickness of the thin part is 50% to 70% of a radial thickness of the abutment facing part 5F.SELECTED DRAWING: Figure 1

Description

Technical Field

[0005] , , ,

[0001] The present invention relates to a seal ring used for sealing a fluid in a device that utilizes the fluid pressure of a fluid such as a hydraulic working fluid, such as an automatic transmission (hereinafter referred to as AT) or a continuously variable transmission (hereinafter referred to as CVT).

Background Art

[0002] In devices such as AT and CVT, a seal ring for sealing the working fluid is attached at key points. For example, it is attached to a pair of spaced annular grooves provided on a rotating shaft inserted through a shaft hole of a housing, receives the working fluid supplied from an oil passage between both annular grooves on the side surfaces and inner peripheral surfaces of both seal rings, and seals the side walls of the annular grooves and the inner peripheral surface of the housing on the opposite side surfaces and outer peripheral surfaces. Each seal surface in the seal ring maintains the hydraulic pressure of the working fluid between both seal rings while slidingly contacting the side wall of the annular groove and the inner peripheral surface of the housing respectively. When assembling the seal ring into the annular groove, it is necessary to expand (enlarge) the inner diameter dimension of the seal ring to be greater than or equal to the outer diameter dimension of the rotating shaft by expanding the mating surface of the seal ring. When the seal ring is expanded, stress may concentrate at positions facing the mating surface.

[0003] In recent years, with the miniaturization of devices, the seal ring tends to have a smaller diameter. Regarding a small-diameter seal ring, for example, Patent Document 1 describes a seal ring that suppresses problems caused by expansion when assembling a small-diameter ring onto a rotating shaft by providing a thin portion in the inner diameter portion of the seal ring.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, there has been an increasing adoption of seal rings made of polyphenylene sulfide (hereinafter referred to as "PPS") resin, which has excellent wear resistance, in applications where the critical PV value (product of peripheral speed (V) and surface pressure (P)) is low. For example, in the case of small-diameter seal rings with an outer diameter of φ30 mm or less, even if a relatively flexible (low elasticity) material is used, the resistance is worse than that of seal rings with an outer diameter exceeding φ30 mm. Therefore, in small-diameter seal rings made of PPS resin, which is a relatively highly elastic resin material (hereinafter referred to as small-diameter PPS seal rings), there is a need to further improve resistance by expanding the diameter.

[0006] This invention was made to address these problems, and aims to provide a seal ring that improves resistance to being assembled into an annular groove, even when it is a small-diameter PPS seal ring. [Means for solving the problem]

[0007] The seal ring of the present invention is a seal ring having a single joint, being a molded article of a polyphenylene sulfide resin composition, having a flexural modulus of 10,000 MPa or less and a flexural strain exceeding 2.0%, and having thin-walled portions on the inner circumferential surface sides of the ring at positions facing the joint, wherein the radial thickness of the ring is reduced, and the radial thickness of the thin-walled portions is 50% to 70% of the radial thickness at the position facing the joint. Here, the thin-walled portions on both sides of the position facing the joint are formed in regions that are separated from each other.

[0008] The above-mentioned seal ring is characterized by having a bending modulus of 8500 MPa or less and a bending strain of 2.5% or more.

[0009] The above-mentioned seal ring is characterized by having an outer diameter of φ30 mm or less.

[0010] The above-mentioned seal ring is an injection-molded body and is characterized by having a gate mark from the injection molding process at a position opposite to the above-mentioned joint. [Effects of the Invention]

[0011] The seal ring of the present invention is a seal ring having a single joint, and is a molded body of a polyphenylene sulfide resin composition. It has a flexural modulus of 10,000 MPa or less and a bending strain exceeding 2.0%, thus exhibiting excellent toughness. Furthermore, it has thin-walled sections on both sides of the inner circumferential surface of the ring opposite the joint (hereinafter referred to as the joint-facing section) that reduce the radial thickness of the ring. Since the radial thickness of the thin-walled section is 50% to 70% of the radial thickness of the joint-facing section, stress can easily escape to the thin-walled section when the ring diameter is expanded. This improves the resistance of the seal ring when it is assembled into an annular groove, even if it is a small-diameter PPS seal ring.

[0012] Since the seal ring has an outer diameter of φ30mm or less, it can be applied to smaller devices.

[0013] The seal ring is an injection-molded product, and even if it has a gate mark from the injection molding process on the mating surface, force is less likely to concentrate around the gate mark, which is structurally weaker, when the ring expands in diameter. This suppresses the concentration of force around the gate mark due to the expansion of the ring during assembly. Furthermore, a seal ring with good molding balance can be obtained. [Brief explanation of the drawing]

[0014] [Figure 1] This is a plan view showing an example of a seal ring of the present invention. [Figure 2] This is an enlarged view of part A of the seal ring in Figure 1. [Figure 3] Figure 1 is a perspective view of the seal ring. [Figure 4] This is a side view of the assembly jig and a schematic diagram of the jig-through test. [Figure 5] This is a plan view showing the shape of the seal ring after heat fixing. [Modes for carrying out the invention]

[0015] An example of the seal ring of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a plan view of the seal ring, and Figure 2 is an enlarged view of part A in Figure 1. The seal ring 1 shown in Figure 1 is an annular body with a circular outer diameter and a substantially rectangular cross-section. The outer circumferential surface 2 and the inner circumferential surface 3 of the ring are surfaces parallel to the axial direction of the seal ring 1. The corners between the inner circumferential surface 3 and the ring side surfaces 4 (both sides) may be provided with straight or curved chamfers.

[0016] The seal ring 1 is a cut-type PPS resin ring having a single joint 5 where both ends in the circumferential direction face each other. It expands in diameter due to elastic deformation and is fitted into the annular groove of the rotating shaft. In a free state without external force, the seal ring 1 is set to have approximately the same outer diameter as the sealing surface (inner wall of the housing), and it adheres tightly to the sealing surface due to the pressure of the sealing fluid. The shape of the joint 5 can be a straight cut shape, an angle cut shape, etc., but it is preferable to adopt the composite step cut shape shown in Figure 1 because it provides excellent sealing performance for the sealing fluid.

[0017] The seal ring 1 has multiple V-shaped recesses 4a along the circumferential direction of the ring at the inner diameter ends of both sides 4 of the ring. One side of the seal ring 1 is a sliding surface with the side wall surface of the annular groove, and the V-shaped recesses 4a formed on the ring side 4 (sliding surface) are non-contact areas with the side wall surface. By providing the recesses 4a, fluid can flow out to the sliding surface in an appropriate manner through the recesses. Specifically, the boundary between the sliding surface X and the recess 4a between adjacent recesses 4a is a continuous shape, while the boundary between the sliding surface Y on the outer diameter side of the recess 4a and the recess 4a is a discontinuous shape (step). Therefore, fluid flows out easily to the sliding surface X, but less easily to the sliding surface Y compared to the sliding surface X. When fluid flows out to the sliding surfaces X and Y, a fluid film such as an oil film is formed on the sliding surfaces, which reduces rotational torque and wear. Furthermore, suppressing flow to the sliding surface Y leads to low leakage. This recess can be formed on one side or both sides of the ring, as needed. The shape of the recess may also be other than the shape described above.

[0018] The seal ring 1 has a plurality of thin portions 6 that reduce the radial thickness of the ring (hereinafter also simply referred to as "thickness") on the inner circumferential surface side of the ring. The thin portion 6 is formed by reducing the radial thickness while maintaining the outer diameter of the seal ring 1. The radial thickness other than the thin portion 6 is a non-thin portion 7 that is thicker than the thin portion 6. The mating portion 5F of the seal ring 1 is the non-thin portion 7, and the thin portions 6 are formed on both circumferential sides thereof. The non-thin portion 7 is formed between the thin portions 6 adjacent to each other in the circumferential direction, and the same number or approximately the same number as the thin portions 6 are formed. The thin portions 6 and the non-thin portions 7 are alternately provided along the circumferential direction of the ring. Note that the number of the thin portions 6 and the non-thin portions 7 is not limited to the configuration of FIG. 1. In FIG. 1, the side surface of the step portion 71 of the non-thin portion 7 is formed at a position lower (narrower in width) than the ring side surface 4, but it may also be an extension surface of the ring side surface 4. When the axial width of the non-thin portion 7 is formed to be thin, it is configured not to contact the side wall surface of the annular groove. Also, this may be used as the protruding surface during the injection molding of the seal ring 1. In the seal ring 1 of FIG. 1, the thickness of the thin portion 6 and the thickness of the non-thin portion 7 are each constant.

[0019] Note that the thickness of the thin portion 6 and the thickness of the non-thin portion 7 do not have to be constant respectively. In this specification, when the thickness in one thin portion 6 is not constant, the thickness of the thin portion 6 is the thickness of the region where the thickness of the thin portion 6 is the smallest. When the thickness in one non-thin portion 7 is not constant, the thickness of the non-thin portion 7 is the thickness of the region where the thickness of the non-thin portion 7 is the largest. Note that the outer diameter center point of the seal ring 1 and the inner diameter center point of the non-thin portion 7 are the same.

[0020] As described above, the seal ring 1 is partially thinned while maintaining the outer diameter, that is, only the inner diameter of the seal ring 1 is enlarged to partially reduce the thickness. Therefore, the adhesion to the inner circumferential surface of the housing can be maintained, and the sealing performance is less likely to deteriorate. Also, since the amount of strain generated in the thin portion is reduced, the resistance due to the diameter expansion can be improved.

[0021] As shown in Fig. 2, for the sealing ring of the present invention, the thickness B of the thin portion 6 is 50% to 70% of the thickness C of the non-thin portion 7. By setting the ratio of these thicknesses within a predetermined numerical range, as shown in the embodiments described later, the resistance to diameter expansion can be improved. Further, the thickness B of the thin portion 6 is preferably 55% to 70% of the thickness C of the non-thin portion 7, and more preferably 55% to 65%. Specifically, the thickness B of the thin portion 6 is 0.9 mm to 2.3 mm.

[0022] The step portion 71 located on the inner peripheral side of the virtual curved surface extending the ring inner peripheral surface 3 of the thin portion 6 in the non-thin portion 7 will be described. The step portion 71 is formed with an upper curved surface 71a arranged on the inner peripheral side and a lower curved surface 71b arranged on the outer peripheral side at one end in the circumferential direction, and the upper curved surface 71a and the lower curved surface 71b are similarly formed at the other end. At each end, the upper curved surface 71a and the lower curved surface 71b are connected via a plane. Note that the upper curved surface 7a1 and the lower curved surface 71b may be directly connected without passing through a plane. Also, one end and the other end of the step portion 71 may be formed only by a plane instead of a curved surface.

[0023] The axial width of the step portion will be described based on Fig. 3. Fig. 3(a) is a perspective view of the sealing ring shown in Fig. 1, and Fig. 3(b) is an enlarged view of the D portion of Fig. 3(a). As shown in Fig. 3(b), the side surface 71c of the step portion 71 in the non-thin portion 7 is a concave surface formed lower by a depth E than the ring side surface 4. And since both side surfaces of the step portion 71 are formed lower by a depth E than the ring side surface 4, the width of the step portion 71 is 2E smaller than the width of the thin portion 6. Note that the two side surfaces 71c, 71c of the step portion 71 may be formed to have different depths from the ring side surface 4, or only one side surface may be a concave surface and the other side surface may be an extension surface of the ring side surface 4. Also, it is not necessary to form concave surfaces on both side surfaces.

[0024] The PPS resin composition used to form the seal ring of the present invention has a flexural modulus of 10,000 MPa or less and a flexural strain exceeding 2.0%. Having such bending characteristics allows the seal ring to undergo elastic deformation during assembly, improving its resistance. From the viewpoint of resistance, the flexural modulus is preferably 8,500 MPa or less, more preferably 7,000 MPa or less, and even more preferably 5,500 MPa or less. On the other hand, a flexural modulus of 3,500 MPa or more is preferable.

[0025] Furthermore, from the viewpoint of durability, the bending strain is preferably 2.5% or more, more preferably 3.0% or more, and even more preferably 3.5% or more. On the other hand, the bending strain is preferably 5.0% or less.

[0026] The flexural modulus and bending strain can be measured by a three-point bending test using a specimen conforming to ASTM D790 (127 mm × 12.7 mm × 3.1 mm thick), with a support distance of 50 mm and a crosshead speed of 1.3 mm / min. In this specification, the flexural modulus and bending strain refer to values ​​obtained from tests conducted at room temperature (23°C).

[0027] Here, we consider why small-diameter seal rings with an outer diameter of φ30 mm or less have lower resistance to expansion than seal rings with an outer diameter exceeding φ30 mm. When the outer diameter of a seal ring is small, such as φ30 mm or less, the ratio of the amount of expansion during installation to the outer diameter is likely to be larger than that of seal rings with an outer diameter exceeding φ30 mm. Therefore, small-diameter seal rings tend to experience greater strain during expansion, resulting in lower resistance to expansion. For example, a seal ring of about φ50 mm has an expansion ratio of 110% or less, and a seal ring of about φ40 mm has an expansion ratio of 115% or less, but a seal ring of φ30 mm or less will have an expansion ratio of 120% or more, resulting in lower resistance to expansion.

[0028] In the present invention, when the thickness of the thin-walled portion is 70% or less of the thickness of the non-thin-walled portion, the surface pressure on the side of the seal ring does not become excessive, making abnormal wear less likely. Furthermore, a predetermined sealing area can be secured, resulting in excellent sealing performance (low leakage). On the other hand, when the thickness of the thin-walled portion is 50% or more of the thickness of the non-thin-walled portion, stress can easily escape to the thin-walled portion, and the amount of strain in the thin-walled portion does not become large. As a result, even small-diameter PPS seal rings with an expansion ratio of 120% or more of the present invention have improved resistance when assembled into annular grooves such as rotating shafts.

[0029] The outer diameter of the seal ring can be freely set, and from the viewpoint of application to small hydraulic equipment, it is preferably φ30 mm or less, more preferably φ25 mm or less, and even more preferably φ20 mm or less. Considering durability, the outer diameter of the seal ring is preferably φ15 mm to 30 mm, more preferably φ15 mm to 25 mm, and even more preferably φ15 mm to 20 mm. By providing a thin-walled portion, the seal ring of the present invention can be applied to smaller hydraulic equipment, which is difficult to apply to molded articles of PPS resin compositions used in conventional seal rings.

[0030] The seal ring of the present invention is an injection-molded body of a resin composition, and the gate mark 8 is formed at the gate where molten resin is injected during injection molding (see Figure 1). The position of the gate mark is not particularly limited, but it is preferable to form it on the inner circumference of the ring from the viewpoint of ensuring sealing performance and eliminating the need for post-processing. Furthermore, as shown in Figure 1, from the viewpoint of flow balance in injection molding, it is preferable that the gate mark 8 be located in the center of the unfolded length of the seal ring 1 on the inner circumference surface 3 of the ring. Specifically, the gate mark 8 is formed on the inner circumference surface of the mating facing portion 5F. The mating facing portion 5F is a non-thin-walled portion 7, which is also preferable from the viewpoint of durability.

[0031] In this way, by having a gate mark in the non-thin-walled portion in the center of the seal ring's extended length, force is less likely to concentrate around the gate mark, which is structurally weaker, when the ring expands in diameter. This prevents force concentration, especially around the gate mark, when the ring expands in diameter during assembly.

[0032] Furthermore, the gate mark 8 may be located at a position other than the center of the unfolded length of the seal ring 1. Also, the gate mark 8 may be located on the thin-walled portion 6.

[0033] The seal ring of the present invention is a molded article of a PPS resin composition mainly composed of PPS resin, and may contain components other than PPS resin. PPS resin is a crystalline thermoplastic resin having a polymer structure shown in the following formula (1), in which benzene rings are linked by sulfur bonds in the para position. PPS resin has a melting point of about 280°C and excellent chemical resistance, so it can be used even when the oil temperature of the hydraulic fluid being sealed is high. In addition, PPS resin can be crosslinked PPS resin or semi-crosslinked PPS resin obtained by oxidative crosslinking of low molecular weight PPS resin, or linear PPS resin that does not take a crosslinked structure, but in the present invention it can be used without being limited to these molecular structures or molecular weights. Since the diameter is expanded when incorporated into the annular groove, it is preferable to use a linear PPS resin with excellent toughness. Examples of PPS resins that can be used in the present invention include MA-520 and T-4AG (DIC Corporation product name).

[0034] [ka]

[0035] The resin component of the PPS resin composition may be PPS resin alone or may contain other resins. The PPS resin composition may contain, for example, an elastomer. The elastomer may be either a thermosetting elastomer or a thermoplastic elastomer, but a thermoplastic elastomer is preferred as it can increase the toughness of the PPS resin. Examples of thermoplastic elastomers include polyamide elastomers, polyurethane elastomers, polyester elastomers, polystyrene elastomers, and olefin elastomers. It is preferable that the decomposition start temperature of the elastomer is above the molding temperature of the PPS resin (280-320°C). However, decomposition of low molecular weight components during seal ring molding is permitted.

[0036] If necessary, the PPS resin composition can be blended with fibrous reinforcing materials such as carbon fibers, glass fibers, and aramid fibers; spherical fillers such as spherical silica and spherical carbon; scale-like reinforcing materials such as mica and talc; and microfiber reinforcing materials such as potassium titanate whiskers. Additionally, solid lubricants such as PTFE resin, graphite, tungsten disulfide, molybdenum disulfide, and boron nitride; sliding reinforcing materials such as calcium phosphate and calcium sulfate; and colorants such as carbon powder, iron oxide, and titanium oxide can also be blended. These can be blended individually or in combination.

[0037] The flexural modulus and bending strain of the seal ring of the present invention are appropriately set depending on the type and amount of PPS resin, and the type and amount of components (such as elastomers and fibrous reinforcing materials) added to the PPS resin.

[0038] The means of mixing and kneading the above raw materials are not particularly limited. For example, PPS resin alone may be used, and carbon fibers, glass fibers, etc., may be side-fed and kneaded using a twin-screw extruder or the like. Alternatively, only the powdered raw materials may be dry-mixed using a Henschel mixer, ball mixer, ribbon blender, Reidige mixer, Ultra Henschel mixer, etc., and then melt-kneaded using a melt extruder such as a twin-screw extruder to obtain molding pellets. For the molding method, injection molding is preferable because it is easy to form complex joint shapes and recesses on the sides of the ring. In addition, treatments such as annealing may be applied to the molded product to improve its physical properties. [Examples]

[0039] The raw materials for the resin compositions used in the examples and comparative examples are listed below. (1)PPS resin [PPS] (2) Glass fiber [GF]

[0040] Using the above raw materials, injection molding pellets were prepared by melt-kneading using a twin-screw extruder. The glass fiber content in Examples 1-3 and Comparative Examples 1 and 2 was 30% by mass, while the glass fiber content in Comparative Example 3 was 40% by mass.

[0041] (1) Bending test Using the pellets described above, test specimens conforming to ASTM D790 (127 mm × 12.7 mm × 3.1 mm thick) were prepared. Three-point bending tests were then conducted using these specimens with a support distance of 50 mm and a crosshead speed of 1.3 mm / min, and the flexural modulus and bending strain were measured. Table 1 shows the raw material composition, flexural modulus, and bending strain of each test specimen.

[0042] [Table 1]

[0043] (2) Assembly jig through test (seal ring diameter expansion test) The assembly jig pass-through test will be explained using Figure 4. Figure 4(a) is a side view of the assembly jig (tapered jig), and Figure 4(b) is a schematic diagram of the assembly jig pass-through test of the seal ring.

[0044] The dimensions of the tapered jig 12 used in the test are as follows, and it is used to expand the inner diameter of the seal ring by 1.25 times (expansion ratio of 125%) (see Figure 4(a)). L: 147.0 mm Dl: 27.6mm Ds: 21.0mm

[0045] Using the above pellets, seal rings for use in the examples and comparative examples were manufactured by injection molding, and their outer diameter was adjusted to φ26 mm by heat fixing. The shape of the heat-fixed seal ring is as shown in Figure 5, with an outer diameter of φ26 mm, an inner diameter of φ22 mm, and a width of 1.9 mm. It has a stepped portion on the inner circumference with a radial length of 0.3 mm and a depth of 0.3 mm (on both sides), and the joint is a composite step cut. The inner circumference of this seal ring was further processed using a milling machine to create a thin-walled portion, and 100 seal rings each were manufactured for each example and comparative example. The shape of the seal ring after the further processing and the position of the non-thin-walled portion correspond to Figure 1. Using a tapered jig 12, as shown in Figure 4(b), 100 seal rings 11 each for each example and comparative example were inserted into the tapered jig 12 at a speed of 1 mm / s, and the presence or absence of resistance and the number of resistances were evaluated. The test results and the ratio of the thickness of the thin-walled portion to the thickness of the non-thin-walled portion (ratio of thin-walled portion) are shown in Table 2.

[0046] [Table 2]

[0047] As shown in Table 2, Examples 1-3, where the ratio of thin-walled sections (thickness of thin-walled section / thickness of non-thin-walled section × 100) was 50% to 70%, had a flexural modulus of 8300 MPa and a flexural strain of 2.5%, and there were 0 samples that were unresistant. On the other hand, Comparative Examples 1 and 2, where the ratio of thin-walled sections was greater than 70%, both had a flexural modulus of 8300 MPa and a flexural strain of 2.5%, similar to Examples 1-3, but had 4 and 9 samples that were unresistant, respectively. Comparative Example 3, similar to Example 1, had a ratio of thin-walled sections of 50%, but had a flexural modulus of 11600 MPa and a flexural strain of 2.0%, and had 7 samples that were unresistant.

[0048] The results in Table 2 show that even small-diameter PPS seal rings have resistance when assembled into an annular groove when the flexural modulus is 8300 MPa, the flexural strain is 2.5%, and the proportion of the thin-walled section is between 50% and 70%. However, even with a flexural modulus of 8300 MPa and a flexural strain of 2.5%, small-diameter PPS seal rings lack resistance when assembled into an annular groove when the proportion of the thin-walled section is greater than 70%. Thus, by combining the bending characteristics and the proportion of the thin-walled section within a suitable range for the seal ring, the resistance when assembled into an annular groove can be improved. [Industrial applicability]

[0049] The seal ring of the present invention has improved resistance to being assembled into an annular groove, even when it is a small-diameter PPS seal ring, and is therefore particularly suitable for use as a seal ring to seal hydraulic fluid in annular passages of small hydraulic equipment. Furthermore, it is not limited to hydraulic equipment and is suitable for use as a seal ring that has a gap and is installed in an annular groove by expanding its diameter. [Explanation of symbols]

[0050] 1, 11 sealing rings 2. Outer surface of the ring 3. Inner surface of the ring 4 Ring side 4a recess 5 joints 5F Opposite section (joint opposite section) 6. Thin-walled section 7 Non-thin wall section 71 Stepped section 71a Upper curved surface 71b Lower curved surface 71c side 8 Gate marks 12. Tapered jig

Claims

1. A seal ring having a single joint, The seal ring is a molded article of a polyphenylene sulfide resin composition, has a flexural modulus of 10,000 MPa or less, and a flexural strain exceeding 2.0%, and has thin-walled portions on the inner circumferential surface side of the ring that reduce the radial thickness of the ring in separate regions on both sides from the position facing the joint. A seal ring characterized in that the radial thickness of the thin-walled portion is 50% to 70% of the radial thickness at the position facing the joint.

2. The seal ring according to claim 1, characterized in that the flexural modulus is 8500 MPa or less and the flexural strain is 2.5% or more.

3. The seal ring is characterized in that its outer diameter is φ30 mm or less, as described in claim 1 or 2.

4. The seal ring is an injection-molded body and is characterized in that it has a gate mark from the injection molding process at a position opposite to the joint, as described in claim 1 or 2.

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