Chain tensioner

Abstract

To prevent working fluid for a chain tensioner from leaking from an interval between a stepped hole accommodating a relief valve and a male screw member.SOLUTION: A chain tensioner includes an elastic body 48 for hermetically sealing an interval between a stepped hole 34 of a cylinder 9 and a male screw member 44. An O-ring or the like for hermetically sealing the interval between the male screw member and the stepped hole at a position nearer to a valve seat 39 in a screw axial line direction than a male screw portion 45 of the male screw member 44 and a female screw portion 42 of the stepped hole 34 is adopted as the elastic body 48.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a chain tensioner that keeps the tension of a chain for driving a camshaft of an engine constant, and more particularly to a chain tensioner having a structure that absorbs fluctuations in the chain tension with a hydraulic damper.

Background Art

[0002] An automobile engine generally transmits the rotation of a crankshaft to a camshaft via a timing chain (hereinafter referred to as a "chain"), and the rotation of the camshaft opens and closes valves in a combustion chamber. In order to keep the tension of the chain within an appropriate range, a tension adjusting device including a chain guide swingably provided about a fulcrum shaft and a chain tensioner that presses the chain via the chain guide is used.

[0003] As a chain tensioner provided in the tension adjusting device, there is known a hydraulic type including a cylinder, a plunger slidably inserted inside the cylinder, a return spring that biases the plunger in a direction protruding from the cylinder, a pressure chamber formed behind the plunger in the cylinder, and an oil supply passage that introduces hydraulic oil into the pressure chamber, and a check valve that allows only the flow of hydraulic oil from the oil supply passage side to the pressure chamber side is disposed in the oil supply passage.

[0004] In the case of this type of hydraulic chain tensioner, when the tension of the chain increases during engine operation, the plunger moves in the direction in which it is pushed into the cylinder (hereinafter referred to as the "pushing direction") by the tension of the chain, absorbing the tension of the chain. At this time, the hydraulic oil in the pressure chamber flows out to the outside of the pressure chamber through the leakage gap between the sliding surfaces of the plunger and the cylinder, and a damping action occurs due to the viscous resistance of the hydraulic oil, so the plunger moves slowly. Here, when the pressure in the pressure chamber becomes higher than the pressure in the oil supply passage, the check valve closes, and the damping action is ensured by closing the pressure chamber. On the other hand, when the tension of the chain decreases during engine operation, the plunger moves in the direction in which it protrudes from the cylinder (hereinafter referred to as the "protruding direction") by the biasing force of the return spring, absorbing the slack of the chain. At this time, the check valve opens, and the hydraulic oil flows into the pressure chamber from the oil supply passage, so the plunger moves quickly. The hydraulic oil is supplied from the engine. Therefore, when the engine stops, the supply of the hydraulic oil stops, and the hydraulic damper cannot be generated, and the chain tensioner is pushed in. To prevent this, a mechanism (no-back mechanism) is adopted so that the plunger is not pushed in beyond a certain amount. Also, a relief valve is provided to prevent the chain from becoming over-tensioned when the chain suddenly tightens. The relief valve has a valve body, a valve spring that biases the valve body in the valve-closing direction, and a valve seat that receives the biased valve body. When the pressure in the pressure chamber exceeds the set pressure of the relief valve, the relief valve opens, and the pressure escapes from the pressure chamber to the outside of the cylinder.

[0005] As this type of hydraulic chain tensioner, there are an internal type in which the cylinder is bolted to the engine block and an external type in which the flange portion of the cylinder is bolted to the outside of the engine cover.

[0006] Conventionally, in an external type chain tensioner, its cylinder is inserted into a tensioner mounting hole in the engine cover. A stepped hole is formed from the flange portion toward the inside of the cylinder, and a relief valve is accommodated in this stepped hole. By screwing a male threaded member into the female threaded portion of the stepped hole, the relief valve is clamped between the male threaded member and the step portion of the stepped hole. When the relief valve opens, the hydraulic oil flowing out from the relief valve returns to the oil passage on the engine cover side. Since a gasket is sandwiched between the engine cover and the flange portion, leakage of hydraulic oil from between them is prevented. Also, a seal adhesive is applied to the male threaded portion of the male threaded member. This seal adhesive is for preventing hydraulic oil from leaking from the screw clearance between the female threaded portion of the stepped hole and the male threaded portion of the male threaded member (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, since the seal adhesive applied to the male threaded portion of the male threaded member is larger than the aforementioned screw clearance, when screwing into the stepped hole, it cannot all enter the screw clearance, and the overflowed seal adhesive accumulates on the flange portion side. At that time, if there is a portion that is not filled with the seal adhesive in the screw clearance, a minute gap can be formed, and there is a concern that hydraulic oil may leak to the outside from the screw clearance due to the pressure when the relief valve opens.

[0009] Therefore, the problem to be solved by this invention is to prevent the hydraulic oil of the chain tensioner from leaking between the stepped hole accommodating the relief valve and the male threaded member.

Means for Solving the Problems

[0010] To achieve the above object, the present invention provides a cylinder, a plunger slidably inserted into the cylinder, a return spring for biasing the plunger in a direction protruding from the cylinder, a check valve disposed in the cylinder, an oil supply passage for introducing hydraulic oil into a pressure chamber formed between the check valve and the plunger, an oil discharge passage for discharging the hydraulic oil from the pressure chamber to the outside of the cylinder, and a relief valve for opening and closing the oil discharge passage. The relief valve includes a valve body, a valve spring for biasing the valve body in a valve closing direction, and a valve seat for receiving the biased valve body. The cylinder has a stepped hole for accommodating the relief valve, and the stepped hole has an internal thread portion and a stepped portion facing the valve seat in the axial direction of the thread axis of the internal thread portion. The oil discharge passage communicates from the pressure chamber to the outside of the cylinder via the stepped hole. In a chain tensioner in which the relief valve is fixed by screwing a male thread portion of a male threaded member from the outside of the cylinder into the internal thread portion, an elastic body for sealing between the male threaded member and the stepped hole is further provided at a position closer to the valve seat side than the male thread portion and the internal thread portion in the axial direction of the thread axis.

[0011] According to the above configuration, when the relief valve is in an open state, the hydraulic oil flows toward the outside of the cylinder through the valve hole of the valve seat. At this time, a part of the hydraulic oil flowing out from the relief valve goes toward the male threaded member side through the space between the relief valve and the stepped hole. However, since there is an elastic body for sealing between the male threaded member and the stepped hole at a position closer to the valve seat side than the male thread portion and the internal thread portion in the axial direction of the thread axis, it is possible to prevent the hydraulic oil from leaking between the stepped hole and the male threaded member. This is because when the male threaded member is screwed in, the contact state of the elastic body with the male threaded member and the stepped hole is ensured to be a stable adhesive state on the surface by the pressing force from the male threaded member. In this way, it is possible to prevent the hydraulic oil of the chain tensioner from leaking from the screw clearance between the stepped hole accommodating the relief valve and the male threaded member.

[0012] Specifically, the relief valve has an end face that contacts the male screw member and an outer peripheral end portion whose outer diameter increases as it moves away from the male screw member in the screw axis direction from the end face. The male screw member has a tightening face that contacts the end face of the relief valve and a sealing face that contacts the elastic body at a position closer to the male screw portion side than the tightening face in the screw axis direction. The sealing face of the male screw member is in the shape of a flat surface along a direction perpendicular to the screw axis. It is preferable that the elastic body pressed from the sealing face of the male screw member is in close contact with the sealing face, the outer peripheral end portion of the relief valve, and the stepped hole. In this way, when the male screw member is screwed in, the relief valve is pushed and fixed toward the stepped portion of the stepped hole by its tightening face, and at the same time, the elastic body is pushed by its sealing face, and while guiding the inner diameter side of the elastic body at the outer peripheral end portion of the relief valve, it can be pushed between the outer peripheral end portion and the stepped hole to pressurize the elastic body. As a result, the pressed elastic body is in a state of being stably in close contact with the sealing face of the male screw member, the outer peripheral end portion of the relief valve, and the stepped hole. Also, since the sealing face of the male screw member is in the shape of a flat surface along a direction perpendicular to the screw axis, the elastic body can be strongly pressed against the outer peripheral end portion of the relief valve by the sealing face of the male screw member to make it in close contact with the outer peripheral end portion and the stepped hole. Further, by adopting a sealing face that contacts the elastic body at a position closer to the male screw portion side than the tightening face of the male screw member, the sealing face can be moved away from the relief valve to form a space for arranging the elastic body.

[0013] In addition, the stepped hole has a sealing seat portion formed in a stepped shape that faces the end face of the male screw member in the screw axis direction at a position closer to the stepped portion side than the female screw portion in the screw axis direction. It is preferable that the elastic body pressed against the end face of the male screw member is in close contact with the end face and the sealing seat portion of the stepped hole. In this way, the space between the male screw member and the stepped hole can be sealed only by squeezing the elastic body between the sealing seat portion of the stepped hole and the end face of the male screw member in the screw axis direction, and it becomes unnecessary to make the elastic body in close contact with the relief valve.

[0014] Further, the relief valve has an end face that contacts the male screw member and an outer peripheral end portion whose outer diameter increases as it moves away from the male screw member in the screw axis direction. The male screw member has a tightening surface that contacts the end face of the relief valve and a sealing surface formed in a tapered shape whose diameter increases as it moves toward the male screw portion side in the screw axis direction from the tightening surface. It is preferable that the elastic body pressed from the sealing surface of the male screw member is in close contact with the sealing surface, the outer peripheral end portion of the relief valve, and the stepped hole. In this way, when the male screw member is screwed in, the relief valve is pushed and fixed toward the step portion of the stepped hole by its tightening surface, and the elastic body is pushed by its sealing surface. Further, while guiding the inner diameter side of the elastic body at the outer peripheral end portion of the relief valve, the elastic body can be pushed between the outer peripheral end portion and the stepped hole to pressurize the elastic body. As a result, the pressed elastic body is in a state of being stably in close contact with the sealing surface of the male screw member, the outer peripheral end portion of the relief valve, and the stepped hole. Further, since the sealing surface of the male screw member is tapered as described above, it becomes easy to push the elastic body between the outer peripheral end portion of the relief valve and the stepped hole while expanding the inner diameter of the elastic body with the sealing surface of the male screw member. Further, since the sealing surface of the male screw member is tapered such that its diameter increases as it moves toward the male screw portion side from the tightening surface, the sealing surface can be moved away from the relief valve to form a space for arranging the elastic body.

[0015] Furthermore, it further includes a seal retainer sandwiched between the male screw member and the relief valve. The relief valve has an end face that contacts the seal retainer. The male screw member has a tightening face that contacts the seal retainer and a seal face that contacts the elastic body at a position closer to the male screw portion side than the tightening face in the screw axis direction. The seal retainer protrudes toward the inner periphery of the stepped hole so as to face the gap between the relief valve and the inner periphery of the stepped hole in the screw axis direction and also to face the seal face of the male screw member in the screw axis direction. The elastic body pressed from the seal face of the male screw member is preferably in close contact with the seal face, the seal retainer, and the stepped hole. In this way, when the male screw member is screwed in, the seal retainer is sandwiched between the tightening face and the relief valve, and the relief valve is pushed and fixed toward the stepped portion of the stepped hole. At the same time, the elastic body can be pressed against the seal retainer by the seal face to pressurize the elastic body. As a result, the pressed elastic body is in a state of being stably in close contact with the seal face of the male screw member, the seal retainer, and the stepped hole. Also, since the seal retainer protrudes toward the inner periphery of the stepped hole so as to face the gap between the relief valve and the inner periphery of the stepped hole in the screw axis direction and also to face the seal face of the male screw member in the screw axis direction, the elastic body can be strongly pressurized to increase the contact area between the seal face, the stepped hole, the seal retainer, and the elastic body, thereby enhancing the sealing performance. Also, by adopting a seal face that contacts the elastic body at a position closer to the male screw portion side than the tightening face of the male screw member, the seal face can be moved away from the relief valve, and a space for arranging the elastic body can be formed.

[0016] The elastic body is preferably an O-ring. When an O-ring is adopted as the elastic body, the elastic body pressed from the seal face of the male screw member can be easily compressed following the surface shape of any contact partner, so it is easy to ensure a contact area with any contact partner.

[0017] Also, a sealant may be applied to the male thread portion of the male thread member. By doing so, loosening of the male thread member can be prevented by the sealant. Since the working oil is sealed upstream of the above-mentioned screw clearance by the elastic body, there is no concern that the working oil will leak outside the cylinder even if the sealant is incomplete, and the sealing performance by the sealant is not questioned. In the present invention, whether or not to use a sealant can be arbitrarily selected.

[0018] A flange portion is formed on the outside of the cylinder, the stepped hole is formed from the flange portion toward the inside of the cylinder, the cylinder is inserted into the tensioner mounting hole of the engine cover, and the flange portion is preferably bolted to the outside of the engine cover. By doing so, the working oil of the chain tensioner bolted to the engine cover by the flange portion does not leak from between the male thread member and the flange portion, so that oil contamination of the engine cover can be prevented even if the leak inspection process is omitted.

Advantages of the Invention

[0019] As described above, by adopting the above configuration, the present invention can prevent the working oil of the chain tensioner from leaking from between the stepped hole accommodating the relief valve and the male thread member.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0021] The first embodiment as an example of the present invention will be described with reference to FIGS. 1 to 4.

[0022] The chain tensioner 1 according to the embodiment shown in FIG. 1 is provided in the chain transmission device shown in FIG. 2. In this chain transmission device, a sprocket 3 fixed to the crankshaft 2 of the engine and a sprocket 5 fixed to the camshaft 4 are connected via a chain 6, and the chain 6 transmits the rotation of the crankshaft 2 to the camshaft 4. The rotation of the camshaft 4 opens and closes a valve (not shown) in the combustion chamber.

[0023] A chain guide 8 that is swingably supported about a fulcrum shaft 7 is in contact with the chain 6. The chain tensioner 1 presses the chain 6 via the chain guide 8.

[0024] As shown in FIG. 1, the chain tensioner 1 includes a cylindrical cylinder 9 having one end closed and the other end open, and a plunger 10 slidably inserted in the cylinder 9 in the axial direction. The cylinder 9 has an inner wall surface 11 along a virtual cylindrical surface. Here, the "axial direction" refers to the direction along the center line of the virtual cylindrical surface.

[0025] A flange portion 12 is formed on the outside of the cylinder 9. The flange portion 12 has a butting surface 13 that extends in a direction perpendicular to the axial direction. As shown in FIG. 2, the cylinder 9 is inserted into the tensioner mounting hole 15 of the engine cover 14 with its open end facing inward within the engine cover 14. The flange portion 12 is fixed to the outside (outer surface) of the engine cover 14 with bolts 16. A gasket 17 for preventing the leakage of hydraulic oil is sandwiched between the butting surface 13 of the flange portion 12 and the outer surface of the engine cover 14.

[0026] As shown in FIG. 1, a check valve 18 is incorporated in the cylinder 9, and a pressure chamber 19 is formed between this check valve 18 and the plunger 10. Further, an oil supply passage 20 for introducing hydraulic oil into the pressure chamber 19 is formed in the cylinder 9 via the check valve 18.

[0027] The oil supply passage 20 consists of an oil introduction hole 21 for introducing hydraulic oil from the outside of the cylinder 9 and a reservoir chamber 22 that is connected to the downstream side of the oil introduction hole 21 and is formed adjacent to the upstream side of the check valve 18. The reservoir chamber 22 is formed between the check valve 18 and the closed end of the cylinder 9. The oil introduction hole 21 opens into the reservoir chamber 22. The inlet (not shown) of the oil introduction hole 21 opens into the butting surface 13 of the flange portion 12 and communicates with the oil passage on the engine cover 14 (see FIG. 2) side. The hydraulic oil supplied from an oil pump (not shown) is introduced into the pressure chamber 19 via the oil introduction hole 21, the reservoir chamber 22, and the check valve 18 in this order as shown in FIG. 1.

[0028] The check valve 18 has a seat 23, a ball 24, and a retainer 25. The seat 23 is cylindrical with a valve hole at its center that communicates between the oil supply passage 20 and the pressure chamber 19. The seat 23 is press-fitted and fixed within the cylinder 9. The seat 23 has a tapered seat surface at the end on the pressure chamber 19 side of the valve hole. The ball 24 is movably provided between a closed valve position in contact with the seat surface of the seat 23 and an open valve position separated from the seat surface. The flow of hydraulic oil from the oil supply passage 20 side to the pressure chamber 19 side is allowed, but the flow of hydraulic oil from the pressure chamber 19 side to the oil supply passage 20 side is prohibited.

[0029] The plunger 10 is formed in a bottomed cylindrical shape with an open insertion end into the cylinder 9. A minute leakage gap 26 is formed between the outer peripheral surface of the plunger 10 and the fitting surface of the inner wall surface 11 of the cylinder 9. When the plunger 10 moves in the direction of being pushed into the cylinder 9, the hydraulic oil in the pressure chamber 19 flows out of the open end of the cylinder 9 to the outside of the cylinder 9 through the leakage gap 26.

[0030] An internal thread 27 is formed on the inner periphery of the insertion portion of the plunger 10 into the cylinder 9. A screw rod 29 having an external thread 28 corresponding to the internal thread 27 on its outer periphery is incorporated into the plunger 10. One end of the screw rod 29 protrudes from the plunger 10, and the protruding end abuts against the seat 23. The external thread 28 and the internal thread 27 are formed in a serrated shape in which the flank angle of the pressure side flank that receives pressure when a load in the direction of pushing the plunger 10 into the cylinder 9 is applied is larger than the flank angle of the play side flank. Such external thread 28 and internal thread 27 can adopt, for example, those with a flank angle of 65° for the pressure side flank and a flank angle of 7° for the play side flank, or those with a flank angle of 75° for the pressure side flank and a flank angle of 15° for the play side flank. Also, an axial play of about 1 mm or less is provided between the external thread 28 and the internal thread 27.

[0031] A return spring 30 is incorporated between the plunger 10 and the screw rod 29. One end of the return spring 30 is supported by the screw rod 29, and the other end presses the plunger 10 via a spring seat 31. Due to this pressing, the plunger 10 is biased in the direction of protruding from the cylinder 9. The protruding end of the plunger 10 from the cylinder 9 abuts against the chain guide 8 as shown in FIG. 2, and presses the chain 6 via the chain guide 8.

[0032] As shown in FIGS. 1 and 3, the chain tensioner 1 includes an oil drain passage 32 that discharges hydraulic oil from the pressure chamber 19 to the outside of the cylinder 9, and a relief valve 33 that opens and closes the oil drain passage 32.

[0033] The oil drain passage 32 is composed of a stepped hole 34 formed from the flange portion 12 toward the inside of the cylinder 9, and an outlet passage 35 branched from the stepped hole 34. The outlet passage 35 communicates with the oil passage on the engine cover 14 side.

[0034] The relief valve 33 has a valve body 36, a valve spring 37 that biases the valve body 36 in the valve closing direction, a valve retainer 38 that receives the valve spring 37, and a valve seat 39 that receives the biased valve body 36. The valve seat 39 has a valve hole and a seat surface on which the valve body 36 seats. The valve seat 39 and the valve retainer 38 are fitted together and assembled into a valve case that houses the valve body 36 and the valve spring 37. The valve body 37 is movably provided between a valve closing position (the position shown in the figure) in contact with the seat surface of the valve seat 39 and a valve opening position separated from the seat surface of the valve seat 39. A groove portion for air bleeding recessed from the seat surface of the valve seat 39 may be formed.

[0035] The stepped hole 34 communicates between the outer peripheral surface of the flange portion 12 and the pressure chamber 19, and has a shape in which the hole diameter is enlarged on the outer peripheral surface side of the flange portion 12 and the hole diameter is reduced on the pressure chamber 19 side. The relief valve 33 is housed in the large-diameter hole portion of the stepped hole 34.

[0036] The small-diameter hole portion of the stepped hole 34 communicates with the valve hole of the valve seat 39 and opens into the pressure chamber 19. The outlet passage 35 communicates from the inner periphery of the large-diameter hole portion of the stepped hole 34 to the abutting surface 13. A plurality of outlet ports 40 of the relief valve 33 are formed in the valve retainer 38. A gap 41 is formed between the outlet port 40 and the outlet passage 35.

[0037] The oil drain passage 32 communicates outside the cylinder 9 via the small-diameter hole portion of the stepped hole 34, inside the relief valve 33, the gap 41, and the outlet passage 35 in this order from the pressure chamber 19. When the pressure in the pressure chamber 19 becomes greater than a preset pressure, the valve body 36 separates from the seat surface of the valve seat 39, and the relief valve 33 is in an open valve state where it opens the oil drain passage 32, allowing the working oil to escape from the pressure chamber 19 to the outside of the cylinder 9.

[0038] The stepped hole 34 has an internal thread portion 42 formed in its large-diameter hole portion and a stepped portion 43 facing the valve seat 39 in the axial direction of the screw of the internal thread portion 42. The relief valve 33 is fixed by screwing the external thread portion 45 of the external thread member 44 into the internal thread portion 42 of the stepped hole 34.

[0039] As shown in FIG. 4, a seal adhesive 46 is interposed in the screw clearance between the external thread portion 45 and the internal thread portion 42. The seal adhesive 46 mainly aims to prevent loosening of the external thread member 44 and secondarily aims to block the screw clearance. As the seal adhesive 46, an appropriate one such as an acrylic resin may be adopted.

[0040] With the sealant 46 applied to the male thread portion 45 of the male thread member 44, when a screwdriver tool (not shown) is connected to the hexagonal hole 47 of the male thread member 44 and the male thread portion 45 is screwed into the female thread portion 42, as shown in FIG. 4, the sealant 46 is fed between the male thread portion 45 and the female thread portion 42. At this time, since the viscous sealant 46 is applied in a larger amount than the aforementioned thread clearance, it does not all enter the thread clearance but overflows and accumulates on the outer periphery of the flange portion 12, resulting in an incomplete filling with a minute clearance remaining. When sealing between the stepped hole 34 and the male thread member 44 only with the sealant 46, incomplete filling cannot be tolerated. This is because when hydraulic oil flows through the clearance 41 between the relief valve 33 and the outlet passage 35 shown in FIG. 3, if hydraulic oil leaks from the thread clearance, it will cause conspicuous oil stains on the engine cover 14. In particular, in the case of a motorcycle engine cover, the leaked hydraulic oil falling on the road surface may cause tire slip, so it is required to prevent it reliably. Although it is possible to confirm whether the sealant is properly filled by performing a leak inspection, the process is time-consuming.

[0041] Therefore, in this chain tensioner 1, as shown in FIGS. 1 and 3, an elastic body 48 for sealing between the male thread member 44 and the stepped hole 34 is provided at a position closer to the valve seat 39 side in the axial direction of the thread than the male thread portion 45 and the female thread portion 42.

[0042] The elastic body 48 is composed of an O-ring. Also, the elastic body is not limited to an O-ring, and it may be an elastic body in the shape of a washer or the like, or a liquid gasket.

[0043] The relief valve 33 has an end face 49 that contacts the male thread member 44 and an outer peripheral end portion 50 whose outer diameter increases as it moves away from the male thread member 44 in the axial direction of the thread from the end face 49.

[0044] The end face 49 of the relief valve 33 is formed on the valve retainer 38. This end face 49 is in the shape of a flat surface along a direction perpendicular to the screw axis direction. The outer peripheral end portion 50 of the relief valve 33 is formed in an R chamfer shape on the outer periphery of the valve retainer 38. The purpose of forming the outer peripheral end portion 50 on the relief valve 33 is to press the inner diameter side of the elastic body 48 and guide the elastic body 48 between the relief valve 33 and the stepped hole 34. The purpose of forming the outer peripheral end portion 50 on the valve retainer 38 is to relieve stress concentration when the valve retainer 38 is formed into a bottomed cylindrical shape by pressing.

[0045] The male screw member 44 has a tightening surface 51 that contacts the end face 49 of the relief valve 33 and a sealing surface 52 that contacts the elastic body 48 at a position closer to the male screw portion 45 side in the screw axis direction than the tightening surface 51.

[0046] The tightening surface 51 of the male screw member 44 is a portion that presses the end face 49 of the relief valve 33 in the screw axis direction. This tightening surface 51 is in the shape of a flat surface along a direction perpendicular to the screw axis direction and is provided with a smaller diameter than the end face 49 of the relief valve 33. The sealing surface 52 of the male screw member 44 is in the shape of a flat surface along a direction perpendicular to the screw axis and is provided with a larger diameter than the outer peripheral end portion 50 of the relief valve 33.

[0047] The accommodation of the relief valve 33 in the stepped hole 34 and the arrangement of the elastic body 48 can be carried out in the same process. That is, the valve seat 39 of the relief valve 33 is placed on the stepped portion 43 of the stepped hole 34, the inner diameter side of the elastic body 48 contacts the outer peripheral end portion 50 of the relief valve 33, and the elastic body 48 is arranged between the outer peripheral end portion 50 and the stepped hole 34 so that the outer diameter side of the elastic body 48 contacts the inner periphery of the stepped hole 34 (see the dashed-dotted line in Fig. 3). In this state, the male screw portion 45 of the male screw member 44 is screwed into the female screw portion 42. The end face 49 of the relief valve 33 can be pushed in the screw axis direction by the tightening surface 51 of the male screw member 44 to be screwed in, and the relief valve 33 can be pressed against the stepped portion 43 of the stepped hole 34 in the screw axis direction. At this time, the elastic body 48 is pushed by the sealing surface 52 of the male screw member 44 to be screwed in and is pushed into the space between the outer peripheral end portion 50 of the relief valve 33 and the cylindrical surface portion 53 between the female screw portion 42 of the stepped hole 34 and the outlet passage 35, and the elastic body 48 can be crushed so as to be in close contact with the sealing surface 52, the outer peripheral end portion 50, and the cylindrical surface portion 53. When the tightening torque when screwing in the male screw member 44 reaches a predetermined value, the elastic body 48 is brought into a contact state in which it exhibits a predetermined sealing performance as drawn by the solid line in Fig. 3. That is, the elastic body 48 pressed from the sealing surface 52 of the male screw member 44, the sealing surface 52, the outer peripheral end portion 50 of the relief valve 33, and the cylindrical surface portion 53 of the stepped hole 34 can be brought into a stable surface contact state, and the relief valve 33 can be fixed.

[0048] Note that the height difference and diameter difference in the screw axis direction between the tightening surface 51 and the sealing surface 52 are set so that the elastic body 48 can be arranged in the compressed state drawn by the solid line in Fig. 3 without expanding the hole diameter of the stepped hole 34 from the inner diameter of the thread crest of the female screw portion 42.

[0049] Also, the elastic body 48 only needs to have at least in the contact portion an elasticity that can make the contact region in which it comes into close contact with the corresponding contact partners (sealing surface 52, outer peripheral end portion 50, cylindrical surface portion 53) due to the screwing in of the male screw member 44 into a stable surface contact state, and is not limited to the above-described O-ring.

[0050] The operation example of the chain tensioner 1 will be described (see FIGS. 1 and 2).

[0051] When the tension of the chain 6 increases during engine operation, the plunger 10 is moved in the pushing direction by the tension of the chain 6 to absorb the tension of the chain 6. At this time, a damping force is generated by the viscous resistance of the working oil flowing out from the pressure chamber 19 through the leakage gap 26. Further, the screw rod 29 rotates with respect to the plunger 10 while repeating forward and backward movements within the range of the axial gap between the female screw 27 and the male screw 28 due to the vibration of the chain 6, so that the plunger 10 moves slowly.

[0052] On the other hand, when the tension of the chain 6 decreases during engine operation, the plunger 10 is moved in the protruding direction by the biasing force of the return spring 30 to absorb the slack of the chain 6. At this time, the check valve 18 opens and the working oil flows into the pressure chamber 19 from the oil supply passage 20, so that the plunger 10 moves quickly.

[0053] When the engine stops, the tension of the chain 6 may increase depending on the stop position of the camshaft 4. In this case, since the chain 6 does not vibrate, the female screw 27 of the plunger 10 is received by the male screw 28 of the screw rod 29, and the position of the plunger 10 is fixed. Therefore, when the engine is restarted, slack of the chain 6 is less likely to occur, and smooth engine starting is possible.

[0054] Further, when the engine stops, the oil pump that supplies the working oil to the oil supply passage 20 also stops. At this time, the check valve 18 holds the working oil in the reservoir chamber 22, and it is possible to prevent the working oil in the reservoir chamber 22 from flowing out into the pressure chamber 19. Therefore, when the engine is restarted, the working oil in the reservoir chamber 22 flows into the pressure chamber 19, and the pressure chamber 19 is quickly filled with the working oil. As a result, it is possible to suppress a decrease in the damping action immediately after the engine is restarted.

[0055] Also, when the engine resonates and the tension of the chain 6 suddenly increases, the relief valve 33 opens to release the pressure in the pressure chamber 19, preventing the over-tension of the chain 6.

[0056] The chain tensioner 1 is as described above (see FIGS. 1 and 3). When the relief valve 33 is in the open state, the hydraulic oil enters the relief valve 33 from the valve hole of the valve seat 39 and flows out of the cylinder 9 via the outlet 40, the gap 41, and the outlet passage 35. At this time, a part of the hydraulic oil flowing out from the outlet 40 of the relief valve 33 to the gap 41 heads toward the male screw member 44 side, but there is an elastic body 48 that seals between the male screw member 44 and the stepped hole 34 at a position closer to the valve seat 39 side in the screw axis direction than the male screw portion 45 and the female screw portion 42. Here, when the male screw member 44 is screwed in, the contact state between the elastic body 48 and the seal surface 52, the contact state between the elastic body 48 and the outer peripheral end portion 50 of the relief valve 33, and the contact state between the elastic body 48 and the stepped hole 34 are respectively ensured to be stable contact states on the surface by the pressing force from the male screw member 44. Therefore, this chain tensioner 1 can prevent the hydraulic oil from leaking from the screw clearance between the stepped hole 34 accommodating the relief valve 33 and the male screw member 44.

[0057] Further, this chain tensioner 1 (see FIG. 3) has an end face 49 where the relief valve 33 contacts the male screw member 44, and an outer peripheral end portion 50 whose outer diameter increases as it moves away from the male screw member 44 in the screw axis direction from the end face 49. The male screw member 44 has a tightening surface 51 that contacts the end face 49 of the relief valve 33, and a sealing surface 52 that contacts the elastic body 48 at a position closer to the male screw portion 45 side than the tightening surface 51 in the screw axis direction. Since the elastic body 48 pressed from the sealing surface 52 of the male screw member 44 is in close contact with the sealing surface 52, the outer peripheral end portion 50 of the relief valve 33, and the stepped hole 34, when the male screw member 44 is screwed in, the relief valve 33 is pushed and fixed toward the stepped portion 43 of the stepped hole 34 by the tightening surface 51, and the elastic body 48 is pushed by the sealing surface 52. While guiding the inner diameter side of the elastic body 48 with the outer peripheral end portion 50 whose outer diameter of the relief valve 33 is changed as described above, it can be pressed into the elastic body 48 by being pushed between the outer peripheral end portion 50 and the stepped hole 34. As a result, the pressed elastic body 48 is in a state of being stably in close contact with the sealing surface 52 of the male screw member 44, the outer peripheral end portion 50 of the relief valve 33, and the stepped hole 34.

[0058] In addition, since the sealing surface 52 of the male screw member 44 is in the form of a flat surface along a direction perpendicular to the screw axis, the elastic body 48 can be strongly pressed against the outer peripheral end portion 50 of the relief valve 33 by the sealing surface 52 of the male screw member 44 to be in close contact with the outer peripheral end portion 50 and the stepped hole 34.

[0059] In addition, by adopting the sealing surface 52 that contacts the elastic body 48 at a position closer to the male screw portion 45 side than the tightening surface 51 of the male screw member 44, the chain tensioner 1 can move the sealing surface 52 away from the relief valve 33 and form a space for arranging the elastic body 48.

[0060] Further, since the elastomer 48 of this chain tensioner 1 is an O-ring, the elastomer 48 pressed from the seal surface 52 of the male screw member 44 can be easily compressed following the surface shape of the contact partner (seal surface 52, outer peripheral end portion 50, stepped hole 34) for any contact partner, so it is easy to secure a contact area with any contact partner.

[0061] Also, since a seal adhesive 46 is applied to the male screw portion 45 of the male screw member 44 of this chain tensioner 1 (see FIGS. 3 and 4), the loosening of the male screw member 44 can be prevented by the seal adhesive 46. Even if the filling of the seal adhesive 46 is incomplete, since there is the elastomer 48, there is no concern that the working oil leaks out of the cylinder 9 from between the stepped hole 34 and the male screw member 44. Therefore, regardless of the sealing performance by the seal adhesive 46, the leak inspection process for inspecting this sealing performance is unnecessary.

[0062] Also, this chain tensioner 1 has a flange portion 12 formed on the outside of the cylinder 9 (see FIGS. 1 to 3), the stepped hole 34 is formed from the flange portion 12 toward the inside of the cylinder 9, the cylinder 9 is inserted into the tensioner mounting hole 15 of the engine cover 14, and although it is an exterior type in which the flange portion 12 is bolted to the outside of the engine cover 14, since the working oil does not leak between the male screw member 44 and the flange portion 12, even if the leak inspection process is omitted, the oil stain on the engine cover 14 can be prevented.

[0063] The second embodiment of this invention is shown in FIG. 5. In the following, only the differences from the first embodiment will be described.

[0064] The stepped hole 60 shown in FIG. 5 has a seal seat portion 61 at a position closer to the step portion 43 side than the female screw portion 42 in the screw axis direction. The seal seat portion 61 expands the hole diameter of the stepped hole 60 at a position between the outlet passage 35 and the female screw portion 42, and is formed in a stepped shape facing the end face 63 of the male screw member 62 in the screw axis direction. The seal seat portion 61 and the end face 63 of the male screw member 62 are each in a flat surface shape along a direction perpendicular to the screw axis direction. When the elastic body 64 is disposed on the seal seat portion 61 and the male screw member 62 is screwed in, the elastic body 64 is pressed in the screw axis direction against the end face 63 of the male screw member 62 and pressed against the seal seat portion 61 of the stepped hole 60. Therefore, the elastic body 64 pressed against the end face 63 of the male screw member 62 is in close contact with the end face 63 and the seal seat portion 61.

[0065] According to the second embodiment, it is possible to seal between the male screw member 62 and the stepped hole 60 only by crushing the elastic body 64 in the screw axis direction between the seal seat portion 61 of the stepped hole 60 and the end face 63 of the male screw member 62, and it becomes unnecessary to bring the elastic body 64 into close contact with the relief valve 33.

[0066] The elastic body 64 is composed of a gasket along a direction perpendicular to the screw axis direction. Such an elastic body 64 is preferable in that it can be brought into a surface contact state by a simple compression deformation of being crushed between the facing end face 63 and the seal seat portion 61, but it is also possible to employ an O-ring, resin, etc. instead of the gasket.

[0067] As such a gasket, it is preferable to use a sheet such as a rubber sheet or a joint sheet punched into an annular shape. Such an elastic body 64 has an advantage that it is less likely to shrink in the screw axis direction compared to an O-ring, and thus the tightening torque of the male screw member 62 is less likely to become unstable. Note that the joint sheet is obtained by uniformly mixing rubber, polyamide fiber, glass fiber, expanded graphite, etc. and then pressure-rolling with a heating roll. Such a gasket is not limited to a soft gasket made of a single material, and may be a gasket sheet obtained by punching a gasket sheet in which a core material such as a joint sheet or a metal thin plate is coated with a resin such as polytetrafluoroethylene (PTFE).

[0068] The third embodiment according to the present invention is shown in FIG. 6.

[0069] The male screw member 70 according to the third embodiment has a tightening surface 71 and a sealing surface 72 formed in a tapered shape with a diameter increasing as it goes from the tightening surface 71 toward the male screw portion 45 side in the screw axis direction. The elastic body 73 pressed from the sealing surface 72 of the male screw member 70 is in close contact with the sealing surface 72, the outer peripheral end portion 50 of the relief valve 33, and the inner periphery of the stepped hole 34.

[0070] According to the third embodiment, the elastic body 73 is disposed between the outer peripheral end portion 50 of the relief valve 33 and the stepped hole 34 (see the dashed-dotted line in the figure). When the male screw member 70 is screwed in, since the sealing surface 72 of the male screw member 70 is tapered with a diameter increasing as it goes from the tightening surface 71 toward the male screw portion 45 side in the screw axis direction, it becomes easy to push the elastic body 73 between the outer peripheral end portion 50 of the relief valve 33 and the stepped hole 34 while expanding the inner diameter of the elastic body 73 with the sealing surface 72.

[0071] Also, according to the third embodiment, since the sealing surface 72 of the male screw member 70 is tapered with a diameter increasing as it goes from the tightening surface 71 toward the male screw portion 45 side, the sealing surface 72 can be moved away from the relief valve, and a space for disposing the elastic body 73 can be formed.

[0072] The fourth embodiment according to the present invention is shown in FIGS. 7 to 8.

[0073] The fourth embodiment includes a seal retainer 81 sandwiched between a male screw member 80 and a relief valve 33. The seal retainer 81 is in a disk shape along a direction perpendicular to the screw axis. The end surface 49 of the relief valve 33 contacts the seal retainer 81. The tightening surface 82 of the male screw member 80 contacts the seal retainer 81.

[0074] The male screw member 80 has a sealing surface 84 formed in a tapered shape with a diameter increasing in the direction of the male screw portion 85 from the tightening surface 82 so as to contact the elastic body 83 at a position closer to the male screw portion 85 side than the tightening surface 82 in the screw axis direction. For this reason, the sealing surface 84 can be moved away from the relief valve 33, and a space for arranging the elastic body 83 can be formed. Note that the formation site of the sealing surface 84 is closer to the male screw portion 85 side by the thickness of the seal retainer 81 compared to the third embodiment, and accordingly, the male screw portion 85 is shortened.

[0075] The seal retainer 81 protrudes toward the inner periphery of the stepped hole 34 so as to face the gap 41 between the relief valve 33 and the inner periphery of the stepped hole 34 in the screw axis direction and also to face the sealing surface 84 of the male screw member 80 in the screw axis direction. The diameter of the seal retainer 81 is set to be equal to the outer diameter of the relief valve 33. For this reason, the peripheral edge of the seal retainer 81 faces the cylindrical surface portion 53 of the stepped hole 34 with a fitting gap.

[0076] When the elastic body 83 is arranged between the seal retainer 81 and the stepped hole 34 and the male screw member 80 is screwed in, the tightening surface 82 sandwiches the seal retainer 81 between the end surface 49 of the relief valve 33, presses and fixes the relief valve 33 toward the step portion 43 of the stepped hole 34, and the sealing surface 84 presses the elastic body 83 against the seal retainer 81 to pressurize the elastic body. As a result, the elastic body 83 pressed from the sealing surface 84 of the male screw member 80 is in close contact with the sealing surface 84, the seal retainer 81, and the inner periphery of the stepped hole 34 as shown in FIG. 8. Here, the point that the sealing surface 84 of the male screw member 80 is tapered and presses the elastic body 83 while expanding the inner diameter of the elastic body 83 is the same as that of the third embodiment.

[0077] According to the fourth embodiment, since the seal retainer 81 protrudes toward the inner circumference of the stepped hole 34 facing the clearance 41 between the relief valve 33 and the inner circumference of the stepped hole 34 in the screw axis direction and also faces the seal surface 84 of the male screw member 80 in the screw axis direction, when pressing the elastic body 83 against the outer peripheral end portion 50 of the relief valve 33, the elastic body 83 can be strongly pressurized to increase the contact areas of the seal surface 84, the stepped hole 34, the seal retainer 81, and the elastic body 83, thereby enhancing the sealing performance.

[0078] In each of the above-described embodiments, a sawtooth type using a screw rod as a non-back mechanism is exemplified, but other types such as a registering type may be adopted, or the non-back mechanism may be omitted.

[0079] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. Therefore, the scope of the present invention is indicated by the scope of claims rather than the above description, and all modifications within the meaning and scope equivalent to the scope of claims are intended to be included.

Explanation of Reference Numerals

[0080] 1 Chain tensioner 9 Cylinder 10 Plunger 12 Flange portion 14 Engine cover 15 Tensioner mounting hole 18 Check valve 19 Pressure chamber 20 Oil supply passage 30 Return spring 32 Oil drain passage 33 Relief valve 34, 60 Stepped hole 36 Valve body 37 Valve spring 38 Valve retainer 39 Valve seat 42 Female screw portion 43 Step portion Male thread member 44, 62, 70, 80 Male thread part 45, 85 Seal adhesive 46 Elastomer 48, 64, 73, 83 End face of relief valve 49 Outer peripheral end of relief valve 50 Tightening surface 51, 71, 82 Sealing surface 52, 72, 84 Seal seat part 61 End face of male thread member 63 Seal retainer 81

Claims

1. A cylinder, a plunger slidably inserted into the cylinder, a return spring for biasing the plunger in a direction protruding from the cylinder, a check valve disposed in the cylinder, an oil supply passage for introducing hydraulic oil into a pressure chamber formed between the check valve and the plunger, an oil drain passage for discharging the hydraulic oil from the pressure chamber to the outside of the cylinder, and a relief valve for opening and closing the oil drain passage. The relief valve has a valve body, a valve spring for biasing the valve body in a valve closing direction, and a valve seat for receiving the biased valve body. The cylinder has a stepped hole for accommodating the relief valve, and the stepped hole has a female thread portion and a stepped portion facing the valve seat in the screw axis direction of the female thread portion. The oil drain passage communicates from the pressure chamber to the outside of the cylinder via the stepped hole. In the chain tensioner in which the relief valve is fixed by screwing a male thread portion of a male thread member from the outside of the cylinder into the female thread portion. The chain tensioner further includes an elastic body for sealing between the male thread member and the stepped hole at a position closer to the valve seat side than the male thread portion and the female thread portion in the screw axis direction. The relief valve has an end face that contacts the male thread member, and an outer peripheral end portion whose outer diameter increases as it moves away from the male thread member in the screw axis direction from the end face. The male thread member has a tightening surface that contacts the end face of the relief valve, and a sealing surface that contacts the elastic body at a position closer to the male thread portion side than the tightening surface in the screw axis direction. The sealing surface of the male thread member is in the shape of a flat surface along a direction perpendicular to the screw axis. The chain tensioner is characterized in that the elastic body pressed by the sealing surface of the male thread member is in close contact with the sealing surface, the outer peripheral end portion of the relief valve, and the stepped hole.

2. A cylinder, a plunger slidably inserted into the cylinder, a return spring for biasing the plunger in a direction protruding from the cylinder, a check valve disposed in the cylinder, an oil supply passage for introducing hydraulic oil into a pressure chamber formed between the check valve and the plunger, an oil drain passage for discharging the hydraulic oil from the pressure chamber to the outside of the cylinder, and a relief valve for opening and closing the oil drain passage. The relief valve has a valve body, a valve spring that biases the valve body in the valve closing direction, and a valve seat that receives the biased valve body. The cylinder has a stepped hole that houses the relief valve, and the stepped hole has a female threaded portion and a stepped portion that faces the valve seat in the axial direction of the thread axis of the female threaded portion. The oil drain passage communicates from the pressure chamber to the outside of the cylinder via the stepped hole. In the chain tensioner in which the relief valve is fixed by screwing the male threaded portion of the male threaded member into the female threaded portion from the outside of the cylinder. The chain tensioner further includes an elastic body that seals between the male threaded member and the stepped hole at a position closer to the valve seat side than the male threaded portion and the female threaded portion in the axial direction of the thread axis. The stepped hole has a seal seat portion formed in a stepped shape that faces the end face of the male threaded member in the thread axis direction at a position closer to the stepped portion side than the female threaded portion in the axial direction of the thread axis. The chain tensioner is characterized in that the elastic body pressed against the end face of the male threaded member is in close contact with the end face and the seal seat portion of the stepped hole.

3. A cylinder, a plunger slidably inserted into the cylinder, a return spring that biases the plunger in a direction protruding from the cylinder, a check valve disposed in the cylinder, an oil supply passage that introduces hydraulic oil into a pressure chamber formed between the check valve and the plunger, an oil drain passage that discharges the hydraulic oil from the pressure chamber to the outside of the cylinder, and a relief valve that opens and closes the oil drain passage. The relief valve has a valve body, a valve spring that biases the valve body in the valve closing direction, and a valve seat that receives the biased valve body. The cylinder has a stepped hole that houses the relief valve, and the stepped hole has a female threaded portion and a stepped portion that faces the valve seat in the axial direction of the thread axis of the female threaded portion. The oil drain passage communicates from the pressure chamber to the outside of the cylinder via the stepped hole. In the chain tensioner in which the relief valve is fixed by screwing the male threaded portion of the male threaded member into the female threaded portion from the outside of the cylinder. The chain tensioner further includes an elastic body that seals between the male threaded member and the stepped hole at a position closer to the valve seat side than the male threaded portion and the female threaded portion in the axial direction of the thread axis. The relief valve has an end face that contacts the male threaded member and an outer peripheral end portion whose outer diameter increases as it moves away from the male threaded member in the screw axis direction from the end face. The male threaded member has a tightening surface that contacts the end face of the relief valve and a sealing surface formed in a tapered shape whose diameter increases as it moves toward the male threaded portion side in the screw axis direction from the tightening surface. A chain tensioner, characterized in that the elastic body pressed from the sealing surface of the male threaded member is in close contact with the sealing surface, the outer peripheral end portion of the relief valve, and the stepped hole.

4. A cylinder, a plunger slidably inserted into the cylinder, a return spring that biases the plunger in a direction protruding from the cylinder, a check valve disposed in the cylinder, an oil supply passage that introduces hydraulic oil into a pressure chamber formed between the check valve and the plunger, an oil discharge passage that discharges the hydraulic oil from the pressure chamber to the outside of the cylinder, and a relief valve that opens and closes the oil discharge passage. The relief valve has a valve body, a valve spring that biases the valve body in a closing direction, and a valve seat that receives the biased valve body. The cylinder has a stepped hole that houses the relief valve, and the stepped hole has a female threaded portion and a stepped portion that faces the valve seat in the screw axis direction of the female threaded portion. The oil discharge passage communicates from the pressure chamber to the outside of the cylinder via the stepped hole. In a chain tensioner in which the relief valve is fixed by screwing a male threaded portion of a male threaded member from the outside of the cylinder into the female threaded portion. An elastic body that seals between the male threaded member and the stepped hole at a position closer to the valve seat side than the male threaded portion and the female threaded portion in the screw axis direction. Further provided with a seal retainer sandwiched between the male threaded member and the relief valve. The relief valve has an end face that contacts the seal retainer. The male threaded member has a tightening surface that contacts the seal retainer and a sealing surface that contacts the elastic body at a position closer to the male threaded portion side than the tightening surface in the screw axis direction. The seal retainer projects toward the inner periphery of the stepped hole so as to face the clearance between the relief valve and the inner periphery of the stepped hole in the screw axis direction and also to face the seal surface of the male screw member in the screw axis direction. The chain tensioner, wherein the elastic body pressed from the seal surface of the male screw member is in close contact with the seal surface, the seal retainer, and the stepped hole. **Claim 5** The chain tensioner according to any one of claims 1 to 4, wherein the elastic body is an O-ring. **Claim 6** The chain tensioner according to any one of claims 1 to 5, wherein a seal adhesive is applied to the male screw portion of the male screw member. **Claim 7** The chain tensioner according to any one of claims 1 to 6, wherein a flange portion is formed on the outside of the cylinder, the stepped hole is formed from the flange portion toward the inside of the cylinder, the cylinder is inserted into a tensioner mounting hole of an engine cover, and the flange portion is bolted to the outside of the engine cover.

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