JP5638979B2 - Chain tensioner - Google Patents

Description

  The present invention relates to a chain tensioner used for maintaining tension of a timing chain that drives a camshaft of an automobile engine.

  In general, an engine of an automobile transmits rotation of a crankshaft to a camshaft through a timing chain (hereinafter referred to as “chain”), and opens and closes a valve of a combustion chamber by the rotation of the camshaft. Here, in order to keep the chain tension within an appropriate range, a tension adjusting device composed of a chain guide provided so as to be able to swing around a fulcrum shaft and a chain tensioner that presses the chain via the chain guide is often used. It is done.

  As a chain tensioner incorporated in this tension adjusting device, a plunger is slidably inserted in a cylindrical cylinder with one end open and the other end closed, and the plunger is urged in a direction protruding from the cylinder. A return spring is formed, the plunger is formed in a bottomed cylindrical shape with an open end into the cylinder, and an oil supply passage is provided for introducing hydraulic oil into a pressure chamber surrounded by the plunger and the cylinder. An end of the oil supply passage on the pressure chamber side is opened at the closed end of the cylinder, and a check valve that allows only the flow of hydraulic oil from the oil supply passage side to the pressure chamber side is provided at the closed end of the cylinder. A valve seat that fits the valve to the inner periphery of the cylinder; a valve body that opens and closes a valve hole formed in the valve seat; and a retainer that holds the valve body; Those configuration is known (Patent Document 1).

  When the chain tension increases during engine operation, the chain tensioner moves in the direction in which the plunger is pushed into the cylinder (hereinafter referred to as “push-in direction”) due to the chain tension, and absorbs the chain tension. At this time, the hydraulic oil in the pressure chamber flows out through a leak gap between the sliding surface of the plunger and the cylinder, and a damper action is generated by the viscous resistance of the hydraulic oil, so that the plunger moves slowly.

  On the other hand, when the tension of the chain is reduced during engine operation, the plunger moves in a direction protruding from the cylinder (hereinafter referred to as “protruding direction”) by the urging force of the return spring, and absorbs the slackness of the chain. At this time, the check valve is opened and hydraulic oil flows into the pressure chamber from the oil supply passage, so that the plunger moves quickly.

  The chain tensioner also stops the oil pump when the engine is stopped, so that the oil level of the working oil in the oil supply passage is lowered and air is accumulated in the oil supply passage. Thereafter, when the engine is restarted, the air in the oil supply passage flows into the pressure chamber, and the inflowed air is accumulated in the plunger. When a load in the pushing direction is applied to the plunger in this state, air accumulated in the plunger is compressed and the plunger moves, so that there is a problem that the damper action of the chain tensioner is lowered.

  Therefore, in order to suppress the decrease in the damper action, the chain tensioner is provided with a screw hole that penetrates the cylinder in the radial direction, and a screw is screwed into the screw hole, and from the pressure chamber through the screw gap between the screw and the screw hole. Air is exhausted to the outside of the cylinder. Here, when air accumulates in the pressure chamber, the air accumulates in the upper portion of the pressure chamber. Therefore, the air release screw and the screw hole must be disposed in the upper portion of the pressure chamber.

  With regard to the arrangement of the air vent screw and screw hole, when the chain tensioner is attached to the engine cover, the cylinder is inserted into the tensioner attachment hole formed in the engine cover, and the flange on the outer periphery of the rear end of the cylinder is attached to the engine cover. The flange is fixed to the engine cover by using a plurality of through-holes and a plurality of bolts provided in advance on the flange. Therefore, the mounting angle around the axis of the cylinder when the mounting is completed is constant, and the position of the upper part of the cylinder can be determined at the design stage. Had to place.

  On the other hand, the inventor of the present invention forms a male thread on the outer periphery of the cylinder as a chain tensioner excellent in workability for mounting to the engine cover, while forming a female thread on the inner periphery of the tensioner mounting hole. A chain tensioner that is attached to an engine cover by engaging a male screw on the outer periphery with a female screw on the inner periphery of a tensioner attachment hole is proposed (Patent Document 2).

  This chain tensioner is provided with a male thread for attachment to the engine cover directly on the outer periphery of the cylinder. Therefore, it is not necessary to prepare a separate bolt when attaching the tensioner, and the attachment workability to the engine cover is excellent.

JP 2008-281171 A JP 2010-90988 A

  However, since the chain tensioner of Patent Document 2 is screwed into the tensioner mounting hole while rotating the cylinder, the mounting angle around the axis of the cylinder when the mounting is completed varies depending on the phase of the screw and the tightening force. When completed, the position of the top of the cylinder is not constant. Therefore, even if the air vent screw and screw hole as in Patent Document 1 described above are employed, the air vent screw and screw hole may not reach the upper portion of the pressure chamber when the tensioner is completely attached. In this case, there is a problem in that the air release screw and screw hole do not function.

  The problem to be solved by the present invention is to effectively discharge air from a pressure chamber in a chain tensioner of a type in which a cylinder is screwed into a tensioner mounting hole.

  In order to solve the above problems, a male screw is formed on the outer periphery of a cylindrical cylinder whose one end is open and the other end is closed, and is engaged with a female screw formed on the inner periphery of the tensioner mounting hole of the engine cover. A plunger is slidably inserted in the cylinder in the axial direction, a return spring is provided to urge the plunger in a direction protruding from the cylinder, and the plunger is formed in a bottomed cylindrical shape with an insertion end into the cylinder opened. An oil supply passage for introducing hydraulic oil into a pressure chamber surrounded by the plunger and the cylinder, and an end portion of the oil supply passage on the pressure chamber side is opened at the closed end of the cylinder. Provided with a check valve that allows only the flow of hydraulic oil from the oil supply passage side to the pressure chamber side, and the check valve is fitted to the inner periphery of the cylinder; In a chain tensioner composed of a valve body that opens and closes a valve hole formed in the valve seat and a retainer that holds the valve body, one end communicates with the pressure chamber between the valve seat and the fitting surface of the cylinder. A plurality of axial passages are provided at intervals in the circumferential direction, and a circumferential passage for communicating the plurality of axial passages is provided between the valve seat and the fitting surface of the cylinder, and the circumferential passage is disposed outside the cylinder. A radial passage communicating with the cylinder is provided in the cylinder, and the air in the pressure chamber is discharged to the outside of the cylinder through the axial passage, the circumferential passage, and the radial passage.

  In this way, a plurality of air vent axial passages provided between the valve seat and the fitting surface of the cylinder are arranged at intervals in the circumferential direction, so that they are screwed into the tensioner mounting holes while turning the cylinder. Even when the installation angle of the cylinder around the center of the cylinder is not constant when the tensioner installation is completed, one of the axial passages is located at the top of the cylinder, and the air in the pressure chamber is effective through the axial passage. Can be discharged.

  As the plurality of axial passages, for example, axial grooves formed on the fitting surface of the valve seat with respect to the inner periphery of the cylinder can be employed. In this way, the axial groove can be processed with higher accuracy than when the axial groove is formed on the cylinder side, and the air bleeding characteristics can be managed with higher accuracy. When the axial groove is formed in a V-shaped cross section, the cross-sectional area of the axial groove can be reduced as compared with the case where the cross-sectional arc shape or the cross-sectional square shape is used, and hydraulic oil consumption associated with the provision of the axial passage Can be suppressed. Furthermore, when the lead angle is provided in the axial groove, the groove length of the axial groove becomes longer than the axial length of the fitting surface, so that the flow resistance of the hydraulic oil in the axial passage can be further increased. It becomes possible.

  As the plurality of axial passages, axial grooves formed in a fitting surface with respect to the outer periphery of the valve seat of the cylinder may be employed. If the cylinder is formed by aluminum die casting, the axial groove can be formed at the same time as the aluminum die casting, thereby reducing the machining cost of the axial groove.

  As the circumferential passage, for example, a circumferentially extending recess formed at the axial end of the fitting surface with respect to the inner periphery of the cylinder of the valve seat can be employed. If it does in this way, the process of a recessed part will be easier than the case where a circumferential direction channel | path is formed in the cylinder side, and it is low-cost. You may employ | adopt the circumferential groove | channel formed in the fitting surface with respect to the outer periphery of the valve seat of the said cylinder as the said circumferential path.

  As the radial passage, for example, a straight hole that penetrates the peripheral wall of the cylinder in the radial direction can be adopted. When the diameter of the straight hole is 0.8 mm or less, the flow resistance of the hydraulic oil flowing through the straight hole can be ensured, and the consumption of the hydraulic oil can be suppressed.

  As the radial passage, a screw gap between a screw hole penetrating the peripheral wall of the cylinder in the radial direction and a screw screwed into the screw hole may be employed. If it does in this way, since the cross-sectional area is small and length is long, it becomes possible to suppress the consumption of hydraulic fluid effectively. As for the screw, it is possible to use a bolt with a head as in Patent Document 1. However, if a set screw with a male screw formed over the entire length is used, the screw screw part is lengthened by the amount that there is no screw head. Therefore, it is possible to more effectively suppress the consumption of hydraulic oil.

  In the chain tensioner according to the present invention, a plurality of axial passages for releasing air provided between the valve seat and the fitting surface of the cylinder are arranged at intervals in the circumferential direction. Even when the mounting angle around the cylinder center is not constant when the tensioner installation is completed by screwing in, one of the axial passages is located at the top of the cylinder, and the pressure chamber air passes through the axial passage. Can be effectively discharged.

Front view showing a chain transmission apparatus incorporating a chain tensioner according to an embodiment of the present invention Sectional view along the line II-II in FIG. FIG. 2 is an enlarged cross-sectional view of the vicinity of the fitting surface of the valve seat and cylinder. (A) is a front view of the valve seat shown in FIG. 3, (b) is a side view of (a). Enlarged sectional view showing an example in which the circumferential passage shown in FIG. 3 is provided on the cylinder side Enlarged sectional view showing an example in which the axial passage shown in FIG. 3 is provided on the cylinder side (A) is a front view showing an example in which a lead angle is provided in the axial passage shown in FIG. 4, and (b) is a side view of (a). FIG. 3 is an enlarged cross-sectional view showing another example of the radial passage shown in FIG. (A) is a front view which shows the other example of the valve seat shown in FIG. 4, (b) is a side view of (a).

  FIG. 1 shows a chain transmission device incorporating a chain tensioner 1 according to an embodiment of the present invention. In this chain transmission device, a sprocket 3 fixed to an engine crankshaft 2 and a sprocket 5 fixed to a camshaft 4 are connected via a chain 6, and the chain 6 rotates the crankshaft 2. This is transmitted to the camshaft 4, and the valve (not shown) of the combustion chamber is opened and closed by the rotation of the camshaft 4.

  The chain 6 is in contact with a chain guide 8 that is swingably supported around the fulcrum shaft 7, and the chain tensioner 1 presses the chain 6 through the chain guide 8.

  As shown in FIG. 2, the chain tensioner 1 includes a cylindrical cylinder 9 that is open at one end and closed at the other end, and a plunger 10 that is slidably inserted into the cylinder 9 in the axial direction. The cylinder 9 is inserted into the tensioner mounting hole 12 of the engine cover 11 with the opening end facing the engine cover 11. In the cylinder 9, a male screw 13 and a cylindrical surface 14 are formed on the outer periphery of a portion inserted into the tensioner mounting hole 12. The cylindrical surface 14 is located closer to the opening end of the cylinder 9 than the male screw 13 and has a smaller diameter than the outer diameter of the male screw 13.

  On the other hand, on the inner periphery of the tensioner mounting hole 12, an internal thread 15 that engages with an external thread 13 on the outer periphery of the cylinder 9 and a cylindrical surface 14 on the outer periphery of the cylinder 9 in order from the outer surface side to the inner surface side of the engine cover 11. A screw pilot hole 17 that forms an annular oil sump 16 and a cylindrical surface 18 that fits with the cylindrical surface 14 on the outer periphery of the cylinder 9 are formed. An oil outlet of an oil hole 19 formed in the engine cover 11 is opened in the screw prepared hole portion 17.

  The cylinder 9 is formed with an oil supply passage 21 for introducing hydraulic oil from the outside of the cylinder 9 into the pressure chamber 20 surrounded by the cylinder 9 and the plunger 10, and the oil passes through the oil hole 19 of the engine cover 11. Hydraulic oil supplied from a pump (not shown) is introduced into the pressure chamber 20 through the oil reservoir 16 and the oil supply passage 21 in order.

  Here, the oil supply passage 21 includes a recess 21B formed on the inner bottom surface of the cylinder 9 and a radial straight hole 21A extending from the outer periphery of the cylinder 9 to the recess 21B. The end of the pressure chamber 20 (that is, the recess 21 </ b> B) of the oil supply passage 21 is open to the closed end of the cylinder 9. A check valve 22 that allows only the flow of hydraulic oil from the oil supply passage 21 side to the pressure chamber 20 side is incorporated at the closed end of the cylinder 9.

  As shown in FIG. 3, the check valve 22 includes a valve seat 23 fitted to the inner periphery of the cylinder 9, a spherical valve body 25 that opens and closes a valve hole 24 formed in the valve seat 23, and the valve body And a retainer 26 for holding 25. On the outer periphery of the valve seat 23, there are provided a cylindrical surface 27 fitted to the inner periphery of the cylinder 9 and a flat surface 28 formed at right angles to the axis of the cylinder 9 so as to contact the inner bottom surface of the cylinder 9. ing.

  A plurality of axial passages 29 are formed between the fitting surfaces of the valve seat 23 and the cylinder 9 at intervals in the circumferential direction. Here, the axial passage 29 is formed on the fitting surface of the valve seat 23 with respect to the inner periphery of the cylinder 9, that is, on the outer peripheral cylindrical surface 27 of the valve seat 23 as shown in FIGS. 4 (a) and 4 (b). It is an axial groove. As shown in FIG. 3, each axial groove is formed over the entire length of the cylindrical surface 27 so that one end thereof communicates with the pressure chamber 20. These axial grooves are V-shaped in cross section.

  Here, as shown in FIGS. 4A and 4B, the axial passage 29 is formed so that the interval between the adjacent axial passages 29 is 90 degrees or less. Regardless of the surrounding mounting angle, any axial passage 29 is preferably located at the top of the cylinder 9. As such an arrangement of the axial passages 29, there may be mentioned one in which four or more axial passages 29 are arranged at equal intervals in the circumferential direction.

  As shown in FIG. 3, a circumferential passage 30 that connects the axial passage 29 to each other is provided between the fitting surfaces of the valve seat 23 and the cylinder 9. Here, the circumferential passage 30 is in the circumferential direction formed at the axial end of the fitting surface of the valve seat 23 with respect to the inner periphery of the cylinder 9, that is, at the axial end of the cylindrical surface 27 of the outer periphery of the valve seat 23. It is an extending recess.

  The recess is formed so as to form an annular space surrounded by the valve seat 23 and the cylinder 9 in a state in which the valve seat 23 is fitted to the inner periphery of the cylinder 9. The plurality of axial passages 29 arranged in communication with each other communicate with each other. As such a circumferential passage 30, for example, as shown in FIG. 5, it is possible to adopt a circumferentially extending recess formed on the fitting surface of the cylinder 9 with respect to the valve seat 23. When the recess formed on the valve seat 23 side is employed as shown in FIG. 3, the recess is easily processed, and the cost is low.

  As shown in FIG. 3, the cylinder 9 is provided with a radial passage 31 that allows the circumferential passage 30 to communicate with the outside of the cylinder 9. Here, the radial passage 31 is a straight hole that penetrates the peripheral wall of the cylinder 9 in the radial direction, and has a diameter of 0.8 mm or less, and constitutes an orifice that restricts the flow of hydraulic oil. Thus, by setting the diameter of the straight hole to 0.8 mm or less, the flow resistance of the hydraulic oil flowing through the straight hole can be ensured, and the consumption of the hydraulic oil can be suppressed. In addition, the radial outer end of the straight hole opens in the cylindrical surface 14 on the outer periphery of the cylinder 9, and the radial inner end of the straight hole is fitted to the valve seat 23 of the cylinder 9 so as to communicate with the circumferential passage 30. Open to the mating surface.

  As shown in FIG. 2, a minute leak gap 32 is formed between the sliding surfaces of the plunger 10 and the cylinder 9 so that the hydraulic oil in the pressure chamber 20 flows out through the leak gap 32. It has become.

  A hexagonal head 33 for engaging a spanner is formed at the closed end of the cylinder 9, and a spanner (not shown) can be applied to the hexagonal head 33 so that the male screw 13 can be tightened. ing. A gasket 34 is sandwiched between the hexagonal head 33 and the engine cover 11. The gasket 34 seals between the hexagonal head 33 and the engine cover 11, and prevents hydraulic oil from leaking to the outside of the engine cover 11 through the screw gap between the male screw 13 and the female screw 15.

  The plunger 10 is formed in a bottomed cylindrical shape whose opening end into the cylinder 9 is open, and a female screw 35 is formed on the inner periphery thereof. A screw rod 37 having a male screw 36 that engages with the female screw 35 on the outer periphery is incorporated in the plunger 10. One end of the screw rod 37 protrudes from the plunger 10, and the protruding end is in contact with the valve seat 23 in the cylinder 9.

  The male screw 36 and the female screw 35 are formed in a sawtooth 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. Yes.

  A return spring 38 that urges the plunger 10 in a direction protruding from the cylinder 9 is incorporated in the pressure chamber 20. The return spring 38 is a coil spring, one end of which is supported by the screw rod 37 and the other end urges the plunger 10. The plunger 10 is in contact with the chain guide 8 at the protruding end from the cylinder 9.

  Next, an operation example of the chain tensioner 1 will be described.

  When the tension of the chain 6 is reduced during the operation of the engine, the plunger 10 moves in the protruding direction by the urging force of the return spring 38 and absorbs the slack of the chain 6. At this time, the check valve 22 is opened, and the hydraulic oil supplied from the oil pump flows into the pressure chamber 20 through the oil supply passage 21, so that the plunger 10 moves quickly.

  On the other hand, when the tension of the chain 6 increases during engine operation, the plunger 10 moves in the pushing direction by the tension of the chain 6 and absorbs the tension of the chain 6. At this time, the screw rod 37 rotates with respect to the plunger 10 while repeating the forward and backward movements within the range of the axial gap between the female screw 35 and the male screw 36 due to the vibration of the chain 6. Further, since the hydraulic oil in the pressure chamber 20 flows out through the leak gap 32 between the sliding surfaces of the plunger 10 and the cylinder 9 and a damper action is generated by the viscous resistance of the hydraulic oil, the plunger 10 moves slowly. To do.

  When the engine is stopped, the tension of the chain 6 may increase depending on the stop position of the camshaft 4. In this case, the chain 6 does not vibrate, so that the internal thread 35 of the plunger 10 is received by the external thread 36 of the screw rod 37. Ten positions are fixed. Therefore, when the engine is restarted, the chain 6 is hardly slackened, and the engine can be started smoothly.

  When the engine is stopped, the oil pump is stopped, the oil level of the hydraulic oil in the oil hole 19 and the oil supply passage 21 is lowered, and air is accumulated in the oil hole 19 and the oil supply passage 21. Therefore, when the engine is restarted, the air in the oil hole 19 and the oil supply passage 21 flows into the pressure chamber 20. In this case, the air mixed in the pressure chamber 20 flows into the axial passage 29 and the circumferential passage. 30 and the radial passage 31 are discharged to the outside of the cylinder 9, and a decrease in the damper action due to the air in the pressure chamber 20 is suppressed.

  Further, during the operation of the engine, a flow of hydraulic oil is formed from the plurality of axial passages 29 toward one circumferential passage 30 and one radial passage 31. When air is mixed as bubbles in the hydraulic oil introduced from the oil supply passage 21 into the pressure chamber 20, the air is mixed with the hydraulic oil, and the axial passage 29, the circumferential passage 30, the radial passage 31, It is discharged through.

  By the way, the chain tensioner 1 is mounted by screwing into the tensioner mounting hole 12 while rotating the cylinder 9, so that the mounting angle around the axis of the cylinder 9 when the mounting is completed varies depending on the phase of the screw and the tightening force. When the operation is completed, the position of the upper part of the cylinder 9 is not constant. However, the chain tensioner 1 has a plurality of axial passages 29 for releasing air between the fitting surfaces of the valve seat 23 and the cylinder 9 at intervals in the circumferential direction. Regardless of the mounting angle, any one of the axial passages 29 is located at the top of the cylinder 9, and the air in the pressure chamber 20 can be effectively discharged through the axial passages 29.

  As shown in the above-described embodiment, when the axial groove formed on the fitting surface of the valve seat 23 with respect to the inner periphery of the cylinder 9 is used for the axial passage 29, as shown in FIG. The axial groove can be processed with higher accuracy than when the groove is formed, and the air bleeding characteristics can be managed with high accuracy. Here, if the axial passage 29 of the above embodiment is formed by rolling, stable machining accuracy can be obtained, and the cost is lower than that of forming by cutting.

  As the axial passage 29, as shown in FIG. 6, an axial groove formed on a fitting surface of the cylinder 9 with respect to the outer periphery of the valve seat 23 can be adopted. In this case, when the cylinder 9 is formed by aluminum die casting, if the cylinder 9 is formed simultaneously with the aluminum die casting, the machining cost of the axial groove can be suppressed.

  As shown in the above embodiment, when an axial groove is employed as the axial passage 29, the axial groove is formed in a cross-sectional circle when formed in a V-shaped cross section as shown in FIGS. 4 (a) and 4 (b). The cross-sectional area of the axial groove can be reduced as compared with the case of the arc shape or the cross-sectional square shape, and the increase in the consumption amount of hydraulic oil accompanying the provision of the axial passage 29 can be suppressed. In this case, as shown in FIGS. 7A and 7B, when the lead angle is provided in the axial groove, the groove length of the axial groove becomes longer than the axial length of the fitting surface. It is possible to further increase the flow resistance of the hydraulic oil in the direction passage 29.

  In the above embodiment, the radial passage 31 has been described by taking, as an example, a straight hole that penetrates the peripheral wall of the cylinder 9 in the radial direction. However, as shown in FIG. 8, a screw that penetrates the peripheral wall of the cylinder 9 in the radial direction. A hole 39 may be provided, and a screw 40 may be screwed into the screw hole 39, and a screw gap between the screw hole 39 and the screw 40 may be used as the radial passage 31. In this case, since the screw gap has a small cross-sectional area and a long length, the screw gap functions as an orifice having a larger flow resistance than the straight hole, and the consumption of hydraulic oil can be more effectively suppressed. Here, for the screw 40, it is possible to use a bolt with a head, but as shown in FIG. 8, if a set screw having a male screw formed over the entire length is used, the screw 40 has no head, Since the screw part of screw 40 can be lengthened, it is possible to suppress consumption of hydraulic oil more effectively.

  In the above embodiment, in order to increase the flow resistance of the axial passage 29, an axial groove is adopted as the axial passage 29. However, as shown in FIGS. 9A and 9B, the outer periphery of the valve seat 23 is used. A plurality of D-cut portions 41 formed by cutting a part of the circumference along a plane are provided on the cylindrical surface 27 of the cylinder surface 27 at intervals in the circumferential direction, and between the D-cut portion 41 and the inner periphery of the cylinder 9. An axial passage 29 may be formed.

DESCRIPTION OF SYMBOLS 1 Chain tensioner 9 Cylinder 11 Engine cover 12 Tensioner attachment hole 13 Male screw 15 Female screw 20 Pressure chamber 21 Oil supply passage 22 Check valve 23 Valve seat 24 Valve hole 25 Valve body 26 Retainer 27 Cylindrical surface 29 Axial passage 30 Circumferential passage 31 Radial direction Passage 38 Return spring 39 Screw hole 40 Screw

Claims (10)

An external thread that engages with an internal thread (15) formed on the inner periphery of a tensioner mounting hole (12) of an engine cover (11) on the outer periphery of a cylindrical cylinder (9) that is open at one end and closed at the other end A return spring (13) is formed, a plunger (10) is slidably inserted in the cylinder (9) in the axial direction, and the plunger (10) is urged in a direction protruding from the cylinder (9). 38), the plunger (10) is formed into a bottomed cylindrical shape with an opening end into the cylinder (9), and is surrounded by the plunger (10) and the cylinder (9). 20) is provided with an oil supply passage (21) for introducing hydraulic oil, and an end of the oil supply passage (21) on the pressure chamber (20) side is opened at the closed end of the cylinder (9), so that the cylinder (9 ) At the closed end of the oil supply passage (21) A check valve (22) that allows only the flow of hydraulic oil from the pressure chamber (20) to the pressure chamber (20) side is provided, and the check valve (22) is fitted to the inner periphery of the cylinder (9). A chain tensioner composed of a valve body (25) for opening and closing a valve hole (24) formed in the valve seat (23) and a retainer (26) for holding the valve body,
Between the fitting surfaces of the valve seat (23) and the cylinder (9), a plurality of axial passages (29) having one end communicating with the pressure chamber (20) are provided at intervals in the circumferential direction.
Only one circumferential passage (30) for communicating the plurality of axial passages (29) with each other is provided between the fitting surfaces of the valve seat (23) and the cylinder (9),
The cylinder (9) is provided with only one radial passage (31) for communicating the circumferential passage (30) with the outside of the cylinder (9),
During engine operation, a flow of hydraulic oil is formed from the plurality of axial passages (29) toward the one circumferential passage (30) and the radial passage (31), and the plurality of axial passages are formed. (29), and the air in the pressure chamber (20) is discharged to the outside of the cylinder (9) through the one circumferential passage (30) and the radial passage (31). Chain tensioner.   The chain tensioner according to claim 1, wherein the plurality of axial passages (29) are axial grooves formed in a fitting surface (27) with respect to the inner periphery of the cylinder (9) of the valve seat (23).   The chain tensioner according to claim 2, wherein the axial groove has a V-shaped cross section.   The chain tensioner according to claim 3, wherein a lead angle is provided in the axial groove.   The chain tensioner according to claim 1, wherein the plurality of axial passages (29) are axial grooves formed on a fitting surface of the cylinder (9) with respect to an outer periphery of the valve seat (23).   The chain tensioner according to claim 5, wherein the cylinder (9) is formed by aluminum die casting, and the axial groove is formed by the aluminum die casting.   The circumferential passage (30) is a circumferentially extending recess formed at an axial end of the fitting surface (27) with respect to the inner periphery of the cylinder (9) of the valve seat (23). 6. The chain tensioner according to any one of 6 above.   The chain tensioner according to any one of claims 1 to 7, wherein the radial passage (31) is a straight hole having a diameter of 0.8 mm or less penetrating the peripheral wall of the cylinder (9) in the radial direction.   The radial passage (31) is a screw gap between a screw hole (39) passing through a peripheral wall of the cylinder (9) in a radial direction and a screw (40) screwed into the screw hole (39). To 7. The chain tensioner according to any one of 7 to 7.   The chain tensioner according to claim 9, wherein the screw (40) is a set screw having a male screw formed over its entire length.

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