JP2010121667A - Automatic tensioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic tensioner capable of preventing excessive expansion of bellows when replacing a belt of an engine without requiring highly accurate management. <P>SOLUTION: In this automatic tensioner 11, the lower outer periphery of a sleeve 16 is suitable for a sleeve fitting recessed part 17 formed at the bottom 14 of a cylinder 15; the inside of the cylinder 15 is partitioned into a pressure chamber 19 and a reservoir chamber 20 by slidably inserting a rod 18 into the sleeve 16; a spring seat 21 is fixed to the upper end of the rod 18; a return spring 27 is arranged for energizing its spring set 21; and vertically expandable cylindrical rubber bellows 22 is arranged for covering an annular opening between the spring seat 21 and the cylinder 15. The spring seat 21 is formed with an air vent 36 for communicating the reservoir chamber 20 with outside air, and an air bleeding plug 37 for manually switching opening-closing is arranged in an outside air side end part of its air vent 36. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an auto tensioner used for maintaining the tension of a belt for driving an automobile auxiliary machine such as an alternator.

  The auxiliary shafts of automobiles, such as car air conditioners and water pumps, are connected to a crankshaft of an engine by a belt and are driven by the crankshaft via the belt. In order to keep the tension of this belt within an appropriate range, a pulley arm that can swing around a fulcrum shaft, a tension pulley attached to the pulley arm, and a pulley arm in a direction to press the tension pulley against the belt are generally attached. A tension adjusting device consisting of an auto tensioner is used.

  As an auto tensioner incorporated in this tension adjustment device, hydraulic oil is stored in a cylinder having a bottom at the bottom, and the outer periphery of the lower portion of the sleeve is fitted into a sleeve fitting recess formed at the bottom of the cylinder, and a rod is placed in the sleeve. The cylinder is slidably inserted in the axial direction to divide the inside of the cylinder into a pressure chamber and a reservoir chamber, a spring seat is fixed to the upper end of the rod, and the spring seat is urged in the direction in which the volume of the pressure chamber increases. The thing provided with the return spring is known (patent documents 1 and 2).

  This auto tensioner absorbs fluctuations in belt tension as the spring seat moves to a position where the biasing force of the return spring balances with the belt tension.

  Further, the lower part of the pressure chamber and the lower part of the reservoir chamber communicate with each other via a first passage provided with a check valve that allows only the flow of hydraulic oil from the reservoir chamber side to the pressure chamber side. When the rod moves in the direction in which the pressure increases, the check valve opens, and hydraulic oil flows from the reservoir chamber side to the pressure chamber side through the first passage. Therefore, the rod moves quickly in the direction in which the volume of the pressure chamber increases.

  In addition, the upper part of the pressure chamber and the upper part of the reservoir chamber communicate with each other via a second passage provided with a throttle that restricts the flow rate of the hydraulic oil, and when the rod moves in a direction in which the volume of the pressure chamber is reduced, The hydraulic fluid in the room flows out through the second passage. At this time, since the flow rate of the hydraulic oil flowing through the second passage is limited by the throttle and a damper action occurs, the rod moves slowly.

  In addition, this auto tensioner has an annular opening between the spring seat and the cylinder covered with a cylindrical rubber bellows that can be expanded and contracted vertically, and the upper part of the bellows is fitted to the outer periphery of the spring seat with a tightening margin. The lower part of the cylinder is fitted to the outer periphery of the cylinder with an allowance, and the hydraulic oil in the reservoir chamber is sealed by the bellows.

  In this auto tensioner, when replacing the belt of the engine, the rod may move excessively in the direction in which the volume of the pressure chamber is reduced.In this case, if a mechanism for absorbing the pressure change in the reservoir chamber is not provided, The bellows expands excessively due to the pressure increase in the reservoir chamber, and hydraulic oil may leak from the upper or lower portion of the bellows.

Therefore, in the auto tensioner described in Patent Document 3, in order to absorb the pressure change in the reservoir chamber, a vent hole that communicates the reservoir chamber and the outside air is formed in the spring seat, and the vent on the outside air side end portion is formed. A vent with a slit is incorporated in a rubber partition that separates the reservoir chamber side from the outside air side. In the auto tensioner, when the pressure in the reservoir chamber becomes larger than a preset pressure, the vent slit opens to release the pressure in the reservoir chamber to the outside air, thereby preventing excessive expansion of the bellows.
Special Table 2000-504395 JP 2007-16932 A JP 2007-315562 A

  However, when a vent is used, when the pressure in the reservoir chamber increases and the vent slit opens, the pressure in the reservoir chamber decreases, but does not decrease to the external pressure. Therefore, if the pressure at which the vent slit opens (hereinafter referred to as “vent opening pressure”) is large, the bellows will remain inflated, the fitting strength of the upper and lower portions of the bellows may be reduced, and hydraulic oil may leak. There is.

  On the other hand, if the vent opening pressure is small, the bellows bulge can be reliably suppressed. However, the vent slit repeatedly opens and closes due to pressure oscillations in the reservoir chamber that occur during engine operation, causing the hydraulic fluid in the reservoir chamber to flow. There is a problem of rapid evaporation and reduction.

  Therefore, when the vent is used to absorb the pressure change in the reservoir chamber, it is necessary to manage the opening pressure of the vent with high accuracy, which is complicated.

  The problem to be solved by the present invention is to provide an auto tensioner that can prevent excessive expansion of the bellows when replacing the belt of the engine without requiring high accuracy control.

  In order to solve the above-described problems, a vent hole for communicating the reservoir chamber and the outside air is formed in the spring seat, and an air vent plug that is manually opened and closed is provided at an end of the vent hole on the outside air side. In this way, when replacing the belt of the engine, the pressure in the reservoir chamber can be released to the outside air by opening the air vent plug, and excessive expansion of the bellows can be prevented. Further, by closing the air vent plug during engine operation, it is possible to reliably prevent the working oil from evaporating in the reservoir chamber.

  The air vent plug includes, for example, a screw that is screw-engaged with a female screw formed on the inner periphery of the outside end of the vent hole, and a gasket that is sandwiched between the head of the screw and the spring seat. The thing of a structure can be employ | adopted. When the screw is loosened, this air vent plug creates a gap in the gasket portion, so that the pressure in the reservoir chamber can be released to the outside air via the gap and the screw gap between the screws. Further, when the screw is tightened, the gap in the gasket portion can be closed and the reservoir chamber can be sealed.

  In addition, as the air vent plug, for example, a plug body that is detachably fitted to an end portion on the outside air side of the vent hole can be employed. This air vent plug can release the pressure in the reservoir chamber to the outside air by removing the plug body from the vent hole. Further, by attaching the plug body to the vent hole, the end portion on the outside air side of the vent hole can be closed to seal the reservoir chamber.

  When a plug body that is detachably fitted to the end portion of the vent hole on the outside air side is employed as the air vent plug, a head portion having a larger diameter than the inner diameter of the end portion of the vent hole on the outside air side is provided on the plug body. And preferred. If it does in this way, when attaching a plug to a vent, since the head of a plug serves as a stopper, it can prevent that a plug immerses in a vent and cannot be removed.

  Further, when a plug body that is detachably fitted to the end of the vent hole on the outside air side is employed as the air vent plug, a protrusion that extends in the circumferential direction on the outer periphery of the insertion portion of the plug body into the vent hole It is preferable that a plurality of ridges are formed at intervals in the axial direction, and the protrusions are fitted to the inner periphery of the vent hole with an allowance. In this case, the outer periphery of the insertion portion of the plug body into the vent hole is formed as a cylindrical surface without protrusions, and the cylindrical surface is fitted with a tight margin on the inner periphery of the vent hole with a smaller force. The plug body can be attached and detached.

  In the case of adopting a plug body that is detachably fitted to the end portion of the vent hole on the outside air side as the air vent plug, the plug body may be formed of rubber or resin.

  In addition, the air vent plug is formed, for example, at a cylinder body fitted into an end portion on the outside air side of the vent hole, a ball accommodated in the cylinder body, and an end portion on the outside air side of the cylinder body. Further, it is possible to adopt a configuration comprising a spring that presses the ball against an inward flange. When the ball is pushed in from the outside air side, this air vent plug creates a gap between the ball and the flange, so that the pressure in the reservoir chamber can be released to the outside air through the gap. When the push-in of the ball is released, the space between the ball and the flange is closed by the force of the spring, so that the reservoir chamber is sealed.

  The end portion on the outside air side of the vent hole may be opened on the upper surface of the spring seat as described in Patent Document 3, but if it is opened on the outer periphery of the spring seat, foreign matter in the outside air enters the vent hole. It becomes difficult to enter the reservoir chamber.

  An annular passage formed between the sliding surfaces of the rod and the sleeve, and an oil passage communicating with the reservoir chamber through the passage through the inside of the rod and the inside of the spring seat. The electromagnetic on-off valve of the oil passage can be incorporated in the spring seat. If it does in this way, the movement of the spring seat to the direction which the volume of a pressure chamber reduces can be prevented by closing an electromagnetic on-off valve. Therefore, when this auto tensioner is used in an engine that is driven and started by a motor generator connected to the belt, the belt is slipped when the engine is started by starting the engine with the electromagnetic on-off valve closed. It becomes possible to prevent.

  When the belt of the engine is replaced, the autotensioner of the present invention can release the pressure in the reservoir chamber to the outside air by opening the air vent plug to prevent excessive expansion of the bellows. Further, this auto tensioner manually opens and closes the air vent plug regardless of the pressure in the reservoir chamber, so that high accuracy control is not required.

  FIG. 1 shows a belt transmission device of an engine corresponding to an idling stop in which an engine is started by rotating a crankshaft 2 with a belt 1 driving an automobile auxiliary machine. The belt 1 is stretched over a crank pulley 3 attached to a crankshaft 2, a motor pulley 5 attached to a rotating shaft 4 of a motor generator, and an auxiliary pulley 7 attached to a rotating shaft 6 of an auxiliary machine. Yes.

  When the engine is started, the rotation shaft 4 of the motor generator rotates as a drive shaft, and the rotation is transmitted from the motor pulley 5 to the crank pulley 3 via the belt 1 so that the crankshaft 2 rotates. On the other hand, during engine operation, the crank pulley 3 rotates as a drive shaft, and the rotation is transmitted from the crank pulley 3 to the accessory pulley 7 and the motor pulley 5 via the belt 1 to drive the accessory and the motor generator. . At this time, the motor generator functions as a generator (generator).

  The belt 1 is in contact with the tension pulley 8 between the crank pulley 3 and the motor pulley 5. The portion with which the tension pulley 8 contacts is on the slack side during rotation of the engine because the crankshaft 2 rotates as the drive shaft, and when starting the engine, the rotation shaft 4 of the motor generator rotates as the drive shaft, so the tension side It becomes.

  The tension pulley 8 is attached to a pulley arm 10 supported so as to be swingable about a fulcrum shaft 9 fixed to an engine block (not shown). One end of the auto tensioner 11 according to the first embodiment of the present invention is connected to the pulley arm 10 via a connecting shaft 12, and the other end of the auto tensioner 11 is supported by a fulcrum shaft 13 fixed to the engine block. . The auto tensioner 11 urges the pulley arm 10 in a direction in which the tension pulley 8 is pressed against the belt 1.

  As shown in FIG. 2, the auto tensioner 11 has a cylinder 15 having a bottom 14 at a lower portion, and hydraulic oil is stored in the cylinder 15. A sleeve 16 is inserted into the cylinder 15 coaxially with the cylinder 15, and a lower outer periphery of the sleeve 16 is fitted into a sleeve fitting recess 17 formed on the bottom 14 of the cylinder 15. A rod 18 is slidably inserted in the sleeve 16 in the axial direction, and the cylinder 15 is partitioned into a pressure chamber 19 and a reservoir chamber 20 by the rod 18 and the sleeve 16.

  The upper end of the rod 18 is fixed to the spring seat 21. The annular opening between the spring seat 21 and the cylinder 15 is covered with a cylindrical rubber bellows 22 that can be vertically expanded and contracted. An upper lip 23 extending in the circumferential direction is formed on the upper inner periphery of the bellows 22, and the upper lip 23 is fitted into an upper lip groove 24 on the outer periphery of the spring seat 21 with a tightening margin. A lower lip 25 extending in the circumferential direction is also formed on the lower inner periphery of the bellows 22, and the lower lip 25 is fitted into the lower lip groove 26 on the outer periphery of the cylinder 15 with a tightening margin.

  A return spring 27 is incorporated between the spring seat 21 and the bottom 14 of the cylinder 15. The lower end of the return spring 27 is supported by the bottom 14 of the cylinder 15, and the upper end presses the spring seat 21. By the pressing, the spring seat 21 is urged in the direction in which the volume of the pressure chamber 19 increases. Yes.

  The rod 18 includes a sliding shaft portion 18C that slides below the retaining ring 28 attached to the upper inner periphery of the sleeve 16, and a small-diameter shaft that projects from the sleeve 16 above the sliding shaft portion 18C. A portion 18B and a large-diameter shaft portion 18A continuous above the small-diameter shaft portion 18B. Here, the small diameter shaft portion 18B is a portion having a smaller diameter than the inner diameter of the retaining ring 28, and the large diameter shaft portion 18A is a portion having a larger diameter than the inner diameter of the retaining ring 28.

  The rod 18 is locked at the lower end of the large-diameter shaft portion 18A with a retaining ring 28, thereby restricting the movement stroke of the rod 18 in the direction in which the volume of the pressure chamber 19 is reduced. By locking the upper end with the retaining ring 28, the movement stroke of the rod 18 in the direction in which the volume of the pressure chamber 19 increases is regulated.

  A first passage 29 that communicates the lower portion of the pressure chamber 19 and the lower portion of the reservoir chamber 20 is formed between the fitting surfaces of the sleeve fitting recess 17 and the sleeve 16. In addition, a check valve 30 for preventing the flow of hydraulic oil in the first passage 29 from the pressure chamber 19 side to the reservoir chamber 20 side is incorporated in the lower portion of the sleeve 16.

  The upper part of the pressure chamber 19 and the upper part of the reservoir chamber 20 communicate with each other via the second passage 31. The second passage 31 has an annular throttle gap 32 formed between the sliding surface of the sleeve 16 and the rod 18, and passes through the inside of the rod 18 and the spring seat 21 from the throttle gap 32 in order. The oil passage 33 communicates with the oil passage 33.

  Here, an O-ring 34 is attached to the outer periphery of the sliding shaft portion 18 </ b> C, and the space between the sliding surface of the sliding shaft portion 18 </ b> C and the sleeve 16 is sealed by the O-ring 34. In addition, an end of the oil passage 33 on the pressure chamber 19 side is opened below the O-ring 34 on the outer periphery of the sliding shaft portion 18C. The throttle gap 32 constitutes a throttle that limits the flow rate of hydraulic oil in the second passage 31.

  The spring seat 21 incorporates an electromagnetic on-off valve 35 that opens and closes the second passage 31 by switching between energization and non-energization.

  As shown in FIG. 3, the spring seat 21 is formed with a vent hole 36 for communicating the reservoir chamber 20 and the outside air. The vent hole 36 includes two holes intersecting inside the spring seat 21, the end on the reservoir chamber 20 side opens on the lower surface of the spring seat 21, and the end on the outside air opens on the outer periphery of the spring seat 21. ing.

  An air vent plug 37 that is manually opened and closed is provided at an end portion of the vent hole 36 on the outside air side. The air vent plug 37 is a ring 38 that is sandwiched between a screw 38 that is screw-engaged with a female screw formed on the inner periphery of the outside end of the vent hole 36, and a head 38 a of the screw 38 and the outer periphery of the spring seat 21. And gasket 39. The head 38 a of the screw 38 has a larger diameter than the inner diameter of the end of the vent hole 36 on the outside air side.

  When the screw 38 is loosened, the air vent plug 37 creates a gap in the gasket 39, so that the pressure in the reservoir chamber 20 can be released to the outside air through the gap and the screw gap of the screw 38. Further, when the screw 38 is tightened, the gap of the gasket 39 can be closed and the inside of the reservoir chamber 20 can be sealed.

  Next, an operation example of the auto tensioner 11 will be described. When starting the engine, the auto tensioner 11 is used in a state in which the electromagnetic opening / closing valve 35 is energized and the second passage 31 is closed, and during operation of the engine, the energization to the electromagnetic opening / closing valve 35 is interrupted. 2. Used with the passage 31 open.

  When the tension of the belt 1 becomes small during engine operation, the spring seat 21 moves relative to the cylinder 15 to a position where the tension of the belt 1 and the urging force of the return spring 27 are balanced, and the slack of the belt 1 is absorbed. At this time, since the volume of the pressure chamber 19 increases, the hydraulic oil flows from the reservoir chamber 20 to the pressure chamber 19 through the first passage 29, and the spring seat 21 moves quickly.

  When the tension of the belt 1 increases during engine operation, the spring seat 21 moves relative to the cylinder 15 to a position where the tension of the belt 1 and the urging force of the return spring 27 are balanced, and absorbs the tension of the belt 1. At this time, since the volume of the pressure chamber 19 is reduced, the hydraulic oil flows from the pressure chamber 19 side to the reservoir chamber 20 side through the second passage 31, and the flow rate of the hydraulic oil is limited by the throttle gap 32, and the damper action. Therefore, the spring seat 21 moves slowly.

  When starting the engine, the portion of the belt 1 that contacts the tension pulley 8 becomes the tension side, so the tension of the belt 1 increases rapidly, but the electromagnetic on-off valve 35 closes the second passage 31, The spring seat 21 is prevented from moving in the direction in which the volume of the pressure chamber 19 is reduced. Therefore, the position of the tension pulley 8 is fixed, and the belt 1 is unlikely to slip.

  In addition, when replacing the belt 1 of the engine, the auto tensioner 11 has a stroke end on the side where the volume of the pressure chamber 19 is reduced (that is, the lower end of the large-diameter shaft portion 18A of the rod 18 is locked by the retaining ring 28. The rod 18 may move to a position where the bellows 22 are not expanded. At this time, in order to prevent excessive expansion of the bellows 22, the screw 38 is loosened to release the pressure in the reservoir chamber 20 to the outside air. Further, during the operation of the engine, the screw 38 is tightened in order to prevent the working oil in the reservoir chamber 20 from evaporating.

  When replacing the belt 1 of the engine, the auto tensioner 11 can release the pressure in the reservoir chamber 20 to the outside air by loosening the screw 38 and prevent the bellows 22 from excessively expanding. Further, since the auto tensioner 11 opens and closes the air vent plug 37 by the operation of the screw 38 regardless of the pressure in the reservoir chamber 20, high accuracy control is not required.

  Further, in the auto tensioner 11, the end portion on the outside air side of the vent hole 36 is opened on the outer periphery of the spring seat 21, and therefore, the end portion on the outside air side of the vent hole 36 is opened on the upper surface of the spring seat 21. As a result, foreign matter in the outside air is less likely to enter the vent hole 36 and less likely to enter the reservoir chamber 20.

  Next, an auto tensioner according to a second embodiment of the present invention will be described. Portions corresponding to the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 4, an air vent plug 40 that is manually opened and closed is provided at an end of the vent hole 36 on the outside air side. The air vent plug 40 includes a plug body 41 that is detachably fitted to an end portion of the vent hole 36 on the outside air side. A head 41 a having a larger diameter than the inner diameter of the end of the vent hole 36 on the outside air side is provided at the end of the plug body 41 on the outside air side.

  In the plug body 41, a plurality of protrusions 42 extending in the circumferential direction are formed on the outer periphery of the portion inserted into the vent hole 36 at intervals in the axial direction. In a state before the plug body 41 is inserted into the vent hole 36, the outer diameter of the protrusion 42 is larger than the inner diameter of the end of the vent hole 36 on the outside air side, and the plug body 41 is inserted into the vent hole 36. Thus, the protrusion 42 is fitted to the inner periphery of the air hole 36 with a tightening margin. The outer diameter of the portion between the adjacent protrusions 42, 42 of the plug body 41 is smaller than the inner diameter of the end of the vent hole 36 on the outside air side. Such a plug body 41 may be formed of rubber or resin.

  The air vent plug 40 can release the pressure in the reservoir chamber 20 to the outside air by removing the plug body 41 from the vent hole 36. Further, by attaching the plug body 41 to the vent hole 36, the end of the vent hole 36 on the outside air side can be closed and the inside of the reservoir chamber 20 can be sealed.

  When replacing the belt 1 of the engine, the auto tensioner can release the pressure in the reservoir chamber 20 to the outside air by removing the plug 41 and prevent the bellows 22 from excessively expanding. In addition, the auto tensioner does not require high accuracy control because the air vent plug 40 is opened and closed by the attachment / detachment operation of the plug body 41 regardless of the pressure in the reservoir chamber 20.

  In this auto tensioner, when the plug body 41 is attached to the vent hole 36, the head portion 41a of the plug body 41 abuts on the outer periphery of the spring seat 21 and functions as a stopper, so that the plug body 41 is immersed in the vent hole 36. Can be prevented from being removed.

  Further, in this auto tensioner, the protrusion 42 on the outer periphery of the plug body 41 is fitted to the inner periphery of the vent hole 36 with a tightening margin, so that the outer periphery of the insertion portion of the plug body 41 into the vent hole 36 is protruded. The plug body 41 can be attached and detached with a smaller force than when a cylindrical surface without 42 is provided and the cylindrical surface is fitted to the inner periphery of the vent hole 36 with a tightening margin.

  Next, an auto tensioner according to a third embodiment of the present invention will be described. Portions corresponding to the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 5, an air vent plug 50 that is manually opened and closed is provided at an end portion on the outside air side of the vent hole 36. The air vent plug 50 includes a cylindrical body 51 fitted into an end portion on the outside air side of the vent hole 36, a ball 52 accommodated in the cylindrical body 51, and an inner portion formed at an end portion on the outside air side of the cylindrical body 51. It consists of a spring 54 that presses the ball 52 against the facing flange 53.

  When the ball 52 is pushed into the air vent plug 50 from the outside air side, a gap is formed between the ball 52 and the flange 53, so that the pressure in the reservoir chamber 20 can be released to the outside air through the gap. In addition, when the push of the ball 52 is released, the gap between the ball 52 and the flange 53 is closed by the force of the spring 54, so that the inside of the reservoir chamber 20 is sealed.

  When replacing the belt 1 of the engine, the auto tensioner can release the pressure in the reservoir chamber 20 to the outside air by pushing the ball 52 and prevent the bellows 22 from being excessively expanded. In addition, the auto tensioner does not require high accuracy control because the air vent plug 50 is opened and closed by the operation of the ball 52 regardless of the pressure in the reservoir chamber 20.

Front view showing a belt transmission device incorporating an auto tensioner according to an embodiment of the present invention. 1 is an enlarged sectional view of the auto tensioner shown in FIG. FIG. 2 is an enlarged cross-sectional view in the vicinity of the air vent plug of FIG. FIG. 3 is an enlarged sectional view showing a modification of the air vent plug of FIG. The expanded sectional view which shows the other modification of the air vent plug of FIG.

Explanation of symbols

11 Auto tensioner 14 Bottom 15 Cylinder 16 Sleeve 17 Sleeve fitting recess 18 Rod 19 Pressure chamber 20 Reservoir chamber 21 Spring seat 22 Bellows 23 Upper lip 25 Lower lip 27 Return spring 29 First passage 30 Check valve 31 Second passage 32 Restriction gap 33 Oil passage 35 Electromagnetic on-off valve 36 Ventilation hole 37 Air vent plug 38 Screw 38a Screw head 39 Gasket 40 Air vent plug 41 Plug body 41a Plug body head 42 Projection 50 Air vent plug 51 Cylindrical body 52 Ball 53 Flange 54 Spring

Claims (10)

The hydraulic oil is stored in a cylinder (15) having a bottom (14) at the bottom, and the lower outer periphery of the sleeve (16) is fitted into a sleeve fitting recess (17) formed on the bottom (14) of the cylinder (15). The rod (18) is slidably inserted in the sleeve (16) in the axial direction to divide the cylinder (15) into a pressure chamber (19) and a reservoir chamber (20), and the rod (18) A spring seat (21) is fixed to the upper end, and a return spring (27) is provided to urge the spring seat (21) in the direction in which the volume of the pressure chamber (19) increases, and pressure is applied from the reservoir chamber (20) side. The pressure chamber (19) and the reservoir chamber (20) communicate with each other via a first passage (29) provided with a check valve (30) that allows only the flow of hydraulic oil to the chamber (19) side. A throttle (32) is provided to limit the oil flow rate. A cylindrical shape that communicates with the pressure chamber (19) and the reservoir chamber (20) through two passages (31), and that can be expanded and contracted vertically to cover the annular opening between the spring seat (21) and the cylinder (15). Rubber bellows (22), and the upper part (23) of the bellows (22) is fitted to the outer periphery of the spring seat (21) with a tight margin, and the lower part (25) of the bellows (22) is fitted to the cylinder ( 15) In an auto tensioner that is fitted to the outer periphery with a tightening margin,
The spring seat (21) is formed with a vent hole (36) communicating the reservoir chamber (20) and the outside air, and an air vent plug that is manually opened and closed at the end of the vent hole (36) on the outside air side. An auto tensioner provided with (37).   The air vent plug (37) includes a screw (38) that is screw-engaged with an internal thread formed on the inner periphery of the outside end of the vent hole (36), a head (38a) of the screw (38), and the The auto tensioner according to claim 1, comprising a gasket (39) sandwiched between the spring seats (21).   The auto tensioner according to claim 1, wherein the air vent plug (40) is a plug body (41) detachably fitted to an end portion on the outside air side of the vent hole (36).   The auto tensioner according to claim 3, wherein the plug (41) is provided with a head (41a) having a diameter larger than an inner diameter of an end of the vent hole (36) on the outside air side.   A plurality of protrusions (42) extending in the circumferential direction are formed on the outer periphery of the insertion portion of the plug body (41) into the vent hole (36) at intervals in the axial direction, and the protrusions (42) are formed through the passages. The auto tensioner according to claim 3 or 4, wherein the autotensioner (36) is fitted to the inner periphery of the pore (36) with a tightening margin.   The autotensioner according to any one of claims 3 to 5, wherein the plug (41) is made of rubber.   The autotensioner according to any one of claims 3 to 5, wherein the plug (41) is made of resin.   A cylinder (51) in which the air vent plug (50) is fitted into an end portion on the outside air side of the vent hole (36), a ball (52) accommodated in the cylinder (51), and the cylinder The auto tensioner according to claim 1, further comprising a spring (54) for pressing the ball (52) against an inward flange (53) formed at an end on the outside air side of the body (51).   The auto tensioner according to any one of claims 1 to 8, wherein an end on the outside air side of the vent hole (36) is opened to an outer periphery of the spring seat (21).   The second passage (31) is connected to the annular throttle gap (32) formed between the sliding surfaces of the rod (18) and the sleeve (16), and the inside of the rod (18) from the throttle gap (32). And an oil passage (33) communicating with the reservoir chamber (20) in order through the inside of the spring seat (21), and the electromagnetic on-off valve (35) of the second passage (31) is connected to the spring seat ( The auto tensioner according to any one of claims 1 to 9, which is incorporated in 21).

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