Lash adjuster

Abstract

To prevent entry of air included in working oil of an oil supply passage into a lash adjuster and thus maintain a function of the lash adjuster.SOLUTION: A body 11 includes: a body circumferential groove 15 recessed on an outer peripheral surface of a peripheral wall 14 over the whole circumference; a body hole 16 penetrating through the peripheral wall 14 and opening on a back surface 33 of the body circumferential groove 15; and a peripheral surface upper part 36 disposed above the body circumferential groove 15 on the outer peripheral surface of the peripheral wall 14. The peripheral surface upper part 36 of the peripheral wall 14 of the body 11 includes air vent grooves 38, 38A, 38B extending from a lower end communicating with the body circumferential groove 15 to an upper end communicating with the atmosphere on a front surface of a cylinder head 90.SELECTED DRAWING: Figure 4

Description

Technical Field

[0004] , ,

[0005] , ,

[0001] The present disclosure relates to a lash adjuster.

Background Art

[0002] Patent Document 1 discloses a lash adjuster including a cylindrical body and a plunger slidably fitted in the body. The body is fitted inside a mounting recess opening on the surface of a cylinder head. A body hole is formed through the peripheral wall of the body. A plunger hole is formed through the peripheral wall of the plunger. In a state where the body is fitted inside the mounting recess, the body hole faces the oil supply passage of the cylinder head, and hydraulic oil flowing through the oil supply passage through the body hole and the plunger hole is supplied into the lash adjuster. The plunger changes the amount of protrusion from the body by the hydraulic pressure of the hydraulic oil. A rocker arm supported by the plunger changes the swing fulcrum position according to the variation of the plunger, and automatically adjusts the valve clearance of the valve to be pressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, air such as bubbles may stay in the oil supply passage together with the hydraulic oil. If the air in the oil supply passage enters the high-pressure chamber of the body, the rigidity of the hydraulic oil filled in the high-pressure chamber decreases, so that the adjustment of the valve clearance by the lash adjuster may not be properly performed.

[0005] Therefore, an object of the present disclosure is to prevent air in the oil supply passage from entering the lash adjuster and maintain the function of the lash adjuster. [Means for solving the problem]

[0006] The lash adjuster of this disclosure comprises a cylindrical body and a plunger fitted into the body, wherein the body has a bottom wall, a peripheral wall rising from the bottom wall, a body peripheral groove recessed around the entire circumference of the peripheral wall, a body hole penetrating the peripheral wall and opening to the back surface of the body peripheral groove, and a peripheral upper surface positioned above the body peripheral groove on the peripheral surface of the peripheral wall, wherein the body is fitted into a mounting recess opening to the surface of the cylinder head so that the peripheral upper surface is in contact with the inner peripheral surface of the mounting recess, and the body peripheral groove is in communication with the oil supply passage of the cylinder head, hydraulic fluid is supplied to the interior from the oil supply passage through the body hole, and the plunger reciprocates and slides against the body by the hydraulic pressure of the hydraulic fluid, wherein the peripheral upper surface of the peripheral wall is provided with an air vent groove extending from a lower end communicating with the body peripheral groove to an upper end communicating with the atmosphere on the surface of the cylinder head. [Effects of the Invention]

[0007] According to this disclosure, it is possible to prevent air from the fuel supply passage from entering the lash adjuster and to maintain the function of the lash adjuster. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a cross-sectional view of a valve train including a lash adjuster according to Embodiment 1 of the present disclosure. [Figure 2] Figure 2 is a cross-sectional view of the lash adjuster according to Embodiment 1. [Figure 3] Figure 3 is a front view of the body of the lash adjuster according to Embodiment 1. [Figure 4] Figure 4 shows the relationship between the extension direction of the air vent groove and the flow direction of the hydraulic fluid flowing through the lubrication passage, with the lash adjuster of Embodiment 1 fitted into the mounting recess. [Figure 5]Figure 5 is a front view of the body of the lash adjuster according to Embodiment 2. [Figure 6] Figure 6 is a rear view of the body of the lash adjuster according to Embodiment 2. [Modes for carrying out the invention]

[0009] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described. The lash adjuster in this disclosure is (1) A lash adjuster comprising a cylindrical body and a plunger fitted inside the body, wherein the body has a bottom wall, a peripheral wall rising from the bottom wall, a body peripheral groove recessed around the entire circumference of the peripheral wall's outer surface, a body hole penetrating the peripheral wall and opening to the back surface of the body peripheral groove, and an upper peripheral surface on the outer surface of the peripheral wall positioned above the body peripheral groove, wherein the body is fitted into a mounting recess opening to the surface of the cylinder head so that the upper peripheral surface is in contact with the inner peripheral surface of the mounting recess, and the body peripheral groove is in communication with the oil supply passage of the cylinder head, hydraulic fluid is supplied to the interior from the oil supply passage through the body hole, and the plunger reciprocates and slides against the body by the hydraulic pressure of the hydraulic fluid, wherein an air vent groove is provided on the upper peripheral surface of the peripheral wall, extending from a lower end communicating with the body peripheral groove to an upper end communicating with the atmosphere on the surface of the cylinder head.

[0010] With the above configuration, air accumulated in the fuel supply passage is discharged into the atmosphere through the air vent groove, thereby preventing air from entering the lash adjuster. As a result, the valve clearance adjustment function of the lash adjuster is properly maintained.

[0011] (2) Preferably, the air vent groove is formed on the upper part of the circumferential surface of the circumferential wall so as to extend in a spiral shape in the circumferential direction.

[0012] According to the above configuration, it is possible to effectively suppress the hydraulic oil flowing through the oil supply passage from leaking to the atmosphere side through the air bleeding groove.

[0013] (3) It is preferable that the air bleeding groove is formed on the upper part of the peripheral surface of the peripheral wall so as to extend in either the clockwise or counterclockwise direction when viewed from above.

[0014] According to the above configuration, it is possible to apply a lash adjuster in which an air bleeding groove extending in either the clockwise or counterclockwise direction is formed according to the flow direction of the hydraulic oil flowing through the oil supply passage, and the air in the oil supply passage can be quickly discharged from the air bleeding groove to the atmosphere.

[0015] (4) The air bleeding groove may be formed on the upper part of the peripheral surface of the peripheral wall so as to extend in both the clockwise and counterclockwise directions when viewed from above.

[0016] According to the above configuration, it is possible to cope with specification changes such as a change in the flow direction of the hydraulic oil flowing through the oil supply passage, and the versatility and expandability can be enhanced.

[0017] (5) It is preferable that the lower end of the clockwise air bleeding groove and the lower end of the counterclockwise air bleeding groove coincide.

[0018] According to the above configuration, even if an air bleeding groove extending in both the clockwise and counterclockwise directions is formed, the air in the oil supply passage is smoothly discharged to the atmosphere through the air bleeding groove.

[0019] (6) It is preferable that the body hole of the peripheral wall is arranged at a position overlapping a vertical virtual line passing through the lower end of the air bleeding groove when viewed from the opening direction of the body hole.

[0020] According to the above configuration, the air in the oil supply passage smoothly enters the air bleeding groove and is efficiently discharged from the air bleeding groove to the atmosphere.

[0021] [Details of Embodiments of the Present Disclosure] Specific examples of the present disclosure will be described below with reference to the drawings. However, the present invention is not limited to these examples and is intended to be included in the claims, with all modifications in the sense and scope equivalent to the claims.

[0022] <Embodiment 1> The lash adjuster 10 in Embodiment 1 of this disclosure is a hydraulic lash adjuster and is provided in the valve train of an internal combustion engine.

[0023] (Valve train) As shown in Figure 1, the valve train comprises a cam 71 mounted on a camshaft 70 that rotates in sync with the internal combustion engine, a valve stem 81 mounted on a valve body 80, a rocker arm 60 that presses against the valve stem 81 by oscillating in accordance with the rotation of the cam 71, and a lash adjuster 10 that pivotably supports one end of the rocker arm 60.

[0024] The valve stem 81 is inserted into a through-hole 92 connected to the intake or exhaust port 91 of the cylinder head 90, and is biased by a coil spring 82 in a direction that closes the valve body 80. When the cam 71 rotates, the rocker arm 60 swings, and the valve stem 81 reciprocates within the through-hole 92, thereby causing the valve body 80 to open and close the intake or exhaust port 91.

[0025] The rocker arm 60 is supported at one end by the lash adjuster 10, and the other end is in contact with the valve stem 81. The cam 71 is rotatably in contact with a roller 61 provided between the one end and the other end.

[0026] (Structure of the lash adjuster) The lash adjuster 10 is inserted into a mounting recess 93 that opens on the upper surface of the cylinder head 90, with its axis oriented vertically. The mounting recess 93 communicates with the oil supply passage 94 (oil gallery) of the cylinder head 90. Hydraulic fluid flows through the oil supply passage 94 in the direction of the thickness of the paper in Figure 1.

[0027] As shown in Figure 2, the lash adjuster 10 comprises a bottomed cylindrical body 11 and a bottomed cylindrical plunger 12 housed within the body 11 so as to be able to reciprocate and slide vertically.

[0028] The plunger 12 consists of a disc-shaped bottom wall 17 and a peripheral wall 18 that rises from the outer circumference of the bottom wall 17 and tapers to a roughly hemispherical shape at its upper end. The upper end of the peripheral wall 18 of the plunger 12 is a support portion 19, and one end of the rocker arm 60 is supported on the hemispherical outer surface of the support portion 19 (see Figure 1). A top hole 21 is provided through the upper end of the support portion 19 in the vertical direction.

[0029] A plunger circumferential groove 24 is recessed around the entire circumference of the peripheral wall 18 of the plunger 12. The peripheral wall 18 of the plunger 12 is provided with a plunger oil hole 25 that penetrates the peripheral wall 18 in the thickness direction and opens to the back surface of the plunger circumferential groove 24. A circular valve hole 26 is provided in the radial center of the bottom wall 17 of the plunger 12, penetrating in the vertical direction.

[0030] The body 11 consists of a disc-shaped bottom wall 13 that is slightly larger than the bottom wall 17 of the plunger 12, and a circumferential wall 14 that rises from the outer circumference of the bottom wall 13. A body circumferential groove 15 is recessed around the entire circumference of the outer surface of the circumferential wall 14 of the body 11. The body circumferential groove 15 has a back surface 33 that runs in the vertical direction, and an upper side surface 34 and a lower side surface 35 that expand radially outward from the upper and lower ends of the back surface 33, respectively.

[0031] The peripheral wall 14 of the body 11 is provided with a body hole 16 that penetrates the peripheral wall 14 in the thickness direction and opens to the inner surface 33 of the body circumferential groove 15. As shown in Figure 3, the outer circumferential surface of the peripheral wall 14 of the body 11 has an upper circumferential surface 36 that extends around its entire circumference above the body circumferential groove 15. The upper circumferential surface 36 of the body 11 is a larger diameter circumferential surface portion than the inner surface 33 of the body circumferential groove 15, and its lower end intersects with the upper side surface 34 of the body circumferential groove 15. In addition, a retainer mounting groove 37 is recessed around the entire circumference of the outer circumferential surface of the peripheral wall 14 of the body 11 at the upper end of the peripheral wall 14, which is above the upper circumferential surface 36. A retainer 50 that restricts the upward movement of the plunger 12 is attached to the retainer mounting groove 37 (see Figure 2).

[0032] An air vent groove 38 is recessed in the upper circumferential surface 36 of the body 11, extending spirally in the circumferential direction from the lower end communicating with the body circumferential groove 15 to the upper end communicating with the retainer mounting groove 37. The air vent groove 38 has a V-shaped or U-shaped cross-section and is formed by machining or the like. In this embodiment 1, one air vent groove 38 is formed on the upper circumferential surface 36, extending almost completely around the entire height from the lower end to the upper end. The lower end of the air vent groove 38 opens to the upper side surface 34 of the body circumferential groove 15. The upper end of the air vent groove 38 opens to the lower side surface 39 of the retainer mounting groove 37.

[0033] When the body 11 is viewed from above, the extension direction L2 (see Figure 4) of the air vent groove 38 extending from the lower end to the upper end corresponds to the flow direction L1 of the hydraulic fluid flowing through the oil supply passage 94, and in the illustration, it is set to a counterclockwise direction. Depending on the flow direction L1 of the oil supply passage 94, the extension direction L2 of this air vent groove 38 may also be set to a clockwise direction.

[0034] The lower end of the air vent groove 38 is positioned directly above the body hole 16 so as to coincide with the body hole 16 in the circumferential direction. The upper end of the air vent groove 38 is positioned approximately at the same location as the lower end of the air vent groove 38 in the circumferential direction. As shown in Figure 3, when the body 11 is viewed from the front from the opening direction of the body hole 16, the body hole 16 is positioned so as to coincide with a virtual line VL in the vertical direction passing through the lower end of the air vent groove 38.

[0035] As shown in Figure 2, a high-pressure chamber 27 is provided in the lower part of the body 11, between the plunger 12 and its bottom wall 17. Inside the plunger 12, a low-pressure chamber 22 is partitioned above the bottom wall 17. The high-pressure chamber 27 houses a spherical valve body 28 that can move vertically to open and close the valve hole 26, a cage 29 that holds the valve body 28, a first spring 31 consisting of a compression coil spring housed in the cage 29 and biasing the valve body 28 toward the valve hole 26, and a second spring 32 consisting of a compression coil spring interposed between the outer peripheral edge of the cage 29 and the bottom wall 13 of the body 11 and biasing the plunger 12 upward. The valve body 28 is biased upward by the first spring 31 to close the valve hole 26.

[0036] (Assembly structure and operation of lash adjusters) When the lash adjuster 10 is fitted into the mounting recess 93, the upper end of the plunger 12 is positioned to protrude above the surface of the cylinder head 90. The upper end of the air vent groove 38, although located in the mounting recess, communicates with the atmosphere on the surface of the cylinder head 90 through a gap G formed radially outward of the retainer 50. The lower end of the air vent groove 38, together with the body circumference groove 15, communicates with the oil supply passage 94 of the cylinder head 90.

[0037] The hydraulic fluid flowing through the oil supply passage 94 of the cylinder head 90 is supplied to the low-pressure chamber 22 via the body circumferential groove 15, body hole 16, plunger circumferential groove 24, and plunger oil hole 25. Also, when the valve body 28 descends against the biasing force of the first spring 31 and the valve hole 26 opens, hydraulic fluid is filled from the low-pressure chamber 22 to the high-pressure chamber 27 through the valve hole 26.

[0038] When the internal combustion engine is driven, the cam 71 rotates and the rocker arm 60 is pressed from above via the roller 61. This presses the plunger 12 against one end of the rocker arm 60, causing it to move downward relative to the body 11 and compressing the hydraulic fluid in the high-pressure chamber 27. As the pressure in the high-pressure chamber 27 increases, the hydraulic fluid flows out through the gap between the plunger 12 and the circumferential walls 14 and 18 of the body 11 towards the plunger circumferential groove 24. As a result, the overall length of the lash adjuster 10 is shortened by the amount of hydraulic fluid that flows out of the high-pressure chamber 27. In addition, the increase in pressure in the high-pressure chamber 27 causes the hydraulic fluid (body 11 and plunger 12) to become rigid, defining the support position of the lash adjuster 10 relative to the rocker arm 60.

[0039] As the cam 71 rotates further and the pressing force from the cam 71 acting on the rocker arm 60 decreases, the plunger 12, receiving pressure from the high-pressure chamber 27 and the biasing force of the second spring 32, rises, and the upper end of the plunger 12 protrudes significantly from the body 11. As the pressure in the high-pressure chamber 27 decreases, the valve body 28 moves away from the valve hole 26, opening the valve hole 26, and hydraulic fluid flows from the low-pressure chamber 22 to the high-pressure chamber 27, extending the overall length of the lash adjuster 10. In this way, the lash adjuster 10 supports the rocker arm 60 in the correct position, adjusting the valve clearance between the cam 71 and the rocker arm 60 to be virtually zero.

[0040] Now, air bubbles and other particles may accumulate in the oil supply passage 94 of the cylinder head 90 along with the hydraulic fluid. If air enters the high-pressure chamber 27, the rigidification of the lash adjuster 10 may not be properly achieved, and there is a concern that the valve clearance adjustment function of the lash adjuster 10 may be impaired.

[0041] However, in this embodiment 1, the air in the oil supply passage 94 enters the air vent groove 38 and is discharged into the atmosphere from the air vent groove 38 (the image of the air is shown by the symbol A in Figure 4). In particular, in this embodiment 1, as shown in Figure 4, the extension direction L2 of the air vent groove 38, which extends from the lower end to the upper end, is oriented in a direction that is obtuse with respect to the flow direction L1 of the hydraulic fluid flowing through the oil supply passage 94. The flow direction L1 of the hydraulic fluid corresponds to the rotation direction of the body 11 within the mounting recess 93. Therefore, the air that accumulates near the opening of the body hole 16 rises smoothly from the lower end to the upper end of the air vent groove 38 and is quickly discharged into the atmosphere.

[0042] As described above, according to this embodiment 1, air accumulated in the fuel supply passage 94 is discharged to the atmosphere through the air vent groove 38, thereby preventing air from entering the lash adjuster 10. As a result, the valve clearance adjustment function of the lash adjuster 10 is properly maintained.

[0043] Furthermore, the air vent groove 38 is formed on the upper part 36 of the circumferential surface of the peripheral wall 14 of the body 11, extending spirally in the circumferential direction. This effectively prevents the hydraulic fluid flowing through the oil supply passage 94 from leaking out into the atmosphere through the air vent groove 38. In particular, since the extension direction L2 of the air vent groove 38 is oriented at an obtuse angle with respect to the hydraulic fluid flow direction L1, the hydraulic fluid is less likely to rise up through the air vent groove 38 and is more likely to enter the body hole 16.

[0044] Furthermore, since the air vent groove 38 is formed on the upper part 36 of the circumferential surface of the peripheral wall 14 of the body 11, extending in either a clockwise or counterclockwise direction when viewed from above, air from the fuel supply passage 94 can be quickly discharged into the atmosphere through the air vent groove 38.

[0045] Furthermore, since the body hole 16 is positioned to coincide with a virtual vertical line VL passing through the lower end of the air vent groove 38 in a front view of the body 11, air from the fuel supply passage 94 enters the air vent groove 38 without obstruction and is discharged more efficiently from the air vent groove 38 into the atmosphere.

[0046] <Embodiment 2> Embodiment 2 of this disclosure differs from Embodiment 1 in that, as shown in Figures 5 and 6, two air vent grooves 38A and 38B extending in different directions are recessed in the peripheral wall 14 of the body 11. Since the other aspects are the same as Embodiment 1, the same reference numerals are used for components identical or corresponding to those in Embodiment 1, and redundant descriptions are omitted. The two air vent grooves are composed of a first air vent groove 38A that extends in a counterclockwise spiral direction when viewed from above the body 11, and a second air vent groove 38B that extends in a clockwise spiral direction. Both the first air vent groove 38A and the second air vent groove 38B are formed to extend approximately around the entire height of the upper circumferential surface 36, from their lower ends that open to the upper side surface 34 of the body circumferential groove 15 to their upper ends that open to the lower side surface 39 of the retainer mounting groove 37. As shown in Figure 5, the lower ends of the first air vent groove 38A and the second air vent groove 38B are in communication with each other directly above the body hole 16. The upper ends of the first air vent groove 38A and the second air vent groove 38B are symmetrically arranged on both sides in the circumferential direction, separated by a virtual line VL that runs vertically through the lower ends of the first air vent groove 38A and the second air vent groove 38B. In this embodiment 2, the dashed line VL passes through the center of the body hole 16. As shown in Figure 6, when the body 11 is viewed from the side opposite to the side where the body hole 16 opens, the first air vent groove 38A and the second air vent groove 38B intersect each other in an X shape at the center of the upper part 36 of the circumferential surface in the height direction.

[0047] When the lash adjuster 10 is fitted into the mounting recess 93, the upper ends of the first air vent groove 38A and the second air vent groove 38B communicate with the atmosphere on the surface of the cylinder head 90, and the lower ends of the first air vent groove 38A and the second air vent groove 38B communicate with the oil supply passage 94 of the cylinder head 90 together with the body circumference groove 15 (see Figure 1, although this is Embodiment 1). Here, regardless of the direction of the hydraulic fluid flow direction L1 in the oil supply passage 94, the extension direction L2 of either the first air vent groove 38A or the second air vent groove 38B, extending from its lower end to its upper end, can be oriented in a direction that forms an obtuse angle with the hydraulic fluid flow direction L1. As a result, air accumulated near the opening of the body hole 16 is efficiently and quickly discharged from either the first air vent groove 38A or the second air vent groove 38B into the atmosphere on the surface of the cylinder head 90.

[0048] According to Embodiment 2, the lash adjuster 10 can be assembled to the cylinder head 90 without having to worry about the flow direction L1 of the hydraulic fluid flowing through the oil supply passage 94. Therefore, it can accommodate specification changes such as a change in the flow direction L1 of the hydraulic fluid flowing through the oil supply passage 94, thereby increasing versatility and expandability. In particular, since the lower ends of the first air vent groove 38A and the second air vent groove 38B are aligned, air in the oil supply passage 94 can be discharged to the atmosphere without obstruction from either the first air vent groove 38A or the second air vent groove 38B.

[0049] [Other embodiments of this disclosure] Embodiments 1 and 2 disclosed herein should be considered in all respects to be illustrative and not restrictive. In Embodiments 1 and 2 described above, the air vent groove was configured to have a length that approximately completed one full rotation around the upper part of the circumferential surface of the body's peripheral wall. In contrast, in other embodiments, the air vent groove may be configured to have a length of approximately half a rotation, approximately one and a half rotations, or approximately two rotations around the upper part of the circumferential surface of the body's peripheral wall. From the viewpoint of moldability and air venting efficiency, it is preferable that the air vent groove be configured to have a length that approximately completed one full rotation around the upper part of the circumferential surface of the body's peripheral wall. However, the length of the air vent groove is not particularly limited to the lengths described above. In Embodiments 1 and 2 described above, the upper end of the air vent groove reached the upper end of the circumferential surface so as to communicate with the retainer mounting groove. In contrast, in the other embodiments, the upper end of the air vent groove does not need to communicate with the retainer mounting groove and does not need to reach the upper end of the circumferential surface. In short, the upper end of the air vent groove only needs to be formed on the upper circumferential surface so as to communicate with the atmosphere on the surface of the cylinder head. [Explanation of Symbols]

[0050] 10...Lash adjuster 11…Body 12…Plunger 13…Bottom wall (of the body) 14…(body) peripheral wall 15… Grooves around the body 16…Body holes 17…Bottom wall (of the plunger) 18…(The) surrounding wall of the plunger 19...Support part 21...apex hole 22... Low-pressure room 24…Plunger surrounding groove 25…Plunger oil hole 26… Valve opening 27…High-pressure room 28… Valve body 29... Cage 31…First Spring 32…2nd Spring 33…back side 34…Upper side 35…Lower side (of the groove around the body) 36... Upper part of the perimeter 37…Retainer mounting groove 38, 38A, 38B... Air vent groove 39…Lower side (of the retainer mounting groove) 50…Retainer 60... Rocker arm 61... Laura 70... Camshaft 71... Cam 80... Valve body 81… Valve stem 82... Coil spring 90... Cylinder head 91... Exhaust port 92…Through hole 93…Mounting recess 94... Refueling route A... Air image G... Gap L1... Flow direction L2… Direction of extension VL…Virtual Line

Claims

1. It comprises a cylindrical body and a plunger fitted inside the body, The body comprises a bottom wall, a peripheral wall rising from the bottom wall, a body circumferential groove recessed around the entire circumference of the peripheral wall's outer surface, a body hole penetrating the peripheral wall and opening to the inner surface of the body circumferential groove, and an upper circumferential surface portion of the peripheral wall positioned above the body circumferential groove on its outer surface. A lash adjuster is provided in which the body is fitted into a mounting recess opening on the surface of the cylinder head, the upper part of the circumferential surface facing the inner circumferential surface of the mounting recess so as to be in contact with it, and the circumferential groove of the body is in communication with the oil supply passage of the cylinder head, hydraulic fluid is supplied to the interior from the oil supply passage through the hole in the body, and the plunger reciprocates and slides against the body by the hydraulic pressure of the hydraulic fluid, A lash adjuster is provided with an air vent groove on the upper part of the circumferential surface of the circumferential wall, extending from a lower end communicating with the body circumferential groove to an upper end communicating with the atmosphere on the surface of the cylinder head.

2. The lash adjuster according to claim 1, wherein the air vent groove is formed on the upper part of the circumferential surface of the circumferential wall so as to extend spirally in the circumferential direction.

3. The lash adjuster according to claim 2, wherein the air vent groove is formed on the upper part of the circumferential surface of the circumferential wall so as to extend in either a clockwise or counterclockwise direction when viewed from above.

4. The lash adjuster according to claim 2, wherein the air vent groove is formed on the upper part of the circumferential surface of the circumferential wall so as to extend in both clockwise and counterclockwise directions when viewed from above.

5. The lash adjuster according to claim 4, wherein the lower end of the clockwise air vent groove and the lower end of the counterclockwise air vent groove coincide.

6. The lash adjuster according to any one of claims 1 to 5, wherein the body hole in the peripheral wall is positioned so as to coincide with a virtual line in the vertical direction passing through the lower end of the air vent groove when viewed from the opening direction of the body hole.

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