Lash adjuster

Abstract

Even when the bubble rate in the hydraulic fluid supplied to the lash adjuster is relatively high, functional loss can be suppressed. [Solution] The lash adjuster 10 comprises a cylindrical body 11, a plunger 12 having a bottom wall 17 and a peripheral wall 18 and slidably positioned within the body 11 to move in the axial direction, forming a high-pressure chamber 27 between itself and the body 11 and a low-pressure chamber 22 inside, with a valve hole 26 in the bottom wall 17 that connects the high-pressure chamber 27 and the low-pressure chamber 22, and a valve body 28 positioned within the high-pressure chamber 27 that opens and closes the valve hole 26 by moving toward and away from a valve seat 26A formed on the opening edge of the valve hole 26 on the lower surface of the bottom wall 17, and a bubble coupling portion 50 is provided around the valve seat 26A to combine fine bubbles in the hydraulic fluid and increase the bubble diameter.

Description

Technical Field

[0001] This disclosure relates to a lash adjuster.

Background Art

[0002] Patent Document 1 discloses a conventional lash adjuster. In this type of lash adjuster, so-called air biting may occur where air flows into the high-pressure chamber. In this case, when the lash adjuster receives a pressing force from the rocker arm side, the air in the high-pressure chamber cannot be compressed and rigidified, and the function of stably supporting the rocker arm is impaired. The lash adjuster of Patent Document 1 forms a tapered surface that rises toward the valve hole on the lower surface of the bottom of the plunger, so as to collect the air bubbles in the high-pressure chamber around the valve seat and make it easier for them to escape to the low-pressure chamber, suppressing the occurrence of functional loss.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The mechanisms for generating air biting are as follows. One is when there is insufficient oil volume in the low-pressure chamber, that is, when the low-pressure chamber is filled with air. In this case, the working oil flows into the high-pressure chamber from the valve hole so that the working oil is properly supplied to the low-pressure chamber, and the air is discharged from the valve hole to the low-pressure chamber in exchange, thereby being eliminated.

[0005] Another possibility is a relatively high bubble ratio in the hydraulic fluid. For example, if bubbles are drawn in along with the hydraulic fluid in an oil pan strainer, hydraulic fluid with a relatively high bubble ratio will flow through the oil supply passage. Such hydraulic fluid contains relatively small bubbles. The smaller the diameter of the bubbles, the lower their buoyancy rate. Therefore, when hydraulic fluid with a relatively high bubble ratio flows into the high-pressure chamber, the small bubbles within it are difficult to discharge into the low-pressure chamber. Consequently, if hydraulic fluid with a relatively high bubble ratio is continuously supplied, the small bubbles that are difficult to discharge will also continuously flow in and gradually accumulate in the high-pressure chamber. If these small bubbles accumulate at the outer edge of the high-pressure chamber, discharge becomes even more difficult, which may lead to a loss of function in the lash adjuster.

[0006] This disclosure aims to address the problem of suppressing functional loss even when the bubble rate in the hydraulic fluid supplied to the lash adjuster is relatively high.

[0007] A lash adjuster according to one embodiment of the present disclosure comprises a cylindrical body, a plunger having a bottom wall and a peripheral wall and slidably disposed within the body in the axial direction, forming a high-pressure chamber between itself and the body and a low-pressure chamber inside, and having a valve hole in the bottom wall that connects the high-pressure chamber and the low-pressure chamber, and a valve body disposed within the high-pressure chamber that opens and closes the valve hole by moving toward and away from a valve seat formed on the opening edge of the valve hole on the lower surface of the bottom wall, wherein a bubble coupling portion is provided around the valve seat to combine with fine bubbles in the hydraulic fluid and increase the bubble diameter. [Effects of the Invention]

[0008] According to this disclosure, functional loss can be suppressed even when the bubble rate in the hydraulic fluid is relatively high. [Brief explanation of the drawing]

[0009] [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 magnified view of the main part of Figure 2. [Figure 4] Figure 4 is a diagram illustrating the operation of the lash adjuster in Embodiment 1. [Figure 5] Figure 5 is a diagram illustrating the lash adjuster of Embodiment 2, showing a magnified view of the main parts. [Figure 6] Figure 6 is a diagram illustrating the lash adjuster of Embodiment 3, showing a magnified view of the main parts. [Modes for carrying out the invention]

[0010] [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; a plunger having a bottom wall and a peripheral wall, slidably disposed within the body in the axial direction, forming a high-pressure chamber between itself and the body and a low-pressure chamber inside, with a valve hole in the bottom wall connecting the high-pressure chamber and the low-pressure chamber; and a valve body disposed within the high-pressure chamber, which opens and closes the valve hole by moving toward and away from a valve seat formed on the opening edge of the valve hole on the lower surface of the bottom wall, wherein a bubble coupling portion is provided around the valve seat to combine with fine bubbles in the hydraulic fluid and increase the bubble diameter.

[0011] According to the above configuration, the bubble coupling section can combine the fine bubbles that flow into the high-pressure chamber, thereby increasing the bubble diameter. Furthermore, since the bubble coupling section can combine the fine bubbles that flow into the high-pressure chamber around the valve seat, the enlarged bubbles can be efficiently discharged from the valve opening. Therefore, even if fine bubbles are mixed in the hydraulic fluid, functional loss can be suppressed.

[0012] (2) In (1) above, the bubble bonding portion may be a recess provided on the lower surface of the bottom wall. This configuration makes it possible to realize a bubble bonding portion with a simple structure that can be easily formed. The recess can store air with a relatively simple structure. Furthermore, the lash adjuster can be manufactured by forging, cutting, etc. For this reason, if the bubble bonding portion is a recess on the lower surface of the bottom wall, it is possible to simultaneously form the concave bubble bonding portion when manufacturing the plunger by these processing methods such as forging and cutting, making manufacturing easy.

[0013] (3) In (2) above, the recess is preferably an annular groove that surrounds the entire circumference of the valve seat. With this configuration, fine bubbles in the hydraulic fluid that flow into the high-pressure chamber through the valve hole are well coupled and enlarged in the recess around the entire circumference of the valve hole, making it difficult for them to reach the outer edge of the high-pressure chamber. As a result, the formation of bubble accumulation at the outer edge of the high-pressure chamber where bubbles are difficult to discharge can be suppressed, and functional loss can be suppressed.

[0014] (4) In any of (1) to (3) above, a retainer is provided which is attached to the lower surface of the bottom wall and holds the valve body, and the bubble coupling portion is provided between the contact portion with the retainer in the radial direction on the lower surface of the bottom wall and the valve seat. In this case, fine bubbles in the hydraulic fluid that flow into the high-pressure chamber through the valve hole are more likely to be coupled and enlarged in diameter by the bubble coupling portion inside the retainer. For example, if fine bubbles are outside the retainer and remain at the outer edge of the high-pressure chamber, they are more difficult to discharge compared to when they remain towards the center. In this case, the fine bubbles can be coupled and enlarged in diameter at the outer edge of the high-pressure chamber. Also, bubbles outside the retainer are more likely to remain outside the retainer because their movement toward the valve hole is easily obstructed by the retainer. In contrast, if the bubble coupling portion is inside the retainer, fine bubbles are more likely to be coupled and enlarged in diameter inside the retainer and less likely to flow out to the outside of the retainer. As a result, air bubbles can be continuously expelled, and functional loss can be suppressed.

[0015] (5) In any one of the above (1) to (4), the bubble coupling portion may be provided adjacent to an inclined surface that slopes upward toward the valve seat. According to this configuration, bubbles enlarged in diameter at the bubble coupling portion can be well guided in the direction of the valve seat by the inclination of the adjacent inclined surface, and the discharge of bubbles can be promoted.

[0016] (6) In any one of the above (1) to (4), the bubble coupling portion may be provided on an inclined surface that slopes upward toward the valve seat. According to this configuration, bubbles enlarged in diameter at the bubble coupling portion can be well guided in the direction of the valve seat by the inclination of the inclined surface, and the discharge of bubbles can be promoted.

[0017] [Details of Embodiments of the Present Disclosure] Specific examples of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to this exemplification, and is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0018] <Embodiment 1> The lash adjuster 10 of Embodiment 1 of the present disclosure is a hydraulic lash adjuster and is provided in the valve actuating device of an internal combustion engine.

[0019] (Valve Actuating Device) As shown in FIG. 1, the valve actuating device includes a cam 71 provided on a camshaft 70 that rotates in synchronization with the internal combustion engine, a valve stem 81 provided on a valve body 80, a rocker arm 60 that presses the valve stem 81 by swinging in response to the rotation of the cam 71, and a lash adjuster 10 that swingably supports one end of the rocker arm 60.

[0020] The valve stem 81 is inserted into a through-hole 92 connected to an 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.

[0021] 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.

[0022] (Structure of the lash adjuster) The lash adjuster 10 is inserted with its axis oriented vertically into a mounting recess 93 that opens on the upper surface of the cylinder head 90. The mounting recess 93 communicates with the oil supply passage 94 of the cylinder head 90. The oil supply passage 94 is a flow path formed inside the cylinder head 90. The oil supply passage 94 supplies hydraulic fluid, which is lubricating oil, to various parts of the internal combustion engine, including the lash adjuster 10. The oil supply passage 94 communicates with an oil pump (not shown) upstream. Pressure from this oil pump acts on the hydraulic fluid in the oil supply passage 94. The hydraulic fluid flows through the oil supply passage 94 according to the pressure difference.

[0023] 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. The lash adjuster 10 extends when the plunger 12 moves in a direction that protrudes relative to the body 11, and retracts when the plunger 12 moves in the opposite direction.

[0024] The body 11 consists of a disc-shaped bottom wall 13 and a peripheral wall 14 rising from the outer circumference of the bottom wall 13. A body peripheral groove 15 is recessed around the entire circumference of the outer peripheral surface of the peripheral wall 14 of the body 11. A body hole 16 is opened at the back of the body peripheral groove 15, penetrating the peripheral wall 14 of the body 11 in the thickness direction. The outer peripheral surface of the peripheral wall 14 slidably contacts the inner peripheral surface of the mounting recess 93 when the lash adjuster 10 is fitted into the mounting recess 93. In addition, a restricting member R is attached to the upper end of the peripheral wall 14 of the body 11 to restrict the upward movement of the plunger 12 (see Figure 2).

[0025] 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. A recess 12A that is recessed upward is formed in the lower part of the plunger 12. A retainer 29, which will be described later, is press-fitted into the recess 12A.

[0026] 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 valve hole 26 with a circular cross-section is provided in the radial center of the bottom wall 17 of the plunger 12, penetrating vertically. A valve seat 26A is formed at the opening edge of the valve hole 26 on the lower surface of the bottom wall 17. The valve hole 26 is opened and closed by the movement of a valve body 28 (described later) toward and away from the valve seat 26A.

[0027] 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 the 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 retainer 29 that holds the valve body 28, a first spring 31 consisting of a compression coil spring housed in the retainer 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 retainer 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. The valve body 28 moves vertically in accordance with the balance between the hydraulic pressure fluctuations in the high-pressure chamber 27 and the biasing force of the first spring 31, opening and closing the valve hole 26. When the valve hole 26 of the lash adjuster 10 is open, the hydraulic fluid in the low-pressure chamber 22 flows through the valve hole 26 to the high-pressure chamber 27.

[0028] The retainer 29 has a so-called hat-shaped (brimmed cap-shaped) external form that opens upward. The valve body 28 is housed in the space inside the retainer 29. The retainer 29 houses the valve body 28 while allowing it to move as the valve hole 26 opens and closes. The retainer 29 has multiple notches formed circumferentially and evenly spaced to connect the internal and external spaces and allow the inflow and outflow of hydraulic fluid. The retainer 29 is mounted on the lower surface of the bottom wall 17 of the plunger 12. In detail, the retainer 29 has a cylindrical portion 29A that is bottomed and houses the valve body 28, and a flange-shaped portion 29B that extends outward from the upper end of the cylindrical portion 29A. The cylindrical portion 29A and the flange-shaped portion 29B are arranged coaxially on the central axis of the retainer 29.

[0029] The retainer 29 is press-fitted into the recess 12A at the lower part of the plunger 12 at the outer peripheral edge of the flange-like portion 29B. As shown in Figure 2, when the retainer 29 is press-fitted into the recess 12A, it contacts the lower surface of the bottom wall 17 at the contact portion C. In this disclosure, "contact" at the contact portion includes the state in which the upper end of the retainer is slightly separated from the lower surface of the bottom wall, assuming that the retainer 29 is press-fitted into the recess 12A at the outer edge of the flange-like portion 29B as in this embodiment. In other words, the contact portion in this disclosure is the part in which the upper end of the retainer and the lower surface of the bottom wall of the plunger are closest.

[0030] As shown in Figure 3, a sloped portion 40 is formed on the lower part of the bottom wall 17. More specifically, the sloped portion 40 is formed on the opening edge of the valve hole 26 on the high-pressure chamber 27 side. The sloped portion 40 forms an inclined surface that widens as it extends downwards at the opening edge of the valve hole 26. In other words, the inclined surface formed by the surface of the sloped portion 40 is an annular inclined surface that extends towards the center as it goes upwards from the lower surface of the bottom wall 17. In this embodiment, the sloped portion 40 forms an inclined surface with a straight cross-section. The valve seat 26A is set on the inclined surface formed by the sloped portion 40.

[0031] The lash adjuster 10 is equipped with a bubble coupling portion 50. The bubble coupling portion 50 couplings fine bubbles in the hydraulic fluid to increase the bubble diameter. As shown in Figure 3, the bubble coupling portion 50 is provided around the valve seat 26A. More specifically, in this embodiment, the bubble coupling portion 50 is a recess provided on the lower surface of the bottom wall 17. The bubble coupling portion 50 is an annular groove in which the lower surface of the bottom wall 17 is recessed upward. The bubble coupling portion 50 surrounds the entire circumference of the valve seat 26A. The annular groove, the bubble coupling portion 50, is formed substantially coaxially with the central axis of the valve hole 26.

[0032] As shown in Figures 3 and 4, the bubble bonding portion 50 is formed on the inclined surface portion 40. More specifically, the bubble bonding portion 50 is formed on the inclined surface of the inclined surface portion 40. In other words, the bubble bonding portion 50 opens to the surface of the inclined surface portion 40 on the radially central side. That is, the bubble bonding portion 50 in this embodiment is a groove that opens in two directions: towards the center and downward.

[0033] (The action of the lash adjuster) As shown in Figures 1 and 2, when the lash adjuster 10 is fitted into the mounting recess 93, the body circumferential groove 15 in the body 11 is positioned to face the oil supply passage 94. The hydraulic fluid in the oil supply passage 94 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.

[0034] 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.

[0035] 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.

[0036] If air bubbles enter the high-pressure chamber 27 along with the hydraulic fluid, there is a risk of air trapping occurring within the high-pressure chamber 27. In the lash adjuster 10, air bubbles that enter the high-pressure chamber 27 float up and gather around the valve seat 26A, and are discharged into the low-pressure chamber 22 when the valve is opened. Specifically, when the valve hole 26 is opened and hydraulic fluid flows into the high-pressure chamber 27, the air bubbles around the valve seat 26A escape to the low-pressure chamber 22, being replaced by the hydraulic fluid flowing from the low-pressure chamber 22 into the high-pressure chamber 27. However, if the air bubbles in the hydraulic fluid are so-called microbubbles, as described above, they are difficult to float up in the hydraulic fluid and are difficult to escape to the low-pressure chamber 22 against the flow of hydraulic fluid entering through the gap between the valve body 28 and the valve seat 26A.

[0037] In this first embodiment, the lash adjuster 10 is equipped with a bubble coupling portion 50. The bubble coupling portion 50 is provided in the area surrounding the valve seat 26A. More specifically, the bubble coupling portion 50 is formed on a slope of the inclined surface portion 40 that slopes upward toward the valve seat 26A. As a result, as shown in Figure 4, bubbles in the hydraulic fluid flowing in from the gap between the valve body 28 and the valve seat 26A pass through the gap along the slope of the inclined surface portion 40, then their flow velocity decreases and they accumulate in the bubble coupling portion 50. The fine bubbles accumulated in the bubble coupling portion 50 combine with each other, gradually increasing the bubble diameter. Bubbles whose diameter exceeds a certain size flow from the bubble coupling portion 50 toward the inclined surface portion 40, and when the valve opens, they slip between the valve seat 26A and the valve body 28 and are discharged toward the low-pressure chamber 22. Furthermore, since the bubble coupling portion 50 is formed on the slope of the slope portion 40, the enlarged bubble is well guided from the bubble coupling portion 50 toward the valve seat 26A, thereby promoting the discharge of the bubble.

[0038] As described above, according to this embodiment 1, the bubble coupling portion 50 can combine the fine bubbles that have flowed into the high-pressure chamber 27, thereby increasing the bubble diameter. Furthermore, since the bubble coupling portion 50 can combine the fine bubbles that have flowed into the high-pressure chamber 27 around the valve seat 26A, the enlarged bubbles can be efficiently discharged from the valve hole 26. Therefore, the lash adjuster 10 can suppress functional loss even when the bubble ratio in the supplied hydraulic fluid is relatively high.

[0039] Furthermore, in the lash adjuster 10, the bubble bonding portion 50 is a recess provided on the lower surface of the bottom wall 17 of the plunger 12. Therefore, the lash adjuster 10 can be formed simultaneously during the manufacturing of the plunger 12, for example, by forging, cutting, etc. In this way, the lash adjuster 10 can realize a bubble bonding portion with a simple structure that can be easily formed.

[0040] Furthermore, the lash adjuster 10 is equipped with a retainer 29 that is mounted on the lower surface of the bottom wall 17 of the plunger 12 and holds the valve body 28. The bubble coupling portion 50 is provided between the contact portion with the retainer 29 in the radial direction on the lower surface of the bottom wall 17 and the valve seat 26A. With this configuration, fine bubbles in the hydraulic fluid that flow into the high-pressure chamber 27 through the valve hole 26 are easily coupled and enlarged in diameter by the bubble coupling portion 50 inside the retainer 29 and are less likely to move to the outside of the retainer 29. As a result, the lash adjuster 10 is easily discharged into the low-pressure chamber 22, and the accumulation of bubbles outside the retainer 29 can be suppressed, thereby suppressing loss of function.

[0041] Furthermore, in the lash adjuster 10, the bubble coupling portion 50 is an annular groove that surrounds the entire circumference of the valve seat 26A. As a result, fine bubbles in the hydraulic fluid that flow into the high-pressure chamber 27 through the valve hole 26 are well coupled and enlarged in the bubble coupling portion 50 around the entire circumference of the valve hole 26, making it difficult for them to reach the outer edge of the high-pressure chamber 27. Consequently, the lash adjuster 10 can suppress the formation of bubble accumulation at the outer edge of the high-pressure chamber 27 where bubbles are difficult to discharge, thereby suppressing functional loss.

[0042] Furthermore, in the lash adjuster 10, the bubble coupling portion 50 is provided on the slope of the surface of the inclined portion 40. This slope is inclined upward toward the valve seat 26A. Therefore, the lash adjuster 10 can effectively guide the enlarged bubble in the bubble coupling portion 50 toward the valve seat 26A by the inclination of the slope, thereby promoting the discharge of the bubble.

[0043] <Embodiment 2> Embodiment 2 of this disclosure, as shown in Figure 5, replaces the bubble coupling portion 50 of Embodiment 1 with a bubble coupling portion 250. The bubble coupling portion 250 is similar to the bubble coupling portion 50 of Embodiment 1 in that it is a recess provided on the lower surface of the bottom wall 17, located around the valve seat 26A. The bubble coupling portion 250 differs from Embodiment 1 in that it is provided adjacent to the inclined surface portion 40. Otherwise, it is the same as Embodiment 1, so the same reference numerals are used for components that are the same as or equivalent to those in Embodiment 1, and redundant explanations are omitted.

[0044] As shown in Figure 5, the bubble coupling portion 250 is adjacent to the radially outer side of the lower end of the inclined surface portion 40. As a result, the bubble coupling portion 250 has a groove shape that opens only downwards. The bubble coupling portion 250 accumulates bubbles in its inner space as bubbles that flow into the high-pressure chamber 27 float up in the hydraulic fluid. The bubble coupling portion 250 is set to be a space of sufficient size to function adequately as a lash adjuster even when the entire inner space is filled with air.

[0045] In this embodiment, the fine bubbles that flow into the high-pressure chamber 27 rise to the surface before reaching the outer edge of the high-pressure chamber 27, and remain in the bubble coupling section 250, where they sequentially combine to form larger bubbles. When air accumulates in the bubble coupling section 250, newly flowing bubbles can rise to the surface and combine with the air in the bubble coupling section 250 at an early stage. As the bubbling process progresses and bubbles begin to leak out of the bubble coupling section 250, the leaked bubbles are guided along the slope of the inclined surface 40 toward the valve seat 26A, similar to Embodiment 1, thereby promoting the discharge of bubbles.

[0046] <Embodiment 3> Embodiment 3 of this disclosure, as shown in Figure 6, is provided with a bubble coupling portion 250 similar to that of Embodiment 2. The bubble coupling portion 250 is provided adjacent to the inclined surface portion 340. Unlike the inclined surface portion 40 of Embodiments 1 and 2, which has a straight inclined surface on its surface, the inclined surface portion 340 has an arc-shaped inclined surface on its surface. In detail, the arc-shaped inclined surface formed on the surface of the inclined surface portion 340 is a so-called R-chamfered inclined surface that smoothly connects the inner circumferential surface of the valve hole 26 and the lower surface of the bottom wall 17. In this case as well, the same functions and effects as those of each of the above embodiments are achieved. Furthermore, since the angle of inclination of the arc-shaped inclined surface gradually changes so that the angle of inclination becomes larger as it goes upward, bubbles leaking from the bubble coupling portion 350 can be effectively guided to the area around the valve seat 26A.

[0047] [Other embodiments of this disclosure] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The bubble coupling portion only needs to be provided around the valve seat and have the function of coupling fine bubbles in the hydraulic fluid to increase the bubble diameter; its configuration and other aspects are not limited to those exemplified in the above embodiments. If the bubble bonding portion is a recess, its shape is not limited to the groove shape exemplified in each of the above embodiments, but may be a simple hole (bottomed hole). In this case, the bubble bonding portion may consist of only one bottomed hole, or it may consist of multiple bottomed holes. If the bubble bonding portion consists of multiple bottomed holes, each bottomed hole may be arranged in a ring around the valve seat so as to surround the valve seat. One example of a bubble bonding area is one in which the surface of the area around the valve seat on the lower surface of the plunger's bottom wall is made rough. In this case, other microbubbles that rise to the surface can sequentially come into contact with and bond with microbubbles that are attached to and caught on the rough surface, thereby increasing their diameter. [Explanation of Symbols]

[0048] 10...Lash adjuster 11…Body 12…Plunger 13...Bottom wall 14...Peripheral wall 17...Bottom wall 18...Peripheral wall 22... Low-pressure room 26… Valve opening 26A…Valve seat 27…High-pressure room 28… Valve body 29…Retainer 50, 250, 350... Bubble bonding part C…Contact site

Claims

1. A cylindrical body, A plunger having a bottom wall and a peripheral wall, slidably positioned within the body in the axial direction, forming a high-pressure chamber between itself and the body, and a low-pressure chamber inside, with a valve hole in the bottom wall connecting the high-pressure chamber and the low-pressure chamber, A lash adjuster comprising a valve body disposed in the high-pressure chamber and opening and closing the valve hole by moving toward and away from a valve seat formed on the opening edge of the valve hole on the lower surface of the bottom wall, A lash adjuster is provided with a bubble coupling portion around the valve seat, which combines fine bubbles in the hydraulic fluid to increase the bubble diameter.

2. The lash adjuster according to claim 1, wherein the bubble bonding portion is a recess provided on the lower surface of the bottom wall.

3. The lash adjuster according to claim 2, wherein the recess is an annular groove that surrounds the entire circumference of the valve seat.

4. It is equipped with a retainer that is attached to the lower surface of the bottom wall and holds the valve body, The lash adjuster according to claim 1, wherein the bubble bonding portion is provided between the contact portion with the retainer in the radial direction on the lower surface of the bottom wall and the valve seat.

5. The lash adjuster according to any one of claims 1 to 4, wherein the bubble bonding portion is provided adjacent to an inclined surface that slopes upward toward the valve seat.

6. The lash adjuster according to any one of claims 1 to 4, wherein the bubble bonding portion is provided on an inclined surface that slopes upward toward the valve seat.

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