Lash adjuster and method for manufacturing a lash adjuster

Abstract

This product provides a lash adjuster that can ensure an appropriate leak-down value in response to temperature changes. [Solution] The lash adjuster 10 comprises a cylindrical body 11 and a cylindrical plunger 12 slidably disposed within the body 11. A high-pressure chamber 35 is provided between the body 11 and the plunger 12, and a low-pressure chamber 26 is provided inside the plunger 12. A valve hole 34 is provided on the bottom surface of the plunger 12, connecting the high-pressure chamber 35 and the low-pressure chamber 26. A leak passage 38 is provided between the inner circumferential surface of the body 11 and the outer circumferential surface of the plunger 12, through which the hydraulic fluid filled in the high-pressure chamber 35 leaks. Either the body 11 or the plunger 12 has a bimetallic portion 39 that deforms in a direction that narrows the leak passage 38 in response to a rise in temperature.

Description

Technical Field

[0001] The present disclosure relates to a lash adjuster and a method for manufacturing a lash adjuster.

Background Art

[0002] The lash adjuster described in Patent Document 1 includes a cylindrical body and a plunger slidably disposed within the body. A leak passage through which hydraulic oil can leak is defined between the inner peripheral side of the body and the outer peripheral side of the plunger. The plunger has a dividable structure and includes a first member that is the lower part of the plunger and forms the leak passage, and a second member that is the upper part of the plunger. The first member is made of a material having a larger linear expansion coefficient than that of the body. Further, the first member and the second member are made of different materials. In Patent Document 1, the first member is deformed according to a temperature change to change the size of the leak passage. Specifically, the first member reduces the leak passage at high temperatures and enlarges the leak passage at low temperatures. By the deformation of the first member, the hydraulic oil flows out through the leak passage, and the leak-down value at which the plunger descends is adjusted.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above, in order to change the linear expansion coefficients of the body and the first member that define the leak passage, they were made of different materials. On the other hand, a lash adjuster that can adjust an appropriate leak passage with respect to temperature changes was also desired by an approach different from Patent Document 1. Therefore, the present disclosure aims to provide a lash adjuster that can ensure an appropriate leak-down value in response to temperature changes. [Means for solving the problem]

[0005] The lash adjuster of this disclosure comprises a cylindrical body and a cylindrical plunger slidably disposed within the body, wherein a high-pressure chamber is provided between the body and the plunger, a low-pressure chamber is provided within the plunger, a valve hole is provided on the bottom surface of the plunger that connects the high-pressure chamber and the low-pressure chamber, a leak passage is provided between the inner circumferential surface of the body and the outer circumferential surface of the plunger through which the hydraulic fluid filled in the high-pressure chamber leaks, and either the body or the plunger has a bimetallic portion that deforms in a direction that narrows the leak passage in response to a rise in temperature. [Effects of the Invention]

[0006] According to this disclosure, it is possible to provide a lash adjuster that can ensure an appropriate leak-down value against temperature changes. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a partial cross-sectional view of a valve train including a lash adjuster according to Embodiment 1. [Figure 2] Figure 2 is a cross-sectional view of the lash adjuster according to Embodiment 1. [Figure 3] Figure 3 is an enlarged cross-sectional view of the main part of the plunger in the lash adjuster of Embodiment 1. [Figure 4] Figure 4 is an enlarged cross-sectional view showing the state in which the plunger deforms outward, narrowing the leak passage, in the lash adjuster of Embodiment 1 at high temperatures. [Figure 5] Figure 5 is an enlarged cross-sectional view showing the state in which the plunger deforms inward to widen the leak passage at low temperatures in the lash adjuster of Embodiment 1. [Figure 6]Figure 6 is an enlarged cross-sectional view of the main body of the lash adjuster according to Embodiment 2. [Figure 7] Figure 7 is an enlarged cross-sectional view showing the state in which the body of the lash adjuster of Embodiment 2 deforms inward, narrowing the leak passage, when the temperature is high. [Figure 8] Figure 8 is an enlarged cross-sectional view showing the state in which the body of the lash adjuster of Embodiment 2 deforms outward to widen the leak passage at low temperatures. [Modes for carrying out the invention]

[0008] [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) The device comprises a cylindrical body and a cylindrical plunger slidably disposed within the body, wherein a high-pressure chamber is provided between the body and the plunger, a low-pressure chamber is provided within the plunger, a valve hole is provided on the bottom surface of the plunger that connects the high-pressure chamber and the low-pressure chamber, a leak passage is provided between the inner circumferential surface of the body and the outer circumferential surface of the plunger through which the hydraulic fluid filled in the high-pressure chamber leaks, and either the body or the plunger has a bimetallic portion that deforms in a direction that narrows the leak passage in response to a rise in temperature.

[0009] According to the configuration described in (1) above, an appropriate leak-down value can be ensured in response to temperature changes. Specifically, at high temperatures, the viscosity of the hydraulic fluid decreases and the amount of hydraulic fluid flowing through the leak passage increases, but the bimetallic part deforms in a direction that narrows the leak passage. At low temperatures, the viscosity of the hydraulic fluid increases and the amount of hydraulic fluid flowing through the leak passage decreases, but the bimetallic part deforms in a direction that widens the leak passage. Therefore, even if the viscosity of the hydraulic fluid decreases or increases due to temperature changes, the amount of hydraulic fluid flowing through the leak passage can be kept constant.

[0010] (2) In the lash adjuster according to (1) above, the plunger can be divided into a bottom wall member and a peripheral wall member. The peripheral wall member has a support portion with a narrowed tip. A top hole that opens into the low-pressure chamber is provided at the tip of the support portion. The bottom wall member has a bottom wall and a peripheral wall rising from the bottom wall. It is preferable that the bimetal portion is provided on the peripheral wall of the bottom wall member.

[0011] If the plunger is an inseparable integral type, due to the presence of the support portion with a narrowed tip, there is a situation where it is difficult to perform processing for the bimetal portion on the inner peripheral side of the plunger. However, according to the configuration of (2) above, since the plunger can be divided into a bottom wall member and a peripheral wall member, the bimetal portion can be formed on the peripheral wall of the bottom wall member without any problems.

[0012] (3) In the lash adjuster according to (1) above, the bimetal portion is configured such that the surface side facing the leak passage is the first peripheral surface portion, and the surface side facing the side opposite to the leak passage is the second peripheral surface portion. It is preferable that the carbon content of the first peripheral surface portion is higher than the carbon content of the second peripheral surface portion.

[0013] According to the configuration of (3) above, the first peripheral surface portion has a higher carbon content than the second peripheral surface portion, and the first peripheral surface portion has a smaller linear expansion coefficient than the second peripheral surface portion. Therefore, due to the difference in carbon content, the leak passage can be narrowed in response to temperature changes to ensure an appropriate leak-down value.

[0014] (4) In the lash adjuster according to (3) above, it is preferable that the first peripheral surface portion is configured as a carburized layer and the second peripheral surface portion is configured as a non-carburized layer. [[ID=***]] [[ID=***]]

[0015] [[ID=***]] According to the configuration of (4) above, the bimetal portion can be easily formed by carburization. For example, the cost can be suppressed compared to the case where the first peripheral surface portion and the second peripheral surface portion are made of different materials. Also, the durability of the bimetal portion can be ensured.

[0016] (5) In the lash adjuster according to (4) above, when the bottom wall member is subjected to carburizing and quenching treatment, it is preferable that the carbon content of the first circumferential surface portion is at least twice the carbon content of the second circumferential surface portion.

[0017] According to the configuration of (5) above, the amount of the hydraulic fluid flowing through the leak passage can be made an appropriate amount with respect to the temperature change. Thereby, a more appropriate leak-down value can be ensured with respect to the temperature change.

[0018] (6) In the lash adjuster according to (1) above, the bimetal portion is configured such that the surface side facing the leak passage is the first circumferential surface portion, and the surface side facing the side opposite to the leak passage is the second circumferential surface portion, and it is preferable that the first circumferential surface portion is a hardened surface harder than the second circumferential surface portion.

[0019] According to the configuration of (6) above, for example, the first circumferential surface portion can be made a hardened surface by various methods such as carburizing and quenching treatment, nitriding treatment, or bonding.

[0020] (7) A method for manufacturing the lash adjuster according to (6) above, the method including: a step of forming the hardened surface by performing a surface treatment on one of the surfaces of the body and the plunger; and a step of forming the second circumferential surface portion by cutting and removing the hardened surface formed on the surface of the body or the plunger facing the side opposite to the leak passage. It is preferable to have these steps.

[0021] According to the manufacturing method of (7) above, when performing the surface treatment for forming the hardened surface, it is not necessary to perform a treatment for preventing hardening on the surface of the body or the plunger facing the side opposite to the leak passage, and the cost can be reduced.

[0022] (8) A method for manufacturing a lash adjuster as described in (5) above, preferably comprising the steps of: forming a carburized layer on the surface of the bottom wall member by applying the carburizing and quenching treatment to the bottom wall member; and forming the second circumferential surface by cutting and removing the carburized layer formed on the surface of the circumferential wall facing the opposite side of the leak passage.

[0023] According to the manufacturing method described in (8) above, when performing the carburizing and quenching treatment, it is not necessary to apply a carburizing treatment to the surface of the peripheral wall facing the opposite side of the leak passage, thereby reducing costs.

[0024] [Details of the embodiments of this disclosure] Specific examples of embodiments of this disclosure will be described below with reference to the drawings. However, the present invention is not limited to these examples and is intended to include all modifications within the meaning and scope equivalent to the claims as defined by the claims.

[0025] [Embodiment 1] The lash adjuster 10 according to this embodiment 1 is a hydraulic lash adjuster and, as shown in Figure 1, is applied to the valve train of an internal combustion engine. The lash adjuster 10 has an overall shape that extends in the axial direction. In the following description, unless otherwise specified, "outside" and "inside" refer to the outside and inside of the lash adjuster 10 in the radial direction (direction perpendicular to the axial direction). In Figures 3-5, the outside is indicated by OUT and the inside by IN.

[0026] (Valve train) As shown in Figure 1, the valve train includes, in addition to the lash adjuster 10, a valve 92 that opens and closes the intake or exhaust port 91 of the cylinder head 90, a cam 93 that rotates in sync with the engine, and a rocker arm 94 that transmits the movement of the cam 93 to the valve 92. The lash adjuster 10 plays the role of automatically adjusting the clearance between the cam 93 and the rocker arm 94 using hydraulic pressure.

[0027] The valve 92 has a valve stem 97 that is slidably inserted into a valve guide 95 of the cylinder head 90. The lower end of the valve 92 is configured as a valve body 96 facing an intake or exhaust port 91. A valve spring 98 is provided around the valve stem 97. The valve 92 is biased by the valve spring 98, causing the valve body 96 to close the intake or exhaust port 91.

[0028] The rocker arm 94 is supported at one end by a support portion 27 of the lash adjuster 10 (described later), and its other end is positioned in contact with the upper end of the valve stem 97. A rotatable roller 99 is provided between the one end and the other end of the rocker arm 94. The roller 99 is in contact with a cam 93 positioned above it.

[0029] (Lash Adjuster 10) The lash adjuster 10 is inserted into a mounting hole 100 provided on the upper surface of the cylinder head 90. A lubrication passage 101 communicates with the inner surface of the mounting hole 100. As shown in Figure 2, the lash adjuster 10 comprises a body 11, a plunger 12, a valve body 13, a first spring 14, and a second spring 15.

[0030] The body 11 is formed in a bottomed cylindrical shape that is open upwards. The body 11 has a disc-shaped bottom 16 and a circumferential portion 17 that rises from the outer circumference of the bottom 16. An outer circumferential groove 18 is provided on the outer circumferential surface of the circumferential portion 17 along its entire circumference. Near the upper end of the inner surface of the outer circumferential groove 18, a body oil hole 19 is formed that penetrates radially (in the wall thickness direction of the circumferential portion 17) from the inner surface of the outer circumferential groove 18 to the inner surface. An inner circumferential groove 20 is formed on the inner surface of the circumferential portion 17 along its entire circumference, corresponding to the opening position on the inner surface side of the body oil hole 19. A retainer 21 is attached to the upper end of the circumferential portion 17 to prevent the plunger 12 from coming out upwards.

[0031] The plunger 12 is formed in a bottomed cylindrical shape and is housed within the body 11 so as to be slidable in the vertical direction. The upper end of the plunger 12 is positioned to protrude from the upper end of the body 11. The plunger 12 is vertically separable into a bottom wall member 22 and a peripheral wall member 23. The peripheral wall member 23 constitutes the upper peripheral wall portion of the plunger 12. The bottom wall member 22 has a bottom wall 24 and a peripheral wall 25 rising from the bottom wall 24. The peripheral wall 25 constitutes the lower peripheral wall portion of the plunger 12. The upper end of the peripheral wall 25 is connected to the lower end of the peripheral wall member 23 by interlocking grooves. The inner diameter of the upper end of the peripheral wall 25 is set to be the same size as the inner diameter of the lower end of the peripheral wall member 23.

[0032] The internal space of the plunger 12 is configured as a low-pressure chamber 26, partitioned by a bottom wall member 22 and a peripheral wall member 23. The bottom wall 24 of the bottom wall member 22 is formed in a disc shape smaller than the bottom 16 of the body 11. A support portion 27 having a hemispherical outer surface is provided at the upper end (top) of the peripheral wall member 23. The support portion 27 slidably supports one end of the rocker arm 94. A top hole 28 is provided at the upper end of the support portion 27, penetrating vertically.

[0033] The upper end of the peripheral wall member 23 is provided with an annular band portion 29 that protrudes outward in a thick manner along its entire circumference. The outer circumferential surface of the annular band portion 29 is in slidable contact with the inner circumferential surface of the upper end of the peripheral portion 17 of the body 11 in the vertical direction. The outer circumferential surface of the peripheral wall member 23 is provided with a plunger circumferential groove 30 that defines the lower end surface of the annular band portion 29 along its entire circumference.

[0034] The peripheral wall member 23 has a plunger oil hole 31 that penetrates radially (in the wall thickness direction of the peripheral wall member 23) from the groove back surface to the inner surface of the plunger circumferential groove 30. The plunger oil hole 31 is located at the upper end of the plunger circumferential groove 30. The plunger oil hole 31 is located above the body oil hole 19.

[0035] The hydraulic fluid supplied from the oil supply passage 101 of the cylinder head 90 is stored in the low-pressure chamber 26 via the outer circumferential groove 18, the body oil hole 19, the plunger circumferential groove 30, and the plunger oil hole 31.

[0036] The peripheral wall 25 has a protruding wall 32 that extends downward from the bottom wall 24. The protruding wall 32, together with the lower surface of the bottom wall 24, forms a recess 33. A cage 36, which will be described later, is press-fitted into the recess 33. A circular valve hole 34 is provided in the radial center of the bottom wall 24 of the bottom wall member 22, penetrating vertically.

[0037] A high-pressure chamber 35 is formed in the lower part of the body 11 between the plunger 12 and the bottom wall member 22. Hydraulic fluid stored in the low-pressure chamber 26 flows into the high-pressure chamber 35 through the valve hole 34. The high-pressure chamber 35 is provided with a spherical valve body 13, a hat-shaped cage 36, and compression coil springs, a first spring 14 and a second spring 15. The cage 36 houses the valve body 13 in its inner space and is press-fitted into a recess 33 with its opening facing the valve hole 34. Multiple notches 37 are formed in the cage 36 at equal intervals in the circumferential direction. Each notch 37 connects the space inside and outside the cage 36, allowing hydraulic fluid to flow in and out. The second spring 15 is positioned between the outer peripheral edge of the cage 36 and the bottom 16 of the body 11 and biases the plunger 12 upward.

[0038] The valve body 13 is housed within the high-pressure chamber 35. A first spring 14 is positioned between the cage 36 and the valve body 13 in the space inside the cage 36. The valve body 13 is biased upward by the first spring 14, allowing the valve hole 34 to be opened and closed.

[0039] With the plunger 12 housed in the body 11, a radial gap is defined between the inner surface of the peripheral portion 17 of the body 11 and the outer surface of the peripheral wall 25 of the plunger 12. This gap forms a leak passage 38 along the entire circumference. The lower end of the leak passage 38 opens to the high-pressure chamber 35, and the upper end opens to the inner peripheral groove 20 and the plunger peripheral groove 30.

[0040] As shown in Figure 3, a bimetallic portion 39 is provided on the peripheral wall 25. The bimetallic portion 39 has a first peripheral surface portion 40 on the outer peripheral surface side of the peripheral wall 25 facing the leak passage 38, and a second peripheral surface portion 41 on the inner peripheral surface side of the peripheral wall 25 opposite to the leak passage 38. In addition, the bimetallic portion 39 has a main body portion 42 that constitutes a non-carburized layer, which will be described later, in the main part of the peripheral wall 25 in the thickness direction, excluding the outer peripheral surface side and the inner peripheral surface side.

[0041] The bimetal portion 39 of this embodiment 1 is manufactured, for example, by the following procedure. First, the bottom wall member 22 is placed in a carburizing furnace heated to approximately 800 degrees and gas carburized. This forms a carburized layer over the entire surface of the bottom wall member 22. After quenching the bottom wall member 22, the carburized layer formed on the inner circumferential surface side of the circumferential wall 25 is scraped off. This forms a second circumferential surface portion 41 on the inner circumferential surface side of the circumferential wall 25, from which the carburized layer has been removed. A first circumferential surface portion 40 is formed on the outer circumferential surface side of the circumferential wall 25, with the carburized layer remaining. In this embodiment 1, the carbon content of the first circumferential surface portion 40 is set to 0.8% by weight. The coefficient of linear expansion of the first circumferential surface portion 40 at this time is 11.1 × 10⁻⁶. -6 The temperature is / ℃. Furthermore, the carbon content of the second circumferential surface 41 is set to 0.2% by weight. The coefficient of linear expansion of the second circumferential surface 41 is greater than that of the first circumferential surface 40, at 11.7 × 10⁻⁶. -6 The temperature is / ℃. The first circumferential surface portion 40 is a hardened surface that is harder than the second circumferential surface portion 41. In this embodiment 1, the plunger 12 is made of S20C, which is a carbon steel with a carbon content of 0.2 wt%.

[0042] (Basic operation of the Lash Adjuster 10) Next, the basic operation of the lash adjuster 10 will be explained. The cam 93 rotates, and the nose portion 102 of the cam 93 moves away from the roller 99, closing the valve 92. A force acts on the plunger 12 from the second spring 15 toward the rocker arm 94. This maintains the support portion 27 in contact with one end of the rocker arm 94. Furthermore, as the plunger 12 advances toward the rocker arm 94, the volume of the high-pressure chamber 35 expands, the valve body 13 moves to the open position, and the hydraulic fluid stored in the low-pressure chamber 26 flows into the high-pressure chamber 35 through the valve hole 34. This maintains pressure balance between the high-pressure chamber 35 and the low-pressure chamber 26, and the valve body 13 returns to the closed position, closing the valve hole 34.

[0043] As the cam 93 rotates further and the nose portion 102 presses against the roller 99, the valve 92 opens. The support portion 27 is pressed against one end of the rocker arm 94, and a force acts on the plunger 12 in the direction of sinking into the body 11. Since the valve hole 34 is blocked by the valve body 13, the sinking of the plunger 12 into the body 11 is suppressed. However, a compressive force acts on the high-pressure chamber 35, and the hydraulic fluid stored in the high-pressure chamber 35 flows out through the leak passage 38. As a result, the volume of the high-pressure chamber 35 decreases, the plunger 12 sinks into the body 11 (leak-down), and the overall length of the lash adjuster 10 is shortened. In this state, the body 11 and the lash adjuster 10 become rigid, so the rocker arm 94 is stably supported by the lash adjuster 10. The hydraulic fluid is divided into three parts: one that leaks out to the outside through the leak passage 38 and the body oil hole 19; one that returns to the low-pressure chamber 26 through the leak passage 38 and the plunger oil hole 31; and another that leaks out to the outside from the low-pressure chamber 26 through the top hole 28 to lubricate one end of the rocker arm 94.

[0044] (Function of the bimetallic part 39) The viscosity of the hydraulic fluid changes with temperature. Therefore, the amount of hydraulic fluid leaking from the leak passage 38 is affected by temperature changes. As a result, the amount of sinking of the plunger 12 relative to the body 11 (leak-down value) is affected by temperature changes. Specifically, at high temperatures, the viscosity of the hydraulic fluid decreases, making it easier to leak from the leak passage 38. Conversely, at low temperatures, the viscosity of the hydraulic fluid increases, making it less likely to leak from the leak passage 38. For these reasons, in this embodiment 1, a bimetallic section 39 is provided to ensure an appropriate leak-down value with respect to temperature changes.

[0045] For example, at high temperatures, hydraulic fluid is prone to leaking from the leak passage 38, so it is necessary to narrow the leak passage 38 to ensure an appropriate leak-down value. In this embodiment 1, since the first circumferential surface portion 40 of the bimetal portion 39 is a carburized layer, the coefficient of linear expansion of the second circumferential surface portion 41 is larger than that of the first circumferential surface portion 40. Therefore, as shown in Figure 4, at high temperatures, the bimetal portion 39 can deform to expand outward, approaching the body 11 (the circumferential wall member 23 is not shown in Figure 4). As a result, the bimetal portion 39 can narrow the leak passage 38, and the amount of hydraulic fluid leaking from the leak passage 38 can be suppressed. This allows the lash adjuster 10 to ensure an appropriate leak-down value at high temperatures.

[0046] In contrast, at low temperatures, hydraulic fluid is less likely to leak from the leak passage 38, so it is necessary to widen the leak passage 38 to ensure an appropriate leak-down value. As described above, the coefficient of linear expansion of the peripheral wall 25 is greater for the second peripheral surface portion 41, which is the inner peripheral surface, than for the first peripheral surface portion 40, which is the outer peripheral surface. As shown in Figure 5, at low temperatures, unlike at high temperatures, the bimetal portion 39 can deform to shrink inward, away from the body 11 (the peripheral wall member 23 is not shown in Figure 5). As a result, the bimetal portion 39 can widen the leak passage 38, increasing the amount of hydraulic fluid that leaks from the leak passage 38. This allows the lash adjuster 10 to ensure an appropriate leak-down value even at low temperatures.

[0047] In this first embodiment, the carbon content of the first circumferential surface portion 40 is adjusted to be four times that of the second circumferential surface portion 41, so that the bimetal portion 39 deforms in response to temperature changes as described above. However, if the bimetal portion 39 is formed by a carburizing and quenching treatment such as gas carburizing, the bimetal portion 39 can be deformed in response to temperature changes and an appropriate leak-down value can be ensured if the carbon content of the first circumferential surface portion 40 is twice that of the second circumferential surface portion 41. At a minimum, if the carbon content of the first circumferential surface portion 40 is twice that of the second circumferential surface portion 41, the bimetal portion 39 can be deformed in response to temperature changes.

[0048] In this embodiment 1, the bimetal portion 39 is formed by removing the carburized layer on the inner surface of the peripheral wall 25 from the carburized and hardened bottom wall member 22. If the plunger is not separable into the peripheral wall member and the bottom wall member, the cutting tool would need to pass through the top hole to cut the inner surface of the carburized and hardened plunger, making it difficult to form the bimetal portion on the plunger. In contrast, in this embodiment 1, the plunger 12 is separable into the peripheral wall member 23 and the bottom wall member 22, making it easier to form the bimetal portion 39 on the plunger 12.

[0049] In this embodiment 1, the carbon content of the first and second circumferential surfaces 40 and 41 of the circumferential wall 25 is adjusted to control the coefficient of thermal expansion and form the bimetallic portion 39 on the bottom wall member 22. Even if the carburized layer on the inner circumferential surface of the carburized and quenched bottom wall member is not removed and a member made of a material with a different coefficient of thermal expansion is press-fitted into the inner circumferential side of the circumferential wall, deformation of the plunger in response to temperature changes will occur. However, using a member made of a different material to change the coefficient of thermal expansion would incur costs such as changes in the manufacturing process and capital investment. In contrast, in this embodiment 1, the bimetallic portion 39 can be provided while the bottom wall member 22 is made of the same material, thereby reducing costs. Furthermore, the durability of the plunger 12 can be ensured more effectively than by press-fitting a member made of a different material.

[0050] In this embodiment 1, the lash adjuster 10 is manufactured by a manufacturing method that includes the steps of applying a carburizing and quenching treatment to the bottom wall member 22, and forming a second circumferential surface portion 41 by cutting and removing the carburized layer from the surface of the circumferential wall 25 facing the opposite side of the leak passage 38. This makes it possible to provide the second circumferential surface portion 41 without applying a carburizing agent or other anti-carburizing treatment to the surface of the circumferential wall 25 facing the opposite side of the leak passage 38 when applying the carburizing and quenching treatment.

[0051] [Embodiment 2] Embodiment 2 of this disclosure differs from Embodiment 1 in that, as shown in Figure 6, the bimetal portion 39 is provided on the body 11 instead of the plunger 12. Since the rest is the same as Embodiment 1, the same reference numerals are used for components identical or equivalent to those in Embodiment 1, and redundant descriptions are omitted.

[0052] In Embodiment 2, the bimetal portion 39 is formed by machining or other processes on the carburized and quenched body 11. Specifically, the body 11 is placed in a carburizing furnace heated to approximately 800 degrees Celsius and gas carburized. After quenching the body 11, the carburized layer on the outer circumferential surface side of the peripheral portion 17 is removed by grinding. As a result, a first peripheral portion 40, which is a carburized layer, is formed on the inner peripheral surface side facing the leak passage 38, and a second peripheral portion 41, from which the carburized layer has been removed, is formed on the outer circumferential surface side opposite the leak passage 38. The carbon content of the first peripheral portion 40 and the second peripheral portion 41 are the same as in Embodiment 1. The coefficients of linear expansion of the first peripheral portion 40 and the second peripheral portion 41 are also the same. In this Embodiment 2, the body 11 is made of S20C, a carbon steel with a carbon content of 0.2% by weight.

[0053] As shown in Figure 7, at high temperatures, the bimetallic portion 39 deforms to curve inward, approaching the plunger 12. This allows the bimetallic portion 39 to narrow the leak passage 38, thereby suppressing the amount of hydraulic fluid leaking from the leak passage 38. As a result, the lash adjuster 10 can maintain an appropriate leak-down value even at high temperatures.

[0054] In this second embodiment, as shown in Figure 8, at low temperatures, the bimetal portion 39 deforms to curve outward, away from the plunger 12. As a result, the bimetal portion 39 can widen the leak passage 38, increasing the amount of hydraulic fluid leaking out of the leak passage 38. This allows the lash adjuster 10 to maintain an appropriate leak-down value even at low temperatures.

[0055] [Other embodiments of this disclosure] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. In this first embodiment, the bimetallic portion was formed by removing the carburized layer from the inner circumferential surface of the bottom wall member that had undergone carburizing and quenching treatment. In contrast, in other embodiments, the bimetallic portion may be provided by press-fitting a member made of a material with a different coefficient of thermal expansion into the inner circumferential side of the peripheral wall of the bottom wall member. In these two embodiments, the carburized layer was cut away when forming the second circumferential surface. In contrast, in other embodiments, the carburized layer may not be completely removed, and a portion of the carburized layer may remain as part of the second circumferential surface. In these embodiments 1 and 2, the first circumferential surface is formed by carburizing and quenching. In contrast, in other embodiments, the first circumferential surface may be formed by nitriding. The point is that any treatment is applied so that the first circumferential surface becomes a harder surface than the second circumferential surface. [Explanation of Symbols]

[0056] 10...Lash adjuster 11…Body 12…Plunger 13… Valve body 14…First Spring 15…2nd Spring 16...bottom 17…periphery 18…Outer circumferential grooves 19…Body oil holes 20...Internal circumferential groove 21…Retainer 22...Bottom wall member 23... Peripheral wall member 24...Bottom wall 25...peripheral wall 26... Low-pressure room 27...Support part 28...apex hole 29… Circular belt section 30…Plunger surrounding groove 31…Plunger oil hole 32...projection wall 33…dent 34… Valve opening 35…High-pressure room 36... Cage 37... Notch 38... Leakage 39...Bimetal section 40...First circumferential part 41…Second peripheral surface part 42...Main body 90... Cylinder head 91... Intake or exhaust port 92... Valve 93... Cam 94... Rocker arm 95... Valve guide 96... Valve body 97… Valve stem 98… Valve springs 99... Laura 100…Mounting holes 101... Refueling route 102... Nose section

Claims

1. It comprises a cylindrical body and a cylindrical plunger slidably disposed within the body, A high-pressure chamber is provided between the body and the plunger. A low-pressure chamber is provided inside the plunger. A valve hole is provided on the bottom surface of the plunger, which connects the high-pressure chamber and the low-pressure chamber. A leak passage is provided between the inner circumferential surface of the body and the outer circumferential surface of the plunger, through which the hydraulic fluid filled in the high-pressure chamber leaks. A lash adjuster wherein either the body or the plunger has a bimetallic portion that deforms in a direction that narrows the leak passage in response to a rise in temperature.

2. The plunger is divisible into a bottom wall member and a peripheral wall member, The aforementioned peripheral wall member has a support portion that tapers towards the tip, The tip of the support portion is provided with a top hole that opens into the low-pressure chamber. The bottom wall member has a bottom wall and a peripheral wall rising from the bottom wall. The lash adjuster according to claim 1, wherein the bimetal portion is provided on the peripheral wall of the bottom wall member.

3. The lash adjuster according to claim 1, wherein the bimetal portion is configured such that the side facing the leak passage is a first circumferential surface and the side facing the opposite side of the leak passage is a second circumferential surface, and the carbon content of the first circumferential surface is greater than the carbon content of the second circumferential surface.

4. The lash adjuster according to claim 3, wherein the first circumferential portion is configured as a carburized layer and the second circumferential portion is configured as a non-carburized layer.

5. When the bottom wall member is subjected to carburizing and quenching treatment, The lash adjuster according to claim 4, wherein the carbon content of the first circumferential surface is twice or more the carbon content of the second circumferential surface.

6. The bimetal portion is configured such that the side facing the leak passage is the first circumferential surface, and the side facing the opposite side from the leak passage is the second circumferential surface. The lash adjuster according to claim 1, wherein the first circumferential surface is a hardened surface that is harder than the second circumferential surface.

7. A method for manufacturing a lash adjuster according to claim 6, A step of forming the hardened surface by applying a surface treatment to the surface of either the body or the plunger, A method for manufacturing a lash adjuster, comprising the step of forming the second circumferential surface portion by cutting and removing the hardened surface formed on the surface of the body or the plunger facing the opposite side of the leak passage.

8. A method for manufacturing a lash adjuster according to claim 5, The process of forming a carburized layer on the surface of the bottom wall member by applying the carburizing and quenching treatment to the bottom wall member, A method for manufacturing a lash adjuster, comprising the step of forming the second circumferential surface by cutting and removing the carburized layer formed on the surface of the circumferential wall facing the opposite side of the leak passage.

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