Lash adjuster

Abstract

To provide a lash adjuster which can secure oil supply by suppressing blockage of a body hole caused by air bubbles and can maintain functions.SOLUTION: A lash adjuster 10 includes a cylindrical body 11, and a cylindrical plunger 12 arranged in the body 11 so as to be reciprocally slidable with respect to the body 11. The body 11 includes a bottom wall 13, a peripheral wall 14 rising from the bottom wall 13, a body circumferential groove 15 recessed over the entire circumference on an outer peripheral surface of the peripheral wall 14, and a body hole 16 opened to an innermost surface of the body circumferential groove 15 and supplying oil to the plunger 12. The body 11 has an uneven shape (recessed groove 15A) on an edge of the body hole 16 in the body circumferential groove 15.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a lash adjuster including a cylindrical body and a plunger arranged to be reciprocally slidable within the body. The body is fitted into a mounting recess that opens onto the surface of a cylinder head. A body hole is formed through the circumferential wall of the body. A plunger hole is formed through the circumferential wall of the plunger. With the body fitted into the mounting recess, hydraulic oil (oil) flowing through an oil supply passage in the cylinder head is supplied into the lash adjuster through the body hole and plunger hole. The plunger changes the amount of protrusion from the body. A rocker arm supported by the plunger changes the position of its swing fulcrum in accordance with fluctuations in the amount of protrusion of the plunger, automatically adjusting the valve clearance of the valve it presses. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-222007 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, air bubbles may be mixed in with the oil in the oil supply passage. These bubbles flow through the oil supply passage along with the oil. The air bubbles can accumulate in areas of the oil supply passage where the flow is slow, forming large clumps. If these trapped air bubbles block the body holes of the lash adjuster, oil cannot be introduced into the interior. This could prevent the lash adjuster from properly performing its function of adjusting the valve clearance.

[0005] Therefore, an object of the present disclosure is to provide a lash adjuster that can prevent blockage of body holes by air bubbles, ensure oil supply, and maintain functionality. [Means for solving the problem]

[0006] The lash adjuster of the present disclosure includes a cylindrical body and a cylindrical plunger disposed within the body so as to be slidable back and forth relative to the body, the body having a bottom wall, a peripheral wall rising from the bottom wall, a body circumferential groove recessed along the entire outer circumferential surface of the peripheral wall, and a body hole that opens into the innermost surface of the body circumferential groove and supplies oil to the plunger, and the body has an uneven shape on the edge of the body hole in the body circumferential groove. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to prevent the blockage of body holes due to air bubbles, ensure oil supply, and maintain functionality. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a valve train including a lash adjuster according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a main part of the valve train of the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing the lash adjuster of the first embodiment. [Figure 4] FIG. 4 is a side view showing the body of the lash adjuster of the first embodiment. [Figure 5] FIG. 5 is a diagram for explaining the operation of the lash adjuster of the first embodiment. [Figure 6] FIG. 6 is a side view showing the body of the lash adjuster of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. The lash adjuster according to the present disclosure comprises: (1) A device comprising a cylindrical body and a cylindrical plunger arranged within the body so as to be able to slide back and forth relative to the body, wherein the body has a bottom wall, a peripheral wall rising from the bottom wall, a body circumferential groove recessed around the entire outer surface of the peripheral wall, and a body hole opening into the innermost surface of the body circumferential groove and supplying oil to the plunger, and the body has an uneven shape on the edge of the body hole in the body circumferential groove.

[0010] According to the above configuration, the uneven shape of the inner surface of the body circumferential groove at the edge of the body hole prevents air bubbles from adhering to the inner surface. This prevents air bubbles from clogging the body hole even if air bubbles accumulate around the edge of the body hole, ensuring a stable oil supply. As a result, the lash adjuster according to the present disclosure can maintain its functionality.

[0011] (2) The uneven shape is formed by at least one of a recess and a protrusion provided on the rear surface of the body circumferential groove, and at least one of the recess and the protrusion extends circumferentially on the rear surface of the body circumferential groove and intersects with the opening edge of the body hole. According to the above configuration, the recessed or protruding portion can be formed simultaneously with machining the outer peripheral surface of the body, facilitating manufacturing.

[0012] (3) The width of at least one of the recess and the protrusion may be smaller than the diameter of the opening of the body hole. According to the above configuration, the oil flow path formed by the concave and convex shape can be reliably connected to the body hole.

[0013] (4) Preferably, a plurality of at least one of the recessed portions and the protruding portions are arranged in parallel. According to the above configuration, redundancy of the oil supply passages connected to the body holes can be ensured, and the function of the lash adjuster can be maintained more reliably.

[0014] [Details of the 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, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0015] <Embodiment 1> The lash adjuster of the first embodiment of the present disclosure is provided in a valve train of an internal combustion engine, as shown in Figures 1 and 2. The lash adjuster 10 is attached to an attachment recess 93 formed in a cylinder head 90.

[0016] As shown in FIG. 1, the valve gear 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.

[0017] The valve stem 81 is inserted into a through-hole 92 that communicates with an intake or exhaust port 91 of a 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 moves back and forth within the through-hole 92, thereby causing the valve body 80 to open and close the intake or exhaust port 91.

[0018] One end of the rocker arm 60 is supported by the lash adjuster 10, and the other end is abutted against the valve stem 81. A cam 71 is arranged in rotatable contact with a roller 61 provided between the one end and the other end.

[0019] As shown in Figures 1 and 2, the cylinder head 90 has an oil supply passage 94 and a mounting recess 93. The oil supply passage 94 is formed inside the cylinder head 90. The oil supply passage 94 supplies oil to various parts of the internal combustion engine. The oil supply passage 94 communicates with an oil pump (not shown) on the upstream side. Pressure from this oil pump acts on the oil in the oil supply passage 94. The oil flows through the oil supply passage 94 in accordance with the pressure difference.

[0020] The mounting recess 93 is a bottomed hole with a circular cross section that opens to the surface of the cylinder head 90. As shown in Figures 1 and 2, the mounting recess 93 is formed so that part of its internal space overlaps part of the space within the oil supply passage 94, and is in communication with the oil supply passage 94. The mounting recess 93 is located above the oil supply passage 94, and air bubbles that have accumulated in the oil supply passage 94 can be located on the mounting recess 93 side, which is the upper side of the oil supply passage 94.

[0021] 1 and 2, the lash adjuster 10 is fitted into the mounting recess 93. When fitted into the mounting recess 93, the lash adjuster 10 protrudes into the oil supply passage 94 from diagonally above the oil supply passage 94. As shown in FIG. 2, the lash adjuster 10 protrudes into the oil supply passage 94 to a position beyond the center of the inner diameter of the oil supply passage 94. The lash adjuster 10 is rotatable along the inner circumferential surface of the mounting recess 93. The lash adjuster 10 rotates within the mounting recess 93 due to vibrations of the internal combustion engine, changes in the magnitude of the force received from the rocker arm 60, fluctuations in the oil pressure within the oil supply passage 94, etc.

[0022] As shown in FIG. 3, the lash adjuster 10 includes a cylindrical body 11 with a bottom, and a cylindrical plunger 12 with a bottom that is housed within the body 11 and is capable of sliding back and forth in the vertical direction. The plunger 12 is made up of a disk-shaped bottom wall 17 and a peripheral wall 18 that rises from the outer periphery of the bottom wall 17 and has an upper end that is narrowed into a substantially hemispherical shape. The upper end of the peripheral wall 18 of the plunger 12 serves as a support portion 19, and one end of a rocker arm 60 is supported by the hemispherical outer periphery of the support portion 19 (see FIG. 1). A top hole 21 is provided at the upper end of the support portion 19 so as to pass through in the vertical direction.

[0023] A plunger circumferential groove 24 is recessed around the entire periphery of the outer circumferential surface of the peripheral wall 18 of the plunger 12. A plunger oil hole 25 is provided in the peripheral wall 18 of the plunger 12, penetrating the peripheral wall 18 in the thickness direction and opening 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.

[0024] The body 11 is made up of a disk-shaped bottom wall 13 that is slightly larger than the bottom wall 17 of the plunger 12, and a peripheral wall 14 that rises from the outer periphery of the bottom wall 13. When the lash adjuster 10 is attached to the attachment recess 93, the outer peripheral surface of the peripheral wall 14 comes into contact with the inner peripheral surface of the attachment recess 93. The peripheral wall 14 is formed with a body circumferential groove 15, a body hole 16, and a recessed groove 15A.

[0025] The body circumferential groove 15 is recessed around the entire circumferential direction in the outer circumferential surface of the peripheral wall 14. The back surface of the body circumferential groove 15 has a substantially uniform outer diameter within a range of a predetermined width in the axial direction of the body 11. The body circumferential groove 15 is disposed in a position facing the oil supply passage 94 from within the mounting recess 93 when the lash adjuster 10 is fitted within the mounting recess 93. The body circumferential groove 15 forms a gap between its back surface and the inner circumferential surface of the mounting recess 93, through which oil can flow. The body hole 16 penetrates the peripheral wall 14 and opens at the back surface of the body circumferential groove 15. A plurality of body holes 16 are provided. In this embodiment, the plurality of body holes 16 are disposed at equal intervals in the circumferential direction of the peripheral wall 14. Specifically, two of the plurality of body holes 16 are provided at an interval of 180° in the circumferential direction of the peripheral wall 14. A retainer 50 is attached to the upper end of the peripheral wall 14 of the body 11 to prevent the plunger 12 from slipping out upward.

[0026] The recessed groove 15A corresponds to the concave-convex shape and recessed portion according to the present disclosure. As shown in FIGS. 3 and 4, the recessed groove 15A is recessed radially inward from the rear surface of the body circumferential groove 15, forming a step. The recessed groove 15A is connected to the edge of the body hole 16 in the body circumferential groove 15. The recessed groove 15A is formed at a position approximately equivalent to the center position of the body hole 16 in the axial direction of the body 11. The recessed groove 15A extends circumferentially on the rear surface of the body circumferential groove 15 and intersects with the opening edge of the body hole 16. More specifically, the recessed groove 15A extends circumferentially in an annular shape on the rear surface of the body circumferential groove 15 so as to pass through the body hole 16. The recessed groove 15A is formed simultaneously when the body circumferential groove 15 is machined. As shown in FIG. 4, the width W1 of the recessed groove 15A is smaller than the opening diameter D of the body hole 16. The width W1 of the groove may be, for example, 1 / 3 or more and 1 / 2 or less of the opening diameter D of the body hole. The depth H1 of the groove may be set to be approximately equal to the width W1. It is preferable that the depth H1 of the groove is greater than the width W1.

[0027] As shown in FIG. 3 , a high-pressure chamber 27 is defined in the lower part of the body 11, between the plunger 12 and the bottom wall 17. A low-pressure chamber 22 is defined above the bottom wall 17 within the plunger 12. The high-pressure chamber 27 contains a spherical valve element 28 that can move vertically to open and close the valve hole 26, a cage 29 that holds the valve element 28, a first spring 31 made of a compression coil spring that is housed in the cage 29 and urges the valve element 28 toward the valve hole 26, and a second spring 32 made of a compression coil spring that is interposed between the outer circumferential edge of the cage 29 and the bottom wall 13 of the body 11 and urges the plunger 12 upward. The valve element 28 is urged upward by the first spring 31 to close the valve hole 26.

[0028] As described above, the lash adjuster 10 of this embodiment is fitted into the mounting recess 93 of the cylinder head 90. The lash adjuster 10 fitted into the mounting recess 93 is disposed so that the upper end of the plunger 12 protrudes above the surface of the cylinder head 90. The upper end of the plunger 12 supports one end of the rocker arm 60. The body 11 faces the oil supply passage 94 at the body circumferential groove 15.

[0029] Oil flowing through the oil supply passage 94 of the cylinder head 90 is supplied to the low-pressure chamber 22 from the body circumferential groove 15 facing the oil supply passage 94, via the body hole 16, the plunger circumferential groove 24, and the plunger oil hole 25. In addition, the valve body 28 descends against the biasing force of the first spring 31, and with the valve hole 26 open, oil is filled from the low-pressure chamber 22 through the valve hole 26 into the high-pressure chamber 27.

[0030] When the internal combustion engine is running, the cam 71 rotates and the rocker arm 60 is pressed from above via the roller 61, so that the plunger 12 is pressed against one end of the rocker arm 60 and moves downward relative to the body 11, compressing the oil in the high-pressure chamber 27. As the pressure in the high-pressure chamber 27 increases, the oil in the high-pressure chamber 27 flows out toward the plunger circumferential groove 24 through between the peripheral walls 14, 18 of the plunger 12 and the body 11. As a result, the overall length of the lash adjuster 10 is shortened by the amount of oil that flows out from the high-pressure chamber 27. Furthermore, the increase in pressure in the high-pressure chamber 27 rigidifies the oil (body 11 and plunger 12), and the support position of the lash adjuster 10 relative to the rocker arm 60 is determined.

[0031] As the cam 71 further rotates and the pressing force from the cam 71 acting on the rocker arm 60 decreases, the plunger 12, which receives the pressure in 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. The drop in pressure in the high-pressure chamber 27 causes the valve element 28 to move away from the valve hole 26, opening the valve hole 26, allowing oil to flow from the low-pressure chamber 22 to the high-pressure chamber 27 and extending the overall length of the lash adjuster 10. In this way, the lash adjuster 10 supports the rocker arm 60 at an appropriate position, thereby adjusting the valve clearance between the cam 71 and the rocker arm 60 to essentially zero.

[0032] There may be air bubbles mixed in the oil in the oil supply passage 94. The air bubbles mixed in the oil are carried by the flow of the oil and circulate through the oil supply passage 94. The lash adjuster 10 is attached to a mounting recess 93 formed above the oil supply passage 94, and protrudes downward from the upper surface of the oil supply passage 94. A lash adjuster 10 positioned in this manner blocks air bubbles in the oil supply passage 94, making it easy for air bubble pool A to form.

[0033] When the lash adjuster 10 rotates within the mounting recess 93, the body hole 16 may be positioned facing the air bubble trap A. In this case, the body hole 16 is covered by the air bubble trap A (see FIG. 2). However, in this embodiment, the innermost surface of the body circumferential groove 15 is formed with the concave-convex groove 15A according to the present disclosure. This concave-convex shape prevents the air bubble trap A from adhering to the innermost surface of the body circumferential groove 15. In other words, when the concave-convex shape is present, the surface tension at the interface with the oil reduces the contact area of ​​the air bubble trap A when it comes into contact with the body circumferential groove 15 compared to when it comes into contact with a smooth surface. This makes it easier for the lash adjuster 10 to avoid blockage of the body hole 16 by the air bubble trap A, ensuring a stable supply of oil to the interior. As a result, the lash adjuster 10 is more likely to maintain its functionality.

[0034] Furthermore, the recessed groove 15A, which has an uneven shape, is formed by depressing the inner surface of the body circumferential groove 15. Therefore, as shown in FIG. 5, even if an air bubble reservoir A accumulates and comes into contact with the inner surface of the body circumferential groove 15, surface tension prevents the air bubble reservoir A from entering the inner space of the recessed groove 15A. This keeps the inner space of the recessed groove 15A filled with oil. Furthermore, the recessed groove 15A extends circumferentially around the body circumferential groove 15 and intersects with the opening edge of the body hole 16. This forms an oil flow path in the inner space of the recessed groove 15A that communicates with the body hole 16. Therefore, even if the air bubble reservoir A covers the body hole 16, the body hole 16 is prevented from being completely blocked by the air bubbles. Even if the body hole 16 of the lash adjuster 10 becomes covered with air bubbles, the supply of oil from the oil supply passage 94 to the body hole 16 via the recessed groove 15A is ensured. As a result, the supply of oil to the inside of the lash adjuster 10 continues, preventing the lash adjuster 10 from losing its functionality due to internal oil consumption.

[0035] As described above, the lash adjuster 10 according to embodiment 1 has recessed groove 15A formed as an uneven shape on the edge of body hole 16, which makes it difficult for air bubbles to adhere to the inner surface of body circumferential groove 15. As a result, lash adjuster 10 can prevent air bubbles from clogging body hole 16, ensuring a steady supply of oil to the interior. This allows lash adjuster 10 to maintain its functionality.

[0036] Furthermore, in the lash adjuster 10, the concave and convex shape according to the present disclosure is formed by the recessed groove 15A, which serves as a recess. Therefore, the lash adjuster 10 can easily form the concave and convex shape.

[0037] Furthermore, in lash adjuster 10, recessed groove 15A extends circumferentially along the inner surface of body circumferential groove 15 and intersects with the opening edge of body hole 16. Therefore, when manufacturing lash adjuster 10 by rotating body 11 around an axis using lathe machining or the like, recessed groove 15A can be formed at the same time as forming body circumferential groove 15, making it even easier to manufacture.

[0038] Furthermore, in the lash adjuster 10, the width W1 of the recessed groove 15A is smaller than the opening diameter D of the body hole 16. More specifically, the width W1 of the recessed groove 15A is set so that the relationship 1 / 3D≦W1≦1 / 2D holds true with respect to the opening diameter D of the body hole 16. Therefore, the lash adjuster 10 can reliably connect the oil flow path formed by the internal space of the recessed groove 15A to the body hole 16.

[0039] <Embodiment 2>

[0040] 6, the second embodiment of the present disclosure differs from the first embodiment in that the body 211 has a concave-convex shape and a convex rib 215A as a convex portion according to the present disclosure. Since the second embodiment is otherwise similar to the first embodiment, the same reference numerals are used to designate the same or corresponding components as those in the first embodiment, and redundant explanations will be omitted.

[0041] As shown in FIG. 6, the body 211 has a ridge 215A. The ridge 215A protrudes radially outward from the innermost surface of the body circumferential groove 15, forming a step. Similar to the recessed groove 15A in the first embodiment, the ridge 215A extends circumferentially on the innermost surface of the body circumferential groove 15 and intersects with the opening edge of the body hole 16. More specifically, the ridge 215A extends in a ring shape in the circumferential direction on the innermost surface of the body circumferential groove 15 so as to pass through the body hole 16. The ridge 215A is formed simultaneously when the body circumferential groove 15 is machined.

[0042] As shown in FIG. 6, two ridges 215A are provided. The two ridges 215A extend parallel to each other and spaced apart in the axial direction. Each ridge 215A is connected to the edge of the body hole 16 in the body circumferential groove 15. Each ridge 215A is formed on both axial sides of the body 211, sandwiching the center of the body hole 16. As shown in FIG. 6, the width W2 of each ridge 215A is smaller than the opening diameter D of the body hole 16. Furthermore, the height H2 of the ridge 215A is set to be approximately equal to the width W1. Note that the width W2 and height H2 of the ridge can be greater than or equal to one-third and less than one-half of the opening diameter D of the body hole, similar to a recessed groove, for example. The height H2 of the ridge is preferably greater than the width W2. Furthermore, as shown in FIG. 6, a recessed groove-like space 215B having a depth equal to the height H2 of the ridge 215A is formed between the two ridges 215A. The width W3 of the space 215B is approximately equal to the width W3 of the ridge 215A. The width W3 of the groove-like space formed between such multiple ridges is preferably smaller than the height H2 of each ridge (depth of the groove-like space).

[0043] According to the second embodiment, by forming the ridge 215A as the uneven shape according to the present disclosure, it is possible to prevent the air bubble trap A from adhering to the inner surface of the body circumferential groove 15. This makes it easier to avoid clogging of the body hole 16 by the air bubble trap A, ensures the supply of oil to the interior, and makes it easier to maintain the function of the lash adjuster.

[0044] Furthermore, the ridge 215A, which has a concave-convex shape, protrudes from the innermost surface of the body circumferential groove 15. Therefore, even if an air bubble trap A accumulates, the step between the protruding end of the ridge 215A and the innermost surface of the body circumferential groove 15 prevents the air bubble from contacting the innermost surface of the body circumferential groove 15. Furthermore, two ridges 215A are formed, and a groove-like space 215B is formed between them. This space 215B functions similarly to the groove 15A in the first embodiment, and functions as an oil flow path that communicates with the body hole 16. This ensures the supply of oil from the oil supply passage 94 to the body hole 16, preventing the lash adjuster from losing its function.

[0045] [Another embodiment of the present disclosure] The above-described embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. In the above embodiments, the concave grooves and convex ridges serving as the concave and convex shapes (concave and convex portions) were formed with a certain length, such as grooves and ridges. In contrast, the concave and convex shapes according to the present disclosure may be hole-shaped, protrusion-shaped, or the like. That is, the concave and convex shapes may be formed in a concave and convex shape at the edge of the body hole in the body circumferential groove. Furthermore, the concave and convex shapes may be fine concave and convex shapes such as matte finish and hairline finish. Even if the irregularities have a length, they do not necessarily have to be annular. The irregularities may be formed only on the edge of the body hole. The irregularities may extend in a direction other than the circumferential direction, such as an axial direction. The irregularities may extend in a different direction, such as a radial direction. When the uneven shape according to the present disclosure is a groove, the number of grooves may be two or more. When the uneven shape according to the present disclosure is a ridge, the number of grooves may be one, or three or more. The uneven shape may be a combination of a recess and a protrusion, for example, a combination of a groove and a ridge. [Explanation of symbols]

[0046] 10...Lash adjuster 11,211...Body 12...Plunger 13...Bottom wall 14...Peripheral wall 15...Body circumferential groove 15A…Concave groove (uneven shape) 16...Body hole 17...Bottom wall 18...Peripheral wall 19...Support part 21...apex hole 22...Low pressure chamber 24...Plunger circumferential groove 25...Plunger oil hole 26...Valve orifice 27...Hypertensive chamber 28...Valve body 29…Cage 31...1st Spring 32...Second spring 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...Fuel line 215A…Convex strip (uneven shape) 215B...Space between ridges (uneven shape) A: Air bubble accumulation D...Body hole opening diameter H1: Groove depth H2: Height of the ridge W1: Groove width W2: Width of the ridge

Claims

1. a cylindrical body; and a cylindrical plunger disposed within the body so as to be reciprocally slidable relative to the body, the body has a bottom wall, a peripheral wall rising from the bottom wall, a body circumferential groove recessed along the entire outer circumferential surface of the peripheral wall, and a body hole opening into a deep surface of the body circumferential groove and supplying oil to the plunger, The body has an uneven shape on an edge of the body hole in the body circumferential groove.

2. the concave-convex shape is formed by at least one of a concave portion and a convex portion provided on a deep surface of the body circumferential groove, 2. The lash adjuster according to claim 1, wherein at least one of the recessed portion and the protruding portion extends circumferentially on a deep surface of the body circumferential groove and intersects with an opening edge of the body hole.

3. The lash adjuster according to claim 2 , wherein a width of at least one of the recessed portion and the protruding portion is smaller than an opening diameter of the body hole.

4. 4. The lash adjuster according to claim 2, wherein a plurality of at least one of the recessed portion and the protruding portion are arranged in parallel.

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