JP2006348837A - Cylinder head cover supporting structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure of supporting a cylinder head cover formed of a low-rigidity material into a bowl shape and mounted on a cylinder head to cover the upper face of the cylinder head, wherein the cylinder head cover using a member specific for the cylinder head is supported at its upper portion and at its outer peripheral skirt portion with ease of maintenance and no leakage of lubricating oil from the outer peripheral skirt portion of the cylinder head cover. <P>SOLUTION: The cylinder head cover is supported by the member integrally fixed to the cylinder head of an internal combustion engine. The outer peripheral skirt portion of the cylinder head cover abuts on the peripheral edge of the cylinder head via a seal member having close contact with the inside/outside face thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a support structure for attaching a cylinder head cover to a cylinder head, and more particularly to a support structure suitable for attaching a cylinder head cover made of a material having low rigidity such as resin. The support structure of the present invention can also be applied to attachment of a thin metal cylinder head cover.

  As a conventional example of attaching a plastic cylinder head cover to the cylinder head, the cylinder head cover is fixed in a suspended state by fixing the center upper part of the cylinder head cover to the receiving column erected on the cylinder head via an elastic member. The thing which has arrange | positioned packing to the joint surface of a skirt part and a cylinder head is disclosed (for example, refer patent document 1). The resin cylinder head cover is more likely to be deformed due to pressure fluctuations in the cylinder head cover or the like than a metal one. In this conventional example, since the holding of the outer peripheral skirt portion of the cylinder head cover is planar, it is difficult to improve the sealing performance against fluctuations in the pressure in the cover.

  As an example in which the conventional example is further improved, a liquid gasket is interposed between the flange at the outer peripheral skirt portion of the cylinder head cover and the cylinder head in the suspension type resin cylinder head cover similar to the above. An example is known in which the gasket head adhesiveness is used to prevent the cylinder head cover from being separated or displaced between the outer peripheral skirt and the cylinder head when the cylinder head cover is deformed (see, for example, Patent Document 2). However, it takes time to apply the liquid gasket, and it takes time to cure, so the working efficiency is low. Furthermore, once cured, the engine cannot be reused after being disassembled, and it is necessary to apply a new liquid gasket every time it is disassembled for maintenance or the like.

  In addition, conventionally, a semicircular recess serving as a relief for inserting a tool for machining a camshaft bearing portion is provided for each camshaft, so that the shape of the edge of the cylinder head end is complicated. . For this reason, after closing the said recessed part of a cylinder head using the plug body of the elastic body produced separately, the cylinder head cover was attached to the cylinder head (for example, patent document 3). This method has a problem that it takes time to manufacture and attach a separate plug.

Japanese Utility Model Publication No. 63-19575 Japanese Utility Model Publication No. 58-57540 Japanese Utility Model Publication No. 62-24033.

  The present invention is based on the prior art only for the purpose of fixing the upper part of the cylinder head cover when the cylinder head cover made of a low rigidity material such as resin or the thin metal cylinder head cover which is easily deformed is attached to the cylinder head. The support structure for the upper part of the cylinder head cover that uses the members that are inherent to the cylinder head is provided, and the outer periphery hem of the cylinder head cover that is suspended is removed. It is an object of the present invention to provide a support structure for an outer peripheral skirt portion that does not cause lubricating oil leakage from the portion and is easy to maintain. It is another object of the present invention to provide a simple means for closing a semicircular recess provided for the convenience of processing the bearing without using a separate plug.

  The present invention solves the above-mentioned problems, and the invention according to claim 1 is a cylinder head cover support structure that is formed in a bowl shape and is attached to a cylinder head so as to cover the upper surface of the cylinder head. An upper portion is supported by a cylinder head of an internal combustion engine, and an outer peripheral skirt portion of the cylinder head cover is in contact with a peripheral portion of the cylinder head through a seal member in close contact with the inner and outer surfaces thereof. It is.

  According to a second aspect of the present invention, in the cylinder head cover support structure according to the first aspect, a groove portion is formed in the peripheral portion of the cylinder head facing the outer peripheral skirt portion of the cylinder head cover, and the cross section is formed in a concave shape. In addition, the seal member is accommodated in the groove portion, and the outer peripheral skirt portion of the cylinder head cover is accommodated in the groove portion.

  According to a third aspect of the present invention, in the support structure of the cylinder head cover according to the first or second aspect, the member that supports the cylinder head cover is a holder that holds a valve operating device disposed in the cylinder head. An insertion hole for inserting a spark plug is formed in the holder, and an opening is formed at a position of a cylinder head cover corresponding to the insertion hole. The cylinder head cover is formed around the opening via a seal member. It is supported on the outer periphery of the spark plug insertion hole.

  According to a fourth aspect of the present invention, in the support structure for a cylinder head cover according to the first to third aspects, the member that supports the cylinder head cover supports two camshafts arranged in the cylinder head. A plurality of bearings are formed, and an approximate trapezoidal recess is formed in the facing part of the cylinder head located in the direction of the camshaft. The portion to be formed is formed so as to close the concave portion.

  According to the first aspect of the present invention, the seal member is brought into contact between the inner and outer side surfaces of the cylinder head cover outer peripheral skirt and the cylinder head, and the sealing performance is secured on the side of the cylinder head cover outer peripheral skirt. Even if the expansion / contraction deformation occurs, the state in contact with the seal member can be maintained, and the sealing performance is not deteriorated, so that the lubricating oil does not leak.

  According to the second aspect of the present invention, the seal member having a concave cross section is accommodated in the groove portion of the cylinder head, and the outer peripheral hem portion of the cylinder head cover is accommodated in the concave portion of the seal member. The seal member can be formed as an integral member, and the assemblability can be improved.

  According to the invention of claim 3, the periphery of the opening provided at the position of the cylinder head cover corresponding to the spark plug insertion hole of the holder holding the valve operating device is surrounded by the outer periphery of the spark plug insertion hole of the holder via the seal member. Therefore, the support portion of the cylinder head cover can be made larger and the support can be strengthened as compared with the prior art.

  According to the invention of claim 4, a recess that becomes a relief at the time of machining the camshaft bearing portion provided on the side surface of the cylinder head located in the camshaft direction is formed in an approximate trapezoidal recess including both the bearing portions of the two camshafts, Since the cylinder head cover has a shape corresponding to the approximate trapezoidal concave portion, there is no need to use a plug to close the concave portion, and when a recess portion for machining is provided corresponding to each camshaft. In comparison, the sharp curved shape of the edge can be reduced, and the sealing performance can be prevented from being deteriorated by the sharp curved portion. In addition, the shape of the seal member can be simplified and the number of manufacturing steps can be reduced. In addition, compared with the case where semicircular recesses for clearance during machining are provided corresponding to each camshaft, the area of the approximate trapezoidal recess of the present application is large. Further reduction in weight of the manufactured cylinder head can be achieved.

  FIG. 1 is a top view of a cylinder head 1 of an in-line three-cylinder internal combustion engine according to the first embodiment of the present invention. An intake cam shaft 2 and an exhaust cam shaft 3 are rotatably held by the cylinder head 1. In the figure, the position of each camshaft is indicated by a center line. A cam chain chamber 4 is provided near the end of the cylinder head 1. One lower camshaft holder 6 is formed integrally with the cylinder head 1 adjacent to the cam chain chamber 4. Three spark plug mounting holes 9 are provided on the upper surface of the cylinder head 1. Three lower camshaft holders 11 having the same shape and surrounding the spark plug mounting hole 9 are formed integrally with the cylinder head 1.

  The intake camshaft 2 and the exhaust camshaft 3 are supported by the four lower camshaft holders 6 and 11, their end portions project into the cam chain chamber 4, and the respective driven sprockets are fixed to the end portions. Is done. A drive sprocket is fixed to the crankshaft, the driven sprocket is driven via a cam chain, and the camshafts 2 and 3 are thereby driven.

  Around each of the spark plug mounting holes 9, there are four valve mounting portions, two of which are intake valve mounting portions 14, and the other two are exhaust valve mounting portions 15. The intake port 16 can be seen on the side of the intake valve mounting portion 14 in the figure. A gasket mounting groove 19 is provided in the peripheral edge 18 on the upper surface of the cylinder head.

  FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 and shows the end of the cylinder head 1 as seen from the cam chain chamber 4. In the drawing, the intake camshaft 2 and the exhaust camshaft 3 are indicated by two-dot chain lines. In addition, the outer peripheral circles of the intake camshaft driven sprocket 22 and the exhaust camshaft driven sprocket 23 at each shaft end are indicated by two-dot chain lines. An approximate trapezoidal recess 20 is formed in the opposite portion of the cylinder head located in the direction of the cam shaft, which serves as a relief when machining the journal bearing portion on the lower cam shaft holder side of the cam shaft. Details will be described later in connection with FIGS. The gasket mounting groove 19 is also curved along the peripheral edge of the approximate trapezoidal recess 20. As shown in FIG. 2, one side of the cylinder head is high and the other side is low. The intake camshaft 2 side is high and the exhaust camshaft 3 side is low.

  FIG. 3 is a top view of the cylinder head cover 25 covering the upper part of the cylinder head. The cylinder head cover 25 is made of synthetic resin. Three spark plug insertion openings 25a are provided on the upper surface. This is provided at a position corresponding to the spark plug mounting hole 9 of the cylinder head.

  4 is a sectional view taken along line IV-IV in FIG. 3, FIG. 5 is a sectional view taken along line V-V in FIG. 3, and FIG. 6 is a sectional view taken along line VI-VI in FIG. Three spark plug insertion openings 25a can be seen on the upper surface of the cylinder head cover 25 of FIG. The bulging portion at the end of the cylinder head cover is a cam chain chamber 25 b on the cylinder head cover 25 side that is continuous with the cam chain chamber 4 of the cylinder head 1. An outer peripheral skirt portion of the cam chain chamber 25b of the cylinder head cover is an extending portion 25c extending toward the cylinder head so as to fit in the recessed portion so as to close the approximate trapezoidal recessed portion 20 of the cylinder head 1.

  7 is a cross-sectional view taken along the line VII-VII of FIG. 1 in a state where the cylinder head 1 of FIG. 1 is covered with the cylinder head cover 25, and shows a cross section of the cam shaft holder assembly 5 adjacent to the cam chain chamber 4. . The cam shaft holder assembly 5 includes a lower cam shaft holder 6, an upper cam shaft holder 7, a pair of long bolts 8 x, and a pair of short bolts 8 y, and the upper cam shaft holder 7 is bolted to the lower cam shaft holder 6. The intake camshaft insertion hole 5a and the exhaust camshaft insertion hole 5b are formed by fastening through 8x and 8y.

  In the drawing, an approximate trapezoidal recess 20 on the periphery of the cylinder head on the cam chain chamber 4 side located on the front side of the camshaft holder assembly 5 is depicted by a one-dot chain line. The edge of the approximate trapezoidal recess 20 is formed lower than the peripheral edge 18 of the other part of the upper surface of the cylinder head. This approximate trapezoidal concave portion 20 includes journal bearing portions 6a and 6b that are cut into the lower camshaft holder 6 in the manufacturing stage of the cylinder head alone before the camshaft holder assembly is assembled, and later shown in FIG. When machining the journal bearings 11a and 11b to be cut into the lower camshaft holder 11, the cutouts are provided for escape so as not to obstruct the insertion of the cutting tool.

  FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG. 1 in a state where the cylinder head 1 is covered with the cylinder head cover 25, and shows a cross section of the camshaft holder assembly 10 including the spark plug mounting hole 9. . The camshaft holder assembly 10 includes a lower camshaft holder 11, an upper camshaft holder 12, a pair of long bolts 13x, and a pair of short bolts 13y. The upper camshaft holder 12 is bolted to the lower camshaft holder 11. Fastened via 13x and 13y, an intake camshaft insertion hole 10a and an exhaust camshaft insertion hole 10b are formed. The journal bearing parts 11a and 11b of the lower camshaft holder 11 are parts cut from the approximate trapezoidal recess 20 side.

  A spark plug 21 is mounted in the center spark plug mounting hole 9. An intake valve mounting portion 14 and an exhaust valve mounting portion 15 are visible on the left and right of the spark plug 21. An intake port 16 and an exhaust port 17 are visible on the left and right outside of the cylinder head.

  The outer peripheral skirt portion 25d of the cylinder head cover 25 is inserted and mounted in a gasket mounting groove 19 provided in the peripheral edge portion 18 on the upper surface of the cylinder head via a large elastic gasket 26. The periphery of the three spark plug insertion openings 25a provided on the upper surface of the cylinder head cover 25 is sandwiched between the upper camshaft holder 12 and the flange portion 28b of the head cover fixing member 28 via small elastic gaskets 27, respectively. These are fastened to the lower camshaft holder 11 by bolts 13x. The cylinder head cover 25 is supported by the cylinder head 1 by fixing around the three spark plug insertion openings 25a.

  9 is a plan view of a large elastic gasket 26 interposed between the outer peripheral skirt 25d of the cylinder head cover and the gasket mounting groove 19, and FIG. 10 is a view of the gasket of FIG. 11 is an enlarged sectional view taken along line XI-XI in FIG. As shown in FIG. 10, the front side of the elastic gasket 26 is shaped along the edge of the approximate trapezoidal recess 20 on the upper surface of the cylinder head. As can be seen in FIG. 11, the inner groove 26a of the large elastic gasket 26 is provided with two left and right protrusions 26b. As a result, the cylinder head cover 25 is prevented from coming off upward, and even if the outer peripheral skirt 25d of the cylinder head cover 25 expands or contracts in the outward or inward direction, the sealing performance is achieved by either the inner or outer protrusion Is secured.

  12 is a plan view of a small elastic gasket 27 interposed around the spark plug insertion opening 25a of the cylinder head cover 25, and FIG. 13 is an XIII-XIII enlarged sectional view of FIG. As shown in FIG. 13, the inner groove 27a of the small elastic gasket 27 is also provided with two protrusions 27b on both sides. As a result, even if the cylinder head cover 25 expands or contracts in any direction, the sealing performance is secured by any one of the protrusions.

  FIG. 14 is a view of the upper camshaft holder 12 which is one member sandwiching the small elastic gasket 27. (A) is a top view, (b) is BB sectional drawing of (a). The upper camshaft holder 12 is provided with a spark plug insertion hole 12a through which the spark plug 21 is inserted. Further, insertion holes 12x and 12y for inserting the above-described large and small bolts 13x and 13y are provided, and the bolt 13x inserted into the insertion hole 12x is used for tightening the small elastic gasket 27.

  FIG. 15 is a view of the head cover fixing member 28 which is the other member sandwiching the small elastic gasket 27 interposed in the spark plug insertion opening 25a. (A) is a top view, (b) is BB sectional drawing of (a), (c) is CC sectional drawing of (a). The head cover fixing member 28 is provided with a spark plug insertion opening 28a through which the spark plug 21 is inserted. The small elastic gasket 27 is sandwiched between flange portions 28b around the head cover fixing member 28. An insertion hole 28x for inserting a bolt 13x for fastening the small elastic gasket 27 is provided. The bolt 13x passes through the head cover fixing member 28 and the upper camshaft holder 12 and is screwed to the lower camshaft holder 11.

  The cylinder head cover mounting structure described in detail above seals the cylinder head cover made of a material such as plastic, which has low rigidity and cannot be fastened by direct contact with a bolt, through an elastic body such as rubber. It can be attached to the cylinder without impairing the performance. This mounting structure can also be applied to the mounting of a cylinder head cover made of a thin metal material that is easily deformed.

The following effects are brought about by the above embodiment.
(1) The large elastic gasket (seal member) 26 is in contact between the cylinder head 1 and both the inner and outer side surfaces of the cylinder head cover outer peripheral skirt 25d, and the sealing performance is secured on the side surface of the cylinder head cover outer peripheral skirt 25d. Even when expansion / contraction deformation occurs due to a pressure change in the cylinder head cover 25-, the state in contact with the seal member can be maintained, and there is no fear of leakage of the lubricating oil.
(2) Since the large elastic gasket (seal member) 26 having a concave cross section is accommodated in the groove portion 19 of the cylinder head and the outer peripheral skirt portion 25d of the cylinder head cover is accommodated in the inner groove recess portion 26a of the seal member 26, The seal members that are in contact with both the inner and outer side surfaces of the outer peripheral skirt portion 25d can be formed as a single body, and assemblability can be improved.
(3) The upper camshaft around the spark plug insertion opening 25a provided in the cylinder head cover 25 corresponding to the spark plug insertion hole 12a of the upper camshaft holder is interposed via a small elastic gasket (seal member) 27. Since it is supported on the outer peripheral portion of the spark plug insertion hole 12a of the holder, the support portion of the cylinder head cover 1 can be enlarged as compared with the prior art, and the support can be strengthened.
(4) A recess serving as a relief when machining the camshaft journal bearing portion is formed in the approximate trapezoidal recess 20 including both journal bearing portions 6a, 6b, 11a and 11b of the two camshafts, and the shape of the cylinder head cover is as described above. Since the extended portion 25c has a shape corresponding to the approximate trapezoidal concave portion 20, it is not necessary to use a separately prepared plug for closing the concave portion, and a relief concave portion for processing is provided corresponding to each camshaft. Compared to the case, the sharp curved portion shape of the edge portion can be reduced, and the sealing performance due to the sharp curved portion can be prevented. Further, the shape of the large elastic gasket (seal member) 26 can be simplified to reduce the number of manufacturing steps. Further, since the area of the approximate trapezoidal recess 20 is large, the surface area of the lightweight cylinder head cover 25 can be increased to further reduce the weight of the cylinder head 1 made of metal.

  FIG. 16 is a view according to the second embodiment of the present invention, and shows a partial cross section of a camshaft holder including a spark plug mounting hole. This embodiment differs from the first embodiment in an upper cam holder 30, a head cover fixing member 31, and a pair of upper and lower O-rings 32 interposed between these members and the cylinder head cover 25. Parts other than those described above are the same as those in the first embodiment, and the same members as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

  An O-ring mounting groove 30b is provided on the upper surface of the periphery of the spark plug insertion hole 30a of the upper camshaft holder 30 of the present embodiment. An O-ring mounting groove 31c is provided on the lower surface of the flange portion 31b surrounding the outer periphery of the spark plug insertion opening 31a of the head cover fixing member 31. Both O-ring mounting grooves 30b and 31c are provided at positions corresponding to the top and bottom in the assembled state. The cylinder head cover 25 is sandwiched between the upper camshaft holder 30 and the head cover fixing member 31 via the O-rings 32 that are respectively inserted into the O-ring mounting grooves 30b and 31c. , 31 are fastened to the lower camshaft holder, and the cylinder head cover 25 is fixed to the cylinder head 1.

  In the present embodiment, the above-described O-ring 32 ensures the sealing performance of the support portion of the cylinder head cover 25. Further, since the O-ring of this embodiment is easier to obtain than the small elastic gasket 27 of the first embodiment, it helps to reduce the cost.

  FIG. 17 is a diagram according to the third embodiment of the present invention, and shows an enlarged cross section of the outer peripheral skirt holding structure of the cylinder head cover. This embodiment differs from the first embodiment in the dimensions of the peripheral portion of the lower cam holder 40, the cross-sectional shape of the large elastic gasket 41, and the outer peripheral skirt portion 42a of the cylinder head cover 42. Parts other than those described above are the same as those in the above embodiments, and the same members as those in the above embodiments are denoted by the same reference numerals.

  A continuous wall portion 40a and intermittent protrusions 40b are provided on the outer peripheral portion of the lower camshaft holder 40 of the present embodiment. Each of these is a portion cast integrally with the lower camshaft holder 40. FIG. 2B is a sectional view taken along the line BB in FIG. 2A, and shows only the continuous wall portion 40a and the intermittent projection 40b. A large elastic gasket 41 is mounted between the continuous wall portion 40a and the intermittent projection 40b. As seen in the cross section of the gasket 41, the upper end flange provided in each of the above-described embodiments is omitted. Further, since the position of the large-sized elastic gasket 41 is raised as compared with the above-described embodiments, the outer peripheral skirt portion 42a of the cylinder head cover 42 is shortened.

  In the present embodiment, since one portion sandwiching the elastic gasket 41 is an intermittent protrusion, oil can be easily removed compared to the above-described embodiments, and oil retention can be prevented.

1 is a top view of a cylinder head 1 of an in-line three-cylinder internal combustion engine according to a first embodiment of the present invention. It is II-II sectional drawing of FIG. FIG. 3 is a top view of a cylinder head cover 25 that covers an upper portion of the cylinder head. It is IV-IV sectional drawing of FIG. It is VV sectional drawing of FIG. It is VI-VI sectional drawing of FIG. FIG. 7 is a cross-sectional view taken along the line VII-VII in FIG. 1 in a state where the cylinder head cover 25 is put on the cylinder head 1 in FIG. 1. FIG. 5 is a cross-sectional view taken along line VIII-VIII in FIG. 1 in a state where the cylinder head cover 25 is put on the cylinder head 1 in FIG. 1. FIG. 3 is a plan view of a large elastic gasket 26 interposed between an outer peripheral skirt 25d of the cylinder head cover and a gasket mounting groove 19; It is the figure which looked at the gasket of FIG. 9 from the arrow X direction. It is XI-XI cross-sectional enlarged view of FIG. 3 is a plan view of a small elastic gasket 27 interposed around a spark plug insertion opening 25a of a cylinder head cover 25. FIG. It is XIII-XIII expanded sectional drawing of FIG. FIG. 6 is a diagram of the upper camshaft holder 12. 4 is a diagram of a head cover fixing member 28. FIG. It is a figure which concerns on 2nd Embodiment of this invention, and the partial cross section of the camshaft holder containing a spark plug mounting hole is shown. It is a figure which concerns on 3rd Embodiment of this invention, and the expanded cross section of the outer periphery skirt part holding structure of a cylinder head cover is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Cylinder head, 2 ... Intake cam shaft, 3 ... Exhaust cam shaft, 4 ... Cam chain chamber, 6 ... Lower cam shaft holder, 6a ... Journal bearing part, 6b ... Journal bearing part, 7 ... Upper cam shaft holder, 8x ... bolt, 9 ... spark plug mounting hole, 11 ... lower camshaft holder, 11a ... journal bearing, 11b ... journal bearing, 12 ... upper camshaft holder, 12a ... spark plug insertion hole, 12x ... bolt insertion hole , 13x ... bolt, 18 ... peripheral edge of cylinder head upper surface, 19 ... gasket mounting groove, 20 ... approximate trapezoidal recess, 21 ... spark plug, 25 ... cylinder head cover, 25a ... spark plug insertion opening, 25b ... cam chain chamber, 25c ... extended portion, 25d ... outer peripheral skirt, 26 ... large elastic gasket, 26a ... inner groove, 26b ... ridge, 27 ... small elastic gasket, 27a ... inner groove, 27b ... ridge, 28 ... head cover fixing member , 28a ... Ignition Lug insertion opening, 28b ... flange portion, 28x ... bolt insertion hole.

Claims (4)

In the support structure of the cylinder head cover which is formed in a bowl shape and is attached to the cylinder head so as to cover the cylinder head upper surface
The upper part of the cylinder head cover is supported by the cylinder head of the internal combustion engine,
A cylinder head cover support structure, wherein an outer peripheral skirt portion of the cylinder head cover is in contact with a peripheral portion of the cylinder head via a seal member in close contact with the inner and outer surfaces thereof. A groove is formed on the peripheral edge of the cylinder head facing the outer peripheral skirt of the cylinder head cover,
2. The support structure for a cylinder head cover according to claim 1, wherein the seal member having a concave cross section is accommodated in the groove portion, and the outer peripheral skirt portion of the cylinder head cover is accommodated in the groove portion. The member that supports the cylinder head cover is a holder that holds a valve operating device disposed in the cylinder head,
The holder is formed with an insertion hole for inserting a spark plug, and an opening is formed at the position of the cylinder head cover corresponding to the insertion hole,
3. The support structure for a cylinder head cover according to claim 1, wherein the cylinder head cover is supported on an outer periphery of a spark plug insertion hole of the holder through a seal member around the opening. The member that supports the cylinder head cover is formed with a plurality of bearing portions that support two camshafts arranged in the cylinder head,
In the opposed part of the cylinder head located in the direction of the camshaft, an approximate trapezoidal recess is formed that serves as a relief when the bearing part is processed,
4. The support structure for a cylinder head cover according to claim 1, wherein a portion corresponding to the concave portion of the cylinder head cover is formed so as to close the concave portion.

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