JP5999964B2 - EGR device - Google Patents

Description

  The present invention relates to an EGR device, and more particularly to an EGR device having a configuration in which an EGR gas recirculation passage is provided in a cylinder head from a side surface where an exhaust port is opened to an EGR valve mounting side surface.

  2. Description of the Related Art Recently, an EGR (Exhaust Gas Recirculation) is mounted on an internal combustion engine (hereinafter also referred to as “engine”) of an automobile for the purpose of reducing nitrogen oxide (NOx) generated during combustion. This is because part of the exhaust gas extracted from the exhaust system (hereinafter referred to as “EGR gas”) is mixed into the intake air to reduce the oxygen concentration, thereby reducing the combustion temperature and suppressing the generation of NOx. It has the effect of reducing loss. Here, an apparatus for realizing EGR is referred to as an EGR apparatus.

  Since the EGR device returns a part of the exhaust gas to the intake side, it is necessary to provide an EGR gas recirculation passage that communicates from the exhaust system to the intake system. For example, if the EGR gas recirculation passage is installed by providing a pipe that passes from the exhaust manifold to the outside of the cylinder head, the number of parts increases, the cost increases, and the layout space around the engine increases. The problem of not becoming.

  In order to cope with this problem, Patent Document 1 provides an EGR gas recirculation passage in the cylinder head, and forms a groove on one side of the cylinder head that connects the EGR gas recirculation passage and the exhaust port. An invention is disclosed in which an EGR gas passageway (a “second EGR passage” in Patent Document 1) is formed that connects the EGR gas recirculation passage in the cylinder head and the exhaust port by covering.

JP 2001-342907 A

  In Patent Document 1, since there is no pipe arranged outside the cylinder head, the number of parts is reduced and the bulk of the engine itself is also eliminated. However, the EGR gas passage that communicates with the EGR gas recirculation passage formed in the cylinder head and the exhaust port covers the groove provided on the side surface of the cylinder head with the connecting flange plate of the exhaust manifold and the lid plate integral with the exhaust manifold. Formed with.

  The members such as the connecting flange plate and the lid plate integrated with the connecting flange plate are plate-like members having a certain area, and the exhaust gas discharged from the exhaust port collides with the normal direction of the plate-like member. Then, there arises a problem that the plate-like member is vibrated and noise is generated when the exhaust gas, which is an extremely high temperature and high pressure and further pulsating gas, collides.

  The present invention is an EGR device that has been conceived in view of the above-described problems, and includes a gasket formed between a groove formed on the side surface of the cylinder head, a connecting flange of an exhaust manifold that serves as a lid for the groove, and a lid portion integrated with the flange. By sandwiching a plurality of the gaskets and making a notch in the gasket, the passage of the EGR gas formed by the groove and the lid portion and the exhaust port are communicated with each other on the side of the cylinder head.

More specifically, the EGR apparatus of the present invention is
A side surface where the exhaust port opens has a through hole communicating with the exhaust port, and a recessed groove extends in the crankshaft direction from the through hole,
A cylinder head provided at the end of the recessed groove with an inlet of an EGR gas recirculation passage formed from the side surface toward a side surface on which an EGR valve is disposed;
A gasket having a lid that covers the recessed groove;
An EGR device having a coupling flange disposed on the gasket, fixing the exhaust pipe, and provided with a lid portion covering the recessed groove,
Communication means for communicating the exhaust port and the through hole from the side surface side is provided ,
The gasket is at least two or more gaskets including first and second gaskets arranged to overlap from the side surface side,
The communication means is a notch provided in the first gasket that communicates the exhaust port and the through hole from the side surface side .

  In the EGR apparatus according to the present invention, the exhaust gas discharged from the exhaust port does not directly collide with the connecting flange of the exhaust manifold and the lid unit integrated with the exhaust manifold, but collides with two gaskets disposed therebetween. . The gasket close to the cylinder head side is provided with a notch so that a communication gap is formed between the exhaust ports. Therefore, when high-temperature and high-pressure exhaust gas collides, the exhaust gas can escape to the exhaust port.

  Moreover, since the passageway of the EGR gas has a communication gap with respect to the exhaust port through which a large amount of exhaust gas flows, it can be said that the exhaust port side sucks exhaust gas that collides with the gasket. Therefore, when the configuration according to the present invention is used, an effect that noise is not generated can be obtained.

  Further, since the gasket (second gasket) on the side far from the cylinder head separates the EGR gas communication path and the lid part of the connecting flange, in particular, condensed water is generated in the EGR gas communication path, and the exhaust gas Even if it becomes a strongly acidic liquid, the connecting flange does not corrode. In other words, if a highly corrosion-resistant material such as stainless steel is used for the second gasket, the connecting flange does not need to use an expensive material having strong corrosion resistance, and the effect of contributing to cost reduction can be obtained. Can do.

  In addition, when the communication means is formed by notching all the gaskets sandwiched between the connecting flange and the cylinder head, the cross-sectional area of the communication means becomes wider and the exhaust gas escapes to the exhaust port side. It becomes easy. This can further reduce noise generation as a result. However, since the inner surface of the connecting flange is directly exposed to the exhaust gas atmosphere in the communication gap, it is necessary to subject the exposed surface to rust prevention treatment.

It is a top view which shows the structure of the cylinder head carrying the EGR apparatus which concerns on this invention. FIG. 2 is a partially enlarged view of FIG. 1. It is the figure seen from one side of a cylinder head. It is a figure showing the AA cross section of FIG. It is a figure which shows other embodiment. It is a figure which shows embodiment at the time of notching all the gaskets.

  The EGR apparatus of the present invention will be described below with reference to the drawings. The following description exemplifies an embodiment of the present invention, and changes within the scope of the present invention are included in the technical scope of the present invention without departing from the spirit of the present invention. Needless to say.

(Embodiment 1)
FIG. 1 shows a part of a plan view of a cylinder head 1 of an engine equipped with an EGR device 10 of the present invention as viewed from the head cover side. FIG. 2 is a partially enlarged view of FIG. Reference numeral 2 represents a cylinder. Although two cylinders are shown in FIG. 1, the number of cylinders is not limited to this. In the present embodiment, description will be made assuming that there are at least three cylinders. That is, the cylinder 2a and the cylinder 2b are arranged in this order, and the cylinder 2c (not shown in FIG. 1) is arranged on the opposite side of the cylinder 2b from the cylinder 2a. Reference numeral 3 denotes a line parallel to the arrangement direction of the crankshaft.

  The side surface 1a is a side surface on the side where the exhaust ports 4a and 4b are opened. This side is also called “one side”. Intake ports 5a and 5b are opened on the side surface 1b opposite to the side surface 1a. The side surfaces perpendicular to the side surfaces 1a and 1b are defined as side surfaces 1c and 1d. In addition, the side surface 1c shows an upper side surface in FIG. The side surface 1d is the opposite side surface, but is not shown. The upper surface of the cylinder head is 1e, and the lower surface is 1f. The upper surface 1e of the cylinder head is the side on which the head cover is disposed, and the lower surface 1f of the cylinder head is the side on which the cylinder block is disposed (see FIG. 3).

  The EGR device 10 of the present invention is disposed between a cylinder head 1, a connecting flange 14 for fixing an exhaust manifold 12 connected to the cylinder head 1, an exhaust manifold 12 and a connecting flange 14, and the cylinder head 1. And at least two gaskets 16 and 18.

  An exhaust port 4 (4a, 4b, etc.) extending from the combustion chamber of the cylinder 2 is formed in the cylinder head 1. An exhaust pipe 6 (6a, 6b, etc.) is connected to the exhaust port 4 respectively. The exhaust port 4 and the exhaust pipe 6 are connected by connecting the connecting flange 14 and the cylinder head 1, which connect the exhaust pipes 6 corresponding to the cylinders 2 together, with a plurality of fastening bolts 15. An exhaust manifold 12 is formed by the connecting flange 14 and the exhaust pipe 6. The exhaust pipe 6 and the connecting flange 14 are connected to each other at a joint 7 (see FIG. 2) by brazing or the like.

  Gaskets 16 and 18 are sandwiched between the exhaust manifold 12 and one side surface 1a of the cylinder head 1. Details regarding the gasket will be described later.

  The cylinder head 1 includes a combustion chamber, an intake port 5 (5a, 5b, etc.) that guides intake air to the combustion chamber, an exhaust port 4 that serves as a passage for discharging exhaust gas from the combustion chamber, and a valve mechanism that controls opening and closing of these ports. (Not shown) is one of the components of the engine. The cylinder head 1 is connected to a cylinder block (not shown) in which a cylinder in which a piston moves up and down is formed. As described above, the cylinder head 1 has the exhaust port 4 opened on one side surface 1a. Since the cylinder is arranged along the crankshaft, the exhaust port 4 also opens on one side surface 1a of the cylinder head 1 along the crankshaft.

  In the EGR device 10 of the present invention, the inlet 22 of the EGR gas recirculation passage 20 is provided at the end of one side surface 1 a of the cylinder block 1. The EGR gas recirculation passage 20 is formed in the cylinder head 1 toward a side surface on which an EGR valve (not shown) is disposed. Here, the “side surface on which the EGR valve is disposed” refers to a side surface having an outlet (not shown) of the EGR gas recirculation passage 20 provided in the cylinder head 1, and the four side surfaces (1a to 1a to 1) of the cylinder head 1. In addition to 1d), the upper and lower surfaces (1e, 1f) of the cylinder head 1 may be included. This is because a part of the EGR gas recirculation passage 20 may pass through the head cover and the cylinder block, and may not necessarily be configured only in the cylinder head 1.

  On one side surface 1 a of the cylinder head 1, the exhaust port 4 a closest to the inlet 22 of the EGR gas recirculation passage 20 is the exhaust port 4 at the end of the plurality of cylinders 2. The exhaust manifold 12 is formed so that the adjacent exhaust pipes 6 are as close as possible to reduce the size of the engine and to warm up the exhaust gas catalyst (not shown) connected to the exhaust manifold 12 as early as possible.

  Accordingly, the exhaust port 4a of the end cylinder 2a is formed with a curved portion 4s so as to approach the exhaust port 4b of the adjacent cylinder 2b from the outlet of the combustion chamber. In other words, the center line 2ac of the cylinder 2a and the center line 6ac of the exhaust port 6a do not coincide with each other and are shifted. For example, the center line 2bc of the cylinder 2b matches the center line 6bc of the exhaust port 6b.

  Therefore, the exhaust gas exiting from the combustion chamber is directed to the opening 4ao (see FIG. 2) of the exhaust port 4a along the curved portion 4s provided in the exhaust port 4a.

  In the EGR device 10 of the present invention, the through hole 24 is provided from one side surface 1a in the curved portion 4s of the exhaust port 4a of the cylinder 2a at the end. This through-hole 24 can also be formed in the cylinder head 1 formed with a mold by post-processing with a drill. Of course, the through hole 24 may be a through hole 24 formed by another method instead of a drill. The through hole 24 is a hole for taking out the EGR gas from the exhaust port 4a. Therefore, the opening on the exhaust port 4a side of the through hole 24 is called an inlet 24i (see FIG. 2) of the through hole 24, and the opening on one side surface 1a of the cylinder head 1 is called an outlet 24o of the through hole 24.

  On one side surface 1 a of the cylinder head 1, a recessed groove 26 is formed from the inlet 22 to the through hole 24 of the EGR gas recirculation passage 20. The recessed groove 26 includes an inlet 22 of the EGR gas recirculation passage 20 at one end and an outlet 24o of the through hole 24 at the other end.

  Reference is now made to FIG. FIG. 3 is a view of the cylinder head 1 as viewed from one side surface 1a. The exhaust port 4 has three openings (4ao, 4bo, 4co). A through hole 24 is provided on the side surface 1c side of the exhaust port 4a at the end of the exhaust port 4 provided side by side (this is referred to as “outside” of the exhaust port 4a). The inlet 22 of the EGR gas recirculation passage 20 is formed at the end of one side surface 1 a of the cylinder head 1. Here, the end portion of one side surface 1 a indicates the space between the outlet 24 o of the through hole 24 and the other side surface 1 c of the cylinder head 1.

  The recessed groove 26 is formed as a region including the outlet 24o of the through hole 24 and the inlet 22 of the EGR gas recirculation passage 20 at both ends. The width 26 w of the recessed groove 26 is not particularly limited as long as it includes the diameters of the outlet 24 o of the through hole 24 and the inlet 22 of the EGR gas recirculation passage 20. For example, the width from the outlet 24 o of the through hole 24 to the inlet 22 of the EGR gas recirculation passage 20 may not be the same. However, a shape that provides resistance to the flow of EGR gas is not preferable. For example, the width 26w of the recessed groove 26 is suddenly narrowed in the middle.

  Since the recessed groove 26 is formed on one side surface 1a of the cylinder head 1, it can be said that it is formed in the crankshaft direction. In this case, the crankshaft direction may be formed in one side surface 1a toward the outside of the exhaust port 4a, and may be inclined toward the upper surface 1e or the lower surface 1f of the cylinder head.

  Referring again to FIGS. 1 and 2, the depth 26 d (see FIG. 2) of the recessed groove 26 is preferably set so that the sectional area of the recessed groove 26 is equal to or larger than the sectional area of the through hole 24. This is to reduce the flow resistance as much as possible with respect to the flow of EGR gas. The depth 26 d of the recessed groove 26 refers to the distance from the surface of one side surface 1 a of the cylinder head 1 to the bottom 26 b of the recessed groove 26.

  Gaskets 16 and 18 are sandwiched between the cylinder head 1 and the exhaust manifold 12. The gaskets 16 and 18 are members for ensuring airtightness between the cylinder head 1 and the exhaust manifold 12, and are sheet-like members having a thickness of about 0.5 to 1 mm formed of stainless steel. In the EGR device 10 of the present invention, two gaskets (16, 18) are used. In this embodiment, a case where there are two gaskets will be described. However, at least two gaskets may be used, and three or more gaskets may be used.

  The two gaskets (16, 18) are referred to as a first gasket 16 and a second gasket 18 from the side close to the surface of one side surface 1a of the cylinder head 1. The first and second gaskets (16, 18) are provided with holes (16b, 18a, 18b, etc.) having substantially the same diameter as that of the opening 4o at a portion corresponding to the opening 4o of the exhaust port 4. As will be described later, since the first gasket 16 is provided with a notch 16z on the cylinder 2a side, there is no hole having substantially the same diameter as the opening 4ao of the exhaust port 4a.

  In the second gasket 18, no hole is formed in a portion corresponding to the recessed groove 26 formed in one side surface 1 a of the cylinder head 1. This is because the passage of EGR gas is formed by covering the recessed groove 26 with the second gasket 18. A portion of the gasket corresponding to the recessed groove 26 is defined as a second gasket lid portion 18m. Since the first gasket 16 has a notch 16z, which will be described later, there is no first gasket lid. The passage of EGR gas is referred to as an EGR gas communication passage 30. In other words, the EGR gas communication passage 30 is an EGR gas passage that communicates the outlet 24 o of the through hole 24 and the inlet 22 of the EGR gas recirculation passage 20 by the recessed groove 26 and the second gasket lid portion 18 m of the second gasket 18. Yes (see FIG. 2).

  The first gasket 16 is provided with a notch 16z extending from the outlet 24o of the through hole 24 to the opening 4ao of the adjacent exhaust port 4a. That is, the opening 4ao of the exhaust port 4a adjacent to the outlet 24o of the through hole 24 originally communicates within the exhaust port 4a, but also communicates with the notch 16z on one side surface 1a side. That is, the notch 16z of the first gasket 16 forms a communication gap that connects the opening 4ao of the exhaust port 4a and the through hole 24 from the one side surface 1a side. This communication gap is a communication means.

  Referring to FIG. 3, the width 16zw of the notch 16z in the first gasket 16 may or may not be the same width from the outlet 24o of the through hole 24 toward the opening 4ao of the exhaust port 4a. Also good. The second gasket 18 is not provided with such a notch. The cutout 16z only needs to be long enough to form a communication gap that connects the opening 4ao of the exhaust port 4a and the through hole 24. However, as shown in FIG. 3, it may be extended to a length including the inlet 22 of the EGR gas recirculation passage 20.

  Referring to FIGS. 1 and 2 again, the exhaust manifold 12 is fastened so that the gaskets 16 and 18 are sandwiched between one side surface 1 a of the cylinder head 1. The exhaust manifold 12 includes the connecting flange 14 and the exhaust pipe 6 as described above. The connecting flange 14 is formed with a lid body portion 14m that covers the recessed groove 26 of the cylinder head 1 and the gasket lid portion. Since the lid part 14m has a width that covers the recessed groove 26, the rigidity is reduced at this part.

  Referring to FIG. 3, the fastening bolt 15 of the connecting flange 14 is disposed so as to surround the recessed groove 26. The AA cross section of FIG. 3 is shown in FIG. FIG. 4 shows a cross section of the recessed groove 26 formed on one side surface 1a of the cylinder head 1, the connecting flange 14 of the exhaust manifold 12, and the two gaskets 16 and 18 sandwiched therebetween.

  The gaskets (16, 18) and the connecting flange 14 are fastened to the cylinder head 1 with fastening bolts 15. The lid portion 14m, which is a portion corresponding to the recessed groove 26 of the coupling flange 14, is formed with a bead having a cross-sectional mountain shape. Thus, the rigidity can be improved by forming the connecting flange 14 (the lid portion 14m) of the portion where the recessed groove 26 is formed in a mountain-shaped cross section.

  Referring to FIGS. 3 and 4 at the same time, the peripheral portion of the coupling flange 14 is provided with a folded portion 14g that is bent in a direction perpendicular to the surface of one side surface 1a of the cylinder head 1. By doing in this way, the rigidity of connecting flange 14 itself can also be improved.

  With reference to FIGS. 1 and 2 again, the operation of the EGR device 10 of the present invention will be described. The EGR device 10 of the present invention extracts part of the exhaust gas as EGR gas from the exhaust port 4 of one cylinder 2 of the plurality of cylinders. Specifically, EGR gas is collected from the through hole 24 of the exhaust port 4a of the cylinder 2a. Since the exhaust gas from the cylinder 2a is discharged every combustion cycle, it has pulsation. In other words, exhaust gas having pulsation is introduced from the through hole 24 into the EGR gas communication path 30 (the recessed groove 26), flows along the EGR gas communication path 30, and recirculates from the inlet 22 of the EGR gas recirculation path 20 to the EGR gas recirculation. It flows through the passage 20.

  Here, it is the second gasket (18) that uses the recessed groove 26 as a sealed space and the EGR gas communication passage 30. However, the rigidity of the second gasket 18 is much lower than that of a portion through which EGR gas flows, such as the through hole 24 provided in the cylinder head 1. Therefore, each time high-temperature and high-pressure EGR gas flows into the EGR gas communication path 30, it undergoes pressure deformation. Since this pressure deformation is periodic, it is recognized as an abnormal sound having a specific frequency.

  However, if the first gasket 16 is provided with a notch 16z (communication gap: communication means) communicating between the recessed groove 26 and the opening 4ao of the exhaust port 4a as in the present invention, Since part of the EGR gas that has flowed into the EGR gas communication passage 30 (the recessed groove 26) from the outlet 24o escapes to the opening 4ao side of the exhaust port 4a, the second gasket (18) is not deformed, and an abnormal noise with a specific frequency is obtained. Does not occur.

  Further, since the second gasket 18 separates the EGR gas communication passage 30 and the lid portion 14m of the connecting flange 14 in particular, condensed water is generated in the EGR gas communication passage 30 and is strongly acidic by the exhaust gas. Even if it becomes liquid, the connecting flange 14 does not corrode. That is, the connection flange 14 does not need to use an expensive material having strong corrosion resistance such as stainless steel, and can use an inexpensive material such as an iron material, which contributes to cost reduction.

  As described above, since the EGR gas communication passage 30 is provided in the cylinder head 1 in the EGR device 10 of the present invention, members for handling the EGR gas can be omitted, and the number of assembly steps can be reduced. I can do it. Further, an EGR gas communication passage 30 (concave groove 26) that connects a through hole 24 provided in the exhaust port 4 for taking out EGR gas and an inlet 22 of the EGR gas recirculation passage 20 provided in the cylinder head 1 and the exhaust port 4a. Since the opening 4ao is communicated with the communication means (communication gap), the EGR gas collides with the second gasket lid portion 18m or the like which is the lid of the recessed groove 26, or has a specific frequency generated by resonance or the like. Abnormal noise can be eliminated.

  The point of the present invention is to suppress the “sounding” generated by the pulsating EGR gas by connecting the through hole 24 and the exhaust port 4 on the side surface 1 a side of the cylinder head 1. Therefore, instead of making the notch 16z in the first gasket 16, a part of the surface portion of the cylinder head 1 may be cut to form a communication gap so that the recessed groove 26 and the opening 4ao of the exhaust port 4a communicate with each other. .

  In this case, the communication means (communication gap) is a communication groove 28 that connects the first gasket 17 without a notch, the recessed groove 26 provided on one side surface 1a of the cylinder head 1 and the exhaust port 4a ( (See FIG. 5). Further, since the communication groove 28 is formed by cutting a part of the cylinder head 1, the first gasket 17 does not need to be provided with a notch. Accordingly, the first gasket 17 may be formed with the first gasket lid portion 17m corresponding to the recessed groove 26. Further, in this case, one gasket may be used, and the second gasket 18 may be omitted.

(Embodiment 2)
FIG. 6 shows an EGR apparatus according to the present embodiment. The same parts as in FIG. 2 use the same reference numerals. In the present embodiment, the communication means is formed by notching all the gaskets. FIG. 6 shows a state in which the first gasket 16 having a notch and the second gasket 19 having a notch (19z) are used as gaskets.

  The notch 19z applied to the second gasket 19 may have the same shape as the first notch 16z. Moreover, a different shape may be sufficient. However, at least both gaskets are notched at the portion of the communication means (communication gap) for communicating the recessed groove 26 and the opening 4ao of the exhaust port 4a.

  Thus, by making a cut in both the two gaskets, the cross-sectional area of the communication means (here, the communication gap formed by the cut 16z and the cut 19z) for communicating the recessed groove 26 and the exhaust port 4 is reduced. Become wider. Then, more exhaust gas that has passed through the through hole 24 can escape to the exhaust port 4 side. Therefore, even if the exhaust gas pressure is high, the generation of abnormal noise can be suppressed.

  With such a configuration, the communication gap is formed by one side surface 1 a of the cylinder head 1 and the inner surface 14 i of the connecting flange 14. The inner surface 14i of the connecting flange 14 is a surface facing the notches (16z, 19z) and is directly exposed to the exhaust gas. Therefore, in the case of such a configuration, a rust prevention treatment is performed on a portion exposed to the exhaust gas. The rust prevention treatment is carried out by forming a rust prevention layer on the inner surface 14i of the connecting flange 14 by plating or coating. Further, the rust prevention treatment may extend to the inner surface 14mi of the lid body portion 14m.

  Or you may form all the flanges 14 for connection using the material which has rust prevention property, such as a stainless steel material. That is, here, “to be subjected to rust prevention treatment” includes forming the connecting flange 14 with a rust-proof material.

  The present invention can be suitably used for an engine equipped with an EGR device.

DESCRIPTION OF SYMBOLS 1 Cylinder head 1a One side surface (cylinder head) 2 Cylinder 3 Crankshaft arrangement direction 4 Exhaust port 4s Exhaust port curved part 4ao etc. Exhaust port opening 5 Intake port 6 Exhaust pipe 7 Junction point 10 EGR apparatus 12 Exhaust manifold 14 Connecting flange 14i (Inside of connecting flange) inner surface (surface facing notch)
14g Folding part 14m Lid part 14mi Inner surface of lid part 16 First gasket 16z Notch 16zw Notch width 16m First gasket lid part 17 (first gasket without notch)
18 2nd gasket 18m 2nd gasket cover part 19 (2nd gasket with a notch)
19z Notch 20 EGR gas recirculation passage 22 EGR gas recirculation passage inlet 24 Through hole 24i Through hole inlet 24o Through hole outlet 26 Recessed groove 26b Recessed groove bottom 26d Recessed groove depth 28 Recessed groove 30 EGR gas communication path

Claims (1)

A side surface where the exhaust port opens has a through hole communicating with the exhaust port, and a recessed groove extends in the crankshaft direction from the through hole,
A cylinder head provided at the end of the recessed groove with an inlet of an EGR gas recirculation passage formed from the side surface toward a side surface on which an EGR valve is disposed;
A gasket having a lid that covers the recessed groove;
An EGR device having a coupling flange disposed on the gasket, fixing the exhaust pipe, and provided with a lid portion covering the recessed groove,
Communication means for communicating the exhaust port and the through hole from the side surface side is provided ,
The gasket is at least two or more gaskets including first and second gaskets arranged to overlap from the side surface side,
The EGR device, wherein the communicating means is a notch provided in the first gasket that communicates the exhaust port and the through hole from the side surface side .