WO2024084540A1

WO2024084540A1 - Internal combustion engine

Info

Publication number: WO2024084540A1
Application number: PCT/JP2022/038528
Authority: WO
Inventors: 大片岡; 渉永田; 浩平那須
Original assignee: 本田技研工業株式会社
Priority date: 2022-10-17
Filing date: 2022-10-17
Publication date: 2024-04-25

Abstract

Provided is an internal combustion engine that is able to suppress the accumulation of combustion gas, improve the compression ratio of the combustion chamber, reduce an unburned gas component, and also contribute to improved fuel efficiency.　This internal combustion engine 4 comprises a crankcase 40, a cylinder block 42 forming a cylinder part 42a, a cylinder head 43, and a gasket 90 interposed between the cylinder block and the cylinder head, wherein a plurality of through-holes 48 for insertion of stud bolts 49 around the cylinder part are formed in the cylinder block and the cylinder head, the gasket comprises a cylinder hole 91 corresponding to the cylinder part and a plurality of bolt holes 92 corresponding to the through-holes, a second bolt hole and a second through-hole 48B corresponding thereto are positioned symmetrically about the cylinder hole with respect to a first bolt hole and a first through-hole 48A corresponding thereto, and the gasket is configured such that the shapes of the first bolt hole and the second bolt hole are dissimilar so that positional adjustment is possible for the direction Z connecting the centers of the first through-hole and the second through-hole.

Description

Internal combustion engine

The present invention relates to an internal combustion engine in which a gasket is interposed between the cylinder block and the cylinder head.

In recent years, research and development has been conducted into improving fuel efficiency, which contributes to energy efficiency, in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy.
2. Description of the Related Art For the purpose of improving fuel efficiency of an internal combustion engine, for example, Patent Document 1 listed below discloses an internal combustion engine in which a gasket is interposed between a cylinder block and a cylinder head.
In the following Patent Document 1, the holes provided in the gasket for passing oil are shown to be elliptical in shape, but the through holes for the stud bolts are all circular in shape.
In order to align the cylinder block and the cylinder head, knock pins are fitted into the through holes of the stud bolts, but in order to make it easier to attach the gasket to the knock pins, it is necessary to enlarge the cylinder hole of the gasket that corresponds to the cylinder part of the cylinder. This causes the volume of the combustion chamber to expand due to the space on the inner edge side of the cylinder hole, resulting in problems such as stagnation of combustion gas and a decrease in the compression ratio of the combustion chamber.

Japanese Utility Model Application Publication No. 5-073360 (Fig. 1)

Incidentally, in this technology for improving fuel efficiency, a challenge is to suppress the accumulation of combustion gas injected into the combustion chamber and improve the compression ratio of the combustion chamber.
In order to solve the above problems, the present invention aims to provide an internal combustion engine that can suppress the stagnation of combustion gas injected into the combustion chamber, improve the compression ratio of the combustion chamber, and reduce unburned gas components, thereby contributing to improved fuel efficiency.

In order to solve the above problems, the internal combustion engine of the present invention comprises:
A crankcase in which a crankshaft is rotatably supported;
a cylinder block connected to the crankcase and forming a cylinder portion;
a cylinder head connected to the cylinder block and having an intake port and an exhaust port formed therein;
In an internal combustion engine having a gasket interposed between the cylinder block and the cylinder head,
a plurality of through holes through which stud bolts are inserted are formed around the cylinder portion in the cylinder block and the cylinder head;
The gasket has a cylinder hole corresponding to a cylinder portion of the cylinder block,
a plurality of bolt holes including a first bolt hole and a second bolt hole corresponding to the plurality of through holes;
the second bolt hole and the second through hole corresponding thereto are positioned symmetrically with respect to the cylinder hole as a center with respect to the first bolt hole and the first through hole corresponding thereto;
The gasket is characterized in that the hole shapes of the first bolt hole and the second bolt hole are different from each other so as to enable position adjustment in a direction connecting the centers of the first through hole and the second through hole.

According to the above configuration,
Since the gasket can be precisely interposed between the cylinder block and the cylinder head by adjusting the positions of the first bolt hole and the second bolt hole relative to the cylinder block in the direction connecting the centers of the first through hole and the second through hole, the relative positional accuracy of the gasket with the cylinder block can be improved. As a result, the inner edge of the cylinder hole of the gasket can be positioned close to the periphery of the cylinder portion, which suppresses the accumulation of combustion gas injected into the combustion chamber and improves the compression ratio of the combustion chamber, thereby realizing a reduction in unburned gas components and ultimately contributing to improved fuel efficiency.

According to a preferred embodiment of the present invention,
The first bolt hole is circular and the second bolt hole is oval.
Therefore, the relative position of the oval second bolt hole with respect to the first bolt hole can be adjusted to more accurately interpose the gasket between the cylinder block and the cylinder head, improving the accuracy of the relative position of the gasket with the cylinder block. As a result, the inner edge of the cylinder hole of the gasket can be positioned close to the periphery of the cylinder section, which suppresses the accumulation of combustion gas injected into the combustion chamber and improves the compression ratio of the combustion chamber, thereby reducing unburned gas components and contributing to improved fuel efficiency.

According to a preferred embodiment of the present invention,
The major axis of the second bolt hole is oriented toward the center of the first bolt hole.
Since the long axis of the oval shape of the second bolt hole is oriented toward the center of the circular shape of the first bolt hole, the relative position of the oval shaped second bolt hole with respect to the first bolt hole can be more easily adjusted, and the gasket can be more accurately interposed between the cylinder block and the cylinder head, improving the accuracy of the relative position of the gasket with the cylinder block. As a result, the inner edge of the cylinder hole of the gasket can be more easily positioned close to the periphery of the cylinder portion, so that the stagnation of the combustion gas injected into the combustion chamber can be suppressed and the compression ratio of the combustion chamber can be improved. Therefore, the unburned gas component can be reduced, which contributes to improved fuel efficiency.

According to a preferred embodiment of the present invention,
The width of the second bolt hole in the minor axis direction is equal to the diameter of the first bolt hole.
Since the width of the oval shape of the second bolt hole in the short axis direction is equal to the diameter of the circle shape of the first bolt hole, the gasket can be prevented from being rotated around the first bolt hole. Therefore, the relative positional accuracy of the gasket with the cylinder block can be improved. As a result, the inner edge of the cylinder hole of the gasket can be positioned closer to the periphery of the cylinder portion more reliably, so that the stagnation of the combustion gas injected into the combustion chamber can be suppressed and the compression ratio of the combustion chamber can be improved. Therefore, the unburned gas component can be reduced, which contributes to improved fuel efficiency.

According to the internal combustion engine of the present invention,
Since the gasket can be precisely interposed between the cylinder block and the cylinder head by adjusting the positions of the first bolt hole and the second bolt hole relative to the cylinder block in the direction connecting the centers of the first through hole and the second through hole, the relative positional accuracy of the gasket with the cylinder block can be improved. As a result, the inner edge of the cylinder hole of the gasket can be positioned close to the periphery of the cylinder portion, which suppresses the accumulation of combustion gas injected into the combustion chamber and improves the compression ratio of the combustion chamber, thereby realizing a reduction in unburned gas components and ultimately contributing to improved fuel efficiency.

1 is a schematic right side view of a motorcycle equipped with a power unit including an internal combustion engine according to an embodiment of the present invention. FIG. 2 is a right side view from a crankcase to a head cover of the internal combustion engine of the power unit of FIG. 1 . 3 is a right side cross-sectional view from a crankcase to a head cover of an internal combustion engine of a power unit, shown in the same orientation as FIG. 2 . 4 is a front view of the gasket taken along the line IV-IV in FIG. 3. A corresponding portion of the cylinder block is indicated by a two-dot chain line. FIG. 5 is an enlarged view of a portion V in FIG. 4, and shows a schematic diagram of a relationship between a predetermined through hole and a predetermined stud bolt with respect to a bolt hole of a gasket. FIG. 5 is an enlarged view of a portion VI in FIG. 4, and is a schematic diagram showing the relationship of a through hole, a knock pin, and a stud bolt with respect to a first bolt hole of a gasket. FIG. 7 is an enlarged view of a portion VII in FIG. 4, and is a schematic diagram showing the relationship between the through hole, the knock pin, and the stud bolt with respect to the second bolt hole of the gasket. FIG. 4 is an enlarged cross-sectional view of a portion VIII in FIG. 3 .

An internal combustion engine according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG.
In the description and claims of this specification, the directions of front, back, left, right, up and down, etc., are based on the directions of a vehicle equipped with a power unit having an internal combustion engine according to this embodiment. Specifically, the vehicle in this embodiment is a scooter-type motorcycle (hereinafter, simply referred to as a "motorcycle").
In the drawings, arrows FR, LH, RH, and UP indicate the front, left, right, and upper sides of the vehicle, respectively.

FIG. 1 shows an outline of a right side view of a motorcycle 1 equipped with a power unit 3 having an internal combustion engine according to this embodiment.
The motorcycle 1 has a front body 1F and a rear body 1R connected via a low floor portion 1C. A body frame 2 forming the skeleton of the vehicle body is generally composed of a down tube 21 and a main pipe 22.
That is, a down tube 21 extends downward from a head pipe 20 at the front part 1F of the vehicle body, bends horizontally at its lower end and extends rearward below the floor part 1C, and a pair of left and right main pipes 22 are connected to its rear end. The main pipes 22 pass through a rising part 22a that rises diagonally rearward from the connecting part, then bend approximately horizontally at a predetermined height and extend rearward.

A fuel tank and a storage box (not shown) are supported by the main pipe 22, and the riding seat 11 is disposed above them.
At the front portion 1F of the vehicle body, a handlebar 12 is provided above and journalled on a head pipe 20, and a front fork 13 extends below and has a front wheel 14 journalled at its lower end.

A bracket 23 protrudes from the rising portion 22a of the main pipe 22, and a power unit side bracket 33 is attached to the bracket 23 via a link member 24, so that a swing-type power unit (hereinafter simply referred to as the "power unit") 3 is connected and supported so as to be able to swing up and down together with the rear wheel 15.
That is, the motorcycle 1 of this embodiment employs an upper link support structure for the power unit 3.

The power unit 3 has a forced air-cooled, single-cylinder, four-stroke cycle internal combustion engine 4 mounted in the front part of its unit case 30, which forms the crankcase 40 of the internal combustion engine 4. The internal combustion engine 4 supports a crankshaft 41, whose axis is aligned in the vehicle width direction, in a freely rotatable manner in the crankcase 40.

The internal combustion engine 4 also includes a cylinder block 42 that is connected to the crankcase 40 and forms a cylinder section (cylinder bore) 42a, a cylinder head 43 that is connected to the cylinder block 42 and forms a combustion chamber 65 between it and the cylinder section 42a, and an intake port 45 and an exhaust port 46 are formed (see FIG. 3), and a head cover 44 that covers the cylinder head 43. The cylinder block 42, cylinder head 43, and head cover 44 are mounted on the power unit 3 with the cylinder block 42, cylinder head 43, and head cover 44 tilted forward to a nearly horizontal position.

The cylinder block 42 and the cylinder head 43 are fastened together to the crankcase 40 by stud bolts 49 that are inserted into a plurality of through holes 48 provided between them (see FIG. 2).
The stud bolts 49 are inserted from above downward through a plurality of through holes 48 (four in this embodiment) that are drilled parallel to the cylinder axis X in the cylinder block 42 and the cylinder head 43 so as to surround the cylinder portion 42 a and the combustion chamber 65, and are fastened to the crankcase 40. A nut 49 a (see FIG. 2 ) is fastened to the upper end of the stud bolt 49.

The unit case 30 of the power unit 3 extends from the internal combustion engine 4 to the left rear and constitutes a transmission case section 31 that houses a belt-type continuously variable transmission, and the rear wheel 15 is journaled on a reduction gear mechanism 32 provided at the rear of the transmission case 31. As shown in FIG. 1, a rear cushion 16 is interposed between the rear end of the unit case 30 and the rear of the main pipe 22.

A throttle body 52 connected to an intake pipe 51 extending from the inlet of the intake port 45 at the top of the cylinder head 42 of the internal combustion engine 4, and an air cleaner 53 connected to the throttle body 52 are disposed on the upper part of the power unit 3.
An exhaust pipe 55 connected to the outlet of the exhaust port 46 at the bottom of the cylinder head 42 bends rearward and extends rearward along the right side of the vehicle, and is connected to a muffler 56 on the right side of the rear wheel 15. The muffler 56 is attached to the unit case 30 via a muffler stay 56a.

The front portion 1F of the vehicle body is covered at the front and rear by a front cover 17a and a rear cover 17b, and the center portion of the handlebar 12 is covered by a handlebar cover 17c.
A step plate 17d is attached to the floor portion 1C, and lower side covers 17e are provided extending downward along the left and right edges of the step plate 17d.

The rear body 1R is connected to the upper rear part of the step plate 17d, and a body cover 17f is placed over the main pipe 22 from the front to the left and right sides, and the seat 11 can be opened and closed to cover the upper opening of the body cover 17f. In a side view, the rear part of the body cover 17f tapers diagonally upward and rearward, and a rear fender 18 extends diagonally downward from the rear part to cover the rear wheel 15 from above.

FIG. 2 is a right side view from the crankcase 40 to the head cover 44 of the internal combustion engine 4 of the power unit 3. As shown in FIG.
The internal combustion engine 4 of this embodiment is of a forced air-cooled type, and the right side of the crankcase 40 is covered with a fan cover 70. The fan cover 70 has a cooling air intake window 71 opened around the axis of the crankshaft 41, and a rotating fan (not shown) is provided inside the cooling air intake window 71 concentrically with the crankshaft 41.
The cylinder block 42 and the cylinder head 43 are covered with a shroud 72 indicated by a two-dot chain line, and the shroud 72 is in communication with a fan cover 70. Outside cooling air is taken in through a cooling air intake window 71 by a rotary fan that rotates together with the crankshaft 41, and is forced into the shroud 72 via the fan cover 70, where it cools the cylinder block 42 and the cylinder head 43 and is then discharged.

The internal combustion engine 4 of this embodiment also employs an SOHC type valve system, and a cam chain 62 that rotates the camshaft 61 by the rotation of the crankshaft 41 is installed between the driven sprocket 61a of the camshaft 61 of the valve train 60 provided in the cylinder head 43 and the drive sprocket 41a of the crankshaft 41. A cam chain chamber 63 (see FIG. 4) for this purpose is provided on the side of the crankcase 40, cylinder block 42, and cylinder head 43, and in this embodiment, is provided next to and connected to the left side of the cylinder section 42a.

3 is a right side cross-sectional view from the crankcase 40 to the head cover 44 of the internal combustion engine 4 of the power unit 3, shown in the same orientation as FIG.
The crankshaft 41 is rotated clockwise in FIG. 2 by the back and forth movement of the piston 35 which slides within a cylinder portion 42a provided in a cylinder block 42 and oriented substantially in the front and rear direction.
At the upper end of the cylinder head 43 , between the head cover 44 and the cylinder head 43 , a camshaft 61 is supported rotatably in parallel with the crankshaft 41 .

A combustion chamber 65 of the internal combustion engine 4 is provided within the cylinder head 43, and the combustion chamber 65 is provided with an intake valve 85 and an exhaust valve 86 for controlling the intake and exhaust within the combustion chamber. The intake valve 85 and the exhaust valve 86 each have their lift amount and opening/closing timing controlled by a cam surface 64 provided on the camshaft 61 in accordance with the rotation of the camshaft 61.
In other words, the rotational torque of the crankshaft 41, which is driven to rotate in a clockwise direction in Figures 2 and 3 as the piston 35 moves up and down, is transmitted to the camshaft 61 via the cam chain 62 that is wound around it, and the intake valve 85 and exhaust valve 86 open and close the intake valve orifice 66 of the intake port 45 and the exhaust valve orifice 67 of the exhaust port 46 at a predetermined timing with respect to the combustion stroke of the internal combustion engine 4.

In order for the intake valve 85 and the exhaust valve 86 to open and close properly at the predetermined timing, the tension of the cam chain 62 must always be kept at an appropriate level.
However, vibrations may occur in the cam chain 62 due to a sudden change in the rotational speed of the crankshaft 41 caused by a sudden acceleration or deceleration by the driver, or due to a change in the running resistance from the road surface.

In this embodiment, as viewed from the right side as shown in FIG. 2, clockwise rotation of the drive sprocket 41a causes the cam chain 62 to run while meshing with the drive sprocket 41a and driven sprocket 61a, with the upper cam chain 62a on the side sent from the drive sprocket 41a to the driven sprocket 61a being slack, and the lower cam chain 62b on the side pulled by the drive sprocket 41a being tight.

In order to prevent the above-mentioned vibration of the cam chain 62 and provide a constant tension, the internal combustion engine 4 is provided with a cam chain tensioner mechanism 80 that presses on the slack side of the cam chain 62, i.e., the upper cam chain 62a, to maintain tension in the cam chain 62. It is equipped with a tensioner slipper 81 that presses on the cam chain 62 to guide it in sliding motion, and a screw-type tensioner 82 that presses on the tensioner slipper 81.

On the other hand, an oil pan 47 (see FIGS. 2 and 3) is provided below the crankcase 40.
In addition, an oil pump (not shown) driven by the power of the crankshaft 41 is provided inside the crankcase 40. When the oil pump is driven by the crankshaft 41, engine oil stored in the oil pan 47 is sucked in through a strainer (not shown) and sent from the oil pump through multiple oil passages to various parts of the internal combustion engine 4.
A portion of the oil is sent to the cylinder head 43 via an oil supply passage, which is a through-hole gap 48c (see Figure 5) between the inner surface of a specific through hole 48C of the multiple through holes 48 and the outer surface of a specific stud bolt 49C that passes through it, and is used for lubricating and cooling the valve mechanism 60 inside the cylinder head 43.

In addition, reference numeral 57 in FIG. 2 denotes an _O2 sensor for exhaust gas.
Furthermore, reference numeral 33 denotes a power unit side bracket for the upper link support structure of the power unit 3 described above.

In this embodiment, a metal gasket 90 is interposed between the cylinder block 42 and the cylinder head 43 which are fastened together by the stud bolts 49 .
The gasket 90 may be made of a material other than metal, such as resin.
FIG. 4 is a front view of the gasket 90 taken along the line IV-IV in FIG. 3, with the corresponding portion of the cylinder block 42 indicated by a two-dot chain line.
The mating surface 42b of the cylinder block 42 has a cylinder portion 42a opening approximately in the center, and four through holes 48 for inserting stud bolts 49 parallel to the cylinder axis X are formed around the cylinder portion 42a. As shown in FIG. 4, the gasket 90 has a cylinder hole 91 corresponding to the cylinder portion 42a of the cylinder block 42, as well as four bolt holes 92 corresponding to the four through holes 48.

The cylinder head 43, which is connected to the mating surface 42b (see Figure 3) via a gasket 90, also has four through holes 48 drilled at the same positions parallel to the cylinder axis X. The tips of the stud bolts 49 inserted from the front of the cylinder head 43 pass through the through holes 48 in the cylinder head 43 and the through holes 48 in the cylinder block 42 and are screwed into the crankcase 40, fastening and fixing the cylinder head 43 and the cylinder block 42 to the crankcase 40 (see Figure 2).

In this embodiment, the gasket 90 is provided with a cam chain chamber opening 93 corresponding to the cam chain chamber 63 on the left side of the cylinder hole 91 .
Two of the four bolt holes 92 are located between the cam chain chamber opening 93 and the cylinder hole 91, and the remaining two bolt holes 92 are located symmetrically about the cylinder hole 91 from each of the bolt holes 92.

In other words, as shown in FIG. 4, the cylinder block 42 with the gasket 90 interposed between it and the cylinder head 43 has a cylinder section 42a to which the cylinder hole 91 of the gasket 90 corresponds, and a cam chain chamber 63 is provided to the left of that, with two of the four through holes 48 located between the cam chain chamber 63 and the cylinder section 42a, and the remaining two through holes 48 are provided in symmetrical positions around the cylinder section 42a of each of the through holes 48. Therefore, the bolt holes 92 of the gasket 90 are also positioned symmetrically around the cylinder hole 91 corresponding to the cylinder section 42a, in line with the through holes 48.

A knock pin 95 is fitted into a first through hole 48A, which is one (the upper one in this embodiment) of the two through holes 48 located between the cam chain chamber 63 and the cylinder portion 42a, for precisely aligning and assembling the cylinder block 42 and the cylinder head 43. The lower through hole 48 may be the first through hole 48A.
The through hole 48 located symmetrically with respect to the first through hole 48A and the cylinder hole 91 serves as a second through hole 48B into which a knock pin 95 is fitted.

One of the two bolt holes 92 on the cam chain chamber opening 93 side, that is, the upper side in this embodiment, is a first bolt hole 92A, through which a knock pin 95 inserted into the first through hole 48A is inserted, and the bolt hole 92 symmetrically positioned about the cylinder hole 91 is a second bolt hole 92B, through which a knock pin 95 inserted into the second through hole 48B is inserted.
As described above, if the lower through hole 48 on the cam chain chamber 63 side is designated as the first through hole 48A, and the through hole 48 located symmetrically about the cylinder bore 91 is designated as the second through hole 48B, the lower of the two bolt holes 92 on the cam chain chamber opening 93 side becomes the first bolt hole 92A, and the bolt hole 92 located symmetrically about the cylinder bore 91 becomes the second bolt hole 92B.

Of the two bolt holes 92 other than the first bolt hole 92A and the second bolt hole 92B, in this embodiment, the upper bolt hole 92 on the opposite side of the cylinder hole 91 from the cam chain chamber opening 93 is used to insert a specified stud bolt 49C which passes through the aforementioned specified through hole 48C.
FIG. 5 is an enlarged view of the V portion in FIG. 4, and shows a schematic diagram of the relationship between a predetermined through hole 48C and a predetermined stud bolt 49C with respect to the bolt hole 92 of the gasket 90. As shown in FIG.
As shown in FIG. 5, a through-hole gap 48c is provided between the inner surface of a specific through-hole 48C and the outer surface of a specific stud bolt 49C. This gap 48c communicates with an oil pump (not shown) in the crankcase 40 and serves as a supply path for oil used to lubricate and cool the valve mechanism 60 in the cylinder head 43.
The predetermined through hole 48C and the predetermined stud bolt 49C may be provided corresponding to the other bolt hole 92 of the two bolt holes 92 other than the first bolt hole 92A and the second bolt hole 92B.

FIG. 6 is an enlarged view of portion VI in FIG. 4, and shows the relationship of the first through hole 48A, the knock pin 95, and the stud bolt 49 with respect to the first bolt hole 92A of the gasket 90, by means of two-dot chain lines.
7 is an enlarged view of portion VII in FIG. 4, and shows the relationship of the second through hole 48B, the knock pin 95, and the stud bolt 49 to the second bolt hole 92B of the gasket 90, using two-dot chain lines.
As shown in Figures 6 and 7, in this embodiment, the cylinder block 42 and the cylinder head 43 are precisely aligned with each other by a knock pin 95 that is inserted into the through hole 48 on the mating surface 42b of the cylinder block 42 and the through hole 48 on the mating surface 43b (see Figure 3) of the cylinder head 43, and are assembled with high precision.

The knock pin 95 is hollow cylindrical, with a stud bolt 49 inserted into the hollow hole. The cylinder block 42 and the cylinder head 43 are fastened to the crankcase 40 by the stud bolt 49 which passes through the through hole 48 and the knock pin 95 .
At this time, the gasket 90 is interposed between the cylinder block 42 and the cylinder 43 .

As shown in Figures 6 and 7, in this embodiment, the knock pin 95 is fitted into a pair of the first through hole 48A and the second through hole 48B which correspond to the first bolt hole 92A and the second bolt hole 92B of the gasket 90.
In other words, the first bolt hole 92A and the second bolt hole 92B of the gasket 90 are set to correspond to the first through hole 48A and the second through hole 48B into which the pair of knock pins 95 are fitted.

The first bolt hole 92A has a hole shape that allows the knock pin 95 of the corresponding first through hole 48A to be inserted with clearance, and the second bolt hole 92B has a hole shape that allows the knock pin 95 of the second through hole 48B that is paired with the first through hole 48A to be inserted with clearance.

The gasket 90 has first bolt holes 92A and second bolt holes 92B with different hole shapes so as to enable position adjustment in direction Z (see FIG. 4) connecting the centers of the first through holes 48A and the second through holes 48B.
Therefore, the positions of the first bolt hole 92A and the second bolt hole 92B relative to the cylinder block 42 in direction Z connecting the centers of the first through hole 48A and the second through hole 48B can be adjusted, and the gasket 90 can be precisely set in a desired position before being interposed between the cylinder block 42 and the cylinder head 43.

Figure 8 is an enlarged cross-sectional view of part VIII in Figure 3. As shown in the figure, the gasket 90 interposed between the cylinder block 42 and the cylinder head 43 must be positioned so that the inner edge 91a of the cylinder hole 91 of the gasket 90 is positioned radially outward from the cylinder axis X beyond the periphery 42b of the cylinder portion 42a so as not to enter the cylinder portion 42a of the cylinder block 42 and the combustion chamber 65 of the cylinder head 43.

However, when the inner edge 91a of the cylinder hole 91 of the gasket 90 is recessed, the space S extending from the combustion chamber 65 on the inner peripheral side of the inner edge 91a increases, making it easier for the combustion gas introduced into the combustion chamber 65 to stagnate. In addition, the increased volume of the combustion chamber 65 causes a decrease in the compression ratio, which leads to an increase in unburned gas components and a decrease in fuel efficiency, so it is desirable to suppress the volume of the space S.
Therefore, in order to reduce the space S on the inner side of the inner edge 91a of the cylinder hole 91 of the gasket 90, it is necessary to improve the relative positional accuracy of the gasket 90 with respect to the cylinder block 42 and position the inner edge 91a of the cylinder hole 91 of the gasket 90 as close as possible to the peripheral edge 42aa of the cylinder portion 42a.

In this embodiment, as described above, the relative positions of the first bolt hole 92A and the second bolt hole 92B relative to the cylinder block 42 can be adjusted, and the gasket 90 can be set precisely in a desired position and then interposed between the cylinder block 42 and the cylinder head 43, so that the inner edge 91a of the cylinder hole 91 of the gasket 90 can be positioned close to the peripheral edge 42aa of the cylinder portion 42a.
As a result, the volume of the space S can be reduced, the stagnation of the combustion gas injected into the combustion chamber 65 can be suppressed, and the compression ratio of the combustion chamber 65 can be improved, thereby reducing the unburned gas components, which ultimately contributes to improved fuel efficiency.

To explain this embodiment in more detail, as shown in FIGS. 4, 6 and 7, the first bolt hole 92A is circular, and the second bolt hole 92B is oval.
By adjusting the relative position of the oval-shaped second bolt hole 92B with respect to the first bolt hole 92A, the gasket 90 can be more precisely interposed between the cylinder block 42 and the cylinder head 43, thereby improving the accuracy of the relative position of the gasket 90 with respect to the cylinder block 42.
As a result, the inner edge 91a of the cylinder hole 91 of the gasket 90 can be positioned close to the periphery 42aa of the cylinder portion 42a, thereby reducing the space S, suppressing the accumulation of the combustion gas injected into the combustion chamber 65, and improving the compression ratio of the combustion chamber 65. This reduces the amount of unburned gas, which in turn contributes to improved fuel efficiency.

In this embodiment, as shown in FIGS. 4 and 7, the direction P of the major axis L of the second bolt hole 92B is oriented toward the center C of the first bolt hole 92A.
In this way, the direction P of the long axis L of the oval shape of the second bolt hole 92B is directed toward the center C of the circle of the first bolt hole 92A, so that the relative position of the oval shaped second bolt hole 92B with respect to the first bolt hole 92A can be more easily adjusted and the gasket 90 can be more precisely interposed between the cylinder block 42 and the cylinder head 43, thereby improving the accuracy of the relative position of the gasket 90 with the cylinder block 42.
As a result, the inner edge 91a of the cylinder hole 91 of the gasket 90 can be more easily positioned close to the periphery 42aa of the cylinder portion 42a, thereby reducing the space S, suppressing the accumulation of the combustion gas injected into the combustion chamber 65, and improving the compression ratio of the combustion chamber 65. This reduces the amount of unburned gas, which in turn contributes to improved fuel efficiency.

Furthermore, a feature of this embodiment is that, as shown in Figs. 4 and 7, the width W of the second bolt hole 92B in the direction of the minor axis M is equal to the diameter D of the first bolt hole 92A.
The width W of the oval shape of the second bolt hole 92B in the direction of the minor axis M is equal to the diameter D of the circle of the first bolt hole 92A, so that the gasket 90 can be prevented from being rotated around the first bolt hole 92A and being inserted therein. This improves the accuracy of the relative position of the gasket 90 with respect to the cylinder block 42.
As a result, the inner edge 91a of the cylinder hole 91 of the gasket 90 can be positioned closer to the peripheral edge 42aa of the cylinder portion 42a, thereby reducing the space S, suppressing the accumulation of the combustion gas injected into the combustion chamber 65, and improving the compression ratio of the combustion chamber 65. This reduces the amount of unburned gas, which in turn contributes to improved fuel efficiency.

Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and may take various forms within the gist of each claim. For example, the vehicle on which it is mounted is not limited to a scooter-type motorcycle as shown in the embodiment, the internal combustion engine is not limited to one provided in a swing-type power unit as in the embodiment, and may be an internal combustion engine fixed to a vehicle frame, and while the left and right, front and rear have been described according to the illustrations for ease of explanation, for example, the left and right may be reversed.

1...motorcycle, 2...body frame, 3...power unit (swing type power unit), 4...internal combustion engine, 30...unit case, 31...transmission case portion, 32...reduction mechanism, 35...piston, 40...crankcase, 41...crankshaft, 41a...driving sprocket, 42...cylinder block, 42a...cylinder portion, 42aa...periphery, 43...cylinder head, 43b...mating surface, 45...intake port, 46...exhaust port, 47...oil pan, 48...through hole, 48A...first through hole, 48B...second through hole, 48C...predetermined through hole, 48c...through hole gap, 49...stud bolt 49C...specified stud bolt, 49a...nut, 60...valve mechanism, 61...camshaft, 61a...driven sprocket, 62...cam chain, 63...cam chain chamber, 64...cam surface, 65...combustion chamber, 66...intake valve port, 67...exhaust valve port, 85...intake valve, 86...exhaust valve, 90...gasket, 91...cylinder hole, 91a...inner edge, 92...bolt hole, 92A...first bolt hole, 92B...second bolt hole, 93...cam chain chamber opening, 95...knock pin, X...cylinder axis, S...space, L...long axis, P...direction (of long axis L), M...short axis, W...width, C...center, D...diameter, Z...direction connecting centers

Claims

a crankcase (40) in which a crankshaft (41) is rotatably supported;
a cylinder block (42) connected to the crankcase (40) and forming a cylinder portion (42a);
a cylinder head (43) connected to the cylinder block (42) and having an intake port (45) and an exhaust port (46) formed therein;
An internal combustion engine (4) comprising a gasket (90) interposed between the cylinder block (42) and the cylinder head (43),
A plurality of through holes (48) through which stud bolts (49) are inserted are formed around the periphery of the cylinder portion (42a) in the cylinder block (42) and the cylinder head (43),
The gasket (90) has a cylinder hole (91) corresponding to the cylinder portion (42a) of the cylinder block (42),
a plurality of bolt holes (92) including a first bolt hole (92A) and a second bolt hole (92B) corresponding to the plurality of through holes (48);
the second bolt hole (92B) and the second through hole (48B) corresponding thereto are positioned symmetrically with respect to the cylinder hole (91) with respect to the first bolt hole (92A) and the first through hole (48A) corresponding thereto,
an internal combustion engine, characterized in that the first bolt hole (92A) and the second bolt hole (92B) have different hole shapes so as to enable position adjustment in a direction (Z) connecting the centers of the first through hole (48A) and the second through hole (48B).
2. The internal combustion engine of claim 1, wherein said first bolt hole (92A) is circular and said second bolt hole (92B) is oval.
3. The internal combustion engine of claim 2, wherein the major axis (L) of said second bolt hole (92B) is oriented toward the center (C) of said first bolt hole (92B).
4. The internal combustion engine according to claim 3, wherein a width (W) of the second bolt hole (92B) in the minor axis (M) direction is equal to a diameter (D) of the first bolt hole (92A).